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Presenter: Jerard William Roche

Faculty Sponsor: Jonathan Woodruff

School: UMass Amherst

Research Area: Geology and Earth Sciences

Session: Poster Session 4, 2:15 PM - 3:00 PM, 163, C1

ABSTRACT

Salt marshes are vertically zonated ecosystems in which tidal elevation dictates sediment and vegetation distribution across the marsh platform. As marshes grow, environmental markers are preserved in the marsh’s sediments and peat, allowing for the reconstruction of paleoelevation and past relative sea-level (RSL) change. While the use of microfossils is the most well-established proxy, this study evaluates the potential use of elemental geochemistry and physical sediment properties to serve as additional proxies for paleo-elevation reconstruction through the establishment of a modern analog. To examine these relationships, surface samples and their elevations were collected at the Cousins River Salt Marsh in Freeport, Maine. Each sample was analyzed for organic content using loss on ignition, bulk density, and X-ray fluorescence to determine its elemental composition. Statistical analysis was performed using Partitioning Around Medoids (PAM) clustering in R-Studio to group samples based on their properties and elevation on the marsh, with an Adjusted Rand Index (ARI) used to evaluate how well these clusters matched known tidal elevation zones. Analyses revealed that bromine and organic content were positively correlated, with higher elevation zones containing increasingly greater concentrations. In contrast, silicon and bulk density were positively correlated with each other, but exhibited increasingly higher concentrations at lower elevations. These correlations indicate that elemental geochemistry and physical sediment properties can reflect tidal inundation gradients across the Cousins River Salt Marsh, establishing a modern relationship that can be used in future studies to infer paleo-elevation and RSL change from marsh sediment cores at this site.