Distribution Of Benthic Foraminifera Research Articles

Distribution of Benthic Foraminifera in the Marine Estuary of the Guadalquivir River (SW Spain): A Preliminary Report

Three zones are differentiated in the marine sector of the Guadalquivir estuary (SW Spain), according to a multidisciplinary analysis (water, sediment, foraminifera). Both salinities and pH increase from the innermost areas (zone 1: Ammonia tepida) to the mouth (zone 3: Ammonia beccarii), with an intermediate zone 2 (Ammonia beccarii-Triloculina trigonula). Both density and diversity are low to very low, except near the transition between zones 2 and 3. Planktonic foraminifera decrease sea Ward from zone 1 to zone 3.

Distribusi Foraminifera Bentonik Hidup dalam Hubungannya dengan Sedimen Dasar Laut di Selat Sumba, Nusa Tenggara Timur

Marine geological survey of Ekspedisi Widya Nusantara (EWIN) LIPI 2016 was conducted by using RV Baruna Jaya VIII in the Sumba Waters from 4 to 26 August 2016. One of the aim of this survey is to understand the sea floor surface sediment characteristics and its influence to the benthic foraminifera distribution. Seven sediment samples were collected from sea floor surface in Sumba Strait, at the different location and depth using grabbing method with box corer. The samples have analyzed for the foraminifera content, sediment grain size, organic matter and carbonate content, and chemical element by XRF method. The living benthic foraminifera distribution increase to the east of the research area, which have higher content of the organic material and Fe, Rb, Zr, Zn and Sr elements in the sediment. The benthic foraminifera distribution most abundance founded at the depth of 800-1000 m with sediment types are sandy coarse silt to sandy very coarse silt.Keywords: Benthic foraminifera, distribution, sea floor sediment, Sumba Strait.

Distribusi Foraminifera Bentonik Hidup dalam Hubungannya dengan Sedimen Dasar Laut di Selat Sumba, Nusa Tenggara Timur

Marine geological survey of Ekspedisi Widya Nusantara (EWIN) LIPI 2016 was conducted by using RV Baruna Jaya VIII in the Sumba Waters from 4 to 26 August 2016. One of the aim of this survey is to understand the sea floor surface sediment characteristics and its influence to the benthic foraminifera distribution. Seven sediment samples were collected from sea floor surface in Sumba Strait, at the different location and depth using grabbing method with box corer. The samples have analyzed for the foraminifera content, sediment grain size, organic matter and carbonate content, and chemical element by XRF method. The living benthic foraminifera distribution increase to the east of the research area, which have higher content of the organic material and Fe, Rb, Zr, Zn and Sr elements in the sediment. The benthic foraminifera distribution most abundance founded at the depth of 800-1000 m with sediment types are sandy coarse silt to sandy very coarse silt.Keywords: Benthic foraminifera, distribution, sea floor sediment, Sumba Strait. DOI: 10.33332/jgsm.2019.v20.1.17-26

Distribusi Foraminifera Bentonik Hidup dalam Hubungannya dengan Sedimen Dasar Laut di Selat Sumba, Nusa Tenggara Timur

Marine geological survey of Ekspedisi Widya Nusantara (EWIN) LIPI 2016 was conducted by using RV Baruna Jaya VIII in the Sumba Waters from 4 to 26 August 2016. One of the aim of this survey is to understand the sea floor surface sediment characteristics and its influence to the benthic foraminifera distribution. Seven sediment samples were collected from sea floor surface in Sumba Strait, at the different location and depth using grabbing method with box corer. The samples have analyzed for the foraminifera content, sediment grain size, organic matter and carbonate content, and chemical element by XRF method. The living benthic foraminifera distribution increase to the east of the research area, which have higher content of the organic material and Fe, Rb, Zr, Zn and Sr elements in the sediment. The benthic foraminifera distribution most abundance founded at the depth of 800-1000 m with sediment types are sandy coarse silt to sandy very coarse silt.Keywords: Benthic foraminifera, distribution, sea floor sediment, Sumba Strait.

Distribusi Foraminifera Bentonik Hidup dalam Hubungannya dengan Sedimen Dasar Laut di Selat Sumba, Nusa Tenggara Timur

Marine geological survey of Ekspedisi Widya Nusantara (EWIN) LIPI 2016 was conducted by using RV Baruna Jaya VIII in the Sumba Waters from 4 to 26 August 2016. One of the aim of this survey is to understand the sea floor surface sediment characteristics and its influence to the benthic foraminifera distribution. Seven sediment samples were collected from sea floor surface in Sumba Strait, at the different location and depth using grabbing method with box corer. The samples have analyzed for the foraminifera content, sediment grain size, organic matter and carbonate content, and chemical element by XRF method. The living benthic foraminifera distribution increase to the east of the research area, which have higher content of the organic material and Fe, Rb, Zr, Zn and Sr elements in the sediment. The benthic foraminifera distribution most abundance founded at the depth of 800-1000 m with sediment types are sandy coarse silt to sandy very coarse silt.Keywords: Benthic foraminifera, distribution, sea floor sediment, Sumba Strait. DOI: 10.33332/jgsm.2019.v20.1.17-26

Early to middle Holocene development of the Tsushima Warm Current based on benthic and planktonic foraminifera in the Nakdong River delta (southeast Korea)

Fossil benthic and planktonic foraminifera from a part of core ND-02 and the published data of core ND-01 from the Nakdong River delta, southeast Korea were analyzed to evaluate the impact of the Tsushima Warm Current on coastal environments in the Korea/Tsushima Strait between Korea and Japan during the early to middle Holocene. Based on cluster analysis, four sample clusters (A, B, C, and D), suggestive of a landward–seaward gradient of environmental conditions, can be defined. According to the spatio-temporal and cluster distributions of benthic foraminifera in faunal compositions, the landward occurrence of benthic foraminifera was delimited in the inner part of the Nakdong River delta at ∼8–7 ka. The common occurrence of warm-water planktonic foraminifera suggests that this maximum landward expansion of benthic foraminifera within the delta was caused by the intensification of the Tsushima Warm Current in addition to sea level rise during the early to middle Holocene. Changes in both marine biota and sedimentation were reported in the coastal areas of southwestern Japan in that period. They were also caused by a precursor of the enhanced Tsushima Warm Current at ∼8 ka. Thus, the evolution of the Tsushima Warm Current during the early to middle Holocene is important for understanding various phenomena in the coastal environments of the Korea/Tsushima Strait.

Benthic foraminifera distribution in the modern sediments of the Southeastern Baltic Sea with respect to North Sea water inflows

Benthic foraminifera distribution in the modern sediments of the Southeastern Baltic Sea with respect to North Sea water inflows

Epifaunal Foraminifera in an Infaunal World: Insights Into the Influence of Heterogeneity on the Benthic Ecology of Oxygen-Poor, Deep-Sea Habitats

A reduction in dissolved oxygen availability in marine habitats is among the predicted consequences of increasing global temperatures. An understanding of past oxygenation is critical for predictions of future changes in the extent and distribution of oxygen minimum zones (OMZs). Benthic foraminifera have been used to assess changes in paleo-oxygenation, and according to prevailing thought, oxygen-poor marine benthic habitats are dominated by sediment-dwelling infaunal foraminifera, while more oxygenated environments are populated with more epifaunal taxa. However, in this study we found elevated densities of epifaunal taxa in oxygen-poor habitats. A series of sixteen multicores were taken on depth transects (360-3000 m) across an OMZ in the Southern California Bight to investigate the ecology of living (rose Bengal stained) benthic foraminifera. Dissolved oxygen concentrations in bottom water at sampling sites varied from 21 mol/l to 162 mol/l. Sampling focused on bathymetric highs in an effort to collect seafloor surface materials with coarse sediments in areas not typically targeted for sampling. Mean grain size varied from about 131m (gravelly sand) to about 830μm (coarse sand with fine gravel). Vertical distribution patterns (0-2 cm) were consistent with those of conspecifics reported elsewhere, and reconfirm that Cibicidoides wuellerstorfi and Hanzawaia nipponica have a living preference at or near the sediment-water interface. As expected, assemblages were dominated by infaunal taxa, such as Uvigerina and Bolivina, traditionally associated with the supersaturated, unconsolidated mud, characteristic of OMZ habitats, suggesting that these taxa are not sensitive to substrate type. However, despite dysoxic conditions (21 mol/l to 28 mol/l ), epifaunal taxa comprised as much as 36 percent of the stained population at the five sites with the coarsest mean grain size, while other measured environmental parameters remained relatively constant. We suggest that these epifaunal taxa, including C. wuellerstorfi, prefer habitats with coarse grains that allow them to remain at or above the sediment-water interface. These results suggest that seafloor habitat heterogeneity contributes to the distribution of benthic foraminifera, including in low-oxygen environments. We submit that paleo-oxygenation methods that use epifaunal indicator taxa need to reconsider the dissolved oxygen requirements of epifaunal taxa.

Effect of seawater temperature, pH, and nutrients on the distribution and character of low abundance shallow water benthic foraminifera in the Galápagos.

In order to help predict the effects of anthropogenic stressors on shallow water carbonate environments, it is important to focus research on regions containing natural oceanographic gradients, particularly with respect to interactions between oceanography and ecologically sensitive carbonate producers. The Galápagos Archipelago, an island chain in the eastern equatorial Pacific, spans a natural nutrient, pH, and temperature gradient due to the interaction of several major ocean currents. Further, the region is heavily impacted by the El Niño—Southern Oscillation (ENSO) and the Galápagos exhibited widespread coral bleaching and degradation following the strong ENSO events of 1982–1983 and 1997–1998. These findings are coupled with reports of unusually low abundances of time-averaged benthic foraminiferal assemblages throughout the region. Foraminifera, shelled single-celled protists, are sensitive to environmental change and rapidly respond to alterations to their surrounding environment, making them ideal indicator species for the study of reef water quality and health. Here, statistical models and analyses were used to compare modern shallow water benthic foraminiferal assemblages from 19 samples spanning the Galápagos Archipelago to predominant oceanographic parameters at each collection site. Fisher α diversity indices, Ternary diagrams, Canonical Correspondence Analysis, regression tree analysis and FORAM-Index (FI; a single metric index for evaluating water quality associated with reef development) implied a combined impact from ENSO and upwelling from Equatorial Undercurrent (EUC) waters to primarily impact foraminiferal abundances and drive assemblage patterns throughout the archipelago. For instance, repeated ENSO temperature anomalies might be responsible for low foraminiferal density, while chronically high nutrients and low aragonite saturation and low pH—induced by EUC upwelling and La Niña anomalies—likely inhibited post-ENSO recovery, and caused foraminiferal assemblages to exhibit a heterotrophic dominance in the southern archipelago. What resulted are low FI values in the southern collection sites, indicating environments not conducive to endosymbiont development and/or recovery.

Changes in the distribution of Uvigerinidae species over the past 775 kyr: Implications for the paleoceanographic evolution of the Japan Sea

The distribution of benthic foraminifera of the Uvigerinidae family, which are abundant in middle to upper Pleistocene samples from the Yamoto Basin in the Japan Sea, have been analyzed quantitatively and used for paleoceanographic interpretations. Twenty-three Uvigerinidae species are reported from IODP Site U1426, 6 of which are present in at least three or more samples with 10% or more abundance and considered as dominant species. The abundance and ecological preferences of dominant Uvigerinidae species, comprised of Uvigerina mediterranea, Uvigerina yabei, Uvigerina sp.1, Uvigerina peregrina suggest dysoxic conditions, with high influx of organic matter between 775 and 475 ka in response to the enhanced flow of the Tsushima Warm Current. The end of MIS 13 marked the onset of more extreme glacial interglacial climate cycles in the Japan Sea. Glacial interglacial alternations of Uvigerina peregrina and Trifarina angulosa from 475 ka to the Holocene indicate major fluctuations in circulation and productivity within this semi-enclosed basin. Both U. peregrina and T. angulosa respond to 100 kyr variability, reflecting the paleoclimatic shift and global ice volume changes associated with the Middle Pleistocene Transition.

Depth distribution of benthic foraminifera in the middle and deeper sublittoral to uppermost bathyal zones northwest of Okinawa, Japan

Depth distribution of benthic foraminifera in the middle and deeper sublittoral to uppermost bathyal zones northwest of Okinawa, Japan

A Study of Co-occurrences of Foraminifera and Mussels in a Polluted Nova Scotian Wetland, Atlantic Canada

Abstract Studies of foraminiferal assemblages in intertidal marshes and subtidal creeks usually rely upon sediment samples collected along transects, such that associations with other organisms often go unnoticed. We show that ecologically useful data can be obtained by sampling that is stratified by substrate and microenvironment. The tidal wetland at Lower LaHave, Nova Scotia, Atlantic Canada (44º16′37.39″N, 64º19′46.45″W, area ∼1 km2) comprises mostly sandy sediment occupied largely by the low marsh grass Spartina alterniflora. The wetland is situated next to LaHave Estuary, which is polluted with domestic waste. Microenvironments within the marsh were sampled for total (living + dead) foraminiferal assemblages. The mass of dried sediment examined at each site was used to calculate the foraminiferal number (FN, number of foraminiferal tests per gram of sediment). Sediment samples from the intertidal grass beds reflect a typical low- to high-marsh zonal distribution of benthic foraminifera [FN = 24.7 ± 16.6 g−1 (mean ± standard deviation); n = 716 tests]. Samples from a tidal channel yielded few tests (FN = ∼0.3 ± 0.7 g−1; n = 22). Clutches of the mussel Mytilus edulis occurred in areas of strong current action within the channel and on lower energy slip-off slopes. Mussel clutches from the channel base yielded few tests (FN = ∼0.7 ± 0.7 g−1; n = 25), mostly Miliammina fusca. Clutches from slip-off slopes yielded a significantly richer assemblage (FN = 8.7 ± 4.6 g−1; n = 229) dominated by Elphidium umbilicatulum. We concluded that mussel clutches in low energy areas can be suitable habitat for E. umbilicatulum, either associated with structural complexity of the clutches or with waste products excreted by mussels that may stimulate growth of bacteria or microalgae upon which the foraminifera feed. The results from this study provide a baseline for examining the biotic impact of remediation of the LaHave River on the Lower LaHave wetland.

Distribution of benthic foraminifera along the Iranian coast

This study focuses on the distribution of benthic foraminifera along the Iranian coast of the Gulf, extending over 1000 km from the northeast close to Shatt Al-Arab/Arvand Rud to the southeast near the Strait of Hormuz where it connects to the Indian Ocean. The Gulf is a naturally stressed environment due to extremes of salinity and temperature and anthropogenically affected by rapid urbanization, maritime transport, desalination plants, and oil platforms. Historical records and distributional studies have commonly underestimated the benthic foraminiferal diversity in the Gulf. Thirty-two samples collected from depths between 20 and 45 m were analyzed for total (unstained) foraminiferal assemblages. A total of 221 benthic foraminiferal species and subspecies belonging to 69 genera, 34 families, and 6 orders were recognized. The assemblages are dominated by hyaline taxa (49%) and porcelaneous foraminifera (36%), while agglutinated foraminifera represent only a minor part (15%). The ten most abundant species are Nonion sp. 1 (5.8%), Quinqueloculina sp. 1 (4.7%), Asterorotalia dentata (4.2%), Bolivina cf. B. persiensis (3.9%), Asterorotalia sp. 3 (3.5%), Rotalinoides gaimardi (3.4%), Ammonia sp. 1 (3.3%), Quinqueloculina sp. 8 (3.3%), Bolivina cf. B. striatula (3.0%), and Nonion sp. 2 (2.8%). We speculate that increase of finer sediments (mud), availability of nutrients, and the presence of oxygen are factors controlling the diversity and distribution of benthic foraminifera. The current thermal regime in the Gulf has been cited as a model for the tropical ocean in 2090–2099. In light of it, foraminiferal assemblage structure, composition, and distribution may provide an insight into the nature of biotic response to future climate change in the Gulf region under conditions of global warming and a baseline for future comparison within and beyond the Gulf. This study also updates the knowledge on the types and distributions of benthic foraminiferal groups in this poorly known area.

Abundance and distribution of benthic foraminifera as indicators of the quality of the sedimentary environment in a subtropical lagoon, Gulf of California

Abundance and spatial distribution of benthic foraminifera were used to evaluate the impacts of anthropogenic activities on sediment quality in a coastal lagoon in the Gulf of California. In 1985 and 2013, 27 samples of superficial sediments were collected. The foraminifera genera Ammonia, Cribroelphidium, Quinqueloculina and Peneroplis were dominant in both years. The abundance of Ammonia increased from 41% to 60%, while Peneroplis abundance decreased from a maximum of 50% in 1985 to 7% in 2013. The greater abundance of Ammonia and the greater spatial coverage of Ammonia and Cribroelphidium suggest a marked environmental deterioration in the quality of the sedimentary environment, which contrasts with studies of trace elements in the sediment of this lagoon. The Foram Stress Index indicates that sediment quality has deteriorated over time, likely due to the effects of anthropogenic activities around the lagoon.

Benthic foraminiferal distribution and biofacies in the shelf part of Bay of Bengal, east coast of India

The environmental conditions that determine the benthic foraminiferal biofacies in the shelf part of Bay of Bengal are identified in the present study. The possible variables such as water depth, nature of sediments and substrate, salinity, dissolved oxygen and hydrodynamic factors are evaluated. A total of 23 surface sediment samples were collected at different water depth from the study area and were subjected to foraminiferal analysis and sediment characterisation. Altogether, 147 species belonging to 59 genera and 6 orders are identified, only 22 species are abundant. Cluster (Q-mode and R-mode) analysis of the abundant species resulted in the identification of four distinct biofacies which are correlated with environmental variables. The shallowest biofacies from 0 to 38 m water depth is represented by Ammonia beccarii, Amphistegina radiata, Asterorotalia pulchella and Elphidium crispum, which are associated with sandy sediment. The second biofacies from 38 to 83 m water depth is characterised by Cibicides wuellerstorfi, Quinqueloculina seminula, Quinqueloculina lamarckiana, Quinqueloculina vulgaris, Quinqueloculina agglutinans, Rotalinoides compressiuscula and Textularia agglutinans and the nature of sediments varies from slightly muddy sand to muddy sand. The third middle shelf biofacies from 83 to 150 m water depth is composed of Asterorotalia dentata, Cassidulina laviegata, Cibicides subhaidingerii and Lenticulina thalmani that are found in muddy sand sediment. The fourth outer shelf biofacies consisting chiefly of Bolivina ordinaria, Brizalina spathulata, Bulimina aculeata, Cancris communis, Siphouvigerina proboscidea and Uvigerina parvula exists from the depth of 150–200 m and related to sandy mud sediment. Two Paleo strandlines are identified at the depths of 49 m and 105 m, respectively, from the occurrence of relic forms along with soft coral sclerites. The shallower part of the seafloor up to 30 m depth is dominated by sandy sediments, reflecting the prevalence of high-energy conditions. On the other hand, the deeper part contains sediments with more mud content formed in low-energy conditions. The spatial distribution of benthic foraminifera in this shelf region is chiefly controlled by the nature of sediments and the bathymetry. However, another factor, such as dissolved oxygen, salinity, temperature and hydrodynamic conditions, seems to have an influence on the composition of benthic foraminiferal biofacies.

The Lower Paleogene Biostratigraphic Scale of the Northern Pacific Based on Deep-Water Benthic Foraminifera

Based on the stratigraphic distribution of benthic foraminifera in the lower bathyal–abyssal sediments uncovered by boreholes drilled under the framework of the Deep Sea Drilling Project (DSDP) and Ocean Drilling Project (ODP) in the Northern and Southern Pacific, the Lower Paleogene biostratigraphic zonal scale based on deep-water benthic foraminifera is proposed. The proposed scale includes eight subdivisions: six zones and two subzones. The boundaries of the zonal subdivisions are determined by biotic events (appearance or disappearance (extinction)) of stratigraphically important taxa and are correlated to the zonal scales based on planktonic foraminifera and calcareous nanoplankton. Most of these events are considered to be subglobal.

Environmental controls on the distribution of living (stained) benthic foraminifera on the continental slope in the Campos Basin area (SW Atlantic)

Abstract Living (stained) benthic foraminifera from deep-sea stations in the Campos Basin, southeastern Brazilian continental margin, were investigated to understand their distribution patterns and ecology, as well as the oceanographic processes that control foraminiferal distribution. Sediments were collected from 1050 m to 1950 m of water depth during the austral winter of 2003, below the Intermediate Western Boundary Current (IWBC) and the Deep Water Boundary Current (DWBC). Based on statistical analysis, vertical flux of particulate organic matter and the grain size of sediment seem to be the main factors controlling the spatial distribution of benthic foraminifera. The middle slope (1050 m deep) is characterized by relatively high foraminiferal density and a predominance of phytodetritus-feeding foraminifera such as Epistominella exigua and Globocassidulina subglobosa. The occurrence of these species seems to reflect the Brazil Current System (BCS). The above-mentioned currents are associated with the relatively high vertical flux of particulate organic matter and the prevalence of sandy sediments, respectively. The lower slope (between 1350 and 1950 m of water depth) is marked by low foraminiferal density and assemblages composed of Bolivina spp. and Brizalina spp., with low particulate organic matter flux values, muddy sediments, and more refractory organic matter. The distribution of this group seems to be related to episodic fluxes of food particles to the seafloor, which are influenced by the BCS at the surface and are deposited under low deep current activity (DWBC).

Diversity and distribution of benthic foraminifera in the Al-Kharrar Lagoon, eastern Red Sea coast, Saudi Arabia

High-resolution benthic foraminiferal study was carried out on the surficial bottom sediments of the Al-Kharrar Lagoon (KL), north of Rabigh City, eastern Red Sea coast, Saudi Arabia. One hundred thirty surface sediments samples were collected from the lagoon during March 2014 to investigate the benthic foraminiferal diversity, abundance, distribution and controlling factors. The lagoon’s water environmental parameters such as temperature, salinity, dissolved oxygen and pH,water depth, sediment grain size, organic matter and carbonate were also studied. Statistical techniques were applied to test the reliability of collected data and to facilitate the interpretation. The results showed that faunal density and diversity were with averages of 135±300 dead tests/g and 23±10 displaying the highest values (3000 and 44) only in some intertidal areas, respectively. The Q-mode cluster analysis as well as the spatial distribution of the benthic foraminifera allowed the division of KL into five environmental biotopes such as the southern tip, the mid-eastern side, the inlet, the whole intertidal-subtidal and, the deeper area. These biotopes were dominated by five major assemblages such as an intertidal assemblage (Quinqueloculina seminula-Q. laevigata and Affinetrina quadrilateralis-Neorotalia calcar), an inlet Amphistegina lessonii assemblage, an intertidal-subtidal assemblage (Peneroplis planatus-Coscinospira hemprichii-Sorites orbiculus) and deep-water assemblage (Spiroloculina communis-Triloculina serrulata-T. trigonula). The canonical correspondence analysis indicated that the intertidal-subtidal assemblage is positively correlated with high salinity, temperature, and bioclastic sandy substrates with algal mats, sea-grasses and macro-algae, reflecting their preferences to warm, dry climatic conditions. The deep-water assemblage showed positive relationships with pH, deep muddy substrates enriched in organic matter, and negatively correlated with high temperature and salinity. The inlet assemblage is also correlated with the deeper waters where hard to coarse-grained substrates predominate.

The distribution of benthic foraminifera in Bel Torrente submarine cave (Sardinia, Italy) and their environmental significance

The use of benthic foraminifera as ecological indicators in submarine caves of temperate seas have never been studied before and it represents a new approach, verified by this research. The Bel Torrente submarine cave (Gulf of Orosei, Sardinia, Italy) was surveyed by GUE (Global Underwater Explorers) scuba divers in order to georeferencing the cave before positioning the sampling stations, from the entrance to 430 m inside the cave. A total of 15 water samples were collected to investigate abiotic parameters (temperature, salinity, pH) while 15 sediment samples were collected to analyze grain size and benthic foraminifera. Benthic foraminifera, investigated for the first time in a submarine cave of temperate areas, were exclusively found from the entrance to 300 m inside the cave. Species distribution and assemblage diversity have been found to be correlated to the environmental gradient towards the inner cave, mainly due to the decreasing of temperature and salinity and the increasing of the flow energy. Water acidification seems responsible for the transition from a calcareous hyaline-dominated assemblage to an agglutinant-dominated one, occurring between 120 and 150 m from the entrance. Common taxa of the Sardinian coastal marine area are present only close to the entrance of the cave, while species found in the inner part are nearly exclusively epifaunal clinging/attached or infaunal taxa, with tolerance for wide variability of environmental parameters, such as Gavelinopsis praegeri, and opportunist infaunal taxa such as Eggerella advena. The agglutinant taxa found in the cave are conversely very rare in coastal marine assemblages of the area. This suggests a very efficient dispersal mechanism for the colonization of the caves, involving probably juvenile foraminifera at a “propagule” stage.

Changes in standing stock and vertical distribution of benthic foraminifera along a depth gradient (58–2750 m) in the southeastern Arabian Sea

Benthic foraminifera are a reliable proxy to reconstruct past oceanographic conditions. The ecological preferences of benthic foraminifera are usually studied from the core-top samples. The habitat of living benthic foraminifera, however, can be much deeper. Here, we document the vertical distribution of living benthic foraminifera from the Gulf of Mannar, Southeastern Arabian Sea, to find out the sediment depth that contains representative living assemblage and to understand the relationship between ecological parameters and foraminiferal abundance. Additionally, as the region has a well-developed oxygen minimum zone, we also assess the effect of dissolved oxygen, organic carbon (%Corg) and other associated parameters on living benthic foraminifera. The multi-core samples were collected along a longitudinal transect covering the shelf, and slope (58–2750 m), during the post southwest monsoon season. We report that at stations where dissolved oxygen is low (≤1.5 mL/L), >85% of the total living benthic foraminiferal population is confined to the top 0–1 cm section of the sediment and the average living depth decreases up to 0.6 cm. However, in the well-oxygenated waters, especially in the lower slope region, a substantial fraction of the total living benthic foraminiferal population inhabits deeper sections of the sediments. The calcareous benthic foraminifera dominates the foraminiferal population both within and outside the oxygen minimum zone. The absolute abundance of agglutinated benthic foraminifera is more on the continental slope, as compared to the shelf. The infaunal and epifaunal calcareous and agglutinated foraminifera show a different trend. We report that while the bottom water dissolved oxygen and depth controls the absolute abundance of benthic foraminifera, both the %Corg and ambient temperature, affect the relative abundance of living calcareous and agglutinated benthic foraminifera in the Gulf of Mannar.