PARTICULATE ORGANIC CARBON IN THE SEAFLOOR SEDIMENTS OF THE BLACK SEA AS AN INDICATOR OF ANTHROPOGENIC IMPACT ON THE MARINE GEOLOGICAL AND ECOLOGICAL SYSTEM

• Дата: 2025
• Автори: Насєдкін, Є.І., Ємельянов, В.О., Федорончук, Н.О.
• Формат: Стаття
• Мова: Українська
• Опубліковано: Institute of Geological Sciences, NAS of Ukraine 2025
• Теми: particulate organic carbon; Black Sea geoecosystem; geologicalecological subsystem of the seafloor sediments; anthropogenic impact marker
• Онлайн доступ: http://geojournal.igs-nas.org.ua/article/view/345248
• Назва журналу: Geological journal

This publication presents the results of experimental studies of particulate organic carbon including black carbon particles in the seafloor sediments of the Black Sea as an indicator of anthropogenic impact, its intensity and possible sources. The aim of the research is to study the quantitative and qualitative characteristics of particulate organic carbon extracted from the seafloor sediments of the Black Sea as a possible indicator of anthropogenic load on the marine geoecosystem. The studies were conducted in the shelf areas and the continental slope of the Black Sea in the eastern, western and southwestern parts of the basin, namely in the exclusive economic zones (EEZs) of Romania and Georgia, and the littoral part of the shelf of Ukraine (Odesa region). The particulate organic carbon were isolated from samples of seafloor sediments in 2020-2024 as a by-product in laboratory studies of microplastics. Samples were taken in various areas of the Black Sea: in the exclusive economic zones (EEZs) of Romania and Georgia during research cruises on the R/V “Mare Nigrum” within the framework of the DOORS H2020 International Project, as well as in the littoral part of the Ukrainian shelf (Odesa region). Sampling at the shelf and continental slope was carried out using Van-Veen Grab and multicorer at sea depths of 30–1080 m, in the littoral part – within the beach. The upper layer of seafloor sediments with a thickness of 5 cm was tested (in some cases to study the vertical distribution of particles − with a thickness of 10 cm). In the littoral part of the northwestern shelf, an aqueous suspension from the wave formation zone was tested by filtration with a net having a pore size of 25 μm. To isolate particulate organic carbon from the sediment, the method of density separation in a saturated solution of zinc chloride with a density of ρ = 1.8 g/cm3 was used. The study of the morphology of the particles was carried out using an optical microscope, and physicochemical identification was carried out using a Raman spectrometer. The black carbon particles are present in the upper layer of all studied areas of the Black Sea geoecosystem – the eastern shelf of the coast of Georgia, the western shelf and continental slope in the EEZ of Romania and the littoral region of the northwestern shelf on the coast of Ukraine. Quantitative dominance of particulate organic carbon is observed off the coast of Georgia, where its content ranges roughly from 10% to 65% of the fraction <1 mm with a density ρ = 1.8 g/cm3. The highest concentration is recorded in the zone of terrigenous runoff of the Rioni and Khobi rivers. On the Romanian shelf, the amount of particulate organic carbon is much lower (about from 1% to 15% of the fraction <1 mm with a density ρ = 1.8 g/cm3), and on the littoral of the northwestern shelf of Ukraine, The particulate organic carbon particles are distributed locally (about from 1% to 5% of the fraction <1 mm with a density of ρ = 1.8 g/cm3). Such features are in general consistent with the intensity of the anthropogenic load on the geoecosystem of the Black Sea in these areas. Morphologically, spherical shapes prevail on the Georgian shelf, which may be due to their spillage during transportation or the specifics of their genesis (combustion products, molten polymer particles, bitumen). The Romanian shelf and continental slope are characterized by sharply different particle sizes and the presence of pyroplastics – particles that morphologically correspond to the black carbon particles, but according to the results of Raman spectroscopy they are polymers that have undergone thermal action. Analysis of the vertical distribution of particulate organic carbon on the Georgian shelf showed a significant increase in the amount of particulate organic carbon in the surface layer (0−5 cm) compared to the subsurface layer (5−10 cm), which most likely reflects the period of intensification of human activity with the accumulation of the corresponding layer of sediments, although it can be caused by diagenetic accumulation processes. Identification of particulate organic carbon by Raman spectroscopy indicates that the isolated particles belong to coal, soot or bitumen, but laboratory experiments on the amount of soluble (bituminous) components showed their minimum amount in the composition of the isolated particles of particulate organic carbon. The obtained results allow us to better understand the anthropogenic impact on the formation of the layers of the geological environment of the geoecosystem at the border with the aquatic ecological subsystem, as well as the influence of hydrological, geological and anthropogenic factors on the processes of the black carbon inflow into the Black Sea geoecosystem. The particulate organic carbon including black carbon particles can become one of the promising indicators of anthropogenic impact on the marine geoecosystem, the degree of its intensity and possible sources, and in addition, carry certain information on the historical and cultural direction of economic activity in the catchment areas. Acknowledgement. This research was supported by the European Union Horizon 2020 DOORS project (Developing Optimal and Open Research Support for the Black Sea, No 101000518), and was conducted according to the thematic plans of the SSI “Center for Problems of Marine Geology, Geoecolology and Sedimentary Ore Formation of the NAS of Ukraine” and the Institute of Geological Sciences of the NAS of Ukraine).