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Abstract. Measurements of dissolved organic carbon (DOC), nitrogen (DON), and phosphorus (DOP) concentrations are used to characterize the dissolved organic matter (DOM) pool and are important components of biogeochemical cycling in the coastal ocean. Here, we present the first edition of a global database (CoastDOM v1; available at https://doi.org/10.1594/PANGAEA.964012, Lønborg et al., 2023) compiling previously published and unpublished measurements of DOC, DON, and DOP in coastal waters. These data are complemented by hydrographic data such as temperature and salinity and, to the extent possible, other biogeochemical variables (e.g. chlorophyll a, inorganic nutrients) and the inorganic carbon system (e.g. dissolved inorganic carbon and total alkalinity). Overall, CoastDOM v1 includes observations of concentrations from all continents. However, most data were collected in the Northern Hemisphere, with a clear gap in DOM measurements from the Southern Hemisphere. The data included were collected from 1978 to 2022 and consist of 62 338 data points for DOC, 20 356 for DON, and 13 533 for DOP. The number of measurements decreases progressively in the sequence DOC > DON > DOP, reflecting both differences in the maturity of the analytical methods and the greater focus on carbon cycling by the aquatic science community. The global database shows that the average DOC concentration in coastal waters (average ± standard deviation (SD): 182±314 µmol C L−1; median: 103 µmol C L−1) is 13-fold higher than the average coastal DON concentration (13.6±30.4 µmol N L−1; median: 8.0 µmol N L−1), which is itself 39-fold higher than the average coastal DOP concentration (0.34±1.11 µmol P L−1; median: 0.18 µmol P L−1). This dataset will be useful for identifying global spatial and temporal patterns in DOM and will help facilitate the reuse of DOC, DON, and DOP data in studies aimed at better characterizing local biogeochemical processes; closing nutrient budgets; estimating carbon, nitrogen, and phosphorous pools; and establishing a baseline for modelling future changes in coastal waters. 

Abstract. In the current era of rapid climate change, accuratecharacterization of climate-relevant gas dynamics – namely production,consumption, and net emissions – is required for all biomes, especially thoseecosystems most susceptible to the impact of change. Marine environmentsinclude regions that act as net sources or sinks for numerous climate-activetrace gases including methane (CH4) and nitrous oxide (N2O). Thetemporal and spatial distributions of CH4 and N2O are controlledby the interaction of complex biogeochemical and physical processes. Toevaluate and quantify how these mechanisms affect marine CH4 andN2O cycling requires a combination of traditional scientificdisciplines including oceanography, microbiology, and numerical modeling.Fundamental to these efforts is ensuring that the datasets produced byindependent scientists are comparable and interoperable. Equally critical istransparent communication within the research community about the technicalimprovements required to increase our collective understanding of marineCH4 and N2O. A workshop sponsored by Ocean Carbon and Biogeochemistry (OCB)was organized to enhance dialogue and collaborations pertaining tomarine CH4 and N2O. Here, we summarize the outcomes from theworkshop to describe the challenges and opportunities for near-futureCH4 and N2O research in the marine environment. 

Abstract. Large-scale climatic forcing is impactingoceanic biogeochemical cycles and is expected to influence the water-columndistribution of trace gases, including methane and nitrous oxide. Our abilityas a scientific community to evaluate changes in the water-column inventoriesof methane and nitrous oxide depends largely on our capacity to obtain robustand accurate concentration measurements that can be validated acrossdifferent laboratory groups. This study represents the first formalinternational intercomparison of oceanic methane and nitrous oxidemeasurements whereby participating laboratories received batches of seawatersamples from the subtropical Pacific Ocean and the Baltic Sea. Additionally,compressed gas standards from the same calibration scale were distributed tothe majority of participating laboratories to improve the analytical accuracyof the gas measurements. The computations used by each laboratory to derivethe dissolved gas concentrations were also evaluated for inconsistencies(e.g., pressure and temperature corrections, solubility constants). Theresults from the intercomparison and intercalibration provided invaluableinsights into methane and nitrous oxide measurements. It was observed thatanalyses of seawater samples with the lowest concentrations of methane andnitrous oxide had the lowest precisions. In comparison, while the analyticalprecision for samples with the highest concentrations of trace gases wasbetter, the variability between the different laboratories was higher:36% for methane and 27% for nitrous oxide. In addition, thecomparison of different batches of seawater samples with methane and nitrousoxide concentrations that ranged over an order of magnitude revealed theramifications of different calibration procedures for each trace gas.Finally, this study builds upon the intercomparison results to developrecommendations for improving oceanic methane and nitrous oxide measurements,with the aim of precluding future analytical discrepancies betweenlaboratories.