Abstract

We quantify the transport of inorganic carbon from the continental shelf to the deep ocean in Dense Shelf Water (DSW) from the Mertz and Ninnis Polynyas along the Adélie Land coast in East Antarctica. Observations of total dissolved inorganic carbon (TCO₂) from two summer hydrographic surveys in 2015 and 2017 were paired with DSW volume transport estimates derived from a coupled ocean‐sea ice‐ice shelf model to examine the fate of inorganic carbon in DSW from Adélie Land. Transports indicate a net outflow of 227 ± 115 Tg C year^‐1 with DSW in the post‐glacial calving configuration of the Mertz Polynya. The greatest outflow of inorganic carbon from the shelf region was delivered through the northern boundary across the Adélie and Mertz Sills, with an additional transport westward from the Mertz Polynya. Inorganic carbon in DSW is derived primarily from inflowing TCO₂‐rich modified Circumpolar Deep Water; local processes (biological productivity, air‐sea exchange of CO₂, and the addition of brine during sea ice formation) make much smaller contributions. This study proposes that Dense Shelf Water export serves as a continental shelf pump for CO₂ and is a pathway to sequester inorganic carbon from the shallow Antarctic continental shelf to the abyssal ocean, removing CO₂ from atmospheric exchange on the timescale of centuries.

Plain Language Summary

Dense waters formed on the Antarctic continental shelf flow into bottom waters that spread throughout the global ocean. These dense shelf waters play an important role in transporting material from the middle and upper layers of the water column to the abyssal ocean. By combining observations and model simulations, we track the transport of dissolved CO₂ in these dense shelf waters from the continental shelf to the deep ocean from the Mertz and Ninnis Polynyas in East Antarctica. We find the largest contributor of dissolved CO₂ to dense shelf water formed in this region is the CO₂‐rich mid‐layers that move onto the continental shelf from offshore. Once on the shelf, local processes in the upper water column further enrich these waters with dissolved CO₂ before their subsequent descent into bottom waters and the abyssal ocean. Our findings highlight the importance of the CO₂‐rich mid‐layers, rather than upper ocean shelf processes, in driving the conditions for carbon sequestration in the deep ocean.

This (paywalled) article appeared on the American Geophysical Union website at https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2020JC016302