HOLOCENE CLIMATE CHANGE RECORDED IN A ROCKY MOUNTAIN SPELEOTHEM: ASSESSING SHIFTING DROUGHT DYNAMICS IN THE WESTERN US FROM 5.7 KA TO PRESENT

Tree ring records show cool-season droughts in the western US have been characterized by three spatial patterns over the past 500 years. These patterns are “western-wide drought”, “wet north/dry south”, and “dry north/wet south”, and each has been shown to persist on timescales of decades to centuries. Evidence suggests that the occurrence of these three varieties of drought is driven by internal climate variability with secondary influence by sea surface temperatures. However very few high-resolution records of western US precipitation extend beyond the tree ring record (~1400 CE), limiting the timeframe in which these patterns of natural climate variability can be reconstructed. Here we use speleothem trace element and stable isotope data to construct a Holocene paleoclimate record for Titan Cave (TC), northern Wyoming, extending the hydroclimate record of the northern Rockies and providing the opportunity to assess longer-term natural climate variability in this region. The TC-7 speleothem grew over the past ~3.1 ka. The proxies exhibit strong correlations with several coeval climate records, including regional snowpack as recorded by tree rings, suggesting the speleothem records winter precipitation patterns in the northern Rockies. Decreased snowpack and dry conditions at TC correlate to warmer sea surface temperatures in the Gulf of Alaska and the positive phase of the Pacific Decadal Oscillation. Comparison of speleothem 𝛿¹⁸O with the 𝛿¹⁸O of Bison Lake sediments from central Colorado suggests all three patterns of western US drought have persisted during intervals of the late Holocene. Specifically, the north/south wet/dry winter precipitation dipole in the Rocky Mountains was established by at least 3.1 ka, and multiple, centuries-long “western-wide” droughts occurred throughout the record, most notably from 2.2 – 2 ka during the Roman Warm Period. A second TC stalagmite that grew from ~5.7 ka to ~1965 CE will be used to replicate and extend the TC-7 record. Additional dating indicates that several TC stalagmites grew during the mid-Holocene and Last Interglacial and thus can provide records of winter precipitation variability in the northern Rockies during those past warm intervals.