Exploring sand ridge formation and preservation in a semi-enclosed tideless basin, Puck Bay, Baltic Sea

Sand ridges are primarily associated with tide- and storm-dominated continental shelves, as documented in various studies. However there is a knowledge gap regarding the development and presence of such features in a semi-enclosed bays of non-tidal intra-continental seas. In the Puck Bay area, part of the Gulf of Gdańsk in the southern Baltic Sea, the field of large sand ridges, aligned obliquely to the shoreline, is present at water depths ranging between 5 m and 27 m. The ridges extend up to 5,000 m in length and 250–350 m in width, following a general SSW–NNE orientation. This field was characterised through high-resolution hydroacoustic data analysis, including bathymetry, backscatter and seismic profiling, complemented by ground-truthing samples such as surface sediments, vibrocores and video recordings. The sand ridges form two series apparent in seabed morphology, each with a distinct ridge axis orientation. High-resolution seismic data revealed the internal structure of the sand ridges, showing varying stages of their development and preservation. Parts of the sand ridges are well-preserved in their original structure, while the most distal parts, at the greatest water depths, are truncated. These parts are buried beneath younger sediments and no longer outlined in the seabed morphology.

For the first time, a system of sand ridges associated with the Holocene transgression in the southern Baltic Sea is documented, providing new perspectives on their evolution in a semi-enclosed bay of an intra-continental sea. The discovery of these ridges in the shallow, low-energy Puck Bay is unforeseen, suggesting that distinct hydrodynamic and morphodynamic conditions existed in the region in the past.