Monday, January 25, 2010, 12:00PM - 1:00PM
U.S. Geological Survey and INSTAAR Affiliate
Full title: "Upper Colorado snowpack variations during the last 10,000 years: a decade-to-century reconstruction from lake-carbonate d18O."
Seasonal snowpack is the primary source of the Upper Colorado River, a watershed that provides critical water resources to 7 states. Management of this resource has relied on ~50-years of instrumental measurements that reflect a relatively limited range of climatic variability. Presented here are two ~10,000-year oxygen isotope (d18O) records from the sedimentary carbonate of alpine lakes (>3000 m a.s.l.) in northwest Colorado. The two continuous d18O-stratigraphies have unprecedented decade-to-century scale temporal resolution compared with previous paleoclimatic records from this region and provide important new detail for better understanding recent hydroclimatic extremes and range of variability. Bison Lake, 3255 m a.s.l., has lake-water d18O sensitivity to variations in inflow which is annually dominated by snowpack depth. Nearby Yellow Lake, 3140 m a.s.l., has lake-water d18O sensitivity to summer evaporation which is closely linked to summer temperatures. The sedimentary d18O data record past lake-water d18O and indicate that during the early to middle Holocene there was a considerably reduced snowpack, warmer/drier summers, and possibly a more 18O-enriched moisture source to the region, a likely reflection of the influence of seasonal solar insolation trends on regional synoptic climate patterns. After ~3500 Cal yr BP, a series of abrupt negative excursions in Bison-d18O indicate amplified seasonality and unprecedented increases in snowpack depth that correspond with the increasing influence of ENSO on western North America. Similar patterns continue through the last millennia, when Bison-d18O indicate sustained maximum snowpack corresponding with variable and/or intensified ENSO, which culminate during the late 19th century. The influence of natural external and internal climate forcing mechanisms evident in these new Holocene records emphasizes that climate model based future projections of Upper Colorado water availability include an accurate ability to simulate the tropical Pacific’s response to anthropogenic climate forcing.