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We succeeded in determining the Ce isotopic composition (138Ce/142Ce) in seawater with an error of 2σm = 0.3–0.7 of e unit. In this study, 1000–3000 L of seawater samples were passed through MnO2 fibers to concentrate Ce and Nd for precise measurement of their isotope ratios. Four surface seawater samples of the northwestern Pacific and a coastal sample in Tokyo Bay were analyzed. Most Ce isotope ratios in the surface water showed positive eCe values (+ 0.8 to + 1.4) in the northwestern Pacific Ocean. These values indicate that Ce in the surface water originates from the continental crust preferentially over mantle-derived materials. We examined binary mixing model between the continental crust and mid-ocean ridge basalt. However the model could not explain both isotopic compositions and concentrations, which implies that the atmospheric input was a possible pathway for Ce into the ocean. A negative eCe value was observed in Tokyo Bay, suggesting mantle-derived sources.

This paper presents the first in situ flow-through chemical analyzer using a chemiluminescence (CL) method in the deep sea to a depth of 5200 m. The analyzer, called GAMOS (Geochemical Anomalies MOnitoring System), determines the concentration of dissolved manganese continuously using a H 2 O 2 –luminol CL method. A detection limit of 0.23 nM was obtained. The GAMOS was used successfully for hydrothermal plume observation.

We present here the detailed vertical profiles of dissolved ( Our dissolved Ag concentrations (4.2–8.0 pmol/kg) in the surface waters are significantly higher than those reported previously for other locations, and it appears that the variability of Ag in the surface waters is greater than an order of magnitude. Although many factors are involved in controlling the Ag concentration in the surface waters, removal by biological uptake appears to be particularly important. Although there may be some indication of anthropogenic sources in the surface waters, it seems to be local, and the large-scale contamination of Ag in the ocean is not seen in our data.

Using manganese-impregnated fiber extraction and high-efficiency gamma counting techniques, we measured the distribution of 228Ra and 226Ra in surface waters near the coast of Japan and in the western North Pacific. There is no evidence in our data that any significant amount of 228Ra is added to open ocean surface waters from the coastal waters around Tokyo Bay. High 228Ra concentrations (> 10 dpm/103 kg), were observed along the Kuroshio Current as compared to 200 km. Along ∼40°N where an eastward flow of the ‘Kuroshio Extension’ prevails, an advective flow of > 0.1 knot is consistent with the observation of nearly constant 228Ra along the track. The geographical distribution pattern of 228Ra is clearly different from that of atmospherically derived 210Pb. Thus the 228Ra in surface water serves as a useful tracer that accompanies fluvially and coastally derived elements during their subsequent lateral transport toward the central gyre.