INVESTIGATING THE UTILITY OF ISOTOPE PROXIES FOR SEA-LEVEL VARIABILITY IN THE SOUTH ATLANTIC OCEAN

High-resolution records of relative sea level are severely lacking in the Southern Hemisphere. This project investigates the potential for a multi-proxy approach to sea-level reconstruction at two salt-marsh sites in central Argentina. Salt marshes can be depositional environments, accumulating centuries to millennia of sediment making them exceptional archives of past sea-level proxies. The dominant component of salt marsh sediments is primarily derived from autochthonous vascular vegetation generally delineated into strict tidal-inundation-based elevation zones. Due to the differing degrees of isotopic fractionation imparted by plants in each zone, δ¹³C values or organic tissues and sediments often vary across zones. Similarly, spatial variation in marsh surface water δ¹⁸O values can exist due to changes in the relative contribution of seawater (saline) vs. meteoric (fresh) waters and potentially recorded in the shells of calcareous plankton such as foraminifera.

Isotopic signatures of both bulk sediment and calcareous foraminifera will be analyzed using a set of modern shore-perpendicular sampling transects to develop a proxy dataset and test the sensitivity of these proxies to variation in tidal inundation. Fossil samples will be analyzed from four cores to assess the temporal application of the proxy to reconstruct past sea level. Isotopic analyses of calcareous foraminifera found in salt marshes and their utility as a relative sea-level proxy has never previously been investigated and represents a potentially novel methodology for sea-level reconstruction. Furthermore, this project contributes to an ongoing investigation of the mechanisms driving ice sheet changes on centennial and millennial timescales from a global sampling network, focusing on the contributions of the Greenland Ice Sheet (GIS) and Western Antarctic Ice Sheet (WAIS) to sea-level variability and ultimately developing a latitudinal gradient of sea level along the Atlantic coast. The proposed research has the potential to promote pioneer advancements in sea-level reconstruction techniques on a regional and global scale.