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Antarctic sea ice melts to new record low

Sea ice levels in the Antarctic have reached a record low for the second time in the last five years, a phenomenon dissected by researchers in a new study.

(CN) — After decades of modest but steady increases, researchers in the Antarctic recorded a new low in sea ice at the southern pole in February — the second instance in five years since scientists began using satellite data to track ice levels in the late 1970s.

According to a study published Tuesday in the journal Advances in Atmospheric Sciences, sea ice covering the South Pole's surrounding waters stretched fewer than 2 million square kilometers for the first time, including “significantly lower than normal” ice coverage in the Bellingshausen/Amundsen and Weddell seas and the western Indian Ocean sector of the Southern Hemisphere.

While the alarming rate of ice melting in the Arctic has been widely reported, the Antarctic has been relatively stable by comparison and sea ice levels there have steadily grown an average of about 1% each year since the 1970s.

But that trend was interrupted in 2017, when the Southern Hemisphere saw a record minimum of sea ice extent. February's measurement marks the second record low in five years, and the lowest level since satellites began observing the poles in 1978. Scientists also noted an overall 30% decrease in ice from a baseline average derived between 1981 and 2010.

The pendulum swing of Antarctic sea ice coverage in such a relatively short time drove researchers at Sun Yat-sen University and Southern Marine Science Engineering Guangdong Laboratory in China to learn more about the phenomenon.

To understand the recent deviations, researchers used a sea ice budget analysis to calculate exactly how the freezing and thawing process has occurred in Antarctica since 1979. This analysis involved calculating ice inputs versus outputs within a cyclical system on the Southern Hemisphere, as well as factoring in thermodynamics.

The study found that summer heat is transported through natural processes to specific areas, such as the Bellingshausen/Amundsen and Weddell seas. Outside of seasonal temperature shifts, researchers also found that the greater absorptive capability of ice than unfrozen seawater causes a “vicious cycle” of melting.

These separate processes combine in the spring, when increased sunlight melts the ice while the natural water flow carries chunks of ice to tropical waters, which speeds up the melting process, according to the study.

Researchers found that thinner ice in key areas also contributes to this increased melting trend. The thinner ice freeboard, or the measured thickness of the ice that appears above the waterline, in the Amundsen Sea becomes more easily affected by La Nina winds that carry warmer temperatures from South America to the tropics, which later melts the ice carried that direction.

These processes result in a region containing the most annual atmospheric variability of anywhere in the Southern Hemisphere. Researchers concluded that this region — dubbed the Amundsen Sea low — was the source of the recent increasing melting trend in the Antarctic, catalyzed by both seasonal shifts and physical thermodynamic processes.

With the culprit in their sights, researchers want to examine the phenomenon more thoroughly, according to Jinfei Wang, a co-author of the study.

“If tropical variability is having such an impact, it’s that location that need to be studied next,” Wang said in a statement.

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Categories / Environment, Science

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