Deep-sea Benthic Foraminifera Research Articles

Astronomically forced paleoclimate and sea-level changes recorded in the continental margin of the South China Sea over the past ∼23 m.y.

The Earth has witnessed the emergence of continental-sized ice sheets, starting with Antarctica and gradually extending to both hemispheres over the past 40 million years. These ice accumulations have had a dramatic impact on both paleoclimate and sea level, substantially influencing sediment deposition in the continental margins. However, understanding sediment accumulation on an orbital scale in continental margins remains limited because of the scarcity of high-resolution, chronologically constrained sedimentary records. Here, we conducted a highly resolved cyclostratigraphic analysis based on natural gamma radiation (GR) series in depth domain at the continental margin of the South China Sea. We established a 22.8 m.y.-long high-resolution astronomical time scale spanning from the Miocene to the Quaternary by tuning the GR records to the global deep-sea benthic foraminifera carbon isotope curves and the 405 k.y. eccentricity cycles. The m.y.-scale sea-level changes since the Miocene were reconstructed through the sedimentary noise modeling of the 405-k.y.-tuned GR series. These reconstructions aligned with regional and global sea-level changes. The phase correlation between the filtered 1.2 m.y. cycles of sea-level change curves (dynamic noise after orbital tuning and ρ1 median models) from δ13Cbenthic and tuned GR series and the 1.2 m.y. obliquity amplitude modulation cycles revealed a shift from an anti-phase to an in-phase relationship across the middle Miocene climate transition (ca. 13.8 Ma), suggesting extensive expansion of the Antarctic ice sheet played a key role. In addition, a shift from an in-phase to an anti-phase relationship during the late Miocene (ca. 8 Ma and 5.3 Ma), indicating ephemeral expansion of the Arctic ice sheets or the changes in carbon cycle involving the terrestrial and deep ocean carbon reservoirs, might be the primary driver of eustatic changes. Furthermore, obliquity forcing and changes in meridional gradients in insolation that transported poleward flux of heat, moisture, and precipitation increased ice accumulation in both pole ice sheets and nonlinearly transferred high-latitude signals to low-latitude regions. This phenomenon is supported by the observation of strong obliquity signals in low latitude during global climate cooling interval. Our results suggest that m.y.-scale sea-level variations respond to astronomically induced climate change and ice sheet dynamics of both poles. This work contributes a highly resolved low-latitude geological archive to the future reconstruction of paleoclimate evolution on a global scale.

Recent Deep-Sea Benthic Foraminifera from an Active Volcanic Area: First Insights around Nishinoshima, Northwest Pacific

Recent Deep-Sea Benthic Foraminifera from an Active Volcanic Area: First Insights around Nishinoshima, Northwest Pacific

Miocene deep-sea benthic foraminifera from the Atlantic and Indian oceans: diversity patterns and palaeoceanography

During the early to middle Miocene of the Atlantic and Indian Oceans there were variations in species diversity of the lower bathyal to abyssal plain (3-4.4 km) benthic foraminifcral assemblages allhough, overall, diversity remained high and comparable with that of the modern environment. The early Miocene was a period of palaeoceanographic change and this has previously been documented both through studies of stable isotopes and the rate of appearances or disappearances of taxa (whether evolutionary or ecological). The diversity oscillations appear to represent shorter period change. The lowest diversities are associated with the peak abundance of bolivinids. Other variations cannot be correlated from one site to another and are thought to represent local environmental changes. During the early-middle Miocene, the diversity of the Atlantic abyssal plain was lower than that of the Indian and Pacific Oceans possibly indicating significant diversity differences between ocean basins. On the basis of limited data, it is possible to speculate that the species diversity of the Miocene was perhaps higher than that of today.

Santonian deep sea benthic foraminifera from IODP Site U1513, Mentelle Basin (SW Australia): Reactions of benthic foraminiferal assemblages to surface water cooling at southern high latitudes

International Ocean Discovery Program (IODP) Expedition 369 recovered a stratigraphically complete, Santonian-aged, pelagic sedimentary sequence at Site U1513 on the Naturaliste Plateau (33°47.6084′S, 112°29.1338′E) at ~2800 m water depth. The site was located at ~60°S paleolatitude in Cretaceous times. A total of 59 samples studied from Holes 1513A and 1513B yielded 140 calcareous and nine agglutinated benthic foraminiferal taxa. Gavelinellids (Notoplanulina, Gavelinella, Anomalinoides) and Gyroidinoides spp., are the most abundant taxa overall and also dominate most samples. We also report 382 foraminiferal stable isotopic measurements and infer cooling [of ~5 °C in surface waters and 2 °C at the seafloor] based on changes in δ18O values for benthic and planktonic taxa through the Santonian at Site U1513. Inferred cooling was accompanied by changes in planktonic and benthic foraminiferal assemblages. At Site U1513, benthic foraminiferal taxonomic richness declines by 15 species (from 20– 25 to 5–10 taxa) towards the upper Santonian. Within this interval, epifaunal, oxic foraminifera diminish in absolute and relative abundance, and there is a parallel relative increase in opportunistic taxa and infaunal foraminifera. Changes in benthic foraminiferal communities indicate a shift from oligotrophic to eutrophic conditions in the bottom water despite the general cooling trend. This paper explores the causes and effects of the paleoenvironmental changes in the bottom waters.

Some like it cool: Benthic foraminiferal response to Paleogene warming events

Long-term climatic trends of the Paleogene were interrupted by global perturbations of the carbon cycle, commonly associated with warming of surface and bottom waters and ecosystem disturbance. Most of these perturbations occurred in the Paleocene - Eocene greenhouse climate, but others were superimposed on the transition of greenhouse-to- icehouse conditions during the middle to late Eocene. Here we analyze deep-sea benthic foraminifera to focus on the impact of Paleogene warming events on ocean bottom water ecosystems. We compare changes in assemblage diversity (Fisher-α index) across nine warming events at 16 locations (ocean drilling sites and land sections; 25 case studies) by applying the Epps-Singleton and Fligner-Killeen non-parametric statistical tests. Generally, diversity decreased whereas the coefficient of variation increased during warming events, but not all changes were statistically significant. The declines in diversity may have been due to adaptation to stressed conditions, whereas the higher coefficients of variation may have been caused by unstable environmental conditions. The most severe events, the Paleocene-Eocene Thermal Maximum (PETM, ~56 Ma) and Eocene Thermal Maximum 2 (ETM2, ~53.7 Ma), had a higher impact on bottom water ecosystems, as shown in major drops in diversity. Regression analysis of data for ODP Sites 1262 and 1263 (SE Atlantic) shows that only up to 62% of the variability of benthic foraminiferal diversity at these sites depends on δ 13 C and δ 18 O values, indicating that changes in diversity were not exclusively determined by the magnitude of the events as defined by the magnitude of changes in carbon isotope excursion and temperature. No major changes in diversity were identified during middle Eocene warming events, and post-event diversity became significantly more stable, suggesting that the overall cooler middle Eocene conditions supported higher faunal diversity and stability of benthic foraminiferal assemblages. • Declined diversity at warming events correlated to magnitude and local factors. • Background climate conditions influenced the impact of warming on marine biota. • Cooler middle Eocene conditions promoted higher diversity of benthic foraminifera.

Biotic responses of deep-sea benthic foraminifera in the equatorial Indian Ocean during the Quaternary: Influence of the ballasting effect on organic matter by calcareous plankton skeletons

We investigated Quaternary benthic foraminifera in core GPC1803 in the eastern equatorial Indian Ocean since ~740 ka to examine the relationship between benthic foraminiferal fauna and ballasting of particulate organic matter (POM) by calcareous plankton skeletons. Because plankton skeletons affect POM sinking in the water column as ballasts, ballasting of POM by biominerals may play an important role to linkage between the surface and deep-sea paleoceanography. We consider this scheme, based on faunal analysis of benthic foraminifera. From multidimensional scaling (MDS) of fossil benthic foraminifera, we recognized two MDS axes. Based on the scores of MDS axis 1, we subdivided our study period into five intervals and identified two major faunal transitions at ~370 ka and ~ 210 ka. After ~210 ka, the food supply to the seafloor increased with an increase in the past flux of calcareous plankton skeletons. A positive correlation between the benthic foraminifera accumulation rate and the carbonate mass accumulation rate existed during ~600–370 ka and after ~210 ka. It is reasonable to suppose that the increase in calcareous plankton skeletons stimulated more efficient vertical transport of POM through the water column due to the positive ballasting effect on POM. The ~370–210 ka period seemed to represent a transitional phase in food supply. Prior to ~370 ka, alternations among three seasonal food supply-related species were generally observed along with glacial–interglacial variations probably under lower food supply, compared with the after ~210 ka period; however, alternations among these three species became obscure and intermittent after ~370 ka. The nearly continuous common occurrences of these seasonal food supply-related species before ~370 ka might have been enhanced by a lower past flux of calcareous plankton skeletons. Scenario of ballasting of POM by biomineral might explain long-term changes of carbonate corrosivity in the Indian Ocean, similarly in the Atlantic and eastern equatorial Pacific Oceans, during the mid-Brunhes dissolution interval. • Quaternary deep-sea benthic foraminifera in the equatorial Indian Ocean • Positive relationship between BFAR and carbonate MAR after ~210 ka • Common occurrences of seasonal food supply-related species before ~370 ka • Changes in the influence of ballasting of POM by calcareous plankton

Palaeoecological significances of deep-sea benthic foraminifera from Cascadia Margin, North East Pacific Ocean

The strong relationship between benthic foraminifera’s habitat and morphological characteristics to their surrounding environment are dominant component in marine community. This study attempts to understand the significance of benthic foraminifera in ecological importance and paleoceanographic reconstructions at Cascadia Margin, NE Pacific Ocean during the Pleistocene. The quantitative analyses of deep sea benthic foraminifera, particularly Bulimina exilis, Cibicides kullenbergi, Elphidium batialis, Epistominella exigua and Uvigerina proboscidea generally show higher abundances in the studied interval. The Gas Hydrate Stability Zone in the Cascadia Margin at ∼1200 ka to 162 ka (GHSZ; ∼240–70 mbsf) is related to low temperature and high-pressure conditions which are responsible for lower abundances of benthic foraminifera across that interval. The Alaska Current, North Pacific Current and California Current, also known as Eastern Boundary Currents (EBC), play a major role in the transportation of suspended sediments and coastal upwelling throughout the coast across the ∼650 to 450 ka and ∼35 to 2 ka intervals. The relative abundance rate of benthic foraminiferal community decreases with increasing core depth, indicating the influence of less ventilated and nutrient-enriched North Pacific Intermediate Water (NPIW). The present study also signifies the disappearance of benthic faunas throughout the Early–Middle Pleistocene Transition (EMPT, 1250–700 ka, Clark et al., 2006) period due to increased cyclic seasonality and decreased food supply, with few species (Bolivina alata, Bolivina spathulata, Cibicides wuellerstorfi, Epistominella exigua, Gavelinopsis lobatulus and Uvigerina peregrina) being exceptions.

2020 Joseph A. Cushman Award to Ellen Thomas

Research Article| January 31, 2021 2020 Joseph A. Cushman Award to Ellen Thomas Laia Alegret; Laia Alegret University of Zaragoza Zaragoza, Spain Search for other works by this author on: GSW Google Scholar Bruce W. Hayward; Bruce W. Hayward Geomarine Research Auckland, New Zealand Search for other works by this author on: GSW Google Scholar R. Mark Leckie; R. Mark Leckie University of Massachusetts Amherst, MA, USA Search for other works by this author on: GSW Google Scholar Paul N. Pearson Paul N. Pearson Cardiff University Cardiff, Wales, UK Search for other works by this author on: GSW Google Scholar Author and Article Information Laia Alegret University of Zaragoza Zaragoza, Spain Bruce W. Hayward Geomarine Research Auckland, New Zealand R. Mark Leckie University of Massachusetts Amherst, MA, USA Paul N. Pearson Cardiff University Cardiff, Wales, UK Publisher: Cushman Foundation for Foraminiferal Research First Online: 10 Mar 2021 Online ISSN: 1943-264X Print ISSN: 0096-1191 Journal of Foraminiferal Research (2021) 51 (1): 1–3. https://doi.org/10.2113/gsjfr.51.1.1 Article history First Online: 10 Mar 2021 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Laia Alegret, Bruce W. Hayward, R. Mark Leckie, Paul N. Pearson; 2020 Joseph A. Cushman Award to Ellen Thomas. Journal of Foraminiferal Research 2021;; 51 (1): 1–3. doi: https://doi.org/10.2113/gsjfr.51.1.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyJournal of Foraminiferal Research Search Advanced Search View largeDownload slideView largeDownload slide Ellen Thomas is the recipient of the 2020 Joseph A. Cushman Award for Excellence in Foraminiferal Research for her lifetime dedication to the study of foraminifera and her outstanding contributions in this field. She is a leading authority on deep-sea benthic foraminifera, especially their taxonomy and curation, evolutionary history, and multiple applications. Additionally, the award recognizes her multiple collaborative studies that have been at the forefront of international efforts to reconstruct past climates. Ellen completed her education at the University of Utrecht with a general background in classical geology and micropaleontology and... You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Composition and diversity patterns of deep sea benthic foraminifera from the Panama basin, eastern equatorial Pacific

Environmental controls affecting the composition and distribution of deep sea benthic foraminifera were analyzed in the Panama Basin (Eastern Equatorial Pacific). For this study, results of the analysis of a new set of 33 core-top samples from the upper-lower slope (714–3819 mbsf) were integrated with previous data from this area.The composition of the foraminiferal assemblages resembles a typical deep sea association, illustrating a close relationship with dissolved oxygen at the seafloor and indirectly with surface productivity. Low oxygen content and organic matter influx, as inferred in the eastern Panama Basin, are connected to terrigenous supply and seasonal upwelling on the Panama Bight and southern Costa Rica. Buliminids, bolivinids, and Epistominella spp. are common elements of the continental slope. In addition, physiographic aspects such as the type of substrate, turbidity fluxes, and bottom currents also exert control over some of the described taxa and defined morphogroups. A broad exploration of the infaunal/epifaunal relationships in the basin does not suggest a clear relationship with dissolved oxygen content. However, there are fluctuations in the proportion of some of the defined epifaunal morphogroups and selected taxa (e.g. Cibicidoides wuellerstorfi, Chilostomella oolina, and Hoeglundina elegans, among others) along the Carnegie Ridge. These changes are explained by the variable physiographic features (surface upwelling, strong bottom currents) that coalesce in this part of the Panama Basin.Furthermore, re-evaluation of the foraminiferal morphogroups in two deep sea cores that comprised the last 25 ky, indicate that some taxa of the recent samples (Cassidulina spp. and Siphouvigerina peregrina, among others) reacted to paleoproductivity and bottom current fluctuations at the end of the Last Glacial Maximum and the Younger Dryas.Despite the lack of ecological data in the foraminiferal assemblages for a large proportion of the Panama Basin, the application of selected taxa or morphogroups as proxies for paleoceanographic conditions is promising.

Deep-sea benthic foraminifera at a bauxite industrial waste site in the Cassidaigne Canyon (NW Mediterranean): Ten months after the cessation of red mud dumping

Deep-sea benthic foraminifera at a bauxite industrial waste site in the Cassidaigne Canyon (NW Mediterranean): Ten months after the cessation of red mud dumping

Latest Oligocene to earliest Pliocene deep-sea benthic foraminifera from Ocean Drilling Program (ODP) Sites 752, 1168 and 1139, southern Indian Ocean

Abstract. Deep-sea benthic foraminifera provide important markers of environmental conditions in the deep-ocean basins where their assemblage composition and test chemistry are influenced by ambient physical and chemical conditions in bottom-water masses. However, all foraminiferal studies must be underpinned by robust taxonomic approaches. Although many parts of the world's oceans have been examined, over a range of geological timescales, the Neogene benthic foraminifera from the southern Indian Ocean have only been recorded from a few isolated sites. In this study, we have examined 97 samples from Neogene sediments recovered from three ODP sites in the southern Indian Ocean (Sites 752, Broken Ridge; 1139, Kerguelan Plateau; 1168, west Tasmania). These data cover a range of palaeolatitudes and water depths during the Miocene. More than 200 species of benthic foraminifera were recorded at each site and, despite their geographic and bathymetric separation, the most abundant taxa were similar at all three sites. Many of these species range from late Oligocene to early Pliocene demonstrating relatively little faunal turnover of the most abundant taxa during the key palaeoclimatic shifts of the Miocene. We illustrate and document the occurrence of the 52 most abundant species (i.e. those with >1 % abundance) encountered across the three study sites.

Deep-sea benthic foraminifera record of the last 1500 years in the North Aegean Trough (northeastern Mediterranean): A paleoclimatic reconstruction scenario

A 1500-year, high-resolution deep-sea benthic foraminifera record from the Athos Basin of the North Aegean Trough (northeastern Mediterranean) has been analyzed for the development of a paleoclimatic scenario. The data analysis points out that the quantity and quality of the seafloor's organic matter could be a crucial controlling factor for the faunal succession. During 550–1000 AD (within the Medieval Climate Anomaly), the relatively high benthic foraminiferal accumulation rates together with the predominance of meso-eutrophic taxa, such as Bolivina dilatata/spathulata, may be interpreted as the result of high precipitation. Consequently, increased riverine discharges into the North Aegean Sea and the associated warm climatic conditions appear to persist for a long time and are related to a negative phase of the North Atlantic Oscillation. Later on, the establishment of an oligo-mesotrophic seafloor environment is documented by the diminishing benthic foraminiferal accumulation rates associated with an increment in the abundances of Gyroidinoides altiformis. During a colder phase of the Little Ice Age (17th century), the relative abundances of the opportunistic foraminiferal species Bulimina inflata and Bulimina marginata can be related to high marine productivity, most probably due to enhanced winter mixing conditions. Finally, during the last 100 years, a faunal shift to eutrophication preferent species, and the persistent occurrence of Chilostomella mediterranensis, reflects a pronounced change in trophic conditions, characterized by high amounts of potentially low-quality organic matter in the seafloor, which are the result of a gradual temperature increase accompanied with enhanced terrigenous inputs.

A New biological proxy for deep-sea paleo-oxygen: Pores of epifaunal benthic foraminifera

The negative consequences of fossil fuel burning for the oceans will likely include warming, acidification and deoxygenation, yet predicting future deoxygenation is difficult. Sensitive proxies for oxygen concentrations in ancient deep-ocean bottom-waters are needed to learn from patterns of marine deoxygenation during global warming conditions in the geological past. Understanding of past oxygenation effects related to climate change will better inform us about future patterns of deoxygenation. Here we describe a new, quantitative biological proxy for determining ocean paleo-oxygen concentrations: the surface area of pores (used for gas exchange) in the tests of deep-sea benthic foraminifera collected alive from 22 locations (water depths: 400 to 4100 m) at oxygen levels ranging from ~ 2 to ~ 277 μmol/l. This new proxy is based on species that are widely distributed geographically, bathymetrically and chronologically, and therefore should have broad applications. Our calibration demonstrates a strong, negative logarithmic correlation between bottom-water oxygen concentrations and pore surface area, indicating that pore surface area of fossil epifaunal benthic foraminifera can be used to reconstruct past changes in deep ocean oxygen and redox levels.

Environmental instability during the latest Paleocene at Zumaia (Basque-Cantabric Basin): The bellwether of the Paleocene-Eocene Thermal Maximum

The Paleocene-Eocene transition is well represented in the bathyal Zumaia section (Basque-Cantabric Basin, Northern Spain), where numerous studies have documented the sedimentological, environmental and biotic effects of the Paleocene-Eocene Thermal Maximum (PETM). The extinction of more than half of the species of deep-sea benthic foraminifera has been previously reported, but the triggering causes and the exact sequence of events leading the to the extinction event still remain uncertain. The combined study of benthic foraminifera and geochemical proxies allowed us to assess the consequences of an extreme, global warming event, and to investigate its environmental precursors, with special attention to the analysis of the uppermost Paleocene.Geochemical and micropaleontological data indicate that environmental instability started ~42.6 kyr before the onset of the carbon isotope excursion (CIE) that officially marks the Paleocene/Eocene boundary. Perturbations during the late Paleocene include fluctuations in trophic and redox conditions, as well as in detrital input. Previous studies on calcareous nannofossils suggest that early warming started during the last ~18.8–12 kyr of the Paleocene. The gradual but rapid disappearance of benthic foraminifera reveals significant environmental stress during the last ~12 kyr of the Paleocene, and the main phase of extinction of benthic foraminifera coincided with the onset of the negative CIE. The gradual onset of the extinction is recorded across an interval with high % CaCO3 content, suggesting that carbonate corrosiveness was not the main trigger of the extinctions. Geochemical and micropaleontological data point to oligotrophy and increased temperatures in surface waters prior to the onset of the CIE. The increasing food demand of benthic foraminifera due to accelerated metabolic rates at higher temperatures was exacerbated by more oligotrophic conditions during the last ~12 kyr of the Paleocene, possibly triggering the gradual but rapid extinction, which culminated during the onset of the CIE, when carbonate dissolution was pervasive at Zumaia. Dilution of carbonate-rich material by terrigenous matter, combined with effects of dissolution, resulted in a very low % CaCO3 content in the lowermost 350 cm of the Eocene. The environmental changes observed during the late Paleocene are the bellwether of the PETM, and are in line with the early warming recorded prior to the PETM at other locations.

Presence of Foraminifera of Superfamily Komokioidea (Order Astrorhizida) in Colombian deep Caribbean waters.

Research regarding deep-sea benthic foraminifera in the Colombian Caribbean requires further development given the complete lack of information related to the different groups that constitute associations and the ecological functions they fulfill. For this purpose, a taxonomic description of Superfamily Komokioidea was composed from macrofauna samples from between 1,215 m and 3,179 m depth, obtained during the research cruise ANH-COL 4 and COL 5 carried out in 2014. Results showed foraminifera belonging to the three families: Komokiidae, Baculellidae, and Normaninidae, inclu-ding five genera (Lana, Komokia, Ipoa, Normaninam, and Catena) and five species (Lana neglecta, Komokia multiramosa, Normanina conferta, Ipoa fragila, and Catena piriformis). This study presents knowledge regarding deep-sea Colombian Caribbean benthic foraminifera, which to date have not been recorded from this region. Their depth distribution when compared with other studies from the Atlantic and Pacific, allows the expansion of taxonomic inventories and the characterization of biodiversity within poorly explored regions.

Ecology of deep-sea benthic foraminifera in the North Atlantic during the last glaciation: Food or temperature control

In this study, we explore the paleoecology of nineteen species and two species-groups of deep-sea benthic foraminifera in relation to bottom water temperature and food supply in the central North Atlantic during the last glaciation, ~60,000–28,000years BP. The study is based on core SO82-02GGC, taken from 1730m water depth on the western flank of Reykjanes Ridge. The climate of the investigated period was extremely unstable, interrupted by thirteen warmings and coolings, the so-called Dansgaard-Oeschger events. At SO82-02GGC, surface and bottom water temperatures varied with up to 5°C between the warm interstadials and the cold stadials. Surface productivity, as indicated by the flux of planktic foraminifera, varied with a factor of up to ten. The Dansgaard-Oeschger events had a significant impact on the benthic foraminiferal faunas, which experienced up to 70% replacement between the interstadials and stadials. Multivariate analysis reveals that the investigated species can be separated into two groups. Group 1, including Bulimina costata, Brizalina subspinescens, Epistominella decorata and Trifarina angulosa, was attracted to higher temperatures and high food supply. Group 2, including Pullenia bulloides, Valvulineria laevigata, and Melonis barleeanus, was attracted to colder water and low food supply. Three species belonging to the cold group, Cibicidoides wuellerstorfi, Oridorsalis umbonatus and Eponides tumidulus are almost exclusively confined to sediments rich in ice rafted detritus. A few species including Nonionella iridea and Epistominella vitrea show opportunistic behaviour. Most species are epifaunal to shallow-infaunal and live today in oligotrophic to mesotrophic habitats. Our investigations indicate that temperature was the primary factor responsible for the relative abundance and main grouping of species. However, four species show little influence by temperature and several, perhaps most, were clearly also affected by food supply.

WITHDRAWN: Ecology of deep-sea benthic foraminifera in the North Atlantic during the last glaciation: Food or temperature control

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Deep-sea benthic foraminiferal turnover across early Eocene hyperthermal events at Northeast Atlantic DSDP Site 550

Several extreme warming events, called hyperthermals, superimposed the warming trend of the early Paleogene. Deep-sea benthic foraminifera suffered major extinction during the most severe of those events, the Paleocene–Eocene Thermal Maximum, but their response to the following, less severe hyperthermals has been documented at very few locations. We evaluate and compare the benthic foraminiferal assemblages across ETM2 and H2 events at DSDP Site 550 in the NE Atlantic Ocean. The CIE and carbonate dissolution were more severe during ETM2 than during the H2 event.Early Eocene benthic foraminiferal assemblages were moderately diverse and strongly dominated by calcareous taxa, and they consisted of mixed infaunal and epifaunal morphogroups. They responded similarly to ETM2 and H2 events, showing a decrease in absolute abundance, an increase in the relative abundance of agglutinated taxa, indicative of more carbonate-corrosive waters, and a marked decrease in the percentage of Bolivinoides decoratus, suggesting a lower food supply during hyperthermals. However, some differences in their response were also noted. Oligotrophic taxa such as Nuttallides truempyi and Quadrimorphina profunda increased in relative abundance during early ETM2, whereas Globocassidulina subglobosa and Osangularia sp. 1, opportunistic species which may indicate pulsed food inputs, peaked during the H2 event. We conclude that both hyperthermal events represent a general disruption of an overall meso-oligotrophic environment, with less food reaching the seafloor combined with increased CaCO3 corrosivity of bottom waters. We did not find clear evidence for decreasing primary productivity during the hyperthermal events, and the apparent low food delivery to the seafloor may have been related to an increase in benthic foraminiferal metabolic rates due to the higher temperatures, with a more severe lack of food during ETM2 than during H2. The benthic foraminiferal response thus appears to be scaled to the magnitude of hyperthermals.

Stable isotope composition of deep-sea benthic foraminifera under contrasting trophic conditions in the western Mediterranean Sea

We have evaluated the environmental and biological processes affecting the stable oxygen and carbon isotope composition of live (Rose Bengal stained) and dead (unstained) tests of different benthic foraminiferal species from the western Mediterranean Sea. Samples were retrieved from comparable water depths but contrasting trophic regimes, comprising the meso- to eutrophic Alboran Sea and the oligo- to mesotrophic Mallorca Channel. The recorded isotope signatures mirror the average microhabitat depth of each species and reflect the specific gradients in pore water δ13C of dissolved inorganic carbon (δ13CDIC) and oxygen. Maximum δ13CDIC pore water gradients of up to − 2.3‰ were estimated under the influence of meso- to eutrophic conditions in the Alboran Sea. The δ13C signal of Uvigerina mediterranea reflects the opportunistic behavior of this species as its δ13C is shifted to more negative values at higher organic matter fluxes. Accordingly, the δ13C signal of U. mediterranea appears particularly suitable as a proxy for quantitative reconstructions of past trophic conditions. Previously reported ontogenetic increase of stable isotope values is confirmed for buliminid taxa (genera Uvigerina and Globobulimina), while it is largely absent in rotaliid taxa (genera Cicidides, Cibicidoides, and Melonis). Particularly strong metabolic fractionation is observed in small specimens of Uvigerina peregrina overprinting the pore-water δ13CDIC signal and resulting in steep ontogenetic δ13C gradients. The δ18O values of epifaunal taxa, which thrive under high dissolved oxygen concentrations, and the shallow to intermediate infaunal Melonis barleeanum, are up to 1.2‰ lower relative to equilibrium calcite. In epifaunal taxa, this depletion can be attributed to enhanced fractionation at high concentrations of metabolically utilizable oxygen.

Three-dimensional observation of foraminiferal cytoplasmic morphology and internal structures using uranium–osmium staining and micro-X-ray computed tomography

Abstract Benthic foraminifera are common protists that inhabit a broad environmental range of the seafloor. Because of their large biomass, these organisms play crucial roles in biogeochemical cycles, but our knowledge of their ecology and cell biology are still limited. One reason is that the calcareous or agglutinated tests (shells) of foraminifera hamper observing or measuring the cytoplasm from outside the organism. Here, we report the three-dimensional (3-D) observation of the cytoplasm and several ultrastructures of deep-sea benthic foraminifera using the combined techniques of micro-X-ray computed tomography (CT) and the osmium- and uranium-based cytoplasm-staining methods that are standard protocols for transmission electron microscope (TEM) observation. Osmium and uranium bind to organic membranes, proteins, and nucleic acids, rendering them visible by X-rays due to their high X-ray attenuation and enabling their reconstruction as 3-D images. This methodology revealed not only the external cellular morphology but also vacuoles and plugs inside the cell. Furthermore, volumetric calculation of cytoplasm and vacuoles is possible using the obtained CT data to evaluate their biomass and roles of vacuoles. Our method offers rapid (less than an hour in this study) evaluation of whole single or multiple foraminiferal cells and can be applied to investigate the biology and ecology of the foraminifera and other testate eukaryotes whose internal features are obscured by their external test structures.