Pollen analysis of a late-glacial and Holocene sediment core from Mono Lake, Mono County, California

Pollen analysis of a 752-cm core from Mono Lake, Mono County, California indicates generally high lake levels 11,600-7000 C-14 yr B.P., moderate lake levels until ca. 4000 C-14 yl. B.P., and fluctuating levels to the present. Drying events, with lake levels near or below the historic minimum are dated ca. 8800, 4000, 2400, and 1100 C-14 yr B.P. Chronologic control is provided by six radiocarbon dates and six volcanic ashes. The rate of upland vegetation change is greatest 11,000, 4000, and 1130 C-14 Yr B.P, Juniperus and Sequoaidendron pollen declines 11,000 yr B.P., marking the transition from late-glacial-juniper woodland to Holocene steppe. High values (5-20%) of Sequoaidendron pollen are unique to this study and may indicate the presence of these trees east of the Sierra crest. The pollen-based reconstructions of climate are generally cooler and wetter than today, with relatively dry but cool climate during the early Holocene. The contrast between higher lake levels and more arid vegetation during the early Holocene can be explained by insolation-driven seasonality. Greater summer insolation produced summer drought, but lower winter insolation led to greater snowpack, greater spring runoff, and higher lake levels. Increased Artemisia and other Compositae pollen percentages mark the establishment of modern vegetation ca. 2000 C-14 yr B.P. During the late Holocene, the pollen-based reconstructions of climate generally match the Mono Lake fluctuations proposed by Stine (1990), but fewer fluctuations are recorded. (C) 1999 University of Washington.