North American Rocky Mountain Hydroclimate: Holocene patterns and variability at multi-decadal to millennial time scales

Abstract:

A network of western North American lake sediment isotope records (calcium carbonate-δ¹⁸O) developed during the past decade provides substantial evidence of Pacific ocean-atmosphere forcing of precipitation variability during the Holocene. We present an overview of the eighteen lake carbonate-δ¹⁸O records located in the North American Rocky Mountains with a new compilation of modern lake water isotope measurements to characterize their sensitivity to variations in precipitation-δ¹⁸O and fractionation effects by evaporation. Comparative analysis of the carbonate-δ¹⁸O records that reflect precipitation isotope (δ¹⁸O) values (i.e., precipitation “isometers”) indicates a sequence of time-varying in-phase and antiphase patterns between northern and southern regions during the Holocene that provide evidence for a highly non-stationary influence of Pacific ocean-atmosphere processes on the hydroclimate of western North America. We identify a prominent precipitation-δ¹⁸O dipole, which was sustained for ~2000 years between ~3.5 and 1.5 ka. The dipole contrasts with divergent earlier Holocene patterns and appears to indicate the onset of linkages between northern and tropical Pacific ocean-atmosphere dynamics as we know them today. These observations are informed by previous research on North Pacific precipitation-δ¹⁸O. Further investigation of short (observational) and long (Holocene) time scale patterns are needed to improve our understanding of the processes that 1) drive regional precipitation-δ¹⁸O responses to Pacific Ocean-atmosphere variability, and 2) cause varying internal ocean-atmosphere responses to external climate forcing.