DOI: 10.5061/dryad.kh18932k0
title: Data from: The hydroclimate and environmental response to middle Miocene warming in the southwestern U.S.A.: Stable isotope evidence

description: 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 with
 the benthic δ18O record. We interpret these data as recording an overall
 winter-wet climate during the MCO and MCT, but that precipitation
 seasonality varied in response to changes in global climate during this
 period. The further correlation with carbonate δ13C suggests that plant
 productivity was driven by the amount of wintertime precipitation.
 Comparison with middle Miocene climate model simulations reveals that
 higher CO2 drives a shift towards wintertime precipitation. Though
 paleogeographic changes may obscure a direct comparison to modern warming,
 overall, our findings suggest that prolonged global warmth may be
 associated with increased wintertime precipitation and greater primary
 productivity in northern New Mexico. These datasets contain the original
 data associated with these records and in support of the
 conclusions. 
description: # 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
 height (m) * Age (Ma) * Carbonate d18O (‰) * Carbonate d13C (‰) * Sample
 tye * Member * Section * Height within section (m) #### File:
 S2\_Dataset\_40Ar39Ar\_Intensities.xlsx **Description:** Argon isotope
 intensity data collected for 40Ar/39Ar analysis. This dataset is split
 into three sheets, and the column names for each sheet as well as their
 meaning and units are detailed below. ##### Variables * Sheet 1 (Summary
 Data) includes summary data for each dated tephra sample * Sample--the
 name of each tephra sample * L#--Lab identifier * Irrad--Irradiation
 identifier * Min--Mineral analyzed * Calculation--Type of calculation used
 to calculate the mean age * n--Number of grains included in the
 calculation of the mean age * MSWD--Mean Square Weighted Deviation *
 Age--Mean age in Ma * 2-sigma--Uncertainty on the mean age (in Ma) * Name
 of Ash--The name of the ash as used in Spaur et al. (2025) * Sheet 2
 (Ratio Data) includes the 40Ar/39Ar analytical data * ID--Grain ID for
 each irradiated sanidine sample * Power--in watts * 40Ar/39Ar--measured
 ratio of 40Ar to 39Ar * 37Ar/39Ar--measured ratio of 37Ar to 39Ar *
 36Ar/39Ar--measured ratio of 36Ar to 39Ar (reported as 10^-3) *
 39ArK--measured 39Ar derived from 39K (reported as 10^-15 mol) *
 K/Ca--ratio of K to Ca * 40Ar*--Radiogenic argon (%) * Age--Grain age (in
 Ma) * 1sigma--uncertainty of the age measurement (in Ma) * Sheet 3
 (Intensity Data) includes the Argon intensity data and related meta data *
 Run_ID--internal reference number for the analytical sequence *
 Sample--sanidine sample * Run_Date--date on which the sample was analyzed
 (in MM/DD/YY) * Run_Hour--hour in which the sample was analyzed * Columns
 E-N--Ar intensities of sample 40Ar, 39Ar, 38Ar, 37Ar, and 36Ar and
 associated errors (1-sigma) (reported as femtoamperes (fA)) * Columns
 O-P--Measured 40Ar/36Ar of air standard divided by 295.5 and associated
 error * Columns Q-Z--Ar intensities of blank 40Ar, 39Ar, 38Ar, 37Ar, and
 36Ar and associated errors (1-sigma) (reported as femtoamperes (fA)) *
 Columns AA-AB--Percentage of total 40Ar that is radiogenic argon and
 associated error * Columns AC-AE--Age and age error and error associated
 with the J-factor considered (see below) (in Ma) * Column AF--Measured
 Ar39 (in mol) * Column AG--Irradiation identifier * Columns
 AH-AI--J-factor, a measure of the neutron dose related to sample
 irradiation and associated error * Columns AJ-AK--decay factors for Ar37
 and Ar39 * Columns AL-AX--Correction factors for interfering isotopes of
 Ca39, Ca38, Ca36, K38, K40, K37, and P36 and associated errors (1-sigma) *
 Column AY--decay constant for 40K * Columns AZ-BA--40Ar/36Ar and 40Ar/38Ar
 constants in air #### File: S3\_Dataset\_tephrachronology\_results.xlsx
 **Description:** Locations of ashes used in tephrochonology for this study
 (sheet 1) and results of electron-microprobe analysis of volcanic glass
 shards from Espanola Basin and similar or correlative tephra layers (sheet
 2). ##### Variables * Sheet 1 * Samples--Sample name * Ash--name of tephra
 bed * UTM coordinates--Easting and Northing in NAD83 * Decimal
 Degrees--Latitude (°N) and Longitude (°E) * Description--field description
 of the sampled tephra bed * Sheet 2 (note that n.r. = not reported) *
 Sample--Sample name * Reference--Publication that provides the reference,
 dated tephra * Columns C-O--Major and minor oxides (weight %, normalized
 to 100% oxide total) * Original analytical total--sum of oxide weights
 prior to normalization * Similarity coefficient--used to quantitatively
 compare the tephra samples where 1.0000 represents a perfect match. Any
 value above 0.93 is considered an acceptable correlation. All similarity
 coefficients are calculated using concentrations of Si, Al, Fe, Ca and Ti
 oxides * Statistical distance--used to quantitatively compare tephra
 samples. Values of &lt;4 are indistinguishable, &lt;10 is a strong match
 #### File: S4\_Dataset\_Meteoric\_water\_isotope\_data.xlsx
 **Description:** Modern water stable isotope (d18O and d2H) data from Ojo
 Sarco, NM, including precipitation and groundwater data, and from northern
 New Mexico streams. Sheet 2 has data from precipitation samples collected
 at Ojo Sarco. Stable isotope data are reported relative to VSMOW. Sheet 3
 has data shallow groundwater samples collected at Ojo Sarco. Sheet 4 has
 data from regional streams sampled in northern New Mexico. ##### Variables
 * Sheet 2 (Ojo Sarco Precip) * Sampling Date--date on which the sample was
 collected from the precipitation sampler * d18O--ratio of 18O to 16O
 normalized to VSMOW and reported in per mille (‰) * d18O--1 sigma
 uncertainty (‰) * d2H--ratio of 2H to 1H normalized to VSMOW and reported
 in per mille (‰) * d2H--1 sigma uncertainty (‰) * Precipitation
 amount--collected precipitation, reported in mm * Notes--any comments
 recorded by the observer * Sheet 3 (Ojo Sarco Groundwater) * Sampling
 Date--date on which the sample was collected from the precipitation
 sampler * d18O--ratio of 18O to 16O normalized to VSMOW and reported in
 per mille (‰) * d18O--1 sigma uncertainty (‰) * d2H--ratio of 2H to 1H
 normalized to VSMOW and reported in per mille (‰) * d2H--1 sigma
 uncertainty (‰) * Sheet 4 (Stream Samples) * Sample Name--name of sample *
 Sampling Date--date of sample collection (in MM/DD/YY) * Sampling Latitude
 (°N)--in WGS84 coordinates * Longitude (°E)--in WGS84 coordinates *
 d18O--ratio of 18O to 16O normalized to VSMOW and reported in per mille
 (‰) * d18O--1 sigma uncertainty (‰) * d2H--ratio of 2H to 1H normalized to
 VSMOW and reported in per mille (‰) * d2H--1 sigma uncertainty (‰)