Antarctic sea ice is a dynamic material that forms during winter and floats away and melts during the summer. Due to this dynamic phenomenon, the ocean around Antarctica enlarges, doubling the size of the continent in the winter months reaching over 18 million sq km (Science Daily 2020). The sea ice plays an important role in maintaining the earth’s energy balance and sustaining the Antarctic ecosystem that supports wide varieties of rare plant and animal species. Understandably, losing sea ice may negatively impact the global temperature as a whole and local ecosystem in particular.
Recently, a team of researchers of various institutions including a scientist from National Centre for Polar and Ocean Research, Goa, found in their study that in the last five years the summer sea ice in the Weddell Sea sector of Antarctic has decreased by roughly one million sq km. The Weddell Sea contains the largest amount of Antarctic multiyear sea ice (Parkinson and Cavalieri 2020). It is located in a relatively frigid region; hence even in summer months sea ice survives here. The amount of sea ice in this sector has been monitored from the 1970s.
John Turner, climate scientist at British Antarctic Survey Antarctic and lead author of a recently published study in June 2020, says that sea ice has been a continuous source of surprise for them. Opposed to the Arctic, sea ice around the Antarctic had been increasing since the 1970s. Then it has rapidly decreased to record low levels, with the greatest decline seen in the Weddell Sea. This area now has a third less sea ice, which is likely to impact ocean circulation and marine life (Cockburn 2020).
What were the reasons behind sea ice loss?
Researchers have cited two primary reasons behind significant sea ice loss in the Weddell Sea. First, is intense and unseasonal storms while the other is the Maud Rise polynya. Due to low pressure over the southern Weddell Sea and high pressure over the South Atlantic, September witnessed high speed westerly winds over northwest Weddell Sea, says research paper. The warm air resulted in the melting of the sea ice.
Secondly, the development of a polynya–a large area of open water within the sea ice, also contributed to the ice loss. The re-development of polynya was also the result of westerly winds of record strength. The ice free conditions allowed the ocean to absorb more energy which resulted in higher ocean temperatures and consequently slowing down in the formation of new ice. The situation still persists even today. The study reveals that between 2015-2016 and 2016-2017, there was the largest decrease in summer sea ice extent in the 40 year record (Fig.1).
What will be the impact?
We all know that the Antarctic sea ice ecosystem supports many plants and animal species. Tiny ice algae, krill, seals and whales are highly adaptive to the sea ice. These all make a food chain that built the great Antarctic ecosystem. Any anomaly in the sea ice concentration will adversely affect the food chain. Krill–shrimp like crustaceans found in huge swarms, is the keystone species in the Antarctic. Krill eat microscopic algae, while blue whales, seals, penguins, albatrosses and seabirds eat krill. In this way, these are the engines of the ocean ecosystem. The ice loss removes ice algae and there is a report which says that over the past 40 years, populations of adult Antarctic krill have declined by 70 to 80 per cent in Weddell Sea and in the waters around the Antarctic Peninsula (Thompson 2016). Hence, the sustainability of the sea ice concentration is necessary to sustain this vital ecosystem. However, researchers are not sure if the Weddell Sea ice will be restored to what it was before 2016.
This story is drawn from a study published in the Geophysical Research Letter, 16 June, 2020. The research paper citation is Turner J., M. V. Guarino, J. Arnatt, B. Jena and G. J. Marshall. 2020. Geophysical Research Letters, Advancing Earth and Space Sciences, 47(11): 1-11. Available at: https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2020GL087127
1. Cockburn H. 2020. Climate crisis: Antarctica’s Weddell Sea Lost Area of Ice Twice The Size of Spain Over Last Five Years, Independent, June 17. Available at: https://www.independent.co.uk/environment/climate-crisis-antarctica-weddell-sea-ice-loss-melt-global-warming-a9571926.html
2. Parkinson C. L. and D. J. Cavalieri. 2012. Antarctic Sea Ice Variability and Trends: 1979–2010, The Cryosphere, 6: 871-880. Available at: https://tc.copernicus.org/articles/6/871/2012/
3. ScienceDaily. 2020. Antarctic Sea Ice Loss Explained in New Study, June 17. Available at: https://www.sciencedaily.com/releases/2020/06/200617121458.htm
4. Turner J., M. V. Guarino, J. Arnatt, B. Jena and G. J. Marshall. 2020. Geophysical Research Letters, Advancing Earth and Space Sciences, 47(11): 1-11. Available at: https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2020GL087127