INTEGRATED HIGH-PRECISION ANALYSES OF HOLOCENE RELATIVE SEA-LEVEL CHANGES - LESSONS FROM THE COAST OF MAINE

A suite of salt-marsh peat samples from four sites along the coast of Maine (Wells, Phippsburg, Gouldsboro, and Machiasport) has been analyz ed using high-precision techniques to determine local relative sealeve l trends and to evaluate proposed along-coast warping. A spatially var iable set of relative sea-level records in Maine would have important implications For geophysical models that predict the response of the l ithosphere during deglaciation and postglacial isostatic relaxation. T hese models are often at odds with observed relative sea-level indicat ors near the margins of former glaciation, including those from Maine. Assemblages of agglutinated benthic foraminifera occur in vertical zo nes on the surface of modern salt marshes in Maine and can be used to accurately locate farmer mean high water levels in cores. Additional t ools in this study include accelerator mass spectrometer C-14 dating o f individual plant fragments and precise leveling of elevations. The a mplification of M(2) tidal range in the Gulf of Maine and the Bay of F undy during the Holocene is modeled and applied to the mean high water data yielding best-estimate envelopes of mean tide level change for e ach location. Average long-term (thousands of years) mean tide level r ise did not exceed approximate to 2 mm/yr at any time during the Late Holocene at Wells, Phippsburg, and Machiasport. Between 4.5 and 3 ka ( calibrated [cal]), the apparent rate of rise at Gouldsboro was higher than at any other site studied, This along-coast variation in the rate of mean tide level rise may reflect time of deglaciation, neotectonic s, or differential isostatic adjustments, Between 8 and 5 ka (call, on ly south-central Maine (Phippsburg) has a good record of relative sea- level change. At this locality, the rate of mean tide level rise was 5 .0-8.8 mm/yr for the period 7.8-5.3 ha (cal), which may have resulted from collapse of a glacial forebulge, A slight acceleration of mean ti de level rise has occurred during the past millennium in Gouldsboro an d Machiasport. If 12 m downwarping in easternmost Maine occurred, as s uggested in other publications, it must have happened prior to 5.7 ka (cal).