Morphology and Late Pleistocene-Holocene Sedimentation of the Strait of İstanbul (Bosphorus): A review

The Bosphorus (Istanbul Strait) is natural strait that connects the Black Sea with the Aegean Sea via the Sea of Marmara and Dardanelles Strait. It is a 31 km long and 3.5 km wide winding channel, with an irregular bottom morphology. It has depressions up to -110 m deep, and two sills with depths of -35 and -58 m in the south and north, respectively.Presently, a two-layer water exchange exists through the strait, with the Mediterranean and Black Sea waters forming the lower and upper layers, respectively. The Bosphorus channel extends as shelf valleys on the Black Sea and Sea of Marmara shelves. However, it operated as a river valley or an estuary during the stadial low-stand periods.The infill sedimentary succession of the Bosphorus channel is up to ∼100 m thick above the Palaeozoic-Cretaceous basement with an irregular topography. The oldest sediments are sandy to muddy fluvial-lacustrine facies of late Pleistocene age, which are preserved only in up to -160 m-deep scoured depressions of the basement. They are overlain by mid-late Holocene estuarine-marine shelly sandy to muddy sediments with patches of bioherms and shelly lag deposits.The Bosphorus outlet areas of the Black Sea and Sea of Marmara are characterized by a submarine fan and a shelf valley, respectively. The fan system in the Black Sea started depositing ∼900 yr after the initial vigorous marine water incursion at ∼8.4 14C kyr BP. On the Marmara shelf, extension of the Bosphorus channel is a sinuous shelf valley with a channel-leveé complex, which was deposited by the Black Sea outflow during the 11-10 14C kyr BP. Catastrophic floodings of the Sea of Marmara by torrential Black Sea outflows during the Greenland Interstadial melt water pulses, as well as the strong Mediterranean current towards the Black Sea during the interglacial periods, were responsible for carving the Bosphorus channel and the shelf valleys, as well as removing the sediments belonging to the earlier periods.

Spatial analysis of seasonal patterns in sea surface temperature and salinity distribution in the Black Sea (1992-2017)

Sea water temperature and water salinity one of the most important environmental factors of the marine ecosystems. Both of them plays an important role in forming suitable environment for marine living organisms and have a great impact on species biodiversity. Our goal for this paper was to identify spatial patterns of interannual variations in the salinity and temperature fluctuations to understand possibilities of future change of the Black Sea ecosystem and its impact on fisheries. We used temperature and salinity data from CMEMS for the 1992-2017 time period. All downloaded data was processed by QGIS 3.14 and R 4.0.3. We found that the temperature regime of the Black Sea in different periods of the year is determined by three main factors - the depth of the shelf zone, the influence of river runoff, and water circulation due to currents. The average salinity of the Black Sea waters is 19 ‰, areas with lower salinity are located near the west shore, due to the flows from the largest rivers (Dnieper, Dniester, Danube) bringing a large amount of fresh water to the Black Sea. The area with higher salinity is located in the south- west due to the water exchange of the Black Sea with the saltier Sea of Marmara (∼ 26 ‰) through the Bosphorus. The currents of the Black Sea pick up the salty water of the Sea of Marmara and slowly moving the water column against the clockwise, carry it across the entire Black Sea, thereby increasing its average salinity.