How statistical physics illuminates sea ice, a key part of Earth’s climate system – @theU

Since beginning to study polar sea ice at NASA in 1975, mathematician Ken Golden has helped document alarming shifts in seasonal variation, the thin crust covering the Arctic oceans. and Antarctica.

There is far less ice now, and since then, the University of Utah scientist has spent most of his career applying statistical mechanics—the physics of phase transitions and complex collective behavior in systems like gases and magnets—to better understand the role climate change plays in the world. the disappearance of our polar ice sheets. The stakes can’t get higher as the effects accelerate. In recent decades, according to Golden, the extent of Arctic sea ice has halved.

U Mathematician Ken Golden

“Not in the last million years, like on a geophysical scale, not in a thousand years, but in the last 30 or 40 years. A few months ago, even in Antarctica, we just saw a new record low,” Golden said in the opening remarks at the May 17 Climate Summit hosted by the Centers for Disease Control and Prevention. Wilkes Climate Science & Policy hosted by the U University of Science. “But just like throwing a stone into a pond, there will be ripple effects, and the bigger the stone, the bigger the ripples and the wider they spread. The extent of sea ice we’ve lost in the Arctic is about two-thirds the area of ​​the contiguous United States and is probably the largest change in Earth’s surface due to planetary warming. It was a big rock.”

The part of Earth’s climate system with snow and ice, known as the cryosphere, is experiencing severe disruption as the planet continues to warm. Ice still covers 9% to 15% of Earth’s ocean surface, but the trend is ominous.

IMAGE CREDIT: University of Utah

Mathematician U Ken Golden, left, drills into sea ice during his 2014 expedition to the North Pole.

A leading sea ice researcher, Golden co-wrote a view published this week by Nature that explains the physics of the cryosphere. According to Golden, a distinguished professor in the Department of Mathematics who has completed 18 polar research expeditions, improving our ability to understand and model the behavior of sea ice is a central issue in the physics of oceans. Earth’s climate system.

Not just ice

Aside from holding water, sea ice sheets have little in common with the frozen blocks in your refrigerator.

“As a material, sea ice is a hierarchical, multi-level composite with complex structures on length scales from tenths of a millimeter to tens of kilometers, and it exhibits rich dynamics. on the scale of the Arctic Ocean,” wrote Golden in the piece’s opening essay. published in the journal Nature Reviews Physics. “A key modeling challenge is how to use the data on the smaller scale structure to find out the efficient properties of sea ice on a larger scale relative to climate models and procedure.»

In other words, what can we learn about the planet from examining small structures in sea ice? Golden believes in a lot of things, not just about climate, but about all other areas of science and engineering where the math is similar, such as in bones, medical imaging, carbon sequestration, substance semiconductors and even high-tech composites with exotic properties.

Sea ice serves as a powerful habitat for organisms ranging from apex predators and birds to algae that live inside saltwater inclusions of sea ice, which feed on nutrient-packed seawater. Nutrients flowing through channels and passages of salt water can percolate through the ice.

How does sea ice affect the climate?

It also plays an important role in regulating the climate system because it affects ocean currents and the reflection of solar radiation back into space, measured by a property known as albedo. While the ice reflects this energy, seawater as well as melt ponds on sea ice will absorb it. That means the planet could warm even more quickly as the sea ice shrinks, exposing the water surface, absorbing more and reducing the planet’s albedo, according to Golden.

“It forms a very thin layer of glacial boundary between the two main geophysical fluids on Earth—the ocean and the atmosphere,” he said at a 2021 Frontiers in Science lecture. “And so, it mediates the exchange of heat, gases and momentum between them. Both the melting and freezing of sea ice play a very important role in global ocean circulation and form the main pathways by which the polar regions communicate with the rest of the oceanic system. world, as well as the global climate system.”

What’s so special about the year?

Golden is best known for developing a mathematical theory he calls the «Rule of Five», which was the first application of the classical model in statistical mechanics to the physics of sea ice – to determine and predicts the “on-off” switch for how the liquid flows through the ice. Based on the permeation model used in the development of an invisibility coating that makes an aircraft invisible to radar, the rule holds that liquids can move vertically when the volume fraction of saline exceeds the permeation threshold. 5% permeation, which corresponds to a critical temperature of –5°C for a typical salinity of 5 parts per thousand.

IMAGE CREDIT: University of Utah

Ken Golden, a U mathematician who studies sea ice, applies green dye to an iceberg during his 2014 expedition to the North Pole.

Golden wants to see the far-reaching and widely applicable ideas of statistical mechanics used more to explore the cryosphere.

“Statistical physics has seen widespread success and has become an important branch of modern physics,” Golden wrote in his essay. “However, while it provides such a natural framework for formulating and addressing key questions in the physics of sea ice, and opens up a host of powerful ideas and methods, it used only in certain contexts, albeit with unusual success. «

Other contributors are Alison Banwell of the Collaborative Institute for Research in Environmental Sciences (CIRES), physicist Justin Burton of Emory University, Claudia Cenedese of Woods Hole Oceanographic Institution and Jan Åström of Åbo Akademi University in Finland.

Cendese’s work illuminates the iceberg; Banwell looked at how meltwater on the surface caused the collapse of the ice shelf; Åström examines the ice melt disaster; and Burton discuss “ice mélange,” a collection of floating icebergs that can clog fjords and waterways, and affect sea level rise.

Read more about Golden’s sea ice research


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