Lake oxygen isotopes as recorders of North American Rocky Mountain hydroclimate: Holocene patterns and variability at multi-decadal to millennial time scales

Lake sediment oxygen isotope records (calcium carbonate-delta O-18) in the western North American Cordillera developed during the past decade provide substantial evidence of Pacific ocean-atmosphere forcing of hydroclimatic variability during the Holocene. Here we present an overview of 18 lake sediment delta O-18 records along with a new compilation of lake water delta O-18 and delta H-2 that are used to characterize lake sediment sensitivity to precipitation delta O-18 in contrast to fractionation by evaporation. Of the 18 records, 14 have substantial sensitivity to evaporation. Two records reflect precipitation-delta O-18 since the middle Holocene, Jellybean and Bison Lakes, and are geographically positioned in the northern and southern regions of the study area. Their comparative analysis indicates a sequence of time-varying north-south precipitation-delta O-18 patterns that is evidence for a highly non-stationary influence by Pacific ocean-atmosphere processes on the hydroclimate of western North America. These observations are discussed within the context of previous research on North Pacific precipitation-delta O-18 based on empirical and modeling methods. The Jellybean and Bison Lake records indicate that a prominent precipitation-delta O-18 dipole (enriched-north and depleted-south) was sustained between-3.5 and 1.5 ka, which contrasts with earlier Holocene patterns, and appears to indicate the onset of a dominant tropical control on North Pacific ocean-atmosphere dynamics. This remains the state of the system today. Higher frequency reversals of the north-south precipitation-delta O-18 dipole between-2.5 and 1.5 ka, and during the Medieval Climate Anomaly and the Little Ice Age, also suggest more varieties of Pacific ocean-atmosphere modes than a single Pacific Decadal Oscillation (PDO) type analogue. Results indicate that further investigation of precipitation-delta O-18 patterns on short (observational) and long (Holocene) time scales is needed to improve our understanding of the processes that drive regional precipitation-delta O-18 responses to Pacific ocean-atmosphere variability, which in turn, will lead to a better understanding of internal Pacific ocean-atmosphere variability and its response to external climate forcing mechanisms. Published by Elsevier B.V.