EARLY-HOLOCENE LIMNOLOGICAL AND CLIMATIC VARIABILITY IN THE NORTHERN GREAT-PLAINS

Information on the timing and direction of climatic and environmental change on a millennial scale exists for many regions of North America, whereas little is known about decadal-to centennial-scale variability . Here we present a high-resolution analysis of diatom-inferred salini ty from a site in the Northern Great Plains to reconstruct multidecada l-and centennial-scale climatic patterns during the early Holocene. Th e diatom-inferred salinity indicates a transition from fresh to highly saline conditions between c. 13 400 and 7700 cal. yr BP, which sugges ts a major shift in climate from wet to dry conditions. The overall tr end toward increasing salinity is interrupted by several freshwater in tervals between c. 9800 and 7950 cal. yr BP, which may be the result o f an increase in the frequency of monsoonal flow from the Gulf of Mexi co. The early Holocene is considered to be a time of rapid change in c limate and vegetation within the Holocene. Although rates of change in the Moon Lake diatom assemblages were high during parts of the early Holocene, in general the rate of change was as great or greater during the last two millennia. This finding may be the result of a generally directional change in climate in the early Holocene, in contrast to s horter-term fluctuations and little directionality in the late Holocen e.