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Effects of Antibiotics on Microbiome and Density of Fecal Pellets in the Copepod Tigriopus koreanus
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Adaptive Nonlinear Proportional–Integral–Derivative Control of a Continuous Stirred Tank Reactor Process Using a Radial Basis Function Neural Network
No full textTemperature control in a continuous stirred tank reactor (CSTR) poses significant challenges due to the process’s inherent nonlinearities and uncertain parameters. This study proposes an innovative solution by developing an adaptive nonlinear proportional–integral–derivative (NPID) controller. The nonlinear gain that dynamically scales the error fed to the integrator is enhanced for optimized performance. The network’s ability to approximate nonlinear functions and its online learning capabilities are leveraged by effectively integrating an NPID control scheme with a radial basis function neural network (RBFNN). This synergistic approach provides a more robust and reliable control strategy for CSTRs. To assess the proposed method’s feasibility, a set of simulations was conducted for tracking, disturbance rejection, and parameter variations. These results were compared with those of an adaptive RBFNN-based PID (APID) controller under identical conditions. The simulations indicated that the proposed method achieved reductions in maximum overshoot of 33.7% and settling time of 54.2% for upward and downward setpoint changes and 27.2% and 5.3% for downward and upward setpoint changes compared to the APID controller. For disturbance changes, the proposed method reduced the peak magnitude (Mpeak) by 4.9%, recovery time (trcy) by 23.6%, and integral absolute error by 16.2%. Similarly, for parameter changes, the reductions were 3.0% (Mpeak), 26.4% (trcy), and 24.4% (IAE).33Yscopu
Hydrogen-enriched black smoker venting on a basaltic edifice within a non-transform offset (NTO) of the slow-spreading Central Indian Ridge
No full textDiverse styles of hydrothermal activity along the slow spreading ridges reflect variations in rock types, heat sources, and faulting associated with detachment settings. These include high temperature (>300 ℃) hydrothermal systems driven by cooling magmas and/or variable mixtures of gabbro and peridotite, as well as low- to moderate-temperature hydrothermal activity resulting from the cooling of ultramafic and mafic lithosphere, which has been reported in both slow- and ultraslow-spreading ridges. Along the middle section of the Central Indian Ridge (8˚S-16 ˚S), which exhibits typical slow-spreading ridge morphology, several hydrothermal vent sites have been identified, particularly in off-axis ridge settings. During the MI2023 expedition aboard RV ISABU by KIOST, a new vent site, SAERO, was discovered at a plume-only location situated at the southern end of an extended non-transform offset (NTO) between segment 3-1 and segment 3-2. Plume signals suggest high temperature venting with ultramafic-influenced characteristics, as indicated by a high CH4/dissolved Mn ratio. However, the volcanic edifice hosting the SAERO vent site is composed of basaltic pillow lava with no observed ultramafic and gabbroic rocks. The SAERO site comprises several high temperature black smokers with a maximum venting temperature of 360 ℃. Preliminary gas analysis of vent fluids reveals substantial H2 concentrations in the end-member fluid, comparable to values observed in ultramafic-influenced hydrothermal systems such as the Rainbow and Von Damm hydrothermal fields, despite the site being located on basalt. The high H2 abundance suggests hydrothermal fluid reaction with ultramafic rocks in the subseafloor before discharge. However, fluid-basalt reactions occurring at very high temperatures cannot be ruled out, as seen in the case of Piccard hydrothermal vent field. The discovery of the SAERO vent site expends our understanding of geodiversity of hydrothermal venting along slow-spreading ridges and highlights the complexity of subseafloor fluid-rock interactions in these environments.1
Gabbro-dominated basement at high-temperature ultramafic-hosted hydrothermal systems: insights from Onnuri vent field, Central Indian Ridge
No full textThe composition of hydrothermal fluid in high-temperature (>200°C) ultramafic-hosted systems is strongly influenced by seawater interaction with basement rocks. The widely accepted "plum-pudding" model envisions the basement of these systems as small (<1 km²) gabbro intrusions ("plums") within peridotite-dominated matrix ("pudding"). However, direct petrological evidence supporting this model remains scarce due to limited accessibility to deep sections in these systems.
The Onnuri Oceanic Core Complex (OCC), located at 11°25'S on the Central Indian Ridge (CIR), provides a rare glimpse into the internal structure of a high-temperature ultramafic-hosted hydrothermal system, exposing its deep interior (up to 1,100 meters) along two extensive slopes. We conducted a comprehensive exploration of the Onnuri OCC, including dredging along the detachment fault surface and rock sampling via remotely operated vehicle (ROV) along the detachment fault and both the northeastern and southeastern slopes. Our findings reveal a significant lithological difference between the detachment fault surface and the steep slopes. The former is dominated by ultramafic rocks and diabase with minor gabbro, while the latter is composed primarily of gabbro with minor diabase and basalt. These results suggest a core-carapace structure for Onnuri, characterized by a gabbroic core overlain by a thin ultramafic carapace. This structure contrasts sharply with the "plum-pudding" model, which assumes limited volumes of gabbro, challenging its applicability as the dominant basement model for high-temperature ultramafic-hosted systems.
The zero-magnesium endmember composition of hydrothermal fluids from Onnuri supports a mafic-ultramafic hybrid reaction zone. Elevated hydrogen concentrations indicate active serpentinization, while moderately elevated CO2 suggests a magmatic gas contribution. Dissolved silica and hydrogen concentrations are consistent with chlorite-magnetite-talc-fluid equilibria, indicating interaction with both olivine and plagioclase. Additionally, high K and Li concentrations point to reactions with mafic/gabbroic source rocks. The compositional similarity between Onnuri vent fluids and other ultramafic-hosted high-temperature systems, along with seismic evidence of gabbroic cores beneath similar systems, suggests that gabbro plays a significant role in shaping fluid chemistry in these environments.1
Covariance of Marine Nucleocytoplasmic Large DNA Viruses with Eukaryotic Plankton Communities in the Sub-Arctic Kongsfjorden Ecosystem: A Metagenomic Analysis of Marine Microbial Ecosystems
No full textNucleocytoplasmic large DNA viruses (NCLDVs) infect various marine eukaryotes. However, little is known about NCLDV diversity and their relationships with eukaryotic hosts in marine environments, the elucidation of which will advance the current understanding of marine
ecosystems. This study characterizes the interplay between NCLDVs and the eukaryotic plankton community (EPC) in the sub-Arctic area using metagenomics and metabarcoding to investigate NCLDVs and EPC, respectively, in the Kongsfjorden ecosystem of Svalbard (Norway) in April and June 2018. Gyrodinium helveticum (Dinophyceae) is the most prevalent eukaryotic taxon in the EPC in April, during which time Mimiviridae (31.8%), Poxviridae (25.1%), Phycodnaviridae (14.7%) and Pandoraviridae (13.1%) predominate. However, in June, the predominant taxon is Aureococcus anophagefferens (Pelagophyceae), and the NCLDVs, Poxviridae (32.9%), Mimiviridae (29.1%), and Phycodnaviridae (18.5%) appear in higher proportions with an increase in Pelagophyceae, Bacillariophyceae, and Chlorophyta groups. Thus,
differences in NCLDVs may be caused by changes in EPC composition in response to environmental changes, such as increases in water temperature and light intensity. Taken together, these findings are particularly relevant considering the anticipated impact of NCLDV-induced EPC control mechanisms on polar regions and, therefore, improve the understanding of the Sub-Arctic Kongsfjorden ecosystem.1
Sound Production Characteristics of the Chorus Produced by Small Yellow Croaker (Larimichthys polyactis) in Coastal Cage Aquaculture
No full textRecent advances in passive acoustic monitoring (PAM) have markedly improved the ability to study marine soundscapes by enabling long-term, non-invasive monitoring of biological sounds across large spatial and temporal scales. Among aquatic organisms, fish are primary contributors to biophony, producing sounds associated with feeding, reproduction, and social behavior. However, the majority of previous research has focused on individual vocalizations, with limited attention to collective acoustic phenomena such as fish choruses. This study quantitatively analyzes choruses produced by the small yellow croaker (Larimichthys polyactis), an ecologically and commercially important species in the Northwest Pacific Ocean. Using power spectral density (PSD) analysis, we examined long-term underwater recordings from a sea cage containing approximately 2000 adult small yellow croakers. The choruses were centered around ~600 Hz and exhibited sound pressure levels 15–20 dB higher at night than during the day. These findings highlight the ecological relevance of fish choruses and support their potential use as indicators of biological activity. This study lays the foundation for incorporating fish choruses into soundscape-based PAM frameworks to enhance biodiversity and habitat monitoring.11Ysciescopu
Sequential Evolution of Changjiang Diluted Water and Its Impact on Stratification and Phytoplankton Blooms in the East China Sea During Summer 2020
No full textThe Changjiang Diluted Water (CDW) plays a crucial role in shaping the hydrography and ecosystem dynamics of the East China Sea (ECS), particularly during summer when freshwater discharge enhances stratification and modulates biogeochemical processes. Despite its importance, the detailed progression of CDW and its short-term impacts remain poorly understood due to the limited availability of high-resolution observations. Using high-resolution in situ observations from the Ieodo Ocean Research Station in summer 2020, we examined the sequential evolution of CDW and its effects on the upper-ocean structure and phytoplankton blooms. CDW evolution was categorized into six distinct phases, characterized by abrupt shifts in salinity and stratification, driven by monsoonal winds, tides, and typhoon-induced mixing. CDW intrusion formed a persistent barrier layer that suppressed vertical mixing and trapped surface heat, leading to increased sea surface temperatures. Nutrient influx from CDW, enriched in nitrate and phosphate, promoted the proliferation of diatoms relative to picoplankton and dinoflagellates, although all groups increased during the CDW-influenced period. Internal wave-induced mixing facilitated nutrient replenishment from deeper layers, partially alleviating phosphate deficiency inherent in CDW and enhancing phytoplankton productivity. Typhoon Bavi disrupted stratification through strong vertical mixing, resulting in a high-salinity state that differed from preintrusion hydrography. This study provides a time-resolved view of CDW-driven variability and demonstrates how episodic freshwater inputs, coupled with physical forcing, regulate stratification, nutrient supply, and ecosystem response in the ECS.11Nsciescopu
A Study on Efficient Evaluation Methods for Electromagnetic Exposure to the Human Body from Electronic Article Surveillance Systems
No full textThis study proposes a method to improve the electromagnetic exposure evaluation procedures for fixed large-scale human-proximity devices, referred to as Electronic Article Surveillance (EAS) systems. The conventional evaluation approach involves measuring magnetic field values at 45 points and calculating the average, which is inefficient in terms of time and cost. To address this issue, a method to reduce the number of measurement points was proposed. Magnetic field values as a function of distance were analyzed for an ideal line current source. Furthermore, magnetic field distributions for the two representative EAS methods, Acousto-Magnetic (AM) and Radio-Frequency (RF), were analyzed through simulations and measurements. Based on these findings, an optimized evaluation method is suggested, which involves measuring three representative points located at 85 cm, 115 cm, and 145 cm heights at a 30 cm distance from the antenna center to derive the average value.11Nsciescopuskc
Species-specific toxic responses of marine phytoplankton to metals leached from cobalt-rich ferromanganese crusts
No full textCobalt-rich ferromanganese (Fe-Mn) crusts are minerals distributed on the slope of a seabed mountain from a depth of 400 to 7000 m. These crusts are considered a next-generation deep-sea mineral resource with abundant industrially useful metals and rare earth elements. However, the ecological impact of deep-sea mining activity on the marine ecosystem has not been fully elucidated. In this study, the effects of Fe-Mn crust leachate were assessed using three different marine phytoplankton as experimental species. Overall, Chlorella sp. showed a dose-dependent increase of growth, while Thalassiosira weissflogii showed a tendency toward dose-dependent growth inhibition in response to the leachate samples. No significant effects were observed on Synechococcus elongatus growth rate. These results imply a species-specific sensitivity to the leachates, potentially associated with variations in accumulated metal compositions and antioxidant responses to the leachate. Although species-specific, our results indicate that mining activity on Fe-Mn crusts could have adverse ecological consequences. These experimental species have the potential to serve as biomarkers for Fe-Mn crust mining activities.11Ysciescopu
Changes in the Speed of the Kuroshio in Response to Asian Monsoon Wind Stress Variability
No full textSeasonal variations in wind stress impact the velocity of the upper layer of the Kuroshio over the East China Sea (ECS–Kuroshio). The dynamics of this process, which involves vorticity adjustments in the baroclinic jet that is induced by local Ekman pumping over the jet, can be attributed to any of the wind stress components acting upon the jet: 1) wind stress relative to the sea surface current; 2) the along-stream wind stress component, which causes nonlinear Ekman pumping due to the effective Coriolis parameter; and 3) the wind stress curl over the jet. This study examines the contribution of these wind stress components to seasonal variability in the current velocity of the upper layer of the ECS–Kuroshio mainly using a satellite-based surface geostrophic-velocity time series and wind stress data. The results showed that the magnitudes of the first and second wind stress components are comparable, but the third component is negligible. The rate of change in the surface speed of the ECS–Kuroshio in response to seasonal variability in the along-stream wind stress was approximately 1.5–2.1 m s−1 (N m−2)−1. This rate of change is approximately 3–4 times as large as that obtained using a numerical model in a previous study, which did not consider the first and third components of wind stress. Consequently, our results showed that the response of the ECS–Kuroshio speed to seasonal wind stress variability is influenced not only by the effect of nonlinear Ekman pumping but also by the effect of wind stress relative to the surface current.
Significance Statement
The Kuroshio is driven by the westerlies and trades over the North Pacific for interannual–interdecadal variabilities, while driven by the Northeast Asian monsoon over the Kuroshio for seasonal variability. The former mechanism is known as a remote process through baroclinic Rossby waves, while the latter mechanism is uncertain. This study aims to clarify a local mechanism driving seasonal variability. Following the vorticity response to nonlinear Ekman pumping over the Kuroshio, we analyzed observational data and concluded that seasonal variability in the Kuroshio speed is influenced by the wind stress relative to the sea surface current and the along-stream wind stress component, both being almost equivalent in amplitude. This implies that seasonal-variability modulations in the Northeast Asian monsoon can drive the interannual–interdecadal Kuroshio speed variabilities.11Nsciescopu