Seismic Images of Shallow Waters over the Shatsky Rise in the Northwest Pacific Ocean

Recent studies have demonstrated the ability of seismic oceanography to reveal finescale vertical structures of water column in the oceans based on multichannel seismic (MCS) reflection data. Such information can clarify the dynamic processes of mixing, exchange, and translation of water mass and energy. In this study, we present four MCS lines and satellite data to show high-resolution seismic images of shallow waters over the Shatsky Rise in the Northwest Pacific Ocean, where the Kuroshio Extension passes and bifurcates. One of our MCS transects crossed the center of an anticyclonic warm eddy on August 28, 2010, confirmed by satellite data such as sea level anomaly (SLA), geostrophic current anomaly (GCA), and sea surface temperature anomaly (SSTa). The seismic image showed that the eddy vertical structure featured a bowl-like shape and onion-like internal layering. The slightly tilted (< 0.5°) surface of the eddy was 400 m below the sea surface, indicating a subsurface eddy. The eddy was inferred to have a radius of 50 km and a maximum thickness of 500 m. Other MCS sections demonstrated the submesoscale structure of oceanfronts, characterized by the dipping reflectors (> 2°–3°) at the boundaries between water masses with differing properties. In addition, the discrepancies in SLA, GCA, and SSTa between water masses resulted in different seismic reflectivities. The water masses with high SLA, anticyclonic GCA and positive SSTa featured high-amplitude, continuous, clear-layered, and non-linear reflections, whereas those with low SLA, cyclonic GCA, and negative SSTa were associated with weak, fragmented, less stratification, and more linear reflectors.