View
3
Download
0
Category
Preview:
Citation preview
1
CHEMICAL CHARACTERIZATION OF
DISSOLVED ORGANIC MATTER IN
RELATION WITH HYDROGRAPHY IN
THE ARCTIC OCEAN
A Thesis submitted to the Committee on Graduate Studies
in Partial Fulfillment of the Requirements for the Degree of Master of
Science in the Faculty of Arts and Science.
TRENT UNIVERSITY
Peterborough, Ontario, Canada
(c) Copyright by Zhiyuan Gao 2016
Environmental and Life Science M.Sc. Graduate Program
January 2017
ii
ABSTRACT
Chemical characterization of dissolved organic matter in
relation with hydrography in the Arctic Ocean
Zhiyuan Gao
In this thesis, water mass distribution of dissolved organic matter (DOM)
characteristics (i.e. molecular weight, fluorescent components, thiols and humic
substances concentration) was observed in the Arctic Ocean. For the first time, DOM
molecular weight (MW) in Beaufort Sea was assessed using asymmetrical flow field-
flow fractionation, as well as the first monitoring of thiols and humic substances (HS)
using cathodic stripping voltammetry (CSV) in the Arctic Ocean. Based on
fluorescence property, DOM characterization was carried out using parallel factor
analysis – excitation-emission matrices. Pacific winter waters in the Canada Basin
showed higher MW DOM associated with higher fluorescence intensity. High HS was
associated with the Arctic outflow waters in top 300 m of the Canadian Arctic
Archipelago. Interestingly, maximum thiol concentration was associated with the
subsurface chlorophyll-a maximum at most sites, but not universal along the study area.
Comparable distributions of CSV-based HS and humic-like fluorescent components
suggest similar sources/ processes in the Arctic Ocean. The findings in this thesis
suggested DOM characteristics could be used as fingerprints in tracing water masses in
the Arctic Ocean.
iii
Keywords
DOM, Cathodic stripping voltammetry, Asymmetrical flow field-flow fractionation,
PARAFAC-EEMs, Molecular weight, Thiols, Humic substances
iv
Acknowledgements
I would like to express my gratitude to my supervisor Dr. Céline Guéguen for the
wonderful graduate project opportunity to explore the north as well as her patient
guidance and helpful engagement through the learning process of this master thesis. I
would like to give special thanks to my committee member Dr. Peter Lafleur and Dr.
David A. Ellis and other faculties at Trent University for the help and assistant in this
thesis. Furthermore, I would like to thank Northern Scientific Training Program,
Canada Research Chair Program (CG), National Sciences and Engineering Research
Council of Canada (CG), Geotraces and ArcticNet programs for funding my project
and the assistantship from crew member and fellow scientists of CCGS Amundsen and
Louis S. St-Laurent. Also, I would like to thank my family and my friends, who have
supported me throughout entire process, both by keeping me harmonious and helping
me putting pieces together. I will be grateful forever for your love.
v
Table of Content
ABSTRACT……… ...................................................................................................... ii
Acknowledgements ...................................................................................................... iv
Table of Content……………………………...………………………………………. v
List of figures and tables ............................................................................................. vii
List of Abbreviations and Symbols .............................................................................. ix
Chapter 1. The chemical nature of dissolved organic matter and its current situation
in the Arctic Ocean ........................................................................................................ 1
1.1 Introduction .....................................................................................................................1
1.2 Importance of DOM and monitoring methods ................................................................2
1.3 The hydrology in the Arctic Ocean ...................................................................................5
1.4 Objectives of my study .....................................................................................................7
Reference ...............................................................................................................................9
Figures and tables ............................................................................................................... 16
Chapter 2. Size distribution of absorbing and fluorescing DOM in Beaufort Sea,
Canada Basin ............................................................................................................... 18
Abstract ............................................................................................................................... 19
2.1 Introduction .................................................................................................................. 20
2.2 Methods ........................................................................................................................ 22
2.2.1 Sampling station ..................................................................................................... 22
2.2.2 Asymmetrical Flow field flow fractionation ........................................................... 22
2.2.3 Chromophoric dissolved organic matter (CDOM) and Fluorescent DOM (FDOM) 24
2.3 Results and Discussion .................................................................................................. 26
2.3.1 Hydrographical parameters ................................................................................... 26
2.3.2 Molecular weight depth distribution ..................................................................... 26
2.3.4 Optical Properties .................................................................................................. 27
2.3.5 Relationship between fluorescence properties and MW ...................................... 30
2.4 Conclusions ................................................................................................................... 31
Reference ............................................................................................................................ 33
vi
Figures and tables ............................................................................................................... 41
Chapter 3. Determination of thiols, humic substances and fluorescent dissolved
organic matter during the 2015 Canadian Arctic GEOTRACES cruises .................... 50
Abstract ............................................................................................................................... 51
3.1 Introduction .................................................................................................................. 52
3.2 Methods ........................................................................................................................ 54
3.2.1 Sampling ................................................................................................................. 54
3.2.2 Reagents ................................................................................................................. 54
3.2.3 Instrumentation ..................................................................................................... 55
3.2.4 Fluorescent dissolved organic matter (FDOM) ...................................................... 57
3.3 Results ........................................................................................................................... 57
3.3.1 Water mass definition ............................................................................................ 57
3.3.2 CSV-based DOM characterization .......................................................................... 59
3.3.3 FDOM characterization .......................................................................................... 59
3.3.4 DOM and water masses ......................................................................................... 60
3.3.5 Principal Components Analysis .............................................................................. 62
3.4 Conclusion ..................................................................................................................... 63
Reference ............................................................................................................................ 65
Figures and tables ............................................................................................................... 71
Chapter 4. Conclusion ............................................................................................. 77
4.1 Molecular weight of DOM ............................................................................................. 77
4.2 Composition of DOM .................................................................................................... 78
4.2.1 Fluorescent dissolved organic matter .................................................................... 78
4.2.2 Thiols and humic substances distribution .............................................................. 80
4.3 Conclusions and future directions ................................................................................ 80
Reference ............................................................................................................................ 82
Figures and tables ............................................................................................................... 84
vii
List of figures and tables
Figures
Figure 1.1 Map of the study area ................................................................................ 16
Figure 1.2 Potential temperature as a function of Salinity. A:2014 JOIS Cruise; B: 2015
GEOTRACES Cruise .................................................................................................. 17
Figure 2.1 Sampling locations in Beaufort Sea, Canada Basin .................................. 41
Figure 2.2 AF4 fractograms of CB29 (400m depth; black) and CB28b (1000m depth;
gray) ............................................................................................................................ 42
Figure 2.3 A) Potential temperature and B) FDOM as a function of salinity (Sp) at the
four study sites (Figure 2.1). ASW - Arctic surface waters, PSW – Pacific summer
water, PWW – Pacific winter water, FSB – Fram Strait Branch water, BSB – Barents
Sea Branch water ........................................................................................................ 43
Figure 2.4 MW depth profiles in Beaufort Sea ........................................................... 44
Figure 2.5 Depth distribution of A) a254, (B) a355, and (C) S275-295 ............................. 45
Figure 2.6 Individual components identified by PARAFAC (A- marine humic-like C1,
B- protein-like C2 and C- terrestrial humic-like C3) .................................................. 46
Figure 2.7 Depth distribution of A) Total Fluorescence Intensity (TF), B) marine
humic-like C1, C) protein-like C2 and D) terrestrial humic-like C3 .......................... 47
Figure 2.8 Change in TF vs CDOM MW ................................................................... 48
Figure 2.9 Correlation between MW and fluorescence components (A) C1; (B) C2; (C)
C3; (D) Change in fluorescence abundance with increasing DOM MW ................... 49
Figure 3.1 Sampling locations in Canada Basin and Canadian Arctic Archipelago,
Study transect highlighted in red area ......................................................................... 72
viii
Figure 3.2 (A) Potential temperature as a function of salinity (Sp) at all depths; (B)
Salinity, (C) Potential temperature and (D) Fluo sensor (Chlorophyll-a) distribution
along the transect (Figure 3.1) .................................................................................... 73
Figure 3.3 Distribution of thiol groups (A), humic substances (B), FDOM (C-F) along
the transect (Figure 3.1) .............................................................................................. 74
Figure 3.4 Excitation emission matrices identified by PARAFAC (A-C: humic-like; D:
protein-like) ................................................................................................................. 75
Figure 3.5 PCA models and score plots on all depths (A-B) and samples in top 100m
(C-D); SW: surface waters, OW: Arctic outflow waters, DW: deep waters; Lsd:
Lancaster Sound, CAA: Canadian Arctic Archipelago, CB: Canada Basin ............... 76
Figure 4.1 (A) Vertical distribution of terrestrial humic-like component in Canada
Basin, Canadian Arctic Archipelago and Lancaster Sound; (B) Vertical distribution of
protein-like components and Chl-a signal in all samples from both cruise ................ 85
Tables
Table 3.1 Repeatability, reproducibility, limit of detections and recovery of the CSV
method ......................................................................................................................... 71
Table 4.1 Fluorescent components identified in JOIS cruise and GEOTRACES cruise.
..................................................................................................................................... 84
ix
List of Abbreviations and Symbols
AF4 - Asymmetrical field flow fractionation
AIW - Arctic intermediate water
ASW - Arctic surface water
BS - Barrow Strait
BSB - Barents Sea Branch water
CAA - Canadian Arctic Archipelago
CB - Canada Basin
CDOM - Chromophoric dissolved organic matter
CSV - Cathodic stripping voltammetry
DOM - Dissolved organic matter
EEMs - Excitation emission matrices
FDOM - Fluorescent dissolved organic matter
FSB - Fram Strait Branch water
HS - humic substances
Lsd - Lancaster Sound
x
LsdSW - Lancaster Sound surface water
MW - Molecular weight
NADW - North Atlantic deep water
OW - Arctic outflow water
PARAFAC - Parallel factor analysis
PSW - Pacific summer water
PWW - Pacific winter water
1
Chapter 1. The chemical nature of dissolved organic
matter and its current situation in the Arctic Ocean
1.1 Introduction
Dissolved organic matter (DOM) is one of the largest reservoirs of organic
molecules (Bushaw et al., 1996) and plays an important role in the global carbon
cycling (Carlson and Hansell, 2014; Mopper and Kieber, 2002). As the most abundant
pool, marine DOM is involved in affecting light penetration (Stedmon et al., 2000),
serving as a food supplement (Cole et al., 2006) and energy transport (Baylor and
Sutcliffe Jr, 1963), as well as regulating trace metal speciation (De Schamphelaere et
al., 2004; Hirose, 2007; Yamashita and Jaffé, 2008).
The difference between DOM and particulate organic matter is only operationally
defined. The definition recommended by the Joint Global Ocean Flux studies is that
DOM is a group of substances passed through a pre-combusted glass fiber (GF) filters
(Knap et al., 1996), while in this study, 0.7 µm GF/F filters were used for the onboard
filtration of marine DOM.
DOM contains a variety of well-defined compounds, including proteins, lipids and
carbohydrates (Leenheer and Croué, 2003; Nebbioso and Piccolo, 2013; Schumacher
et al., 2006). A big part of DOM (13 - 32%, Chanudet et al., 2006) consists of humic
substances (HS), which are heterogeneous in nature and largely refractory in the aquatic
system (Thurman, 2012). While the structure of the DOM complex remains largely
unknown, some organic groups (i.e. thiols and HS) formed strong complexation with
2
trace metals such as Cd, Cu, Fe and Mo (Hunter and Boyd, 2007; Kinniburgh et al.,
1996; Pernet-Coudrier et al., 2013; Yang and Berg, 2009).
It is not easy to understand the fate of DOM due to its various sources and multiple
sinks in aquatic systems. In the marine environment, DOM is mostly formed in-situ
through photosynthesis and metabolism by bacteria and phytoplankton (Aluwihare et
al., 1997; Aslam et al., 2012; Jiao et al., 2010; Teira et al., 2001). Allochthonous source
of DOM was also important. River discharges (i.e Mackenzie River input to Beaufort
Sea, Arctic Ocean) constitute an important source of DOM in coastal areas (Bélanger
et al., 2006; Guéguen et al., 2005) and therefore influence the distribution and
composition of marine DOM (Rachold et al., 2004; Walker et al., 2009; Yang et al.,
2013). Lobbes et al., (2000) reported considerable amounts of DOM released from the
Russian rivers into Arctic Ocean. The major sinks of DOM include photochemical and
microbial mineralization (Brinkmann et al., 2003; Dainard et al., 2015; Helms et al.,
2008; Miller and Moran, 1997; Zhou and Wong, 2000). In this thesis, DOM distribution
and composition would be monitored in the Arctic Ocean, which will help us further
understand the fate of DOM in the area.
1.2 Importance of DOM and monitoring methods
The optical properties (i.e. absorbance and fluorescence) of DOM are important
factors affecting its behavior in the marine environment. The light absorbing
chromophoric dissolved organic matter (CDOM; Coble, 1996; Stedmon et al., 2000)
enhances primary production (Arrigo and Brown, 1996) and serves as a protection layer
in the surface water by absorbing harmful radiation such as ultraviolet radiations (Hill,
2008). However, high levels of light absorption may result in competition with
3
phytoplankton for the amount and quality of available light resource, which may
impede primary production (Bidigare et al., 1993; Kowalczuk et al., 2003; Thrane et
al., 2014). Based on the absorption spectrum, information on relative CDOM
concentration (absorption coefficient at a specific wavelength at 254 or 355 nm, Chen
et al., 2004; Dainard and Guéguen, 2013; Granskog et al., 2007), as well as molecular
size and aromaticity (spectral slope S, Helms et al., 2008; Stedmon et al., 2011), could
be determined.
In addition to absorbing properties, DOM can be characterized by its fluorescing
properties (FDOM, Coble, 1996; Mopper and Schultz, 1993). The fluorescence
excitation emission matrices (EEMs, Coble, 1996) had been proved to be capable of
differentiating humic-like DOM of terrestrial or marine origin (Coble, 1996). The
coupling with parallel factor analysis (PARAFAC) allows to decompose EEMs into
more detailed fluorescent components (Dainard and Guéguen, 2013; Guo et al., 2011;
Murphy et al., 2008). For example, a PARAFAC model consisted of marine (M peak,
Coble, 1996) and terrestrial (A and C peak, Coble, 1996) humic-like, protein-like (T
peak, Coble, 1996) fluorescent components was validated for DOM samples in Arctic
Ocean (Dainard and Guéguen, 2013; Guéguen et al., 2014; Walker et al., 2009).
DOM – metal complexation is of vital importance in the marine environment,
which had been demonstrated to be related with aromaticity and DOM molecular size
(Benoit et al., 2001; Guo and Santschi, 2007; Laglera and van den Berg, 2003; Louis
et al., 2014; Nierop et al., 2002; Sun et al., 1997; Wu et al., 2004). Thus, assessment
on the molecular weight (MW) could help us better understand the function of DOM
4
in the ocean system. There were multiple ways of determining DOM MW, like
ultrafiltration (Guo and Santschi, 2007; Pokrovsky et al., 2012), high pressure size
exclusion chromatography (HPSEC, Conte and Piccolo, 1999; Zhou et al., 2000) and
asymmetrical flow field flow fractionation (AF4, Guéguen and Cuss, 2011; Lin et al.,
2016; Stolpe et al., 2014, 2010). However, ultrafiltration only gives a single MW cutoff
separation while AF4 could provide a continuous and detailed MW distribution.
HPSEC and AF4 were both proved to be capable of detecting DOM MW with rapid
throughput and high accuracy. But HPSEC is limited in the size range and choice of
buffers (Liu et al., 2006; Narhi, 2013), while AF4 displays broad dynamic range and is
capable of running under high salinity condition (Cao et al., 2009; Narhi, 2013), which
is more applicable for marine DOM. Besides, AF4 is capable of maintaining the
original DOM composition without the high pressure applied in HPSEC system.
Moreover, only a few researchers applied AF4 on the marine DOM (Hassellöv, 2005;
Lin et al., 2016; Stolpe et al., 2014, 2010) and for the first time, AF4 was selected as
the detector for marine DOM MW in the Arctic Ocean in this thesis.
Besides DOM MW, available organic ligands are another important factors
affecting DOM-metal complexation. Some metal-binding agents are fluorescent and
can be determined by fluorimeter (McIntyre and Guéguen, 2013; Tani et al., 2003; Wu
et al., 2001; Yamashita and Jaffé, 2008). For example, HS was involved with iron
solubility and measured as humic-like type fluorescent components in north Pacific
Ocean (Tani et al., 2003). But not all the organic ligands are fluorescent, like thiols,
however, thiol groups (i.e. GSH) showed great binding affinity with metals in the
aquatic system (Hunter and Boyd, 2007; Kinniburgh et al., 1996; Yang and Berg, 2009).
5
Thus, methods other than EEMs are needed for the non-fluorescing organic ligands (i.e.
thiols). High performance liquid chromatography (HPLC) and cathodic stripping
voltammetry (CSV) have been applied in detecting thiols in ocean studies (Kading,
2013; Laglera and van den Berg, 2003; Pernet-Coudrier et al., 2013; Swarr et al., 2016).
Although HPLC analysis features high resolution in thiol determination, time
consuming thiol derivatization is required (Kading, 2013; Swarr et al., 2016; Tang et
al., 2003). On the other hand, CSV technique allows the determination of GSH
(Kawakami et al., 2006) without extensive sample preparation (Marie et al., 2015;
Pernet-Coudrier et al., 2013). Regarding refractory organic matter in the aquatic
systems, HS could be characterized as humic-like components based on its fluorescing
property (Tani et al., 2003) and detected by CSV (Whitby and Van den Berg, 2014).
But the comparison between humic-like fluorescent components and CSV-based HS
remains unknown, and this comparison will provide novel insights on marine DOM
composition in this thesis. For the simultaneous detection purpose of thiols and HS in
seawater samples (Marie et al., 2015; Pernet-Coudrier et al., 2013), CSV is used in this
thesis.
1.3 The hydrology in the Arctic Ocean
The Arctic Ocean (Fig 1.1) serves as a channel between the Pacific Ocean and the
Atlantic Ocean. Pacific-origin water flows into Beaufort Sea via Bering Strait while
Atlantic-origin deep water enters through Fram Strait Branch and Barents Sea Branch.
Canadian Arctic Archipelago (CAA) and other passages like Smith Sound serve as
exiting pathways for Arctic waters into the North Atlantic Ocean.
6
Surface waters in the Canada Basin (CB) are controlled by a strong wind-driven
circular current, the Beaufort Gyre (Woodgate, 2013), accumulating freshwater from
sea ice melting and Eurasian and American river inputs. With the contribution of
summer ice melting inputs, Pacific summer water (PSW) is formed, which is on the top
of a saline and cold Pacific winter water (PWW). The great difference in salinity and
temperature (Fig 1.2A) impeded the vertical exchange between PSW and PWW.
Underlying Pacific waters, saline and warm Atlantic waters was found below 400 m.
For the spatial distribution, sub-surface Pacific waters flowed eastwards through CAA
and encountered warm and saline Atlantic waters at Lancaster Sound where they join
the thermocline circulation at Baffin Bay.
Four main water masses (Carmack et al., 2015; McLaughlin et al., 2011, 2004;
Melling et al., 2008; Michel et al., 2006; Rudels et al., 2012; Woodgate, 2013) are
identified based on the temperature/salinity (T/S) diagram (Fig 1.2):
Surface waters (SW) occupy the top 30 m and include the Arctic surface
waters (ASW) in CB and western and Lancaster Sound surface waters
(LsdSW).
Arctic Outflow waters (OW) are found in the top 300 m (excluding SW).
OW encompasses the PSW and PWW in CB.
In CB, Atlantic-derived Arctic intermediate water (AIW) are found
underlying Pacific waters, a temperature maximum near 400 m
characterizes Fram Strait Branch (FSB) waters while lower temperature
characterizes Barents Sea Branch (BSB) water.
7
Deep layers near Lancaster Sound are occupied by North Atlantic Deep
waters (NADW).
The Arctic Ocean is undergoing rapid changes due to global warming (Purkey and
Johnson, 2010; Shimada et al., 2006). Increased river discharges in Arctic Ocean
(Peterson et al., 2002) may bring more terrestrial influence to the Arctic Ocean, while
change in sea ice cover (Comiso et al., 2008) may make a difference in DOM
composition and distribution. Although, remote sensing techniques have been applied
in DOM monitoring in Arctic Ocean (Matsuoka et al., 2013), in-situ sampling and
assessment of DOM in Arctic Ocean are still required and will provide better insights
into the Arctic Ocean under global warming issues.
1.4 Objectives of my study
For the purpose of monitoring DOM distribution in the Arctic Ocean, DOM MW,
optical properties and metal-binding ligands (i.e. thiols and HS) concentration would
be determined in samples collected in CB and CAA during the Joint Ocean Ice Studies
(JOIS) cruise (September 2014) and the Canadian Arctic GEOTRACES cruises (July-
September 2015).
Two major research questions will be solved in this thesis:
Is the distribution of DOM characteristics associated with water masses of
different origin?
Is there a connection between voltammetry-based HS and humic-like
fluorescent component?
8
For the first time, AF4 system will be applied to assess marine DOM MW in the
Arctic Ocean, as well as the first monitoring of thiols and humic substances. Besides,
a novel comparison between voltammetry-based HS and humic-like fluorescent
components will be conducted.
Since the Arctic Ocean is highly stratified and consisted of waters from Pacific and
Atlantic origin, the DOM characteristics (i.e. DOM MW, CDOM, thiol and HS) are not
homogeneously distributed throughout the Arctic Ocean. Tracing water masses by
DOM characteristics will improve the understanding of water circulation, fate and
transport of DOM in the Arctic. The DOM monitoring conducted in this thesis will
provide unique insights on the DOM distribution and composition in the Arctic Ocean.
At the same time, DOM MW, thiols and HS concentrations, CDOM (including FDOM)
will be studied as fingerprints to distinguish water masses of different origin.
9
Reference
Aluwihare, L., Repeta, D., Chen, R., 1997. A major biopolymeric component to
dissolved organic carbon in surface sea water. Nature.
Arrigo, K., Brown, C., 1996. Impact of chromophoric dissolved organic matter on UV
inhibition of primary productivity in the sea. Mar. Ecol. Prog. Ser.
Aslam, S., Underwood, G., Kaartokallio, H., Norman, L., 2012. Dissolved
extracellular polymeric substances (dEPS) dynamics and bacterial growth during
sea ice formation in an ice tank study. Polar Biol.
Baylor, E.R., Sutcliffe Jr, W.H., 1963. Dissolved Organic Matter in Seawter as a
source of Particulate Food. Limnol. Oceanogr. 8, 369–371.
Bélanger, S., Xie, H., Krotkov, N., Larouche, P., Vincent, W.F., Babin, M., 2006.
Photomineralization of terrigenous dissolved organic matter in arctic coastal
waters from 1979 to 2003: Interannual variability and implications of climate
change. Global Biogeochem. Cycles 20, 1–13. doi:10.1029/2006GB02708
Benoit, J.M., Mason, R.P., Gilmour, C.C., Aiken, G.R., 2001. Constants for mercury
binding by organic matter isolates from the Florida Everglades. Geochim.
Cosmochim. Acta 65, 4445–4451. doi:10.1016/S0016-7037(01)00742-6
Bidigare, R., Ondrusek, M., Brooks, J., 1993. Algal Pigments in the Caribbean Sea.
Geophys. Res.
Brinkmann, T., Sartorius, D., Frimmel, F., 2003. Photobleaching of humic rich
dissolved organic matter. Aquat. Sci.
Bushaw, K., Zepp, R., Tarr, M., Schulz-Jander, D., 1996. Photochemical release of
biologically available nitrogen from aquatic dissolved organic matter.
Cao, S., Pollastrini, J., Jiang, Y., 2009. Separation and characterization of protein
aggregates and particles by field flow fractionation. Curr. Pharm.
Carlson, C.A., Hansell, D.A., 2014. DOM Sources, Sinks, Reactivity, and Budgets,
in: Biogeochemistry of Marine Dissolved Organic Matter: Second Edition. pp.
65–126. doi:10.1016/B978-0-12-405940-5.00003-0
Carmack, E.C., Haine, T.W.N., Bacon, S., Bluhm, B.A., Lique, C., Melling, H.,
Polyakov, I. V, Straneo, F., Timmermans, M., Williams, W.J., 2015. Freshwater
and its role in the Arctic Marine System: Sources, disposition, storage, export,
and physical and biogeochemical consequences in the Arctic and global oceans
675–717. doi:10.1002/2015JG003140.Received
Chanudet, V., Filella, M., Quentel, F., 2006. Application of a simple voltammetric
method to the determination of refractory organic substances in freshwaters.
Anal. Chim. Acta 569, 244–249. doi:10.1016/j.aca.2006.03.097
Chen, Z., Li, Y., Pan, J., 2004. Distributions of colored dissolved organic matter and
10
dissolved organic carbon in the Pearl River Estuary, China. Cont. Shelf Res. 24,
1845–1856. doi:10.1016/j.csr.2004.06.011
Coble, P.G., 1996. Characterization of marine and terrestrial DOM in seawater using
excitation-emission matrix spectroscopy. Mar. Chem. 51, 325–346.
doi:10.1016/0304-4203(95)00062-3
Cole, J.J., Carpenter, S.R., Pace, M.L., Van De Bogert, M.C., Kitchell, J.L., Hodgson,
J.R., 2006. Differential support of lake food webs by three types of terrestrial
organic carbon. Ecol. Lett. 9, 558–568. doi:10.1111/j.1461-0248.2006.00898.x
Comiso, J., Parkinson, C., Gersten, R., 2008. Accelerated decline in the Arctic sea ice
cover. Geophys. Res.
Conte, P., Piccolo, A., 1999. High pressure size exclusion chromatography (HPSEC)
of humic substances: molecular sizes, analytical parameters, and column
performance. Chemosphere.
Dainard, P.G., Guéguen, C., 2013. Distribution of PARAFAC modeled CDOM
components in the North Pacific Ocean, Bering, Chukchi and Beaufort Seas.
Mar. Chem. 157, 216–223. doi:10.1016/j.marchem.2013.10.007
Dainard, P.G., Guéguen, C., McDonald, N., Williams, W.J., 2015. Photobleaching of
fluorescent dissolved organic matter in Beaufort Sea and North Atlantic
Subtropical Gyre. Mar. Chem. 177, 630–637.
doi:10.1016/j.marchem.2015.10.004
De Schamphelaere, K. a C., Vasconcelos, F.M., Tack, F.M.G., Allen, H.E., Janssen,
C.R., 2004. Effect of dissolved organic matter source on acute copper toxicity to
Daphnia magna. Environ. Toxicol. Chem. 23, 1248–1255. doi:10.1897/03-184
Granskog, M.A., Macdonald, R.W., Mundy, C.J., Barber, D.G., 2007. Distribution,
characteristics and potential impacts of chromophoric dissolved organic matter
(CDOM) in Hudson Strait and Hudson Bay, Canada. Cont. Shelf Res. 27, 2032–
2050. doi:10.1016/j.csr.2007.05.001
Guéguen, C., Cuss, C.W., 2011. Characterization of aquatic dissolved organic matter
by asymmetrical flow field-flow fractionation coupled to UV-Visible diode array
and excitation emission matrix fluorescence. J. Chromatogr. A 1218, 4188–
4198. doi:10.1016/j.chroma.2010.12.038
Guéguen, C., Cuss, C.W., Cassels, C.J., Carmack, E.C., 2014. Absorption and
fluorescence of dissolved organic matter in the waters of the Canadian Artic
Archiipelago, Baffin Bay, and the Labrador Sea. J. Geophys. Res. Ocean. 119,
2034–2047. doi:10.1002/2013JC009173.Received
Guéguen, C., Guo, L., Tanaka, N., 2005. Distributions and characteristics of colored
dissolved organic matter in the Western Arctic Ocean. Cont. Shelf Res. 25,
1195–1207. doi:10.1016/j.csr.2005.01.005
Guo, L., Santschi, P.H., 2007. Ultrafiltration and its Applications to Sampling and
Characterisation of Aquatic Colloids, in: Environmental Colloids and Particles:
11
Behaviour, Separation and Characterisation. pp. 159–221.
doi:10.1002/9780470024539.ch4
Guo, W., Yang, L., Hong, H., Stedmon, C., Wang, F., Xu, J., 2011. Assessing the
dynamics of chromophoric dissolved organic matter in a subtropical estuary
using parallel factor analysis. Mar. Chem.
Hassellöv, M., 2005. Relative molar mass distributions of chromophoric colloidal
organic matter in coastal seawater determined by Flow Field-Flow Fractionation
with UV absorbance and. Mar. Chem.
Helms, J.R., Stubbins, A., Ritchie, J.D., Minor, E.C., Kieber, D.J., Mopper, K., 2008.
Absorption spectral slopes and slope ratios as indicators of molecular weight,
source, and photobleaching of chromophoric dissolved organic matter.
Limonology Oceanogr. 53, 955–969. doi:10.4319/lo.2008.53.3.0955
Hill, V.J., 2008. Impacts of chromophoric dissolved organic material on surface
ocean heating in the Chukchi Sea. J. Geophys. Res. 113, 1–10.
doi:10.1029/2007JC004119
Hirose, K., 2007. Metal-organic matter interaction: Ecological roles of ligands in
oceanic DOM. Appl. Geochemistry 22, 1636–1645.
doi:10.1016/j.apgeochem.2007.03.042
Hunter, K., Boyd, P., 2007. Iron-binding ligands and their role in the ocean
biogeochemistry of iron. Environ. Chem.
Jiao, N., Herndl, G.J., Hansell, D.A., Benner, R., Kattner, G., Wilhelm, S.W.,
Kirchman, D.L., Weinbauer, M.G., Luo, T., Chen, F., Azam, F., 2010. Microbial
production of recalcitrant dissolved organic matter: long-term carbon storage in
the global ocean. Nat. Rev. Microbiol. 8, 593–9. doi:10.1038/nrmicro2386
Kading, T., 2013. Distribution of thiols in the northwest Atlantic Ocean.
Kawakami, S.K., Gledhill, M., Achterberg, E.P., 2006. Determination of
phytochelatins and glutathione in phytoplankton from natural waters using
HPLC with fluorescence detection. TrAC - Trends Anal. Chem. 25, 133–142.
doi:10.1016/j.trac.2005.06.005
Kinniburgh, D., Milne, C., Benedetti, M., 1996. Metal ion binding by humic acid:
application of the NICA-Donnan model. Environmental.
Knap, A., Michaels, A., Close, A., Ducklow, H., 1996. Protocols for the joint global
ocean flux study (JGOFS) core measurements. JGOFS, Repr.
Kowalczuk, P., Cooper, W., Whitehead, R., Durako, M., 2003. Characterization of
CDOM in an organic-rich river and surrounding coastal ocean in the South
Atlantic Bight. Aquat. Sci.
Laglera, L.M., van den Berg, C.M.G., 2003. Copper complexation by thiol
compounds in estuarine waters. Mar. Chem. 82, 71–89. doi:10.1016/S0304-
4203(03)00053-7
12
Leenheer, J., Croué, J., 2003. Peer reviewed: characterizing aquatic dissolved organic
matter. Environ. Sci. Technol.
Lin, H., Chen, M., Zeng, J., Li, Q., Jia, R., Sun, X., Zheng, M., Qiu, Y., 2016. Size
characteristics of chromophoric dissolved organic matter in the Chukchi Sea. J.
Geophys. Res. Ocean. doi:10.1002/2016JC011771
Liu, J., Andya, J., Shire, S., 2006. A critical review of analytical ultracentrifugation
and field flow fractionation methods for measuring protein aggregation. AAPS J.
Lobbes, J., Fitznar, H., Kattner, G., 2000. Biogeochemical characteristics of dissolved
and particulate organic matter in Russian rivers entering the Arctic Ocean.
Geochim. Cosmochim. Acta.
Louis, Y., Pernet-Coudrier, B., Varrault, G., 2014. Implications of effluent organic
matter and its hydrophilic fraction on zinc (II) complexation in rivers under
strong urban pressure: Aromaticity as an inaccurate indicator. Sci. Total Environ.
Marie, L., Pernet-Coudrier, B., Waeles, M., Gabon, M., Riso, R., 2015. Dynamics and
sources of reduced sulfur, humic substances and dissolved organic carbon in a
temperate river system affected by agricultural practices. Sci. Total Environ.
537, 23–32. doi:10.1016/j.scitotenv.2015.07.089
Matsuoka, A., Hooker, S., Bricaud, A., Gentili, B., 2013. Estimating absorption
coefficients of colored dissolved organic matter (CDOM) using a semi-analytical
algorithm for southern Beaufort Sea waters: application to.
McIntyre, A.M., Guéguen, C., 2013. Binding interactions of algal-derived dissolved
organic matter with metal ions. Chemosphere 90, 620–626.
doi:10.1016/j.chemosphere.2012.08.057
McLaughlin, F.A., Carmack, E.C., Macdonald, R.W., Melling, H., Swift, J.H.,
Wheeler, P.A., Sherr, B.F., Sherr, E.B., 2004. The joint roles of Pacific and
Atlantic-origin waters in the Canada Basin, 1997-1998. Deep. Res. Part I
Oceanogr. Res. Pap. 51, 107–128. doi:10.1016/j.dsr.2003.09.010
McLaughlin, F.A., Carmack, E.C., Proshutinsky, A., Krishfield, R.A., Guay, C.K.,
Yamamoto-Kawai, M., Jackson, J.M., Williams, B., Williams, W.J., Williams,
B., Williams, W.J., 2011. The Rapid Response of the Canada Basin to Climate
Forcing: From Bellwether to Alarm Bells. Oceanography 24, 146–159.
doi:10.5670/oceanog.2011.66
Melling, H., Agnew, T., Falkner, K., 2008. Fresh-water fluxes via Pacific and Arctic
outflows across the Canadian polar shelf. Arctic–Subarctic Ocean.
Michel, C., Ingram, R.G., Harris, L.R., 2006. Variability in oceanographic and
ecological processes in the Canadian Arctic Archipelago. Prog. Oceanogr. 71,
379–401. doi:10.1016/j.pocean.2006.09.006
Miller, W., Moran, M., 1997. Interaction of photochemical and microbial processes in
the degradation of refractory dissolved organic matter from a coastal marine
environment. Limnol. Oceanogr.
13
Mopper, K., Kieber, D.J., 2002. Photochemistry and the Cycling of Carbon, Sulfur,
Nitrogen and Phosphorus. Biogeochem. Mar. Dissolved Org. Matter 455–489.
doi:10.1016/B978-012323841-2/50011-7
Mopper, K., Schultz, C., 1993. Fluorescence as a possible tool for studying the nature
and water column distribution of DOC components. Mar. Chem.
Murphy, K.R., Stedmon, C.A., Waite, T.D., Ruiz, G.M., 2008. Distinguishing
between terrestrial and autochthonous organic matter sources in marine
environments using fluorescence spectroscopy. Mar. Chem. 108, 40–58.
doi:10.1016/j.marchem.2007.10.003
Narhi, L., 2013. Biophysics for therapeutic protein development.
Nebbioso, A., Piccolo, A., 2013. Molecular characterization of dissolved organic
matter (DOM): A critical review. Anal. Bioanal. Chem. 405, 109–124.
doi:10.1007/s00216-012-6363-2
Nierop, K., Jansen, B., Verstraten, J., 2002. Dissolved organic matter, aluminium and
iron interactions: precipitation induced by metal/carbon ratio, pH and
competition. Sci. Total Environ.
Pernet-Coudrier, B., Waeles, M., Filella, M., Quentel, F., Riso, R.D., 2013. Simple
and simultaneous determination of glutathione, thioacetamide and refractory
organic matter in natural waters by DP-CSV. Sci. Total Environ. 463–464, 997–
1005. doi:10.1016/j.scitotenv.2013.06.053
Peterson, B., Holmes, R., McClelland, J., 2002. Increasing river discharge to the
Arctic Ocean.
Pokrovsky, O., Shirokova, L., Zabelina, S., 2012. Size fractionation of trace elements
in a seasonally stratified boreal lake: control of organic matter and iron colloids.
Aquatic.
Purkey, S.G., Johnson, G.C., 2010. Warming of global abyssal and deep Southern
Ocean waters between the 1990s and 2000s: Contributions to global heat and sea
level rise budgets. J. Clim. 23, 6336–6351. doi:10.1175/2010JCLI3682.1
Rachold, V., Eicken, H., Gordeev, V., 2004. Modern terrigenous organic carbon input
to the Arctic Ocean. Org. carbon.
Rudels, B., Anderson, L., Eriksson, P., Fahrbach, E., Jakobsson, M., Jones, E.P.,
Melling, H., Prinsenberg, S., Schauer, U., Yao, T., 2012. Observations in the
Ocean, in: ARCTIC CLIMATE CHANGE: THE ACSYS DECADE AND
BEYOND. pp. 117–198. doi:10.1007/978-94-007-2027-5_4
Schumacher, M., Christl, I., Vogt, R., Barmettler, K., 2006. Chemical composition of
aquatic dissolved organic matter in five boreal forest catchments sampled in
spring and fall seasons. Biogeochemistry.
Shimada, K., Kamoshida, T., Itoh, M., Nishino, S., Carmack, E., McLaughlin, F.,
Zimmermann, S., Proshutinsky, A., 2006. Pacific Ocean inflow: Influence on
14
catastrophic reduction of sea ice cover in the Arctic Ocean. Geophys. Res. Lett.
33, 3–6. doi:10.1029/2005GL025624
Stedmon, C.A., Amon, R.M.W., Rinehart, A.J., Walker, S.A., 2011. The supply and
characteristics of colored dissolved organic matter (CDOM) in the Arctic Ocean:
Pan Arctic trends and differences. Mar. Chem. 124, 108–118.
doi:10.1016/j.marchem.2010.12.007
Stedmon, C., Markager, S., Kaas, H., 2000. Optical properties and signatures of
chromophoric dissolved organic matter (CDOM) in Danish coastal waters.
Estuar. Coast. Shelf Sci.
Stolpe, B., Guo, L., Shiller, A.M., Hassellöv, M., 2010. Size and composition of
colloidal organic matter and trace elements in the Mississippi River, Pearl River
and the northern Gulf of Mexico, as characterized by flow field-flow
fractionation. Mar. Chem. 118, 119–128. doi:10.1016/j.marchem.2009.11.007
Stolpe, B., Zhou, Z., Guo, L., Shiller, A.M., 2014. Colloidal size distribution of
humic- and protein-like fl uorescent organic matter in the northern Gulf of
Mexico. Mar. Chem. 164, 25–37. doi:10.1016/j.marchem.2014.05.007
Sun, L., Perdue, E.M., Meyer, J.L., Weis, J., 1997. Use of elemental composition to
predict bioavailability of dissolved organic matter in a Georgia river. Limnol.
Oceanogr. 42, 714–721. doi:10.4319/lo.1997.42.4.0714
Swarr, G.J., Kading, T., Lamborg, C.H., Hammerschmidt, C.R., Bowman, K.L.,
2016. Dissolved Low-Molecular Weight Thiol Concentrations from the U.S.
GEOTRACES North Atlantic Ocean Zonal Transect. Deep Sea Res. Part I
Oceanogr. Res. Pap. 116, 77–87. doi:10.1016/j.dsr.2016.06.003
Tang, D., Shafer, M.M., Vang, K., Karner, D.A., Armstrong, D.E., 2003.
Determination of dissolved thiols using solid-phase extraction and liquid
chromatographic determination of fluorescently derivatized thiolic compounds.
J. Chromatogr. A 998, 31–40. doi:10.1016/S0021-9673(03)00639-3
Tani, H., Nishioka, J., Kuma, K., Takata, H., 2003. Iron (III) hydroxide solubility and
humic-type fluorescent organic matter in the deep water column of the Okhotsk
Sea and the northwestern North Pacific Ocean. Deep Sea Res.
Teira, E., Pazó, M.J., Serret, P., 2001. Dissolved organic carbon production by
microbial populations in the Atlantic Ocean. Limnol.
Thrane, J., Hessen, D., Andersen, T., 2014. The absorption of light in lakes: negative
impact of dissolved organic carbon on primary productivity. Ecosystems.
Thurman, E., 2012. Organic geochemistry of natural waters.
Walker, S.A., Amon, R.M.W., Stedmon, C.A., Duan, S., Louchouarn, P., 2009. The
use of PARAFAC modeling to trace terrestrial dissolved organic matter and
fingerprint water masses in coastal Canadian Arctic surface waters. J. Geophys.
Res. Biogeosciences 114. doi:10.1029/2009JG000990
15
Whitby, H., Van den Berg, C.M.G., 2014. Evidence for copper-binding humic
substances in seawater. Mar. Chem. 173, 282–290.
doi:10.1016/j.marchem.2014.09.011
Woodgate, R., 2013. Arctic Ocean Circulation: Going Around At the Top Of the
World. Nat. Educ. Knowl. Proj. 4, 1–12.
Wu, F., Evans, D., Dillon, P., Schiff, S., 2004. Molecular size distribution
characteristics of the metal-DOM complexes in stream waters by high-
performance size-exclusion chromatography (HPSEC) and high-resolution
inductively coupled plasma mass spectrometry (ICP-MS). J. Anal. At. Spectrom.
19, 979. doi:10.1039/b402819h
Wu, F., Midorikawa, T., Tanoue, E., 2001. Fluorescence properties of organic ligands
for copper (II) in Lake Biwa and its rivers. Geochem. J.
Yamashita, Y., Jaffé, R., 2008. Characterizing the interactions between trace metals
and dissolved organic matter using excitation-emission matrix and parallel factor
analysis. Environ. Sci. Technol. 42, 7374–7379. doi:10.1021/es801357h
Yang, L., Guo, W., Hong, H., Wang, G., 2013. Non-conservative behaviors of
chromophoric dissolved organic matter in a turbid estuary: Roles of multiple
biogeochemical processes. Estuar. Coast. Shelf Sci.
Yang, R., Berg, C. van den, 2009. Metal complexation by humic substances in
seawater. Environ. Sci. Technol.
Zhou, L., Wong, J., 2000. Microbial decomposition of dissolved organic matter and
its control during a sorption experiment. J. Environ. Qual.
Zhou, Q., Cabaniss, S., Maurice, P., 2000. Considerations in the use of high-pressure
size exclusion chromatography (HPSEC) for determining molecular weights of
aquatic humic substances. Water Res.
16
Figures and tables
Figure 1.1 Map of the study area
17
Figure 1.2 Potential temperature as a function of Salinity. A:2014 JOIS Cruise; B: 2015 GEOTRACES Cruise
18
Chapter 2. Size distribution of absorbing and fluorescing
DOM in Beaufort Sea, Canada Basin
Zhiyuan Gao1, Céline Guéguen2,*
1 Environmental and Life Sciences Graduate program, Trent University, ON, Canada
2 Chemistry Department, Trent University, ON, Canada
*Corresponding author: Tel: +1 (705) 748 1011; Fax: +1 (705) 748 1625; email:
celinegueguen@trentu.ca
19
Abstract
The molecular weight (MW) of dissolved organic matter (DOM) is considered as an
important factor affecting the bioavailability of organic matter and associated chemical
species. Chromophoric DOM (CDOM) MW distribution was determined, for the first
time, in the Beaufort Sea (Canada Basin) by asymmetrical flow field-flow fractionation
(AF4) coupled with online diode array ultra violet-visible photometer and offline
fluorescence detectors. The apparent MW ranged from 1.07 kDa to 1.45 kDa, congruent
with previous studies using high performance size exclusion chromatography and
tangential flow filtration. Interestingly, a minimum in MW was associated with the
Pacific Summer Waters, while higher MW was associated with the Pacific Winter
Waters. The Arctic Intermediate Waters did not show any significant change in MW
and fluorescence intensities distribution between stations, suggesting homogeneous
DOM composition in deep waters. Three fluorescence components including two
humic-like components and one protein-like component were PARAFAC-validated.
With the increase of MW, protein-like fluorescence component became more dominant
while the majority remained as marine/microbially derived humic-like components.
Overall, it is concluded that water mass origin influenced DOM MW distribution in the
Arctic Ocean.
Keywords
DOM, Asymmetrical flow field-flow fractionation (AF4), Molecular weight,
PARAFAC-EEMs
20
2.1 Introduction
Dissolved organic matter (DOM), usually measured as dissolved organic carbon
(DOC), is a major carbon pool in aquatic systems (Amon and Benner, 1994; Benner et
al., 1992; Jiao et al., 2010). DOM serves as a source of food for microorganisms (Cole
et al., 2006), contributing to the food web and energy transport (Baylor and Sutcliffe
Jr, 1963). DOM also plays an important role in regulating the speciation and
distribution of trace metals such as Cu, Hg, Fe and Zn (Hirose, 2007; De Schamphelaere
et al., 2004; Yamashita and Jaffé, 2008). Previous studies showed that increased Cu-
binding affinity was observed with increasing DOM molecular weight (MW) in natural
waters (Midorikawa and Tanoue, 1998; Wu and Tanoue, 2001). High MW DOM
complexation was favoured by metals with high binding strength while low MW DOM
was preferentially bound by weak binding strength metals (Wu et al., 2004). Besides
affecting metal binding affinity, DOM MW could influence its uptake by
microorganisms (Guo and Santschi, 2007; Sun et al., 1997). For example, high MW
oceanic DOM was favoured by bacterial utilization (Amon and Benner, 1996), boosting
growth rates of some bacterial group and algae (Tulonen et al., 1992).
The heterogeneous nature of DOM requires the use of complementary analytical
techniques. The absorbance and fluorescence properties of DOM have been
increasingly used in differentiating allochthonous and autochthonous DOM sources
(Stedmon et al., 2003) and tracing riverine supply into the ocean system (Fichot et al.,
2013; Fichot and Benner, 2012; Guéguen et al., 2011, 2012a; Nelson et al., 2010;
Stedmon et al., 2011). The ultraviolet-visible absorbance properties of chromophoric
dissolved organic matter (CDOM) have been used as molecular size and aromaticity
21
proxies (Guéguen and Cuss, 2011; Helms et al., 2008). Excitation emission matrix
(EEM; Coble, 1996) technique coupled to parallel factor analysis (PARAFAC; Murphy
et al., 2008) have been used to facilitate the identification and quantification of
independent fluorescent classes such as protein-like, microbially derived and terrestrial
humic-like in marine studies (Dainard and Guéguen, 2013; Guo et al., 2011; Murphy
et al., 2008). Asymmetrical flow field-flow fractionation (AF4) is a chromatographic-
like method that has been recently applied to investigate the sources and dynamics of
DOM in aquatic systems (Boehme and Wells, 2006; Guéguen and Cuss, 2011; Lin et
al., 2016; Stolpe et al., 2010, 2014). For example, Lin et al., (2016) showed that the 1-
10 kDa CDOM fraction was influenced by terrestrial input. Stolpe et al., (2014)
concluded that the small MW DOM (2-3 nm) in surface northern Gulf of Mexico
originated from terrestrial sources whereas the larger MW DOM (>6 nm) was protein-
rich and freshly produced.
The Arctic regions are undergoing rapid changes in air temperatures, river
discharge, sea ice extent and permafrost integrity (Frey and McClelland, 2009;
Overland and Wang, 2013; Peterson et al., 2002; Schuur et al., 2009; Shimada et al.,
2006). Continued climate change will likely have profound effect on carbon cycle.
Documenting the composition and distribution of DOM (i.e. MW and optical properties)
could provide valuable insights into the biogeochemical carbon cycle.
In this study, DOM samples were collected at four sites and five water masses in
Beaufort Sea: Arctic Surface Water (ASW), Pacific Summer Water (PSW), Pacific
Winter Water (PWW) and Arctic Intermediate Waters (AIW) including Fram Strait
Branch (FSB) waters and Barents Sea Branch (BSB) water (Carmack et al., 2015;
22
McLaughlin et al., 2011; 2004; Rudels et al., 2012; Woodgate et al., 2005). The DOM
MW distribution in the Arctic Ocean was assessed, for the first time, using
asymmetrical flow field-flow fractionation (AF4) coupled with online diode array ultra-
violet/visible photometer and offline fluorescence detectors.
2.2 Methods
2.2.1 Sampling station
A total of 88 samples, including 20 samples for MW analysis, were collected at 4
sites (CB28b, CB29, CB50 and CB51; Fig. 2.1) in Beaufort Sea in September 2014 as
part of the Joint Ocean Ice Studies cruise. Water samples were collected at depths
ranging from 5 m to 1000 m at each site using Niskin bottles mounted on a rosette
together with a conductivity – temperature – depth profiler and immediately filtered
using pre-combusted (450 ℃ for 4 h) 0.7 µm glass fiber filters (GF/F, Whatman) and
stored in the dark at 4 ℃ in pre-combusted amber glass vials until measurement. The
AF4 based MW distribution was carried out on samples collected at 10 m, sub-
chlorophyll maximum (i.e. 50 - 68 m), salinity 33.1 (i.e. 148 - 161 m) and temperature
maximum (i.e. 414 – 433 m) and 1000 m at each site. High-resolution vertical profiles
of humic-like fluorescent DOM (FDOM), primarily derived from terrestrial sources,
were also acquired using a WET Labs probe (WETStar Ex/Em 370/460 nm) at each
site.
2.2.2 Asymmetrical Flow field flow fractionation
MW distribution was assessed using an asymmetrical flow field-flow fractionation
(AF4) system within 10 days of collection to avoid MW alteration (Guéguen and Cuss,
23
2011). AF4 is carried out using an AF2000 Focus fractionation system (Postnova
Analytics, Landsberg, Germany) which includes two PN1130 HPLC pumps to control
the axial and focus flows, a PN1610 syringe pump to control the crossflow rate, and a
PN7505 degasser to remove gas from the carrier solution prior to introduction to the
pumps (Guéguen and Cuss, 2011). Absorbance scan was recorded from 270 nm to 700
nm, using an on-line diode array ultra-violet/visible photometer (Shimadzu SPD-
M20A). The fractionation system is equipped with a 300 Da polyethersulfone
membrane (Guéguen and Cuss, 2011; Guéguen et al., 2013; Zhou and Guo, 2015). It
should be noted that DOM smaller than 300 Da will not retained on the AF4 membrane
and thus not measured. The pH and conductivity of the NaCl carrier solution matched
that of the Arctic samples (20 mS/cm, pH 7.9) to preserve the native chemical
environment of DOM.
The AF4 system was operated under the following conditions: detector flow rate at
0.35 mL/min, focusing at 0.15 mL/min focus flow rate for 7 min, elution at 2.20
mL/min cross flow rate for 13 min. MQ blank were performed under the same operating
conditions between DOM samples to avoid any cross contamination. In order to get
accurate MW distribution, the AF4 system was calibrated at 254 nm using a log-log
calibration based on four macromolecules laser grade rhodamine B (479 Da),
bromophenol blue (692 Da), cytochrome C (12,400 Da) and lysozyme (14,300 Da)
twice a day, at the beginning and the end of each day (Guéguen and Cuss, 2011). The
simultaneous multi wavelength measurements of the online absorbance detector allow
us to accurately determine the retention of each of the four macromolecules in a single
injection. The retention time at 254 nm was used to estimate the CDOM MW at peak
24
maximum intensity (Guéguen and Cuss, 2011; Lin et al., 2016; Stolpe et al., 2010,
2014). For example, a typical calibration recorded at 254 nm was log (Time) = (0.1634
± 0.0086) * Log (MW) + (0.4831 ± 0.0228) (r2 = 0.999). The smallest and largest
macromolecules (rhodamine-B and lysozyme, respectively) were eluted at 8.680 ±
0.165 (n = 10) and 14.759 ± 0.503 min (n = 10), respectively. It can be noted that the
retention time (i.e. MW) of the Beaufort samples was 4.8% higher (n = 20) at 350 nm
than at 254 nm, confirming the higher MW of aromatic CDOM (Cuss and Guéguen,
2013). A typical chromatogram (Fig. 2.2) showed a very sharp peak representing the
void peak with unfocused and small MW materials and a smooth peak containing the
focused and eluted material.
In terms of repeatability, MW of bromophenol blue sodium salt (Sigma-Aldrich®)
was measured daily (n = 10) and was within 6% of the recommended MW (669 Da).
The relative standard deviation of MW of Suwannee River natural organic matter (n =
5) was 3% (or 85 Da). Similar precision was reported in earlier work (Guéguen and
Cuss, 2011).
2.2.3 Chromophoric dissolved organic matter (CDOM) and Fluorescent DOM (FDOM)
Chromophoric dissolved organic matter (CDOM) samples were allowed to warm
to room temperature before analyzing on a Shimadzu UV 2550 spectrophotometer.
Milli-Q water was measured between each samples to avoid carry-over. A slit width
of 0.5 nm was applied, with an absorbance acquisition interval of 1 nm. The measured
absorbance at wavelength λ was converted to absorption coefficient a (m-1) as
following Eq (1):
25
𝑎𝜆 = 2.303𝐴𝜆/ 𝑙 (1)
where 𝑎𝜆 is the absorption coefficient at wavelength λ , 𝐴𝜆 is the instrumental
absorbance signal, l is the path-length of the optical cell in meters (i.e. 10 cm).
Absorbance coefficient at 254 nm (a254) and 355 nm (a355) were used as indicator for
CDOM concentration in natural samples (Chen et al., 2004; Dainard and Guéguen,
2013; Granskog et al., 2007; Penru et al., 2013).
Three dimensional excitation-emission fluorescence matrices (EEMs) were
generated by measuring fluorescence intensity across excitation wavelengths ranging
from 250 to 500 nm and emission wavelengths ranging from 300 to 600 nm through
successive scans with a Fluoromax-4 Jobin Yvon spectrofluorometer. Excitation and
emission slit widths were set to 5 nm. Blank Milli-Q EEMs were measured daily to
correct background and scatter peak. Before loading samples, a cuvette was rinsed to
avoid cross contamination and scanned at excitation 270 nm and emission 280 – 500
nm for confirmation. All EEMs were normalized to Raman units (R.U.) by dividing the
signal at all Ex/Em pairs by the integrated area under the Raman water peak at
excitation 350 nm using a daily acquired Milli-Q blank EEM (Lawaetz and Stedmon,
2009). Absorption spectra were obtained for all natural seawater samples to make sure
the intensity were within the linear range (A250 < 0.05).
Parallel factor analysis (PARAFAC) was carried out on 88 EEMs (20 AF4 fractions
and 68 bulk) in Matlab using the DOMFluor (Stedmon and Bro, 2008) and DrEEM
toolboxes (Murphy et al., 2013). The model was constrained to nonnegative values and
run for three to ten components. The appropriate number of components was
26
determined by split-half and Tucker congruence coefficient analyses. Percent
fluorescence was calculated as follows:
C1% =𝐶1
(𝐶1+𝐶2+𝐶3) (2)
2.3 Results and Discussion
2.3.1 Hydrographical parameters
Five main water masses were found based on the temperature/salinity (T/Sp)
diagram (Fig. 2.3A): Arctic surface waters (ASW) in the top 50 m (Sp < 30 and -1.5 ℃
< T < -0.5 ℃) were influenced by river runoff (Cory et al., 2007; Pegau, 2002; Walker
et al., 2009), primary production (Fouilland et al., 2007; Hill and Cota, 2005), sea ice
formation and melt (Logvinova et al., 2016; Walker et al., 2009), and photobleaching
(Bélanger et al., 2006); Pacific summer waters (PSW, 30 < Sp < 32) were characterized
by a temperature maximum (T ~ -0.8 ℃; Steele et al., 2004); Pacific winter water
(PWW, Sp ~ 33.1) was characterized by a temperature minimum (T ~ -1.4°C;
McLaughlin et al., 2004) and a terrestrial humic-like maximum (Fig. 2.3B) (Guéguen
et al., 2012b); Deeper layers (> 400 m) were dominated by Atlantic-derived Arctic
intermediate water (AIW). A temperature maximum near 400 m characterized Fram
Strait Branch waters (FSB; Sp ~ 34.8, T ~ 0.6 °C) while lower temperature
characterizes the Barents Sea Branch waters (BSB; Sp ~ 34.8, T ~ 0 °C) (McLaughlin
et al., 2004; Woodgate et al., 2005).
2.3.2 Molecular weight depth distribution
Natural marine CDOM MW ranged from 1.07 kDa to 1.45 kDa (Fig. 2.4),
congruent with previous studies on DOM MW using AF4, high performance size
27
exclusion chromatography and tangential flow filtration (Beckett et al., 1992; Everett
et al., 1999; Guéguen and Cuss, 2011; Huguet et al., 2010; Landry and Tremblay, 2012;
Penru et al., 2013; Stolpe et al., 2010). For example, colloidal DOM MW averaged 1.4
± 0.4 kDa in Northern Gulf of Mexico (Stolpe et al., 2010). Higher MWs (1.62-2.52
kDa) were reported for colloidal DOM in Chukchi Sea (Lin et al., 2016). The average
MW reported in Beaufort Sea agreed with values reported for fulvic acids (Beckett et
al., 1987; Guéguen and Cuss, 2011), confirming that fulvic acids are good proxy for
marine DOM (Tipping et al., 2015).
Average CDOM MW (1.37 ± 0.01 kDa) in ASW was remarkably consistent across
the study area. This contrasts with the halocline complex and deeper layers where
significant MW differences were found (Fig. 2.4). Compared to ASW, the CDOM MW
in PSW was lower, likely due to the influence of sea ice melt waters rich in low MW
DOM (Logvinova et al., 2016). CDOM MW increased again in PWW, which resulted
from the interactions with C-rich shelf bottom sediment (Moore et al., 1983)
remobilizing high MW DOM (Skoog et al., 1996). Below the halocline complex, lower
MW CDOM (~1.21 kDa) was found with the saline Atlantic waters. The BSB MW was
relatively consistent (1.27 ± 0.06 kDa), confirming the CDOM homogeneity in deeper
layer.
2.3.4 Optical Properties
The a254 and a355 values (Fig. 2.5A-B) compared well with previous Arctic studies
(Dainard and Guéguen, 2013; Spencer et al., 2009). Relatively low a254 and a355 values
(2.444 and 0.2014 m-1, respectively) were found in ASW likely due to photobleaching
(Guéguen et al., 2016; Logvinova et al., 2015) and/or sea ice melt (Logvinova et al.,
28
2015) in surface waters. Similar trends were previously observed (Dainard and
Guéguen, 2013; Stedmon et al., 2011). The PSW-PWW waters were characterized by
high CDOM values (Fig. 2.5A-B), congruent with previous studies. As proxy for
molecular size and aromaticity (Guéguen and Cuss, 2011; Helms et al., 2008), S275-295
ranged from 0.018 to 0.033 nm-1 (Fig. 2.5C), congruent with previous Arctic DOM
studies (Fichot et al., 2013). Although S275-295 was not significantly correlated with
AF4-based MW in this study, the increase in S275-295 (i.e. decrease in MW) from PSW
to deeper waters was consistent with the overall vertical decrease in AF4-based MW
(Fig. 2.4).
Three fluorescent components (Fig. 2.6) were PARAFAC-validated and reported
in previous studies (Dainard and Guéguen, 2013; Kowalczuk et al., 2009; McIntyre and
Guéguen, 2013; Singh et al., 2010; Stedmon and Markager, 2005; Walker et al., 2009).
Component C1 displayed a maximum excitation wavelength at 305 nm and emission
wavelength at 410 nm, similar as to peak M (Coble, 1996), representing marine humic-
like component or biological and microbial origin DOM (Shimotori et al., 2012;
Yamashita et al., 2008). This component was widely found in both freshwater and
marine systems (Dainard and Guéguen, 2013; Kowalczuk et al., 2009; McIntyre and
Guéguen, 2013; Singh et al., 2010; Walker et al., 2009). Component C2 showed a
maximum excitation wavelength at < 280 nm and emission wavelength at 330 nm,
which was similar to peak T, traditionally considered as protein-tryptophan-like
component (Coble, 1996). Tryptophan-like component was linked to biological
production (Coble et al., 1998) and commonly found among different aquatic systems
(Dainard and Guéguen, 2013; McIntyre and Guéguen, 2013; Stedmon and Markager,
29
2005). Component C3 had maximum excitation wavelengths at < 270 nm and 365 nm
and a maximum emission wavelength at 465 nm. This component was comparable to
peaks A and C (Coble, 1996). Despite of its terrestrial origin, similar components have
been reported along a large salinity scale (Dainard and Guéguen, 2013; Kowalczuk et
al., 2009; Stedmon and Markager, 2005; Walker et al., 2013).
Total fluorescence intensity (TF=C1+C2+C3) as well as the fluorescent component
(C1, C2 and C3) intensities (Fig. 2.7) were within the ranges reported earlier (Dainard
and Guéguen, 2013; Guéguen et al., 2014; Walker et al., 2009). TF was relatively stable
within each water mass except in ASW likely due to the influence of biological
activities and sea ice melt. Maximum TF and humic-like intensities (C1 and C3) were
associated with PWW (150 m; Fig. 2.7A-B, D), consistent with CDOM distribution
(Fig. 2.5). Similar distributions were found in previous studies (Dainard et al., 2015;
Guéguen et al., 2007, 2012b; Nakayama et al., 2011). Low TF in ASW is likely due to
enhanced photobleaching (Dainard et al., 2015; Guéguen et al., 2016; Logvinova et al.,
2016) associated with a greater influence of DOM-poor sea ice melt waters (Belzile et
al., 2002) in surface waters. The prominent FDOM (and CDOM; Fig. 2.5) maximum
at PWW was due to humic-rich materials brought by injection of cold saline shelf
waters (Guéguen et al., 2007; Moore et al., 1983; Woodgate et al., 2005). No significant
difference in humic-like fluorescence intensities was found in FSB and BSB between
sites (0.0137 ± 0.0014 r.u. for C1; 0.0090 ± 0.0010 r.u. for C3), suggesting
homogeneous humic-like intensity in deeper layers. Protein-like C2 intensity maximum
(Fig. 2.7C) was associated with the highly productive (Arrigo et al., 2008; Fouilland et
al., 2007; Hill and Cota, 2005) ASW, confirming the biological origin of protein-like
30
component. Lower C2 intensities were associated with the PSW-PWW complex and
Atlantic-derived waters. Homogeneous distribution (p > 0.05) was observed in AIW.
2.3.5 Relationship between fluorescence properties and MW
Despite a 40% difference in TF (0.042 vs 0.060 r.u., p < 0.05; Fig. 2.8), ASW and
PWW showed similar average CDOM MW values (1.37 vs 1.38 kDa) (Fig. 2.8). PWW
was largely associated with the increase in aromatic CDOM (low S275-295; Fig. 2.5C)
and humic-like FDOM (Fig. 2.7) due to sediment interactions (Guéguen et al., 2007;
Moore et al., 1983). Although FDOM concentration and composition did not
significantly influence MW in ASW and PWW, the significant decrease in MW from
PWW and AIW was associated with a dramatic decrease in humic-like intensities (p <
0.05). Similarly, PSW and BSB displayed comparable mean MW values (1.27 kDa in
both water masses) but a 39 % reduction (p < 0.05) in TF in BSB. Together these results
showed that a change in MW does not necessarily mean a change in TF. This contrasts
with previous studies where higher TF, and particularly higher humic-like intensities,
was generally associated with higher MW material (Cuss and Guéguen, 2013; Huguet
et al., 2010). Because the PARAFAC-validated components cannot be attributed to
pure compounds but to a group of compounds sharing similar fluorescence properties,
it is possible that a change in the concentration and/or nature of fluorescing compounds
affects the fluorescence efficiency and therefore FDOM signal without changing MW.
Furthermore, Stolpe et al. (2014) showed that protein-like fluorescence (275/340 nm)
in marine waters had a size distribution that was very different from the size distribution
of CDOM measured at 254 nm. Further studies should be carried out to assess the
influence of absorbing and fluorescing DOM composition on MW.
31
In terms of fluorescence composition in bulk samples (Fig. 2.9A-C), humic-like C1%
and C3% decreased with increasing MW (r2 = 0.38 and 0.40, respectively). This
contrasts with protein-like C2% which was more abundant at higher MW (r2 = 0.41;
Fig. 2.9D). The change in size distribution between protein- and humic-like FDOM
was also found in the northern Gulf of Mexico (Stolpe et al., 2014) where humic-like
components dominated small size marine DOM while protein-like DOM was enriched
in larger MW DOM. Similarly, increase in protein-like component was observed with
decreasing S275-295 (i.e. increase in MW) in North Pacific seawater studies (Helms et al.,
2013). Despite of variation in S275-295, humic-like components were found to be
dominant (> 50%) throughout the study area (Dainard and Guéguen, 2013).
2.4 Conclusions
For the first time, asymmetrical flow field-flow fractionation system was applied in
the Arctic Ocean to assess CDOM MW distribution in relation with optical properties
and water masses. The CDOM MW ranged from 1.07 to 1.45 kDa, consistent with
earlier works. The vertical distribution of CDOM MW and optical properties showed
some water-mass related distribution pattern. DOM in Arctic surface waters displayed
similarity in MW and fluorescence intensity across the study area. PWW formed in
from ice formation and freshwater injection, showed higher MW CDOM associated
with higher fluorescence intensity. Protein-like fluorescence became more dominant as
MW increased, but humic-like components remained dominant throughout the water
column.
32
Acknowledgments
This work was supported by the Northern Scientific Training Program, Canada
Research Chair Program (CG) and National Sciences and Engineering Research
Council of Canada (CG). The field program on the Louis S. St-Laurent was funded by
the U.S. National Science Foundation’s Beaufort Gyre Observation System and the
Department of Fisheries and Oceans Canada. We gratefully acknowledge the support
of C. Wylie, S. Zimmerman and W. Williams for field assistance in the JOIS cruise.
We thank the captain and crew of the CCGS Louis S. Saint-Laurent and the other
participants of the cruise.
33
Reference
Amon, R. M. W., Benner, R. 1994. Rapid cycling of high-molecular-weight dissolved
organic matter in the ocean, Nature, 369(6481), 549–552,
doi:10.1038/369549a0.
Amon, R. M. W. and Benner, R. 1996. Bacterial utilization of different size classes of
dissolved organic matter, Limnol. Oceanogr., 41(1), 41–51,
doi:10.4319/lo.1996.41.1.0041.
Arrigo, K. R., van Dijken, G., Pabi, S. 2008. Impact of a shrinking Arctic ice cover on
marine primary production, Geophys. Res. Lett., 35(19),
doi:10.1029/2008GL035028.
Baylor, E. R., Sutcliffe Jr, W. H. 1963. Dissolved Organic Matter in Seawater as a
source of Particulate Food, Limnol. Oceanogr., 8, 369–371.
Beckett, R., Jue, Z., Giddings, J. 1987 Determination of molecular weight
distributions of fulvic and humic acids using flow field-flow fractionation,
Environ. Sci. Technol., 21(3), 289–295, doi:10.1021/es00157a010.
Beckett, R., Wood, F. J., Dixon, D. R.1992. Size and chemical characterization of
pulp and paper mill effluents by flow field‐flow fractionation and resin
adsorption techniques, Environ. Technol., 13(12), 1129–1140,
doi:10.1080/09593339209385252.
Bélanger, S., Xie, H., Krotkov, N., Larouche, P., Vincent, W. F., Babin, M.2006.
Photomineralization of terrigenous dissolved organic matter in arctic coastal
waters from 1979 to 2003: Interannual variability and implications of climate
change, Global Biogeochem. Cycles, 20(4), 1–13, doi:10.1029/2006GB02708.
Belzile, C., Gibson, J. A. E., Vincent, W. F., 2002. Colored dissolved organic matter
and dissolved organic carbon exclusion from lake ice: Implications for irradiance
transmission and carbon cycling, Limnol. Oceanogr., 47(5), 1283–1293,
doi:10.4319/lo.2002.47.5.1283.
Benner, R., Pakulski, J. D., McCarthy, M., Hedges, J. I., Hatcher, P.G., 1992. Bulk
chemical characteristics of dissolved organic matter in the ocean, Science,
255(5051), 1561–1564, doi:10.1126/science.255.5051.1561.
Boehme, J., Wells, M. 2006 Fluorescence variability of marine and terrestrial
colloids: Examining size fractions of chromophoric dissolved organic matter in
the Damariscotta River estuary, Mar. Chem., 101(1–2), 95–103,
doi:10.1016/j.marchem.2006.02.001.
Chen, Z., Li, Y., Pan, J. 2004. Distributions of colored dissolved organic matter and
dissolved organic carbon in the Pearl River Estuary, China, Cont. Shelf Res.,
24(16), 1845–1856, doi:10.1016/j.csr.2004.06.011.
Coble, P. G. 1996. Characterization of marine and terrestrial DOM in seawater using
excitation-emission matrix spectroscopy, Mar. Chem., 51(4), 325–346,
34
doi:10.1016/0304-4203(95)00062-3.
Coble, P. G., Del Castillo, C. E., Avril, B. 1998. Distribution and optical properties of
CDOM in the Arabian Sea during the 1995 Southwest Monsoon, Deep. Res. Part
II, 45(10–11), 2195–2223, doi:10.1016/S0967-0645(98)00068-X.
Cole, J. J., Carpenter, S. R., Pace, M. L., Van De Bogert, M. C., Kitchell, J. L.,
Hodgson, J. R. 2006. Differential support of lake food webs by three types of
terrestrial organic carbon, Ecol. Lett., 9(5), 558–568, doi:10.1111/j.1461-
0248.2006.00898.x.
Cory, R. M., McKnight, D. M., Chin, Y. P., Miller, P., Jaros, C. L. 2007. Chemical
characteristics of fulvic acids from Arctic surface waters: Microbial
contributions and photochemical transformations, J. Geophys. Res.
Biogeosciences, 112(4), doi:10.1029/2006JG000343, 2007.
Cuss, C.W., Guéguen, C. 2013. Distinguishing dissolved organic matter at its origin:
Size and optical properties of leaf-litter leachates. Chemosphere 92, 1483-1489.
Dainard, P. G., Guéguen, C. 2015. Distribution of PARAFAC modeled CDOM
components in the North Pacific Ocean, Bering, Chukchi and Beaufort Seas,
Mar. Chem., 157, 216–223, doi:10.1016/j.marchem.2013.10.007, 2013.
Dainard, P. G., Guéguen, C., McDonald, N. and Williams, W. J.: Photobleaching of
fluorescent dissolved organic matter in Beaufort Sea and North Atlantic
Subtropical Gyre, Mar. Chem., 177, 630–637,
doi:10.1016/j.marchem.2015.10.004.
Everett, C. R., Chin, Y. P., Aiken, G. R., 1999. High-pressure size exclusion
chromatography analysis of dissolved organic matter isolated by tangential-flow
ultrafiltration, Limnol. Oceanogr., 44(5), 1316–1322,
doi:10.4319/lo.1999.44.5.1316.
Fichot, C. G., Benner, R. 2012 The spectral slope coefficient of chromophoric
dissolved organic matter (S275-295) as a tracer of terrigenous dissolved organic
carbon in river-influenced ocean margins, Limnol. Oceanogr., 57(5), 1453–1466,
doi:10.4319/lo.2012.57.5.1453.
Fichot, C. G., Kaiser, K., Hooker, S. B., Amon, R. M. W., Babin, M., Bélanger, S.,
Walker, S. A, Benner, R., 2013. Pan-Arctic distributions of continental runoff in
the Arctic Ocean., Sci. Rep., 3, 1053, doi:10.1038/srep01053.
Fouilland, E., Gosselin, M., Rivkin, R. B., Vasseur, C., Mostajir, B., 2007. Nitrogen
uptake by heterotrophic bacteria and phytoplankton in Arctic surface waters, J.
Plankton Res., 29(4), 369–376, doi:10.1093/plankt/fbm022.
Frey, K., McClelland, J. 2009. Impacts of permafrost degradation on arctic river
biogeochemistry, Hydrol. Process. 23, 169-182.
Granskog, M. A., Macdonald, R. W., Mundy, C. J., Barber, D. G. 2007. Distribution,
characteristics and potential impacts of chromophoric dissolved organic matter
(CDOM) in Hudson Strait and Hudson Bay, Canada, Cont. Shelf Res., 27(15),
35
2032–2050, doi:10.1016/j.csr.2007.05.001.
Guéguen, C., Cuss, C. W. 2011 Characterization of aquatic dissolved organic matter
by asymmetrical flow field-flow fractionation coupled to UV-Visible diode array
and excitation emission matrix fluorescence, J. Chromatogr. A, 1218(27), 4188–
4198, doi:10.1016/j.chroma.2010.12.038.
Guéguen, C., Cuss, C.W., Chen, W. 2013. Asymmetrical flow field-flow fractionation
and excitation-emission matrix spectroscopy combined with parallel factor
analyses of riverine dissolved organic matter isolated by tangential flow
ultrafiltration. Int. J. Environm. Anal. Chem.
doi:10.1080/03067319.2013.764415.
Guéguen, C., Guo, L., Yamamoto-Kawai, M., Tanaka, N. 2007. Colored dissolved
organic matter dynamics across the shelf-basin interface in the western Arctic
Ocean, J. Geophys. Res. - Oceans, 112, C05038, doi:10.1029/2006JC003584,.
Guéguen, C., Granskog, M. A., McCullough, G., Barber, D. G., 2011.
Characterisation of colored dissolved organic matter in Hudson Bay and Hudson
strait using parallel factor analysis, J. Mar. Syst., 88(3), 423–433,
doi:10.1016/j.jmarsys.2010.12.001.
Guéguen, C., Burns, D. C., McDonald, A., Ring, B. 2012a. Structural and optical
characterization of dissolved organic matter from the lower Athabasca River,
Canada, Chemosphere, 87(8), 932–937,
doi:10.1016/j.chemosphere.2012.01.047.
Guéguen, C., McLaughlin, F. A., Carmack, E. C., Itoh, M., Narita, H., Nishino, S.
2012b. The nature of colored dissolved organic matter in the southern Canada
Basin and East Siberian Sea, Deep. Res. Part II, 81–84, 102–113,
doi:10.1016/j.dsr2.2011.05.004, 2012b.
Guéguen, C., Cuss, C. W., Cassels, C. J., Carmack, E. C. 2014 Absorption and
fluorescence of dissolved organic matter in the waters of the Canadian Artic
Archipelago, Baffin Bay, and the Labrador Sea, J. Geophys. Res. Ocean.,
119(3), 2034–2047, doi:10.1002/2013JC009173.
Guéguen, C., Mokhtar, M., Perroud, A., McCullough, G., Papakyriakou, T., 2016.
Mixing and photoreactivity of dissolved organic matter in the Nelson/Hayes
estuarine system (Hudson Bay, Canada), J. Mar. Syst., 161, 42–48,
doi:10.1016/j.jmarsys.2016.05.005.
Guo, L., Santschi, P. H., 2007 Ultrafiltration and its Applications to Sampling and
Characterisation of Aquatic Colloids, in Environmental Colloids and Particles:
Behaviour, Separation and Characterisation, pp. 159–221.
Guo, W., Yang, L., Hong, H., Stedmon, C. A., Wang, F., Xu, J., Xie, Y. 2011.
Assessing the dynamics of chromophoric dissolved organic matter in a
subtropical estuary using parallel factor analysis, Mar. Chem., 124(1–4), 125–
133, doi:10.1016/j.marchem.2011.01.003.
36
Helms, J. R., Stubbins, A., Ritchie, J. D., Minor, E. C., Kieber, D. J., Mopper, K.
2008. Absorption spectral slopes and slope ratios as indicators of molecular
weight, source, and photobleaching of chromophoric dissolved organic matter,
Limonology Oceanogr., 53(3), 955–969, doi:10.4319/lo.2008.53.3.0955.
Helms, J. R., Stubbins, A., Perdue, E. M., Green, N. W., Chen, H., Mopper, K. 2013.
Photochemical bleaching of oceanic dissolved organic matter and its effect on
absorption spectral slope and fluorescence, Mar. Chem., 155, 81–91,
doi:10.1016/j.marchem.2013.05.015.
Hill, V., Cota, G., 2005. Spatial patterns of primary production on the shelf, slope and
basin of the Western Arctic in 2002, Deep Sea Res II, 52(24–26), 3344–3354.
Hirose, K. 2007. Metal-organic matter interaction: Ecological roles of ligands in
oceanic DOM, Appl. Geochemistry, 22(8 SPEC. ISS.), 1636–1645,
doi:10.1016/j.apgeochem.
Huguet, A., Vacher, L., Saubusse, S., Etcheber, H., Abril, G., Relexans, S., Ibalot, F.,
Parlanti, E. 2010. New insights into the size distribution of fluorescent dissolved
organic matter in estuarine waters, Org. Geochem., 41(6), 595–610,
doi:10.1016/j.orggeochem.2010.02.006.
Jiao, N., Herndl, G. J., Hansell, D. A., Benner, R., Kattner, G., Wilhelm, S. W.,
Kirchman, D. L., Weinbauer, M. G., Luo, T., Chen, F., Azam, F. 2010 Microbial
production of recalcitrant dissolved organic matter: long-term carbon storage in
the global ocean., Nat. Rev. Microbiol., 8(8), 593–9, doi:10.1038/nrmicro2386.
Kowalczuk, P., Durako, M. J., Young, H., Kahn, A. E., Cooper, W. J., Gonsior, M.
2009. Characterization of dissolved organic matter fluorescence in the South
Atlantic Bight with use of PARAFAC model: Interannual variability, Mar.
Chem., 113(3–4), 182–196, doi:10.1016/j.marchem.2009.01.015.
Landry, C., Tremblay, L. 2012. Compositional differences between size classes of
dissolved organic matter from freshwater and seawater revealed by an HPLC-
FTIR system, Environ. Sci. Technol., 46(3), 1700–1707,
doi:10.1021/es203711v.
Lawaetz, A. J., Stedmon, C. A. 2009. Fluorescence intensity calibration using the
Raman scatter peak of water, Appl. Spectrosc., 63(8), 936–940,
doi:10.1366/000370209788964548.
Lin, H., Chen, M., Zeng, J., Li, Q., Jia, R., Sun, X., Zheng, M., Qiu, Y. 2016. Size
characteristics of chromophoric dissolved organic matter in the Chukchi Sea, J.
Geophys. Res. Ocean., doi:10.1002/2016JC011771.
Logvinova, C. L., Frey, K. E., Mann, P. J., Stubbins, A., Spencer, R. G. M. 2015.
Assessing the potential impacts of declining Arctic sea ice cover on the
photochemical degradation of dissolved organic matter in the Chukchi and
Beaufort Seas, J. Geophys. Res. G Biogeosciences, 120(11), 2326–2344,
doi:10.1002/2015JG003052.Logvinova, C. L., Frey, K. E., Cooper, L. W. 2016.
The Potential Role of Sea Ice Melt in the Distribution of Chromophoric
37
Dissolved Organic Matter in the Chukchi and Beaufort Seas, Deep Sea Res. Part
II Top. Stud. Oceanogr., 130, 28–42, doi:10.1016/j.dsr2.2016.04.017.
McIntyre, A. M., Guéguen, C.2013. Binding interactions of algal-derived dissolved
organic matter with metal ions, Chemosphere, 90(2), 620–626,
doi:10.1016/j.chemosphere.2012.08.057.
McLaughlin, F. A., Carmack, E. C., Macdonald, R. W., Melling, H., Swift, J. H.,
Wheeler, P. A., Sherr, B. F., Sherr, E. B. 2004. The joint roles of Pacific and
Atlantic-origin waters in the Canada Basin, 1997-1998, Deep. Res. Part I
Oceanogr. Res. Pap., 51(1), 107–128, doi:10.1016/j.dsr.2003.09.010.
Midorikawa, T., Tanoue, E. 1998. Molecular masses and chromophoric properties of
dissolved organic ligands for copper(II) in oceanic water, Mar. Chem., 62(3–4),
219–239, doi:10.1016/S0304-4203(98)00040-1.
Moore, R. M., Lowings, M. G., Tan, F. C. 1983. Geochemical Profiles in the Central
Arctic Ocean: Their Relation to Freezing and Shallow Circulation, J. Geophys.
Res., 88(c4), 2667–2674, doi:10.1029/JC088iC04p02667,.
Murphy, K. R., Stedmon, C. A., Waite, T. D., Ruiz, G. M. 2008. Distinguishing
between terrestrial and autochthonous organic matter sources in marine
environments using fluorescence spectroscopy, Mar. Chem., 108(1–2), 40–58,
doi:10.1016/j.marchem.2007.10.003.
Murphy, K. R., Stedmon, C. A., Graeber, D., Bro, R. 2013. Fluorescence
spectroscopy and multi-way techniques. PARAFAC, Anal. Methods, 5(23),
6557, doi:10.1039/c3ay41160e.
Nakayama, Y., Fujita, S., Kuma, K., Shimada, K. 2011. Iron and humic-type
fluorescent dissolved organic matter in the Chukchi Sea and Canada Basin of the
western Arctic Ocean, J. Geophys. Res., 116, 16, doi:10.1029/2010jc006779.
Nelson, N. B., Siegel, D. A., Carlson, C. A., Swan, C. M. 2010. Tracing global
biogeochemical cycles and meridional overturning circulation using
chromophoric dissolved organic matter, Geophys. Res. Lett., 37(3), n/a-n/a,
doi:10.1029/2009GL042325.
Overland, J., Wang, M. 2013 When will the summer Arctic be nearly sea ice free?,
Geophys. Res. Lett., 40, 2097-2101, 10.1002/grl.50316
Pegau, W. S. , 2002. Inherent optical properties of the central Arctic surface waters, J.
Geophys. Res., 107(C10), 1–7, doi:10.1029/2000JC000382.
Penru, Y., Simon, F. X., Guastalli, A. R., Esplugas, S., Llorens, J., Baig, S., 2013.
Characterization of natural organic matter from Mediterranean coastal seawater,
J. Wat. Supply Res. Technol., 62(1), 42–51, doi:10.2166/aqua.2013.U3.
Peterson, B., Holmes, R., McClelland, J. 2002. Increasing river discharge to the
Arctic Ocean, Science, 298, 5601, 2171-2173.
De Schamphelaere, K.A.C., Vasconcelos, F. M., Tack, F. M. G., Allen, H. E.,
38
Janssen, C. R. 2004. Effect of dissolved organic matter source on acute copper
toxicity to Daphnia magna., Environ. Toxicol. Chem., 23(5), 1248–1255,
doi:10.1897/03-184.
Schuur, E., Vogel, J., Crummer, K., Lee, H. 2009. The effect of permafrost thaw on
old carbon release and net carbon exchange from tundra, Nature 459, 556-559.
Shi, Y. X., Mangal, V., Guéguen, C. 2016. Influence of dissolved organic matter on
dissolved vanadium speciation in the Churchill River estuary (Manitoba,
Canada), Chemosphere, 154, 367–374, doi:10.1016/j.chemosphere.2016.03.124,
2016.
Shimada, K., Kamoshida, T., Itoh, M., Nishino, S., Carmack, E., McLaughlin, F.,
Zimmermann, S., Proshutinsky, A. 2006. Pacific Ocean inflow: Influence on
catastrophic reduction of sea ice cover in the Arctic Ocean, Geophys. Res. Lett.,
33(8), 3–6, doi:10.1029/2005GL025624.
Shimotori, K., Watanabe, K., Hama, T. 2012. Fluorescence characteristics of humic-
like fluorescent dissolved organic matter produced by various taxa of marine
bacteria, Aquat. Microb. Ecol., 65(3), 249–260, doi:10.3354/ame01552.
Singh, S., D’Sa, E. J., Swenson, E. M., 2010. Chromophoric dissolved organic matter
(CDOM) variability in Barataria Basin using excitation-emission matrix (EEM)
fluorescence and parallel factor analysis (PARAFAC), Sci. Total Environ.,
408(16), 3211–3222, doi:10.1016/j.scitotenv.2010.03.044.
Skoog, A., Hall, P. O. J., Hulth, S., Paxéus, N., Rutgers Van Der Loeff, M.,
Westerlund, S. 1996. Early diagenetic production and sediment-water exchange
of fluorescent dissolved organic matter in the coastal environment, Geochim.
Cosmochim. Acta, 60(19), 3619–3629, doi:10.1016/0016-7037(96)83275-3.
Spencer, R. G. M., Aiken, G. R., Butler, K. D., Dornblaser, M. M., Striegl, R. G.,
Hernes, P. J. 2009. Utilizing chromophoric dissolved organic matter
measurements to derive export and reactivity of dissolved organic carbon
exported to the Arctic Ocean: A case study of the Yukon River, Alaska,
Geophys. Res. Lett., 36(6), doi:10.1029/2008GL036831.
Stedmon, C. A., Bro, R. 2008. Characterizing dissolved organic matter fluorescence
with parallel factor analysis: a tutorial, Limnol. Oceanogr. Methods, 6, 572–579,
doi:10.4319/lom.2008.6.572.
Stedmon, C. A., Markager, S. 2005. Resolving the variability of dissolved organic
matter fluorescence in a temperate estuary and its catchment using PARAFAC
analysis, Limnol. Oceanogr., 50(2), 686–697, doi:10.4319/lo.2005.50.2.0686.
Stedmon, C. A., Markager, S., Bro, R. 2003. Tracing dissolved organic matter in
aquatic environments using a new approach to fluorescence spectroscopy, Mar.
Chem., 82(3–4), 239–254, doi:10.1016/S0304-4203(03)00072-0.
Stedmon, C. A., Amon, R. M. W., Rinehart, A. J., Walker, S. A. 2011. The supply
and characteristics of colored dissolved organic matter (CDOM) in the Arctic
39
Ocean: Pan Arctic trends and differences, Mar. Chem., 124(1–4), 108–118,
doi:10.1016/j.marchem.2010.12.007.
Steele, M., Morison, J., Ermold, W., Rigor, I., Ortmeyer, M. 2004. Circulation of
summer Pacific halocline water in the Arctic Ocean, J. Geophys. Res., 109(C2),
1–18, doi:10.1029/2003JC002009.
Stolpe, B., Guo, L., Shiller, A. M., Hassellöv, M. 2010. Size and composition of
colloidal organic matter and trace elements in the Mississippi River, Pearl River
and the northern Gulf of Mexico, as characterized by flow field-flow
fractionation, Mar. Chem., 118(3–4), 119–128,
doi:10.1016/j.marchem.2009.11.007.
Stolpe, B., Zhou, Z., Guo, L., Shiller, A. M. 2014. Colloidal size distribution of
humic- and protein-like fluorescent organic matter in the northern Gulf of
Mexico, Mar. Chem., 164, 25–37, doi:10.1016/j.marchem.2014.05.007.
Sun, L., Perdue, E. M., Meyer, J. L., Weis, J. 1997. Use of elemental composition to
predict bioavailability of dissolved organic matter in a Georgia river, Limnol.
Oceanogr., 42(4), 714–721, doi:10.4319/lo.1997.42.4.0714.
Tipping, E., Lofts, S., Stockdale, A. 2015. Metal speciation from stream to open
ocean: modelling v. measurement, Environ. Chem., doi:10.1071/EN15111.
Tulonen, T., Salonen, K., Arvola, L. 1992. Effects of different molecular weight
fractions of dissolved organic matter on the growth of bacteria, algae and
protozoa from a highly humic lake, Hydrobiologia, 229(1), 239–252,
doi:10.1007/BF00007003.
Walker, S. A., Amon, R. M. W., Stedmon, C. A., Duan, S., Louchouarn, P. , 2009.
The use of PARAFAC modeling to trace terrestrial dissolved organic matter and
fingerprint water masses in coastal Canadian Arctic surface waters, J. Geophys.
Res. Biogeosciences, 114(4), doi:10.1029/2009JG000990.
Walker, S. A., Amon, R. M. W., Stedmon, C. A., 2013. Variations in high-latitude
riverine fluorescent dissolved organic matter: A comparison of large Arctic
rivers, J. Geophys. Res. Biogeosci., 118(4), 1689–1702,
doi:10.1002/2013JG002320.
Woodgate, R. A., Aagaard, K., Swift, J. H., Falkner, K. K., Smethie, W. M. 2005.
Pacific ventilation of the Arctic Ocean’s lower halocline by upwelling and
diapycnal mixing over the continental margin, Geophys. Res. Lett., 32(18), 1–5,
doi:10.1029/2005GL023999.
Wu, F., Tanoue, E. 2001. Molecular mass distribution and fluorescence
characteristics of dissolved organic ligands for copper(II) in Lake Biwa, Japan,
Org. Geochem., 32(1), 11–20, doi:10.1016/s0146-6380(00)00155-8.
Wu, F., Evans, D., Dillon, P., Schiff, S. 2004. Molecular size distribution
characteristics of the metal-DOM complexes in stream waters by high-
performance size-exclusion chromatography (HPSEC) and high-resolution
40
inductively coupled plasma mass spectrometry (ICP-MS), J. Anal. At.
Spectrom., 19(8), 979, doi:10.1039/b402819h.
Yamashita, Y., Jaffé, R.2008. Characterizing the interactions between trace metals
and dissolved organic matter using excitation-emission matrix and parallel factor
analysis, Environ. Sci. Technol., 42(19), 7374–7379, doi:10.1021/es801357h.
Yamashita, Y., Jaffé, R., Maie, N., Tanoue, E. 2008. Assessing the dynamics of
dissolved organic matter (DOM) in coastal environments by excitation emission
matrix fluorescence and parallel factor analysis (EEM-PARAFAC), Limnol.
Oceanogr., 53(5), 1900–1908, doi:10.4319/lo.2008.53.5.1900.
41
Figures and tables
Figure 2.1 Sampling locations in Beaufort Sea, Canada Basin
42
Figure 2.2 AF4 fractograms of CB29 (400m depth; black) and CB28b (1000m depth; gray)
43
Figure 2.3 A) Potential temperature and B) FDOM as a function of salinity (Sp) at the four study sites (Figure 2.1). ASW -
Arctic surface waters, PSW – Pacific summer water, PWW – Pacific winter water, FSB – Fram Strait Branch water, BSB –
Barents Sea Branch water
44
Figure 2.4 MW depth profiles in Beaufort Sea
45
Figure 2.5 Depth distribution of A) a254, (B) a355, and (C) S275-295
46
Figure 2.6 Individual components identified by PARAFAC (A- marine humic-like C1, B- protein-like C2 and C- terrestrial
humic-like C3)
47
Figure 2.7 Depth distribution of A) Total Fluorescence Intensity (TF), B) marine humic-like C1, C) protein-like C2 and D)
terrestrial humic-like C3
48
Figure 2.8 Change in TF vs CDOM MW
49
Figure 2.9 Correlation between MW and fluorescence components (A) C1; (B) C2; (C) C3; (D) Change in fluorescence
abundance with increasing DOM MW
50
Chapter 3. Determination of thiols, humic substances and
fluorescent dissolved organic matter during the 2015
Canadian Arctic GEOTRACES cruises
Zhiyuan Gao1, Céline Guéguen2,*
1 Environmental and Life Sciences Graduate program, Trent University, ON, Canada
2 Chemistry Department and Trent School of the Environment, Trent University, ON,
Canada
*Corresponding author: Tel: +1 (705) 748 1011; Fax: +1 (705) 748 1625; email:
celinegueguen@trentu.ca
51
Abstract
Distribution of thiols, humic substances (HS) and fluorescent dissolved organic matter
(FDOM) were determined in seawater samples from Canada Basin and Canadian Arctic
Archipelago (CAA) by differential pulse cathodic stripping voltammetry (DP-CSV)
and excitation-emission matrix (EEM). The simultaneous determination of thiols and
HS by DP-CSV featured high repeatability (RSD, 0.64 % for GSH, 0.60 % for HS),
high recovery (~ 100% for both) and low LOD (1.12 nM for GSH, 21.19 µg C/L for
HS). The thiol concentration ranged from 8 to 78 nM (glutathione equivalent) and HS
ranged from 31 to 222 µg C/L, congruent with ranges reported in CSV-based seawater
studies. Three humic-like (C1-C3) and one protein-like (C4) components identified and
validated using parallel factor analysis (PARAFAC) have been reported in previous
ocean studies. The distributions of voltammetry-based HS and humic-like components
(C1 and C2) along CAA were similar, whereas thiol and protein-like component C4
were closely related in the top 100 m depth. Maximum thiol concentrations were
associated with chlorophyll-a maximum, confirming the biogenic origin of thiols. The
distribution and concentrations of thiols, HS and FDOM varied between four distinct
water masses (i.e. surface waters, Arctic outflow waters, Arctic intermediate waters and
North Atlantic deep waters) with the lowest levels associated with the surface waters,
likely due to photobleaching and sea ice melt dilution. The concentrations in HS and
FDOM in the Arctic outflow waters decreased from western to eastern CAA, reflecting
the influence of DOM-rich Pacific derived waters.
Keywords
DOM, Cathodic stripping voltammetry, Thiols, Humic substances, PARAFAC-EEMs
52
3.1 Introduction
Dissolved organic matter (DOM) is one of the major carbon groups in the ocean
system, contributing to energy transport and food supplement. DOM plays a significant
role in regulating the speciation and distribution of trace metals, such as Cu, Fe and Hg,
affecting their bioavailability and toxicity (Hirose, 2007; Stockdale et al., 2011; Wen
et al., 1999). For example, the photolysis of iron-siderophore complexes increases the
availability of Fe uptake by planktonic assemblages (Barbeau et al., 2001). DOM was
reported to be an important complexing agent for Hg (Benoit et al., 2001) whereas
terrestrial humic substances (HS) were responsible for reduction of copper toxicity in
the seawater (Kogut and Voelker, 2001).
Low molecular weight sulphur-containing DOM (i.e. thiols) is one of the most
important organic ligands for metal binding (Benoit et al., 2001; Laglera and van den
Berg, 2003), with thiourea, cysteine and glutathione (GSH) being the most common
thiol groups in marine environment (Ahner et al., 2002; al-Farawati and Van Den Berg,
2001; Dupont et al., 2006; Kading, 2013; Tang et al., 2000). Algal culture studies have
shown that thiols are biologically produced as a response to the increase of free metal
ion concentrations in aquatic systems (Ahner et al., 2002; Dupont and Ahner, 2005;
Leal et al., 1999). High performance liquid chromatography (HPLC) and cathodic
stripping voltammetry (CSV) have been applied in detecting thiol abundance in ocean
studies (Kading, 2013; Laglera and van den Berg, 2003; Pernet-Coudrier et al., 2013).
Although HPLC analysis featured high resolution in thiol determination, time-
consuming thiol derivatization is required (Kading, 2013; Swarr et al., 2016; Tang et
al., 2003). On the other hand, the CSV technique allows the determination of GSH
53
(Kawakami et al., 2006) without extensive sample preparation (Marie et al., 2015;
Pernet-Coudrier et al., 2013). The limit of detection (LOD) of CSV-based thiol
determination (1 nM; Pernet-Coudrier et al., 2013) is compatible with the natural range
of seawater thiol compounds (10 to 410 nM; Le Gall and van den Berg, 1993; Marie et
al., 2015; Pernet-Coudrier et al., 2013).
Humic substances (HS), consisting of fulvic and humic acids (Coble, 1996; Harvey
et al., 1983; Rashid, 2012), are considered as the refractory fraction of DOM and
comprise 10-50 % of total organic carbon (Harvey et al., 1983). The two main sources
of marine HS in the marine domain are: allochthonous part of terrestrial origin
(Guéguen et al., 2005; Meyers-Schulte and Hedges, 1986; Opsahl et al., 1999; Opsahl
and Benner, 1997) and autochthonous part produced in-situ through photo-oxidation
and biological processes (Harvey et al., 1984; Kieber et al., 1997; Shimotori et al., 2012;
Yamashita and Tanoue, 2008). HS can be characterized by its fluorescence property as
humic-like components (Coble, 1996) and detected through electrochemical techniques
like CSV (Pernet-Coudrier et al., 2013; Whitby and Van den Berg, 2014). However,
the comparison between humic-like components and CSV-based HS remained to be
shown.
Regarding metal binding capability, documenting the concentration and
distribution of their main ligands (i.e. thiols and HS) will provide valuable insights into
distribution of DOM and associated trace metals. For the first time, differential pulse
cathodic stripping voltammetry (DP-CSV) was applied on samples collected in the
Canada Basin and Canadian Arctic Archipelago as part of the 2015 Canada Arctic
54
GEOTRACES cruises. Comparison between CSV-based HS and humic-like
components will provide novel insights into DOM distribution in the Arctic Ocean.
3.2 Methods
3.2.1 Sampling
Eleven sites (Fig 3.1) in the Canadian Arctic Archipelago (9 sites) and Canada
Basin (2 sites) were sampled in July and August, 2015 (leg 2) and September, 2015
(leg 3b) as part of the 2015 Canadian Arctic GEOTRACES cruise program. Water
samples were collected using Niskin bottles mounted on a trace metal rosette together
with a conductivity – temperature – depth profiler (Fig 3.2A). Samples were
immediately filtered using pre-combusted (450 ℃ for 4 h) glass fiber filters (GF/F,
Whatman) and stored in the dark at 4 ℃ in pre-combusted amber glass vials for ~2
months. Duplicate samples for voltammetry analysis were acidified to pH 1.95 with 50
µL HCl immediately after filtration and analyzed within the recommended preservation
time (i.e. 2 months; Pernet-Coudrier et al., 2013).
3.2.2 Reagents
Milli-Q water (Millipore, Fisher scientific) was used for rinsing glass cells and
fluorescence cuvette, and preparation of stock and working solutions. HCl (CALEDON)
and NaOH (J.T.Baker) were used to acidify and adjust pH during voltammetric analysis.
The choice of standards is an important factor affecting the CSV-based thiol
concentration. Several thiol groups have been previously used as standards, resulting
in huge difference in the reported concentrations. For example, 50 nM of GSH-
equivalent thiol compounds was found in ocean studies (Le Gall and van den Berg,
55
1993), while a range of 0.7 – 3.6 nM of thiourea-equivalents thiol compounds was
found in English Channel and North Sea studies (al-Farawati and Van Den Berg, 2001).
In this study, glutathione (GSH) was used as a standard for thiol groups (Pernet-
Coudrier et al., 2013). GSH stock solution (oxidized, Sigma-Aldrich) was prepared in
Milli-Q water and stored in dark at 4 ℃ and diluted daily to 20 µM; the pH was adjusted
to 1.95 by adding 2 % HCl. Suwannee river fulvic acid (SRFA) (1S101F; International
Humic Substances Society) was selected as a standard to quantify HS in voltammetry
analysis (Pernet-Coudrier et al., 2013). SRFA stock solution (251 mg C/L) was
prepared in NaOH (~ 0.01 M) for better dissolution and diluted to 150 mg C/L, adjusted
to pH 1.95 before using as the working solution.
3.2.3 Instrumentation
Voltammetry analysis was carried out using a Metrohm uAutolab Type III
potentiostat/galvanostat coupled with a three electrode basis 663 VA stand (Metrohm)
controlled by Autolab GPES software version 4.9. A static mercury drop electrode
(SMDE) was applied in the electrochemical cell as working electrode with the mercury
drop at size one (r0 = 1.41 × 10-4 m). A Ag/AgCl (3 mol/L, Fluka) electrode and a glass
carbon rod (Metrohm) were used as reference and auxiliary electrodes, respectively. A
PTFE stirrer was used with a rotation rate of 1500 rpm for the purpose of better purging
and deposition. A daily calibrated dual channel pH meter (accumet) was used during
the measurement. The DP-CSV method was based on Pernet-Coudrier et al. (2013).
Briefly, 25 mL of seawater samples was loaded into a voltammetric glass cell and 100
µL of 100 ppm Mo solution (EMD) was added to amplify HS signal. A 600-s N2
purging period was applied, followed by a 120-s deposition time with deposition
56
potential at 0.00 V with stirring. After deposition, a 5-s rest time was applied and
stripping scan using differential pulse mode started from 0.0 V to -0.6 V, where the
step potential was 2 mV and amplitude was 60 mV. The range of current was
determined automatically by the GPES software.
Repeatability, reproducibility, LOD and recovery (Table 3.1) experiments were
conducted on freshly made artificial seawater (Stein, 1979) without EDTA and trace
metal solution. The artificial seawater was adjusted in conductivity and pH to match
that of natural seawater samples. Repeatability calculated as 10 consecutive
measurements of artificial seawater (2.50 nA and 32.11 nA) was 0.64 %, 0.60 % for
GSH and HS, respectively. The CSV reproducibility obtained after 10 consecutive
measurements of one sample was 40.75 nM and 672.05 µg C/L for GSH and HS,
respectively. LODs were calculated as 3 times the standard deviation of 10 consecutive
measurements, which were 1.12 nM and 21.19 µg C/L, respectively for GSH and HS
(Table 3.1). Repeatability, reproducibility and LODs are comparable to previous study
(Marie et al., 2015; Pernet-Coudrier et al., 2013). Recovery was assessed by measuring
artificial seawater with known concentration of GSH and HS (10.3 nM and 168 µg C/L,
respectively). The recovery was ~ 100% for both GSH and HS.
Though the presence of HS was reported to overlap the GSH signal in CSV (Le
Gall and van den Berg, 1993), seawater contains low DOM concentration (i.e. < 1 ppm;
Carlson and Hansell, 2014) which is not enough to obscure GSH signal.
57
3.2.4 Fluorescent dissolved organic matter (FDOM)
Three dimensional excitation-emission fluorescence matrices (EEMs) were
generated by measuring fluorescence intensity across excitation wavelengths (Ex)
ranging from 250 to 500 nm and emission wavelengths (Em) ranging from 300 to 600
nm through successive scans with a Fluoromax-4 Jobin Yvon spectrofluorometer.
Excitation and emission slit widths were set to 5 nm. Blank Milli-Q EEMs were
measured daily to correct background and scatter peaks. Between each sample, the
quartz cuvettes were thoroughly rinsed with Milli-Q and scanned at Ex/Em 270/280 –
500 nm. The absence of significant fluorescent intensity at 300-500 nm confirmed the
cleanliness of the cuvette. All EEMs were normalized to Raman units (R.U.) by
dividing the signal at all Ex/Em pairs by the integrated area under the Raman water
peak at Ex 350 nm using a daily acquired Milli-Q blank EEM (Lawaetz and Stedmon,
2009).
Parallel factor analysis (PARAFAC) was carried out in Matlab using the
DOMFluor (Stedmon and Bro, 2008) for the decomposition of EEMs dataset. The
model was constrained to nonnegative values and run for three to ten components. The
appropriate number of components was determined by split-half and Tucker
congruence coefficient analyses.
3.3 Results
3.3.1 Water mass definition
Arctic Ocean serves as a conduit between the Pacific Ocean and the Atlantic Ocean.
Pacific-derived water exits the Canada Basin through Canadian Arctic Archipelago
58
(CAA), Barrow Strait (BS) and other passages like Jones Sound and Smith Sound into
North Atlantic Ocean (Woodgate, 2013). The current description of water masses is
based on previous works in CB (Carmack et al., 2015; McLaughlin et al., 2011, 2004;
Rudels et al., 2012; Woodgate, 2013) and CAA (Melling et al., 2008; Michel et al.,
2006; Woodgate, 2013). Three main water masses were found (Fig 3.2A):
Surface waters (SW; top 30 m). Surface waters (ASW) in CB and western CAA
were highly affected by runoff and ice melt (Cory et al., 2007; Logvinova et
al., 2016; Walker et al., 2009) and characterized by a low salinity and cold
temperature (Tp < 2 ℃ and Sp < 32; Fig 3.2B-C), while Lancaster Sound
surface waters (LsdSW) were affected by warmer and saline Atlantic waters
(Tp > 2 ℃ and Sp > 32). Chlorophyll showed relative low level in ASW while
it is relatively higher with LsdSW (Fig 3.2D).
Arctic outflow waters (OW; T < 0 ℃ and Sp < 33.7) (Azetsu-Scott et al., 2010;
Tang et al., 2004). OW occupied the top 300 m (excluding SW) and included
chlorophyll maximum along the section (Fig 3.2D). OW also encompassed
Pacific summer waters (T ~ - 0.8℃; Fig 3.2C) and Pacific winter waters (Sp ~
33.1) in CB. OW is affected by Canadian rivers input and ice melting in CAA
(Michel et al., 2006; Myers, 2005).
Deep waters (DW; T > 0 ℃ and Sp > 34). Warm and saline Atlantic origin
waters dominated the deep layers (> 300 m) with low level bioactivity (i.e. low
chlorophyll, Fig 3.2D). Arctic intermediate waters (AIW; > 400 m, Sp > 34.5)
were observed in CB and western CAA, whereas North Atlantic deep waters
(NADW; T ~ 2 ℃) was found in Lancaster Sound (Lsd).
59
3.3.2 CSV-based DOM characterization
The CSV-based thiol concentration of all samples ranged from 8 to 78 nM (Fig
3.3A) with an average of 21.9 nM (GSH equivalent), congruent with CSV-based
studies (Le Gall and van den Berg, 1993; Marie et al., 2015; Pernet-Coudrier et al.,
2013). HS of all samples ranged from 31 to 222 µg C/L (Fig 3.3B) with an average of
94 µg C/L and fell into the range reported earlier (Pernet-Coudrier et al., 2013; Whitby
and Van den Berg, 2014). Assuming that the dissolved organic carbon (DOC)
concentration was 90 µM in surface Western Arctic Ocean (Cai et al., 2011), the
abundance of HS represented between 2.8 % and 20.5 % of DOC, which was
comparable to previous studies (Chanudet et al., 2006; Weishaar et al., 2003).
3.3.3 FDOM characterization
Four components were identified and validated in PARAFAC model (Fig 3.4). The
cross validated PARAFAC components were compared with the online repository of
published PARAFAC components (Tucker congruence > 0.95; Murphy et al., 2014).
All components were previously found.
Components C1 to C3 were reported previously and considered as humic-like as
their maximum emission wavelengths were above 400 nm. C1 showed an excitation
wavelength at < 250 nm and 370 nm, an emission wavelength at 460 nm, which is close
to traditionally considered UV/visible terrestrial humic-like components (Coble, 1996).
The longest maximum emission wavelength of C1 suggested its elevated degree of
aromaticity (Stedmon et al., 2003). Despite of its terrestrial origin, similar components
had been found in open ocean studies (Dainard and Guéguen, 2013; Guéguen et al.,
2014; Walker et al., 2009). C2 and C3 showed a primary excitation wavelength
60
maximum at < 250 nm, a secondary excitation maximum at 310 nm and a maximum
emission at ~ 400 nm. These two components were identified as a combination of UV
humic-like and marine humic-like components (Coble, 1996), which were observed in
both terrestrial and marine systems (Dainard and Guéguen, 2013; McIntyre and
Guéguen, 2013; Stedmon et al., 2007; Walker et al., 2009). C4 featured a peak at Ex/Em
275/325 nm, which is similar to tryptophan-like fluorescence component (Coble, 1996)
associated with biological production (Coble et al., 1998). This component had been
reported widely in aquatic studies (Dainard and Guéguen, 2013; McIntyre and Guéguen,
2013; Stedmon et al., 2007; Stedmon and Markager, 2005).
The intensity ranges of four fluorescence components (C1: 0.014 to 0.039 r.u.; C2:
0.007 to 0.031 r.u.; C3: 0.005 to 0.032 r.u.; C4: 0.001 to 0.079 r.u.; Fig. 3.3C-F) agreed
with reported studies in the Arctic Ocean (Dainard and Guéguen, 2013; Guéguen et al.,
2014; Stedmon et al., 2007; Stedmon and Markager, 2005; Walker et al., 2009).
3.3.4 DOM and water masses
Thiol concentration (Fig 3.3A) increased from SW (16.87 ± 5.29 nM) to the
subsurface chlorophyll-a maximum depth (27.18 ± 5.59 nM). Maximum thiol
concentrations were coincident with chlorophyll-a maximum, but not universal along
the transect. The similar biological origin of thiol compounds was also reported in the
English Channel (al-Farawati and Van Den Berg, 2001) and North Atlantic Ocean
(Swarr et al., 2016). High HS concentrations (Fig 3.3B) were associated with the top
300 m through the study area and the highest HS concentrations were found in Viscount
Melville Sound (~150m) and in BS bottom waters. For deep layers, low level thiol
compounds and HS was found from 500 m to 1,000 m in AIW, except a DOM-rich
61
source was observed over 1,000 m, likely due to shelf break sediment interactions
(Hioki et al., 2014; Nebbioso and Piccolo, 2013; Shi et al., 2016). In NADW,
homogeneous distribution of thiol compounds and HS was observed, but the average
thiol concentration from 300 m to 1,000 m was higher than that of AIW (22.59 ± 3.63
nM vs. 15.90 ± 3.74 nM, p < 0.05) while HS (< 50 µg C/L) remained similar.
In terms of FDOM intensities (Fig 3.3C-F), humic-like C1 and C2 showed similar
distribution throughout the study area, suggesting similar processes affecting their
distribution as previously reported in CAA (Guéguen et al., 2014). High C1 and C2
intensities were found to be associated with the subsurface Pacific haloclines in CB,
occupying the top 300 m excluding ASW, the similar distribution was reported
previously in the Arctic Ocean (Dainard et al., 2015; Guéguen et al., 2012, 2007; Hioki
et al., 2014; Nakayama et al., 2011). A significant lateral reduction in C1-C2 intensities
in top 300 m near Lsd is caused by mixing with less humified Atlantic-origin waters
(Guéguen et al., 2014). Low C1 and C2 intensities (0.019 and 0.012 r.u. respectively)
in SW may be caused by enhanced photobleaching (Bélanger et al., 2006; Dainard et
al., 2015) and FDOM-poor sea ice contribution (Logvinova et al., 2016). Almost
identical vertical distribution (C1 and C2) in top 300 m from CB to BS suggested that
photo degradation is limited due to extensive sea ice cover in western CAA (Fransson
et al., 2009). However, the UV humic-like C3 (peak A; Coble, 1996) displayed different
distribution in western CAA. For protein like C4, higher intensities in SW and OW
were found in western CAA than in eastern CAA (0.023 vs 0.017 r.u., p < 0.05). Since
similar protein-like component had been reported to be linked to biological production
62
(Coble et al., 1998), the eastward decrease confirmed Pacific waters in western CAA
were more nutrients-rich (Michel et al., 2006) than eastern CAA waters.
In DW, a decreasing trend was observed for C1-C4 from 300 m to 1,000 m in
BAW, this contrasted with the distribution of FDOM in NADW, where identical
distribution was observed at relatively low level.
3.3.5 Principal Components Analysis
Principal components analysis (PCA) was carried out using samples from all
depths (Fig 3.5A) and using samples collected in the top 100 m (Fig 3.5C).
Five variables (HS, FDOM C1- C4) were selected in PCA on all depths. Principal
components 1 (PC1) and 2 (PC2) explained 39% and 25% of total variance (Fig 3.5A).
Humic-like C2 (A/M peak) and protein-like C4 were closely related (negative PC2
values), suggesting similar processes affecting both PARAFAC components. Both
components C2 and C4 were previously reported to be linked to microbial or bioactivity
production (Coble et al., 1998; Shimotori et al., 2012). On the other hand, voltammetry-
measured HS and humic-like components (C1 and C3) were in close proximity
(positive PC2 values), confirming the humic character of C1 and C3. The PCA revealed
differences in DOM characteristics between three main water masses (i.e. SW, OW and
DW) (Fig 3.5B). The DW and SW samples were clustered together in the left quadrants
whereas the OW samples were further on the right side of the score plot. SW took over
the top left quadrant while the DW samples dominated the bottom left quadrant, except
those affected by shelf sediments leaching in deep CB sites (> 1,000 m).
63
When considering all variables (i.e. GSH, HS and C1-C4) in the top 100 m (Fig
3.5C), the influence from intense biological activity (i.e. chlorophyll maximum), sea
ice contribution and river discharge could be revealed. The first and second principal
components accounted for 36% and 20% of the total variance explained, respectively.
Humic-like fluorescent components (C1 – C3) displayed negative PC2 loadings
whereas protein-like C4 and GSH concentration showed positive PC2 loadings. The
closer proximity of protein-like C4 and voltammetry-measured GSH concentration in
the top 100 m suggested similar biological origin. Interestingly, a trend moving from
CB to Lsd was observed in the score plots (Fig 3.5D), supporting the observation that
Pacific waters in CB were more nutrients-rich and productively (Michel et al., 2006)
than Atlantic waters in Lsd.
3.4 Conclusion
The distribution of FDOM, thiols and HS showed significant spatial changes
between eastern Canada Basin to Lancaster Sound and great stratification throughout
the entire depth. The ranges of GSH (8 to 78 nM) and HS (31 to 222 µg C/L) determined
by CSV were consistent with previous studies, suggesting that CSV-based DOM
characterization is suitable for marine studies. Four fluorescent components including
three humic-like (C1- C3) and one protein-like components (C4) were identified and
previously reported. Maximum thiol concentration was associated with the subsurface
chlorophyll-a maximum, but not universal along CAA. HS and humic-like fluorescent
components showed similar distribution, whereas thiols groups (i.e. GSH) was
observed to be closely related to protein-like C4. For the first time, thiols and HS were
measured in the Arctic Ocean by CSV and the method was proved to be capable in
64
marine studies, enabling the future monitoring of these important metal-binding ligands,
which will help better understand the distribution of trace metals in the Arctic Ocean.
Acknowledgments
This work was supported by the Canada Research Chair Program (CG) and National
Sciences and Engineering Research Council of Canada (CG). The field program on the
CCGS Amundsen was funded by Geotraces and ArcticNet. We thank Roger François,
Philippe Tortell, Jay Cullen, Richard Nixon and, the captain and crew of the CCGS
Amundsen.
65
Reference
Ahner, B.A., Wei, L., Oleson, J.R., Ogura, N., 2002. Glutathione and other low
molecular weight thiols in marine phytoplankton under metal stress. Mar. Ecol.
Prog. Ser. 232, 93–103. doi:10.3354/meps232093
al-Farawati, R., Van Den Berg, C.M., 2001. Thiols in coastal waters of the western
North Sea and English Channel. Environ. Sci. Technol. 35, 1902–1911.
Azetsu-Scott, K., Clarke, A., Falkner, K., Hamilton, J., Jones, E.P., Lee, C., Petrie, B.,
Prinsenberg, S., Starr, M., Yeats, P., 2010. Calcium carbonate saturation states in
the waters of the Canadian Arctic Archipelago and the Labrador Sea. J.
Geophys. Res. Ocean. 115, 1–18. doi:10.1029/2009JC005917
Barbeau, K., Rue, E., Bruland, K., Butler, A., 2001. Photochemical cycling of iron in
the surface ocean mediated by microbial iron (III)-binding ligands. Nature.
Bélanger, S., Xie, H., Krotkov, N., Larouche, P., Vincent, W.F., Babin, M., 2006.
Photomineralization of terrigenous dissolved organic matter in arctic coastal
waters from 1979 to 2003: Interannual variability and implications of climate
change. Global Biogeochem. Cycles 20, 1–13. doi:10.1029/2006GB02708
Benoit, J.M., Mason, R.P., Gilmour, C.C., Aiken, G.R., 2001. Constants for mercury
binding by organic matter isolates from the Florida Everglades. Geochim.
Cosmochim. Acta 65, 4445–4451. doi:10.1016/S0016-7037(01)00742-6
Cai, W.-J., Bates, N.R., Guo, L., Anderson, L.G., Mathis, J.T., Wannikof, R., Hansel,
D. a., Chen, L., Zemiletov, I.P., 2011. Carbon Fluxes Across Boundaries in the
Pacific Sector of the Arctic Ocean in a Changing Environment. Pacific Arct.
Sect. Status Trends 46, 1–38.
Carlson, C.A., Hansell, D.A., 2014. DOM Sources, Sinks, Reactivity, and Budgets,
in: Biogeochemistry of Marine Dissolved Organic Matter: Second Edition. pp.
65–126. doi:10.1016/B978-0-12-405940-5.00003-0
Carmack, E.C., Haine, T.W.N., Bacon, S., Bluhm, B.A., Lique, C., Melling, H.,
Polyakov, I. V, Straneo, F., Timmermans, M., Williams, W.J., 2015. Freshwater
and its role in the Arctic Marine System: Sources, disposition, storage, export,
and physical and biogeochemical consequences in the Arctic and global oceans
675–717. doi:10.1002/2015JG003140.Received
Chanudet, V., Filella, M., Quentel, F., 2006. Application of a simple voltammetric
method to the determination of refractory organic substances in freshwaters.
Anal. Chim. Acta 569, 244–249. doi:10.1016/j.aca.2006.03.097
Coble, P.G., 1996. Characterization of marine and terrestrial DOM in seawater using
excitation-emission matrix spectroscopy. Mar. Chem. 51, 325–346.
doi:10.1016/0304-4203(95)00062-3
Coble, P.G., Del Castillo, C.E., Avril, B., 1998. Distribution and optical properties of
CDOM in the Arabian Sea during the 1995 Southwest Monsoon. Deep. Res. Part
66
II Top. Stud. Oceanogr. 45, 2195–2223. doi:10.1016/S0967-0645(98)00068-X
Cory, R.M., McKnight, D.M., Chin, Y.P., Miller, P., Jaros, C.L., 2007. Chemical
characteristics of fulvic acids from Arctic surface waters: Microbial
contributions and photochemical transformations. J. Geophys. Res.
Biogeosciences 112. doi:10.1029/2006JG000343
Dainard, P.G., Guéguen, C., 2013. Distribution of PARAFAC modeled CDOM
components in the North Pacific Ocean, Bering, Chukchi and Beaufort Seas.
Mar. Chem. 157, 216–223. doi:10.1016/j.marchem.2013.10.007
Dainard, P.G., Guéguen, C., McDonald, N., Williams, W.J., 2015. Photobleaching of
fluorescent dissolved organic matter in Beaufort Sea and North Atlantic
Subtropical Gyre. Mar. Chem. 177, 630–637.
doi:10.1016/j.marchem.2015.10.004
Dupont, C.L., Ahner, B. a., 2005. Effects of copper, cadmium, and zinc on the
production and exudation of thiols by Emiliania huxleyi. Limnol. Oceanogr. 50,
508–515. doi:10.4319/lo.2005.50.2.0508
Dupont, C.L., Moffett, J.W., Bidigare, R.R., Ahner, B.A., 2006. Distributions of
dissolved and particulate biogenic thiols in the subartic Pacific Ocean. Deep.
Res. Part I Oceanogr. Res. Pap. 53, 1961–1974. doi:10.1016/j.dsr.2006.09.003
Fransson, A., Chierici, M., Nojiri, Y., 2009. New insights into the spatial variability
of the surface water carbon dioxide in varying sea ice conditions in the Arctic
Ocean. Cont. Shelf Res. 29, 1317–1328. doi:10.1016/j.csr.2009.03.008
Guéguen, C., Cuss, C.W., Cassels, C.J., Carmack, E.C., 2014. Absorption and
fluorescence of dissolved organic matter in the waters of the Canadian Artic
Archiipelago, Baffin Bay, and the Labrador Sea. J. Geophys. Res. Ocean. 119,
2034–2047. doi:10.1002/2013JC009173.Received
Guéguen, C., Guo, L., Tanaka, N., 2005. Distributions and characteristics of colored
dissolved organic matter in the Western Arctic Ocean. Cont. Shelf Res. 25,
1195–1207. doi:10.1016/j.csr.2005.01.005
Guéguen, C., Guo, L., Yamamoto-Kawai, M., Tanaka, N., 2007. Colored dissolved
organic matter dynamics across the shelf-basin interface in the western Arctic
Ocean. J. Geophys. Reserach - Ocean. 112, Citation No. C05038.
Guéguen, C., McLaughlin, F.A., Carmack, E.C., Itoh, M., Narita, H., Nishino, S.,
2012. The nature of colored dissolved organic matter in the southern Canada
Basin and East Siberian Sea. Deep. Res. Part II Top. Stud. Oceanogr. 81–84,
102–113. doi:10.1016/j.dsr2.2011.05.004
Harvey, G., Boran, D., Piotrowicz, S., Weisel, C., 1984. Synthesis of marine humic
substances from unsaturated lipids. Nature.
Harvey, G.R., Boran, D.A., Chesal, L.A., Tokar, J.M., 1983. The structure of marine
fulvic and humic acids. Mar. Chem. 12, 119–132. doi:10.1016/0304-
4203(83)90075-0
67
Hioki, N., Kuma, K., Morita, Y., Sasayama, R., Ooki, A., Kondo, Y., Obata, H.,
Nishioka, J., Yamashita, Y., Nishino, S., Kikuchi, T., Aoyama, M., 2014.
Laterally spreading iron, humic-like dissolved organic matter and nutrients in
cold, dense subsurface water of the Arctic Ocean. Sci. Rep. 4, 6775.
doi:10.1038/srep06775
Hirose, K., 2007. Metal-organic matter interaction: Ecological roles of ligands in
oceanic DOM. Appl. Geochemistry 22, 1636–1645.
doi:10.1016/j.apgeochem.2007.03.042
Kading, T., 2013. Distribution of thiols in the northwest Atlantic Ocean.
Kawakami, S.K., Gledhill, M., Achterberg, E.P., 2006. Determination of
phytochelatins and glutathione in phytoplankton from natural waters using
HPLC with fluorescence detection. TrAC - Trends Anal. Chem. 25, 133–142.
doi:10.1016/j.trac.2005.06.005
Kieber, R.J., Hydro, L.H., Seaton, P.J., 1997. Photooxidation of triglycerides and
fatty acids in seawater: Implication toward the formation of marine humic
substances. Limnol. Oceanogr. 42, 1454–1462. doi:10.4319/lo.1997.42.6.1454
Kogut, M.B., Voelker, B.M., 2001. Strong copper-binding behavior of terrestrial
humic substances in seawater. Environ. Sci. Technol. 35, 1149–1156.
doi:10.1021/es0014584
Laglera, L.M., van den Berg, C.M.G., 2003. Copper complexation by thiol
compounds in estuarine waters. Mar. Chem. 82, 71–89. doi:10.1016/S0304-
4203(03)00053-7
Lawaetz, A.J., Stedmon, C.A., 2009. Fluorescence intensity calibration using the
Raman scatter peak of water. Appl. Spectrosc. 63, 936–940.
doi:10.1366/000370209788964548
Le Gall, A., van den Berg, C.M.G., 1993. Cathodic Stripping Voltammetry of
Glutathione in Natural Waters 118.
Leal, M.F.C., van Vasconcelos M. Teresa S. D., B. den C.M.G., Vasconcelos,
M.T.S.D., van den Berg, C.M.G., 1999. Copper-induced release of complexing
ligands similar to thiols by Emiliania huxleyi in seawater cultures. Limnol.
Ocean. 44, 1750–1762. doi:10.4319/lo.1999.44.7.1750
Logvinova, C.L., Frey, K.E., Cooper, L.W., 2016. The Potential Role of Sea Ice Melt
in the Distribution of Chromophoric Dissolved Organic Matter in the Chukchi
and Beaufort Seas. Deep Sea Res. Part II Top. Stud. Oceanogr. 130, 28–42.
doi:10.1016/j.dsr2.2016.04.017
Marie, L., Pernet-Coudrier, B., Waeles, M., Gabon, M., Riso, R., 2015. Dynamics and
sources of reduced sulfur, humic substances and dissolved organic carbon in a
temperate river system affected by agricultural practices. Sci. Total Environ.
537, 23–32. doi:10.1016/j.scitotenv.2015.07.089
McIntyre, A.M., Guéguen, C., 2013. Binding interactions of algal-derived dissolved
68
organic matter with metal ions. Chemosphere 90, 620–626.
doi:10.1016/j.chemosphere.2012.08.057
McLaughlin, F.A., Carmack, E.C., Macdonald, R.W., Melling, H., Swift, J.H.,
Wheeler, P.A., Sherr, B.F., Sherr, E.B., 2004. The joint roles of Pacific and
Atlantic-origin waters in the Canada Basin, 1997-1998. Deep. Res. Part I
Oceanogr. Res. Pap. 51, 107–128. doi:10.1016/j.dsr.2003.09.010
McLaughlin, F.A., Carmack, E.C., Proshutinsky, A., Krishfield, R.A., Guay, C.K.,
Yamamoto-Kawai, M., Jackson, J.M., Williams, B., Williams, W.J., Williams,
B., Williams, W.J., 2011. The Rapid Response of the Canada Basin to Climate
Forcing: From Bellwether to Alarm Bells. Oceanography 24, 146–159.
doi:10.5670/oceanog.2011.66
Melling, H., Agnew, T., Falkner, K., 2008. Fresh-water fluxes via Pacific and Arctic
outflows across the Canadian polar shelf. Arctic–Subarctic Ocean.
Meyers-Schulte, K.J., Hedges, J.I., 1986. Molecular evidence for a terrestrial
component of organic matter dissolved in ocean water. Nature 321, 61–63.
doi:10.1038/321061a0
Michel, C., Ingram, R.G., Harris, L.R., 2006. Variability in oceanographic and
ecological processes in the Canadian Arctic Archipelago. Prog. Oceanogr. 71,
379–401. doi:10.1016/j.pocean.2006.09.006
Murphy, K.R., Stedmon, C.A., Wenig, P., Bro, R., 2014. OpenFluor- an online
spectral library of auto-fluorescence by organic compounds in the environment.
Anal. Methods 6, 658–661. doi:10.1039/c3ay41935e
Myers, P.G., 2005. Impact of freshwater from the Canadian Arctic Archipelago on
Labrador Sea Water formation. Geophys. Res. Lett. 32, 1–4.
doi:10.1029/2004GL022082
Nakayama, Y., Fujita, S., Kuma, K., Shimada, K., 2011. Iron and humic-type
fluorescent dissolved organic matter in the Chukchi Sea and Canada Basin of the
western Arctic Ocean. J. Geophys. Res. 116, 16. doi:10.1029/2010jc006779
Nebbioso, A., Piccolo, A., 2013. Molecular characterization of dissolved organic
matter (DOM): A critical review. Anal. Bioanal. Chem. 405, 109–124.
doi:10.1007/s00216-012-6363-2
Opsahl, S., Benner, R., 1997. Distribution and cycling of terrigenous dissolved
organic matter in the ocean. Nature. doi:10.1038/386480a0
Opsahl, S., Benner, R., Amon, R.M.W., 1999. Major flux of terrigenous dissolved
organic matter through the Arctic Ocean. Limnol. Oceanogr. 44, 2017–2023.
doi:10.4319/lo.1999.44.8.2017
Pernet-Coudrier, B., Waeles, M., Filella, M., Quentel, F., Riso, R.D., 2013. Simple
and simultaneous determination of glutathione, thioacetamide and refractory
organic matter in natural waters by DP-CSV. Sci. Total Environ. 463–464, 997–
1005. doi:10.1016/j.scitotenv.2013.06.053
69
Rashid, M., 2012. Geochemistry of marine humic compounds.
Rudels, B., Anderson, L., Eriksson, P., Fahrbach, E., Jakobsson, M., Jones, E.P.,
Melling, H., Prinsenberg, S., Schauer, U., Yao, T., 2012. Observations in the
Ocean, in: ARCTIC CLIMATE CHANGE: THE ACSYS DECADE AND
BEYOND. pp. 117–198. doi:10.1007/978-94-007-2027-5_4
Shi, Y.X., Mangal, V., Guéguen, C., 2016. Influence of dissolved organic matter on
dissolved vanadium speciation in the Churchill River estuary (Manitoba,
Canada). Chemosphere 154, 367–374. doi:10.1016/j.chemosphere.2016.03.124
Shimotori, K., Watanabe, K., Hama, T., 2012. Fluorescence characteristics of humic-
like fluorescent dissolved organic matter produced by various taxa of marine
bacteria. Aquat. Microb. Ecol. 65, 249–260. doi:10.3354/ame01552
Stedmon, C.A., Bro, R., 2008. Characterizing dissolved organic matter fluorescence
with parallel factor analysis: a tutorial. Limnol. Oceanogr. Methods 6, 572–579.
doi:10.4319/lom.2008.6.572
Stedmon, C.A., Markager, S., Bro, R., 2003. Tracing dissolved organic matter in
aquatic environments using a new approach to fluorescence spectroscopy. Mar.
Chem. 82, 239–254. doi:10.1016/S0304-4203(03)00072-0
Stedmon, C.A., Thomas, D.N., Granskog, M., Kaartokallio, H., Papadimitriou, S.,
Kuosa, H., 2007. Characteristics of dissolved organic matter in baltic coastal sea
ice: Allochthonous or autochthonous origins? Environ. Sci. Technol. 41, 7273–
7279. doi:10.1021/es071210f
Stedmon, C. a., Markager, S., 2005. Tracing the production and degradation of
autochthonous fractions of dissolved organic matter using fluorescence analysis.
Limnol. Oceanogr. 50, 1415–1426. doi:10.4319/lo.2005.50.5.1415
Stein, J., 1979. Handbook of phycological methods: culture methods and growth
measurements.
Stockdale, A., Tipping, E., Hamilton-Taylor, J., Lofts, S., 2011. Trace metals in the
open oceans: Speciation modelling based on humic-type ligands. Environ.
Chem. 8, 304–319. doi:10.1071/EN11004
Swarr, G.J., Kading, T., Lamborg, C.H., Hammerschmidt, C.R., Bowman, K.L.,
2016. Dissolved Low-Molecular Weight Thiol Concentrations from the U.S.
GEOTRACES North Atlantic Ocean Zonal Transect. Deep Sea Res. Part I
Oceanogr. Res. Pap. 116, 77–87. doi:10.1016/j.dsr.2016.06.003
Tang, C.C.L., Ross, C.K., Yao, T., Petrie, B., DeTracey, B.M., Dunlap, E., 2004. The
circulation, water masses and sea-ice of Baffin Bay. Prog. Oceanogr. 63, 183–
228. doi:10.1016/j.pocean.2004.09.005
Tang, D., Hung, C.-C., Warnken, K.W., Santschi, P.H., 2000. The distribution of
biogenic thiols in surface waters of Galveston Bay. Limnol. Oceanogr. 45, 1289–
1297. doi:10.4319/lo.2000.45.6.1289
70
Tang, D., Shafer, M.M., Vang, K., Karner, D.A., Armstrong, D.E., 2003.
Determination of dissolved thiols using solid-phase extraction and liquid
chromatographic determination of fluorescently derivatized thiolic compounds.
J. Chromatogr. A 998, 31–40. doi:10.1016/S0021-9673(03)00639-3
Walker, S.A., Amon, R.M.W., Stedmon, C.A., Duan, S., Louchouarn, P., 2009. The
use of PARAFAC modeling to trace terrestrial dissolved organic matter and
fingerprint water masses in coastal Canadian Arctic surface waters. J. Geophys.
Res. Biogeosciences 114. doi:10.1029/2009JG000990
Weishaar, J., Aiken, G., Bergamaschi, B., Fram, M., Fujii, R., Mopper, K., 2003.
Evaluation of specific ultra-violet absorbance as an indicator of the chemical
content of dissolved organic carbon. Environ. Sci. Technol. 37, 4702–4708.
doi:10.1021/es030360x
Wen, L.S., Santschi, P., Gill, G., Paternostro, C., 1999. Estuarine trace metal
distributions in Galveston Bay: Importance of colloidal forms in the speciation
of the dissolved phase. Mar. Chem. 63, 185–212. doi:10.1016/S0304-
4203(98)00062-0
Whitby, H., Van den Berg, C.M.G., 2014. Evidence for copper-binding humic
substances in seawater. Mar. Chem. 173, 282–290.
doi:10.1016/j.marchem.2014.09.011
Woodgate, R., 2013. Arctic Ocean Circulation: Going Around At the Top Of the
World. Nat. Educ. Knowl. Proj. 4, 1–12.
Yamashita, Y., Tanoue, E., 2008. Production of bio-refractory fluorescent dissolved
organic matter in the ocean interior. Nat. Geosci.
71
Figures and tables
Table 3.1 Repeatability, reproducibility, limit of detections and recovery of the CSV method
GSH HS
Repeatability Average 2.50 nA 32.11 nA
n = 10 Stdev 0.016 nA 0.192 nA
RSD % 0.64 0.60
Reproducibility Average 40.75 nM 672.05 µg C/L
n = 10 Stdev 0.375 nM 7.062 µg C/L
RSD % 0.92 1.05
Recovery % Average 100.81 101.29
n = 3 Stdev 0.74 1.78
Limit of detection
deposition time 120 s
1.12 nM 21.19 µg C/L
72
Figure 3.1 Sampling locations in Canada Basin and Canadian Arctic Archipelago, Study transect highlighted in red area
73
Figure 3.2 (A) Potential temperature as a function of salinity (Sp) at all depths; (B) Salinity, (C) Potential temperature and
(D) Fluo sensor (Chlorophyll-a) distribution along the transect (Figure 3.1)
74
Figure 3.3 Distribution of thiol groups (A), humic substances (B), FDOM (C-F) along the transect (Figure 3.1)
75
Figure 3.4 Excitation emission matrices identified by PARAFAC (A-C: humic-like; D: protein-like)
76
Figure 3.5 PCA models and score plots on all depths (A-B) and samples in top 100m (C-D); SW: surface waters, OW:
Arctic outflow waters, DW: deep waters; Lsd: Lancaster Sound, CAA: Canadian Arctic Archipelago, CB: Canada Basin
77
Chapter 4. Conclusion
Dissolved organic matter (DOM) was monitored over two consecutive years (i.e.
2014 and 2015) in the Arctic Ocean. Samples were collected aboard the CCGS Louis
S. Saint-Laurent (Joint Ocean Ice Studies JOIS cruise, September 2014) and the CCGS
Amundsen (Canadian Arctic GEOTRACES cruises, July-September 2015). DOM
Molecular weight (MW) was assessed using asymmetrical flow field-flow fractionation
(AF4), DOM characterization was carried out using Parallel factor analysis
(PARAFAC) – Excitation-emission matrices (EEMs) and concentrations of thiols and
humic substances was monitored using cathodic stripping voltammetry (CSV).
Two research questions were solved in this thesis:
Is the distribution of DOM characteristics associated with water masses of
different origin?
Is there a connection between voltammetry-based HS and humic-like
fluorescent component?
4.1 Molecular weight of DOM
For the first time, AF4 system was used in detecting DOM MW (JOIS cruise) in
Arctic waters. The DOM MW ranged from 1.07 to 1.45 kDa, consistent with earlier
studies using field-flow fractionation, high performance size exclusion
chromatography and tangential flow filtration (Beckett et al., 1992; Everett et al., 1999;
Guéguen and Cuss, 2011; Huguet et al., 2010; Landry and Tremblay, 2012; Penru et
al., 2013; Stolpe et al., 2010). The vertical distribution of DOM MW showed water-
78
mass related distribution pattern. DOM in Arctic surface waters displayed similarity in
MW. A minimum in MW was associated with the Pacific summer waters, while higher
MW was associated with Pacific winter waters. Arctic intermediate waters did not show
any significant change in MW in the area.
It is noted that there were some limitations in applying AF4 system to determine
DOM MW in seawater samples. For example, the 300 Da membrane used in the system
prevented molecules less than 300 Da to be focused and thus analysed. As fulvic acids
are good proxy for marine DOM (Tipping et al., 2015), the small molecules (< 300 Da)
are not signficant compared to the natural range of marine DOM. The molecules used
in the calibration solution did not exactly resemble natural DOM, thus the application
of more representative standards is needed for future work. The presence of salts in
samples and AF4 eluent was one of the issues affecting AF4 system. Although
extensive cleaning between samples allowed us to minimize salt built-up in the AF4
system, running seawater samples still resulted in a short life of membrane. A future
focus on pre-treatment (e.g. solid phase extraction) for seawater desalt process may
provide novel information. Furthermore, the preservation time (i.e. 10 days) was too
short to allow a large scale monitoring using in-lab measurements. An onboard AF4
using miniature AF4 channel should be developed in future oceanographic studies.
4.2 Composition of DOM
4.2.1 Fluorescent dissolved organic matter
The PARAFAC-validated fluorescent components in this study were found in
previous Arctic studies (Dainard and Guéguen, 2013; Guéguen et al., 2014; Stedmon
79
and Markager, 2005; Walker et al., 2009). Table 4.1 summarized the fluorescent
components identified in both cruises. C1-JOIS and C2-Geotraces both contained
marine humic-like component M peak (Coble, 1996). Protein-like (C2-JOIS and C4-
Geotraces) and terrestrial humic-like (C3-JOIS and C1-Geotraces) were identified in
both PARAFAC models. Humic-like C3 was only found in Geotraces dataset.
With the influence of sea ice contribution and river inputs, Pacific waters occupied
the top 400 m while saline and warm Atlantic waters stayed underneath. The great
difference in salinity and temperature impeded the vertical exchange between different
water masses, resulting in the Pacific haloclines in top 400 m. As Arctic waters flowed
through CAA, the haloclines became weak while the Pacific waters merged with
Atlantic waters. Humic-like component (A and C peak) was widely used to track the
movement of water mass due to its terrestrial origin (Walker et al., 2009), since similar
component had been observed in both two cruises, a comparison of vertical distribution
pattern of this terrestrial component in different sites was shown in Figure 4.1. In order
to discriminate the difference between sites, the signal had been normalized to the
surface ones. A strong halocline was observed at CB site and it weakened as water
flowing eastwards to Lancaster Sound. For protein-like component, similar vertical
distribution patterns on all samples collected in two years were observed with
fluorescence probe signal, which was associated with the chlorophyll-a concentration
(Fig. 4.1B). This observation supported the previous findings on the biological origin
of protein-like components (Coble et al., 1998).
80
4.2.2 Thiols and humic substances distribution
Thiols and humic substances (HS) concentrations were monitored the first time in
the Arctic Ocean, the ranges of thiols (8 - 78 nM GSH-equivalent) and HS (31 - 222
µg C/L) determined by CSV were consistent with previous marine studies (Le Gall and
van den Berg, 1993; Marie et al., 2015; Pernet-Coudrier et al., 2013; Whitby and Van
den Berg, 2014). Interestingly, maximum thiol concentration was associated with the
subsurface chlorophyll-a maximum for most sites, but not universal along Canadian
Arctic Archipelago. Highest HS concentration was associated with Arctic outflow
waters in top 300 m. Comparable distributions of CSV-based HS and humic-like
fluorescent components suggest the close proximity between each other.
Filella, (2014) showed that the concentrations of CSV-based thiols are greatly
affected by the choice of standards, a consistency in standards would be very helpful.
Alternatively, calibrating each CSV standard (GSH, cysteine, thioacetamide, thiourea)
against each other would be recommended for future study. Besides, novel information
would be revealed if CSV-based metal ligands concentrations were analyzed together
with the trace metal distribution in the area.
4.3 Conclusions and future directions
Overall, water mass related distribution of DOM fingerprints (i.e. DOM MW,
FDOM and CSV-based DOM) was observed in the study. The range of DOM MW
determined by AF4 system was similar to those done by high performance size
exclusion chromatography and tangential flow filtration. CSV-based thiols and HS
concentration was consistent with other marine studies and provided comparable trends
81
to previous work by HPLC. The results (i.e. DOM MW, thiol and HS distribution)
supported AF4 and CSV-based DOM analysis are suitable for marine studies.
For the future project, in-situ measurement and field work focus are required for a
larger scale monitoring. Miniature AF4 channel and onboard CSV measurement could
make it possible for future in-situ monitoring. A large scale future ocean monitoring on
DOM MW and CSV-based DOM would provide valuable insights on the fate and
transport of DOM, thus help us better understand global carbon cycle.
82
Reference
Beckett, R., Wood, F.J., Dixon, D.R., 1992. Size and chemical characterization of
pulp and paper mill effluents by flow field‐flow fractionation and resin
adsorption techniques. Environ. Technol. 13, 1129–1140.
doi:10.1080/09593339209385252
Coble, P.G., 1996. Characterization of marine and terrestrial DOM in seawater using
excitation-emission matrix spectroscopy. Mar. Chem. 51, 325–346.
doi:10.1016/0304-4203(95)00062-3
Coble, P.G., Del Castillo, C.E., Avril, B., 1998. Distribution and optical properties of
CDOM in the Arabian Sea during the 1995 Southwest Monsoon. Deep. Res. Part
II Top. Stud. Oceanogr. 45, 2195–2223. doi:10.1016/S0967-0645(98)00068-X
Dainard, P.G., Guéguen, C., 2013. Distribution of PARAFAC modeled CDOM
components in the North Pacific Ocean, Bering, Chukchi and Beaufort Seas.
Mar. Chem. 157, 216–223. doi:10.1016/j.marchem.2013.10.007
Everett, C.R., Chin, Y.P., Aiken, G.R., 1999. High-pressure size exclusion
chromatography analysis of dissolved organic matter isolated by tangential-flow
ultrafiltration. Limnol. Oceanogr. 44, 1316–1322. doi:10.4319/lo.1999.44.5.1316
Filella, M., 2014. Understanding what we are measuring: standards and quantification
of natural organic matter. Water Res.
Guéguen, C., Cuss, C.W., 2011. Characterization of aquatic dissolved organic matter
by asymmetrical flow field-flow fractionation coupled to UV-Visible diode array
and excitation emission matrix fluorescence. J. Chromatogr. A 1218, 4188–
4198. doi:10.1016/j.chroma.2010.12.038
Guéguen, C., Cuss, C.W., Cassels, C.J., Carmack, E.C., 2014. Absorption and
fluorescence of dissolved organic matter in the waters of the Canadian Artic
Archiipelago, Baffin Bay, and the Labrador Sea. J. Geophys. Res. Ocean. 119,
2034–2047. doi:10.1002/2013JC009173.Received
Huguet, A., Vacher, L., Saubusse, S., Etcheber, H., Abril, G., Relexans, S., Ibalot, F.,
Parlanti, E., 2010. New insights into the size distribution of fluorescent dissolved
organic matter in estuarine waters. Org. Geochem. 41, 595–610.
doi:10.1016/j.orggeochem.2010.02.006
Landry, C., Tremblay, L., 2012. Compositional differences between size classes of
dissolved organic matter from freshwater and seawater revealed by an HPLC-
FTIR system. Environ. Sci. Technol. 46, 1700–1707. doi:10.1021/es203711v
Le Gall, A., van den Berg, C.M.G., 1993. Cathodic Stripping Voltammetry of
83
Glutathione in Natural Waters 118.
Marie, L., Pernet-Coudrier, B., Waeles, M., Gabon, M., Riso, R., 2015. Dynamics and
sources of reduced sulfur, humic substances and dissolved organic carbon in a
temperate river system affected by agricultural practices. Sci. Total Environ.
537, 23–32. doi:10.1016/j.scitotenv.2015.07.089
Penru, Y., Simon, F.X., Guastalli, A.R., Esplugas, S., Llorens, J., Baig, S., 2013.
Characterization of natural organic matter from Mediterranean coastal seawater.
J. WATER SUPPLY Res. Technol. 62, 42–51. doi:10.2166/aqua.2013.U3
Pernet-Coudrier, B., Waeles, M., Filella, M., Quentel, F., Riso, R.D., 2013. Simple
and simultaneous determination of glutathione, thioacetamide and refractory
organic matter in natural waters by DP-CSV. Sci. Total Environ. 463–464, 997–
1005. doi:10.1016/j.scitotenv.2013.06.053
Stedmon, C.A., Markager, S., 2005. Resolving the variability of dissolved organic
matter fluorescence in a temperate estuary and its catchment using PARAFAC
analysis. Limnol. Oceanogr. 50, 686–697. doi:10.4319/lo.2005.50.2.0686
Stolpe, B., Guo, L., Shiller, A.M., Hassellöv, M., 2010. Size and composition of
colloidal organic matter and trace elements in the Mississippi River, Pearl River
and the northern Gulf of Mexico, as characterized by flow field-flow
fractionation. Mar. Chem. 118, 119–128. doi:10.1016/j.marchem.2009.11.007
Tipping, E., Lofts, S., Stockdale, A. 2015. Metal speciation from stream to open
ocean: modelling v. measurement, Environ. Chem., doi:10.1071/EN15111.
Walker, S.A., Amon, R.M.W., Stedmon, C.A., Duan, S., Louchouarn, P., 2009. The
use of PARAFAC modeling to trace terrestrial dissolved organic matter and
fingerprint water masses in coastal Canadian Arctic surface waters. J. Geophys.
Res. Biogeosciences 114. doi:10.1029/2009JG000990
Whitby, H., Van den Berg, C.M.G., 2014. Evidence for copper-binding humic
substances in seawater. Mar. Chem. 173, 282–290.
doi:10.1016/j.marchem.2014.09.011
84
Figures and tables
Table 4.1 Fluorescent components identified in JOIS cruise and GEOTRACES cruise.
JOIS cruise (ex/em) GEOTRACES cruise (ex/em) Traditionally (Coble, 1996) (ex/em)
Component 1 C1 (305/410) M peak
Component 2 C2(<280/330) C4 (275/325) T peak
Component 3 C3(<270 and 365/465) C1 (250 and 370/460) A and C peak
Component 4 C2 (<250 and 310/400) A and M peak
Component 5 C3 (<250/400) A peak
85
Figure 4.1 (A) Vertical distribution of terrestrial humic-like component in Canada Basin, Canadian Arctic Archipelago and
Lancaster Sound; (B) Vertical distribution of protein-like components and Chl-a signal in all samples from both cruise
Recommended