Trace metals in speleothems: LA-ICP-MS vs synchrotron techniques

Andrea Borsato,the University of Newcastle, Australia

Acknowledgment: S. Frisia, R. Belli (Newcastle), J. Hellstrom, J.Woodhead (Melbourne), I.J. Fairchild (Birmingham), V.Johnston (Trento), S.Eggins (Canberra),M.Cotte, M.Salomè, J.Susini, A. Somogyi (Grenoble),

1. SR applications in speleothem science

2. Soft vs. hard X-ray

3. Sample preparation, spatial resolution,

4. Spectral interference

5. Detection limits and measurable elements

6. Calibration

7. Examples and environmental interpretation

OUTLINE 1. Synchrotron RadiationTechniques

►XRF: X-ray fluorescence spectroscopy

qualitative/quantitative elemental composition,

2D/3D mapping (micro – nano scale)

► XAS: X-ray absorption spectroscopy,

► XANES: X-ray absorption near-edge structure,

chemical state (valence) of a given element, 2D mapping

► XRD: X-ray diffraction

mineralogy, crystalline µ-structures, 2D/3D mapping

► X-ray excited optical luminescence

SR applications in speleothem science

Synchrotron Radiation X-ray fluorescence (SR-XRF)

• The absorption of a X-ray

radiation of a specific energy

(greater than the ionization

potential) results in the re-

emission of a radiation

(photon).

• The emitted energy is equal

to the energy difference of the

two orbitals involved (K, L

and M lines)

• Synchrotron X-ray source is

unique for its brillance and

tunability

European Synchrotron Radiation Facility, Grenoble

Beamline ID21 (soft) ID22 (hard) .• Excitation energy (tunable): 2-9 keV 6-65 keV• Operation mode : vacuum air

• Beam size (resolution): 0.2 - 1.5 µm 1.0 – 2.0 µm

• Acquisition time: 0.5 – 10 sec 1 - 15 sec

• Detection limits: 0.5 - 50 ppm 0.06 - 0.16 ppm

• Detectable elements: Z<26 (Fe) K-lines 14<Z<72 (Hf) K-lines

Z<64 (Gd) L-lines 72<Z L-lines

SR-XRF: ESRF ID21 and ID22 beamlines configuration

investigation area:8 x 8 mm

Double polished wafer 200 µm-thick

Sample holder ID21

Polished wafer up to 10 mm-thick

investigation area:22 x 7 mm

ESRF Beamline ID21: soft X-Ray 2-9 keV

P Kα

Na

Kα

Mg

KαAl

Kα

Si

Kα

Sr

LαS Kα

Cl Kα

scattering

O

Kα

Soft X-Ray fluorescence spectrum (excitation 2.9 keV)

Spectral interference

Incoming beam

Sample Main detector

ESRF Beamline ID22: hard X-Ray 6-65 keV

Al-foil

ID22 Fluorescence spectrum

CaKα+β

Sr Kα

Mo

FeKα

CuKα

CrKα

Sr Kβ

ZnKβ

PbLβ

ZnKα

PbLα

NiKα

Hard X-Ray fluorescence spectrum (excitation 23 keV)

Spectral interference

BrLα

UMα

SR-XRF Measurable elements

(Fairchild & Treble, Quat. Sci. Rev. 2009)

Solutes

Solutes intermediates

Colloidal intermediates

Colloidal

Particles

Atomic n° 11 12 13 14 15 16 17 19 20 22 23 24 25 26 28 29 30 35 38 39 42 56 57 58 60 82 90 92

Element Na Mg Al Si P S Cl K Ca Ti V Cr Mn Fe Ni Cu Zn Br Sr Y Mo Ba La Ce Nd Pb Th U

Soft SR-XRF

hc hc √ √ √ √ hc hc √ hc hc hc hc hc x x x x hc x x hc x x x hc x x

Hard SR-XRF

x x x x x x x x √ hc hc hc hc hc √ √ √ hc √ √ hc hc hc hc hc √ hc hc

Calibration: from XRF intensity data (Ii) into concentrations (Ci)

3,,det,0

,

CaCOEXRFi

d

Eii i

AliEAl

i

AbseGICI ⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅====⋅⋅⋅⋅−−−−

σσσσηηηηµµµµ

3,,det,

3,,det,

,

,

CaCOEXRFi

d

E

CaCOKCaXRFKCa

d

KCa

KCa

i

Cai

i

AliEAl

i

AlKCaAl

Abse

Abse

I

ICC

⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅

⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅====

⋅⋅⋅⋅−−−−

−−−−−−−−

⋅⋅⋅⋅−−−−

−−−−

−−−−

−−−−

σσσσηηηη

σσσσηηηη

µµµµ

αααααααα

µµµµ

αααα

αααα

αααα

I0 incoming intensity

G geometry factor

detection efficiency

absorption within the Al foils

cross section for the given characteristic X-ray line of element I

AbsEi CaCO3 self-absorption within the matrix, considered to be 100% CaCO3 (calcite)

iEdet,η

AliEAl de

⋅− ,µ

XRFi ,σ

(Borsato et al., Geoc. Cosmoc. Acta. 2007)

This standardization method seem to be accurate for Mg, P, Zn, and Pb, whereas Cu and Y are

underestimated by a factor of 10 and 5 respectively with respect to ICP-MS. Y is also underestimated

with respect to ion probe data. This discrepancy is likely to result from the fact that Y is usually near the

detection limit of XRF in the sample. For Cu the discrepancy could be due to its association with highly

concentrated particles. Standardization is thus to be considered with caution, and needs future work.

1.2 0.59 0.23 14.9 0.045 0.8 0.21±0.57 ±0.42 ±0.59 ±1.3 ±0.05 ±0.25 ±0.10

80.5 1.63 0.74 0.22 15.5 0.049 1.07 0.24

±14 ±0.77 ±0.40 ±0.14 ±1.9 ±0.07 ±0.32 ±0.14

1.1-4.6 657 106 3.3 3.05 14.8 0.30 0.32

4.6-8.0 560 80 2.5 1.85 16.5 0.18 0.16

103/4 5.5-7.0 532 85 15.9

128 5.7-6.7 422 60 15.1 0.21

ICP-MS bulk sample

Ion microprobe

5.5-8 567±5944 & 95

µ-XRF

32 1.8 - 5

Y Br PbZn Fe Cu SrScan Mg PDepth

(mm)

In order to reduce the systematic error resulting from the uncertainty of the thickness of

the Al foil, ICP-MS bulk Sr concentrations are compared with Sr XRF measurements.

This allow to solve the equation for Sr and quantifying the absorption within the Al foil.

(Borsato et al., GCA. 2007)

Examples: Volcanic S-layer in stalagmite SV1 (Savi cave, Trieste, Italy)

(Frisia et al. EPSL, 2005) C) the record of volcanogenic sulphate

in the Greenland GISP2 ice core

(Frisia et al. EPSL, 2005)

S-sulphate2.482 keV

S-sulphite

Examples: Sulphur X-ray AbsorptionNear Edge Structure (XANES) spectra

Frisia et al. / Journal of Volcanology and Geothermal Research 2008

Tambora

1815

Krakatoa

1883Ekla

1947

Examples: Sulphur record in ER78 stalagmite

•Stalagmite ER78: cicli chimici dei diversi elementi distanziati come le lamine visibili (50–100 µm).

•I picchi di P, Cu, Zn, Pb, Br, Y corrispondono a minimi di Sr (tasso di crescita minimo)

0.5

0.60.7

0.8

Fe

(p

pm

)

12

14

16

18

Sr

(pp

m)

0

2

4

Zn

(p

pm

)

0.1

0.2

0.3

0.4

Cu

(p

pm

)

0.0

0.3

0.6

Y (

pp

m)

0.0

0.4

0.8

Pb

(p

pm

)0.6

1.2

1.8

Br

(pp

m)

5.8 6.0 6.2 6.4 6.6 6.8

Distance from top (mm)

50

90

130

P (

pp

m)

• The elemental markers are spaced apart as

the visible laminae.

• The P peaks are aligned with the Cu, Zn,

Pb, Br, Y peaks and with Sr troughs.

(Borsato et al., Geoc. Cosmoc. Acta. 2007)Examples: Trace element in annuallaminated stalagmite ER78

(Borsato et al., Geoc. Cosmoc. Acta. 2007)Examples: Trace element in annuallaminated stalagmite ER78

The peak intensities of Y > Zn, Cu, Pb > P and Br reflect the

selectivity of transport via colloids and incorporation.

0

2

4

Zn (

ppm

)

12

13

14

15

1875 1885 1895 1905 1915 1925

Te

mp

era

ture

(°C

)

Year

0

0.2

0.4

0.6

Y (

ppm

)

0

0.2

0.4

Cu (

ppm

)

0

0.2

0.4

0.6

0.8

Pb (

ppm

)

10

15

20

Sr

(ppm

)

500

1000

1500

Pre

cip

itatio

n(m

m/y

ear)

0.00

0.05

0.10

1875 1885 1895 1905 1915 1925

Thic

k. (

mm

)

Approximate year

a

b

The maximum (red lines) and minimum (black lines) annual

concentrations for Zn, Y, Pb, Cu and Sr .The period with higher

maximum values for all the elements correspond to

deforestation coinciding with pre-WW1 military activities.

Examples: Trace element in annual laminated stalagmite Obi84

Obir cave (Austria)

stalagmite Obi84.

The speleothem have

a distinct Zn- (3400 to

5000 ppm) and Pb-

(500 to 770 ppm)

enrichment related to

local host-rock

mineralization.

(Fairchild et al. Geol.Soc.

London, Spec. Publ. 2010)

XRF maps (excitation 23 keV): 8 annual visible laminae, formed during autumn,

take the form of annual packages or individual ‘event laminae’ enriched in Zn and Pb

and separated by almost inclusion-free calcite. The excitation of crystallites at

different depths (100 – 150 µm) caused a pseudo-3D image.

Growth direction 200 µm

1. Ablation system, sample preparation, resolution,

2. Interference by molecules and ions

3. Elemental fractionation and mass-load matrix effects

4. Mass resolution, detection limits and measurable elements

5. Background, calibration and standards

6. Riproducibility and adjacent scans correlation

7. Examples and environmental interpretation

OUTLINE 2. Laser Ablation ICP Mass Spectrometry

• Ablation system: ArF excimer, Nd:YAG (Nd-doped Y Al garnet) • Wavelenghth: 193nm, 213 nm, 266 nm• Laser size: spot (10-200 µm ) or slit (10-30 µm x 100-200 µm )• Laser pulse rate: 10-30 Hz• Carrier gas: He and Ar

• Acquisition time (single element): 2-100 ms

• Scan speed: 5-20 mm/s

• Integration: 5 to 20-points

• Final resolution: 10 - 50 µm

• Investigation area*: 90 x 60 mm

Ablation system, sample preparation, spatial resolution

Polished slab up to 12 mm-thick

Sample chamber

Standard housing

(Jochum et al., Chem.Geol. 2012)

Mass (u) Mass (u)

Interference by molecules and multiply charged ions

Isotope Interference isotopes

23Na+ 46Ca+24Mg+ 48Ca++27Al+ 14N13C+29Si+ 12C17O+, 13C16O+, 14N2

1H+30Si+ 12C18O+, 14N16O+33S+ 16O17O+, 16O2

1H+34S+ 16O18O+39K+ 38Ar1H+52Cr+ 40Ar12C+53Cr+ 40Ar13C+55Mn+ 40Ar15N+57Fe+ 40Ca16O1H+68Zn+ 28Si40Ar+, 38Ar14N16O+

Bold: interference >10%

Interference by molecules and multiply charged ions

Matrix compoundsCa++, CaO+, CO+

Carrier compoundsAr+

(semplified from Jochum et al., Chem.Geol. 2012)

Mass resolution, detection limits and measurable elements

(Jochum et al., Chem.Geol. 2012)

Most studies utilised

quadrupole or sector-

field ICP-MS in the low

mass resolution mode

(M/∆M of ~ 300)

Suitable isotopes and mass resolution

Elemental fractionation

Several elements, such as Zn, Cu, Cd

and Pb, show an increase in signal

intensity as a function of ablation time.

The elemental fractionation is related to

the size of the ablated particles and is

particularly important for laser systems

with wavelengths >266. Laser systems

with shorter wavelengths (213 and 193

nm) generate particles with a lower size

(<150 nm) reducing elemental

fractionation.

Elemental fractionation and mass-load matrix effects

Fractionation factors (ratios of the total counts determined in the

second half of the measurements to the counts of the first half and

normalized to Ca) (Fryer et al., Canad. Miner., 1995) for different

elements, matrix and spot sizes (Jochum et al., Chem.Geol. 2012)

213 nm 193 nm

�N

IST

610

�N

IST

614

�bac

kgro

und

�bac

kgro

und

�bac

kgro

und

�re

sin

�S

ampl

e

Background, calibration and standards

�N

IST

610

�N

IST

614

�bac

kgro

und

�bac

kgro

und

�bac

kgro

und

�re

sin

Background, calibration and standards

Signalnoise

edge effect

�S

ampl

e

memory effect

background drift

signal drift

Background, calibration and standards

Elemental fractionation and mass-load matrix effects

ICP-MS and SR-XRF detection limits

(Fairchild & Treble, Quat. Sci. Rev. 2009)

Solutes

Solutes intermediates

Colloidal intermediates

Colloidal

Particles

Atomic n° 11 12 13 14 15 16 17 19 20 22 23 24 25 26 28 29 30 35 38 39 42 56 57 58 60 82 90 92

Element Na Mg Al Si P S Cl K Ca Ti V Cr Mn Fe Ni Cu Zn Br Sr Y Mo Ba La Ce Nd Pb Th U

isotope 25 27 29 31 34 39 43 49 51 53 55 57 60 65 66 88 89 95 138 139 140 146 208 232 238

LA-ICP-MSLowR

x 0.2 1 50 4 20 x x 10 0.2 0.05 1 0.2 10 1 0.1 0.5 x 0.01 0.01 0.05 0.010.000

50.001 0.001 0.003 0.0002 0.0002

LA-ICP-MSMedR

x 0.3 1 50 2 100 x 2 30 x x 0.03 0.1 0.03 0.1 0.1 2 x 0.1 0.001 x 0.01 x x x 0.001 0.0005 0.0005

Soft SR-XRF

hc hc √ √ √ √ hc hc √ hc hc hc hc hc x x x x hc x x hc x x x hc x x

Hard SR-XRF

x x x x x x x x √ hc hc hc hc hc √ √ √ hc √ √ hc hc hc hc hc √ hc hc

(ICP-MS detection limits from Jochum et al., Chem.Geol. 2012)

0

1

2

3

4

5

6

7

8

9

10

-80

-60

-40

-20

0

20

40

60

80

100

0 10 20 30 40 50 60

Ba

(p

pm

)

Sr

(pp

m)

Sr line0a Sr line1a Sr line2aBa line0a Ba line1a Ba line2a

Phase1 Phase3 Phase4Phase2

Distance (mm)

Savi Cave stalagmite. Unpublished data

Riproducibility: parallel line scans – solutes

Three line scans spaced 0.5 mm apart

0.0

0.1

0.2

0.3

0.4

0.5

0.6

-100

-50

0

50

100

150

200

0 10 20 30 40 50 60

U (

pp

m)

P (

pp

m)

P line0a P line1a P line2a

U line0a U line1a U line2a

Distance (mm)

Savi Cave stalagmite. Unpublished data

Riproducibility: parallel line scans – solutes intermediates

Three line scans spaced 0.5 mm apart

Phase1 Phase3 Phase4Phase2

Combined SR-XRF and LA-ICP-MS analyses

Age: 4.3 Myr (J. Woodhead,

preliminary U/Pb data).

LA-ICP-MS trace element

variability across two

elongated columnar calcite

crystals (Phase-1 and -3)

interrupted by a stromatolite-

like layer (Phase-2, pale blue

bar highlight).

High concentration of Y, Mn,

Al, and P in Phase-2

(Frisia et al., Clim. Past 2012)

Growth directionWinbirra Cave, Nullarbor (AUS)Stalagmite FS04

Synchrotron radiation micro XRF maps for S, Mg, Si and P. Sulphur is present as

sulphate (XANES), and silicon is in amorphous silica form.

(Frisia et al., Clim. Past 2012)

Stromatolite-like layer in FS04 (phase 2)

dissolution

Thin section showing micrite filling

dissolution voids in the columnar

crystals, and micrite filling the voids

and the depressions between crystal

terminations.

Winbirra Cave, Nullarbor (AUS) Dissolution and micritisation in stalagmite MO1 – age 3.9 Ma

(Frisia et al., Clim. Past 2012)

SR-XRF maps (pixel size 2 µm) for S, P,

and Si. Note that S, P and Si are all

associated with micrite.

SEF diagram constructed by comparing elemental composition in the host rock and in

speleothem FS04. The red arrows highlight the elemental enrichment in phase 2 with

respect to the average values in columnal calcite phases 1 and 3. Error bars (1SD) are

shown for phase 2 only.(Frisia et al., Clim. Past 2012)

Speleothem enrichment factor (SEF)

• LA-ICP-MS is the most commonly used micro-analytical technique in speleothem science combining low detection limits and high spatial resolution (10–100 µm).

For the correct use in paleoclimate reconstructions the issues of mass interferences, elemental fractionation, mass-load matrix effects and calibration protocols have to be addressed;

• The ultra-high spatial resolution (0.2-1 µm) of SR-XRF allow the detection of ca. 10 elements in standard setting. Mapping confirm the lateral continuity of the elemental distribution in banded and laminated samples.

The measure of a more complete suite of elements as well as the quantification of the data still need technical improvement.

• Mineralogical, crystallographic and textural characteristics have to be considered when planning the analyses and interpreted the data.

Conclusions

• Borsato, A., Frisia, S., Fairchild, I.J., Somogyi, A., & Susini, J., (2007). Trace element distribution in annual

stalagmite laminae mapped by micrometer-resolution X-ray fluorescence: implications for incorporation of

environmentally significant species, Geochim. Cosmoch. Acta 71: 1494–1512.

• Fairchild, I.J. & Treble, P.C. (2009). Trace elements in speleothems as recorders of environmental change.

Quaternary Science Reviews, 28, 449-468.

• Fairchild, I.J., Spötl, C., Frisia, S., Borsato, A., Susini, J., Wynn, P.M., Cauzid, J., & EIMF. (2010). Petrology and

geochemistry of annually laminated stalagmites from an Alpine cave (Obir, Austria): seasonal cave physiology. In:

Pedley, H.M.& Rogerson, M. (eds) Tufas and Speleothems: Unravelling the Microbial and Physical Controls.

Geological Society, London, Special Publications 2010; v. 336; p. 295-321.

• Fairchild, I.J. & Baker, A. (2012). Speleothem Science. From Process to Past Environment. Wiley Blackwell.

• Frisia, S., Borsato, A., Fairchild, I.J., Susini, J., (2005). Variations in atmospheric sulphate recorded in stalagmites

by synchrotron micro XRF and XANES analyses. Earth and Planetary Science Letters, 235: 729-740.

• Frisia, S., Borsato, A., & Susini, J., (2008). Synchrotron radiation applications to past volcanism archived in

speleothems: An overview. Journ. of Vulcanology and Geothermal Research, 177, 1: 96-100.

• Frisia, S., Borsato, A., Drysdale, R.N., Paul, B., Greig, A. & Cotte, M., (2012). A re-evaluation of the

palaeoclimatic significance of phosphorus variability in speleothems revealed by high-resolution synchrotron

micro XRF mapping. Clim. Past, 8, 2039–2051, 2012.

• Fryer, B.J., Jackson, S.E., Longerich, H.P., (1995). The design, operation and role of the laser-ablation microprobe

coupled with an inductively coupled plasma-mass spectrometer (LAM-ICP-MS) in the Earth sciences. The

Canadian Mineralogist 33, 303–312.

• Jochum K.P., Scholz D., Stoll B., Weis U., Wilson, S.A., Yang Q., Schwalb A., Börner N., Jacob D.E., Andreae

M.O., (2012). Accurate trace element analysis of speleothems and biogenic calcium carbonates by LA-ICP-MS.

Chemical Geology 318–319: 31–44.

• Treble, P., Shelley, J. M. G., & Chappell, J. (2003). Comparison of high resolution subannual records of trace

elements in a modern (1911-1992) speleothem with instrumental climate data from southwest Australia. Earth and

Planetary Science Letters, 216, 141-153.

Essential reference lists