Overview
- An international team published observational evidence in Nature Climate Change showing Antarctic Intermediate Water (AAIW) stopped freshening and grew saltier, denser and deeper beginning around 2015–2016 and accelerating through 2016–2024.
- The authors link the change to a sharp drop in Antarctic sea ice that reduced seasonal meltwater and to increased upward movement of warmer, saltier deep water into the intermediate layer.
- The result is a measured salinity rise of about 0.0048 grams per kilogram per decade across the Southern Ocean with larger regional signals, based on Argo float records and satellite and atmospheric data.
- Scientists warn the altered AAIW could weaken ocean layering, push more excess heat and carbon into different ocean reservoirs, and influence large currents such as the Atlantic overturning system, but the size and timing of those impacts remain uncertain.
- Researchers say the rapid reversal — the last comparable basin‑scale switch dates to roughly 130,000 years ago — exposes gaps in observations and models and calls for expanded monitoring and improved climate‑ocean simulations.