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Show J. Piatt Bradbury and R. M. Forester U. S. Geological Survey, Box 25046 MS 980, Federal Center, Denver, Colorado 80225 A DIATOM AND OSTRACODE RECORD OF CLIMATE AND HYDROLOGY FOR THE PAST 200 KY FROM OWENS LAKE, CALIFORNIA Diatoms and ostracodes from lake sediments beneath Owens Lake playa, Inyo County, California, ( 36.5° N. x 118° W. elev. 1080 m) document a nearly continuous high- resolution paleolimnological record of climate and hydrologic change for the past 200 ky based on a chronology established by radiocarbon dates, tephrochronology, and paleomagnetic excursions. The Owens River, originating in the Sierra Nevada, feeds the Owens Lake basin. With sufficient precipitation and runoff, Owens Lake overflows and becomes fresh. During dry climates, alkaline groundwater from springs issuing along graben faults dominates the hydrochemistry of the basin to produce shallow saline lakes and marshes. Freshwater planktic diatoms ( especially species of Stephanodiscus), north temperate or boreal ostracodes ( Cytherissa lacustris), plagioclase feldspar- rich sediments with high magnetic susceptibility, and Juniperus- lype pollen characterized glacial climates 175- 120 ka at Owens Lake. Alpine glaciers descended from the Sierra Nevada crest to the Owens Valley floor during this time and the lake was surrounded by a juniper forest. Saline diatoms ( Campylodiscus clypeus) and ostracodes ( Limnocythere sappaensis) dominated in the interglacial period after 120 ka, but there were several episodes between 100 ka and 50 ka with abundant freshwater diatoms that represented interstadial climatic conditions. Particularly wet, but non- glacial conditions occurred between 70 ka and 65 ka that may correlate to oxygen isotope stage ( OIS) 4. Between 50 ka and 25 ka, saline diatoms and ostracodes declined and warm- season Aulacoseira species indicate episodes of significant summer precipitation in the hydrologic balance of Owens Lake prior to the last glacial maximum. By 25 ka, glacial environments were again characterized by abundant Juniperus, plagioclase feldspar, Stephanodiscus, and cold- water ostracodes. Generally arid Holocene climates were recorded in Owens Lake by short- term fluctuations of saline and freshwater diatoms, desiccation, and oolitic sediments barren of diatoms. Comparison of diatom- based paleolimnological records from Owens Lake ( 36.5° N) and Tule Lake ( 42° N) in California shows antithetical lacustrine changes for the past 180 ky. At Tule Lake, the penultimate glacial episode, OIS 6, was dominated by species of Fragilaria indicating marsh conditions and a relatively dry, cold climate. Owens Lake, on the other hand, was characterized by Stephanodiscus species of open, fresh- water lake environments that imply increased precipitation in the Sierra Nevada watershed to the west. During OIS 5, Owens Lake had shallow water, saline diatoms whereas Tule Lake was dominated by Aulacoseira indicating warm, open, fresh- water conditions. OIS 2 limno- climatic conditions at Owens Lake were similar to those of the penultimate glaciation. In contrast, at Tule Lake glacial climates produced fluctuating marsh and open water habitats under cold, seasonally variable climates. The Holocene at Owens Lake was generally so dry that diatoms were only poorly preserved. At Tule Lake, however, Aulacoseira again became dominant with Fragilaria indicating an interplay of local marsh and open water environments. The antithetical nature of the Tule and Owens Lake paleolimnological records may relate to the N- S- N displacement of westerly storm tracks as glacial and interglacial climates alternate. |
