Collaborative Research: Deglacial and Holocene Environmental Change in California's Headwaters: Insights from High-Resolution Sedimentary Records from Mono Lake

Overview We propose to develop precisely dated geochemical and biological proxy records from newly recovered Mono Lake sediment cores, in order to reconstruct deglacial and Holocene climate change in the Eastern Sierra Nevada (California). The proxy records will be interpreted in the framework of absolute changes in lake level from shoreline facies and geomorphic features, to construct continuous records of changes in lake chemistry, biological productivity, physical limnology, and terrestrial environmental change. The chronology of the sediment cores will be a significant focus, applying 40Ar/39Ar on tephras and radiocarbon dating of macrofossils and pollen sorted by flow cytometry. Climate is expected to be the major driver of paleoenvironmental changes in our records, driven on long timescales by the termination of the last glacial period and the rise and fall of northern hemisphere summer insolation. Intrabasin volcanic processes may be a secondary driver, especially of changes in nutrient levels and biological productivity. Intellectual Merit Well-dated lake sediment cores provide one of the few terrestrial archives available to extend the record of climate change in the West into the Holocene and terminal Pleistocene. Mono Lake is located on the eastern side of the Sierra Nevada of California, and is highly sensitive to changes in the amount of precipitation falling in the Sierra Nevada, the most important water source for much of California. Interpretation of the proposed geochemical and biological proxy records from lake cores within the framework of the lake-level curves will provide continuous records of lake level and productivity that are tied to absolute lake levels. A sub-centennial-precision age model for the records will allow accurate correlation of terrestrial climate conditions in the West to global records for the first time. This will allow us to shed light on the climate mechanisms controlling Western climate between the waning of the great continental ice sheets and the droughts and pluvials of the last 2000 years, which have been examined in detail in tree-ring records. Broader Impacts The work proposed here lays important groundwork for future long-core drilling at Mono Lake, which holds promise for transforming our understanding of regional and global terrestrial change over the last million years, including the volcanic and tectonic history, as well as climatic change. The pollen dating method described builds on pilot projects supervised by Zimmerman in her role as terrestrial age model expert at CAMS, and is the first systematic application of flow cytometry to terrestrial paleoclimate reconstructions we know of, within the framework of an independent chronology. Demonstration of the technique has the potential to encourage the production of lacustrine records of Western paleoclimate with the age resolution of U-series dated speleothem records, which are rare in the western US. The proposed work is also highly complementary to on-going work of Zimmerman on Sierra Nevada alpine glaciation. The project provides support for two early career female scientists (Zimmerman and Ivory), a Masters student (Hodelka) and undergraduates at UK and Brown. This is the initiation of the first domestic project for McGlue, facilitating incorporation of the research into undergraduate classes and fieldtrips, including a biannual course in glacial and Quaternary geology that will use the eastern Sierras for a paleolimnological field exercise. In addition, McGlue is co-PI on a new NSF-IUSE GEOPATHS proposal (Award # 1600399), which endeavors to expose the students from the UK-STEAM Academy (high schoolers from under-represented groups) to the geosciences through short internships, and funds have been requested to support development STEAM internship exercises centered around the Mono Lake Basin.