Establishing Paleoclimate Variation From Major and Trace Elements and Stable Isotopes in a Tufa Deposit, Wisconsin

By Liz Forbes

Whitman College, Walla Walla WA


This study examines the paleoclimate from Middle to Late Holocene of southwest Wisconsin by analyzing the compositional and isotopic variation of a spring-deposited tufa mound consisting primarily of calcium carbonate.  Two drill cores of 3.58 and 1.38 meters length were analyzed for trace elements and stable isotopes (δ 13C, δ 18O).  Mg/Ca, Ba/Ca, Sr/Ca and δ13C values within the tufa reflect the wetness or dryness of the climate, with high ratios and δ13C values corresponding to dry periods.  δ18O values reflect temperature, with high δ18O indicating high paleotemperature.  Results showthat southern Wisconsin was dry and warm prior to ~4,500 yr BP and has experienced a general increase in moisture and decrease in temperature for the past 6,000 years.