Patricia L. Yager
description
Transcript of 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).
05/26/05 DOE Workshop, Belmont, MD
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
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05/26/05 DOE Workshop, Belmont, MD
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
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Hemiaulus hauckiiwith endosymbionts
Hemiaulus indicus with Richelia intracellularis
Plus many other free-living or endosymbiotic cyanobacteria and Bacteria(Karl et al., Biogeochemistry, 2002
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Trichodemsium
Diazotrophs
Courtesy of SERC
Courtesy of R. Shipe
Courtesy of P. Lundgren and B. Bergman
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http://web.uconn.edu/mcbstaff/benson/Frankia/N2fix.htm
But here’s the catch: The nitrogenase enzyme
needs iron
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Amazon River (looking south)
(Tg y-1)Jickells et al. (Science 2005)
Where does the iron going into the ocean come from?
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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
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Dust from Africa•Sensitive to climate and land use•Max flux: May-Sept•Deposition site depends on ITCZ
Africa
Brazil
Africa
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Jickells et al. (Science 2005)
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“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
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Long Term Variability of Barbados Dust: The Link to Climate
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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/ )
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).
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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
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Atlantic Cruise Tracks
MP 1Jan-Feb 2001
MP3June-August 2001
M/P 8April - May 2003
MANTRA/PIRANA Biocomplexity
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MANTRA/PIRANA - MP02 - Pacific Cruise 1 -
4/9/2001-4/30/2001
MP05 - Pacific Cruise 2 - 6/25/2002-7/19/2002
MP06 - Pacific Cruise 3 - 9/22/2002-10/16/2002
MP09 - Pacific Cruise 4 - 7/13/2003-8/23/2003
The Subtropical Pacific
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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
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Location and Size of the Amazon River Plume Based on Monthly Climatologies of Satellite Derived K490
MP1
MP8
MP3
DelVecchio and Subramaniam,
2004
05/26/05 DOE Workshop, Belmont, MD
∆pCO2 (air-sea)(calculated from discrete DIC & ALK surface samples)
Cooley and Yager (JGR submitted)
The river plumeconverts an oceanic source to a sink
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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
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y = 56.84x + 312.58
R2 = 0.9899
y = 50.62x + 178.46
R2 = 0.9501
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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
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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
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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)
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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)
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Subramaniam et al. (Nature in review)
Tricho biomass linked to dust
Richelia abundance •clearly linked to river
Subramaniam et al. (Nature in review) 05/26/05 DOE Workshop, Belmont, MD
Subramaniam et al. (Nature in review)
Depth integrated N2-fixation
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Subramaniam et al. (Nature in review)
Biological carbon drawdownCarbon drawdown
is dominated by diatom-
endosymbionts.
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Trichodesmium
Heterotrophic bacteria
Diatoms with Richelia
GrazersPicoplankton
Phytoplankton community structure matters
Subramaniam et al. (Nature in review)
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Mass Flux at 200m y = -40.034x + 1464.9
R2 = 0.9228
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Salinity (PSS)
Mass Flux (mg/d/m2)
See also Deuser et al. (1988)
Courtesy of A. Subramaniam
05/26/05 DOE Workshop, Belmont, MD
Location and Size of the Amazon River Plume Based on Monthly Climatologies of Satellite Derived K490
MP1
MP8
MP3
DelVecchio & Subramaniam,
2004
05/26/05 DOE Workshop, Belmont, MD
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.
Subramaniam et al. (Nature in review)
05/26/05 DOE Workshop, Belmont, MD
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.
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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?
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).
05/26/05 DOE Workshop, Belmont, MD
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
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05/26/05 DOE Workshop, Belmont, MD
Sarah Cooley
The Role of the Amazon Plume in the Western Tropical Atlantic Ocean
Inorganic Carbon Budget
05/26/05 DOE Workshop, Belmont, MD