This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: The Antarctic Intermediate Water (AAIW)—a vast layer of fresh water spanning much of the Southern Hemisphere's ocean—has rapidly reversed its long-term trends in salinity and density, according to new research. The AAIW helps store carbon, supply oxygen and drive global ocean currents.
The AAIW plays a role in heat, freshwater and carbon redistribution around the planet. The international research team says its findings, published in Nature Climate Change, show we may have underestimated the extent of deep-ocean warming and rising sea levels. Led by associate professor Bishakhdatta Gayen (University of Melbourne and the Indian Institute of Science (IISc)) and Ph.D. student Kaushik Mishra (IISc), with co-author professor Alberto Naveira Garabato (University of Southampton (UK)), the paper describes how, from 1995 to 2015, the AAIW was kept healthy by the Antarctic summer ice melt.
From 2016 to 2024, that trend abruptly reversed when reduced freshwater input led the layer to become saltier, denser and deeper. It is the first direct observational evidence of this change in AAIW properties. The team analyzed data from the global Argo program—a network of around 4,000 robotic floats that sample the upper oceans—as well as satellite and atmospheric data sets.
Associate professor Gayen said the last time the AAIW switched was at the end of the last interglacial period, around 130,000 years ago, when there was very little ice in the Antarctic. "That transition took thousands of years, not two decades," associate professor Gayen said. "The Antarctic region is the freshwater engine of oceans around the globe.
Melting Antarctic sea ice influences circulation thousands of kilometers away. Until 2016, the seasonal summer melt was triple the Amazon River's entire annual flow of roughly 6,600 cubic km (1.7 quadrillion gallons). "From 2016, Antarctic sea ice shrank to record lows.
This abruptly choked off that critical seasonal surge and the meltwater delivery dropped to roughly double the Amazon's annual flow." He said oceans act as a 'climate buffer,' absorbing and redistributing most of the excess heat and a large share of human CO₂ emissions, storing them for decades to centuries and thereby slowing and moderating atmospheric warming and its immediate impacts. "If the altered AAIW changes the way surface water is carried down into deeper layers, it could affect how much carbon the ocean locks away—although the magnitude and timing are uncertain," he said. "This could be the tipping point for the Atlantic Ocean and the AAIW current, leading to larger, longer-lasting changes to the climate in the Southern Hemisphere." Mishra said the abrupt reversal reveals a critical missing feedback loop.
Extract — continue reading at the source.
