TERRAPUB Journal of Oceanography

Journal of Oceanography, Vol. 57 (No. 3), pp. 315-322, 2001

Biogeochemical Variation in Dimethylsulfide, Phytoplankton Pigments and Heterotrophic Bacterial Production in the Subarctic North Pacific during Summer

Kazushi Aranami1*, Shuichi Watanabe1, Shizuo Tsunogai1, Masato Hayashi2, Ken Furuya2 and Toshi Nagata3

1Laboratory of Marine and Atmospheric Geochemistry, Graduate School of Environmental Earth Science, Hokkaido University, Sapporo 060-0810, Japan
2Depertment of Aquatic Bioscience, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Yayoi, Bunkyo, Tokyo 113-8657, Japan
3Ocean Research Institute, The University of Tokyo, Minami-dai, Nakano, Tokyo 164-8639, Japan

(Received 6 July 2000; in revised form 25 December 2000; accepted 28 December 2000)

Abstract: Dimethylsulfide (DMS), chlorophyll a (Chl-a), accessory pigments (fucoxanthin, peridinin and 19´-hexanoyloxyfucoxanthin), and bacterial production (BP) were measured in the surface layer (0-100 m) of the subarctic North Pacific, including the Bering Sea, during summer (14 July-5 September, 1997). In surface seawater, the concentrations of DMS and Chl-a varied widely from 1.3 to 13.2 nM (5.1 ± 3.0 nM, mean ± S.D., n = 48) and from 0.1 to 2.4 mg L-1 (0.6 ± 0.6 mg L-1, n = 24), respectively. In the subarctic North Pacific, DMS to Chl-a ratios (DMS/Chl-a) were higher on the eastern side than the western side (p < 0.0001). Below the euphotic zone, DMS/Chl-a ratios were law and the correlation between DMS and Chl-a was relatively strong (r2 = 0.700, n = 27, p < 0.0001). In the euphotic zone, DMS/Chl-a ratios were higher and the correlation between DMS and Chl-a was weak (r2 = 0.128, n = 50, p = 0.01). The wide variation in DMS/Chl-a ratios would be at least partially explained by the geographic variation in the taxonomic composition of phytoplankton, because of the negative correlation between DMS/Chl-a and fucoxanthin-to-Chl-a ratios (Fuc/Chl-a) (r2 = 0.476, n = 26, p = 0.0001). Furthermore, there was a positive correlation between DMS and BP (r2 = 0.380, n = 19, p = 0.005). This suggests that BP did not represent DMS and dimethylsulfoniopropionate (DMSP) removal by bacterial consumption but rather DMSP degradation to DMS by bacterial enzyme.

*Corresponding author E-mail: kazushi@ees.hokudai.ac.jp

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