Holocene record of precipitation seasonality from lake calcite δ 18 O in the central Rocky Mountains, United States
A context for recent hydroclimatic extremes and variability is provided by a ∼10 k.y. sediment carbonate oxygen isotope (δ 18 O) record at 5–100 yr resolution from Bison Lake, 3255 m above sea level, in northwestern Colorado (United States). Winter precipitation is the primary water source for the alpine headwater lake in the Upper Colorado River Basin and lake water δ 18 O measurements reflect seasonal variations in precipitation δ 18 O. Holocene lake water δ 18 O variations are inferred from endogenic sedimentary calcite δ 18 O based on comparisons 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 δ 18 O values, and vice-versa. Early to middle Holocene δ 18 O values are higher, implying a rain-dominated seasonal precipitation balance. Lower, more variable δ 18 O values after ca. 3500 yr ago indicate a snow-dominated but more seasonally variable precipitation balance. The middle to late Holocene δ 18 O record corresponds with records of El Niño Southern Oscillation intensification that supports a teleconnection between Rocky Mountain climate and North Pacific sea-surface temperatures at decade to century time scales.