Modeling deep ocean shipping noise in varying acidity conditions

Area of Science:

• Oceanography
• Acoustics
• Environmental Science

Background:

• Seawater chemistry is changing, with probable decreases in pH.
• Shipping noise is a significant anthropogenic sound source in the ocean.
• Sound propagation in the ocean is influenced by absorption and environmental conditions.

Purpose of the Study:

• To analyze potential future changes in ambient shipping noise in the North Pacific.
• To investigate the impact of changing seawater chemistry, specifically pH, on underwater sound propagation.
• To quantify the effects of reduced sound absorption on noise levels.

Main Methods:

• Utilized a simplified acoustic propagation model for the North Pacific.
• Focused on low-frequency sound (0.1-1 kHz) relevant to shipping noise.
• Employed ray physics to compare sound energy attenuation from volume absorption and seafloor interaction.

Main Results:

• Decreasing pH is predicted to reduce the sound absorption coefficient in near-surface waters.
• A potential increase of a few decibels in ambient shipping noise over 100 years is projected.
• These noise increases are most pronounced in very quiet areas distant from noise sources.
• Effects are smaller in regions closer to shipping lanes.

Conclusions:

• Ocean acidification may lead to a measurable, albeit small, increase in underwater shipping noise in specific regions.
• The findings highlight the complex interplay between ocean chemistry and acoustic environments.
• Further research with more sophisticated models may refine these predictions for different ocean basins.