CENTENNIAL-SCALE COUPLING OF HOLOCENE CLIMATE IN THE SOUTHEASTERN VOLGA BASIN TO NORTH ATLANTIC POLEWARD HEAT TRANSPORT

The hydrological response of the Volga River watershed to abrupt climatic change is not well constrained in paleoclimate proxy records. Model forecasts under various global warming scenarios suggest a significant reduction in summer precipitation for the southern sector by the end of this century, but local precipitation is highly dependent on synoptic-scale weather regimes, which are not well reproduced by climate models. Furthermore, strong interannual variability has masked any signal from anthropogenic warming over recent decades. Accurate risk assessment for the Volga River watershed, including the Caspian Sea, is therefore limited by uncertainty regarding the predominant climate dynamic controls on seasonal precipitation at decadal and longer timescales. To reconstruct multidecadal trends in paleoprecipitation, we utilized ICP-OES instrumentation to measure major cation concentrations (Mg and Sr) at 344 points along the growth axis of a stalagmite from Kinderlinskaya Cave, which grew between 11.8–1.8 ka. Elemental ratios of Mg/Ca and Sr/Ca in speleothems have been shown to reflect aquifer residence time, as well as prior calcite precipitation (PCP) in the epikarst during intervals of persistent climatic aridity. Our Mg/Ca data suggest that local precipitation is paced by the reduction in June insolation at 55°N from ~10 ka to present, which we interpret to reflect stronger continental heating and convective storms during the Early–Middle Holocene. Following the disintegration of northern-hemisphere ice sheets at 6.8 ka, centennial-scale trends in Mg/Ca and Sr/Ca are highly correlated to those in previously determined carbon- and oxygen-isotope values, which are proxies for warm-season rainfall and cold-season temperature, respectively. This relationship implies a close coupling of winter warming and summer aridity (enhanced PCP) over the past seven millennia, which may serve as an analog for future climate. Comparing our data to Holocene records from the North Atlantic Ocean, we find that poleward oceanic heat transport is the major dynamic control on hydroclimate in the Volga River basin. The two regions are linked via a persistent strengthening of southwesterly winds over Eurasia that is initially forced by higher sea-surface temperature and latent heat transfer in the Nordic Seas.