Deep Seawater Research Articles

Geochemical Characteristics of Trace Elements and Mineralization Model of the Ediacaran-Early Cambrian Phosphorites, South China.

As a nonrenewable resource, phosphate rock is an important support for the development and survival of the national economy. The regional distribution and output of phosphate rock in China are extremely uneven, and the amount of high-quality ore resources is relatively poor, which seriously restricts the development and utilization of phosphate rock resources in China. This paper briefly summarizes the distribution characteristics of phosphate rock resources and summarizes the characteristics and research progress of Ediacaran-early Cambrian phosphorus mineralization types, geological characteristics, and deposit genesis of the Yangtze platform in South China. The Ediacaran-early Cambrian sedimentary phosphorite deposits in China are mainly distributed in Yunnan, Guizhou, Hubei, Sichuan and Hunan provinces of the Yangtze platform, in which the early Cambrian phosphate deposits are also rich in rare earth elements, associated with uranium, nickel, molybdenum, vanadium, and other beneficial metal elements. The increase of atmospheric oxygen content at the Ediacaran-Cambrian boundary may have promoted the extensive oxygenation of the late Neoproterozoic oceans, so the Ediacaran-early Cambrian oceans generally showed a reductive environment, and there may be dynamic chemical stratification of the oxidation zone-sulfide zone-iron zone. Up to the early Cambrian, the redox stratified structure of Precambrian seawater may still be inherited, showing that the surface water is an oxidizing environment, changing to a reduction environment, and even wedge-shaped sulfide water is developed at the bottom of the deep basin. The main phosphorus sources are deep phosphorus-rich seawater, continental weathering, and deep hydrothermal activity of Ediacaran-early Cambrian marine sedimentary phosphorite deposits in South China. The genetic mechanisms of phosphorite deposits in the Yangtze platform in South China are mainly biogenic, upwelling phosphorus-forming theory, mechanical mineralization, and syn-sedimentary hot water mixed genesis. In the future, it is still necessary to further explore the internal relationship between phosphorus deposits and major geological events, the in situ analysis of microstructure of phosphate rock ores, and the genetic mechanism of phosphate deposits and the reconstruction of paleo-marine environment.

New records and five new species of sipunculans (Sipuncula) from the central and northwestern Mexican Pacific

Sipuncula are marine unsegmented worms that can be found in benthic habitats, from shallow to deep-sea waters. In Mexico these worms have been scarcely studied. Among nine studies in the entire Mexican Pacific coasts, seven are from the central and northwestern Mexican Pacific. For over 80 years, only 24 species have been recorded. To improve the knowledge of the sipunculans from the central and northwestern Mexican Pacific, 501 specimens from three scientific collections of Mexico were revised. The specimens were collected by diverse methods from intertidal, subtidal, and bathyal depths (~1000 m), from 27 locations along the central and northwestern Mexican Pacific. Sixteen taxa belonging to nine genera and five families were identified. One species is recorded for the first time in the Mexican Pacific and five new species are described, one from intertidal and shallow subtidal depths: Phascolosoma (Phascolosoma) azteca sp. nov.; two from subtidal depths: Phascolion (Lesenka) salgadoi sp. nov. and Sipunculus (Sipunculus) bastidai sp. nov.; and two from bathyal depths: Apionsoma (Apionsoma) silviae sp. nov. and Apionsoma (Edmondsius) hendrickxi sp. nov.

Design and Experimental Study of 50 kW Ocean Thermal Energy Conversion Test Platform Based on Organic Rankine Cycle

In recent years, clean and renewable energy sources have received much attention to balance the contradiction between resource needs and environmental sustainability. Among them, ocean thermal energy conversion (OTEC), which consists of surface warm seawater and deep cold seawater, can rely on thermal cycling to generate electricity and has great potential in alleviating the energy crisis. In this paper, the design and experiment study of a 50 kW OTEC platform is proposed. Thermodynamic modeling, calculation, optimization, and engineering calibration of the system were carried out, and the thermal efficiency reached 2.63% to meet the power generation demand. Experiments were also carried out by using a heat pump unit to simulate hot and cold seawater environments, and data on the stable operation of the system were obtained, with the grid-connected power reaching 47.5 kW and a thermal efficiency of 2.46%. The accuracy of the design scheme is verified, and the theoretical basis and data support are provided for the practical development and application of ocean thermal energy conversion.

Deep sea treasures - Insights from museum archives shed light on coral microbial diversity within deepest ocean ecosystems

Deep sea benthic habitats are low productivity ecosystems that host an abundance of organisms within the Cnidaria phylum. The technical limitations and the high cost of deep sea surveys have made exploring deep sea environments and the biology of the organisms that inhabit them challenging. In spite of the widespread recognition of Cnidaria's environmental importance in these ecosystems, the microbial assemblage and its role in coral functioning have only been studied for a few deep water corals. Here, we explored the microbial diversity of deep sea corals by recovering nucleic acids from museum archive specimens. Firstly, we amplified and sequenced the V1–V3 regions of the 16S rRNA gene of these specimens, then we utilized the generated sequences to shed light on the microbial diversity associated with seven families of corals collected from depth in the Coral Sea (depth range 1309 to 2959 m) and Southern Ocean (depth range 1401 to 2071 m) benthic habitats. Surprisingly, Cyanobacteria sequences were consistently associated with six out of seven coral families from both sampling locations, suggesting that these bacteria are potentially ubiquitous members of the microbiome within these cold and deep sea water corals. Additionally, we show that Cnidaria might benefit from symbiotic associations with a range of chemosynthetic bacteria including nitrite, carbon monoxide and sulfur oxidizers. Consistent with previous studies, we show that sequences associated with the bacterial phyla Proteobacteria, Verrucomicrobia, Planctomycetes and Acidobacteriota dominated the microbial community of corals in the deep sea. We also explored genomes of the bacterial genus Mycoplasma, which we identified as associated with specimens of three deep sea coral families, finding evidence that these bacteria may aid the host immune system. Importantly our results show that museum specimens retain components of host microbiome that can provide new insights into the diversity of deep sea coral microbiomes (and potentially other organisms), as well as the diversity of microbes writ large in deep sea ecosystems.

Rapid, contamination-less, and efficient environmental DNA filtration system

Due to the sporadic distribution and trace amount of environmental DNA (eDNA) in deep-sea water, in the context of biodiversity monitoring, large volumes of filtration and multiple filtration replicates are required for eDNA metabarcoding. To address issues tied to the use of multiple filtration devices and large filtration volumes (e.g., contamination, time consumption, etc.), we have developed two systems for simple, rapid, and contamination-less filtration simultaneously that allow for the processing of multiple sample replicates from large volumes of water. First, the water from a Niskin bottle was filtered directly using a solenoid pump. Second, the pumped deep-sea water, using the siphon effect, was directly filtered by a filtration device driven by water pressure. This system can process 24 replicates simultaneously without the need for expensive equipment and active driving force. Compared with conventional filtering methods, e.g., peristaltic pumps, the proposed systems reduce filtration time, minimizing contamination, and enabling the simultaneous acquisition of multiple replicates. Overall, the systems presented here provide an effective approach for eDNA metabarcoding analysis, particularly for the filtration of large volumes of water containing small amounts of eDNA, such as deep-sea water.•The present systems reduce filtration time and contamination without water having to be transferred.•Simultaneous multiple replicates improve the efficiency and reliability of biodiversity assessments.

Metocean conditions at two Norwegian sites for development of offshore wind farms

This paper examines metocean data from NORA3, a state-of-the-art wind and wave hindcast dataset for Northern Europe. Two offshore Norwegian areas, Utsira Nord (UN) and Sørlige Nordsjø II (SN2), are investigated. Both areas offer significant potential for the offshore wind sector. UN is situated in deep-sea water, suitable for floating offshore wind turbines. In contrast, SN2 lies in intermediate waters and ranks among the North Sea’s most promising regions allocated for offshore wind. Data from NORA3, originally on a 3-km resolution grid, are resampled into unstructured grids spanning from 1982 to 2022. This refined dataset offers a climatology time scale with superior spatial and temporal resolution compared to most other hindcast and reanalysis databases. The study examines mean wind speed and direction across seven levels, ranging from 10 m to 750 m above the surface. Analyses of extreme wind and wave conditions have been conducted. Results reveal that UN experiences higher extreme wave heights than SN2 while the extreme wind speeds may be substantially larger at SN2 than UN. Moreover, this study establishes joint distribution models that encompass several parameters, including mean wind speed, significant wave height, wave spectral peak period, and direction difference between wind and waves. Thus, this metocean data is valuable for designing and analyzing floating wind farms over their lifecycles.

The effects of atmospheric nitrogen deposition in coral-algal phase shifts on remote coral reefs

Remote seawater has been considered a potential refuge for corals in the face of anthropogenic disturbances. However, these remote areas may receive increased atmospheric N deposition, and the ecological consequences remain unclear. This field survey revealed coral-algal phase shifts in the mid-north of the South China Sea. These shifts were observed in 44%, 13.6%, and 26.5% of the sampled reef sites at depths of 1-4 m, 5-8 m, and 10-15 m, respectively. Over 50% of sections in the deeper depths hosted fewer corals compared to shallower areas, coinciding with a higher abundance of macroalgae in the deeper layers. Furthermore, based on long-term observation of atmospheric N flux, laboratory experiments were conducted to explore the cause of coral declines. The results indicate that N supply efficiently promoted macroalgae growth. The saturation of N absorption by macroalgae occurred within 2 weeks, leading to nutrient accumulation in seawater, especially nitrate, which had a direct impact on corals. While moderate N fluxes appeared to mitigate coral bleaching, high N fluxes, even with a balanced P supply or medium level of nutrients with an imbalanced N/P ratio, can both increase the susceptibility of corals to heat bleaching. This study explains the coral-algal phase shift in remote and relatively deep seawater and improves understanding of the cause-and-effect relationship between atmospheric N deposition and coral reef decline.

Ichthyoplankton in the northern part of the Black Sea under prolongation of summer hydrological season in 2020

The species diversity and spatial distribution of ichthyoplankton in the shelf and deep-sea waters of the northern half of the Black Sea near the Crimean Peninsula and the shores of the Caucasus under the conditions of prolongation of the summer hydrological season 2020 for September–October are presented. The high temperatures of the upper layer of the sea, peculiar of the summer spawning season, caused a continuation of productive spawning of warm-water fish. Eggs and larvae of 19 species from 12 families were identified in the ichthyoplankton. The maximum number of eggs was 302 ind./m2, and larvae — 58 ind./m2. Eggs and larvae of the mass commercial species Engraulis encrasicolus (L., 1758) dominated, whose share in the total population was 92.9 and 84.2% respectively. The highest abundance of ichthyoplankton corresponded to areas with minimal dynamic activity and maximum warming within the limits of coastal-shelf quasi-stationary anticyclonic vortices characteristic of the summer hydrological season.

Mechanism of island dolostones formation in the Cretaceous calcitic ocean: Insights from the Mid-Pacific Guyots

Dolomite is common in carbonate successions. There is an ongoing debate about the origin of ancient massive dolostones. Recent studies suggest widespread syndepositional and early-burial dolomitisation by normal and near-normal seawater, in the rock record, than previously recognised. Seawater dolomitisation is ubiquitous in Cenozoic islands but Cretaceous counterparts are rare, except for Resolution and Allison guyots, Mid-Pacific Mountains. We explored their dolomitisation conditions and the implications on our understanding of Cretaceous normal seawater syndepositional and near-surface dolomitisation. Integrating geochemical and borehole data reveals temporal overlap between 87Sr/86Sr ages of dolomites, and K/Ar and 40Ar/39Ar ages of the basement. Dolomites near basaltic basement exhibit 42-times Fe-enrichment compared to normal seawater dolomites. Host-rock thermal modelling suggested that δ18Odol temperatures are ∼18–29 °C higher than concurrent temperatures. Seismic interpretation and seismic facies forward modelling demonstrate a spatial overlap between dolomites and magmatic sills in both guyots. Accordingly, magmatically driven hydrothermal dolomitisation is proposed, which promoted dolomitisation by providing high heat flow, increasing seawater circulation, and overcoming limited dolomitisation potential of Cretaceous seawater. The H2O–CO2–SO2–HCl-rich magmatic-hydrothermal acidic fluids would mix with seawater causing slight modification by leaching Mg and Fe from basaltic basement. Consequently, magmatically active Cretaceous islands had greater potential for seawater dolomitisation than counterparts with ceased magmatism, due to increased heat flux and slight increase in Mg:Ca of dolomitising fluids. Our findings imply that deep-seated island dolostones don't only form by deep cold seawater below calcite saturation depth. Instead, magmatism appears crucial in this study and potentially other locations (e.g. Xisha Islands). The absence of dolostones in other Cretaceous islands supports previous models of reduced effectiveness of massive dolomitisation by Cretaceous normal seawater, questioning interpretations of syndepositional and near-surface dolomitisation. Thus, caution is advised when interpreting these dolomites by considering additional factors (dolomite geometry, geological settings, and dolomitisation age), as they may share characteristics with syndepositional and near-surface normal seawater dolomites.

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.

Broccoli Cultivated with Deep Sea Water Mineral Fertilizer Enhances Anti-Cancer and Anti-Inflammatory Effects of AOM/DSS-Induced Colorectal Cancer in C57BL/6N Mice.

This study aimed to determine the alleviating effect of broccoli grown with deep sea water mineral (DSWM) fertilizer extracted from deep sea water on the development of colorectal cancer in C57BL/6N mice treated with AOM/DSS. Naturaldream Fertilizer Broccoli (NFB) cultured with deep sea water minerals (DSWM) showed a higher antioxidant effect and mineral content. In addition, orally administered NFB, showed a level of recovery in the colon and spleen tissues of mice compared with those in normal mice through hematoxylin and eosin (H&E) staining. Orally administered NFB showed the inhibition of the expression of inflammatory cytokine factors IL-1β, IL-6, TNF, IFN-γ, and IL-12 while increasing the expression of IL-10. Furthermore, the expression of inflammatory cytokines and NF-κB in the liver tissue was inhibited, and that of inflammatory enzymes, such as COX-2 and iNOS, was reduced. In the colon tissue, the expression of p53 and p21 associated with cell cycle arrest increased, and that of Bcl-2 associated with apoptosis decreased. Additionally, the expression of Bax, Bad, Bim, Bak, caspase 9, and caspase 3 increased, indicating enhanced activation of apoptosis-related factors. These results demonstrate that oral administration of broccoli cultivated using DSWM significantly restores spleen and colon tissues and simultaneously inhibits the NF-κB pathway while significantly decreasing cytokine expression. Moreover, by inducing cell cycle arrest and activating cell apoptosis, they also suggest alleviating AOM/DSS-induced colon cancer symptoms in C57BL/6N mice.

Vertical distribution of microplastic along the main gate of Indonesian Throughflow pathways

Even though Pacific – Indian Ocean exchange [Indonesian Throughflow (ITF)] has been measured for the last three decades, the measurements of microplastic in the region is very limited. This study was the initial investigation of the vertical distribution of microplastic in the deep-sea areas across the ITF Pathway. Niskin water samples were utilized to obtain the samples from a water column in a range of 5 to 2450 m. A total of 924 microplastic particles with an average abundance of 1.062 ± 0.646. n/L were found in the water column. Our findings indicate that water temperature and water density are the most significant factors correlated to the microplastic concentration. This study will be the first report discussing the distribution of microplastics in the deep-sea water column that could be highly significant in determining the fate and transport of microplastic within Indonesian waters that exits into the Indian Ocean.

Fontisubflavum oceani gen. nov., sp. nov., isolated from the deep-sea cold seep water of South China Sea.

In this study, we report a Gram-stain-negative, rod-shaped, atrichous and aerobic bacterial strain named CSW1921T, which was isolated from the deep-sea water of a cold seep in South China Sea. Growth of strain CSW1921T occurred at 10.0-35.0 °C (optimum, 30 °C), pH 5.0-10.0 (optimum, pH 8.0-9.0) and with 0-9.0 % (w/v) NaCl (optimum, 1.0-2.0 %). Phylogenetic tree analysis based on 16S rRNA gene sequence or the genomic sequence indicated that strain CSW1921T belonged to the family Rhodobacteraceae and was closely related to Rhodophyticola porphyridii MA-7-27T (97.5 % sequence similarity). Genomic analysis indicated that strain CSW1921T contains a circular chromosome of 3 592 879 bp with G+C content of 60.5 mol%. The predominant respiratory quinone of CSW1921T was ubiquinone-10. The polar lipids of CSW1921T contained phosphatidylglycerol, three unidentified aminolipids, two unidentified phospholipids and two unidentified lipids. The major fatty acids of strain CSW1921T contained C16 : 0, C18 : 1 ω7c 11-methyl and summed feature 8 (C18 : 1 ω7c). The average nucleotide identity, DNA-DNA hybridization and average amino acid identity values between strain CSW1921T and members of its related species were 68.02-69.08 %, 12.7-12.9 % and 46.87-48.08 %, respectively, which were lower than the recommended threshold values for bacterial species or genus delineation. Phylogenetic, physiological, biochemical and morphological analyses suggested that strain CSW1921T represents a novel genus and a novel species of the family Rhodobacteraceae, and the name Fontisubflavum oceani gen. nov., sp. nov. is proposed with the type strain CSW1921T (=MCCC 1K08371T=KCTC 92834T).

The study of phytoplankton in the Banggai Deep Sea: The study case of Banggai Upwelling Dynamics and Ecosystem Experiment (BUDEE)

The upwelling process in the Banggai deep-sea water occurs yearly during the east monsoon. The upwelling process is characterized by low surface water temperatures compared to the surrounding waters, high nutrient values of phosphate, nitrate, and silicate, and high values of primary productivity. The aim of this research was to determine the types of phytoplankton that are abundant in the Banggai deep-sea waters during the upwelling process. Phytoplankton sampling was conducted at 36 stations using a phytoplankton net from a depth of 150 m to the water surface. The mesh size of the phytoplankton net was 80 µm with a net length of 100 cm. Phytoplankton samples were preserved using 4% formalin. Based on the research results, the highest total abundance of phytoplankton was found at station 13 (315.457 cells.m-3), followed by stations 20 (234.746 cells.m-3), 26 (213.865 cells.m-3), station 14 (202.371 cells.m-3), station 18 (196.983 cells.m-3) and station 46 (187397 cells.m-3). Meanwhile, the other stations had an abundance of <150,000 cells/m3. The highest abundance at station 13 was dominated by the genera Bellerochea (64.068 cells.m-3), Chaetoceros (42.407 cells.m-3) and Nitzschia (35.390 cells.m-3). The high abundance of phytoplankton at Station 13 was due to upwelling.

Age and genesis of the Tongshan banded iron formation in the Zhongtiao region, North China Craton

Banded iron formations (BIFs) occur extensively within the late Neoarchean supracrustal successions of the North China Craton (NCC). The Zhongtiao region is located on the southern margin of the NCC and is a terrane that may host BIFs. The region is well known for exposed early Precambrian rocks, such as the Sushui Complex, which can be divided into three lithological units: Neoarchean tonalite-trondhjemite-granodiorite (TTG) rocks, Paleoproterozoic multi-phase granitoids, and supracrustal rocks (i.e., the Sushui Group). Despite previous studies focused on the granites within the Sushui Complex, limited information is available on the supracrustal rocks and the potential for associated BIFs that have undergone amphibolite-facies metamorphism. Here, for the first time, we conduct petrological, geochronological, and geochemical studies on a newly discovered BIF layer (i.e., the Tongshan BIF) and the associated metamorphosed volcanic and sedimentary rocks in the Sushui Group. This study constrains the formation age of the Tongshan BIF, its source characteristics, and the redox state of the depositional environment. SHRIMP zircon U–Pb analyses on biotite plagioclase gneiss (the footwall rock of the BIF) demonstrate that the Tongshan BIF was formed at ca. 2583.1 ± 9.8 Ma. The Tongshan BIF, occurrs in a volcano-sedimentary succession, and may have been deposited in a continental margin arc along the southern segment of the NCC and may best be considered as an Algoma-type BIF. Given a 2.58 Ga depositional age for the Tongshan BIF and the Sushui Group, and the more restricted depositonal nature of Algoma-type BIFs, this work highlights the potential for the identification of additional BIF layers in the Zhongtiao region.Two distinctive sedimentary facies are recognized in the Tongshan BIF based on mineral composition: an oxide facies BIF, composed of magnetite and quartz, and a silicate facies BIF, composed of magnetite, amphibole, and quartz. The Tongshan BIF displays distinct seawater-like, shale-normalized REY characteristics, including super-chondritic Y/Ho ratios, HREE enrichment relative to LREE, and positive La, Gd, and Y anomalies. Consistently positive Eu anomalies are also observed, indicating the influence of a high-T hydrothermal input. No true negative Ce anomalies occur in the Tongshan BIF, suggesting a dominantly anoxic water column contemporaneous to deposition. Further, the lack of true negative Ce anomalies extensively occurring in the Tongshan BIF is consistent with other BIFs observed globally, and confirms that ferruginous (anoxic and Fe-rich) conditions were maintained in deep seawater before to the GOE.

Discovery of Prevalent Ciliophora, Discoba, and Copepoda Protists in Deep Sea Water by In Situ Nucleotide Extraction

Deep-sea eukaryotic microorganisms play a vital role in degrading organic matter and geochemically cycling elements in the deep ocean. However, the impact of sampling methods on detection of these microorganisms under high hydrostatic pressure remains uncertain. In this study, we compared a traditional water sampling method using a Niskin bottle, an in situ microbial filtration and fixation method (ISMIFF), and a multiple in situ nucleic acid collection (MISNAC) method to exhibit differences in the community structures that were collected at ~590–3100 m in the South China Sea (SCS). The classification and biodiversity indices of 18S rDNA Illumina sequencing reads from the V9 variation region revealed higher diversity for MISNAC DNA absorption column samples compared to others. Importantly, the relative abundance of Ciliophora (19.49%), Copepoda (23.31%), and Diplonemea (10.67%) was higher in MISNAC adsorption column samples, while Retaria (48.86%) were dominant in the MISNAC membrane samples. This indicates that MISNAC columns might collect more DNA in situ for the naked protists, while Retaria with a carbonate shell were more likely retained on the membrane. In conclusion, MISNAC is an effective method for DNA collection of deep-sea eukaryotic microorganisms and provides valuable materials for studying deep-sea microbial ecosystems.

Exploring the Effect of Deep-Sea Water on the Therapeutic Potential of the Anti-Inflammatory Response in an Indomethacin-Induced Gastric Ulcer Rat Model.

Gastric ulcers are often exacerbated by factors such as nonsteroidal anti-inflammatory drugs (NSAIDs) and inflammation, and they have a substantial impact on a significant portion of the population. Notably, indomethacin is recognized as a prominent contributor to ulcers. This study investigated this potential method, with normalization to the anti-inflammatory and antiulcer properties of deep-sea water (DSW)-derived mineral water, using an indomethacin-induced gastric ulcer model in rats. The study involved four groups (n = 6 rats/group): normal control group (CON), indomethacin-only group (IND), indomethacin with trace mineral water group (TM), and indomethacin with high magnesium low sodium water group (HMLS). For three weeks, the CON and IND groups consumed tap water, while the TM and HMLS groups had access to mineral water. Gastric ulcers were induced on the final day using indomethacin, for all groups except the CON group. The results demonstrated that HMLS intake significantly improved gastric mucosal damage, preserved mucin stability, and increased gastric thickness, indicating its potential to prevent and alleviate indomethacin-induced gastric ulcers. Furthermore, HMLS consumption led to the upregulation of key genes associated with inflammation and a reduction in inflammatory cytokines. These findings suggest that DSW-derived mineral water, and particularly its high Mg2+ content, may offer promising health benefits including anti-inflammatory and anti-ulcer properties.

Isolation and characterization of bacteria from the gut of a mesopelagic copepod Cephalophanes reflugens (Copepoda: Calanoida)

Abstract The mesopelagic calanoid copepod Cephalophanes reflugens is characterized by its large eyes with semi-parabolic reflectors. It is hypothesized that the eyes aid in finding crustacean carcasses as food in poor deep-sea light and oligotrophic conditions. Here, the crustacean carcasses-associated luminous, chitin-degrading bacteria may play a vital role in detecting and digesting foods by the copepod. In this study, we collected adult female C. reflugens (n = 9) from the mesopelagic layers off southwestern Japan in the Pacific Ocean and obtained a total of 47 bacterial isolates from the gut contents. None of the isolates were luminescent, but almost half of the isolates were chitinolytic. Based on the 16S rRNA gene sequences, these chitinolytic bacteria were identified as members of the genus Vibrio, Photobacterium and Pseudoalteromonas. In culture experiments at 15°C, most of the chitinolytic isolates efficiently utilized colloidal chitin as the sole carbon source and degraded the carapace strip of shrimp (Litopenaeus vannamei). Some isolates showed these chitinoclastic activities even at low temperatures (<5°C), equivalent to that of the deep-sea waters. The present results imply that chitin-degrading bacteria significantly contribute to chitin digestion in the gut of C. reflugens, whereas the involvement of luminous bacteria in the feeding mechanism remains unidentified.

Oxidative Dissolution of Sulfide Minerals Tends to Accumulate More Dissolved Heavy Metals in Deep Seawater Environments than in Shallow Seawater Environments.

Deep-sea mining magnifies the release of heavy metals into seawater through oxidative dissolution of seafloor massive sulfide (SMS). At present, there is little information about how the metals released into seawater might be affected by the mineral assemblages, seawater conditions, and solid percentages. Here, leaching experiments were carried out to examine the behavior of three sulfides from the Southwest Indian Ridge, under conditions that replicated deep and shallow seawater environments at three solid-liquid ratios. The results demonstrated that sphalerite dissolved rapidly, and the metals released in both experimental conditions were comparable, potentially reflecting galvanic interactions between the sulfide minerals. Large quantities of the released metals were removed from the solutions when hydrous ferric oxides formed, especially for shallow seawater conditions. A comparison of metal concentrations in the leachates with the baseline metal concentrations in natural seawater indicated that most of the released metals, when diluted with seawater, would not have widespread impacts on ecosystems. Based on the obtained unique oxidative dissolution properties of each SMS at variable solid-liquid ratios, targeted wastewater discharge treatments are proposed to minimize impacts from the dissolved metals. This study will support the development of robust guidelines for deep-sea mining activities.

Theoretical analysis on temperature-lifting cycle for ocean thermal energy conversion

A significant obstacle to the widespread large-scale utilization of ocean thermal energy is the low temperature of the heat source, which restricts the turbine inlet to saturated steam conditions and results in notably reduced turbine efficiency. In this paper, a novel temperature-lifting based Ocean Thermal Energy Conversion cycle (OTEC) is proposed. The cycle combines the second-type absorption heat pump and the Rankine power cycle to overheat the working fluid at the turbine inlet using both surface and deep seawater, thereby mitigating the adverse effects of low surface seawater temperatures on energy conversion. The thermodynamic model is developed for this proposed cycle, 22 wet working fluids are selected for the Rankine sub-cycle. A comparative analysis with the traditional Rankine cycles is conducted to evaluate the cycle performance. The results show that the overheated temperature at the turbine inlet reaches up to 44.7 °C relying on the ocean thermal energy. In contrast to the traditional Rankine cycle, the proposed cycle achieved an average thermal efficiency improvement of 40 % and a substantial increase in exergy efficiency, ranging from 17.99–57.58 % to 32.83–68.88 %. The economic analysis reveals that the optimal cost is reduced by 38 % compared to the Rankine cycle, leading to a lower levelized cost of energy, down from 0.18 $/kWh to 0.13 $/kWh. This novel cycle offers an economically efficient and easily implementable approach to enhance low-grade thermal energy conversion.