Physical oceanography of the Prydz Bay region of Antarctic waters

Abstract

Hydrographic data from four major Australian cruises to the Prydz Bay region are interpreted to show features of the large-scale circulation that remain consistent across a number of years. A large cyclonic gyre, extending from within the Bay to the Antarctic Divergence north-west of the Bay, is recognised in all of the data. It is associated with a relatively narrow coastal current that runs from the southern limits of Prydz Bay past the Amery Ice Shelf, and continues westward after leaving the Bay (becoming very strong, with currents exceeding 1 m s −1) along the MacRobertson Land shelf. Part of the current flows offshore near 63°E, while another (unknown) fraction continues westward. Data from a number of current-meter moorings deployed within the Bay and on the MacRobertson Land shelf lend support to the interpretation of gross features of the circulation. Coherences between different vertical levels show that the shelf waters respond barotropically to variations of a few days period or more. Little coherence with winds measured at Davis and Mawson stations was evident. Diurnal variations are strong near the shelf edge, and are associated with substantial encroachment of (modified) Circumpolar Deep Water over the shelf break. Dense water production within Prydz Bay appears to mimic processes occurring within the Weddell Sea, involving the intrusion of modified Circumpolar Deep Water over the shelf, and its mixing with High Salinity Shelf Water (and Ice Shelf Water) promoted by marginal or unstable conditions below the intrusions. No observations of dense plumes leaving Prydz Bay have been obtained. Instead, this paper tests the hypothesis, dynamically, that locally formed Antarctic Bottom Water observed near the foot of the continental slope at 62°E in 1974, had its origin in Prydz Bay. An integral model of the descent of a dense plume over a sloping boundary, also incorporating the fully non-linear equation of state of seawater, implies an origin either within Prydz Bay or to the west of the Bay.