A. Schröder-Ritzrau

Plankton in the Norwegian-Greenland Sea: from living communities to sediment assemblages —an actualistic approach

A synoptic study is carried out to reconstruct the development of the plankton community in the late Quaternary in the Norwegian-Greenland Sea. It comprises quantitative analyses of coccolithophores, dinoflagellate cysts, diatoms and radiolarians. An actualistic approach is applied to evaluate the different fossil records of these plankton groups. The preliminary results of the current investigation are reported here.The composition and distribution of living communities of coccolithophores are presented as an example. A close relationship between the distribution of regional groups and surface water masses is observed. Seasonal vertical fluxes of coccolithophores and radiolarians through the water column show similar patterns within different years. However, diatoms are highly variable, both in absolute fluxes and species composition. The differentiation of sporadic and periodic processes is evident only after several years of observation. During settling and sedimentation biotic and abiotic processes such as grazing, dissolution and lateral transport alter the assemblages.Investigation of death assemblages in surface sediments reveals that in spite of these alteration processes the abundance and species distribution are related to surface water masses. Higher abundances and diversities are usually found in sediments underlying the warm Norwegian Current. Concentrations decrease to the north-west towards the cold polar water masses.The sediment assemblages of all groups are strongly altered relicts of former living communities. They are characterized by distinct changes in species composition and absolute abundances related to palaeo-oceanographic development. Their variation through the sedimentary record is used to distinguish four ecostratigraphic units during the late Weichselian and Holocene.

Distribution, Export and Alteration of Fossilizable Plankton in the Nordic Seas

The present study gives an overview of recent research results concerning the distribution of living fossilizable plankton groups (coccolithophores, diatoms, dinoflagellate cysts, radiolarians and planktic foraminifers) in the water column of the Nordic Seas. Information is combined with results of sediment trap investigations on fluxes and the species composition of these fossilizable plankton groups in the Nordic Seas and their relation to oceanographic conditions. In order to validate spatial and temporal occurrence patterns of the plankton assemblages, their fluxes were monitored with sediment traps over several years in three different oceanic regions, characterized by the major surface water masses of the Nordic Seas. In addition, the alteration processes on settling plankton assemblages were investigated at three water depths.

Distribution of Calcareous, Siliceous and Organic-Walled Planktic Microfossils in Surface Sediments of the Nordic Seas and their Relation to Surface-Water Masses

The distribution of calcareous, siliceous and organic-walled planktic microfossils has been investigated in surface sediments from the Nordic Seas, Planktic foraminifers, coccolithophores, radiolarians, diatoms and dinoflagellate cysts generally reflect major oceanographic domains in the distribution of sediment assemblages, The occurrence of fossilizable plankton in the water column and in sediments has been compared to describe processes which alter the composition of assemblages.

The Potential of Synoptic Plankton Analyses for Paleoclimatic Investigations: Five Plankton Groups from the Holocene Nordic Seas

Five plankton groups, including diatoms, radiolarians, coccolithophores, foraminifers, and dinoflagellate cysts, were synoptically analyzed in six sediment cores and two sediment traps from the Norwegian-Greenland Sea and the North Atlantic in order to provide more detailed insights into the paleoclimatic and paleoceanographic evolution and the development of plankton assemblages of the northern North Atlantic during the last 15, 000 years. Based on Q-mode factor analyses, cold, warm, transitional, and relict assemblages were calculated for each of the plankton groups. Data from the different plankton groups complement one another, although they are not always consistent. However, the multiple plankton-group data set is able to bridge intervals in which single groups lack preservation or the ability to react to changes. Synoptically interpreted, the results provide a detailed picture of the response of plankton assemblages to environmental changes during the time period investigated, which includes the Bolling/ Allerod interstadial, the Younger Dryas cold spell, Termination IB, and, in all likelihood, also the “8, 200 Event”, and the Hypsithermal (approximately 8-4 14C ky BP).

Present and Past Oceanographic Controls of Sediment Formation in the North Atlantic-Arctic Gateway (A Critical Appraisal of SFB 313 Scientific Results)

This concluding chapter presents a critical appraisal of the research carried out within the framework of SFB 313. We will try to outline the scientific perspectives and problems as well as our approach to their solution. Moreover, we shall describe the scientific highlights of the results and define areas where we followed questionable assumptions and therefore failed to achieve what we had hoped for. A complete documentation of the various activities of SFB 313 (including an overview of research cruises, etc.) can be found in Schafer and Schroder-Ritzrau (1999).