Scientists in the Antarctic have been documenting subglacial lakes for miles, buried under the ice for miles. They have discovered more than 400 of them and even investigated some and found evidence of living and long-dead life forms. But despite their ubiquity at the bottom of the world, no one really saw if sub-glacial lakes were common under the Greenland ice sheet. So far.
So far only four subglacial lakes have been documented in Greenland. This week, an impressive poll in Nature Communications added another 56 new maritime candidates. And the researchers behind this survey believe that this is only the beginning. As in the Antarctic, subglacial lakes could play a key role in Greenland's lower abdomen. Some of them might even affect the movement of the ice above as they fill up and drain off.
"I'm sure this is the tip of the iceberg in terms of what can be found," co-author Stephen Livingston, a glaciologist at Sheffield University, said Earther.
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They would not see any obvious signs of them going over the ice, but there are a few ways researchers can discover subglacial lakes. In Antarctica, many were spotted using satellites such as NASA's ICESat (and its recently launched replacement ICESat-2), which repeatedly flew over the same portions of the ice to measure small elevation changes – which was interpreted as a result of subterranean lakes filling and drain.
Where lakes are less active, so to speak, scientists have other means to discover them. For example, you can shoot radio waves through the ice and use their reflections to create an image of the underlying bedrock. In the mid-nineties, for example, the researchers were able to identify the occurrence of Lake Vostok, a 4,000 square kilometer subglacial lake buried near the South Pole.
This latter approach helped scientists discover the most new – albeit much smaller – subglacial lakes in Greenland. The authors drew on the extensive database of radio echo sounding data (RES) collected from 1993 to 2016 by Operation IceBridge, a NASA-led aerial survey of the Earth's polar regions. From this, they identified 54 sub-glacial maritime candidates or regions where the waves that bounce back produce a "brighter" signal indicating accumulated water at the bottom of the ice sheet. Eleven of these lakes have been observed for at least a decade of RSE data, which enhances researchers' confidence in lake longevity.
"At least on the decade scale, these lakes seem to be relatively stable," Livingston said.
Two more active-looking lakes were discovered using high-resolution topographic maps of the icy surface of Greenland. In total, these 56 maritime candidates are between 0.2 and 5.9 km long. With the exception of the two active lakes in the southwest, most fell into three distinctive groups in central eastern, northern and northwestern Greenland.
The lakes in central Greenland tended to coincide with geothermal foci, suggesting geothermal energy. Interior has played a role in its creation. The low number of active lakes that scientists have documented are closer to the edge of the ice sheet, where a significant surface melt occurs in summer, suggesting that they may be recharged when meltwater seeps from the surface to the bedrock ,
The question arises as to whether climate change, which is melting faster and faster across Greenland's surface, could affect the activity of some of these lakes and thus the movement of ice over them. Livingston said it was too early to say anything, but understanding the connection between the lakes and the movement of the ice above them is an important area for future research.
There is much more to do than just documenting the existence of these lakes. Livingston noted that although the data from Operation IceBridge are extensive, they cover only a "small percentage" of Greenland ice sheet. He suggests that many more lakes can be found by taking a closer look at these topographic maps, which researchers continue to do.
After all, scientists can now begin to study individual lakes that have been found. Perhaps in a few years' time they will prepare to try one, as recently a team in the Antarctic has done. Who knows what they might discover in its waters?