Tests Of Benthic Foraminifera Research Articles

Threads of microbial activity on quasi-anoxic environments: Case studies from Oligocene to Miocene of the Central Paratethys

Microbial activity can be expressed in a wide range of products and forms including boring structures, biofilm-like subproducts, and framboidal pyrite precipitates. Microendolithic structures, in particular, are found in carbonate hardgrounds including tests of planktonic and benthic foraminifera and their traces can provide an extra paleoenvironmental marker of relative paleobathymetry, oxygenation, and environmental stress. Variegated traces of microbial activity including microborings, framboidal pyrite bacterial subproducts, and probable biofilms were herein studied in tests of benthic foraminifera from dysphotic to aphotic, shelf to an upper bathyal hypoxic environment. Collected material is from 6 localities in the Central Paratethys area, the Czech Republic (LOM-1 Mikulov, Hevlín), Slovakia (DNV, LKŠ-1), and Hungary (Rozalia), ranging from Rupelian to Serravalian. Microendolithic morphology was examined from resin casts obtained from the tests resulting in a total of ten ichnospecies and four other forms for which it was only possible to establish affinity on higher ranks. Levels of oxygen depletion were estimated from Benthic Foraminifera Oxygen index (BFOI). The bacterial origin of pyrite was inferred by morphology, grain size, and ẟS34 values. The number of observed microboring structures gradually reduce with the decrease of oxygen content, while the precipitation of framboidal pyrite were increasing at the same time. Biofilm-like structures, apart from the suggestive morphology, also showed an enriched content of elemental iron, sulfur, and phosphorus. Raman spectroscopy shows similarities with organic pigment spectra and is still under investigation.

Benthic Foraminiferal Mn/Ca as Low‐Oxygen Proxy in Fjord Sediments

AbstractFjord systems are typically affected by low‐oxygen conditions, which are increasing in extent and severity, forced by ongoing global changes. Fjord sedimentary records can provide high temporal resolution archives to aid our understanding of the underlying mechanisms and impacts of current deoxygenation. However, such archives can only be interpreted with well‐calibrated proxies. Bottom‐water oxygen conditions determine redox regime and availability of redox‐sensitive trace elements such as manganese, which in turn may be recorded by manganese‐to‐calcium ratios (Mn/Ca) in biogenic calcium carbonates (e.g., benthic foraminifera tests). However, biological influences on Mn incorporation (e.g., species‐specific Mn fractionation, ontogeny, living and calcification depths) are still poorly constrained. We analyzed Mn/Ca of living benthic foraminifera (Bulimina marginata, Nonionellina labradorica), sampled at low‐ to well‐oxygenated conditions over a seasonal gradient in Gullmar Fjord, Swedish West coast (71–217 μmol/L oxygen (O2)), by laser‐ablation ICP‐MS. High pore‐water Mn availability in the fjord supported Mn incorporation by foraminifera. B. marginata recorded contrasting Mn redox regimes sensitively and demonstrated potential as proxy for low‐oxygen conditions. Synchrotron‐based scanning X‐ray fluorescence nanoimaging of Mn distributions across B. marginata tests displayed Mn/Ca shifts by chambers, reflecting bottom‐water oxygenation history and/or ontogeny‐driven life strategy preferences. In contrast, Mn/Ca signals of N. labradorica were extremely high and insensitive to environmental variability. We explore potential biologically controlled mechanisms that could potentially explain this species‐specific response. Our data suggest that with the selection of sensitive candidate species, the Mn/Ca proxy has potential to be further developed for quantitative oxygen reconstructions in the low‐oxygen range.

Natural arsenic-rich spring waters discharging from the Austin Chalk, North-Central Texas, USA: Mineral and chemical evidence of pyrite oxidation followed by reductive dissolution of neo-formed Fe(III) oxides/oxyhydroxides

The chemical composition of acidic springs with elevated arsenic (As) concentrations discharging from the Cretaceous Austin Chalk in North-Central Texas, USA, along with the mineralogy of ochreous precipitates associated with these springs, was investigated to evaluate the source of the arsenic. Water samples were collected from the springs for chemical analysis and bedrock (i.e., Austin Chalk) and local soil samples were taken for mineralogical and chemical analyses. The mean (±1σ) pH of the spring waters is 6.3 ± 0.68. The spring waters also exhibit low redox potentials (Eh = −100 ± 70 mV), high iron (Fe) concentrations (40 mg kg−1), elevated As concentrations (up to 105 μg kg−1), moderate total dissolve solids (TDS) values (780 mg kg−1 ≤ TDS ≤1380 mg kg−1), and a sulfurous odor. Arsenic concentrations are highest where the springs discharge, but subsequently decreases with flow beyond the spring orifices. Scanning electron microscopy (SEM) of samples of the Austin Chalk from the field site revealed that pyritization of planktonic and benthic foraminifera tests is a common feature of these aquifer rocks, and that the pyrite occurs largely as framboids. Electron microprobe analysis of the pyrite grains indicate that early diagenetic forms consist chiefly of Fe and sulfur (S) in nearly stoichiometric proportions (i.e., ∼45 and 50 wt % respectively, for Fe and S), whereas late diagenetic and/or weathered forms are largely Fe (∼60 wt %) with minimal S contents (∼0.1 wt%). Arsenic is distributed evenly in both phases (∼0.2 wt %) but is absent in the surrounding carbonate matrix. The spring water compositions along with the mineralogy of the aquifer rocks and the ochreous precipitates are consistent with the source of the elevated dissolved As concentrations being the result of oxidation and chemical weathering of As-bearing pyrite that occurs within the Austin Chalk and overlying soils/sediments as recharging meteoric water reacts with these materials. We employ a simple 1-D reactive transport model that supports As-bearing pyrite oxidation by O2(aq) in recharging meteoric waters, adsorption of mobilized As onto the resulting neo-formed Fe(III) oxides/oxyhydroxides, followed by reductive dissolution of the neo-formed Fe(III) oxides/oxyhydroxides and re-release of the adsorbed into the groundwater as the likely geochemical processes responsible for the elevated As concentrations measured in the studied springs.

Fractal analysis highlights analogies in arenaceous tubes of Sabellaria alveolata (Metazoa, Polychaeta) and agglutinated tests of foraminifera (Protista).

Bioconstructions of Sabellaria alveolata (Polychaeta Sabellariidae) from southern Sicily (Central Mediterranean) were sampled and analysed through a multidisciplinary approach in order to unravel the construction pattern of arenaceous tubes and explore possible analogies existing between the worm tubes and the agglutinated tests of benthic foraminifera (Protista). Scanning Electron Microscopy and Energy Dispersive Spectroscopy analyses were carried out on entire tubes as well as sectioned ones. Results show that arenaceous tubes are built following a rigorous architectural framework, based on selection and methodical arrangement of the agglutinated grains, and show surprising analogies with the test microstructure previously observed in agglutinated foraminifera. The grain distribution detected in both model species bioconstructions was analysed using a fractal numerical model (Hausdorff fractal dimension). Collected data show that in both organisms the grains were distributed according to a fractal model, indicating that the evolutionary process may have led to finding the same optimal constructive strategy across organisms with an independent evolutionary history, notwithstanding different geometrical scales. Furthermore, in sectioned tubes we observed microplastic fragments agglutinated within the arenaceous wall and in the inter-tube area. This unexpected finding shows that marine animals can be affected by microplastic pollution not only in soft tissues, but also engineered hard structures, and suggests the problem is more pervasive than estimated so far.

DISTRIBUTION OF BENTHIC FORAMINIFERA IN THE CORAL REEFS ECOSYSTEM OF PULAU BIDONG, TERENGGANU, SOUTHERN SOUTH CHINA SEA

A study on the distribution of benthic foraminiferal species in the surface sediments of coral reefs was carried out in Pulau Bidong in the southern South China Sea (SCS). Samples were collected at 12 sites around Pulau Bidong at water depths ranging from 5 m to 30 m. Live (rose bengal stained) and optimally preserved empty tests of benthic foraminifera were analysed based on their chamber and apertural characteristics observed under binocular microscope (Leica Zoom 2000). The results revealed that 32 genera of benthic foraminifera were found in the coral reefs sediments. Amphistegina was the most abundant genus with relative abundance of 68% and frequently recorded at depths of between 10-15 m and 25-30 m. Other common genera that were found were Calcarina, Elphidium, Heterolepa, Heterostegina, Quinqueloculina, Peneroplis and Triloculina. These genera showed depth distribution preference in the shallow water zone (5 m depth). The highest diversity index (2.3) and number of taxa (26 genera) were recorded at station W2, located at the western part of Pulau Bidong. The lowest diversity index (0.2) and number of taxa (seven genera) were recorded at station S3, located at the southern part of Pulau Bidong. The frequency distribution and diversity of benthic foraminifera in the study area were related to water depth.

Complex Rupture of the 2015 Mw 8.3 Illapel Earthquake and Prehistoric Events in the Central Chile Tsunami Gap

Abstract On 16 September 2015, the Mw 8.3 Illapel megathrust earthquake broke the subduction contact of the Nazca plate beneath the South American plate, causing unexpectedly high tsunami waves that strongly impacted the coast along the Coquimbo region in central–northern Chile. Here, we report results from a postearthquake and tsunami survey, evidencing a complex coastal geological response driven by the near coast and near trench seismic patches that ruptured during this event. Systematically, high tsunami run-ups, up to 10–11 m a.s.l., were measured on the western coast of the Punta Lengua de Vaca Peninsula in front of the near trench rupture patch, whereas tsunami run-ups up to 5–6 m were measured close to the near coast rupture patch. Detailed measurements conducted in the Coquimbo area revealed tsunami run-ups systematically higher than 6–6.5 m and up to 7.8 m. Field observations of bleached coralline algae supported by ulterior laboratory experiences were compared with geodetic measurements that evidenced complex and variable alongshore uplift-subsidence responses of the coast, suggesting a relative consistency with respect to its modern geomorphological configuration. From the analysis of pit dug in the Tongoy area, which was strongly impacted by this last tsunami, we evaluated distinctive sandy layers with benthic foraminifera tests interbedded between alluvial fine sediments, which we interpreted as paleotsunami events dated before 1108 ± 77 C.E., shortly before 1346 ± 50 C.E., and approximately 1473 ± 37 C.E. In addition to the historical massive tsunamis that occurred in 1730, 1877, and 1922 C.E. in central and northern Chile, we interpreted prehistoric tsunamis revealed here as events triggered by large megathrust earthquake ruptures, evidencing the high exposition of these coasts to near fields as well as to distant tsunamis produced along the Chilean subduction margin but also in the pan-Pacific region.

Impact of methane seepage dynamics on the abundance of benthic foraminifera in gas hydrate bearing sediments: New insights from the South China Sea

The stable isotopic composition of benthic foraminifera tests is widely used to trace past methane release events. However, gaps in our knowledge on the ecology of benthic foraminifera at methane seeps impede the utility of test composition as proxy of methane emission histories and the influence of redox zonation on the local fauna. Here, we use sediment geochemistry and foraminiferal assemblages of a seep area of the South China Sea to reveal that seepage duration and intensity affect benthic foraminifera. Taxa tolerating eutrophic conditions like Uvigerina thrive at times of reduced seepage when aerobic methanotrophy is favored. In contrast, intense methane seepage leads to high sulfide levels, and a positioning of the sulfate-methane transition zone close to the seafloor. At these times, bottom waters may become oxygen depleted and benthic foraminifera will decline. This study provides (1) the means to understand how seepage dynamics control the distribution of benthic foraminifera and (2) new constraints on the use of foraminifera as paleoceanographic proxies, including possible mechanisms of mass mortality in the geological past.

Quantifying Diagenesis, Contributing Factors, and Resulting Isotopic Bias in Benthic Foraminifera Using the Foraminiferal Preservation Index: Implications for Geochemical Proxy Records

AbstractGeochemical records generated from the calcite tests of benthic foraminifera, especially those of the genera Cibicidoides and Uvigerina, provide the basis for proxy reconstructions of past climate. However, the extent to which benthic foraminifera are affected by postdepositional alteration is poorly constrained. Furthermore, how diagenesis may alter the geochemical composition of benthic foraminiferal tests, and thereby biasing a variety of proxy‐based climate records, is also poorly constrained. We present the Foraminiferal Preservation Index (FPI) as a new metric to quantify preservation quality based on objective, well‐defined criteria. The FPI is used to identify and quantify trends in diagenesis temporally, from late Pliocene to modern coretop samples (3.3–0 Ma), as well as spatially in the deep ocean. The FPI identifies the chemical composition of deep‐ocean water masses to be the primary driver of diagenesis through time, while also serving as a supplementary method of identifying periods of changing water mass influence at a given site. Additionally, we present stable isotope data (δ18O, δ13C) generated from individual Cibicidoides specimens of various preservation quality that demonstrate the likelihood of significant biasing in a variety of geochemical proxy records, especially those used to reconstruct past changes in ice volume and sea level. These single‐test data further demonstrate that when incorporating carefully selected tests of only the highest preservation quality, robust paleorecords can be generated.

Holocene methane emissions in the South-Western part of the Okhotsk Sea (on the basic of carbon isotopes in the tests of benthic foraminifera)

We report several negative carbon stable isotope excursions in benthic foraminifera in a gas-bearing core LV50-05, collected from an area of active methane venting on the Eastern Slope of Sakhalin Island, the Okhotsk Sea. Within the study area, four methane events (ME) are established in Holocene: short-term ME-1 (700-900 yr BP) and ME-2 (from 1200 to 1400 yr BP), long-term ME-3 (2500-4700 yr BP) and ME-4 (7400-10000 yr BP).

Burial-induced oxygen-isotope re-equilibration of fossil foraminifera explains ocean paleotemperature paradoxes

Oxygen-isotope compositions of fossilised planktonic and benthic foraminifera tests are used as proxies for surface- and deep-ocean paleotemperatures, providing a continuous benthic record for the past 115 Ma. However, visually imperceptible processes can alter these proxies during sediment burial. Here, we investigate the diffusion-controlled re-equilibration process with experiments exposing foraminifera tests to elevated pressures and temperatures in isotopically heavy artificial seawater (H218O), followed by scanning electron microscopy and quantitative NanoSIMS imaging: oxygen-isotope compositions changed heterogeneously at submicrometer length scales without any observable modifications of the test ultrastructures. In parallel, numerical modelling of diffusion during burial shows that oxygen-isotope re-equilibration of fossil foraminifera tests can cause significant overestimations of ocean paleotemperatures on a time scale of 107 years under natural conditions. Our results suggest that the late Cretaceous and Paleogene deep-ocean and high-latitude surface-ocean temperatures were significantly lower than is generally accepted, thereby explaining the paradox of the low equator-to-pole surface-ocean thermal gradient inferred for these periods.

Does the recent pool of benthic foraminiferal tests in fjordic surface sediments reflect interannual environmental changes? The resolution limit of the foraminiferal record

Benthic foraminifera tests (living + dead) and conductivity, temperature and depth (CTD) records in Hornsund Fjord (SW Spitsbergen) were studied over five non-consecutive summer seasons during 2002–2011. The data indicated significant changes in the abundance of benthic foraminifera, species composition and the variability of hydrological and micro-environmental conditions in this fjord. The increased inflow of Atlantic Water (AW) resulted in higher foraminiferal biodiversity and a greater number of rare species; however, many of these were fragile and were thus poorly preserved in the sediment. Cold years significantly reduced species richness in the fjord centre, while more stable hydrological conditions with a predominance of opportunistic foraminifera were noted at the fjord head. Elphidium excavatum f. clavata and Cassidulina reniforme exhibited sensitivity to salinity changes and food supply. The dynamic foraminiferal response to hydrological changes led to the conclusion that the annual foraminiferal flux, compounded by the poor preservation of fragile individuals, significantly changed the spatial and interannual composition of the foraminiferal tests remaining in the sediment. Furthermore, only mature individuals are representative of yearlong or multi-year fjord conditions, since the juveniles that bloom during their maximum growth periods in spring can die out under poor summer and winter conditions. The findings of this study indicated that the upper 8 cm of the sediment in the intense depositional systems of the Svalbard fjords provide good representation of recently departed benthic foraminifera, because of their mobility in surface sediments and further sediment compaction. Hence, the corresponding 10- to 15-year resolution in palaeoceanographic investigations seems to be the most reliable.

Carbonate Sediment Production, Transport, and Supply To A Coral Cay At Raine Reef, Northern Great Barrier Reef, Australia: A Facies Approach

Abstract Coral cays are low-lying (typically 2 mm grain size) and the relative abundances of foraminifera and coral grains. Gravelly coral-dominated sediment is concentrated at the reef margins, whereas facies on and around the leeward cay are dominated by the sand-size tests of benthic foraminifera. Mud is absent in reef sediments and reflects the prevailing high-energy wave-dominated setting as well as a paucity of mud producers. Benthic foraminifera tests are the major sediment component, constituting an average proportion of 39% (range: 2–77%). Sediment derived from the skeletal remains of corals (24%, 1–65%), mollusks (15%, 3–30%), Halimeda (14%, 4–36%), and coralline algae (6%, 0–20%) are present in lesser volumes. Foraminifera content is highest (> 40%) on tidally emergent algal pavement, where they live in greatest abundance, and on the cay shorelines, where their tests are deposited and comprise the bulk of beach sand (36–63%). A comparison of the Raine Island data with other exposed modern reefs and platforms of the central and western Pacific shows that occurrence and distribution of facies types is broadly consistent. Beyond these sedimentological data, the taphonomy of foraminifera at Raine Island indicates that tests are vulnerable to destruction due to abrasion when transport and reworking is prolonged. Therefore the foraminifera-rich facies adjacent to and on the cay, disjunct from the source zones, as well as taphonomic evidence, imply that transport from the outer reef flat to the cay must be relatively quick. These short temporal links between ecological source zones and depositional landforms are likely to have important ramifications for the contemporary management of reef-associated landforms (e.g., cays) in the future.

A new model for biomineralization and trace-element signatures of Foraminifera tests

Abstract. The Mg/Ca ratio of Foraminifera calcium carbonate tests is used as proxy for seawater temperature and widely applied to reconstruct global paleo-climatic changes. However, the mechanisms involved in the carbonate biomineralization process are poorly understood. The current paradigm holds that calcium ions for the test are supplied primarily by endocytosis of seawater. Here, we combine confocal-laser scanning-microscopy observations of a membrane-impermeable fluorescent marker in the extant benthic species Ammonia aomoriensis with dynamic 44Ca-labeling and NanoSIMS isotopic imaging of its test. We infer that Ca for the test in A. aomoriensis is supplied primarily via trans-membrane transport, but that a small component of passively transported (e.g., by endocytosis) seawater to the site of calcification plays a key role in defining the trace-element composition of the test. Our model accounts for the full range of Mg/Ca and Sr/Ca observed for benthic Foraminifera tests and predicts the effect of changing seawater Mg/Ca ratio. This places foram-based paleoclimatology into a strong conceptual framework.

EMP and SIMS studies on Mn/Ca and Fe/Ca systematics in benthic foraminifera from the Peruvian OMZ: a contribution to the identification of potential redox proxies and the impact of cleaning protocols

Abstract. In this study we present an initial dataset of Mn/Ca and Fe/Ca ratios in tests of benthic foraminifera from the Peruvian oxygen minimum zone (OMZ) determined with SIMS. These results are a contribution to a better understanding of the proxy potential of these elemental ratios for ambient redox conditions. Foraminiferal tests are often contaminated by diagenetic coatings, like Mn rich carbonate- or Fe and Mn rich (oxyhydr)oxide coatings. Thus, it is substantial to assure that the cleaning protocols are efficient or that spots chosen for microanalyses are free of contaminants. Prior to the determination of the element/Ca ratios, the distributions of several elements (Ca, Mn, Fe, Mg, Ba, Al, Si, P and S) in tests of the shallow infaunal species Uvigerina peregrina and Bolivina spissa were mapped with an electron microprobe (EMP). To visualize the effects of cleaning protocols uncleaned and cleaned specimens were compared. The cleaning protocol included an oxidative cleaning step. An Fe rich phase was found on the inner test surface of uncleaned U. peregrina specimens. This phase was also enriched in Al, Si, P and S. A similar Fe rich phase was found at the inner test surface of B. spissa. Specimens of both species treated with oxidative cleaning show the absence of this phase. Neither in B. spissa nor in U. peregrina were any hints found for diagenetic (oxyhydr)oxide or carbonate coatings. Mn/Ca and Fe/Ca ratios of single specimens of B. spissa from different locations have been determined by secondary ion mass spectrometry (SIMS). Bulk analyses using solution ICP-MS of several samples were compared to the SIMS data. The difference between SIMS analyses and ICP-MS bulk analyses from the same sampling sites was 14.0–134.8 μmol mol−1 for the Fe/Ca and 1.68(±0.41) μmol mol−1 for the Mn/Ca ratios. This is in the same order of magnitude as the variability inside single specimens determined with SIMS at these sampling sites (1σ[Mn/Ca] = 0.35–2.07 μmol mol−1; 1σ[Fe/Ca] = 93.9–188.4 μmol mol−1). The Mn/Ca ratios in the calcite were generally relatively low (2.21–9.93 μmol mol−1) but in the same magnitude and proportional to the surrounding pore waters (1.37–6.67 μmol mol−1). However, the Fe/Ca ratios in B. spissa show a negative correlation to the concentrations in the surrounding pore waters. Lowest foraminiferal Fe/Ca ratios (87.0–101.0 μmol mol−1) were found at 465 m water depth, a location with a strong sharp Fe peak in the pore water next to the sediment surface and respectively, high Fe concentrations in the surrounding pore waters. Previous studies found no living specimens of B. spissa at this location. All these facts hint that the analysed specimens already were dead before the Fe flux started and the sampling site just recently turned anoxic due to fluctuations of the lower boundary of the OMZ near the sampling site (465 m water depth). Summarized Mn/Ca and Fe/Ca ratios are potential proxies for redox conditions, if cleaning protocols are carefully applied. The data presented here may be rated as base for the still pending detailed calibration.

Boron isotopes and B/Ca in benthic foraminifera: Proxies for the deep ocean carbonate system

Accurate records of the state of the ocean carbonate system are critical for understanding past changes in pCO 2, ocean acidification and climate. The chemical principles underlying the proxy of oceanic pH provided by the boron isotope ratio of foraminiferal carbonate are relatively well understood, but the proxy's reliability has been questioned. We present 76 new Multi-Collector Inductively-Coupled Plasma Mass Spectrometry (MC-ICPMS) δ 11B measurements on a range of benthic foraminifera from 23 late-Holocene samples from the Atlantic that reaffirm the utility of the δ 11B-pH proxy. Our boron isotope measurements on ~ 10 benthic foraminifera tests typically yield a precision of ~ ± 0.25‰ at 2 s.d. (equivalent to ~ ± 0.03 pH units). δ 11B values of epifaunal species are within analytical uncertainty of those predicted from a simple model assuming sole incorporation of B(OH) 4 − from seawater and no vital effects, using the independently determined fractionation factor of 1.0272 between 11B/ 10B of aqueous boron species. Infaunal foraminifera are consistent with this model, but record the combined effects of lower pore-water δ 11B and pH. No influence of partial dissolution or shell size on δ 11B is observed. We have also measured the B/Ca ratios of the same samples. For individual Cibicidoides species, B/Ca shows a good correlation with Δ[CO 3 2−], but the B/Ca of different co-occurring species morphotypes varies considerably. These effects are not seen in δ 11B, which may therefore provide a more robust proxy of the ocean carbonate system. Whilst in theory δ 11B and B/Ca can be combined to provide a quantitative reconstruction of alkalinity and dissolved inorganic carbonate (DIC), in practice this is precluded by propagated uncertainties. δ 11B data give significant constraints on foraminifera calcification mechanisms, and seem most simply explained by incorporation of B(OH) 4 − into a HCO 3 − pool, which is then completely incorporated in foraminiferal CaCO 3. Our demonstration of the predictable variation of δ 11B with pH, across a wide range of species and locations, provides confidence in the application of MC-ICPMS measurements of foraminiferal δ 11B to reconstruct past changes in the ocean carbonate system.

BENTHIC FORAMINIFERAL BIOFACIES IN TEMPERATE CARBONATE SEDIMENT IN THE WESTERN PONTINE ARCHIPELAGO (TYRRHENIAN SEA, ITALY)

Recent foraminiferal assemblages are identified in 70 grab samples from 20–380 m depth in the Pontine Archipelago (Tyrrhenian Sea, Italy). All broken and relict tests of benthic foraminifera and other bioclastic sediments were counted for each sample, in order to provide a more complete description of the benthic community. Hierarchical cluster analysis (HCA) was performed on the relative abundances (live + dead) of 53 taxa of benthic foraminifera that were common in the samples. Q-mode HCA recognizes three distinct foraminiferal biofacies, each associated with a particular bioclastic lithofacies: 1) the Asterigerinata-Lobatula-Rosalina biofacies occurs at 20–150 m and is dominated by benthic foraminifera, most notably epiphytic species such as Asterigerinata mamilla , Lobatula lobatula , and Rosalina bradyi ; other bioclasts include rhodoliths, bryozoans, and echinoid spines, which constitute the rhodalgal lithofacies; 2) the Cassidulina carinata biofacies at intermediate depths of 100–250 m includes benthic and planktonic foraminifera among branches of bryozoans that constitute the bryomol lithofacies; also present are high percentages of reworked glauconitic tests of shallow-water taxa (e.g., Elphidium , Lobatula , and Asterigerinata ), possibly related to Late Quaternary sea-level still-stands; 3) the Uvigerina-Bulimina biofacies at 200–380 m, that is characterized by Uvigerina mediterranea and Bulimina marginata ; in addition to benthic and planktonic foraminifera, it has a molechfor lithofacies of bivalves and gastropods.

The ecology and distribution of benthic foraminifera at the Håkon Mosby mud volcano (SW Barents Sea slope)

To investigate a possible influence of submarine methane seepage on benthic foraminiferal communities, Rose Bengal stained (“live”) and empty tests of benthic foraminifera were studied from the sediment surface down to 15 cm sub-bottom depth of 12 sites at the Håkon Mosby mud volcano (HMMV). In addition, one reference site well away from the seep sites, but from similar water depths and the same general hydrographic setting was occupied for comparison. The HMMV is located at 1265 m water depth on the SW Barents Sea continental slope. Distinct living foraminiferal associations at the HMMV are linked to specific sedimentary, microbial, and macrofaunal habitats. In the center of the crater, and in crater areas completely covered by bacterial mats, Cassidulina reniforme is the only, albeit rare, living species. Below the top few millimeters, sediments are anoxic and devoid of living specimens. At the rim of the mud volcano, at sites densely populated by pogonophoran tube worms, three benthic foraminiferal associations are found; (i) a Fontbotia wuellerstorfi–Lobatula lobatula association living attached to the upper parts of pogonophoran tubes, which protrude into oxic water, (ii) a diverse Cassidulina neoteretis association populating dysoxic sediments of the surface centimeter, and (iii) a species-poor Bolivina pseudopunctata association colonizing the subsurface sediments down to four centimeters. Generally, we did not find endemic or seep indicative species or associations at the HMMV. However, the HMMV live faunas dominated by B. pseudopunctata are not found at the reference site nor are they described from comparable water depths and environments without gas seepages from the Norwegian-Greenland Seas. In the center and outer rim of the mud volcano, a C. neoteretis–Reophax guttifer dead association, similar to the one at the reference site, characterizes an assemblage of strongly corroded and partly displaced tests. At bacterial mat sites, a C. reniforme dead association corresponds to the living one. Thus both the living and the dead associations are indicative of a specific bacterial mat environment at the HMMV.

Isotopic composition of a large photosymbiotic foraminifer: Evidence for hypersaline environments across the Great Australian Bight during the late Pleistocene

Analysis of carbon and oxygen isotopic compositions of large benthic foraminifera tests ( Marginopora vertebralis) that lived in the Great Australian Bight during the late Pleistocene, reveal that the tests are enriched by 1 to 3‰ in both 18O and 13C relative to modern specimens from the same region. The intolerance of M. vertebralis for cool waters negates lower ocean water temperature as an explanation for such high δ 18O values. The oxygen isotopic compositions are thus interpreted to reflect tests secreted in hypersaline waters of up to 56 ppt salinity, concentrated from seawater by evaporation. M. vertebralis thrives today in waters of similar salinity at Shark Bay, Western Australia. The Pleistocene sedimentary assemblage supports an interpretation that environments broadly similar to those in outer modern-day Shark Bay were wide spread across the Great Australian Bight during portions of marine isotope stages 2, 3 and 4. The high δ 13C values of the Pleistocene M. vertebralis are interpreted to reflect enhanced photosynthetic activity that depletes dissolved carbonate in 12C in such shallow, saline settings. These hypersaline environments formed during periods of lower sea-level when shallow-waters (< 20 m depth) extended from the shoreline over ~ 100 km across what is currently a relatively deep shelf. This study indicates that shelf bathymetry was a critical determinant of past environments of deposition across the Great Australian Bight.

Serial Mg/Ca and Sr/Ca chronologies across single benthic foraminifera tests

We used secondary ion mass spectrometry (SIMS) to analyse Mg/Ca and Sr/Ca across four individual tests of the benthic foraminifera Hyalinea balthica, collected ‘live’ from a site on the NW European shelf with seasonal variations in bottom water temperature (> 4 °C). Test growth is episodic and we have produced chronologies of Mg/Ca and Sr/Ca variations between consecutive chambers. Chronologies do not correlate well between replicate specimens although in one case the seasonal Mg/Ca trend is in reasonable agreement with estimated seawater temperature variations. We also observe significant intra-chamber hetereogeneity even within the outermost test chamber which is deposited nominally as a single event and has not been thickened during the addition of subsequent chambers. Mg/Ca and Sr/Ca also vary significantly between tests of similar size which were collected at the same time. SIMS can be used to analyse single specimens from sediment samples in which foraminifera are rare or to selectively target pristine calcite in diagenetically altered individuals. Our observation that Mg and Sr can vary significantly between foraminifera tests of the same size indicates a potential pitfall of this approach.

Paleoenvironmental changes in the northern shelf of the Sea of Okhotsk during the Holocene

The combined micropaleontological (spores and pollen, diatoms, benthic foraminifers), lithologic, and isotopic-geochemical analysis of sediments from the northern shelf of the Sea of Okhotsk recovered by hydrostatic corer from the depth of 140 mbsl elucidated environmental changes in this part of the basin and adjacent land areas during the last 12.7 thousands cal. years. Geochronological scale of the core is established using the acceleration mass-spectrometry method for radiocarbon dating of benthic Foraminifera tests. The first insignificant warming in the northern part of the sea after glaciation occurred in the mid-Boreal time (9.6 ka ago) but not at the onset of the Holocene. The strongest warming in the region took place in the mid-Atlantic epoch to reach climatic optimum in the second half of the Subboreal (6 to 2.5 ka ago). A cooling in the northern shelf and adjacent land areas is established at the beginning of the Subatlantic (2.5 ka). A comparison of results obtained for Core 89211 with dated hydrological and climatic changes in central and southern parts of the Sea of Okhotsk (Gorbarenko et al., 2003, 2004) is used for a high-resolution analysis of climatic fluctuations in the study region and other areas of the basin during deglaciation and the Holocene.