Holocene environmental and climatic change in the Northern Great Plains recorded in the geochemistry of sediments in Pickerel Lake, South Dakota

The sediments in Pickerel Lake, northeastern South Dakota, provide a contin uous record of climatic and environmental change for the last 12000 yr. Sed iments deposited between 12 and 6 ka (radiocarbon) show extreme variations in composition, oxygen and carbon isotopic composition of bulk carbonate, c arbon isotopic composition of organic matter, and magnetic susceptibility. These variations reflect changes in sources of moisture, regional vegetatio n types, precipitation-evaporation balance, ground- and surface-water influ x, water residence time, erosion, lake productivity, water level, and water temperature. The total carbonate content of late Pleistocene sediments ste adily increased from <20% at the base of the core to as much as 80% in sedi ments deposited between 11 and 9 ka. By about 8 ka, the total carbonate con tent of the sediments had declined to about 40% where it remained with litt le variation for the past 8 kyr, suggesting relatively stable conditions. T here are marked increases in values of delta(13)C and delta(18)O in bulk ca rbonate, and delta(13)C of organic matter, in sediments deposited between 1 0 and 6 ka as evaporation increased, and the vegetation in the watershed ch anged from forest to prairie. This shift toward more O-18-enriched carbonat e may also reflect a change in source or seasonality of precipitation. Duri ng this early Holocene interval the organic carbon (OC) content of the sedi ments remained relatively low (2-3%), but then increased rapidly to 4.5% be tween 7 and 6 ka, reflecting the rapid transition to a prairie lake. The OC content fluctuates slightly between 4 and 6% in sediments deposited over t he past 6 kyr. Like OC and total carbonate. most variables measured show li ttle variation in the 13 m of sediment deposited over the past 6 kyr, parti cularly when compared with early Holocene variations. Although the magnetic susceptibility of this upper 13 m of sediment is generally low (<10 SI uni ts), the upper six meters of the section is marked by striking 1 m cycles ( ca. 400-500 yr periodicity) in susceptibility. These cycles are interpreted as being due to variations in the influx of eolian detrital-clastic materi al Century-scale cyclic variations in different proxy variables for aridity and eolian activity from sediments deposited over the past 2000 yr in othe r lakes in the northern Great Plains, as well as in sand dune activity, sug gest that aridity cycles were the dominant feature of late Holocene climate of the northern Great Plains. (C) 2000 Elsevier Science Ltd and INQUA. All rights reserved.