Date of Award
Campus Access Dissertation
Doctor of Philosophy (PhD)
Environmental Sciences/Environmental, Earth & Ocean Sciences
The study of the paleoclimate of the Gulf of Maine (GOM) is of particular importance to help limit the potential impacts of human-induced climate change. Marine mollusk shell mineralogy and inorganic elemental and isotopic composition reflect specific physical characteristics of the environment in which the mollusk lives (e.g., temperature and salinity). This multiple monograph dissertation includes three research chapters, in which I explore the paleoclimate of the GOM during the recent Holocene (past 5000 years) using archaeological (dead-collected) mollusk shells at shell middens sites at Turner Farm, Maine and Nantucket Island, Massachusetts.
The overarching goal of this work is to provide a deeper understanding of the recent Holocene GOM climate by investigating the relationship between bivalve shell growth and environmental conditions using paleoenvironmental proxies. I examined growth rate and used trace element-based paleoenvironmental proxies at four occupation periods at the Turner Farm site in Maine. I conducted an aquaculture-based experiment using three species of bivalve native to the GOM to examine the relationship between shell and water stable isotopic composition as a proxy for seawater temperature. Finally, I reconstructed sea surface temperature (SST) using stable isotopic data at my study sites to evaluate spatial and temporal trends of historic temperature conditions in the GOM.
From this work, I determined that: (1) At the Turner Farm site (Maine), growth rate and Mg/Ca and Sr/Ca ratios indicate a strong temperature control on shell growth during the Medieval Warm Period; (2) interactions between temperature and salinity influenced δ18O composition of experimentally reared M. arenaria, M. mercenaria, and C. virginica rendering the data ineffective for use in developing species-specific paleothermometers; (3) Gulf of Maine SST results, reconstructed from δ18O of archaeological shell material, correspond to known historic climatic events, such as the Medieval Warm Period and Little Ice Age; and (4) these findings, in total, verify local and regional temporal differences and their influence on growth rate, and stable isotopic as well as elemental composition of midden shells; supporting the use of geochemical paleoenvironmental proxies in combination with archaeological data to successfully reconstruct the climate history of the GOM over the last 5000 years.
Johnston, Amy Elizabeth, "Paleoclimate Reconstruction of the Gulf of Maine During the Recent Holocene (Past 5000 Years) Using Archaeological Mollusk Shells" (2020). Graduate Doctoral Dissertations. 563.