Testing tree-ring cellulose δ 18 O with water isotopes for Holocene lake δ 18 O interpretations in the central Rocky Mountains USA

Abstract

Stable isotopes of water preserved in geologic archives, primarily as oxygen (δ¹⁸O), have proven critical for documenting Earth’s climatic and hydrologic systems past and present. However, timescale differences of water isotope inputs to proxy systems and the signal embedded in long paleorecords often confound translation to observed hydroclimatic metrics. Here, a unique 20-year dataset of meteorology, hydrology, and the isotopic composition of weekly meteoric and surface water samples (δ¹⁸O, δ²H) are combined with paleoclimate δ¹⁸O data from tree-ring cellulose and lake carbonate to better understand proxy signals of Upper Colorado river basin drought. Annual tree-ring cellulose δ¹⁸O from Picea engelmannii growing within a glacier-fed creek and a spring discharge area were used to derive annual source water δ¹⁸O using a cellulose source-water isotope model. Comparisons with the monitoring record indicates that tree-ring cellulose δ¹⁸O tracks variations in wet and dry hydroclimatic extremes. Source water isotopes are shown to reflect the hydroclimate of the current year and some number of previous years as an effective moisture-discharge proxy rather than a precipitation isotope proxy. Results contextualize Holocene lake carbonate δ¹⁸O data. The contemporary-to-paleo comparison identifies changes in seasonal precipitation extremes during recent millennia and several earlier arid and monsoon-dominated Holocene periods that exceed the arid maximum of the calibration period.