delta ¹³ C variations of loess organic matter as a record of the vegetation response to climatic changes during the Weichselian

CNRS/CEA, Laboratoire des Sciences du Climat et de l'Environnement, Gif sur Yvette, France

This paper presents high-resolution records of ¹³ C/ ¹² C ratios of organic matter from two loess sequences in northwestern Europe. Our analysis is the first attempt to use organic matter delta ¹³ C as a record of the response of vegetation to climatic variations in an area where climatic changes were not strong enough to induce a radical change in vegetation cover. Over the last climatic cycle, the vegetation of the Rhine Valley showed a strong predominance of C3 plants. Thus, the small delta ¹³ C variations, with an amplitude of only 1.5 per mil to 3 per mil, are interpreted as corresponding to fluctuations in water supply and atmospheric CO ₂ concentration variations rather than to the ratio of C4 to C3 vegetation. Furthermore, loess sequences accumulated at high rates and allow high correlation with climatic proxy data, like the Greenland Ice Sheet Project 2 (GISP2) delta ¹⁸ O and the variations in CO ₂ concentration recorded in the Vostok ice core. The delta ¹³ C constitutes a reliable and complementary proxy to study small climatic stresses endured by vegetation during the Weichselian in northwestern Europe. Moreover, by using absolute age control and correlations between global (Vostok-CO ₂ ) or semi-global (GISP2-delta ¹⁸ O) climate effects, delta ¹³ C values of organic matter in loess sequences offer a new tool to establish a refined chronology in continental sequences.

This record provided courtesy of AGI/GeoRef.

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