Author(s): Pat Langhorne
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Abstract: The presence of ice shelves around 44% of the coastline of Antarctica means that the coastal sea ice in this region is influenced by processes that take place at the base of ice shelves. In particular, theoretical studies estimate that basal meltwater may contribute as much as 0.2 m to the sea ice thickness over significant portions of the sea ice cover. Thus the sea ice in the vicinity of an ice shelf forms due to heat transfer to two heat sinks: the atmosphere and the ocean. The reason the ocean can act as a heat sink is that it, in turn, has interacted with an ice shelf. Over the past decade we have conducted a number of experiments that examine the contribution that platelet ice makes to the landfast sea ice of McMurdo Sound, Antarctica. Our winter measurements have conclusively linked the presence of loose platelet ice in the water column with its incorporation into the sea ice cover. To explain the appearance of ice crystals in the water column we examine the oceanographic changes as autumn progresses into winter. From mid winter a layer develops at the ice-water interface that eventually becomes 10s of meters thick and is 10s of mK below its in situ freezing point. We estimate the contribution to the sea ice cover by heat rejection to an oceanic sink and find that it is significant and of the order of magnitude predicted by models. While progress towards understanding and quantifying the contribution of ice shelves to the ocean and sea ice has been made, there are still many mysteries.
Year: 2008