Composition Of Foraminiferal Assemblages Research Articles

A dynamic subtropical coastal hotspot of benthic foraminifera in the Southeastern Mediterranean indicates early-stage tropicalization

Due to ongoing ocean warming, subtropical environments are becoming accessible to tropical species. Among these environments are the vermetid reefs of the Southeastern Mediterranean (SEM). In the last decades, these valuable coastal habitats witnessed the proliferation of numerous alien species of tropical origin. Among the meiofauna thriving on these reefs are benthic foraminifera, single cell marine organisms that make a significant contribution to global carbonate production. It has been widely recognized that benthic foraminifera, among other invasive species, thrive in the macroalgal cover, and it has been suggested that their populations are becoming a significant new source of sediment substrate. Here, we report on the first systematic assessment of the population size of the benthic foraminifera, allowing a comparison with data from the native tropical habitat of these species. Our study is based on a seasonal sampling of benthic foraminifera from confined sampling areas at four sites along the vermetid reef platforms of the Israeli SEM coast. Our survey reveals a patchy distribution of each species with peak population densities exceeding 100,000 specimens per m2, making the SEM a hotspot of benthic foraminifera, with population densities comparable to tropical coral reef environments. The assemblages of the SEM hotspot are dominated by cosmopolitan foraminiferal taxa and tropical invaders from the Indo-Pacific (e.g., Amphistegina lobifera, Pararotalia calcariformata, soritids, and Hauerina diversa). In contrast to foraminiferal hotspots in the tropics, which are completely dominated by larger symbiont-bearing taxa, the SEM hotspot stands out due to high abundances of non-symbiont-bearing species Textularia agglutinans and small miliolids. An intriguing observation is the significant heterogeneity in composition and density of foraminiferal assemblages between the vermetid reefs' southern and northern areas (Israel), indicating that the productivity of the dominant species are also modulated by local yet unknown environmental factors.

Towards an Integrated and Accurate Planktonic-Foraminiferal-Deduced Bio-Chrono-Stratigraphic Framework of Late Quaternary Mediterranean Marine Cores

The late Quaternary is a key stratigraphic interval as it encompasses the Late Glacial to Holocene transition, which is characterized by a series of pronounced centennial climate oscillations and subsequent short-term events of paleoceanographic variability. Across this stratigraphic interval, significant turnovers and faunal changes in the composition and abundance of planktonic foraminiferal assemblages are well-documented through their high-resolution quantitative analysis performed in the south Aegean core NS-18. The identification of 10 synchronous bioevents among the Mediterranean sub-basins allows accurate inter-basinal correlations over the study time interval, thus contributing to the development of a robust chronostratigraphic framework for this setting. Moreover, the identification and timing of additional 20 diachronous bioevents, in conjunction with the already established bio-ecozonation scheme of the Aegean Sea, provide a continuous record of faunal changes (in terms of species-specific distributional abundances) which can be used as an additional locally expressed biochronological tool for the eastern Mediterranean deep-sea cores. The present study certainly indicates that the cause-and-effect relationships between the paleoceanographic/paleoclimatic perturbations and biological response require a highly resolved regional chronostratigraphy.

Environmental Signatures Preserved in Extremely Shallow-Water Benthic Foraminiferal Assemblages From Oman, Arabian Sea

Abstract The composition and preservation state of testate foraminiferal assemblages is of highest importance for paleoenvironmental and paleoclimatic reconstructions. Nearshore coastal areas, however, are often subject to harsh conditions, being shaped by continuous wave action and exposed to turbulence, erosion, and dynamic processes of sediment reworking. Situated at the interface between land and water, the environmental signatures preserved in assemblages of benthic foraminifera from coastal environments are therefore prone to taphonomic alterations, which potentially bias the fossil record and compromise accurate reconstructions. In this study, we have analysed the composition and preservation of benthic foraminifera from a suite of extremely shallow-water habitats along the Dhofar coastline (Oman) to document the structure of assemblages and illustrate their species richness. Our analyses show that extremely shallow foraminiferal assemblages from the southern coast of Oman retain the environmental signatures of their habitats despite intense environmental processes, making them useful for paleoenvironmental studies. Features of these signatures are recorded in the structural composition, species richness, dominance, and diversity indices of foraminiferal communities, in addition to numerical abundances of shell preservation groups.

Impact of submarine karst sulfur springs on benthic foraminiferal assemblage in sediment of northern Adriatic Sea

PurposeThis work highlights the sedimentary characteristics and the role of submarine sulfur-rich karstic springs in the distribution of benthic foraminifera in the northern part of the Adriatic Sea (Bay of Koper). Little is known about how local conditions such as temperature and sulfur bursts may influence sediment properties, benthic habitat variability, and composition of foraminiferal assemblages. Here we compare the distribution of total and living benthic assemblages in surface sediment samples collected from a funnel-shaped depression created by submarine sulfur springs.Materials and methodsSampling was performed at water depths between 24.6 and 32.2 m in fine-grained sandy silt to silty sand (partially washed). Sedimentological, mineralogical, and geochemical analyses of the sediment were carried out and the distribution of benthic foraminifera living around the springs was studied.Results and discussionIn general, sediment characteristics (i.e., mineralogical, geochemical, and organic content) around the sulfur springs do not show prominent deviations from the marine surface sediment of the area; however, some differences exist among depressions of different depths. Deeper depressions in the lower parts probably extend to older continental sediments of Late Pleistocene age with alluvial features, while shallower depressions were formed entirely in Holocene marine sediments typical of a wider area. Only one of the five samples (M05) contained living foraminifera in sufficient abundance for biocenosis research. The benthic foraminiferal assemblages of moderate diversity are composed of opportunistic species. Elphidium translucens, Ammonia ex gr. tepida, Haynesina depressula, and Porosononion granosum dominate, while A. neobeccarii, Reussella spinulosa, and Textularia bocki are subordinate.ConclusionsThe distribution and diversity of foraminifera in the sediment near sulfur springs can be explained by several factors and their interactions. The intensity of the spring discharge affects the mixing/oxygenation of the sediment, the shape of spring depressions, and the granulometry of the coarser sediment around the springs. Sediment characteristics indicate different types of sediment origin. This is related to and can be explained by the depth of spring depressions.

Cretaceous southern high latitude benthic foraminiferal assemblages during OAE 2 at IODP Site U1516, Mentelle Basin, Indian Ocean

At Site U1516 (Mentelle Basin, southeast Indian Ocean, offshore western Australia), the International Ocean Discovery Program (IODP) Expedition 369 recovered an almost complete pelagic record of the Upper Cretaceous, including the Oceanic Anoxic Event 2 (OAE 2). To better understand paleoenvironmental changes across OAE 2, 32 samples were analysed for benthic foraminiferal abundance data that represent one of the few benthic foraminiferal datasets spanning the OAE 2 in the southern high latitudes.The OAE 2 interval at Site U1516 is characterized by an interval of low CaCO3 content that contains a prominent positive Carbon Isotope Excursion (CIE). The record of the OAE 2 can be subdivided in pre OAE 2, pre max-CIE, low CaCO3, and post low CaCO3 intervals. Through the Cenomanian–Turonian boundary, we document an extreme decline in benthic foraminifera during OAE 2, that is followed by a profound repopulation event in the post low CaCO3 interval.Benthic foraminiferal assemblages indicate an outer neritic to upper bathyal depositional environment. During the pre OAE 2 and pre max-CIE intervals, calcareous deep-water gavelinellids, lingulogavelinellids and gyroidinids are dominant. In the low-carbonate interval, the microfossil record documents a substantial increase in radiolaria and foraminifera are almost absent as only three out of nine samples contain benthic foraminifera. Changes in benthic foraminiferal assemblage composition are documented in the initial low CaCO3 interval, underlying the maximum CIE and associated interferences. Comparison of the pre- and post-CIE benthic foraminiferal assemblages highlights a distinct repopulation event during the post max- CIE interval mainly represented by the conspicuous increase in abundance of agglutinated taxa and Conorboides. Compared to other southern high latitude records, the dataset collected at Site U1516 represents one of the most complete benthic foraminiferal records across the OAE 2 that registers the Late Cretaceous environmental changes in the Southern Hemisphere.

Upper Jurassic to Lower Cretaceous benthic foraminifera from South Tibet (Tethyan Himalayas): systematic, biostratigraphic, and palaeoecologic implications

The present study represents the first attempt to described foraminiferal fauna of the Gucuo Locality and is among the first work to illustrate the Upper Jurassic to Lower Cretaceous benthic foraminifers of South Tibet. The material consists in a combination of unpublished data on the Gucuo Section and published data on the Gyangze; Weimei, and Bandingsi sections.A total of 239 specimens have been currently recorded in the Upper Jurassic to Lower Cretaceous Menkadun and Gucuo formations of the Gucuo locality. To facilitate further researches on foraminifers from the Tethyan Himalayas, a total of 59 species from 38 genera have currently been repertory and described. Among the recorded specimens, a few species are significant biostratigraphic markers used to identify and constrain the age of four foraminiferal assemblages. The Textularia aff. haeusleri assemblage contains a few numbers of agglutinated species very similar to the one described in the Oxfordian to Kimmeridgian Nupra Formation of the Thakkola Region. The Tithonian Trochammina quinqueloba assemblage is a widespread biostratigraphic horizon recorded in both southern and northern parts of South Tibet, as well as in the Indian and the Proto-Atlantic oceans. The Berriasian to Valanginian Trochammina abrupta assemblage contains typical Early Cretaceous foraminifers. It confirms the Jurassic/Cretaceous boundary should be delineated at the base of the shale Unit of the Gucuo Formation, although it was previously attributed to the base of the volcaniclastic sandstone units using ammonite data. This latest being currently associated to the Valanginian to Hauterivian Ammobaculites crepinae–Textularia bettenstaedti foraminiferal assemblage.A palaeoecological reconstruction along a southwest to northeast transect of South Tibet, Himalayas, is proposed to understand the composition and dynamic of foraminiferal assemblages along with palaeoenvironmental changes. The morphogroup approach has been selected as the best methods to illustrate both sea-level and oxic changes. The northern tectonic zone of South Tibet is associated with the abundance of deep-water agglutinated foraminifers, which suggests a deep environment beyond the shelf break. The southern tectonic zone of South Tibet is rich in typical species of shallow environment and was located on the neritic shelf. The morphogroup analysis reveals localized, periodic disaerobic conditions on the sea-floor. The Jurassic to Cretaceous Boundary interval was associated with a drop of the sea-level, whereas the rise in diversity and abundance of marginal-sea taxa during the Valanginian to Hauterivian times underline a higher sea-level and a pulse in the development of epeiric seas in the southern part of South Tibet.

Nutrients and hydrography explain the composition of recent Mediterranean planktonic foraminiferal assemblages

The composition of planktonic foraminiferal assemblages in surface sediments of the Mediterranean Sea shows a pronounced zonal gradient. This gradient is different from what is observed in the open ocean, indicating that the assemblage composition may respond to environmental variables other than the otherwise dominant surface water temperature. Here we make use of a dataset of census counts of 18 taxonomic categories in 124 surface-sediment samples extracted from the ForCenS database to understand the main environmental factors affecting the composition of recent Mediterranean planktonic foraminiferal assemblages. The tested explanatory variables include temperature, salinity, chlorophyll, nitrate and phosphate concentrations in the surface waters, temperature, nitrate and phosphate concentrations at depth and thermal, salinity and density vertical gradients. The composition of the assemblages is aligned along two environmental gradients and redundancy analysis reveals that the tested variables explain a large portion (>70%) of the variance in the compositional data. The first environmental gradient reflects the nutrient content in the deep waters, affecting nutrient availability in the productive zone, while the second gradient is driven by higher (northern area) and lower (southern area) upward nutrient advection due to differences in density stratification, conditioned by the regional hydrography. Although sea surface temperature is the most reconstructed environmental variable from fossil assemblages of planktonic foraminifera, it seems to play a secondary role in the Mediterranean Sea. This, has implications for reconstructions of past oceanographic conditions in this region, opening up the possibility to reconstruct productivity instead, or next to, temperature.

Latest Hauterivian foraminiferal and calcareous nannofossil assemblages and bioevents from the Pseudothurmannia beds (Central Western Carpathians, Slovakia): A prelude to the Faraoni event

A diverse and abundant assemblage of deep-water agglutinated foraminifera (DWAF) has been recovered from an uppermost Hauterivian ammonite-rich horizon (Pseudothurmannia ohmi Biozone) from the Central Western Carpathians. The section records the last occurrence of the calcareous nannofossil species Litraphidites bollii (Thierstein) preceding the Faraoni anoxic level. Various morphogroups of agglutinated foraminifera show changes in response to trophic regime shift and decreasing oxygenation of the bottom and pore waters in a relatively short time-series. The DWAF data were compared with calcareous nannofossil assemblages and foraminifera analysed from thin sections (calcareous benthic and planktonic foraminifera). Four ecozones were identified, each with a specific taxonomic composition of foraminiferal assemblages. The zone-to-zone changes include fluctuations in the richness and relative abundance of morphogroups and planktonic foraminifera, and dwarfism in certain groups of foraminifera.

One Tree Reef Foraminifera: a relic of the pre-colonial Great Barrier Reef

Abstract Benthic Foraminifera are important elements of coral reef ecosystems and valuable proxies for monitoring reef health in the face of local, regional and global stressors. Here Foraminifera preserved in a sediment core from the One Tree Reef (OTR) lagoon on the southern Great Barrier Reef (GBR) are used to quantify ecological changes associated with European colonization (early 1800s) and the subsequent industrialization of Australia (1950s onward). Core samples are compared to published benthic grab samples from three reefs to compare spatial and temporal variation. Standard measures of richness, diversity and foraminiferal assemblage composition indicate significant differences between the Recent assemblages of OTR lagoon and those from Heron and Wistari reef lagoons. However, there is no discernible change in the OTR lagoon core assemblages from the last four centuries in any of the richness or diversity indices examined. While benthic grabs likely undersample infaunal Foraminifera relative to core samples, these foraminiferal assemblages indicate the OTR lagoon contains a living example of a pre-colonial GBR lagoon ecosystem. Without cores from Heron and Wistari it is unknown if their foraminiferal assemblages have changed due to recent anthropogenic activity or if they have always been distinct.

A Multiparametric Approach to Unravelling the Geoenvironmental Conditions in Sediments of Bay of Koper (NE Adriatic Sea): Indicators of Benthic Foraminifera and Geochemistry

The Bay of Koper is influenced by agricultural, urban, and port activities, therefore pollution from trace metals is a concern. A total of 20 sediment samples obtained from four 10-cm sediment cores were analyzed. Element concentration in the sediment of the bay was determined spatially and temporally from the recent surface to depth. The results were correlated with the composition and diversity of the benthic foraminiferal assemblages. Major element concentrations indicate natural lithogenic origin (which is also confirmed by mineralogical features). The benthic foraminiferal assemblages in sediment samples, although mainly composed of representatives of the Rotaliida, show moderate to high species diversity and are dominated by the pollution tolerant speciesAmmonia pakinsoniana,Haynesinasp.,Valvulineria bradyanaand the non-keelElphidiumsp. and subordinated byAmmonia tepidaandHaynesina depressula. Canonical correspondence analysis (CCA) on foraminiferal species and trace element concentrations shows a possible control of some potential toxic elements (i.e., Cu, Ni, Pb, Zr, Cr, As) on the diversity and taxonomic composition of foraminiferal assemblages. Nevertheless, foraminiferal diversity and dominance in the bay are related to sediment characteristics such as sediment grain size, and the amount of terrigenous inflow rather than to the element concentrations of sediments. This study evaluated ecological conditions by using the Foram-AMBi and EcoQS indices. The values of the Foram-AMBI index reflect the good to moderate quality of ecological conditions, whereas high to poor ecological statuses were interpreted by calculating EcoQS.

Linkages Between East China Sea Deep‐Sea Oxygenation and Variability in the East Asian Summer Monsoon and Kuroshio Current Over the Last 400,000 years

AbstractThe East China Sea (ECS) seasonally receives a high organic input due to the terrestrial organic matter influx, which is controlled by the East Asian Summer Monsoon (EASM), and the increased productivity driven by upwelling of the subsurface Kuroshio Current (KC). Changes in benthic foraminiferal assemblage composition in combination with paleoceanographic proxy data (CaCO3 (%), TOC (%), δ13Cpf, and δ18Obf) are used to reconstruct bottom water oxygenation and organic export flux variability over the last 400 kyr in the ECS. Multivariate analyses of benthic foraminiferal census data identified six biofacies characteristic of varying environmental conditions. These results suggest that enhanced EASM precipitation and KC upwelling directly influenced organic export flux and bottom water oxygen content in the ECS. The ECS bottom water was suboxic during Marine Isotope Stage (MIS) 11 to 8; suboxic to dysoxic between MIS 7 and 6, strongly dysoxic between mid‐MIS 5 and 4, and exhibited high variability between MIS 3 and 1. Spectral analysis of relative abundances of representative genera Quinqueloculina (oxic), Bulimina (suboxic), and Globobulimina (dysoxic) reveals a robust 23 kyr signal, which we attribute to precessionally‐paced changes in surface productivity and bottom water oxygenation related to KC variability over the past 400 kyr.

Benthic foraminiferal carbon cycling in coastal zone sediments: The influence of the assemblage structure and jellyfish detritus

Jellyfish carrion is an important carbon source to the benthic ecosystem that is expected to increase in some regions in the future, but its potential impact on sediment biochemical processes is not fully understood. Benthic foraminifera play important carbon processing roles in marine ecosystems but little is known about how they process carbon within fjords, or how jellyfish detritus on the sediment may affect this role. This study is the first to use 13C-labelled algae to quantify how jellyfish detritus may alter benthic foraminiferal microalgal-carbon uptake (C-uptake) from the inner to outer fjord. To assess potential mechanisms for variations in C-uptake, foraminiferal biomass, density, and assemblage composition, in addition to the sediment O2 dynamics and environmental parameters (e.g. sediment total organic carbon [TOC] content) were investigated. Benthic foraminiferal C-cycling strongly varied within the fjord with 20-times higher C-uptake rates at the inner-fjord location compared to the locations further outwards. This difference was likely caused by the higher foraminiferal biomass and relative abundances of Bulimina marginata and Nonionella turgida at the inner location. Strong differences in foraminiferal assemblage structure amongst the locations were not explained by major differences in the investigated environmental parameters. Changes in sediment O2 dynamics suggested that jellyfish detritus obstructed O2 diffusion into the sediment. A potential effect of these changes on the C-uptake was only observed at the inner location, indicating the effect of jellyfish detritus on foraminiferal C-uptake rates was little and dependent on the benthic foraminiferal assemblage composition (e.g. the presence of B. marginata). This suggests that the areas in coastal zones where the highest amounts of organic carbon are being processed may also be the most sensitive to changes in the sediment O2 dynamics, which would make them vulnerable to changes in riverine input and anthropogenic organic carbon enrichment.

Atypical, high-diversity assemblages of foraminifera in a mangrove estuary in northern Brazil

Abstract. Mangrove forests are extremely productive ecosystems, are sources and sinks of organic carbon, and provide essential services both to the marine environment and people. We have studied the composition and species richness of modern benthic foraminiferal assemblages from mangrove swamps along the Mamanguape River in Paraíba, northern Brazil. Sampling points for foraminifera were selected to acquire information on the composition of foraminiferal assemblages from dense mangrove stands collected along a river transect. Almost 100 species of benthic foraminifera were identified within the shallow mangrove habitats. The large number of identified mangrove taxa is the highest recorded so far for true mangrove habitats. The high species richness rivals shallow-water assemblages recorded from nearby offshore and reef environments and indicates that a particularly large number of species is capable of growing and flourishing under multiple stressor conditions. Numerical analysis of the faunal assemblages shows that specific taxa, which were previously known to be uncommon in mangrove environments, are abundant in the Mamanguape River estuary. The atypical foraminiferal fauna found in the Mamanguape River estuary resembles shallow-water offshore assemblages, is characterized by high percent abundances of perforate and miliolid taxa, and contains only very few of the otherwise typical and numerically abundant agglutinated mangrove taxa. The unusual structure of the assemblages recorded provides insight into what combination of environmental variables controls their composition and novel perspectives to reconstruct past mangrove environments. Distribution, diversity, and species-specific analysis will provide guidance on the use of Brazilian mangrove foraminifera as indicators for the strength of tidal activity, pollution, and anoxia in coastal waters and sea-level reconstructions.

Paleoceanographic evolution of the Japan Sea during the Pleistocene – A benthic foraminiferal perspective

We reconstructed the paleoceanographic evolution of the Japan Sea over the Pleistocene using benthic foraminiferal and organic geochemical records from sediment cores recovered at IODP Site U1426, which was drilled at a water depth of 900 m on the Oki Ridge in the southern Japan Sea. The dominant benthic foraminiferal biofacies and the assemblage composition, total organic and inorganic carbon, coarse fraction percentages indicate a notable reduction in primary productivity between 2150 and 1700 ka, due to the restricted supply of nutrients from the northern Pacific Ocean through the northern connecting strait. The inflow of the Tsushima Warm Current via the southern strait began after 1700 ka and marked a major change in the productivity regime of the Japan Sea, as shown by the increased abundance of calcareous foraminifera and enhanced CaCO3 (%). A marked shift in productivity occurred during the Middle Pleistocene Transition, as indicated by the dominance of low-oxygen tolerant species, and a higher influx of total organic carbon (%). The onset of more extreme glaciation at ~490–470 ka coincident with the Mid-Brunhes Event was linked to marked changes in foraminiferal assemblage composition, reflecting major changes in sea-level, oxygen availability at the seafloor, and carbonate compensation depth during intense glacial-interglacial cycles. Productivity changes were also modulated by 23 kyr variability, related to precessional insolation forcing at low latitudes, and superimposed on the 41 and 100 kyr variability, linked to high-latitude climate fluctuations.

Bottom-water deoxygenation at the Peruvian margin during the last deglaciation recorded by benthic foraminifera

Abstract. Deciphering the dynamics of dissolved oxygen in the mid-depth ocean during the last deglaciation is essential to understand the influence of climate change on modern oxygen minimum zones (OMZs). Many paleo-proxy records from the eastern Pacific Ocean indicate an extension of oxygen-depleted conditions during the deglaciation, but the degree of deoxygenation has not been quantified to date. The Peruvian OMZ, one of the largest OMZs in the world, is a key area to monitor such changes in near-bottom-water oxygenation in relation to changing climatic conditions. Here, we analysed the potential to use the composition of foraminiferal assemblages from the Peruvian OMZ as a quantitative redox proxy. A multiple regression analysis was applied to a joint dataset of living (rose-bengal-stained, fossilizable calcareous species) benthic foraminiferal distributions from the Peruvian continental margin. Bottom-water oxygen concentrations ([O2]BW) during sampling were used as the dependant variable. The correlation was significant (R2=0.82; p<0.05), indicating that the foraminiferal assemblages are rather governed by oxygen availability than by the deposition of particulate organic matter (R2=0.53; p=0.31). We applied the regression formula to three sediment cores from the northern part of the Peruvian OMZ between 3 and 8∘ S and 997 and 1250 m water depth, thereby recording oxygenation changes at the lower boundary of the Peruvian OMZ. Each core displayed a similar trend of decreasing oxygen levels since the Last Glacial Maximum (LGM). The overall [O2]BW change from the LGM and the Holocene was constrained to 30 µmol kg−1 at the lower boundary of the OMZ.

Saltmarsh foraminifera in the subarctic White Sea: Thrive in summer, endure in winter

Abundance and diversity of intertidal benthic foraminifera decreases towards the poles. Well studied in the temperate zone, saltmarsh foraminiferal assemblages have only recently received attention at higher latitudes. We report modern foraminifera, including the taxonomy, abundance, and zonation, from a pristine saltmarsh in the subarctic White Sea, northern Europe. We sampled 10 stations (surface sediment, two replicates) from two high-tide flats covered with lush halophytic plants. Nine foraminiferal species found exhibited distinct vertical zonation confined to certain elevation levels. The high marsh assemblage comprised arenaceous Balticammina pseudomacrescens, Trochammina inflata, Jadammina macrescens, and monothalamous Ovammina opaca. This is the northernmost location where the first two species have been encountered alive. The low marsh assemblage was dominated by Miliammina fusca and Elphidium williamsoni. Summer abundances of live foraminifera were surprisingly higher than on other subarctic saltmarshes studied, mostly 100–500 and up to 3000 per 10 cm³. In winter, under a 40 cm of ice, the abundances were only 15–20 ind./10 cm³, but the species richness was the same. Unlike summer specimens of calcareous foraminifera, which are always brightly colored, winter Elphidium williamsoni all had bleak colorless cytoplasm, suggesting they discard kleptoplasts and abandon algal diet. We conclude that the insulating blanket of fast ice, which hardly moves on saltmarshes, prevents elimination of foraminifera in the harshness of winter, whereas the intense continental heating in summer lets them thrive on White-Sea saltmarshes. The composition of foraminiferal assemblages under local climatic conditions may thus deviate substantially from the latitudinal trend.

Foraminiferal-based biotic indices to assess the ecological quality status of the Gulf of Gabes (Tunisia): Present limitations and future perspectives

Abstract Biotic indices are tools to assess the ecological status of marine systems, and can be based on different metrics (such as ecological groups, specific diversity). The present study applies five biotic indices based on living (stained) benthic foraminiferal assemblages to assess ecological conditions in a wide area of the Mediterranean Sea in the heavily polluted Gulf of Gabes and along the western and eastern coasts of the Djerba Island, with the eastern coast considered as “pristine”. The applied indices are based on epiphytic foraminifera e.g., the “long versus short life span” index (ILS) and the modified FoRAM-Index (FI’), benthic foraminiferal assemblage composition and diversity, e.g., the Tolerant Species index (TSstd), the Foram Stress Index (FSI), the diversity Index (exp(H’bc)) and the newly developed Foram-AZTI Marine Biotic Index (Foram-AMBI). This latter index was tested using species of benthic foraminifera presently assigned to ecological groups in the Mediterranean Sea. All indices confirm good ecological conditions eastern of Djerba. The FI’ and ILS, % TSstd, FSI, indicate a severe anthropogenic impact especially in the central part of the Gulf of Gabes, next to the phosphate industry of Skhira and along the western coast of Djerba Island and confirm direct observations and geochemical data. The indices based on epiphytic foraminifera seem to better reflect actual environmental conditions in the investigated region because of the extended Posidonia oceanica meadow in the area. The exp(H’bc) reflects lower degrees of pollution. The application of the Foram-AMBI index presents limitations that prevent its current use. It strongly underestimates the pollution impact along the Tunisian coast, and additional work is needed to increase the number of species attributed to ecological groups and to possibly modify the coefficients to be used in its equation.

Cenomanian to Coniacian sea-level changes in the Lower Benue Trough (Nkalagu Area, Nigeria) and the Eastern Dahomey Basin: palaeontological and sedimentological evidence for eustasy and tectonism

AbstractThe Benue Trough formed in close relation to the opening of the South Atlantic and experienced sea-level fluctuations of different magnitudes during the Cenomanian to Coniacian interval. We identify depositional environments from outcrop sections and a drilling as control record. Lines of evidence for the interpretation include facies analyses, foraminiferal assemblage composition (P/B-ratio) and the presence of planktonic deep-water indicators. While the analysis of the well data from the Dahomey Basin indicates a continuous deep-water (bathyal) environment, the succession in the Nkalagu area of the Lower Benue Trough evolved in a different and more complex way. Beginning with latest Cenomanian shoreface to shelf deposits, a long period of subsidence lasted until the middle Turonian when pelagic shales and calcareous turbidites were deposited at upper to middle bathyal depths. These conditions continued during late Turonian and Coniacian times. The general deepening trend of the Lower Benue Trough was mainly controlled by tectonic subsidence and was superimposed by eustatic sea-level changes, resulting in periodically changing palaeowater depths. We were able to identify eight sea-level rises and falls that can be attributed to 405 kyr eccentricity cycles. The amplitudes of the sea-level changes were most likely in the range of several tens to a few hundred metres. The deposition of carbonate turbidites at Nkalagu was probably triggered by eustatic sea-level lowstands.

Impact of bottom water currents on benthic foraminiferal assemblages in a cold-water coral environment: The Moira Mounds (NE Atlantic)

Abstract Strong bottom currents play a key role in cold-water coral environments by shaping their morphology and providing the necessary food for the corals to thrive. This study investigates the differences between living and dead benthic foraminiferal assemblages in such environments, more precisely on the Moira Mounds (NE Atlantic). A specific focus is to understand the role of currents and their influence on the taphonomy of benthic foraminiferal assemblages. Here, we analyze high-resolution sediment grain size distributions coupled with benthic foraminiferal assemblage composition to assess how much deep-sea bottom currents affect benthic foraminiferal assemblages. We suggest that the dead benthic foraminiferal assemblage consists of a reworked glacial fauna associated with contemporary species. Reworked glacial species (Elphidium excavatum, Sigmoilopsis schlumbergeri) are the most abundant. Dominant species that are present almost exclusively in the living assemblage (Alabaminella weddellensis, Nonionella iridea, Trifarina spp.) are associated with high phytodetritus input, possibly as a response to the later phase of the North-east Atlantic spring bloom. Dead assemblages are further characterized by the scarcity of organic-walled agglutinated foraminifera in comparison to living assemblages. Sediment grain size distributions show that the downslope Moira Mounds consist of well-sorted fine sand, typical of contourite deposits in the area. Grain size distributions and the average Shannon diversity of living and dead foraminiferal assemblages indicate that the coral cover offers a sheltered environment, baffling eroded sediment and preventing post-mortem transport of dead foraminifera. We conclude that cold-water coral environments provide a valuable paleoenvironmental archive by trapping sediment in an otherwise non-depositional system.

Reef shallowing is a critical control on benthic foraminiferal assemblage composition on nearshore turbid coral reefs

Declining water quality represents a major threat to the coral reefs of Australia's Great Barrier Reef (GBR). Due to their close proximity to river point sources, reefs situated on the inner-shelf of the GBR are widely perceived to be most susceptible to the increased discharge of nutrients and sediments from coastal catchments, many of which have been modified since European settlement. However, the impact and magnitude of water quality change on the GBR's inner-shelf reefs remains unclear. Much of the uncertainty can be attributed to a paucity of long-term records with which to assess ecological and environmental change over appropriate reef-building timescales. Here, we present benthic foraminiferal palaeo-records from three proximal nearshore turbid-zone reefs located within the central region of the GBR. Bayesian age-depth modelling was used to identify the core intervals corresponding to the timing of European settlement in the region (c. 1850 CE), enabling the investigation of: (1) the composition and variability of benthic foraminiferal assemblages during reef shallowing towards sea level; and (2) whether any signal of increased nutrient and sediment inputs, as the result of historical land-use change, can be discerned on the most nearshore reefs of the central GBR. Multivariate analyses identified two assemblage groups, delineated by a significant increase in the relative abundance of Pararotalia spp. up-core. Our results suggest that post-European settlement associated increases in nutrient and sediment inputs are unlikely to have driven the observed shifts in benthic foraminiferal assemblage composition. Rather, we interpret changes in the composition of benthic foraminiferal assemblages as being linked to changes in hydrodynamic energy, light availability and the carbonate content of reef-matrix sediments during reef shallowing towards sea level. Our findings support the hypothesis that nearshore turbid-zone reefs have a higher resistance to increased nutrient and sediment inputs than those located further offshore, towards the inner/mid-shelf boundary of the GBR.