COASTAL WETLANDS EVOLUTION AT THE LEADING EDGE OF THE MARINE TRANSGRESSION: JARRETT BAY, NORTH CAROLINA

Peat moisture and ash contents, macro-vegetative remains, δ13C biogeochemical signatures, and four radiocarbon dates from a series of cores were used to document the development of an irregularly-flooded brackish marsh in upper Jarrett Bay, North Carolina. Jarrett Bay lies in a drowned incised channel, and is a tidal tributary of Core Sound. Unidirectional landward migration and marsh surface aggradation at pace with rising sea-level characterized the developmental history of the marsh. Rising sea-level initiated tidal wetland development directly over upland soils in upper Jarrett Bay. A basal peat 2.72 m below the extant marsh surface was radiocarbon dated to 5,710 ± 142 years B.P., yielding a long-term average sea-level rise rate of 0.48 mm/yr. Peat moisture and ash content isopleths defined three peat strata: a subaerial stratum of about 1 m thickness with a gradual increase in mineral content proceeding upward; a middle organic-rich stratum of about 1 m thickness; and a lowermost stratum below about 2 m depth with a gradual decrease in mineral content proceeding upward. Moisture content isopleths in all three strata generally dip seaward. Alterations in hydrodynamics accompanying the evolution of Core Sound presumably induced formation of the three peat strata. Vegetative remains and δ13C biogeochemical signatures indicate that Juncus roemerianus has dominated the extant marshes since their inception. Drowned peat overlain by estuarine mud was recovered in Jarrett Bay; bayside erosion accompanying sea-level rise converted these former wetlands to subtidal habitat.