TERRAPUB Journal of Oceanography

Journal of Oceanography, Vol. 54 (No. 5), pp. 495-508, 1998

Satellite and Ship Observations of Kuroshio Warm-Core Ring 93A off Sanriku, Northwestern North Pacific, in Spring 1997

Sei-ichi Saitoh1, Denzo Inagake2, Kousei Sasaoka1, Joji Ishizaka3, Yukihiro Nakame4 and Toshiro Saino5

1Faculty of Fisheries, Hokkaido University, 3-1-1, Minato-cho, Hakodate 041-8611, Japan
2Fisheries Oceanographic Division, Tohoku National Fisheries Research Institute, 3-27-5, Shinhama-cho, Shiogama, Miyagi 985-0001, Japan
3National Institute of Resources and Environment, 16-3, Onogawa, Tsukuba 305-8569, Japan
4Hokkaido Kushiro Fisheries Experimental Station, 2-6, Hama-cho, Kushiro 085-0024, Japan
5Institute for Hydrospheric-Atmospheric Sciences, Nagoya University, Chikusa-ku, Nagoya 464-8601, Japan

(Received 31 March 1998; in revised form 27 July 1998; accepted 29 July 1998)

Abstract: Synoptic ship and satellite observations were performed of the Kuroshio warm-core ring (KWCR) 93A and its adjacent waters, off Sanriku, northwestern North Pacific, between early April and late June 1997. The temporal and spatial distribution of chlorophyll a(Chl-a) and sea surface temperature in the study area were analyzed using data from ADEOS Ocean Color and Temperature Scanner (OCTS) and NOAA Advanced Very High Resolution Radiometer (AVHRR). The objective of this study was to describe the temporal and spatial variability of the spring bloom and understand its relationship with the changes in the hydrographic structure of these waters in and around KWCR 93A. The maximum value of Chl-aconcentration in the ring was less than 1 mg/m3 during April. The spring bloom in the ring occurred early in May and the relatively high maximum (>1.0 mg/m3) continued from early in May to mid-June. In late June, a ship-observed surface Chl-aconcentration of less than 0.4 mg/m3 suggests that the spring bloom had already declined in and around KWCR 93A. Double spiral structures of warm and cold streamers appeared from late April to mid-May, which may have an influence on the occurrence of the spring bloom in and around the ring. In this episodic event, the warm streamer can maintain the available potential energy of the ring and the strength of upwelling around the ring. The cold streamer provided water with a high Chl-aconcentration to the surface layer of the ring. In order to understand the temporal and spatial variability of Chl-adistribution in the ring, the behavior of the warm and cold streamers needs to be taken into consideration.

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