title: Nitrification and its influence on biogeochemical cycles from the equatorial Pacific to the Arctic Ocean.
abstract: We examined nitrification in the euphotic zone, its impact on the nitrogen cycles, and the controlling factors along a 7500 km transect from the equatorial Pacific Ocean to the Arctic Ocean. Ammonia oxidation occurred in the euphotic zone at most of the stations. The gene and transcript abundances for ammonia oxidation indicated that the shallow clade archaea were the major ammonia oxidizers throughout the study regions. Ammonia oxidation accounted for up to 87.4% (average 55.6%) of the rate of nitrate assimilation in the subtropical oligotrophic region. However, in the shallow Bering and Chukchi sea shelves (bottom ⩽67 m), the percentage was small (0-4.74%) because ammonia oxidation and the abundance of ammonia oxidizers were low, the light environment being one possible explanation for the low activity. With the exception of the shallow bottom stations, depth-integrated ammonia oxidation was positively correlated with depth-integrated primary production. Ammonia oxidation was low in the high-nutrient low-chlorophyll subarctic region and high in the Bering Sea Green Belt, and primary production in both was influenced by micronutrient supply. An ammonium kinetics experiment demonstrated that ammonia oxidation did not increase significantly with the addition of 31-1560 nm ammonium at most stations except in the Bering Sea Green Belt. Thus, the relationship between ammonia oxidation and primary production does not simply indicate that ammonia oxidation increased with ammonium supply through decomposition of organic matter produced by primary production but that ammonia oxidation might also be controlled by micronutrient availability as with primary production.
authors.affiliation: Department of Marine Ecosystem Dynamics, Atmosphere and Ocean Research Institute, The University of Tokyo, Chiba, Japan.
authors.forename: Takuhei
authors.initials: T
authors.lastname: Shiozaki
authors.affiliation: Department of Marine Ecosystem Dynamics, Atmosphere and Ocean Research Institute, The University of Tokyo, Chiba, Japan.
authors.forename: Minoru
authors.initials: M
authors.lastname: Ijichi
authors.affiliation: Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo, Japan.
authors.forename: Kazuo
authors.initials: K
authors.lastname: Isobe
authors.affiliation: Department of Ocean Sciences, Tokyo University of Marine Science and Technology, Tokyo, Japan.
authors.forename: Fuminori
authors.initials: F
authors.lastname: Hashihama
authors.affiliation: Department of Aquatic Bioscience, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo, Japan.
authors.forename: Ken-Ichi
authors.initials: K
authors.lastname: Nakamura
authors.affiliation: Department of Ocean Sciences, Tokyo University of Marine Science and Technology, Tokyo, Japan.
authors.forename: Makoto
authors.initials: M
authors.lastname: Ehama
authors.affiliation: School of Marine Biosciences, Kitasato University, Kanagawa, Japan.
authors.forename: Ken-Ichi
authors.initials: K
authors.lastname: Hayashizaki
authors.affiliation: Department of Aquatic Bioscience, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo, Japan.
authors.forename: Kazutaka
authors.initials: K
authors.lastname: Takahashi
authors.affiliation: Department of Marine Ecosystem Dynamics, Atmosphere and Ocean Research Institute, The University of Tokyo, Chiba, Japan.
authors.forename: Koji
authors.initials: K
authors.lastname: Hamasaki
authors.affiliation: Department of Aquatic Bioscience, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo, Japan.
authors.forename: Ken
authors.initials: K
authors.lastname: Furuya
mesh_terms: D000641:Ammonia / Q000378:metabolism; D001105:Archaea / Q000235:genetics / Q000378:metabolism*; D001110:Arctic Regions; D058465:Nitrification; D058458:Nitrogen Cycle; D010084:Oxidation-Reduction; D010140:Pacific Ocean
chemical_list: D000641:Ammonia