Calibration of the 14C time scale to >40 ka by 234U–230Th dating of Lake Lisan sediments (last glacial Dead Sea)

Abstract

A new comparison of 14C dates with 234U-230Th ages is presented of aragonites from Lake Lisan, the last Glacial Dead Sea, between ∼20–52 cal-ka-BP. The Lisan data are coincident with the coral based 14C-calendar age calibration through the continuous portion of the curve to 23.5 cal-ka-BP, and with the additional ‘checkpoints’ at ∼30 and ∼40 cal-ka-BP. The agreement with the corals provides evidence for the accuracy of the U-Th and 14C ages, and indicates that Lisan aragonites can potentially be used to generate a nearly continuous record of the atmospheric 14C variations through this crucial time interval. The Lisan data are compared with other records older than 25 cal-ka-BP from Lake Suigetsu, Japan, North Atlantic foraminifera, South African cave deposits and tufa from Spain. Over some age intervals the records show broad agreement, over other intervals they diverge. All agree that 14C ages were ∼2.5±0.5 ka younger than calendar ages between 20–32 cal-ka-BP. For ages >32 cal-ka-BP, the Lake Suigetsu data indicate small differences between 14C ages and calendar ages of less than 1.5 ka. The other records broadly agree that 14C ages are too young by ∼3±1 ka from 32–39 cal-ka-BP. At ∼40 cal-ka-BP, the foraminifera show equal 14C and calendar ages, while the corals, Lisan aragonites and the Spanish tufa indicate a large age difference of 4–5 ka. A recent paleomagnetic study of the Lisan Formation indicates that the high calendar-14C age difference at ∼40 cal-ka-BP may be associated with the Laschamp paleomagnetic excursion.