Terrestrial response to Dansgaard-Oeschger cycles and Heinrich events : the lacustrine record of Les Echets, south-eastern France

Abstract: Marine Isotope Stage (MIS) 3 was an interval characterized by large and abrupt temperature changes on a millennial time scale, the so-called Dansgaard-Oeschger (DO) cycles and Heinrich events. Evidence for this high-frequency climate variability has been identified in many marine and ice core records. Reconstructions from continental Europe, however, are still too scarce to form a comprehensive environmental picture for this time interval. In this thesis, high-resolution multi-proxy sedimentological, geochemical and chronological analyses were conducted on two long sediment sequences from the site of Les Echets, France. The main objective of this study was to determine the extent and nature of the lacustrine response to the rapid climate variability of MIS 3 and 2. The results indicate that the lake underwent recurrent shifts in lake status that closely followed temperature variations associated with DO cycles and Heinrich events which occurred between ca 60-20,000 years BP. Organic matter elemental and isotopic results indicate that most of the organic matter is mainly autochthonous suggesting that increased lake organic primary productivity commenced during DO interstadials. DO stadials and Heinrich events on the other hand are clearly marked by a reduction in productivity, organic matter oxidation and an increase in catchment erosion indicators. The results discussed in this thesis provide new insights into the response of a terrestrial ecosystem to millennial-scale climate variability and highlight the potential of multi-proxy studies in lake sediment research. This research also demonstrates that the Les Echets site may represent a potential link between the more fragmented central and northern continental European sites and marine and terrestrial records from the Mediterranean region.