The elusive 8.2 ka event in speleothems from southern France

Abstract

The Holocene is generally considered a climatically stable period, yet a prominent perturbation occurred around 8.2 ka BP. Evidence of its impacts has been identified in many palaeoclimate archives across Europe. However, outside the Atlantic seaboard, no clear high-resolution signal for this event has emerged from southwestern Europe. Here, we investigate the potential impact of the 8.2 ka event in southern France through high-resolution multiproxy analyses of two speleothems from the Ardèche region. Variations in Mg / Ca and Sr / Ca of the speleothem calcite are mainly attributed to the prior calcite precipitation effect and indicate switches between drier and wetter conditions. The δ13C signal is likely influenced by soil development and biological activity, integrating both regional climate conditions and local geomorphology and hydrology. The pattern of speleothem δ18O changes do not correlate with regional palaeotemperature reconstructions and is therefore more likely related to hydrology, such as variations in the seasonality of karst recharge and/or the moisture source. During the 8.2 ka event, no distinct geochemical anomaly is recorded by the Ardèche speleothems, suggesting either a limited climatic impact in southern France or a lack of sensitivity of these speleothem proxies to respond to an event of this magnitude. While the muted δ18O response may be explained by its insensitivity to temperature changes and buffering by Mediterranean influences at the time, the absence of a clear hydrological response in Mg / Ca, Sr / Ca and δ13C remains unresolved. Therefore, despite a likely southward displacement of the mid-latitude westerlies induced by the 8.2 ka event, the Ardèche region may have remained under their influence, preventing a marked shift towards drier conditions. Consistent with other records from southern France, the lack of significant changes in our results that time challenges the spatial extent and uniformity of the impacts of the 8.2 ka event across western Europe.