| Autor: |
Trower, Elizabeth J., Hibner, Brianna M., Lincoln, Tyler A., Dodd, Jacqueline E., Hagen, Cedric J., Cantine, Marjorie D., Gomes, Maya L. |
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| Zdroj: |
Geophysical Research Letters; 8/16/2024, Vol. 51 Issue 15, p1-11, 11p |
| Abstrakt: |
The measured carbon isotopic compositions of carbonate sediments (δ13Ccarb) on modern platforms are commonly 13C‐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 δ13Ccarb values 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 δ13CDIC values on a modern carbonate platform. These data demonstrate that δ13Ccarb values on modern platforms are broadly representative of seawater, but only after accounting for the recent decrease in the δ13C value of atmospheric CO2 and shallow seawater DIC due to anthropogenic carbon release, a phenomenon commonly referred to as the 13C Suess effect. These findings highlight an important, yet overlooked, aspect of some modern carbonate systems, which must inform their use as ancient analogs. Plain Language Summary: Carbon isotope values of carbonate minerals (δ13Ccarb) are an important archive of information about Earth's carbon cycle in the geological past. To interpret this archive, we must understand how to identify carbonate rocks in which preserved δ13Ccarb values are representative of global trends. This effort has long been challenged by a puzzling observation in modern shallow water carbonate‐producing environments like the Bahamas: δ13Ccarb values of some sediments in these settings are higher than we predict they should be relative to δ13C values of seawater. These unexpectedly high δ13Ccarb values potentially suggest that δ13Ccarb values in carbonate rocks deposited in similar environments reflect local, rather than global processes, questioning the application of this important and long‐used tool. We measured hourly changes in seawater chemistry on a shallow marine carbonate platform and observed evidence of two key effects: (a) daily variation in δ13C values driven by photosynthesis, and (b) the recent change in the δ13C value of atmospheric CO2 and shallow seawater due to anthropogenic carbon release (the 13C Suess effect). Our data show that δ13Ccarb values of shallow marine carbonates are broadly representative of seawater, but only if we account for the 13C Suess effect. Key Points: Diurnal changes in carbonate chemistry occur, but cannot fully explain the unexpectedly high δ13Ccarb values of ooid sand on Caicos PlatformThe 13C Suess effect is primarily responsible for the offset between predicted and expected δ13Ccarb values on Caicos PlatformConsideration of the 13C Suess effect is critical for interpretations of modern carbonate sediments as analogs for the rock record [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
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