Antarctic Polar Front Zone in the Western Scotia Sea—Summer 1975

Abstract

The component of the FDRAKE-75 data obtained by the R/V Conrad in the western Scotia Sea reveals a definite sequence of thermohaline stratification zones encountered on passing from Antarctic to Sub-antarctic waters. A Polar Front Zone, displaying multiple temperature minima, separates the Antarctic Zone, characterized by a single intense T-min above 200 m, from the Subantarctic Zone with its nearly isohaline layer from 100 m to over 400 m. The Antarctic Zones of the Weddell and the Scotia Seas aye separated by a cold, relatively homogeneous zone situated in the southern Scotia Sea called the Weddell-Scotia Confluence. The boundaries of the Polar Front Zone are highly meandered and isolated eddies of Subantarctic water may occur within the zone. The main axis of the Antarctic Circumpolar Current apparently lies close to the Subantarctic boundary of the, Polar Front Zone, while a secondary axis is associated with the southern limit of the Polar Front Zone. Inspection of the Islas Orcadas and Melville data, the western section of the FDRAKE-75 data set, also shows a meandered Polar Front Zone. It further suggests the possibility of eddies of Polar Front Zone water within the Subantarctic Zone. The thick, nearly isohaline layer of the Subantarctic Zone possesses a weak negative salinity gradient (at least within a few hundred kilometers of the Polar Front Zone). It is proposed that this structure is a remnant of a winter period homogeneous layer, which is altered from above by summer sea-air interaction and from below by upward mixing of Antarctic water introduced into the Subantarctic Zone by cross-frontal isopycnal exchange. This latter process may cool and freshen the overall characteristics of the Subantarctic water in relation to expected characteristics by local sea-air factors.