NASA Explains Why Sea Ice Cover Around Antarctica Is Increasing

Washington: Why has the sea ice cover surrounding Antarctica been increasing slightly, in sharp contrast to the drastic loss of sea ice occurring in the Arctic Ocean? A new NASA-led study has found the geology of Antarctica and the Southern Ocean are responsible.

The researchers used satellite radar, sea surface temperature, land form and bathymetry (ocean depth) data to study the physical processes and properties affecting Antarctic sea ice.

They found that two persistent geological factors -- the topography of Antarctica and the depth of the ocean surrounding it -- are influencing winds and ocean currents, respectively, to drive the formation and evolution of Antarctica's sea ice cover and help sustain it.

"Our study provides strong evidence that the behaviour of Antarctic sea ice is entirely consistent with the geophysical characteristics found in the southern polar region, which differ sharply from those present in the Arctic," said lead researcher Son Nghiem of NASA's Jet Propulsion Laboratory, Pasadena, California.

The study was published in the journal Remote Sensing of Environment.

The researchers analysed radar data from NASA's QuikScat satellite from 1999 to 2009 to trace the paths of Antarctic sea ice movements and map its different types.

They focused on the 2008 growth season, a year of exceptional seasonal variability in Antarctic sea ice coverage.

Their analyses revealed that as sea ice forms and builds up early in the sea ice growth season, it gets pushed offshore and northward by winds, forming a protective shield of older, thicker ice that circulates around the continent.

The persistent winds, which flow down slope off the continent and are shaped by Antarctica's topography, pile ice up against the massive ice shield, enhancing its thickness.

This band of ice, which varies in width from roughly 100 to 1,000 kms, encapsulates and protects younger, thinner ice in the ice pack behind it from being reduced by winds and waves.

The team also used QuikScat radar data to classify the different types of Antarctic sea ice.

Older, thicker sea ice returns a stronger radar signal than younger, thinner ice does. They found the sea ice within the protective shield was older and rougher (due to longer exposure to wind and waves), and thicker (due to more ice growth and snow accumulation).

As the sea ice cover expands and ice drifts away from the continent, areas of open water form behind it on the sea surface, creating "ice factories" conducive to rapid sea ice growth, the researchers said.