Séminaire
Mass loss from the West Antarctic ice shelves and glaciers has been linked to basal melt by ocean heat flux. The Totten Glacier on the Sabrina Coast (East Antarctica), which holds a 3.5 m sea-level change equivalent, also experiences rapid mass loss. Here we show for the first time that warm Modified Circumpolar Deep Water (MCDW) enters the cavity beneath the Totten Ice Shelf through a newly discovered deep channel, driving rapid basal melt (> 10 m year-1) and presumably triggering the mass loss of the Totten Glacier. MCDW is not only found in this deep channel but is widespread on the continental shelf, forming a warm (> 0.3°C) and saline (34.5–34.6) bottom layer overlaid by cold (freezing point) and fresh (34.3) Winter Water. The absence of Dense Shelf Water comes as a surprise given the relatively high rates of sea-ice production in the Dalton Polynya, east of the Totten Ice Shelf. Using a simple model driven by observed forcing, we show that freshwater input from basal melt of the Moscow University Ice Shelf (upstream of the Dalton Polynya) suppresses Dense Shelf Water formation. Consequently, MCDW is not eroded by polynya activity and floods the continental shelf. We show that the same process is underway in the Amundsen Polynya, where basal melt of Pine Island and Thwaites ice shelves inhibits dense water formation in the Amundsen Sea. Our study indicates that the ocean conditions on the Sabrina Coast more resemble those found in West Antarctica than those typical of East Antarctica, where cold and dense waters dominate the continental shelf.
jean-baptiste.sallee@locean-ipsl.upmc.fr