An Integrated Multi-Isotope and Element Distribution Study of the Irish Biosphere
Citation:
RYAN, SASKIA, An Integrated Multi-Isotope and Element Distribution Study of the Irish Biosphere, Trinity College Dublin.School of Natural Sciences.GEOLOGY, 2017Download Item:
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Abstract:
Geochemical variation in major and trace element concentrations and multiple isotope systems (87Sr/86Sr, δ18O, δ2H, δ13C, δ15N) are explored within the Irish biosphere. This is done through the analysis of an array of environmental sample media, including vegetation, tree cores, soils, streamwaters and archaeological human remains. This integrated and comprehensive approach informs on spatial and temporal geochemical changes in the biosphere and demonstrates how local and regional characteristic values can be used as a proxy for element provenance and geographical discrimination.
87Sr/86Sr are employed by a wide range of science-based disciplines including geology, environmental science, archaeology and forensic science for multiple applications including geochronology, element cycling, geochemical fingerprinting and tracing the mobility of pre-historic humans and animals. For archaeological provenance studies, there are a number of potential limitations associated with the use of 87Sr/86Sr as a tracer, including possible contributions from multiple geochemical reservoirs, a lack of environmental reference baseline data and a general gap in understanding how different geochemical proxies may complement 87Sr/86Sr data. These challenges are examined by this research using case studies from selected sites in Ireland.
This thesis has revealed the following new insights: (1) The 87Sr/86Sr of vegetation progressively diverges from a marine 87Sr/86Sr value with increasing distance from the coast along coastal transects. (2) Geochemical topsoil datasets (including Na, Ca and Mg cation concentrations) further demonstrate a high marine element-contribution along the western coastal perimeter of Ireland and in areas covered by blanket peat. (3) Surface waters exhibit clear binary mixing between atmospheric and minerogenic end-members. (4) Tree core records illustrate a small but marked change in 87Sr/86Sr values in the mid-20th century, taken to reflect the introduction and intensive use of modern fertiliers. (5) Statistically, soil-parent materials derived from both bedrock and Quaternary sediments can control the 87Sr/86Sr distribution within the environment. (6) Rare earth elements (REE) in the plant-soil-streamwater interface demonstrate complex fractionations between media. (7) Isotope biosphere variations in Ireland can be successfully applied to answer questions relating to past human subsistence and mobility.
The implications of this research are that local biologically-available 87Sr/86Sr ranges should not be inferred from geological proxies in areas proximal to the coast and regions subject to high levels of precipitation or from intensively farmed land. It is also shown that the ability to use isotopic variation to study past human provenance is greatly improved by using combined isotope systems (87Sr/86Sr, δ18O, δ2H, δ13C, δ15N).
Sponsor
Grant Number
Trinity Postgraduate Studentship
Fulbright GSI Geoscience Scholarship
Author's Homepage:
http://people.tcd.ie/ryans22Description:
APPROVED
Author: RYAN, SASKIA
Advisor:
Crowley, QuentinPublisher:
Trinity College Dublin. School of Natural Sciences. Discipline of GeologyType of material:
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