Foraminiferal biostratigraphy of the lower Miocene Hamzian and Arashtanab sections (NW Iran), northern margin of the Tethyan Seaway

Lower Miocene strata exposed in the Khoy-Bostan Abad area (NW Iran) document marine platform environments. Paleontological and lithological characteristics of these deposits were investigated to develop detailed bio- and lithostratigraphic frameworks. The shallow marine units, composed of bioclastic carbonates in Bostan Abad and mixed siliciclastic carbonates in Khoy area, were deposited under different local tectonic regimes. Relatively diverse assemblages of benthic foraminifera from these shallow marine units were studied to establish a high resolution biostratigraphy in the context of the standard shallow benthic zonation of Western Tethys. The co-occurrence of Miogypsina intermedia Drooger and Borelis melo curdica (Reichel) characterizes Zone SBZ25, indicating a Burdigalian age as also indicated by planktonic foraminifera.     

Molecular evidence for an independent origin of modern triserial planktonic foraminifera from benthic ancestors

Gallitellia vivans is the only Recent representative of the triserial planktonic foraminiferal family Guembelitriidae. The origin and evolution of this interesting albeit poorly known family are enigmatic. To elucidate the phylogenetic relationships between G. vivans and other planktonic foraminifera, we sequenced the small subunit ribosomal DNA (SSU rDNA) for comparison to our extensive database of planktonic and benthic species. Our analyses suggest that G. vivans represents a separate lineage of planktonic foraminifera, which branches close to the benthic rotaliids Stainforthia and Virgulinella. Both genera resemble Gallitellia in general morphological appearance, having elongate triserial tests at least in their early ontogenic stages. The divergence time of G. vivans is estimated at ca. 18 Ma (early Miocene), suggesting an origin independent from the Cretaceous and Paleogene triserial planktonic foraminifera. Our study thus indicates that modern triserial planktonic foraminifera are not related to the Cretaceous–Paleogene triserial species, and that the sporadic occurrences in the fossil record are not the result of poor preservation, but reflect multiple transitions from benthic to planktonic mode of life.     

Of volcanoes and insects: the impact of the Puyehue–Cordon Caulle ash fall on populations of invasive social wasps, Vespula spp.

Volcanic eruptions have important effects on terrestrial ecosystems. The biotic effects of volcanic ash on insect populations vary from widespread and catastrophic to subtle and localized. Volcanic eruptions may increase insect mortality through the effects of the ash plume, and these vary by taxon or specific biological features. The Puyehue–Cordon Caulle Volcanic Complex is the most recent eruption in Patagonia. Here we explore and describe the effects of the eruption of this volcanic complex on invasive Vespula spp. populations. These wasps are very abundant social hymenoptera that have recently invaded Patagonia. We placed baited traps following the gradient of deposited ash, and revisited them once a week during February to April. No wasps were caught where ash deposition levels exceeded 3.0 cm. The number of wasps caught in sites with minimal ash deposits was similar to that of previous years. In locations where ash layers are intermediate, a few wasps were observed, but only during the peak of wasp abundance. We show that Vespula spp. populations were severely affected by the ash deposition and plume, caused by this eruption. These results show catastrophic effects of ash deposition over a large area, even at great distances from the eruption epicenter. We conclude that wasp mortality explained by the volcanic eruption may reach distant areas, and cause local extinction. In areas where active volcanoes are common, invasive insects may encounter an additional obstacle in their invasion success.     

Cytological Observations of the Large Symbiotic Foraminifer Amphisorus kudakajimensis Using Calcein Acetoxymethyl Ester

Large benthic foraminifera are unicellular calcifying reef organisms that can form symbiotic relationships with a range of different microalgae. However, the cellular functions, such as symbiosis and calcification, and other aspects of cellular physiology in large benthic foraminifera are not fully understood. Amphisorus kudakajimensis was used as a model to determine the detailed cellular characteristics of large benthic foraminifera. We used calcein acetoxymethyl ester (calcein AM) as a fluorescent indicator for live confocal imaging. We demonstrated that calcein AM is a useful fluorescent indicator to stain the fine network of reticulopodia and the cytoplasm in living A. kudakajimensis. We showed that at least two types of reticulopodia exist in A. kudakajimensis: the straight bundle of reticulopodia that spreads from the aperture and the fine reticulopodia along the surface of the aperture and chamber walls. The cytoplasm in outer chambers was highly branched and contained a few dinoflagellates. In contrast, the inner chamberlets contained condensed cytoplasm and many dinoflagellates, suggesting that the cytoplasm of A. kudakajimensis performs different functions based on its location within the large test. Our confocal detailed image analysis provides real-time cellular morphology and cell physiology of living foraminifera.     

Distribution of ostracod and benthic foraminiferal assemblages during the last 550 kyr in the East-Corsica basin,western Mediterranean Sea: A paleo-environmental reconstruction

The study of Quaternary sediments covering the last 550 kyr from the borehole GDEC-4-2, East-Corsica basin, was performed through the study of benthic meiofaunal assemblages (ostracoda and benthic foraminifera) whose distribution responds to climate changes, and glacial–interglacial variability in particular. The interglacial ostracod group is mainly composed of the Argilloecia acuminata, Cytheropteron alatum, Henryhowella sp., Polycope sp. and Cytherella sp., which indicate an enhanced surface productivity and possibly high bottom water temperature during these warm intervals. Benthic foraminifera, such as Hoeglundina elegans, Sigmoilopsis schlumbergeri, Bigenerina nodosaria and Hyalinea balthica are predominant during interglacial periods and also show an increasing surface productivity associated to warm intervals. Increase in surface productivity would contribute to an enhanced export of organic matter to sea floor at the GDEC-4-2 site during interglacial periods. The bottom temperature drop coupled with the important sedimentary inputs (associated to a significant quantity of refractory organic matter) during glacial periods was highlighted by the predominance of ostracoda, such as Paradoxostoma sp., Cytheropteron testudo, Bathycythere vanstraateni, Macrocypris sp., Echinocythereis echinata and benthic foraminifera as Bolivina spathulata, Bulimina costata, and Bulimina marginata. The distribution of some benthic foraminifera species describing a turnover system allowed the characterization of the last three climate cycles (MIS 8–9, MIS 6–7, MIS 1–5) probably marked by changes of bottom water paleoceanographic conditions in terms of temperature, salinity, bottom current intensity and surface productivity. The cyclic variations of the allochthonous group recorded over the last 550 kyr suggest a major role played by the eustatic factor, with the latter possibly favouring down slope transport. The distribution of this group allowed thus establishing a link between shelf-basin sediment transfer and climate, with enhanced shelf-basin sediment transfer during glacial low stands.     

Benthic foraminifera associated with the invasive ascidian, Didemnum sp. A

The invasive ascidian, Didemnum sp. A, first appeared in New England bays and harbors in the early 1990s, and in the waters around Cape Cod in 1993. While ship traffic was the likely vector introducing the species, its origin and precise date and location of its introduction are presently unknown. Colony surfaces of Didemnum sp. A appear very clean and not favorable substrates for epibiota settlement, but closer inspection revealed the presence of benthic foraminifera. During 2003 and 2004, 52 samples of Didemnum sp. A and other ascidians were collected to determine whether or not the foraminiferal assemblages might also be non-native and thus provide a potential clue to the place of origin of Didemnum sp. A. Sample locations included the New England coast from Connecticut to Maine (with a concentration in the Cape Cod area), northern California, Zeeland, The Netherlands, and Shakespeare Bay, New Zealand. From New England samples, 18 species of benthic foraminifera were identified. The most common species represented were Cornuspira involvens, C. planorbis, Elphidium galvestonense, E. margaritaceum, Glabratellina lauriei, Miliolinella subrotunda, Quinqueloculina bicornis, and Rosalina floridana. Foraminiferal assemblages on Didemnum sp. A from other regions sampled were composed of the same cosmopolitan species found in New England, plus other species which were indigenous to each region. Because no exotic foraminifera species were found it is concluded that Didemnum sp. A likely did not introduce non-native foraminifera originating from their native habitats into the New England region.     

Benthic foraminifera at a scallop aquaculture site in Minonosok Bay,the sea of Japan

The species composition and distribution of benthic foraminifera at a scallop aquaculture site in shallow Minonosok Bay (southern Primorye) were studied. Ninety-three species of benthic foraminifera were found in Minonosok Bay in 1998 and 83 species in 2000; representatives of the families Elphidiidae, Discorbidae, Trochamminidae, and Ataxophragmiidae dominated. In 1998, the calcareous species Cribroelphidium frigidum was most abundant; in 2000, calcareous Protelphidium asterotuberculatum and arenaceous species Trochammina inflata and Eggerella advena were dominant. The effect of scallop cultivation on the distribution of benthic foraminifera was local. The species composition and population density of foraminifera directly under scallop cages were decreased, compared to areas of the bay where there were no mariculture operations.     

Oxygen respiration rates of benthic foraminifera as measured with oxygen microsensors

Oxygen respiration rates of benthic foraminifera are still badly known, mainly because they are difficult to measure. Oxygen respiration rates of seventeen species of benthic foraminifera were measured using microelectrodes and calculated on the basis of the oxygen fluxes measured in the vicinity of the foraminiferal specimens. The results show a wide range of oxygen respiration rates for the different species (from 0.09 to 5.27 nl cell⁻¹ h⁻¹) and a clear correlation with foraminiferal biovolume showed by the power law relationship: R = 3.98 10⁻³ BioVol^0.88 where the oxygen respiration rate (R) is expressed in nl O₂ h⁻¹ and in μm³ biovolume (BioVol) (n = 44, R² = 0.72, F = 114, p < 0.0001). The results expressed per biovolume unit (1.82 to 15.7 nl O₂ 10⁻⁸ μm⁻³ h⁻¹) allow us to compare our data with the previous published data showing similar ranges. A comparison with available data for other microbenthos groups (nematodes, copepods, ostracods, ciliates and flagellates) suggests that benthic foraminifera have a lower oxygen respiration rates per unit biovolume. The total contribution of benthic foraminifera to the aerobic mineralisation of organic matter is estimated for the studied areas. The results suggest that benthic foraminifera play only a minor role (0.5 to 2.5%) in continental shelf environments, which strongly contrasts with their strong contribution to anaerobic organic matter mineralisation, by denitrification, in the same areas.     

Biogeographic distribution of rudists and benthic foraminifera: An approach to Campanian-Maastrichtian palaeobiogeography of Turkey

Transgressive sequences of Campanian-Maastrichtian Stages in Turkey generally begin with medium- to coarse-grained clastics and continue with shallow marine limestones, reefal limestones and then open marine rhythmic fine-grained clastics. These mixed siliciclastic-carbonate sequences are observed on three main platforms known as Rhodope-Pontide (RPP), Anatolide-Tauride (ATP) and Arabian (AP). New species of the rudist genera Gorjanovicia, Radiolites, Sauvagesia, Durania and Sabinia are observed on the RPP. Yvaniella and Ugarella are only found on this platform. Orbitoides gruenbachensis Papp is the most abundant species of benthic foraminifera on the RPP. Cideina soezerii (Sirel), Dizerina anatolica Meriç, Helicorbitoides boluensis Sirel, Ilgazina unilateralis Erdo?an, Nummofallotia kastamonica Özgen-Erdem, Selimina spinalis ?nan, Sirelina orduensis Meriç and ?nan, Smoutina cruysi Drooger are also observed on this platform. Rudist and benthic foraminifera on the ATP have both high diversity and abundance in comparison with RPP and AP faunas. Genus and species diversity of the rudist fauna is quite high: 17 genera and 36 species are described. New rudist genera such as Darendeella, Kurtinia and Balabania and many new species of Radiolitidae and Hippuritidae may be restricted to this platform. Characteristic larger benthic foraminifera contain 18 genera and 37 species. Among benthic foraminifera Loftusia ketini Meriç, L. turcica Meriç and Av?ar, Postomphalocyclus merici ?nan and Pseudoedomia hekimhanensis Görmü? are also likely restricted to this platform. Rudist diversity on the AP is poor. Four endemic genera (Vautrinia, Dictyoptychus, Paracaprinula and Hatayia) and two species (Hippurites syriaca Vautrin, Pironaea syriaca Vautrin) characterize the fauna on this platform. Loftusia diversity and abundance among the benthic foraminifera is quite high. Arnaudella grossouvreii Douvillé, Discyclina schlumbergeri Munier-Chalmas, Loftusia harrisoni Cox, L. elongata Cox, L. matsumaruii Meriç and Görmü? and Pseudorbitolina marthae Douvillé are only documented from southeastern Anatolia. Biogeographic distributions of rudist and benthic foraminifera show different faunal associations on the three main platforms (RPP, ATP and AP). Our data from both rudist and benthic foraminifera indicate that different faunal associations and existence of restricted genera and species may be associated with a deep marine barrier to circulation during the Campanian-Maastrichtian. Southern and northern branches of the Neotethyan Ocean are considered to be barriers in preventing migration of the species.     

Carbon and oxygen isotope geochemistry of live (stained) benthic foraminifera from the Aleutian Margin and the Southern Australian Margin

Comparisons of ambient bottom-water geochemistry and stable isotopic values of the tests of living (stained) calcareous benthic foraminifera from the North Pacific (on the Aleutian Margin, water depth 1988 m) and Murray Canyons group in the Southern Indian Ocean (Australian Margin, water depths 2476 m and 1634 m) provide modern environmental analogs to calibrate paleoenvironmental assessments. Consistent with the hypothesis that microhabitat preferences influence foraminiferal isotopic values, benthic foraminifera from both margins were depleted in ¹³C with respect to bottom-water dissolved inorganic carbon (DIC). The carbon isotope values of deep infaunal foraminifera (Chilostomella oolina, Globobulimina pacifica) showed greater differences from estimates of those of DIC than shallow benthic foraminifera (Bulimina mexicana, Bolivinita quadrilatera, Pullenia bulloides). This study provides new isotopic and ecological information for B. quadrilatera. The mean Δδ¹³C value, defined as foraminiferal δ¹³C values minus estimated ambient δ¹³C values from the Aleutian Margin, is 0.97‰ higher for G. pacifica than the mean from the Murray Canyon. This difference may result either from genetic or biological differences between the populations or from differences in environmental isotopic influences (such as pore water differences) that were not accounted for in the equilibrium calculations. These analyses provide calibration information for the evaluation of bottom water conditions and circulation patterns of ancient oceans based on fossil foraminiferal geochemistry.     

Heterosteginapapyracea Seguenza du Miocène du Corridor Sud-Rifain (Maroc) : biométrie et particularités paléoécologiques

Biometric study of the inner features of Heterostegina specimens preserved in tortonian sediments of the oued Yhoudi member allows to confirm the presence of species Heterostegina papyracea Seguenza, 1880. Analysis of both large and small components of the foraminiferal assemblage in all examined samples establishes the dominant character of species Heterostegina papyracea Seguenza (more than 60% of total benthic foraminifera). The assemblage of small benthic foraminifera associated with the Heterostegina is different from that described from Recent sediments, as well as from Miocene sediments of Calabria and Spain. In order to explain this result, two hypotheses can be put forward: (1) the Tortonian Heterostegina from Morocco proliferated abundantly in very shallow environments in association with small foraminifera (i.e. abundant Ammonia beccarii). (2) Because of powerful tidal currents in the South Rifian Corridor, Heterostegina tests were probably transferred after death. This transfer could possibly be due to the narrowness of the South Rifian Corridor in the Early Late Tortonian and its position between the Atlantic and the Mediterranean. Similar cases foraminiferal displacements are also known from modern basins. This study illustrates the difficulties in reconstructing the paleogeography of the studied area and the importance of considering all available components of the assemblage.     

The anthropogenic impact on the western French coasts as revealed by foraminifera: A review

Coastal benthic foraminifera are widely studied as indicators of environmental disturbance. This paper presents a synthesis of the studies that showed correlations between foraminiferal assemblages and various environmental problems along the western French coasts. Pollution in coastal environments may be chronic, resulting from current activities, or may result from accidental events. All the studies show that foraminifera may be used as indicators of pollution after deconvoluting from natural impacts. The most sensitive foraminifera identified by these studies are Haynesina germanica, Ammonia tepida, Cribroelphidium excavatum, bolivinids and Eggerelloides scabrus.     

Paleoenvironmental changes across the Cenomanian/Turonian Boundary Event (Oceanic Anoxic Event 2) as indicated by benthic foraminifera from the Demerara Rise (ODP Leg 207)

This study is based on Cenomanian to lower Turonian sediments of Ocean Drilling Program (ODP) Sites 1258, 1259, 1260, and 1261 from the Demerara Rise (Leg 207, western tropical Atlantic, off Suriname) that are oriented along a paleodepth transect. Studied sediments include the Cenomanian/Turonian Boundary Event (CTBE) or Oceanic Anoxic Event 2 (OAE 2) and consist of laminated black shales with TOC values between 5% and 10% below and above OAE 2 and up to 29% within the OAE 2 interval. Benthic foraminiferal assemblages in this eutrophic environment are generally characterized by low diversities and strong fluctuations of abundances, indicating oxygen depletion and high organic matter fluxes. Dominant taxa at all sites are Bolivina anambra, Gavelinella dakotensis, Tappanina sp., Praebulimina prolixa, and Neobulimina albertensis. Based on the positive stable carbon isotope excursion characteristics of OAE 2 we subdivided the studied successions into three intervals: (1) the interval below OAE 2; (2) the carbon isotope excursion reflecting OAE 2; and (3) the interval above OAE 2. In the bathymetrically shallower Sites 1260 and 1261 benthic foraminiferal assemblages indicate anoxic to sometimes slightly dysoxic bottom-water conditions below the OAE 2 interval. The bathymetrically deepest Site 1258, in contrast, reflects more oxygenated bottom waters with an almost continuous occurrence of benthic foraminifera. It is therefore suggested that the shallower sites were located within the oxygen minimum zone (OMZ), whereas Site 1258 was below the OMZ. During OAE 2 anoxic conditions prevailed at the shallower sites. At Site 1258 benthic foraminifera indicate severe dysoxic but not anoxic conditions. This pattern is proposed to reflect a strengthening of the OMZ possibly related to increased primary production during OAE 2. A short-term repopulation event of benthic foraminifera in the lower third of the OAE 2 interval was observed at all sites, reflecting a brief bottom-water oxygenation event. This short-lived event parallels a surface-water cooling and is probably equivalent to the “Plenus Cool Event” in Europe and the “benthonic zone” in the U.S. Western Interior. The benthic foraminifera of a ~0.5 Ma interval following OAE 2 still indicate oxygen depletion of bottom waters. Subsequently, however, a strong increase in benthic foraminiferal abundance and diversity reflects better oxygenation of the bottom-water masses, probably related to a weakening of the OMZ due to decreasing organic matter flux.     

Siphodinarella costata n. gen., n. sp., a new benthic foraminifer from the Coniacian of the Adriatic Carbonate Platform (Slovenia, Croatia)

A new benthic foraminifer is described as Siphodinarella costata n. gen., n. sp. from Coniacian shallow-water platform-interior carbonates of Slovenia and Croatia. The new foraminifer is found in skeletal wackestone in association with small benthic foraminifera, thaumatoporellaceans, and calcimicrobes (Decastronema, Girvanella-type tubes). The existence of an internal siphon in Siphodinarella n. gen. is interpreted as an entosolenian tube and discussed in terms of its generic and suprageneric importance.     

Benthic foraminiferal assemblages of the Cretaceous platform carbonate succession in the Yavca area (Bolkar Mountains, S Turkey): biostratigraphy and paleoenvironments

The microbiostratigraphic analysis of the three outcrop sections from the Cretaceous inner platform carbonate succession in the Yavca area (Bolkar Mountains) allows to recognize the four local benthic foraminiferal zones. These are: (1) Voloshinoides murgensis and Praechrysalidina infracretacea Cenozone in the Lower Aptian; (2) Pseudorhapydionina dubia and Biconcava bentori Cenozone in the Middle-Upper Cenomanian; (3) Ostracoda and Miliolidae Interval Zone in the probable Turonian, represented by dolomitized limestones without any significant markers; (4) Moncharmontia compressa and Dicyclina schlumbergeri Cenozone in the Coniacian-Santonian. The benthic foraminiferal assemblages correspond to those in other areas of the Mediterranean realm, with the exception of a lack of alveolinids and orbitolinids due to unfavorable environmental conditions (inner platform, restricted shelf). After the regionally well-known emergence during the late Aptian, Albian and early Cenomanian, very shallow subtidal to intertidal conditions were re-established during the middle-late Cenomanian time. The Coniacian-Santonian benthic foraminiferal assemblage shows an increase in diversity and abundance as a result of open marine influence, confirmed by the presence of larger foraminifera (Dicyclina), Rotaliidae and radiolitid fragments. Thaumatoporella and Aeolisaccus-bearing wackestone intercalations still indicate the existence of sporadic restricted environment conditions. The Cretaceous shallow-water platform carbonate succession of the Yavca area is conformably overlain by gray pelagic limestones with calcispheres and planktonic foraminifera. The Campanian flooding of the Bolkar Da? carbonate platform resulted in drowning of the pre-existing biota and facies.     

Benthic foraminiferal paleoenvironmental reconstruction from the Upper Coniacian-Lower Campanian succession in north-western Tunisia

Quantitative analysis of benthic foraminifera is used to characterize the paleoenvironments of the Upper Coniacian-Lower Campanian succession in the Jbil section of north-western Tunisia. Foraminiferal parameters and benthic foraminiferal assemblages show that the studied section includes four distinct paleoenvironmental phases. From oldest to youngest, these are as follows: (1) an interval with a Praebulimina reussi assemblage with infaunal ratios as high as 96.1%. High abundances of P. reussi, reflecting an increase in organic matter flux to the seafloor (meso-to eutrophic) under oxygenated bottom-water conditions. (2) An interval characterized by a Gavelinella costulata assemblage with mixed infaunal/epifaunal foraminifera with higher Fisher's alpha values (ranging from 4 to 15.2), reflecting mesotrophic conditions in an outer shelf environment. (3) An interval with a Gaudryina laevigata assemblage indicative of a middle to outer shelf environment; there is a considerable increase in infaunal agglutinated foraminifera, as well as a relatively abundant and moderately diversified oxic/suboxic foraminifera. (4) The final interval occurs in the lower Campanian (the Globotruncana ventricosa Zone) and includes a Bolivinoides decoratus assemblage reflecting an outer shelf to upper bathyal environment. It contains a higher planktonic percentage and biodiversity with a slight increase in dysoxic species; the mixed infaunal/epifaunal content (57.6 to 73.3%) reflects mesotrophic conditions. Four well-recognized major sea-level falls are matched by the dual signatures of eustatic sea-level changes. These are coincident with the results of this study, which represent the first documentation of these events in Tunisian faunal and paleoenvironmental changes, at the following boundaries: Coniacian/Santonian, intra-Santonian, Santonian/Campanian, and intra-early Campanian.     

Spatial Patterns in the Distribution,Diversity and Abundance of Benthic Foraminifera around Moorea (Society Archipelago,French Polynesia)

Coral reefs are now subject to global threats and influences from numerous anthropogenic sources. Foraminifera, a group of unicellular shelled organisms, are excellent indicators of water quality and reef health. Thus we studied a set of samples taken in 1992 to provide a foraminiferal baseline for future studies of environmental change. Our study provides the first island-wide analysis of shallow benthic foraminifera from around Moorea (Society Archipelago). We analyzed the composition, species richness, patterns of distribution and abundance of unstained foraminiferal assemblages from bays, fringing reefs, nearshore and back- and fore-reef environments. A total of 380 taxa of foraminifera were recorded, a number that almost doubles previous species counts. Spatial patterns of foraminiferal assemblages are characterized by numerical abundances of individual taxa, cluster groups and gradients of species richness, as documented by cluster, Fisher α, ternary plot and Principal Component Analyses (PCA). The inner bay inlets are dominated by stress-tolerant, mostly thin-shelled taxa of Bolivina, Bolivinella, Nonionoides, Elongobula, and Ammonia preferring low-oxygen and/or nutrient-rich habitats influenced by coastal factors such as fresh-water runoff and overhanging mangroves. The larger symbiont-bearing foraminifera (Borelis, Amphistegina, Heterostegina, Peneroplis) generally live in the oligotrophic, well-lit back- and fore-reef environments. Amphisteginids and peneroplids were among the few taxa found in the bay environments, probably due to their preferences for phytal substrates and tolerance to moderate levels of eutrophication. The fringing reef environments along the outer bay are characterized by Borelis schlumbergeri, Heterostegina depressa, Textularia spp. and various miliolids which represent a hotspot of diversity within the complex reef-lagoon system of Moorea. The high foraminiferal Fisher α and species richness diversity in outer bay fringing reefs is consistent with the disturbance-mosaic (microhabitat heterogeneity) hypothesis.Calculations of the FORAM Index (FI), a single metric index to assess reef vitality, indicate that all fore- and most back-reef environments support active carbonate accretion and provide habitat suitability for carbonate producers dependent on algal symbiosis. Lowest suitability values were recorded within the innermost bays, an area where natural and increasing anthropogenic influences continue to impact the reefs. The presence of habitat specific assemblages and numerical abundance values of individual taxa show that benthic foraminifera are excellent recorders of environmental perturbations and good indicators useful in modern and ancient ecological and environmental studies.     

A Decline in Benthic Foraminifera following the Deepwater Horizon Event in the Northeastern Gulf of Mexico

Sediment cores were collected from three sites (1000–1200 m water depth) in the northeastern Gulf of Mexico from December 2010 to June 2011 to assess changes in benthic foraminiferal density related to the Deepwater Horizon (DWH) event (April-July 2010, 1500 m water depth). Short-lived radioisotope geochronologies (²¹⁰Pb, ²³⁴Th), organic geochemical assessments, and redox metal concentrations were determined to relate changes in sediment accumulation rate, contamination, and redox conditions with benthic foraminiferal density. Cores collected in December 2010 indicated a decline in density (80–93%). This decline was characterized by a decrease in benthic foraminiferal density and benthic foraminiferal accumulation rate (BFAR) in the surface 10 mm relative to the down-core mean in all benthic foraminifera, including the dominant genera (Bulimina spp., Uvigerina spp., and Cibicidoides spp.). Cores collected in February 2011 documented a site-specific response. There was evidence of a recovery in the benthic foraminiferal density and BFAR at the site closest to the wellhead (45 NM, NE). However, the site farther afield (60 NM, NE) recorded a continued decline in benthic foraminiferal density and BFAR down to near-zero values. This decline in benthic foraminiferal density occurred simultaneously with abrupt increases in sedimentary accumulation rates, polycyclic aromatic hydrocarbon (PAH) concentrations, and changes in redox conditions. Persistent reducing conditions (as many as 10 months after the event) in the surface of these core records were a possible cause of the decline. Another possible cause was the increase (2–3 times background) in PAH’s, which are known to cause benthic foraminifera mortality and inhibit reproduction. Records of benthic foraminiferal density coupled with short-lived radionuclide geochronology and organic geochemistry were effective in quantifying the benthic response and will continue to be a valuable tool in determining the long-term effects of the DWH event on a larger spatial scale.     

Stable isotopic study of Oligocene-Miocene sediments from DSDP Site 354, Equatorial Atlantic

The oxygen- and carbon-isotope compositions of planktic and benthic foraminifera and calcareous nannofossils from Middle Oligocene-Early Miocene Equatorial Atlantic sediments (DSDP Site 354) indicate two important paleoceanographic changes, in the Late Oligocene (foraminiferal Zone P.21) and in the Early Miocene (foraminiferal Zone N.5). The first change, reflected by a δ¹⁸O increase of 1.45‰ inGlobigerina venezuelana, affected only intermediate pelagic and not surface, deep or bottom waters. The second change affected surface and intermediate waters, whereas deep and bottom waters showed only minor fluctuations. In the case of the former the isotope effect of the moderate ice accumulation on the Antarctic continent is amplified in the Equatorial Atlantic by changes in the circulation pattern. The latter paleoceanographic change, reflected by a significant increase in¹⁸O in both planktic and benthic forms (about 1.0‰ and 0.5‰, respectively), may have been caused by ice volume increase and temperature decrease. Both oxygen- and carbon-isotope compositions indicate a marked depth-habitat stratification for planktic foraminifera and calcareous nannofossils. Three different dwelling groups are recognized: shallowGlobigerinoides, Globoquadrina dehiscens, Globorotalia mayeri and nannofossils; intermediateGlobigerina venezuelana; and deepCatapsydrax dissimilis. The comparison of foraminifera and calcareous nannofossils suggests that the isotopic compositions of nannofossils are generally controlled by the same parameters which control the isotopic composition of shallow-dwelling foraminifera, but the former are more enriched in¹⁸O.