North Atlantic palaeointensity stack since 75ka (NAPIS–75) and the duration of the Laschamp event

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Abstract
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 field strength exhibits some oscillations, with a first 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 field strength seems to slowly increase to the upper limit of the studied interval. In the 10–20 kyr interval some differences exist between individual records, and fine–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 five cores, appears to be about 1500 years, consistent with a recent suggestion on the origin of geomagnetic excursions.