An isotopic paleotemperature record for late Wisconsinan time in northeast Iowa

Isotopic temperatures and 230Th/234U ages have been determined for a stalagmite from Cold Water Cave, Iowa, some 50 km west of the Driftless Area. Calcite is now being deposited in this cave under conditions of isotopic equilibrium. The stalagmite, which was continuously deposited during the interval 25,000 to 6000 B.P., shows a pronounced temperature minimum at about 17,000 ± 2000 B.P. This is synchronous with the maximum Woodfordian advance of the Lake Michigan glacial lobe. During the growth of this speleothem, the temperature of the cave fell and then rose over a range of about 5°C. If the parent seepage waters obeyed the relationship δD = 8 δ18O, as observed for Wisconsin age Antarctic ice and other paleowaters, then the minimum temperature reached was about 2°C. Rates of temperature change accompanying the last glacial advance and retreat in this region are estimated to range between −0.6 and ±1°C/103 yr.