The densest waters of Antarctica have reduced dramatically over recent decades, in part due to man-made impacts on the climate,Australian scientists said Friday.

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 researcherSteve Rintoul, from the Australian government’s science body theCommonwealth 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 Rintoulsaid 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.