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The deep-water area in the central Bohai Sea (BS) serves as a spawning ground and nursery for fish, shrimp, and crabs. Frequent hypoxia will affect the ecological environment in the central BS. Data from an on-site investigation of the central BS in the spring and summer of 2022 were used to analyze the relevant factors generating the occurrence of hypoxia in the central BS through the eutrophication index E, apparent oxygen consumption (AOU), and Spearman correlation. The hypoxia area was largely distributed in the study area's deep water section, and stratification was the main cause of hypoxia at the bottom. Organic matter mineralization, degradation, and biological respiration further exacerbated the hypoxia. In the summer of 2022, temperature stratification was the dominant factor influencing hypoxia. • Temperature stratification affects the exchange of dissolved oxygen between bottom and surface in central Bohai Sea of 2022. • Weak hydrodynamics and low wind speed in central Bohai Sea in summer provide the basis for the occurrence of hypoxia. • Eutrophication in study area leads to an increase in phytoplankton density, their life activities consume dissolved oxygen. • Organic matter degradation and mineralization in central Bohai Sea promoted by rising temperature, aggravated the hypoxia. [ABSTRACT FROM AUTHOR]

The Sargassum bloom has severely impacted the ecological environment of the East China Sea and the Yellow Sea, causing significant economic losses. In recent years, deep learning has seen extensive development due to its outstanding feature extraction capabilities. However, the deep learning process typically involves a large number of parameters and computations. To address this issue, this paper proposes a lightweight deep learning network based on the U-Net framework, called SLWE-NET, which uses lightweight modules to replace the feature extraction modules in U-Net. In this experiment, SLWE-Net performed the best in both extraction accuracy and model lightweight. Compared to the formal U-Net, the number of parameters decreased by 65.83 %, the model size reduced from 94.97 MB to 32.51 MB, and the mIoU increased to 93.81 %. Therefore, the method proposed in this paper is beneficial for Sargassum extraction and provides a basis for operational monitoring. • The SLWE-Net model is an effective model for Sargassum detection through satellite images. • Using VoVNet as the feature extraction module of the model can better extract the target and achieve higher accuracy. • In terms of Sargassum extraction accuracy, SLWE-Net outperforms traditional spectral vegetation indices. • SLWE-Net has achieved notable advancements in model lightweight by decreasing parameter count and computation complexity. [ABSTRACT FROM AUTHOR]

In the oil industry, oil spills occur due to offshore rig explosions, ship collisions, and other reasons. It is crucial to accurately and rapidly identify oil spills to protect marine ecosystems. Synthetic aperture radar (SAR) can all-weather and all-time work and provide a wealth of polarization information for identification of oil spills based on semantic segmentation model. However, the performance of classifiers in the semantic segmentation model has become a significant challenge to improving recognition ability. To solve this problem, an improved semantic segmentation model named DRSNet was proposed, which uses ResNet-50 as the backbone in DeepLabv3+ and support vector machines (SVM) as the classifier. The experiment was conducted using ten polarimetric features from SAR images and results demonstrate that the DRSNet performs best compared to other semantic segmentation models. Current work provides a valuable tool to enhance maritime emergency management capabilities. • Ten key polarimetric features are used for oil spill detection. • ResNet-50 as the backbone in encoder of DeepLabv3+, can get more feature map extraction. • SVM as the classifier can trained by the more sufficiently feature map to identify oil spill pixels. [ABSTRACT FROM AUTHOR]

The Greenland ice sheet melting status is critical for global sea level rise and climate change. Based on the CryoSat-2 altimetry data from 2011 to 2021, the 5 km × 5 km DEMs of the Greenland ice sheet were derived by adopting the kriging interpolation method. Then the changes in elevation and volume of the ice sheet were calculated by using the intersection method. The changes in the ice sheet were analysed, and the results show that: (1) The accuracy of the Greenland DEMs obtained based on satellite altimetry data is region-dependent, with better accuracy in inland areas and higher elevation errors in marginal areas. (2) The inland area elevation remains unchanged basically or even shows an increasing trend, and there is an apparent melting trend in the marginal area, especially on the west coast. The contribution of the ice sheet melting mainly comes from elevations below 2000 m. (3) The main body of the Greenland ice sheet is melting with an elevation change rate of −13.27 ± 0.86 cm·a−1 and a volume change rate of −202.47 ± 14.8 km³·a−1. The rate of the Greenland ice sheet thinning has slowed down compared with the changes from 2003 to 2009. [ABSTRACT FROM AUTHOR]

The risk caused by different environmental factors in the navigation of ships is not uniform. The univariant (e.g., sea fog), covariant (e.g., wind and waves), and spatially restricted (e.g., offshore distance) risk factors present a complex non-linearity impact on the navigation of ships. This means that a comprehensive evaluation of the environmental risk for navigation should consider the risk characteristics of different factors. In this paper, a non-linear spatial multi-criteria decision (SMCD) method-based evaluation framework was developed to evaluate the potential environmental risk of navigating ships. (1) Non-linear weight adjustment and risk decision functions were proposed to spatially evaluate the comprehensive risk and avoid diluting the critical impact of high-risk factors. (2) The double thresholds standardization approach was developed to construct the risk association between different tonnage ships and environmental factors. (3) The developed methods were used in the Bohai and Yellow Seas as a case study to verify the validity and practicability. The quantitative analysis, historical accident matching (82% accident matching rate), and a real accident case proved the validity of the developed model. • A nonlinear spatial multi-criteria decision model is proposed for maritime safety. • The potential risk of marine environment factors on ships is assessed spatially. • The spatial risk with different risk-causing features are fairly emphasized. • The risk tolerance of different ships is analyzed and considered in the evaluation. [ABSTRACT FROM AUTHOR]

Refrigerant injection is a good method for reducing the exhaust temperature of a single-screw refrigeration compressor (SSRC). In this paper, an accurate method is proposed to calculate the variation of the injection area for different initial positions and different sizes of injection holes. Furthermore, a mathematical model describing the internal working process of an SSRC with liquid refrigerant injection (LRI) is established to evaluate the performance of an SSRC and heat pump with a variety of injection hole geometries and working conditions. This theoretical model is verified by comparing the calculation results with experimental data. The results show that LRI can markedly reduce the exhaust temperature and improve the performance of the SSRC and heat pump to some extent. The injection-hole radius is the most important factor affecting the performance of the compressor and heat-pump system. The variations of different performance parameters of the SSRC and heat pump at low ambient temperature can be obtained. This work provides a theoretical method for optimizing the injection process in SSRCs. • A mechanical model is proposed to accurately calculate the injection area of the SSRC. • A mathematical model is developed to study the performance of compressor with LRI. • The performance of heat pump with liquid refrigerant injection is experimentally studied. • The effects of the different injection parameters on the performance of the heat pump are compared. [ABSTRACT FROM AUTHOR]