A new approach to classification of 40 years of Antarctic sea ice concentration data

Abstract

In this paper, we present a characterization of Antarctic sea ice based on the classification of annual sea ice concentration (SIC) data from 1979 to 2018. A clustering algorithm was applied to provide a climatological description of significant annual cycles of SIC and their spatial distribution around the Southern Ocean. Based on these classification results, we investigate the variability of SIC cycles on decadal and inter-annual time scales. First, we discuss significant spatial shifts of SIC cycles during 1979-1998 and 1999-2018. In the Weddell Sea and in large parts of the Ross Sea, we observed higher SIC during the summer season, and an extension of sea ice cover in winter compared to the long-term average. Second, we introduce the Climatological Sea Ice Anomaly Index (CSIAI), which is an annual measure for year-round sea ice anomalies of the Southern Ocean and its regional sub-sectors. By relating selected years of significant sea ice conditions (1981, 2007 and 2014) with atmospheric influences, we demonstrate that the CSIAI is very useful for assessing interannular Antarctic SIC variability. Positive and negative sea ice anomalies can be qualitatively explained by atmospheric circulation anomalies in the years 1981 and 2007. However, in 2014, the year with the largest observed sea ice extent in our time series, we found that this positive sea ice anomaly was surprisingly not associated with a stationary and inter-seasonally persistent pattern of circulation anomaly. This suggests that sub-seasonal to seasonal circulation anomalies and ocean-related processes favoured the formation of the sea ice maximum in 2014. With this study we provide additional information on the long-term annual SIC variability around Antarctica. Furthermore, our classification approach and its results have potential for application in the evaluation of sea ice model results.

The Antarctic Marginal Ice Zone and Pack Ice Area in CMEMS GREP Ensemble Reanalysis Product

“…After record maxima successively occurred in 2012, 2013, and 2014, Antarctic sea ice decreased below the long-term average in 2015, with unprecedented record low minima in 2016, 2017 and 2018 (Parkinson, 2019). However, the recent decrease does not signify a change in the sign of the long-term trend, which remains positive over the period 1979-2019, though with lower magnitude compared to the 1979-2015 trend (Wachter et al, 2021).…”

Editorial for the Special Issue “Remote Sensing of the Polar Oceans”

“…Satellite passive microwave observations have been used to monitor SIC and SIE since the 1970s by measuring sea ice and open water brightness temperature (TB). Since then, several products have been developed to improve our understanding of the sea ice cover in both polar hemispheres [3,4], allowing us to estimate its decrease in the Arctic Ocean [20] and its enormous variability of the Southern Ocean [5,6]. However, this information is characterized by a certain level of inaccuracy due to retrieval and sensor noise, and may be less accurate during summer when sea ice and open-water TB values are similar.…”

“…Polar regions have undergone significant changes over the past 40 years, impacting the global climate [1,2]. Sea ice is rapidly changing (in terms of extent, concentration, and, especially, thickness), both in the Arctic and in the Southern Ocean [3][4][5][6]. This affects climate and biogeochemical cycles, ocean circulation and stratification, as well as the ocean-atmosphere exchange of momentum, heat and gases [7,8].…”

The Role of the Pacific‐Antarctic Ridge in Establishing the Northward Extent of Antarctic Sea‐Ice

“…The Southern Ocean (SO) can be characterized by large variations in SIC and SIE at both local and regional scales. For example, observations of the Bellingshausen Sea (in the Pacific sector of the SO) show strong decrease during the last four decades (Parkinson & Cavalieri, 2012; Stammerjohn et al., 2012; Wachter et al., 2021). However, the opposite occurred in the Ross Sea, where a slight increase in SIC and SIE was observed (Aulicino et al., 2014; Comiso et al., 2017; Parkinson, 2019).…”