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The majority of Earth’s freshwater is contained within the ice that envelops Antarctica. As the ocean and atmosphere become warmer, that ice is disintegrating at an alarming rate with sea levels and global currents altering in consequence. To comprehend the possible consequences, scholars must grasp precisely how swiftly the ice is vanishing and what factors are causing its retreat.

The West Antarctic ice sheet, an unstable stretch adjacent to the Amundsen Sea, is one of the most significant sources of unpredictability in climate forecasts. Historical records reveal that it has been gradually diminishing since the 1940s, yet vital information is lacking. Utilizing ecological data obtained from ice samples, tree rings, and corals, researchers at the University of Washington customized a climate model for Antarctica and conducted simulations to discern how shifting weather patterns influence ice melt.

The findings, released on Sept. 10 in Nature Geoscience, were unexpected. For years, scientists have theorized that westerly winds were transporting warm water toward the ice sheet, accelerating ice melt. The new research challenges the existing storyline, directing attention towards winds originating from the north instead.

“We recognize that the Earth is warming on average, but that by itself doesn’t justify ice loss in Antarctica,” stated Eric Steig, a UW professor of Earth and space sciences. “To predict future scenarios, we must understand the particulars of what is transpiring now, and crucially, whether we are linked to it.”

The Antarctic ice sheet encompasses an expanse greater than that of the U.S. and Mexico combined. If the Western Hemisphere segment were to melt, global sea levels could rise by up to 20 feet. The ice sheet is held in position by ice shelves, extensions of ice that reach into the ocean. Free-floating sea ice blankets the surfaces of the surrounding waters.

To investigate weather patterns in Antarctica, where there are fewer meteorological stations than in much of the globe, researchers employ computer simulations that utilize the available data sources. Nonetheless, these models frequently lack region-specific data, hindering the precision of their predictions.

During the last century, westerly winds across high latitudes of the Southern Hemisphere have intensified due to anthropogenic climate change. Indirect indications also hinted that this trend was contributing to West Antarctic ice loss. However, when the researchers examined that hypothesis, inconsistencies arose.

“We expected to validate what the climate models indicated, which was that westerly winds were intensifying near Antarctica’s coast,” remarked Gemma O’Connor, lead author and postdoctoral researcher at UW’s oceanography department. “However, there was no indication of westerly winds gaining strength in this sector of Antarctica.”

O’Connor’s doctoral research investigated how proxy data—historical records from ice cores, trees, and coral—can disclose past weather patterns, including wind. Her findings revealed that the force required to elucidate the accelerating melt rates was still absent from the analysis.

In this new research, scholars executed a series of high-resolution ice-ocean simulations to determine which climatic patterns were instigating ice shelf melting in this essential section of Antarctica. They introduced a wind pattern for five-year intervals, gauged the mass loss from the ice, and repeated this procedure 29 times. Each iteration represented a unique wind pattern. Data from the 30 simulations indicated that northerly winds consistently heightened ice loss, whereas westerlies did not have the same impact.

The northerly winds, which blow powerfully across Antarctica, were rearranging the sea ice that encircles Antarctica, sealing small but significant gaps known as polynyas.

“Sea ice serves as a highly effective insulator, keeping the ocean relatively warmer compared to the air,” explained Kyle Armour, a UW professor of oceanography and atmospheric and climate sciences. “When northerly winds close off the polynyas, it diminishes ocean heat loss, leading to warmer waters and increased melting of ice shelves beneath the surface.”

Polynyas function like pores on the icy surface of the ocean. When they are obstructed, excess heat cannot escape. As the ice shelf dissolves, fresh water mixes with saline ocean water. A density gradient is established between the lighter, fresher water and the open ocean. This gradient drives a current that pulls in additional warm ocean water from miles away, hastening ice shelf melt.

Researchers posit that greenhouse gas emissions could be energizing the northerly winds. Initial studies indicate that human-induced climate change is diminishing air pressure over the Amundsen Sea. This region houses a significant low-pressure center that drives many of Antarctica’s weather patterns. As it becomes even lower, wind speeds from the north escalate.

“This mechanism establishes a link between West Antarctic ice loss and anthropogenic climate change, albeit through a different mechanism than previously believed,” O’Connor stated. This is crucial, the researchers emphasized, because if emissions are contributing to ice loss, then perhaps reducing them could mitigate it.

“I believe the work Gemma has accomplished will lead to a complete
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“A breakthrough in the comprehension of what influences the melting of Antarctic ice,” stated Armour. “We had numerous hypotheses regarding the winds that travel from the west to the east, yet the northern winds were not even considered. We were mistaken by 90 degrees.”

Additional contributors comprise LuAnne Thompson, a professor of oceanography at UW; Mira Berdahl, a research scientist in Earth and space sciences at UW; Yoshihiro Nakayama, an assistant professor of engineering at Dartmouth College; Shuntaro Hyogo, a graduate researcher in environmental science at Hokkaido University; and Taketo Shimada, a graduate researcher in environmental science at Hokkaido University.

This study received funding from the Washington Research Foundation, the University of Washington eScience Institute, the U.S. National Science Foundation, a Calvin professorship in oceanography, the Japanese Ministry of Education, Culture, Sports, Science, and Technology, the Inoue Science Foundation, the NASA Sea Level Change Team, the John Simon Guggenheim Memorial Foundation, and JST SPRING.

For additional details, reach out to Gemma O’Connor at [email protected].

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