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This paper synthesizes, compares, and discusses acoustic data pertaining to the presence of gas in sediments within the Polish Exclusive Economic Zone in the southern Baltic Sea, which are scattered among different journals, some of which are difficult to access and therefore have limited availability to a wider group of readers. It includes data collected between the 1970s and the present day, collected using different acoustic measurement devices. A majority of reported acoustic manifestations of gas presence in sediments in the Polish EEZ take the form of acoustic blanking followed by layer enhancement, acoustic turbidity, and increased acoustic energy absorption. The observed morphological structures related to gas presence are pockmarks (shallow and buried-17 km 2), gas-saturated sediments, gas pockets, and gas chimneys. The estimated total area of acoustic manifestation of shallow gas in the Polish EEZ is around 700 km 2. Geochemical analyses of surface sediments demonstrated strong correlation with acoustic data and revealed that methane occurs at relatively shallow depths compared with other regions of the Baltic Sea.

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Three ex situ pore water sampling procedures (I – rhizon samplers, II – centrifugation of sediment subsamples collected from different sediment depths without core sectioning, III – core sectioning and centrifugation of sediment sections) were compared to indicate factors that may affect concentrations of pore water constituents (ammonia and sulfides). The methods were selected and modified in such a way as to determine how the concentrations are affected by different factors related to sampling procedures, e.g. contact with atmospheric air, filtration and sediment core disturbance. They were tested on nine sediment cores collected at one site in the southern Baltic Sea. The concentration of ammonia in pore water from centrifuged sediment sections was significantly higher compared to pore water extracted by rhizons – probably due to the impact of changing pH. The factor with the greatest impact on the H2S/HS– concentration in the analyzed pore water was the contact with atmospheric air and/or the extrusion of sediments from a core liner. Rhizons proved to be the best option for sampling pore waters analyzed for H2S/HS– and NH4+/NH3. In the case of H2S/HS– we noticed the smallest loss of the analyzed constituents. For ammonia, the centrifugation of the whole sediment sections was likely to cause interferences in the indophenol blue method.

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