With the acceleration of global warming, polar sea ice is melting at an unprecedented pace. As a result, ocean currents are becoming unstable, and analysts say polar seas will swing more violently and grow more unstable going forward.
Axel Timmermann, director of the Institute for Basic Science (IBS) Center for Climate Physics and distinguished professor at Pusan National University, and his team said that ultra–high-resolution Earth system model simulations show that human-caused warming rapidly melts sea ice, which will further intensify the ocean's "mesoscale horizontal stirring." The findings were published in the international journal Nature Climate Change on the 5th.
"Mesoscale horizontal stirring" is a large-scale mixing of water created by wind, currents, and eddies within the ocean. On scales of tens to hundreds of kilometers, seawater is churned horizontally, spreading heat and nutrients and affecting the dispersion of pollutants such as plankton, fish eggs and larvae, and microplastics.
However, directly observing these changes in the polar oceans is not easy. In particular, quantitatively identifying how global warming affects small-scale currents and marine ecosystems in the polar regions remains a difficult task. This is because observations are limited by geographic constraints, and satellite data cannot capture mesoscale ocean processes in detail.
To address this, the team used the IBS supercomputer Aleph to run simulations with an ultra–high-resolution climate model (CESM-UHR). Comparing scenarios with atmospheric carbon dioxide concentrations set at current levels, double, and quadruple, they found that as carbon dioxide increased, seas along the Arctic and Antarctic coasts heaved more violently. The more warming intensified, the more clearly mesoscale horizontal stirring increased.
Quantifying this phenomenon showed that the rapid decline of sea ice due to global warming strengthens currents and turbulence in future Arctic Ocean and Antarctic coastal waters, accelerating the horizontal stirring of seawater.
The researchers found that the reasons for the intensified stirring differ between the Arctic and the Antarctic. In the Arctic Ocean, as sea ice decreases, winds push the seawater more strongly, strengthening surface circulation and turbulence, whereas along the Antarctic coast, the influx of freshwater from melted sea ice increases density differences in seawater, intensifying current strength and stirring.
Lee Junyi, a professor at the Pusan National University Climate Change Research Institute and the corresponding author of the paper, said, "The increase in future polar ocean horizontal stirring could have major impacts on polar marine ecosystems, including the survival of fish eggs and larvae."
Axel Timmermann said, "Our research group is currently developing a next-generation Earth system model that more effectively integrates climate and life," adding, "This will enhance our understanding of how polar ecosystems respond to global warming."
References
Nature Climate Change (2025), DOI: https://doi.org/10.1038/s41558-025-02471-2