The hydroclimate and environmental response to middle Miocene warming in the southwestern U.S.A.: Stable isotope evidence

Predictions for the southwestern US with warming often suggest increased aridity. We investigate the sedimentary record of the Miocene Climate Optimum and Transition (MCO and MCT; ~17-14 Ma) in northern New Mexico to understand the impact of warmer global temperatures and higher pCO2 on southwestern hydroclimate. The MCO and MCT comprised a globally warmer period with elevated pCO2 similar to end-of-the-century (~400-800 ppm) projections. We present new stable isotope (δ18O and δ13C) records of vadose-zone and groundwater terrestrial carbonates and of modern precipitation, stream, and groundwater from the Española basin in northern New Mexico and establish a high-resolution age model using new 40Ar/39Ar ages. We interpret δ18O as reflecting the balance between summertime monsoonal and wintertime precipitation and δ13C as a reflection of plant productivity. Terrestrial carbonate δ18O is lowest during the MCO and MCT and is correlated with terrestrial carbonate δ13C and anti-correlated wi..., , # Data from: The hydroclimate and environmental response to middle Miocene warming in the southwestern U.S.A.: Stable isotope evidence

Dataset DOI: [10.5061/dryad.kh18932k0](10.5061/dryad.kh18932k0)

## Description of the data and file structure

We collected sedimentary samples of authigenic carbonates from the Santa Fe Group of the Rio Grande Rift to measure for stable isotopes of oxygen and carbon. We also collected tephra layers to isolate sanidine grains for Ar-Ar analysis as well as for tephrochronology. Lastly, we collected precipitation, shallow groundwater, and stream water samples for analysis of oxygen and hydrogen isotopes.

### Files and variables

#### File: S1\_Dataset\_Isotope\_data.xlsx

**Description:** Stable isotope data for all samples included in this study. Dataset includes carbonate d18O and d13C (reported relative to VPDB), stratigraphic height, calculated age, sample type, and geologic section and member.

##### Variables

* Sample ID
* Composite stratigraphic...,