Antarctic sea ice loss is making a vital ocean layer saltier, denser, and deeper

The oceans' ability to store heat and carbon could be affected by changes unfolding beneath Antarctic waters. Sea ice loss there has been making a vast subsurface water layer saltier and denser while pushing it deeper, with potential consequences far beyond Antarctica.

Here's what to know

A study published in Nature documented changes in Antarctic Intermediate Water, according to Gizmodo. This cold, oxygen-rich, relatively fresh water mass develops near Antarctica, roughly 2,300-4,000 feet below the surface.

But after Antarctic sea ice reached a record high in 2014, a sharp decline began in 2016, reducing that freshwater supply. That fresh water helps keep the layer's salinity low and arrives as sea ice melts each Southern Hemisphere summer.

Lead author Bishakhdatta Gayen, a professor and researcher affiliated with the University of Melbourne and the Centre for Atmospheric and Oceanic Sciences in Bengaluru, India, noted that a comparable transformation last occurred roughly 130,000 years ago.

"That transition took thousands of years, not two decades," Gayen said in a statement quoted by Gizmodo.

Why does it matter?

How much the deep ocean warms depends in part on Antarctic Intermediate Water, which separates the cold depths from warmer surface waters. The water mass also moves toward the tropics through three oceans — the Indian, Pacific, and Atlantic — transporting nutrients, oxygen, carbon, and heat.

Changes to that circulation could influence storm paths, precipitation patterns, and sea levels in different regions, potentially affecting communities far from Antarctica. It could also hasten sea ice loss, creating a feedback loop that makes the intermediate layer progressively saltier.

A 2025 satellite analysis identified a substantial rise in the salinity of the Southern Ocean's surface waters since 2015. A separate study published in 2024 found that Antarctica's unusually low sea ice coverage in 2023 intensified heat escaping from the ocean and increased storminess.

What's being done?

For their study, Gayen and his colleagues analyzed observations from the global Argo program, which uses close to 4,000 robotic floats to record salinity and temperature within the top 1.2 miles of ocean water, according to Gizmodo.

Their analysis found that the intermediate layer's core salinity is increasing by approximately 0.00008 ounces of salt for every pound of water (equivalent to 0.005 grams per kilogram) each decade. The measurements were analyzed together with satellite and atmospheric datasets.

While those numbers might sound insignificant, over time, that shift can change the water mass's density and behavior. The researchers emphasized that studying these deep-water changes could improve predictions of climate feedback loops and preparations for a hotter planet.

Where can I learn more?

The changes beneath Antarctica have been unfolding alongside shifts in ocean heat, salinity, and ice cover around the world.

• Antarctic sea ice reached its third-smallest winter peak in 48 years, raising concerns among experts.

• Southern Ocean climate models overstated clouds yet missed heat, observations from an Antarctic voyage indicated.

• Greenland and Antarctica lost 11.3 trillion tons of ice over the longest satellite record.

• During marine heat waves, polar seas absorbed 11% more CO2, rather than less.

• The Mediterranean has been becoming warmer and saltier faster, with changes reaching the sea floor.

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