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Abstract Dissolved inorganic carbon (DIC) and its stable carbon isotope (δ13C‐DIC) are valuable parameters for studying the aquatic carbon cycle and quantifying ocean anthropogenic carbon accumulation rates. However, the potential of this coupled pair is underexploited as only 15% or less of cruise samples have been analyzed forδ13C‐DIC because the traditional isotope analysis is labor‐intensive and restricted to onshore laboratories. Here, we improved the analytical precision and reported the protocol of an automated, efficient, and high‐precision method for ship‐based DIC andδ13C‐DIC analysis based on cavity ring‐down spectroscopy (CRDS). We also introduced a set of stable in‐house standards to ensure accurate and consistent DIC andδ13C‐DIC measurements, especially on prolonged cruises. With this method, we analyzed over 1600 discrete seawater samples over a 40‐d cruise along the North American eastern ocean margin in summer 2022, representing the first effort to collect a large dataset ofδ13C‐DIC onboard of any oceanographic expedition. We evaluated the method's uncertainty, which was 1.2 μmol kg−1for the DIC concentration and 0.03‰ for theδ13C‐DIC value (1σ). An interlaboratory comparison of onboard DIC concentration analysis revealed an average offset of 2.0 ± 3.8 μmol kg−1between CRDS and the coulometry‐based results. The cross‐validation ofδ13C‐DIC in the deep‐ocean data exhibited a mean difference of only −0.03‰ ± 0.07‰, emphasizing the consistency with historical data. Potential applications in aquatic biogeochemistry are discussed.
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This content will become publicly available on November 12, 2025
Using DIC‐δ 13 C Pair to Constrain Anthropogenic Carbon Increase in the Southeastern Atlantic Ocean Over the Most Recent Decade (2010–2020)
Abstract The southeastern Atlantic Ocean is a crucial yet understudied region for the ocean absorption of anthropogenic carbon (Canth). Data from the A12 (2020) and A13.5 (2010) cruises offer an opportunity to examine changes in dissolved inorganic carbon (DIC), its stable isotope (δ13C), and Canthover the past decade within a limited region (1∼3°E, 32∼42°S). For the decade of 2010–2020, Canthinvasion was observed from the sea surface down to 1,200 m based on both DIC and δ13C data. The mean Canthincrease rate (1.08 ± 0.26 mol m−2 yr−1) during this period accelerated from 0.87 ± 0.05 mol m−2 yr−1during the previous period (1983/84–2010). The δ13C‐based Canthincrease closely matches the DIC‐based estimation below 500 m but is 26% higher in the upper ocean. This discrepancy is likely due to δ13C's longer air‐sea exchange timescale, seasonal variability in the upper ocean, and the chosen ratio of anthropogenically induced changes in δ13C and DIC. Finally, column inventory changes based on the two methods also exhibit very similar mean Canthuptake rates. The paired DIC concentration and stable isotope dataset may enhance our ability to constrain Canthaccumulation and its controlling mechanisms in the ocean.
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- Award ID(s):
- 2023545
- PAR ID:
- 10579558
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Oceans
- Volume:
- 129
- Issue:
- 11
- ISSN:
- 2169-9275
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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