The Conditions of Sedimentation of Gdańsk Bay Sediments (Baltic Sea, Poland) in the Light of Lithological Features and Carbon Content

Abstract

The research has been carried out for many years, the aim of which is to thoroughly identify sedimentation conditions in the area of the Gulf of Gdańsk. This process is conditioned by many factors, among which the quantity, type and quality of sedimentary material subject to sedimentation, the dynamics of the reservoir, its depth as well as the morphology of the bottom should be mentioned. Research sediments were collected in April 2014, during a research cruise on ORP Heweliusz. Sediment cores with a length of approx. 25 cm were taken in parts of the basin characterized by a different bathymetry, dynamics and a different distance from the main sources of supply of the terrigenous material. The GD core was taken from the Gdańsk Deep, the PB from the Puck Bay and the other two cores within the Gdansk Deep slope: UP near Hel and VR at the level of the Vistula estuary. The sediments from collected cores were subjected to wet sieve analysis and pipette analysis. The obtained results allowed to determine the type of lithological sediment and the calculation of graining indices, on the basis of which the interpretation of the sedimentation conditions was carried out. In the sediments, the carbon content was determined using the Perkin Elmer 2400 CHNS / O elemental analyzer. It was found that clayey silts and silty clays dominated in the PB, UP, GD core throughout the profile. Only in the VR core, there was a clayey sand, which proved that the sedimentation environment is more dynamic, conditioning the deposition and the periodic redeposition of sediments. It is the shallowest located station near the source of supply with terrigenous sediments (estuary of the Vistula). In the surface layer of the cores, the total organic carbon (TOC) content exceeds 4.7% and reaches up to 8.3%. The lowest TOC content, ranging from 0.8 to 2%, was found in the VR core. The total inorganic carbon (TIC) ranged from 0.18% (VR) to 1.77% (UP). In all profiles, both carbon forms decreased with depth. The greatest dynamics of changes in the surface layer of sediments (10 cm) characterized the UP core (4.1–6.6%), while the smallest changes characterized the PB station (4.7–4.9%). The parameter relations indicate a close relationship between the carbon content and the dynamics of the sedimentation environment and the proximity of the power sources.