Collapsing Antarctic Ice Shelves
Warming From Above and Below
Antarctica holds approximately 90 percent of the world’s freshwater, locked away in ice. The mean thickness of the Antarctic ice is 2.2 km (just under 1.4 miles) due to the massively thick continental ice cap and its associated glaciers. However, along the coasts of this southernmost continent, the Antarctic ice sheets extend out over the coastal seas, forming thick, floating ice shelves.
Several of these prominent ice shelves collapsed during the past 50 years, and conventional thinking has been that the primary culprit for these collapses was atmospheric warming. Now, mounting evidence indicates the Antarctic ice shelves are under attack from above by atmospheric warming and undermined from below by oceanic warming.
But ocean warming is a relative term. In Antarctic waters, a temperature of zero degrees Celsius (32 degrees Fahrenheit) is warm. Yes, this is the freezing point of water, but it only applies to freshwater. Seawater freezes at -2 degrees Celsius (28.4 degrees Fahrenheit) due to its salinity. So, Antarctic ice-shelf temperature dynamics require the saltwater under the ice to remain below the freezing point of freshwater, thus keeping the ice from melting.
