Seasonal change in chlorophyll a profiles in the Tohoku sea area [Japan]
1996
Yokouchi, K. (Tohoku National Fisheries Research Inst., Shiogama, Miyagi (Japan)) | Tomosada, A. | Matsuo, Y. | Inagake, D.
As a preliminary study on the feasibility to transform surface chlorophyll maps produced by ocean color sensors into maps of the primary production, 430 vertical profiles of chlorophyll alpha observed off the Tohoku region were fitted into a combination of Gaussian and exponential functions to calculate a depth-integrated chlorophyll alpha content from the surface to 200 m. The profiles were taken mainly in 34-40 degrees N, 140-146 degrees E during 20 cruises from February 1989 to January 1995. Seasonal fluctuations of chlorophyll alpha concentrations were much larger in the two water masses of the transition area than in Kuroshio waters, although observations were too few to determine any seasonal trends in the Oyashio waters and in the coastal area. The spring bloom started earlier in warmer waters than in colder waters of the transition area. Maximum concentration of chlorophyll alpha at the surface was larger in colder waters than in warmer waters, whilst the yearly cumulative amount was similar in both waters. Seasonal change of the chlorophyll alpha profiles in the transition area occurred. The winter homogeneous profile changed to a stratified one with a surface layer maximum during the spring bloom. In summer a subsurface maximum was observed, and in autumn a relatively small increase of chlorophyll alpha occurred at the surface. In spite of a one to two month time lag during the spring bloom, highly significant relationships between the surface concentration and the depth-integrated chlorophyll alpha content suggest that the surface chlorophyll maps can be useful to transform into production maps by using light-production models in the Tohoku sea area
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