Summary
This study evaluates geological archives and a suite of proxy methods to identify and date past storm-surge events along the Halland coast, southwest Sweden, with a modern analogue site at Löderup in Scania. Using GIS-based site selection, targeted fieldwork and laboratory analyses including dating methods, we tested which coastal settings and methods best record overwash deposits and whether the geological record can extend the instrumental storm-surge record.
We found that storm-surge overwash deposits in the form of coarse sand, gravel and shell-rich beds with sharp erosional contacts are present at several investigated sites. Field visits and understanding of the local sedimentological and geomorphological context are vital to interpreting the data and in the selection of the most suitable proxies. The event layers are identifiable by sedimentological analysis, significantly aided by CT imagery, which provides high-resolution structural detail and grain detection. Geochemical proxies and luminescence profiling provide additional information on shifts in sediment source or energy.
Sandy strandplains record fewer events than coastal meadows, but their thicker beds may on the other hand allow reconstruction of hydraulic conditions during the depositional events. Individual events are more easily distinguished in coastal meadows with fine-grained sediment, and they likely provide a more comprehensive, but still incomplete record.
The dating methods show that the sediments are young, most are less than 100 years old. The chronological resolution of the records is so far low; luminescence dating is at its younger limit and lead-caesium dating requires additional analysis to yield more precise ages. The methods nevertheless provide ages consistent with each other, in stratigraphic order, and agree with observations of modern material (polymers) in the sediments.
The recovered geological record from the investigated sites is thus generally Young and discontinuous, largely overlapping the 20th – 21st centuries rather than producing continuous multi-centennial sequences. The number of event layers at a single site does not provide a complete record of events during this time. Many storms are not preserved: local morphology, sediment supply and meteorological-hydrological conditions strongly control whether an event is recorded.
Building a robust regional storm-surge chronology therefore requires sampling multiple sites across different settings and integrating several proxies. To go further back in time, sites in coastal wetlands or lagoons could be targeted. If combined with hydrodynamic modelling and historical/instrumental data, storm-surge reconstruction from geological archives has the potential to improve event attribution and support coastal risk assessments.