From Individual Plankton Cells To Pelagic Marine Ecosystems And To Global Biogeochemical Cycles

Abstract

It is often assumed that the biological CO2 pump in the oceans is essentially driven by the upward flux of NO3, so that the potential export of biogenic carbon from the upper ocean is stoichiometrically equivalent to N-derived phytoplankton new production. The steady-state/stoichiometry model does not consider that ecosystem dynamics have a significant influence on the export or sequestration of biogenic carbon. Contrary to this assumption, there are several cases where ecosystems do have a significant effect on the export and sequestration of biogenic carbon. These include the fixation of nitrogen gas in the upper layer of the ocean (phytoplankton and coral reefs), the export of carbon by organisms with high carbon content (thecate dinoflagellates, coccolithophores, foraminifers, pteropods), the production of long-lived dissolved organic matter, and the fact that the pathways of export may differ in length and complexity. This is considered within the context of a general typology of pelagic marine ecosystems, based on the various possible combinations linking standing stock to production of phytoplankton: (1) production and standing stock dominated by large cells (e.g. upwelling, ice-edge and episodic blooms); (2) production by small and large cells, standing stock dominated by large cells (e.g. exceptional blooms); (3) production and standing stock of small and large cells (e.g. spring bloom in the North Atlantic); (4) production by small and large cells, standing stock dominated by small cells (e.g. Alaskan Gyre in the North Pacific); (5) production and standing stock dominated by small cells (e.g. oligotrophic ocean). These five types of ecosystems correspond to different modes of phytoplankton production (as controlled by hydrodynamics) and different structures (as reflected in the standing stocks), which influence the pathways of carbon export and sequestration as well as the renewable marine resources.