A Continental Shelf Pump for CO2 on the Adélie Land Coast, East Antarctica

Dense Shelf Water (DSW) supplied from Antarctic coastal polynyas is a key component of the global meridional overturning circulation, contributing to the formation of Antarctic Bottom Water. The export of DSW from the continental shelf acts as a conduit for the offshore transport of CO₂ thereby connecting the atmosphere and the surface waters with the deep ocean. In this study, the export of inorganic carbon with DSW from the Mertz and Ninnis Polynyas on the Adélie Land Coast in East Antarctica is quantified, and the implications for Southern Ocean biogeochemistry and carbon export are discussed. Shipboard observations from two summer surveys in 2015 and 2017 were paired with model-derived DSW transport estimates to explore the offshore and cross-shelf fluxes of inorganic carbon. The largest flux of inorganic from the shelf region was exported through the northern boundary across the Adélie and Mertz Sills, with an additional westward transport from the Mertz through the D’Urville Trough Sill. The source of inorganic carbon to DSW is derived mainly from inflowing modified Circumpolar Deep Water, with additional contributions from brine rejection during sea ice formation. This work suggests that Dense Shelf Water export serves as a continental shelf pump for CO_2, representing an important transport pathway from the shallow Antarctic continental shelf to the deep ocean.