You’ve heard that the Arctic ice cap has shrunk, and that there are sea lanes open in the northern summer that had not been open previously, and on and so forth.
Since the start of the satellite record in 1979, scientists have observed the continued disappearance of older “multiyear” sea ice that survives more than one summer melt season. Some scientists suspected that this loss was due entirely to wind pushing the ice out of the Arctic Basin — a process that scientists refer to as “export.” In this study, Ron Kwok and Glenn Cunningham at NASA’s Jet Propulsion Laboratory in Pasadena, Calif., used a suite of satellite data to clarify the relative role of export versus melt within the Arctic Ocean.*
Some of the ice in the arctic is “mutiyear sea ice,” or essentially, a floating glacier, in that the ice consists of material built up over multiple winters and not melted away during the summer. The ice flows through the Arctic in a fairly regular pattern, with MYI observed being “exported” through various routes throughout the year. Most of this process occurs because of winds and currents, but an increasing amount seems to be accounted for by in situ melting. Scientists looked at a 17 year record of data collected by polar-observing satellites and instruments such as NASA’s Quick Scatterometer, the Ice, Cloud and land Elevation Satellite, the Advanced Microwave Scanning Radiometer, and the European Space Agency’s European (ERS)-1 and -2 satellites.
The researchers demonstrate that between 1993 and 2009 a significant amount of MYI, about 1,400 cubic kilometers, was lost due to melt. They further demonstrate that the rate of this melting has increased through time.
One data set showed that over a 17-year period about 947,000 square kilometers, which amounts to 32% percent of the MYI that had disappeared, was lost in the Beaufort Sea due to melt. Calculations using estimate of ice thickness from 2004 to 2009 show a melt loss of 1,400 cubic kilometers (about 20% percent of the total loss by volume).
In other words, of the loss that happens every year, more is due to melt than previously thought, and this amount seems to be increasing. This has several implications. For example, ice that is blown out of the arctic sea melts in a more dispersed fashion, but extensive in situ melting means an influx of much more fresh water into the Arctic marine environment. This can influence oceanic circulation.
The last year of the study showed a dramatic drop in MYI melt. This is not because less sea ice disappeared that year, but the reasons are not explored in detail. Also, the study only accounts for roughly half of the disappearing ice, because it is not geographically comprehensive. Further studies of other regions where ice melts need to be carried out and integrated with this one.
Kwok, R., & Cunningham, G. (2010). Contribution of melt in the Beaufort Sea to the decline in Arctic multiyear sea ice coverage: 1993-2009 Geophysical Research Letters, 37 (20) DOI: 10.1029/2010GL044678