The Arctic ice may be disappearing, but until not long ago in Antarctica the opposite was the case. However, in February that trend was broken and the extent of ice in the southern hemisphere reached a record low, the second in five years.
According to satellite data, the extent of Antarctic sea ice was below two million square kilometers for the first time since observations of the poles from space began in 1978.
This Tuesday, in an article published in Advances in Atmospheric, a team of researchers from Sun Yat-sen University and the Marine Science and Engineering Laboratory of South Guangdong (Zhuhai), in China, has analyzed this event in search of its causes, although they remain unclear.
In recent years, global warming is causing a rapid decline in the extent of sea ice in the Arctic, but so far, at the other pole of the Earth, Antarctic ice has increased by about one percent per decade since the late 1970s.
In 2017 this trend was broken and the sea ice of the southern hemisphere registered its historical minimum that now, five years later, has been repeated.
On February 25, 2022, at the end of summer in the southern hemisphere, data showed that there was significantly less than normal ice in the Bellingshausen/Amundsen Seas, the Weddell Sea, and the western Indian Ocean.
Besides, across the region, sea ice extent was 30% lower than the average for the three-decade reference period 1981-2010.
In recent years, many causes have been proposed to explain the variability of Antarctic sea ice, but there is still no scientific consensus and the phenomenon remains theoretical and unexplored.
The appearance of a new minimum in sea ice extent in such a short period of time prompted Chinese researchers to study what had happened and why.
After analyzing the satellite data, they observed that in summer thermodynamics dominates the processes that cause sea ice to melt, producing anomalies in the transport of heat towards the pole in the Bellingshausen/Amundsen seas, the western Pacific Ocean and the eastern Weddell Sea. in particular.
Global infrared radiation, light, temperature and albedo (the “whiteness” of a surface. The whiter it is, the greater the reflection of said radiation, and the darker it is, the greater the absorption).
“Sea ice is whiter than unfrozen dark sea, so there is less reflection of heat and more absorption, which in turn produces a vicious circle that melts more sea ice and produces more heat absorption», explains the climatologist and co-author of the study Qinghua Yang.
However, in spring, both thermodynamics and dynamics contribute to the state of sea ice extent.
The authors noted that, according to data from the US National Oceanographic and Atmospheric Administration (NOAA), the new record for Antarctic sea ice reduction coincided with two climatological phenomena: La Niña and a positive Southern Annular Mode (SAM).
The SAM is a belt of strong westerly winds or low pressure that surrounds the continent and moves north or south, while La Niña describes a weather pattern of powerful winds that forcefully blow warm water from the surface of the ocean from South America to Indonesia in the tropics.
These two phenomena affect the low of the Amundsen Sea (ASL), a center of low atmospheric pressure over the southern end of the Pacific Ocean and off the coast of West Antarctica.
Therefore, “if tropical variability has such an impact, that is the place to study”, concludes Jinfei Wang, co-author of the work.