Direct velocity measurements in the Subantarctic Front and over Campbell Plateau, southeast of New Zealand

Abstract

Flow variability in the Subantarctic Front (SAF) and over the Campbell Plateau, southeast of New Zealand, is examined using data from a current meter mooring array along with conductivity‐temperature‐depth (CTD) and satellite altimetry data. These data are part of an ongoing study of ocean climate variability in the region. Contrasting flow regimes were found with very energetic and highly variable flows in the SAF flowing along the Subantarctic Slope and much weaker flows over the Campbell Plateau. Currents up to 75 cm s−1 were observed in the core of the SAF, while flows over the plateau were typically less than 10 cm s−1. Estimates of the total bottom referenced transport from three CTD sections across the SAF varied between 48 and 68 Sv. Transports were also estimated using TOPEX/Poseidon altimetry sea truthed with the CTD data. The resulting 8‐year time series exhibited high variability resulting from current meanders and eddy activity. One event in the record appeared to be the result of a cyclonic eddy passing through the mooring array. This event was modeled using an idealized geostrophic eddy. The simulation reproduces the main features observed in the current meter records and the surface topography from the TOPEX/Poseidon altimeter. Inspection of the TOPEX/Poseidon data suggests that large cyclonic and anticyclonic eddies occur in the frontal region with a frequency of around 9 yr−1.