Where today a 1.4 kilometer thick ice sheet rests, vegetation once grew, as the examination of a 55 year old drill core from the secret military base “Camp Century” shows. Traces of plants and other analysis results show that Greenland has lost most of its ice sheet at least once in the last million years. The study thus illustrates the sensitivity of the Greenland ice masses to warming and thus also emphasizes the risk associated with anthropogenic climate change. Because the meltwater in Greenland is causing sea levels to rise and has the potential to cause widespread flooding on earth, say the scientists.
It looks like eternal ice: The largest island on earth is shaped by gigantic glaciers, which in some places are over three kilometers thick. The Greenland ice sheets formed over a long period of time and over the past 2.6 million years have repeatedly gone through periods of growth and shrinkage – that much seems clear. But so far there are only a few more precise indications of the icy development history in the course of the Pleistocene. However, against the background of anthropogenic climate change, they could be important. Studies show that the warming in the far north is already drastically gnawing at the ice masses of Greenland. Information about the extent of past thaws can thus provide important information on the extent of the ice loss and thus the extent of the meltwater inflow into the oceans in the future.
Rediscovered sample material
The new insight into the development of the Greenland ice is based on the examination of sample material with an unusual history. It comes from a hole drilled in Camp Century in 1966. The real purpose of the secret US military camp in northwest Greenland was to station nuclear missiles under the ice. As a camouflage, the army declared the camp as a polar science station – and research was actually carried out. This resulted in a 1.4 kilometer deep drilling through the ice to the shelf below Camp Century. During the investigations at the time, however, the scientists concentrated on the ice, but paid less attention to the “dirty” end of the drill core. So the samples finally slumbered in a freezer – until they were rediscovered by chance in 2017. The international research team headed by Andrew Christ from the University of Vermont in Burlington then turned to examining the samples.
As they now report, they found traces of plant materials in addition to sand and rock. “What we discovered were delicate plant structures – perfectly preserved. They are traces of what once lived on the surface of the earth, ”says Christ. The findings showed that the area in northwest Greenland was not always covered by a thick layer of ice in the recent geological past. Instead, there was apparently once a landscape with tundra vegetation, the findings show.
The at least temporary absence of ice was also confirmed by the results of further analyzes: the researchers were able to prove that the soil was once exposed to the sky based on the ratio of isotopes of the elements aluminum and beryllium in the sand from the samples. Because they only form in quartz material when it is hit by cosmic rays. Another test used clues from rare forms of oxygen found in the ice within the sediment. They show that the precipitation did not fall at the height of the current surface of the ice sheet, but at a level without ice cover.
Sensitive masses of ice
The results of the investigation also enabled rough conclusions to be drawn about the time frame in which the ice had been lost. Accordingly, there was apparently an ice-free period in the early Pleistocene, but what is particularly interesting is a phase rich in vegetation during the last 1.1 million years. As the scientists report, the results fit in with earlier findings from ice cores from central Greenland, which also suggested that the ice sheet had disappeared there for some time in the recent geological past. It is therefore becoming apparent that global warming, such as that which occurred during the Pleistocene, could lead to the loss of a large part or even the entire Greenland ice sheet, the researchers sum up.
As they emphasize, the region thus appears to be more sensitive than previously assumed – which appears particularly worrying against the background of current climate change. “Our study shows that the Greenland Ice reacted more intensely to natural global warming than we previously thought. It should now be noted that the warming of the planet by mankind is far exceeding the natural rate, ”says Christ. His colleague Paul Bierman adds: “Greenland may seem far away, but the ice there could melt quickly and lead so much water into the oceans that New York, Miami, Dhaka – choose a city – will be flooded,” he says Scientists in conclusion.
Source: University of Vermont, Article: PNAS, doi: 10.1073 / pnas.2021442118