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Nutrient and diatom dynamics during late winter and spring in the Oyashio region of the western subarctic Pacific Ocean

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Title: Nutrient and diatom dynamics during late winter and spring in the Oyashio region of the western subarctic Pacific Ocean
Authors: Sugie, Koji Browse this author
Kuma, Kenshi Browse this author →KAKEN DB
Fujita, Satoshi Browse this author
Nakayama, Yuta Browse this author
Ikeda, Tsutomu Browse this author →KAKEN DB
Keywords: Nutrient
Iron
spring bloom
Si:N ratio
Diatom
western subarctic Pacific Ocean
Issue Date: Sep-2010
Publisher: Elsevier
Journal Title: Deep Sea Research Part II: Topical Studies in Oceanography
Volume: 57
Issue: 17-18
Start Page: 1630
End Page: 1642
Publisher DOI: 10.1016/j.dsr2.2010.03.007
Abstract: We investigated the nutrient and diatom dynamics during late winter and spring (9-March to 1-May 2007) in the Oyashio region as part of the OECOS-WEST research cruises. Macronutrients, iron, chlorophyll a (Chl-a) and biogenic silica (BSi) concentrations in the upper mixed layer varied remarkably ranges were 1.88-18.8 μmol L^[-1] for NO3+NO2, 0.64-1.85 μmol L^[-1] for PO4, 3.14-35.7 μmol L^[-1] for Si(OH)4, 0.14-0.54 nmol L^[-1] for D-Fe, 0.64-24.6 nmol L^[-1] for T-Fe, 0.30-17.4 μg L^[-1] for Chl-a, and 0.34-14.1 μmol L^[-1] for BSi. Mixed layer depth (MLD) also varied from 8-190 m during the cruises. The growth rate of in situ phytoplankton communities, dominated by centric diatoms, varied in shipboard culture experiments from 0.55 d^[-1] for iron-replete to 0.14 d^[-1] for iron-limited conditions. A relationship between BSi and Chl-a concentrations indicates that the in situ diatom community in the warmer water system (>4℃) was heavily silicified, probably due to iron-limitation. The in situ macronutrient and dissolved iron concentrations below the MLD and estimated macronutrient concentrations during winter were negatively correlated to temperature (1-6℃), that is to the relative proportion of warm modified Kuroshio Water mixed into the colder Oyashio water system. The rate of decrease in Si(OH)4 per ℃ increase was greater than the rates for NO3+NO2 and PO4 for both in situ and estimated winter values. These results suggest that the spring bloom in the cold water system with high macronutrients and iron concentrations would progress rapidly and intensely, and then be terminated by nitrogenous nutrient depletion. However, the diatom bloom in warmer waters with lower macronutrients and iron concentrations would be terminated by Si- and/or iron-limitation of heavily-silicified diatoms. In the OECOS study, variation of macronutrients and iron due to the surface intrusions of several water masses and modification from different chemical conditions during winter were the most important factors regulating the progression, magnitude and probably fate of the spring phytoplankton bloom in the Oyashio region.
Type: article (author version)
URI: http://hdl.handle.net/2115/48858
Appears in Collections:環境科学院・地球環境科学研究院 (Graduate School of Environmental Science / Faculty of Environmental Earth Science) > 雑誌発表論文等 (Peer-reviewed Journal Articles, etc)

Submitter: 杉江 恒二

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