Greenland: Tracking down "lost" lakes

Discovery of 56 subglacial lakes clarifies discrepancy between observations and model

Under the ice sheet of Greenland are hidden many subglacial lakes - so far they were hidden. © NASA / GSFC, Reto Stockli / Blue Marble
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But they do exist: So far researchers have been puzzling why there are hardly any subglacial lakes under the ice of Greenland - and so many in the Antarctic. Now the discovery of as many as 56 such lakes under the Greenland Ice Sheet provides the answer: they have simply not been recognized. The new discoveries now provide valuable insights into the behavior of the thawing Greenland Ice, as the researchers report in the journal "Nature Communications".

The ice sheets of Antarctica and Greenland appear powerful and massive. But under the ice there are ponds, lakes and even whole networks of liquid water. Using radar mappings and seismic measurements, scientists in the Antarctic have tracked down more than 400 such subglacial lakes. The range spans from huge and ancient Lake Vostok to smaller, dynamically filling and emptying waters.

Where are the subglacial lakes?

Strange, however: Also in Greenland, the ice base is thawed in many places, which is why there numerous subglacial lakes would have to exist. But so far researchers have discovered countless meltwater pools on the Greenland ice and a deep ravine under the ice sheet, but only four rather small subglacial lakes. But where is the rest?

In order to track down the missing lakes, Jade Bowling from Lancaster University and his colleagues have carried out the first comprehensive "search" of subglacial lakes in Greenland. They evaluated radar data from the NASA operation IceBridge, as well as satellite data and topographic models of surface changes to the ice sheet.

Location and size of the newly discovered subglacial lakes. Bowling et al. Nature Communications, CC-by-sa 4.0

Missing lakes spotted

And they came to fruition: their evaluations revealed the presence of 56 hitherto unrecognized lakes under the Greenland ice. Their sizes vary from 200 meters in length to almost six kilometers in length making them on average eight times smaller than their counterparts in the Antarctic, as Bowling and his team report. Three quarters of these subglacial lakes are also under relatively slow-moving ice. display

However, the newly discovered lakes are not evenly distributed, but concentrate mainly in three areas: the northwest, north and, above all, east of the center. The largest lakes appear along the subglacial mountain range in eastern Greenland, while at the edge of the Greenlandic eiche, smaller and possibly shorter-lived lakes can be found,

Topography determines distribution

The scientists attribute this distribution to the specific conditions at the bottom of the ice sheet: "In the east of Greenland, the ground is very rough and the meltwater can collect and be stored there well", explains Co-author Stephen Livingstone of the University of Sheffield. This steeper relief therefore promotes the formation of larger subglacial lakes. In the north, on the other hand, a patchwork of thawed and frozen ice underside only allows smaller lakes.

"This study has for the first time enabled us to get an idea of ​​where lakes are forming under the Greenland ice sheet, " says Bowling. "This is important to assess their influence on the sub-glacial hydrological system and ice flow." The findings from the newly discovered lakes could also help improve the future behavior of the greenland ice predict.

Mysteries Empty in the south and west

However, it is still unclear why the researchers have found hardly any lakes among the fastest thawing and flowing glaciers in Greenland. "In the southern and western sectors of the Greenland ice sheet, there are large amounts of meltwater every summer, " explain Bowling and his team. This also penetrates to the ice base, as confirmed by radar measurements.

However, the scientists suspect that the amount of melt water in particular causes the water to make its way and flow off more effectively. As a result, lakes could be formed only temporarily. However, it is also possible that the lakes in these areas are overlooked because the many superficial meltwater disturb the measurements, the researchers say. Quite the riddle of the missing lakes is not yet solved, but the first step is done. (Nature Communications, 2019; doi: 10.1038 / s41467-019-10821-w)

Source: Lancaster University

- Nadja Podbregar