Animal-Borne Metrics Enable Acoustic Detection of Blue Whale MigrationHighlights d Acoustic monitoring reveals patterns in population-level blue whale song production d Tag-derived metrics provide behavioral context for distinct diel patterns in song d When integrated, tag and acoustic metrics reveal an acoustic signature of migration d Key to discerning timing, plasticity, and drivers of a dispersed migration

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A discrete wavelet transform was applied to satellite altimetry data for the period 1992–2007 off California to decompose the SSH signal into inter‐annual, annual, semi‐annual and shorter period components. For the lowest frequency (inter‐annual) component, a system of alternating quasi‐zonal jets was detected. The jet system was delineated by a north‐south series of quasi‐zonal bands of co‐rotating eddies; that is, the eddies were embedded in a shearing zonal flow. The direction of eddy rotation alternated between adjacent bands. The temporal behavior of the jet system showed the existence of quasi‐stationary states and transitions between them. Observed non‐linear effects of the evolution of the jets included southward drift at about 0.2 cm sec−1, deviations of the jets from the zonal direction, and re‐forming of the jet system through decay and merging of eddy chains.

The capability of the reconstruction scheme developed in Part I is demonstrated here through three practical applications. First, the nonlinear regression model is used to reproduce the upper-layer three-dimensional circulation of the eastern Black Sea from model data distorted by white and red noises. Second, the quasigeostrophic approximation is used to reconstruct the shallow water circulation pattern in an open domain with various sampling strategies. Third, the large-scale circulation in the Southern Ocean is reproduced from the First Global Atmospheric Research Program (GARP) Global Experiment (FGGE) drifter data with noncontrollable noise statistics. All three cases confirm that the theoretical approach is robust to various noise-to-signal ratios, number of observations, and station disposition. Using the simplified open boundary condition for analyzing long-term observational data is recommended because the nonlinear regression procedure requires considerable computer resources.

Low-frequency sound from large vessels is a major, global source of ocean noise that can interfere with acoustic communication for a variety of marine animals. Changes in vessel activity provide opportunities to quantify relationships between vessel traffic levels and soundscape conditions in biologically important habitats. Using continuous deep-sea (890 m) recordings acquired ∼20 km (closest point of approach) from offshore shipping lanes, we observed reduction of low-frequency noise within Monterey Bay National Marine Sanctuary (California, United States) associated with changes in vessel traffic during the onset of the COVID-19 pandemic. Acoustic modeling shows that the recording site receives low-frequency vessel noise primarily from the regional shipping lanes rather than via the Sound Fixing and Ranging (SOFAR) channel. Monthly geometric means and percentiles of spectrum levels in the one-third octave band centered at 63 Hz during 2020 were compared with those from the same months of 2018–2019. Spectrum levels were persistently and significantly lower during February through July 2020, although a partial rebound in ambient noise levels was indicated by July. Mean spectrum levels during 2020 were more than 1 dB re 1 μPa2 Hz–1 below those of a previous year during 4 months. The lowest spectrum levels, in June 2020, were as much as 1.9 (mean) and 2.4 (25% exceedance level) dB re 1 μPa2 Hz–1 below levels of previous years. Spectrum levels during 2020 were significantly correlated with large-vessel total gross tonnage derived from economic data, summed across all California ports (r = 0.81, p < 0.05; adjusted r2 = 0.58). They were more highly correlated with regional presence of large vessels, quantified from Automatic Identification System (AIS) vessel tracking data weighted according to vessel speed and modeled acoustic transmission loss (r = 0.92, p < 0.01; adjusted r2 = 0.81). Within the 3-year study period, February–June 2020 exhibited persistently quiet low-frequency noise and anomalously low statewide port activity and regional large-vessel presence. The results illustrate the ephemeral nature of noise pollution by documenting how it responds rapidly to changes in offshore large-vessel traffic, and how this anthropogenic imprint reaches habitat remote from major ports and shipping lanes.

[1] A new interpretation of SSH anomalies propagating in the California Current System as weakly nonlinear Rossby waves (RWs) is suggested. Satellite altimetry and float data were used to extract annual and semi-annual components of RWs from a multi-scale altimetry signal and estimate their kinematic characteristics. Different propagation regimes for the waves were identified by propagation speed, wave steepness and length of spatial phase coherence (SPC). A transition from a SSH field dominated by waves to a turbulent-like field was detected in the saturation regime. The recurrence period for wave behavior was estimated as about 105-120 (195-210) days for the semiannual (annual) component. The propagation speed and length of SPC decreased when wave steepness increased, and westward propagation halted during the saturation regime.Citation: Ivanov, L. M., C. A. Collins, T. M. Margolina, and