Pockmarks and associated fresh submarine groundwater discharge in the seafloor of Puck Bay, southern Baltic Sea.

This is the first well-documented report on the occurrence of pockmarks in Puck Bay. Pockmarks in the seafloor of Puck Bay were discovered during a hydroacoustic survey carried out in 2020. They are located at a depth of 25-27 m in the southwestern part of the bay. Significant depletion of chloride (Cl-) concentrations in sediment pore water was found within the depressions. Most likely, the formation of pockmarks was due to groundwater flow through the Miocene-Pleistocene system of aquifers, which extends from land to the bay area. One-dimensional modeling of vertical Cl- concentration profiles in pore water revealed the upward flow of freshened groundwater within the pockmarks. The magnitude of submarine groundwater discharge (SGD) was estimated to vary from 1.53·10-2 to 18·10-2 L·m-2·h-1. The effect of groundwater seepage was also observed at 3 cm above the seafloor within the pockmarks, which was identified as a decrease in salinity of approximately 0.12 PSU compared to reference sites. Furthermore, due to the effect of water advection, SGD can be detected even several meters above the seafloor as a decrease in salinity values within the thermocline layer.

First basin scale spatial-temporal characterization of underwater sound in the Mediterranean Sea.

Anthropogenic underwater noise is an emergent pollutant. Despite several worldwide monitoring programs, only few data are available for the Mediterranean Sea, one of the global biodiversity hotspots. The results of the first continuous acoustic programme run at a transnational basin scale in the Mediterranean Sea are here presented. Recordings were done from March 2020 to June 2021, including the COVID-19 lockdown, at nine stations in the Northern Adriatic Sea. Spatial-temporal variations of the underwater sound are described, having one third octave band sound pressure levels (SPLs) from 10 Hz to 20 kHz as metrics. Higher and more variable SPLs, mainly related to vessel traffic, were found close to harbours, whereas Natura 2000 stations experienced lower SPLs. Lower values were recorded during the lockdown in five stations. Median yearly SPLs ranged between 64 and 95 as well as 70 and 100 dB re 1 µPa for 63 and 125 Hz bands, respectively. These values are comparable with those previously found in busy shallow EU basins but higher levels are expected during a business-as-usual period. This is a baseline assessment for a highly impacted and environmental valuable area, that needs to be managed in a new sustainable blue growth strategy.

First assessment of underwater sound levels in the Northern Adriatic Sea at the basin scale.

The protection of marine habitats from human-generated underwater noise is an emerging challenge. Baseline information on sound levels, however, is poorly available, especially in the Mediterranean Sea. To bridge this knowledge gap, the SOUNDSCAPE project ran a basin-scale, cross-national, long-term underwater monitoring in the Northern Adriatic Sea. A network of nine monitoring stations, characterized by different natural conditions and anthropogenic pressures, ensured acoustic data collection from March 2020 to June 2021, including the full lockdown period related to the COVID-19 pandemic. Calibrated stationary recorders featured with an omnidirectional Neptune Sonar D60 Hydrophone recorded continuously 24 h a day (48 kHz sampling rate, 16 bit resolution). Data were analysed to Sound Pressure Levels (SPLs) with a specially developed and validated processing app. Here, we release the dataset composed of 20 and 60 seconds averaged SPLs (one-third octave, base 10) output files and a Python script to postprocess them. This dataset represents a benchmark for scientists and policymakers addressing the risk of noise impacts on marine fauna in the Mediterranean Sea and worldwide.

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

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.

BIAS: A Regional Management of Underwater Sound in the Baltic Sea.

Management of the impact of underwater sound is an emerging concern worldwide. Several countries are in the process of implementing regulatory legislations. In Europe, the Marine Strategy Framework Directive was launched in 2008. This framework addresses noise impacts and the recommendation is to deal with it on a regional level. The Baltic Sea is a semienclosed area with nine states bordering the sea. The number of ships is one of the highest in Europe. Furthermore, the number of ships is estimated to double by 2030. Undoubtedly, due to the unbound character of noise, an efficient management of sound in the Baltic Sea must be done on a regional scale. In line with the European Union directive, the Baltic Sea Information on the Acoustic Soundscape (BIAS) project was established to implement Descriptor 11 of the Marine Strategy Framework Directive in the Baltic Sea region. BIAS will develop tools, standards, and methodologies that will allow for cross-border handling of data and results, measure sound in 40 locations for 1 year, establish a seasonal soundscape map by combining measured sound with advanced three-dimensional modeling, and, finally, establish standards for measuring continuous sound. Results from the first phase of BIAS are presented here, with an emphasis on standards and soundscape mapping as well as the challenges related to regional handling.

Directionality of the ambient noise field in an Arctic, glacial bay.

The directionality of ambient noise in an Arctic tidewater glacier bay was measured using two horizontally spaced, broadband hydrophones. Segments of noise were divided into two frequency bands and analyzed for arrival angle. These data show that different classes of source radiate noise in distinct spectral bands and are spatially diverse. A previously unidentified source, the interaction of surface gravity waves with underside of ice ledges at the periphery of icebergs, is described. The generation of noise by ice-wave interaction suggests that surface waves should be measured if ambient noise is to be used to monitor ice dynamics in glacial fjords.