LATE HOLOCENE SEA LEVEL IN SOUTHERN PAMLICO SOUND: NEW DATA FROM SALTMARSH CORES ON WESTERN POINT, CEDAR ISLAND, NC

Cores from Western Point, Cedar Island, North Carolina constrain the Late Holocene relative sea-level history for southern Pamlico Sound. Radiocarbon dated plant macrofossils from basal saltmarsh peats overlying sand provide chronological control. Samples were analyzed for organic matter content, and agglutinated foraminifera tests were separated, identified and counted. Marsh surface elevations were referenced to NAVD 88 by total station leveling to the NGS benchmark on Cedar Island. The modern marsh foraminiferal assemblage was determined by analyzing surface samples from a transect of known elevation; throughout the transect the marsh surface is vegetated by Juncus roemerianus (black needlerush). As has been found elsewhere in Pamlico Sound, this Juncus-dominated marsh lies slightly below local mean sea level (-0.11 to -0.03 m LMSL). Abundant foraminifera in the modern assemblage include Ammoastuta inepta, Tiphotroca comprimata, Jadammina macrescens, Arenoparella mexicana, and Trochammina inflata. We have acquired marsh cores as deep as 3.25 m below local mean sea level (LMSL), but thus far the deepest peat sample found to contain saltmarsh foraminifera is from 2.31 m below LMSL. The dominant foraminifera species observed in the basal peat of cores analyzed thus far are Jadammina macrescens, Ammoastuta inepta, Tiphotroca comprimata, and Trochammina inflata. This basal peat assemblage closely resembles that of the modern marsh surface, suggesting deposition under conditions similar to those prevailing at the study site today. Although additional radiocarbon dates are pending, our results bracket relative sea level in southern Pamlico Sound between 2.10 and 1.60 m below LMSL during the interval from 1,690 to 1,410 cal years before present. Although this range overlaps the high-resolution sea-level curve from northern Pamlico Sound published by Kemp et al. (2011, PNAS, 108:11017-11022), the data in hand suggest a slower rate of subsidence in southern Pamlico Sound than in northern Pamlico Sound. This pattern is in general agreement with published models of glacial isostatic adjustment for coastal North Carolina (Engelhart et al., 2011, Geology, 39:751-754).