In recent news, the Covid-19 pandemic and subsequent lockdowns resulted in a significant reduction in noise pollution on the earth’s surface. Interestingly, this had a parallel effect in the underwater world where human-made sounds, also known as anthrophony, substantially decreased over a prolonged period. This article explores components of oceanic acoustics, the change in noise levels during modern times, the impact of anthrophony on marine life, and ongoing research on ocean soundscapes.
Understanding Oceanic Acoustics
There are three broad elements that make up the soundscape of the oceans: geophony, biophony, and anthrophony.
1. Geophony represents the sounds generated by non-biological natural activities such as earthquakes, waves, and the bubbling of underwater features.
2. Biophony pertains to the noises created by living creatures in the ocean.
3. Anthrophony refers to the sounds produced by humans, with shipping noise being a significant contributor.
According to a 2021 report titled ‘The Soundscape of the Anthropocene Ocean’ published in the Science Journal, before the industrial era, the underwater soundscape was dominated by geophony and biophony. Today, however, anthrophony interferes and alters these naturally occurring components.
Noise Levels in Current Geological Era
The Anthropocene era, the current geological epoch characterized predominantly by significant human impact on the environment, has seen noisier oceans than pre-industrial times. During the initial days of the Covid-19 pandemic, several ocean sound monitors recorded a drop in decibels (dB). For instance, hydrophones at Canada’s Neptune Ocean Observatory notched an average decrease of 1.5 dB in the yearly mean weekly noise power spectral density at 100 hertz.
The Impact of Anthrophony on Marine Life
Anthrophony has considerable short and long-term effects on the marine ecosystem. In the short term, it disrupts the auditory signal processing of marine animals, negatively impacting their ability to forage for food, evade predators, or attract mates. Over time, sustained noise pollution can lead to population thinning in underwater species.
The International Quiet Ocean Experiment (IQOE)
The IQOE is a global scientific initiative aimed at encouraging research to improve understanding of ocean soundscapes and the impact of sound on marine organisms. Launched in 2015, the program will continue through 2025.
During the Covid-19 pandemic, the IQOE team collected large amounts of data and is currently developing methods to make this ocean acoustic information more comparative. Ultimately, this data will be merged into a global dataset to establish trends in ocean sound and assess the effects of the pandemic on underwater acoustics.
The IQOE project has identified and utilized over 200 non-military hydrophones (underwater microphones) in oceans worldwide. Although these hydrophones are primarily located along the coasts of the USA and Canada, their presence is gradually increasing in other regions worldwide, particularly Europe.
Understanding Hydrophones
Hydrophones function similarly to microphones, capturing sound in water rather than air. Most hydrophones operate based on a special property of certain ceramics that generate a small electrical current when subjected to changes in underwater pressure.
When submerged, a ceramic hydrophone produces low-voltage signals across various frequencies in response to underwater sounds from any direction. By amplifying and recording these signals, hydrophones can measure ocean sounds with remarkable precision.
