Community Structure and Dynamics of Phytoplankton in the Western Subarctic Pacific Ocean: A Synthesis |
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| Authors: | Hongbin Liu Koji Suzuki Hiroaki Saito |
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| Institution: | (1) Louisiana Universities Marine Consortium, 8124 Hwy 56, Chauvin, LA, 70344, U.S.A.;(2) Graduate School of Environmental Earth Science, Hokkaido University, Kita-ku, Sapporo 060-0810, Japan;(3) Tohoku National Fisheries Research Institute, Fisheries Research Agency, Shinhama-cho, Shiogama 985-0001, Japan |
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| Abstract: | The phytoplankton community in the western subarctic Pacific (WSP) is composed mostly of pico- and nanophytoplankton. Chlorophyll
a (Chl a) in the <2 μm size fraction accounted for more than half of the total Chl a in all seasons, with higher contributions of up to 75% of the total Chl a in summer and fall. The exception is the western boundary along the Kamchatka Peninsula and Kuril Islands and the Oyashio
region where diatoms make up the majority of total Chl a during the spring bloom. Among the picophytoplankton, picoeukaryotes and Synechococcus are approximately equally abundant, but the former is more important in term of carbon biomass. Despite the lack of a clear
seasonal variation in Chl a concentration, primary productivity showed a large seasonal variation, and was lowest in winter and highest in spring. Seasonal
succession in the phytoplankton community is also evident with the abundance of diatoms peaking in May, followed by picoeukaryotes
and Synechococcus in summer. The growth of phytoplankton (especially >10 μm cell size) in the western subarctic Pacific is often limited by
iron bioavailability, and microzooplankton grazing keeps the standing stock of pico- and nano-phytoplankton low. Compared
to the other HNLC regions (the eastern equatorial Pacific, the Southern Ocean, and the eastern subarctic Pacific), iron limitation
in the Western Subarctic Gyre (WSG) may be less severe probably due to higher iron concentrations. The Oyashio region has
similar physical condition, macronutrient supply and phytoplankton species compositions to the WSG, but much higher phytoplankton
biomass and primary productivity. The difference between the Oyashio region and the WSG is also believed to be the results
of difference in iron bioavailability in both regions.
This revised version was published online in July 2006 with corrections to the Cover Date. |
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| Keywords: | Phytoplankton community structure iron limitation zooplankton grazing HNLC western subarctic Pacific picophytoplankton |
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