The western Pacific ADCP Program started in January 1997 as part of J-GOOS (Japanese Global Ocean Observing System) Program by using a huge mineral transport ship operated mainly between Japan and Australia. This program is planned to continue for more than 10 years under the financial support of the Japanese government. It is expected that surface velocity data obtained repeatedly along the ship track serve as data to predict the large meander of the Kuroshio south of Honshu, Japan and the initiation of El Nino. In this paper, the observation system is briefly introduced and the accuracy and error problems of velocity measurement are discussed. Finally the first commercial cruise data are presented as a typical example of observation data.

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Horizontal and vertical chlorophyll-a distributions in the Kii Channel, Japan were revealed using field observational data and the averaged chlorophyll-a concentration in the euphotic layer was estimated. The ocean color image by OCTS taken at nearly the same time reproduces well the surface distirbution of chlorophyll-a concentration in the Kii Channel. Such a fact suggests that we can clarify the temporal and spatial variations in chlorophyll-a distribution in the coastal sea from ocean color images by satellites if we have an empirical relationships between the chllorophyll-a concentration at the sea surface and that in the euphotic layer.

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I have currently worked on the chemistry and geochemistry of the ocean with special focus on seawater for which the Prize of the Oceanographic Society of Japan was awarded in 1998. Coincidentally, during the last few decades, my work is closely followed by the world-wide development of new analytical and sampling techniques that enabled us to establish the oceanic distributions of almost all the elements existing in seawater. It seems that a long desire of world chemical oceanographers is now going to be achieved. Nevertheless, kinetics that govern the present-day elemental composition and distribution are not well understood as yet, because fluxes to and out of the ocean are poorly quantified for most elements. Exceptions are natural radionuclides that have served as useful tracers to determine how the elements behave in the ocean (Nozaki, 1991). By coupling knowledge from the natural radionuclides and those of elements with similar chemical reactivities, for example, ²27Ac versus lanthanide, the dynamic aspects of geochemical cycling in the ocean will be better elucidated. This is an aspect described in this article.

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Variability, control factors and adaptive significance of the diel feeding rhythm (DFR) of copepods were examined in the Oyashio region. All the species examined, which were dominant copepods, showed DFR. The increase in feeding rate was observed at dusk, and the decrease was at dawn or several hours before sunrise. These showed the timing of the increase in feeding rate was triggered by light cycle but the decrease was controlled by not only light cycle but also other factors, e.g., circadian rhythm. However, the timing of the change in feeding rate was variable by species and developmental stages. Diel amplitude in feeding rate also showed variations by species and stages. DFR is thought to be available to decrease the risk of visual predation because of the inconspicuous body during the day with low gut contents. In order to examine this hypothesis, the cost of DFR was determined by a simple DFR model. The model revealed that large species, which were vulunerable to the visual predation, paid more cost on DFR than small one. The prey selectivity experiments on full- and empty-gut copepods showed consistent results on the hypothesis that fish selected more on full-gut copepods than the empty-gut one. These results show that DFR is the behavior to reduce the risk of visual predation. Variations in the DFR by species are the results of the trade-off between foraging and survival.

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