MEPS 353:81-88 (2008)  -  doi:10.3354/meps07151

In situ observation of phytoplankton productivity by an underwater profiling buoy system: use of fast repetition rate fluorometry

Tetsuichi Fujiki1,2,5,*, Takuji Hosaka1,2, Hideshi Kimoto3, Takashi Ishimaru4, Toshiro Saino1,2

1Hydrospheric Atmospheric Research Center, Nagoya University, Chikusa-ku, Nagoya 464-8601, Japan
2Japan Science and Technology Agency, Kawaguchi Center Building, 4-1-8, Honcho, Kawaguchi, Saitama 332-0012, Japan
3Kimoto Electric Co., Ltd., 3-1 Funahashi-cho, Tennoji-ku, Osaka 543-0024, Japan
4Faculty of Marine Science, Tokyo University of Marine Science and Technology, 4-5-7, Konan, Minato-ku, Tokyo 108-8477, Japan
5Present address: Mutsu Institute for Oceanography, Japan Agency for Marine-Earth Science and Technology, 690 Kitasekine, Sekine, Mutsu, Aomori 035-0022, Japan

ABSTRACT: To gain a better understanding of variability in phytoplankton productivity in the oceans, we developed an underwater profiling buoy system that uses a fast repetition rate (FRR) fluorometer. We used the profiling buoy system to observe phytoplankton productivity in Sagami Bay, Japan, from 15 April to 10 May 2005. During the observation period, chlorophyll a (chl a) concentration increased gradually, peaking at >5 mg chl a m–3 at a depth of 10 m, indicating the occurrence of phytoplankton blooms. Gross oxygen production (PO2), as determined by FRR fluorometry, increased with the development of phytoplankton blooms and peaked at 49.4 mmol O2 m–2 h–1 on 2 May 2005, when both the chl a concentration and surface irradiance were high. To validate FRR-based PO2, the light-utilization efficiency of a water column (ψO2) was calculated and compared with previous values determined for this location by the oxygen evolution method. The ψO2 derived from FRR fluorometry showed good agreement with those by the oxygen evolution method, suggesting that FRR fluorometry was able to roughly estimate in situ daily PO2. Our profiling buoy system has potential benefits for the measurement of oceanic phytoplankton productivity at a high resolution.

KEY WORDS: FRR fluorometry · Gross oxygen production · Phytoplankton blooms · Profiling buoy system

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Cite this article as: Fujiki T, Hosaka T, Kimoto H, Ishimaru T, Saino T (2008) In situ observation of phytoplankton productivity by an underwater profiling buoy system: use of fast repetition rate fluorometry. Mar Ecol Prog Ser 353:81-88

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