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  1. Abstract

    The timing and mechanisms of past hydroclimate change in northeast Mexico are poorly constrained, limiting our ability to evaluate climate model performance. To address this, we present a multiproxy speleothem record of past hydroclimate variability spanning 62.5 to 5.1 ka from Tamaulipas, Mexico. Here we show a strong influence of Atlantic and Pacific sea surface temperatures on orbital and millennial scale precipitation changes in the region. Multiple proxies show no clear response to insolation forcing, but strong evidence for dry conditions during Heinrich Stadials. While these trends are consistent with other records from across Mesoamerica and the Caribbean, the relative importance of thermodynamic and dynamic controls in driving this response is debated. An isotope-enabled climate model shows that cool Atlantic SSTs and stronger easterlies drive a strong inter-basin sea surface temperature gradient and a southward shift in moisture convergence, causing drying in this region.

     
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  2. Cave carbonate minerals are an important terrestrial paleoclimate archive. A few studies have explored the potential for applying carbonate clumped isotope thermometry to speleothems as a tool for constraining past temperatures. To date, most papers utilizing this method have focused on mass-47 clumped isotope values (Δ47) at a single location and reported that cave carbonate minerals rarely achieve isotopic equilibrium, with kinetic isotope effects (KIEs) attributed to CO2 degassing. More recently, studies have shown that mass-47 and mass-48 CO2 from acid digested carbonate minerals (Δ47 and Δ48) can be used together to assess equilibrium and probe KIEs. Here, we examined 44 natural and synthetic modern cave carbonate mineral samples from 13 localities with varying environmental conditions (ventilation, water level, pCO2, temperature) for (dis)equilibrium using Δ47-Δ48 values, in concert with traditional stable carbon (δ13C) and oxygen (δ18O) isotope ratios. Data showed that 19 of 44 samples exhibited Δ47-Δ48 values indistinguishable from isotopic equilibrium, and 18 (95 %) of these samples yield Δ47-predicted temperatures within error of measured modern temperatures. Conversely, 25 samples exhibited isotopic disequilibria, 13 of which yield erroneous temperature estimates. Within some speleothemsamples, we find Δ47-Δ48 values consistent with CO2 degassing effects, however, the majority of sampleswith KIEs are consistent with other processes being dominant. We hypothesize that these values reflect isotopicbuffering effects on clumped isotopes that can be considerable and cannot be overlooked. Using a Raleigh Distillation Model, we examined carbon and oxygen isotope exchange trajectories and their relationships with dual clumped isotope disequilibria. Carbon isotope exchange is associated with depletion of both Δ47 and Δ48 relative to equilibrium, while oxygen isotope exchange is associated with enrichment of both Δ47 and Δ48 relative to equilibrium. Cave rafts collected from proximate locations in Mexico exhibit the largest averagedepartures from equilibrium (ΔΔ47 = − 0.032 ± 0.007, ΔΔ48 = − 0.104 ± 0.035, where ΔΔi is the measured value – the equilibrium value). This study shows how the Δ47-Δ48 dual carbonate clumped isotope framework can be applied to a variety of tcave carbonate mineral samples, enabling identification of isotopic equilibria and therefore quantitative application of clumped isotope thermometry for paleoclimate reconstruction, or alternatively, constraining the mechanisms of kinetic effects. 
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    Free, publicly-accessible full text available February 1, 2025
  3. This archived Paleoclimatology Study is available from the NOAA National Centers for Environmental Information (NCEI), under the World Data Service (WDS) for Paleoclimatology. The associated NCEI study type is Cave. The data include parameters of speleothems with a geographic location of Mexico. The time period coverage is from 62500 to 5858 in calendar years before present (BP). See metadata information for parameter and study location details. Please cite this study when using the data. 
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  4. This archived Paleoclimatology Study is available from the NOAA National Centers for Environmental Information (NCEI), under the World Data Service (WDS) for Paleoclimatology. The associated NCEI study type is Cave. The data include parameters of speleothems with a geographic location of Mexico. The time period coverage is from 1117 to -67 in calendar years before present (BP). See metadata information for parameter and study location details. Please cite this study when using the data. 
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