The coastline in the Jastrzębia Góra area can be divided into three major zones of general importance: a beach and barrier section, a cliff section, and a section protected by a heavy hydrotechnical construction. These areas are characterised by a diverse geology and origin, and hence different vulnerability to erosion. In addition, observations have demonstrated a different pace of erosion within each zone. Based on the results obtained by remote sensing methods (analysis of aerial photographs and maps), it has been determined that the coastline in the barrier area, i.e., to the west of Jastrzębia Góra, moved landwards by about 130 m, in a period of 100 years, and 80 m over about 50 years. A smaller displacement of the shoreline could be observed within the cliff. Between the middle of the twentieth and the start of the twenty-first centuries the shore retreated by about 25 m. However, in recent years, an active landslide has led to the displacement of the uppermost part of the cliff locally up to 25 m. Another issue is, functioning since 2000, a heavy hydrotechnical construction which has been built in order to protect the most active part of the cliff. The construction is not stable and its western part, over a distance of 50 m, has moved almost 2 m vertically downwards and c. 2.5 m horizontally towards the sea in the past two years. This illustrates that the erosional factor does not comprise only marine abrasion, but also involves land-based processes determined by geology and hydrogeology. Changes in the shoreline at the beach and barrier part are constantly conditioned by rising sea levels, the slightly sloping profile of the sea floor and low elevation values of the backshore and dune areas. Cliffs are destroyed by mass wasting and repetitive storm surges that are responsible for the removal of the colluvium which protects the coast from adverse wave effects. Presumably, mass movements combined with groundwater outflow from the cliff, plus sea abrasion cause destabilisation of the cliff protection construction.

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The impact of climate change on European society is an issue of increasing concern on the agenda of European regional development policy. Using sea-level rise and changing flood-prone areas as an example of climate-change impact, this paper reviews an approach to stakeholder communication developed in the Baltic Sea Region. The application of climate- and sea-level change scenarios in spatial planning, as well as the communication between scientists and stakeholders, was integrated into a set of tools called the ‘decision support frame’ (DSF), which focuses especially on uncertainty aspects. By specifically addressing the communication process the DSF distances itself from pure computer-based decision-making. The city of Gdańsk is a good example where a combination of climate-change models, maps and various discussion rounds led to a communication process that has integrated several planning authorities and decision-makers.

New 2D high resolution seismic and hydro-acoustic data demonstrate the presence of methane in the shallow sediments and its origin in the Pomeranian Bight, southern of the Baltic Sea area. Various shallow gas features were identified in the Gryfice block, along the inverted Trzebiatów fault zone, including chimneys, bright spots, acoustic blanking, pockmarks, and polarity reversal. Structural and stratigraphic interpretation with support of seismic attributes was carried out to show the potential of fluid migration pathways from the Upper Triassic formation reservoirs to shallow sediments below seabed and helps in explanation of how this natural gas escapes to the sea bottom. Amplitude-vs-offset (AVO) analysis verified remnants of free gas existence in the Upper Triassic potential reservoir and helped locating free gas deposits within sediments. Hydro-acoustic data illustrated the gas chimneys’ anomalies and corresponding free gas accumulation in Pleistocene to Quaternary successions. Leaking of gas to sea surface was also proved by exposure of pockmarks on multibeam (bathymetry) data. We combine seismic, hydro-acoustic data and information on petroleum system from previous studies to explain signatures of free gas and its migration from lower reservoirs to shallow sediments.

<p>Presence of methane in the shallow sediments of the southern Baltic Sea area is a well-known phenomenon. In the Polish Exclusive Economic Zone (Polish EEZ), the observations were mostly based on hydroacoustic data, as well as sediment and water sampling. However, majority of the occurrences were reported in the eastern part of the EEZ (e.g., Gulf of Gdansk). Here we focus on the western part of the Polish EEZ (Pomeranian Bight) and combination of both hydroacoustic and seismic data to provide evidences of free gas in the shallow sediments.</p><p>Our study area is located in the inverted part of the Permo-Mesozoic Polish Basin, so called Mid-Polish Swell, with the main inversion-related fault zones: Adler-Kamień and Trzebiatów faults, rooted in the pre-Permian basement (Devonian, Carboniferous?).  Both the Permian and Paleozoic rocks are a proven hydrocarbon exploration play, with an ongoing exploration at the structural trend extending further onshore towards SE. We use seismic data acquired during the RV Maria S. Merian cruise in 2016 (cruise MSM52) with the co-located sub-bottom sediment profiler (Parasound) data.</p><p>Various signatures of shallow gas were identified across the seismic section including gas chimneys, shallow bright spots, seafloor polarity reversal and acoustic blanking. Seismic attributes were used to highlight and support interpretation of shallow gas anomalies. Anomalous zones in seismic data were observed in both the Cretaceous, Jurassic and Triassic section in the vicinity of the Adler-Kamień and Trzebiatów fault zones. Parasound data illustrated corresponding free gas accumulation in Pleistocene to Quaternary successions. Amplitude versus offset (AVO) analysis was carried out at two locations of the assumed gas chimney. The gradient analysis from angle gathers shows clearly amplitude variations with increasing offset due to existence of gas in the formation, in addition, free gas amplitude anomalies were highlight in the intercept vs gradient crossplot.</p><p>Our data indicate existence of potential fluid migration pathways from the Permian-Paleozoic reservoirs to shallow sediments below the seabed and helps in explanation of how this free gas escapes to the sea bottom.</p><p>This study was funded by the Polish National Science Centre grant no UMO-2017/27/B/ST10/02316. Cruise MSM52 has been funded by German Science Foundation DFG and Federal Ministry of Education and Research (BMBF). We thank Federal Institute for Geosciences and Natural Resources (BGR) for their support during seismic data acquisition and sharing the data.</p>