GROUND-TEMPERATURE CONTROLS ON RACEMIZATION-DERIVED PALEOTEMPERATURE ESTIMATES FOR THE LAST GLACIATION IN CENTRAL EUROPE

Arrhenius parameters of amino acid racemization are derived for glutamic acid, aspartic acid, phenylalanine, and valine in the terrestrial gastropod genera Succinea, Pupilla, and Trichia. Measured D/L values and independent radiocarbon and luminescence age estimates are incorporated into kinetic models of racemization in order to calculate effective diagenetic temperatures for intervals of time during the late Pleistocene in the central Europe. Estimates based on initial glutamic acid Arrhenius parameters and measured D/L values in fossil Succinea shells collected from a loess profile at Nussloch, Germany (present mean annual air temperature=10 °C), suggest that the last glacial maximum (ca. 20 – 25 ka) temperature was -6 ± 12 °C, the period from 25 – 35 ka was -2 ± 11 °C, 35 – 60 ka estimated temperatures were 1 ± 12 °C, and the period corresponding to oxygen-isotope stage 3 (ca. 25 – 60 ka) was 0 ± 11 °C. Comparable effective temperature estimates are calculated based on alloisoleucine/isoleucine data, but aspartic acid results suggest significantly lower paleotemperatures. Ongoing refinement of racemization kinetics for amino acids measured in Succinea, Pupilla, and Trichia will lead to reduction in the error estimates and allow us to calculate late Pleistocene paleotemperatures at loess localities in Germany, Czech Republic, Hungary, and Serbia.

It should be noted that we are reporting calculated ground (paleo)temperatures, which are not directly comparable with mean annual air temperatures. The temperature that a shell experiences in the ground has a strong control on the rate of racemization of amino acids in the shell carbonate matrix. We have recently undertaken a program of installing ground temperature data loggers at depths from one to three meters throughout the study area. While these data are not yet available, multi-year ground temperature data will allow us to determine the relationship between temperatures at depth and surface air temperatures. These data will also enable us to correct our calculated effective diagenetic temperatures for changing burial depths and varying sedimentation rates as loess progressively accumulated.