Analyzing saltmarsh organic carbon to reconstruct Late Holocene sea level in coastal North Carolina

Nina Shmorhun
Advisor: Don Barber, BMC Geology and Environmental Studies

As sea level rises on temperate coasts, salt marshes deposit layers of peat that can record various paleo-environmental conditions including temperatures, precipitation and the rate of sea level rise. Thick and continuous peat deposits represent a dynamic equilibrium among the rates of sea level rise, organic matter production and fine-grained sediment supply. Analyses of the organic matter and mineral sediment content of peat core samples provide us with an accurate method for reconstructing the varying rates of sea level rise through time. In the past century, salt marshes situated along the US East Coast have responded to the accelerating sea level rise, and analyses of older, deeper saltmarsh peat deposits allow the recent acceleration to be placed in a longer context. In order to extend and refine the record of sea level fluctuations over the last 4,000 years (i.e. the Late Holocene), fieldwork and lab work is being conducted. The fieldwork involves collecting new cores from salt marshes in Core Sound (Oyster Creek and Jarrett Bay) and southern Pamlico Sound (Sand Hill Point, West Bay) and surveying the elevations of marsh surfaces at the core sites. The lab work involves analyses of organic carbon concentrations in the newly obtained cores, as well as in previously collected cores from Croatan Sound. The concentration of organic carbon in peat is determined using the loss-on-ignition method. Samples from near the base of the marsh peat will be submitted for radiocarbon dating to provide age control. The new data from our saltmarsh peat cores will be combined with other researchers’ results to extend the high-resolution sea level curve for coastal North Carolina. The scientific importance of this work is the improvement of future sea-level rise predictions by generating data that can be used to work out the relationship between Late Holocene temperature and sea level. These results also allow us to gain a better understanding of how salt marshes grow as sea level rises. This information is essential to coastal managers so that they can come up with wetland or terrestrial restoration plans to allow salt marshes to continue to exist at the coast.