Temperature and salinity beneath Ronne Ice Shelf, Antarctica

Abstract

Salinity and temperature measurements have been made beneath Ronne Ice Shelf, Antarctica. Access to the seawater was gained by hot‐water drilling through 562 m of ice at a site 300 km from the ice front. The ice column is composed of 516 m of meteoric‐origin ice, underlain by 31 m of consolidated saline ice, with a further 15 m of unconsolidated slush at the base. The 360‐m‐deep water column beneath the ice shelf consists broadly of a 210‐m layer of Ice Shelf Water (ISW) at a potential temperature of −2.30°C and salinity 34.53, overlying a 100‐m‐thick layer of modified Western Shelf Water (−2.03°C, 34.64). The layers are separated by a weak 50‐m‐thick pycnocline. Isotopic analyses of water samples support this interpretation of the water types. Comparison of the data with published oceanographic observations from the shore lead indicate that the source of the water is either the western Berkner shelf or north of the ice front in the Ronne Depression. The measurements from the drill site broadly match predictions from a simple plume model of the sub‐ice‐shelf water circulation. In that model the basal slope of the ice shelf plays a central role in determining the properties of the ISW plume. With the exception of the upper few tens of meters the temperature and salinity of the entire water column vary by about 0.04°C and 0.03 on tidal timescales, and there is evidence for a longer‐term drift, presumably connected with shifts in the larger‐scale circulation. There is also much variability from internal wave activity. The salinity and deuterium budgets indicate that the meltwater fraction in the ISW observed at the drill site was between 5.3 and 6.5‰, in reasonable agreement with values previously found for ISW in the open ocean.