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The eruption of the Miyake‐jima Volcano (34.08°N, 139.53°E) in the Izu Islands, Japan, 180 km SSW of Tokyo, began on 8 July 2000. A substantial amount of NH3 gas was found to be emitted from the Miyake‐jima Volcano together with SO2 gas and that geochemically significant quantities of aerosol particles composed of ammonium sulfate form in the plume. Through the use of satellite images, the additional atmospheric deposition of ammonium sulfate caused an increase of phyto‐plankton in the nutrient‐deficient region south of the Kuroshio. The emission of volcanic gases from the Miyake‐jima has likely been modifying the marine air quality as well as the open ocean ecosystem over parts of the western North Pacific for the past several years.

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Strong phytoplankton blooms are occasionally observed around a recurvature point of typhoon tracks in the western subtropical Pacific. These are noteworthy events in subtropical regions where both nutrient concentrations and biological production are persistently low. We investigated the response of phytoplankton to typhoon passage using a numerical model with/without biogeochemical processes. The model reproduced the observed patch‐like phytoplankton bloom around a recurvature point of Typhoon Keith in 1997. The strong bloom is caused by the typhoon‐centered upwelling of nutrient‐rich water from below the euphotic layer, which supplies the nutrients required for phytoplankton growth, resulting in higher chlorophyll‐a concentrations. Biogeochemical processes then play essential roles in determining the response after the passage of typhoons in subtropical regions.