Distribution Of Foraminifera Research Articles

Distribution and Abundances of Planktic Foraminifera and Shelled Pteropods During the Polar Night in the Sea-Ice Covered Northern Barents Sea

Planktic foraminfera and shelled pteropods are important calcifying groups of zooplankton in all oceans. Their calcium carbonate shells are sensitive to changes in ocean carbonate chemistry predisposing them as an important indicator of ocean acidification. Moreover, planktic foraminfera and shelled pteropods contribute significantly to food webs and vertical flux of calcium carbonate in polar pelagic ecosystems. Here we provide, for the first time, information on the under-ice planktic foraminifera and shelled pteropod abundance, species composition and vertical distribution along a transect (82°–76°N) covering the Nansen Basin and the northern Barents Sea during the polar night in December 2019. The two groups of calcifiers were examined in different environments in the context of water masses, sea ice cover, and ocean chemistry (nutrients and carbonate system). The average abundance of planktic foraminifera under the sea-ice was low with the highest average abundance (2 ind. m–3) close to the sea-ice margin. The maximum abundances of planktic foraminifera were concentrated at 20–50 m depth (4 and 7 ind. m–3) in the Nansen Basin and at 80–100 m depth (13 ind. m–3) close to the sea-ice margin. The highest average abundance (13 ind. m–3) and the maximum abundance of pteropods (40 ind. m–3) were found in the surface Polar Water at 0–20 m depth with very low temperatures (–1.9 to –1°C), low salinity (<34.4) and relatively low aragonite saturation of 1.43–1.68. The lowest aragonite saturation (<1.3) was observed in the bottom water in the northern Barents Sea. The species distribution of these calcifiers reflected the water mass distribution with subpolar species at locations and depths influenced by warm and saline Atlantic Water, and polar species in very cold and less saline Polar Water. The population of planktic foraminifera was represented by adults and juveniles of the polar speciesNeogloboquadrina pachydermaand the subpolar speciesTurborotalita quinqueloba. The dominating polar pteropod speciesLimacina helicinawas represented by the juvenile and veliger stages. This winter study offers a unique contribution to our understanding of the inter-seasonal variability of planktic foraminfera and shelled pteropods abundance, distribution and population size structure in the Arctic Ocean.

Development of an intertidal foraminifera training set for the North Sea and an assessment of its application for Holocene sea-level reconstructions

Regional datasets of the vertical distribution of intertidal foraminifera are useful to reconstruct Holocene sea-level changes from fossil foraminifera in estuaries and salt marshes. In this paper, we present a new foraminiferal dataset from the Ythan Estuary (Scotland) and combine it with data from eight other coastal sites from England, Denmark and Germany to produce a regional modern training set for the North Sea. We recognise a correlation between foraminifera and tidal elevation which makes the foraminifera suitable as sea-level indicators. We subdivide the data into subregional training sets and develop WA and WAPLS transfer functions. Applying a variety of statistical methods, including detrended canonical analysis, cross-validation by bootstrapping and leave-one-site-out, and the modern analogue technique, we establish the most appropriate transfer function from which to reconstruct early Holocene sea-level changes in a sediment core from the western North Sea coast. Results show that the subregional England/Scotland training set provides the most appropriate sea-level reconstructions, with decimetre-scale uncertainties. The techniques we use in this study, that consider both the modern and fossil assemblages to determine the best training set and transfer function, are suggested as a template for the development of regional transfer functions based on foraminifera and other intertidal microfossils.

The spatial distribution of benthic foraminifera in the Pearl River Estuary, South China and its environmental significance

Thirty surface sediment samples were collected from the Pearl River Estuary, South China, and benthic foraminifera were analyzed in order to understand the relationship between foraminiferal assemblages and environmental parameters. Multivariate analyses showed that the foraminferal assemblages (i.e., abundance and diversity) are correlated with the hydro-sedimentary gradients within the estuary. In addition, the dominant faunal composition seems to be largely influenced by food availability and trace metal contamination in surface sediments. A comparison with historical data from 1980s demonstrated that the foraminiferal abundance and diversity in the lower estuary have dramatically decreased over the last three decades, together with a significant shift in the dominant species. This is most likely due to the cumulative impacts of eutrophication and Cu contamination caused by human activities in the Pearl River basin. This work confirms the value of benthic foraminifera as bio-indicators in polluted estuarine environments.

Testing the applicability of random forest modeling to examine benthic foraminiferal responses to multiple environmental parameters

The main environmental variables controlling benthic foraminiferal distributions were identified and used to assess their influence on ecological indices developed as predictors of Ecological Quality Status (EcoQS) in marine ecosystems. Gradient forest and random forest models were applied to assess the predictive value of a selection of abiotic (environmental) and biotic (foraminifera) variables in a costal marine area in the central Adriatic Sea (Italy). This approach yields evidence that the predictor variables sand, silt, Pollution Load Index, and TN have the greatest influence on the distribution of benthic foraminifera in this area. In addition, we identify thresholds for the most important environmental variables that influence ecological indices. These findings contribute to efforts to determine how to best improve sediment quality and environmental stability for marine conservation. Further application of these approaches represents a useful tool for policymakers to survey the diversity of marine organisms and to improve the ability to protect and restore marine ecosystems by identifying predictors of diversity and identifying key thresholds in these predictors.

Systematic of the Early-Miocene (Burdigalian) Ostracoda from Northeastern Semnan, Central Iran

Seven genera and seventeen species of marine Ostracoda are reported for the first time from the Attari section (Qom Formation), northeast of the Semnan, Central Iran. In this section, the Qom Formation outcrops with 280 m thickness lies on the Eocene volcanic and under the Upper Red formation. According to the distribution of index foraminifera, there is conspicuous similarity between larger bentic foraminifera assemblages of the Qom Formation foraminifera and those of the Zagros basin, such as Borelis melo curdica the age of Qom Formation in the Attari section is Early Miocene (Burdigalian). The Miocene and even Oligocene Ostracoda fauna, relatively similar to the Attari section, have been reported from the Mediterranean area and the Proto- Indo- Pacific Ocean. The presence of one species with Paratethian origin in the Qom Formation is strong evidence that during the Burdigalian stage, the sea way between Central Iran and Paratethys basin still existed.

Influence of Bottom Water Parameters on the Distribution of Benthic Foraminifera from the Gulf of Mannar, Off Tiruchendur, Southeast Coast of India

Foraminifera are found in all marine environments, but they are very particular about the congenial environment for their reproduction, diversity and abundance. To understand the influence of bottom water parameters on the distribution of foraminifera from the shallow shelf region of Bay of Bengal, off Tiruchendur, Southeast Coast of Tamil Nadu, sediment and bottom water samples were collected at 27 stations, along three traverses viz. from off Veerapandianpattinam, off Tiruchendur and from off Alandurai, ranging in depths from 1.6m to 18.5m. The samples were collected during three seasons representing, summer (May 2016), pre monsoon (October 2016) and winter (January 2017) and thus the total samples amounted to 81. A total of 105 species of foraminifera have been identified from 47 genera, 32 families, 16 superfamilies and 4suborders. Among these 105 foraminiferal species, five were found to be widespread and abundant viz. Ammonia beccarii, A. tepida, Asterorotalia inflata, Nonioniodes boueanum and Quinqueloculina seminulam. Various bottom water parameters such as temperature, salinity, dissolved oxygen and pH were determined and correlated with the foraminiferal population. Temporally, higher temperature, salinity, dissolved oxygen and pH of bottom water observed during summer (May 2016) were congenial for higher population in the study area. Optimum conditions for the higher population and abundance of foraminifera are: Temperature: > 32.0°C, Dissolved oxygen: >6.0 mg/l, Salinity: >32 ppt and pH>8.1.

Subsurface and Infaunal Foraminifera of Kemaman-Chukai Mangrove Swamps, East Coast Peninsular Malaysia

This study analysed the distribution and abundance of dead and live (Rose Bengal stained) infaunal foraminifera from three short cores taken at three locations in the mangrove swamps of Kemaman-Chukai, Terengganu, Malaysia. Eighteen agglutinated taxa were recorded in assemblages dominated by Arenoparrella mexicana, Haplophragmoides wilberti and Miliammina fusca; and of these, only two taxa were recorded as live. The distribution of subsurface and infaunal foraminifera varied from core to core, as did their depth of occurrence. Core 1 (seaward core) was dominated by sandy deposits, relatively high salinity (32 ppt), and extensive crab mounds, displayed very low numbers of dead foraminifera inconsistently throughout the core, while no infaunal foraminifera were observed, indicating intense bioturbation by mangrove crabs. In Core 2 (middle core), even though the numbers of live foraminifera decreased down-core, the number of dead or subsurface foraminifera were inconsistent, indicating taphonomic loss of the tests. Core 3 (landward core) however, displayed ideal foraminiferal distribution patterns required in the palaeo sea-level reconstruction (with less taphonomic loss and decreasing number of infaunal foraminifera downcore). Because of the similarity displayed in the foraminiferal assemblages in the 0–1 cm and 10–11 cm intervals, the surface sample (0–1 cm) should be an acceptable basis for down-core reconstructions in this study. Live (Rose Bengal stained) infaunal foraminifera, though observed at 40–41 cm depth, are not considered abundant enough to influence the dead assemblage in the subsurface sediment and its applicability for palaeoenvironmental and sea-level reconstructions. Therefore, it is possible for palaeo sea-level to be reconstructed based on foraminiferal assemblages preserved in the Kemaman-Chukai mangrove swamps.

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.

Distribution and relative abundance of dominant benthic foraminifera and their palaeoecological significance from beach cores sediment in Kerala coast, India

The study on 365 sediment subsamples have been analyzed for benthic foraminifera from beach cores sediment in Kerala coast, India. The recent benthic foraminiferal faunal record that reveals the paleoecological preferences of the different benthic foraminiferal species are reported in this study. A total of 38 species belonging to 22 genera were identified from the study. For benthic foraminiferal faunal study, dry samples were sieved over 125 μm-size sieve and split into suitable aliquots to obtain ~250 specimens of benthic foraminiferal species identified and counted. The recent benthic foraminiferal faunal record assemblages were dominated by species are Ammonia beccarii followed by Ammonia gaimardii, Cancris oblongus, Discopulvinulina bertheloti, Gyroidinoides nitidula, Gyroidinoides cibaoensis and Quinqueloculina seminulum etc. The most dominant genus like Ammonia was recorded in all the samples from the study. Benthic foraminiferal species are utilized for biostratigraphy for several years and have also been confirmed very constructive in paleoceanographic and paleoclimatological modernization. This study, benthic foraminifera the major contributor to the marine biotic community is largely employed as an important tool for paleoclimatic reconstruction for high fossilization potential and a wide range of geographical distribution.

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.

Distribution of benthic foraminifera in an oceanic (Darwinian) barrier reef lagoon, Bora Bora, French Polynesia

Bora Bora, French Polynesia, represents the classic oceanic (Darwinian) barrier reef system, complete with a deep and extensive lagoon. The foraminiferal faunas of such oceanic barrier reef lagoons have never been studied in detail. How they relate to atoll lagoons and more broadly to coral reef lagoons in general is not known. Back-reef lagoon samples from Bora Bora were studied for their foraminiferal content. The fauna contains sparse larger symbiont bearing foraminifera, and most samples are dominated by a textulariid fauna of mainly Textularia gr. sp. 1, Textularia gr. foliacea and Textularia oceanica. Statistical analyses revealed three main assemblages, a Textularia-dominated deep central lagoon assemblage, an outer shallow lagoon assemblage characterised by abundant porcelaneous taxa, and a narrow embayment assemblage with abundant Elphidium. Although the species at Bora Bora are common to the Pacific Ocean, the Textularia-dominated assemblages are markedly different from the lagoon assemblages reported from atoll and non-oceanic barrier reef lagoons in the Pacific. These unique assemblages are hypothesised to have evolved due to interactions of the central volcanic island with the lagoon system, likely via the run-off of fine sediment and nutrients. Thereby, the prerequisites for abundant larger, symbiont-bearing foraminifera, which prefer clear, nutrient-poor waters, are largely unavailable. Despite similar substrates and facies, differences between species compositions indicate subtly different disconnected western and eastern deep lagoon environments, possibly due to differences in connectivity to the open ocean. This study provides the first detailed account of the foraminifera from the lagoon of an oceanic barrier reef lagoon.

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.

Investigating the benefits and costs of spines and diet on planktonic foraminifera distribution with a trait-based ecosystem model

Planktonic foraminifera are important calcifiers in the modern ocean. Despite this importance, the main functions of foraminifera's test and ornamentation such as spines are unclear. Spinose species dominate the planktonic foraminifera population in subtropical oligotrophic gyres, while non-spinose species dominate in deeper waters and at high latitudes suggesting that spines help foraminifera in food-limited areas. Here we take a novel approach to investigate the benefits of spines on foraminifera foraging using a 0-D trait-based ecosystem model. The model considers the traits of size, calcification, spines, passive feeding, and diet. We assess how the presence of spines impact foraminifera diet and fitness via a series of simulated environments representing oligo, meso- and eutrophic settings at different temperatures. We find that independent of diet, non-spinose taxa need to be more size-generalist predators than other zooplankton species to maintain their population. In contrast, spinose species benefit from a relatively higher surface-to-volume ratio compared to non-spinose species, which allows them to be as generalist as other zooplankton groups. In agreement with observations, we find that herbivory is the most successful diet in cold environments, while carnivory allows foraminifera to be more successful in warm environments.

Latitudinal Differentiation among Modern Planktonic Foraminiferal Populations of Central Mediterranean: Species–Specific Distribution Patterns and Size Variability

Studies of the spatial distribution and size of modern planktonic foraminifera are still lacking in the Mediterranean Sea. In this study, 17 core-top sediments collected from a north-south transect along the central Mediterranean have been analyzed for planktonic foraminiferal content, in terms of their distributional pattern and intraspecific size variability. Among the analyzed planktonic foraminiferal species, Globigerina bulloides and Globigerinoides ruber (w) were the most abundant, presenting an antagonistic behavior and an overall decreasing trend in their average size values from Adriatic to Ionian sub-basins. Intraspecific differences have been also documented for G. ruber (w), with the dominant sensu stricto morphotype to present generally higher frequencies and more constant shell sizes than sensu lato. The greater size variability of the latter is possibly related to its adaptation in particular hydrographic conditions based on its depth habitat preference and ecological characteristics to reach the (sub)optimum growth conditions. The rest of the species occur in minor percentages and show on average 11% increase with decreasing latitude characterized by distinct species-specific size variations along the transect. Our results show that the relationship between planktonic foraminifera shell size and abundance or sea surface temperature are either absent or weaker than previously reported for other regions and that in central Mediterranean assemblages’ size may be mainly related to nutrient availability. Besides the environmental parameters (sea surface temperature, primary productivity, water depth, stratification), the possible hidden cryptic diversity, still lingers to be consistently determined, could give a better understanding of the geographic and morphological differentiation within the Mediterranean planktonic populations.

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.

The Occurrence and Distribution of Benthic Foraminifera in Tropical Waters Along the Strait of Malacca

Foraminifera are shelled single-celled protists that are found in all marine environments. Benthic foraminifera either live in sediments or attach to surfaces on the seafloor. Understanding the distribution and ecological response of benthic foraminifera is crucial, as they can indicate past and current ocean conditions. However, the benthic foraminifera distribution along the busy Strait of Malacca, which connects the Indian Ocean (north) to the Java Sea (south), is undersampled. In this study, we collected 24 surface samples from the northern Strait of Malacca to understand the distribution of foraminifera assemblages in shallow tropical waters. A total of 49 species of benthic foraminifera were identified. Calcareous hyaline species dominated the assemblages, with an extremely low occurrence of calcareous porcelaneous species. The common calcareous hyaline taxa were Asterorotalia pulchella, Pseudorotalia schroeteriana, Discorbinella bertheloti, Ammonia tepida, and Heterolepa praecincta. Cluster analysis categorised the foraminiferal assemblages into three major groups. The first cluster (Group A) consisted of a more diverse assemblage of hyaline and agglutinated species that inhabited a mean water depth of 45 m. The second cluster represented a population that inhabited deeper water environments (average water depth of 59 m). Finally, the third cluster (Group C) consisted of a foraminifera assemblage that inhabited shallow coastal environments (average depth of 22 m) with higher organic matter enrichment. The multivariate canonical correspondence analysis (CCA) showed that the foraminiferal assemblages reflected the shallow to deep water transition in the Malacca Strait. Water depth, which defines the depositional environment, had a greater influence on foraminifera distribution here than organic matter and salinity.

Biostratigraphy and Paleoenvironments of the Oligocene Deposits (Qom Formation) in the Neyzar Area (Southeast of Salafchegan), Iran

The Qom Formation deposits, located at 12 km southeast of Salafchegan (N: 34° 21′ 26″ and E: 50° 32′ 14″), have a thickness of 110 m. The formation includes thin, and medium-to-thick bedded limestone, as well as shale, overlying the Lower Red Formation (early Oligocene) above an erosional unconformity. Its upper boundary is covered by alluvium sediments. Biostratigraphic distributions of benthic Foraminifera were used to determine the age and paleoenvironmental conditions of the Qom Formation. Two assemblage zones were recognized. Assemblage zones 1 and 2 were indicative of a Rupelian–Chattian age. The inner shelf (restricted and semi-restricted lagoons) and middle shelf (open marine) settings were formed on an open shelf platform. Euphotic conditions were dominant during the early and late Rupelian in the studied area. During the middle Rupelian, photic conditions were variable between euphotic and mesophotic to oligophotic. During the early and middle Chattian, photic conditions varied between oligophotic, mesophotic to oligophotic, and euphotic. During the late Chattian, mesophotic-oligophotic conditions were dominant. Additionally, a high level of salinity (40–50 and > 50 psu) was present in the studied area during the early Rupelian. The level of salinity varied from normal (30–40 psu) to hypersaline (40–50 psu) during the late Rupelian. Salinity during early and late Chattian subages was normal (30–40 psu). However, hypersaline (40–50 and > 50 psu) and normal (30–40 psu) conditions were present in the middle Chattian. Eutrophic to mesotrophic-oligotrophic conditions were found in the early Rupelian age. However, mesotrophy-oligotrophy dominated during the middle and late Rupelian and Chattian ages. In addition, the paleo-water depth of the Qom Sea fluctuated from < 10 m to > 20 m. Foralgal and foramol associations are dominant in the studied area during the Rupelian-Chattian ages. The general depositional environment of the Qom Formation is associated with seagrass meadows.

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.

Distribution and environmental implications of planktonic foraminifera in the surface sediments of southwestern part of Bay of Bengal, India

Distribution and environmental implications of planktonic foraminifera in the surface sediments of southwestern part of Bay of Bengal, India

Vertical distribution of planktic foraminifera through an oxygen minimum zone: how assemblages and test morphology reflect oxygen concentrations

Abstract. Oxygen-depleted regions of the global ocean are rapidly expanding, with important implications for global biogeochemical cycles. However, our ability to make projections about the future of oxygen in the ocean is limited by a lack of empirical data with which to test and constrain the behavior of global climatic and oceanographic models. We use depth-stratified plankton tows to demonstrate that some species of planktic foraminifera are adapted to life in the heart of the pelagic oxygen minimum zone (OMZ). In particular, we identify two species, Globorotaloides hexagonus and Hastigerina parapelagica, living within the eastern tropical North Pacific OMZ. The tests of the former are preserved in marine sediments and could be used to trace the extent and intensity of low-oxygen pelagic habitats in the fossil record. Additional morphometric analyses of G. hexagonus show that tests found in the lowest oxygen environments are larger, more porous, less dense, and have more chambers in the final whorl. The association of this species with the OMZ and the apparent plasticity of its test in response to ambient oxygenation invites the use of G. hexagonus tests in sediment cores as potential proxies for both the presence and intensity of overlying OMZs.