Unraveling the signals of sea level and storminess of the past millennium (southern North Sea; SEASTORM)
Final Report Abstract
The overarching objective of our project was to unravel the signals of regional sea level and storminess of the southern North Sea during the past millennium and under the conditions of future global warming. In order to address this objective, we combined high-resolution proxy data from active salt marshes and fossil polder deposits with results from regional model experiments. We found that the sediment sequences of foreland salt marshes document the response of coastal depositional processes to changing climate. In this context, we have established robust chronologies for the active salt marshes by combining various absolute and relative age dating methods with XRF core scanning data for the inter-correlation of the study sites. Mean marsh accretion rates range from 1.16 to 1.75 cm yr^-1, suggesting a high resilience of salt marshes to ongoing sea-level rise as long as sediment availability and natural flooding dynamics are maintained. End-member modelling of bulk grain-size distributions allowed for unravelling and quantification of natural and anthropogenic depositional processes. Periodic fluctuations in various element ratios on decadal timescales suggest a close linkage between local sediment accretion and large-scale atmosphere-ocean climate oscillations, and related storm-surge frequency and intensity. The abundance of abnormally grown tests of the salt marsh foraminifer Entzia macrescens between the year 1950 and the late 1980s documented increased environmental stress in a phase of amplified North Sea storm climate. Results from downscaling of global climate model simulations provided a 1000 year-long high-resolution extreme sea level (ESL) record for the North Sea, which showed large variations on interannual to centennial timescales without preferred oscillation periods. Downscaling of a large ensemble of anthropogenic climate change simulations showed, that ESLs increase with atmospheric CO2 levels, even without considering a rise in background sea level. Increase of local sea level of up to 0.5 m is found along the western shorelines of Germany and Denmark for ESLs of 20–50 years return periods. In summary, our findings have important implications for adapting coastal protection strategies.
Publications
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Evolution of a salt marsh in the southeastern North Sea region – Anthropogenic and natural forcing. Estuarine, Coastal and Shelf Science, 218(c(2019, 3)), 268-277.
Müller-Navarra, Katharina; Milker, Yvonne; Bunzel, Dorothea; Lindhorst, Sebastian; Friedrich, Jana; Arz, Helge & Schmiedl, Gerhard
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The long-term variability of extreme sea levels in the German Bight. Ocean Science, 15(3), 651-668.
Lang, Andreas & Mikolajewicz, Uwe
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Extreme high sea levels in the German Bight. PhD thesis, Universität Hamburg, 109 pp.
Lang, A.
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Integrated stratigraphy of foreland salt-marsh sediments of the south-eastern North Sea region. Newsletters on Stratigraphy, 53(4), 415-442.
Bunzel, Dorothea; Milker, Yvonne; Müller-Navarra, Katharina; Arz, Helge Wolfgang; Friedrich, Jana; Lahajnar, Niko & Schmiedl, Gerhard
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Rising extreme sea levels in the German Bight under enhanced $${{\mathrm {CO}}_2}$$ levels: a regionalized large ensemble approach for the North Sea. Climate Dynamics, 55(7-8), 1829-1842.
Lang, Andreas & Mikolajewicz, Uwe
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North Sea salt marshes and their response to changing storm-climate conditions over the last century. PhD thesis, Universität Hamburg, 93 pp.
Bunzel, D.
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North Sea salt-marsh archives trace past storminess and climate variability. Global and Planetary Change, 198(c(2021, 3)), 103403.
Bunzel, Dorothea; Milker, Yvonne; Müller-Navarra, Katharina; Arz, Helge Wolfgang & Schmiedl, Gerhard
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Determination and quantification of sedimentary processes in salt marshes using end‐member modelling of grain‐size data. The Depositional Record, 9(1), 4-29.
Lenz, Nina; Lindhorst, Sebastian & Arz, Helge W.
