Elk Lake pollen record

The pollen record from Elk Lake is interpreted in climatic terms by three different numerical approaches. The paleoclimatic record inferred for Elk Lake can be described as a sequence of climatic zones, separated by short transitional intervals: (1) the cold and dry late glacial zone (11,600-11,000 varve yr), (2) the cool and moist early Holocene zone (10,000-8500 varve yr), (3) the warm and dry middle Holocene zone (7800-4500 varve yr), and (4) the warm and moist late Holocene zone (3500 varve yr to present). Two large-scale controls of this climatic sequence can be inferred from paleoclimatic model experiments. The first is the effect of the Laurentide ice sheet on surface winds and temperatures; this influence was strongest prior to 9 ka. This control was replaced by the amplified seasonal cycle of solar radiation between 12 and 6 ka that increased summer temperature and net radiation and decreased effective moisture. Mesoscale controls on the climate of the Itasca region possibly include a lake effect during the various stages of Lake Agassiz and subtle changes in atmospheric circulation during the prairie period (about 8000 to 4000 varve yr).