Late Quaternary vegetation history of the southern Owens Valley region, Inyo County, California

摘要

This study analyzes the pollen, spores, and algae in the upper 90 m section of a mostly continuous, well dated, 323 m core (OL-92) from Owens Lake, southeastern California. The entire core has produced a paleoclimatic record for the past ∼800 ka. The 90 m interval dates from ∼9 ka to ∼151 ka beginning with the penultimate glaciation and ending during the termination of the last glaciation. The record shows high amplitude fluctuations in the abundances of pine, juniper, saltbush, sagebrush, chenopods/amaranths, and Ambrosia-type pollen. High percentages of juniper pollen with low percentages of desertscrub pollen during the intervals ∼150 ka to ∼120 ka and 73 ka to ∼20 ka alternate with low juniper pollen and relatively high percentages of desertscrub and oak pollen during the intervals ∼118 ka to ∼103 ka and ∼18 ka ∼10 ka and into the Holocene. Sagebrush pollen varies with juniper pollen but has a tendency to lead it in time. Pine and fir pollen tends to vary inversely with juniper over the long term. These trends are interpreted as vegetation change in response to glacial-interglacial cycles: During cold-wet glacial climates there was a downslope expansion of juniper woodland and sagebrush scrub, contraction of Sierra Nevada mixed conifer forest, and displacement of warm desertscrub, suggesting average temperature and precipitation departures from modern values ranging from -2°C to -6°C and from +100 mm to +350 mm. Conversely under warmer and drier interglacials warm desert shrubs expanded their range in the lowlands, juniper and sagebrush retreated upslope, and the Sierran forests expanded. Estimated average temperature and precipitation departures from modern values ranged from -0.5°C to +3.7°C and +13 to -26 mm. Comparison of the pollen spectra spanning the penultimate and ultimate glacial maxima shows the former to have been longer and more intense, in accord with the Sierra Nevada glacial record. Similarly, the higher abundances of Ambrosia pollen during the last interglaciation, compared to the Holocene, indicate warmer temperatures in the former. The presence of high oak percentages also during the last interglaciation suggest an expansion of the summer monsoon. Finally, the match of the juniper curve with the marine oxygen isotope chronostratigraphy suggests a link between vegetation change in the southern Owens Valley and global climate.