To facilitate the development of surface-type methane hydrate resources in the Sea of Japan, we conducted an ocean environmental baseline survey and assessed the current status of megabenthos in the area. Sampling within the target area yielded only the dead shells of deep-sea bivalves with shell lengths of approximately 80 mm; no information on living individuals was obtained. It is believed that both the depth and quantity of the sediment samples collected by the existing samplers were insufficient. Therefore, we designed and fabricated four types of samplers capable of collecting large amounts of sediment through repeated sampling during a single dive of a remotely operated vehicle. The proposed sediment-sampling technique was tested on the deep-sea floor. The samplers successfully repeated the sediment-sampling, with one sampler completing 25 samplings during a single dive. A live bivalve approximately 80 mm in shell length and presumed to be Conchocele sp., was successfully collected. The developed samplers represent a potentially valuable technology for environmental impact assessments associated with deep-sea resource development.

This study investigates the biogeochemical cycling of nine trace metals (Al, Mn, Fe, Co, Ni, Cu, Zn, Cd, Pb) across the Pacific Ocean, aiming to elucidate the processes that govern their distribution in seawater. By examining their vertical sectional distributions in the North and South Pacific, the Bering Sea, and the Sea of Japan, the study evaluates how terrestrial and anthropogenic inputs influence marine environments. Results show that, in mid- to deep water layers, nutrient-type elements (Ni, Cu, Zn, Cd) are controlled not only by water circulation and biogeochemical cycling but also by scavenging. Ratios of nutrient-type elements to phosphate and apparent oxygen utilization indicate that scavenging significantly affects their distribution. Furthermore, the horizontal distribution of trace metals in deep layers highlights the influence of sediment-water exchange on the seawater composition.