About cheese, sea ice and a warmer Arctic
Top image: Sea ice in northern Svalbard. Photo: Eva Therese Jenssen/UNIS.
The Arctic Ocean has been frozen for a long time. It is difficult to say exactly how long. But the wildlife we find on the underside of the ice bears a clear testimony that the ice cover has lasted long enough for different species to have developed very special adaptations to be able to live in, on or just under the ice. Most spectacular are perhaps the amphipods we find inside the melting channels in the ice. These are facing an uncertain future as the ice in the Arctic melts. One might think that last year’s summer, autumn and winter with a lot of ice around Svalbard gave these animals a little respite. Unfortunately, this is not the case.
5 October 2020
Text by Professor Jørgen Berge – UiT The Arctic University of Norway, UNIS and NTNU.
The ice in the Arctic Ocean is like a Swiss cheese – it is full of holes. The holes, or rather the canals, are formed when the seawater freezes and excretes salt. Then a kind of highly concentrated brine is formed which melts through the ice and “drips” into the sea below. Inside a fjord, this cooled brine that sinks to the bottom is the most important factor in filling up salt and cold water inside threshold fjords. Billefjorden is a good example of such a fjord. The groundwater there maintains a temperature of -1.8 ° C all year round. As the brine melts through the ice, a network of channels is formed inside the ice. These canals serve as an excellent habitat for the amphipods that live all or part of their lives in the ice.
Since 2006, we have used Rijpfjorden on Nordaustlandet, Svalbard as a kind of climate laboratory and a counterpart to the relatively warm and eventually quite “Atlanticised” Kongsfjorden. Rijpfjorden has an annual ice cover, and there is little trace of either Atlantic water masses or Atlantic organisms. Rijpfjorden is the realm of polar cod – and just a few years ago also with a bustling life of amphipods that are otherwise found associated with the ice in the Arctic Ocean. When we in the years 2007-2011 were on our annual expeditions up to Rijpfjorden to retrieve the sea observatories used to monitor the marine environment, they were often full of amphipods that in the absence of ice found a temporary home at the observatory. On the large ball that holds the observatory up (the yellow ball in the picture of the research ship Helmer Hanssen) we could often find several hundred such amphipods. Many were also caught by the sediment traps at the observatory.
Last summer and autumn there were a lot of ice around Svalbard. We never got into Rijpfjorden due to ice in the autumn of 2019, which meant that the observatory put out in the autumn of 2018 had to stand for two years until we came up now in September to retrieve it. The observatory had then stood in a fjord that had been ice-covered almost continuously for about 18 months until the ice melted and withdrew in late summer 2020.
Would this mean that we would again be able to observe amphipods from the freshly melted ice clinging to the observatory when it came up? Unfortunately, that was not the case. And the reason for this is to be found in the fact that sea ice and cheese also have another similarity – it actually matters what kind of ice we are talking about.
Although we had a lot of ice in the Arctic Ocean and north of Svalbard last autumn, there was very little multi-year ice (ice that has “survived” at least one summer season) north of Svalbard. Almost all the ice was first-year ice. Inside Rijpfjorden, despite very low temperatures throughout the summer and autumn of 2019, it had the effect that almost no old ice drifted in, and thus also very few of the animals that live on the underside of the ice. In other words, it is not done in one cold summer to change the system back to the condition it had 10-15 years ago.