The authors thank an anonymous reviewer for helping to improve the manuscript. The authors thank Drs. Sachihiko Itoh and Takahiro Tanaka for performing the turbulence observations during the cruises. The authors thank Prof. Mike Gregg for suggesting the importance of fall-rate variability. The authors also thank the captain, officers, and crews of R/V Hakuho-maru, R/V Tansei-maru, and R/V Shinsei-maru. This study is partially supported by KAKENHI 25257206, JP15H05818, JPH05817, JP15K21710, and 23710002.
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