Stoichiometric buffering of organic carbon export in the future and during last glacial period

Katsumi Matsumoto, University of Minnesota, Minneapolis, MN, United States and Tatsuro Tanioka, University of California Irvine, Earth System Science, Irvine, CA, United States
Ocean biogeochemists traditionally assume that phytoplankton biomass is composed of carbon (C), nitrogen (N), and phosphorus (P) in some fixed stoichiometry. Most global analyses and models of ocean biogeochemistry thus employ some fixed C:N:P stoichiometry, typically the Redfield ratio, for organic matter export. However, there is really no theoretical basis for the fixed ratio, and recent large-scale studies indicate that C:N:P ratio varies significantly on basin scales. The field has begun to explore how to represent flexible phytoplankton stoichiometry in global biogeochemical models and what the implications are for the global carbon cycle. Because the C:N:P ratio of organic matter is the gear by which nutrients drive the biological pump, the C:N:P variability has potentially significant implications on the global carbon cycle. Here we apply a power law formulation of flexible stoichiometry to an earth system model of intermediate complexity under a future warming scenario as well as glacial conditions. We demonstrate the importance of both physiology and taxonomy in driving local C:N:P variability and the importance of Antarctic sea ice in driving global C:N:P variability. This stoichiometric variability in turn buffers carbon export from changing as one might expect from nutrient export alone.