Possible causes of sediment dynamics and mixing in western Baltic Sea basins

Transcription

1 Tauber, F. (2012), BSH, BSBD Possible causes of sediment dynamics and mixing in western Baltic Sea basins Dennis Bunke Thomas Leipe, Matthias Moros & Helge W. Arz

2 Tauber, F. (2012), BSH, BSBD Introduction Shallow mud basins influenced by wind-driven waves and currents Water exchange with North Sea through Danish straits and with Bornholm Basin No considerable direct fluvial input Arkona Basin 2

3 Tauber, F. (2012), BSH, BSBD Introduction Shallow mud basins influenced by wind-driven waves and currents Water exchange with North Sea through Danish straits and with Bornholm Basin No considerable direct fluvial input Deposition areas with up to 11 m thick Holocene mud Arkona Basin Final sink or only intermediate and long-term storage for imported material? Bonecker, P. (unpubl.) 3

4 Objectives SECOS: The service of sediments in German coastal seas Evaluating the function of marine benthic systems in the context of human use Service functions of the Baltic Sea Quantify the inventory and mass accumulation rates of lithogenic, biogenic and anthropogenic matter Grain size TOC, TIC, N, S, P, Hg, Biogenic silica (SiO2) Ca, Cr, Cu, Fe, Mn, Pb, Zn, As Radionuclide dating ( 2 Pb, 137 Cs) of short cores to estimate sedimentary mixing depths, lateral transports and rates of erosion and deposition Temporal and spatial distribution patterns History of anthropogenic impacts (last years) Linkage with observational and modelling results of small-scale mixing and transport processes 4 Sediment dynamic (within and between basins) Overlapping of natural mixing (Bio-/Hydroturbation) and anthropogenic impact

5 Geochemical mapping Arkona Basin / Pomeranian Bight Mercury as good example of anthropogenic pollution Positive correlation with organic-rich fine material Military dumping site from WWII Resuspension and lateral Arkona transport Basin of / contaminants Pomeranian Bight Hg content Leipe, T. & Naumann, M. (unpubl.) 5

6 Geochemical profiling Arkona Basin / Pomeranian Bight Arkona Basin / Pomeranian Bight Hg content Leipe, T. & Naumann, M. (unpubl.) 6

7 Sediment fabric analysis Fine-scale X-radiographs reveal trace fossils and layers of storm and inflow events Sedimentary structure is partly overprinted by burrowing organisms living in surface sediments Station 17-7 (Arkona Basin) Station 57- (Mecklenburg Bight) 1 cm 9 Thanks to Aki Kallonen, University of Helsinki

8 Depth [cm] Bioturbation Chlorophyll measurements indicate a high bioturbation down to 3 cm depth and a medium bioturbation down to 6 cm depth in the Arkona Basin Chl a [µg/ml] Recent main species (abundance/biomass) Bivalvia Macoma balthica Polychaeta Scoloplos armiger Bivalvia Arctica islandica 9 Morys, C. (unpubl.) Gogina, M.

9 Hydroturbation First particle resuspension at 7- cm/s Storm events like XAVER (Dec 2013) are powerful enough to reach and resuspend bottom sediments in the Arkona Basin Wind velocity [m/s] resuspension of first particles (cm/s) resuspension of particles sand silt sandy silt july 2014 oct 2014 mean grain size grain size (µm) N-S current velocity at 42 m depth [cm/s] Salinity at 43 m depth [PSU] STOLT OB LB MB AB TW 0 5 Dec 6, Morys, C. & Brodte, E.-M. (unpubl.) MARNET, BSH (2013) Prien, R. (2013)

10 SALINITY [PSU] Hydroturbation Inflow events cause strong bottom currents that follow the morphology of the Baltic Sea floor cm/s Seifert, T. (1997) 13 Prien, R. (2013)

11 Anthropogenic impact Sediment mixing by bottom trawling and construction activities at the sea floor Deep Sea Conservation Coalition 14 EnBW Baltic 2

12 Conclusion Western Baltic Sea basins are at least intermediate storage for imported material on a centennial scale Sediments affected by various mixing processes Ongoing bioturbation of surface sediments with changing intensity Episodic resuspension and lateral transport caused by storm and inflow events In-depth disturbance due to human activities Goal to distinguish between individual impacts of these processes needs further investigations Thank you for your attention! 16