Scientists have revealed new details of the icy depths

Deeper understanding of the Antarctic floor.

Researchers have gained new information about how the formation of subsurface ice in Antarctica promotes the circulation of cold, dense water that sinks to the ocean floor, an important aspect of global water circulation.

The team from Hokkaido University The Institute of Low Temperatures, the Arctic Research Center and the Faculty of Fisheries, in collaboration with researchers from the Japan National Institute of Polar Research and the Japan Aerospace Exploration Agency, made the findings, which were published in the journal Achievements of science.

The seas surrounding Antarctica, where significant amounts of sea ice form, are critical to the circulation of water in the world’s oceans, connecting the Atlantic, Pacific and Indian oceans. When sea ice forms, it repels salt, resulting in dense, cold water that sinks to the sea floor.

Much of the deep ocean floor, known as the global abyss, is flooded with this water, known as Antarctic Bottom Water (AABW), which is the coldest and densest body of water in the global circulation. Understanding the mechanism by which AABW develops and how global warming will affect the formation is critical as the global ocean circulation influences global climate.

“We found surprising new results about the shape of sea ice growth at a key site of AABW production, near Cape Darnley in Antarctica, with potentially large implications for other regions,” says Kei Oshima of the Hokkaido team. He explains that satellite monitoring and data from moored sensors in the ocean have shown the importance of underwater ice, called Frazil ice, in producing dense, cold water. This ice forms below the surface when water is cooled below freezing by strong winds and turbulence. Cooling can occur at amazing depths of 80 meters or more.

Their key importance is that they cover the area where water is cooled by strong winds from the very cold Antarctic, especially in open water areas in the pack ice called polynyas.

“It’s important to know that such an important process is happening underwater, revealing an aspect of the circulatory system that has been at least partially hidden from view,” Kay says.

The researchers also suggest that Frazil ice may incorporate sediment on the sea floor and release it as the ice melts. This may provide new insights into the cycling of nutrients that fertilize plankton and affect the overall biological productivity of Antarctic waters.

“Our next step is to incorporate these new processes into our understanding of Southern Ocean biogeochemistry and carbon cycling, which will require significant new fieldwork and research,” Kay concludes.

Reference: “Dominant Frazil Ice Production in the Cape Darnley Polynya Leading to Antarctic Bottom Water Formation” by Kei I. Oshima, Yasushi Fukamachi, Masato Ito, Kazuki Nakata, Daisuke Shimizu, Kazuya Ono, Daiki Nomura, Gen Hashida, and Takeshi Tamura, 19 October 2022, Achievements of science.
DOI: 10.1126/sciadv.adc9174

The research was funded by the Ministry of Education, Culture, Sports, Science and Technology of Japan, the Japan Antarctic Research Expedition, the Japan Aerospace Exploration Agency, the European Space Agency, the National Institute of Polar Research and[{” attribute=””>Hokkaido University.