When you envision what it looks like around the North Pole, you probably imagine a pristine layer of ice floating on top of the Arctic Ocean, so thick that polar bears can walk on it. What you might not realize is that the sea ice is actually not one big piece of ice stretching across the entire Arctic. Cracks open and close all the time, making the sea ice cover resemble a jigsaw puzzle with pieces continuously changing their shape. A recent study showed that the Arctic has been warming nearly four times faster than the rest of the planet in the past 40 years. And warmer temperatures in the Arctic mean more windstorms. Strong winds can cause breakup events: Wind is pushing the ice and it rips open, exposing the seawater below. The counterparts to those cracks are called ridges: Ice blocks are being pushed up onto the sea ice and they form long stretches, like how plate tectonics create mountain ridges such as the Alps and Himalayas. Both ridges and open cracks can be quite small, but it is also common that the cracks become dozens of kilometers wide and hundreds of kilometers long. They can even stretch across the entire Arctic. And these large features impact two very different environments: The ocean below the sea ice and the atmosphere above.
Arctic sea water and Arctic air have very different temperatures and moisture levels, and the sea ice cover separates these two environments effectively. The sea water is about -1.8°C, which is quite warm compared to the atmosphere. The air above the sea ice is as cold as down to -40°C, and it is extremely dry. Wherever the sea ice cracks though, those two environments – water and air – collide.
In the forming crack, the “warm” surface water evaporates quickly, and it rises. So-called Arctic sea smoke forms, making it look like the ocean is steaming. The sea smoke removes both heat and moisture from the ocean and brings it into the atmosphere. The air over the crack warms up locally, and it becomes much moister than over solid sea ice. But this evaporation process does not just affect the air – the sea water changes, too. Because it is exposed to the extremely cold air above, a thin layer of new ice forms on top of it. When sea ice forms it releases salt that is contained in the seawater. The seawater below the newly formed sea ice therefore becomes saltier. So, saltier seawater below cracks, and warmer, moister air above are the outcomes of the sea ice breaking up in the Arctic. But how is this relevant for us?
Most of us live far away from the Arctic, and we will never see the sea ice cracking in person. But what happens in the Arctic, does not stay in the Arctic. A recent study was able to reproduce the cracking during an especially strong breakup in 2013. The figure shows the satellite footage after several days of cracks forming in the ice covering the Beaufort Sea during that breakup. With more cracking occurring due to global warming, the effects on atmosphere and sea become stronger. Locally increasing salt contents can impact the Arctic Ocean’s ecology for which the full extent is not yet known. It is likely that changes in the Arctic will not just have regional, but global impacts. Marine food availability for example is dependent on the ocean’s ecology, and we rely on the fishing industry to provide food. And a thinning ice cover due to rising air temperatures will affect the global climate in multiple ways. This, together with more frequent wind-induced breakup events, will contribute to an even faster decline in sea ice in the Arctic. The ultimate jigsaw puzzle is not only changing the shape of its pieces, but eventually there won’t be any puzzle pieces left.
 Rantanen, M., Karpechko, A.Y., Lipponen, A. et al. The Arctic has warmed nearly four times faster than the globe since 1979. Communications Earth & Environment 3, 168 (2022). https://doi.org/10.1038/s43247-022-00498-3
 Rheinlænder, J.W., Davy, R., Ólason, E., Rampal, P., Spensberger, C., Williams, T.D., Korosov, A., and T. Spengler. Driving mechanisms of an extreme winter sea ice breakup event in the Beaufort Sea. Geophysical Research Letters 49 (2022). e2022GL099024. https://doi.org/10.1029/2022GL099024