Antarctic ocean currents have slowed since 1990s, sparking fears of collapse
Watch: Isobel Ewing reports on how deep ocean circulation (thermohaline circulation) has slowed by 30 percent since the 1990s, and could collapse completely. Credits: Video: Newshub - Photo: Getty Images. New research has found the circulation of deep ocean waters around Antarctica has already slowed by 30 percent since the 1990s. An Australian study published in Nature Climate Change on Friday has found the deep ocean currents in waters surrounding Antarctica have slowed radically, sparking fears it could be about to collapse. Deep ocean currents (or thermohaline circulation) refers to the natural mixing, rising and sinking of cold/warm, salty/fresh waters, kilometres below the surface. Dr Christian Ohneiser from University of Otago / Ōtākou Whakaihu Waka said the study points to widespread impacts from Antarctic glacial melt. "The super-cold, salty, dense waters flow into the ocean abyss (+4000m) out of sight and out of mind, but their influence is felt around the world because they drive the global ocean circulation system which redistributes heat and nutrients around the globe," he said. This new study confirms Australian research from March, whose models suggested these delicate currents could slow down by 40 percent in the year 2050. As melting glaciers release more fresh water into Antarctica's oceans, it reduces how much water sinks - because salt water is denser - which in turn slows ocean currents. "The work paints a grim picture that the production of these vital, dense cold waters is slowing most likely because of freshwater input from melting ice," said Dr Ohneiser. He added scientists should pay more attention to this isolated part of the world, because so much is unknown. "The Southern Ocean is one of the least instrumented and studied oceans in the world with only a few decades of data; the record is patchy at best." NIWA's top marine physicist, Dr Craig Stevens, said slowing currents could affect the whole world. "It is a subtle interplay of meltwater, wind and sea ice formation. This change in oxygenation will shift the way the planet's oceans work for centuries to come," he said. Dr Stevens argued the research makes the need to reduce greenhouse gas emissions even more urgent. The 2022 research showed Antarctic ice melting has increased six-fold over the last 30 years. Dr Ariaan Purich from Monash University in Melbourne said it was much-needed science. "Gunn and colleagues provide important observational evidence of a freshening of the ocean around the Antarctic coast, caused by melting ice shelves." Dr Purich agreed with Dr Stevens about the consequences. "While they might seem far away, changes occurring around the Antarctic margins will affect the climate and sea levels experienced here in Australia for decades to come."