Heat from Below: How the Ocean is Wearing Down the Arctic Sea Ice

Marine researchers refer to the increasing influx of warm Atlantic water masses into the Arctic Ocean as ‘Atlantification’. To date, this process has mainly been investigated from an oceanographic perspective. In two new studies, AWI sea-ice physicists have, for the first time, estimated the effects of the input of heat on the sea-ice growth in the Arctic. Of note here: in those places where the sea ice completely melts in summer, in the following winter the sea releases especially large amounts of heat into the atmosphere. As a result, the sea freezes so rapidly that it compensates for the summertime ice losses. “Young, thin sea ice conducts heat significantly better than thick ice, and therefore less effectively protects the sea from cooling. At the same time, more water freezes on the bottom of the ice, which is why thin ice grows more quickly than thick ice,” explains AWI sea-ice physicist Dr Robert Ricker.

The important winter growth no longer takes place as smoothly in all marginal seas, as Ricker and colleagues found using long-term data on the thickness, concentration and drift of Arctic sea ice. “We analysed satellite data from the ESA Climate Change Initiative and found that in the period from 2002 to 2019, less and less sea ice formed, especially in the Barents Sea and Kara Sea,” Ricker reports. In the East Siberian Sea, as well as in the Beaufort and Chukchi Seas, on the other hand, the winter ice production is still high enough to compensate for the losses in summer.

To determine the cause of these varying regional trends, the researchers simulated the interaction between the ocean, ice, wind, and air temperature for the past four decades using two coupled ice-ocean models. Both simulations led to the same conclusion. “The warm water masses that flow from the North Atlantic into the Arctic Ocean are responsible for slowing or even preventing ice growth in the Barents and Kara Seas. If new ice does form, it’s significantly thinner than before,” says Ricker, adding: “If Atlantification persists to this extent, and the winter temperatures in the Arctic continue to rise, in the long term we will also see changes in the regions of the Arctic Ocean further east. In that case, the ice cover in the Arctic Ocean will decline and become thinner and more fragile than it already is.