The research vessel carried out a deep dive near the trench.
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海沟 (literally 'sea ditch') is the geological term — long, narrow depressions on the ocean floor, generally over 6,000 m deep, formed at subduction zones. Famous examples: 马里亚纳海沟 (Mariana), 菲律宾海沟 (Philippine), 日本海沟 (Japan).