A MULTI-PROXY CHARACTERIZATION OF THE HOLOCENE DRY PERIOD FOR TWO SITES FROM SOUTH-CENTRAL MINNESOTA

Kimble Pond and Sharkey Lake are two small glacial lakes in south-central Minnesota that provide a continuous high-resolution record of paleoclimate throughout the Holocene. In both lakes sediment-magnetic parameters (magnetic susceptibility, ARM/IRM, hysteresis parameters) show an increase in coarse-grained magnetic minerals during the early to mid-Holocene dry period between 4000 - 9000 yrs. B.P. (cal. 14C), and large changes in these parameters suggest highly variable lake conditions during this period. The drier conditions are confirmed by low-resolution pollen analyses, which show a decrease in the ratio of arboreal / non-arboreal pollen. Lake productivity, as inferred by biogenic silica analyses, was high during this dry interval. Charcoal concentrations are low throughout most of the Holocene, but show a significant peak between 3000 - 4000 yrs B.P., indicating increased fire frequency when increased moisture availability led to more abundant fuel supply. A comparison of the various paleo-climate proxies shows that sedimentological and magnetic proxies tend to respond rapidly to changing watershed conditions, while pollen and charcoal analyses present a smoother record and are likely to indicate regional changes.