Circulation and production of Cape Darnley Bottom Water on the continental slope off the Cape Darnley polynya, East Antarctica

Abstract

The circulation and water properties of Cape Darnley Bottom Water (CDBW), which is a component of Antarctic Bottom Water (AABW) produced in the Cape Darnley polynya, were investigated using results of mooring measurements and hydrographic data collected by a ship-based conductivity-temperature-depth (CTD) profiler and instrumented elephant seals. CDBW was transported northwestward on the western flank of a gully located in Wild Canyon. As CDBW descended down the slope, its thickness increased from $\sim$100 m to $\sim$600 m. The basic properties of CDBW were determined near the Antarctic Slope Front (ASF), where modified shelf water (mSW) intrudes below the dense part of Circumpolar Deep Water (CDW) and mixes with the overlying CDW to produce CDBW. mSW is shown to be the mixture of 40–45 % CDW, 30–40 % winter water (WW), and 20–25 % shelf water (SW) produced in the Cape Darnley polynya. Compared with CDBW produced in 2008, CDBW produced in 2018 and 2019 was colder and less saline. The enhanced influence of dense WW, which is locally produced on the shelf, is suggested to drive the year-to-year variability of CDBW’s salinity, at least in these three years. Water properties indicate that CDBW basically corresponds to a water mass in a transition layer between mSW and CDW. The annual mean transport of mSW contained in CDBW was estimated to be 0.26–$1.2\times 10^6$ m${}^3$ s⁻¹