ISOTOPE DATA FROM ICE STATION WEDDELL - IMPLICATIONS FOR DEEP-WATER FORMATION IN THE WEDDELL SEA

Helium isotope data (He-3/He-4 ratios and He-4 concentrations) and (H2 O)-O-18/(H2O)-O-16 ratios obtained from stations occupied during the d rift of Ice Station Weddell (February to June 1992) are used, together with hydrographic data, to study formation of deep and bottom water i n the western Weddell Sea. The data indicate deep and bottom water for mation along the entire track of the ice station (71.4 to 65.8 degrees S, approximate to 53 degrees W). Ice Shelf Water (ISW) seems to contr ibute significantly to the formation of Weddell Sea Deep Water (WSDW) and Weddell Sea Bottom Water (WSBW) in the southern part of the drift track, Toward the north, the fraction of ISW contained in WSDW/WSBW de creases, This trend is overlaid by high ISW fractions in the deep and bottom waters found in the vicinity of the Larsen Ice Shelf, The fract ion of Western Shelf Water (WSW) in WSBW shows the opposite trend, inc reasing from south to north, The combined fraction of ISW and WSW in w aters with potential temperatures below 0 degrees C is about 20%, corr esponding to a roughly 200 m thick layer, Overall, WSW seems to contri bute approximately 2 to 3 times more water than ISW to the water colum n below the 0 degrees C isotherm, Using the estimated flow of ISW over the sill north of the Filchner Depression of 1 Sv [Foldvik et al,, 19 85a] together with the ratio of WSW plus Winter Water (WW) to ISW, we calculate a value of about 5 Sv for the formation rate of WSBW with a potential temperature of -0.7 degrees C, About one third of this flux represents near-surface waters (WSW/WW) which have recently been equil ibrated with the atmosphere, whereas pure ISW contributes about 10%.