Fujii^{1, 2}, Masahiko, Yukihiro Nojiri¹, Yasuhiro Yamanaka^{3, 4} and Michio J. Kishi^{3, 4}

¹National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba 305-8506, Japan, Tel: +81-29-850-2769, Fax: +81-29-851-4732, E-mail: fujii.masahiko@nies.go.jp, ²JSPS, Tokyo, Japan, ³FRSGC, Yokohama, Japan and ⁴Hokkaido University, Hokkaido, Japan

Simulated seasonal and interannual variations in physical and biogeochemical processes at the subarctic North Pacific time-series station KNOT (44°N, 155°E)

A fifteen-compartment marine ecosystem model based on the NEMURO (North pacific Ecosystem Model Used for Regional Oceanography) was applied to Station KNOT (44°N, 155°E) in the Western North Pacific (WNP). The simulation successfully reproduced seasonal features in the observed physical and biogeochemical processes at KNOT. The simulated physical environments at the surface were quite different between El Niño and La Niña years, consistent with the observed. The simulated annual-mean biogeochemical processes, however, did not show clear difference year by year. Thus, the model successfully reproduced interannual variations in the physical processes but not in the biogeochemical processes. This implied that horizontal advection and/or specific biogeochemical changes, both of which were not included in the model, were also effective to the interannual variations in the biogeochemical processes. The simulated results were compared with those at Stations A7 (41.5°N, 145.5°E) in WNP and OSP (Ocean Station Papa; 50°N, 145°W) in the Eastern North Pacific. The simulated seasonal variability in the biogeochemical processes at KNOT and A7 was larger than at OSP, resulting from the larger seasonal variability in the physical processes in WNP. The simulated spring diatom bloom was smaller and surface nutrient concentrations in summer were higher at KNOT than at A7 although both stations were located in WNP. This might arise from the severer iron limitation on the photosynthesis by diatoms at KNOT than at A7. The simulated interannual variability was smaller at KNOT than at OSP and A7, implying less sensitivity to the ENSO Event at KNOT.