New Terrestrial Temperature and Precipitation Reconstructions Spanning the Last 135 Kyrs from Natural Trap Cave, Wyoming

The scarcity of long-term terrestrial paleoclimate archives (103 to 105 years), especially from the Rocky Mountain region of the Western USA, poses great challenges to our understanding of continental climate change since the last interglacial period (i.e., the Eemian). In western North America, caves and rock shelters can serve as excellent repositories of environmental information for the late-Quaternary. Natural Trap Cave is a 23 m deep sinkhole located at the foot of the Big Horn Mountains (Wyoming) containing a wealth of fossils preserved in the cave sediments that span over the last ~135 kyrs. Deposited over time from surface soil erosion, the cave sediments provide a unique opportunity to generate continuous paleoclimate records in the continental U.S. since the prior interglacial period. An ~5-meter-thick section within the primary excavation pit of the cave was sampled at 1-cm intervals and archived for palynological and geochemical analysis. Pollen and bulk isotopic records from this section showed floristic shifts in the dominant pollen types (grasses, sagebrush, pines) that were associated with changes in aridity and season of precipitation through the late Pleistocene and Holocene, providing a strong foundation for further work using biomarkers and other, more sensitive environmental proxies.

Here, we expand on these environmental records by using brGDGT and leaf-wax δ2H records to reconstruct temperature and precipitation regimes in northern Wyoming over the past ~135 kyrs. Our results show that Eemian summers were warmer and wetter compared to the Holocene, and that temperatures have decreased steadily until the Last Glacial Maximum. The early-Holocene was marked by wet winters accompanied by hot and dry summers followed by declining summer temperatures and precipitation rates towards present. Our results on the Eemian-Holocene temperature and precipitation comparisons are in good agreement with other paleoclimate-based results as well as with model simulations for the region.