Seasonal and Interannual Variability in the Location, Structure and Transport of Antarctic Circumpolar Current Fronts South of Australia

John A. Church, Antarctic CRC & CSIRO Division of Marine Research, Hobart, Australia
Richard Coleman, Antarctic CRC & Department of Geography and Environmental Studies, University of Tasmania, Hobart, Australia
Neil J. White, Antarctic CRC & Division of Marine Research, Hobart, Australia
Stephen R. Rintoul, Antarctic CRC & Division of Marine Research, Hobart, Australia

Abstract:

Six full depth CTD sections have been completed across the Southern Ocean south of Australia between 1991 and 1996. These sections have been complemented by ongoing repeat XBT sections during austral summer (November to March) and a two year deployment of moored instruments measuring the transport of the Sub-Antarctic Front of the Antarctic Circumpolar Current (the Sub-Antarctic Flux and Dynamics Experiment). The repeat CTD sections have been used to derive a relationship between upper ocean temperatures and dynamic height thus allowing dynamic height to be estimated from the repeat XBT sections. These in situ data sets were used to define a synthetic geoid which was combined with TOPEX/POSEIDON and ERS-1/2 altimeter data mapped to the locations of the repeat XBT and CTD tracks to estimate the seasonal and interannual variability in the location, structure and transport of Antarctic Circumpolar Current fronts south of Australia. The altimeter data implies the latitude of the SubAntarctic Front varies by about 1.5 deg. for the repeat CTD section (143.5 degE) but increases to 2.3-3 deg. only two degrees further east at the repeat XBT section where the width of the front can change by a factor of two. The annual surface height variations are less than 10% of the total variability and the annual surface current variations are typically less than 0.1 ms-1. The total eastward transport south of Australia (assuming barotropic fluctuations on the seasonal time scale) varies by ~10 Sv. After averaging the transport estimates over 50 days, the standard deviation of the transport is about 10 Sv if barotropic motions are assumed or 4 Sv if baroclinic motions are assumed. The altimeter estimates will be compared with estimates of the transport variability from the in situ data sets.