2024 Issue №3

Based on underwater video footage and diver observations, along with previously obtained lithological data, four types of benthic landscapes have been identified on the section of the underwater coastal slope near Cape Taran. The high mosaic distribution of lithofacies and the varying degrees of macrophyte coverage of the seabed have been confirmed. The boulder-block pavement within the euphotic layer of the sea was maximally covered by macrophytes, with Polysiphonia nigrescens as the dominant species. The lower boundary of macrophyte distribution was recorded at a depth of 19 meters, which is significantly deeper than previously believed. Macrophytes can be recommended for use in regional environmental monitoring. The presence of an ecologically significant aggregation of macrophytes near Cape Taran, the largest in the Russian sector of the southeastern Baltic, combined with the high lithofacial diversity of the seafloor, provides strong justification for establishing a marine protected area in this region.

The spatial and temporal distribution of suspended matter in the southeastern part of the Baltic Sea was studied in the context of the transition from oxygenated to anoxic conditions. Semi-enclosed water bodies, such as the shallow Baltic Sea, play a key role in the global carbon cycle. Carbon-containing particles, both organic and inorganic, settle within the total suspended matter, making it important to understand the patterns of its distribution. The main sources of suspended matter in the southeastern part of the Baltic Sea are primary production and abrasion processes in the coastal zone. From the intensively mixed coastal zone, the suspended matter is transported to the Gdańsk Deep, where benthic nepheloid layers indicate complex sedimentation conditions, suggesting that this area cannot be considered a simple carbon sink. Intermediate nepheloid layers form during the seasonal shift from oxygenated to anoxic conditions, especially when local maxima of dissolved hydrogen sulfide detach from the seabed. The concentration of dissolved oxygen in the water varies significantly depending on the season, both in the surface and bottom layers, reaching its peak in winter and spring and its minimum in summer and autumn.