Helena Alexanderson

Storm surges combine the power of two natural hazards, strong winds and flooding, and can have devastating effects on people, infrastructure, and nature in coastal areas. Ongoing global changes, including rising sea levels and shifting storm patterns, are expected to increase both the frequency and amplitude of such events in the future. There are, however, significant regional variations and some trends are uncertain. To improve our understanding of the factors and processes that control coastal flooding and increase our ability to assess future risks at time scales relevant for coastal management, we require storm surge records that extend back beyond the instrumental era.
In this pilot study we have explored the coastal sedimentary record at several sites along the coast of Halland and Scania in southern Sweden with the aim of identifying past storm surges. Sites with both known storm surge deposits (e.g. from storm Babet in October 2023) and sites expected to contain traces of older events were investigated. A range of sedimentological, geochemical and dating methods have been applied and tested to evaluate what works best for these types of deposits, including X-ray fluorescence (XRF), X-ray computed tomography (CT), carbon/nitrogen (C/N) isotope analysis, luminescence and 210Pb dating, and grain-size analysis.
Storm surge deposits at the studied sites include massive sandy beds or laminae that differ in grain size and/or composition from the normal accumulation, heavy-mineral lamination, and massive shell beds. Most geochemical and dating results are still pending, but preliminary data indicate that at least the upper parts of the studied stratigraphies are young (<100 years) as also indicated by the presence of polymer fibres in some of the sediments. Our results so far indicate that beach meadows may be the most promising setting in terms of number of events recorded (possibly up to nine at site Rosendal), while sandy berm beaches may contain traces of fewer events, but with deposits that are thicker and more easily traceable inland and alongshore.