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From June to August 2018, the eruption of Kīlauea volcano on the island of Hawai‘i injected millions of cubic meters of molten lava into the nutrient-poor waters of the North Pacific Subtropical Gyre. The lava-impacted seawater was characterized by high concentrations of metals and nutrients that stimulated phytoplankton growth, resulting in an extensive plume of chlorophyll a that was detectable by satellite. Chemical and molecular evidence revealed that this biological response hinged on unexpectedly high concentrations of nitrate, despite the negligible quantities of nitrogen in basaltic lava. We hypothesize that the high nitrate was caused by buoyant plumes of nutrient-rich deep waters created by the substantial input of lava into the ocean. This large-scale ocean fertilization was therefore a unique perturbation event that revealed how marine ecosystems respond to exogenous inputs of nutrients. 

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.