EXTENDING TEPHROCHRONOLOGY FROM THE TERRESTRIAL ENVIRONMENT TO THE MARINE ENVIRONMENT: A CASE STUDY FROM CORE MD99-2269, N ICELAND SHELF

An abundance of traceable and dated tephra-markers from Icelandic volcanoes offer a unique opportunity for high-resolution, land-sea correlations. Here we attempt to correlate the tephrochronology of a marine sediment core MD99-2269 (Lat: 66.37.53 N, Long: 20.51.16 W, water depth 365 m, length 2530 cm) from the N Iceland shelf to the terrestrial tephrochronological record of Iceland. Core MD99-2269 contains one visible tephra-marker (Saksunarvatn) and an abundance of cryptotephra (microscopic tephra-markers). Important considerations when attempting a land-sea correlation are: 1) How well can we distinguish individual single eruptions from each other. 2) Once identified, how well constrained are the absolute ages of the tephra. Tephras ages are often based on radiocarbon dated terrestrial deposits where ages may vary widely. We have pooled together previously published ages for the Hekla 3 and Hekla 4 tephras and combine them using the R-combined feature in Oxcal to estimate the radiocarbon age for the respective tephras. For MD99-2269 tephras are identified to specific eruptions by their geochemical fingerprint, thereby creating a chronostratigraphic marker. We construct a tephrochronological age model using multiple tephras from eruptions of the Hekla, Grimsvotn, and Snaefellsjokull volcanoes. An independent radiocarbon based age model is obtained for MD99-2269. To augment the 25 AMS radiocarbon dates from MD99-2269 we have through paleomagnetic synchronization transferred an additional 18 AMS radiocarbon dates from East Greenland core MD99-2322 (Lat. 67°08.18 N, Long. 30°49.67W, water depth 714 m, length 2635 cm) to their equivalent depths in MD99-2269. The combined 43 AMS radiocarbon dates are pooled together to create a single age model (converted to cal BP yr with standard 400 yr reservoir correction) for the two cores. This poster compares the radiocarbon based age model with a purely tephrochronological age model. We will examine whether differences between the two can be used to infer reservoir age changes.