Abundance Of Foraminifera Research Articles

MIOCENE NERITIC BENTHIC FORAMINIFERAL COMMUNITY DYNAMICS, CALVERT CLIFFS, MARYLAND, USA: SPECIES POOL, PATTERNS AND PROCESSES

ABSTRACTThe presence/absence and abundance of benthic foraminifera in successive discrete beds (Shattuck “zones”) of the Miocene Calvert and Choptank formations, exposed at the Calvert Cliffs, Maryland, USA, allows for investigation of community dynamics over space and time. The stratigraphic distribution of benthic foraminifera is documented and interpreted in the context of sea-level change, sequence stratigraphy, and the previously published distribution of mollusks. Neritic benthic foraminiferal communities of four sea-level cycles over ∼4 million years of the middle Miocene, encompassing the Miocene Climatic Optimum and the succeeding middle Miocene Climate Transition, are dominated by the same abundant species. They differ in the varying abundance of common species that occur throughout most of the studied section and in the different rare species that appear and disappear. Transgressive systems tracts (TSTs) have higher species diversity than highstand systems tracts (HSTs) but much lower density of specimens. In contrast to some previous research, all beds in the studied section are interpreted as being from the inner part of a broad, low gradient shelf and were deposited at water depths of less than ∼50 m. It is suggested that species are recruited from a regional species pool of propagules throughout the duration of TSTs. Recruitment is curtailed during highstands leading to lower diversity in the HSTs.

Planktic Foraminiferal and Pteropod Contributions to Carbon Dynamics in the Arctic Ocean (North Svalbard Margin)

Planktic foraminifera and shelled pteropods are some of the major producers of calcium carbonate (CaCO3) in the ocean. Their calcitic (foraminifera) and aragonitic (pteropods) shells are particularly sensitive to changes in the carbonate chemistry and play an important role for the inorganic and organic carbon pump of the ocean. Here, we have studied the abundance distribution of planktic foraminifera and pteropods (individuals m–3) and their contribution to the inorganic and organic carbon standing stocks (μg m–3) and export production (mg m–2day–1) along a longitudinal transect north of Svalbard at 81° N, 22–32° E, in the Arctic Ocean. This transect, sampled in September 2018 consists of seven stations covering different oceanographic regimes, from the shelf to the slope and into the deep Nansen Basin. The sea surface temperature ranged between 1 and 5°C in the upper 300 m. Conditions were supersaturated with respect to CaCO3(Ω > 1 for both calcite and aragonite). The abundance of planktic foraminifera ranged from 2.3 to 52.6 ind m–3and pteropods from 0.1 to 21.3 ind m–3. The planktic foraminiferal population was composed mainly of the polar speciesNeogloboquadrina pachyderma(55.9%) and the subpolar speciesTurborotalita quinqueloba(21.7%),Neogloboquadrina incompta(13.5%) andGlobigerina bulloides(5.2%). The pteropod population was dominated by the polar speciesLimacina helicina(99.6%). The rather high abundance of subpolar foraminiferal species is likely connected to the West Spitsbergen Current bringing warm Atlantic water to the study area. Pteropods dominated at the surface and subsurface. Below 100 m water depth, foraminifera predominated. Pteropods contribute 66–96% to the inorganic carbon standing stocks compared to 4–34% by the planktic foraminifera. The inorganic export production of planktic foraminifera and pteropods together exceeds their organic contribution by a factor of 3. The overall predominance of pteropods over foraminifera in this high Arctic region during the sampling period suggest that inorganic standing stocks and export production of biogenic carbonate would be reduced under the effects of ocean acidification.

Investigation of sedimentary records of Hurricane Irma in sinkholes, Big Pine Key, Florida

Few paleotempestological studies have focused on coastal sinkholes, a common feature in Florida, which can receive and preserve storm overwash sediments. The major goal of this research is to improve our understanding of the characteristic signatures of storm sediments in sinkholes thereby determining reliability of these environments as proxies for hurricanes. Hurricane Irma as a category 5 storm provides an excellent case study for characterizing storm deposits in sinkholes on Big Pine Key. We cored at four sinkholes along a 350 m transect normal to the shoreline. Core sediments were characterized using physical description, short-lived radioisotope dating, sediment grain size analysis, loss-on-ignition, microfossil analysis, and x-ray fluorescence elemental analysis. We found that Irma deposits had higher abundances of marine foraminifera, less total organic matter and elevated Si/Al and Ca/Ti ratios, compared to pre- or post-Irma sediments. In addition, there was a thinning of the storm sediments along the inland transect. Consequently, we propose that sinkholes, particularly those that are closer to the shoreline, can provide reliable sites for paleotempestology studies.

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.

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

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

Paleoenvironmental changes and biotic response to Aptian–Albian episodes of accelerated global change: Evidence from the western margin of the proto-North Atlantic (central-eastern Mexico)

The Aptian–Albian interval represents a time of distinctive atmospheric and oceanic changes. A major perturbation of the carbon cycle induced by intense volcanic activity produced episodes of environmental change affecting the abundance and evolution of marine plankton. Several studies based on pelagic and hemipelagic sections have used biostratigraphic events and carbon isotope stratigraphy tools to identify biotic responses to environmental perturbations. Few studies have included Aptian–Albian planktic microfossil communities and paleoenvironmental changes in Mexico, a region that was part of the western proto-North Atlantic margin. The aim of this study is to interpret paleoenvironmental and paleoceanographic conditions through a microfacies analysis of a carbonated succession of the Tamaulipas Formation from central-eastern Mexico (Tampico-Misantla Basin), within a temporal framework based on planktic foraminiferal and colomiellids biostratigraphy.The studied section, 92 m thick, consists of a continuous pelagic succession. Facies contain abundant planktic microfossils and span the stratigraphic interval between the Globigerinelloides blowi and Ticinella praeticinensis Zones. The Aptian/Albian Boundary in the studied section was established on the highest occurrence (HO) of planktic foraminifera such as Paraticinella rohri and the presence of Microhedbergella spp., followed by the lowest occurrence (LO) of colomiellids such as Colomiella recta.Detailed quantification of microfossil assemblages reveals variations in abundance of planktic foraminifera, radiolarians, praecolomiellids, colomiellids, dinocyst and echinoderm fragments. These variations related to fabric characterization and bioturbation indexes allow us to infer fluctuations in ancient trophic conditions in the water column, which might be associated with episodes of global environmental change such as Oceanic Anoxic Events.

Foraminiferal Abundance at the Western Water of Kai Islands, Molucca Province, Related to Oceanographic Condition

Foraminifera is a single-celled marine organism known as a potential proxy for (paleo)environment and (paleo)oceanography conditions. It also has been widely used as an indicator of coral reef health. We analyzed microfauna foraminifera from nine core top of marine sediments. Marine sediments have been collected by gravity core from western Water of Kai Islands, on board Geomarin III of MGI. The study aims to understand the microfaunal community and the oceanographical condition of Kai islands. The result indicates the high abundance and diversity of foraminifera, comprised of 95 species, including 28 species of planktonic and 67 benthic species. Planktonic type is very dominant (95.4% on average), typical for a bathyal environment. The dominant species are Neogloboquadrina dutertrei (21.21% on average), Globorotalia menardii (16.67% on average), Globigerina bulloides (11.73%), and Pulleniatina obliqueloculata (7.83%). Those are indicator species for a high productivity environment. However, Globigerinoides ruber, an oligotrophic warm water type, is also abundant (13.86% on average). Furthermore, the dominant genera of benthic types are Bolivina, Bulimina, dan Uvigerina (1.2% on average). This finding indicates relatively eutrophic and warm water conditions of west waters surrounding Kai Islands, with dysoxic bottom water conditions.

The relationship between paleoclimate change and paleosedimentary environment identification in coastal areas

Based on the close relationship between paleoclimate change and paleosedimentary environment, the relationship and influence between paleoclimate change and paleosedimentary environment identification in coastal areas were further studied. Taking the coastal areas of Zhejiang Province as the study area, the soil samples of the coastal areas of Zhejiang Province were collected by BZK1 borehole, and the samples were preliminarily treated and identified by optical microscope. The foraminifera, Ostracoda, and grain size were identified, and the paleosedimentary environment was analyzed by mapping. The results show that the coastal strata in Zhejiang can be divided into four stages according to the changes of sporopollen assemblage, species distribution, abundance, and diversity of foraminifera and Ostracoda. Since the late Pleistocene, the general trend of climate change in the study area is warm-wet, warm-wet and warm-wet, and gradually turns to cold-dry, which is consistent with the change of sea level fluctuation. According to the general trend of paleoclimate change in the study area, the paleosedimentary environment of the study area is further analyzed by the characteristics of grain size parameters and grain size composition. According to the depth, the sediments can be divided into seven stages. Since late Pleistocene, the sediments are mainly silt. The changing process of hydrodynamic conditions during deposition is medium energy-medium low energy-medium energy-medium low energy-medium energy. The changes of sedimentary facies are as follows: shore shallow lake, flood plain, shallow lake beach bar, lake swamp, flood plain, and shallow sea swamp.

Microfacies Characterizations and Paleoenvironment of Upper Part of Qamchuqa Formation from Chwarqauran Section, Sulaimaniyia Area, Kurdistan Region, Iraq

The Qamchuqa Formation was studied in Chwarqauran section, Sulaimanyia, Kurdistan region, Northeastern Iraq. The lithology of the formation contains limestone throughout the whole section except for one bed of dolomite at the Middle part. Twenty-four slides were prepared from 24 rock samples that were taken from this section to discriminate the petrography and fossil content. The petrographic study shows four main microfacies including lime mudstone, wackestone, packstone, and floatstone. Additionally, there are four sub microfacies: bioclast wackestone, miliolid wackestone, bioclast packstone and orbitolinid packstone. However, the fossil content shows the abundance of benthic foraminifera against the planktonic. All the microfacies indicate facies zone 7, 8 and 9A which reflect deposition in the platform interior between the tidal flat to the mid ramp and back reef environment

The Adıyaman Group carbonate succession on the northern Arabian Plate (southeastern Turkey): A review of lithostratigraphy, foraminiferal biostratigraphy, depositional environments and sequence stratigraphic evolution

Abstract This study presents a new stratigraphic framework for the Adiyaman Group succession developed on the northern margin of the Arabian Platform. This Upper Cretaceous carbonate sequence, distributed widely in outcrop and subsurface rocks in the southeast Anatolia region, is investigated in terms of lithostratigraphy, biostratigraphy, microfacies analysis and sequence stratigraphy. The sequence is divided into six lithostratigraphic units, which in ascending order are the Karabogaz, Saytepe, Saydere, Sayindere, Beloka and Sanli formations. Based on examination of benthic and planktonic foraminifera, the Adiyaman Group ranges in age from late Santonian to early late Campanian. The Saytepe, Beloka and Sanli formations are characterized by benthic foraminifers, while the Karabogaz, Saydere and Sayindere formations are defined by planktonic foraminifers. Following a detailed microfacies analysis, the Adiyaman Group carbonates are interpreted to have been deposited in settings that range from deep shelf to lagoonal depositional environments. Sequence stratigraphic studies identified three successive third-order depositional sequences that are separated by sequence stratigraphic surfaces. Sequence boundaries are correlated to global cycle boundaries. The abundance and diversity of foraminifera are interpreted as a function of relative sea-level changes. This study provides revisions in stratigraphic nomenclature that rely on precise biostratigraphic data.

Early Miocene larger benthic foraminifera from the northwestern Tethyan Seaway (NW Iran): new findings on Shallow Benthic Zone 25.

The lower Miocene marine units of NW Iran (Hamedan–Miandoab area) were studied to establish a high-resolution biostratigraphy framework in the context of European standard biozonation (SBZ zonal scheme). The units are dominated by larger and small benthic foraminifera together with coralline algae and corals. Due to its position in the Tethyan Seaway between the Mediterranean and Indo-Pacific, the investigated area has high significance in palaeobiogeography. Seven species of benthic foraminifera were described, including Miogypsina globulina, Amphistegina bohdanowiczi, Elphidium crispum, Elphidium sp. 1, Borelis curdica, Austrotrillina asmariensis, and Peneroplis thomasi. The occurrence of Miogypsina globulina in the shallow-marine carbonates of the studied sections documents the Burdigalian SBZ 25 Zone. Austrotrillina asmariensis and Peneroplis thomasi occur with M. globulina. Simultaneously, their stratigraphical range is extended to the Burdigalian in the Middle East. Based on the discovery of lower Miocene deposits in the Hamedan–Miandoab area (previously mapped as Oligocene–Miocene units), the stratigraphy of northwest Central Iran is revised. The biostratigraphic results also present a more precise chronology for the marine transgression in the study area, initiating in the late early Miocene. The coralline algal assemblages and the abundance and diversity of larger benthic foraminifera indicate that shallow-marine Qom Formation got deposited in tropical to subtropical warm waters.

Paleoceanographic evolution of the Japan Sea during the Pleistocene – A benthic foraminiferal perspective

We reconstructed the paleoceanographic evolution of the Japan Sea over the Pleistocene using benthic foraminiferal and organic geochemical records from sediment cores recovered at IODP Site U1426, which was drilled at a water depth of 900 m on the Oki Ridge in the southern Japan Sea. The dominant benthic foraminiferal biofacies and the assemblage composition, total organic and inorganic carbon, coarse fraction percentages indicate a notable reduction in primary productivity between 2150 and 1700 ka, due to the restricted supply of nutrients from the northern Pacific Ocean through the northern connecting strait. The inflow of the Tsushima Warm Current via the southern strait began after 1700 ka and marked a major change in the productivity regime of the Japan Sea, as shown by the increased abundance of calcareous foraminifera and enhanced CaCO3 (%). A marked shift in productivity occurred during the Middle Pleistocene Transition, as indicated by the dominance of low-oxygen tolerant species, and a higher influx of total organic carbon (%). The onset of more extreme glaciation at ~490–470 ka coincident with the Mid-Brunhes Event was linked to marked changes in foraminiferal assemblage composition, reflecting major changes in sea-level, oxygen availability at the seafloor, and carbonate compensation depth during intense glacial-interglacial cycles. Productivity changes were also modulated by 23 kyr variability, related to precessional insolation forcing at low latitudes, and superimposed on the 41 and 100 kyr variability, linked to high-latitude climate fluctuations.

Petrological, geochemical, and microfacies analysis of the Sylhet limestone, Bengal Basin, Bangladesh: implication for depositional environment and diagenesis

The fossiliferous Sylhet limestone formation of the Eocene age in the Bengal Basin is important for scientific and geoheritage study. This formation is exposed in the two locations of Bengal Basin; however, it is least studied. In this study, petrological, geochemical, and microfacies analysis of the Sylhet limestone was carried out by analyzing twenty-eight (28) samples from the two exposed sections and two underground (boreholes) in the Bengal Basin. The microscopic and XRD analysis shows that the calcite is the most dominant mineral in the studied samples along with some amount of dolomite, siderite, ankerite, pyrite, and quartz. The presence of the crystal structure of calcite, dolomite, quartz, and pyrite was confirmed through SEM-EDX. Geochemical results show that the samples are composed of high CaO (14.296 to 53.326%) with a significant amount of Fe2O3 (0.095 to 18.482%), Al2O3 (0.664 to 7.357%), K20 (0.83 to 2.274%), MgO (0.157 to 8.109%), and SiO2 (0.08 to 0.451%). Beside the major oxides, some minor and trace elements including Sr, Mn, Zr, Zn, Sc, Co, V, Ba, Ni, and Cu were also measured. Among these, Sr, V, Mn, and Cu concentration within the Sylhet limestone directly indicates its depositional environment at a shallow continental shelf in open marine condition and its diagenetic change to convert as dolomitic limestone. Geochemical characteristics indicate that the Sylhet limestone is highly dolomitized with high Ca/Mg ratio and was deposited in a low-energy shallow continental shelf marine depositional environment. Higher values of the Ca/Mg ratio of the studied samples also confirm lower salinity during its deposition. The presence of silica in the limestone was observed with a positive/negative correlation with Ca which implies that the silica is derived either from a terrestrial source due to increases of sediment supply during the Middle Eocene for the consequences of the Indo-Asian plate Himalayan Collision or dissolution from the siliceous shells of fossils that replace the calcite. Eight (08) microfacies (MFT) types were identified based on abundance of foraminifera or calcareous algae (e.g., Nummulites sp., Discocyclina sp., Alveolina sp., Quinqueloculina sp., Cibicides sp., Lenticulina sp., Ovulites sp.) which are similar to grainstone/packstone carbonate of 18 standard microfacies types (SMF 18). The observed SMF was deposited under restricted to open marine carbonate platform of shallow water depth at different hydrodynamic conditions.

Holocene Interactions Between Glacier Retreat, Sea Ice Formation, and Atlantic Water Advection at the Inner Northeast Greenland Continental Shelf

AbstractDuring the past four decades significant decrease in Arctic sea ice and a dramatic ice mass loss of the Greenland Ice Sheet (GIS) has been coincident with global warming and an increase in atmospheric CO2. In Northeast Greenland significant mass loss from the outlet glaciers Nioghalvfjerdsbræ (79NG) and Zachariæ Isstrøm (ZI) and intensive seasonal breakup of the local Norske Øer Ice Barrier (NØIB) have also been observed since 2000. In order to better understand the processes driving these modern changes, studies of paleoclimate records are important and of major societal relevance. A multiproxy study including organic‐biogeochemical and micropaleontological proxies was carried out on a marine sediment core recovered directly in front of 79NG. Data from Core PS100/270 evidenced a strong inflow of warm recirculating Atlantic Water across the Northeast Greenland shelf from the early Holocene between ~10 and 7.5 ka. An overall high in phytoplankton productivity occurred within a stable sea ice margin regime, accompanied by 79NG retreat most probably triggered by peak solar insolation and changes in the local ocean circulation. Enhanced basal melt of the underside of 79NG at ~7.5 ka then led to the total disintegration of the ice shelf. The released freshwater would have driven water column stratification and promoted the formation of the local landfast ice barrier, which is shown by lowered biomarker values and foraminifera abundances toward the end of the early Holocene. Near perennial sea ice conditions with short summers and 79NG retreat to the inner fjord then prevailed from ~7.5 to ~0.8 ka.

Evolution of the Oligotrophic West Pacific Warm Pool During the Pliocene‐Pleistocene Boundary

AbstractThis study investigates the development of oligotrophic conditions, thickening, and zonal and meridional contraction of the West Pacific Warm Pool (WPWP) during the Pliocene. It has been hypothesized that the evolution of the WPWP and the establishment of strong equatorial Pacific zonal gradients are closely related to the narrowing of the Indonesian Gateway (IG) as well as the closure of the Central American Seaway (CAS). However, the timing of the development of these events remains unclear. Here we report Pliocene‐to‐Recent relative abundances of planktic foraminifera at Deep Sea Drilling Project (DSDP) Site 214 in the eastern Indian Ocean and at Ocean Drilling Program (ODP) Site 807, in the western Pacific. A comparison of the abundance of mixed‐layer species (MLS) from both sites indicates a pronounced increase in their population between ~3.15 and 1.6 Ma. There is a contemporaneous decrease in the Globigerinita glutinata population during this time, which together with the MLS data suggest the development of oligotrophic conditions in the western tropical Pacific. Our data suggest that the oligotrophic WPWP, resembling present‐day conditions, developed around 3.15 Ma and was closely linked to the gradual constriction of the IG.

Variable Kuroshio Current intrusion into the northern South China Sea over the last 7.3 kyr

The branch intrusion of the Kuroshio Current (KC) into the northern South China Sea (SCS) has a significant effect on temperature, salinity, circulation, and eddy generation. However, the study of Holocene hydrological changes and the historical influence of the KC in this region is limited. Here, we report high-resolution sea surface temperature (SST) and δ18Osw (as a proxy for sea surface salinity, SSS) records based on paired Mg/Ca ratios and δ18O analyses of the planktonic foraminifera Globigerinoides ruber combined the Pulleniatina obliquiloculata and G. sacculifer/G. ruber ratios from core 05E306 (22°0.06′ N, 118°59.64′ E; water depth = 1440 m) in the northern SCS. By comparing these data with records from cores located within and outside of the main KC flow pathway, we evaluate the spatiotemporal evolution of the KC in this region over the last 7.3 kyr. The strongest influence was observed from 6.1 to 5.3 ka, recorded as an abrupt increase in SST and SSS with remarkably increased P. obliquiloculata abundance (37.4%) and G. sacculifer/G. ruber ratios (3.18). During the following period, 5–2.5 ka, SST decreased by 0.4–1.1 °C with an associated decrease in δ18Osw, indicating a weakened KC. After 2.5 ka, the influence of the KC on the northern SCS strengthened; however, the high SST record still exhibits a spatial constraint in the longitude distribution of the KC during this period of strongest intrusion. Moreover, the abundance of planktonic foraminifera in the study area more strongly correlates with SSS than SST. The δ18Osw records in core 05E306 show a freshening trend after 5.7 ka, which is inconsistent with the declining East Asian Summer Monsoon precipitation record but consistent with the Holocene freshening trend recorded in the Western Pacific. This suggests that hydrological variability of the northern SCS is mainly influenced by the Western Pacific Ocean.

Changes in sea surface hydrography and productivity in the western equatorial Atlantic since the last interglacial

Scientific projections point to the increase of greenhouse gas levels in the atmosphere will turn the oceans warmer and, consequently, the upper layer of the thermohaline circulation will get thicker, restricting the productivity areas. Oligotrophic conditions will tend to prevail, and expanding the range of proxy data in oligotrophic oceans, across different climate scenarios, has the potential to improve predictions of climate models about how primary productivity will respond. Still, the variability of past primary production in the equatorial Atlantic remains elusive. We used organic-walled dinoflagellate cysts (dinocysts) assemblages to reconstruct changes in the sea surface hydrography and productivity in the western equatorial Atlantic over the last ~130 kyr. Four dinocysts assemblages were defined: open ocean, river outflow, neritic and nutricline assemblages. Multiple proxies were used to support the environmental changes evidenced by the observed variations in the dinocyst assemblages, such as the X-ray fluorescence (XRF) Ti/Ca ratio, and planktonic foraminifera abundances. We observed glacial-interglacial as well as the millennial-scale changes in the dinocyst assemblages. A clear glacial-interglacial pattern was marked by more autotrophs dinocysts over the interglacials and the prevalence of heterotrophs dinocysts during the glacial period. We pointed out the interchange of autotrophs assemblages (nutricline and open ocean) over the interglacials intervals, denoting divergences in nutrient availability. During the last glacial period, precipitation events occurred in northeastern Brazil due to southward displacements of the Intertropical Convergence Zone (ITCZ). The increase of precipitation boosted the freshwater input to the adjacent ocean, and the dinocyst assemblages oscillated in response to such freshwater/salinity changes. Over the glacial period, dinocysts with different nutritional requirements (autotrophs and heterotrophs) varied following the ITCZ displacements. Thus, in this study, we showed the influence of ocean-atmospheric processes on the ocean and investigated the productivity in an oligotrophic region over distinct past climatic backgrounds.

Structure Community and Distribution of Benthic Foraminifera in the Waters of Bagan Tanjungbalai Village Asahan Regency North Sumatera Province

This research was conducted in March 2019 in the waters of Bagan Tanjungbalai Village Asahan Regency North Sumatera Province. The purpose of the study were to analyze the community structure and distribution of benthic foraminifera. Determination of the research was purposive sampling of 4 station with 3 sampling points where the distance each sampling point was 50 meters wich were based on the initial sampling point. In the study area were found 24 species of foraminifera. The study showed that composition of sediment organic matter involved 4.97 - 15.26%, while the abundance of benthic foraminifera was between 13690 - 28571 ind/m2. Defferences of the abundance of benthic foraminifera at each station obtained a significant value of 0.01 or p < 0.05, which means a difference the abundance of benthic foraminifera beetwen stations,but not significant. While the relative abundance between sampling is only 0.15-21.00%, while the relative sedimentation rate between sampling is 15.38 - 33.02%.

Sedimentary response to sea level and climate changes in the inner sea of Maldives carbonate platform over the past 30 kyr

We applied AMS 14C dates, Mg/Ca estimated sea surface temperature (SST), planktonic foraminiferal abundance, coarse component and X-ray diffraction mineral composition analyses for an International Ocean Discovery Program (IODP) sediment Hole U1467C in the Maldives inner sea, to reveal factors that affected the depositional process in the Maldives inner sea over the past 30 kyr. We found that the linear sedimentation rate (LSR) in Holocene (6.8 cm/kyr) was obviously higher than that in glacial period (3.45 cm/kyr); the average SST during the Holocene was 2–3°C higher than that in glacial stage. High abundance of planktonic foraminifera occurred during the glacial period, which was consistent with the variation of pelagic biogenic component. Reef-sourced material showed apparent high percentage during the Holocene (43.5%), in contrast to the low values during the glacial stage (20.7%). Terrigenous matter, only accounting for a small percentage in carbonate platform, was relatively high during the glacial period than that in the Holocene. We therefore conclude that reef-sourced material, dominated in the glacial-interglacial sediment sources, was mainly affected by sea level and climate changes. During glacial stage, sea level low-stand and weakened weathering in Maldives limited the input of the eroded material into the inner sea, resulting in low LSR; while the Holocene high sea level accompanied with rapid growth of the reef atoll and enhanced weathering, brought more reef-sourced material to the inner sea, leading to increased LSR and lowered abundance of planktonic foraminifera. The sea level and climate-controlled reef-sourced material changes are the key to understand the sedimentary process of the Maldives inner sea. Our study will shed some light on the evolution of glacial-interglacial sedimentary process of carbonate platform.

Benthic foraminifera and brachiopods from a marine cave in Spain: environmental significance

Sediment samples from a marine cave in the Murcia region (eastern Spain) were analysed for grain size, total benthic foraminiferaand dead brachiopoda to obtain environmental information through physical and ecological data in order to understandthe benthic communities of cave environments and their ecological significance. A total of 100 foraminiferal and 7 brachiopodspecies were classified, highlighting the first occurrence in the western Mediterranean of Gwynia capsula (Jeffreys, 1859). Statistical analysis applied to foraminiferal data allowed the identification of three assemblages characterised by decreasing species diversity along the cave. This corresponded to a similar separation recognisable through changes in brachiopod species abundance and well-correlated with cave morphology. The relative abundance of epifaunal clinging-attached foraminifera as well as the rate of cave and sciaphilic/coralligenous Brachiopoda, thought to be representative of the degree of separation from marine conditions,were found to be highly correlated, increasing towards the inner cave. Our hypothesis was that despite the different lifestyles ofthese two groups, the strict correlation of environmental factors (i.e. light, nutrients, sediment texture, water parameters) changingalong the length of the cave determines a comprehensive environmental gradient, causing an increase in environmental stress that has similar effects on the different taxonomic groups.