Meteoric 10Be in lake sediment cores as a measure of climatic and erosional change
Jensen, Rachel Elizabeth
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Developing tools that trace Earth-surface processes is necessary to quantify the complex controls on geomorphological, geochemical, and climate records. This thesis explores the potential of one such tool, meteoric 10 Be. The delivery of meteoric 10 Be to the surface varies with precipitation and its adsorption to sediment has proven useful in studies of erosion. These characteristics indicate that meteoric 10 Be in lake sediments varies under changing climate and changing sediment influx, making it a potential recorder of past climate and landscape processes. To examine the controls on meteoric 10 Be concentrations in lake sediments, we develop a model that predicts concentrations of 10 Be in lake sediments as a function of atmospheric flux, sedimentation rate, and terrigenous input. The model was applied to two published datasets of 10 Be profiles in lake sediments from different settings to assess the sensitivity of individual controls on 10 Be concentration. Results show that while a variety of environmental conditions influence 10 Be in lake sediments, these can be quantified with surprisingly simple parameters. Assessment of the relative importance of model parameters requires the comparison of 10 Be concentrations in well-dated lake cores to independent paleoenvironmental proxies. We further validate this model and explore the application of meteoric 10 Be in lake archives, by exploring a new system, Blacktail Pond in Northern Yellowstone, for which a wealth of paleoenvironmental data exists. We present new meteoric 10 Be data in the core, and compare to model predictions based on sedimentation rates of both autochthous and allocthonous sediments and changes in the flux of meteoric 10 Be with precipitation. Surprisingly, patterns of measured 10 Be concentrations in Blacktail Pond sediments show little relationship to predicted concentrations, despite being of similar magnitude. Based on this analysis, we suggest that small lake systems may be most problematic for 10 Be analyses as they are most sensitive to changing 10 Be concentrations relative to changes in model parameters. This work provides a new quantitative framework to assess the control of sedimentation rates, inputs of allocthonous sediments, and hydroclimate in determining the 10 Be concentrations measured in lake sediments, and highlights the potential and limitations of meteoric 10 Be in quantifying past environmental changes.