MELBOURNE, July 16 (Xinhua) -- The deepest layer of the Southern Ocean is shrinking faster than scientists realised, with the rate of change accelerating over the past decade, new research reveals.
This is globally significant because Antarctic Bottom Water (AABW), a cold, dense water mass that fills up to 40 percent of the global ocean volume, drives Earth's currents and regulates climate, according to a statement released by the Australian Antarctic Program Partnership (AAPP) on Wednesday.
By carrying oxygen to the deep ocean, locking away heat and carbon, and driving part of the global "conveyor belt" of ocean circulation, it provides a buffer against global heating, according to the study published in Geophysical Research Letters.
A circumpolar analysis of AABW, the ocean's deepest water mass, found its volume fell by about 3 percent between 2002 and 2023, with the rate of decline increasing fourfold after 2015.
"We show the recent increase in AABW loss coincides with a rapid decline in Antarctic sea ice since 2016, and AABW volume anomalies are strongly correlated with variability in sea ice extent," said lead author James Wyatt of the AAPP at Australia's University of Tasmania (UTAS).
The researchers report simultaneous warming, freshening (becoming less salty), loss of oxygen and shrinking volume in AABW, indicating "a slowdown of deep-ocean overturning."
"These multiple signs provide strong evidence that climate change is already altering the deepest parts of the world's oceans, with long-term consequences for ocean circulation, heat transport and carbon storage," said study co-author, UTAS Prof Nathan Bindoff. ■
