Benthic Foraminiferal Populations Research Articles

Intermediate water variability of the subtropical Northeastern Atlantic during 490–424 ka (late MIS 13 and MIS 12)

High-resolution foraminiferal stable isotopes and benthic foraminiferal faunal records of IODP Site U1391 drilled off the western Iberian margin were adopted to reconstruct intermediate water variability of the subtropical Northeastern Atlantic during the late Marine Isotope Stage (MIS) 13 and MIS 12. Five faunal turnovers were recognized based on multivariate statistical analyses of benthic foraminiferal census data from the size fraction >125 μm. The dominance of Uvigerina peregrina parva and Melonis barleeanum coincides with high benthic foraminiferal accumulation rates (BFAR), high benthic δ13C and the presence of dark-colour sediments during the final stage of MIS 13, also accompanied by frequent occurrences of Planulina ariminensis, an indicator of Mediterranean Outflow Water (MOW), which indicates MOW-related high oxic and mesotrophic to slightly eutrophic bottom water environments. MIS 12c and MIS 12b are characterized by Bulimina mexicana assemblage, together with low BFAR, high benthic δ13C and the presence of light-colour sediments, revealing mesotrophic and well‑oxygenated seafloor conditions associated with the possible advection of Glacial North Atlantic Intermediate Water (GNAIW) to the studied site. A prominent increase in organic matter supply and a slight decrease in dissolved oxygen concentration during MIS 12a were reflected by more abundant Bulimina aculeata, higher BFAR, lower benthic δ13C and the darker-colour sediments relative to MIS 12c-b. A shift in the dominant species and significantly decreased benthic δ13C, suggest an increased influence of southern-sourced waters (SSW) and a decreased influence of GNAIW during MIS 12a. During the early Termination V (TV), infaunal taxa mainly composed of B. aculeata, Bulimina exilis, Nonionella turgida, Brizalina sp. and Uvigerina proboscidea dominate the benthic foraminiferal population, which may be attributed to eutrophic and poorly‑oxygenated bottom water environment strongly influenced by SSW. During the late TV, N. turgida rapidly became the predominant taxa, and its predominance was probably the result of further reduction in dissolved oxygen concentration.

Annual dynamics of benthic foraminiferal populations in the Tramandaí-Armazém Lagoon, southern Brazil

Abstract Modern coastal environments are considered highly selective and dynamic, not only due to the natural variability of physical and chemical parameters, but also because of anthropogenic contamination. Our study aims to identify environmental and/or anthropogenic factors influencing benthic foraminiferal abundances over a period of one year in the Tramandai-Armazem Lagoon, southern Brazil. Assemblages were composed exclusively of agglutinated species assigned to the genera Trochammina, Trochamminita, Ammotium, Haplophragmoides and Miliammina. Total abundances varied throughout the year, reaching the highest values during the wetter months of March and July, when living and dead assemblages became dominated by Ammotium salsum. This pattern is likely related to salinity fluctuations due to changes in freshwater input that, consequently, affected the amount of organic matter (e.g., phytodetritus) brought into the lagoon by surrounding drainages. To assess the impact of anthropogenic pollution, we evaluated total relative abundances of deformed tests in the Tramandai-Armazem Lagoon. Relative abundances of deformed tests were the highest during the months of January and March, when contaminant (e.g., sewage) discharge was probably increased due to the seasonal population growth in the region.

Inner Shelf Substrate Characteristics and Their Impacts on the Distribution of Recent Benthic Foraminifera from the Southern Part of Gulf of Mannar, Southeast Coast of India

The present study elaborates the relationship between sediment characteristics and benthic foraminiferal population distribution from off the coast of Theresapuram, Sippikulam, Mookaiyur and Valinokkam representing the southern part of Gulf of Mannar, Southeast coast of India. A systematic collection of sediment and bottom water samples were made at 28 sampling stations, keeping seven samples each, along the four traverses. The samples were collected for three seasons, representing pre-monsoon (October), post-monsoon/winter (January) and summer (April) and thus the collections amounted to a total of 84 samples. The benthic foraminiferal studies from the sediments collected have led to the recognition of 124 benthic foraminiferal species belonging to 59 genera, 39 families and 21 super families of 5 suborders. Among the 124 species, Ammonia beccarii, A. tepida, Asterotalia infllata, Elphidium advenum, Noninoides boueanum, and Quinqueloculina seminulum are considered to be abundant and widespread in the present study area. It has been observed that the maximum population is observed during summer (April) with 2335 specimens and the minimum with 1934 specimens during monsoon (October). Spatially, the middle segment (stations 3-5) of all traverses of all the collections encounter with relatively higher population. Impact of spatial and seasonal variation in substrate characteristics on the benthic foraminiferal population revealed that the calcium carbonate content shows a positive correlation with the fauna of the study area and the organic matter content has somewhat inverse relationship with the population abundance. In the present study, organic matter content is not an effective factor that controls the population abundance, but along with other parameters plays a supporting role. Out of 12 possible sediment types of Trefethen’s classification, the sediments in the study area fall only in three types’ viz., sand, siltysand and claysand. The most favourable substrate for higher benthic foraminiferal population seems to be siltysand. In general, the benthic foraminiferal population of the present study is directly proportional to the calcium carbonate content of the sediments along with lower organic matter (0.7 -0.93%) and the accommodative substrate for higher reproduction is silty sand.

Benthic foraminiferal assemblages and test accumulation in coastal microhabitats on San Salvador, Bahamas

Abstract. Benthic foraminiferal populations were studied in a shallow bay of San Salvador Island, the Bahamas. Surface sediments and marine macrophytes were collected from 14 sample sites along a 500 m transect at Grahams Harbour to investigate the foraminiferal assemblage in each microhabitat and to test the link between dead foraminiferal test accumulation patterns and living epiphytic and sedimentary foraminiferal assemblages, macrophyte distribution, and environmental gradients. The analyses include grain size measurements, macrophyte biomass quantification, and qualitative and quantitative studies of benthic foraminifera. The foraminifera found attached to macrophytes differed between macrophyte habitats. However, a correlation between these living communities and the dead assemblages in the sediments at the same sites could not be observed. Principal component analysis (PCA) and redundancy analysis (RDA) suggest that the presence of the macroalgae Halimeda explains 16 % of the residual faunal variation in the dead foraminiferal assemblage after the effects of sorting according to fall speed are partialled out. The RDA also reflects a positive correlation between foraminifera larger than 1.0 mm in diameter and the 0.25–0.5 mm sediment grain size, indicating sedimentological processes as the main factor controlling the sedimentary epiphytic foraminiferal assemblages. These sedimentary processes overprint most effects of ecological features or macrophyte-specific association.

Assessing the environmental significance of benthic foraminiferal morpho-groups from the northern high latitudinal regions

The spatial distribution of benthic foraminiferal morpho-groups has been documented from the Kongsfjorden-Krossfjorden, to assess its environmental significance. Benthic foraminiferal abundance increases from the inner-most fjord towards the mouth in Kongsfjorden. The calcareous forms dominate the benthic foraminiferal population in Kongsfjorden as compared to Krossfjorden. The agglutinated benthic foraminifera are relatively more abundant in Krossfjorden. The rounded symmetrical benthic foraminifera are the dominant morpho-group, due to the high energy conditions and generally well-oxygenated waters. A significant positive correlation between the relative abundance of rounded symmetrical benthic foraminifera and water depth, however, suggests the influence of factors other than turbulence. A more significant positive correlation is observed between the relative abundance of agglutinated rounded symmetrical benthic foraminifera and water depth. The relative abundance of calcareous angular asymmetrical benthic foraminifera is significantly negatively correlated with water depth. The significant correlation between foraminiferal parameters and water depth, suggests that melt-water and glacial calving, as well as associated changes in the sedimentation rate, grain size, pH and organic carbon, affect benthic foraminifera in high latitudinal fjords. The difference in the surface distribution of calcareous and agglutinated benthic foraminiferal morpho-groups implies their differential response to ambient conditions.

Mudbank off Alleppey, India: A bane for foraminifera but not so for carbon burial

Calm conditions and extensive fishing, during monsoon season in the mudbank off Alleppey (Kerala), India creates a unique environment, associated with high suspended particulate matter. The effect of processes associated with mudbank formation, on benthic foraminifera, however, has not been documented. We have studied, seasonal foraminiferal distribution, to understand foraminiferal response to physico-chemical changes associated with the mudbank formation. Additionally, seasonal changes in total carbon, calcium carbonate (CaCO3), organic carbon (Corg) and Corg/nitrogen (Corg/N) were also measured to understand the effect of mudbank formation on carbon burial. We report a low foraminiferal abundance in the mudbank. Benthic foraminiferal diversity is also low in the mudbank, during both pre-monsoon and monsoon season, clearly suggesting a stressed environment. Agglutinated foraminifera dominate the living benthic foraminiferal population in the mudbank, suggesting that the area is carbonate undersaturated and under fresh-water influence. Ammobaculites dilatatus and Ammobaculites exiguus are the dominant agglutinated species abundant in the mudbank and thus can be used to reconstruct past changes in the mudbank. The CaCO3 is consistently low during all seasons, at one of the core mudbank stations. The %Corg is, however, higher in the core mudbank as well as the northern peripheral region. The Corg/N is consistently uniform at all the stations indicating a similar source of organic matter in all the seasons. The higher %Corg and constant Corg/N suggest, that food availability and its source is not a major factor affecting benthic foraminifera in the mudbank. Instead, increased turbidity and low bottom water salinity are the main cause of seasonally stressed environment in the mudbank. Additionally, Corg degradation coupled with fresh water influx induced drop in bottom water pH is responsible for low foraminiferal population in mudbank region, in all the seasons. The reduced calcareous benthic foraminiferal abundance, however, does not affect the carbon burial in the mudbank, due to higher %Corg.

Foraminifera from the upper Campanian Pierre Shale methane cold-seeps, South Dakota

Investigations into ancient benthic foraminiferal populations are limited, particularly in the Late Cretaceous methane cold-seeps of the Western Interior Seaway. Poorly lithified shale samples (400 cc) from 8 methane cold-seeps and one coeval non-seep locality from the upper Campanian Pierre Shale in South Dakota were disaggregated, sieved, and examined for specimens (>150 μm). Seeps yielded between 100 and 148 specimens per locality. The foraminiferal populations found at seeps and the single non-seep locality contain many of the same species. The most abundant benthic genera found at late Campanian seeps in South Dakota include Guardryina, Haplophragmoides, Trochammina, buliminids (Buliminella and Praebulimina), Lagena, and Gavelinella. Planktic foraminiferal assemblages are much less diverse and dominated by Globigerinelloides. Only two seeps and the non-seep locality contain biserial species, these localities fall in the Baculites compressus zone. The foraminifera from both seeps and the non-seep have Shannon-Weiner (ln) and Fisher's diversity indices that show that the foraminiferal populations are of moderate diversity with a small peak in seeps from the Baculites compressus Zone. Agglutinate to calcareous ratios are consistent for nearly all seep localities, however, one seep locality (AMNH loc. 3528a) and the non-seep sample render a slightly higher percentage of agglutinated species, these localities are within the Baculites compressus Zone. We conclude that, like their modern counterparts: 1) there is no evidence of unique physiological differences between seep and non-seep foraminifera, 2) the species found in seep environments are most likely more tolerant of seep conditions, and 3) there are no seep obligate species.

Changes in standing stock and vertical distribution of benthic foraminifera along a depth gradient (58–2750 m) in the southeastern Arabian Sea

Benthic foraminifera are a reliable proxy to reconstruct past oceanographic conditions. The ecological preferences of benthic foraminifera are usually studied from the core-top samples. The habitat of living benthic foraminifera, however, can be much deeper. Here, we document the vertical distribution of living benthic foraminifera from the Gulf of Mannar, Southeastern Arabian Sea, to find out the sediment depth that contains representative living assemblage and to understand the relationship between ecological parameters and foraminiferal abundance. Additionally, as the region has a well-developed oxygen minimum zone, we also assess the effect of dissolved oxygen, organic carbon (%Corg) and other associated parameters on living benthic foraminifera. The multi-core samples were collected along a longitudinal transect covering the shelf, and slope (58–2750 m), during the post southwest monsoon season. We report that at stations where dissolved oxygen is low (≤1.5 mL/L), >85% of the total living benthic foraminiferal population is confined to the top 0–1 cm section of the sediment and the average living depth decreases up to 0.6 cm. However, in the well-oxygenated waters, especially in the lower slope region, a substantial fraction of the total living benthic foraminiferal population inhabits deeper sections of the sediments. The calcareous benthic foraminifera dominates the foraminiferal population both within and outside the oxygen minimum zone. The absolute abundance of agglutinated benthic foraminifera is more on the continental slope, as compared to the shelf. The infaunal and epifaunal calcareous and agglutinated foraminifera show a different trend. We report that while the bottom water dissolved oxygen and depth controls the absolute abundance of benthic foraminifera, both the %Corg and ambient temperature, affect the relative abundance of living calcareous and agglutinated benthic foraminifera in the Gulf of Mannar.

Benthic foraminiferal response to changes in mining pattern: a case study from the Zuari estuary, Goa, India

Being sensitive to environmental changes, foraminifera have been extensively used to monitor pollution level in the marine environment, including the effect of mining in coastal areas. In the Goa state of India, the rejects from opencast mining on land largely find their way to the estuaries, as washout during monsoon. Additionally, the Mormugao Port at the mouth of the Zuari estuary is the hub of activities due to the transport of ore from hinterland areas by barges and its subsequent loading for export. On the directive of the Supreme Court of India, all the mining-related activities abruptly stopped throughout India, including that in Goa in 2012, and got reinstated in 2015. Therefore, it provided a fit case to test the effectiveness of benthic foraminifera as an indicator of environmental impact due to mining activities. A total of ten surface sediment samples from five locations in Zuari estuary were collected from a depth range of 4.5–8.5 m in the years of 2013 and 2016 and were analyzed for both the living (stained) and dead benthic foraminifera. The year 2013 represents a time interval immediately after the closure of extensive mining activity, and the sampling during 2016 represents minimal mining. The living benthic foraminiferal abundance was higher (19–54/g sediment) during 2013 and decreased substantially during 2016 (3–22/g sediment), suggesting an adverse effect of activities associated with mine closure on benthic foraminifera. Additionally, the relative abundance of Ammonia was also significantly low during the year 2016. The temporal variation in dead foraminifera was, however, different than that of the living foraminifera. The differential response was attributed to the terrigenous dilution as a result of change in sedimentation rate. Therefore, we conclude that living foraminifera correctly incorporate the changes in mining pattern and may be used as an effective tool to monitor the impact of mining. We further suggest that the potential counter effect of terrigenous dilution on total and living benthic foraminiferal population should be considered while interpreting temporal variations in foraminiferal abundance in marginal marine settings.

WITHDRAWN: Benthic Foraminiferal Assemblage Formation: Theory and Observation for the European Arctic Margin

Abstract We use theory and observation to determine how benthic foraminiferal populations living in a range of sedimentary microenvironments are translated into fossil assemblages along the continental margin of the European Arctic. We examine downcore stained (cell tracker green and rose Bengal) and total species shell abundances through the sediment mixing (bioturbation) zone. This, in combination with porewater geochemical measurements, allows us to establish zones of production and destruction for species’ shells, and deduce how the fossil record is being generated by the living community. For many taxa, shell production is high in the upper, oxic, sedimentary layer, but destruction in this zone is also high. Hence, contribution to the fossil record is biased to more infaunal populations and species. Taxa producing near, or below, the anoxic boundary of the sediments are particularly important to the developing fossil record of the fjord environment. We find that taxon relative and absolute abundances change continuously through the biologically active sediment profile. This has implications for reconstructing paleoenvironments using benthic foraminiferal assemblages, and potentially for the geochemistry of individual fossil taxa.

Benthic foraminiferal assemblage formation: Theory and observation for the European Arctic Margin

We use theory and observation to determine how benthic foraminiferal populations living in a range of sedimentary microenvironments are translated into fossil assemblages along the continental margin of the European Arctic. We examine downcore stained (cell tracker green and rose Bengal) and total species shell abundances through the sediment mixing (bioturbation) zone. This, in combination with porewater geochemical measurements, allows us to establish zones of production and destruction for species’ shells, and deduce how the fossil record is being generated by the living community. For many taxa, shell production is high in the upper, oxic, sedimentary layer, but destruction in this zone is also high. Hence, contribution to the fossil record is biased to more infaunal populations and species. Taxa producing near, or below, the anoxic boundary of the sediments are particularly important to the developing fossil record of the fjord environment. We find that taxon relative and absolute abundances change continuously through the biologically active sediment profile. This has implications for reconstructing paleoenvironments using benthic foraminiferal assemblages, and potentially for the geochemistry of individual fossil taxa.

Species diversity variations in Neogene deep-sea benthic foraminifera at ODP Hole 730A, western Arabian Sea

Deep-sea benthic foraminifera are an important and widely used marine proxy to understand paleoceanographic and paleoclimatic changes on regional and global scales, owing to their sensitivity to oceanic and climatic turnovers. Some species of benthic foraminifera are sensitive to changes in water mass properties whereas others are sensitive to organic fluxes and deep-sea oxygenation. Benthic faunal diversity has been found closely linked to food web, bottom water oxygen levels, and substrate and water mass stability. The present study is aimed at analyzing species diversity trends in benthic foraminifera and their linkages with Indian monsoon variability during the Neogene. Species diversity of benthic foraminifera is examined in terms of number of species (S), information function (H), equitability (E) and Sanders’ rarefied values, which were combined with relative abundances of high and low productivity benthic foraminifera at Ocean Drilling Program Hole 730A, Oman margin, western Arabian Sea. The Oman margin offers the best opportunity to understand monsoon-driven changes in benthic diversity since summer monsoon winds have greater impact on the study area. The species diversity was higher during the early Miocene Climatic Optimum (∼17.2–16.4 Ma) followed by a decrease during 16.4–13 Ma coinciding with a major increase in Antarctic ice volume and increased formation of Antarctic Bottom Water. All the diversity parameters show an increase during 13–11.6 Ma, a gradual decrease during 11.6–9 Ma and then an increase with a maximum at 7 Ma. Thereafter the values show little change until 1.2 Ma when all the parameters abruptly decrease. The benthic foraminiferal populations and diversity at Hole 730A were mainly driven by the Indian monsoon, and polar waters might have played a minor or no role since early Neogene period as the Arabian Sea is an enclosed basin.

Deep-sea benthic foraminiferal changes in the eastern Indian Ocean (ODP Hole 757B): Their links to deep Indonesian (Pacific) flow and high latitude glaciation during the Neogene

This study analyses 26.5 Ma record of deep-sea benthic foraminifera from 194 samples from Ocean Drilling Program Hole 757B (latitude 17°01.458' S, longitude 88°10.899' E, water depth of 1652.1 m) located on the Ninetyeast Ridge, southeastern Indian Ocean below equatorial divergence zone. The data document important changes in benthic foraminiferal population at Hole 757B since the late Oligocene. The welloxygenated, oligotrophic species including Cibicides cicatricosus, C. pseudoungerianus and Oridorsalis umbonatus were dominant during the late Oligocene to the early Miocene. These species began to decline as site 757 moved northward into the influence of the Indonesian Throughflow (ITF) beneath surface and subsurface water masses from the Pacific Ocean. Cibicides cicatricosus and C. pseudoungerianus disappeared in the late Miocene (10-8 Ma) at Hole 757B. The lower bathyal to abyssal species Nuttallides umbonifera shows a major increase at ~11.5 Ma coinciding with a significant increase in Neodymium (Nd) isotope values, indicating substantial transport of deep Pacific water to the Indian Ocean through the Indonesian seaway. Nuttallides umbonifera decreases drastically during 3-2.8 Ma, though the Nd isotope values do not show a decrease. We relate this change to a low sample resolution in the latter study. This event coincides with the final closure of the Indonesian seaway and a switch in shallow ITF source from warm, saline South Pacific to cool, fresh North Pacific thermocline water, which triggered global cooling and major expansion of Northern Hemisphere glaciation.

Benthic Foraminiferal response to sea level change in the mixed siliciclastic‐carbonate system of southern Ashmore Trough (Gulf of Papua)

Ashmore Trough in the western Gulf of Papua (GoP) represents an outstanding modern example of a tropical mixed siliciclastic‐carbonate depositional system where significant masses of both river‐borne silicates and bank‐derived neritic carbonates accumulate. In this study, we examine how benthic foraminiferal populations within Ashmore Trough vary in response to sea level–driven paleoenvironmental changes, particularly organic matter and sediment supply. Two 11.3‐m‐long piston cores and a trigger core were collected from the slope of Ashmore Trough and dated using radiocarbon and oxygen isotope measurements of planktic foraminifera. Relative abundances, principal component analyses, and cluster analyses of benthic foraminiferal assemblages in sediment samples identify three distinct assemblages whose proportions changed over time. Assemblage 1, with high abundances of Uvigerina peregrina and Bolivina robusta, dominated between ∼83 and 70 ka (early regression); assemblage 2, with high abundances of Globocassidulina subglobosa, dominated between ∼70 and 11 ka (late regression through lowstand and early transgression); and assemblage 3, with high abundances of neritic benthic species such as Planorbulina mediterranensis, dominated from ∼11 ka to the present (late transgression through early highstand). Assemblage 1 represents heightened organic carbon flux or lowered bottom water oxygen concentration, and corresponds to a time of maximum siliciclastic fluxes to the slope with falling sea level. Assemblage 2 reflects lowered organic carbon flux or elevated bottom water oxygen concentration, and corresponds to an interval of lowered siliciclastic fluxes to the slope due to sediment bypass during sea level lowstand. Assemblage 3 signals increased off‐shelf delivery of neritic carbonates, likely when carbonate productivity on the outer shelf (Great Barrier Reef) increased significantly when it was reflooded. Benthic foraminiferal assemblages in the sediment sink (slopes of Ashmore Trough) likely respond to the amount and type of sediment supplied from the proximal source (outer GoP shelf).

Foraminiferal and ostracod ecological patterns in coastal environments of SE Andros Island (Middle Aegean Sea, Greece)

A comparative study of recent epiphytal ostracod and benthic foraminiferal populations was conducted in August 2001, at two gulfs (Korthi and Kastro) located at the southeastern part of Andros Island (middle Aegean Sea, Greece). Thirty samples (representing living macro-benthic algae and seagrasses) from both gulfs were studied and a total of 34 ostracod species and 60 benthic foraminiferal species were identified. In the gulf of Korthi both benthic foraminiferal and epiphytal ostracod assemblages were characterized by high abundances of Amphistegina lessonii and Xestoleberis spp., respectively, therefore the performed Q-mode cluster analysis verified the presence of a Normal Environment Biofacies (NE). Declined Environment (DE) and Stressed (SE) Environment Biofacies were recognized in the gulf of Kastro, an area more affected by anthropogenic activities. Several deformed foraminiferal specimens have been documented in the assemblages from both gulfs, but malformed tests are significantly increased in SE Biofacies of Kastro gulf. This study suggests that great accumulations of A. lessonii (35–60%) associated with high frequencies of Xestoleberis communis and/or Xestoleberis decipiens and high species diversities can be used as bioindicators of coastal health.

Benthic foraminifera from a recent, shallow-water hydrothermal environment in the Aeolian Arc (Tyrrhenian Sea)

Benthic foraminiferal assemblages from sediments around active or recently active hydrothermal vents in the Aeolian Arc have been investigated in four areas with different hydrothermal mineralization and seafloor exhalative activity at depths between ∼60 and ∼300 m. Active hydrothermal spots were distinguished from the surrounding sediments by direct observations by a Remotely Operated Vehicle (ROV) and subsequent seafloor sampling. Samples were taken at different water depths and are characterized by a number of mineralogies reflecting the changing temperature of the hydrothermal fluids. Overall, benthic foraminifera are absent from sites with high-temperature hydrothermal emissions, and their distribution at sites of low-temperature emissions is very patchy, depending on the physical and/or chemical conditions reflecting differences in temperature and composition of the emitted fluids. In the Secca del Capo area, which is free from recent emission activity, the benthic foraminiferal population is indicative of a normal marine environment, with Globocassidulina subglobosa, Cassidulina crassa, and Gavelinopsis lobatulus. In the Basiluzzo, Secca dei Pesci, and Panarea areas, which are characterized by different degrees of hydrothermal activity, three distinct assemblages have been recognized. The first assemblage is dominated by Ammodiscus catinus, Glomospira charoides, and Glomospira gordialis and indicates hydrothermal influence. The second assemblage, with Lobatula lobatula, Asterigerinata mamilla, Rosalina globularis, and Quinqueloculina spp. as main constituents, indicates a seagrass environment influenced by diffuse emissions. The third assemblage with abundant A. catinus, Ammoglobigerina globigeriniformis, G. gordialis and Haplophragmoides canariensis suggests low pH conditions resulting from acidic hydrothermal emissions, leading to the dissolution of calcium carbonate tests.

Benthic foraminifera associated with a hydrocarbon seep in the Rockall Trough (NE Atlantic)

Recent benthic foraminiferal assemblages in surface sediments of the Rockall Trough (NE Atlantic) have been qualitatively and quantitatively studied in order to investigate the effects of hydrocarbon seepage on benthic foraminiferal populations. Species diversity and abundance data have been examined in samples of similar lithology collected from hydrocarbon seep and non-seep (control) areas at a water depth of about 1000 m. Three species groups with different environmental preferences can be recognized. Group 1 dominates seep samples, and includes species tolerant to hydrocarbon emission, especially Angulogerina bradyana. In contrast, the less tolerant Group 2 species are weakly represented at seeps but dominate control samples. Group 3 species occur in low frequencies in both seep and non-seep samples. Furthermore, the measurement of species diversity (Shannon–Wiener and Simpson indices) demonstrates a difference in foraminiferal occurrence and frequencies between the seep and non-seep sites. Thus, the benthic foraminiferal distribution pattern is guided by different sensitivities of the species to hydrocarbons, reduced bottom-water oxygen usually associated with seepage and/or to a relatively elevated organic matter content in the sediment.

Relationship between benthic foraminifera and food resources in South San Francisco Bay, California, USA

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 297:131-145 (2005) - doi:10.3354/meps297131 Relationship between benthic foraminifera and food resources in South San Francisco Bay, California, USA Amy E. Lesen* Department of Integrative Biology and Museum of Paleontology, University of California, Berkeley, California 94720-3140, USA Present address: Department of Math and Science, Pratt Institute, 200 Willoughby Avenue, Brooklyn, New York 11205, USA *Email: alesen@pratt.edu ABSTRACT: Foraminifera are amongst the most abundant known protists found in marine habitats, and are ecologically important constituents of the benthic meiofauna. The seasonality of San Francisco Bay, USA, makes it an ideal system in which to study the relationships between primary production, organic matter fluxes, and food resources for the benthos. Samples were collected at one site at a depth of 8.8 m in South San Francisco Bay on monthly cruises for 2 yr from November 1999 through November 2001. Each month, water column parameters (chlorophyll concentration) and sediment parameters (chlorophyll, total organic carbon, nitrogen, amino acids, bacterial abundance) were measured, and benthic foraminiferal population size and biovolume was counted and calculated. Water column chlorophyll peaked in the spring of 2000 and 2001, and the fall of 2000, with sediment parameters peaking 1 to 3 mo later. The benthic foraminiferal standing crop peaked during the spring of both study years, and showed a large peak in the fall of 2001 dominated by the small-sized foraminifer Fursenkoina pontoni. The data strongly suggest that benthic foraminifera increase in number following phytoplankton blooms when many kinds of sediment organic matter also increase. Foraminiferal biovolume does not necessarily follow this pattern, especially when peaks in standing crop mainly consist of small-sized individuals. Foraminiferal biovolume and standing crop generally increase when the sediment C:N ratio increases, suggesting that benthic foraminiferal populations in South San Francisco Bay may be exploiting a detrital food source in addition to recently deposited fresh phytoplankton. Thus, foraminifera are probably quick to exploit sediment organic matter, and may be important remineralizers of nutrients in this system. KEY WORDS: Benthic ecology · Foraminifera · Marine protists · Population dynamics · Food webs · Estuarine ecology · Meiofauna · Organic matter Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 297. Online publication date: August 01, 2005 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2005 Inter-Research.

Recent turbidite deposition in the eastern Atlantic: Early diagenesis and biotic recovery

An interface core taken in Capbreton canyon shows a succession of sedimentary facies interpreted as classical Bouma turbiditic sequences. Activities of 234Th and 210Pb suggest that the deposition of the most recent turbidite was triggered by the violent storm that affected the Atlantic coast of southern France on the 27th of December 1999, about four months before the sampling of the core. This turbidite allows us to study the ongoing diagenesis of the new sediment layer and of the previous sediment-water interface, which has been buried and only slightly eroded. A study of benthic foraminiferal populations informs us about the rate of benthic ecosystem recovery after such a major ecosystem disturbance event. The composition of the benthic foraminiferal fauna suggests that the benthic ecosystem in Capbreton canyon remains in an early stage of colonization. The rare agglutinant taxon Technitella melo appears to be the first colonizing species. It is suggested that Technitella melo is advantaged by the food-impoverished conditions in the days following turbidite deposition. Almost all of the turbidite layer and the previous oxic sediment-water interface contain reduced dissolved metal species and were anoxic. The buried interface contains Fe- and Mn-oxides inherited from its recent oxic past. The reduction of manganese oxides was in progress at the time of core collection. The reduced Mn remained trapped in the sediment as Mn-containing carbonates. Iron-oxides did not undergo significant reductive dissolution. The top of the newly deposited turbidite formed an oxic layer, which was rapidly enriched in metal-oxides. The enrichment of manganese oxides was mostly due to the oxidation of dissolved Mn2+, which diffused from below. The enrichment of iron oxides is explained both by the oxidation of the upward flux of dissolved Fe2+, and by the input of detrital iron oxide after, or as a result of the turbidite deposition.

Distribution of benthic foraminiferal populations in surface sediments of the Saguenay Fjord, before and after the 1996 flood

In the summer of 1996, a ‘flash’ flood occurred in the Saguenay-Lac-St-Jean region (Quebec) leading to the deposition, in less than 2 days, of an estimated 6–15×10 6 m 3 of sediments at the head of the Saguenay Fjord. In order to evaluate the impact of such a sedimentary event on the benthic meiofauna, foraminiferal analyses were performed in surface sediment at eight stations in 1994, 1997, 1998 and 1999 along the main axis of the fjord. A 10-cm sedimentary sequence taken from a box core collected in 1997 from the deepest part of the fjord and spanning the last ca. 35 years provides a reference state for pre-flood foraminiferal assemblages. A significant change in foraminiferal assemblages is observed downcore, with the decrease of Spiroplectammina biformis relative to Adercotryma glomerata. 210Pb measurements suggest that this change occurred during the late 1970s. Surface samples (0–1 cm) collected between 1997 and 1999 in the inner basin also reveal a decrease of S. biformis percentages. Given the relative stability of this environment, such a change in faunal assemblages could be related to reduced industrial waste inputs or to a differential preservation of taxa. The 1996 flood had a major negative impact on the concentration and species diversity of benthic populations near the head of the fjord (Baie des Ha! Ha!), where the flood material is up to 50 cm thick. However, two years after the flood, benthic foraminiferal populations recolonized the sediments in the Saguenay Fjord.