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Abstract The stable isotope ratio of dissolved inorganic carbon (δ13C‐DIC) is a valuable tracer for investigating carbon cycling in aquatic environments. However, its potential remains underutilized due to limited data availability. Fewer than 15% of cruise samples are analyzed forδ13C‐DIC, as isotope analysis using isotope ratio mass spectrometry is labor‐intensive and restricted to onshore laboratories. We present over 3500δ13C‐DIC measurements from the 2023 Global Ocean Ship‐based Hydrographic Investigations Program A16N cruise in the North Atlantic. Notably, three‐quarters of these measurements were conducted onboard using a CO2extraction device coupled with cavity ring‐down spectroscopy, a more efficient and cost‐effective method. This extensive dataset providesδ13C‐DIC values with spatial resolution comparable to other ocean carbonate chemistry and biogeochemical parameters. This dataset supports improved quantification of anthropogenic CO2uptake and storage, and may facilitate the development of algorithms to estimateδ13C‐DIC in under sampled regions.
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A High‐Precision Analytical Technique for Dissolved N 2 Isotopes in Aquatic Systems: Biogeochemical Applications and Determination of Solubility Equilibrium Isotope Effects
ABSTRACT RationaleThe isotopic composition of dissolved dinitrogen gas (δ15N‐N2) in water can offer a powerful constraint on the sources and pathways of nitrogen cycling in aquatic systems. However, because of the large presence of atmosphere‐derived dissolved N2in these systems, high‐precision (on the order of 0.001‰) measurements of N2isotopes paired with inert gas measurements are required to disentangle atmospheric and biogeochemical signals. Additionally, the solubility equilibrium isotope fractionation of N2and its temperature and salinity dependence are underconstrained at this level of precision. MethodsWe introduce a new technique for sample collection, processing, and dynamic dual‐inlet mass spectrometry allowing for high‐precision measurement of δ15N‐N2and δ(N2/Ar) with simultaneous measurement of δ(40Ar/36Ar) and δ(Kr/N2) in water. We evaluate the reproducibility of this technique and employ it to redetermine the solubility equilibrium isotope effects for dissolved N2across a range of temperatures and salinities. ResultsOur technique achieves measurement reproducibility (1σ) for δ15N‐N2(0.006‰) and δ(N2/Ar) (0.41‰) suitable for tracing biogeochemical nitrogen cycling in aquatic environments. Through a series of air–water equilibration experiments, we find a N2solubility equilibrium isotope effect (ε = α/1000 − 1, where α = (29N2/28N2)dissolved/(29N2/28N2)gas) in water of ε(‰) = 0.753 − 0.004•TwhereTis the temperature (°C), with uncertainties on the order of 0.001‰ over the temperature range of ~2°C–23°C and salinity range of ~0–30 psu. We find no apparent dependence of ε on salinity. ConclusionsOur new method allows for high‐precision measurements of the isotopic composition of dissolved N2and Ar, and dissolved N2/Ar and Kr/N2ratios, within the same sample. Pairing measurements of N2with inert gases facilitates the quantification of excess N2from biogeochemical sources and its isotopic composition. This method allows for a wide range of applications in marine, coastal, and freshwater environments to characterize and quantitatively constrain potential nitrogen‐cycling sources and pathways and to differentiate between physical and biological isotope signals in these systems.
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- Award ID(s):
- 2122427
- PAR ID:
- 10652362
- Publisher / Repository:
- Rapid Communications in Mass Spectrometry
- Date Published:
- Journal Name:
- Rapid Communications in Mass Spectrometry
- Volume:
- 39
- Issue:
- 19
- ISSN:
- 0951-4198
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1002/rcm.10094
