Beryllium isotopes as tracers of Lake Lisan (last Glacial Dead Sea) hydrology and the Laschamp geomagnetic excursion

The content of the cosmogenic isotope ¹⁰Be (t_1/2=1.39 Ma) in lacustrine sediments that deposit in lakes with a large watershed is susceptible to both climate and cosmogenic production rate variations. In order to distinguish between these two controls, we measured ¹⁰Be and major elements in several sections of the annually laminated sediments of the Lake Lisan (the last Glacial precursor of the Dead Sea) that are composed of detrital sediments and primary (evaporitic) aragonites. The sections were selected to represent regional hydrology and climate as reflected by different lake configurations (level rise, drop and high-stands) and rapid change in the ¹⁰Be production rate during the Laschamp geomagnetic excursion.Since the short-lived cosmogenic "sister" of ¹⁰Be, ⁷Be (t_1/2=53.3 d) has virtually no recycled component, the recycled ¹⁰Be in Lake Lisan detrital sediments was evaluated by measuring ⁷Be in their modern equivalents: modern flood suspended matter, dust and mud cracks.Our results demonstrate that although the recycled ¹⁰Be component is significant, secular variations in the ¹⁰Be concentration in Lake Lisan sediments correlate with hydrological variations and geomagnetic excursions.