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Title: Timing of Pedogenic Carbonate Formation in Fine‐Grained Soils: Decoupled T(Δ 47 ) and δ 18 O w Seasonal Bias
Abstract Historically, clumped isotope thermometry (T(∆47)) of soil carbonates has been interpreted to represent a warm‐season soil temperature based dominantly on coarse‐grained soils. Additionally, T(∆47) allows the calculation of the oxygen isotope composition of soil water (δ18Ow) in the past using the temperature‐dependent fractionation factor between soil water and pedogenic carbonate, but previous work has not measured δ18Owvalues with which to compare to these archives. Here, we present clumped isotope thermometry of modern soil carbonates from three soils in Colorado and Nebraska, USA, that have a fine‐to‐medium grain size, contain clay, and are representative of many carbonate‐bearing paleosols preserved in the rock record. At two of the three sites, Briggsdale, CO and Seibert, CO, T(∆47) overlaps with mean annual soil temperature (MAST), and the calculated δ18Owoverlaps within uncertainty with measured δ18Owat carbonate bearing depths. At the third site, in Oglala National Grassland, NE, mean T(∆47) is 8–11°C warmer than MAST, and the calculated δ18Owhas a significantly higher isotope value than any observations of δ18Ow. At all three sites, even in the fall season, δ18Owvalues at carbonate bearing depths overlap with spring rainfall δ18Ow, and there is little to no evaporative enrichment of δ2Hwand δ18Owvalues. These data challenge long‐held assumptions that all pedogenic carbonate records a warm‐season bias, and that δ18Owat carbonate‐bearing depths is affected by evaporative enrichment.  more » « less
Award ID(s):
2023385
PAR ID:
10585196
Author(s) / Creator(s):
; ; ;
Publisher / Repository:
American Geophysical Union
Date Published:
Journal Name:
Paleoceanography and Paleoclimatology
Volume:
40
Issue:
2
ISSN:
2572-4517
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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