ON THE TEMPORAL VARIABILITY OF THE TRANSPORT THROUGH DRAKE PASSAGE

A recently obtained series of bottom pressure measurements from variou s positions in the Drake Passage (DP) has been used to estimate the tr ansport variability of the Antarctic Circumpolar Current (ACC) under t he assumption that the variability is predominantly barotropic and thu s proportional to the north-minus-south pressure difference, The stand ard deviations in derived transport range from 5.3 Sv in 1993 to 8.9 S v in 1990 (10-day filter; 1 Sv = 10(6) m(3) s(-1)). All values are les s than the 10 Sv (IO-day filter) obtained during the International Sou thern Ocean Studies (ISOS) program at DP between the mid 1970s and ear ly 1980s [Whitworth and Peterson, 1985]. Although some of this discrep ancy is due to differences in procedure in dealing with gaps in the da ta, our data suggest that the ACC transport can be persistently less v ariable over several years than was previously thought. In particular, the ISOS data set contains two large-amplitude changes in pressure di fference over timescales less than 2 weeks, while no similar events we re observed in the more recent data. Although the more recent pressure gauges were deployed at different positions to those used in ISOS, th eir reliability as indicators of ACC transport changes has been establ ished by examination of simultaneous pressure measurements within DP.