The ocean acts as a significant sink for atmospheric carbon dioxide (CO₂), regulating global climate. The biological carbon pump (BCP) transfers organic carbon, fixed in the euphotic zone via phytoplankton photosynthesis, to the deep ocean. This mechanism is believed to have played a crucial role in regulating atmospheric CO₂ during the glacial-interglacial transitions. However, paleo-records show that the export production preserved in the sediment is not high enough to explain the tens of ppm CO₂ drawdown. On the other hand, field observations have shown that the ratio of dissolved organic carbon (DOC) to dissolved organic phosphorus (DOP) and the ratio of dissolved organic nitrogen (DON) to DOP increase with depth, suggesting a preferential remineralization of organic phosphorus, compared to nitrogen and carbon, and also suggesting a rapid recycling of phosphorus in the surface ocean. Consequently, preferential remineralization of organic phosphorus alleviates phosphorus limitation and enhance carbon sequestration, offering another explanation for the glacial-interglacial atmospheric CO₂ oscillations. Our model results show that CO₂ concentration can be drawn down by 121.35 ppm when both DOP and particulate organic phosphorus (POP) are allowed to be preferentially remineralized compared to DON/DOC and PON/POC.

biological carbon pump, ocean carbon cycle, preferential remineralization, inverse model