Sea ice cover in the Southern Hemisphere is extremely variable, from summer to winter and from millennium to millennium, according to a new study. Overall, sea ice has been on the rise for about 10,000 years, but with some exceptions to this trend. Researchers uncovered these findings by examining the chemistry of a 54,000-year-old South Pole ice core.

Dominic Winski, a research assistant professor at the UMaine Climate Change Institute, spearheaded a project that uncovered new information about millennia of sea ice variability, particularly across seasons, in the Southern Hemisphere by examining the chemistry of a 54,000-year-old South Pole ice core.

The Southern Ocean experiences the largest seasonal difference in sea ice cover in the world, with Antarctica surrounded by 18.5 million-square-kilometers of sea ice in the winter and only 3.1 million-square-kilometers of it in the summer. According to researchers, this seasonal disparity in sea ice has a significant influence on regional and global climate, yet scientists for years knew relatively little about the extent of sea ice variation in the Southern Hemisphere before 1979.

When a team of scientists recently retrieved the deepest and oldest ice core from the South Pole and analyzed it, Winski saw an opportunity to learn more about seasonal and overall changes in sea ice in the Southern Hemisphere throughout the Holocene — the last 11,400 years. The CCI research assistant professor and his colleagues decided to examine the chemistry of the ice core, particularly its sea salt concentrations, to learn more about sea ice variability in the region.

Karl Kreutz, a UMaine professor of Earth and climate sciences, and researchers from Dartmouth College, South Dakota State University, the University of Washington and the University of Colorado Boulder participated in the project. Geophysical Research Letters published the paper detailing their findings.

The team capitalized on the massive seasonal variations in Southern Ocean climate in order to create a sea ice record showing distinct summer and winter variability. They combined this information with a state-of-the-art atmospheric chemistry model to link the ice core measurements with sea ice variability. The result is a detailed record of Southern Ocean sea ice revealing major fluctuations, especially in wintertime sea ice.

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