Dan Hammarlund

Pollen records from 21 sites were used to reconstruct Holocene hydrological changes in northern Fennoscandia. The inferred dominance of maritime-type Betula-forests from c. 9600 BP onwards indicate an oceanic climate in the region during the early Holocene, with high amounts of precipitation and low seasonal contrasts. This interpretation is supported by oxygen isotope records obtained on lacustrine carbonates from Abisko, northern Sweden. Enrichment of O-18 during the early Holocene suggests enhanced zonal circulation and a pronounced influence of Atlantic air-masses in northern Sweden. The pattern of Pinus expansion in the area was time-transgressive, ranging from 9200-8000 BP in the extreme north-east to 7900-5500 BP in the western and south-western parts of the region. The replacement of Betula-forests by Pinus-forests indicates a climatic change towards drier summers and increased seasonality. At Abisko, a close correlation between regional Pinus expansion and depletion of (1)8O in lacustrine carbonates suggests that the expansion of Pinus was triggered by a gradual attenuation of the influence of westerlies. Thus, in large-scale palaeohydrological terms, the early expansion of Pinus in the north-easternmost parts of Fennoscandia as compared to the successively later expansion in the west and south-west may reflect a gradually decreasing influence of Atlantic air-masses in northern Fennoscandia during the early and mid Holocene.