Reshaping and redirection of a tomographic impulse by local and distant undersea mountains

For the past 2 years, the 75-Hz pseudo-impulse from the Kauai Beacon has been captured on hydrophones maintained at Wake Island to enforce the Comprehensive Test Ban Treaty, sampling a 3000-km span of the North Mid-Pacific Subtropical Ocean Basin. Considering the curvature of the Earth, the source and receiver sit well below the horizon and the bulk of the acoustic energy is trapped in the deep ocean waveguide. The acoustic propagation becomes diffuse as the sound passes over the Mid-Pacific Mountains, which rise up into the Deep Sound Channel (DSC). The reception at Wake Island is made atop a steep bathymetric feature known as a Guyot—an undersea volcanic mountain that quickly rises from the deep seafloor but terminates well below the sea surface, and in this case below the DSC axis too. Models of the propagation processes are examined, specifically with the goal of interpreting the observed energy distribution at the receiver to correctly track the timing of the bulk-energy arrival, and thus deep ocean temperature. Results, cast in terms of deep ocean temperature changes, show a strong deviation in 2024 (much warmer than seasonally predicted) due to the transition into La Ninota.