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Paleoclimatology

Thawing Climate History

During the interglacial Eemian Period, which occured approximately between 130,000 and 115,000 years ago, polar temperatures were significantly warmer than at present, with sea levels 4-6 meters higher. This period offers a perfect benchmark for current global warming models, which predict a temperature rise of 2.4°C per century.
Yet little is known about Eemian evolution—including the sequence of changes in polar ice caps and ocean currents. Crucial evidence of this period and its transition into the last Ice Age is buried deep below the Greenland ice cap as thin layers of ice, each representing annual snowfall, compacted over tens of thousands of years. Each of these layers contains a trove of information about previous atmospheric and environmental conditions in polar regions.
To retrieve this evidence, the NEEM project (North Greenland EEMian Ice Drilling), led by the University of Copenhagen (Denmark), but made up of a team of scientists from 14 countries1 including CNRS researchers,2 is established at a remote base in northwestern Greenland. The site of this ambitious project, drilling to ice older than that of any previous study, was chosen by radar prospection for optimal conditions: it had to be above an ice divide, where the oldest ice is located, and on a flat bedrock to ensure the undisturbed preservation of the layers.
NEEM began deep drilling in June 2009, using its own non-polluting drill fluid developed with CNRS scientists. By the summer's end, NEEM had reached a depth of 1757.84 meters—establishing a new world record for single-season deep-ice core drilling. It now hopes to reach the annual Eemian ice layers by the end of summer 2010. Each of these layers is on average 7 mm thick and found close to the bedrock, 2542 meters below the surface.
The samples brought to the surface are analyzed by stable water isotope ratios, revealing the temperatures prevalent at the time in Greenland, and the regional sources of the precipitations.
Gases trapped between snow crystals and the particulates they contain tell us about atmospheric conditions, notably greenhouse gas levels. But more information can be obtained from chemical and biological material, like bacteria, or by measuring both ice crystal structures and bore-hole temperatures.
The ice reached last summer dates from 38,500 years ago. First analyses show the site at that time received the heaviest precipitations in the summer, and reveal the nature of climatic variations prevalent over the Labrador Sea and Baffin Bay.

Graham Tearse

Notes :

1. The United States, Belgium, Canada, China, Denmark, France, Germany, Iceland, Japan, Korea, the Netherlands, Sweden, Switzerland, and the United Kingdom.
2. From INSU-CNRS, CEA, Versailles St. Quentin University, Joseph Fourier University (Grenoble), with the support of the French national research agency (ANR), and the French polar institute (IPEV).

Contacts :

Valérie Masson-Delmotte
LSCE, Gif-sur-Yvette.
Valerie.Masson@lsce.ipsl.fr


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