Thermohaline structure and variability in the Terra Nova Bay polynya, RossSea

Hydrological measurements from three cruises during the summers 1994/95, 19 95/96 and 1997/98 in the western sector of the Ross Sea allow summer and ye ar to year changes in heat and salt content in the Terra Nova Bay polynya t o be analysed. Changes in the surface layer (upper pycnocline) followed the expected seasonal pattern of warming and freshening from the beginning to the end of the summer. These near-surface changes, expressed as net heating and salting rate, were about 11 W m(-2) and -6 mg salt m(-2) s(-1). The he ating changes were substantially lower than the estimated heat supplied by the atmosphere during the summer, which underlines the importance for this season of the advective component carried by the currents in the total heat budget. The year to year differences were about one or two orders of magni tude smaller than the seasonal changes in the surface layer. In the interme diate and deep layers, the summer heat and salt variability were of the sam e order as or one order higher than from one summer to the nest. The differ ences in sign and magnitude for the heat change in the upper and in the low er pycnocline indicate a weak connection in the summer period between the s urface heat fluxes and the deep waters. A local source of very cold water ( with temperatures below the surface freezing point) of about 0.3 Sv has bee n detected close to the Terra Nova Bay coast. It arose out of the interacti on of the shallow-intermediate layers of High Salinity Shelf Water with the coastal glaciers. The presence and the variability of this cold water poin t to the significant role of the thermohaline properties of Terra Nova Bay waters in controlling the floating glacier by governing the basal melting p rocesses.