Observed variability of water properties and transports on the World Ocean Circulation Experiment SR1b section across the Antarctic Circumpolar Current

Abstract

R/V Hespe ´rides occupied the World Ocean Circulation Experiment SR1b repeat section across the Scotia Sea in February 1995, February 1996, and February 1998. On each cruise the same set of 21 hydrographic stations with characteristic spacing <20 nautical miles was visited. The results of the three surveys display a characteristic zonation of water masses in the region, which is defined by four hydrographic fronts. The net geostrophic transport of the Antarctic Circumpolar Current (ACC) across SR1b, computed with reference to the deepest common depth of each pair of adjacent stations, is similar in all three cruises, 144 Sv in February 1995, 131 Sv in February 1996, and 134 Sv in February 1998, and compares well with earlier computations of the ACC transport across Drake Passage. A close comparison of the vertical distributions of water properties on SR1b reveals changes in the structure of the ACC that are linked to undersampled current mesoscale activity, as suggested by infrared satellite images contemporary to the cruises. The most remarkable features are several ‘‘hydrographic discontinuities’’ observed in the Antarctic Zone south of the Southern ACC Front (SACCF), which are believed to be signatures of eddies produced east of the Shackleton Fracture Zone. The paper further addresses the different contribution of each ACC zonal band to the net geostrophic transport across SR1b on each Hespe ´rides occupation.