CHARACTERIZATION OF THE ANTARCTIC POLAR FRONTAL ZONE TO THE NORTH OF SOUTH GEORGIA IN SUMMER 1994

The Polar Front (PF) forms the southern boundary to the Polar Frontal Zone (PFZ) along the northern edge of the Antarctic Circumpolar Curren t (ACC). In a number of areas the position of the PF (and thus the PFZ ) is known to be influenced by topographic steering, while local bathy metry has also been implicated in the movement and retention of variou s associated mesoscale features. In this paper we examine the structur e and position of the PF as it passes over the rugged bathymetry to th e north of the Scotia Sea. Results are presented from an oceanographic transect crossing the PF to the northwest of South Georgia and from a pair of shorter transects south of the PF but north and east of the f irst. Associated with the PF was a narrow, high-speed flow embedded in broader, slower moving regions. This high-speed flow was found to hav e a geostrophic component of velocity that was slower than estimates f or other regions of the PF. Comparisons with output from recent oceano graphic models were found to be consistent with the physical observati ons. A second examination of the region after a period of 30 days sugg ested that the surface expression of the PF had shifted southward by a pproximately 35 km but that the PF was essentially in the same positio n over the southern edge of the Maurice Ewing Bank. An advanced very h igh resolution radiometer image taken during the cruise provided addit ional information about the position of the surface expression of the PF and the extent of mesoscale features that were present to the north of the study area. Immediately to the north of South Georgia, water i n the eastward flow of the ACC meets colder, more saline water flowing west along the north coast of the island. The area where these two fl ows meet was found to be variable over the 30-day timescale of the cru ise. This area is known to be of major biological significance, and va riability in the local oceanography is possibly of crucial importance to many predator species breeding at the northern end of South Georgia .