Theses and Dissertations - Department of Geological Sciences

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Browsing Theses and Dissertations - Department of Geological Sciences by Subject "Archaeology"

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    δ15n in mollusk shells as a potential paleoenvironmental proxy for nitrogen loading in chesapeake bay
    (University of Alabama Libraries, 2014) Black, Heather Dawn; Andrus, C. Fred T.; University of Alabama Tuscaloosa
    Crassostrea virginica is one of the most common oyster species in North America and is frequently found in archaeological sites and sub-fossil deposits, especially in the eastern US. Although there have been several sclerochronological studies on δ13C and δ18O in the shells of this species, little is known about δ15N stored within the shells, which could potentially be a useful paleoenvironmental proxy to determine nitrogen loading and the subsequent anthropogenic impacts within an area. In order to potentially serve as paleoenvironmental proxies for N loading, bivalve shells' organic matter needs to remain chemically unaltered. Since ancient peoples cooked most archaeological shells before depositing them in shell middens, it is necessary to determine if prehistoric cooking methods alter either %N or δ15N stored within the shells. Twenty C. virginica oysters and twenty-two Mercenaria spp. clams were treated to five different prehistoric cooking methods: direct exposure to hardwood coals, roasting above hardwood coals, roasting in a dry oven, boiling in freshwater, or boiling in seawater. Each shell was bisected through the resilifer with one half treated with one of the five prehistoric cooking methods and the remaining half serving as a control. With the exception of roasting above the hardwood coals, prehistoric cooking methods do not significantly alter either %N or δ15N within the shells. Those shells roasted above the coals were typically enriched in both %N and δ15N , which is likely an effect of smoke coming from the hardwood coals and infiltrating pore spaces within the outer layers of the shell. Ninety archaeological C. virginica shells ranging in age from ~120 to 3,400 years old and thirty-two modern C. virginica shells were collected in Chesapeake Bay at the Smithsonian Environmental Research Center in Edgewater, Maryland. One valve from each shell was sub-sampled and the calcite powder was analyzed (without acidification pretreatment) using an EA-IRMS system equipped with a CO2 trap to determine the %N and δ15N content of the shells. Comparison of %N and δ15N in C. virginica shells from the six different time periods studied show relatively constant values from ~3,400 years ago to 1820 AD. Between 1820 and 1890, there are rapid increases in both %N and δ15N in the shells, which continue to exponentially increase in value to the modern shells. The increases in %N and δ15N are correlated with increased anthropogenic impact due to human population, sewage discharge, and urbanization in Chesapeake Bay at this time. Therefore, it is likely that C. virginica shells can be used as a paleoenvironmental proxy to measure the anthropogenic impact of a specific area over time. However, the constant, relatively low %N and δ15N values from ~3,400 years ago to 1820 AD compared to the increased N concentrations and enriched δ15N shells from the modern periods could be influenced by diagenetic alteration of the shell after burial in the midden. It is possible that the shells are losing N and preferentially losing 15N over time. More research is necessary to determine if bivalve shells are geochemically stable with regard to N over time or if diagenesis is likely to have occurred in these shells.
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    Clams and climate: implications for measuring seasonality in the marine bivalve, saxidomus gigantea
    (University of Alabama Libraries, 2016) Bassett, Christine Nicole; Andrus, C. Fred T.; University of Alabama Tuscaloosa
    Sclerochronological and sclerochemical analysis of shellfish remains from archaeological sites afford the opportunity to understand environmental change and its impacts on human populations through time. During the Late Holocene in the Gulf of Alaska, the paleoenvironmental record reflects fluctuating marine conditions throughout the region. The effects of changes in regional climate patterns, as well as human responses to such change, however, can exhibit great variability locally. In the Kodiak archipelago in the Gulf of Alaska, changing environmental conditions, population growth, technological transitions, and contact with other communities likely promoted the transition from needs based maritime hunting and gathering to surplus-based, semi-permanent villages. The precise role of climate in this transition is understudied. Few paleoclimate reconstructions are available for the Kodiak archipelago and while climate reconstructions for the Gulf of Alaska are not uncommon, regional climate reconstructions are often insufficient for archaeological research. Many climate reconstructions lack sub-annual resolution and cannot produce a detailed understanding of seasonal behaviors in human populations. Sclerochronological and sclerochemical analysis of shellfish remains from archaeological sites in the archipelago may provide additional paleoenvironmental information. Measuring and comparing the length of seasonal shell growth in select species of bivalves may complement stable oxygen isotope analysis, together providing a more precise paleoclimate reconstruction. This research utilizes the growth of Saxidomus gigantea, abundant both on modern and ancient coastlines to provide information about the length of its growing seasons. To measure seasonality, a total of 25 modern samples were collected from Alaska and British Columbia and the number of circalunidian growth lines were counted between annual winter growth lines confirmed by oxygen isotope analysis. Clams collected from Alaska grew a total of 143±34 days while the Canadian clams grew 273±14 days. Additionally, oxygen isotope values were more positive from annual winter growth lines from Alaskan samples than Canadian samples. This method was then applied to three archaeological samples collected from the Rice Ridge site (KOD-363), the Uyak site (KOD-145), and the Settlement Point site (AFG-105), which grew an average of 166±22, to confirm that these methods can be applied to archaeological samples through time to detect spatial and temporal changes in seasonality. These results suggest that changes in sea surface conditions and seasonality are detectable both spatially and temporally through detailed sclerochronological and sclerochemical analysis of shellfish remains from archaeological sites and offer the potential to reconstruct marine environmental conditions throughout the Holocene.
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    δ¹⁵N as a potential proxy for anthropogenic nitrogen loading in Charleston harbor, South Carolina
    (University of Alabama Libraries, 2016) Payne, Taylor Norris; Andrus, C. Fred T.; University of Alabama Tuscaloosa
    Bivalve shell geochemistry can serve as a useful indicator of changes in coastal environments. There is increasing interest in developing paleoenvironmental proxies from mollusk shell organic components. Numerous studies have focused on how the δ15N obtained from bivalve tissues and shells can be used to trace present-day wastewater input into estuaries. However, comparatively little attention has been paid to tracing the impact of anthropogenic nitrogen loading into estuaries over time. By measuring historic levels of δ15N in the organic fraction of oyster shells (Crassostrea virginica) from archaeological sites around Charleston Harbor and comparing those levels to the δ15N content of modern shells, it is possible to assess how nitrogen has fluctuated historically in the area. Whole-shell samples from the Woodland Period (~1400-800 BP), 18th, 19th, and 20th centuries, and modern controls were measured for %N and δ15N. δ15N was found to not vary significantly with time. The highest δ15N values came from shells dated to the mid and late 19th century. Mean modern δ15N (8.6‰) were found to be similar to mean Woodland Period δ15N (8.5‰). This is in contrast to studies done by Black (2014), but similar to a study done by Darrow et al. (2016). This information could help understand how large-scale anthropogenic nitrogen loading has affected coastal ecosystems over time and guide future remediation. Furthermore, this project will help refine and improve this novel proxy of past environmental conditions.