Assessing the influence of Subantarctic calcification on the global distribution of alkalinity

The Great Calcite Belt (GCB) in the Subantarctic region of Southern Ocean (SO) is an area of elevated calcification by coccolithophores. Through the production of calcium carbonate, coccolithophores may influence air-sea CO2 uptake and contribute ballast to sinking organic matter. Subantarctic mode water (SAMW) formed in the region of the GBC travels north in the lower thermocline; the nutrient content and upwelling of these waters at low latitudes influences global ocean productivity. Consistent with elevated calcification in the GBC, we observe a signature decrease in salinity normalized potential alkalinity in oceanographic observations of SAMW. The chemical composition of SAMW is modified by phytoplankton residing in the SAMW formation region of the SO, where coccolithophores compete for nutrient resources with diatoms. While the role of nutrient content exported in SAMW has been previously considered, modifications to SAMW alkalinity from calcification has received much more limited attention. Simulations with the ocean component of the Community Earth System Model suggest that calcification in the GCB has a significant impact on global alkalinity distributions. These results have implications for future oceanic conditions in the SO where calcification may be impaired by ocean acidification, among other rearrangements to the phytoplankton community.