Geomagnetic field intensity changes in Sweden between 9000 and 450 cal BP: extending the record of “archaeomagnetic jerks” by means of lake sediments and the pseudo-Thellier technique

Abstract

The pseudo-Thellier technique was applied to recover relative palaeointensity (PT-RPI) estimates from four piston cores retrieved from a Holocene lake sediment sequence in the province of Småland, central southern Sweden. A time–depth model between 11,000 and 450 cal BP was based on a combination of calibrated radiocarbon ages and the ages of established palaeomagnetic secular variation (PSV) features that were transferred from a varve-dated regional master curve. In Fennoscandia, significant peaks in geomagnetic field intensity occurred at ∼8400, ∼6400, 3900 and 2800 cal BP. The maximum field intensity at 2800 cal BP was associated with the most rapid change in the direction of the geomagnetic vector. While the high-resolution sedimentary data show that significant century scale increases and decreases in relative field intensity between 4000 and 2000 cal BP were associated with abrupt changes (jerks) in the direction of the geomagnetic vector, archaeomagnetic jerks younger than 2000 years were not reproduced in this multiple sediment core study. On the other hand, the PT-RPI reconstructions display century to millennial scale trends between 5000 and 450 cal BP that are coherent with archaeomagnetic data sets from western Europe and Central Asia. This agreement indicates that palaeointensity may be used as a relative dating technique across this region. Fennoscandian PSV and RPI records for the earlier Holocene do not show the same rapid style of vector movement, which suggests that northern Europe has been affected by a more turbulent geodynamo since ∼4000 cal BP.