Reconstructing Radiocarbon Reservoir Ages North of Iceland During the Last Millennium: Implications for Ocean Circulation and Climate Change

In this study we provide radiocarbon reservoir ages for the north Icelandic shelf waters for intervals during the last millennium based on annually banded molluscs. The master shell chronology is based on long-lived bivalves (Arctica islandica L.), which were live-caught in 2006 in 80 m water depth. We have successfully cross-matched fossil A. islandica shells with the modern chronology establishing a continuous shell chronology for most of the last millennium. Based on these data, we calculate Delta R values (deviation from the modelled global mean surface ocean reservoir age of about 40514C years) to infer the relative position of the Polar Front. The oceanic Polar Front is now situated in the Denmark Strait between Greenland and Iceland where the relatively warm and saline waters from the North Atlantic flow clockwise around Iceland as the Irminger Current and mix with the relatively cold and low saline waters of the East Icelandic Current. The position of the Polar Front is intimately linked to North Atlantic Deep Water convection sites and the North Atlantic meridional overturning circulation, and these strong oceanic and atmospheric gradients make this region particularly sensitive to climate change. Our initial results compare well with nearby sediment- based Delta R records, and the combined data set suggests that the Polar Front location was highly dynamic from AD 1000 to 1300, and during the most recent period (AD 1800 to 1950). From AD 1300 to 1800, during the Little Ice Age, the Delta R values were stable and showed little variability, suggesting that the Polar Front moved southward of the north Icelandic shelf during this interval. The implications of these findings are discussed with respect to the interpreted palaeoceanographic evolution of the north Icelandic shelf during the last millennium.