Breaking Records: The Antarctic Sea Ice Extent Hits an All-time Low

By SaGHAA Team

In 2021, Antarctic sea ice retreated sooner than anticipated starting from early September but the negative anomalies became larger until mid-November and changed little until mid-December, and sea ice extent rapidly decreased exceeding two standard deviations of the climatology on 8 February. Compared to 2017, the SIE in 2022 had a slower recovery in late February, leading to the new record minimum.

Introduction

Antarctic sea ice is a vital component of the Earth's climate system, playing a crucial role in regulating the planet's temperature and influencing ocean currents. In recent years, scientists have observed a record low in sea ice extent (SIE) in the Antarctic raising concerns about its potential impacts on the environment and the organisms that rely on it. In this article, we will delve into the latest research concerning the decline of Antarctic Sea ice and the factors causing it.

 

         

    Image Source: Flickr

 The Meltdown: Status of Antarctic Sea Ice Extent

Antarctic Sea ice extent hit a new record for the season’s lowest SIE of 1.9 million sq km in February 2022 since record-keeping began in 1978; 0.17 million sq km lower than the previous record low set in 2017 (Wang, et al., 2022). Sea ice is a feature of high-latitude oceans such as polar regions and its most common measure is extent; defined as the area covered with an ice concentration of at least 15 per cent. This extent increases and decreases with the seasons.  Even the slightest change in Antarctic Sea ice cover can affect the exchange of moisture, heat and gases between the atmosphere and ocean freshwater input, ocean circulation, local weather systems, and global climate. Contrary to the rapid decline of the Arctic Sea ice extent (SIE) in the context of global warming (Serreze and Meier, 2019), Antarctic SIE displays a modest increasing trend of ~1.0 per cent ± 0.5 per cent per decade since late 1978 (Parkinson, 2019), masking significant interannual and regional variations (Stammerjohn and Maksym, 2016; Yuan et al., 2017; Maksym, 2019).

Figures used in this study involve daily sea ice concentration (SIC) data during 1979-2022 from National Snow Ice Data Center (NSIDC). Daily sea ice drift (SID) during 1979–2020 and weekly quick look SID since 2021 are also obtained from the NSIDC. Hourly sea level pressure (SLP), air temperature, surface net shortwave and longwave radiative fluxes, surface latent heat, and sensible heat fluxes are obtained from the ERA5 reanalysis (ECMWF, 2018; Wang, et al., 2022).

 

  Source: Climate.gov Media, 14 March 2022 https://www.climate.gov/media/14290

Uncovering the Meltdown: Causes Leading to Lowest SIE

One reason for this is that the Antarctic Sea ice retreated earlier than normal, starting from early September 2021. The negative anomalies became larger until mid-November, and then sea ice exhibited a steadily decreasing rate until mid-December of 2021 and dropped quickly, exceeding two standard deviations (SDs) of the climatology on 8 February 2022 (Wang et al., 2022). Significant negative SIC anomalies in summer were located in the western Amundsen Sea, eastern Ross Sea, west of Antarctic Peninsula, northern Weddell Sea, and north-western Indian Ocean sector, while the SIC anomalies in spring were negative in most sectors, basically confined in the western Weddell Sea, the Bellingshausen Sea, and the eastern Indian Ocean.

In summer, thermodynamic processes dominate the sea ice melting through poleward heat transport anomalies in the Bellingshausen/Amundsen Seas, eastern Weddell Sea, and the western Pacific Ocean and positive net shortwave radiation anomalies with albedo–temperature feedback. In spring, dynamic and thermodynamic processes contribute to sea ice tendency together. Dynamic ice loss exists in the Amundsen Sea where northward ice motion pushes more ice to the lower latitudes and increases melting, especially in the Amundsen Sea and the Ross Sea. Thermodynamic contributions including poleward heat transport, shortwave radiation, and sensible and latent heat flux anomalies melt sea ice in the Weddell Sea. Meanwhile, thinner sea ice freeboard along the coast of the Amundsen Sea is also critical to the summer melting. All these atmospheric impacts originate from the intensity and position of Amundsen Sea Level (ASL) and ocean warming, proving the deductions made by Raphael and Handcock (2022).

According to the NOAA Climate Prediction Center, the monthly Antarctic Oscillation (AAO) index and Oceanic Niño Index show that the new record Antarctic SIE minimum happened during a combination of positive Southern Annular Mode (SAM) and La Niña. Both of these modes lead to a deepened ASL (Yu et al., 2015; Fogt and Marshall, 2020). Fogt et al. (2011) revealed that when a La Niña (El Niño) is concurrent with a positive (negative) SAM, the impact of ENSO is significant on South Pacific atmospheric circulation. Stammerjohn et al. (2008) investigated the relationship between these combined impacts and the sea ice retreat/advance and showed a similar result to the in-phase condition in Fogt et al. (2011), with significant ice responses, particularly in the western Antarctic Peninsula and the southern Bellingshausen Sea. In addition, the Indian Ocean Dipole, Interdecadal Pacific Oscillation, and the Atlantic Multidecadal Oscillation are all important factors contributing to the Antarctic Sea ice decline in the spring 2016 (Eayrs et al., 2021).  Besides studying the physical cause of the difference in the SIC distribution between 2016-17 and 2021-22 can help us understand the physical causes of the interannual variability of the Antarctic Sea ice. Hence, the impacts of tropical variability and large-scale climate modes should be further studied (Wang, et al., 2022).

Bottomline

Studies on the consequences of the lowest Antarctic sea ice extent are currently underway. Researchers are investigating the impact of this phenomenon on the delicate ecosystem of the region, as well as its effects on global weather patterns and sea levels. As the sea ice in the Antarctic plays a crucial role in regulating the Earth's climate, it is important to understand the potential consequences of its decline. The findings from these studies will provide crucial information for decision-makers to develop effective strategies to mitigate the effects of climate change in the region and beyond.

References

Climate.gov Media, 14 March 2022 https://www.climate.gov/media/14290

ECMWF, 2018: ERA5 hourly data on single levels from 1979 to present. Available online from https://cds.climate.copernicus.eu/cdsapp#!/dataset/reanalysis-era5-single-levels?tab=overview

Eayrs, C., X. C. Li, M. N. Raphael, and D. M. Holland, 2021: Rapid decline in Antarctic sea ice in recent years hints at future change. Nature Geoscience, 14, 460−464, https://doi.org/10.1038/s41561-021-00768-3   

Fogt, R. L., and G. J. Marshall, 2020: The southern annular mode: Variability, trends, and climate impacts across the southern hemisphere. WIREs Climate Change, 11, e652, https://doi.org/10.1002/wcc.652.

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