Fundamental processes affecting aquatic rare earth element chemistry; new experimental and empirical observations towards a proxy for anthropogenic change

Lawrence, Michael Glen (2007). Fundamental processes affecting aquatic rare earth element chemistry; new experimental and empirical observations towards a proxy for anthropogenic change PhD Thesis, School of Physical Sciences, University of Queensland.

       
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Author Lawrence, Michael Glen
Thesis Title Fundamental processes affecting aquatic rare earth element chemistry; new experimental and empirical observations towards a proxy for anthropogenic change
School, Centre or Institute School of Physical Sciences
Institution University of Queensland
Publication date 2007
Thesis type PhD Thesis
Supervisor Prof Ken Collerson
Total pages 1 v.
Language eng
Subjects 260000 Earth Sciences
Abstract/Summary Previous research has indicated that coral can be used as an in situ biogeochemical archive of palaeoclimatic and paleaoenvironmental change. The rare earth elements have been used in geologic and groundwater studies as provenance indicators, and recent observations suggest that their concentrations in coral may show a secular change. It has further been proposed that the change in coral rare earth element concentration over time is indicative of anthropogenic change. In this thesis, I examine the use of the rare earth elements and yttrium (REY), with a view towards further establishing the REY as a widely accepted proxy for change in the near-shore ocean environment. The thesis takes a fundamental approach to that goal. I first develop methods for the analysis of the REY in fresh and saline water. Then I apply these methods to the understanding of REY behaviour in freshwater catchments and through the estuary. In the course of these experiments, I discovered that the REY do indeed show provincial behaviour in freshwater, and that aspects of the REY pattern can be altered due to anthropogenic change in the environment. I also discovered further aspects of REY chemistry that had, hitherto, not been explicitly stated. These include the pseudo conservative behaviour (relative to the other REY) of europium and gadolinium during estuarine mixing and the correlation of the cerium anomaly with reduced iron, signalling the importance of pore water to the overall biogeochemical budget of the coastal ocean. These experimental observations lead to the conclusion that from theoretical prediction at least, the REY may indeed be suitable tools for investigating palaeoclimatic or palaeoenvironmental change (anthropogenic or otherwise) in coral (and other proxies) that were subject to such change. Only after establishing this framework did I attempt to analyse a coral core, from which temporal variability of the REY content was investigated. Prior to trace element analysis, the coral core chronology was established, and the core examined for diagenetic alteration. The coral core was then analysed by laser ablation ICP-MS. I compare the baseline and flood event REY patterns and concentration throughout the core, especially in the pre- and post-European periods (pre- and post-1860). However, despite flood events and baseline REY incorporation resulting in distinct REY patterns, there is no evidence to suggest a secular change in either the concentration of the REY or a shift in the shape of the REY pattern (for either the flood events or the baseline winter incorporation) that could indicate an alteration of the REY supply to the location of this coral core. This contrasts with recent results from coral under the influence of the Burdekin River discharge, suggesting that inland agricultural activity (largely grazing) apparently has a more detrimental effect on coastal water quality than crop agriculture along the shore. My research has demonstrated that aspects of REY chemistry may indeed provide useful proxies for anthropogenic or environmental change. Especially the cerium, europium and gadolinium anomalies and in some cases Y/Ho fractionation may eventually become useful features to investigate. However, while the analytical protocol developed for this study was able to obtain in situ REY data for a coral, I was unable, in the coastal coral selected for this study, to discover any evidence for secular change. Further studies are required along the entire North Queensland shore to carefully map out the areas that are most threatened by deteriorating water quality.
Keyword Yttrium
Rare earth metals
Chemical oceanography
Water chemistry
Marine sediments
Additional Notes Variant title : Aquatic rare earth element chemistry

 
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Created: Fri, 21 Nov 2008, 16:25:37 EST