LATE HOLOCENE SEA-LEVEL RECONSTRUCTION FOR THE LOFOTEN ISLANDS, NORWAY USING SEDIMENT RECORDS FROM ISOLATION BASINS

In northern Norway, records that define general trends of relative sea level (RSL) change throughout the Holocene have been developed, with sea level in this area lowering ~10m over the past c. 6800 cal yr BP. However, the rate and magnitude of this lowering in the Lofoten Islands are poorly defined during the late Holocene. This study analyzes sediment cores from two isolation basins in the Lofoten Islands, Farstadvatnet and Upper Storfjordvatnet, to characterize changes in marine influence throughout each sediment record in order to develop new sea-level index points and refine existing late Holocene RSL curves. Isolation basins are coastal lakes characterized by their past connection to and isolation from the sea due to RSL changes driven by post-glacial isostatic adjustments. These basins provide a continuous record of sedimentation that is useful in reconstructing RSL changes. Sediment cores were analyzed for changes in magnetic susceptibility, carbon, nitrogen, sulfur, carbon isotopes of organic matter, and diatom assemblages, which reflect changes in salinity and water column characteristics. These data define four distinct litho-chemostratigraphic facies (A-D), which are interpreted to reflect glacio-marine, marine, brackish, and lacustrine phases of sedimentation in each basin. Our record from Farstadvatnet indicates a period of glacio-marine depositional conditions (from the base of the core to c. 9700 cal yr BP). This was followed by a long period of brackish to marine depositional conditions (c. 9700 – 4000 cal yr BP), followed by complete isolation c. 4000 cal yr BP. A similar sequence was found in Storfjordvatnet and radiocarbon samples are currently being processed. The data from Farstadvatnet indicate a RSL lowering rate of ~1.15 mm/yr. These results have implications for understanding the evolution of this coastal system, where RSL likely influenced early Viking-age settlements in this area (c. AD 800-1050, 1150-800 cal yr BP), and for understanding how it will change in the future.