Cibicidoides Wuellerstorfi Research Articles

Deciphering Paleoceanographic Shifts Inferred from the Foraminiferal Record of the Western Svalbard Slope (Bellsund Drift) over the Past Century

The objective of this study was to reconstruct the last century’s climatic oscillations in the Arctic region around the Fram Strait using high-resolution analysis of foraminiferal assemblages as proxies for surface and deep-water mass properties. In this area, warm Atlantic water masses are advected to the Arctic Ocean through the West Spitsbergen Current, representing the northernmost tip of the Global Thermohaline Circulation. The interaction between the cold Arctic and the warm Atlantic water masses significantly influences the entire foraminiferal community. Planktic species such as Neogloboquadrina pachyderma and Turborotalita quinqueloba are respectively used as indicators of cold Arctic water and warm Atlantic water masses. Among the main benthic species, Cibicidoides wuellerstorfi, Epistominella exigua, and Oridorsalis tener stand out, serving as proxies for the bottom water mass current velocity and paleoproductivity. The paleoenvironmental reconstruction obtained with the foraminiferal assemblages, together with data from satellite monitoring of the sea ice extent and the long-term record of the annual temperature of the West Spitsbergen Current measured over the last 50 years, support the evidence of a progressively rising heat influx into the Arctic Ocean due to an increasing Atlantic water inflow, forcing the consequent decay of the sea ice extent.

Abundance and distribution of recent benthic foraminifera from the southwestern part of the Bay of Bengal

Foraminifers are ubiquitous and abundant organisms in the marine environment, sensitive to different environmental variables such as pH, dissolved oxygen, salinity, temperature, organic matter and substrate. In the present study, environmental variables and benthic foraminiferal assemblages from 32 surface sediment samples belonging to different water depths were studied to understand the shelf and slope environment of the southwestern Bay of Bengal. Statistical methods such as cluster and principal component analysis (PCA) were used to infer the relationship existing among various foraminiferal assemblages, bathymetry, sediment and bottom water characteristics. Statistical analysis yielded four assemblages, of which assemblage-I is dominated by Nonion faba, Rotalidium annectens, Asterorotalia pulchella, Elphidium crispum, and Amphistegina radiata, and is confined to the shallowest inner shelf region (5 to 35 m water depth) with sandy sediments indicating high-energy condition. Assemblage-II is marked by the abundance of Cibicidoides wuellerstorfi, Hanzawaia concentrica, Quinqueloculina agglutinans, Quinqueloculina seminula, Quinqueloculina lamarckiana, Ammonia beccarri, and Ammonia tepida which are associated with the middle shelf region (water depth 35 to 70 m) with sandy to slightly muddy sand sediments. Assemblage-III is dominated by Asterorotalia dentata, Quinqueloculina venusta, Cancris communis, Cassidulina laevigata, and N. costiferum which occur at a depth of 70 to 170 m in the outer shelf, and are highly associated with slightly muddy sand to muddy sand. Whereas, assemblage -IV includes Uvigerina mediterranea, Bolivina dilatata, Bolivina robusta, and Bulimina marginata foraminiferal species that are abundant in the upper slope (170–244 m water depth) and are confined to muddy sand and sandy mud with low dissolved oxygen in the bottom water. The above assemblages depict that the abundance and distribution of foraminifera are largely controlled by substrate, energy conditions and environmental variables such as temperature, salinity, organic matter and dissolved oxygen.

The Effect of Seawater Carbonate Chemistry on the Stable Isotope Composition of Cibicidoides wuellerstorfi and Other Cibicidoides Species

AbstractThe δ13C composition of Cibicidoides wuellerstorfi and other Cibicidoides spp is an important tool to reconstruct past changes in the deep ocean carbon cycle. The species are expected to match the δ13C of ambient dissolved inorganic carbon (DIC), although it has been recognized that substantial offsets can occur. Here, I present a compilation of modern δ13C and δ18O data for named Cibicidoides species in combination with fully resolved carbonate chemistry at each core location. The data show for C. wuellerstorfi that the offset from the expected value in both carbon (∆13C) and oxygen (∆18O) is correlated with seawater carbonate chemistry. The result is comparable to, but not identical with, published culture experiments in which marine organisms were grown under variable pH‐conditions. Overall, ∆13C in C. wuellerstorfi correlates positively with carbonate saturation, [DIC], and temperature. The three variables together explain 47.1% of the variation in ∆13C. The trend for ∆18O is similar, except that the effect of temperature has been removed through correction with a published δ18O‐temperature equation. Up to 35% of the remaining variation in ∆18O can be explained by ambient carbonate chemistry. Data for other named Cibicidoides species are broadly similar, but are too sparse for a detailed analysis. The results indicate that strongly negative ∆13C occurs predominantly in the deep Atlantic in response to a combination of low [DIC], low temperature, and undersaturation within the lysocline. Implications for paleoceanographic reconstructions are discussed.

Amino acid racemization in Neogloboquadrina pachyderma and Cibicidoides wuellerstorfi from the Arctic Ocean and its implications for age models

Abstract. We report the results of amino acid racemization (AAR) analyses of aspartic acid (Asp) and glutamic acid (Glu) in the planktic Neogloboquadrina pachyderma, and the benthic Cibicidoides wuellerstorfi, foraminifera species collected from sediment cores from the Arctic Ocean. The cores were retrieved at various deep-sea sites of the Arctic, which cover a large geographical area from the Greenland and Iceland seas (GIS) to the Alpha and Lomonosov ridges in the central Arctic Ocean. Age models for the investigated sediments were developed by multiple dating and correlation techniques, including oxygen isotope stratigraphy, magnetostratigraphy, biostratigraphy, lithostratigraphy, and cyclostratigraphy. The extent of racemization (D/L values) was determined on 95 samples (1028 subsamples) and shows a progressive increase downcore for both foraminifera species. Differences in the rates of racemization between the species were established by analysing specimens of both species from the same stratigraphic levels (n=21). Aspartic acid (Asp) and glutamic acid (Glu) racemize on average 16 ± 2 % and 23 ± 3 % faster, respectively, in C. wuellerstorfi than in N. pachyderma. The D/L values increase with sample age in nearly all cases, with a trend that follows a simple power function. Scatter around least-squares regression fits are larger for samples from the central Arctic Ocean than for those from the Nordic Seas. Calibrating the rate of racemization in C. wuellerstorfi using independently dated samples from the Greenland and Iceland seas for the past 400 ka enables estimation of sample ages from the central Arctic Ocean, where bottom water temperatures are presently relatively similar. The resulting ages are older than expected when considering the existing age models for the central Arctic Ocean cores. These results confirm that the differences are not due to taxonomic effects on AAR and further warrant a critical evaluation of existing Arctic Ocean age models. A better understanding of temperature histories at the investigated sites, and other environmental factors that may influence racemization rates in central Arctic Ocean sediments, is also needed.

Benthic foraminifera in high latitude contourite drift systems (North Atlantic: Björn, Gardar and Eirik drifts)

Benthic foraminifera colonize a wide range of marine environments including contourite drift systems. Contourites form elongated sedimentary bodies deposited under persistent contour-parallel bottom currents, and certain suspension-feeding foraminifera benefit from the entrained nutrient load. Their distribution patterns have been shown to be highly valuable for reconstructing ocean circulation at mid-latitudes. However, comparable faunal studies from the high-latitude North Atlantic, a crucial region for global ocean circulation and the widespread deposition of contourites drifts, are missing. This study examines foraminiferal faunas >250 μm from surface samples of the Björn and Gardar drifts in the Iceland Basin and the Eirik Drift south off Greenland. It serves as baseline for understanding the biogeographic patterns of benthic foraminifera from high latitude contourites.The results show that four types of suspension-feeding species characterize different hydrodynamic environments. Bottom currents <3 cm s−1 at the Björn Drift sustain assemblages rich in the finely branching, erect species Saccorhiza ramosa and Rhizammina algaeformis, which capture food particles with a pseudopodial net. The northern Gardar Drift displays intermediate flow velocities up to 10 cm s−1 and is determined by tubular branching and facultative suspension-feeding species such as Rhabdammina abyssorum. Assemblages with abundant Rhabdammina abyssorum and Hoeglundina elegans colonize the southern detached and finer grained Gardar Drift. The Eirik Drift off Greenland with flow velocities of 12 to 22 cm s−1 displays a fauna different from the contourites of the Iceland Basin. Assemblages with attached Cibicidoides wuellerstorfi and Heterolepa broeckhiana largely determine the benthic community. Also attached species, but composed primarily of Cibicides lobatulus, Cibicides refulgens, and Cibicidoides pachyderma, settle at the Greenland continental margin in high energy areas with velocities up to 40 cm s−1.

High Precision Femtosecond Laser Ablation ICP‐MS Measurement of Benthic Foraminiferal Mn‐Incorporation for Paleoenvironmental Reconstruction: A Case Study From the Plio‐Pleistocene Caribbean Sea

AbstractClosure of the Central American Seaway (CAS) and hydrology of the Caribbean Sea triggered Northern Hemisphere Glaciation and played an important role in the Pliocene to modern‐day climate re‐establishing the deep and surface ocean currents. New data on Mn/Ca obtained with femtosecond laser ablation inductively coupled plasma mass spectrometry on well‐preserved tests of the epibenthic foraminifer Cibicidoides wuellerstorfi and infaunal C. mundulus contribute to the interpretation of paleoenvironmental conditions of the Caribbean Sea between 5.2 and 2.2 Ma (million years) across the closure of the CAS. Hydrothermal activity at the Lesser Antilles may be a primary source of Mn in the well‐oxygenated Plio‐Pleistocene Caribbean Sea. Incorporation of Mn in the benthic foraminifer shell carbonate is assumed to be affected by surface ocean nutrient cycling, and may hence be an indicator of paleoproductivity.

Response of benthic foraminifera to environmental successions of cold seeps from Vestnesa Ridge, Svalbard: Implications for interpretations of paleo-seepage environments

This paper presents the results of a study on the response of living benthic foraminifera to progressing environmental successions in a cold-seep ecosystem. Sediment samples were collected from Vestnesa Ridge (79°N, Fram Strait) at ~1200 m water depth. The distribution of live (Rose Bengal-stained) foraminifera were analyzed in the upper sediment layers in relation to pore water biogeochemical data together with the distribution of sulfur-bacterial mats and Siboglinidae tubeworms. At methane cold seeps, the process of environmental succession is strongly connected to the duration and strength of methane seepage and the intensity of methane-related biological processes, e.g, aerobic and anaerobic oxidation of methane (MOx and AOM, respectively). The results show that the distribution patterns of benthic foraminifera change according to the progressing environmental succession. The benthic foraminifera seemed to thrive in sediments with a moderate activity of seepage, dominated by MOx, i.e, at an early stage of seepage or when seepage decreases at a late stage of the succession. Species composition of the foraminiferal fauna under these conditions was similar to the control sites (outside of pockmarks with no seepage); the dominant species being Melonis barleeanus and Cassidulina neoteretis. In sediments with strong seepage and high AOM activity, the hostile environmental conditions due to the presence of toxic sulfide caused a reduction in the foraminiferal population, and samples were almost barren of foraminifera. In environments of moderate methane seepage, the presence of chemosynthetic Siboglinidae tube worms potentially support communities of the epibenthic species Cibicidoides wuellerstorfi. Despite the very different environmental conditions, the foraminiferal assemblages were very similar (or nearly absent). Therefore, the foraminiferal faunas cannot be used as exclusive indicators of past strength of methane seepage in palaeoceanographic interpretations.

Deglacial restructuring of the Eastern equatorial Pacific oxygen minimum zone

Oxygenation in the Eastern Equatorial Pacific is responsive to ongoing climate change in the modern ocean, although whether the region saw a deglacial change in extent or position of the Oxygen Minimum Zone remains poorly constrained. Here, stable isotopes from the shells of an Oxygen Minimum Zone-dwelling planktic foraminifer are used to reassess the position of the mid-water Oxygen Minimum Zone relative to both the thermocline and benthos. Oxygen isotopes record a rapid shoaling of the Oxygen Minimum Zone towards the thermocline associated with Heinrich Stadial 1 and persisting through the deglaciation. Meanwhile, carbon isotope similarities between Oxygen Minimum Zone-dwelling Globorotaloides hexagonus and benthic Cibicidoides wuellerstorfi suggest a shared source water through the deglaciation. Results support a direct role for the Eastern Equatorial Pacific in venting carbon to the atmosphere through the deglaciation, a deglacial expansion of the Oxygen Minimum Zone, and a restructuring of mid-water oxygen and carbon dynamics from the glacial to Holocene intervals.

The marine environmental evolution in the northern Norwegian Sea revealed by foraminifera during the last 60 ka

Both planktonic and benthic foraminifera were identified in a sediment core collected from the northern Norwegian Sea to reconstruct the paleoceanographic evolution since the last glaciation. The assemblages and distribution patterns of dominant foraminiferal species with special habitat preferences indicated that three marine environments occurred in the northern Norwegian Sea since 62 ka BP: (1) an environment controlled by the circulation of the North Atlantic Current (NAC); (2) by polynya-related sinking of brines and upwelling of intermediate water surrounding the polynya; (3) by melt-water from Barents Sea Ice Sheet (BSIS). At 62–52.5 ka BP, a period with the highest summer insolation during the last glaciatial period, intensification of the NAC led to higher absolute abundances and higher diversity of foraminiferal faunas. The higher abundance of benthic species Cibicidoides wuellerstorfi indicates bottom water conditions that were well-ventilated with an adequate food supply; however, higher abundances of polar planktonic foraminiferal species Neogloboquadrina pachyderma (sin.) indicate that the near-surface temperatures were still low. During mid-late MIS 3 (52.5–29 ka BP), the marine environment of the northern Norwegian Sea alternately changed among the above mentioned three environments. At 29–17 ka BP during the last glacial maximum, the dominant benthic species Bolivina arctica from the Arctic Ocean indicates an extreme cold bottom environment. The BSIS expanded to its maximum extent during this period, and vast polynya formed at the edge of the ice sheet. The sinking of brines from the formation of sea ice in the polynyas caused upwelling, indicated by the upwelling adapted planktonic species Globigerinita glutinata. At 17–10 ka BP, the northern Norwegian Sea was controlled by melt-water. With the ablation of BSIS, massive amounts of melt water discharged into the Norwegian Sea, resulting in strong water column stratification, poor ventilation, and an oligotrophic bottom condition, which led to a drastic decline in the abundance and diversity of foraminifera. At 10–0 ka BP, the marine environment was transformed again by the control of the NAC, which continues to modern day. The abrupt decrease in relative abundance of Neogloboquadrina pachyderma (sin.) indicates a rise in near-surface temperature with the strengthening of the NAC and without the influence of the BSIS. Citation : Wang W G, Zhao M W, Yang J C, et al. The marine environmental evolution in the northern Norwegian Sea revealed by foraminifera during the last 60 ka. Adv Polar Sci, 2021, 32(3): 210-220, doi: 10.13679/j.advps.2021.0020

Oxygen Isotope Offsets in Deep-Water Benthic Foraminifera

ABSTRACT Despite the extensive use of the benthic foraminiferal oxygen isotope composition (δ18O) as a proxy for paleoclimatic reconstructions, uncertainties remain regarding the consistency of interspecies offsets and the environmental factors controlling 18O fractionation. We investigated δ18O offsets of some frequently used Uvigerina, Bulimina, and Cibicidoides species in core top samples from different hydrographic and sedimentary regimes in the South China Sea, Makassar Strait, and Timor Strait/Eastern Indian Ocean. The δ18O values of the epifaunal taxa Cibicidoides mundulus and Cibicidoides wuellerstorfi showed no significant offset in all investigated regions, whereas shallow infaunal Cibicidoides species exhibited higher variability and were less reliable. We found no offsets between species of Uvigerina and Bulimina and assume that these genera can be measured together and/or substituted. Our results show that epifaunal taxa are close to equilibrium with ambient seawater and thus provide more reliable records of past ice volume and/or bottom water temperature variations than infaunal taxa. Offsets among equilibrium calcite, epifaunal taxa, and infaunal taxa are not constant “vital effects” but are influenced by changing gradients in bottom to pore water pH and carbonate ion concentrations that depend on deep-water ventilation and export flux of particulate carbonate and organic carbon. Offsets between epifaunal and infaunal taxa varied between 0.58 and 0.73‰, depending on regional bottom and pore water conditions. Our findings highlight the importance of regional and temporal variations in organic carbon flux/degradation and dissolution of calcite that may lead to slight under- or overestimates of the amplitude of δ18O fluctuations, especially during times of rapidly changing calcite-saturation of bottom and pore water.

Benthic foraminiferal response to orbital-scale variability in primary productivity off the Portuguese margin over the last 1.3 Myr

Detailed analyses of benthic foraminiferal fauna and planktonic foraminiferal stable carbon isotopes at IODP Site U1391 were performed to reconstruct orbital-scale variability in primary productivity off the Portuguese margin over the last 1.3 Myr. Q-mode factor analysis of benthic foraminiferal census data from the >250 μm fraction reveals four assemblages, which is mainly controlled by the organic matter flux to the seafloor deriving from surface water productivity. The Sphaeroidina bulloides assemblage accounts for nearly half of the total variance, consisting of S. bulloides, the agglutinated taxa and Lenticulina as major components and Cibicidoides robertsonianus, Planulina ariminensis and Uvigerina peregrina parva as subsidiary species. Cibicidoides wuellerstorfi and Bulimina mexicana are important accessory species of the Cibicidoides pachyderma-dominated assemblage. The miliolids assemblage is dominated by miliolids and B. mexicana with Uvigerina mediterranea as the important associated species. The Praeglobobulimina ovata assemblage is represented by P. ovata along with Globobulimina affinis, Melonis pompiloides, Melonis barleeanum and U. peregrina parva as important accessory species. High productivity often occurs during the interglacial stages and is characterized by the S. bulloides assemblage with subsidiary P. ovata assemblage, while low productivity often occurs during the glacial stages and is marked by the miliolids assemblage and the C. pachyderma assemblage. In addition to the distinct glacial/interglacial variations, there is a long-term decreasing trend in primary productivity recorded by benthic foraminifera, which is supported by a broadly increasing trend in the sediment redness (a*). Continuous wavelet analysis of high productivity-related Factor 1 loading (the S. bulloides assemblage) suggests that variations in primary productivity have a middle Pleistocene transition (MPT)-related shift in cyclicity from the ~41-kyr dominant cycle prior to the MPT to the ~100-kyr dominant cycle after the MPT. Cross-spectral analyses between the Factor 1 loading record and δ18O of Globigerina bulloides reveal the control of global ice volume changes on primary productivity. The high coherency between the Factor 1 loading record and δ13C of G. bulloides on the glacial/interglacial timescale suggests that primary productivity off the Portuguese margin may be largely affected by nutrient availability which was related to the Iberian surface hydrographic changes associated with changes in global ice volume.

Deep Thermohaline Circulation Across the Closure of the Central American Seaway

AbstractThe closure of the Central American Seaway (CAS) resulted in changes of ocean‐climate dynamics since the late Miocene following the uplift of northern Andes. Reconstructing the bottom‐water temperatures (BWTs) of the Caribbean Sea illustrates feedbacks of the closure on the ocean‐climate system including deep‐water dynamics of the Caribbean Sea. Here, Mg/Ca‐derived BWTs of the Plio‐Pleistocene Caribbean Sea from the benthic foraminifer Cibicidoides wuellerstorfi are presented for the first time and interpreted along with Na/Ca and Sr/Ca as proxies of salinity and continental input, respectively. Our results highlight several warm (93, Gi15‐19, and N1) and cool (92, M2, Gi20, and CN4) marine isotope stages (MISs). Accordingly, changes in the circulation of deep‐water masses during the CAS closure developed in four main time intervals: (I) between 5.2 and 4.1 Ma (million years ago) BWT was ~1.1°C, (II) 4.1–3.2 Ma ~2.1°C, (III) 3.2–2.7 Ma ~2.7°C, and (IV) 2.7–2.2 Ma ~2.1°C. Relatively higher, gradually increased temperatures between 3.2 and 2.7 Ma correspond to late Pliocene warmth and restricted inflow of Pacific waters into the Caribbean due to shoaling of the CAS. In addition, Sr/Ca values reveal gradually escalating terrigenous input until 2.7 Ma most likely related to the increased river discharge in response to the Andean uplift. The gradual decrease of the BWTs from 2.7 Ma may have resulted from the onset of Northern Hemisphere Glaciation. Overall, BWTs match with previous sea surface temperatures from the planktic foraminifer Neogloboquadrina dutertrei. The BWTs presented here confirm intensified thermohaline circulation during the overall Pliocene warmth with increased bottom‐water Na/Ca values indicating enhanced salinity.

Technical note: Single-shell &amp;lt;i&amp;gt;δ&amp;lt;/i&amp;gt;&amp;lt;sup&amp;gt;11&amp;lt;/sup&amp;gt;B analysis of &amp;lt;i&amp;gt;Cibicidoides wuellerstorfi&amp;lt;/i&amp;gt; using femtosecond laser ablation MC-ICPMS and secondary ion mass spectrometry

Abstract. The boron isotopic composition (δ11B) of benthic foraminifera provides a valuable tool to reconstruct past deep-water pH. As the abundance of monospecific species might be limited in sediments, microanalytical techniques can help to overcome this problem, but such studies on benthic foraminiferal δ11B are sparse. In addition, microanalytics provide information on the distribution of δ11B at high spatial resolution to increase the knowledge of biomineralization processes, for example. For this study, we investigated the intra- and inter-shell δ11B variability of the epibenthic species Cibicidoides wuellerstorfi, which is widely used in paleoceanography, by secondary ion mass spectrometry (SIMS) and femtosecond laser ablation multicollector inductively coupled plasma mass spectrometry (LA-MC-ICPMS). While the average δ11B values obtained from these different techniques agree remarkably well with bulk solution values to within ±0.1 ‰, a relatively large intra-shell variability was observed. Based on multiple measurements within single shells, the SIMS and LA data suggest median variations of 4.8 ‰ and 1.3 ‰ (2σ), respectively, while the larger spread for SIMS is attributed to the smaller volume of calcite being analyzed in each run. When analytical uncertainties and volume-dependent differences in δ11B variations are taken into account for these methods, the intra-shell variability is estimated to be on the order of ∼3 ‰ and ∼0.4 ‰ (2σ) on a ∼20 and 100 µm scale, respectively. In comparison, the δ11B variability between shells exhibits a total range of ∼3 ‰ for both techniques, suggesting that several shells need to be analyzed for accurate mean δ11B values. Based on a simple resampling method, we conclude that ∼12 shells of C. wuellerstorfi must be analyzed using LA-MC-ICPMS to obtain an accurate average value within ±0.5 ‰ (2σ) to resolve pH variations of ∼0.1. Based on our findings, we suggest preferring the conventional bulk solution MC-ICPMS over the in situ methods for paleo-pH studies, for example. However, SIMS and LA provide powerful tools for high-resolution paleoreconstructions, or for investigating ontogenetic trends in δ11B.

Foraminiferal Ecology and Role in Nitrogen Benthic Cycle in the Hypoxic Southeastern Bering Sea

Southeastern Bering Sea is one of the highest surface productivity area in the open ocean due to strong upwelling along the Bering canyon. However, the benthic geochemistry and organisms living in the area have been largely overlooked. In August 2017, surface sediment was sampled from four stations along a transect at depths between 1536 and 103 meters in the Bering canyon with JAMSTEC R/V Mirai. Bottom-water hypoxia was recorded in the two deepest stations (1536 and 536 m). At these stations, the oxygen penetrated down to 5 mm in the sediment due to siltier and much organic-rich sediments in the deeper stations while oxygen penetration was about 20 mm at stations 103 and 197 meters deep with coarse-grained sediment stations. Foraminiferal number of species and abundances were higher in the Unimak pass depression station E2 (197 m). Abundance did not change significantly between stations, suggesting that foraminiferal densities are not affected by the hypoxic conditions but are rather controlled by organic matter and nutrients availability. At the upper bathyal and middle bathyal stations, living foraminiferal communities were in general dominated by Uvigerina peregrina, Nonionella pulchella, Elphidium batialis, Globobulimina pacifica, Reophax spp., and Bolivina spathulata while the shallower stations exhibited large densities of Uvigerina peregrina, Cibicidoides wuellerstorfi, Recurvoidella bradyi, Globocassidulina subglobosa, and Portatrochammina pacifica. More than 50% of the individuals have a potential to accumulate nitrate in their cell (from 3 to 648 mmol/L; which is from 100 to 4000 times larger than the highest concentration measured in pore water). Onboard denitrification measurements confirmed that B. spathulata, N. pulchella and G. pacifica could reduce nitrate through denitrification and foraminiferal denitrification could contribute over 6% to benthic nitrate reduction at the southeast Bering Sea. Although the foraminiferal contributions were smaller than those measured at other hypoxic areas, our study quantitatively revealed the significance of eukaryotic microbes on benthic nitrogen cycles at this area.

ОСОБЕННОСТИ РАСПРЕДЕЛЕНИЯ БЕНТОСНЫХ ФОРАМИНИФЕР И ЕСТЕСТВЕННЫХ РАДИОНУКЛИДОВ В ДОННЫХ ОСАДКАХ СЕВЕРНОЙ АТЛАНТИКИ

The analysis of the relationship of benthic foraminifera and of natural radionuclides (232Th, 238U and 226Ra) distribution in the deep-water sediments of the North Atlantic in the section of 60○N crossing the arctic front is fulfilled. A oppositely directed correlation between the distribution of natural radionuclides in sediments and Alabaminella Weddellensis (Rs = 0.8) and Cibicidoides wuellerstorfi (Schwager, 1866) (Rs = –0.68) species occupying different ecological niches was revealed. The weighted radiation dose is calculated. The dose values obtained are in the range of 0.63–2.16 μGr/hour. It is assumed that under the conditions of measured background radiation, the effect of radiation hormesis in foraminifera manifests itself, stimulating their development.

Insights into the ecology of epibenthic calcareous foraminifera from a colonization study at 4000 m (Station M) in the NE Pacific Ocean

Benthic foraminifera are an abundant and important component of modern and ancient deep-sea ecosystems, and these single-celled organisms generate a fossil record that facilitates the assessment of paleoceanographic changes through time. Despite recent advances in taxonomic and ecological information about deep-sea foraminifera, many basic questions remain, requiring a better understanding of ecological tolerances, morphologic plasticity, and distribution of deep-sea foraminiferal species. This study focuses on the phylogenetics, morphology, and colonization dynamics of deep-sea foraminifera at abyssal Station M in the eastern Pacific Ocean. After 368 days at 4000 m on the Pacific Ocean seafloor, 546 foraminifera ~80% of which were calcareous species, occupied elevated substrate experiments. Genetic analyses of the most abundant calcareous foraminiferal taxon indicate that this trochospiral species is a morphological variant of Cibicidoides wuellerstorfi (referred to as C. wuellerstorfi var. lobatulus). Although Pyrgo and other milioline foraminifera are commonly found within sediments, two morphological variants of Pyrgo colonized elevated substrates at the Station M study site. Many Pyrgo spp. and C. wuellerstorfi var. lobatulus, were covered in an organic cyst, perhaps as a feeding structure. These results suggest that these calcareous foraminifera are able to flourish in deep-sea settings where hard substrates are available, and may be more widely distributed and diverse in lower bathyal and upper abyssal habitats when elevated substrates are present.

Paleocirculation and Ventilation History of Southern Ocean Sourced Deep Water Masses During the Last 800,000 Years

AbstractMost conceptual models of ocean circulation during past glacial periods invoke a shallowed North Atlantic‐sourced water mass overlying an expanded, poorly ventilated Southern Ocean (SO)‐sourced deep water mass (Southern Component Water or SCW), rich in remineralized carbon, within the Atlantic basin. However, the ventilation state, carbon inventory, and circulation pathway of SCW sourced in the Pacific sector of the SO (Pacific SO) during glacial periods are less well understood. Here we present multiproxy data—including δ18O and δ13C measured on the benthic and planktic foraminifera Cibicidoides wuellerstorfi, and Neogloboquadrina pachyderma, and productivity proxies including percent CaCO3, total organic carbon, and Ba/Ti—from a sediment core located in the high‐latitude (71°S) Pacific SO spanning the last 800 kyr. Typical glacial δ13C values of SCW at this core site are ~0‰. We find no evidence for SCW with extremely low δ13C values during glacials in the high‐latitude Pacific SO. This leads to a spatial gradient in the stable carbon isotope composition of SCW from the high‐latitude SO, suggesting that there are different processes of deep‐ and bottom‐water formation around Antarctica. A reduced imprint of air‐sea gas exchange is evident in the SCW formed in the Atlantic SO compared with the Pacific SO. A spatial δ13C gradient in SCW is apparent throughout much of the last 800,000 years, including interglacials. A SO‐wide depletion in benthic δ13C is observed in early MIS 16, coinciding with the lowest atmospheric pCO2 recorded in Antarctic ice cores.

The effect of matrix interferences on in situ boron isotope analysis by laser ablation multi-collector inductively coupled plasma mass spectrometry.

Boron isotope analysis of marine carbonates by laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) offers the potential for rapid sample throughput, and the means to examine micron-scale variations in the δ11 B signatures of fossil skeletons and shells/tests of marine organisms. Existing studies demonstrate an acceptable level of reproducibility is achievable, but also typically show a level of accuracy outside the limits required by most applications. Here we investigate matrix interference effects as a cause of inaccuracy and imprecision. Analyses were performed on a standard format Thermo Scientific Neptune Plus MC-ICP mass spectrometer coupled to a New Wave Research 193 nm ArF laser ablation system. The effects of matrix interference on δ11 B analysis were investigated through analyses of a set of reference materials with differing B/Ca ratios. Three approaches to correct for matrix-induced effects were trialled: (1) use of matrix-matched standards, (2) utilisation of the relationship between δ11 B inaccuracy and11 B/43 Ca, 11 B/40 ArCa4+ or 11 B/Cainterference from three reference materials with known δ11 B values and varying B/Ca ratios, and (3) direct characterisation of the (sloping) interference itself. Matrix interference from scattered Ca ions on 10 B can impede both the accuracy and the reproducibility of δ11 B analysis by LA-MC-ICP-MS. Based on analyses of two in-house reference materials, deep sea coral PS69/3181 and inorganic calcite UWC-1, we find approach 2, following the 11 B/Cainterference relationship, gives the best mean accuracies (within 0.4‰ of solution values) and external reproducibilities (± 0.5‰ 2 SD for PS69/3181). This approach has been applied to analyses of an annual growth cycle of a Siderastrea siderea coral and eight Cibicidoides wuellerstorfi benthic foraminifera. Both coral and foraminifera data match solution MC-ICP-MS analyses within reported uncertainties. LA-MC-ICP-MS can produce accurate and precise δ11 B data to a 0.5‰ (2σ) level on <0.3 ng B after correction for Ca interference effects.

Epifaunal Foraminifera in an Infaunal World: Insights Into the Influence of Heterogeneity on the Benthic Ecology of Oxygen-Poor, Deep-Sea Habitats

A reduction in dissolved oxygen availability in marine habitats is among the predicted consequences of increasing global temperatures. An understanding of past oxygenation is critical for predictions of future changes in the extent and distribution of oxygen minimum zones (OMZs). Benthic foraminifera have been used to assess changes in paleo-oxygenation, and according to prevailing thought, oxygen-poor marine benthic habitats are dominated by sediment-dwelling infaunal foraminifera, while more oxygenated environments are populated with more epifaunal taxa. However, in this study we found elevated densities of epifaunal taxa in oxygen-poor habitats. A series of sixteen multicores were taken on depth transects (360-3000 m) across an OMZ in the Southern California Bight to investigate the ecology of living (rose Bengal stained) benthic foraminifera. Dissolved oxygen concentrations in bottom water at sampling sites varied from 21 mol/l to 162 mol/l. Sampling focused on bathymetric highs in an effort to collect seafloor surface materials with coarse sediments in areas not typically targeted for sampling. Mean grain size varied from about 131m (gravelly sand) to about 830μm (coarse sand with fine gravel). Vertical distribution patterns (0-2 cm) were consistent with those of conspecifics reported elsewhere, and reconfirm that Cibicidoides wuellerstorfi and Hanzawaia nipponica have a living preference at or near the sediment-water interface. As expected, assemblages were dominated by infaunal taxa, such as Uvigerina and Bolivina, traditionally associated with the supersaturated, unconsolidated mud, characteristic of OMZ habitats, suggesting that these taxa are not sensitive to substrate type. However, despite dysoxic conditions (21 mol/l to 28 mol/l ), epifaunal taxa comprised as much as 36 percent of the stained population at the five sites with the coarsest mean grain size, while other measured environmental parameters remained relatively constant. We suggest that these epifaunal taxa, including C. wuellerstorfi, prefer habitats with coarse grains that allow them to remain at or above the sediment-water interface. These results suggest that seafloor habitat heterogeneity contributes to the distribution of benthic foraminifera, including in low-oxygen environments. We submit that paleo-oxygenation methods that use epifaunal indicator taxa need to reconsider the dissolved oxygen requirements of epifaunal taxa.

Lithium isotopic composition of benthic foraminifera: A new proxy for paleo-pH reconstruction

The lithium isotopic composition of foraminifera is an established tracer of long-term changes in the global silicate weathering cycle, following the assumption that foraminifera faithfully record the lithium isotopic composition (δ7Li) of seawater. In this study, we demonstrate by utilising benthic foraminifera (Amphistegina lessonii) that were cultured under decoupled pH-[CO32–] conditions, that foraminifera δ7Li is strongly dependent on pH. This is reinforced with δ7Li data from globally distributed core-top samples of Cibicidoides mundulus and Cibicidoides wuellerstorfi, which show the same negative correlation with pH. The dependency of δ7Li on pH is perhaps a surprising result given that lithium speciation in seawater is independent of both pH and carbonate ion speciation. The dependence of lithium incorporation on growth rate was assessed by measuring the calcium isotopic composition; no growth rate dependent incorporation was observed. Instead, we propose that the strength of the 6Li and 7Li hydration spheres (and hence their respective desolvation energy) is pH-dependent, resulting in a significant isotopic fractionation during the incorporation of lithium into foraminifer calcite. The core-top derived δ7Li-pH calibration is used to demonstrate the applicability of this δ11B-independent pH proxy in reconstructing deglacial variations in pH in the South Pacific. The use of foraminifera δ7Li to compliment δ11B-based pH reconstructions has the potential to provide insight into time-dependent variations in porewater/seawater δ11B, temperature and salinity, which were previously unresolvable.