Acoustic investigations of shallow gas in the southern Baltic Sea (Polish Exclusive Economic Zone): a review

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 km2), 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 km2. 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.