A study of early Holocene climate changes in Småland, Sweden, with focus on the '8.2 kyr event'

Sammanfattning: Three sediment cores, each 1.5 meters in length, obtained from Lake Byestadsjön in the province of Småland, southern Sweden were studied with high resolution mineral magnetic measurements, carbon content, pollen analysis and XRF analysis. The aim was to reconstruct the early Holocene environment, with focus on the period between 9000-7000 cal yr BP, and thereby conclude if the 8200 cal yr BP cooling event affected the region or not. The results are further compared to other proxies from nearby sites and the NorthGRIP oxygen isotope ice core record from Greenland. The chronology was obtained by radiocarbon dating of three levels and by adopting dates from earlier studies by mineral magnetic correlation. The results obtained from the detailed mineral magnetic measurements indicates that the most commonly used magnetic parameter χ (mass specific magnetic susceptibility) is highly influenced by the production of single domain magnetite particles by magnetotactic bacteria within the lake. These bacteria are favoured by sub-oxic conditions and are sensitive to changes in the environment. Three distinct changes in limonology, as interpreted from the mineral magnetic analyses, are seen at 8400, 8200 and 8000 cal yr BP, respectively. The response in forest composition, as reflected by the pollen analysis, indicates that the first environmental disturbance was the most severe and the following two were less pronounced. There is an noticeable 200 year period between the three deteriorations seen in Småland. By comparing the results with the NorthGRIP ice core record it is obvious that the 8200 cooling event is part of a much more complex climatic deterioration period, but only one distinct cooling of about 100-150 years often referred to in most literature. The magnetic signals obtained from Lake Byestadsjön might reflect a much more complex “8.2 kyr event” than has so far been revealed.