ABSTRACT. We present two new high-resolution sediment records from the southwestern Iceland and Norwegian Seas that were dated by numerous 14C ages up to 5414C ka BP. Based on various lines of evidence, the local 14C 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 6180 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 14C ages between 20 and 54 i4C ka BP. Generally the results confirm the 14C 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 14C shifts after 4514C 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 14C and 10Be production, giving rise to excess 14C in the atmosphere of up to 1200%o.

Six relative palaeointensity records from the north Atlantic Ocean were stacked together to produce a new record for the last 75 kyr (NAPIS-75). Five of these records have been previously correlated at millennial scale and placed on the GISP2 age scale, the sixth record was tied to the others using magnetic susceptibility. From 75 ka the eld strength exhibits some oscillations, with a rst minimum ca. 65 ka, followed by a progressive increase to a broad maximum centred at ca. 48 ka. There is then a well-marked low at 40 ka, corresponding to the directional anomaly of the Laschamp event. Another intensity low, observed at ca. 34 ka, corresponds in age to the Mono Lake event. After a high at 33 ka and two lows at 30 and 24 ka with a broad maximum between, the eld strength seems to slowly increase to the upper limit of the studied interval. In the 10{20 kyr interval some di¬erences exist between individual records, and ne-scale details are not always resolved. In the 20{75 kyr interval, on the other hand, well-resolved millennial-scale features are superimposed to the broader trends. The duration of the Laschamp event, which is recorded directionally in ve cores, appears to be about 1500 years, consistent with a recent suggestion on the origin of geomagnetic excursions.