HOLOCENE ENVIRONMENTAL-CHANGE IN THE ABISKO REGION OF NORTHERN SWEDENRECORDED BY THE MINERAL MAGNETIC STRATIGRAPHY OF LAKE-SEDIMENTS

Combined mineral magnetic, geochemical and palynological analyses were undertaken on Holocene sediment sequences recovered from lakes in the Abisko region of northern Sweden. The absence of the Karsa glacier in the Early and Mid-Holocene is reflected in downstream lake sediment s equences by zones of gyttja clay that experienced post-depositional ma gnetite (Fe3O4) dissolution and greigite (Fe3S4) authigenesis, due to organic matter decomposition and sulphate reduction. Between 3,000 and 2,500 C-14 yrs BP the Karsa glacier reformed and the accumulation of sediment with a higher minerogenic content took place, with the result that magnetite was preserved in the sediments. The mineral magnetic p roperties of different sediment types (algal/detrital gyttja) deposite d in two lakes in the Abisko valley record the same climatic deteriora tion between 3,000 and 2,500 C-14 yrs BP, although these lakes have be en isolated from a glacial influence during the Holocene. Gyttja depos ited during the Early and Mid-Holocene was also subjected to magnetite dissolution (and greigite authigenesis in one lake) until the regiona l climate deteriorated between 3,000 and 2,500 C-14 years BP. Due to c limate induced alterations in vegetation the limnology of the lakes ch anged and magnetite became preserved in the sediments.