Summertime water masses off the northern Larsen C Ice Shelf, Antarctica

We report on oceanographic observations made at the northern end of Larsen C Ice Shelf in the western Weddell Sea. It appears that the Larsen C continental shelf is flushed not by High Salinity Shelf Water from the southern continental shelf, but by Modified Weddell Deep Water (MWDW) flowing across the shelf break. MWDW is observed at the ice front, having tracked west along the northward facing slopes of depressions that reach to the shelf break. Ice Shelf Water observed near the ice front is not, however, derived from MWDW directly, but from MWDW pre-conditioned by winter cooling and by salinification from sea ice production. If the ice shelf base generally is being melted only by pre-conditioned MWDW, then, contrary to recent suggestions, changes in the temperature of the deep Weddell Sea are unlikely to have a major impact on melt rates at the base of Larsen C Ice Shelf.