A deep ocean acoustic noise floor, 1-800 Hz

Area of Science:

• Oceanography
• Acoustics
• Marine geophysics

Background:

• The deep ocean acoustic noise floor is crucial for understanding ambient soundscapes.
• Limited data exists on vertical noise distribution near the seafloor in deep ocean environments.

Purpose of the Study:

• To measure the vertical distribution of the ocean's acoustic noise floor near the seafloor.
• To characterize the acoustic properties of the deep ocean soundscape.

Main Methods:

• Deployment of an acoustic array extending 987m from a depth of 5048m in the eastern North Pacific.
• Measurement of ambient noise levels across a range of frequencies.

Main Results:

• The acoustic noise floor is depth-independent between 1-6 Hz.
• Above 6 Hz, noise increases due to shipping, then decreases (∼f⁻² from 40-800 Hz).
• Acoustic energy is concentrated in a narrow horizontal beam near the seafloor, narrowing with frequency.

Conclusions:

• Deep ocean noise characteristics are influenced by surface wave radiation and distant shipping.
• Vertical noise profiles near the seafloor show distinct frequency-dependent patterns.
• The measured noise floor is comparable to historical data despite different experimental conditions.