Ambient seismic noise (ASN) recorded by ocean bottom seismometers allows us to perform coda wave interferometry without using active sources. We analyzed two-year ASN recordings from five ocean bottom stations in the northwestern Pacific Ocean basin (depth > 5,500 m), and measured the relative velocity variation (\(\delta\)v/v) near the seafloor. The most important finding is an extremely low variation in \(\delta\)v/v (around -0.05%), which likely responds to a significant pressure drop at sea level and subsequently affects an anomaly at the ocean bottom (over -400 Pa) in December 2013. Furthermore, several major phases of the velocity change show delayed-correlation with the sea level pressure variations. A poroelastic simulation with adjusted ocean bottom variables supports the pressure factor mainly drives the variation in \(\delta\)v/v. Our study suggests the potential use of seismic signals to monitor oceanic and atmospheric processes by tracking variations in the oceanic pressure field.