Major controls on storm surge flooding: sea-level rise, climate or coastal landforms? Insights from the coastal sedimentary record of southern Baltic Sea

Lowland coasts, accounting for ca. 30% of the global coastline, are significantly threatened by the climate change, related sea-level rise and enhanced storminess. However, the role of key factors controlling the frequency and extent of extreme storm surges of inundation regime are not yet fully understood. In the present research we seek for the answer what are factors governing the susceptibility of the coast to storm surge flooding: is it coastal landforms development, storminess or rising sea-level?

            The southern Baltic Sea coast presents an ideal target for the research on the frequency and intensity of catastrophic storm surge flooding as it is nontidal/microtidal sea, where major water level fluctuations are related to well-documented past sea-level changes and storm surge floodings. Moreover, it is located in the area highly sensitive to latitudinal shifts in North Atlantic Oscillation and changes of the westerly storm tracks. Furthermore, the southern Baltic coast has recently been identified as the region where the storm surge flooding overtopping coastal barriers is one of the highest in the world and is expected to increase in the near future together with the climate change.

             We documented the longest to date, high-resolution sedimentary succession from the Polish coastal wetland located at Mechelinki, Puck Bay within the Gulf of Gdańsk at the southern Baltic sea coast. There, high-resolution records of extreme storm surge flooding of inundation regime within two periods: 3.6-2.9 ka BP and from ca. 0.7 ka BP until present, are preserved. The studied wetland succession, including sedimentary archive of storm surges, has been analyzed by sedimentological (grain size, loss-on-ignition, micromorphology), geochronological (¹⁴C, ²¹⁰Pb, ¹³⁷Cs), geochemical (XRF), mineralogical (heavy minerals) and micropaleontological (diatoms) methods. The results indicated that both periods were characterized by high-frequency storm surge flooding in order of 1.3 – 4.2 events per century. They are correlated to widely recognized enhanced storminess periods in NW Europe and took place during both rising and fluctuating sea levels. Our results show that the storm surge driven coastal inundation frequency and extent largely depend on the development of coastal barriers (e.g., beach ridges). Thus, in the context of the future coastal storm surge hazard, the protection of existing coastal barriers should be the prime concern.

The research project CatFlood is funded by National Science Centre, Poland, OPUS grant nr: 2018/29/B/ST10/00042