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Evidence of Changes in Aridity in the Upper Mississippi Basin
Dean, W.E., T.S. Ahlbrandt, R.Y. Anderson, and J.P. Bradbury
Complete Scientific Reference

Elk Lake Sediment Data and Data Description from the WDC Paleoclimatology archive.

Summary:
For larger viewing image, please click image. The distribution of the vegetation present in Minnesota today reflects both north-south and east-west climate gradients (figure to the right), and identifies this as an important region for studies of past drought and climate variability. Lakes sediments from Elk Lake, in the headwaters region of the Upper Mississippi Basin (northeastern Minnesota), record variations in climate and other environmental factors over time scales of years to millennia. Elk Lake sediments are layered in varves, which make it possible to reconstruct information on climate variability with annual resolution. Sediment cores taken from the lake bottom have been used to generate a regional record of aridity based on the chemical, sedimentological, and biological characteristics of the sediments. Changes in varve thickness as well as the abundances of wind-blown quartz-rich silt and clay (quartz values increase under dry conditions), or the sodium from plagioclase feldspar (under dry conditions, retained in soil until washed or blown into lakes) are indicative of regionally wet and dry conditions. Increases in the remains of the diatom Aulacoseira indicate windy conditions, commonly accompanying increased aridity.

The Elk Lake record, spanning almost 11,000 years, shows that conditions were warmer, drier, and windier between 8000 and 6000 year ago as inferred from For larger viewing image, please click image. increases in varve thickness, sage pollen, quartz abundance, sodium levels, and the diatom Aulacoseira (figure to the right). Similar changes in the sediment composition between 4800 and 4300 years ago are indicative of another interval of dry conditions. The subsequent decrease in varve thickness, sage pollen, quartz abundance, sodium levels, and Aulacoseira, reflects an overall trend to moister conditions from 4000 to 1000 years ago. High amplitude changes in sediment composition over the last 1500 years are also interpreted to reflect a number of shorter but equally severe intervals of dry conditions (see Dean, 1997 for details on this work).

For more details on Elk Lake paleoenvironmental studies, click here.

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