Scientists using deep-diving Argo floats have pinpointed the reason behind Antarctica's dramatic sea ice contraction starting in 2016. The decline stems from a violent release of pent-up heat from ocean depths, triggered by shifting winds and salinity changes. This discovery highlights the ocean's key role in sea ice variability.
Antarctica's sea ice expanded from the 1970s until around 2016, despite ongoing climate change. Then it suddenly shrank and has not recovered, as warmer temperatures affected the Southern Ocean. Earle Wilson, a polar oceanographer at Stanford University and lead author of a new study, attributes this to ocean dynamics involving salinity, winds, and vertical mixing. “One of the key takeaways from the study is that the ocean plays a huge role in sort of modulating how sea ice can vary from year to year, decade to decade,” Wilson said, as first reported by Grist. Argo floats, torpedo-shaped instruments about human-sized, repeatedly dove thousands of feet to measure temperature and salinity before surfacing to relay data via satellite. In Antarctic waters, cold surface layers over warmer, saltier depths created stratification from increased precipitation, trapping heat below and allowing more ice formation. Around 2016, stronger winds pushed fresher surface waters away from the continent and churned up the deep heat. “What we witnessed was basically this very violent release of all that pent-up heat from below that we linked to the sea ice decline,” Wilson explained. These winds, possibly intensified by climate change, may also have fragmented the ice through compression and waves. Zachary Labe, a climate scientist at Climate Central not involved in the study, noted that both atmospheric and oceanic warming contribute to the change since 2016, with deeper ocean warmth playing a significant role. The sea ice loss threatens coastal ice shelves that buttress the Antarctic ice sheet, potentially accelerating its melt and contributing to global sea level rise of up to 190 feet if fully lost. Scientists call for expanded monitoring networks in the region amid rapid changes. Wilson predicts a long-term negative trend for sea ice, though short-term fluctuations remain possible.