Abby Letts
Dr. Don Barber
Geology Department

The effect of volcanic eruptions on carbon burial rates in salt marshes

Saltmarshes sequester large quantities of carbon due to the anaerobic conditions in coastal wetland soils. Deep saltmarsh peat layers can also provide proxy records of past environmental conditions at the coast. This summer research project investigates how and why carbon accumulation/burial rates have varied over the last two thousand years in the saltmarshes of eastern North America. I am analyzing the carbon concentration and stable carbon isotopic composition in salt marsh organic matter from cores in North Carolina, Delaware, and Massachusetts. Preliminary studies of cores from the study area suggest correspondence between volcanic eruptions and a subsequent drop in organic carbon content. My analyses target these intervals of known climate variations. The analyses will test hypotheses regarding the climate mechanisms by which large explosive volcanic eruptions induce the observed marsh responses; e.g., reduced organic matter preservation due to increased decomposition and/or reduced belowground plant growth.

Differential decomposition of belowground biomass fragments will be analyzed at sites with varying salinities, elevations and and plant communities (e.g., Juncus, Spartina alterniflora or S. patens). Marsh vegetation comprises multiple organic fractions with different carbon isotope ratios. Measurements of these ratios will help determine whether changes in organic material production or preservation are associated with the drop in organic carbon content. The organic carbon content and carbon isotopic composition of the marsh peat will be compared across different time intervals and also among different coastal regions. Along with the carbon analyses described above, the studied marsh cores will be analyses for C/N ratio, bulk density and loss-on-ignition. Lastly selected samples will be submitted for radiocarbon dating in order to strengthen the core chronology.  Overall, the project aims to elucidate how effective saltmarshes are carbon sinks, and why carbon burial rates vary in response to short-lived climate perturbations.