Enrichment of silicate and CO 2 and circulation of the bottom water in the Weddell Sea

Abstract

Deep and bottom water from the Enderby Basin, which is strongly enriched in silicate, enters the Weddell Sea off Kapp Norvegia parallel to the coast. However, the bottom water in this region originates from the northern Weddell Sea, indicating a southward return flow of bottom water west of the prime meridian. The eastern Weddell Sea margin was identified as the place where a significant silicate enrichment (at least 15 μmol kg -1) and a weak CO 2 enrichment of the bottom water occurs, related to a regional recirculation cell. The deep and bottom water continue their course through the Weddell Sea along the base of the continental slope, where further to the west they are underridden by a thin layer of new, silicate-poor bottom water. A silicate maximum and weak TCO 2 maximum are formed at the interface between deep and bottom water at approximately 4000 m. This silicate maximum occurs in the central Weddell Sea as well. This indicates an exchange of the deep water between the boundaries and the interior of the Weddell basin; the northwestern Weddell Sea was identified as an important site for this. Bottom layer enrichment of CO 2 in the central Weddell Sea (3 μmol kg -1) is comparable to that in the eastern Weddell Sea, but silicate enrichment in the former is much less than in the latter. The extent of bottom layer enrichment suggests that about 2% of the primary production reaches the seafloor, supporting the view that the biological pump mechanism in this area is effectively transporting downward a significant amount of CO 2.