Hydroclimate Variability in the Southwestern US Since the Last Interglacial: Insights From Cave Paleodata and Process Studies

Abstract:

Cave records from the Southwestern US reveal a rich history of hydroclimate variability. In southeastern Arizona, we have developed a set of isotopic reconstructions of paleoclimate that include high-resolution records from several key intervals spanning the last glacial cycle (129 kyr BP to present). From monitoring studies in several caves, we infer that a significant control on the oxygen isotope content of dripwater is the balance between summer and winter precipitation. This balance varies among caves, and the response time is different between drips within caves. Speleothem records from both the Holocene (4 overlapping datasets) and the last interglacial (2 non-overlapping) show relatively high oxygen isotope values that most likely reflect a stronger monsoon directly forced by high summer insolation. This inference is consistent with other paleoclimate datasets and with forced model simulations of past intervals. We also observe elevated oxygen isotope values that approach Holocene levels around 14 and 52 kyr BP, which can only partly be linked to insolation forcing but are consistent with some other datasets. All records show substantial decade-century scale variability exceeding that of the past century; this variability can partially be correlated among late Holocene records. We show that caves with seasonally different infiltration rates may yield very different isotopic histories, because of the lack of correlation between summer and winter rainfall amounts. Finally, we find that carbon isotope records are highly variable, but poorly correlated even among samples from the same cave, and that growth rates do not seem to vary with moisture. Taken together, these records show an interplay among seasonally specific forcings over interannual-millennial time scales on Southwestern hydroclimate.