HOLOCENE RELATIVE SEA LEVELS OF THE U.S. ATLANTIC COAST: IMPLICATIONS FOR GLACIAL ISOSTATIC ADJUSTMENT MODELS

The relative sea-level (RSL) data from the U.S. Atlantic coast are an independent constraint on the accuracy of glacial isostatic adjustment (GIA) models. We have constructed a quality-controlled database of Holocene sea-level index points for the U.S. Atlantic coast, which is sub-divided into 16 areas based on distance from the Laurentide Ice Sheet. The observations show spatial variability related to the removal of the Laurentide Ice Sheet and document a decreasing rate of RSL rise through the Holocene. RSL rise during the Holocene has been highest in the mid-Atlantic region. Predictions of RSL for these areas are generated using two ice models (ICE-5G and ICE-6G) coupled to an existing model of mantle viscosity (VM5a). We identified significant misfits from Massachusetts to South Carolina using the initial mantle viscosity profile, regardless of ice model, although ICE-6G provides some improvement for northern Massachusetts to New York. Modifying the viscosity profile by decreasing the upper mantle viscosity by 50% removes the discrepancy between observations and predictions along the mid-Atlantic coastline from southern Massachusetts to the inner Chesapeake. There is no improvement from the Eastern Shore of Virginia to South Carolina, and the previously good agreement with data from Maine is destroyed. We believe that further refinement of the model may be able to resolve these misfits.