Multi-proxy speleothem record of climate instability during the early last interglacial in southern Turkey

Abstract

A stalagmite from Dim Cave in southern Turkey contains a climate record documenting rapid and significant changes in amounts of precipitation between ~132 ka and ~128 ka, during the penultimate glacial – interglacial transition. Some U–Th dates have been compromised by carbonate dissolution but rigorous selection and tuning to δ18O records from other speleothems has generated a robust age model. Growth rate was initially very slow but a rapid increase at ~129 ka was accompanied by strong negative trends in δ18O and δ13C, a combination implying the onset of much wetter conditions. Isotopic values at ~129 ka suggest that groundwater recharge rates and biogenic activity in the soil zone exceeded those of the early Holocene. A significant isotopic enrichment event at ~128 ka, during which there was alternating aragonite and calcite deposition, documents a strong drying event with a duration of ~200 years. A concurrent decrease in 87Sr/86Sr ratios indicates increased groundwater residence times and the cumulative evidence suggests amounts of rainfall fell from well above to slightly below present-day levels. Similar δ18O enrichment events are present in coeval speleothem records from southwest France and the Northern Alps, and these, together with pollen evidence from Italy, Greece and the Iberian margin of drier conditions at this time, imply that a climate anomaly extended across the northern Mediterranean borderlands. The timing, duration and structure of this episode are consistent with marine evidence of strong North Atlantic cooling early in the last interglacial and there is a resemblance to the Holocene 8.2 ka event recorded globally in many proxy-climate archives.