Masters Thesis

Study of Summer Lake, OR BB3-I core via biogeochemical molecular and isotopic analysis for Paleoclimate Reconstruction

The purpose of this study is to test models of millennial-scale climate response to hemispheric-scale drivers during the late Pleistocene in northwestern North America. Towards this end, a 12.5-10.5 mbgs section of the BB3-I core, spanning 38-35 ka in age and taken from Summer Lake Basin, Oregon, USA, was investigated using lipid molecular stratigraphy and compound specific carbon isotope analysis. Previous climate proxy studies on this core segment, including those based on Corg/N, ostracode taxonomy, palynology, and environmental magnetism, divided the core segment into four intervals of alternating warmer/wetter and cooler/drier climate corresponding to Dansgaard-Oeschger (D-O) Interstadials #8 and #7 and the successive stadials. Carbon isotope ratios ranged from -24.5 to -42.4 ‰ indicating that as expected, all plants represented by the leaf waxes followed the C3 photosynthetic pathway. ACL25-33 (Average Chain Length) and CPI23-35 (Carbon Preference Index) values in the sediment samples associated with the D-O interstadials were higher (30.31 -29.61) than the ACL values for the stadials, particularly the one that followed IS#7, indicating the dominance of terrestrial-sourced vegetation during interstadials and aquatic vegetation during stadials. Similarly, Paq values were lower during interstadials and vice-versa indicating an increased terrestrial component of organic matter rather than organics of strictly lacustrine origin. Furthermore, a preference for terrestrial origin in interstadial samples was found in the odd carbon-numbered, long-chain n-alkanes with the younger stadial sample identified to be exclusively aquatic/lacustrine. These results support the teleconnection hypothesis of climate response to late Pleistocene millennial-scale climate change in the North American Great Basin wherein warmer temperatures in the North Atlantic drive wetter, warmer Great Basin climates and vice-versa.

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