Session: 04-06-02 Underwater Vehicles and Subsea Communications II

Submission Number: 181549

Sound Source Characteristics of an Operating Polymetallic Nodule Mining Vehicle and Application for Environmental Impact Assessment 

Deep water has long been considered a silent world, yet anthropogenic noise generated by deep-sea mining activities may affect the hearing and communication of marine organisms. The potential impact depends strongly on both the source level of the mining noise and the ambient noise conditions. In this study, we measured the source level of a prototype polymetallic nodule collector vehicle for traveling test and the deep-sea ambient noise. The collector vehicle was remotely operated from a floating barge in shallow water, and its closest point of approach (CPA) to the hydrophone was determined acoustically. The CPA distance was verified by a diver based on visible track marks. Results showed that the dominant frequency components contributing to the acoustic energy were within 90–110 Hz and several narrowband tones around 1.2 kHz. The low-frequency component originated from crawler movement, while the higher harmonics were generated by hydraulic pumps. The received levels of these two sources were comparable. The overall broadband source level was estimated to be 161 dB rms re 1 μPa, which is similar to that of a small fishing vessel. Independent measurements of deep-water ambient noise were conducted at the west contract area of DORD approved in ISA at CCZ in 2021. The ambient noise level within 10 Hz to 20 kHz band was 95.6 dB in average, ranged from 92.6 to 96.2 dB rms re 1 μPa, The detectable distance of the collector vehicle from 1738 m to 2630 m. These results suggest that the detectable range varies considerably depending not only on anthropogenic noise but also on natural fluctuations in ambient noise caused by storms and rainfall. The source levels of major anthropogenic sound sources in the ocean are roughly 160 dB for a small vessel, 190 dB for a container ship, and 220 dB for an air gun, which are comparable to or higher than that of the collector vehicle. It should be noted that the collector vehicle operates on the seabed, whereas most anthropogenic noise sources are located near the sea surface. Therefore, noise exposure mapping of seabed-based sources is essential for future environmental impact assessments. Furthermore, acceptable noise exposure thresholds for deep-sea organisms remain unknown. International collaboration will be crucial to fill these knowledge gaps.

Presenting Author: Tomonari Akamatsu Research Organization for Nano & Life Innovation, Waseda University,

Presenting Author Biography: Professor at the Research Organization for Nano & Life Innovation, Waseda University. Ph.D. (Agriculture). Specializes in underwater bioacoustics. Completed master's program of Physics at Tohoku University Graduate School of Science, Ph.D. (Agriculture, Nihon University). Since 1989-2019, he has been a researcher at the Fisheries Research and Education Agency (formerly, Fisheries Research Agency). He was a visiting researcher at the National Institute of Polar Research, and the University of Kentucky's Department of Biological Sciences. He served as a Director of Ocean Policy Research Division and a Senior Researcher at the Sasakawa Peace Foundation during 2020-2024. Specializes in bioacoustics, marine acoustics, and marine mammal studies. Member of the International Organization for Standardization TC43 Technical Committee, member of specialist grounp of cetaceans and sirenians of IUCN, and Environmental Impact Review Advisory Committee member.

Authors:

Chisato Murakami Deep Ocean Resources Development Co., Ltd.
Akira Koizumi Deep Ocean Resources Development Co., Ltd.
Takashi Kamoshida AquaSound Inc.
Aki Miyagi AquaSound Inc.
Tomonari Akamatsu Research Organization for Nano & Life Innovation, Waseda University,