The Quaternary development as a trigger for the distribution of habitats in the North Sea and the Baltic Sea
Christian-Albrechts-University, Kiel
Richter, P.P.1; Schwarzer, K.1; Heinrich, C.1; Reimers, H.-C.2, Zeiler, M.3 1
Institute of Geosciences, Sedimentology, Coastal and Continental Shelf Research, Christian Albrechts-University, Kiel 2State Agency for Agriculture, Environment and Rural Areas Schleswig-Holstein (LLUR), Flintbek 3Federal Maritime and Hydrographic Agency(BSH), Hamburg
Institute of Geosciences
Sedimentology, Coastal and Continental Shelf Research
Introduction The different geological and morphological evolution of the non tidal Baltic Sea and tide dominated North Sea determine sediment distribution patterns as well as morphodynamic conditions. A comparison of both areas (Fig.1) provides a good example to elucidate the role of different geological histories for the development of habitats. Surveys, employing hydroacoustic systems (multibeam echosounder (only coastal waters), side-scan sonar) supplemented by groundtruthing (grab sampling, UW-video), were carried out to investigate the sea floor. Geological evolution of North Sea and Baltic Sea The Saalian Ice sheet covered the area of today’s Baltic Sea and the whole German Bight, whereas the ice sheet of the Weichselian glaciations did not reach the area of the southwestern and southern North Sea (Fig.1). Morainic material of Weichselian age is limited to the Baltic Sea. In the southern North Sea area periglacial conditions prevailed at that time. Weichselian melt water deposits form the base of the Holocene sequence. They are overlain by a thin cover (2-3m) of holocene deposits (Zeiler et al. 2000). The rivers Ems, Weser, and Elbe formed a glacial spillway draining into the North Sea basin, cutting into older glacial deposits (Saalian ice age). This process formed the flank of Sylt Outer Reef.
Fig. 1: Maximum extent of the inland ice sheets during Saale- and Weichselain glaciations. The lower courses of the rivers Ems, Weser and Elbe were forming a common spillway into the North Atlantik via the North Sea (Berner and Streif 2000; modified)
Fig. 3. Detailed map of Adlergrund with strongly heterogenious Side Scan Sonar mosaic (from Schwarzer & Diesing, 2006).
TYPE
Fig. 2: Distribution of sediments, stone fields and Side Scan Sonar Mosaics, including FFH sanctuaries, of the german Baltic Sea (based on Hermansen and Jensen (2000)).
Sylt Outer Reef
Results and Discussion As a result of the last glaciation, the Baltic Sea is characterised by numerous sills and basins originating from the last glacial period with a comparatively large relief. The basins function as sinks for fine-grained sediments (silt and clay), whilst sandy material is deposited in shallower areas (Fig. 2). This leads to a widespread patchy and heterogeneous distribution pattern (Fig. 2 + Fig. 3). The rather shallow southern North Sea shows poor distinctive morphological variations. Reworking processes of glacial deposits have progressed far more than in the Baltic Sea and there is a lack of significant abrasion platforms as they can be found in parts of the southern Baltic Sea. This leads to a much less patchy distribution pattern (Fig 4.), although locally reworked pleistocene material appears. There are major morphological differences which provide very dissimilar framework conditions for the differentiation of geo-habitats. The Baltic Sea developed a wide range of sub-habitats interlocked at the small-scale, whereas the North Sea exhibits larger scale habitat distribution patterns. Contact: Dr. Peter P. Richter Institute of Geosciences Sedimentology, Coastal and Continental Shelf Research Christian-Albrechts-Universität, Kiel Otto-Hahn Platz 1, 24118 Kiel Tel.: +49 (0)431 880-2877 Fax: +49 (0)431 880-4376
[email protected] http://www.ifg.uni-kiel.de/936.html
Fig. 4: Distribution of sediments (after Figge, 1981) of the North Sea, stone fields and Side Scan Sonar Mosaics in the german EEZ of the North Sea.
References: Berner, U. & Streif, H. (2000). Klimafakten. Der Rückblick - ein Schlüssel für die Zukunft. - 238 S.; Stuttgart (E. Schweizerbart´sche Verlagsbuchhandlung). Figge, K. (1981). Sedimentverteilung in der Deutschen Bucht. Deutsches Hydrographisches Institut, Karte Nr. 2900 (mit Begleitheft) Hermansen, B. & J. B. Jensen (2000). Digital Sea Bottom Map around Denmark. Geological Survey of Denmark (GEUS). Schwarzer, K. and Diesing, M. (2006). Abschlussbericht – Erforschung der FFH-Lebensraumtypen Sandbank und Riff in der AWZ der deutschen Nordund Ostsee. M Zeiler; J Schulz-Ohlberg,; K Figge (2000): Mobile sand deposits and shoreface sediment dynamics in the inner German Bight (North Sea) Acknowledgements: Data result from the projects: a) Full coverage sediment mapping in the North- and Baltic Sea by applying different hydroacoustic systems. Cooperation with the Federal Maritime and Hydrographic Agency (BSH). b) Compilation of marine Habitats in the Baltic Sea (several projects). Cooperation with State Agency for Agriculture, Environment and Rural Areas Schleswig-Holstein (LLUR) c) BfN project: Erforschung der FFH-Lebensraumtypen Sandbank und Riff in der AWZ der deutschen Nord- und Ostsee
