Ocean System Research Articles

Roly-poly inspired tribo-electromagnetic energy harvester toward sustainable ocean energy harvesting

With the increasing global population, the demand for energy has also risen significantly. However, the utilization of fossil fuels for the purpose of energy production has resulted in the release of carbon emissions, accelerating the global warming. Therefore, the demand for carbon-free and renewable energy sources, which can replace the fossil fuels, is growing. In this study, a roly-poly-structure-inspired hybridized energy generator (RPHG) is demonstrated by combining a roly-poly triboelectric nanogenerator with an electromagnetic generator. By utilizing the RPHG, multiple vibrations can be induced from an external force due to the recovering force originated by the roly-poly structure of the RPHG. Consequently, the RPHG is capable of harvesting multiple vibrations from a single input vibration. To optimize the electrical performance of the RPHG, the effects of the substrate shape and the number of polytetrafluoroethylene balls into the electrical output is investigated. Also, the effect of the center of gravity on the electrical output generated from the RPHG is theoretically and experimentally confirmed. As a result, the average vibration number is increased from 2.6 to 25.1 with the 20 polytetrafluoroethylene balls when the tilted substrate with a tilted angle of 170° is applied to the RPHG, compared to the electrical output is generated from the RPHG with a flat substrate. The synergistic effect of the hybridization is demonstrated by comparing the charging speeds of a capacitor and the RPHG shows the fastest speed for charging the capacitor. Furthermore, our RPHG generates 2.45 and 19.29 times higher electrical output than the roly-poly triboelectric nanogenerator (RP-TENG) and electromagnetic generator, respectively. The proposed RPHG demonstrates the 195% higher conversion efficiency in terms of energy compared to the power owing to its unique structure. Also, although the RP-TENG and TENG without roly-poly structure (NRP-TENG) generate similar electrical power, the RP-TENG generates 242% higher electrical energy than NRP-TENG, showing the great potential to harvest the mechanical energy due to the roly-poly structure. As an application, a self-powered ocean wave monitoring system is implemented using the RPHG and it successfully detects strong, calm, and gentle waves. These results show the great potential of the RPHG to harvest vibration and ocean wave energy. Hence, we expect our RPHG to be a promising energy-harvesting solution for generating carbon-free energy.

Multivariate Upstream Kuroshio Transport (UKT) Prediction and Targeted Observation Sensitive Area Identification of UKT Seasonal Reduction

Variation and seasonal reduction in the Upstream Kuroshio Transport (UKT) have important impacts on surrounding climate and oceanic circulation systems. Therefore, reliable UKT prediction is crucial. In this paper, we propose an intelligent UKT prediction model, KuroshioNet, which is firstly pre-trained with simulation data generated by the Regional Ocean Modeling System (ROMS) and then fine-tuned with reanalysis data of the Simple Ocean Data Assimilation (SODA). Operating at a five-day time resolution and a 0.5°spatial resolution, KuroshioNet has the capability to predict multivariate fields associated with upstream Kuroshio, including 3D variables like velocity, temperature, as well as salinity and 2D variables like sea surface height. Subsequently, the UKT is computed from the predicted fields. We evaluate and analyze the experimental results, which show that KuroshioNet has a lead time of 55 days for UKT prediction. In order to enhance the physical interpretability of KuroshioNet, we conduct an ablation experiment to evaluate the impact of each predictor on prediction skill. It demonstrates that selecting zonal velocity, meridional velocity, temperature, salinity, and SSH contributes to UKT prediction by KuroshioNet. Besides, by analyzing model performance and visualizing what the convolutional kernels learn, we find that KuroshioNet, which has learned from ROMS data, is capable of obtaining better initial performance and acquiring more active kernels to better learn the features in SODA data. Furthermore, we identify the targeted observation sensitive area of UKT seasonal reduction by KuroshioNet with the saliency map method, which is situated to the east of upstream kuroshio. The sensitive area is consistent with the result identified by numerical models and yields 38.1% improvement on prediction demonstrated by observing system simulation experiments.

The Ophiolite-Hosted Cu-Zn VMS Deposits of Tuscany (Italy)

Several Jurassic, ophiolite-hosted Cu-Zn VMS deposits occur in Tuscany. They are hosted by tectonic units of oceanic affinity (Ligurian Units), such as the well-known deposits of nearby Liguria. Industrial production was small and definitively ceased in the 1960s. Locally, massive ore (chalcopyrite-bornite-chalcocite) with an exceptionally high grade was found. The Montecatini Val di Cecina mine exploited the largest “bonanza” and, for few decades in the 19th century, became one of the most profitable copper mines in Europe. This study provides an updated review of these deposits. Tuscan Cu-Zn VMSs mostly occur in proximity of the contact between the serpentinite-gabbro basement and the overlying basalts. Chalcopyrite-pyrite stockworks occur in serpentinite-gabbro cut by dolerite dykes, while the largest massive sulphide bodies are hosted by polymictic-monomictic breccias at the base of pillow basalts. Early chalcopyrite ores were mechanically–chemically reworked and upgraded to bornite-rich nodular ore embedded in a chlorite, calcic amphibole, Fe-rich serpentine, quartz, andradite, ilvaite, and xonotlite assemblage. This bornite-rich ore contains substantial amount of sphalerite and pyrite and ubiquitous grains of clausthalite, hessite, tellurium, and gold. They represent a prime example of the sub-seafloor portion of a hybrid mafic-ultramafic oceanic hydrothermal system formed in an OCC along the slow spreading ridge of the Jurassic Piedmont-Ligurian Ocean. The peculiar mineralogical–textural character of the bornite-rich ore was driven by an interface coupled dissolution–precipitation process mediated by fluids.

Evolution of the Neo-Tethys traced by Late Triassic to Early Cretaceous marine remnants in the eastern segment of the Yarlung-Tsangpo suture zone, southern Tibet

Widely distributed siliceous mélanges in the Yarlung-Tsangpo suture zone preserve significant information of the Neo-Tethys and subduction-accretion processes. Similar ophiolites and siliceous mélanges are well exposed in the Xigaze and Zedong areas, however, their relationship including age assignments, depositional environments, and accretionary process remains vague. Based on radiolarian biostratigraphy (56 species belonging to 35 genera), black cherts from the Carnian to the Norian (Late Triassic), red cherts from the Aalenian to Bathonian (Middle Jurassic), and siliceous mudstones of the Berriasian (Early Cretaceous) are distinguished from siliceous mélange in the Zedong area. Values of Al/(Al + Fe + Mn) indicate that the siliceous rocks are biogenic silica derived. The diagrams of Al2O3/(Al2O3 + Fe2O3) vs Fe2O3/TiO2 and Al2O3/(Al2O3 + Fe2O3) vs LaN/CeN indicate siliceous rocks were deposited far from the ridge. Weak positive Ce anomaly and low ratio of LaN/CeN indicate that siliceous rocks were deposited in a deep-sea basin proximal to terrigenous sources. Comprehensive summary of studies on Bainang siliceous mélange, Xigaze ophiolite, Zedong ophiolite, and Zedong siliceous mélange reconstructs the Ocean Plate Stratigraphy (OPS) and the evolution of the Neo-Tethys since the Late Triassic till the Early Cretaceous. Mélanges in Xigaze and Zedong were formed in different intra–oceanic subduction-accretion systems at different times in the Neo-Tethys Ocean during the Cretaceous.

Stable Chromium Isotope Fractionation During the Alteration of Abyssal Peridotite: Implications for Marine Chromium Isotope Mass Balance

AbstractThe stable chromium isotope system has been widely used as a redox proxy to reconstruct the oxygenation history of ocean atmosphere systems. However, the Cr isotope mass balance in modern oceans (i.e., inputs and outputs) remains poorly constrained. To investigate the influence of seawater‐peridotite reaction on the global marine Cr isotope mass balance, we report high‐precision Cr isotope data (δ53Cr) on a series of fresh and altered abyssal peridotites from the Gakkel Ridge and the Southwest Indian Ridge (SWIR). The least altered peridotites give a δ53Cr value of −0.08 ± 0.06‰ (2SD, n = 4) for the oceanic mantle which is consistent with the established δ53Cr of the Bulk Silicate Earth. Compared to fresh peridotites, a subset of altered peridotites exhibit a loss of isotopically light Cr with relatively positive δ53Cr values (up to 0.04‰). These altered peridotites are characterized by significant Cr loss and likely have been subject to serpentinization. By contrast, seafloor weathering has limited influence on the Cr concentrations and isotopic compositions of the altered peridotites. Monte Carlo (MC) simulations of marine alteration suggest a net Cr flux into seawater from altered abyssal peridotites of ∼3.5 × 108 mol/yr, which is on the same order of magnitude as the riverine input flux of 108–109 mol/yr. Furthermore, the MC results suggest that the peridotite‐sourced net Cr flux has a negative δ53Cr signature (−0.33 ± 0.21‰, 2SD). Thus, seawater‐peridotite interactions must be considered when evaluating the modern oceanic Cr isotope mass balance.

Ubiquitous filter feeders shape open ocean microbial community structure and function.

The mechanism of mortality plays a large role in how microorganisms in the open ocean contribute to global energy and nutrient cycling. Salps are ubiquitous pelagic tunicates that are a well-known mortality source for large phototrophic microorganisms in coastal and high-latitude systems, but their impact on the immense populations of smaller prokaryotes in the tropical and subtropical open ocean gyres is not well quantified. We used robustly quantitative techniques to measure salp clearance and enrichment of specific microbial functional groups in the North Pacific Subtropical Gyre, one of the largest ecosystems on Earth. We discovered that salps are a previously unknown predator of the globally abundant nitrogen fixer Crocosphaera; thus, salps restrain new nitrogen delivery to the marine ecosystem. We show that the ocean's two numerically dominant cells, Prochlorococcus and SAR11, are not consumed by salps, which offers a new explanation for the dominance of small cells in open ocean systems. We also identified a double bonus for Prochlorococcus, wherein it not only escapes salp predation but the salps also remove one of its major mixotrophic predators, the prymnesiophyte Chrysochromulina. When we modeled the interaction between salp mesh and particles, we found that cell size alone could not account for these prey selection patterns. Instead, the results suggest that alternative mechanisms, such as surface property, shape, nutritional quality, or even prey behavior, determine which microbial cells are consumed by salps. Together, these results identify salps as a major factor in shaping the structure, function, and ecology of open ocean microbial communities.

Switches between nitrogen limitation and nitrogen–phosphorus co‐limitation in the subtropical North Atlantic Ocean

AbstractConcentrations of bioavailable inorganic nitrogen (N) and phosphorus (P) are simultaneously depleted in the (sub)tropical North Atlantic Ocean, but it remains unclear if phytoplankton growth rates are N limited or N–P co‐limited. Here we present findings from three bottle‐scale experiments using a four‐by‐four matrix of low‐level N and P additions, conducted at one site in the subtropical North Atlantic Ocean. Phytoplankton responses were assessed both in terms of bulk chlorophyll a (Chl a) concentrations and intracellular Chl a of dominant Prochlorococcus and Synechococcus groups. Two matrix experiments suggested that N was independently limiting in situ growth, with no co‐limiting role for P, while the third showed co‐limitation by both N and P in this region. This switch from N limitation to N–P co‐limitation was attributed to an episodic wet deposition event that supplied N, thereby stimulating phytoplankton growth and consuming available P. Such rapid transitions in nutrient limitation in response to environmental forcing might be common in oceanic systems with multiple depleted nutrients.

Simultaneous sensing profiles of beam attenuation coefficient and volume scattering function at 180° using a single-photon underwater elastic-Raman lidar.

Lidar has emerged as a promising technique for vertically profiling optical parameters in water. The application of single-photon technology has enabled the development of compact oceanic lidar systems, facilitating their deployment underwater. This is crucial for conducting ocean observations that are free from interference at the air-sea interface. However, simultaneous inversion of the volume scattering function at 180° at 532 nm (βm) and the lidar attenuation coefficient at 532 nm (K l i d a r m) from the elastic backscattered signals remains challenging, especially in the case of near-field signals affected by the geometric overlap factor (GOF). To address this challenge, this work proposes adding a Raman channel, obtaining Raman backscattered profiles using single-photon detection. By normalizing the elastic backscattered signals with the Raman signals, the sensitivity of the normalized signal to variations in the lidar attenuation coefficient is significantly reduced. This allows for the application of a perturbation method to invert βm and subsequently obtain the K l i d a r m. Moreover, the influence of GOF and fluctuations in laser power on the inversion can be reduced. To further improve the accuracy of the inversion algorithm for stratified water bodies, an iterative algorithm is proposed. Additionally, since the optical telescope of the lidar adopts a small aperture and narrow field of view design, K l i d a r m tends to the beam attenuation coefficient at 532 nm (cm). Using Monte Carlo simulation, a relationship between cm and K l i d a r m is established, allowing cm derivation from K l i d a r m. Finally, the feasibility of the algorithm is verified through inversion error analysis. The robustness of the lidar system and the effectiveness of the algorithm are validated through a preliminary experiment conducted in a water tank. These results demonstrate that the lidar can accurately profile optical parameters of water, contributing to the study of particulate organic carbon (POC) in the ocean.

OPO-CVI: design and implementation of an ocean profiling observation system for wave-powered vertical profiler following an ISO standard

This paper presents the design and implementation of an ISO-compliant ocean profiling observation system for wave-powered vertical profiler. This system aims to provide a comprehensive, scalable, and interoperable solution for high-resolution, real-time oceanic observation. As a part of this system, we introduce a wave-powered vertical profiler, known as “Wave Master,” designed to offer enhanced stability and reliability for long-term oceanic data collection. The core of the paper focuses on the Ocean Profiling Observation Complex Virtual Instrument (OPO-CVI), a comprehensive system developed in alignment with ISO 21851 standard. OPO-CVI seamlessly integrates data collection, transmission, storage, and visualization. Specifically, OPO-CVI addresses the challenges of information isolation, system rigidity, and lack of modularity in traditional ocean profiling methods by standardizing data formats and transmission protocols, allowing for seamless integration of new observation elements, and employing a modular architecture for enhanced scalability and reusability. By offering detailed technical insights into the OPO-CVI architecture and its compliance with ISO 21851 standard, this paper aims to contribute significantly to the advancement of standardized, efficient, and reliable oceanic observation systems.

Horizontally forced initiation of the Izu-Bonin-Mariana subduction zone

The sparsity of a direct record for the moment of subduction zone initiation has led to various models describing the infancy and evolution of modern oceanic subduction systems. Recently, with increases in available samples and geochemical data for subduction zone initiation-to-mature-arc lavas, better constraints on subduction evolution are possible. Here, by systemically modeling the time-space pattern and geochemical characters of forearc magmas with forward numerical modeling, we attempt to search for a best-fit geodynamic scenario where Izu-Bonin-Mariana-type subduction tends to develop. Our modeling and geochemical constraints have identified a necessary and possibly transitory pre-subduction zone initiation trenchward contraction consistent with observed Izu-Bonin-Mariana forearc magma geochemistry. Our results also reveal a typical maturation process for Izu-Bonin-Mariana-type oceanic subductions, controlled by the pace of the upper plate’s rifting and solidification.

Multi-scale spatial features and temporal attention mechanisms: advancing the accuracy of ENSO prediction

The exponential progression in oceanic observational technology has fostered the accumulation of substantial time series data pivotal for predictions in ocean meteorology. Foremost among the phenomena observed is El Niño-Southern Oscillation (ENSO), a critical determinant in the interplay of global ocean atmosphere interactions, with its severe manifestations inducing extreme meteorological conditions. Therefore, precisely predicting ENSO events carries immense gravitas. Historically, predictions hinged primarily on dynamic models and statistical approaches; however, the intricate and multifaceted spatiotemporal dynamics of ENSO events have often impeded the accuracy of these traditional methodologies. A notable lacuna in contemporary research is the insufficient exploration of long-term dependencies within oceanic data and the suboptimal integration of spatial information derived from spatiotemporal data. To address these limitations, this study introduces a forward-thinking ENSO prediction framework synergizing multiscale spatial features with temporal attention mechanisms. This innovation facilitates a more profound exploration of temporal and spatial domains, enhancing the retention of extensive-period data while optimizing the use of spatial information. Preliminary analyses executed on the global ocean data assimilation system dataset attest to the superior efficacy of the proposed method, underscoring a substantial improvement over established methods including SA-convolutional long short-term memory, particularly in facilitating long-term predictions.The source code and datasets are provided. The code is available at https://github.com/tse1998/ENSO-prediction.

Mechanism of methane migration in oceanic hydrate system: Insights from microfluidic investigations

Methane vents and gas hydrate systems coexist extensively in many regions of the world's oceans, posing challenges to the predictions of global carbon budgets and climate. However, the understanding of how methane gas migrates through deep-sea hydrate-bearing sediments and ultimately enters the overlying seawater is still incomplete. To address this issue, we used microfluidic technology to study the pore-scale mechanisms of free gas methane migration under hydrate-forming conditions. The microfluidic device is used to simulate the porous medium in submarine reservoir. The nucleation and growth of hydrates in saturated solution under the condition of methane and water flow were observed. Results indicate that during seepage, methane bubble surfaces continuously undergo the formation and detachment of tinny hydrate fragments, acting like an upward-flowing hydrate seeder. These flowing hydrate-bearing bubbles and hydrate fragments are capable of penetrating the entire oceanic hydrate system. Once captured elsewhere, these hydrate seeds, like other kinetic promoters, can significantly accelerate hydrate evolution at certain locations. Meanwhile, flowing methane repeatedly collides with the trapped hydrate fragments, either leading to the continuous flow of free methane or adsorption to the surface of the trapped hydrate fragments and eventually nucleation. Furthermore, when hydrates occupy the majority of pore channels, free methane gas can migrate through the water film between hydrates and the matrix. These three migration mechanisms may all contribute to the sustained emission of methane gas in natural seafloor hydrate systems.

Basic design optimization of power and desalinated water for hybrid cycle ocean thermal energy conversion system integrated with desalination plant

AbstractOcean thermal energy conversion (OTEC) is a heat engine application that utilizes the Rankine cycle to extract energy from the thermal gradient between surface seawater and deep seawater. Hybrid cycle OTEC (H-OTEC) is a combination of an open cycle desalination system and a closed-cycle power generation system that leverages the features of both cycles. Unlike other desalination technologies that require extensive energy to operate, H-OTEC relies entirely on renewable energy. In addition, a desalination plant can be coupled with the H-OTEC system (H-OTEC + D) to improve its performance. Conventionally, the total heat transfer area of heat exchangers per net power is used as an objective function to achieve optimal performance with the lowest capital expenditure cost. The proposed objective function, unlike the conventional one, considers both power and water. In this study, the optimization of H-OTEC + D and H-OTEC is carried out by minimizing the proposed objective function, considering several independent variables. The performance of both systems is evaluated in terms of the objective function, power consumption, seawater flow rates, and desalination ratio. The findings also indicate the effectiveness of the proposed objective function over the conventional one as an effective tool for maximizing power and desalinated water generation.

Effect of working fluid on the ORC cycle performance of the ocean thermal energy conversion system

Effect of working fluid on the ORC cycle performance of the ocean thermal energy conversion system

Observations reveal onshore acceleration and offshore deceleration of the Kuroshio Current in the East China Sea over the past three decades

The Kuroshio Current (KC) in the East China Sea is one of the most prominent components of the ocean circulation system in the North Pacific. The onshore intensification of the KC is found to drive nutrient-rich upwelling in the shelf regions, induce anomalous warming that leads to coastal marine heatwaves, and reduce the ability of the oceans to absorb anthropogenic carbon dioxide. Based on altimeter and in situ observations, we find an onshore acceleration and offshore deceleration of the KC over the past three decades. This intensification is characterized by a spatial mean onshore acceleration (offshore deceleration) of 0.39 (−0.63) cm s−1 per decade. This phenomenon can be attributed to changes in wind stress curl (WSC) and oceanic stratification over the subtropical North Pacific. The weakened WSC decreases the vertical extent of the KC by reducing its transport and contributes to the offshore deceleration, whereas the enhanced stratification drives the uplift of the KC and contributes to the onshore acceleration. Our findings underscore the importance of establishing and maintaining a long-term monitoring network for the zonal variations of the KC in the future to obtain a comprehensive understanding of the associated impacts.

Composite vertical structures and spatiotemporal characteristics of abnormal eddies in the Japan/East Sea: a synergistic investigation using satellite altimetry and Argo profiles

Mesoscale eddies are omnipresent and play an important role in regulating Earth’s climate and ocean circulation in the global ocean. Here using the combination of satellite altimetry products and Argo float profile data, two types of abnormal eddies are investigated: WCEs(warm cyclonic eddies) and CAEs(cold anticyclonic eddies) with different cores than conventional eddies in the Japan/East Sea. By applying a classification method based on the calculation of the heat content anomalies in the upper ocean, it was found that 10% of the eddies that captured the Argo float profiles exhibited obvious abnormal features. Subsequently, their spatiotemporal distributions and characteristics were analyzed statistically. Three-dimensional structures of abnormal eddies were obtained via the composite analysis method, showing that the warm/cold and light/dense core of the composite WCE/CAE is confined to the upper 100 m of the ocean with a maximum temperature anomaly of approximately +1.0(-1.1)°C. The composite WCE had a double-core salinity structure with a salty core above 50 m and an inferior fresh core. Meanwhile composite CAE had a fresh single-core with a maximum magnitude of -0.05 psu. Abnormal eddies are pervasive in the Japan/East sea, a revaluation of the role of these eddies in ocean circulation and climate systems, such as heat and salt transport, air and sea interaction, and variability in mixed layer depth, is of great importance.

Diurnal to interannual variability in the Northeast Atlantic from hydrographic transects and fixed time-series across the Rockall Trough

The southern entrance to the Rockall Trough is subject to a complex set of dynamic processes, influenced by Atlantic gyre interactions, the North Atlantic Current, slope boundary currents, variable wind stress forcing, mesoscale activity, and a changing supply of modified water masses formed elsewhere in the Atlantic. These processes drive large temporal and spatial variations, and mixing of surface and intermediate water mass properties that advect through the Trough and drive variations in the deeper waters circulating around it. Here, we investigate variability across the southern and central Rockall Trough from standard hydrographic sections (2006–2022) and deepwater moored subsurface measurements, to better understand changes in water column characteristics and water mass modification during advection through the Rockall Trough and track the aftermath of recent freshening events. Rapid and longer-term physical changes are assessed along with spatial variability and watermass interaction. Interannual variability is large across intermediate depths, deeper circulations are regenerated and a salinity core associated with the eastern boundary current is detailed. Establishing, maintaining, monitoring and analysis of observational ocean time-series datasets are a fundamental requirement for managing and conserving crucial biological resources and are key to understanding oceanic and earth system change.

Performance analysis of ocean thermal energy conversion system integrated with waste heat recovery from offshore oil and gas platform

To improve ocean thermal energy conversion (OTEC) system efficiency, four systems utilizing the waste heat recovery from offshore oil and gas platform are proposed, including flue gas boosting OTEC (system I), production water boosting surface seawater OTEC (system II), production water boosting working medium OTEC (system III), and production water boosting vapor OTEC (system IV). The system thermodynamic performance are investigated. The results show that system IV has larger power generation (Wnet), thermal efficiency (ηth) and exergy efficiency (ηex) than others. Compared with single OTEC system, for system IV, Wnet, ηth and ηex are increased by 1569.13 %, 70.35 % and 138.26 %, respectively. For system IV, with the increase of flue gas waste heat quantity from 2000 to 4000 kW, Wnet, ηth and ηex are increased by 562 %, 390 % and 181 % respectively; with the increase of production water waste heat quantity from 0 to 100 kW, Wnet, ηth and ηex are 12.59 %, 5.73 % and 2.86 % respectively. Wnet rises first and then decreases with the increase of evaporation pressure (Peva) or base fluid concentration (xb), presenting an optimal Peva of 1.5 MPa and xb of 0.82 corresponding to the maximum Wnet; Wnet decreases with the increase of condensation temperature.

Deciphering variations in the surficial bacterial compositions and functional profiles in the intersection between North and South Yellow Sea

The coastal ocean systems play paramount role in the nutrient biogeochemistry because of its interconnected environment. To gain a novel insight into coupling relationships between bacterial community, functioning properties and nutrient metabolism, we conducted analysis on the patterns and driving factors of planktonic bacterial functional community across subsurface water of marine ranching near the Yellow Sea in both summer and winter. Illumina HiSeq Sequencing and a corresponding set of biogeochemical data were used to assess distribution patterns of taxa, adaptive mechanism and metabolic function. Results demonstrated that Proteobacteria, Cyanobacteria, Actinobacteriota and Bacteroidota were dominant phyla both in summer and winter. Taxonomic profiles related to nutrient variation were found to be highly correlated with Dissolved Oxygen (DO) and Chlorophyll fluorescence (FLUO), and distinct diversity differences were also found between summer and winter samples. Functional activity in summer associated with the relative abundance of phototrophy and photoautotrophy were the highest in the subsurface water, while in winter the dominant functional properties were mainly include chemoheterotrophy and aerobic_ chemoheterotrophy. A significant difference related to functional activity between summer and winter, mainly representing ligninolysis and iron_respiration. In general, our study provides a framework for understanding the relative importance of environmental factors, temperature variation and nutrient availability in shaping the metabolic processes of aquatic microorganisms, particularly in ocean mariculture systems.

Vertical distribution of epibenthic megafauna of a large seamount west of Cape Verde islands (tropical North Atlantic)

Seamounts are thought to function as hotspots of megafauna diversity due to their topology and environmental characteristics. However, assessments of megafauna communities inhabiting seamounts, including diversity and density, are scarce. In this study, we provide megafauna diversity and density estimates for a recently discovered, not yet characterized seamount region (Boetius seamounts) west of Cape Verde (N17° 16′, W29° 26′). We investigated the distribution of epibenthic megafauna over a large depth gradient from the seamount’s summit at 1400 m down to 3200 m water depth and provided qualitative and quantitative analyses based on quantified video data. In utilizing an ocean floor observation system (OFOS), calibrated videos were taken as a horizontal transect from the north-eastern flank of the seamount, differentiating between an upper, coral-rich region (−1354/−2358 m) and a deeper, sponge-rich region (−2358/−3218 m). Taxa were morphologically distinguished, and their diversity and densities were estimated and related to substrate types. Both the upper and deeper seamount region hosted unique communities with significantly higher megafauna richness at the seamount’s summit. Megafauna densities differed significantly between the upper (0.297 ± 0.167 Ind./m2) and deeper community (0.112 ± 0.114 Ind./m). The seamount showed a vertical zonation with dense aggregations of deep-sea corals dominating the seamount’s upper region and colonies of the glass sponges Poliopogon amadou dominating the deeper region. The results are discussed in light of detected substrate preferences and co-occurrence of species and are compared with findings from other Atlantic seamounts.