Over the past decade, Antarctic sea ice has rapidly declined , dropping to unprecedented annual lows. This trend has triggered drastic changes in a vast layer of the Southern Ocean that plays a critical role in Earth’s climate system and global ocean dynamics.

That’s according to a study published Wednesday in the journal Nature. The findings show that the Antarctic Intermediate Water (AAIW)—a mass of cold, oxygen-rich freshwater that forms around Antarctica at depths of 2,300 to 4,000 feet (700 to 1,200 meters)—is rapidly growing saltier, denser, and deeper.…