Dramatic thinning of Arctic lake ice cuts winter ice season short by 24 days

Researchers have revealed that Arctic lakes have been freezing up later in the year and thawing earlier, which is creating a winter ice season about 24 days shorter than was in 1950.

The research also reveals that climate change has dramatically affected the thickness of lake ice at the coldest point in the season: In 2011, Arctic lake ice was up to 38 centimetres thinner than it was in 1950.

The research team used satellite radar imagery from ESA to determine that 62 per cent of the lakes in the region froze to the bottom in 1992. By 2011, only 26 per cent of lakes froze down to the bed, or bottom of the lake. Overall, there was a 22 per cent reduction in what the researchers call "grounded ice" from 1992 to 2011.

Researchers were able to tell the difference between a fully frozen lake and one that had not completely frozen to the bottom, as satellite radar signals behave very differently, depending on presence or absence of water underneath the ice.

Radar signals are absorbed into the sediment under the lake when it is frozen to the bottom. However, when there is water under the ice with bubbles, the beam bounces back strongly towards the radar system. Therefore, lakes that are completely frozen show up on satellite images as very dark while those that are not frozen to the lake bed are bright.

Researchers used the Canadian Lake Ice Model (CLIMo) to determine ice cover and lake ice thickness for those years before 1991, when satellite images are not available.

The model simulations show that lakes in the region froze almost six days later and broke up about 18 days earlier in the winter of 2011 compared to the winter of 1950. Shorter ice-cover seasons may lead to shifts in lake algal productivity as well as thawing of permafrost under lake beds.

The research has been published in journal The Cryosphere.