An updated Holocene sea-level curve for the Delaware coast

Abstract

Abstract We present an updated Holocene sea-level curve for the Delaware coast based on new calibrations of 16 previously published radiocarbon dates ( Kraft, 1976; Belknap and Kraft, 1977 ) and 22 new radiocarbon dates of basal peat deposits. A review of published and unpublished 137 Cs and 210 Pb analyses, and tide gauge data provide the basis for evaluating shorter-term (10 2 yr) sea-level trends. Paleosea-level elevations for the new basal peat samples were determined from the present vertical zonation of marsh plants relative to mean high water along the Delaware coast and the composition of plant fossils and foraminifera. Current trends in tidal range along the Delaware coast were used to reduce elevations from different locations to a common vertical datum of mean high water at Breakwater Harbor, Delaware. The updated curve is similar to Belknap and Kraft's [J. Sediment. Petrol., 47 (1977) 610–629] original sea-level curve from 12,000 to about 2000 yr BP. The updated curve documents a rate of sea-level rise of 0.9 mm/yr from 1250 yr BP to present (based on 11 dates), in good agreement with other recent sea-level curves from the northern and central U.S. Atlantic coast, while the previous curve documents rates of about 1.3 mm/yr (based on 4 dates). The precision of both estimates, however, is very low, so the significance of these differences is uncertain. A review of 210 Pb and 137 Cs analyses from salt marshes of Delaware indicates average marsh accretion rates of 3 mm/yr for the last 100 yr, in good agreement with shorter-term estimates of sea-level rise from tide gauge records.