DOI: 10.5061/dryad.5hqbzkhc5
title: Data from: Stable isotope evidence for long-term stability of large-scale hydroclimate in the Neogene North American Great Plains

description: The Great Plains of North America host a stark climatic gradient,
 separating the humid and well-watered eastern US from the semi-arid and
 arid western US, and this gradient shapes the region’s water availability,
 its ecosystems, and its economies. This climatic boundary is largely set
 by the influence of two competing atmospheric circulation systems that
 meet over the Great Plains—the wintertime westerlies bring dominantly dry
 air that gives way to moist, southerly air transported by the Great Plains
 Low-Level Jet in the warmer months. Climate model simulations suggest
 that, as CO2 rises, this low- level jet will strengthen, leading to
 greater precipitation in the spring, but less in the summer and, thus, no
 change in mean annual precipitation. Combined with rising temperatures
 that will increase potential evapotranspiration, semi-arid conditions will
 shift eastward, with potentially large consequences for the ecosystems and
 inhabitants of the Great Plains. We examine how hydroclimate in the Great
 Plains varied in the past in response to warmer global climate by studying
 the paleoclimate record within the Ogallala Formation, which underlies
 nearly the entire Great Plains and provides a spatially resolved record of
 hydroclimate during the globally warmer late Miocene. We use the stable
 isotopes of oxygen (δ18O) as preserved in authigenic carbonates hosted
 within the abundant paleosol and fluvial successions that comprise the
 Ogallala Formation as a record of past hydroclimate. Today, and coincident
 with the modern aridity gradient, there is a sharp meteoric water δ18O
 gradient with high (−6 to 0‰) δ18O in the southern Great Plains and low
 (−12 to −18‰) δ18O in the northern Plains. We find that the spatial
 pattern of reconstructed late Miocene precipitation δ18O is
 indistinguishable from the spatial pattern of modern meteoric water δ18O.
 We use a recently developed vapor transport model to demonstrate that this
 δ18O spatial pattern requires air mass mixing over the Great Plains
 between dry westerly and moist southerly air masses in the late
 Miocene—consistent with today. Our results suggest that the spatial extent
 of these two atmospheric circulation systems have been largely unchanged
 since the late Miocene and any strengthening of the Great Plains Low-Level
 Jet in response to warming has been isotopically masked by proportional
 increases in westerly moisture delivery. Our results hold implications for
 the sensitivity of Great Plains climate to changes in global temperature
 and CO2 and also for our understanding of the processes that drove
 Ogallala Formation deposition in the late Miocene.
description: # Stable isotope evidence for long-term stability of large-scale
 hydroclimate in the Neogene North American Great Plains Table S1-Ogallala
 formation authigenic carbonate stable isotope data
 [https://doi.org/10.5061/dryad.5hqbzkhc5](https://doi.org/10.5061/dryad.5hqbzkhc5) This dataset provides all of the carbonate stable isotope data referenced in the study. Please see the associated manuscript for sampling and analytical methods. ## Description of the data and file structure The data in this Table is organized by stratigraphic section. The first tab is a Metadata tab that lists all of the stratigraphic section, their short abbreviation, and the latitude and longitude. Also listed is the paper(s) which first studied the section and provided an age estimate. In each tab (organized alphabetically), there are sixteen columns: Section ID: The two-four letter/number abbreviation for the section. Sample ID: The letter or number combination assigned to each unique sample. Longitude (°E): in decimal degrees Latitude (°N): in decimal degrees delta-13C: The carbon stable isotope value (in delta notation (‰)) relative to the standard VPDB. delta-18C: The oxygen stable isotope value (in delta notation (‰)) relative to the standard VPDB. Height: The stratigraphic height in meters from the base of our measured section. Epoch: The epoch in the Cenozoic corresponding to the sample age. NALMA: North American Land Mammal Age, if provided by the original paper that characterized the section. Age Min: The minimum age of the section in millions of years. Age Max: The maximum age of the section in millions of years. Age Mean: The mean age of the section in millions of years, calculated as the mid-point between the minimum age and the maximum age. Formation: The unit from which the sample was collected. Depositional Type: Facies if provided by the original paper. Material: Type of material collected for later analytical analysis. Notes: Free-form notes collected during field work or later laboratory work. The data in Table S1 are used to calculate the average data in Table 1 in the main text.