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Abstract The El Niño Southern Oscillation and Pacific Decadal Oscillation (PDO) are key drivers of cool‐season precipitation variability in the western United States (US), including the Rocky Mountains. Together, they help modulate the north‐south “precipitation dipole,” a regional climate pattern operating on multi‐decadal timescales leading to dry conditions north of 40°N latitude when the south is wet, and vice versa. We investigate the natural evolution of this climate pattern using two precisely‐dated (5900 years ago to present), multi‐proxy, coeval stalagmite records of hydroclimate from Titan Cave, Wyoming, located just north of the modern‐day dipole transition zone. Consistent trace element and stable isotope records from the two stalagmites reflect the amount and seasonality of regional precipitation, documenting decreased winter snowfall and dry conditions over multi‐decadal intervals characterized by the warm phase of the PDO and more frequent and stronger El Niño events. 

Abstract Freshwater lakes are vital water resources, especially in the context of a changing climate. Supplementing existing hydrological methods to monitor lake levels may greatly improve resource management, particularly in drought‐prone regions. In this study, we performed dual‐isotope (δ¹⁸O and δ²H) calculations to model the hydrological balance of Bear Lake, Utah‐Idaho. The lake is a critical water resource and site for paleoclimate studies of the latest Pleistocene. Using the Craig‐Gordon isotopic mass balance model, we simultaneously constrained unknown fluxes, including groundwater discharge and particularly evaporation, which is typically under‐constrained due to inconsistencies across existing methods. Data from community databases and sampling campaigns in 2022 and 2023 were utilized to derive an evaporation rate of 2.18 × 10⁸ m³/yr (±4.94 × 10⁶ m³/yr, 1σ using δ¹⁸O; ±3.47 × 10⁶ m³/yr, 1σ using δ²H) at a calculated relative humidity of 0.62 above the lake. Detailed analysis of the sensitivity of the model revealed that parameters related to atmospheric moisture, particularly humidity and its isotopic composition, significantly influence evaporation estimates. Using carbonate‐based isotope data, we leveraged this sensitivity to provide insights in the evaporation and humidity at Bear Lake during different time periods. This study shows the potential of using modern water isotopic composition to aid with interpreting carbonate‐based paleoclimate data sets and informing current and future water resource management practices. 

Abstract During the mid‐Holocene (MH: ∼6,000 years Before Present) and Last Interglacial LIG (LIG: ∼129,000–116,000 years Before Present) differences in the seasonal and latitudinal distribution of insolation drove Northern Hemisphere high‐latitude warming comparable to that projected for the end of the 21st century in low emissions scenarios. Paleoclimate proxy records point to distinct but regionally variable hydroclimatic changes during these past warm intervals. However, model simulations have generally disagreed on North American regional moisture patterns during the MH and LIG. To investigate how closely the latest generation of models associated with the Paleoclimate Model Intercomparison Project (PMIP4) reproduces proxy‐inferred moisture patterns during recent warm periods, we compare hydroclimate output from 17 PMIP4 models with newly updated compilations of moisture‐sensitive North American proxy records during the MH and LIG. Agreement is lower for the MH, with models producing wet anomalies across the western United States (US) where most proxies indicate increased aridity relative to the preindustrial period. The models that agree most closely with the LIG proxy compilation display relative wetness in the eastern US and Alaska, and dryness in the northwest and central US. An assessment of atmospheric dynamics using an ensemble of the three LIG simulations that best agree with the proxies suggests that weaker winter North Pacific pressure gradients and steeper summer North Pacific and Atlantic gradients drive LIG precipitation patterns. Our updated compilations and proxy‐model comparisons offer a tool for benchmarking climate models and their performance in simulating climate states that are warmer than present.