Journal of Oceanography, Vol. 55 (No. 6), pp. 667-679, 1999
Takashi Harimoto1,2, Joji Ishizaka3,4 and Rhohei Tsuda1
1Department of Agriculture, Kinki University, 3327-204 Naka, Nara 631-8505, Japan
2Kansai Environmental Engineering Center, Inc., 1-3-5 Aduchi, Chuo, Osaka 541-0052, Japan
3National Institute for Resources and Environment, 16-3 Onogawa, Tsukuba, Ibaraki 305-8569, Japan
4Faculty of Fisheries, Nagasaki University, 1-14 Bunkyo, Nagasaki 852-8521, Japan
(Received 6 July 1998; in revised form 4 June 1999; accepted 7 June 1999)
Abstract: Vertical changes of phytoplankton absorption spectra along 175°E from 48°N to 15°S were examined during spring 1994. The absorption spectra were analyzed using three different approaches; averaging the spectra within same oceanic areas, EOF analysis, and multiple regression analysis. Average spectra showed differences in five oceanic areas; subarctic, Kuroshio, subtropical surface, equatorial surface, and subtropical and equatorial subsurface areas. The distributions of the EOF mode of the variance of absorption spectra and of the pigments estimated by the multiple regression analysis indicated consistent differences of the spectra between those areas. Kuroshio water contains highest chlorophyllaconcentrations and low chlorophyll-a-specific absorption spectra, and this may be caused by the package effect with large phytoplankton cell and by low concentrations of photo-protected carotenoids. Subtropical and equatorial subsurface water showed high absorption at 480 nm and indicated the effects of chlorophyll b. Absorption of the subsurface phytoplankton also showed a shift of the blue peak, possibly caused by the presence of divinyl-chlorophyll a. The consistency of the three different analytical methods indicates that the phytoplankton absorption includes significant information on pigment composition along a north-south vertical section of the central North Pacific.