(Press Release Alfred Wegener Institute) Bremerhaven, 24 January 2012. An international team of researchers has succeeded for the first time in completely reconstructing the layer of the Greenland ice sheet from the Eemian interglacial (130,000 to 115,000 years ago).
Using this ice data, the scientists can now say how warm it became in Greenland at that time and how the ice responded to climate changes. The surprising conclusion of this study appears today in the scientific journal Nature, with air temperatures which were up to eight degrees Celsius higher than in the 21st century, the ice masses shrank far less than presumed compared to today.
Consequently, the Greenland ice sheet also had a far smaller share in the rise in sea level at that time than has so far been assumed. If the current temperature rise in Greenland continues, the reactions of the ice sheet during the course of the Eemian interglacial may be seen as a possible future scenario for the ice masses of the island.
It is said in a Greenland myth that during his first foray onto the island, Eric the Viking was so impressed by the fertile Fjord landscape that he gave the island the name of “Greenland”. Depending on how far the Viking pushed through to the centre of the country in the year 982, he may also have discovered the precursors of the Greenland ice sheet, because as an international research team has now discovered, Greenland was ice free neither during Erik’s lifetime nor some 125,000 years earlier, at the pinnacle of the Eemian interglacial.
On the contrary: the ice sheet has lost around 400 meters since the highest level during the cold period which preceded the Eemian, and at the end of the Eemian interglacial 130,000 to 115,000 years ago was some 130 meters lower than it is today. Its volume had shrunk to a maximum of a quarter in the same period.
The scientists from 14 nations reached this conclusion after having examined the lower part of a 2540 meter long drilled ice core from North Greenland and were able to reconstruct the disturbed and folded layering for the first time.
“We knew that the ice from a depth of 2200 to 2450 meters originated from the Eemian interglacial. The challenge, however, was to “read” this ice because contrary to the younger ice age ice above it, whose individual annual layers rest on top of each other like a cake, the individual layers of the Eemian ice and the layers from the transition to the last ice age had folded into each other like a crumpled tablecloth with a serviette on top”, explains Dr. Ilka Weikusat, expert for ice deformation and microstructures involved in the project from the Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research.
In order to bring order and therefore a temporal sequence into this layered chaos, the scientists measured the Greenland ice sheet with radio waves, examined the physical properties of the ice core, determined the water and oxygen isotope count, checked how much methane the air enclosed in the ice contained and then compared all these values with Eemian data from Antarctica and other places of the world. They were then able to answer their actual questions about temperature and ice conditions on Greenland during the Eemian interglacial.
“Our data show that it was up to eight degrees Celsius warmer during the Eemian interglacial in North Greenland than today”, says project leader Prof. Dorthe Dahl-Jensen from the University of Copenhagen. The fact that the Greenland ice sheet did not react so sensitively to this rise in temperature as so far thought was the good news of the study.
But there was also bad news: “If the Greenland ice sheet did not disappear completely at that time, then this conversely means that the ice masses of the Antarctic were mainly responsible for the sea level being four to eight meters higher during the Eemian interglacial than today”, says Dorthe Dahl-Jensen.
And the project leader also adds: during the Eemian interglacial the snow on the glacier surface melted considerably and repeatedly and the melt water seeped down to the snow layers beneath. The layers of refrozen melt water found by the researchers in the ice core would indicate this.
Dorthe Dahl-Jensen and her NEEM Team (NEEM = North Greenland Eemian Ice Drilling Project) observed a similarly large melt event during their last drillings in the summer of last year. “The warm surface temperatures of the summer of 2012 really surprised us. It rained and as in the Eemian interglacial, the melt water seeped into the depths and froze again“, explains Dorthe Dahl-Jensen.
In her opinion the past summer was an extreme event. Nevertheless, with the forecasted warming of Greenland the probability would rise that such an event will repeat itself in the coming 50 to 100 years and that the climate will take on Eemian-like features.
The new ice and temperature data for Greenland are now to be incorporated in climate models and further improve their prediction accuracy. “These new findings are really exciting. They refute not only all doomsday scenarios according to which the Greenland ice sheet will quickly disappear as a result of a warm period.
They also confirm model calculations which were made over a decade ago at the Alfred Wegener Institute“, says Prof. Heinrich Miller, co-author of the study and Helmholtz professor for glaciology at the Alfred Wegener Institute.
The NEEM Project:
The North Greenland Eemian Ice Drilling Project (NEEM) is an international ice core research project on which scientists from 14 nations are working. The aim of this project was to drill into the ice of North-West Greenland (camp coordinates: 77.45° N 51.06 °W) to such depths that ice layers from the Eemian interglacial are reached. In just two summers the research team with its ice core drill has managed to penetrate through to a depth of 2500 meters –that is down to the bottom of the ice sheet. They recovered the first complete sample of ice which formed in the Eemian interglacial. It contains information on the average temperature at that time, the precipitation and the content of greenhouse gases in the atmosphere. These data are to help to understand the current and future climate developments and to make better predictions.
Participation of scientists from the Alfred Wegener Institute:
Experts from the Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research (AWI) were involved in all sections of the NEEM Project. They participated in the geophysical and glaciological explorations of the drilling site, provided logistic support in Greenland with the research aircraft POLAR 5 and 6, co-developed the drilling technology and assisted in drilling and in the first processing of the drilled ice cores. Finally, their expertise was in demand for the dust and aerosol measurements and in the isotope analysis. AWI glaciologists working in the Greenland drilling camp and in the AWI ice laboratory in Bremerhaven also examined and analysed the physical properties of the drilled ice core.
The Alfred Wegener Institute conducts research in the Arctic and Antarctic and in the high and mid-latitude oceans. The Institute coordinates German polar research and provides important infrastructure such as the research icebreaker Polarstern and stations in the Arctic and Antarctic to the international scientific world. The Alfred Wegener Institute is one of the 18 research centers of the Helmholtz Association, the largest scientific organization in Germany.
The title of the original publication is:
D. Dahl-Jansen et al: Eemian interglacial reconstructed from a Greenland folded ice core, Nature, 24 January 2013
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