INITIAL RESULTS ON THE TEPHRA STRATIGRAPHY IN LACUSTRINE AND SHALLOW MARINE SEDIMENT CORES FROM ICELAND

The climate in Iceland is sensitive to subtle changes in the North Atlantic circulation because of its position at the boundary between the opposing currents: the cold East Greenland Current and the warmer and more saline, Irminger Current. This factor along with high sediment accumulation rates (up to 5 m/ka) makes marine and lake sediments in Iceland well suited for obtaining continuous time-series of critical climate proxies. Consequently, Icelandic sediment sequences are ideal when addressing questions on the timing and magnitude of climate change during the Holocene. Accurate high resolution dating of the sediments underpins stratigraphic correlations and is thus essential for obtaining reliable results. We have collected a number of marine and lacustrine sediment cores on a north-south transect across Iceland in order to delineate a detailed record of Holocene climatic and environmental change.

Holocene explosive basalt to rhyolite volcanism in Iceland has produced numerous tephra fall deposits, which when present in sediments represent an instantaneous marker horizon. Widespread tephra fall deposits of known age, in conjunction with high precision AMS 14C dating, are the foundation for constructing unambiguous high resolution regional chronology across marine and land based sedimentary environments. We have identified several key tephra marker layers in our sediment cores. The Saksunarvatn tephra (10180 cal yr BP) along with a mildly alkaline basalt tephra layer (~ 9500 cal yr BP) and an andesite tephra layer of Hekla composition (~6000 cal yr BP) have been identified in all sediment cores in question and clearly represent chronostratigraphic markers of regional significance. Furthermore, the Vedde ash (11980 cal yr BP) has been identified in two marine cores recovered from sites northwest of the Vestfirdir Peninsula. We have also identified several late Holocene tephra layers in the lacustrine cores, including a young rhyolitic tephra layer with composition indicative of origin within the Torfajokull volcano. This tephra layer is tentatively identified as the rhyolitic component of the Settlement Layer formed at ~870 AD.