Antarctica: Understand effects of negative ice record – 10/03/2023 – Environment

The successive negative sea ice records in Antarctica in 2023 reinforced researchers’ warning about the effects of these decreases in atmospheric circulation and the formation of cyclones and rain.

Among the possible consequences are the change in position and intensity of cyclones, which cause rains like those that hit Rio Grande do Sul recently. Furthermore, if the trend towards warmer waters reduces the formation of sea ice, the impact will reach the food chain, with indirect effects on large animals, such as whales.

Although it is not possible to say what part climate change plays in melting sea ice, experts point out that global warming plays a role in changing the scenario.

The negative record was indicated in preliminary data from the United States National Snow and Ice Data Center (NSIDC) at the end of September. On September 10, there was 1 million km² less sea ice than at the previous low in 1986.

For the head of the geography department at UFRGS (Federal University of Rio Grande do Sul), Francisco Aquino, the changes could mean, in the coming years, changes in the location and intensity of extratropical cyclones.

“We understand that a warmer planet, with an Antarctica with a smaller ice anomaly, intensifies some atmospheric circulations and could increase extreme events”, says the climatologist, known as Chico Glacier for his research in Antarctica.

This is because, according to Aquino, a hotter planet forces a greater contrast in temperature between Antarctica and the subtropical region. “At times, this synchrony triggers cyclones with greater impact or more intense cold waves in Brazil. Therefore, reducing sea ice may be a condition for intensifying extreme events in our hemisphere.”

More heat, including in the oceans, leads to an adjustment in wind circulation, which will change the formation of cyclones. Still, less ice to reflect solar radiation means more heat will be absorbed by the oceans. For Aquino, the same reasoning applies to other regions besides southern Brazil, such as southern South Africa and Australia.

The growth of ice around Antarctica, according to Aquino, may also have been caused by climate change. “The intensification of cyclones, with winds around Antarctica, stirred up the water, maintaining low temperatures and consistency for sea ice.”

In 2015 and 2016, years of a super El Niño, there was the largest ice retreat at the end of winter so far. “That’s what drew our attention to studying the region at that time.”

The ice reductions in Antarctica are reminiscent of what happened in the Arctic three decades earlier. Aquino explains that the ice in the southern hemisphere was not as affected as its counterpart to the north because there was no pressure from continental heat in Europe.

For Ilana Wainer, professor in the department of physical oceanography at the USP Oceanographic Institute, it is possible to relate the decrease in sea ice to warmer oceans. “Since 2014, between 100 and 200 meters below the surface, the water has warmed significantly.”

It is still not possible, however, to fully separate what global warming is from the variations that are already occurring in the Antarctic region. “Climate change happens over a long time, and satellite data for ice began in 1979,” he says.

The researcher recalls that the reduction in sea ice refers to an already known concern about rising sea levels. “Sea ice acts as a buffer for the ice on the coast against storms and violent tides.”

Thus, with less protection, the mantle tends to suffer more from the effects of bad weather — and thaw.

Beyond atmospheric circulation and disaster repositioning, the effects of drastic change can reach a diverse range of non-human life. In addition to episodes such as the death of entire colonies of emperor penguin chicks recorded in a study last year, there is a systemic impact.

At the base of the region’s food chain is Antarctic krill, the main source of food for seals and whales.

“These variations in ocean temperature have little or no direct influence on mammals such as seals, sea lions and whales, but they have a huge indirect effect”, says Eduardo Secchi, researcher at the Ecopelagos/Proantar project, which studies cetaceans.

Krill, a crustacean similar to shrimp, feeds on a specific type of marine microalgae, diatoms, which are attached to the ice. Changes in the stock of this algae can cause a reduction in the quantity of the animal, which is key to the food chain in Antarctica.

“With climate change, the emergence of another type of microalgae, cryptophytes, has been observed under certain conditions,” says Carlos Rafael Mendes, researcher on the Ecopelagos/Proantar project at the Federal University of Rio Grande (Furg).

Because krill do not feed on cryptophytes, their abundance declines, reducing the food and energy supply for top predators such as penguins and whales. Since many species always return to the same regions, looking for food elsewhere requires more energy.

“In the western region of the Antarctic Peninsula, one of the regions on the planet with the highest warming rates, a southward shift in the distribution of penguin colonies that depend on ice has been observed,” says Secchi.