During the anthropogenic interval between 1975 and 1999/2008, the natural pattern of morphologic change with accumulation at active lobes and mild erosion/stability
in non-active stretches of the nearshore has almost completely disappeared (Fig. 4b and d). The Chilia lobe became wave-dominated in this anthropogenic period showing some similarities to the natural St. George lobe regime. Delta front progradation became limited to largest mouths and a submerged platform developed in front of the Old Stambul asymmetric sub-lobe on which a barrier island emerged (i.e., the Musura Island developed since the 1980s; Giosan et al., 2006a and Giosan et al., 2006b). Aiding these morphological processes at the Old Stambul mouth, the continuous extension of the Sulina jetties blocked the southward Selleckchem Caspase inhibitor longshore drift trapping sediment upcoast. The same jetties induced deposition and shoreline progradation in their wave shadow downcoast, south of the Sulina mouth (Giosan et al., 1999), constructing a purely anthropogenic, local depocenter. During the anthropogenic interval, the St. George lobe started to exhibit incipient but clear signs of abandonment (Giosan, 1998, Dan et al., 2009, Dan et al., 2011 and Constantinescu et al., 2013). Erosion of the delta front has
become generalized down to 20–25 m water depth, reaching values over 50 cm/yr in places. The Sacalin barrier island (Fig. 4d) has continued to elongate PLX4032 mouse and roll over and became a spit in the 1970s by connecting with its northern end to the delta plain. During its lifetime, the barrier has effectively transferred eroded sediments downcoast
toward its southern tip (Giosan et al., 2005), the only zone where the delta front remained locally depositional at St. George’s mouth. The sheltered zone downcoast of Sacalin Island remained stable to mildly erosional. For the anthropogenic time interval, the available bathymetric data extends also downcoast beyond Perisor where the nearshore slowly transitions into a largely erosional regime (Fig. 4b). Overall, based on the bathymetric changes discussed above, we estimated that the minimal deposition for the diglyceride delta fringe zone was on the order of 60 MT/yr in natural conditions between 1856 and 1871/1897. In contrast the same parameter for the 1975–1999/2008 was only ∼25 MT/yr. Both these values are surprisingly close to what the Danube has actually delivered to the Black Sea during these intervals (i.e., ∼70 and 25 MT/yr). However, the erosion estimated over the same intervals was ∼30 MT/yr and 120 MT/yr (!) respectively indicating significant loss of sediment. Both accretion and erosion were calculated over the same alongshore span for both time intervals (i.e., Chilia, Sulina-St. George II updrift and downdrift in Fig. 4) assuming that in both cases the bathymetric data extended far enough offshore so that morphologic changes became insignificant beyond that limit.