Lake sediment oxygen isotope records (calcium carbonate-δ18O) 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 δ18O records along with a new compilation of lake water δ18O and δ2H that are used to characterize lake sediment sensitivity to precipitation-δ18O in contrast to fractionation by evaporation. Of the 18 records, 14 have substantial sensitivity to evaporation. Two records reflect precipitation-δ18O 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-δ18O 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-δ18O based on empirical and modeling methods. The Jellybean and Bison Lake records indicate that a prominent precipitation-δ18O dipole (enriched-north and depleted-south) was sustained between ~3.5 and 1.5ka, 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-δ18O dipole between ~2.5 and 1.5ka, 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-δ18O patterns on short (observational) and long (Holocene) time scales is needed to improve our understanding of the processes that drive regional precipitation-δ18O 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.
Bibliographical noteFunding Information:
The U.S. Geological Survey (USGS) Climate and Land Use Change Research and Development supported this research by Anderson and Barron. The National Science Foundation provided support for Berkelhammer ( AGS 1502776 ), Steinman and Abbott ( EAR 090220 ) and Finney ( ARC 0909310 , AGS 040206 ). We appreciate assistance by Paco VanSistine and Jeremy Havens with GIS and figures, Dan Engstrom for radiometric dating interpretations, Shad O'Neel, Eric Klein and Jeff Welker for sharing the 2014 Wolverine snow pit data, David Fisher for sharing the Mount Logan data, Alisa Mast for sharing lake water isotope data from the Flat Tops Wilderness of Colorado, and Nathan Stansell for assistance with lake water collections. We thank Matthew Jones, Natalie Kehrwald and an anonymous reviewer for constructive and helpful comments that greatly improved the manuscript. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
- Climate forcing
- Lake water isotopes
- Western North America