Distribution and mineralogy of carbonate sediments on Antarctic shelves

We analyzed 214 new core-top samples for their CaCO3 content from shelves all around Antarctica in order to understand their distribution and contribution to the marine carbon cycle. The distribution of sedimentary CaCO3 on the Antarctic shelves is connected to environmental parameters where we considered water depth, width of the shelf, sea-ice coverage and primary production. While CaCO3 contents of surface sediments are usually low, high (>15%) CaCO3 contents occur at shallow water depths (150–200m) on the narrow shelves of the eastern Weddell Sea and at a depth range of 600–900m on the broader and deeper shelves of the Amundsen, Bellingshausen and western Weddell Seas. Regions with high primary production, such as the Ross Sea and the western Antarctic Peninsula region, have generally low CaCO3 contents in the surface sediments. The predominant mineral phase of CaCO3 on the Antarctic shelves is low-magnesium calcite. With respect to ocean acidification, our findings suggest that dissolution of carbonates in Antarctic shelf sediments may be an important negative feedback only after the onset of calcite undersaturation on the Antarctic shelves. Macrozoobenthic CaCO3 standing stocks do not increase the CaCO3 budget significantly as they are two orders of magnitude lower than the budget of the sediments. This first circumpolar compilation of Antarctic shelf carbonate data does not claim to be complete. Future studies are encouraged and needed to fill data gaps especially in the under-sampled southwest Pacific and Indian Ocean sectors of the Southern Ocean. ► High CaCO3 contents are found at water depths of 150–200m and 600–900m. ► Carbonate contents are low in high-productivity regions. ► Carbonates in surface sediments are in the form of low-Mg calcite. ► Dissolution of aragonite in the Southern Ocean cannot buffer ocean acidification. ► Macrozoobenthos does not contribute significantly to the CaCO3 budget.