For the first time, scientists have discovered that Antarctica's massive ice sheet is hiding an estuary, where fresh water from rivers mixes with salt water from the ocean.

Hidden at the head of the thick Ross Ice Shelf in West Antarctica, a strange and singular ecosystem could exist in the estuary, researchers said.

"We know in the sub-aerial environment that estuaries are fascinating," said Richard Alley, a glaciologist at Penn State University and co-author of a study.

"You have got a mixture of two very strange environments, so whether you're going to find anything that shakes up the world, I don't know, but it's a fascinating target," said Alley.

The tidal mixing zone sits beneath the end of the Whillans Ice Stream, one of the fast-moving "ice rivers" in West Antarctica.

Ice streams are features that flow quickly compared to the surrounding ice, 'LiveScience' reported.

Researchers announced, earlier this year, that the buried glacial lake contained microbial life.

Estuaries are channels only partly open to the ocean, and a one-kilometre-wide channel snakes inland from the Ross Sea toward Lake Whillans. The river-like channel is about 7 meters deep.

Researchers led by Huw Horgan of Victoria University in New Zealand, found signs of a thin brackish layer of sub-glacial water, ocean water and sediment several kilometres inland of the Whillans Ice Stream grounding line.

The grounding line is where the bottom of a glacier loses contact with land and floats on water.

The study was published in the journal Geology.