TERRESTRIAL ECOSYSTEM RESPONSE TO ABRUPT CLIMATE CHANGES DURING THE PLEISTOCENE-HOLOCENE TRANSITION AT MONO LAKE, CALIFORNIA, USA

Over recent decades, California has experienced major drought and wildfires forced by increased Pacific sea surface temperatures reorganizing ocean-atmosphere interactions over the North Pacific. This in turn threatens terrestrial ecological communities and water resources of California residents. The last major reorganization of precipitation regimes and terrestrial ecosystems in western North America occurred during the Pleistocene – Holocene transition. However, the timing, structure, and forcing of these changes in the central Sierra Nevada and Great Basin are poorly known. We present a well-dated record of pollen, microcharcoal, and the dung fungus Sporormiella from Mono Lake, California to understand the terrestrial ecological response to climate change as vegetation communities developed during the last deglaciation (16 – 9 ka). The pollen record indicates that abrupt climate events inaugurated the transition to new vegetation assemblages as widespread, intense wildfires often heralded the replacement of new zonal vegetation groups. The largest-magnitude turnover in vegetation composition occurred after a period of intense fires during the Younger Dryas-Holocene transition as Juniperus and other arboreal taxa, Artemisia, and the enigmatic Sequoiadendron were replaced by characteristic arid taxa (Sarcobatus, Amaranthaceae, and Ephedra). In conjunction with climate, herbivory by now-extinct megafauna shaped vegetation communities around Mono Lake by keeping Poaceae abundance low until their abrupt decline at 14.8 ka during the warming from Heinrich Stadial 1 to the Bølling Oscillation before final extinction at 11.3 ka, the beginning of early Holocene aridity in the Sierra Nevada. Precipitation during the Bølling–Allerød was marked possibly by increased summer precipitation before aridification occurred during the second half of the Younger Dryas and early Holocene. Comparison with regional proxy records and modern climatology suggest that these moisture changes were associated with the relative strength of the Aleutian low and latitude of the North Pacific High which forced terrestrial ecological change in the eastern Sierra Nevada.