Estimated chronologic ages of benthic microfossil events in ODP Site 105-647 (Table 1)

Benthic foraminifers were examined from the Paleogene of Ocean Drilling Program (ODP) Site 647 and Deep Sea Drilling Program (DSDP) Site 112 in the southern Labrador Sea. The Paleogene sequence of the deep Labrador Sea can be subdivided into seven assemblages, based on the ranges and relative abundance of characteristic taxa. The first occurrences (FOs) and last occurrences (LOs) of important benthic taxa are calibrated to a standard biochronology, by interpolating from our age model for Site 647. The biostratigraphy of Site 647 is used to improve the age estimates of Site112 cores. Fifteen microfossil events in Site 647 also are found in the sedimentary wedge along the Labrador Margin. A comparison of the probabilistic microfossil sequence from the Labrador Margin with that at Site 647 yields four isochronous benthic foraminifer LOs. Two new species are described from Sites 647 and 112: Hyperammina kenmilleri, Kaminski n.sp., and Ammodiscus nagyi Kaminski n.sp. Significant faunal turnovers are observed at the Ypresian/Lutetian and Eocene/Oligocene boundaries. The Ypresian/Lutetian boundary is characterized by a Glomospira-facies and is attributed to a rise in the CCD (carbonate compensation depth) associated with the NP14 lowstand in sea level. The Eocene/Oligocene boundary is delimited by the LO of Spiroplectammina spectabilis and Reticulophragmium amplectens. The change from an Eocene agglutinated assemblageto a predominantly calcareous assemblage in the early Oligocene took place gradually, over a period of about 4 Ma, but the rate of change accelerated near the boundary. This faunal turnover is attributed to changes in the preservationof agglutinated foraminifers, as delicate species disappeared first. Increasingly poorer preservation of agglutinated foraminifers in the late Eocene to earliest Oligocene reflects the first appearance of cool, nutrient-poor deep water in the southern Labrador Sea. The approximately coeval disappearance of agglutinated assemblages along the Labrador Margin was caused by a regional trend from slope to shelf environments, accentuated by the 'mid'-Oligocene lowstand in sea level.

Distribution of benthic foraminifera in surface sediments of the Portuguese continental margin

Living and dead benthic Foraminifera of 26 sediment surface samples from the East Atlantic continental margin (off Portugal) are studied. The stations are located on two profiles off Cape Mondego and off Cape Sines, ranging in water depth from 45 to 3905 meters. The highest values of standing crop are on the shelf (200 m) (up to 420 specimens/10 cm**3). Below 1000 m water depth standing crop is low (5 -24 specimens/10 cm**3). 151species and species groups are distinguished. Most of the living species do occur in a wide depth range. Faunal depth boundaries are at 50/100m, at 600/800 m, and at 1000 m. Results published from the North Atlantic and the East Mediterranean do not differ from those obtained in samples off Portugal. Depth of water (e.g. hydrostatic pressure) or another factor being controlled by depth (e.g. limitation of food supply) seems to be the most important factor of the benthic foraminiferal distribution.

Agglutinated benthic foraminifera of the Upper Cretaceous

A reexamination of the agglutinated benthic foraminiferal microfaunas found in the Upper Cretaceous red and brown clays of DSDP Hole 603B and ODP Holes 640A and 641A allows us to refine the initial shipboard biostratigraphic interpretation and to propose a fourfold zonation that can be used with some precautions in the oceanic realm. By means of various calibrations, an attempt is also made to integrate this zonation in a worldwide chronostratigraphic framework. The resulting chronologic control permits us to discern large differences in the rhythm of red clay deposition on either side of the North Atlantic Ocean.

Eocene benthic foraminifera of DSDP Hole 93-605

This paper describes and illustrates early to middle Eocene benthic foraminifers from northwest Atlantic Site 605, on the continental rise off New Jersey. Benthic foraminiferal faunas are dominated by Bulitnina spp., Nuttallides truempyi, Lenticulina spp., and Cibicidoides spp. Other common taxa include Oridorsalis spp., Gyroidinoides spp., uniserial taxa, arenaceous taxa, and Globocassidulina subglobosa. Together, these taxa usually make up 70% or more of the total fauna. The assemblages are interpreted as indicating a lower bathyal environment of deposition during the Eocene at Site 605. This is corroborated by an independent water depth estimate through backstripping, indicating a water depth for the beginning of the Eocene to late middle Eocene of approximately 2300 to 2000 m.

(Table 2) Species composition of agglutinated foraminifers from the abyssal zone of the Pacific Ocean

The quantitative study of distribution and taxonomic composition of recent living and dead (without plasma) benthic foraminifers revealed three foraminiferal assemblages in bottom sediments of the Pacific Ocean at depths of 3350 to 4981 m. The assemblage dominated by epibenthic Lagenammina difflugiformis, Reophax dentaliniformis, and Saccorhiza ramose occupies slopes of underwater hills. The assemblage with a high share of infaunal Cribrostomoides subglobosum, C. nitidum, and Ammobaculites agglutinans is registered on an abyssal plateau. The assemblage with a significant proportion of large Astrorhiza and Reophax species, which are characterized by active way of life, populates gentle slopes and narrow depressions with potentially strong bottom currents.

Benthic foraminifera in the Arctic Ocean

We examine the quantitative composition of benthic foraminiferal assemblages of Rose Bengal-stained surface samples from 37 stations in the Laptev Sea, and combine this data set with an existing data set along a transect from Spitsbergen to the central Arctic Ocean. Foraminiferal test accumulation rates, diversity, faunal composition and statistically defined foraminiferal associations are analysed for living (Rose Bengal-stained) and dead foraminifers. We compare the results of several benthic foraminiferal diversity indices and statistically defined foraminiferal associations, including Fisher's alpha and Shannon-Wiener diversity indices, Q-mode principal component analysis and correspondence analysis. Diversity and faunal density (standing stock) of living benthic foraminifers are positively correlated to trophic resources. In contrast, the accumulation rate of dead foraminifers (BFAR) shows fluctuating values depending on test disintegration processes. Foraminiferal associations defined by Q-mode principal component analysis and correspondence analysis are comparable. The factor values of the correspondence analysis allow a quantitative correlation between the foraminiferal fauna and the local carbon flux, which may be used as a tool to estimate changes in primary productivity.

Benthic foraminifera off West Africa (1°N to 32°S)

Recent benthic foraminifera (> 125 µm) were investigated from multicorer samples on a latitudinal transect of 20 stations between 1°N and 32°S along the upper slope off West Africa. Samples were selected from a narrow water depth interval, between 1200 and 1500 m, so that changes in water masses are minimized, but changes in surface productivity are important and the only significant environmental variable. Live (Rose Bengal stained) benthic foraminifera were counted from the surface sediment down to a maximum of 12 cm. Dead foraminifera were investigated in the top 5 cm of the sediment only. Five live and five dead benthic foraminiferal assemblages were identified using Q-mode principal component analysis, matching distinct primary productivity provinces, characterized by different systems of seasonal and permanent upwelling. Differences in seasonality, quantity, and quality of food supply are the main controlling parameters on species composition and distribution of the benthic foraminiferal faunas. To test the sensitivity of foraminiferal studies based on the uppermost centimeter of sediment only, a comparative Q-mode principal component analysis was conducted on live and dead foraminiferal data from the top 1 cm of sediment. It has been demonstrated that, on the upper slope off West Africa, most of the environmental signals as recorded by species composition and distribution of the 'total' live and dead assemblages, i.e., including live and dead foraminifera from the surface sediment down to 12 cm and 5 cm, respectively, can be extracted from the assemblages in the top centimeter of sediment only. On the contrary, subsurface abundance maxima of live foraminifera and dissolution of empty tests strongly bias quantitative approaches based on the calculation of standing stocks and foraminiferal numbers in the topmost centimeter.

Communities and microhabitats of living benthic foraminifera from the tropical East Atlantic

Living (Rose Bengal stained) benthic foraminifera were collected with a multicorer from six stations between 2°N and 12°S off West Africa. The foraminiferal communities in the investigated area reflect the direct influence of different productivity regimes, and are characterized by spatially and seasonally varying upwelling activity. At five stations, foraminiferal abundance coincides well with the gradient of surface productivity. However, at one station off the Congo River, the influence of strong fresh water discharge is documented. Although this station lies directly in the center of an upwelling area, foraminiferal standing stocks are surprisingly low. It is suggested that the Congo discharge may induce a fractionation of the organic matter into small and light particles of low nutritional content, by contrast to the relatively fast-sinking aggregates found in the centers of high productivity areas. Quality and quantity of the organic matter seem to influence the distribution of microhabitats as well. The flux of organic carbon to the sea-floor controls the sequence of degradation of organic matter in sediment and the position of different redox fronts. The vertical foraminiferal stratification within sediment closely parallels the distribution of oxygen and nitrate in porewater, and reflects different nutritive strategies and adaptation to different types of organic matter. The epifauna and shallow infauna colonize oxygenated sediments where labile organic matter is available. The intermediate infauna (M. barleeanum) is linked to the zone of nitrate reduction in sediments where epifaunal and shallow infaunal species are not competitive anymore, and must feed on bacterial biomass or on metabolizable nutritious particles produced by bacterial degradation of more refractory organic matter. The deep infauna shows its maximum distribution in anoxic sediments, where no easily metabolizable organic matter is available.