In-phase variation along the Nankai trough in the ocean bottom temperature records of DONET

Abstract Ocean bottom temperature is affected by waves propagating along the seafloor. Understanding fluctuations in ocean bottom temperature caused by such wave phenomena can enhance the accuracy of geophysical observations. If seafloor seismic observation networks such as the Dense Ocean floor Network system for Earthquakes and Tsunamis (DONET), which was installed for earthquake disaster prevention in the Nankai Trough region, can detect ocean waves generated along the continental slope, they may serve broader multidisciplinary research objectives across various ocean bottom seismic networks. Here, we investigated the spatiotemporal characteristics of ocean bottom temperature data recorded by DONET and identified in-phase wave patterns. Our findings reveal that temperature correlations are more strongly dependent on relative water depths than on the horizontal distances between observation sites. Such in-phase variations observed in DONET thermometers suggest that seafloor seismic networks can indeed detect and assess oceanographic phenomena such as wave propagation. Furthermore, we discuss the implications of such wave activity on the accuracy of distributed acoustic sensing (DAS) data used in geophysical studies, highlighting potential applications of DAS in oceanography and its relevance to crustal deformation observation.