Radiocarbon Reservoir Ages as Freshwater-Brine Monitors in Lake Lisan, Dead Sea System
A continuous and high-resolution record of the radiocarbon reservoir age (RA) has been recovered from the primary aragonites that were deposited from the last glacial Lake Lisan. The RA is calculated as the difference between the measured 14C “apparent” age in the aragonite and the atmospheric age at any particular time. The RA shows temporal decreases during the time interval of ~28 to ~18 ka cal BP. This behavior is attributed to a continuous addition of low RA-high bicarbonate freshwater into the high RA-Ca-chloride (low bicarbonate) brine solution filling the lake. The mixing of the brine with freshwater drives the precipitation of CaCO3 in the form of aragonite from the lake epilimnion (surface layer). The runoff-brine mixture in Lake Lisan is also reflected by the Sr/Ca ratios that are positively correlated with the RA. Nevertheless, the 14C content in the epilimnion did not drop at the same rate as the atmospheric value but rather remained nearly constant. We suggest that turbulent mixing with the much saltier hypolimnion (lower layer) across the hypolimnion/epilimnion interface at a depth of about 390 m below sea level, buffered the 14C content as well as the Sr and Ca concentrations in the aragonite precipitating solution. The RA-Sr/Ca related limnological model developed here opens the way to determine the reservoir-age-corrected atmospheric ages of Lisan Formation aragonites beyond 28 ka cal BP.
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