Global Angular Recurrence and Low-Dimensional Stiff Axes in Concatenated NOAA NRS Underwater Ambient Noise

We apply Phase-Mediated Attractor Dynamics (PMAD) to long-term passive acoustic recordings from NOAA Noise Reference Stations (NRS), focusing on global angular recurrence plots (RP) and stiff-axis projections after cosine-delta embedding of 5\,kHz audio segments. Concatenated time series from multiple NRS deployments reveal block-structured recurrence with sharp basin transitions and persistent low effective dimensionality (typically 3--8 stiff axes). Global angular RPs at small phase tolerance ($\varepsilon_\theta \approx 7.8 \times 10^{-2}$) show pronounced diagonal and blocky features inconsistent with uncorrelated red noise, while projection onto the leading stiff axes exposes coherent, banded trajectories over thousands of samples. These findings extend earlier PMAD results from black-hole accretion noise, pulsar timing residuals, solar EUV, and Planck dust maps to underwater ambient soundscapes, suggesting that ocean noise retains unexpectedly organized phase-mediated structure at long timescales.