The ice of Antarctica is finding it increasingly difficult to keep its secrets.
Deep beneath the ice of the East Antarctic Ice Sheet, the world’s largest ice cap, scientists have confirmed the existence of a huge lake of liquid water.
The researchers named it Lake Snow Eagle and believe that the sediments it contains could hold information about the evolution of the Antarctic ice sheet since its very first formation.
“This lake is likely to have a record of the entire history of the East Antarctic Ice Sheet, from its initiation over 34 million years ago, and its growth and evolution through glacial cycles since then,” says University of Texas geophysicist Don Blankenship at the Austin Institute of Geophysics.
“Our observations also suggest that the ice sheet changed significantly around 10,000 years ago, although we don’t know why.”
Although East Antarctica is the coldest place on earth, it is not completely frozen. Hundreds of lakes of liquid water – known as subglacial lakes – have been discovered hidden under the ice that covers the continent.
There are a number of factors at play that allow these reservoirs to exist. The mass of the ice sheet produces pressure that dramatically lowers the freezing point of the water trapped below.
Additionally, the ice cap itself provides insulation from the freezing air, while the rocks below provide a source of gentle heating. Also, if the water is brackish, saturated with salts, this can also lower the freezing point further.
We can detect subglacial lakes using ice-penetrating radar from above. The radar signal propagates through the ice and bounces around, and by comparing the transmitted signal with the returned signal, scientists can study what’s under the ice.
A radar signal bouncing through liquid water is brighter or more reflective than other media.
In the case of Snow Eagle Lake, the first clue was a large depression observed in the ice sheet, revealed by satellite images.
So a research team, led by geophysicist Shuai Yan from the University of Texas at Austin, set out to obtain radar data for the region, as well as measurements of the Earth’s magnetic field, over a three-year period. , from 2016 to 2019.
Analysis of radar data revealed a large spot, deep under the ice, shining brightly. Researchers have confirmed it to be Snow Eagle Lake: one of the largest subglacial lakes ever discovered.
“I literally jumped when I first saw this bright reflection of the radar,” says Yan.
The body of water is about 3.2 kilometers (2 miles) below the ice sheet, and it is significant. It is approximately 42 kilometers in length and 15 kilometers in width, covering an area of 370 square kilometers and containing 21 cubic kilometers of water, with a depth of 200 meters (656 ft).
Snow Eagle Lake sits in a 1.6 mile deep jagged canyon buried under ice, but radar reflections reveal there is more than water in the hidden lake.
At the bottom of the lake is a layer of unconsolidated sediment. Given the time it takes for sediments to build up in these subglacial environments, the team thinks they must have been there for a very long time – perhaps even before the ice sheet formed.
“This lake has been accumulating sediment for a very long time, potentially taking us through the period when Antarctica had no ice at all, until it became frozen,” says Imperial College glaciologist Martin Siegert. from London in the UK.
“We don’t have a single record of all of these events in one place, but the sediments at the bottom of this lake might be ideal.”
Given that it’s trapped under several miles of ice in one of Earth’s most hostile environments, actually traveling to the lake to study it further is likely to prove the next challenge.
The team proposes that a station be set up nearby, to facilitate future efforts to study the mysterious lake and sample its ancient sediments.
The research has been published in Geology.