Methane seeps are widespread seafloor ecosystems shaped by complex physicochemical-biological interactions over geological timescales, and seep microbiomes play a vital role in global biogeochemical cycling of key elements on Earth. However, the mechanisms underlying the coexistence of methane-cycling microbial communities remain largely elusive. Here, high-resolution sediment incubation experiments revealed a cryptic methane cycle in the South China Sea (SCS) methane seep ecosystem, showing the coexistence of sulfate (SO₄^2–)- or iron (Fe)-dependent anaerobic oxidation of methane (AOM) and methylotrophic methanogenesis. This previously unrecognized methane cycling is not discernible from geochemical profiles due to high net methane consumption. High-throughput sequencing and Catalyzed Reporter Deposition-Fluorescence in situ Hybridization (CARD-FISH) results suggested that anaerobic methane-oxidizing archaea (ANME)-2 and -3 coupled to sulfate-reducing bacteria (SRB) carried out SO₄^2–-AOM, and alternative ANME-2 and -3 solely or coupled to iron-reducing bacteria (IRB) might participate in Fe-AOM in sulfate-depleted environments. This finding suggested that ANME could alter AOM metabolic pathways according to geochemical changes. Furthermore, the majority of methylotrophic methanogens belonged to Methanimicrococcus, and hydrogenotrophic and acetoclastic methanogens were likely inhibited by sulfate or iron respiration. Fe-AOM and methylotrophic methanogenesis are overlooked potential sources and sinks of methane in methane seep ecosystems, thus influencing methane budgets and even the global carbon budget in the ocean.

Complex underwater environmental factors, such as turbidity, turbulence, background light, and mobility, pose great challenges to the rapid and stable establishment of underwater wireless optical communication (UWOC) links. Therefore, it is crucial to accelerate the development of fast, high-precision, and robust acquisition, pointing, and tracking (APT) systems to promote the practical application of UWOC. In this work, the YOLOv5s algorithm with strong learning and adaptive abilities and a solar panel receiver with a large detection area are proposed to solve the link alignment issues caused by complex underwater environmental factors. In a 3-m water tank, the turbidity, bubbles-induced turbulence, and background light have less impact on the robust YOLOv5s-based APT system. The average pointing time is merely 5.97 ms, and the average tracking time is merely 229 ms for different underwater environments. When the concentration of Mg(OH) ₂ reaches 3.39 mg/L and the scintillation index of bubbles reaches 0.019, the UWOC link can still be established quickly with a data rate of 1.76 Mbit/s, respectively. Moreover, the APT system can tolerate the illuminance of the background light as low as 0.2 lx. We also conduct a preliminary study on the performance of the system in mobile conditions, which proves the effectiveness of the system and lays a foundation for further research.

The typical strategy for the phase-shifted full-bridge (PSFB) converter is to design a linear compensator based on a small-signal model. However, this approach cannot provide a strongly robust output under changing operating conditions or with perturbations in the converter parameters. In this article, a fixed-frequency pulse width modulation (PWM) based full-order sliding mode controller is proposed to improve the performance of a PSFB converter with diodes in series on the lagging leg. Firstly, to facilitate the application of sliding control laws, we construct a simplified equivalent control model by analyzing the phase-shifted modulation and operating waveforms of the converter. Secondly, we derive strict existence conditions for the sliding phases to ensure that the state trajectories fulfill the requirements. Thirdly, the perturbations of both the external and internal variables are considered in the equivalent control function to improve the stability of the controller. Finally, simulation and experimental results verify that the proposed sliding mode controller provides better dynamic regulation performance and robustness than does a linear controller.

Ultra-Wideband (UWB) positioning, utilizing the Time Difference of Arrival (TDOA) technique, is renowned for its high positioning update rates and centimeter-level accuracy in Internet of Things (IoT) scenarios, such as smart living and smart production. However, achieving such precision requires nanosecond-level synchronization accuracy in UWB network anchors. Inspired by the primary source of synchronization errors—unpredictable future clock deviations—this paper introduces a novel Deferred+3S-KF Wireless Clock Synchronization (WCS) method. It departs from conventional methods which attempt to better predict future clock deviations. Instead, to obtain a more accurate estimate of clock deviation parameters during the tag message arrival period, the calculation for mapping arrival times is deferred until the next Clock Correction Package (CCP) arrives. In this way, with just tens of milliseconds of real-time positioning performance sacrificed, it allows for obtaining minimal measurement uncertainty of the first-order clock deviation parameters of the period (100-150 ps, corresponding to DWM1000 timestamp accuracy). The 3-Stage Kalman Filter (3S-KF) based WCS model is employed in this method to achieve more precise clock deviation tracking and accurate time mapping. Compared to the conventional 3S-KF WCS method, the experimental results demonstrate that our proposed unidirectional (CCPs are only broadcast by the reference anchor, with no response required) deferred+3S-KF WCS method can reduce the static positioning accuracy STD.V by 27.1%, achieving 5.82 cm STD.V, 6.44 cm RMSE, and 9.62 cm ME.

High-precision wave data serve as a foundation for investigating the wave characteristics of the East China Sea (ECS) and wave energy development. Based on the simulating waves nearshore (SWAN) model, this study uses the ERA5 (ECMWF Reanalysis v5) reanalysis wind field data and ETOPO1 bathymetric data to perform high-precision simulations at a resolution of 0.05° × 0.05° for the waves in the area of 25–35° N and 120–130° E in the ECS from 2009 to 2023. The simulation results indicate that the application of the whitecapping dissipation parameter Komen and the bottom friction parameter Collins yields an average RMSE of 0.374 m and 0.369 m when compared to satellite-measured data, demonstrating its superior suitability for wave simulation in shallow waters such as the ESC over the other whitecapping dissipation parameter, Westhuysen, and the other two bottom friction parameters, Jonswap and Madsen, in the SWAN model. The monthly average significant wave height (SWH) ranges from 0 to 3 m, exhibiting a trend that it is more important in autumn and winter than in spring and summer and gradually increases from the northwest to the southeast. Due to the influence of the Kuroshio current, topography, and events such as typhoons, areas with significant wave heights are found in the northwest of the Ryukyu Islands and north of the Taiwan Strait. The wave energy flux density in most areas of the ECS is >2 kW/m, particularly in the north of the Ryukyu Islands, where the annual average value remains above 8 kW/m. Because of the influence of climate events such as El Niño and extreme heatwaves, the wave energy flux density decreased significantly in some years (a 21% decrease in 2015). The coefficient of variation of wave energy in the East China Sea exhibits pronounced regional heterogeneity, which can be categorized into four distinct patterns: high mean wave energy with high variation coefficient, high mean wave energy with low variation coefficient, low mean wave energy with high variation coefficient, and low mean wave energy with low variation coefficient. This classification fundamentally reflects the intrinsic differences in dynamic environments across various maritime regions. These high-precision numerical simulation results provide methodological and theoretical support for exploring the spatiotemporal variation laws of waves in the ECS region, the development and utilization of wave resources, and marine engineering construction.