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MSM51: Forschungsfahrt Maria S. Merian MSM51-2

The cruise is designed to execute seismo- and hydroacoustic surveys, sampling of Holocene sediments in the western, central and northeastern Baltic Sea, and investigate the water column wintertime mixing close to sea-ice limits. The surveys, sediment coring and hydrographic measurements should fill important gaps in existing data sets, which improve our understanding variations in the ventilation of the deeper Baltic, considering not only external climate forcing but also the effects of postglacial sea-level rise and isostatic uplift. In particular, we want to investigate in more detail the impact of the Littorina transgression on the inflow of saline waters into the western Baltic and assess the potential for future diminution of ventilation in the central and northern deeper basins as - due to the geomorphological adjustment - the influence of saline water inflow in these basins is likely to decrease. The role of wintertime deep mixing in deep water oxygenation of northern basins will be studied in detail. Moreover, the western and northeastern regions actually experience increasing erosion of early to mid-Holocene sediments that are transported into the deeper central basins. The response of deeper ventilation and overall ecosystem conditions to such an erosional activity, e.g., organic matter re-suspension and transport of contaminants, cannot be predicted with available data and models. A new sampling and surveying campaign in the northeastern basins during maximum sea ice extent (likely in February) and the deployment of a new vibrocorer system, especially in siltysandy sediment drifts and transgressive deposits outside and close to the deeper basins are, therefore, very important for a more quantitative assessment of Holocene water and sediment budgets as well as to account for the impact of budget changes on the Baltic Sea ecosystem during the Littorina Stage.