Research suggests that up to 60 percent of "Antarctic Bottom Water", the dense water formed around the edges of Antarctica that seeps into the deep sea and spreads out through the world's oceans, has disappeared since 1970.
"This is a response to changes that are happening to climate in the polar regions, both natural and human causes," lead researcher Steve Rintoul, from the Australian government's science body the Commonwealth Scientific and Industrial Research Organisation, told AFP.
"It's not driving changes in climate, it's responding to changes in climate. So it's a signal to us that things are changing around Antarctica."
Scientists are not sure what is causing the phenomenon but Rintoul said the leading hypothesis is that as more of the ice on Antarctica melts around the edges of that continent, it adds fresh water to the ocean.
He said this could be causing the "sinking" of the dense water at high latitudes, a process that has been linked to major changes in climate in the past.