Water Column Research Articles

Adsorption of trace metals onto different plastics during long-term exposure in an estuarine environment: Influence of time, stratified water column, and specific surface area

The pervasive increase of plastics in marine systems and subsequent trace metals (TM) adsorption represents a critical environmental challenge. This long-term study is first to investigate how duration of exposure and stratified water column impact TM adsorption on various plastics in an estuary. We exposed polypropylene (PP), polyethylene (PE), poly(ethylene terephthalate) (PET), and fluorinated ethylene propylene (FEP) to estuarine conditions, categorizing them into three distinct groups to capture diverse human activities: pre-production pellets (Pellets), single-use plastics (SUP) and laboratory plastics (Lab). Plastic and water samples were analyzed before deployment and 1, 4, 7 and 16 months after deployment at three depths in the stratified Krka River estuary (Croatia). We measured TM concentrations, pH and salinity in the water column, and adsorbed TM amounts on plastics. Additionally, we examined plastic sample surfaces by Raman spectroscopy and scanning electron microscopy. TM speciation was modeled from water column data to better explain adsorption processes. Statistical analysis indicates that Zn, Cd, Pb, Ni, and Co adsorption depends on both duration of exposure and stratified water column, while Cu is influenced solely by duration of exposure to estuarine environment. Adsorbed TM amounts varied significantly among the plastic groups (Pellets, SUP and Lab), but not among different polymer types (PP, PE, PET and FEP). A noteworthy observation was the difference in the results of statistical analysis when investigating TM amounts expressed by plastic sample mass and by plastic sample surface area. Results expressed by plastic sample mass showed a difference between SUP group versus Pellets and Lab groups, while results expressed by plastic sample surface area distinguished Pellets group compared to other two groups. Therefore, we suggest presenting TM adsorption results in similar studies both by plastic sample mass and by plastic sample surface area. This approach will improve the understanding of TM adsorption on plastics, and enable more effective comparisons among the scientific literature dealing with plastics of different specific surface areas.

Determining hydraulic parameters using the free jet benches

The free jet bench, developed by Algetec for educational and teaching purposes, provides a controlled environment for analysing phenomena associated with fluid jets. It allows water dynamics to be explored using different types of nozzles, providing crucial data for advanced hydraulic analyses. To this end, the hydraulic efficiency of nozzles with different diameters was evaluated, measuring parameters such as flow velocity, flow rate and jet range. The experiment was carried out at the Hydraulic Irrigation and Hydrology Laboratory (LIHH) at the Agricultural Sciences Centre of the State University of the Tocantins Region of Maranhão (UEMASUL), using the free jet bench available in the laboratory. A completely randomised experimental design was adopted, with four treatments and five replications each, using nozzles with diameters of 4 mm, 6 mm, 8 mm and 10 mm. The results showed that the height of the water column directly influences outlet velocity and pressure. Nozzles with larger diameters had a significant impact on horizontal reach and flow, while smaller nozzles performed less well in these aspects. These findings are key to optimising the selection and design of nozzles in hydraulic systems, improving efficiency and performance in practical applications.

Genome of Methylomonas sp. AM2-LC, representing a methanotrophic bacterial species isolated from water column of a boreal, oxygen-stratified lake

Genome of Methylomonas sp. AM2-LC, representing a methanotrophic bacterial species isolated from water column of a boreal, oxygen-stratified lake

Trophic homogeneity due to seasonal variation in nitrogen in shallow subtropical lakes

Lakes play a crucial role in the nitrogen (N) cycle, and eutrophication disrupts the balance of the nitrogen cycle within lakes, including both the N removal process and the N supplement process. However, the mechanisms by which different nutrient levels affect seasonal nitrogen variations in the water columns are not clear, especially for long-term and large-scale scale studies. In this study, we used 206 independent spatial samples from a total of 108 subtropical shallow lakes from four surveys in the middle and lower reaches of the Yangtze River, as well as time-case study data from Lake Taihu and Lake Donghu of up to 23 and 14 years, respectively, to analyze the changes in summer TN compared to spring (delta TN). Delta TN was significantly negatively correlated with initial spring TN concentrations, with similar trends observed in both space and time. Furthermore, the slopes of spring TN vs. delta TN varied little across lakes in both time and space, suggesting a consistent relationship between initial spring TN and summer TN changes. When initial TN or TN: TP ratio was low, N fixation by algae played a significant role in compensating for summer N removal, thus mitigating summer N reductions; when TN was high or TN: TP ratio was high, ammonia stress reduced the compensatory effect of algae and denitrification played a significant role in summer N removal, thus increasing summer N reductions. Our study suggested that no matter what the initial conditions are, lakes tend to evolve towards a common nutrient status through biological regulation.

Interacting internal waves explain global patterns of interior ocean mixing.

Across the stable density stratification of the abyssal ocean, deep dense water is slowly propelled upward by sustained, though irregular, turbulent mixing. The resulting mean upwelling determines large-scale oceanic circulation properties like heat and carbon transport. In the ocean interior, this turbulent mixing is caused mainly by breaking internal waves: generated predominantly by winds and tides, these waves interact nonlinearly, transferring energy downscale, and finally become unstable, break and mix the water column. This paradigm, long parameterized heuristically, still lacks full theoretical explanation. Here, we close this gap using wave-wave interaction theory with input from both localized and global observations. We find near-ubiquitous agreement between first-principle predictions and observed mixing patterns in the global ocean interior. Our findings lay the foundations for a wave-driven mixing parameterization for ocean general circulation models that is entirely physics-based, which is key to reliably represent future climate states that could differ substantially from today's.

Design and development of a new stand-alone profiler for marine monitoring purposes

Marine pollution is a complex issue that has prompted extensive research. The Mar Menor lagoon, a singular Mediterranean ecological feature, is under pressure from various economic activities, leading to episodes of hypoxia and fish mass mortality. The lagoon is covered by an extensive meadow of submerged vegetation that release oxygen during daylight hours but consumes it during the night. Under exceptional conditions, the water column becomes stratified, with higher oxygen consumption in the deeper layers due to organic matter decomposition. Therefore, continuous high-frequency monitoring of critical parameters affecting the metabolic behaviour of the lagoon is essential. This marine environment has traditionally been monitored with traditional techniques from vessels on a weekly basis, incurring in high costs and yielding limited results. This article introduces the s-Nautilus, a submersible profiler that enables near real-time data transmission in shallow marine environments. It showcases an operational autonomy of two months and significantly reduces installation costs by eliminating the need for on-site infrastructure and personnel. Weighing 21 kg, makes it easy to transport, and it can be equipped with different commercial sensors to monitor various parameters as required. Currently, several s-Nautilus profilers are deployed in the Mar Menor lagoon, collecting data during critical hours, and providing valuable information to the managers of this emblematic environment.

Synthesis of In Situ Marine Calcium Carbonate Dissolution Kinetic Measurements in the Water Column

AbstractCalcium carbonate (CaCO3) dissolution is an integral part of the ocean's carbon cycle. However, laboratory measurements and ocean alkalinity budgets disagree on the rate and loci of dissolution. In situ dissolution studies can help to bridge this gap, but so far published studies have not been utilized as a whole because they have not previously been compiled into one data set and lack carbonate system data to compare between studies. Here, we compile all published measurements of CaCO3 dissolution rates in the water column (11 studies, 752 data points). Combining World Ocean Atlas data (temperature, salinity) with the neural network CANYON‐B (carbonate system variables), we estimate seawater saturation state (Ω) for each rate measurement. We find that dissolution rates at the same Ω vary by 2 orders of magnitude. Using a machine learning approach, we show that while Ω is the main driver of dissolution rate, most variability can be attributed to differences in experimental design, above all bias due to (diffusive) transport and the synthetic or biogenic nature of CaCO3. The compiled data set supports previous findings of a change in the mechanism driving dissolution at Ωcrit = 0.8 that separates two distinct dissolution regimes: rslow = 0.29 · (1 − Ω)0.68(±0.16) mass% day−1 and rfast = 2.95 · (1 − Ω)2.2(±0.2) mass% day−1. Above the saturation horizon, one study shows significant dissolution that cannot solely be explained by established theories such as zooplankton grazing and organic matter degradation. This suggests that other, non‐biological factors may play a role in shallow dissolution.

Alkaline Phosphatase Activity and Phosphatase-Active Bacteria in Lake Baikal Water Column and Major Tributaries

Phosphorus is one of the major biogenic elements. Its inflow facilitates eutrophication of lake water. In aquatic ecosystems, phosphorus is present mostly in organic compounds. Ability of aquatic microorganisms to assimilate phosphorus from organophosphorous compounds results from activity of alkaline phosphatases; activity of these enzymes may be an indicator of the state of the ecosystem, phosphate load, and water quality. In the present work, alkaline phosphatase activity (APA) and abundance of phosphatase-active bacteria (PAB) in Lake Baikal pelagic zone and in the mouths of its major tributaries was studied. In the pelagic zone, APA and PAB abundance decreased with depth, indicating that the main processes of phosphate generation occurred in the trophic layer of the lake. In the main tributaries, both APA and PAB abundance were considerably higher than in the pelagic zone. These results indicate active biochemical processes of transformation of organophosphorous compounds occur in the estuarine zones of the rivers. The degradation processes result in regeneration of phosphates, which are completely incorporated in the biological turnover, providing for phytoplankton development.

Modeling the hydrodynamic wake of an offshore solar array in OpenFOAM

Offshore solar is seen as a promising technology for renewable energy generation. It can be particularly valuable when co-located within offshore wind farms, as these forms of energy generation are complementary. However, the environmental impact of offshore solar is not fully understood yet, and obtaining a better understanding of the possible impact is essential before this technology is applied at a large scale. An important aspect which is still unclear is how offshore solar affects the local hydrodynamics in the marine environment. This article describes the hydrodynamic wake generated by an offshore solar array, arising from the interaction between the array and a tidal current. A computational fluid dynamic (CFD) modeling approach was used, which applies numerical large eddy simulations (LES) in OpenFOAM. The simulations are verified using the numerical model TUDFLOW3D. The study quantifies the wake dimensions and puts them in perspective with the array size, orientation, and tidal current magnitude. The investigation reveals that wake width depends on array size and array orientation. When the array is aligned with the current, wake width is relatively confined and does not depend on the array size. When the array is rotated, the wake width experiences exponential growth, becoming approximately 30% wider than the array width. Wake length is influenced by factors such as horizontal array dimensions and current magnitude. The gaps in between the floaters decrease this dependency. Similarly, the wake depth showed similar dependencies, except for the current magnitude, and only affected the upper meters of the water column. Beneath the array, flow shedding effects occur, affecting a larger part of the water column than the wake. Flow shedding depends on floater size, gaps, and orientation.

Metagenomic insights into bacterial dynamics and niche partitioning in response to varying oxygen gradients in the Arabian Sea oxygen minimum zone (OMZ)

This study investigates the impact of oxygen gradients on bacterial diversity and community composition within the Arabian Sea oxygen minimum zone (OMZ), providing insight into their ecology in this unique environment. Vertical profiling of physicochemical parameters and bacterial community composition was conducted at two stations within the OMZ using Illumina sequencing of the V3-V4 regions of the 16S rRNA gene. The oxygen levels in the water column of the study locations varied from oxic to hypoxic and Station-I exhibited intense anoxic conditions. Bacterial diversity analyses revealed a rich assemblage of 24 bacterial phyla dominated by Proteobacteria, with significant presence of Actinobacteria and Planctomycetes. SIMPER (Similarity percentage) analysis highlights taxa such as Synechococcophycideae, Flavobacteriia in oxic water and Phycisphaerae as significant contributors to community dissimilarity in oxygen-deficient water, emphasizing their ecological roles in nutrient cycling and the impact of oxygen availability on marine biodiversity. Canonical Correspondence Analysis (CCA) further elucidates the relationships between bacterial communities and environmental variables, with oxygen, temperature, and nutrient concentrations playing crucial roles in shaping bacterial community distributions. This research enhances our understanding of microbial ecology in the Arabian Sea OMZ by revealing how microbial communities respond to changing oxygen conditions, providing insights into the ecological dynamics of the region. Furthermore, these findings underscore the need for continued research to predict and mitigate the effects of environmental changes on marine ecosystems, particularly in the context of expanding OMZs and global biogeochemical cycles.

New evidence from the Paleoproterozoic Gunflint Iron Formation for microbially-driven, early diagenetic precipitation of siderite

Petrographic, geochemical, C-, O-, and clumped isotope measurements of drill core samples from the Paleoproterozoic (1.88 Ga) Gunflint Iron Formation containing siderite, ankerite, Fe-silicate clays (dominantly greenalite) and silica, reveal variable but light carbonate δ13C values (-21.3 to -7.87‰, VPDB), with heavy and less variable carbonate δ18O values (20.6 to 24.9‰, VSMOW). These measurements are consistent with a model in which siderite is formed during early diagenesis as a by-product of the metabolism of dissimilatory iron reducing (DIR) microbes that consume Fe(III)-oxide and organic carbon delivered from the water column to the sediment-water interface. This model indicates that the oxygen isotope compositions of reactant Fe-oxide, organic matter and dissolved inorganic carbon were set in equilibrium with seawater at T = 5–35 °C and δ18O = -1.0 to -6.5‰, prior to being metabolized to form siderite. Clumped isotope measurements on Fe-bearing carbonates yield temperatures (T(Δ47)) between 40 °C-132 °C, which constrain δ18Ofluid to values between -6.22 to 7.32‰. These measurements record the onset temperature of DIR followed by low water-to-rock ratio diagenetic recrystallization at elevated temperature. Combined petrographic, chemical, and isotopic measurements reveal that the major phases delivered to the shallow seafloor were a disequilibrium assemblage of Fe-oxide, greenalite, silica, and organic matter that underwent microbially mediated modification to form an assemblage of siderite, greenalite, silica, and later diagenetic ankerite. We contend that observed differences between carbonate derived from Gunflint core and outcrop may be reconciled by removal of siderite during exposure and weathering, leaving outcrop enriched in late diagenetic ankerite.

An experimental study of vortex evolution around an offshore stationary dual-chamber oscillating water column converter

The Oscillating Water Column (OWC) is a promising Wave Energy Converter (WEC) due to its practicality and efficiency. Conventional single-chamber OWCs exhibit constraints in extracting energy over diverse wave periods, while dual-chamber OWCs demonstrate enhanced adaptability, leading to improved energy capture rates. This study investigates an offshore stationary dual-chamber OWC with an underlying transverse channel designed to facilitate wave ingress and augment energy extraction. Experiments across various wave periods reveal that dual-chamber OWCs with transverse channels achieve superior wave energy extraction compared to single-chamber counterparts. Time-resolved particle image velocimetry (TR-PIV) is employed for detailed flow field measurement to elucidate the complex hydrodynamic processes. Analysis of the water column oscillation and flow dynamics reveals an intensified interaction between hydrodynamic processes in the dual chambers, especially with elongated transverse channels. The Ω method is used to examine vortex evolution, indicating heightened complexity in vortex formation within dual-chamber OWCs compared to single-chamber OWCs. Notably, large-scale vortices emerging in the forward chamber impede oscillation and diminish energy extraction efficiency. Optimizing the design of transverse channel entries, frontal walls, and internal chamber corners is crucial to mitigate flow separation and vortex generation, thereby enhancing overall energy extraction performance.

Evaluating drivers and predictability of catch composition in a highly mixed trawl fishery using stacked and joint species distribution models

Evaluating drivers and the predictability of catch is valuable for the management of mixed fisheries. Drivers can represent or help to identify levers for management and predictable catch compositions are a key component of simulation tools and dynamic management strategies. But modelling mixed fisheries can be challenging due to the large number of taxa, and analysis typically focuses on a few key species or highly aggregated taxa.Here we employ seven types of stacked and joint species distribution models to explore the drivers and predictability of trawl-level catches in an ocean prawn trawl fishery, in New South Wales, Australia. Catch data was sourced from an observer program, with 130 taxa able to be modelled. The main drivers of catch composition were latitude, depth, and seasonality represented here by water temperature. Water column mixing, lunar illumination, and fishing effort were also important for some taxa. Up to 60–80 taxa were predicted with good predictive skill (AUC>0.8, >35 % decline in mean absolute error relative to an intercept-only model), and an additional 40–60 taxa were predicted with lower but still useful predictive skill (AUC>0.7, 25–35 % decline in error). However, the level of predictive skill varied considerably among model type.The best framework for prediction was stacked random forests using a hurdle modelling approach, followed by a spatial joint species distribution model. Our results show that predictive models at a fine spatial-temporal and taxonomic resolutions can be a viable information tool for highly mixed fisheries, but these tools ultimately need to be tested against specific management objectives and performance metrics, such as spatial closures and bycatch:target catch ratios.

A benthic source of isotopically heavy Ni from continental margins and implications for global ocean Ni isotope mass balance

Nickel (Ni) is a bio-essential element for phytoplankton in the modern oceans, and yet, the global ocean mass balance of Ni has puzzled scientists for decades. Many estimates of total Ni output flux are larger than the total Ni input flux to the ocean. The measurement of Ni stable isotopes (δ60Ni) in earth materials may inform our understanding of ocean biogeochemistry and redox conditions in both the modern ocean and the geological past. An ocean Ni stable isotope imbalance has also concerned scientists, with a global ocean δ60Ni of +1.4 ‰ which is notably heavier than the major source of Ni to the oceans from rivers. Recent efforts to resolve Ni and δ60Ni imbalances have focused on the role which manganese (Mn) oxides play in marine Ni cycling, both in the water column and in marine sediments. Manganese oxide rich marine sediments can supply isotopically heavy dissolved Ni to porewater fluids and seawater, but the source of the isotopically heavy porewater Ni remains unclear. Here we present porewater trace metal concentrations and δ60Ni from two sites from the continental margin off southern California. Porewater Ni concentrations are up to roughly 100-fold higher than deep seawater concentrations (∼1 μM compared to 10 nM, respectively). Porewater δ60Ni is near 0 ‰ in the subsurface region where Ni concentrations are highest, suggesting dissolution of lithogenic material from sediments. Porewater δ60Ni increases dramatically towards the sediment-water interface with values of up to +2.66 ‰, which to our knowledge are the heaviest Ni isotope compositions ever reported for natural materials. Measurements of porewater and sediment Ni and Mn concentrations suggest that Ni is released to porewaters in the Mn-reducing zone, and then removed by newly precipitated Mn oxides as Mn and Ni move towards the oxygenated zone of sediments. A simple Rayleigh model suggests a Ni isotope fractionation of factor of -0.61 ‰ for Ni sorption onto Mn oxides, while a diffusion-reaction model suggests a Ni isotope fractionation of -1.80 to -0.96 ‰, always with preferential adsorption of lighter Ni isotopes. This flux of Ni toward the sediment-water interface, coupled with preferential removal of lighter Ni isotopes in marine sediments, provides evidence supporting an isotopically heavy benthic source of new Ni to the oceans, which we estimate has a magnitude of 0.65 × 108 to 1.66 × 108 moles/year. We find that a benthic flux such as measured here over just 0.27-2.70 % of the ocean seafloor could mix with the river δ60Ni of +0.8 ‰ to achieve the observed deep ocean δ60Ni of +1.4 ‰. This study reveals the similarities in how rivers and continental margin sediments supply heavy Ni isotopes to the ocean. In both continental rivers and margin sediments, terrigenous Ni is released with an δ60Ni near 0.1 ‰, but lighter isotopes are captured by precipitation onto oxides so that the dissolved flux to the ocean is isotopically heavier than the terrigenous material from which Ni was released, and in the case of margin sediments may be heavier than even bulk seawater δ60Ni. We thus recognize continental margin sediments with active Mn cycling as a ‘new’ source of isotopically heavy dissolved Ni to the ocean.

Potential of CO2 sequestration by olivine addition in offshore waters: A ship-based deck incubation experiment

Ocean alkalinity enhancement is considered as an effective atmospheric CO2 removal approach, but currently, little is known about the carbon sequestration potential of implementing olivine addition in offshore waters. We investigated the effect of olivine addition on the seawater carbonate system by carrying out a deck incubation experiment in the Northern Yellow Sea; the dissolution rate of olivine was calculated based on the increase in seawater alkalinity (TA), and the CO2 sequestration potential was evaluated. The results showed that the dissolution of olivine increased seawater TA and decreased partial pressure of CO2, resulting in oceanic CO2 uptake from the atmosphere through sea-air exchange; it also increased seawater pH and mitigated ocean acidification to a certain extent. The addition of 1 ‰ olivine had a more significant effect on the seawater carbonate system than 0.5 ‰ olivine addition. The average dissolution rate constant of olivine was 1.44 ± 0.15 μmol m−2 d−1. Assuming that olivine settles completely on the seabed due to gravity, the theoretically maximum amount of CO2 removed by applying 1 tonne of olivine per square meter area in the Northern Yellow Sea is only 2.0 × 10−4 t/m2. Therefore, when olivine addition is implemented in the offshore waters, it is necessary to consider reducing the olivine size, prolonging the settling time of olivine in the water column; and spreading olivine in well-mixed waters to prolong the residence time through repeated resuspension, thus increasing its potential in carbon sequestration.

Maximizing oscillating water column efficiency: The impact of vertical plate and guide vane

This study is centered on improving the hydrodynamic efficiency of a conventional Oscillating Water Column (OWC) that has a rectangular cross-section. The OWC chamber is modified by introducing a centrally installed vertical plate, dividing it into two sub-chambers, and further incorporating a quarter-circle guide vane beneath the vertical plate. Physical experiments are conducted under three scenarios: the conventional single-chamber OWC, the OWC with double sub-chambers separated by a vertical plate, and the OWC with both a vertical plate and a guide vane. Hydrodynamic efficiency is examined across varying Power Take-Off (PTO) dampings, incident wave frequencies, and wave heights. Results demonstrate substantial efficiency improvements with the vertical plate, particularly at lower dimensionless wave frequencies. The guide vane also boosts these benefits by preventing vortex formation due to flow separation, resulting in a total average efficiency increase of 42 %. Visual observations highlight the transition from sloshing to piston-like motion induced by the vertical plate, contributing to increased kinetic energy and improved efficiency. The study highlights that basic but effective modifications can substantially enhance OWC efficiency, suggesting promising directions for the development of wave energy conversion technology.

Aquacultural source of nitrous oxide revealed by nitrogen isotopes

The rapid expansion of coastal aquaculture has led to an increase in the coverage of aquaculture ponds, where intense feed-derived nitrogen is causing significant emissions of nitrous oxide (N2O). Multiple N2O production pathways and the relative importance of water column vs. sedimentary production in aquaculture ponds remain uncertain. Clarifying these pathways is vital for sustainable aquaculture development. Using 15N-labeled dissolved inorganic nitrogen, the pathways and rates of N2O production in subtropical aquaculture ponds located in south China, cultivating whiteleg shrimp, Japanese seabass, and giant river prawn, were successfully characterized. Total N2O production rates ranged from 6 to 70 µmol-N m−2 d−1, with the shrimp pond exhibiting the highest total N2O production rates, followed by ponds for seabass and prawn. These differences are primarily due to varying feed amounts causing differences in dissolved nutrients in water column and sediment. Particularly, nutrient and organic matter accumulation at the surface sediment stimulated N2O production. The oxygenated sediment on a centimeter scale could produce substantially more N2O compared to the water column above on a meter scale. Partial denitrification, i.e., nitrate and nitrite reduction to N2O, was more important (> 60 %) for N2O production in aquaculture ponds. The availability of nitrite is likely a major factor driving partial denitrification for both sedimentary and water column N2O production.

Abundant small microplastics hidden in water columns of the Yellow Sea and East China Sea: Distribution, transportation and potential risk

Microplastics (MPs) pose significant concerns for marine ecological security due to their minuteness and ubiquity. However, comprehensive knowledge on their distribution and fate in seawater columns remains limited. This study investigated the abundances and characteristics of MPs across 3–6 water layers in the South Yellow Sea and East China Sea. Results indicate that high-abundance small MPs (< 100 µm) (average 6567 items/m3) were hidden beneath the sea-surface, predominantly fine-grained particles (< 20 µm) and high-density polymers (> 1.03 g/cm3). The total suspended MPs (5.0–834.2 µm) are estimated at 2.9–3.1 × 1017 particles, with most of them occurring in upper layers. In profiles, their distribution varied by physical properties with depth; fragment-shaped and high-density MPs increased in proportion at greater depths, contrasting with fibrous MPs. These MPs originated primarily from the Yangtze River and their winter transport was driven by the Yangtze River Dilution Water, East China Sea Coastal Current, and Yellow Sea Warm Current, resulting in their accumulation in coastal and estuarine regions. Consequently, the Yangtze River Estuary ecosystem faces substantial risks from MP pollution throughout the water column. This work unveils the prevalence of small MPs in coastal water columns and intricate interaction between their fate and hydrodynamic conditions.

The vertical calcification mode of planktonic foraminifera in the Western Pacific Warm Pool

A thorough knowledge of the ecology of planktonic foraminifera throughout the water column is necessary for a reliable reconstruction of the paleooceanographic environment of the upper-middle water column. However, little is known about the planktonic foraminifera in the Western Pacific Warm Pool (WPWP), especially for the deep dwelling species. Here we present the stable oxygen isotope (δ18O) data of eight species collected from vertically stratified plankton tows across 0–500 m water depth from 5 sites in the WPWP during autumn, the vertical mode of foraminiferal calcification is explored. Vertical plankton tows provide more detailed information than other materials, it indicates a wider depth range of foraminiferal calcification than the other sample types. All the species exhibit a complex vertical calcification process that the majority of specimens precipitate their tests out of the depth at which they were obtained. It could be connected to the intricate hydrological conditions in the WPWP and/or the foraminiferal ontogenetic trajectory. Calcification depth range of the investigated species is substantially smaller than their living depth, and most of them prefer to calcify inside the abundant layers. Additionally, we found no clear correlation between foraminiferal test size and shell δ18O for any of the species that were studied at any of the locations.

Paleoenvironmental factors controlling organic-rich formations deposition in the Babouri-Figuil Basin (Northern Cameroon)

The Babouri-Figuil Basin is an intracratonic basin (half-graben) in northern Cameroon that is genetically connected to the Benue Trough from Nigeria, and is an area of interest in terms of petroleum prospectivity. Recent studies highlighted the presence of organic-rich formations in the basin. However, none of these works have identified factors that governed the accumulation of organic matter (OM) in the sediments. The main objective of this work is the characterization of these formations through palynofacies and organic geochemical techniques (total organic carbon - TOC, total sulfur, insoluble residue and biomarkers), in order to determine the organic facies, their depositional environments and the main drivers for organic enrichment in the basin. The current study reveals that black shale and massive claystone lithologies constitute the main organic-rich formations in the basin, with TOC reaching up to 26.08 wt%, being characterized by a dominance of bacterially-derived amorphous OM. Palynofacies and biomarker data revealed that these formations are positively associated with anoxic conditions and a partly highly saline and stratified lake water column. The deposition of organic-rich formations in the Babouri-Figuil Basin was mainly controlled by restriction conditions which developed in connection with the regional tectonic framework. The Lower Cretaceous rifting episode in the West and Central African Rift System (WCARS) basins led to the formation of accommodation space, a reduction in water levels, and the development of anoxic conditions within the basin, facilitating the deposition of organic-rich formations. Therefore, the organic enrichment of the Babouri-Figuil Basin has been predominantly controlled by its tectonic evolution, particularly during the syn-rift phase. This phase created favorable conditions for the deposition and preservation of OM, including the establishment of anoxic conditions. Additionally, the paleoclimate (arid conditions), the development of bacterial biomass, and the basin's paleogeography all played a significant role in this process. The organic-rich formations of the Babouri-Figuil Basin show characteristics of prospective petroleum source rocks (high organic content, high proportion of oil-prone kerogen, significant thickness and lateral extension). The combination of organic-rich formations with sandstone deposits above and extensive claystone/shale deposits on top can indicate the presence of an oil play in the basin. A detailed study with broader sampling is needed to investigate thoroughly the variation of organic facies and the influence of paleoenvironmental factors that control the deposition of thick source rock intervals.