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Scientific result | Paleoclimates

Earthworms Set the Tempo of the Last Glaciation

Through the radiocarbon dating of calcite granules secreted by earthworms, a multidisciplinary team involving LSCE proposed the first precise chronological framework for all thawing phases in the last glacial period.
Published on 29 January 2018

During the last ice age, which started about 110,000 years ago, many swift climate fluctuations were identified through analysis of ice cores and marine sediments. Until recently, these temporary warming periods, also called Dansgaard-Oeschger events (DO), had not been formally and systematically identified or dated on the continents where they occurred.

This has now been achieved, thanks to the loess profile of Nussloch, in the Rhine valley (Germany). For decades, this site has been known as the most complete recording of switches in climate conditions from the last glaciation. It shows that warming phases are associated with the development of characteristic "embryonic" soils called tundra gleys. Humidity and thaw have fostered the proliferation of earthworms, and the worms' carbonated excreta ("granules") are still present in these gleys.

Therefore, the gleys could be dated by measuring the carbon 14 in the granules. Each thaw recorded in ices and marine sediments has found its counterpart on the continent in Nussloch gleys. Even better: the analyses revealed previously unknown, weakly pronounced warming periods.

These results highlight the high sensitivity of loess environments to glacial climate changes and a climate dynamic that is more complex in the mid latitudes than in the high latitudes between -27,000 and 20,000 years. They will likely facilitate the reconstitution of other rapid paleoenvironmental episodes, in regions, or even at a continental scale, as appropriate.

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