Total suspended matter in the Gdansk deep at oxygenated / anoxic conditions in 2018—2023

Abstract

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.