While it’s no secret that Arctic sea ice is steadily declining, sea ice supplies on the other side of the world, in Antarctica, are much more stable. This year, however, the amount of ice covering the sea in Antarctica has fallen to an all-time low since records began in the late 1970s.
Drastic decline in Antarctica
The drastic decline in Antarctic sea ice is the second such event in five years. Researchers have been able to find reasons for this decline, but there are still many unsolved mysteries.
The Arctic ice retreat has been steadily going on for years and is caused by global warming. In Antarctica, on the other hand, sea ice has been growing relatively moderately at about one percent per year since the 1970s — albeit with significant fluctuations and regional variations.
In 2017, this positive trend was interrupted when Antarctic sea ice bottomed out. And now, just five years later, this event is repeating itself.
On February 25, a few days before the end of summer in the southern hemisphere, Chinese researchers calculated that the ice mass in the Arctic Ocean was less than two million square kilometers for the first time. There has never been so little ice in Antarctica since satellite observations of the poles began in 1978. Especially in the Bellingshausen Sea and the Amundsen Sea and in the western Indian Ocean the ice surface had sunk drastically. The total extent of Antarctic sea ice was about 30 percent below the 1981-2010 average.
Causes are complex
The reasons for the fluctuations in Antarctic sea ice are complex – several mechanisms have only been discovered and discussed in recent years. Until now, however, there is no scientific consensus on this and there is a great need for research.
A research group from Sun Yat-sen University and Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai) in China seized the current negative record as an opportunity to take a closer look at the exact causes.
To do this, the researchers analyzed data on the daily portion of Antarctica covered in ice collected between 1979 and 2022 and combined them with data on sea ice anomalies collected during that period by the National Snow and Ice Data Center (NSIDC). ). The scientists discovered that in the summer it is mainly thermodynamic processes that cause the sea ice to melt. Reasons for this are, for example, deviations in the heat transport in the region. In addition, there is an increase in infrared radiation and visible light, which is partly caused by the interaction between the white surface of the sea ice and the radiation.
†Sea ice is whiter than the dark, unfrozen sea, so there is less reflection of heat and more absorption, which in turn melts more sea ice, absorbing more heat, in a vicious circle‘, says climatologist Qinhua Yang, one of the co-authors of the study.
Interaction of different effects
In the spring, the thermodynamic processes are then supplemented by an ice drift towards the tropics. This effect mainly occurs in the Amnundsen Sea and the Ross Sea. The researchers found that the negative record coincided with a combination of La Niña weather effects and a positive Southern Annular Mode (SAM). The latter term describes a strong west-facing wind system, while La Niña describes strong winds that transport warm water from South America to Indonesia.
Both weather systems amplify the Amundsen Sea Low, a low-pressure system building over the South Pacific Ocean off the coast of West Antarctica.
The researchers discovered that the atmospheric influences on the sea ice originate from the intensity and location of this Amundsen Sea layer. † If tropical variability has such an impact, then that location needs to be studied” summarizes Jinfei Wang, who also participated in the investigation.