The mineral magnetic properties of an annually laminated Holocene lake-sediment sequence in northern Sweden

Abstract

Detailed mineral magnetic measurements were conducted on a 9000-year varved lake sediment sequence in northern Sweden (Lake Sarsjön). The results demonstrate that the paramagnetic susceptibility reflects the concentration of detrital minerogenic material in the lake sediments, which is controlled to a large extent by the intensity of the spring snow melt. In contrast, the concentration of ferrimagnetic magnetite (reflected by initial magnetic susceptibility and magnetic hysteresis parameters) is positively correlated to the concentration of organic carbon, which is most likely of an autochthonous origin. This magnetite has magnetic properties that are characteristic of stable single-domain magnetite grains produced by magnetotactic bacteria. The paramagnetic susceptibility record clearly points to a climatic excursion in the early Holocene between 6100± 174 bc and 5700± 167 bc, which can be correlated to an d18O excursion (a cold event) in the Greenland ice cores and lake sediments in southern Germany, and also to a short period of increased glacial activity in Scandinavia. The middle Holocene (4000–1760 bc) is characterized by sediment with a low concentration of detrital minerals and a high organic carbon content, whereas the late Holocene (1760 bc–ad 1918) is marked by more frequent and intense periods of detrital sedimentation.