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

Belmaker, R; Stein, M; Beer, J; Christl, M; Fink, D; Lazar, B

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

Date

2014-08-15

Authors

Publisher

Elsevier Science BV

Abstract

The content of the cosmogenic isotope Be-10 (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 Be-10 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 Be-10 production rate during the Laschamp geomagnetic excursion. Since the short-lived cosmogenic "sister" of Be-10, Be-7 (t(1/2) = 53.3 d) has virtually no recycled component, the recycled Be-10 in Lake Lisan detrital sediments was evaluated by measuring Be-7 in their modern equivalents: modern flood suspended matter, dust and mud cracks. Our results demonstrate that although the recycled Be-10 component is significant, secular variations in the Be-10 concentration in Lake Lisan sediments correlate with hydrological variations and geomagnetic excursions. During periods of moderate variations in Be-10 production rate, the Be-10 concentration in the Lisan detrital sediments positively correlates with lake level, Al + Fe content and the (Al + Fe)/(Ca + Mg) ratio. These correlations suggest that the Be-10 is adsorbed on the fine silicate component (probably clays) of the detrital laminae. The fine silicates together with carbonates were transported to Dead Sea drainage basin mainly as airborne dust that after a short residence time was washed into Lake Lisan as flood suspended matter. We suggest that preferential dissolution of carbonates in the flood suspended matter concentrated the residual fine component leading to the positive correlation between Be-10 and the (Al + Fe)/(Ca + Mg) ratio. During periods of increased water discharge more carbonates were dissolved and hence the Be-10 concentration in the detrital laminae increased. During periods of rapid increase in the Be-10 production rate (e.g. the Laschamp excursion), Be-10 showed a similar to 2 fold increase, beyond the above-mentioned correlations (lake levels and Al + Fe contents). This observation suggests that Lake Lisan can serve as a potential high-resolution archive of Be-10 production rate variations during periods of geomagnetic excursions. © 2014, Elsevier Ltd.

Keywords

Beryllium, Isotopes, Lakes, Dead Sea, Solar activity, Evolution

Citation

Belmaker, R., Stein, M., Beer, J., Christl, M., Fink, D., & Lazar, B. (2014). Beryllium isotopes as tracers of Lake Lisan (Last Glacial Dead Sea) hydrology and the Laschamp geomagnetic excursion. Earth and Planetary Science Letters, 400, 233-242. doi:10.1016/j.epsl.2014.05.049