| Summary: | We present two new high-resolution sediment records from the southwestern Iceland and Norwegian Seas that were dated by numerous (super 14) C ages up to 54 (super 14) C ka BP. Based on various lines of evidence, the local (super 14) C reservoir effect was restricted to 400-1600 yr. The planktic stable isotope records reveal several meltwater spikes that were sampled with an average time resolution of 50 yr in PS2644 and 130 yr in core 23071 during isotope stage 3. Most of the delta (super 18) O spikes correlate peak-by-peak to the stadials and cold rebounds of the Dansgaard-Oeschger cycles in the annual-layer counted GISP2 ice core, with the major spikes reflecting the Heinrich events 1-6. This correlation indicates large fluctuations in the calibration of (super 14) C ages between 20 and 54 (super 14) C ka BP. Generally the results confirm the (super 14) C age shifts as predicted by the geomagnetic model of Laj, Mazaud and Duplessy (1996). However, the amplitude and speed of the abrupt decrease and subsequent major increase of our (super 14) C shifts after 45 (super 14) C ka BP clearly exceed the geomagnetic prediction near 40-43 and 32-34 calendar (cal) ka BP. At these times, the geomagnetic field intensity minima linked to the Laschamp and the Mono Lake excursions and confirmed by a local geomagnetic record, probably led to a sudden increase in cosmogenic (super 14) C and (super 10) Be production, giving rise to excess (super 14) C in the atmosphere of up to 1200 per mil.
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