Nonionellina Labradorica Research Articles

Distribution of Living Benthic Foraminifera in the Baffin Bay and Nares Strait in the Summer and Fall Periods: Relation with Environmental Parameters

Arctic climate warming leads to drastic changes in sea ice dynamics, hence impacting primary productivity but also the benthic communities. Therefore, to assess the response of living benthic foraminifera to contrasting Arctic environments, surface sediments from nine stations were collected during the summer of 2014 and fall of 2015 in the Baffin Bay and Nares Strait. Living standing stock are systematically low in the eastern and western Baffin Bay and much higher in the North Water Polynya and the Kane Basin located at the entrance and in the center of Nares Strait, respectively. High living benthic foraminiferal densities in the NOW reflect higher TOC while the highest density in the Kane Basin coincides with lower TOC but higher C/N and higher δ13Corg. The contribution of agglutinated species is on average very high for the whole study area and dominated by the species Adercotryma glomeratum, Lagenammina arenulata, and Reophax scorpiurus. Calcareous species, dominated by Nonionellina labradorica and Melonis barleeanus, are more abundant in the North Water Polynya and the Kane Basin. The very high living standing stock observed in the Kane Basin might be related to the northern position of the ice arch that summer during 2014 and therefore a particularly scarce sea ice cover might have allowed massive phytoplankton production during that season. In this study, the distribution of living benthic foraminifera is discussed according to several environmental parameters such as water masses, phytoplankton productivity, and organic matter fluxes.

Distribution of recent Benthic foraminifera in Kongsfjorden and Krossfjorden; North-West Svalbard, High Arctic

Benthic foraminifera assemblages from two fjords of Svalbard—Kongsfjorden and Krossfjorden in the High Arctic—have been studied. The foraminifera assemblages show three characteristic assemblages from the two fjords’ glacial proximal, middle and distal parts. The Cassidulina reniforme– Elphidium clavatum, Textularia spp. assemblage dominates the foraminifera fauna near the glacier proximal that indicates increased sedimentation and meltwater runoff; a Nonionellina labradorica– Islandiella helenae– Lobatula lobatula assemblage relates to well-oxygenated and high energy conditions and mainly occupies the middle part; and the Nonionellina labradorica– Islandiella helenae assemblages dominate in the distal region that indicates high surface primary productivity. Krossfjorden contains an oxygen deficiency zone around the middle part characterised by Stainforthia loeblichi. The abundance of Islandiella helenae and Nonionellina labradorica indicates that the high surface primary productivity of Krossfjorden is more than that of Kongsfjorden.

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.

Environmental changes in Krossfjorden, Svalbard, since 1950: Benthic foraminiferal and stable isotope evidence

ABSTRACT Environmental changes for the past ca. 50 years were studied in a short sediment core from inner Krossfjorden, Svalbard, investigating benthic foraminifera and stable isotopes (δ18O, δ13C). A depth–age model based on anthropogenic 137Cs time markers indicates that record covers the period from 1955 to 2007 and has sediment accumulation rates of ca. 0.3 to 1 cm/year. The benthic foraminifera are arctic and/or common in glaciomarine environments. Six fauna assemblages were identified using stratigraphically constrained cluster analysis. Benthic foraminiferal fauna assemblages are mainly dominated by Cassidulina reniforme. Elphidium clavatum is dominant from 1973 to 1986 and 2002 to 2007, likely due to greater turbidity in the water column. We interpret the increased percentages of Spiroplectammina biformis over the same intervals to reflect a slightly lower salinity probably caused by meltwater. During a short time period, 1970 to 1973, Stainforthia concava dominates the benthic foraminiferal fauna interpreted to reflect increased productivity within a marginal ice zone. Other species as Islandiella norcrossi, Nonionellina labradorica, Islandiella helenae, and Melonis barleanus also indicate more nutrient-rich waters are present but not very abundant throughout the record probably due to the glacier proximal position of the study site. The stable isotope record (δ18O) shows lighter values from 2001 to 2007, which seem to correlate well with oceanographic monitoring data showing increasing core temperatures of West Spitsbergen Current.

Drought recorded by Ba∕Ca in coastal benthic foraminifera

Abstract. Increasing occurrences of extreme weather events, such as the 2018 drought over northern Europe, are a concerning issue under global climate change. High-resolution archives of natural hydroclimate proxies, such as rapidly accumulating sediments containing biogenic carbonates, offer the potential to investigate the frequency and mechanisms of such events in the past. Droughts alter the barium (Ba) concentration of near-continent seawater through the reduction in Ba input from terrestrial runoff, which in turn may be recorded as changes in the chemical composition (Ba/Ca) of foraminiferal calcium carbonates accumulating in sediments. However, so far the use of Ba/Ca as a discharge indicator has been restricted to planktonic foraminifera, despite the high relative abundance of benthic species in coastal, shallow-water sites. Moreover, benthic foraminiferal Ba/Ca has mainly been used in open-ocean records as a proxy for paleo-productivity. Here we report on a new geochemical data set measured from living (CTG-labeled) benthic foraminiferal species to investigate the capability of benthic Ba/Ca to record changes in river runoff over a gradient of contrasting hydroclimatic conditions. Individual foraminifera (Bulimina marginata, Nonionellina labradorica) were analyzed by laser-ablation ICP-MS over a seasonal and spatial gradient within Gullmar Fjord, Swedish west coast, during 2018–2019. The results are compared to an extensive meteorological and hydrological data set, as well as sediment and pore-water geochemistry. Benthic foraminiferal Ba/Ca correlates significantly to riverine runoff; however, the signals contain both spatial trends with distance to Ba source and species-specific influences such as micro-habitat preferences. We deduce that shallow-infaunal foraminifera are especially suitable as proxy for terrestrial Ba input and discuss the potential influence of water-column and pore-water Ba cycling. While distance to Ba source, water depth, pore-water geochemistry, and species-specific effects need to be considered in interpreting the data, our results demonstrate confidence in the use of Ba/Ca of benthic foraminifera from near-continent records as a proxy for past riverine discharge and to identify periods of drought.

Influence of modern environmental gradients on foraminiferal faunas in the inner Kongsfjorden (Svalbard)

Kongsfjorden (Svalbard archipelago) is subjected to strong environmental gradients creating high physical and geochemical stress on benthic faunas. The present study aims at understanding the environmental drivers governing benthic foraminifera in the innermost part of the fjord. Surface sediments from 9 stations were sampled during August 2018 along a transect starting at ca. 2 km from the tidewater glacier Kronebreen and ending 12 km seaward. Three biozones were identified in response to disturbances linked to the proximity of the Kronebreen front (i.e., high water turbidity, freshwater, and sediment inputs, reduced organic fluxes). Close to the terminus (proximal biozone), few stress-tolerant and glacier proximal species were present (i.e., Capsammina bowmanni and Cassidulina reniforme). At about 6–8 km from the front (medial biozone), reduced turbidity, and increased organic fluxes, resulted in a higher diversity, and a high abundance of the phytodetritus-indicator Nonionellina labradorica. Relatively high diversity persisted until 12 km from the front due to higher organic inputs and reduced stressful conditions. The distal biozone was dominated by the Atlantic Water (AW) indicator Adercotryma glomeratum, in coherence with the presence of warm and salty AW detected far inside the fjord. Physical stress related to the glacier dynamics appears to favour the establishment of opportunistic species close to the terminus, whereas reduced disturbance away from the glacier induces the establishment of diverse assemblages. Our results show that benthic foraminifera may be effective bioindicators to monitor the long-term retreat of tidewater glaciers induced by climate change in Kongsfjorden.

Living and dead foraminiferal assemblages of the last decades from Kveithola Trough: Taphonomic processes and ecological highlights

We examine the living and dead benthic foraminiferal assemblages from the topmost 10 cm (using 150 μm sieve fraction) of three sedimentological short records collected in the Kveithola Trough (northwest Barents Sea). Our aim is to reconstruct the environmental variations of the last decades, connected to the interaction among the North Atlantic and the Arctic water masses. Our samples are collected at water depths between 150 and 380 m during the Eurofleets2-BURSTER oceanographic cruise, on board of the R/V Polarstern (June 2016).In the Cell Tracker Green (CTG) labelled living foraminiferal fauna, the main species are Pullenia bulloides, Globobulimina auriculata, and Nonionellina labradorica, while in the dead assemblages the main species are Cassidulina neoteretis, Cibicidoides lobatulus, and Cassidulina reniforme (outer, inner, and shelf stations, respectively). The dead foraminiferal assemblages show no significant traceable environmental changes in the Kveithola Trough area occurred during the last ca. 100 years. Conversely, the living foraminiferal fauna shows that this area is subject to variations related to circulation changes and organic matter burial in sediments, to which the biota adapts quickly. Moreover, the species that are only observed in the dead foraminiferal assemblages and not in the living CTG-labelled foraminiferal assemblages (e.g. C. reniforme) are typical of colder water and highlight the ongoing warming of the Arctic area. We find that the preservation of foraminiferal tests may bias the paleontological results. The agglutinated tests are often disintegrated, and the delicate calcareous ones are broken. The environmental conditions (style of sedimentation, bottom currents, interaction with other communities) can weaken the foraminiferal tests and make them prone to breakage or dissolution.

Ecological characteristics and stable isotope compositions of Elphidium batialis Saidova off Hidaka (northern Japan) in the Northwestern Pacific continental margin

We investigated the microhabitats of benthic foraminifera and stable oxygen and carbon isotope compositions of living (stained) Elphidium batialis Saidova off Hidaka (northern Japan) in the Northwestern Pacific continental margin. In the study area, six major species reside in three microhabitats that are vertically distributed within the sediment column. Bolivina spissa, Uvigerina akitaensis, and E. batialis tend to be shallow infauna, whereas Chilostomellina fimbriata and Globobulimina pacifica are deep infauna. Nonionellina labradorica is intermediate infauna. The δ18O values of E. batialis and U. akitaensis increased gradually with the water depth, but those of E. batialis contain a systematic offset by about −1.0 to −1.2‰ to U. akitaensis. This offset range is consistent with that observed in previous fossil studies in the Bering Sea. The δ13C values of U. akitaensis are approximately consistent (−1.1‰ to −0.8‰) with the water depth, whereas those of E. batialis increase with water depth from the shallower sites (−3.0 to −2.0‰) to the deeper sites (−2.0 to −1.6‰). Depending on the water depth, the δ13C values of E. batialis are lower than U. akitaensis by −1.4 to −0.7‰. Elphidium batialis may produce slightly 13C-poor calcite at the severely oxygen-poor water depths of the oxygen minimum zone (OMZ), suggesting that dissolved oxygen level may affect δ13C values of E. batialis during calcite precipitation. It is hypothesized that the δ13C values of E. batialis may contain signals arising from food digestion (or an internal respiration effect) and change the proportion of carbonate ions for calcite precipitation between the DIC values of the ambient pore water and food materials, depending on the dissolved oxygen level on the seafloor. Thus, the δ13C difference between E. batialis and Uvigerina spp. might be useful when inferring the past development of the OMZ and/or changes in the evolution of the North Pacific Intermediate Water in the subarctic North Pacific margin including adjacent marginal seas such as the Bering Sea.

Effectiveness of Fluorescent Viability Assays in Studies of Arctic Cold Seep Foraminifera

Highly negative δ13C values in fossil foraminifera from methane cold seeps have been proposed to reflect episodes of methane release from gas hydrate dissociation or free gas reservoirs triggered by climatic changes in the past. Because most studies on live foraminifera are based on the presence of Rose Bengal staining, that colors the cytoplasm of both live and recently dead individuals it remains unclear if, and to what extent live foraminifera incorporate methane-derived carbon during biomineralization, or whether the isotopic signature is mostly affected by authigenic overgrowth. In this paper, modern foraminiferal assemblages from a gas hydrate province Vestnesa Ridge (∼1,200 m water depth, northeastern Fram Strait) and from Storfjordrenna (∼400 m water depth in the western Barents Sea) is presented. By using the fluorescent viability assays CellTrackerTM Green (CTG) CMFDA and CellHunt Green (CHG) together with conventional Rose Bengal, it was possible to examine live and recently dead foraminifera separately. Metabolically active foraminifera were shown to inhabit methane-enriched sediments at both investigated locations. The benthic foraminiferal faunas were dominated by common Arctic species such as Melonis barleeanus, Cassidulina neoteretis, and Nonionellina labradorica. The combined usage of the fluorescence probe and Rose Bengal revealed only minor shifts in species compositions and differences in ratios between live and recently dead foraminifera from Storfjordrenna. There was no clear evidence that methane significantly affected the δ13C signature of the calcite of living specimens.

Negative δ13C Excursions in Foraminiferal Records: The Holocene History of Methane Events in the Central Sea of Okhotsk

Abstract—Several negative δ13C excursions in benthic foraminifera from gas-bearing core LV50-05 sampled offshore on the eastern slope of Sakhalin Island, Sea of Okhotsk, in an area of active methane seepage record the local history of methane events (ME). The core chronostratigraphy has been contrained from AMS 14C ages and biostratigraphic data. Benthic foraminifera (Nonionellina labradorica and Uvigerina parvocostata) from some core intervals show normal marine δ13C values about –1‰ but some intervals are marked by extremely depleted compositions as low as –34.5‰ δ13C (relative to VPDB). The negative δ13C excursions are interpreted as a record of seabed methane emanation during primary and secondary biomineralization of carbonate foraminifera. The results reveal four Holocene methane events (ME) in the area: two brief (ME-1 at 700–900 yr BP and ME-2 at 1200–1400 yr BP) and two long (ME-3 at 2500–4700 yr BP and ME-4 at 7400–10000 yr BP) events.

Inter fjord variations as a key contributor in the meiobenthic faunal distribution in the Arctic Kongsfjord, Svalbard

The community pattern of meiobenthos in an inner and outer glacial fjord of Kongsfjord was analysed during this study. This study examined the hypothesis that there is a significant difference in the distribution of total meiofauna and the major meiofaunal groups between the inner and outer fjords and it also looked into the effect of environmental variables on their distribution. Meiofaunal abundance and diversity was higher in the inner fjord, indicating that meiofauna can be less sensitive to sediment disturbances caused by glacial activity. Average abundance and biomass of the major meiofaunal groups, namely nematodes (54%) and foraminiferans (37%) were higher in the outer region. 45 species of nematodes representing 20 families were identified during the study, in which Dorylaimopsis sp. (39.55%) and Terschellingia longicaudata (12.53%) had the highest relative abundance. Out of the 56 foraminiferan species belonging to 5 suborders, Nonionellina labradorica (18.30%) and Cassidulina teretis (8.85%) had the highest relative abundance. There are clear and significant changes (ANOSIM) in the assemblage of meiofauna with increasing distance from the glacial front which correlates to environmental variables. Species contributing to differences between inner and outer basins (SIMPER) were also determined. Among nematodes, Chromadorids and Araeolaimids had a tendency to distribute in the inner fjord while Enoplids and Monhysterids were more prevalent in the outer fjord. Sediment organic matter, silt content and pH were the best matching variables (BEST) for the distribution of both nematodes and foraminiferans. The Principal Component Analysis (PCA) revealed that environmental variations have significant patterns in the faunal distribution in Kongsfjord. From this study it can be inferred that the inner fjord has the maximum numerical abundance of meiofauna but the foraminiferans and nematodes were numerically abundant in the outer fjord and there is also significant difference in the distribution of species between the two fjords.

Kleptoplastidic benthic foraminifera from aphotic habitats: insights into assimilation of inorganic C, N and S studied with sub-cellular resolution.

The assimilation of inorganic compounds in foraminiferal metabolism compared to predation or organic matter assimilation is unknown. Here, we investigate possible inorganic-compound assimilation in Nonionellina labradorica, a common kleptoplastidic benthic foraminifer from Arctic and North Atlantic sublittoral regions. The objectives were to identify the source of the foraminiferal kleptoplasts, assess their photosynthetic functionality in light and darkness and investigate inorganic nitrogen and sulfate assimilation. We used DNA barcoding of a ~ 830 bp fragment from the SSU rDNA to identify the kleptoplasts and correlated transmission electron microscopy and nanometre-scale secondary ion mass spectrometry (TEM-NanoSIMS) isotopic imaging to study 13 C-bicarbonate, 15 N-ammonium and 34 S-sulfate uptake. In addition, respiration rate measurements were determined to assess the response of N. labradorica to light. The DNA sequences established that over 80% of the kleptoplasts belonged to Thalassiosira (with 96%-99% identity), a cosmopolitan planktonic diatom. TEM-NanoSIMS imaging revealed degraded cytoplasm and an absence of 13 C assimilation in foraminifera exposed to light. Oxygen measurements showed higher respiration rates under light than dark conditions, and no O2 production was detected. These results indicate that the photosynthetic pathways in N. labradorica are not functional. Furthermore, N. labradorica assimilated both 15 N-ammonium and 34 S-sulfate into its cytoplasm, which suggests that foraminifera might have several ammonium or sulfate assimilation pathways, involving either the kleptoplasts or bona fide foraminiferal pathway(s) not yet identified.

The effects of multiple stressors on the distribution of coastal benthic foraminifera: A case study from the Skagerrak-Baltic Sea region

Abstract Coastal ecosystems are subjected to both large natural variability and increasing anthropogenic impact on environmental parameters such as changes in salinity, temperature, and pH. This study documents the distribution of living benthic foraminifera under the influence of multiple environmental stressors in the Skagerrak-Baltic Sea region. Sediment core tops were studied at five sites along a transect from the Skagerrak to the Baltic Sea, with strong environmental gradients, especially in terms of salinity, pH, calcium carbonate saturation and dissolved oxygen concentration in the bottom water and pore water. We found that living foraminiferal densities and species richness were higher at the Skagerrak station, where the general living conditions were relatively beneficial for Foraminifera, with higher salinity and Ωcalc in the water column and higher pH and oxygen concentration in the bottom and pore water. The most common species reported at each station reflect the differences in the environmental conditions between the stations. The dominant species were Cassidulina laevigata and Hyalinea balthica in the Skagerrak, Stainforthia fusiformis, Nonionella aff. stella and Nonionoides turgida in the Kattegat and N. aff. stella and Nonionellina labradorica in the Oresund. The most adverse conditions, such as low salinity, low Ωcalc, low dissolved oxygen concentrations and low pH, were noted at the Baltic Sea stations, where the calcareous tests of the dominant living taxa Ammonia spp. and Elphidium spp. were partially to completely dissolved, probably due to a combination of different stressors affecting the required energy for biomineralization. Even though Foraminifera are able to live in extremely varying environmental conditions, the present results suggest that the benthic coastal ecosystems in the studied region, which are apparently affected by an increase in the range of environmental variability, will probably be even more influenced by a future increase in anthropogenic impacts, including coastal ocean acidification and deoxygenation.

An overview of cellular ultrastructure in benthic foraminifera: New observations of rotalid species in the context of existing literature

We report systematic transmission electron microscope (TEM) observations of the cellular ultrastructure of selected, small rotalid benthic foraminifera. Nine species from different environments (intertidal mudflat, fjord, and basin) were investigated: Ammonia sp., Elphidium oceanense, Haynesina germanica, Bulimina marginata, Globobulimina sp., Nonionellina labradorica, Nonionella sp., Stainforthia fusiformis and Buliminella tenuata. All the observed specimens were fixed just after collection from their natural habitats allowing description of intact and healthy cells. Foraminiferal organelles can be divided into two broad categories: (1) organelles that are present in all eukaryotes, such as the nuclei, mitochondria, endoplasmic reticulum, Golgi apparatus, and peroxisomes; and (2) organelles observed in all foraminifera but not common in all eukaryotic cells, generally with unknown function, such as fibrillar vesicles or electron-opaque bodies. Although the organelles of the first category were observed in all the observed species, their appearance varies. For example, subcellular compartments linked to feeding and metabolism exhibited different sizes and shapes between species, likely due to differences in their diet and/or trophic mechanisms. The organelles of the second category are common in all foraminiferal species investigated and, according to the literature, are frequently present in the cytoplasm of many different species, both benthic and planktonic. This study, thus, provides a detailed overview of the major ultrastructural components in benthic foraminiferal cells from a variety of marine environments, and also highlights the need for further research to better understand the function and role of the various organelles in these fascinating organisms.

Benthic foraminiferal Mn / Ca ratios reflect microhabitat preferences

Abstract. The Mn / Ca of calcium carbonate tests of living (rose-Bengal-stained) benthic foraminifera (Elphidium batialis, Uvigerina spp., Bolivina spissa, Nonionellina labradorica and Chilostomellina fimbriata) were determined in relation to pore water manganese (Mn) concentrations for the first time along a bottom water oxygen gradient across the continental slope along the NE Japan margin (western Pacific). The local bottom water oxygen (BWO) gradient differs from previous field study sites focusing on foraminiferal Mn / Ca and redox chemistry, therefore allowing further resolution of previously observed trends. The Mn / Ca ratios were analysed using laser ablation inductively coupled plasma-mass spectrometer (ICP-MS), allowing single-chamber determination of Mn / Ca. The incorporation of Mn into the carbonate tests reflects environmental conditions and is not influenced by ontogeny. The inter-species variability in Mn / Ca reflected foraminiferal in-sediment habitat preferences and associated pore water chemistry but also showed large interspecific differences in Mn partitioning. At each station, Mn / Ca ratios were always lower in the shallow infaunal E. batialis, occupying relatively oxygenated sediments, compared to intermediate infaunal species, Uvigerina spp. and B. spissa, which were typically found at greater depth, under more reducing conditions. The highest Mn / Ca was always recorded by the deep infaunal species N. labradorica and C. fimbriata. Our results suggest that although partitioning differs, Mn / Ca ratios in the intermediate infaunal taxa are promising tools for palaeoceanographic reconstructions as their microhabitat exposes them to higher variability in pore water Mn, thereby making them relatively sensitive recorders of redox conditions and/or bottom water oxygenation.

Benthic foraminifera contribution to fjord modern carbon pools: A seasonal study in Adventfjorden, Spitsbergen

The aim of this study was to determine the amount of organic and inorganic carbon in foraminifera specimens and to provide quantitative data on the contribution of foraminifera to the sedimentary carbon pool in Adventfjorden. The investigation was based on three calcareous species that occur commonly in Svalbard fjords: Cassidulina reniforme, Elphidium excavatum and Nonionellina labradorica. Our results show that the species investigated did not contribute substantially to the organic carbon pool in Adventfjorden, because they represented only 0.37% of the organic carbon in the sediment. However, foraminiferal biomass could have been underestimated as it did not include arenaceous or monothalamous taxa. Foraminiferal carbonate constituted up to 38% of the inorganic carbon in the sediment, which supports the assumption that in fjords where non-calcifying organisms dominate the benthic fauna foraminifera are among the major producers of calcium carbonate and that they play crucial roles in the carbon burial process. The results presented in this study contribute to estimations of changes in foraminiferal carbon levels in contemporary environments and could be an important reference for palaeoceanographic studies.

Impact of shelf-transformed waters (STW) on foraminiferal assemblages in the outwash and glacial fjords of Adventfjorden and Hornsund, Svalbard

Summary A new dataset of benthic foraminiferal assemblages from Adventfjorden (tributary fjord of Isfjorden, West Spitsbergen) was compared with the results of a study conducted by Zajączkowski et al. (2010) in Hornsund (West Spitsbergen). According to Nilsen et al. (2016) , Atlantic water inflow to the Isfjorden Trough occurs more readily than to anywhere else along the shelf of Spitsbergen; thus, we compared the foraminiferal assemblages of the outwash Adventfjorden fjord, located in the Isfjorden system, with glacial Hornsund, located in southwest Spitsbergen. Despite the juxtaposition of Adventfjorden and Hornsund the data revealed varying impacts of shelf-transformed water (STW) on the benthic foraminiferal assemblages. Outer and central Adventfjorden was dominated by Adercotryma glomerata, Recurvoides turbinata and Spiroplectammina sp., reflecting the presence of STW, while abundant Melonis barleeanus in the central area of the fjord indicated a large flux of unaltered organic matter. Only the head of the fjord was dominated by the glaciomarine taxa Cassidulina reniforme and Elphidium clavatum. Foraminiferal fauna characteristic of STW-influenced environments (i.e., Nonionellina labradorica and R. turbinata) were also observed in outer Hornsund. However, the glacier-proximal taxa E. clavatum and C. reniforme were dominant throughout the fjord, demonstrating the impacts of meltwater and high sedimentation. Therefore, it is likely that in Hornsund, glacial impact is a major environmental factor, which is stronger than the influence of STW.

Effects of the Younger Dryas climate event recorded in sediment near the western Irish seaboard

Results of analyses of a shallow marine sediment vibrocore from the Atlantic seafloor just west of the Aran Islands, western Ireland, are presented. The sediments range from ~16,000 to younger than 9,000 cal BP in age, based on 14C dating of foraminifers and molluscs. One sample within the core is dated at 12804 ± 125 cal BP and lies a very short distance stratigraphically below a conspicuous horizon containing isolated pebbles and sand‐size clasts, in what is an otherwise fine‐grained sequence of sediment. These outsized clasts are interpreted to be ice‐rafted debris. Approximately coeval with this horizon, the diversity and abundance of foraminifers decrease significantly and the foraminifer Nonionellina labradorica makes its first appearance in the core sediment. Stable isotope analysis shows a significant increase in values of δ18O approaching the horizon containing ice‐rafted debris. These results show the effects of a relatively sudden cooling of this part of the Atlantic Ocean at middle latitudes coincident with, or just after, the onset of the Younger Dryas event and demonstrate the extent of floating icebergs and probable later pack ice as a result of this temperature decrease.

Benthic foraminiferal growth seasons implied from Mg/Ca‐temperature correlations for three Arctic species

AbstractCore‐top sediment samples from Kongsfjorden, Svalbard, and adjacent fjord and shelf areas were collected in order to investigate a potential relationship between Mg/Ca‐ratios of Arctic benthic foraminifera and the ambient bottom water temperatures (BWT). The area is influenced by large seasonal variation in factors such as light and temperature, which is further strengthened by oceanographic shifts, including inflow of relatively warm Atlantic water. Four hydrological seasons have been defined. The studied samples were collected during the years 2005–2010 and comprise data from three hydrological seasons: spring, summer, and autumn. Five common species of cold‐water benthic foraminifera were investigated: Islandiella helenae/norcrossi, Buccella frigida, Nonionellina labradorica, Elphidium clavatum, and Cassidulina reniforme. For E. clavatum and C. reniforme, the investigations failed. For the remaining three species, the Mg/Ca‐temperature correlations initially appeared stochastic holding correlation coefficients between 0.01 and 0.15. However, grouping the data based on seasons gave stronger Mg/Ca‐temperature correlations, indicating specific growing seasons for the three species. The equations represent a starting point for a discussion on seasonality rather than robust, “ready‐to‐use” equations. I. helenae/norcrossi seems to reproduce and grow during summer (July/August) in outer Kongsfjorden. For B. frigida, a Mg/Ca‐temperature correlation is seen both in summer (July/August) and autumn (October/November) samples, indicative of a continuous reproduction/growth‐season lasting from July to November. N. labradorica appears to reproduce and grow during autumn (October/November). The results indicate that temperature reconstructions based on these benthic foraminifera reproduce seasonal temperatures rather than annual average temperatures.

LIVING (STAINED) DEEP-SEA FORAMINIFERA OFF HACHINOHE (NE JAPAN, WESTERN PACIFIC): ENVIRONMENTAL INTERPLAY IN OXYGEN-DEPLETED ECOSYSTEMS

Live (Rose-Bengal stained) deep-sea foraminiferal faunas have been studied at five stations between 500–2000-m depth along the NE Japanese margin (western Pacific) to understand how complex environmental conditions (e.g., oxygen depletion, organic matter) control their structure (i.e., diversity, standing stocks, and microhabitats). All stations are characterized by silty sediments with no evidence of recent physical disturbances. The three stations located between 760–1250 m are bathed by dysoxic bottom waters ( 2.2% DW), only the oxygen-depleted sites are characterized by higher concentrations of sugars, lipids, and enzymatically hydrolysable amino acids (EHAA). Sedimentary contents in chlorophyllic pigments decrease with water depth without any major change in their freshness (i.e., [Chl a/(Chl a + Pheo a)] ratios). Both Uvigerina akitaensis and Bolivina spissa are restricted to the stations bathed by dysoxic waters, proving their oxygen-depletion tolerance. In such conditions, both phytophagous taxa are obviously able to take advantage of labile organic compounds (e.g., lipids and EHAA) contained in phytodetritus. Nonionella stella and Rutherfordoides cornuta survive in oxygen-depleted environments probably via alternative metabolic pathways (e.g., denitrification ability) and a large flexibility in trophic requirements. At stations where oxygen availability is higher (i.e., >70 μmol/L in bottom water) and where bioavailable organic compounds are slightly less abundant, diversity indices remain low, and more competitive species (e.g., Uvigerina curticosta, U. cf. U. graciliformis, Nonionella globosa, Nonionellina labradorica, and Elphidium batialis) are dominant.