A High-Resolution, Holocene Climate Record From the N Iceland Shelf: Benthic and Planktonic Mg/Ca and d18O Records on a Radiocarbon, Tephrochronology and Paleomagnetic Chronostratigraphy

We present a high-resolution Holocene Mg/Ca and d18O record from benthic foraminifera Islandiella norcrossi/helenae and Melonis barleeanus and planktonic foraminifera Neogloboquadrina pachyderma (sin) from the North Iceland shelf core MD99-2269 (Lat: 66.37.53 N, Long: 23.51.16 W, water depth 365 m, length 2530 cm). These allow reconstruction of the upper and bottom water conditions at our site. To place the observed changes on as accurate chronology as possible we have employed a multilevel approach toward deriving our radiocarbon-based chronology. Twenty-five AMS radiocarbon dates were acquired from MD99-2269. To augment these dates, we have through paleomagnetic synchronization transferred an additional 18 AMS radiocarbon dates from East Greenland core MD99-2322 (Lat: 67.08.18 N, Long: 30.49.67 W, water depth 714 m, length 2635 cm) to their equivalent depths in MD99-2269. Forty of the combined 43 AMS radiocarbon dates were pooled together to create a single age model for the two cores. This chronology was then tested for accuracy using the abundance of traceable and dated tephra-markers from Icelandic volcanoes. Core MD99-2269 contains one visible tephra-marker (Saksunarvatn) and an abundance of cryptotephra. Cryptotephra were located by grain counting in the >150 µm size-fraction. Samples from selected tephra peaks were geochemically analyzed at the Nordic Volcanological Institute in Iceland. The geochemical fingerprint identifies each tephra to a specific eruption, providing eight checks on the accuracy of MD99-2269 age model. Offsets are generally less than 200 yrs and suggest that reservoir-age on the NW-Iceland shelf was time dependent during the Holocene. We incorporate this variable reservoir age in our final age model. The temperature variations observed are interpreted as variations in the strength of Irminger water inflow to the N Iceland shelf. These variations versus time will be discussed.