What can models tell us about the global cycles of elements such as carbon, oxygen, phosphorus, nitrogen, and iron?

Humans beings have a major impact on the cycles of elements such as carbon and nitrogen. A major part of my research uses models to characterize these cycles and to estimate the impact of human activity and climate change upon them.

A significant part of my work has been as a participant in the Ocean Carbon Model Intercomparison Project which developed a standard framework for running a simple diagnostic biogeochemical model in different circulation models.

One of the outgrowths of this work has been studies (with Robbie Toggweiler and Irina Marinov) of how the ocean circulation determines the magnitude and sensitivity of carbon pumps.

Another outgrowth of this work has been to use these models to do depletion experiments, simulating the effect of iron fertilization. Iron fertilization has been proposed as a cheap, easy verifiable, controllable and environmentally benign process for offsetting carbon dioxide emissions. Our research argues that this claim may be severely oversold.

References

Gnanadesikan, A., R.D. Slater, N. Gruber and J.L. Sarmiento, Oceanic vertical exchange and new production: A comparison of models and data, Deep Sea Res. II. , 49: 363-401, 2002.

Gnanadesikan, A. J.L. Sarmiento, and R.D. Slater, Effects of patchy ocean fertilization on atmospheric carbon dioxide and biological productivity, Global Biogeochemical Cycles , 17, 1050, doi:10.1029/2002GB001940, 2003.

Toggweiler, J.R., A. Gnanadesikan, S.Carson, R.J. Murnane and J.L. Sarmiento, The strength of carbon pumps in box models, GCMs and the real ocean, Part 1: The solubility pump, Global Biogeochem. Cyc. , 17(1),1026, doi:10.1029/2001GB001401, 2003.

Toggweiler, J.R., R.J. Murnane, S. Carson, A. Gnanadesikan and J.L. Sarmiento, The strength of carbon pumps in box models, GCMs and the real ocean, Part 2: The biological pump, Global Biogeochem. Cyc. 17(1),1027, doi:10.1029/2001GB001841,2003.

Gnanadesikan, A., J.P. Dunne, R.M. Key, K. Matsumoto, J.L. Sarmiento, R.D. Slater and P.S. Swathi, Oceanic ventilation and biogeochemical cycling: Understanding the physical mechanisms that produce realistic distributions of tracers and productivity, Global Biogeochem. Cycles , GB4010, doi:10.1029/2003GB002097, 2004.

Matsumoto, K., J.L. Sarmiento, R.M. Key, J.L. Bullister, K. G. Caldeira, J.-M. Campin, S. C. Doney, H. Drange, M. J. Follows, Y. Gao, A. Gnanadesikan, N. Gruber, A. Ishida, F. Joos, R. M. Key, K. Lindsay, F. Louanchi, E. Maier-Reimer, R. J. Matear, P. Monfray, A. Mouchet, R. G. Najjar, J.C. Orr, G.-K. Plattner, C. L. Sabine, J. L. Sarmiento, R. Schlitzer, R.D. Slater, P.S. Swathi, I. Totterdell, M.-F. Weirig, M. E. Wickett, Y. Yamanaka, and A. Yool, Evaluation of ocean carbon cycle models with data-based metrics, Geophys. Res. Lett., 31, L07303, doi:10.1029/2003GL018970, 2004.

Mignone, B., J.L. Sarmiento, R.D. Slater and A. Gnanadesikan, Sensitivity of sequestration efficiency to mixing processes in the global ocean, Energy, 29, 1467-1478, 2004.

Orr,.J.C., O. Aumont, L. Bopp, S.C. Doney, V.J. Fabry, R.M. Feely, M. Follows, A. Gnanadesikan, A. Ishida, F. Joos, R.M. Key, K. Lindsay, E. Maier-Reimer, R. Matear, P. Monfray, A. Mouchet, R.G. Najjar, G.K. Plattner, C.L. Sabine, J.L. Sarmiento, R. Schlitzer, R.D. Slater, I. Totterdell, M.F. Weirig, Y. Yamanaka, A. Yool, Anthropogenic ocean acidification over the twenty-first century and its impact on calcifying organisms, Nature, 437,681-686, 2005.

Dunne,J.P., R.A. Armstrong, A. Gnanadesikan, J.L. Sarmiento and R.D. Slater, Empirical and mechanistic models for particle export ratio, Global Biogeochemical Cycles, 19, GB4026, doi:10.1029/2004GB002390, 2005.

Mignone, B., A. Gnanadesikan, J.L. Sarmiento and R.D. Slater, Central role of Southern Hemisphere winds and eddies in modulating the oceanic uptake of anthropogenic carbon, Geophys. Res. Lett., 33, L01604, doi:10.1029/2005Gl024464, 2006.

Marinov, I., A. Gnanadesikan, J.R. Toggweiler, J.L. Sarmiento, The Southern Ocean Biogeochemical Divide, Nature, 441,964-967, 2006.

Gnanadesikan, A.,J.L. Russell, and F. Zeng, How does ocean ventilation change under global warming? Ocean Science 3 , 43-53, 2007. Link