Antarctic sea ice
Antarctic sea ice is the
Sea ice that comes from the Southern Ocean melts from the bottom instead of the surface like
Measurements of sea ice
Extent
The Antarctic sea ice cover is highly seasonal, with very little ice in the
Since the ocean off the Antarctic coast usually is much warmer than the air above it, the extent of the sea ice is largely controlled by the winds and currents that push it northwards.[5] If it is pushed quickly, the ice can travel much further north before it melts. Most ice is formed along the coast, as the northward-moving ice leaves areas of open water (coastal latent-heat polynyas), which rapidly freeze.
Thickness
Because Antarctic ice is mainly first-year ice, which is not as thick as multiyear ice, it is generally less than a few meters thick. Snowfall and flooding of the ice can thicken it substantially, and the layer structure of Antarctic ice is often quite complex.
Recent trends and climate change
Sea ice extent in Antarctica varies a lot year by year. This makes it difficult determine a trend, and record highs and record lows have been observed between 2013 and 2023. The general trend since 1979, the start of the
The IPCC AR5 report concluded that "it is very likely" that annual mean Antarctic sea ice extent increased 1.2 to 1.8% per decade, which is 0.13 to 0.20 million km2 per decade, during the period 1979 to 2012.[8]: 7 IPCC AR5 also concluded that the lack of data precludes determining the trend in total volume or mass of the sea ice. The increase in sea ice area probably has a number of causes.[9] These are tied to changes in the southern hemispheric westerly winds, which are a combination of natural variability and forced change from greenhouse gases and the ozone hole. The winds drive sea ice drift, and modelling research suggests that the observed sea ice expansion was driven by changes in the sea ice drift velocity.[10] Another possible driver is
Recent changes in wind patterns, which are connected to regional changes in the number of extratropical cyclones and anticyclones,[12] around Antarctica have advected the sea ice farther north in some areas and not as far north in others.
Atmospheric and oceanic drivers likely have contributed to the formation of regionally varying trends in Antarctic sea-ice extent. For example, temperatures in the atmosphere and Southern Ocean have increased during the period 1979–2004. However, sea ice grows faster than it melts, because of a weakly stratified ocean. Thus, this oceanic mechanism is, among others, contributing to an increase in the net ice production, potentially resulting in more sea ice.[13] Although thickness observations are limited, modelling suggests that observed ice-drift toward the coastal regions makes an additional contribution for dynamical sea-ice thickening during autumn and winter.[14]
Observed autumn and spring trends in the number of extratropical cyclones, anticyclones and blocks, which have a strong thermodynamic control through temperature advection, and a strong dynamic control through ice-drift, on sea-ice extent during the same and also during following seasons are almost everywhere around Antarctica in agreement with the observed, regionally varying, trends in sea-ice extent.[12] Consequently, the near-surface winds steered around weather systems are thought to explain large parts of the inhomogeneous Antarctica sea-ice trends.
The 2021 IPCC AR6 report confirms the observed increasing trend in the mean Antarctic sea ice area over the period from 1979 to 2014 but assesses that there was a decline after 2014, with the least extent reached in 2017, and a following growth.[15] The report then concludes that there is “high confidence” that there is no significant trend in the satellite observed Antarctic sea ice area from 1979 to 2020 in both winter and summer.
In early January 2023, the National Snow and Ice Data Center reported that Antarctic sea ice extent stood at the lowest in the 45-year satellite record—more than 500,000 square kilometers (193,000 square miles) below the previous record (2018), with four of the five lowest years for the last half of December having occurred since 2016.[16]
Implications
Monitoring changes in sea ice is important as this impacts the
Changes in Antarctic sea ice are also important because of implications for atmospheric and oceanic circulation.
[T]he greatest part of this southern continent (supposing there is one), must lie within the polar circle, where the sea is so pestered with ice, that the land is thereby inaccessible.
Captain James Cook. A Voyage Towards the South Pole and Round the World, etc.[19]
The force of moving ice is considerable; it can crush ships that are caught in the ice pack, and severely limits the areas where ships can reach the land, even in summer. Icebreakers, iceports and ice piers are used to land supplies.
See also
References
- ^ a b c d "Understanding climate: Antarctic sea ice extent". NOAA Climate.gov. 14 March 2023. Retrieved 2023-03-26.
- ^ a b Vaughan, D. G.; Comiso, J. C.; Allison, I.; Carrasco, J.; et al. (2013). "Chapter 4: Observations: Cryosphere" (PDF). IPCC AR5 WG1 2013. pp. 317–382.
- ^ NASA (2009-05-22). "Antarctic Sea Ice".
- ^ AP staff. (19 March 2022). "Both of the planet's poles experience extreme heat, and Antarctica breaks records". NPR website Retrieved 27 March 2022.
- ^ Fountain, Henry (22 February 2022). "Sea Ice Around Antarctica Reaches a Record Low". The New York Times. New York City. Retrieved 24 February 2022.
A complex group of factors is at play when it come to Antarctic sea ice. Large-scale atmospheric patterns, often occurring far from the continent, as well as local ocean currents and winds can all increase or reduce sea-ice coverage.
- ^ "Arctic Sea Ice News and Analysis". National Snow & Ice Data Centre. 15 March 2023. Retrieved 26 March 2023.
- .
- IPCC (2013). "Summary for Policymakers"(PDF). IPCC AR5 WG1 2013. pp. 3–29.
- ^ Lynch, Patrick (Oct 7, 2014). "Q&A with NASA's Joey Comiso: What is Happening with Antarctic Sea Ice?". NASA. Archived from the original on 2014-10-11.
- PMID 33594079.
- S2CID 54759501.
- ^ S2CID 134805912.
- .
- S2CID 53678373.
- IPCC (2021). "Chapter 9"(PDF). IPCC AR6 WG1 2021. pp. 1251–1254.
- ^ "Ice down under". 3 January 2023. Archived from the original on 6 January 2023. Fig. 5a
- .
- ^ "Sea Ice and Global Climate". NSIDC. Retrieved 11 Jul 2018.
NSIDC
- ^ Cook, James. (1777). A Voyage Towards the South Pole, and Round the World. Performed in His Majesty's Ships the Resolution and Adventure, In the Years 1772, 1773, 1774, and 1775. In which is included, Captain Furneaux's Narrative of his Proceedings in the Adventure during the Separation of the Ships. Volume II. London: Printed for W. Strahan and T. Cadell. (Relevant fragment)