AMINO-ACID ESTIMATES OF LATITUDINAL TEMPERATURE-GRADIENTS AND GEOCHRONOLOGY OF LOESS DEPOSITION DURING THE LAST GLACIATION, MISSISSIPPI VALLEY, UNITED-STATES

Principles of amino acid paleothermometry are used to estimate paleote mperatures and latitudinal temperature gradients for the period during and following the last glacial maximum in the Mississippi Valley. Gas tropod shells were collected from the Peoria Loess for amino acid anal ysis, and Arrhenius parameters of isoleucine epimerization were determ ined experimentally for the gastropod genera Catinella and Hendersonia . There are 37 radiocarbon and 5 thermoluminescence ages that constrai n the paleotemperature estimates and provide additional chronological data for loess deposition in the region. Amino acid paleotemperature e stimates suggest that the north-south temperature gradient was signifi cantly depressed in the Mississippi Valley for a considerable period d uring the past approximate to 25 k.y. Effective diagenetic temperature estimates indicate that at some time during or following the last gla ciation, the effective-temperature gradient was approximate to 0.3-0.6 degrees C/degree of latitude, which is significantly lower than the m odern mean annual air-temperature gradient of approximate to 0.9 degre es C/degree of latitude. Calculated effective paleotemperatures for th ree localities in Tennessee and Mississippi suggest that temperatures were approximate to 7-13 degrees C lower than present during the perio d from ca, 24 to 16 ka in the lower Mississippi Valley These results p rovide additional evidence for a significant cooling in southern Unite d States continental temperatures during the last glacial maximum.