Dan Hammarlund

Cellulose-inferred lakewater oxygen-isotope records have been obtained from two hydrologically open basins (Lake Spaime and Lake Svartkalstjarn), located on a west east transect across central Sweden, to investigate changes in atmospheric circulation patterns during the Holocene. The Lake Spaime delta O-18 record is sensitive to changes in the seasonal distribution of precipitation in the Scandes Mountains of west-central Sweden, and thus generally portrays variations in delta O-18 of precipitation (delta O-18(P)) that are governed predominantly by the influence of air masses originating from the North Atlantic. In contrast, the Lake Svartkalstjarn delta O-18 record appears to reflect the varying influence of air masses delivering moisture from the North Atlantic and the Baltic Sea. A comparison of inferred changes in delta O-18(P) over the Holocene between the two sites reveals systematic patterns of variability over widely different time scales. These include: (1) a previously recognized long-term regional decline in delta O-18(P), possibly in response to the declining vigour of Northern Hemisphere atmospheric circulation related to decreasing summer solar insolation; (2) newly identified inverse centennial- to millennial-scale delta O-18(P) fluctuations at the two sites that may be linked to changes in modes of atmospheric circulation analogous to those described at interannual to multidecadal time scales by the North Atlantic Oscillation (NAO) index; and (3) a prolonged interval of apparent climatic stability in the mid-Holocene (c. 6300-4200 cal. yr BP) characterized by persistently negative NAO-like circulation.