Chemical patterns in sediments of ancient Theodosius Harbour (Istanbul)

Purpose: The use of fossil fuels, cement production and the reduction of forest areas cause a high amount of CO₂ emissions to the atmosphere which in turn causes the ocean to be acidified. Acidity of seawater can directly change sediment properties. It is expected that the average pH value of the ocean surface water will decrease between 0.3 and 0.5 pH units according to the projection to year 2100. This study aimed to make a contribution to the understanding of long-term pollution trends. In the study, sediment samples from Neolithic Era, Early Byzantine Era and Byzantine Era from archaeological excavations jointly conducted by Istanbul Archaeological Museums and the Istanbul University Department of Conservation of Underwater Cultural Heritages were investigated. Materials and methods: The sediment samples were taken from ancient Theodosius Harbour (5000 BC). Major elements (Si, Al, Fe, Mg, Ca, K, Na, Mn, Ti), rare earth elements (Tb, Yb, Eu, Dy, Tm) and toxic elements (As, Cr, Co, Cu, Ni, Pb and Zn) in sediment samples were determined by X-ray fluorescence spectrometer. The chemical abundance of the ancient sediments was evaluated with the ecological risk factor and geo-accumulation index. Results and discussion: The sediment samples from the Neolithic Era reflect the contribution of both parent rock and also anthropogenic pollution. In the Early Byzantine and Byzantine Era, the development of the industry has increased the basic element concentrations in the environment and potential ecological risk and geo-accumulation indices. As, Cu, Cr, Zn, Ni and Co contents of Neolithic Era samples were found to be lower than Early Byzantine and Byzantine Era. Conclusions: The obtained the results showed that the toxic elements in the Neolithic Era, which the industry never developed, started to rise and increased concentrations of Ni by about two and a half times, Zn four times, Pb two times, Cr two times, Co six times and As three times in the Early Byzantine and Byzantine Eras. The concentrations of major elements (Al, Ba, Ca, Fe, K, Mg, Mn, Na, Si) did not show any significant difference during these three eras.