Sources of low-frequency variability in observed Antarctic sea ice

Creators: Bonan, David B.¹; Dörr, Jakob^{2, 3}; Wills, Robert C. J.⁴; Thompson, Andrew F.¹; Årthun, Marius^{2, 3}

1. California Institute of Technology
2. University of Bergen
3. Bjerknes Centre for Climate Research
4. ETH Zurich

Abstract

Antarctic sea ice has exhibited significant variability over the satellite record, including a period of prolonged and gradual expansion, as well as a period of sudden decline. A number of mechanisms have been proposed to explain this variability, but how each mechanism manifests spatially and temporally remains poorly understood. Here, we use a statistical method called low-frequency component analysis to analyze the spatiotemporal structure of observed Antarctic sea ice concentration variability. The identified patterns reveal distinct modes of low-frequency sea ice variability. The leading mode, which accounts for the large-scale, gradual expansion of sea ice, is associated with the Interdecadal Pacific Oscillation and resembles the observed sea surface temperature trend pattern that climate models have trouble reproducing. The second mode is associated with the central Pacific El Niño–Southern Oscillation (ENSO) and the Southern Annular Mode and accounts for most of the sea ice variability in the Ross Sea. The third mode is associated with the eastern Pacific ENSO and Amundsen Sea Low and accounts for most of the pan-Antarctic sea ice variability and almost all of the sea ice variability in the Weddell Sea. The third mode is also related to periods of abrupt Antarctic sea ice decline that are associated with a weakening of the circumpolar westerlies, which favors surface warming through a shoaling of the ocean mixed layer and decreased northward Ekman heat transport. Broadly, these results suggest that climate model biases in long-term Antarctic sea ice and large-scale sea surface temperature trends are related to each other and that eastern Pacific ENSO variability is a key ingredient for abrupt Antarctic sea ice changes.

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Published by Copernicus Publications on behalf of the European Geosciences Union.

Acknowledgement

David B. Bonan thanks the Nansen Legacy Project for funding part of this research through a visit to the University of Bergen.

Funding

David B. Bonan was supported by the US National Science Foundation Graduate Research Fellowship Program (NSF grant no. DGE-1745301). Jakob Dörr and Marius Årthun were funded by Research Council of Norway project Nansen Legacy (grant no. 276730) and by the Trond Mohn Foundation (grant no. BFS2018TMT01). Robert C. J. Wills was supported by the US National Science Foundation (NSF grant no. AGS-2203543) and the Swiss National Science Foundation (award no. PCEFP2_203376). Andrew F. Thompson was supported by the Office of Naval Research's Multidisciplinary University Research Initiative (grant no. N00014-19-1-2421).

Data Availability

All data in this study are publicly available. Monthly Antarctic sea ice concentration is available through the National Snow and Ice Data Center (https://doi.org/10.7265/efmz-2t65, Meier et al., 2021 b). The ERA5 reanalysis data are available through the Copernicus Climate Change Service (https://doi.org/10.24381/cds.f17050d7, Hersbach et al., 2023). The code for LFCA is available on GitHub (https://github.com/rcjwills/lfca, last access: 29 April 2024) and Zenodo (https://doi.org/10.5281/zenodo.7940013, Wills and Shen, 2023).

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Additional Information

This paper was edited by Jari Haapala and reviewed by three anonymous referees.

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Sources of low-frequency variability in observed Antarctic sea ice

Abstract

Copyright and License

Acknowledgement

Funding

Data Availability

Additional Information

Additional Information

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