Benthic foraminifera of late Quaternary sediments in the northern North Atlantic

Four long sediment cores from locations in the Framstrait, the Norwegian-Greenland Seas and the northern North Atlantic were analysed in a high resolution sampling mode (1 - 2 cm density) for their benthic foraminiferal content. In particular the impact of the intense climatic changes at glacial/interglacial transitions (terminations I and II) on the benthic community have been of special interest. The faunal data were investigated by means of multivariate analysis and represented in their chronological occurence. The most prominent species of benthic foraminifera in the Norwegian-Greenland Seas are Oridorsalis umbonatus, Cibicidoides wuellerstorfi, the group of Cassidulina, Pyrgo rotalaria, Globocassidulina subglobosa and fragmented tubes of arenaceous species. The climatic signal of termination I as well as termination II is recorded in the fossil foraminiferal tests as divided transition from glacial to interglacial. The elder INDAR maximum (individuals accumulation rate = individuals/sq cm * 1.000 y; Norwegian-Greenland Seas: average 3.000 - 6.000 individuals/sq cm * 1.000 y; northern North Atlantic: average 150 individuals/sq cm * 1.000 y) is followed by a period of decreased values. The second, younger maximum reaches comparable values as the elder maximum. The interglacial INDAR are in average 700 individuals/sq cm * 1.000 y in the Norwegian-Greenland Seas and 200 individuals/sq cm * 1.000 y in average in the northern North Atlantic. The occurence of the elder INDAR maximum shows a distinct chronological transgressivity between the northern North Atlantic (12.400 ybp.) and the Framstrait (8.900 ybp.). The time shift from south to north amounts 3.500 yrs., the average expanding velocity 0,78 km per year. Within the Norwegian-Greenland Seas the average expanding velocity amounts 0,48 km per year. This chronological transgressivity is interpreted as impact of the progressive expanding of the North Atlantic and the Norwegian Current during the deglaciation. The dynamic of the faunal development is defined as increasing INDAR per time. The elder INDAR maximum shows in both glacial/interglacial transitions an exponential increase from south to north. Termination II is characterized by a general higher dynamic as termination I. By means of the high resolution sampling density the impact of regional isotopic recognized melt-water events is recognized by an increase of endobenthic and t-ubiquitous species in the Norwegian-Greenland Seas sediments. During termination I the relative minimum between both INDAR maxima occur chronological with an decrease of calculated sea surface temperatures. This is interpreted as indication of the close pelagic - benthic coupling. The climatic signal in the northern North Atlantic recorded in the fossil benthic foraminiferal community shows a lower amplitude as in the Norwegian-Greenland Seas. The occurence of the epibenthic Cibicidoides wuellersforfi allows to evaluate the variability of the bottom water mass. In general at all core locations increasing lateral bottom currents are recognized with the occurence of the second younger INDAR maximum. In comparison with various paleo-climatological data sets fossil benthic foraminifers show a distinct koherence with changes of the atmospheric temperatures, the SSTs and the postglacial sea level increase. The benthic foraminiferal fauna is bound indirectly on and indicative for regional climatic changes, but principal dependent upon global climatic changes.

Investigation of N. pachyderma from the North Atlantic

The shells of the planktonic foraminifer Neogloboquadrina pachyderma have become a classical tool for reconstructing glacial-interglacial climate conditions in the North Atlantic Ocean. Palaeoceanographers utilize its left- and right-coiling variants, which exhibit a distinctive reciprocal temperature and water mass related shift in faunal abundance both at present and in late Quaternary sediments. Recently discovered cryptic genetic diversity in planktonic foraminifers now poses significant questions for these studies. Here we report genetic evidence demonstrating that the apparent 'single species' shell-based records of right-coiling N. pachyderma used in palaeoceanographic reconstructions contain an alternation in species as environmental factors change. This is reflected in a species-dependent incremental shift in right-coiling N. pachyderma shell calcite d18O between the Last Glacial Maximum and full Holocene conditions. Guided by the percentage dextral coiling ratio, our findings enhance the use of d18O records of right-coiling N. pachyderma for future study. They also highlight the need to genetically investigate other important morphospecies to refine their accuracy and reliability as palaeoceanographic proxies.

Flux data in the Greenland Basin

Pelagic processes and their relation to vertical flux have been studied in the Norwegian and Greenland Seas since 1986. Results of long-term sediment trap deployments and adjoining process studies are presented, and the underlying methodological and conceptional background is discussed. Recent extension of these investigations at the Barents Sea continental slope are also presented. With similar conditions of input irradiation and nutrient conditions, the Norwegian and Greenland Seas exhibit comparable mean annual rates of new and total production. Major differences can be found between these regions, however, in the hydrographic conditions constraining primary production and in the composition and seasonal development of the plankton. This is reflected in differences in the temporal patterns of vertical particle flux in relation to new production in the euphotic zone, the composition of particles exported and in different processes leading to their modification in the mid-water layers. In the Norwegian Sea heavy grazing pressure during early spring retards the accumulation of phytoplankton stocks and thus a mass sedimentation of diatoms that is often associated with spring blooms. This, in conjunction with the further seasonal development of zooplankton populations, serves to delay the annual peak in sedimentation to summer or autumn. Carbonate sedimentation in the Norwegian Sea, however, is significantly higher than in the Greenland Sea, where physical factors exert a greater control on phytoplankton development and the sedimentation of opal is of greater importance. In addition to these comparative long-term studies a case study has been carried out at the continental slope of the Barents Sea, where an emphasis was laid on the influence of resuspension and across-slope lateral transport with an analysis of suspended and sedimented material.