#O09 Variable stoichiometry ocean bgc

Abstract

Both laboratory and field populations of pico-sized (< 2 µm) marine phytoplankton exhibit plasticity in their cellular phosphorus, nitrogen, and carbon content in response to changing environmental conditions such as light and nutrient supply. Phylogenetic affiliation is an additional control on pico-phytoplankton cellular C:N:P stoichiometry. Variable carbon to nutrient stoichiometry for marine primary production has important implications for the carbon-climate feedback of the ocean’s biological pump that remain largely unrepresented and unquantified in Earth System Models. We have implemented three new explicit pico-phytoplankton groups (Prochlorococcus, Synechococcus, and pico-eukaryotes) for a total of six phytoplankton functional types with variable C:P stoichiometry within the CESM-BEC ocean biogeochemistry model. Pico-phytoplankton dominate the low-nutrient subtropical ocean gyres with their greater cellular C:P plasticity giving them a competitive advantage over larger plankton (nano-plankton, diatoms) with lower C:P stoichiometry. The pattern of high C:P plankton within the subtropics and lower C:P plankton in the equatorial and polar latitudes reduces the meridional gradient in carbon export predicted by most ocean models that assume a constant Redfield C:N:P stoichiometry. Pico-phytoplankton contribute 10, 4, and 8% to global carbon export for Prochlorococcus, Synechococcus, and pico-eukaryotes, respectively. Future work will add two additional diazotrophic phytoplankton types with implementation of the nine phytoplankton types with variable C:P stoichiometry within the ACME ocean model.