Although the floating ice cap in the Arctic is disappearing due to climate change, in Antarctica, until recently, the opposite was happening: it was expanding. However, in February the lowest values ever recorded were detected. It is the first time that its extension is less than two million square kilometers.
The area of sea ice (or sea ice) in the Arctic is rapidly declining due to global warming. In contrast, at the other pole of the Earth, it had increased by about 1% per decade since the late 1970s, although with significant variations each year and substantial regional differences.
However, bucking this general upward trend in Antarctica, there was a brief but quite marked anomaly in 2017, when the Southern Hemisphere sea ice experienced a record low. On February 25, 2022, just five years later, the lowest values of the Antarctic sea ice were again recorded, this is the first time that its surface has been less than two million square kilometers since they began to be used for satellite observations in 1978.
The data shows significantly lower than normal ice cover in the Bellingshausen and Amundsen seas, the Weddell Sea and the western Indian Ocean. Interestingly, across the region, sea ice extent was 30% below the average for the three-decade baseline period 1981-2010.
Possible causes of thaw
The causes of this variability are complicated. Several mechanisms have been proposed in recent years, but there is still no scientific consensus. Therefore, the appearance of this new record in such a short time led a team of scientists from Sun Yat-sen University and the South Guangdong Marine Science and Engineering Laboratory (both in China) to find out what happened and why. The results of the study are published in the journal Advances in atmospheric science.
Using data from the National Snow and Ice Data Center (NSIDC), the researchers took stock of the state of the sea ice from 1979 to 2022, that is, they examined the amount of frozen water added and lost during this period. with dynamic (processes related to the movement of fluids) and thermodynamic (such as freezing and melting) phenomena.
The scientific team discovered that in summer it is thermodynamics that dominates the processes that cause melting. This occurs through anomalies in poleward heat transport in the Bellingshausen and Amundsen seas, western Pacific Ocean, and eastern Weddell Sea.
At this time, there is also an increase in global infrared radiation and visible light due to positive albedo and temperature feedback. The albedo describes the whiteness of a surface: the whiter it is, the greater the reflection of this radiation, and the darker it is, the greater the absorption.
“Sea ice is whiter than the unfrozen Black Sea, so [en el mar] there is less heat reflection and more absorption“, explains the climatologist Qinghua Yang, co-author of the study. “Which in turn melts more sea ice, producing more heat absorption in a vicious cycle.”.
In the spring, however, thermodynamics and dynamics contribute to the state of the sea ice. In addition to the aforementioned thermodynamic processes, the dynamics of ice loss in the Amundsen Sea cause a northward movement of the sea which pushes more ice to the lower latitudes of the tropics, increasing melting, especially in the Amundsen Sea and Ross Sea.
The climatic phenomena at the origin of the new historical minimum
The authors note that, according to data from the U.S. National Oceanographic and Atmospheric Administration (NOAA), the new record low occurred at the same time as a combination of La Niña and a southern annular mode ( SAM) positive. MAS describes a belt of strong westerly winds or low pressure that encircles the continent and moves north or south, while La Niña describes a weather pattern of strong winds that forcefully blow warm water from the surface of the ocean in the tropics, from South America to Indonesia.
Both phenomena intensify the low atmospheric pressure of the Amundsen Sea. The variability of atmospheric conditions in this region is greater than in any other part of the southern hemisphere. Additionally, the researchers found that all of the atmospheric impacts that affect sea ice size come from the intensity and position of low pressures in the Amundsen Sea.
Thanks to this study, scientists were able to find explanations for the shrinking of the floating ice cap in Antarctica. However, their findings also raised more questions, which they hope to answer in future research. “If tropical variability has such an impact, this is where to study next.concludes Jinfei Wang, one of the other authors of the book.
Wang et al. (2022) “An unprecedented record Antarctic sea ice extent in the 2022 austral summer”Advances in atmospheric science