Sediment budget calculation to estimate Holocene coastal changes on the southwest Baltic Sea (Germany)

Abstract

The tide-less SW Baltic Sea has a paraglacial coast. Alternating Pleistocene cliff sections and Holocene barrier systems separate shallow lagoons from the open sea. More than 300 cores penetrating the Holocene coastal sequence allowed for detailed reconstruction of the palaeogeographic evolution. The sequence formed in response to transgression in the early Holocene (∼ 8000 year BP). The barrier–cliff system evolution is described as four stages. Over these stages, dependencies of sedimentation processes to the rate of sea-level rise are obvious. To reconstruct palaeo-coast configurations, mass balance calculations were applied. Retreating cliff sections are seen as the main source for coastal sediment. Starting from mapped volumes of sand incorporated in barriers, cliff retreat in the last 8000 years is calculated to total 2400 m at maximum. Sediment supply to the coastal zone averaged over the larger part of the Holocene is approximately three times smaller than for the last hundreds years. This signals accelerated rise of sea-level since c. 1000 years and hints on what to expect when sea-level rises faster in the future. Such will cause intensified coastal erosion and eventually the formation of new inlets. A general drowning of the coastal landscape, as observed in the early Holocene is unlikely.