Successfully simulating sea-ice breakups with neXtSIM

A new study led by Jonathan Rheinlænder at the Nansen Center investigates if the sea-ice model neXtSIM can recreate an unusual breakup event in the Arctic to find out what caused it.

During the polar night in 2013, something unusual happened in the Beaufort Sea in the Arctic. Sea ice is normally very thick and resistant that time of year. But in winter 2013, the ice cover cracked open over hundreds of kilometers, coinciding with strong winds. Why did this happen, and what do such breakup events mean for the future of Arctic sea ice? That is what Jonathan Rheinlænder and his colleagues from the Nansen Center, the University of Bergen, and the Université Grenoble Alpes wanted to find out. They used neXtSIM, the sea-ice model developed at the Nansen Center, to see if they could simulate the formation of the cracks occurring in the sea ice during the breakup event. In their recent publication Driving Mechanisms of an Extreme Winter Sea Ice Breakup Event in the Beaufort Sea in Geophysical Research Letters, they were able to reproduce the breakup event. Their results are remarkably close to what satellite images of the breakup show. This is quite extraordinary! “No other sea-ice or climate model is currently able to simulate this type of behaviour”, says Jonathan Rheinlænder. They also found that, in 2013, the combination of specific weather patterns with strong winds, and relatively thin ice caused the sea-ice cover to break up in such a spectacular manner.

What happens in the Arctic during a breakup event?

In the summer months, sea ice melts and the extent of the ice cover shrinks. During winter, more ice forms and the ice cover expands and thickens. Some of the ice survives several of those melting periods, it is called multi-year ice. In the past decades, much of the multi-year ice has been falling victim to melting during the summer months, and the ice cover nowadays is generally thinner and younger than just 50 years ago. During such events as the one in 2013, cracks form in the sea-ice cover over large distances and it breaks apart. This way, the barrier between extremely cold air (down to –40°C) and relatively warm ocean water (ca. –2°C) is disrupted, and a massive amount of heat is released from the ocean into the atmosphere above. This released heat affects the Arctic climate system.

Above: Video of the satellite data on the breakup (left side) and the recreation by neXtSIM (right side).

Breakup events and the future of the Arctic sea ice

One of the more alarming results of the study is that these breakup events can accelerate the loss of multi-year ice in the Beaufort Sea. Jonathan Rheinlænder and his colleagues found that the ice cover becomes more mobile due to the breakup, and more sea ice is transported out of the region than if no breakup event had occurred. “Overall, strong breakup events lead to a thinner and weaker ice cover at the end of the winter season, which makes it even more vulnerable to melting during summer”, says Jonathan Rheinlænder. They also found that as the ice cover becomes thinner, weaker winds can also break up the sea-ice cover. This means that we might see more large breakup events in the future, potentially leading to sea ice starting to melt earlier in the year and accelerating the loss of sea ice in the Arctic. And this is bad news.

Societal relevance of better understanding breakup events

The Arctic sea ice is an important factor influencing the global climate. Global climate models, that researchers use to make projections for the future, cannot capture small-scale processes such as fractures occurring in the ice cover, for example caused by such massive breakup events as in 2013. This means that the effects of such events are not captured in the models, making the projections less reliable. With such breakup events likely becoming more common in the future, it will become even more important to include these processes into global climate models to improve future projections of Arctic sea ice and the effects on the global climate. “Our results suggest that in order to capture such events we need better atmospheric models as well as improving sea ice models used in the climate models”, says Jonathan Rheinlænder.

Improved knowledge on these breakup events will also help to improve weather prediction in the Arctic and provide critical input to people living in the coastal regions. Coastal communities relying on the sea ice as hunting and fishing grounds need to know when and where the ice cover will break up. In addition, safe navigation through ice-affected waters for example for shipping or other offshore activities is only possible with detailed information about where there is ice and where there is open water.

Even though most people live far away from the Arctic, what happens there affects all of us. The sea ice is becoming more vulnerable to melting, and breakups are speeding up that process. To be able to reliably predict sea-ice behaviour, including breakup events, is beneficial both on the local scale, as well as on the global scale, and the sea ice model neXtSIM has once again proven to be valuable for this purpose.

Comparison between satellite information (upper images) on where cracks (also called “leads”) formed during the 2013 breakup event and the simulation by neXtSIM (lower images) showing where the model predicted cracks. Both satellite data and the simulation show very similar locations for the cracks forming over several days.

Source: Rheinlænder et al. (2022), CC BY 4.0.


Geophysical Research Letters:
«Driving mechanisms of an extreme winter sea ice breakup event in the Beaufort Sea»