Temperature variability beneath Ronne Ice Shelf, Antarctica, from thermistor cables

Thermistor cables have been deployed at two sites beneath Ronne Ice Shelf, Antarctica. One site is to the east of a submarine ridge that delineates the eastern boundary of the Ronne Depression, and the other is 100 km to the north, above the eastern slope of the depression. Long records from the cables (up to 22 months) indicate a large difference in the temperature variability at the two sites, being an order of magnitude greater in the Ronne Depression (site 2). Although the records appear otherwise similar, there is no significant correlation between them. The high variability in the site 2 record has allowed the construction of a simple descriptive model of the local oceanographic regime. Winter freezing in the open water north of the ice front generates Western Shelf Water (WSW), a type of High Salinity Shelf Water, which travels southwest beneath the ice shelf, appearing at site 2 as a slope-trapped current at the bottom of the water column. Baroclinic instability in the flow manifests itself in the site 2 temperature record as oscillations on time scales of 5 to 15 days. The disturbances cause a periodic east-west advection of water masses across the Ronne Depression. Site 2 is on the eastern slope of the depression, where the wave-induced eastward motion forces Ice Shelf Water to rise, resulting in periodic ice-platelet formation in the water column, as surmised from conductivity-temperature-depth measurements at the site. The depth of the WSW layer decreases by 40 to 60 m during a 100-day period, starting some 4 months after the beginning of the summer. Assuming an absence of significant WSW production during the summer, the 4-month delay implies a minimum average speed of WSW flow of about 0.02 m s−1. The WSW flux into the Ronne Depression is estimated at 3 × 105 m3s−1.