25 Apr 2023
 | 25 Apr 2023
Status: this preprint is open for discussion.

Sources of low-frequency variability in observed Antarctic sea ice

David B. Bonan, Jakob Dörr, Robert C. J. Wills, Andrew F. Thompson, and Marius Årthun

Abstract. Antarctic sea ice gradually increased from the late 1970s until 2016, when it experienced an abrupt decline. A number of mechanisms have been proposed for both the gradual increase and abrupt decline of Antarctic sea ice, 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 spatial-temporal 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. This mode is associated with periods of abrupt Antarctic sea-ice decline and is related to a weakening of the circumpolar westerlies, which favors surface warming through a shoaling of the ocean mixed layer and decreased northward Ekman heat convergence. Broadly, these results suggest that climate model biases in long-term Antarctic sea-ice and global sea-surface temperature trends are related to each other and that eastern Pacific ENSO variability causes abrupt sea ice changes.

David B. Bonan et al.

Status: open (until 07 Jul 2023)

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David B. Bonan et al.

David B. Bonan et al.


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Short summary
Antarctic sea ice has experienced substantial changes over the last few decades, including a gradual increase since the late 1970s and an abrupt decline in 2016. In this paper, we use a novel statistical method to identify sources of variability in observed Antarctic sea-ice changes. We find that the gradual increase in sea ice is likely related to global temperature trends and periods of abrupt sea ice decline are related to specific flavors of equatorial tropical variability known as ENSO.