Holocene climatic change in Swedish Lapland inferred from an oxygen-isotope record of lacustrine biogenic silica

Holocene climatic variability was studied in a 9500-year lake-sediment sequ ence from the Abisko region in Swedish Lapland, using the oxygen-isotope ra tio in diatom biogenic silica (delta O-18(si)). Oxygen- and hydrogen-isotop e ratios of waters from the Abisko area suggest that in this region the eva porative flux is small and the isotopic composition of most lakes reflects that of the local precipitation. The hydrological setting of the region and sensitivity analysis of isotopic response to changing climatic parameters such as humidity, inflow and evaporation show that the downcore diatom delt a O-18(si) record is primarily controlled by changes in the summer isotopic composition of the lake water. The overall 3.5 parts per thousand depletio n in delta O-18(si) since the early Holocene is interpreted as an increase in the influence of the Arctic polar continental air mass that carries depl eted precipitation. We estimate that this change is associated with a 2.5-4 degreesC cooling that has occurred since the early Holocene. In general, t he diatom delta O-18(si) record resembles the average annual air temperatur e reconstructed for the Greenland ice core GISP2, especially during the pas t 4000 years, with a pronounced cooling starting at 2000 years BP.