Spatial and Temporal Variability of Ambient Underwater Sound in the Baltic Sea

Abstract

During last decades, anthropogenic underwater sound and its chronic impact on marine species have been recognised as an environmental protection challenge. At the same time, studies on the spatial and temporal variability of ambient sound, and how it is affected by biotic, abiotic and anthropogenic factors are lacking. This paper presents analysis of a large-scale and long-term underwater sound monitoring in the Baltic Sea. Throughout the year 2014, sound was monitored in 36 Baltic Sea locations. Selected locations covered different natural conditions and ship traffic intensities. The 63 Hz, 125 Hz and 2 kHz one-third octave band sound pressure levels were calculated and analysed. The levels varied significantly from one monitoring location to another. The annual median sound pressure level of the quietest and the loudest location differed almost 50 dB in the 63 Hz one-third octave band. Largest difference in the monthly medians was 15 dB in 63 Hz one-third octave band. The same monitoring locations annual estimated probability density functions for two yearly periods show strong similarity. The data variability grows as the averaging time period is reduced. Maritime traffic elevates the ambient sound levels in many areas of the Baltic Sea during extensive time periods.

Human impacts and their interactions in the Baltic Sea region

“…As this is a human health issue, the impact on humans is much better studied than the effects on other components of the marine ecosystem. The impact of marine noise caused by human activities (installation and operation of coastal infrastructure, shipping) is also a largely unknown factor of disturbance for fish, mammals 1085 or smaller components of the ecosystem (Ströber and Thomsen 2019;Mustonen et al, 2019). The effects of extensive wind farms on pelagic ecosystems are largely unknown, ranging from creating microhabitats at the hard substrates of the pillar bases (reef effects , Andersson and Öhman, 2010), marine noise during the construction phase, to effects on stratification and downwelling (van Berkel et al, 2020) https://doi.org/10.5194/esd-2021-54 Preprint.…”

“…Oily bilge water release is allowed if their oil content is below 15 ppm and the vessel is not in coastal waters. Discharges of 1915 grey water (wash water from sinks, washing machines etc), emissions of energy (noise, light, heat) to the sea are currently not regulated, but the importance of noise as pollution has been recognized (Mustonen et al, 2019;Jalkanen et al, 2018).…”

Metadata-Driven Universal Real-Time Ocean Sound Measurement Architecture

“…As concern about underwater noise increased, numerous studies have been presented analyzing ocean sound [5], [6], [7], [8]. Commercial off-the-shelf hydrophones used in ocean sound monitoring usually provide raw acoustic data, whether as acoustic recordings or in streaming mode.…”

“…Moored autonomous recorders composed of one or several hydrophones and a recording unit have also been used in large-scale deployments for underwater noise assessment [6], [8], [12]. The autonomy of such devices is mainly reduced by two factors: power and storage capacity.…”

“…In order to correct this loss of amplitude the result of the DFT has to be scaled with the coherent gain (CG). This factor can be calculated as the sum of the window components (W ) normalized by the number of samples (N ), as showed in (7) and (8).…”