patricia l. yager

The impact of nitrogen fixation on carbon sequestration: a

reassessment of the inorganic carbon system in LNLC regions

Patricia L. Yager

University of GeorgiaSchool of Marine Programs

05/26/05 DOE Workshop, Belmont, MD

Conclusion

As we debate the potential costs and benefits of iron fertilization to carbon sequestration, realize that we are already doing it in the tropical and subtropical oligotrophic oceans (albeit indirectly).


Acknowledgments

Collaborators:• Sarah Cooley (UGA)• Doug Capone (USC)• Ajit Subramaniam (LDEO)• Victoria Coales (HPL)• Tony Michaels (USC)• Ed Carpenter (Romberg)• NSF Biocomplexity Team

Funding sources:•DOE C-sequestration •NOAA OGP GCC•NASA ESS •University of Georgia•NSF Biocomplexity

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.


N2-supported new production (Lee et al., 2002)

mol C m-2 y-1

Hood et al., 2000

“only the sinking flux due to new production associated with nitrogen fixation and nutrient inputs from terrestrial and atmospheric sources can be identified as biologically-mediated transport of atmospheric CO2 to the deep ocean”

-Eppley and Peterson, Nature 197905/26/05 DOE Workshop, Belmont, MD





Hemiaulus hauckiiwith endosymbionts

Hemiaulus indicus with Richelia intracellularis

Plus many other free-living or endosymbiotic cyanobacteria and Bacteria(Karl et al., Biogeochemistry, 2002



Trichodemsium

Diazotrophs

Courtesy of SERC

Courtesy of R. Shipe

Courtesy of P. Lundgren and B. Bergman


http://web.uconn.edu/mcbstaff/benson/Frankia/N2fix.htm

But here’s the catch: The nitrogenase enzyme

needs iron


Amazon River (looking south)

(Tg y-1)Jickells et al. (Science 2005)

Where does the iron going into the ocean come from?


River fluxes

sensitive to land use

and hydrology (climate)

The Amazon is one of the fewrivers that impact the oceanbeyond the continental shelf

NASA SeaWIFS




Dust from Africa•Sensitive to climate and land use•Max flux: May-Sept•Deposition site depends on ITCZ

Africa

Brazil

Africa


Jickells et al. (Science 2005)


“In order for a process to qualify as a sink for anthropogenic CO2 emissions, the flux of carbon must have increased relative to its pristine value.”

-Smith and Mackenzie, 1991


Long Term Variability of Barbados Dust: The Link to Climate

0

5

10

15

20

25

30

35

40

45

50

J-65J-66J-67J-68J-69J-70J-71J-72J-73J-74J-75J-76J-77J-78J-79J-80J-81J-82J-83J-84J-85J-86J-87J-88J-89J-90J-91J-92J-93J-94J-95J-96J-97J-98

Mineral Dust (ug/m3)

Major El Niño events: 1972-73, 1982-83, 1986-87, 1991-92, 1997-98NOAA-CIRES Climate Diagnostics Center Multivariate ENSO Index web site:

http://www.cdc.noaa.gov/~kew/MEI/mei.html].

Monthly Means, 1965-1998

Lots of variability, generally coherent from year-to-year.

Courtesy of J. M. Prospero (USGS dust workshop online: http://esp.cr.usgs.gov/info/dust/ )

http://www.cdc.noaa.gov/~kew/MEI/mei.html





What was the longer term rainfall history of the Soudano-Sahel and what are the implications for dust transport?

Prospero & Lamb Science 302: 1024 ‑ 1027, 2003. 7 November 2003

This period of extended drought and increased dust occurs at a time when the global warming trend has become most visible.

Niger River Catchment Rainfall and River Flow

Period of Barbados

Record

CONCLUSION: drought in Africa over the past 30 years was unique in the 20th century – probably dust transport as well.

Courtesy of J. M. Prospero (USGS dust workshop online: http://esp.cr.usgs.gov/info/dust/ )

Carbon sequestration hypotheses:

1) The input of iron associated with aeolian dust and

riverine sources stimulates photosynthesis via

enhanced nitrogen fixation (Biocomplexity Project).

2) The enhanced productivity caused by N2 fixation

yields greater export of biological carbon which, in

turn, draws down the pCO2 of the surface ocean

and increases oceanic uptake of atmospheric CO2

(This grant).


Carbon research questions

Can we predict how indirect iron fertilization (sensitive to climate and

other human activities) will help sequester CO2?

Only if we understand system mechanistically


Atlantic Cruise Tracks

MP 1Jan-Feb 2001

MP3June-August 2001

M/P 8April - May 2003

MANTRA/PIRANA Biocomplexity


MANTRA/PIRANA - MP02 - Pacific Cruise 1 -

4/9/2001-4/30/2001

MP05 - Pacific Cruise 2 - 6/25/2002-7/19/2002



The Subtropical Pacific


Sample Precision: DIC: 0.95 µmol/kg ALK: 2.1 µmol/kg del13DIC: 0.15 pCO2: 1 µatm

Inorganic carbon system

DIC: SOMMA/coulometer ALK: potentiometric titration

Underway pCO2: Equilibrator/LICOR

del13C-DIC: GC/MS


Location and Size of the Amazon River Plume Based on Monthly Climatologies of Satellite Derived K490

MP1

MP8

MP3

DelVecchio and Subramaniam,

2004


∆pCO2 (air-sea)(calculated from discrete DIC & ALK surface samples)

Cooley and Yager (JGR submitted)

The river plumeconverts an oceanic source to a sink


WinterSummer

DICALK

DIC

ALK

Depth profilesSummer data shows significantly lower concentrations at the surface due to presence of the river.

Cooley and Yager (JGR submitted) 05/26/05 DOE Workshop, Belmont, MD

Z

DIC

Production

Summer Winter

Winter SML

Expected

Z Respiration

Winter SML

DIC

Enhanced production? Or enhanced respiration?

SummerExpected Winter

The question is whether there is more or less than predicted by

simple river dilution

S.R. Cooley


y = 56.84x + 312.58

R2 = 0.9899

y = 50.62x + 178.46

R2 = 0.9501

1500

1600

1700

1800

1900

2000

2100

2200

2300

2400

2500

27 28 29 30 31 32 33 34 35 36 37

Salinity

DIC or TA (umol C/kg SW)

Winter SML DIC

Summer SMLDICWinter SML ALK

Summer SMLALKLinear (SummerSML ALK)Linear (SummerSML DIC)

S.R. CooleyCooley and Yager (JGR submitted)

Alkalinity is conservative; DIC is not


Biological/Physical Effects A. Mixing model calculates proportional

contributions of plume, seawater

(Assumes conservative TA, salinity)

B. Calculate predicted DIC

C. Compare predicted, observed DIC

plume seawaterobserved


Cooley and Yager (JGR submitted)

Net community production?The difference between observed and that predicted from mixing alone

Up to 1 mol C m-2

Would be underestimate if include gas exchange:

(0-0.2 mol C m-2)


Aerosol [Fe] clearly linked to ITCZ seasonality

Dissolved [Fe]•uncoupled from atm •clearly linked to river

Subramaniam et al. (Nature in review)

Mean dry deposition of labile Fe: Winter: 0.24 µmol m-2 d-1) Spring: 0.09 µmol m-2 d-1) Summer: 0.06 µmol m-2 d-1)



Tricho biomass linked to dust

Richelia abundance •clearly linked to river

Subramaniam et al. (Nature in review) 05/26/05 DOE Workshop, Belmont, MD


Depth integrated N2-fixation



Biological carbon drawdownCarbon drawdown

is dominated by diatom-

endosymbionts.


Trichodesmium

Heterotrophic bacteria

Diatoms with Richelia

GrazersPicoplankton

Phytoplankton community structure matters



Mass Flux at 200m y = -40.034x + 1464.9

R2 = 0.9228

0

50

100

150

200

250

300

350

31.5 32.0 32.5 33.0 33.5 34.0 34.5 35.0 35.5 36.0

Salinity (PSS)

Mass Flux (mg/d/m2)

See also Deuser et al. (1988)

Courtesy of A. Subramaniam


Location and Size of the Amazon River Plume Based on Monthly Climatologies of Satellite Derived K490

MP1

MP8

MP3

DelVecchio & Subramaniam,

2004


Organic Carbon makes up 5-40% of Total Flux i.e. 5-40% of 150 mg/m2/d = 7.5-60 mg/m2/dOver the area of the Richelia habitat, this is 2 – 15 Tg C y-1

The global mean air-to-sea flux of carbon is 15 mg C/m2/day.



Conclusions

• Nitrogen fixation is clearly linked to iron fertilization.

• The enhanced production yields greater carbon sequestration when the community is dominated by the diatom-diazotroph symbionts found in the river plume.

• This mechanism, in the WTNA region alone, likely accounts for sequestration of up to 15 Tg C yr-1.


Remaining questions

Seasonal and interannual variability versus long-term change in iron flux?

Cooley and Yager (GBC, in prep)

Where does the “export” go?Cooley and Yager (in prep): modeling

Yager (in prep): isotope analysis

Is this a globally significant phenomenon?MMAMBO to NSF

DOE?


Conclusion

As we debate the potential costs and benefits of iron fertilization to carbon sequestration, realize that we are already doing it in the tropical and subtropical oligotrophic oceans (albeit indirectly).


Acknowledgments

Collaborators:• Sarah Cooley (UGA)• Doug Capone (USC)• Ajit Subramaniam (LDEO)• Victoria Coales (HPL)• Tony Michaels (USC)• Ed Carpenter (Romberg)• NSF Biocomplexity Team

Funding sources:•DOE C-sequestration •NOAA OGP GCC•NASA ESS •University of Georgia•NSF Biocomplexity




Sarah Cooley

The Role of the Amazon Plume in the Western Tropical Atlantic Ocean

Inorganic Carbon Budget


patricia l. yager

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