Unraveling the signals of sea level and storminess of the past millennium (southern North Sea; SEASTORM)

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We propose to unravel the signals of regional sea level and storminess of the southern North Sea during the past millennium and under future global warming. The hypothesis to test is that existing proxy-based sea-level reconstructions bear a so far underestimated climate component. In order to address this hypothesis we combine high-resolution proxy data from active salt marshes and fossil polder deposits with results from regional model experiments, which help to understand the relevant mechanisms behind storm flood variability and allow us to estimate the evolution of storm flood variability under climate change. Specifically we want to address the following objectives: 1) Generation of data series of relative sea level and storminess of the past millennium, 2) Evaluation of the impacts of shifts in local storm climate on proxy-based sea-level reconstructions, 3) Validation of the proxy-based data series of storminess, 4) Quantification of extreme storm flood variability in the German Bight and investigation of their associated forcing mechanisms, 5) Estimation of extreme storm flood variability under future global warming, and 6) Investigation of the response of modern salt marsh environments to regional sea-level and climate change.
Both proxy and model approaches will jointly focus on understanding storm flood variability and associated drivers. Sediments of the past century will be cored in naturally grown salt marshes. Fossil marsh sediments from medieval to early modern polders will be further evaluated. Detailed sedimentological and geochemical data will allow for reconstruction of the depositional environments and for the identification of storm-surge layers. Application of a foraminiferal transfer function will deliver information on relative elevation and submergence changes with respect to the tidal frame. The proxy studies will be complemented by regional Earth System Model experiments investigating the climate variability and storm frequency of the North Sea for selected time intervals of the past millennium. These data will be used to study the relationships between decadal variations of extreme sea-level variability in the German Bight and associated large-scale climate variations. The large extreme value variations found in the last millennium simulations have shown that the standard approach to estimate future sea-level extremes does not account for their full variability spectrum and the typical ensemble size is not sufficient to separate signal from noise. We will therefore employ a large ensemble approach to estimate future changes in extreme sea-level statistics, allowing the detection of a potential climate change signal. 
Our project will provide the first attempt to reconstruct the forcing mechanisms and coastal impacts of sea-level variability and storminess of the southern North Sea by directly combining proxy data from sediment archives and climate modeling information.