Polar Regions

Improved understanding of Antarctic sea ice variability and change

The Amundsen Sea Low (ASL) is a dominant feature of atmospheric circulation in the high latitude southern hemisphere. This low pressure center influences winds near Antarctica, and thus also sea ice concentrations. Over the past year, three studies – one modeling and two observational - have significantly expanded our understanding of the complicated relationships between the ASL and Antarctic sea ice.

Late twentieth century Antarctic sea ice concentrations (SIC) shown the significant positive trends in the Ross Sea during austral fall (March-April-May (MAM)). Climate models do not reproduce the observed trends. One of the possible suggested mechanisms for the observed trends is stratospheric ozone loss, which leads to a deepening of the summer (December-January-February (DJF)) ASL and accompanying changes in surface winds. Furthermore, the discrepancy between observed and modeled trends in SIC might be explained if the models do not capture the ASL-SIC relationships.

The first of these studies looked at relationships between austral summer ASL and austral fall SIC in both observations and in the Community Earth System Model (CESM). The CESM captures on both interannual and decadal timescales the observed relationships between strength of the summer ASL and the following fall SIC. Furthermore, the ASL-SIC relationships are such that a deepening ASL due to ozone hole formation should lead to a decrease rather than an increase in MAM SIC. Stratospheric ozone depletion is thus an unlikely candidate for explaining observed MAM SIC increases in the Ross Sea.

ASL variability influences variability in the winds (both location and strength). How this variability in the winds impacts sea ice depends on the location of the sea ice in relation to the location of the ASL – and these vary both seasonally and regionally. Two observational studies explored these relationships. The links between the ASL and sea ice can change from ice advance to ice retreat season. Three important new understandings emerge from this work: 1) the influence of the ASL on sea ice can change signs in some regions depending on the month and season; and 2) the sea ice response to ASL variations is often largest at a lag of some months (rather than at lag 0); and 3) the sea ice response to the ASL can persist for up to 8 months in part through impacts on sea surface temperatures.

These three studies were sponsored by NSF, NOAA and NASA and included researchers from the National Center for Atmospheric Research, the University of California, Columbia University, the University of Tasmania, and the California Institute of Technology.

Holland, M.M., L. Landrum, M.N. Raphael, and R. Kwok, 2018: The regional, seasonal, and lagged influence of the Amundsen Sea Low on Antarctic sea ice. Geophys. Res. Lett., Doi: 10.1029/2018GL080140
Landrum, L., M.M. Holland, M.N. Raphael, and L.M. Polvani, 2017: Stratospheric ozone depletion: An unlikely driver of the regional trends in Antarctic sea ice in austral fall in the late 20th century, Geophys. Res. Lett., Doi: 10.1002/2017GL075618
Raphael, M.N., M.M. Holland, L. Landrum, W.R. Hobbs, 2018: Links between the Amundsen Sea Low and sea ice in the Ross Sea: Seasonal and interannual relationships. Climate Dynamics, Doi: 10.1007/s00382-018-4258-4