Antarctic sea ice, which melts during the summer and grows back during the winter has displayed an alarming aberration this time
Antarctic sea ice, which melts during the summer (December-February) and grows back during the winter (June-August) has displayed an alarming aberration this time.
Sea ice, almost the size of Greenland, has not grown back in the ongoing winter season. In the southern hemisphere, where sea ice grows back from its lowest point has been monitored using satellites for the last 44 years.
In February 2023, Antarctica had also displayed its lowest summer sea ice extent. Replenishment of sea ice is dependent on conditions of the surface ocean and lower atmosphere.
Sea surface warming and a warmer lower atmosphere has reduced the freezing potential, in turn reducing the thermodynamic ice growth (ice absorbs heat from the atmosphere to convert into water).
Moreover, the changed position of the polar vortex is increasing the southerly flow over the Antarctic sea ice. So the atmospheric circulation has also changed because of global warming.
Low sea ice directly impacts the marine ecosystems because their 'primary production' is dependent on sea ice. This will indirectly impact marine life in the higher tropical regions as well. Breeding cycles of species like emperor penguins and Weddell seals are also dependent on sea ice near the coastline.
The recent seasonal cycle of Antarctic sea ice suggests that Antarctic sea ice has transitioned to a different state with less sea ice overall and shorter duration of sea ice. Indications are that this transition is due to anthropogenic global warming.
Less sea ice also means less high albedo surface (one that reflects more sunlight) on the Southern Ocean. This directly warms the ‘upper ocean’. Lower sea-ice cover means less production of Antarctic Bottom Water (overlaying the sea floor), which is a critical element driving the meridional overturning circulation.
This circulation that drives water from north to south and back, brings warmth to various parts of the globe and also carries nutrients necessary to sustain ocean life. Less sea ice overall influences the gas and other exchanges between the ocean and atmosphere.
This includes aerosol production and with it the cloud formation over the Southern Ocean. While we have been hearing news about depleting sea ice for years now, the unusual discovery this year makes it uncertain about how long the resilient Antarctic ecosystem will be able to sustain the impacts of anthropogenic global warming.
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