TERRAPUB Journal of Oceanography

Journal of Oceanography, Vol. 62 (No. 5), pp. 657-666, 2006

Sedimentary Records of Multidecadal-Scale Variability of Diatom Productivity in the Bungo Channel, Japan, Associated with the Pacific Decadal Oscillation

Michinobu Kuwae1*, Azumi Yamashita2, Yuichi Hayami3, Atsushi Kaneda1, Takashige Sugimoto4, Yoshio Inouchi1, Atsuko Amano1 and Hidetaka Takeoka1

1Center for Marine Environmental Studies, Ehime University, Ehime 790-8577, Japan
2Ehime Prefectural Fisheries Experimental Station, Ehime 798-0104, Japan
3Ariake Sea Research Project, Saga University, Saga 840-8502, Japan
4Institute of Oceanic Research and Development, Tokai University, Shizuoka 424-8610, Japan

(Received 24 November 2005; in revised form 23 April 2006; accepted 10 May 2006)

Abstract: In order to examine the responses of primary productivity in the southern coastal sea of Japan to the Pacific Decadal Oscillation (PDO) in the 20th century, sedimentary records of diatom productivity (diatom valve fluxes) were reconstructed using core samples from the Bungo Channel (BC) in southwest Japan. The record of the Thalassionema spp. flux—the best index of fall primary productivity in the BC—indicated a multidecadal-scale duration with a low flux (1943-1982) and those with a high flux (1913-1943 and 1982-2001); apparent shifts were recognized in 1943 and 1982. The shift in 1982 was also recognized in the flux records of other early summer to fall predominant genera in the BC and, previously, in the biogenic silica records from a broad region of the southeast BC. This indicates that in our records, this shift reflects a general trend in the primary production in the southeast BC. A comparison among the Thalassionema spp. flux records, meteorological data from an observatory adjacent to the core site, and the PDO index showed that the flux records were more similar to the PDO index than the other meteorological records, which suggests that the multidecadal-scale variability of the BC primary productivity may be associated with some marine-derived forcing. The bottom intrusions of nutrient-rich water that upwelled from the shelf slope into the BC, the axis movement or the transport of the Kuroshio Current off the BC, and a basin-scale wind stress in the North Pacific might play an important role in this forcing and mediate between the BC primary productivity and the PDO.

*Corresponding author E-mail: mkuwae@sci.ehime-u.ac.jp

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