A 20,000 year flowstone record of Gulf of Mexico sourced moisture in Texas



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Understanding how future atmospheric warming may affect moisture distribution in the American Southwest is becoming increasingly important. To this end, various paleoclimatic proxies have been used to investigate the range of climatic fluctuations forced by natural processes during past periods of warming. As part of this effort, speleothem-based oxygen isotope records have been used to hypothesize the contribution of either Gulf of Mexico (GoM) or Pacific Ocean sourced moisture since the Last Glacial Maximum (LGM) at cave sites across the Southwest. In this study, a new oxygen isotope time series is developed from a flowstone in central Texas as a means to test this hypothesis. Due to significant age reversals in the U-series chronology, multiple age models were created that use a series of assumptions to exclude questionable age determinations. By comparing these age models, portions of the flowstone that are most likely to produce robust chronologies were identified. The rate, timing, and amplitude of oxygen isotope shifts in all of the age models are consistent with the only other Texas speleothem and one of the few GoM sediment cores that cover the same time period and have an oxygen isotope record. These results support the hypothesis that central Texas had a dominant GoM moisture source since the LGM and that speleothems in the region might record this signal. Furthermore, this study developed a novel workflow that could be applied to other flowstone samples, which would allow for greater spatial coverage of speleothem-based paleoclimate reconstructions when high-quality stalagmite samples are not available.