Geochemical signals in Danube Deep-Sea Fan-indicators/ proxies for sedimentological changes in The Black Sea

Abstract

The Black Sea is known as a semi-enclosed basin that lies between south-eastern Europe and western Asia. Since the Last Glacial Maximum, the Black Sea has experienced many climate and environmental changes. The Black Sea is particularly prone to paleoenvironmental variances due to its essentially isolated marginal sea character. Thus, it provides a wonderful opportunity for high-resolution investigations of hydrology and recent climate changes in the watershed. Depending on the global sea level, the Black Sea has been connected to the global sea about 25 times and is isolated again. This last attachment event occurred about 9,000 years ago. The link with the Mediterranean Sea was provided through the straits of Bosphorus and Dardanelles and water inflow started from the Mediterranean Sea. Thus, the Black Sea turned from fresh-water environment to marine environment. The general water equilibrium of the Black Sea is determined by the intake of riverine waters and the narrow Bosporus Strait. In terms of the input of riverine waters, the Danube River has an active and essential role because it is known as one of the mainly advanced deep-sea sedimentary depositional systems which supply a huge amount of sediment inputs However, in recent decades there has been a decrease in the freshwater and thus sediment inflow to the Black Sea by favour of Danube river. The new urban structures formed along the Danube is expected to be the major reason for this. The specific intention of this study was to compare the geochemical and sedimentological imprints between the gravity cores taken during the cruise M142 using the R/V Meteor by the University of Bremen and with the other research to see the slump effects in the area of the Danube paleodelta. The location of the gravity cores was specially chosen inside of the Danube channel-levee system and also from exactly near the channels to see changes in the accumulation ratio caused by the estimated slumping effects during the last glacial. Especially Ca and Ti intensities in the studied cores were analysed and carried out with the help of the Avaa Tech XRF scanner by using two different voltages to determine the mineral contents at the laboratory of MARUM at the University of Bremen. Geochemical and sedimentological changes are observed. Our results showed that the pattern of element changes along the cores is identical (Unit 1-2-3). These gravity cores examined and sampled as the well-recognized series of coccolith layer (Unit 1) on the upper section; dark-colored sediments that are rich in organic matter, known as sapropel sediment (Unit 2), and the other last section described as limnic sediments (Unit 3). However, thicknesses of specific intervals vary depending on the location of sediment burial. Within this study, sediment cores with a quite high recovery rate first time as deep as 147.4 m were analyzed in terms Ti and Ca intensities which enabled to observe the glacial slump effect on the area of deposit and spillover turbidity laminas in the through Danube Deep Sea Fan region older than Holocene sediment sequence.