Development of a rare earth element paleoproxy Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/zp38wg96z

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  • This thesis describes the development of a rare earth element (REE) proxy for paleoceanographic studies of climate change. This work was done in three stages with the goal: (1) To develop a cleaning method that overcomes the problems of REE readsorption; (2) To measure pore water REEs for evaluation of diagenesis, and for comparison to benthic foraminiferal REE:Ca; and (3) To evaluate the REE:Ca of cleaned planktonic and benthic foraminifera as a potential paleoproxy. In developing a novel flow-through method for cleaning foraminiferal calcite for the REE:Ca paleoproxy measurements, it was found that REE contamination is primarily due to a "refractory" phase and not Mn-oxides. Moreover, these contaminants can be removed and primary foraminiferal calcite isolated, although this calcite is shown to be more heterogeneous than previously thought. The first analyses of marine pore water REE concentrations shown here, illuminate several new features of REE biogeochemistry. The flux of REE from marginal sediments is similar to riverine input fluxes, suggesting the residence time of REEs is far less than currently thought. Furthermore, these data indicate that marine REEs are dominantly controlled by dissolved and particulate organic carbon and iron oxides. This is reflected in both the concentration and pattern of REEs measured in pore water. Finally, contrary to some prior conclusions, Ce was found to be only indirectly associated to the oxygen content of water. A REE biogeochemical model is presented which accounts for water column and pore water REE distributions. Finally, the REE:Ca measured in planktonic foraminifera are shown to be a proxy for water mass and potentially for surface ocean biologic activity. Benthic foraminifera REE:Ca are also found to be a proxy for carbon flux to the sea floor. In both cases, these REE proxies are negated if the sediments have undergone intense diagenesis, although, if this has occurred, it is obvious from the REEs measured.
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