Coastal evolution of a Holocene barrier spit (Bug peninsula/NW-Rügen) deduced from geological structure and relative sea-level

The Bug peninsula/NW Rügen located at the south-western Baltic coast has been investigated to study coastal barrier evolution depending on Holocene sea-level rise. In this so far minor explored coastal section 25 sediment cores, seven ground-penetrating radar tracks and six sediment-echosounder tracks were collected from which six depositional facies types were derived. The data show that the recent peninsula consists of an about 10 m thick Holocene sediment sequence, underlain by Pleistocene till or (glaci-) fluviolimnic fine sand. Although no absolute age data could be gathered to estimate the chronostratigraphy of the sedimentary sequence the relation of the depositional facies to the local relative sea-level curve allow the reconstruction of the palaeogeographic evolution of the Bug barrier spit. The marine inundation of the area occurred around 7,000 BC during the Littorina transgression. In this stage the sea level rose rapidly and generated a fast increasing subaquatic accommodation space, where fine clastic material was deposited nearly or below the wave base and levelled the former relief. Accumulative coastal landforms grew to only minor extent because the accommodation space increased faster than it was filled with material from neighbouring eroding cliffs. Since the time the sea-level rise decreased accumulation became more dominant and the main barrier was built up in only some two thousand years. According to the beach ridge formations visible on the barrier´s surface the shoreline development of the Bug peninsula can be divided into two evolutionary stages depending on wave impact, erosion and overwash. Today, the barrier displays a volume of 66.4 million m³ according to a feeder cliff retreat of at about 2000 m. Although the barrier seems to be in maturity stage some features points to instability. Coastal protection measures in the north prevent breakthrough and detachment. Waterway dredging in the south inhibited further elongation and accretion with spits growing from Hiddensee. Without these measures the barrier would disintegrate and be reshaped by inlet generation and increasing erosion in the north and inlet closure and beach progradation in the south.