Modulations of shallow sea wave–related seismic noise revealed during a sea-ice freeze–thaw cycle

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Abstract

As a key component of the marine soundscape, ocean ambient noise has a significant impact on underwater acoustic detection. However, the observational understanding of very low-frequency noise dynamics during sea-ice freeze–thaw cycles in shallow seas remains limited. In this study, we conducted nearly two months of concurrent measurements of sea ice, waves, and ambient noise in the coastal Bohai Sea, capturing a complete sea-ice freeze–thaw cycle.

 Using a newly developed vector hydrophone, we recorded wave-related seismic noise (WRSN) in the 0.1–0.3 Hz band, which showed a strong correlation with wave amplitude. Because sea-ice formation significantly attenuates ocean waves, we observed the WRSN amplitude declining rapidly upon ice formation and recovering to baseline levels after the ice had completely melted. Polarization analysis of the three-dimensional ground motion indicated that the WRSN was generated primarily by local wave-induced vertical seismic waves, supplemented by surface seismic waves propagating from distal sources, both of which were linked to wave activity. 

These findings confirm the effectiveness using of vector hydrophones to monitor coastal WRSN and suggested that diminishing sea ice and increasingly energetic waves under future climate change scenarios may potentially influence shallow-water WRSN, a topic that warrants further investigation.

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