Late Quaternary History of Export Themes or topics ... · • An ultimate goal: explain the Vostok CO 2 record • Where has export production been important? ... • Case studies:

1

Presented by Tom Pedersen at the SOLAS Summer School, Cargése, Corsica, 30 June - 11th July 2003

Late Quaternary History of ExportLate Quaternary History of ExportProduction and BiogeochemicalProduction and BiogeochemicalCycles: How Do We Trace Them Cycles: How Do We Trace Them

and Why?and Why?

Tom PedersenUniversity of Victoria

Canada

[email protected]

Solas Summer School, Cargese, 2003Presented by Tom Pedersen at the SOLAS Summer School, Cargése, Corsica, 30 June - 11th July 2003

• Export production: why is it important?• An ultimate goal: explain the Vostok CO2 record

• Where has export production been important?• Equatorial regions? The Southern Ocean?• Coastal regions? Specific coastal regions?

• Tracing export production and its impact using amultiproxy approach:• organic C concentration and accumulation rate• N isotopes, C isotopes, foraminifera• sedimentary Mo and Ag concentrations

Themes or topics:Themes or topics:


• Case studies: the Vancouver Island and SouthernCalifornian margins

• Global implications:• could changes in hydrography in this area on thewestern margin of the Americas have been ofglobal significance with respect to climate?

• Greenland N2O versus California Margin δ15Nand its link to pCO2

Themes or topics (contThemes or topics (cont’’d):d):


CO2

∆T

CH4

The ultimate objective: To explain these profiles.


Modern difference in CO2concentration, ocean minusatmosphere in boreal winterand summer.

Note the strong efflux ofCO2 in the equatorialPacific region in bothseasons.

Data from Taro Takahashi.


The first The first paleoproxypaleoproxy: : organic carbonorganic carbon

2

Presented by Tom Pedersen at the SOLAS Summer School, Cargése, Corsica, 30 June - 11th July 2003 Presented by Tom Pedersen at the SOLAS Summer School, Cargése, Corsica, 30 June - 11th July 2003

Sedimentaryorganic carbon

concentration inPacific sediments,

wt. %

after Pedersen and Calvert, 1990


Estimated ratesof burial of organiccarbon in sediment coresfrom four locations. Note that the pair of cores from the equatorial Pacific showvery similar and substantialincreases in Corg burial during the last glacial period.


Was the increased export productionWas the increased export productionimplied by the higherimplied by the higher C Corgorg MAR in the MAR in theequatorial Pacific during the LGMequatorial Pacific during the LGMassociated with associated with decreaseddecreased surface- surface-water pCOwater pCO22??


Relative Nutrient UtilizationRelative Nutrient UtilizationPhytoplankton discriminate against 15N (ε ~ 5-6 ‰) when NO3

- isabundant. As NO3

- utilization proceeds with distance from the nitratesource, the residual nitrate becomes isotopically heavier and so doesthe plankton.Discrimination has little effect on δ15N when NO3

- is scarce.

DenitrificationDenitrificationReduction of NO3

- by denitrifying bacteria strongly fractionates theproduct N2 (which is depleted in 15N) from the substrate (ε ~ -30 ‰) .The residual NO3

- becomes progressively enriched as denitrificationproceeds and N2 and N2O are lost to the atmosphere.

NN22 Fixation ( Fixation (δδ1515N of NN of N22 = 0 = 0 ‰‰))Little fractionation occurs: the Norg produced has a δ15N of ~0 ‰.

Nitrogen Isotopes As Nitrogen Isotopes As PaleotracersPaleotracers


3


An example of Rayleigh fractionation applied to nitrogen isotopes.The left panel illustrates the effect of nitrate utilization as NO3

- wellsup and is progressively assimilated by plankton as the surface watermoves away from the point of upwelling (e.g. Equatorial Pacific).

after M.R. Talbot, “Nitrogen Isotopes in Paleolimnology”

Fraction remaining1.0 0

δ15N

+15-20

+5-6

~0

ε ~ 5-6Dissolv

ed NO 3

-Pla

nkton

δ15 N

Presented by Tom Pedersen at the SOLAS Summer School, Cargése, Corsica, 30 June - 11th July 2003Farrell, Pedersen et al., 1995

Calibration of the“relative nitrateutilization” hypothesis

Levitus climatologyNote that the nitratedistribution results from acombination of upwellingalong the equatorialdivergence and lateraladvection in the SouthEquatorial Current westwardfrom upwelling centre alongthe northern coast of Peru.


Modern difference in CO2concentration, ocean minusatmosphere in boreal winterand summer.

Note the strong efflux ofCO2 in the equatorialPacific region in bothseasons.

Data from Taro Takahashi.


Was this picturedifferent in the past?


VNTR01-13GC: 3.1°S, 90.8°WP7GC: 2.6°N, 84.0°WTT199-5-GC26: 2.7°N, 86.0°W

0.5

1.0

1.5

2.0

2.5

0 5 10 15 20 25 30

Org

anic

car

bon,

wt.

%

Age (ka)

last ice age

2

3

4

5

6

7

8

9

10

0 5 10 15 20 25 30

δ15 N

(‰ a

ir)

Age (ka)

Farrell et al. (1995)

Nitrogen isotope profiles (upperpanel) from three cores across theequatorial divergence zone just eastof the Galapagos Islands.

These imply decreased relativenitrate utilization during the lastglacial period. But organic carbonburial was four-fold higher then.How can these be reconciled?

The best explanation is thatincreased upwelling supplied morenitrate than was exported throughenhanced primary production. Thatis, supply exceeded demand, morethan today.


Was this picturedifferent in the past?

Apparently

not!

4



Vancouver Island

Figure courtesy Jennifer McKayPresented by Tom Pedersen at the SOLAS Summer School, Cargése, Corsica, 30 June - 11th July 2003

Vancouver Island Continental MarginVancouver Island Continental Margin

McKay and Pedersen, submitted

Abo

ut tw

o ce

ntur

ies


•• Mo Mo in in oxicoxic seawater is: seawater is:•• relatively conservative and abundant (~ 0.1 relatively conservative and abundant (~ 0.1 µµMM))•• occurs as MoO occurs as MoO44

2-2-

•• But, under But, under anoxicanoxic conditions: conditions:

•• sulphate sulphate reduction yields HSreduction yields HS--

•• at [HS at [HS--] > 11 ] > 11 µµMM, MoO, MoO442-2- is is sulphidizedsulphidized producing producing

mono, mono, didi, tri and , tri and tetrathiomolybdatestetrathiomolybdates, , MoOMoOxx-1-1SS2-2-5-x5-x

•• the the monothio monothio to to trithio trithio species are unstable, sospecies are unstable, sotetrathiomolybdate tetrathiomolybdate becomes progressively dominant. Thisbecomes progressively dominant. Thisspecies is readily scavenged by particlesspecies is readily scavenged by particles•• thus, thus, Mo Mo enrichments in sediments are a proxy forenrichments in sediments are a proxy foranoxic (anoxic (sulphatesulphate-reducing) conditions-reducing) conditions

Molybdenum geochemistry in the ocean: a primerMolybdenum geochemistry in the ocean: a primer




5


A hypothesis:





Core JT96-09, Vancouver Island Continental Marginn-alkanes vs. C and N isotopes; n-alkanes are exclusively derived from(terrestrial) vascular plant waxes

Carbon and nitrogen isotopes as tracers of provenance: a primer

Endmembers:Marine Terrestrial

δ13CPDB ~ -21 ~ -27 (C3 plants)δ15Nair ~ +5-9 ~ +1-3

Example:

MarineMarineTerrestrial Terrestrial

n-al

kane

s





[O2] at 300 m


•Modern fixed N supply to the ocean from rivers and theatmosphere to oceans is ~90-100 Tg yr-1

•But the loss from denitrification and sedimentary Nburial is roughly 200 Tg yr -1

•Thus, excluding N2 fixation, there is a net deficit ofvery roughly ~100 to 110 Tg yr -1.

•This imbalance is partly compensated by N2 fixation,but the integrated contribution from this source is notwell known. Recent estimates (Karl, Gruber, Sarmientoand others) suggest the modern ocean may be close tobeing in balance (but the error bars remain large!).

Consider the modern nitrogen mass balance in the sea:

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Dissolved Oxygen Concentration on the ~27.8 σT Surface

Illustration by Ingrid Hendy


Inferred export production history, NW Mexican Margin

Data of Raja Ganeshram


MD02-2508

15

20

25

30

35

40

45

500 5 10 15 20 25

Reflectance (L*)

MD02-2508

Depth (m)

0 20 40 60 80

-44

-42

-40

-38

-36

-34

GRIP (d18O)

Age (Ka)

CORE MD02-2508 Cruise MONA-IMAGES VIII (June 2002)Location : Western Margin of Baja California

Ref

lect

ance

MD

02-2

508

Grip δ

18O

Greenland-Baja Comparison

Greenland

Northwest Mexico




Was this picture different in the past?


Relative Nutrient UtilizationRelative Nutrient UtilizationPhytoplankton discriminate against 15N (ε ~ 5-6 ‰) when NO3

- isabundant. As NO3

- utilization proceeds with distance from the nitratesource, the product becomes isotopically heavier. Discrimination has little effect on δ15N when NO3

- is scarce.

DenitrificationDenitrificationReduction of NO3

- by denitrifying bacteria strongly fractionates theproduct N2 (which is depleted in 15N) from the substrate (ε ~ -30 ‰) .The residual NO3

- becomes progressively enriched as denitrificationproceeds and N2 and N2O are lost to the atmosphere.

NN22 Fixation ( Fixation (δδ1515N of NN of N22 = 0 = 0 ‰‰))No fractionation occurs: the Norg produced has a δ15N of ~0 ‰.

Nitrogen Isotopes As Nitrogen Isotopes As PaleotracersPaleotracers

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Brandes et al., 1998, GBC


Corg

Opal

0

10

20

30

40

50

4 8 12 200 300 400 500 0.01 0.02 0.03

2 4 6 8 100 200 300 400

1

2

3

Organic Carbon (Wt. %)

Biogenic Opal (Wt. %) Opal MAR (mg/cm2/kyr)

Organic CarbonMAR (mg/cm2/kyr) Ba/Al (Wt. Ratio)

NH8P, 1018 m water depth

Bioturbated

Laminated

Higher exportproduction

Lower exportproduction


6 7 8 9 10

4 3 20

10

20

30

40

50

60

BioturbatedLaminated

δ15N (‰ to Air)

NH8P, 1018 m water depth

1

2

3

δ18O smoothed (‰ to PDB)

δ15N

More

denitrifica

tion

Less denitrification


Los Angeles

Key Coring Sites and Surface Currents, Southern Californian Margin

~ 1 km water depth,below O2 minimum

Presented by Tom Pedersen at the SOLAS Summer School, Cargése, Corsica, 30 June - 11th July 2003 Presented by Tom Pedersen at the SOLAS Summer School, Cargése, Corsica, 30 June - 11th July 2003Hendy and Pedersen, in prep

8


7.8

18.3

6.3

7.2

11.6

140° 130° 120° 110° W

W8709-8PC

W8709-13PC

ODP 1017

NH22P

Midway

Nearshore

Monterey Bay

San Pedro Basin

Gulf of California

20°

30°

40°

50°N

11

14coring site

trap siteδ15N(NO3-) value

Oregon

California

Mexico

0.2 m

l/l

Vanc. Is.

S. Kienast et al., 2002, Paleoceanography

Nitrate δ15N in the California Undercurrent, ~250 m depth


6

8

10

12

14

16

18

20

33.8 34 34.2 34.4 34.6 34.8

δ15Nnitrate (150-350m)

δ15Nnitrate (450-600m)

δ15N

nitra

te

salinity

ETNP

San Pedro Basin

Oregon

Monterey

ETNP

Oregon

Washington

Kienast et al. 2002

Presented by Tom Pedersen at the SOLAS Summer School, Cargése, Corsica, 30 June - 11th July 2003Hendy and Pedersen, in prep


ODP Hole 1017E, S. California Margin1 km water depth

Age,

kyr

ExportProduction

Pore-waterAnoxia

Hendy and Pedersen, in prep

Presented by Tom Pedersen at the SOLAS Summer School, Cargése, Corsica, 30 June - 11th July 2003Bolivina counts by Kevin Cannariatto

Benthic foraminifera aspaleotracers:

•Bolivina spissa tolerates very lowoxygen concentrations.•Note that it becomes a significantcomponent of the total benthicassemblage in the intervals when theδ15N is heavy.•B. spissa grows on the seafloor (inthis case at ~1 km water depth) whilethe δ15N signal is generated in thesurface waters.•Both proxies together imply tightvertical links between surface andintermediate-depth waters.




Was this picture different in the past?

Yes!/Oui!

9


A related issue:A related issue:

Are there implications for global climateAre there implications for global climatebound up in variations in the intensity ofbound up in variations in the intensity ofdenitrificationdenitrification in the NE tropical Pacific and in the NE tropical Pacific andelsewhere?elsewhere?


Hendy and Pedersen, in prep

8

12


Denitrifying bacteria (Denitrifying bacteria (Thiobacillus denitrificansThiobacillus denitrificansand other and other sppspp.) reduce NO.) reduce NO33

-- and produce N and produce N22OOand Nand N22 gases. gases.


Flueckiger et al., Science, 1999

GRIP N2O

CH4

BYRD N2O

GRIP ∆T

D-O 8


Unpublished data, courtesy Jacqueline Flueckiger, University of Bern

12


Altabet et al., 2002Nature

Chlorins12

8

δ15N

δ15N

Greenland δ18Oice

Oman Margin,Arabian Sea

10


Vostok ∆T, deg C

Taylor Dome pCO2

Altabet et al., 2002

δ15N

δ15N

Arabian Sea, Oxygen Minimum Intensity

Arabian Sea, Oxygen Minimum IntensityNB: the timescale for theArabian Sea cores is notindependent, but was derived by correlation toGRIP. It is thusassumption dependent.

High-frequencyvariability ofdenitrificationintensity in the

Arabian Sea

Altabet et al., 2002

812


•• A A multiproxy multiproxy approach is valuable (perhaps mandatory?) in anyapproach is valuable (perhaps mandatory?) in anyattempt to interpretattempt to interpret paleoceanographic paleoceanographic history. history.

•• The equatorial Pacific was unlikely to have been an enhanced CO The equatorial Pacific was unlikely to have been an enhanced CO22sink during glacial periods.sink during glacial periods.

Summary:Summary:

•• Off California and Mexico, late Quaternary climate Off California and Mexico, late Quaternary climatevariations were accompanied by biological variations were accompanied by biological responses in surface responses in surface waters waters andand changes in changes in oxygenation at 1 km depth. oxygenation at 1 km depth.

•• The The multiproxymultiproxy approach strongly implies approach strongly impliesthat the vertical that the vertical CCorgorg flux was a (critical?) flux was a (critical?)factor in modulating the intensity offactor in modulating the intensity ofdenitrificationdenitrification in the northeast subtropical in the northeast subtropicalPacific and probably elsewhere (e.g. ArabianPacific and probably elsewhere (e.g. ArabianSea)Sea)..


•• The coupling of upwelling, export production and The coupling of upwelling, export production and denitrificationdenitrification in the Eastern Tropical North in the Eastern Tropical North Pacific (andPacific (andelsewhere) had global implications for climate.elsewhere) had global implications for climate.

Summary Summary ((contcont’’dd))::


CO2

∆T

CH4

But, the ultimate objective remains. We can perhaps explain partsof these profiles, but we are not yet at a level of comprehensiveunderstanding that can explain the glacial-interglacial cycling.

Moreover, why do there seem to be fixed maxima and minima?This is an extremely important question for which there is atpresent no answer!

Documents

Late Quaternary History of Export Themes or topics ... · • An ultimate goal: explain the Vostok CO 2 record • Where has export production been important? ... • Case studies: