High-resolution late-glacial chronology for the Gerzensee lake record (Switzerland): δ~(18)O correlation between a Gerzensee-stack and NGRIP

摘要

Oxygen-isotope variations were analyzed on bulk samples of shallow-water lake marl from Gerzensee, Switzerland, in order to evaluate major and minor climatic oscillations during the late-glacial. To highlight the overall signature of the Gerzensee δ~(18)O record, δ~(18)O records of four parallel sediment cores were first correlated by synchronizing major isotope shifts and pollen abundances. Then the records were stacked with a weighting depending on the differing sampling resolution. To develop a precise chronology, the δ18O-stack was then correlated with the NGRIP δ~(18)O record applying a Monte Carlo simulation, relying on the assumption that the shifts in δ~(18)O were climate-driven and synchronous in both archives. The established chronology on the GICC05 time scale is the basis for (1) comparing the δ~(18)O changes recorded in Gerzensee with observed climatic and environmental fluctuations over the whole North Atlantic region, and (2) comparing sedimentological and biological changes during the rapid warming with smaller climatic variations during the B?lling/Aller?d period. The δ~(18)O record of Gerzensee is characterized by two major isotope shifts at the onset and at the termination of the B?lling/Aller?d warm period, as well as four intervening negative shifts labeled GI-1e2, d, c2, and b, which show a shift of one third to one fourth of the major δ~(18)O shifts at the beginning and end of the B?lling/Aller?d. Despite some inconsistency in terminology, these oscillations can be observed in various climatic proxies over wide regions in the North Atlantic region, especially in reconstructed colder temperatures, and they seem to be caused by hemispheric climatic variations.