University of Utah mathematicians and climate researchers are creating new models to better comprehend the behavior of sea ice, which is actually more fluid than many may assume.
Sea ice in polar regions is constantly changing. It contracts, expands, shifts, fractures, and reconstitutes, responding to seasonal shifts and rapid climate changes. Instead of being a uniform layer of frozen water atop the ocean, sea ice is a dynamic blend of ice, water, and tiny pockets of air and brine trapped within it.
Recent studies conducted by scientists at the University of Utah are developing innovative models that focus on two major processes within the sea ice framework that have significant impacts on global climate: the heat exchange through sea ice, which connects the ocean and atmosphere thermally, and the dynamics of the marginal ice zone (MIZ), a curvy area of the Arctic sea ice that separates dense ice packs from open ocean.
According to Court Strong, a professor of atmospheric sciences, satellite images over the last 40 years show that the MIZ has expanded by 40% in width and shifted 1,600 kilometers northward.
“Simultaneously, it has moved closer to the North Pole as the sea ice pack has diminished,” said Strong, a co-author of one of the two studies released by Utah scientists recently. “These transformations have primarily occurred during the fall when the sea ice reaches its seasonal low point.”
A pair of studies, one in the Arctic and another in the Antarctic
One of the studies, which modifies a phase transition model typically utilized for alloys and binary mixtures in laboratory settings to analyze MIZ dynamics at the scale of the Arctic Ocean, has been published in Scientific Reports. The second study, appearing in the Proceedings of the Royal Society A, is based on field research in Antarctica and created a model to understand the thermal conductivity of sea ice. The journal cover features an image showing regularly spaced brine channels within the bottom layers of Antarctic sea ice.
Both polar regions have significantly lost ice in recent decades due to human-induced global warming. This loss creates a feedback loop where more solar energy is absorbed by the open ocean instead of being reflected back into space by the ice cover.
Utah mathematics professors Elena Cherkaev and Ken Golden, a noted sea ice researcher, contributed to both studies. The Arctic-focused study by Strong investigates the broader structures of sea ice, while the Antarctic study, led by former Utah postdoctoral researcher Noa Kraitzman, delves into the finer-scale details.
Sea ice behaves less like solid ice and more like a sponge filled with tiny holes containing salty water, known as brine inclusions. When ocean water beneath interacts with the ice, it can create a flow that speeds up heat transfer through the ice, akin to stirring a cup of coffee, according to Golden. The Antarctic study employed advanced mathematical techniques to quantify the extent of this heat-enhancing flow.
Additionally, the thermal conductivity study revealed that newly formed ice, compared to ice that remains frozen year-round, facilitates increased water flow and enhances heat transfer. Current climate models might be underestimating the heat exchange rates through sea ice since they may not fully consider this water flow. By refining these models, scientists can improve predictions on the rate of sea ice melting and its impact on global climate.
Even though the studies focus on different aspects of ice, the underlying mathematical modeling principles are the same, Golden explained.
“The ice is not a continuous body. It consists of numerous floes. It’s a composite material, much like sea ice with tiny brine inclusions, except here we have water with ice.” Golden described the MIZ. “The physics and math are fundamentally similar, merely applied in a different context, allowing us to determine the effective thermal properties on a large scale based on geometry and the characteristics of the floes, much like detailed information about brine inclusions at a very small scale.”
Golden often remarks that what happens in the Arctic does not stay in the Arctic. Changes in the MIZ are influencing climate patterns globally, emphasizing the importance of understanding this area. The MIZ is identified as the segment of the ocean surface where 15% to 80% is covered by sea ice. Areas with more than 80% coverage are classified as pack ice, while those with less than 15% are regarded as the outer edges of open water.
An alarming view from above
“The MIZ is the area around the perimeter of the sea ice, where waves and melting break the ice into smaller pieces,” Strong noted. “Alterations in the MIZ are crucial as they affect how heat is exchanged between the ocean and atmosphere, influencing wildlife in the Arctic, from tiny microorganisms to polar bears, as well as human activities.”
Since improved satellite data became available in the late 1970s, there has been a surge in scientific interest surrounding the MIZ, with the ability to document its changes effectively. Strong was instrumental in figuring out how to utilize satellite images to measure the MIZ and observe concerning changes.
“Over the years, we’ve documented a dramatic 40% widening of the MIZ,” said Strong.
For some time, scientists have regarded sea ice as a “mushy layer.” When a metal alloy melts or solidifies, it passes through a porous or mushy phase in which both liquid and solid forms coexist. The freezing of saltwater is similar, resulting in pure ice with liquid brine pockets, primarily in the bottom few centimeters near the warmer ocean, creating vertical channels colloquially termed “chimneys.”
Strong’s team investigated whether traditional mushy layer physics could apply to the vast regions of the MIZ. The findings suggest this is indeed the case, potentially providing a new perspective on a constantly changing part of the Arctic.
Essentially, the research offers a fresh perspective on the MIZ, viewing it as a large-scale transition area, akin to how ice melts into water. Traditionally, melting has been considered a minor-scale phenomenon, such as at ice floe edges. However, assessing the Arctic as a whole reveals the MIZ as a broad transition area between solid, dense pack ice and open water. This perspective elucidates why the MIZ is not merely a sharp line but a “mushy” region where ice and water exist simultaneously.
“In climate science, we often rely on quite complex models. While they can lead to accurate predictions, they can complicate our understanding of the physical processes at play,” said Strong. “Our aim here was to develop the simplest possible model capable of capturing the changes we’re observing in the MIZ and to analyze that model to gain insights into its behavior and evolving nature.”
This study centered on comprehending the seasonal fluctuations of the MIZ, and the next phase will involve applying this model to gain a deeper understanding of the MIZ trends seen in the recent past.
