LAKE SEDIMENT RECORDS OF LATE HOLOCENE DROUGHT FROM NORTHERN WASHINGTON

The goal of this project is to document regional climate history from lake sediment cores using sedimentological, geochemical and stable isotope studies. This presentation focuses on the sediments covering the last 1,000 years from Lime Lake, a small (<1km2), shallow (15m deep), and hydrologically-open system. We used authigenic CaCO3 precipitated annually during summer whiting events for oxygen and carbon stable isotope studies. These whiting events form mm-scale laminations below ~7m water depth where anoxic conditions prevail year-round. These finely laminated sediments are dated using tephrochronology and radiocarbon measurements on terrestrial macrofossils and charcoal. Surface water stable isotope measurements indicate that the lake is insensitive to evaporation today. The small, well defined catchment is isolated from regional groundwater so the main drivers of oxygen isotopes down core are likely some combination of changes in source water, temperature, and the seasonality of precipitation.