HEAT AND SALT CHANGES ON THE CONTINENTAL-SHELF WEST OF THE ANTARCTIC PENINSULA BETWEEN JANUARY 1993 AND JANUARY 1994

Hydrographic measurements from four cruises between January 1993 and J anuary 1994 over the continental shelf west of the Antarctic Peninsula allow analysis of seasonal changes in heat and salt content of this r egion. Changes above the permanent pycnocline (about 150 m) follow a s easonal pattern of cooling and increasing in salt from summer to winte r and warming and freshening from winter to summer. These near-surface changes expressed as net heating or salting rate, were above 80 W m(- 2) and 4 mg salt m(-2) s(-1). The year to year difference was small co mpared to the seasonal changes. There was no seasonal pattern to the c hanges below the permanent pycnocline; heat and salt content increased or decreased together, with magnitudes about half (50 W m(-2) and 2.0 mg salt m(-2) s(-1)) that observed near the surface. Subpycnocline wa ter warmed (10 W m(-2)) and increased salt (0.5 mg salt m(-2) s(-1)) f rom one January to the next. Exchange of Upper Circumpolar Deep Water (UCDW), an oceanic water mass, and West Antarctic Peninsula modified C ircumpolar Deep Water, a, cooled version of UCDW on the shelf, is resp onsible for these changes. During the exchange process, UCDW cools by loosing heat to the cold, near-surface Winter Water left by the deep m ixing during the previous winter. Subpycnocline heat and salt changes occur as a difference between onshore and vertical diffusion with vert ical diffusivities of (1.0, 0.36) x 10(-4) m(2) s(-1), for heat and sa lt, respectively, and a horizontal diffusivity of 37 m(2) s(-1). The a nnual change is due to a net flux of UCDW onto the shelf during 1993, with most of the exchange occurring fall and winter. Meandering of the Antarctic Circumpolar Current along the shelf break in this area seem s to cause these exchanges. Deep across-shelf cuts in the bottom topog raphy may also play a role.