Long-term variations in the mass and heat transport in the oceanic regime of the Filchner-Ronne Ice Shelf, Antarctica

Long term observations of the flow of dense waters from their area of formation to the abyss of the World Ocean, and the return flow of warm waters, are central to climate research. For the Weddell Sea, an important component of such a system is the formation of High Salinity Shelf Water (HSSW) on the continental shelf north of Ronne Ice Front, the transformation to Ice Shelf Water (ISW) by basal melting of the Filchner-Ronne ice shelf, and the transport of ISW overflowing the shelf break to the deep ocean.

While basal melt-rates are currently low, studies have suggested that they have the potential to increase dramatically in a future, warmer world, although the underlying processes are subject to large uncertainty.

We operate a number of long-term monitoring stations in the oceanic regime of Filchner-Ronne Ice Shelf. We have yearlong oceanographic time series from the area back to 1968. In 1977 we establish the S2 observatory on the Filchner sill, today the longest existing oceanographic time serie from Antarctica. In 1999 we established Site 5 on Ronne Ice Shelf where access to the 402 m water column was gained through the overlying 763-m thick ice shelf using a hot-water drill. In the 2014/15 austral summer, we reoccupied Site 5 and deployed three instrumented moorings for long term monitoring of the oceanic mass and heat transport beneath Ronne Ice Shelf. In addition, we deployed three radars at the snow surface to monitor the melting/freezing rate at the ice shelf base.

Results from the 1968-2015 time series show the sensitivity of the sub-ice shelf circulation to changes in conditions over the continental shelf and the sea ice concentration in the Weddell Sea.