the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 14 Jul 2026
Δ14C and δ13C of DIC dataset from R/V Mirai and NABOS in the Arctic Ocean, with a synthesis of published records from 1979–2021
Abstract. We present a new full-water-column dataset of dissolved inorganic carbon (DIC) Δ¹⁴C, δ¹³C, DIC concentration, and CTD/chemical properties for the Arctic Ocean, obtained on R/V Mirai cruise transects (1999, 2000, 2002, 2006, 2008, 2009) and the 2008 NABOS expedition. In total, 255 new DIC Δ¹⁴C measurements (each with paired δ¹³C and DIC concentration) are reported here, of which 42 are from NABOS 2008. The archived dataset released with this study consists primarily of these unanalyzed data; raw numerical values from earlier published papers are not redistributed. To evaluate the long-term change of Arctic DIC Δ¹⁴C over 1979–2021 are used in the text for citation-based comparison and synthesis analysis. Older values transcribed or extracted from printed pages are treated as contextual information for surveying the time series and vertical structure, not as redistributed individual values. The primary aims of this paper are (i) to release the new Mirai/NABOS data in a long-term-archivable form, (ii) to organise the location, period, region, depth range and water-mass information of the published data, and (iii) by combining the new data with published records, to demonstrate the scientific utility of the full-water-column Arctic DIC Δ¹⁴C structure, including the surface mixed layer, the PWW/halocline, the AW layer and the deep water. The detailed interpretation of the temporal change of the AW layer and of Atlantification is deferred to a companion JGR-Oceans paper (Uchida et al., submitted).
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Status: open (until 06 Sep 2026)
- CC1: 'Comment on essd-2026-493', Anne-Marie Wefing, 06 Aug 2026 reply
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RC1: 'Comment on essd-2026-493', Anonymous Referee #1, 24 Aug 2026
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General comments
This manuscript presents a valuable set of previously unpublished Arctic DIC radiocarbon and stable carbon isotope observations from R/V Mirai and NABOS cruises and attempts to place these measurements in a longer-term Arctic context. The underlying observations are potentially useful, particularly as full-depth DIC Δ14C observations in the Arctic remain relatively sparse.
However, in its current form, I do not think the manuscript yet meets the standard expected for an ESSD data description paper. The main concern is not the value of the observations, but the definition and completeness of the data product. The manuscript combines a relatively small newly released dataset with a larger synthesis of published observations, while much of the scientific interpretation, particularly for the Atlantic Water (AW) layer and Atlantification, is explicitly assigned to a companion JGR-Oceans manuscript. This creates substantial overlap and makes the specific contribution of the ESSD paper difficult to identify. The manuscript itself states that the detailed AW-layer interpretation is deferred to the companion paper, while nevertheless presenting the four-phase AW evolution, its slopes, and the AW plateau in the present manuscript. This substantially erodes the novelty of the companion JGR-Oceans paper, and raises reasonable concerns about salami slicing of a single research project into two publications. The manuscript relies on 1025 observations compiled from published records for its core synthesis analyses, yet only provides citations and DOIs for these historical data without delivering a harmonized, quality-controlled compilation integrated with the 255 newly released measurements. In addition, the present data release appears to be centered on the 255 newly reported isotope measurements, whereas associated CTD, hydrographic, dissolved oxygen, carbonate-system, and other cruise observations are mainly referenced through external cruise records rather than being incorporated into a single analysis-ready product. This represents a significant missed opportunity for an ESSD contribution.
Major comments
- The manuscript needs a much clearer ESSD-specific purpose.The paper should focus on the creation, quality control, documentation, and long-term usability of an Arctic DIC isotope data product rather than on a partial scientific interpretation of the Arctic Δ14C record. At present, the manuscript contains substantial scientific interpretation of SML, PWW, AW, deep-water age, and Atlantification, while the actual data product remains relatively limited. I recommend substantially reducing the process-oriented interpretation and restructuring the manuscript around the data product itself.
- The relationship between this ESSD manuscript and the companion JGR-Oceans paper must be clarified.The current manuscript presents the four-phase AW evolution, including the increase, plateau, rapid decline, and slow decline, although these results are explicitly described as part of the companion JGR-Oceans paper. The same information is repeated in the Results and Conclusions. This raises a fundamental question: what is the distinct scientific contribution of the JGR-Oceans paper if the major AW temporal features and their quantitative characteristics are already presented here? The two papers should be clearly separated. The ESSD paper should establish the dataset, its provenance, processing, uncertainty, validation, and demonstrated utility.
- The manuscript currently reports 255 new Δ14Cmeasurements with paired δ13C and other information, but associated cruise observations such as CTD, bottle-water chemistry, dissolved oxygen, ｐCO2, nutrients, and other hydrographic and geochemical measurements are only referenced through external repositories. For an ESSD publication, I strongly recommend that the authors go one step further and construct an integrated, analysis-ready product aligned with the standards of widely used community reference datasets such as GLODAP.
- The manuscript uses 1025 observations by combining the new data with published records, but explicitly states that the statistics presented from Table 2 onward are based on a synthesis that combines new and published data, rather than on the archived dataset itself.If these 1025 observations are central to the scientific demonstration of the product, I recommend making the full compilation available in ananalysis-ready form, with complete provenance for each record. The target should be a single harmonized Arctic DIC isotope database containing the full set of publicly reusable observations, rather than a new-data file plus a separate literature inventory. Bringing them together would substantially increase the value and reusability of the dataset. ESSD specifically recommends complete source attribution, processing documentation, validation, uncertainty accounting, and accessible data products and codes.
- The synthesis combines Δ14Crecords from severalsources across 1979–2021, generated by different laboratories, AMS facilities, extraction methods and normalization protocols. The only stated harmonization step is conversion to Stuiver & Polach (1977) notation, which addresses reporting convention but not analytical systematic biases. Direct trend calculation from uncalibrated multi-source data undermines the reliability of reported rates such as -2.89‰ yr-1. A dedicated crossover analysis using overlapping stations and depth horizons is necessary to quantify and mitigate inter-measurement biases. For each data source, the authors should document full provenance and processing details: laboratory and analytical method, reference standards and normalization protocols, originally reported analytical uncertainty, all decay and normalization corrections applied, unit and notation conversion procedures, treatment of missing or estimated values, quality-control criteria, whether individual values were digitized from tables, supplementary files or figures, and whether source-specific uncertainties were retained or reassigned.
- The title gives Δ14Cand δ13Cequal prominence, but the scientific analysis is overwhelmingly based on Δ14C. δ13C is mainly presented as a paired measurement and receives limited analysis. The authors are advised to either substantially expand the description and scientific utility demonstration of the δ13C component throughout the manuscript, or revise the title and overall framing to clearly position δ13C as an auxiliary variable accompanying the primary Δ14C radiocarbon dataset.
- The current abstract emphasizes the scientific synthesis and ends by pointing readers toward the companion JGR-Oceans paper. This weakens the identity of the ESSD paper. Besides, the abstract fails to clearly distinguish between the 255 newly released measurements and the 1025-point synthesis dataset compiled from published literature, which may lead readers to incorrectly assume this paper releases a full 1979–2021 dataset. The abstract should be rewritten around the data product.
Minor Comments
- Several quantitative interpretations should be presented more cautiously. For example, the trend analyses are based on highly uneven temporal and spatial sampling, and the manuscript uses both raw-sample regressions and cast-mean regressions. The statistical justification for these choices is currently insufficient. Confidence intervals, regression uncertainty, and sensitivity to sampling strategy should be reported.
- Some interpretations are stronger than the presented data support. For example, near-zero surface Δ14Cvalues are described as indicating “recent freshening”(Table 3). Δ14C alone does not directly demonstrate freshening, such an interpretation requires independent salinity or freshwater-fraction evidence. Similarly, the interpretation of Δ14C and δ13C changes in the Chukchi shelf as direct evidence of photosynthetic uptake and benthic respiration is plausible but should be stated as being consistent with these processes.
- The manuscript contains redundant phrasing, duplicated expressions and occasional awkward long sentences. For example, the manuscript repeatedly explains that published data are not redistributed. This information should be consolidated into one clear data-policy section rather than repeated throughout the Results. A full round of language editing and conciseness improvement is needed.
- There is an arithmetic inconsistency in the Conclusion: the statement in the Line 500-501 “SML Δ14Cdeclined by about 90‰ over 42 years (1987 peak +89‰ → 2021 −7‰)” is incorrect. The period 1987-2021 is 34 years, not 42 years (which would correspond to 1979–2021).
- The authors appropriately disclose their use of Anthropic Claude for language editing, formatting, translation support, and figure preparation. However, multiple factual errors and textual irregularities throughout the manuscript point to insufficient human validation of AI-processed content. Specifically, the citation of Povinec et al. (2011) as evidence for subarctic North Pacific Δ14Cdecline is misapplied, as that work investigates tracer distributions in the southern Indian Ocean, not the subarctic North Pacific. As noted by Anne-Marie Wefing, the reference entry for Payne et al. (2024) lists incorrect co-authors despite bearing an accurate DOI. Widespread redundant phrasing and repetitive statements also indicate incomplete manual revision of AI-edited prose. The the authors should explicitly verify all scientific content, numerical values, and citations against the original sources.
Citation: https://doi.org/10.5194/essd-2026-493-RC1
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My comment concerns the reference to the study by Payne et al. (2024) given in the manuscript. This study is listed in the references with the correct title, journal and doi, but the list of co-authors is not correct. More specifically, two people are listed who are not co-authors of this paper.
I cannot really understand how a mistake like this can happen, given that the doi of the paper is correct. My only explanation is the use of AI to generate this reference. I strongly encourage the authors to use suitable reference management software and to check the list of references carefully.