Late winter oceanography off the Sabrina and BANZARE coast (117–128°E), East Antarctica

Abstract

We report on the late winter oceanography observed beneath the Antarctic sea ice offshore from the Sabrina and BANZARE coast of Wilkes Land, East Antarctica (117–128°E) in September–October 2007 during the Sea Ice Physics and Ecosystem eXperiment (SIPEX). A pilot program using specifically designed ‘through-ice’ conductivity-temperature-depth (CTD) and acoustic Doppler current profiling (ADCP) systems was conducted to opportunistically measure water mass properties and ocean currents at major ice stations. Additional water mass properties across the survey region were collected from Ice-Argo floats deployed during the voyage north of the 3000 m isobath. The mean drift of the floats was along the slope to the west with the Antarctic Slope Current. Vertical profiles of the potential temperature reveal the deepest ( ∼ 350 – 400 m ) winter mixed layer (WML) in the western sector of the survey northwest of the Dalton Iceberg Tongue polynya. The meridional structure of the Antarctic Slope Front, i.e. the monotonic shoaling of the WML across the upper continental slope, is found to be similar to the previous observations in summer. A strong bottom-intensified intrusion of modified Circumpolar Deep Water (mCDW) as warm as 0 °C was detected beneath the fast ice south of the continental shelf break at 118°E. An mCDW intrusion of similar strength was detected near this location in the austral summer of 1996. We hypothesise that there is a persistent supply of mCDW and associated ocean heat flux to this region of the continental shelf that is capable of migrating to the grounding lines of the nearby Totten Glacier and Moscow University Ice Shelf. There was no detection of locally formed dense shelf water capable of forming Antarctic Bottom Water at the shelf break locations sampled despite the number of minor polynyas across this region. Ocean current measurements, limited to a maximum period of 24 h and 50–100 m depth by the relative scarcity of backscatter, found increased mean vertical speeds at the offshore stations (6–17 cm s −1) relative to the shelf break (2.3–6.4 cm s −1). The diurnal variation in the ADCP range reflected the diel migration of zooplankton occurring beneath the sea ice in late winter, with greater range/abundance offshore. Concurrent time series of wind, ocean current and their influence on sea ice drift from global positioning system (GPS) compass measurements were examined but the length of data acquisitions limited the applicability of this analysis.