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Two Millennia of Natural and Anthropogenic Changes of the Polish Baltic Coast  

Andrzej Osadczuk, Ryszard Krzysztof Borówka, and Joanna Dudzińska-Nowak

Changes of the coast are a net result of morphodynamic processes driven by changes in external conditions. Morphodynamics can be understood as feedback between shore topography and hydrodynamics, the latter including bedload transport, which alters the morphology of the coast. The evolution of a marine coast can take various pathways depending on the time scale, shoreline length, geological setting, tectonic underpinnings, type and availability of sediments in the nearshore zone, sea level changes, intensity of waves and currents, and the influence of the adjacent land masses. A spatio-temporal approach (processes of millennial, decadal, annual, and seasonal change) is particularly important for coastal areas built of erosion-prone, poorly consolidated glacial and postglacial deposits. This is the case of the southern Baltic Sea coast where the shore has been and continues to be impacted by geological processes, climatic factors, and anthropogenic activities. The processes involved are shaped primarily by external factors such as wind–wave action, currents, storm surges, precipitation, winter ice cover, and gravitational mass movements. The shoreline response to climate change depends on both the nature of the change and the coastal zone characteristics. Long-term climate changes result in sea level changes. The sea level rise resulting from global warming enhances coastal erosion, particularly where the shore is built by poorly consolidated rocks and deposits. Coastal zones are usually very sensitive to all the external forces, therefore climate change will most likely be the strongest driver and will be the first to impinge on the coast, whereas the most distant changes in the oceans may produce effects delayed by decades or even centuries.


Climate Change and Coastal Processes in the Baltic Sea  

Tarmo Soomere

Various manifestations of climate change have led to complicated patterns of reactions of the Baltic Sea shores to varying hydrodynamic drivers. The northern and western bedrock and limestone coasts of this young water body experience postglacial uplift that is faster than the global sea-level rise. These coastal segments are thus insensitive with respect to changes in hydrodynamic forcing. Sedimentary and easily erodible coasts of the westernmost, southern, and eastern shores of this water body evolve under the impact of relative sea-level rise, changing wave properties and gradual loss of sea ice in conditions of chronic deficit of fine sediment. Several classic features of coastal processes, such as the cut-and-fill cycle of beaches, are substantially modified in many coastal sections. Waves approaching the shore systematically at large angles drive massive alongshore sediment transport in many coastal segments. This transport has led to the development of large sand spits and many relict lakes separated from the sea by coastal barriers. The concept of closure depth is reinterpreted because of frequent synchronization of strong waves and elevated water levels. The gradual loss of sea ice cover endangers most seriously coastal systems around the latitudes of the Gulf of Finland (about 60°N). The combined influence of climatically controlled sea-level rise and intense wave action leads to a gradual increase in eroding sections and the acceleration of coastal retreat on the southern downlifting shores of Poland and Germany. The bidirectional wind forcing has created a delicate balance of sediment on the shores of Latvia and Lithuania. This balance is vulnerable with respect to changes in strong wind directions. The sedimentary shores of Estonia host a number of small beaches that are geometrically protected against typical strong wind directions but are sensitive with respect to storms from unusual directions. Numerical analysis of sediment transport patterns along the eastern shores of the Baltic Sea has identified major changes in the wave directions in the Baltic Proper that can be attributed to manifestations of climate change.