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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 Georgia School of Marine Programs. 05/26/05 DOE Workshop, Belmont, MD. Conclusion.

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Patricia L. Yager

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  1. The impact of nitrogen fixation on carbon sequestration: a reassessment of the inorganic carbon system in LNLC regions Patricia L. Yager University of Georgia School of Marine Programs 05/26/05 DOE Workshop, Belmont, MD

  2. 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

  3. Acknowledgments • Funding sources: • DOE C-sequestration • NOAA OGP GCC • NASA ESS • University of Georgia • NSF Biocomplexity Collaborators: • Sarah Cooley (UGA) • Doug Capone (USC) • Ajit Subramaniam (LDEO) • Victoria Coales (HPL) • Tony Michaels (USC) • Ed Carpenter (Romberg) • NSF Biocomplexity Team 05/26/05 DOE Workshop, Belmont, MD

  4. N2-supported new production (Lee et al., 2002) mol C m-2 y-1 “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 1979 Hood et al., 2000 05/26/05 DOE Workshop, Belmont, MD

  5. Diazotrophs Hemiaulus hauckii with endosymbionts Trichodemsium Courtesy of SERC Courtesy of P. Lundgren and B. Bergman Hemiaulus indicus with Richelia intracellularis Plus many other free-living or endosymbiotic cyanobacteria and Bacteria (Karl et al., Biogeochemistry, 2002 Courtesy of R. Shipe 05/26/05 DOE Workshop, Belmont, MD

  6. But here’s the catch: The nitrogenase enzyme needs iron http://web.uconn.edu/mcbstaff/benson/Frankia/N2fix.htm 05/26/05 DOE Workshop, Belmont, MD

  7. Where does the iron going into the ocean come from? Amazon River (looking south) (Tg y-1) Jickells et al. (Science 2005) River fluxes sensitive to land use and hydrology (climate) 05/26/05 DOE Workshop, Belmont, MD

  8. The Amazon is one of the few rivers that impact the ocean beyond the continental shelf NASA SeaWIFS 05/26/05 DOE Workshop, Belmont, MD

  9. Africa Brazil • Dust from Africa • Sensitive to climate and land use • Max flux: May-Sept • Deposition site depends on ITCZ Africa 05/26/05 DOE Workshop, Belmont, MD

  10. Jickells et al. (Science 2005) 05/26/05 DOE Workshop, Belmont, MD

  11. “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 05/26/05 DOE Workshop, Belmont, MD

  12. Long Term Variability of Barbados Dust: The Link to Climate Lots of variability, generally coherent from year-to-year. Monthly Means, 1965-1998 Major El Niño events: 1972-73, 1982-83, 1986-87, 1991-92, 1997-98 NOAA-CIRES Climate Diagnostics Center Multivariate ENSO Index web site: http://www.cdc.noaa.gov/~kew/MEI/mei.html]. Courtesy of J. M. Prospero (USGS dust workshop online: http://esp.cr.usgs.gov/info/dust/ )

  13. Period of Barbados Record Niger River Catchment Rainfall and River Flow What was the longer term rainfall history of the Soudano-Sahel and what are the implications for dust transport? CONCLUSION: drought in Africa over the past 30 years was unique in the 20th century – probably dust transport as well. This period of extended drought and increased dust occurs at a time when the global warming trend has become most visible. Prospero & Lamb Science 302: 1024 ‑ 1027, 2003. 7 November 2003 Courtesy of J. M. Prospero (USGS dust workshop online: http://esp.cr.usgs.gov/info/dust/ )

  14. Carbon sequestration hypotheses: • The input of iron associated with aeolian dust and riverine sources stimulates photosynthesis via enhanced nitrogen fixation (Biocomplexity Project). • 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). 05/26/05 DOE Workshop, Belmont, MD

  15. 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 05/26/05 DOE Workshop, Belmont, MD

  16. MANTRA/PIRANA Biocomplexity Atlantic Cruise Tracks MP 1 Jan-Feb 2001 MP3 June-August 2001 M/P 8 April - May 2003 05/26/05 DOE Workshop, Belmont, MD

  17. The Subtropical Pacific MP05 - Pacific Cruise 2 - 6/25/2002-7/19/2002 MANTRA/PIRANA - MP02 - Pacific Cruise 1 - 4/9/2001-4/30/2001 MP06 - Pacific Cruise 3 - 9/22/2002-10/16/2002 MP09 - Pacific Cruise 4 - 7/13/2003-8/23/2003 05/26/05 DOE Workshop, Belmont, MD

  18. Inorganic carbon system ALK: potentiometric titration DIC: SOMMA/coulometer Sample Precision: DIC: 0.95 µmol/kg ALK: 2.1 µmol/kg del13DIC: 0.15 pCO2: 1 µatm del13C-DIC: GC/MS Underway pCO2: Equilibrator/LICOR 05/26/05 DOE Workshop, Belmont, MD

  19. 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

  20. ∆pCO2 (air-sea) (calculated from discrete DIC & ALK surface samples) The river plume converts an oceanic source to a sink Cooley and Yager (JGR submitted) 05/26/05 DOE Workshop, Belmont, MD

  21. Depth profiles Summer data shows significantly lower concentrations at the surface due to presence of the river. DIC ALK Winter Summer ALK DIC Cooley and Yager (JGR submitted) 05/26/05 DOE Workshop, Belmont, MD

  22. The question is whether there is more or less than predicted by simple river dilution DIC DIC Summer Expected Winter Expected Winter Summer Respiration Production Z Z Winter SML Winter SML S.R. Cooley Enhanced production? Or enhanced respiration? 05/26/05 DOE Workshop, Belmont, MD

  23. S.R. Cooley Alkalinity is conservative; DIC is not Cooley and Yager (JGR submitted) 05/26/05 DOE Workshop, Belmont, MD

  24. Biological/Physical Effects • Mixing model calculates proportional contributions of plume, seawater (Assumes conservative TA, salinity) • Calculate predicted DIC • Compare predicted, observed DIC observed plume seawater 05/26/05 DOE Workshop, Belmont, MD

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

  26. Aerosol [Fe] clearly linked to ITCZ seasonality 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) • Dissolved [Fe] • uncoupled from atm • clearly linked to river Subramaniam et al. (Nature in review) 05/26/05 DOE Workshop, Belmont, MD

  27. Tricho biomass linked to dust • Richelia abundance • clearly linked to river Subramaniam et al. (Nature in review) Subramaniam et al. (Nature in review) 05/26/05 DOE Workshop, Belmont, MD

  28. Depth integrated N2-fixation Subramaniam et al. (Nature in review) 05/26/05 DOE Workshop, Belmont, MD

  29. Biological carbon drawdown Carbon drawdown is dominated by diatom-endosymbionts. Subramaniam et al. (Nature in review) 05/26/05 DOE Workshop, Belmont, MD

  30. Phytoplankton community structure matters Trichodesmium Diatoms with Richelia Heterotrophic bacteria Grazers Picoplankton Subramaniam et al. (Nature in review) 05/26/05 DOE Workshop, Belmont, MD

  31. Courtesy of A. Subramaniam See also Deuser et al. (1988) 05/26/05 DOE Workshop, Belmont, MD

  32. 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

  33. Subramaniam et al. (Nature in review) Organic Carbon makes up 5-40% of Total Flux i.e. 5-40% of 150 mg/m2/d = 7.5-60 mg/m2/d Over 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. 05/26/05 DOE Workshop, Belmont, MD

  34. 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. 05/26/05 DOE Workshop, Belmont, MD

  35. 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

  36. 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

  37. Acknowledgments • Funding sources: • DOE C-sequestration • NOAA OGP GCC • NASA ESS • University of Georgia • NSF Biocomplexity Collaborators: • Sarah Cooley (UGA) • Doug Capone (USC) • Ajit Subramaniam (LDEO) • Victoria Coales (HPL) • Tony Michaels (USC) • Ed Carpenter (Romberg) • NSF Biocomplexity Team 05/26/05 DOE Workshop, Belmont, MD

  38. The Role of the Amazon Plume in the Western Tropical Atlantic Ocean Inorganic Carbon Budget Sarah Cooley 05/26/05 DOE Workshop, Belmont, MD

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