NASA researchers investigate why
A big question puzzling scientists is why sea ice cover surrounding the continent of Antarctica has been increasing, while a dramatic loss of sea ice is occurring in the Arctic Ocean.
Now, a new NASA-led study may have found the answer.
The team, led by Son Nghiem of NASA’s Jet Propulsion Laboratory, used satellite radar, sea surface temperature, topography, and ocean depth data to study the processes affecting Antarctic sea ice. What they found is that two persistent geological features — the topography of Antarctica and the depth of the ocean surrounding it — are influencing winds and ocean currents to drive the formation, evolution, and preservation of Antarctic sea ice cover.
"Our study provides strong evidence that the behavior 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 Nghiem in a NASA news release.
Scientists have hypothesized several reasons to explain the behavior of Antarctic sea ice, especially since global temperatures continue to increase. But what is protecting Antarctic sea ice has remained a mystery.
Nghiem and his team analyzed radar data from NASA’s QuikScat satellite from 1999 to 2009 to trace the paths of Antarctic sea ice movement and type, focusing on the 2008 growth season — a year that had large seasonal variability.
What they found is the sea ice that forms and builds up early in the sea ice growth season gets pushed offshore and northward by winds. These winds, which are shaped by Antarctica’s topography, pile ice up against the ice shield, enhancing its thickness. This band of ice, which varies in width from 62 to 620 miles (100 to 1,000 kilometers), shields the younger, thinner ice behind the pack from being reduced by winds and waves.
But how does it maintain this ice shield, even in the face of warming atmospheric temperatures?
It turns out that at the peak of the ice growth season, the boundary of the ice shield remains behind a 30 degree Fahrenheit (-1 degree Celsius) temperature line surrounding Antarctica. This temperature line corresponds with the southern Antarctic Circumpolar Current front — a boundary that separates the circulation of cold and warm waters around Antarctica (seen in the above image). The team thinks that this front likely follows deeper under the ocean, maintaining the boundary.
Unfortunately, the Arctic does not have this type of protection, which is why it continues to shrink at global temperatures rise.
The results are published in the journal Remote Sensing of Environment.
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