The Large-Scale Thermohaline Structure of the Ross Gyre

Abstract

This study describes the large-scale thermohaline structure and circulation patterns of the Ross Gyre and is based on a quality controlled data set including about 7,000 historical and modern hydrographic stations. A new regional climatology was obtained through the objective analysys of the data on neutral surfaces. Steric height anomaly maps portray Ross Gyre as a depression south of the mid-ocean ridge between about 170 degrees E and 140 degrees W. The centre of the gyre shifts with depth from about 68 degrees S 164 degrees W in near surface levels to about 63oS 150oW at 1500 meters. Maximum estimate of the geostrophic transport within the gyre is 8.5 Sv near 150 degrees W, a factor of three lower than corresponding estimates for the Weddell Gyre. Data from a quasi-synoptic survey made by three former U.S.S.R vessels in 1985-86 are used for a more detailed description of the gyre's northern, eastern and southern boundaries. Similar to the Weddell Gyre the location of the eastern boundary is controlled by the southward extension of the Antarctic Circumpolar Current core flowing through the Udintsev Fracture Zone with the geostrophic transport of 56 Sv. The Circumpolar Deep Water spreads westwards along the southern limb of the gyre with potential temperatures still as high as 1.6 degrees C at 75 degrees S, 150 degrees W.