Acoustic signature of strong deep-water currents in the vicinity of the New England Seamounts

Abstract

This paper presents some initial findings from the New England Seamount Acoustics (NESMA) Pilot experiment, focusing on the data obtained in April—June 2023 with three moored autonomous noise recorders (MANRs). Two MANRs were each equipped with a tilt current meter (TCM). Unexpectedly strong near-bottom currents were observed at depths of 2500m and 4443m, with the flow speeds reaching 110 cm/s and 80 cm/s, respectively. At 2500 m, recorded current speeds exceeded 20 cm/s approximately 5% of the time throughout the entire eight-week measurement period. Collocated ambient sound measurements revealed episodic large increases in the low-frequency noise intensity. A strong correlation is found between the noise intensity in the 2–20 Hz band and the measured current speed. As expected for flow noise, the intensity and the characteristic frequency of the power spectrum peaks increase with the increasing current speed. Observations of the flow noise by the MANR not equipped with a TCM indicate the presence and timing of strong current events and allow for an estimate of the current speeds at that location. The possible origins of the strong near-bottom currents and the flow noise effect on operation of deep-water acoustic systems will be discussed.