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Master of Science (M.S.)
Year Degree Awarded
Month Degree Awarded
Multiple proxy analysis of lake sediment records are crucial for understanding changes in environmental and climate conditions over historical and geological time. Most recently, the use of biomarker proxies coupled with sedimentological investigations provides a new approach for gaining insight into the lake processes that capture information about past climate change. This approach is applied here to better understand the paleoclimate record from Lake El’gygytgyn in Western Beringia. Multiple organic geochemical compound concentrations were measure as proxies for both aquatic and terrestrial biological productivity. Measurements of n-alkane (plant leaf waxes) as well as concentrations of the compounds arborinol (marker for trees), dinosterol (dinoflagellates), and long chain (C28 – C32) 1,15 n-alkyl diols (eustigmatophyte algae) demonstrate warming conditions around Lake El’gygytgyn during MIS 9 and MIS 11, especially when compared to diatom production and palynological investigations from Melles et al. (2012). These time periods illustrate the presence of extensive forest cover as well as elevated concentrations of all aquatic biomarkers analyzed, corroborating their “super interglacial” designation. Analysis of branched glycerol dialkyl glycerol tetraethers, a relatively new proxy used to estimate mean annual temperatures and soil pH, was applied also suggesting warming conditions during MIS 9 and MIS 11, although further calibration techniques are needed to accurately estimate temperature changes.
Sedimentological results include the analysis of bulk mineralogy, clay mineralogy, iron oxide, and color measurements for the same MIS 8 through MIS 12 interval. The hue color parameter, measured from high resolution core scans, suggests a link to global climate records, with green sediments reflective of cold intervals and red sediments indicative of warmer climate conditions. Validation of the color record was done in part by analyzing the clay mineralogy and the abundances of clay minerals. These data show that clay deposition dominates interglacial periods. Moreover the clay polytypes can be linked to bedrock weathering. Bulk mineralogy measurements allow for the reconstruction of synthetic color spectra which link mineralogy to sediment color. Overprinted on the mineralogical color signal is red color staining from iron oxide minerals, formed within the catchment during wet intervals when increasing amounts of eroded Fe – bearing silicate minerals are available for oxidation. If true, interpretation of the hue record then suggests hue is a proxy for wet/dry conditions within the lake, and when paired with the biomarker analysis shows significant warmer and wetter conditions during MIS 9 and 11. However, the hue record also demonstrates notable variability outside of these two interglacial periods, not recognized by other proxies, are not currently well understood. Overall, the multi-proxy results from this work can be further applied to the longer temporal scale of the Lake El’gygytgyn sediment core, and potentially elucidate climate changes deeper into the Pleistocene, and even into the Pliocene portions of the sediment record.
Isla S. Castañeda