Interannual analysis of noise levels and spectral trends in the marine soundscape of Kongsfjorden, Svalbard

Until recently, the Arctic soundscape remained pristine due to low anthropogenic activity. Climate change and economic interests have rapidly increased underwater noise and may cause irreversible acoustic changes. Understanding environmental, biological, and anthropogenic components of the soundscape is key to predicting variations and impacts. This study presents the first interannual investigation of underwater noise levels at the innermost part of Kongsfjorden, Svalbard, a strategic hydrological and biological area. An autonomous recorder was deployed at 76 m and collected acoustic data between September 2021 and July 2023 (50 % duty cycle). Noise levels were analyzed using power spectral density and sound pressure level metrics in one-third octave frequency bands from 10 Hz to 10 kHz, at different temporal scales. Two main frequency cluster bands were identified, describing the distribution and variability of noise levels. Noise levels were lower in frequencies below 160 Hz, indicating minimal human-generated noise at the mooring site, and the greatest contribution to the spectrum was associated with the environmental component. Environmental variables showed complex and seasonally variable effects on the soundscape. Wind speed was identified as the primary driver, whilst air temperature and salinity contributed significantly during winter, likely due to their impact on water column stratification and acoustic propagation dynamics. Analysis revealed significant interannual differences in noise levels. These findings enhance our understanding of the sources and drivers of underwater sounds in this Arctic fjord, providing a foundation for long-term monitoring of the soundscape within Kongsfjorden.