Epistominella Vitrea Research Articles

Miocene Climatic Optimum and Middle Miocene Climate Transition: a foraminiferal record from the central Ross Sea, Antarctica

Abstract. The Ross Sea record of the Miocene Climatic Optimum (MCO; ∼ 16.9–14.7 Ma) and the Middle Miocene Climate Transition (MMCT; ∼ 14.7–13.8 Ma) provides critical insights into Antarctic ocean–cryosphere interactions during a time of extreme warmth and subsequent cooling. Here we report on Lower to Middle Miocene foraminiferal assemblages from the International Ocean Discovery Program (IODP) Site U1521 on the outer shelf of the central Ross Sea to identify regional shifts in environmental and water mass conditions and trace continental shelf evolution. We identified seven benthic biofacies clusters, dominated by abundant Globocassidulina subglobosa (a proposed indicator of proto-Circumpolar Deep Water, pCDW), Uvigerina cf. U. fueguina (high productivity and enhanced bottom-water currents), Nonionella spp. (high productivity), or Melonis spp. (high productivity) using a Q-mode cluster analysis to develop preliminary regional paleoenvironmental interpretations. Four unique assemblages, including Globobulimina cf. G. auriculata (high productivity and low oxygen), are also identified. Unit IV (representing the early MCO event) is a short-lived (∼ 80 ka), progradational, clast-poor sandy diamictite, likely deposited during deglaciation; the upper part of Unit IV is transitional with overlying Unit III. Unit IV sediments contain the most persistently abundant and diverse foraminiferal assemblages recovered at U1521 because they are mud-rich and diatom-poor, despite very high sedimentation rates. The benthic assemblages shift between Globocassidulina and Uvigerina dominance, suggesting changes in the pCDW influence relative to productivity and/or current activity. We suggest the abundance of Uvigerina (a shelf-edge proxy) in Unit IV records the northward progradation of the Ross continental shelf at this location during the late Early to Middle Miocene. Unit III (MCO) was deposited in an open-marine setting, evident by the ice-rafted detritus or debris (IRD) clast-free, diatom-rich/diatom-bearing muds. The sporadic nature of foraminiferal abundances in Unit III is likely due to intervals of terrigenous mud alternating with more diatom-rich/diatom-bearing muds. As in Unit IV, the muddier lithologies (higher natural gamma ray (NGR) values) are more likely to preserve calcareous foraminifera, whereas the most diatom-rich sediments (lower NGR values) are more corrosive to carbonate. We interpret the muddier intervals as interglacials with incursions of pCDW, as indicated by increased Globocassidulina subglobosa, and sporadic occurrences of rare warmer-water planktic foraminifera. Collectively, these multiple incursions of warmer-water planktic foraminifera provide evidence for polar amplification in the Ross Sea during the MCO and MMCT. The diatom-rich muds are interpreted as glacials during the MCO with open-marine conditions and higher productivity. The dominance of Globobulimina in the upper part of Unit III corresponds with the carbon maximum of Carbon Maxima 2 (CM2) and low-oxygen conditions in the sediments at ∼ 16.1 Ma. Subsequent glaciation (including Mi2, Miocene Isotope event 2), marine-based ice sheet grounding, and erosion on the shallow shelf are recorded by the widespread Ross Sea Unconformity 4 (RSU4; ∼ 15.95–14.2 Ma) at Site U1521. Unit II (MMCT) likely represents sedimentation in the interval between the RSU4 and the Mi3 (Miocene Isotope event 3) glaciation at ∼ 13.9–13.8 Ma. The benthic biofacies composition of Unit II shows a further increase in neritic taxa, including Elphidium magellanicum and Epistominella vitrea, suggesting continued shoaling of the continental shelf, which facilitated the growth of marine-based ice sheets during the Middle Miocene. Our initial correlation between Site U1521 and the ANtarctic geological DRILLing Project (ANDRILL) site, AND-2A, yields similar environmental interpretations, including peak warm events 3 and 4 during the MCO, supported by the foraminifera and unit lithologies. Suspected glacial intervals during the MCO, including Mi2 at the top of Unit III, correlate well with the reconstructed deep-sea estimates of ice volume changes (seawater δ18Osw record) from the Ocean Drilling Program (ODP) Site 1171 on the South Tasman Rise.

Foraminiferal Biostratigraphy of Well Ad, Western Niger Delta

Micropaleontological analysis of sixty (62) ditch cuttings rock samples collected from interval, 7800 feet to 12,002 feet of well AD, located offshore western Niger Delta was carried out for the investigation of their age and paleodepositional environment. Standard methods and techniques of foraminiferal sample processing and analysis were followed to disaggregate the microfauna from the rock matrix. The studied interval is predominantly made up of 80 to 100 % sandstone, minor shale and siltstone with variable textural properties. Foraminifera study revealed well preserved and diverse species dominated by the calcareous benthic forms. A total of seventy-four (74) foraminiferal species were recovered among which fifty (52) two are calcareous benthic, six (6) are agglutinating forms while sixteen (16) are planktonic foraminifera. On the basis of the faunal assemblage, abundance and diversity of the important foraminiferal events, four (4) foraminiferal zones (Valvulineria spp, Brizalina mandoroveensis, Hanzawaia concentrica and Lenticulina inornata) were recognised and correlated with F300 and F500 to assign an early to middle Miocene age for the sediments. Paleoenvironmental deductions were based primarily on the richness and diversity of foraminiferal species categories. The presence or absence of planktonic foraminifera aided in deciphering open ocean environments. The dominant biofacies associations recorded within the studied section of Well-AD is the Ammonia beccarii biofacies defined by the rare to common occurrences of Ammonia beccarii, Bolivina scalpratamiocenica, Florilus atlanticus and Epistominella vitrea. Brizalina mandoroveensis species, Lenticulina inornata, Hanzawaia strattoni, Eponides eshira, Cribroelphidium galvestonensis and Hanzawaia concentrica were also in association. The Ammonia beccarii biofacies is indicative of the Shallow/Inner Neritic Paleoenvironment, while the Inner Neritic/Middle Neritic Setting is characterized by top occurrence of Valvulineria spp, a rich continuous occurrence of Epistominella vitrea. The paleoenvironment of the studied section of Well-AD is dominantly inner to middle neritic with concomitant minor incursion of outer neritic setting.

Does the analysed size fraction of benthic foraminifera influence the ecological quality status and the interpretation of environmental conditions? Indications from two northern Norwegian fjords

The introduction of the European Water Framework Directive has increased the interest in benthic foraminifera as a biomonitoring tool. This prompted the need to standardise the methods used to analyse benthic foraminifera, including which sediment fraction to analyse. In some regions benthic foraminifera produce small (< 125 µm) adult tests, and the current study assessed the effect of analysing the > 63 µm or > 125 µm fraction on determining the Ecological Quality Status (EcoQS) in two fjords in northern Norway. The diversity indices Shannon-Wiener index (H’log2) and Hurlbert’s rarefaction index (ES100), and the multi-metric Norwegian Quality Index (NQI), from both the > 63 µm and > 125 µm fraction resulted in the same or similar EcoQS, reflecting good environmental conditions in both fjords. The same applied to the AZTI’s Marine Biological Index (AMBI), except at one location which had moderate EcoQS. At this location especially, more foraminifera with a tolerant or opportunistic response to organic matter enrichment occurred in the > 63 µm fraction than in the > 125 µm fraction. Hence, the higher H’log2 and ES100 of the > 63 µm fraction can be somewhat misleading as it indicates better environmental conditions, whereas the AMBI indicates more organic matter input. The Stainforthia group and Epistominella vitrea, indicating organic matter enrichment and increased primary productivity were, however, mostly absent in the > 125 µm fraction. Their absence in this fraction could have consequences for monitoring potential anthropogenic pressure factors and identifying long-term changes in environmental conditions when using this fraction. This study suggests the > 125 µm would be mostly sufficient for determining the EcoQS in northern Norway.

Monitoring environmental impacts of fish farms: Comparing reference conditions of sediment geochemistry and benthic foraminifera with the present

Intensive fish farming is a major industry, but the extent of organic matter (OM) and heavy metal pollution by fish farms is debated. This study established in situ reference conditions using geochemical parameters and fossil benthic foraminiferal assemblages in dated sediment cores to identify potential impacts of fish farming in two basins of the inner Øksfjord, Northern Norway. Living (rose Bengal stained) benthic foraminifera were used to assess the present day environmental conditions. The fossil foraminiferal records were compared with the living foraminifera, which in turn were compared with macrofaunal data. Long-term (>100 yrs) sediment core records of the geochemical parameters (TOC63, C/N, δ13CVPDB TOC and heavy metals) and foraminiferal indices (Norwegian Quality Index (fNQI), AZTI’s Marine Biotic Index (fAMBI), fHlog2, ES100) did not indicate an impact from fish farming through time. Long-term changes in foraminiferal absolute abundances and relative abundances of ecological groups (EGs) reflecting organic matter (OM) tolerance suggest that the OM supply slightly increased compared to reference conditions. Relative abundances of Brizalina skagerrakensis and Epistominella vitrea, previously associated with phytodetrital input, suggest a minor increase in primary productivity compared to reference conditions. The Stainforthia group (S. fusiformis and S. feylingi), indicative of OM enrichment, in the living foraminiferal assemblages may indicate a response to fish farming activities, but foraminiferal seasonality could not be excluded as a potential cause. The indices of both fossil and living foraminifera, in addition to the macrofauna showed a good to high Ecological Quality Status (EcoQS) through time and at present. This indicates that environmental conditions have been and still are acceptable.

A short note on a present-day benthic recovery status in the formerly heavily polluted Idefjord (Sweden/Norway)

Idefjord (Skagerrak, North Sea) has had a long pollution history due to a heavy exposure to effluents from sawmills and pulp and paper industry, which had a detrimental effect on fjord life. Earlier we presented a paper on the pollution history and benthic recovery in the fjord by studying sediment geochemistry (TOC and heavy metals) and benthic foraminifera in the sediment cores taken in the inner and the outer Idefjord. At that stage the foraminiferal (~benthic recovery) record was limited to years 2000 (inner fjord) and 2002 (outer fjord), in contrast to pollutant data reaching all the way up to 2014. In this short note we extend the foraminiferal record to year 2014 and fill the gap in the benthic recovery in the inner and the outer fjord over the last 12years. The results show that both inner and outer fjord inlets currently undergo a steady benthic recovery reflected in comeback of transitional and pre-pollution benthic foraminiferal species after 2000–2002 and towards 2014. The recovery is also supported by increasing faunal diversity, low dominance and since 2000–2002 re-appearance of calcareous foraminiferal species (Bulimina marginata, Elphidium spp., Epistominella vitrea, Hyalinea balthica and Lagena spp), which all disappeared during the period of maximum effluent discharges. At the same time, detection of opportunistic newcomers (e.g. Stainforthia fusiformis) and persisting absence of some transitional species such as Ammoscalaria tenuimargo suggests a recolonization by foraminiferal population with a different species composition as compared to the original pre-pollution community either due to changed environmental conditions or/and increased competition.

Ecology of deep-sea benthic foraminifera in the North Atlantic during the last glaciation: Food or temperature control

In this study, we explore the paleoecology of nineteen species and two species-groups of deep-sea benthic foraminifera in relation to bottom water temperature and food supply in the central North Atlantic during the last glaciation, ~60,000–28,000years BP. The study is based on core SO82-02GGC, taken from 1730m water depth on the western flank of Reykjanes Ridge. The climate of the investigated period was extremely unstable, interrupted by thirteen warmings and coolings, the so-called Dansgaard-Oeschger events. At SO82-02GGC, surface and bottom water temperatures varied with up to 5°C between the warm interstadials and the cold stadials. Surface productivity, as indicated by the flux of planktic foraminifera, varied with a factor of up to ten. The Dansgaard-Oeschger events had a significant impact on the benthic foraminiferal faunas, which experienced up to 70% replacement between the interstadials and stadials. Multivariate analysis reveals that the investigated species can be separated into two groups. Group 1, including Bulimina costata, Brizalina subspinescens, Epistominella decorata and Trifarina angulosa, was attracted to higher temperatures and high food supply. Group 2, including Pullenia bulloides, Valvulineria laevigata, and Melonis barleeanus, was attracted to colder water and low food supply. Three species belonging to the cold group, Cibicidoides wuellerstorfi, Oridorsalis umbonatus and Eponides tumidulus are almost exclusively confined to sediments rich in ice rafted detritus. A few species including Nonionella iridea and Epistominella vitrea show opportunistic behaviour. Most species are epifaunal to shallow-infaunal and live today in oligotrophic to mesotrophic habitats. Our investigations indicate that temperature was the primary factor responsible for the relative abundance and main grouping of species. However, four species show little influence by temperature and several, perhaps most, were clearly also affected by food supply.

DOES THE PEB INDEX RESPOND ONLY TO HYPOXIA IN THE MISSISSIPPI DELTA, GULF OF MEXICO?

The frequency of anthropogenic seasonal hypoxia on the continental shelf west of the Mississippi Delta (the Louisiana Bight) has increased since the middle of the 20 th century. This study applies the PEB index, a proxy for hypoxia, to four ~2 m kasten cores taken southwest of Southwest Pass of the Mississippi Delta. The PEB index is defined as the cumulative percent of Protononion atlanticum (= Nonionella atlantica of this study), Nonionella opima, Epistominella vitrea and Buliminella morgani . The PEB index varies little in the shallowest core, KC4 (59 m water depth). Assemblages were strongly dominated by PEB taxa (average 95%), due mainly to the dominance of E. vitrea (average 76%). In core KC3 (75 m), an average PEB value of 84% is also due mainly to E. vitrea (61%). The PEB index of KC3 was consistently higher above 90 cm, a level dated at 1955–1960 ( 210 Pb age estimate), and could reflect an increased influence of hypoxia or an increased rate of sediment accumulation associated with delta progradation. A similar trend characterizes core KC2 (87 m). The PEB index is 18% from 240 cm to 140 cm, increasing up core as the abundance of E. vitrea increases, likely due to delta progradation. Other PEB taxa, B. morgani and N. opima , increase in the top 30 cm of the core, probably due to increased hypoxia between 1952 and 1968 ( 210 Pb age estimate). Core KC1 (473 m) differed from shallower cores in its higher species diversity. Bolivina lowmani, Cassidulina neocarinata , and Bolivina ordinaria each comprise ~15% of assemblages and PEB taxa are rare (average 5%) but increase to 19% in a 30 cm interval attributed to off-shelf transport. We conclude that the PEB index is a useful indicator of anthropogenic hypoxia but dominance of E. vitrea may also be attributable to sedimentological factors related to delta progradation.

Multi-proxy evidence of rainfall variability recorded in subaqueous deltaic deposits off the Adra River, southeast Iberian Peninsula

The Adra River deltaic system, southeast Iberian Peninsula, shows a steep topography and is subjected to strong climatic seasonality. This system has been affected by alternating wet and dry periods, and it has also undergone numerous anthropogenic activities such as deforestation, mining activities, river channel deviations and dam construction, particularly during the last two centuries. Two sediment cores were retrieved off the Adra River, from the western (MS_V9) and eastern (MS_V4) lobes of the subaqueous deltaic deposit. A multi-proxy study was carried out, including grain size, benthic foraminiferal assemblages, magnetic susceptibility and geochemical element analyses, in order to understand the sedimentary expression of recent climatic cycles and anthropogenic interventions in the river basin.Periods of increased deposition of coarse-grained sediments, low absolute abundance of benthic foraminifera and high elemental ratios indicative of terrigenous contributions, were interpreted as periods of increased sediment supply to the shelf. Four flooding events were recorded in core MS_V9 and three events on core MS_V4, of which two were observed in both cores. They were related to periods with major floods that were documented on the southern Iberian Peninsula around 1770–1810 and 1860–1870 AD. On the other hand, sediment core intervals exhibiting increasing proportion of fine-grained sediments and higher abundances of foraminiferal species assigned as successful colonizers (Textularia earlandi) and opportunistic species that feed on bacteria or terrestrial organic matter (Bolivina ordinaria, Bulimina elongata, Eggerelloides scaber and Ammonia beccarii or tepida), indicate the establishment of new environments with new ecological constraints. They were related to significant decreases of terrigenous sediment input during low rainfall or dry periods. The increase of opportunistic species feeding on fresh phytodetritus (Nonionella iridea, Nonionella stella, Nonionella sp., Brizalina dilatata, Epistominella vitrea and Bolivinellina pseudopuntata), under more stable environmental conditions, also point to a stronger marine influence on the prodeltaic environments during these periods. The human interventions on the river basin after 1872 AD, with the deviation of the main river channel to the east, led to a drastic reduction of the sediment exported to the western delta lobe. This study showed that the sedimentation on the Adra subaqueous deltaic deposit was mainly controlled by rainfall variability from 1663 to 1872 AD, and afterwards by anthropogenic interventions.

EFFECTS OF DIFFERENT POTENTIAL FOOD SOURCES ON UPPER-BATHYAL BENTHIC FORAMINIFERA: AN EXPERIMENT WITH PROPAGULES

Research Article| October 01, 2014 EFFECTS OF DIFFERENT POTENTIAL FOOD SOURCES ON UPPER-BATHYAL BENTHIC FORAMINIFERA: AN EXPERIMENT WITH PROPAGULES Christopher J. Duffield; Christopher J. Duffield 4 1Department of Geosciences, University of Oslo, P.O. Box 1047 Blindern, 0316 Oslo, Norway 4Correspondence author. E-mail: c.j.duffield@geo.uio.no Search for other works by this author on: GSW Google Scholar Bente Edvardsen; Bente Edvardsen 2Department of Biosciences, University of Oslo, P.O. Box 1066, Blindern, N-0316 Oslo, Norway Search for other works by this author on: GSW Google Scholar Wenche Eikrem; Wenche Eikrem 2Department of Biosciences, University of Oslo, P.O. Box 1066, Blindern, N-0316 Oslo, Norway3Norwegian Institute for Water Research, Gaustadalléen 21, 0349 Oslo, Norway Search for other works by this author on: GSW Google Scholar Elisabeth Alve Elisabeth Alve 1Department of Geosciences, University of Oslo, P.O. Box 1047 Blindern, 0316 Oslo, Norway Search for other works by this author on: GSW Google Scholar Journal of Foraminiferal Research (2014) 44 (4): 416–433. https://doi.org/10.2113/gsjfr.44.4.416 Article history received: 30 Aug 2013 accepted: 04 Apr 2014 first online: 03 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Christopher J. Duffield, Bente Edvardsen, Wenche Eikrem, Elisabeth Alve; EFFECTS OF DIFFERENT POTENTIAL FOOD SOURCES ON UPPER-BATHYAL BENTHIC FORAMINIFERA: AN EXPERIMENT WITH PROPAGULES. Journal of Foraminiferal Research 2014;; 44 (4): 416–433. doi: https://doi.org/10.2113/gsjfr.44.4.416 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyJournal of Foraminiferal Research Search Advanced Search Abstract A propagule experiment was designed to investigate the effects of different food types and varying sediment depths on the survival and growth of upper-bathyal benthic foraminifera, collected from surface-sediment cores in Oslofjord, Norway. Sediment that passed through a 53-μm sieve was used in the experiment. Any foraminifera >63 μm at the end of the experiment had therefore grown, indicating at least tolerable living conditions. The experiment was arranged into four sub-experiments to test foraminiferal responses to a lack of food input, algal medium, sediment depth (1- vs. 2-cm depth), and different food types. Potential food sources included monospecific algal cultures (the green alga Dunaliella tertiolecta, the haptophyte Emiliania huxleyi, and the diatoms Chaetoceros sp. and cf. Navicula), as well as phytoplankton and zooplankton from net hauls collected at the same sampling site. After six weeks all foraminiferal assemblages showed an increase in abundance, even those which were not fed. This suggests that most species (e.g., Textularia earlandi, Bathysiphon flexilis) were feeding on microbes or detritus already in the sediment. However, the addition of certain phytodetritus increased the abundance, suggesting that some species (e.g., Epistominella vitrea) are dependent on the input of this particular fresh phytodetritus. Conversely, certain types of detritus (E. huxleyi and zooplankton) appear detrimental to most species, except Elphidium excavatum which appeared resistant to the treatments inimicable to other species. Leptohalysis catella was the only species observed to respond positively to net hauls dominated by dinoflagellates. For some species (e.g., Stainforthia fusiformis, Nonionella iridea) the availability of a greater sediment depth stimulates growth more than the input of organic matter. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

The Late Glacial–Holocene record from Central Adriatic Sea: Paleoenvironmental reconstruction based on benthic foraminiferal assemblages

New micropaleontological data coming from three cores collected on the meso-Adriatic continental shelf (Vasto area) are studied. Comparisons to foraminiferal assemblages and radiocarbon dates previously collected from cores in the San Benedetto del Tronto and Tremiti areas allow the correlation of patterns observed in shallow water areas with those in deeper parts of the basin. We focused on the response of benthic foraminifera during the Holocene high-stand, corresponding to the installation of the recent sedimentary and trophic system. An influence of anthropogenic impacts cannot be ruled out; its effects consist of a depletion of oxygen level with a consequent modification of the structure of benthic foraminiferal assemblages. During the glacial/post glacial cycle, three phases, characterized by a total of six foraminiferal biofacies including different species assemblages were recognized. The first phase, from 14 kyr BP to 11 kyr BP, corresponds to the Bölling/Alleröd and Younger Dryas cold event, before the Holocene sea-level rise. During this phase, the continental shelf was characterized by an infralittoral environment with productive waters owing to the proximity of the Po river delta at the edge of the Mid-Adriatic Deep. The second phase, from 11 kyr BP to 4 kyr BP, represents the Holocene sea-level rise and is characterized by a condensed sedimentation spread over the entire basin. The third phase corresponds to the Holocene high-stand, during which time the modern current system became established. During this phase, the eastern portion of the shelf underwent to the central part of the mud-belt, corresponding to the sub-recent conditions. Recent eutrophication resulting from human activities over the last few centuries is evidenced by frequency fluctuations of typically opportunistic taxa such as Nonionella turgida and Epistominella vitrea.

DISTRIBUTION OF LIVING BENTHIC FORAMINIFERA ON THE NORTHERN GULF OF CADIZ CONTINENTAL SHELF

Living (stained) benthic foraminiferal faunas were analyzed in 51 surficial sediment samples taken from the northern Gulf of Cadiz continental shelf between the mouths of the Guadiana and Guadalquivir rivers. The distribution and abundance of 26 species with relative abundance >5% were related to water depth, sediment type, river discharge, water temperature, salinity, turbidity, and primary productivity. Hierarchical classification using R- and Q-mode cluster analyses, and individual distributions, allowed these taxa to be categorized into four general groups. Group 1 is represented by Bolivina ordinaria and Hopkinsina atlantica. These species are linked to river discharge, and are associated with muddy sediments. They are considered the most opportunistic species in the assemblage, and are associated with the limits of productivity. Group 2, contains Ammonia beccarii, Eggerelloides scaber, Elphidium gerthi, Quinqueloculina laevigata, and Q. stelligera, and is characteristic of shallow water depths. Its species are associated with different sediment types and their distribution is influenced by river discharge. Group 3 is dominated by Bulimina aculeata, B. elongata, Elphidium excavatum, E. cuvillieri, Epistominella vitrea, and Rectuvigerina phlegeri. These species display the highest abundances between 30–100 m water depths. They prevail in muds associated with weak hydrodynamics, low oxygenation, and high organic matter. Group 4 includes species that are more abundant in deep stations and is divided into two subgroups. Subgroup 4A includes Bolivina catanensis, B. italica, B. striatula, Cassidulina laevigata, Stainforthia sp., Nouria polymorphinoides, and Nouria sp., with higher abundances in one or two samples. Subgroup 4B, with Brizalina dilatata, B. spathulata, Bulimina marginata, Nonionella iridea, N. stella, and N. turgida, has patchy distribution. Higher abundances of Nonionella species off the Guadiana River are related to low temperature and salinity.

LIVE BENTHIC FORAMINIFERAL FAUNAS ALONG A BATHYMETRICAL TRANSECT (282-4987 M) ON THE PORTUGUESE MARGIN (NE ATLANTIC)

Live benthic foraminifera were studied in eight cores collected along a depth transect ranging 282-4987 m on the Portuguese margin. Total standing stocks (TSS) and species assemblages from both 63-150- and >150-mu m fractions are compared between stations along the transect and with previous live foraminiferal studies from the Bay of Biscay and western Iberian margin. Based on the sedimentary organic matter contents and ecological traits of the retrieved foraminifera, three groups of stations are distinguished: (1) eutrophic upper-slope stations (282-1002 m) with faunas dominated by Uvigerina mediterranea, U. elongatastriata, Melonis barleeanus, Bigenerina nodosaria, Trifarina bradyi, Epistominella vitrea, Cribrostomoides bradyi, and Bolivina robusta, (2) mesotrophic middle- to lower-slope stations (1374-2475 m) with faunas dominated by Uvigerina peregrina, Globobulimina affinis, and Repmanina charoides, and (3) oligotrophic lower-slope and abyssal-plain stations (2908-4987 m) with faunas in the larger size fraction dominated by Cibicides kullenbergi and agglutinated species such as Reophax fusiformis and Recurvoides sp. 1. The smaller size fraction is dominated by opportunistic calcareous species such as Bulimina translucens, Epistominella exigua, and Nuttallides pusillus, along with Reophax fusiformis, but most of these species are diminished at 4987 m, where Reophax fusiformis, Pullenia salisburyi, and various monothalamous agglutinates are dominant. This succession of assemblages probably reflects the increasing scarcity of trophic resources with water depth. This hypothesis is corroborated by 1) the clear decrease of TSS with increasing water depth, and 2) the decreasing sediment phytopigment concentrations towards deeper sites. Moreover, the decreasing percentage of perforate calcareous foraminifera, and increasing percentage of agglutinated foraminifera with water depth, suggests that, in general, perforate calcareous species have higher trophic requirements than agglutinated ones.

Benthic foraminifera as bioindicator for cold-water coral reef ecosystems along the Irish margin

Cold-water coral ecosystems building cold-water carbonate mounds occur worldwide and are especially developed along the European margin, from northern Norway to the Gulf of Cadiz. A remarkable mound province is documented southwest of Ireland along the Porcupine and Rockall Banks. In this area carbonate mounds are formed in water depths between 500 and 1200 m and are often densely settled by cold-water coral ecosystems offering many ecological niches for benthic foraminifera. We investigated total (unstained) benthic foraminiferal assemblages from surface sediments (0–1 cm, >63 μm size fraction) of this region with the aim to trace their distribution patterns and to test if they can be used as bioindicators for facies characterization in different parts of carbonate mound systems. Our quantitative data were further statistically treated with non-metric multidimensional scaling (nMDS) based on Bray–Curtis similarity matrix to highlight community patterns that were not readily apparent. Our results indicate that different benthic foraminiferal assemblages characterize different facies along cold-water carbonate mounds and are related to the environmental conditions and available substrates. The following facies can be described: (1) the Off-Mound Facies is dominated by uvigerinids and other infaunal species; (2) the Dropstone Facies is characterized by infaunal Globocassidulina subglobosa and attached-epifaunal Cibicidoides sp.; (3) the Dead Coral Facies is characterised by epifaunal species (e.g., Planulina ariminensis, Hanzawaia boueana) and infaunal species ( Spiroplectinella wrightii, Angulogerina angulosa, Epistominella vitrea); (4) the Living Coral Facies includes both infaunal and epifaunal species, but is dominated by the epifaunal Discanomalina coronata; and (5) the Sandwave Facies contains high abundances of epifaunal species including D. coronata. Based on this distribution, we propose D. coronata, as an indicator species to identify active mounds and/or living cold-water coral ecosystems. Our results also emphasise the importance of studying the small size fractions that yield many infaunal species. A causal link exists between distribution patterns of benthic foraminifera and cold-water coral facies, thus providing an independent tool to identify and describe the different facies in this setting.

Spatial distribution of live benthic foraminifera in the Rhône prodelta: Faunal response to a continental–marine organic matter gradient

Benthic foraminifera were collected in the Rhône prodelta (Gulf of Lions, Mediterranean Sea), an enriched zone with high organic matter content. In June 2005, sediment cores were sampled at depths ranging from 20 to 100 m. Four distinct foraminiferal assemblages were determined in the study area, reflecting the geographical distribution of the impact of river supply. The living foraminiferal faunas present a typical picture, with strongly impoverished faunas composed exclusively of stress-tolerant taxa ( Fursenkoina fusiformis, Bulimina aculeata, Leptohyalis scottii, and Adelosina longirostra) in the immediate vicinity of the river mouth. This assemblage is well adapted to a high input of continental organic matter and a minimum oxygen penetration depth into the sediment. To the southwest, under the main corridor followed by the river plume, high organic input with a dominantly terrestrial signature (more refractory) may be stressful for many taxa which need organic matter of a more labile quality. In this area, Nonion scaphum, Nonionella turgida and Rectuvigerina phlegeri are present in low densities. On the edge of this area, these taxa show much higher densities. A greater proportion of marine organic carbon could explain their increasing abundances in this area. Towards the east and towards the deepest stations, in the outer part of the enriched zone, biodiversity increases. Faunas at these stations have intermediate densities and contain a number of taxa ( Cassidulina carinata, Epistominella vitrea, Valvulineria bradyana, Nonionella iridea/bradyi) at the deepest stations; Bolivina dilatata/spathulata and Textularia porrecta at the eastern stations) that seem to benefit from more marine organic matter. The comparison of geochemical measurements and foraminiferal data strongly suggests that the spatial distribution of foraminifera in the Rhône prodelta is mainly governed by the quality and the quantity of organic matter reaching the sediment–water interface. Since bottom waters are well oxygenated (215–260 µmol/L), and oxygen penetration into the sediment is less than 1 cm at all stations, benthic ecosystem oxygenation appears to have only a minor impact on regional differences in faunal distribution.

Foraminiferal Evidence of Younger Dryas Age Cooling on the British Columbia Shelf

Cluster analysis of foraminifera from a ~12,000-9000 radiocarbon year old piston core from Goose Island Trough, Queen Charlotte Sound, indicates that a cold interval correlative with the Younger Dryas stadial occurred during a shallow water phase. The reduction in depth was caused by the passage across the area, between 11,500 and 10,000 years BP, of a glacial forebulge associated with the retreat of the Late Wisconsinian ice sheets. Published sedimentological evidence indicate that water depths decreased to ~75-90 m, placing the site above the permanent North Pacific pycnocline (100 m). Low salinity-near glacial conditions, at these depths, between -11,100 and 10,000 years BP were recognized by abundant populations of Cassidulina reniforme and lslandiella helenae. This cold interval has also been recognized in cores from elsewhere in Queen Charlotte Sound. The depressed salinity and temperature may have resulted from a modification of regional weather patterns. Decreased mean continental summer temperatures could have reduced the seasonal influence of the North Pacific High and lengthened that of the Aleutian Low. This would have resulted in a near continuous onshore surface Ekman transport and enhanced coastal runoff, effectively blocking the movement onto the shelf of deep, saline, warm water of the California Undercurrent. The resultant isolated inshore basin comprised of present-day Hecate Strait and Queen Charlotte Sound is tentatively named the "Hecate Sea". By ~10,000 years BP, weather and ocean circulation had returned to near modern patterns as indicated by the disappearance of lslandiella helenae and by the development of an Epistominella vitrea - dominated biofacies.

A note on the genetic similarity between shallow- and deep-water Epistominella vitrea (Foraminifera) in the Antarctic

Many Antarctic species are known to have large bathymetric ranges. However, little is known about the genetic diversity of populations living at different depths. In certain microfauna- and meiofauna-sized taxa, some morphospecies can be divided into several cryptic genetic species. To test whether cryptic diversity is linked with depth of occurrence in Southern Ocean foraminifera, we compared ribosomal DNA sequences of selected calcareous foraminiferal species from shallow localities in McMurdo Sound and deep ones in the Weddell Sea. We found that at least one species, Epistominella vitrea, was genetically almost identical between the two localities, having a bathymetric range of over 1000 m. Our study provides molecular evidence for an extraordinarily large depth migration of Antarctic shelf foraminifera. It also suggests a relationship between populations of foraminifera from widely separated geographic regions of the Southern Ocean.

The influence of seasonal processes on geochemical profiles and foraminiferal assemblages on the outer shelf of the Bay of Biscay

Benthic foraminifera are widely used tools to reconstruct paleoenvironments. They reflect bottom water oxygen concentrations and organic carbon flux. To increase their accuracy as proxies, seasonal variability of foraminiferal populations from the outer shelf of the Bay of Biscay (150 m water depth) was followed over a 3-year period. The selected area is characterized by seasonal variation in organic matter deposition. A strong interaction between organic detritus input, macrofaunal bioturbational activity, the degree of separation of redox zones and the reproduction, growth and migrational response of benthic foraminifera was found. During periods of high labile organic matter input, as occurs during spring bloom conditions, the redox zonation was not well established. Different organic degradation pathways occurred at the same depth intervals in the sediment. Shallow infaunal species reacted in response to the high nutrient content with rapid growth ( Bolivina subaenariensis) or reproduction ( Epistominella vitrea, Bolivina seminuda, Bolivina dilatata/spathulata). Infaunally living foraminifera, Chilostomella oolina and to lesser extent Nonion scaphum, migrated to the sediment surface in reaction the increase organic matter input to the seafloor. This migration could have been induced by the more intensive overlapping of redox zones that were perhaps better separated vertically in winter. However, this migration could also have been triggered by the occurrence of fresh phytodetritus in the sediment, becoming even available in slightly deeper sediment level due to the increased bioturbation activity.

EXPERIMENTAL EFFECTS OF AN ORGANIC MATTER PULSE AND OXYGEN DEPLETION ON A BENTHIC FORAMINIFERAL SHELF COMMUNITY

Foraminiferal assemblages from a shelf environment (32 m water depth) in the northern Adriatic Sea were incubated in 26 mesocosms, in which six different environmental conditions were created. A number of mesocosms were sealed to initiate anoxic conditions, and different doses of organic matter were added under both the oxygenated and anoxic conditions. The mesocosms were harvested three times during an experimental period of two months and foraminifera were studied in the upper 3 cm of the sediment. Certain taxa ( Stainforthia fusiformis, Nouria polymorphinoides, Hopkinsina pacifica, Nonionella turgida ) responded immediately to the anoxic conditions: standing stocks declined and migration towards the sediment-water interface was observed. Other taxa ( Caronia silvestrii, Epistominella vitrea, Acostata mariae ) only reacted to a pulse of organic matter. These taxa are also found in deeper infaunal habitats, but were observed to migrate towards shallower habitats. The quantity of organic matter appeared to be an important factor: the highest dose resulted in higher densities of certain taxa. Some taxa ( H. pacifica, S. fusiformis ) increased in abundance under anoxia when labile organic matter was present. A number of other taxa were not affected by organic flux; perhaps one of these ( N. turgida ) depends on another food source, e.g., bacteria, since it migrated to shallower depth in the anoxic treatments. A last group ( Bolivina spp., Eggerella spp., Bulimina marginata ) appeared to be less affected by or showed no clear response to the induced environmental changes. In total, five different groups of foraminiferal taxa were distinguished, based on their response to the treatments. Oxygen depletion induced strong changes in the vertical distribution and density of the foraminiferal taxa over a short-term period ( 4 weeks).

Effect of seasonal hypoxia on the benthic foraminiferal community of the Louisiana inner continental shelf: The 20th century record

A species census in sediment core samples reveals significant changes in the composition of the Louisiana-shelf benthic foraminiferal community in the past century; these changes can be explained by an increase in the severity of seasonal hypoxia in bottom waters. Agglutinated and porcelaneous orders living in water depths less than 60 m suffered a noticeable decline during this time. In particular, the genus Quinqueloculina was severely affected by the progression of hypoxia, and nearly disappeared from parts of the study area. In contrast, several hyaline taxa, especially Nonionella basiloba, Buliminella morgani, and Epistominella vitrea, tolerated the progressive oxygen depletion well. Results of cluster and principal components analyses of the foraminiferal assemblage data match the observed species distribution trends and indicate that seasonal hypoxia on the Louisiana shelf, related to eutrophication and water stratification, worsened in the past century, even near the outer edge of the present-day zone of spring and summer oxygen depletion. The temporal trends in the foraminiferal record correspond to that of fertilizer use in the U.S. and nitrogen loading in the Mississippi River, suggesting that the anthropogenic factor has been particularly strong in the development of coastal hypoxia since the early 1940s.

Factors influencing recent benthic foraminifera distribution on the Guadiana shelf (Southwestern Iberia)

Benthic foraminiferal assemblages in 24 sediment surface samples collected at water depths ranging from 9 to 103 m on the continental shelf off Guadiana River were analysed, leading to the identification of a total of 270 species. Cluster analyses performed on species with a relative abundance higher than 5% led to the identification of four assemblages. The shallowest assemblage, down to 12 m water depth, is represented by Ammonia beccarii, Asterigerinata mamila, Eggerelloides scaber, Mississipina concentrica, Planorbulina mediterranensis, Elphidium crispum and Quinqueloculina laevigata. A second assemblage between 12 and 40 m water depth is characterised by Bulimina elongata, Cribrononion gerthi and Nonion fabum. The assemblage between 40 and 95 m water depth is characterised by Bolivina dilatata, Epistominella vitrea, Bulimina aculeata, Bolivina ordinaria, Spiroloxostoma croarae and Nonionella iridea. Finally, below a depth of 95 m on the upper outer shelf, an assemblage exists characterised by Brizalina spathulata, Bulimina marginata, Cassidulina minuta, Brizalina subaenariensis, Cassidulina laevigata and Uvigerina peregrina. The spatial distribution of assemblages is closely associated with sea-bottom sedimentary environments and bathymetry. The number of benthic foraminiferal tests, and the distribution of several nearshore species within the two shallowest assemblages are clearly influenced by the outflow of the Guadiana Estuary and by local hydrodynamic conditions. The deeper water assemblages, on the other hand, were found to be more related to low levels of tidal energy, low oxygen environments associated to fine-grained sediments, and cold-water filaments related to seasonal upwelling.