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Abstract The measured carbon isotopic compositions of carbonate sediments (δ13Ccarb) on modern platforms are commonly13C‐enriched compared to predicted values for minerals forming in isotopic equilibrium with the dissolved inorganic carbon (DIC) of modern seawater. This offset undermines the assumption that δ13Ccarbvalues of analogous facies in the rock record are an accurate archive of information about Earth's global carbon cycle. We present a new data set of the diurnal variation in carbonate chemistry and seawater δ13CDICvalues on a modern carbonate platform. These data demonstrate that δ13Ccarbvalues on modern platforms are broadly representative of seawater, but only after accounting for the recent decrease in the δ13C value of atmospheric CO2and shallow seawater DIC due to anthropogenic carbon release, a phenomenon commonly referred to as the13C Suess effect. These findings highlight an important, yet overlooked, aspect of some modern carbonate systems, which must inform their use as ancient analogs.
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Soil Carbon Isotope Values and Paleoprecipitation Reconstruction
Abstract Anthropogenic climate change has significant impacts at the ecosystem scale including widespread drought, flooding, and other natural disasters related to precipitation extremes. To contextualize modern climate change, scientists often look to ancient climate changes, such as shifts in ancient precipitation ranges. Previous studies have used fossil leaf organic geochemistry and paleosol inorganic chemistry as paleoprecipitation proxies, but have largely ignored the organic soil layer, which acts as a bridge between aboveground biomass and belowground inorganic carbon accumulation, as a potential recorder of precipitation. We investigate the relationship between stable carbon isotope values in soil organic matter (δ13CSOM) and a variety of seasonal and annual climate parameters in modern ecosystems and find a statistically significant relationship between δ13CSOMvalues and mean annual precipitation (MAP). After testing the relationship between actual and reconstructed precipitation values in modern systems, we test this potential paleoprecipitation proxy in the geologic record by comparing precipitation values reconstructed using δ13CSOMto other reconstructed paleoprecipitation estimates from the same paleosols. This study provides a promising new proxy that can be applied to ecosystems post‐Devonian (∼420 Ma) to the Miocene (∼23 Ma), and in mixed C3/C4ecosystems in the geologic record with additional paleobotanical and palynological information. It also extends paleoprecipitation reconstruction to more weakly developed paleosol types, such as those lacking B‐ horizons, than previous inorganic proxies and is calibrated for wetter environments.
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- Award ID(s):
- 1812949
- PAR ID:
- 10449967
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Paleoceanography and Paleoclimatology
- Volume:
- 36
- Issue:
- 4
- ISSN:
- 2572-4517
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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