A regime shift in seasonal total Antarctic sea ice extent in the twentieth century

Abstract

ea ice is a critically important component of the very complex Antarctic climate system. Its variability is driven by changes in the atmosphere and ocean, which interact with each other and operate on different timescales 1 . The remote nature of Antarctica means that there are very few in situ measurements of the surrounding atmosphere or ocean where the sea ice forms, and understanding its variability depends largely on satellite observations 2,3 . Satellite measurements of Antarctic sea ice extent indicate weak but statistically significant increases in total sea ice around Antarctica from 1979 to 2016, followed by a sharp decline to below-average values in 2016 and a record low in summer 2017, before returning to average by austral summer 2020. While the total Antarctic sea ice extent exhibits a positive trend 4 (unlike the Arctic sea ice extent 5 ), there is a strong regionality 6 and seasonality 7 to the trends, and they can be of opposite signs, particularly marked by an increase in the Ross Sea and a decrease in the Bellingshausen Sea prior to 2016 1,4 . Analyses of the observed temporal and spatial variability in Antarctic sea ice have been attempted [8][9][10][11][12] , but a thorough understanding is limited because the sparsity of in situ observations and the brevity of the satellite record mean that their temporal uniqueness cannot be easily assessed 13 . Their future change is also uncertain, since coupled climate models used in both the fifth and the recent sixth IPCC assessment reports fail to reproduce the observed increases; instead, most show widespread decreases around Antarctica [14][15][16] .

Record Low Antarctic Sea Ice Cover in February 2022

“…This is supported by sea ice reconstructions from ice cores (Thomas et al., 2019), and data assimilation approaches (Fogt et al., 2022). Most reconstructions suggest that total Antarctic SIE has been declining during the 20th century (Fogt et al., 2022), and it is only after the 1980s that a positive trend is observed. On a regional scale, SIE in the Bellingshausen Sea (Abram et al., 2010) and Indian Ocean (Curran et al., 2003) has been steadily declining during the 20th century.…”

“…Sea ice reconstructions, based on principal component regression of Southern Hemisphere midlatitude temperature and pressure observations, suggest that the 2022 minimum was one of the lowest of the past 100 years (Fogt et al., 2022). This is supported by sea ice reconstructions from ice cores (Thomas et al., 2019), and data assimilation approaches (Fogt et al., 2022).…”

“…Sea ice reconstructions, based on principal component regression of Southern Hemisphere midlatitude temperature and pressure observations, suggest that the 2022 minimum was one of the lowest of the past 100 years (Fogt et al., 2022). This is supported by sea ice reconstructions from ice cores (Thomas et al., 2019), and data assimilation approaches (Fogt et al., 2022). Most reconstructions suggest that total Antarctic SIE has been declining during the 20th century (Fogt et al., 2022), and it is only after the 1980s that a positive trend is observed.…”

Antarctic sea ice over the past 130,000 years, Part 1: A review of what proxy records tell us

“…The slight increase in total extent was the result of opposing trends in different regions of Antarctica, with a large decrease in sea-ice extent in the Amundsen and Bellinghausen seas offset by a large increase in the western Ross Sea (Zwally et al, 2002;Holland and Kwok, 2012;Fan et al, 2014;Jena et al, 2018;Parkinson, 2019). This regional and inter-annual variability has mainly been attributed to the atmospheric climate modes prevailing over the SO, such as the Antarctic Circumpolar Wave (White and Peterson, 1996;Raphael, 2007;Fogt et al, 2022) and the SAM (Kwok and Comiso, 2002;Simpkins et al, 2012;Kohyama and Hartmann, 2015), along with teleconnections to low latitude climate modes such as ENSO (Liu et al, 2002;Yuan, 2004;Hobbs and Raphael, 2010;Deb et al, 2014;Ciasto et al, 2015;Kohyama and Hartmann, 2015;Meehl et al, 2016). After years of increasing extent, there was an exceptional decline in Antarctic sea-ice extent in 2016 (Parkinson et al, 2019), especially in the Weddell and Ross seas (Hao et al 2021).…”

“…The causes of this expansion and subsequent decline are not yet fully understood, but may be related to complementary processes such as deepening of the ozone hole (Ferreira et al, 2015), freshening of surface waters due to ice shelf melt (Bintanja et al, 2013;Rye et al, 2020) or changes in atmospheric circulation, wind stress and thermodynamic processes linked to the Southern Annular Mode (SAM) and El Niño-Southern Oscillation (ENSO) (Hall and Visbeck, 2002;Holland and Kwok, 2012;Matear et al, 2015;Kwok et al, 2016;Turner et al, 2016;Kusahara et al, 2019;Maksym, 2019;Yang et al, 2021;Fogt et al, 2022). Climate models that were part of the Third,Fifth,and Sixth Coupled Model Intercomparison Projects (CMIP3,CMIP5,and CMIP6,respectively), used by the United Nations Intergovernmental Panel on Climate Change (IPCC), have predicted that the WSI extent is expected to decline between 24 and 34% by 2100 (Arzel et al, 2006;Bracegirdle et al, 2008;IPCC, 2013;Roach et al, 2020).…”