Warm air from the north | Polarjournal
El Niño and La Niña cannot be used to predict the state of the ice; that depends on their intensity, and each phenomenon is unique. Image: Michael Wenger

The winter of 2023 saw the lowest ever sea ice extent around Antarctica. A drop in sea ice area compared with average values caused by uuper ocean warming, polar cyclones and atmospheric lows.

Repeated record lows. The retreat of sea ice has continued from summer to summer since 2016. During this period, anomalies remained light in winter until strong warm and wet winds from the north blew southwards over the ice sea. In the journal Geophysical Research Letters, on March 27, an Indo-British research team described this unique phenomenon observed in 2023, attesting the signal of climate change have affected the sea ice in winter for the first time.

As a result, the surface of the sea ice reached a record low, at just bellow 17 million square kilometers. The average value of records over the past 40 years stands at around 19 million square kilometers. This new record follows that of the summer of 2023, when sea ice reached its lowest ever recorded level: 1.79 million square kilometers. And it precedes the second summer record, set this year. “When we have low ice conditions in summer, it has an impact on winter ice extent and vice versa”, explains Babula Jena, the study’s lead author, an ocean physicist in India at the National Center for Polar and Ocean Research (NCPOR).

There were two reasons for the slowing of sea ice recovery in the winter of 2023: first, “the heat and warming of the upper ocean”, he points out, and second, “polar cyclones and southward winds”, he adds. On the one hand, the winds push the ice and, on the other, they activate the upwelling of warm water towards the surface. These two combined actions cause the ice to retreat in phases.

Ice growth was slow during the last austral winter. Image: Dr. Babula Jena / Indian Scientific Expedition to Antarctica

The northerly wind was brought by atypical “explosive” polar cyclones, meaning that they remain stationary over certain Antarctic ocean areas instead of passing through. “It was very exceptional”, notes the researcher. Next, the low-pressure area – which attracts the wind – across the Weddell Sea grew particularly deep, and the atmospheric blocking of the Ross Ice Shelf was particularly strong. The sea ice was therefore more affected by the wind in the Weddell and Ross Sea, where more of 70 % of the record low in winter sea ice extent in 2023 occurred.

“We need more observations and more precise models to know exactly what is going to happen, but it is likely that sea ice will remain at a low level”, explains the physicist. The retreating sea ice in winter has a major impact on the emperor penguins that nest at that time of year, and the krill larvae that overwinter underneath the sea ice. Less ice also means more warming of the ocean under the effect of light energy, modifying oceanic and atmospheric circulations on a global scale.

Camille Lin, PolarJournal

Link to the study : Jena, B., Kshitija, S., Bajish, C.C., Turner, J., Holmes, C., Wilkinson, J., Mohan, R., Thamban, M., 2024. Evolution of Antarctic Sea Ice Ahead of the Record Low Annual Maximum Extent in September 2023. Geophysical Research Letters 51, e2023GL107561. https://doi.org/10.1029/2023GL107561.

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