Fluctuations in atmospheric 14C concentrations beyond the 26 ka of the established 14C calibration have been reported from several proxy records back to ca. 50 ka BP. There are significant differences between the records, highlighting the difficulty to establish an absolute time scale and indicating regional influences on the records. In order to identify 14C fluctuations caused by regional effects in the 14C analysis of sediment core PS2644, north of Iceland, we have measured the 14C concentration of 2 other marine records, core MD 01-2444 off Portugal and coral records ARA 04 from Vanuatu.
In addition, we have extended the detailed 14C analysis (214 dates) of core PS2644 back with 53 new results into MIS 4 (> 70 ka cal BP, GISP2 time scale) to the technical limits of our AMS system beyond 62 ka 14C BP (see Nadeau et al). The reproducibility of many measurement series performed during the last 9 years demonstrates the observed fluctuations in 14C concentrations are a property of core. PS2644. With its time scale based on correlation with the GISP2 δ18O record, PS2644 has provided evidence of large variations in 14C concentrations in the ocean mixed layer north of Iceland. The results show large 14C fluctuations around 55 and 70 ka cal BP, and, a particularly sharp 14C increase, between 46 and 48 ka cal BP, which is reproduced in MD 01-2444.
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