Date of Award
Master of Science in Biological and Environmental Sciences (MSBES)
To investigate spatial and temporal variability of relative sea-level (RSL) changes in southern New England, USA, we reconstructed ~3,300 years of RSL change in lower Narragansett Bay, Rhode Island. We applied a regional-scale, foraminiferal-based Bayesian transfer function to foraminiferal assemblages contained within a ~3.4 m salt-marsh peat sequence recovered at Fox Hill Marsh. To develop the chronology, we obtained 30 accelerator mass spectrometry (AMS) radiocarbon dates from plant macrofossils and identified historical chronological markers of known age using 137Cs, heavy metals, and lead isotope ratios. We combined our geologic reconstruction with local tide gauge measurements from Newport, Rhode Island (1931–2016 CE) and used an Errors-in-Variables Integrated Gaussian Process (EIV-IGP) model to estimate past rates and positions of RSL. Our reconstruction shows RSL rose from –3.9 m at ~1250 BCE reaching 0 m at present (2014 CE) and identifies multiple oscillations of accelerating and decelerating RSL superimposed on this overall rising trend. Sea-level change was also evaluated by removing a linear glacial isostatic adjustment (GIA) contribution of 0.9 mm/yr from our record that we then compared against other detrended sea-level reconstructions in the region to identify climate-driven sea-level trends. This analysis demonstrates that sea level deviated multiple times from stability during the ~3,300-year record, and included oscillations that have been identified at other sites as due to the Medieval Climate Anomaly and Little Ice Age. Further, sea-level was rising at 2.74±0.79 mm/yr in 2014 CE, the fastest century-scale trend in the ~3,300-year record. Apart from the onset of modern rates of rise, the timing of the departures from stability varies from other southern New England and mid-Atlantic records in Connecticut and New York, respectively, with additional oscillations identified in Rhode Island that are not present in the Connecticut record. After considering multiple physical and RSL methodological explanations, we conclude that this may be due to the increased density of radiocarbon dates in our chronology or the resolution of paleomarsh elevation (PME) estimates compared to other RSL reconstructions in the region.
Stearns, Rachel B., "A High-Resolution Reconstruction of Late-Holocene Relative Sea Level in Rhode Island, USA" (2017). Open Access Master's Theses. Paper 1057.