Higher state of the North Atlantic Oscillation during the Last Interglacial (130-115 ka BP): evidence from temperature and hydrology in the Dead Sea 

Abstract

<p>The North Atlantic Oscillation (NAO) is currently the main mode of winter atmospheric variability in the extratropical Northern Hemisphere. It represents the fluctuation of the meridional sea-level pressure gradient in the North Atlantic, with high and low phases defined by high and low pressure gradients, respectively. High (or low) NAO phases are associated with wet and warm (or dry and cold) weather conditions in Northern Europe. In mid latitude regions such as the Mediterranean, this relationship is inverse, producing dry and cold (or wet and warm) conditions. Whether or not the average state of the NAO may have shifted in the past is much debated, with major implications for the understanding of past regional climate. Using a climate model, Felis et al. (2004) showed that the average state of the NAO during the Last Interglacial (130-115 ka BP) was significantly higher than during the pre-industrial period, with a high plateau from ~126 to 118 ka BP. However, proxy-based reconstructions of temperature and rainfall are needed to support this. Here, we use a new method, Brillouin spectroscopy on halite fluid inclusions, to reconstruct the evolution of temperature and hydrology in the Dead Sea, southern Levant, throughout the Last Interglacial. We find lower than modern Dead Sea temperatures and a lowering freshwater influx throughout the last interglacial. Using climate data from the recent decades, we demonstrate that the temperature of the Dead Sea hypolimnion mainly depends on winter air temperature, which is itself anti-correlated with the NAO. We also demonstrate that, during years of very high NAO, rainfall is drastically reduced in the lake catchment. In light of our analysis of modern climate data, the reconstructed cold and dry conditions in the Dead Sea area is consistent with the modelled higher NAO conditions.</p>