June 2025

Oceanography | Vol. 38, No. 2

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terminology was also adopted in recommendations from two

international workshops, one in Dublin in 2016 (Ainslie et al.,

2019) and one in Berlin in 2022 (Martin et  al., 2024), and it

served as the basis for the new ISO project 23990 Underwater

Acoustics—Bioacoustical Terminology via the SATURN

terminology standard.

For passive acoustic processing bands, ADEON adopted inter­

national standard decidecade band terminology (IEC 61260-

1:2014) whereby multiple decidecade bands can be combined

into a single decade band or user selected bands (https://doi.

org/10.6084/m9.figshare.6792359.v2). To achieve high frequency

resolution over a wide frequency range, the ADEON Data

Processing Specification (https://doi.org/10.6084/m9.​figshare.​

12412610.v1) introduced hybrid millidecade bands, with mil­

lidecade bands used at high frequency and 1 Hz bands at low

frequency (Martin et  al., 2021). Finally, two further standards

describe ADEON’s choice of hardware (https://doi.org/​10.6084/

m9.figshare.6809711) and calibration and deployment guidelines

(https://doi.org/10.6084/m9.figshare.6793745).

ADEON RESULTS

Passive Acoustics

A total of 116 TB of passive acoustic data were recorded during

the three-year data collection phase of ADEON. All data were

retrieved, except for August–November of 2019 and 2020 at site

VAC, which were lost due to commercial trawling; these land­

ers were successfully retrieved thanks to their satellite beacons

(Figure 1). Figure 2 summarizes this extensive dataset using

the monthly empirical probability density functions (EPDF) of

the one-minute sound pressure levels (SPL) in various decide­

cade frequency bands. The broadband SPL was computed from

the high-frequency sampling rate data and covers four ADEON

decade bands, which are sum of the decide­

cade bands centered from 10 Hz to 80,000 Hz,

with edge frequencies of 8.91–89,100 Hz. The

peak of the EPDFs for the broadband SPL at

all stations was near 100 dB re 1 µPa². The

two stations closest to shipping lanes (VAC

and HAT) had the highest peak SPLs in their

broadband EPDFs.

The EPDFs for four decidecade bands

shown in Figure 2 present some of the key

features of the OCS soundscape. The 20 Hz

decidecade band had higher levels in win­

ter than in summer due the mating cho­

rus of fin whales, showing that this biologi­

cal contribution is often the most notable part

of the soundscape at 20 Hz. The 20 Hz and

125  Hz decidecade bands at CHB had dis­

torted EPDFs due to the strong effect of flow-​

induced noise on the results. In general, the

125 Hz decidecade band exhibited substantial

contributions from two sources—vessels and

minke whales. The differences between the

summer and winter sound levels at the south­

ern stations (WIL, CHB, SAV, JAX, and BLE)

were caused by the mating chorus of minke

whales in winter. The two northern stations

(VAC and HAT) showed little difference

between summer and winter months due

to the frequent presence of vessels. The two

higher frequency decidecade bands (630 Hz

and 3,150 Hz) both show higher SPLs in

winter and lower levels in summer, associ­

ated with higher mean wind speeds in winter

than in summer.

Several studies of the ADEON soundscape

have provided insight into the contributions

FIGURE 2. An overview of the ADEON soundscape using monthly empiri­

cal probability density functions of one-minute sound pressure levels aver­

aged over all years. The columns are different frequency bands: broadband

(8.91–89,100 Hz) sound pressure level (in dB), and the 20, 125, 630, and 3,150 Hz

decidecade bands. The seven rows are for the seven recording locations. The

colors represent the month, as shown by the legend on the right. A dashed line

at 90 dB provides a reference for comparison between frequency bands and

stations. At VAC, the lander was picked up by fishers in July of 2019 and 2020,

so only data from 2018 are available for August to November. The reference

sound pressure is 1 µPa.