Ice in the polar regions has been under assault from rising ocean and water temperatures. While human-driven climate change is driving widespread weirdness, natural patterns can also lead to chaos.
A prime of example of said chaos was the freakishly low sea ice extent in Antarctica in 2016 and 2017. Ice extent crashed hard everywhere, but particularly in the Weddell Sea near the Antarctic Peninsula. Among the oddities of the austral spring and summer those years was a Netherlands-sized hole in the ice known as a polynya.
Now, new findings published in Geophysical Research Letters show the likely cause of the abnormal conditions were intense, warm winds, which also helped usher in powerful storms that wiped out icepack. The results could help researchers refine their understanding of what the future holds, as temperatures rise and further destroy ice and the ecosystems it supports.
Antarctic sea ice is the oddball of polar ice. The Arctic’s ice has shown a steep decline as the planet has warmed, owing to its location in a largely enclosed ocean. In comparison, the Antarctic’s sea ice extends out from a continent and is much more dynamic. In the years before the huge 2016 crash to a record low, it was at a record high.
From 2015 to 2016, Antarctic sea ice extent dropped a staggering 463,322 square miles (1.2 million square kilometres) – an area twice the size of France. The new research used satellites as well as data collected from autonomous ocean-faring floats to figure out what happened to drive the drop. The findings show the first blow to the ice came in September, when the most powerful storm ever recorded in the Weddell Sea whipped through the region. Relatively warm, gusty winds lashed icepack and broke it up to kickstart melt season.
The heat continued into November, which was the hottest November ever recorded for the region, with temperatures averaging around 5.4 degrees Fahrenheit (3 degrees Celsius) above normal. During that time, the first polynya in nearly 40 years opened in the ice, which allowed dark water to absorb more heat from the sun and contribute to melting. Then another storm struck in December, this time moving the farthest south any storm has moved in the Weddell Sea. And thus, you have the recipe for record sea ice decline. The next year saw similarly shrunken sea ice and an even bigger polynya.
Whether the sudden change represents a new regime in Antarctic sea ice is still an area of very active research, but sea ice is generally expected to decline in the region in the coming decades as climate change emerges more forcefully.
“Variability in Antarctic sea ice extent is very large, and detecting an anthropogenic signal is going to be difficult,” John Turner, a climate expert with the British Antarctic Survey who led the new research, told Gizmodo in an email. “The increase up to 2014 was a surprise, considering the ice loss in the Arctic, and the rapid drop in 2016 added to the long list of questions about Antarctic sea ice. It’s unclear whether the sea ice extent will recover to 2014 values or if this the start of the long-term decline expected as greenhouse gas concentrations increase.”
Turner said that natural forces are likely largely responsible for the sea ice mess of the past five years in Antarctica, though he also noted there’s evidence the ozone hole has influenced storm tracks and winds. He also said that climate change is expected to drive a decline in the region’s sea ice by a third this century. The results also show the risk of natural conditions that can drive ice loss, forming a climate dogpile with human-driven warming to hurt ice. A similar situation played out for Greenland’s land ice last year, when extra sunny skies combined with record heat and dirty snow to drive record melt.
Disappearing sea ice won’t cause sea levels to rise like Greenland’s land ice will (that’s a whole other issue in Antarctica, though). But it could affect ocean circulation patterns and habitats for everything from seals to penguins to krill.
Featured image: NASA Goddard Space Flight Center (Flickr)