Climate variability as seen in two interglacial records from the midwestern USA

Ch.E. Geiss, S.K. Banerjee, University of Minnesota, 100 Union St. S.E., Minneapolis, MN 55455, USA, geis0037@umn.edu

The sediment records from 2 kettle lakes were used to compare the magnetic signature of the Sangamon and Holocene interglacial. Pittsburg Basin in southern Illinois recorded Sangamonian climate variations, while sediment cores from Kirchner Marsh in Minnesota were used to study Holocene variations. Pollen studies from both sites indicate the occurrence of a dry prairie period in both interglacials. The magnetic response to these dry periods is quite different. In Kirchner Marsh the dry period is characterized by increased input of detrital material, which leads to an increase in magnetic susceptibility and SIRM. The magnetic grainsize, as expressed in ARM/SIRM and hystreresis parameters increases during the same period. Pittsburg Basin cores also show an increase in magnetic material, but here the magnetic grainsize deceases during the dry period, and the samples show increased SD and SP contributions. In Kirchner Marsh the sediments deposited during the dry period are most likely redeposited lake sediments that have undergone additional alteration, while Pittsburg Basin prairie sediments seem to be dominated by pedogenic processes. The different response of the two lakes to a similar climatic signal shows the necessity of multiparameter studies that combine magnetic as well as non-magnetic techniques.

Annales Geophysicae Supplement I, V.16, p.C213, 1998