Seasonal Variations in Phytoplankton Biomass and Primary Production

Sea surface chlorophyll a (Fig. 3A) reached a maximum of 15.0 mg/L in Oyashio-transition waters, with a large peak from April to May, and a small increase in August. In contrast, in other waters it was sparse throughout the year, with small seasonal variations (e.g., a slight increase during spring and autumn). Standing stock of chlorophyll a in the euphotic zone (Fig. 3B)

Oyashi o-trans i t ion

Kuroshio

Tosa Bay Continental shelf ECS 3r

Oyashi o-trans i t ion

Kuroshio

Tosa Bay Continental shelf ECS 3r

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Phytoplanton Carbon Cycle

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Figure 3: Seasonal change in (A) surface chlorophyll a (mg/l), (B) standing stock of chlorophyll a in the euphotic zone (mg/m ), (C) daily carbon fixation rate at the sea surface(mgC/m /day), (D) biomass normalized primary production at sea surface (mgC/mgChl/day), (E) daily primary production integrated over the euphotic zone (IPP, mgC/m2/day) of Oyashio waters, Kuroshio waters, Tosa Bay, and continental shelf waters of the East China Sea. Solid lines connect monthly means with standard deviations.

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Figure 3: Seasonal change in (A) surface chlorophyll a (mg/l), (B) standing stock of chlorophyll a in the euphotic zone (mg/m ), (C) daily carbon fixation rate at the sea surface(mgC/m /day), (D) biomass normalized primary production at sea surface (mgC/mgChl/day), (E) daily primary production integrated over the euphotic zone (IPP, mgC/m2/day) of Oyashio waters, Kuroshio waters, Tosa Bay, and continental shelf waters of the East China Sea. Solid lines connect monthly means with standard deviations.

reached a maximum of 265 mg/m2 in Oyashio-transition waters, where it markedly increased during spring and summer; in other waters the mean was about 20 mg/m2, with no remarkable variations during the course of the year.

Primary production at the sea surface (Fig. 3C) reached a maximum of 520mgC/m3/day in Oyashio-transition waters, displaying large seasonal variations with peaks from April to May and in August. In other areas the variations were small, with a slight increase from April to May. Chlorophyll a normalized primary production at the sea surface (Fig. 3D) peaked in Oyashio-transition waters and Kuroshio waters in May, and in Tosa Bay and ECS continental shelf waters in August. IPP (Fig. 3E) ranged from 30 mgC/ m2/day in March in Oyashio-transition waters to 3,980 mgC/m2/day in May in ECS continental shelf waters. IPP varied seasonally in Oyashio-transi-tion waters, with high production from April to August and very low production from September to March. In contrast, seasonal variations in IPP in other areas were not remarkable, with a slight increase in May in Kuroshio waters and Tosa Bay, and increases in both May and August in ECS continental shelf waters. Annual primary production (gC/m2/year) was estimated to be 340 in ECS continental shelf waters, 280 in Tosa Bay, 200 in Oyashio-transition waters, and 110 in Kuroshio waters.

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