A new study by NASA found that the oldest and the thick Arctic sea ice is melting faster than the young and thin (at the edges of the floating ice of the Arctic Ocean).
Usually a thick multi-year ice (over two years) is less susceptible to the melt season, while young ice formed in a short time over the winter, just as quickly melts in the summer. The rapid disappearance of the old ice makes the Arctic sea ice more vulnerable to further melting.
In the new study, the researchers observed the perennial ice, which cover at least 15% of the surface of the Arctic Ocean. The scientists found that the amount of ice is reduced by 15.1% per decade. Thus, the average thickness of the Arctic sea ice cover is reduced due to the melting of thick multi-year ice shell. At the same time, the surface temperature in the Arctic increases, which reduces the period of time when a new young ice formed and can quickly restore the volume of ice many years.
The volume of perennial sea ice reached its record low in winter 2008 — it fell by 55% from the end of the 1970s, when satellite measurements began ice. Multiyear sea ice is then recovered over the next three years: it was 34% more than in 2008. But in the winter 2012 ice again began actively melting.
Scientists do not exclude the existence of a nine-year cycle of melting sea ice. At least, satellite observations have established just such a period. Apparently, a slight recovery of sea ice within three years after he had reached historic lows in 2008, is only a step in a nine-year cycle, and we are waiting for new records melting, while the number of ice with each cycle is reduced.