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Coastal fens like the nature reserve "Hutelmoor und Heiligensee" (north-eastern Germany) are important landscape elements along the southern Baltic coast, which exchange fresh water and brackish water with the Baltic Sea. These exchange processes can be understood as experiments with a natural tracer, which may be used to investigate the hydrologic behaviour of these fen systems. With the establishment of coastal protection measures such as dunes and dikes, the installation of surface drainage and, more recently, also nature conservation measures, the hydrologic regime of these coastal wetlands has constantly altered over the last centuries.The rehabilitated wetland "Hutelnnoor und Heiligensee" is suitable for an analysis of hydrologic change as it has been monitored over the time period since nature conservation measures started in the 1990s. Collected data sets included observation of groundwater levels and electrical conductivities, weather data as well as discharge at the outlet of the drainage catchment. In this article, as a second part of the dual publication, processes and quantified process magnitudes have been identified that govern the salt balance of the study area including its variability in space and time. It was detected that - over the period of rehabilitation - salt water entered the catchment with an episodic storm surge by wave overtopping of dunes in 1995. The intruded brackish water was then diluted, which was a slow process extending over decades. It was governed by local groundwater recharge from precipitation and the inflow of relatively fresh groundwater from the hinterland. It is concluded that salt inputs from the Baltic Sea provide a natural tracer of hydrological processes, which can be readily monitored via electrical conductivity measurements.
Geochemistry and Ar-40/Ar-39 age of Early Carboniferous dolerite sills in the southern Baltic Sea
(2015)
The Early Carboniferous magmatic event in the southern Baltic Sea is manifested by dolerite intrusions. The presumable area in which the dolerite intrusions occur ranges from 30 to 60 km in east-west direction, and is about 100 km in north-south direction. The dolerites were sampled in well D1-1 and investigated by applying chemical analysis and Ar-40/Ar-39 step-heating dating. Dolerites are classified as alkali and sodic, characterized by high TiO2 (3.92, 3.99 wt%) and P2O5 (1.67, 1.77 wt%) and low MgO (4.89, 4.91 wt%) concentrations, enriched in light rare earth elements, originated from an enriched mantle magma source and emplaced in a continental rift tectonic setting. The 351 +/- 11 Ma Ar-40/Ar-39 plateau age for groundmass plagioclase indicates a considerable age gap with the 310-250 Ma magmatism in southern Scandinavia and northern Germany. The magmatic rocks in the Baltic Sedimentary Basin are coeval with alkaline intrusions of NE Poland. Both magmatic provinces lie in the northwestward prolongation of the Pripyat-Dnieper-Donetsk Rift (370-359 Ma) and may constitute a later phase of magmatic activity of this propagating rift system.