A hidden ocean change near Antarctica could have global consequences

What happened

A new paper says the water in a large layer of the Southern Ocean has become saltier. This layer lies about 2,300 to 4,000 feet below the surface and wraps all the way around Antarctica. For decades, this water had been getting fresher, so the switch is a big reversal.

Key numbers and facts

• The study tracked the Southern Ocean from 2004 to 2024 using six separate data sets.
• Antarctic sea ice hit its highest level in the satellite record in 2014. It fell to a record low just two years later, in 2016.
• In 2023, sea ice was about 1 million square miles below the 1981 to 2010 average. That is an area about four times the size of Texas.
• Argo floats, which drift through the ocean and measure salt and density, provided much of the data.

Why the ocean layer matters

The layer is called Antarctic Intermediate Water. It flows north into the Indian, Pacific, and Atlantic oceans. On its way, it carries heat, carbon, oxygen, and nutrients toward the tropics and even across the equator. When sea ice melts, it adds fresh water to the ocean. Less sea ice means less fresh water, so the water becomes saltier.

Why it matters

Changes in this layer can change how the ocean stores and spreads heat. That could affect the climate far from Antarctica. The researchers say this kind of change usually takes thousands of years, but here it is happening in just a few years.

What to watch

• Scientists say more monitoring is needed to track these changes.
• The researchers warn that the effects could be felt within about five years.
• A 2025 study also found rising surface salt levels linked to less sea ice.