Pelagic calcium carbonate production and shallow dissolution in the North Pacific Ocean

Abstract

AbstractPlanktonic calcifying organisms play a key role in regulating ocean carbonate chemistry and atmospheric CO2. Surprisingly, references to the absolute and relative contribution of these organisms to calcium carbonate production are lacking. Here we report quantification of pelagic calcium carbonate production in the North Pacific, providing new insights on the contribution of the three main planktonic calcifying groups. Our results show that coccolithophores dominate the living calcium carbonate (CaCO3) standing stock, with coccolithophore calcite comprising ~90% of total CaCO3production, and pteropods and foraminifera playing a secondary role. We show that pelagic CaCO3production is higher than the sinking flux of CaCO3at 150 and 200 m at ocean stations ALOHA and PAPA, implying that a large portion of pelagic calcium carbonate is remineralised within the photic zone; this extensive shallow dissolution explains the apparent discrepancy between previous estimates of CaCO3production derived from satellite observations/biogeochemical modeling versus estimates from shallow sediment traps. We suggest future changes in the CaCO3cycle and its impact on atmospheric CO2will largely depend on how the poorly-understood processes that determine whether CaCO3is remineralised in the photic zone or exported to depth respond to anthropogenic warming and acidification.