Sea-Level and Ice Sheet History of West Greenland During the Last Millenia

Ice core and other palaeoenvironmental archives from terrestrial and marine settings record several major climate perturbations during the last millennia in Greenland that include the "Medieval Warm Period" and the "Little Ice Age". These changes were associated with variations in ice sheet mass balance and associated changes in ice margin position and ice load. For example, in Disko Bugt (West Greenland), the ice sheet margin is thought to have retreated between AD 600 and AD 1300, before readvancing to a maximum position at c. AD 1750 and then retreating to present. In this poster we present a new methodology for reconstructing high resolution records of RSL change from West Greenland, from which we may infer variations in ice sheet mass balance over decadal to centennial time scales. Our challenge has been to minimise age and altitude uncertainties, which are routinely high in conventional RSL approaches in Greenland and other Arctic areas that relie on shell and isolation basin chronologies. To achieve this, we target thin (0.5 m) salt marsh sediment sequences to provide multiple RSL data points based on AMS radiocarbon dating of terrestrial plant macrofossils and a transfer function based water level reconstruction that uses diatoms and other sedimentological criteria. The transfer function has a typical height uncertainty for each data point of +/- 0.2 m, whilst high precision AMS radiocarbon dates reduce age uncertainty to a little as +/-20 years. We present and compare two salt marsh- based RSL records from West Greenland (Disko Bugt and Kangerlussuaq) that together span the last millennia. Existing models of RSL change during this interval suggest a rise in RSL of up to 8 m since AD 1100. In contrast, our new work indicates a slower and more modest rate of RSL rise during this interval, which at Kangerlussuaq is c. 1.3 mm yr-1. New, high resolution RSL records, such as these, provide targets for geophysical models of ice sheet mass balance change and a long term context for short term geodetic records of crustal motions and ice sheet dynamics.