Masters Thesis

Paleontological, geochemical, and geophysical climate proxies in Late Pleistocene lacustrine sediments from Summer Lake, Oregon, western Great Basin

Paleontological, geochemical, and geophysical data from pluvial Summer Lake, Oregon, western Great Basin are the basis for a high resolution paleoclimate record during a time interval (38-34 ka) including the Mono Lake Excursion, Dansgaard-Oeschger interstadials #8-6, and the end of Heinrich Event 4. The proxies consist of grain-size, Corg/N ratio, ostracode faunal counts, and palynology and build on previously-published proxies based on environmental magnetism. Results from granulometry and geochemical analysis and the presence of the ostracode Cytherissa lacustris consistently demonstrate the correspondence of low lake conditions and colder water temperatures during Dansgaard-Oeschger stadials, one of which also includes the Mono Lake Excursion found both in the lake and ice core records. Palynological variability seen from Atriplex, Rosaceae, high spine and low spine Asteraceae concentrations, and pollen ratios of Juniperus/Dip Pinus and (Rosaceae+Atriplex+Poaceae+Hi Spine+Low Spine Asteraceae)/(Pinus+Picea+Tsuga mertensiana+Sarcobatus) suggest warmer/wetter semi-arid woodland conditions during interstadials 8 and 7 and colder/drier continental montane woodland conditions during stadial periods. These results confirm those of earlier studies at Summer Lake and other Great Basin lakes in western North America with respect to the relationship between millennial-scale temperature changes throughout the northern hemisphere and the response of regional climate in western North America at semitropical latitudes. That is, millennial-scale interstadials are associated with warmer, wetter climates in the Great Basin and vice-versa.

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