Hydrography of the German Bight

Abstract

This paper gives the physical oceanography background for the Bremerhaven Workshop on Biological Effects of Contaminants in the North Sea and the resulting papers contained in the volume. For the water quality bioassays, the benthic community analysis, and the benthic sediment bioassays the relevant hydrographic conditions are described and the results of model simulations carried out for the workshop are presented as well as an evaluation of the oceanographic observations carried out on board RV 'Valdivia' during the workshop. Two main conclusions must be drawn: (1) The German Bight is an area characterized by strong mesoscale variability in physical properties such as fronts, meanders and eddies. This vanabil~ty is also seen in the mobile superficial sediment and the resulting variability of the suspended matter content. (2) During the workshop the hydrographic situation in the German Bight was marked by highly saline inflows to the German Bight from the English Channel. The stations close to the East-Friesian coast are located within the contaminated Continental Coastal Water; the more offshore stations met more or less undiluted water originating from the English Channel, with a high portion of Atlantic Water.

Experimental trials on the feasibility of offshore seed production of the mussel Mytilus edulis in the German Bight: installation, technical requirements and environmental conditions

“…Due to the anti-clockwise tidal currents in the North Sea (Becker et al 1992;Ducrotoy et al 2000) the settled post-larvae may originate from inshore mussel beds along the Lower-Saxonian coast and, in some cases, from the intertidal areas from the Dutch Wadden Sea. Data of larvae numbers determined in the water are equivalent to those reported by Dobretsov and Miron (2001) for the White Sea and Cáceres-Martínez and Figueras (1998) for NW Spain being t1.3 and 1.2 £ 10 3 m ¡3 , respectively.…”

Benthos and demersal fish habitats in the German Exclusive Economic Zone (EEZ) of the North Sea

“…The coastal habitat is characterized by water masses, which are largely influenced by fresh water run-off from rivers resulting in low salinity and high nutrient input (Continental Coastal Water; according to Laevastu 1963). Additionally, water in the coastal habitat is well mixed throughout the year beneath the 20-30-m depth contour (Becker et al 1992) resulting in high seasonal temperature variations (Fig. 6).…”

“…As a consequence, management tools such as the ''Plaice Box'' (a coastal area closed for fishing to protect young plaice) lose effectiveness since juvenile plaice shifted its distribution towards more offshore waters (van Keeken et al 2007). Ehrich et al (2007) found that Becker et al (1992) demersal fish communities in the German Bight shifted from a gadoid-dominated community to a flatfish-dominated community in a period from 1987 to 2005. Distribution shifts in a sense of natural range expansion of, for example, southern species into the German EEZ were also found in the last decades.…”

“…For example, length of summer stratification increased towards the Duck's Bill, where a stable Significance level p \ 0.001 is indicated by * thermal stratification occurs from May to September. Water masses (central North Sea water) in the Duck's Bill habitat were characterized by lower seasonal temperature variation as well as medium salinity and nutrient concentration (Laevastu 1963;Becker et al 1992). Furthermore, stratification processes inhibited sedimentation of organic matter to the bottom and vice versa input of nutrients from bottom waters into upper layers, which resulted in a decreasing trend of TOC and chlorophyll a (Table 4), and hence food supply especially for benthic infauna species, from the coast to the Duck's Bill (Kröncke et al 2004).…”

Introduction to the Bremerhaven Workshop on Biological Effects of Contaminants

“…Experts were invited to prepare background papers in areas where additional knowledge was necessary to interpret the results of the workshop. T h s was especially important for the hydrography of the German Bight (Becker et al 1992). The latest information on migration of the dab in the German Bight (Rijnsdorp et al 1992) is necessary for the correct interpretation of fish disease as a measure of the effects of pollution (see Vethaak 1992).…”