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Chemical oceanographers are concerned with the composition and distribution of elements and isotopes in ocean water. Their determination is a basic study of marine science which not only satisfies human's curiosity but also can help us to understand various oceanographic processes. A focus is placed on global change.

Organic matter in sinking particles from Japan Trench (JT-01) was analyzed by pyrolysis-gas chromatography/mass spectrometry with the following results: The sinking particles produced mainly aromatic hydrocarbons and nitrogen compounds with lesser amounts of phenols, furans, aliphatic hydrocarbons and aliphatic cyanides. Ratios of n-alkanes/n-alkenes and n-alkanes/indole and the production of aromatic hydrocarbons and pyridines were used to determine whether organic matter in particles is fresh or mature. It was concluded that organic matter in the sinking particles from Japan Trench is essentially composed of fresh and matured (i. e., resuspended) ones.

The presence of excess 227 Ac (half-life, 21.8 years) relative to the parent 231 Pa in deep ocean waters indicates its usefulness as a novel tracer of basin-wide circulation and mixing studies on the time scales of less than 100 years. For this purpose, 227 Ac is probably best utilized by coupling with 228 Ra (half-life, 5.75 years), both of which have their significant source in the bottom sediments. Most important is to develop a new method for simultaneous and accurate determination of 227 Ac and 228 Ra in seawater. This may be achieved by combination of MnO 2 -fiber extraction and subsequent α-scintillation counting of 220 Rn and 219 Rn emanated from the fiber. New data on the vertical profiles of 227 Ac and 228 Th (as an indicator of 228 Ra) obtained in the deepest part of the Izu-Ogasawara Trench down to 9,700 m suggest that they are predominantly governed by isopycnal mixing. Within the trench, both nuclides are nearly constant with depth, suggesting that the water is uniformly mixed. This view is consistent with the distributions of other chemical species and radioisotopes whose concentrations are almost identical to those of the deep water at 5000-6000 m depths around this region.