Placing the deep Baltic Sea sediment stratigraphy in a precise chronological framework: Improved paleoenvironmental studies and 14C reservoir age calibration

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Varying climate and human activity altered the Baltic Sea ecosystem and left their footprint in the physical, biological and chemical properties of its sediments. Particularly, the partly fine-laminated sediments from the deep basins are valuable archives of these changes, because of their sub-decadal resolution. Understanding the processes behind the recorded environmental changes requires (i) knowledge about their temporal progression, i.e. the exact timing of the succession of changes within an event and the time-span from event to event, and (ii) to put them in a regional to hemispheric context. This knowledge is for Baltic Sea sediments presently hampered due to centennial-scale chronological uncertainties. Therefore, utilizing the down to sub-decadal environmental information in deep Baltic Sea sediments necessitates their placement in an improved chronological framework. Globally common production rate variations of the cosmogenic radionuclides 10Be and 14C can provide a novel tool for constructing such a framework. A pilot 10Be time-series covering the Mid-Holocene enabled the synchronization of Baltic Sea sediments from the Western Gotland Basin to the absolute dated 14C production record from the IntCal20 calibration curve. This alignment reduced the existing centennial chronological uncertainties to ± 10-15 years. Within this proposal, we aim at the establishment of a continuous decadal-scale 10Be record from sediments of the Western Gotland Basin, as well as its alignment to the atmospheric 14C record for the complete brackish Littorina Stage of the Baltic Sea, i.e. the last 8000 years. In addition, the project will apply the common cosmogenic radionuclide production rate variations to synchronize the new 10Be record to existing cosmogenic radionuclide time-series from sediment and ice core archives in the Circum-Baltic region and across the Northern Hemisphere. Based on the improved chronological constraints, we will determine the progression of physical, chemical and biological proxy responses in Baltic Sea sediments associated with major environmental transitions at sub-decadal precision and place them into a regional to hemispheric context. Such investigations provide significantly improved constraints about possible temporal ranges and amplitudes of Baltic ecosystem responses to contrasting environmental forcing and allow us to better anticipate the effects of the anthropogenic climate change. In addition, comparing the new 10Be-based chronology with systematic offsets in existing 14C dates can enable us the construction of a 14C reservoir age calibration curve and reduce the presently centennial-scale uncertainties of radiocarbon dating in this archive to a few decades.