It’s summer right now in Antarctica. So, you might expect there to be less sea ice (the ice that freezes in the ocean). And indeed, there is. But this year is exceptional in that winds and warmer air and water have reduced sea ice extent to its lowest amount since satellites started measuring in the late 1970s. Unusually high air temperatures to the west and east of the Antarctic Peninsula – 1.5 degrees Celsius above the long-term (30-year record) have played a key role in the demise of the ice. The previous record-breaking sea ice extent minimum happened last year (2022) and wasn’t reached until February 25. The record-breaking sea ice loss this year (2023) was reached on February 13 – and the melting isn’t finished yet.
Looking at the imagery from all available satellite data, Antarctic sea-ice extent shows great variability with time. However, a downward trend to smaller and smaller amounts of summer ice has become visible in the past few years. In the case of 2023, what is happening? Something called the “Southern Annular Mode” (SAM) is a key player as well – it describes variations in air pressure around Antarctica, which influences the continent’s fast-moving winds from the west. SAM is in a “positive” phase right now, meaning the winds are stronger, leading to more storminess. The storminess helps to break up the sea ice and push it North into warmer waters, where it eventually melts. At the moment, this year’s summer ice pack is missing nearly 1 million square kilometers compared to the normal amount there should be – enough to cover the British isles!
Why is this so important? Salt doesn’t freeze so when seawater starts to freeze, it expels salt, making the water below denser and thus easier to sink. This is part of the engine that drives the global ocean conveyor – the mass movement of water that helps regulate energy in the climate system. If the sea ice is gone, it affects this circulation. Sea ice is also very important for life. In the Antarctic, the algae that cling to the underside of the ice are a food source for krill (small crustaceans), which, in turn, are a food source for whales, seals, penguins and other birds. The sea ice is also a platform on which some species, like seals, will haul out and rest. Without the sea ice, an entire ecosystem can collapse. And, ultimately that will affect us all as well.