Thick ice disappeared, Arctic sea ice changes more slowly

According to a new study released by NASA scientist Ron Kwok of the Jet Propulsion Laboratory in Pasadena, California, the Arctic Ocean's sea ice cover has changed since 1958 and has gone from the thickest ice to the oldest. With so little old thick ice, the rate of decrease in ice thickness has slowed. New ice grows faster, but is more vulnerable to weather and wind. The thickness of the ice is therefore more variable than the effect of global warming.

Kwok's research, published today in the journal Letters of research on the environment, combined with decades of declassified submarine measurements from the US Navy with more recent data from four satellites, to create a 60-year record of changes in sea ice thickness in the Arctic . He found that since 1958 the arctic ice cover had lost about two-thirds of its thickness, as it had been on average in the late summer. The old ice has shrunk by nearly 800,000 square miles (over 2 million square kilometers). Today, 70% of the ice cover consists of ice that forms and melts in a single year, what scientists call seasonal ice.

Sea ice of all ages is frozen seawater. However, while sea ice survives during several melt seasons, its characteristics change. Multi-year ice is thicker, stronger and rougher than seasonal ice. It's much less salty than seasonal ice; Arctic explorers used it as drinking water. Satellite sensors observe enough of these differences that scientists can use spatial data to distinguish between two types of ice.

Thinner and weaker seasonal ice is naturally more vulnerable to weather than thick, multi-year ice. It can be moved more easily by the wind, as was the case in the summer of 2013. During this time, the prevailing winds accumulated the layer of ice on the coasts, which made the layer of ice thicker. During months.

The vulnerability of ice can also be demonstrated by the increasing variation in the thickness and extent of sea ice in the Arctic from one year to the next at the same time. during the last decade. In the past, sea ice rarely melted in the Arctic Ocean. Each year, a certain multi-year ice flowed from the ocean into the East Greenland Sea and melted there. Some ice was getting thick enough to survive the melt season and become a multi-year ice. However, as the air temperature in the polar regions has warmed over the last few decades, large amounts of multi – year ice are now melting in the very Arctic Ocean. Much less seasonal ice thickens enough in the winter to survive in the summer. As a result, not only is there less ice overall, but the proportions of multi-year ice compared to seasonal ice have also changed in favor of young ice.

Seasonal ice now reaches a depth of about two meters in winter and melts largely in the summer. This basic scheme will probably continue, said Kwok. "The thickness and coverage in the Arctic are now dominated by the growth, melting and deformation of seasonal ice."

The increase in seasonal ice also means that record changes in ice cover, such as those of the 1990s and the 2000s, will likely be less frequent, Kwok noted. In fact, there has been no new record low sea ice since 2012, despite years of warm Arctic weather. "We have lost so much thick ice that the thickness changes are going to be slower because of the different behavior of this type of ice," Kwok said.

Kwok used the United States Navy's submarine sonar data from 1958 to 2000; satellite altimeters on NASA's ICESat and the European CryoSat-2, covering the period from 2003 to 2018; and scatterometer measurements from NASA's QuikSCAT and the European ASCAT from 1999 to 2017.

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More information:
R Kwok. Thickness of Arctic sea ice, volume and multi-year ice cover: losses and coupled variability (1958-2018), Letters of research on the environment (2018). DOI: 10.1088 / 1748-9326 / aae3ec