Scientists predict the future of Earth’s ice-covered oceans at their rough edges

One of the harshest and most dynamic regions on Earth is the marginal ice zone – the place where ocean waves meet sea ice formed by freezing the ocean’s surface.

A special issue of the journal Philosophical Transactions of the Royal Society A, published today, looks at the rapid advances researchers have made over the past decade in understanding and modeling this challenging environment.

This research is crucial for us to better understand the complex interactions of the Earth’s climate systems. This is because the marginal ice zone plays a role in the seasonal freezing and thawing of the oceans.

A rough place to study

In the Arctic and Antarctic, ocean surface temperatures are consistently below -2℃ – cold enough to freeze and form a layer of sea ice.

At the highest latitudes closer to the poles, sea ice forms a solid, several-meter-thick cap on the ocean that reflects the sun’s rays, cooling the region and driving cool water around the oceans. This makes sea ice a key component of the climate system.

Read more: The Southern Ocean absorbs more heat than any other ocean on Earth, and the effects will be felt for generations

But at lower latitudes, when the ice-covered ocean meets the open ocean, sea ice forms smaller, much more mobile chunks called “floes,” separated by water or a slurry of ice crystals.

This marginal ice zone interacts with the atmosphere above and the ocean below in a very different way than the ice cover closer to the poles.

It’s a challenging working environment for scientists, as a trip to the marginal ice zone around Antarctica in 2017 faced winds of over 90 km/h and waves of over 6.5 m. It’s also difficult to observe from a distance as the floes are smaller than what most satellites can see.

Crushed by waves

The marginal ice zone also interacts with the open ocean via surface waves that travel into the zone from the open waters and act on the ice. The waves can have a destructive effect on the ice sheet, breaking up large floes and making them more vulnerable to melting in summer.

In winter, on the other hand, waves can encourage the formation of “pancake” floes, so named because they are thin slices of sea ice (you can see them in the image above).

But the wave energy itself is lost in interactions with floes, so the waves gradually weaken as they penetrate deeper into the ice marginal zone. This creates wave-ice feedback mechanisms that drive sea ice development in a changing climate.

For example, a trend towards warmer temperatures will weaken the ice sheet, allowing waves to penetrate deeper into ice-covered oceans and cause more breakup, further weakening the ice sheet – and so on.

Scientists studying the dynamics of marginal ice zones aim to improve our understanding of the zone’s role in the dramatic and often puzzling changes the world’s sea ice is undergoing in response to climate change.

In the Arctic Ocean, for example, sea ice coverage “has decreased by about half since the 1980s.” In Antarctica, sea ice coverage has recently had both one of its largest and one of its smallest recorded extents, with the marginal ice zone being a source of annual variability.

Our progress in better understanding these harsh regions revolves around major international research programs conducted by the United States Office of Naval Research and others. These programs involve geoscientists, geophysicists, oceanographers, engineers and even applied mathematicians (like us).

Recent efforts have led to innovative observation techniques such as B. A method for 3D imaging of wave and floe dynamics in the marginal ice zone on board an icebreaker and for capturing waves in the ice from satellite imagery.

They have also led to new models capable of simulating the interaction of waves and ice from the level of individual floes to the overall behavior of entire oceans. The advances have led to a multi-month Australian-led experiment in Antarctica’s ice rim on the new $500 million icebreaker RSV Nuyina, expected next year.

The marginal ice zone will be an increasingly important part of the global sea ice cover in the future as temperatures rise and waves become more extreme.

Despite rapid progress, there is still a long way to go before understanding the feedback processes in the marginal ice zone is translated into improved climate predictions, used for example by the International Panel on Climate Change Assessment Reports.

The inclusion of the marginal ice zone in climate models has been described by one of its leaders as the “holy grail” for the area, and the issue points to closer connections with the broader climate community as the next big direction for the area.

Read more: Ice shelves keep Antarctica’s glaciers from raising sea levels — but they’re crumbling