Abundance and biomass of the benthic infauna of the North Sea

In 1986 participants of the Benthos Ecology Working Group of ICES conducted a synoptic mapping of the infauna of the southern and central North Sea. Together with a mapping of the infauna of the northern North Sea by Eleftheriou and Basford (1989, doi:10.1017/S0025315400049158) this provides the database for the description of the benthic infauna of the whole North Sea in this paper. Division of the infauna into assemblages by TWINSPAN analysis separated northern assemblages from southern assemblages along the 70 m depth contour. Assemblages were further separated by the 30, 50 m and 100 m depth contour as well as by the sediment type. In addition to widely distributed species, cold water species do not occur further south than the northern edge of the Dogger Bank, which corresponds to the 50 m depth contour. Warm water species were not found north of the 100 m depth contour. Some species occur on all types of sediment but most are restricted to a special sediment and therefore these species are limited in their distribution. The factors structuring species distributions and assemblages seem to be temperature, the influence of different water masses, e.g. Atlantic water, the type of sediment and the food supply to the benthos.

(Figure 4) Stratigraphic distribution of planktonic foraminifera in DSDP Hole 93-604

During Deep Sea Drilling Project Leg 93, upper Miocene through Quaternary sediments were continuously cored in Hole 604, located on the upper continental rise of the New Jersey transect (western North Atlantic). A detailed biostratigraphic study of these strata has been made using the vertical distribution of planktonic foraminifers. The Quaternary climatic zonation of Ericson and Wollin (1968) has been tentatively delineated and all the Pliocene zones and subzones (sensu Berggren, 1977) have been recognized. The rate of sedimentation was slow during most of the Pliocene but underwent a significant acceleration in the early Pleistocene. Quantitative variations in the distribution of planktonic foraminifers appear to be influenced by various factors, such as hydrodynamic winnowing resulting from the action of bottom currents and surficial thermal conditions caused by climatic changes. Both dissolution intervals and brief increases in the coarser detrital input seem, most of the time, to be correlated with indications of climatic cooling and may correspond to glacial events or cycles. This chapter delineates a precursor stage in the inception of Northern Hemisphere glaciation at 3 Ma and wide-scale Quaternary glacial-interglacial cycles. Data from a detailed study of Hole 604 are briefly compared with the main sedimentary and microfaunal features of contemporaneous series previously drilled along the east American margin in the northwestern Atlantic. One of the striking observations appears to be the intense redistribution of sediments that affected this region in Neogene-Quaternary times.