Foraminiferal assemblage and statistical analysis of surface sediment samples from the Golfe d'Arguin, Mauritania

With the growing pressure of eutrophication in tropical regions, the Mauritian shelf provides a natural situation to understand the variability in mesotrophic assemblages. Site-specific dynamics occur throughout the 1200 m depth gradient. The shallow assemblages divide into three types of warm-water mesotrophic foraminiferal assemblages, which is not only a consequence of high primary productivity restricting light to the benthos but due to low pore water oxygenation, shelf geomorphology, and sediment partitioning. In the intermediate depth (approx. 500 m), the increase in foraminiferal diversity is due to the cold-water coral habitat providing a greater range of micro niches. Planktonic species characterise the lower bathyal zone, which emphasizes the reduced benthic carbonate production at depth. Although, due to the strong hydrodynamics within the Golf, planktonic species occur in notable abundances through out the whole depth gradient. Overall, this study can easily be compared to other tropical marine settings investigating the long-term effects of tropical eutrophication and the biogeographic distribution of carbonate producing organisms.

Recent benthic foraminifera of the Scotia Sea and Argentine Basin

We investigated 88 surface sediment samples taken with a multiple corer from the southwestern South Atlantic Ocean for their live (Rose Bengal stained) and dead benthic foraminiferal content. Using Q-Mode Principal Component Analysis six live and six dead associations are differentiated. Live and dead association distributions correspond fairly well; differences are mainly caused by downslope transport and selective test destruction. In addition, four potential fossil associations are calculated from the dead data set after removal of non-fossilizable species. These potential fossil associations are expected to be useful for paleoceanographic reconstructions. Environments are described in detail for the live and potential fossil associations and for selected species. Along the upper Argentine continental slope strong bottom currents control the occurrence of live, dead and potential fossil Angulogerina angulosa associations. Here, particles of a high organic carbon flux rate remain suspended. Below this high energy environment live, dead and potential fossil Uvigerina peregrina dominated associations correlate with enhanced sediment organic carbon content and still high organic carbon flux rates. The live A. angulosa and U. peregrina associations correlate with high standing crops. Furthermore, live and dead Epistominella exigua-Nuttallides umbonifer associations were separated. Dominance of a Nuttallides umbonifer potential fossil association relates to coverage by Antarctic Bottom Water (AABW) and Lower Circumpolar Deep Water (LCDW), above the Calcite Compensation Depth (CCD). Three associations of mainly agglutinated foraminifera occur in sediments bathed mainly by AABW or CDW. A Reophax difflugiformis association was found in mud-rich and diatomaceous sediments. Below the CCD, a Psammosphaera fusca association occurs in coarse sediments poor in organic carbon while a Cribrostomoides subglobosus-Ammobaculites agglutinans association covers a more variable environmental range with mud contents exceeding 30%. One single Eggerella bradyi-Martinottiella communis association poor in both species and individuals remains from the agglutinated associations below the CCD if only preservable species are considered for calculation.

Oligocene to early Miocene benthic foraminifera in the eastern Equatorial Pacific

We investigated Oligocene and early Miocene benthic foraminiferal faunas (> 105 µm in size) from Ocean Drilling Program (Leg 199) Site 1218 (4826 m water depth and ~3300 to ~4000 m paleo-water depth) and Site 1219 (5063 m water depth and ~4200 to ~4400 m paleo-water depth) to understand the response of abyssal benthic foraminifera to mid-Oligocene glacial events in the eastern Equatorial Pacific Ocean. Two principal factor assemblages were recognized. The Factor 1 assemblage (common Nuttallides umbonifer) is related to either an influx of the Southern Component Water (SCW), possibly carbonate undersaturated, or a decrease in seasonality of the food supply from the surface ocean. The Factor 2 assemblage is characterized by typical deep-sea taxa living under variable trophic conditions, possibly with a seasonal component in food supply. The occurrence of abyssal benthic foraminifera faunas during the mid-Oligocene depends on either the effect of SCW or the seasonality of food resources. The Factor 1 assemblage was most common near 76Ol-C11r, 73Ol-C10rn and 67Ol-C9n (ca. 30.2, 29.1 and 26.8 Ma respectively by Pälike et al. (2006, doi:10.1126/science.1133822)). This indicates that the effect of SCW increased or the seasonal input of food from the surface ocean to benthic environments was weakened close to these glacial events. In contrast, the huge export flux of small biogenic carbonate particles close to these glacial events might be responsible for carbonate-rich sediments buffering carbonate undersaturation. Changes in deep-water masses or the periodicity of food supply from the surface ocean and variation in surface carbonate production affected by orbital forcing had an impact on the mid-Oligocene faunas of abyssal benthic foraminifera around the intervals of glacial events in the eastern Equatorial Pacific Ocean. The Factor 1 assemblage decreased sharply at ? 30 Ma (29.8 Ma by Pälike et al. (2006), 30.0 Ma by CK95) and returned to dominance after ? 29 Ma (28.6 Ma by Pälike et al. (2006), 28.8 Ma by CK95). It is likely that the effect of SCW (possibly carbonate undersaturated) has intensified since the late Oligocene. The faunal transition of benthic foraminifera in the eastern Equatorial Pacific Ocean at ~29 Ma might be attributable to the influence of Northern Component Water (NCW) input to the Southern Ocean and the subsequent formation of SCW at about that time.

Distribution of diatoms, coccolithophores and planktic foraminifera in the Arabian Sea

The distribution of diatoms, coccolithophores and planktic foraminifers mirrored the hydrographic and trophic conditions of the surface ocean (0-100 m) across the upwelling area off the Oman coast to the central Arabian Sea during May/June 1997 and July/August 1995. The number of diatoms was increased in waters with local temperature minimum and enhanced nutrient concentration (nitrate, phosphate, silicate) caused by upwelling. Vegetative cells of Chaetoceros dominated the diatom assemblage in the coastal upwelling area. Towards the more nutrient depleted and stratified surface waters to the southeast, the number of diatoms decreased, coccolithophore and planktic foraminiferal numbers increased, and floral and faunal composition changed. In particular, the transition between the eutrophic upwelling region off Oman and the oligotrophic central Arabian Sea was marked by moderate nutrient concentration, and high coccolithophore and foraminifer numbers. Florisphaera profunda, previously often referred as a 'lower-photic-zone-species', was frequent in water depths as shallow as 20 m, and at high nutrient concentration up to 14 µmol NO3/l and 1.2 µmol PO4/. To the oligotrophic southeast of the divergence, cell densities of coccolithophores declined and Umbellosphaera irregularis prevailed throughout the water column down to 100 m depth. In general, total coccolithophore numbers were limited by nutrient threshold concentration, with low numbers (<10*10**3 cells/l) at high [NO3] and [PO4], and high numbers (>70*10**3 cells/l) at low [NO3] and [PO4]. The components of the complex microplankton succession, diatoms, coccoliths and planktic foraminifers (and possibly others), should ideally be used as a combined paleoceanographic proxy. Consequently, models on plankton ecology should be resolved at least for the seasonality, to account for the bias of paleoceanographic transfer calculations.