| Summary: | The radiocarbon timescale has been calibrated by dendrochronology back to 11.8 ka cal BP, and extended to 14.8 ka cal BP using laminated marine sediments from the Cariaco Basin. Extension to nearly 23.5 ka cal BP is based on comparison between (super 14) C and U-Th ages of corals. Recently, attempts to further extend the calibration curve to >40 kyr are based on laminated sediments from Lake Suigetsu, Japan, foraminifera in North Atlantic sediments, South African cave deposits, tufa from Spain, and stalagmites from the Bahamas. Here we compare these records with a new comparison curve obtained by (super 234) U- (super 230) Th ages of aragonite deposited at Lake Lisan (the last Glacial Dead Sea). This comparison reveals broad agreement for the time interval of 20-32 ka cal BP, but the data diverge over other intervals. All records agree that Delta (super 14) C values range between approximately 250-450 per mil at 20-32 ka cal BP. For ages >32 ka cal BP, the Lake Suigetsu data indicate low Delta (super 14) C values of less than 200 per mil and small shifts. The other records broadly agree that Delta (super 14) C values range between approximately 250 and 600 per mil at 32-39 ka cal BP. At approximately 42 ka cal BP, the North Atlantic calibration shows low Delta (super 14) C values, while the corals, Lisan aragonites, and the Spanish tufa indicate a large deviations of 700-900 per mil. This age is slightly younger than recent estimates of the timing of the Laschamp Geomagnetic Event, and are consistent with increased (super 14) C production during this event.
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