ESM working group: Meeting notes 2024

Earth System Working Group
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38

Date: 27/3/2025
Chair: @dkhutch

  1. 2025 ACCESS-NRI Community Workshop Training Day Poll:
  • A reminder was given about the poll for training sessions at the 2025 ACCESS-NRI Community workshop training day. Voting is now closed.
  1. Shared Resources and Experiments:
  • ESM project lg87 used nearly all of its 875 KSU allocation for quarter 1. /g/data storage remains at 54.3TB
  • There are often opportunities at the end of the quarter to apply for spare resources from other working groups near the end of each quarter. Having experiments prepared and visible proposals on the Hive forum helps make this possible.
  • Proposals are now open for quarter 2. Do you have any proposals for shared experiments? See guidelines for how to do this. There are often used resources we can access if there are projects to use them.
  1. Science Presentation:

  • Hannah Dawson presented on Using ACCESS CM2 to investigate the role of ocean warming in Antarctic sea ice loss.

  • The in-progress study aims to understand how deeper ocean warming impacts Antarctic sea ice.

Background

  • The past two years have seen record low winter Antarctic sea ice extents, well outside the range of historical observations. Recent work investigating the causes of this decline suggest that the ocean has played a significant contribution to this decline, which may suggest a regime shift.

Experiments

  • Initial condition perturbation experiments with ACCESS-CM2 were run, where warming was applied to the upwelling branch in the ocean restart files. Several warming regions were tested. The final warming area was defined based on a density, temperature, and depth constraints. Ten ensemble members were run branching from different points of the PI control simulation.

Results

  • Over time, subsurface heat added in the Southern Ocean spreads into the surface mixed layers.
  • Significant reductions in sea ice extent and volume were observed, particularly in winter and spring. The response was more pronounced in certain regions, such as East Antarctica.
  • The reductions in sea ice were closely aligned with regions experiencing increased
    ocean temperatures, suggesting a direct link between the warming and sea ice loss.
  • Sea ice declines were driven by increased basal melt rather than decreased freezing rates.
  • Increases in sea surface temperatures and surface air temperatures were observed in the Southern Ocean. Changes were also observed in sea level pressure, however further analysis is required in interpreting the changes.

Future work

  • Future work will investigate into the relative roles of the applied ocean warming and atmospheric feedbacks in the sea ice decline.
  • Other areas for investigation will include understanding the pattern of surface freshening that occurs in the Southern Ocean.

These notes were partially generated by AI. If you notice any errors or omissions please feel free to modify directly, or message @spencerwong.

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