A HOLOCENE RECORD OF PRECIPITATION SEASONALITY FROM BISON LAKE CALCITE-δ18O IN THE CENTRAL ROCKY MOUNTAINS, U.S.A

Context for recent hydroclimatic extremes and variability is provided by a ~10,000 year sediment-carbonate oxygen isotope (δ¹⁸O) record at 5 to 150-yr resolution from Bison Lake, 3255 m a.s.l., northwest Colorado. Bison Lake is located near the summit of the White River Plateau limestone massif (39.764˚N, 107.346˚W, 3255 m asl), and is a headwater of the White River and Deep Creek, both tributaries of the Upper Colorado River. Winter precipitation is the primary water source for the alpine headwater lake. The oxygen and hydrogen isotope ratios of modern lake-water, streams, springs, and snow within the region indicate that lake-water δ¹⁸O values reflect seasonal variations in precipitation δ¹⁸O. Holocene lake-water δ¹⁸O variations are inferred from measurements of endogenic sedimentary-calcite δ¹⁸O that are compared with historic watershed discharge records and tree-ring reconstructions. Drought periods (i.e. drier winters and/or a more rain-dominated seasonal precipitation balance) generally correspond with higher calcite- δ¹⁸O values, and vice versa. Early-to-middle Holocene δ¹⁸O values are higher, implying a rain-dominated seasonal precipitation balance. Lower, more variable δ¹⁸O values after ~3500 Cal BP indicate a snow-dominated but more seasonally variable precipitation balance. The mid-to-late Holocene δ¹⁸O record corresponds with records of ENSO intensification that supports a teleconnection between Rocky Mountain climate and North Pacific sea surface temperatures at decade to century time scales.