LATE HOLOCENE INITIATION AND DEVELOPMENT OF SALTMARSH PEAT DEPOSITS IN CORE SOUND AND SOUTHERN PAMLICO SOUND, NORTH CAROLINA, USA

Peat accumulation allows coastal saltmarshes to persist in place as sea level rises, yet continuous peat build-up requires a dynamic equilibrium among rates of sea level rise, organic matter production, and mineral sediment supply. This interplay of ecogeomorphic processes has produced a range of coastal marsh responses to the changing environmental conditions associated with human activities over the last few centuries, making the relative influence of each process difficult to discern.

Here we examine down-core properties of saltmarsh peat deposited prior to significant human alteration of the adjacent landscape, and we discuss the peat sequences in the context of a high-resolution sea level reconstruction for North Carolina (Kemp et al., 2011, PNAS). We obtained multiple cores from each of four sites in eastern Carteret County: West Bay and North Bay in southern Pamlico Sound, and Oyster Creek and Smyrna Creek in Core Sound. At all four sites Juncus roemarianus dominates both the surface vegetation and the underlying peat material, the tidal range is less than 0.5 m, and salinities range from 5 to 28 ppt. Any differences in suspended sediment among the sites likely result from their proximity to the open waters of Core and Pamlico Sounds; while the North Bay and Smyrna Creek marshes are more sheltered, the West Bay and Oyster Creek sites are more exposed. Dry bulk density (BD) and organic matter content (OM) were analyzed at 2 cm intervals in cores obtained using a Russian peat sampler. Analyses were made by oven-drying volume specific samples and measuring mass loss-on-ignition after 4 hours at 550°C.

Preliminary findings show upward transitions from basal sediment (BD ≥ 0.79±0.06 g/cm3; OM ≤ 10.1±1.7%) into saltmarsh peat (BD = 0.37±0.18 g/cm3; OM = 33.2±17.9%) at depths of 1.3-1.6m below MSL in many cores from the study area. The spatial pattern of this transition seems to indicate extensive lateral marsh expansion as local relative sea level rise accelerated from 0.9mm/year up to 1.5mm/year, from ca. 850 to 1100 AD at onset of the Medieval Climate Anomaly. Further analyses and dates aim to evaluate peat accumulation patterns associated with other minor changes in sea level rise prior to the more rapid and complex environmental changes of the last few hundred years.