The Evolution of Danube Delta After Black Sea Reconnection to World Ocean

Abstract

This chapter presents synthetically the latest progresses made on Danube Delta evolution based on new cores, sedimentological and morphological analyses which together with the newly obtained absolute ages (AMS 14C and OSL) shed a new light upon the delta formation in both its evolutionary phases (chronology) and the growth patterns. It is the first proposed reconstruction of the fluvial delta which succeeds to date delta front advancement (Old Danube lobe: 8/7.5–5.5 ka) into Danube Bay and the formation of the initial spit. Contrary to the former views, for the first time, it is proven that the early stage of delta plain formation preceded with more than a millennium both the inception of the initial spit and the relative stabilization of the sea level. Moreover, the fluvial delta morphology is reinterpreted to show that most of the present landscape is the recent result of fluvial aggradations which followed after the initial topography (former delta plain) was drowned through the concurrent action of subsidence and sea level rise. With regard to the maritime delta, we bring new arguments into the debate concerning the southern delta (composed by lagoons and sandy barriers built by longshore circulation versus deltaic lobes construction and reworking) which demonstrate that a southern distributary (Dunavaţ, derived from Sf. Gheorghe) had an intense activity and formed open-coast lobes during 2.6–1.3 ka. Moreover, the evolution of each of the six open-coast lobes belonging to maritime delta is systematically presented in relation with Danube flow changes with a focus on their chronology, progradation rates and spatial extension. New evidences have been also produced to document the changes induced by the solid discharge reduction on the Danube since the mid-twentieth century, which recently fostered the shifting of the active lobes from asymmetric to deflected (Sf. Gheorghe) or from fluvial dominated to wave influenced (Chilia).