The role of the vertical fluxes of particulate organic matter and calcite in the oceanic carbon cycle: Studies using an ocean biogeochemical general circulation model

Distributions of chemical tracers in the world ocean are well reproduced in an ocean general circulation model which includes biogeochemical processes (biogeochemical general circulation model, B-GCM). The difference in concentration of tracers between the surface and the deep water depends not only on the export production but also on the remineralization depth. Case studies changing the vertical profile of particulate organic matter (POM) flux and the export production show that the phosphate distribution can be reproduced only when the vertical profile of POM flux observed by sediment traps is used. The export production consistent with the observed distribution of phosphate is estimated to be about 10 GtC/yr. Case studies changing the vertical profile of calcite flux and the rain ratio, a ratio of production rate of calcite against that of particulate organic carbon (POC), show that the rain ratio should be smaller than the widely used value of 0.25. The rain ratio consistent with the observed distribution of alkalinity is estimated to be 0.08 to approximately 0.10. This value can be easily understood in a two-box model where the difference of remineralization depth between POC and calcite is taken into account.