Growth and productivity of phytoplankton substantially change organic matter characteristics, which affect bacterial abundance, productivity, and community structure in aquatic ecosystems. We analyzed bacterial community structures and measured activities inside and outside phytoplankton blooms in the western North Pacific Ocean by using bromodeoxyuridine immunocytochemistry and fluorescence in situ hybridization (BIC-FISH). Roseobacter/Rhodobacter, SAR11, Betaproteobacteria, Alteromonas, SAR86, and Bacteroidetes responded differently to changes in organic matter supply. Roseobacter/Rhodobacter bacteria remained widespread, active, and proliferating despite large fluctuations in organic matter and chlorophyll a (Chl-a) concentrations. The relative contribution of Bacteroidetes to total bacterial production was consistently high. Furthermore, we documented the unexpectedly large contribution of Alteromonas to total bacterial production in the bloom. Bacterial abundance, productivity, and growth potential (the proportion of growing cells in a population) were significantly correlated with Chl-a and particulate organic carbon concentrations. Canonical correspondence analysis showed that organic matter supply was critical for determining bacterial community structures. The growth potential of each bacterial group as a function of Chl-a concentration showed a bell-shaped distribution, indicating an optimal organic matter concentration to promote growth. The growth of Alteromonas and Betaproteobacteria was especially strongly correlated with organic matter supply. These data elucidate the distinctive ecological role of major bacterial taxa in organic matter cycling during open ocean phytoplankton blooms.The major ecological function of heterotrophic bacteria in interactions with phytoplankton is mineralization of organic matter for recycling of nutrients and secondary production, which is channeled mainly to the higher trophic levels of aquatic food webs (10, 66). Growth of phytoplankton leads to major changes in organic matter quantity and quality, which results in changes to bacterial community structure, abundance, and productivity (3). Previous studies have shown that bacterial abundance, production, and community structure change markedly during naturally occurring and experimentally induced phytoplankton blooms (16,56,61). These studies pointed to several key phylogenetic groups as actively responding to the blooms and utilizing organic matter derived from phytoplankton. Bacteroidetes and Alpha-and Gammaproteobacteria were reportedly important during the blooms. Their relative contributions to total bacterial abundance and its variability have been studied intensively by using fluorescence in situ hybridization (FISH). However, as abundance is determined by both growth and mortality, changes in bacterial abundance do not always indicate changes in growth. Mainly because of some methodological limitations, little is known about the relative contributions of these key groups to total bacterial production or its va...

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Abstract.A new mechanism of ozone loss is found in the sub-tropical marine boundary layer over the north Pacific. This ozone destruction occurs just after sunrise (hereafter Sunrise Ozone Destruction, SOD) and is commonly found throughout the year. SOD is a predominant ozone loss mechanism in winter, which takes place after sunrise in a few hours with 1-2 ppbv of ozone depletion for 40-50 ppbv of background ozone, while, in summer, SOD is weaker than in winter with small ozone depletion for 10-20 ppbv of background ozone. In summer, daytime ozone destruction (hereafter, DOD) associated with UV photolysis and subsequent HOx reaction is more active. Since DOD is not active in early morning, SOD should be a new ozone loss mechanism. After demonstrating the observational findings, halogen chemistry associated with sea-salt aerosols is described as a possible mechanism.