Spatial and Temporal Variability of Natural Oil Slick Trajectories on the Sea Surface of the South Caspian Sea Revealed by Satellite Data

Oil pollution is the main environmental problem of the Caspian Sea, and a significant contribution to the total oil pollution is made by natural hydrocarbon showings at the seabed. In this paper, we discuss the spatial and temporal variability of the trajectories of natural oil slicks (NOSs) after their emerging to the surface. The study is based on satellite synthetic aperture radar data and data from multispectral satellite sensors in the optical range obtained over 5 years of a survey from 2017 to 2021 in two test areas in the southern part of the Caspian Sea. These areas are a water area near the southwest coast eastward of Cape Sefid Rud (Gilan Province, Iran) and a water area westward of the Cheleken Peninsula, which administratively belongs to Turkmenistan. Natural hydrocarbon seepages at the seabed were discovered in these regions through satellite data. Our main results include the discovery of significant seasonal variability in the NOS distribution directions in both test regions caused by the influence of local winds and surface currents that prevail in different seasons. Various types of NOS distribution trajectories were considered, and assumptions were made on the mechanisms of their formation. The impact of vortex dynamics on the spreading of the NOS and its contribution to the cross-shelf transport of oil pollution was noted.