Benthic Foraminiferal Abundance Research Articles

Response of inner shelf benthic foraminiferal community to different concentrations of dissolved oxygen under laboratory culture experiment

Dissolved oxygen, a vital parameter for a majority of marine organisms, may decline in the near future due to anthropogenic eutrophication in coastal waters. The effect of depleting dissolved oxygen on the marine benthic community is difficult to assess from field studies, as dissolved oxygen often co-varies with several other parameters, especially organic matter. The controlled laboratory culture experiments can help to assess the effect of a specific parameter on marine organisms. Foraminifera constitute a substantial fraction of the marine benthic organisms, and a few species are vulnerable to depleted oxygen. A majority of the previous culture experiments have used isolated specimens of individual benthic foraminiferal species. Although such studies helped to understand the response of individual species to a particular parameter, they have to be scaled up to understand the community-level response of benthic foraminifera. Here, we assess the community-level response of the shallow subtidal benthic foraminiferal community to five different oxygen concentrations (1.67 mL/L to 5.01 mL/L) in a laboratory culture experiment. The living benthic foraminiferal abundance was considerably high at the intermediate oxygen concentration, whereas it decreased at both the lower and higher concentrations. The decreasing dissolved oxygen caused poor preservation of dead benthic foraminifera due to a drop in pH. The relative abundance trend of the species belonging to the same genus was different, suggesting a species-specific response to the dissolved oxygen. The maximum abundance at 2.91 mL/L and the varying response of individual species clearly suggest a non-linear response of the benthic foraminiferal community to the dissolved oxygen.

Cretaceous southern high latitude benthic foraminiferal assemblages during OAE 2 at IODP Site U1516, Mentelle Basin, Indian Ocean

At Site U1516 (Mentelle Basin, southeast Indian Ocean, offshore western Australia), the International Ocean Discovery Program (IODP) Expedition 369 recovered an almost complete pelagic record of the Upper Cretaceous, including the Oceanic Anoxic Event 2 (OAE 2). To better understand paleoenvironmental changes across OAE 2, 32 samples were analysed for benthic foraminiferal abundance data that represent one of the few benthic foraminiferal datasets spanning the OAE 2 in the southern high latitudes.The OAE 2 interval at Site U1516 is characterized by an interval of low CaCO3 content that contains a prominent positive Carbon Isotope Excursion (CIE). The record of the OAE 2 can be subdivided in pre OAE 2, pre max-CIE, low CaCO3, and post low CaCO3 intervals. Through the Cenomanian–Turonian boundary, we document an extreme decline in benthic foraminifera during OAE 2, that is followed by a profound repopulation event in the post low CaCO3 interval.Benthic foraminiferal assemblages indicate an outer neritic to upper bathyal depositional environment. During the pre OAE 2 and pre max-CIE intervals, calcareous deep-water gavelinellids, lingulogavelinellids and gyroidinids are dominant. In the low-carbonate interval, the microfossil record documents a substantial increase in radiolaria and foraminifera are almost absent as only three out of nine samples contain benthic foraminifera. Changes in benthic foraminiferal assemblage composition are documented in the initial low CaCO3 interval, underlying the maximum CIE and associated interferences. Comparison of the pre- and post-CIE benthic foraminiferal assemblages highlights a distinct repopulation event during the post max- CIE interval mainly represented by the conspicuous increase in abundance of agglutinated taxa and Conorboides. Compared to other southern high latitude records, the dataset collected at Site U1516 represents one of the most complete benthic foraminiferal records across the OAE 2 that registers the Late Cretaceous environmental changes in the Southern Hemisphere.

A 600 kyr reconstruction of deep Arctic seawater δ18O from benthic foraminiferal δ18O and ostracode Mg ∕ Ca paleothermometry

Abstract. The oxygen isotopic composition of benthic foraminiferal tests (δ18Ob) is one of the pre-eminent tools for correlating marine sediments and interpreting past terrestrial ice volume and deep-ocean temperatures. Despite the prevalence of δ18Ob applications to marine sediment cores over the Quaternary, its use is limited in the Arctic Ocean because of low benthic foraminiferal abundances, challenges with constructing independent sediment core age models, and an apparent muted amplitude of Arctic δ18Ob variability compared to open-ocean records. Here we evaluate the controls on Arctic δ18Ob by using ostracode Mg/Ca paleothermometry to generate a composite record of the δ18O of seawater (δ18Osw) from 12 sediment cores in the intermediate to deep Arctic Ocean (700–2700 m) that covers the last 600 kyr based on biostratigraphy and orbitally tuned age models. Results show that Arctic δ18Ob was generally higher than open-ocean δ18Ob during interglacials but was generally equivalent to global reference records during glacial periods. The reduced glacial–interglacial Arctic δ18Ob range resulted in part from the opposing effect of temperature, with intermediate to deep Arctic warming during glacials counteracting the whole-ocean δ18Osw increase from expanded terrestrial ice sheets. After removing the temperature effect from δ18Ob, we find that the intermediate to deep Arctic experienced large (≥1 ‰) variations in local δ18Osw, with generally higher local δ18Osw during interglacials and lower δ18Osw during glacials. Both the magnitude and timing of low local δ18Osw intervals are inconsistent with the recent proposal of freshwater intervals in the Arctic Ocean during past glaciations. Instead, we suggest that lower local δ18Osw in the intermediate to deep Arctic Ocean during glaciations reflected weaker upper-ocean stratification and more efficient transport of low-δ18Osw Arctic surface waters to depth by mixing and/or brine rejection.

Benthic Foraminiferal Distribution and their Environmental Significance of Selected Red Sea Coastal Ecosystems, Saudi Arabia

The present study uses benthic foraminiferal abundance and diversity indices in the coastal bottom sediments of the Farasan Island, Southern Cornich of Jeddah (SCJ) and Rabigh areas, Saudi Arabia to identify the ecological controls on their distribution. A total of 20 recent sediment samples were collected from the studied sites. Grain size analysis, CaCO3 content and organic matter were determined. Multivariate analyses were applied to test and represent the diversity indices and distribution of benthic foraminiferal assemblage. Two main benthic foraminiferal assemblages; A and B have been distinguished. The assemblage-A includes a high abundance of T. trigonula (33%), S. communis (30%), Q. bosciana (21%), E. striatopunctatum (18%) with low diversity indices in the Rabigh coastal sediments indicating high ecological stress. The Farasan ecosystem is dominated by sub-assemblage-B1 P. planatus (55%), S. orbiculus (27%), N. calcar (15%), Q. limbata (14%), which totally ranges between 60%-82%, indicating a highly oxic marine environment and normal ecology stress. Sub-assemblage-B2 such as P. planatus (39%),C. hemprichii (26%), V. neostriata (15%),Q. costata (10%) dominate the Southern Corniche of Jeddah (SCJ) with relatively high diversity indices, indicating moderate stress ecology or unstable environmental conditions.The cluster and the canonical correspondence analyses (CCA) indicated that the distribution and diversity pattern of benthic foraminifera are controlled by the enrichment of organic matters, CaCO3 contents, and sediments grain size characteristics. The concept of differentiation between these ecosystems is probably related to several factors, such as seasonal flash floods carrying a considerable amount of dissolved nutrients and mangrove communities on the Rabigh coast. In contrast, it is negligible on the south Jeddah coast and absence on Farasan Island.

High-frequency modification of the central Mediterranean seafloor environment over the last 74 ka

Here we present a high-resolution record of benthic foraminiferal assemblages for the last 74 kyr from the Sicily Channel Ocean Drilling Program Leg 160 Site 963. Benthic foraminiferal results are compared with geochemical (benthic and planktic δ 18 O and δ 13 C) and calcareous plankton data, previously acquired on the same marine core sediments. Within the succession, three benthic foraminifera compositional zones were defined. Temporal changes in the assemblages are interpreted in the context of the modification of subtropical and temperate climate systems that affected the Mediterranean thermohaline circulation. A close connection between bottom conditions in the Sicily Channel and eastern Mediterranean Sea is evident in two intervals, characterized in the ODP Site 963 by reduced oxygen conditions. The first one, around 53–51 ka, is tentatively attributed to the ‘missing’ sapropel S2 while the second, between 35 and 29 ka, is marked by short and recurrent episodes of bottom-water oxygen decrease. Both are related to a weakening of the intermediate circulation in the Sicily Channel connected with relatively high northern hemisphere summer insolation and increase in Nile River discharge, which inhibited vertical mixing and intermediate water ventilation in Eastern Mediterranean Sea. Over the last deglaciation, the African humid period (AHP) and the sea level rise, also influenced the water mass structure in the Sicily Channel and a reduction of the bottom ventilation is suggested by a strong reduction of deep-water Miliolids. Decreased bottom oxygen levels, which testifies for a weakening of intermediate circulation in Sicily Strait, also characterized the interval corresponding to S1 deposition. Yet, the strong decrease of benthic foraminiferal abundance related to a low surface water trophic level, appears to be conditioned by the reduction of trophic levels in the western Mediterranean. The very high relative abundance of U. mediterranea recorded during this interval is explained by the availability of organic matter during a limited short year period and/or the availability of more degraded organic matter from river runoff. In general, compositional data analysis highlighted a quite complex response of benthic foraminifera to paleoclimatic changes. However, changes in the benthic foraminiferal assemblages recorded during the last glacial are coherent with surface paleoproductivity dynamics connected with D-O oscillation, and support oligotrophic, meso-eutrophic and oligo-mesotrophic conditions during the early interstadials, late interstadials and stadials, respectively. • High-resolution ODP963 (Sicily Channel) Last Glacial to Holocene benthic record. • Dansgaard-Oeschger imprints in bottom environments. • Connection between western and eastern Mediterranean dynamics. • Relationships between Levantine Intermediate Water flow and bottom ventilation.

Abrupt changes in the southwest monsoon during Mid-Late Holocene in the western Bay of Bengal

• Variation in southwest monsoon governs the surface circulation of Bay of Bengal. • Reduction in fresh water flux between ∼5.9 and ∼3.7 kyr. • A progressive increase in fresh water flux after ∼3.7 kyr. • Abrupt increase in fresh water flux related to RWP and MWP extreme events. The present work aims to understand the variation in the southwest monsoon (SWM) and the surface water hydrography around the western Bay of Bengal (WBoB). In this study, we used various micropaleontological [planktonic foraminifera relative abundance, planktonic and benthic foraminiferal abundance (PFA and BFA), planktonic/benthic (P/B) ratio], sedimentological [sand %] and oxygen isotope of Globigerinoides ruber (δ 18 O G.ruber ) proxies in a marine sediment core (SK336/3) since last ∼6 kyr before present (BP). The δ 18 O G.ruber , PFA, BFA, and the planktonic foraminifera relative abundance records suggest the reduced freshwater input corresponding to an aridification phase during ∼5.9–3.7 kyr BP, possibly related to the weakening of the SWM in the WBoB. The WBoB has reworded comparatively wetter conditions since ∼3.7 kyr BP suggests increased freshwater input centering around ∼1.8 and ∼0.9 kyr BP, associated with the SWM intensification during the Roman and Medieval Warm Periods (RWP and MWP), respectively. The relative abundance of planktonic foraminifera correlates well with a sand percentage between ∼5.9 and ∼3.7 kyr BP, suggesting a productivity decline due to terrigenous dilution. Significant periodicities of ∼418, ∼165, ∼139, ∼109, ∼97, and ∼86 years are found in the spectral analysis of planktonic foraminiferal relative abundance and δ 18 O G.ruber time-series, corresponding to hydrographic changes in the WBoB due to the influence of solar-driven cyclicity in the SWM during the last ∼6 kyr BP. Comparison of our multi-proxy signatures with other paleo-proxy records during the mid-late Holocene reveals large-scale climate variability in the Northern Hemisphere, related to the changes in solar activity.

Seasonal distribution of benthic foraminifera at Nana Layja, Kachchh, Gujarat – India

Benthic foraminiferal abundance from three sites at Nana Layja from the coast of Kachchh was studied over a period of one year to determine the seasonal variability. All the three sites were dominated by Ammonia beccarii (Brunnich, 1772), Pararotalia calcariformata (Le Calvez, 1949), Elphidium advenum (Haynes, 1973), Eponides repandus (Montfort, 1808) and Quinqueloculina bosciana (d'Orbigny, 1826). These showed considerable seasonal variability at the studied three sites. The maximum total foraminiferal abundance was found on December 2016 while the minimum was observed on June 2017. A. beccarii , P. calcariformata , and E. repandus exhibited a seasonal pattern similar to the total foraminiferal abundance. Whereas, E. advenum and Q. bosciana showed a different pattern of abundance with the minimum and maximum abundances found in December 2016 and June 2017, respectively. Other two rare species recorded were Spiroloculina sp. 1 (Alcide d'Orbigny, 1826) and Rosalina globularis (Alcide d'Orbigny, 1826) in all the seasons. Species diversity analysis showed that the three sites are rich in species variability with a high Shannon−Weiner Index and low Evenness Index. The physicochemical characterization of seawater collected from three sites showed distinct seasonal variations.

Deglacial to Holocene environmental changes in the northern Ligurian Sea: The dual influence of regional climate variability and large-scale intermediate Mediterranean circulation

The sedimentary archives of the Mediterranean Sea record periodic deposits of organic-rich deposits, called sapropels in the eastern basin and organic-rich layers (ORL) in the western basin. Changes in both the Mediterranean circulation and inputs of fresh water through borderlands rivers under more humid climate, are important mechanisms to explain those events. The last ORL and sapropel S1 have different timing, respectively from ~14.5 to 9 Ka and from ~10 to 6 Ka, presumably due to different forcing factors in the western basin (i.e., melting of Alps ice). Here we present a high-resolution study of a marine sediment core located off the mouth of the Var River, one of the most dynamic river system of the northern borderland of the western Mediterranean Sea. We applied a multi-proxy approach based on benthic foraminiferal assemblages, foraminiferal δ18O and δ13C, grain size analyses, organic carbon content and XRF elemental data to decipher the regional climate signals from the basin-scale intermediate circulation signature. Our results do not show large river inputs at the timing of the last ORL deposit. On the opposite, foraminiferal and geochemical evidence indicate that the 11–6 kyr period, concomitant to Sapropel S1 event in the Eastern Mediterranean, was characterised by high river activity and low ventilated bottom waters at the studied location. Additionally, our results characterized the last 6 ka with large scale episodes of more active bottom water ventilation due perhaps to enhanced wind activity under an overall cooler climate.Time series analyses were computed from stable isotopes, Ca/Ti XRF ratio and foraminifera abundances. They show common frequencies peaks (2.2–3, 1.1–1.2, 0.9–1.0, and 0.4–0.5 kyr) most likely related to the solar activity. Also, a specific frequency band (1.5–1.6 kyr) was only recorded in benthic foraminiferal abundance and stable isotopic records. This was preferentially attributed to an oceanic-driven internal forcing.

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

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

A highly diverse living benthic foraminiferal assemblage in the oxygen deficient zone of the southeastern Arabian Sea

The exchange of seawater between the Arabian Sea and the Bay of Bengal, creates a strong seasonality in the southeastern Arabian Sea, including the oxygen deficient zone (ODZ) at intermediate depth. Here, we assess the effect of this strong seasonality on benthic foraminifera living within ODZ of the southeastern Arabian Sea. We delineate five benthic foraminiferal assemblages characterizing different dissolved oxygen levels. A distinct depth zonation in living benthic foraminiferal species is observed within the southeastern Arabian Sea ODZ. Cassidulina laevigata, Cassidulina carinata and Eponides umbonatus dominate shallow depth, hypersaline, oxygen rich, warm water environment with low organic matter (%Corg) availability. The upper slope intense suboxic zone with moderate %Corg abundance, is characterized by Bolivina seminuda, Hopkinsinella glabra and Eubuliminella exilis. A similar suboxic zone, but with high %Corg concentration on the middle slope, is represented by Rotaliatinopsis semiinvoluta, Hopkinsinella glabra and Epistominella exigua. The lower slope (~ 1000–1500 m) assemblage is dominated by rectilinear species, namely Bulimina arabiensis, Bulimina elegans and Bolivina earlandi and represents a comparatively higher dissolved oxygen environment (1–2 mL/L) with high organic carbon at deeper water depths. Bolivina earlandi, Bulimina aculeata and Globocassidulina subglobosa dominate deep-water benthic foraminifera population, where bottom water is oxygen rich (> 2 mL/L) with plenty of organic matter and the lowest bottom water temperature and salinity. The living benthic foraminiferal abundance as well as diversity increases manifold within the southeastern Arabian Sea ODZ and may be attributed to the strong seasonality. The depth habitat of the dominant living benthic foraminifera has also been reported.

Dispersal potential of neritic benthic foraminifera in the coastal areas of the Japanese Islands and its application to paleoenvironmental studies

In this study, we evaluated the dispersal potential of both modern and fossil benthic foraminifera in lagoon and bay environments in the Japanese Islands. Our investigations of living (stained) benthic foraminifera in Maizuru Bay (central Japan) revealed complicated lateral distributions and high temporal variation among common benthic species. Benthic foraminiferal communities in bay environments are often characterized by strong lateral trends in species richness due to frequent fluctuations in the salinity and/or dissolved oxygen content of the hypolimnion. However, our results do not show the existence of similar trends in Maizuru Bay. In fact, the dispersal of opportunistic species during intense coastal winter mixing events may account for this complexity in species diversity and evenness. Sediment trap and plankton tow observations in Lake Nakaumi (southwestern Japan) imply that benthic foraminifera utilize suspended organic matter aggregates as mobile substrates for passive dispersal. Furthermore, we examined three horizons of high fossil benthic foraminiferal abundance in the Aso-kai Lagoon (central Japan) dating to ca. AD 1070, 1400, and 1570, which were nearly coincident with coastal mixing events that were likely caused by enhanced East Asian winter monsoons. Many of the neritic benthic foraminifera in our study region appear to possess high dispersal potential, suggesting that the distribution of opportunistic benthic foraminifera may be useful in inferring the past status of the East Asian winter monsoon.

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

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

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

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

Assessing the ecological preferences of agglutinated benthic foraminiferal morphogroups from the western Bay of Bengal

Agglutinated benthic foraminiferal morphogroups have often been used as a proxy in paleoecological studies. The response of various agglutinated morphogroups may, however, vary regionally. Here we report the ecological preferences of agglutinated morphogroups from the fresh-water influx dominated western Bay of Bengal. The abundance of both living (rose-Bengal stained) as well as dead agglutinated benthic foraminifera and their morphogroups, has been studied in a total of 42 core-top samples from the depth range of 25–2540 m, covering the entire shelf and slope. Agglutinated foraminifera are divided into four morphogroups (A–D). Out of these, two morphogroups, namely B and C are sub-grouped into (B1–B4) and (C1–C2), respectively. We report exceptionally high agglutinated benthic foraminiferal abundance on the slope of the western Bay of Bengal. The depth and temperature affect the total abundance of agglutinated benthic foraminifera. Morphogroups A (tubular), B1 (globular), and B3 (planispiral/trochospiral, only dead) are positively correlated with water depth and negatively correlated with the ambient temperature, suggesting its preference for deeper waters. Both the dead and living assemblages of morphotype B2 as well as C1, are negatively correlated with dissolved oxygen (DO) and positively correlated with organic carbon (%Corg) suggesting its preference for depleted oxygen environment. The morphotype B4 prefers relatively deeper depths. The morphotype C2 (quinqueloculine/milioline forms) is positively correlated with DO, temperature, coarse fraction and organic carbon/nitrogen, and negatively correlated with %Corg and water depth, thus indicating that species belonging to this morphotype prefer shallow water, oxic, coarse-grained environment. The relative abundance of morphogroup D (dead) is negatively correlated with ambient salinity, thus suggesting its preference for hyposaline conditions in the shallow marine environment. The study suggests a clear ecological preference of a majority of the agglutinated morphotypes and morphogroups and thus their potential application in paleoecological interpretations.

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

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

Oceanographic influences on the stability of the Cosgrove Ice Shelf, Antarctica

Ferrero Bay, located in eastern Pine Island Bay (PIB) of the Amundsen Sea Embayment, is one of the largest and southernmost fjords yet studied in Antarctica. High-resolution multibeam swath bathymetric data, chirp sonar sub-bottom profiles, and three Kasten cores were collected in Ferrero Bay during the IB Oden Southern Ocean 2009–2010 cruise (OSO0910). Core KC-15 from the inner bay yielded two carbonate ages providing a minimum age for ice sheet recession from this sector of PIB by ~11 cal. kyr BP. In total, seven additional acid insoluble organic (AIO) fraction radiocarbon ages provide a linear age model with an R2 of 0.99. Variations in magnetic susceptibility, grain size, total organic carbon (TOC) and nitrogen, diatom abundance, and foraminiferal assemblage and abundance are used to interpret glacial history and paleoceanographic conditions. Grounding line retreat was characterized by advection of planktic foraminifera beneath an ice shelf that may have extended across the middle continental shelf. Following initial deglaciation, the Cosgrove Ice Shelf covered Ferrero Bay, and productivity was virtually absent during the mid-Holocene, while benthic foraminifera indicate periodic incursion of warm Circumpolar Deep Water. The ice shelf persisted until 2.3 cal. kyr BP, when TOC and diatom abundance increased as the bay opened and coastal areas deglaciated. Abundant diatoms demonstrate open marine conditions and seasonal sea ice during the recent open water phase, while high benthic foraminiferal abundance indicates active benthos. The retreat of the Cosgrove Ice Shelf was out of phase with Antarctic Peninsula ice shelves and ice-core proxy temperatures, implying that it did not respond to Holocene climate events but rather to the influence of Circumpolar Deep Water and possibly to internal glacial dynamics.

Micropaleontological evidence for redox changes in the OAE3 interval of the US Western Interior: Global vs. local processes

The Coniacian-Santonian interval has been proposed as the youngest of the Cretaceous ocean anoxic events (OAE3), but this designation has long been debated. OAE3 is associated with a long-lasting (∼3 myr) succession of black shales from the central and South Atlantic, Caribbean region, and the North American Western Interior; in the Western Interior it is characterized by an abrupt increase in total organic carbon (TOC) and corresponding trace metal indicators for anoxia. However, the modern concept of OAEs is predicated on detection of global carbon cycle perturbations as recorded by substantial carbon isotope excursions (CIE), and the protracted Coniacian-Santonian black shale interval does not have a large CIE. A more conservative definition of OAE3 might limit the event to the modest positive carbon isotope excursion restricted to the upper Coniacian Scaphites depressus Ammonite Zone. Trace metal proxies suggest that oxygen levels abruptly declined prior to the onset of this CIE in the Western Interior Sea (WIS), but it is unknown whether regional anoxic conditions were confined to sediments/pore waters, or how anoxia may have affected the biota. In an effort to characterize the oxygenation history of the WIS and to better understand the nature of the hypothesized OAE3, we present micropaleontological evidence of declining oxygen in bottom waters prior to the event using benthic foraminifera, which are sensitive to dissolved oxygen. Changes in benthic foraminiferal abundances suggest a decline in oxygen at least 1-myr prior to the CIE (including a nadir immediately below the start of the excursion), improving bottom water oxygen during the CIE, and re-establishment of persistent anoxia following the isotope excursion. Anoxia endured for nearly 3 myr in the central seaway, showing some signs of recovery toward the top of the Niobrara Formation. Our findings suggest that declining oxygen concentrations in the seaway eventually reached a tipping point, after which dissolved oxygen quickly dropped to zero.The late Coniacian CIE is an exception to the trend of declining oxygen in the WIS, and part of a larger pattern in the oxygenation history of the Niobrara Formation which suggests that it does not adhere to standard black shale models. Transgressive periods, including the Fort Hays Limestone and the lower limestone unit of the Smoky Hill Shale (which corresponds to the CIE) are relatively oxic, while periods of highstand (i.e., most of the Smoky Hill) correspond to deteriorating oxygen conditions. This contrasts with the standard black shale model for sea level and oxygen, where transgressions typically correlate with maximum TOC enrichment, interpreted to result from both sediment condensation and oxygen deficiency. The association of global carbon burial/anoxia (as indicated by carbon isotopes) with a regional increase in oxygen and decrease in organic matter preservation is reminiscent of the Cenomanian-Turonian Greenhorn Limestone, which contains OAE2. In both cases, the facies are not typical black shales, but instead have appreciable carbonate content. Western Interior redox trends support the rejection of the original concept of a protracted Coniacian-Santonian OAE3 because it is not a distinct “event.” Increasing local oxygen during the late Coniacian CIE also argues against a narrower OAE designation for this event, because the excursion can't be tied to anoxia here or anywhere else it has been described. Nevertheless, the Late Coniacian Event (as we prefer to call this CIE) still represents an important perturbation of the global carbon cycle. This is emblematic of the shift away from widespread, discrete anoxic events during the ongoing paleoceanographic reorganization of the Late Cretaceous, even as large carbon cycle perturbations continued.

Assessing the suitability of benthic foraminiferal morpho-groups to reconstruct paleomonsoon from Bay of Bengal

Temporal changes in benthic foraminiferal morpho-groups were suggested as an effective proxy to reconstruct past monsoon intensity from the Arabian Sea. Here, in order to test the applicability of temporal variation in morpho-groups to reconstruct past monsoon intensity from the Bay of Bengal, we have documented recent benthic foraminiferal distribution from the continental shelf region of the northwestern Bay of Bengal. Based on the external morphology, benthic foraminifera were categorized into rounded symmetrical (RSBF) and angular asymmetrical benthic foraminifera (AABF). Additionally, a few other dominant groups were also identified based on test composition (agglutinated, calcareous) and abundance (Asterorotalids and Nonions). The relative abundance of each group was compared with the ambient physico-chemical conditions, including dissolved oxygen, organic matter, salinity and temperature. We report that the RSBF are abundant in comparatively warm and well oxygenated waters of low salinity, suggesting a preference for high energy environment, whereas AABF dominate relatively cold, hypersaline deeper waters with low dissolved oxygen, indicating a low energy environment. The agglutinated foraminifera, Asterorotalids and Nonions dominate shallow water, low salinity regions, whereas the calcareous benthic foraminiferal abundance increases away from the riverine influx regions. Food availability, as estimated from organic carbon abundance in sediments, has comparatively less influence on faunal distribution in the northwestern Bay of Bengal, as compared to dissolved oxygen, temperature and salinity. We conclude that the factors associated with freshwater influx affect the distribution of benthic foraminiferal morpho-groups in the northwestern Bay of Bengal and thus it can be used to reconstruct past monsoon intensity from the Bay of Bengal.

Foraminiferal and nannofossil paleoecology and paleoceanography of the Cenomanian–Turonian Eagle Ford Shale of southern Texas

The Upper Cretaceous of central Texas is dominated by a broad, shallow carbonate platform called the Comanche Platform that occupies an important gateway between the epeiric Western Interior Seaway (WIS) of North America to the open-marine Gulf of Mexico/Tethys. We investigated the Cenomanian–Turonian Eagle Ford Shale on and adjacent to the Comanche Platform to determine whether the Eagle Ford Shale has an affinity with the Western Interior, and if so, determine where the transition from Western Interior to open ocean is located. We were also interested in the relationship, if any, between the organic-rich facies of the Eagle Ford and Oceanic Anoxic Event 2 (OAE2). Our work is based on quantitative foraminiferal population counts and associated sedimentary particles (including inoceramid prisms, sand, glauconite, and pyrite grains), calcareous nannofossil assemblages, carbon isotopes, and total organic carbon (TOC) from three sites across a range of paleowater depths: an outcrop in Lozier Canyon in Terrell County, west of Langtry, TX, an outcrop at Bouldin Creek outside of Austin, TX, and Swift Energy's Fasken A #1H core in Webb County, TX.The highest TOC in the Eagle Ford occurs before the onset of OAE2 (6% at Lozier Canyon, 7% at both Bouldin Creek and the Fasken Core) and then declines steadily through the rest of the section (except for a small increase at the end of OAE2 at Lozier and a fairly large post-OAE2 increase at Bouldin Creek). Nannofossil paleoproductivity indicators (%Zeugrhabdotus and %Biscutum) track TOC at Bouldin Creek and in the Fasken Core and display similar trends to those observed in the Western Interior Seaway to the north. Benthic foraminiferal abundances increase as TOC decreases and the lithology shifts from laminated black shale to bioturbated light gray shale; low-oxygen-tolerant infaunal Neobulimina spp. appear first and gradually increase in abundance; epifaunal benthics appear soon after. This oxygenation trend continues through the OAE2 interval and the upper Eagle Ford contains a diverse epi- and infaunal benthic foraminiferal assemblage and macrofossil assemblage. This trend of decreasing TOC and nannofossil paleoproductivity indicators coupled with increasing benthic foraminiferal abundance and diversity (and seafloor oxygenation) corresponds to rising sea level.Based on foraminiferal and nannofossil events, TOC trends, and changes in lithology, both platform sites have a strong affinity with the Western Interior, with Lozier Canyon being the most similar; the Fasken Core bears all the characteristics of an open ocean site, except for the fact that peak TOC occurs before OAE2. This suggests that the oceanographic boundary between WIS and Tethys can be placed on the edge of the Comanche Platform.Productivity was likely driven by bathymetry-induced upwelling caused by restriction between the WIS and Tethys during times of low sea level; as sea level rose, upwelling diminished and productivity decreased. This explains why the Fasken Core, adjacent to the platform margin and in the center of this upwelling zone, displays the same TOC trends as the platform sites. Organic carbon content in the seaway was controlled by stratification and enhanced preservation, but this was also reduced by rising sea level, which is why the two areas show parallel trends.

Aptian–Albian benthic foraminifera from DSDP Site 364 (offshore Angola): A paleoenvironmental and paleobiogeographic appraisal

This work presents a paleoenvironmental and paleobiogeographical appraisal of the benthic foraminiferal assemblages recovered from the Aptian–Albian carbonate-dominated succession of Deep Sea Drilling Project (DSDP) Site 364, located in the Kwanza Basin (offshore Angola). Forty-two species were identified within the studied interval, and their stratigraphic distributions enabled the recognition of two events of diversification, the first within the latest Aptian and the second within the late Albian. Q-mode and R-mode cluster analyses of the benthic foraminifera allowed to recognize three associations (Bathysiphon sp., Gyroidinoides infracretaceus and Kadriayina gradata), which seem to have been mainly controlled by paleobathymetry. The studied fauna is characteristic of neritic to upper bathyal depths. At and/or close to black shale levels low values of benthic foraminiferal abundance and species richness could be indicative of low-oxygen (dysoxic) bottom water conditions. The black shales deposition in Site 364, cores 42 to 39 (likely related to an Aptian dysoxic-anoxic event), occurred at shallow to middle neritic water depths. Some typical tropical/subtropical planktic biostratigraphic markers are missing from specific stratigraphic intervals of Site 364, in which shallow (neritic) water depths were inferred. Their absence from the northern South Atlantic Ocean (north to the Walvis Ridge–Rio Grande Rise) may be rather a result of their deeper-dwelling habitat preferences, than to the influx of colder-water masses from the southern South Atlantic Ocean, as previously reported. Paleobiogeographically, the studied Aptian–Albian benthic foraminifera present a predominant Austral/Transitional affinity, in contrast to the evidence of the planktic foraminifera, which indicate the influence of tropical/subtropical conditions in surface waters.