The impact on atmospheric CO 2 of iron fertilization induced changes in the ocean's biological pump

Abstract. Using numerical simulations, we quantify the impact of changes in the ocean's biological pump on the air-sea balance of CO2 by fertilizing a small surface patch in the high-nutrient, low-chlorophyll region of the eastern tropical Pacific with iron. Decade-long fertilization experiments are conducted in a basin-scale, eddy-permitting coupled physical/biogeochemical/ecological model. In contrast to previous studies, we find that most of the dissolved inorganic carbon (DIC) removed from the euphotic zone by the enhanced biological export is replaced by uptake of CO2 from the atmosphere. Atmospheric uptake efficiencies, the ratio of the perturbation in air-sea CO2 flux to the perturbation in export flux across 100 m, integrated over 10 years, are 0.75 to 0.93 in our patch size-scale experiments. The atmospheric uptake efficiency is insensitive to the duration of the experiment. The primary factor controlling the atmospheric uptake efficiency is the vertical distribution of the enhanced biological production and export. Iron fertilization at the surface tends to induce production anomalies primarily near the surface, leading to high efficiencies. In contrast, mechanisms that induce deep production anomalies (e.g. altered light availability) tend to have a low uptake efficiency, since most of the removed DIC is replaced by lateral and vertical transport and mixing. Despite high atmospheric uptake efficiencies, patch-scale iron fertilization of the ocean's biological pump tends to remove little CO2 from the atmosphere over the decadal timescale considered here.

[1]  P. Falkowski,et al.  Ocean Iron Fertilization--Moving Forward in a Sea of Uncertainty , 2008, Science.

[2]  M. Levasseur,et al.  Ocean Biogeochemical Dynamics , 2007 .

[3]  B. Quéguiner,et al.  Effect of natural iron fertilization on carbon sequestration in the Southern Ocean , 2007, Nature.

[4]  F. Millero.  The marine inorganic carbon cycle. , 2007, Chemical reviews.

[5]  E. Boyle,et al.  Mesoscale Iron Enrichment Experiments 1993-2005: Synthesis and Future Directions , 2007, Science.

[6]  K. Matsumoto,et al.  Model simulations of carbon sequestration in the northwest Pacific by patch fertilization , 2006 .

[7]  L. Bopp,et al.  Globalizing results from ocean in situ iron fertilization studies , 2006 .

[8]  K. Lindsay,et al.  Nitrogen fixation amplifies the ocean biogeochemical response to decadal timescale variations in mineral dust deposition , 2006 .

[9]  George A. Jackson,et al.  The evolution and termination of an iron‐induced mesoscale bloom in the northeast subarctic Pacific , 2005 .

[10]  Ulf Riebesell,et al.  Synthesis of iron fertilization experiments: From the iron age in the age of enlightenment , 2005 .

[11]  David Archer,et al.  Feasibility of ocean fertilization and its impact on future atmospheric CO2 levels , 2005 .

[12]  Corinne Le Quéré,et al.  Role of Marine Biology in Glacial-Interglacial CO2 Cycles , 2005, Science.

[13]  Stephanie Dutkiewicz,et al.  Interactions of the iron and phosphorus cycles: A three‐dimensional model study , 2005 .

[14]  Richard A. Feely,et al.  A global ocean carbon climatology: Results from Global Data Analysis Project (GLODAP) , 2004 .

[15]  Keith Lindsay,et al.  Upper ocean ecosystem dynamics and iron cycling in a global three‐dimensional model , 2004 .

[16]  Taro Takahashi,et al.  Southern Ocean Iron Enrichment Experiment: Carbon Cycling in High- and Low-Si Waters , 2004, Science.

[17]  William Miller,et al.  The decline and fate of an iron-induced subarctic phytoplankton bloom , 2004, Nature.

[18]  E. Boyle,et al.  Modeling the global ocean iron cycle , 2004 .

[19]  N. Gruber,et al.  Offsetting the radiative benefit of ocean iron fertilization by enhancing N2O emissions , 2003 .

[20]  Watson W. Gregg,et al.  Phytoplankton and iron: validation of a global three-dimensional ocean biogeochemical model , 2003 .

[21]  N. Mahowald,et al.  Sensitivity study of meteorological parameters on mineral aerosol mobilization, transport, and distribution , 2003 .

[22]  Stéphane Blain,et al.  An ecosystem model of the global ocean including Fe, Si, P colimitations , 2003 .

[23]  R. Slater,et al.  Effects of patchy ocean fertilization on atmospheric carbon dioxide and biological production , 2003 .

[24]  Corinne Le Quéré,et al.  Dust impact on marine biota and atmospheric CO2 in glacial periods , 2003 .

[25]  P. Boyd,et al.  Will Ocean Fertilization Work? , 2003, Science.

[26]  Q. Schiermeier.  Climate change: The oresmen , 2003, Nature.

[27]  D. Mackey,et al.  Iron in the western Pacific: a riverine or hydrothermal source for iron in the Equatorial Undercurrent? , 2002 .

[28]  F. Joos,et al.  Feedback mechanisms and sensitivities of ocean carbon uptake under global warming: Ocean carbon uptake , 2001 .

[29]  P. Falkowski,et al.  Dis-Crediting Ocean Fertilization , 2001, Science.

[30]  K. Taylor.  Summarizing multiple aspects of model performance in a single diagram , 2001 .

[31]  Gian-Kasper Plattner,et al.  Feedback mechanisms and sensitivities of ocean carbon uptake under global warming , 2001 .

[32]  Andrew J. Watson,et al.  A mesoscale phytoplankton bloom in the polar Southern Ocean stimulated by iron fertilization , 2000, Nature.

[33]  Alexander F. Shchepetkin,et al.  Model evaluation experiments in the North Atlantic Basin : simulations in nonlinear terrain-following coordinates , 2000 .

[34]  S. Doney.  Major challenges confronting marine biogeochemical modeling , 1999 .

[35]  R. Murnane,et al.  Spatial distribution of air‐sea CO2 fluxes and the interhemispheric transport of carbon by the oceans , 1999 .

[36]  F. Joos,et al.  Global warming and marine carbon cycle feedbacks on future atmospheric CO2 , 1999, Science.

[37]  Syukuro Manabe,et al.  Simulated response of the ocean carbon cycle to anthropogenic climate warming , 1998, Nature.

[38]  Raphael Kudela,et al.  A massive phytoplankton bloom induced by an ecosystem-scale iron fertilization experiment in the equatorial Pacific Ocean , 1996, Nature.

[39]  K. Johnson,et al.  Control of community growth and export production by upwelled iron in the equatorial Pacific Ocean , 1996, Nature.

[40]  A. J. Watson,et al.  Testing the iron hypothesis in ecosystems of the equatorial Pacific Ocean , 1994, Nature.

[41]  J. Sarmiento,et al.  Potential of marine macroalgae as a sink for CO2: Constraints from a 3-D general circulation model of the global ocean , 1992 .

[42]  J. Toggweiler,et al.  Downward transport and fate of organic matter in the ocean: Simulations with a general circulation model , 1992 .

[43]  J. Sarmiento,et al.  Three‐dimensional simulations of the impact of Southern Ocean nutrient depletion on atmospheric CO2 and ocean chemistry , 1991 .

[44]  W. Broecker,et al.  Factors limiting the reduction of atmospheric CO2 by iron fertilization , 1991 .

[45]  U. Siegenthaler,et al.  Estimates of the effect of Southern Ocean iron fertilization on atmospheric CO2 concentrations , 1991, Nature.

[46]  S. Fitzwater,et al.  Iron in Antarctic waters , 1990, Nature.

[47]  John H. Martin.  glacial-interglacial Co2 change : the iron hypothesis , 1990 .

[48]  J. Toggweiler,et al.  A new model for the role of the oceans in determining atmospheric PCO2 , 1984, Nature.

[49]  Alexander F. Shchepetkin,et al.  The regional oceanic modeling system (ROMS): a split-explicit, free-surface, topography-following-coordinate oceanic model , 2005 .

[50]  D. Sigman.  6.18 – The Biological Pump in the Past , 2003 .

[51]  Timothy P. Boyer,et al.  World ocean atlas 2001 : objective analyses, data statistics, and figures : CD-ROM documentation , 2002 .

[52]  S. Wakeham,et al.  A new, mechanistic model for organic carbon fluxes in the ocean based on the quantitative association of POC with ballast minerals , 2001 .