קולוקוויום בחוג לגאופיזיקה: Insolation Forcing and Eastern Mediterranean aridity: Evidence from the Dead Sea and implications for climate projections
Prof. Yochanan KushnirCooperative Institute of Climate Applications and Research, Lamont Doherty Earth Observatory
The Mediterranean region stands out among other subtropical regions in its projected drying response to the global rise in atmospheric greenhouse gas concentrations. This drying trend has already emerged out of the normal, random climate variability in the densely populated, semi-arid Eastern Mediterranean (EM). To better understand the dynamical mechanisms responsible for this regional sensitivity, we turn to past protracted EM drying states during warm geological epochs. A unique view of the historical and pre-historical hydroclimate of the EM-Levant has been gleaned from the continued study of the sedimentary and geochemical record left by the lakes that filled the tectonic basin of the Dead Sea. We revisit the Late Quaternary sediment record retrieved during the 2010-2011 Dead Sea Deep Drilling Project (DSDDP). The sediments clearly indicate that the Levant was drier during past warm interglacials than during the adjacent glacials but nonetheless experienced large variations in the intensity of the regional aridity. During each interglacial, extended thick deposits of salts accumulated at the Lake bottom, during millennia of significant regional aridity and severely reduced Mediterranean rains. These dry states were interrupted by extended wet intervals, fed by rains that were supplied by a blend of tropical and Mediterranean moisture. To understand the underlying causes of the EM-Levant interglacial hydroclimate variations, we put the Dead Sea record in the context of the Northern Hemisphere orbital insolation variations and their impact on the global climate system. We show that the changes in EM hydroclimate portrayed by the DSDDP record during the interglacials, are entirely consistent with the response of the North Atlantic Ocean and the overlying atmosphere and surrounding land areas to the changes in the latitudinal insolation gradient, as determined by climate models and evident by surface temperature proxies. This perspective provides new information regarding the dynamical processes responsible for the ongoing, greenhouse gas forced, EM drying.
מארגן האירוע: ד"ר רועי ברקן