AMINO-ACID RACEMIZATION IN FOSSIL GASTROPODS FROM CENTRAL EUROPEAN LOESS: ARRHENIUS PARAMETERS, PALEOTEMPERATURES, AND GROUND-TEMPERATURE CONTROLS

In an effort to reconstruct paleotemperatures during the last glaciation across Europe, we determined the Arrhenius parameters of amino acid racemization for aspartic acid, glutamic acid, valine, phenylalanine, and isoleucine, in the terrestrial gastropod genera Succinea, Trichia, and Pupilla, recovered from Upper Pleistocene loess deposits throughout the region. Combining kinetic models of racemization with independent radiocarbon and luminescence age estimates, we calculate Late-Pleistocene effective diagenetic temperatures and temperature gradients in a transect ranging from Germany and Belgium in northwest Europe, to Hungary and Serbia in southeastern 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. Racemization data suggest that effective paleotemperatures increase from the northwest to the southeast, and indicate that the late Pleistocene temperature gradient may have been steeper than present across the region.

It is important to note that paleotemperatures reported here reflect paleo-ground-temperature conditions. For paleoclimate reconstruction it is necessary therefore to determine the relationship between the calculated ground (> 2m depth) paleotemperatures and surface air temperatures. To assess this relationship across the study region, we have installed ground-temperature recorders at numerous localities at depths ranging from one to three meters. Multi-year ground-temperature measurements allow us to model the relationship between present-day surface air temperature and temperature at depth, which will be applied to the period of loess deposition and shell burial. 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.