Offshore Areas Research Articles

Holocene sedimentary distribution and morphological characteristics reworked by East Asian monsoon dynamics in the Mekong River shelf, South Vietnam

The distribution of Holocene sediments in the Mekong River shelf area was investigated using shallow seismic and core data. The results show that the shelf depositional stratigraphy since the last glacial period can be classified into four depositional units (U1, U2, U3 and U4). The average thickness of the Holocene deposit in the nearshore area of the Mekong River estuary is approximately 20 m and decreases seaward. In addition to a thickened deposit in the palaeo-river channel, two sedimentary centres have developed, namely, the Mekong River estuary and the Cape Ca Mau area. In contrast to nearshore deposition, the Holocene sedimentation rate rapidly decreased offshore, even in the transgressive systems tract. To understand the driving mechanisms for the variation in Holocene deposition, a three-dimensional numerical model and Geographic Information System(GIS)-based model were applied to reconstruct the oceanographic and sediment transport patterns on the South Vietnam shelf. The simulation results reveal that the Mekong River shelf has undergone significant transformations since the Last Glacial Maximum (LGM). During the LGM, the coastline was situated near the shelf break, and as the sea level rose rapidly, the shoreline retreated. When the sea level reached its peak, the modern Mekong Delta emerged. Furthermore, the distribution of Holocene deposits is controlled by monsoon-influenced seasonal variations in currents, resulting in a triangular delta and narrow strip-like subaqueous clinoform. Our simulation results also show obvious erosional capacity in the offshore area, leading to an evident erosional through to the east of Cape Ca Mau and erosion of Pleistocene sediments in the shelf break area. By combining stratigraphic interpretation and oceanographic simulations, our study provides new insights into sediment transport and erosion processes mediated by ocean currents driven by East Asian monsoons.

Comparisons of Underwater Light From Atmospheric and Mechanically Stimulated Bioluminescence Sources in High Arctic Polar Night

AbstractAt high latitudes, polar night is a prolonged period of seasonal darkness with the sun remaining below the horizon throughout the diel cycle for up to 177 days at the North Pole. Along with diffuse atmospheric light from the sun and the moon, bioluminescence is an in‐water light source that can facilitate ecological interactions in an otherwise dim‐light environment. At high latitudes during polar night, bioluminescence rather than sunlight represents a significant portion of the photons available in the pelagic. We investigated depths of transition zones (called the bioluminescence transition depth) in the pelagic light field during polar night, defining the transition of a light field dominated by atmospheric irradiance, to one dominated by bioluminescent point sources. We derived relationships between values of the transition depth, bioluminescence potential, surface irradiance due to atmospheric light and the diffuse attenuation coefficient. We conducted studies for two Svalbard, Norway fjords, as well as for offshore areas located in the shelf‐break, shelf‐slope and in the Arctic basin. Based on our results for two polar nights, the transition from underwater light dominated by atmospheric sources to that dominated by bioluminescence occurs between 10 and 40 m in two Svalbard fjords, and between 18 and 60 m for offshore areas. These transition depths may be of particular importance to understanding how bioluminescence structures planktonic communities both in polar regions and at lower latitudes.

How ethical areas of post-normal science can invigorate mathematics education

Future experts, decision-makers, stakeholders and future citizens – they all go to school, which could be a place to prepare students to facing post-normal problems in their future roles. While the literature on mathematics and science education shows increased interest in post-normal science to critically understand contemporary problems, mathematics is still generally taught as a neutral subject with either correct or wrong answers. In this paper, I lean on post-normal science literature and the slowly growing literature on ethics and mathematics education to develop a framework for identifying how mathematics education can prepare students for ethical aspects of post-normal problems. Three areas of ethics associated with post-normal problems are explored through concepts from ethics and mathematics education: ethical perspectives of the problem, ethical perspectives embedded in knowledge, and ethics in interpersonal care in discussions and care for students’ self-esteem in participatory processes. This framework is used to analyse and discuss three classroom projects to provide examples of what these areas may contain. The projects partly align with post-normal science, and are about clothing and sustainability, traffic safety, and argumentation related to open an offshore area to oil exploitation. The ethical areas are discussed in terms of ethical awareness and democratic practices.

Small microplastic ingestion by the calanoid Centropages furcatus in the Gulf of Thailand

Microplastics could be ingested by many organisms, including zooplankton, involving bioaccumulation and biomagnification mechanisms a cross food webs. The information about microplastic ingestion by zooplankton keeps increasing worldwide. However, it is still limited for particle sizes under 300 μm (small microplastics, SMPs) and in areas such as Southeast Asia, which is considered one of the hotspots for plastic debris. This study aimed to characterize the size, shape, and polymer types of the SMPs ingested by the copepod Centropages furcatus in Si Chang Island (upper Gulf of Thailand). The study spans offshore and coastal waters, with data collected across wet, intermediate, and dry seasons. Using a semi-automated technique for micro-FTIR (Fourier-transform infrared) scanning spectroscopy for particle analysis, we found ingested SMPs in all samples. A total of 750 individuals of the calanoid Centropages furcatus were analyzed, finding 309 plastic particles and an average ingestion value of 0.41 ± 0.13 particles ind−1, one of the highest recorded values. All the particles were fragments, with a predominant size under 50 μm, and polymer types as Polypropylene (PP, 71 %), followed by Ethylene-Propylene-Diene-Monomer (EPDM, 16 %) and Polyethylene (PE, 7 %). Up to 470.2 particles m−3 were estimated to be retained by this calanoid species and potentially available for trophic transfer. The effect of rainfall on SMPs ingestion was inconclusive, with a non-significant observed tendency to higher ingestion values near the coastal area than offshore area, suggesting a decrease in particle exposure due to the runoff effect. Nevertheless, future studies should increase the frequency of surveys to arrive at better conclusions.

Role of BP-ANN in simulating greenhouse gas emissions from global aquatic ecosystems via carbon component-environmental factor coupling

Inland waters (IW), estuarine areas (EA), and offshore areas (OA) function as aquatic systems in which the transport of carbon components results in the release of greenhouse gases (GHGs). Interconnected subsystems exhibit a greater greenhouse effect than individual systems. Despite this, there is a lack of research on how carbon loading and its components impact GHG emissions in various aquatic systems. In this study, we analyzed 430 aquatic sites to explore trade-off mechanisms among dissolved organic carbon (DOC), particulate organic carbon, dissolved inorganic carbon (DIC), and GHGs. The results revealed that IW emerged as the most significant GHG source, possessing a comprehensive global warming potential (GWP) of 0.78 ± 0.08 (10−2 Pg CO2-ep ha−1 year−1) for combined carbon dioxide, methane, and nitrous oxide. This surpassed the cumulative potentials of EA and OA (0.35 ± 0.05 (10−2 Pg CO2-ep ha−1 year−1)). Additionally, structural equation modeling indicated that GHG emissions resulted from a combination of carbon component loading and environmental factors. DOC exhibited a positive correlation with GWPs when influenced by biodegradable DOC. Total alkalinity and pH influenced DIC, leading to elevated pCO2 in aquatic systems, thereby enhancing GWPs. Predictive modeling using backpropagation artificial neural networks (BP-ANN) for GWPs, incorporating carbon components and environmental factors, demonstrated a good fit (R2 = 0.6078, RMSEaverage = 0.069, p > 0.05) between observed and predicted values. Enhancing the estimation of aquatic region feedback to GHG changes was achieved by incorporating corresponding water quality parameters. In summary, this study underscores the pivotal role of carbon components and environmental factors in aquatic regions for GHG emissions. The application of BP-ANN to estimate greenhouse effects from aquatic regions is highlighted, providing theoretical and experimental support for future advancements in monitoring and developing policies concerning the influence of water quality on GHG emissions.

Methanooceanicella nereidis gen. nov., sp. nov., the first oceanic Methanocellaceae methanogen, isolated from potential methane hydrate bearing area offshore southwestern Taiwan.

A novel mesophilic, hydrogenotrophic methanogen, strain CWC-04T, was obtained from a sediment sample extracted from a gravity core retrieved at station 22 within the KP-9 area off the southwestern coast of Taiwan during the ORIII-1368 cruise in 2009. Cells of strain CWC-04T were rod-shaped, 1.4-2.9 µm long by 0.5-0.6 µm wide, and occurred singly. Strain CWC-04Tutilized formate, H2/CO2, 2-propanol/CO2 or 2-butanol/CO2 as catabolic substrates. The optimal growth conditions were 42 °C, 0.17 M NaCl and pH 5.35. The genomic DNA G+C content calculated from the genome sequence of strain CWC-04T was 46.19 mol%. Phylogenetic analysis of 16S rRNA gene revealed that strain CWC-04T is affiliated with the genus Methanocella. The 16S rRNA gene sequences similarities within strains Methanocella arvoryzae MRE50T, Methanocella paludicola SANAET and Methanocella conradii HZ254T were 93.7, 93.0 and 91.3 %, respectively. In addition, the optical density of CWC-04T culture dropped abruptly upon entering the late-log growth phase, with virus-like particles (150 nm in diameter) being observed on and around the cells. This observation suggests that strain CWC-04T harbours a lytic virus. Based on these phenotypic, phylogenetic and genomic results, we propose that strain CWC-04T represents a novel species of a novel genus in the family Methanocellaceae, for which the name Methanooceanicella nereidis gen. nov., sp. nov. is proposed. The type strain is CWC-04T (=BCRC AR10050T=NBRC 113165T).

Prospects for Geological Storage of CO2 in Carbonate Formations of the Adriatic Offshore

Croatia has both significant CO2 emissions from the point sources and a history of oil and gas exploration, and this is why the CCS technology surfaced as a viable solution for curbing CO2 emissions on a national level. Since approximately half of emissions from the stationary industrial sources occur along the Adriatic coastline, the entire offshore area became an exploration target. Regional studies revealed the potential storage plays, one of which is in the aquifer of the Mesozoic carbonate complex with dual porosity extending all along the Croatian offshore area. Three structures were chosen in its central part–Klara, Kate and Perina. For the first two, the models were constructed based on the data from old exploration wells and a regional structural map, while for the Perina structure, a new seismic interpretation was added to better characterise its properties. It came out that the Kate structure appears to be the most prospective in general (45 Mt), with neighbouring Klara as the second (39 Mt), while the initially promising Perina (7 Mt) turned out to be of far lesser importance. The Perina structure case is an example that new seismic interpretation can reduce the capacity estimate if it reveals certain limiting factors, in this case, the limitation of structural closure.

Winds of Change: A Study on the Resource Viability of Offshore Wind Energy in Montenegro

The energy produced from renewable sources (solar, wind, hydro, geothermal, and biomass) provides direct access to clean and safe energy. Offshore wind energy, generated through wind farms, has traditionally relied on fixed structures, whereas innovative floating structures have been commercially applied since 2017. This study investigates offshore areas in Montenegro suitable for wind farm construction. Research on average annual wind speeds has successfully identified a surface area deemed suitable for constructing a wind farm in the Montenegrin part of the Adriatic Sea. Analysis of available bathymetric databases has pinpointed technical solutions for the supporting structures of wind turbines required to construct an offshore wind farm. Applying an assessment method to the defined surface of Montenegrin waters, seven blocks have been identified as suitable for wind farm construction. The research results indicate that wind farms can be built in Montenegrin waters with a technical potential corresponding to a total capacity of 2299.794 MW, which includes 2034.48 MW for floating structures, 126.759 MW for fixed structures, and 138.555 MW for jacket-fixed structures.

Indices and methods for evaluating gross ecosystem product in sea areas: a case study in Changdao County, China

IntroductionCoastal nations heavily rely on their sea areas to achieve sustainable socioeconomic development. Sea areas offer abundant marine ecosystem products and services that are difficult to substitute with industrial goods. Although considerable research has been performed to evaluate the contribution offrom the marine ecosystems to human well-being, systematic and measurable indices are lacking.MethodsTo address this knowledge gap, ecosystem service theory was used to establish a framework for assessing the gross ecosystem product (GEP) of a sea area, which represents the total monetary value of final ecosystem products directly and indirectly used by people within a specific administrative jurisdiction in one year. To evaluate marine GEP, three primary indices, i.e., material products, regulating products, and cultural products, were employed, and they consist of eight secondary indices. Material products in the sea area include aquatic products and oxygen products; regulating products include carbon sequestration, climate regulation, waste treatment, and coastal protection; and cultural products include leisure and recreation, and seascape-added value. The marine GEP was calculated for the administrative sea areas of Changdao County, which is located in the Yellow Sea-Bohai Sea transitional zone.Results and discussionOur analysis indicated that from 2017 to 2019, the marine GEP in Changdao ranged between 32.59 and 33.35 billion Chinese yuan (CNY). Regulating products contributed two-thirds of this total value. However, over the three-year period, the marine GEP underwent a 5.64% decrease in Changdao. Specifically, the value of material products increased by 38.85% while that of regulating and cultural products decreased by 9.16% and 15.87%, respectively. Notably, the spatial distribution of ecosystem product values in Changdao displayed two prominent trends: (1) higher values along the coastal sea areas of islands and lower values in offshore sea areas; and (2) higher values in coastal areas of southern islands and lower values in coastal areas of northern islands. Marine GEP may serve as a comprehensive indicator for assessing the sustainability of marine ecosystem. Combining the assessment of both marine and terrestrial GEP facilitates an understanding of how marine and terrestrial ecosystems interact in coastal regions. Furthermore, the combined use of marine GEP and GDP helps better evaluate and sort the level of green development of coastal nations and regions.

An investigation on the vibrations of a flexible net excited by irregular waves and irregular boundary deformations

Aquaculture cages located in offshore areas typically contain frames and flexible nets. The cages are typically subjected to irregular waves and the frames may deform irregularly over time. Since the nets are tied on the frames, when the frames deform over time, the boundaries of the nets change. In this study, a large flexible net subjected to irregular waves and irregular boundary deformations is theoretically simulated. The irregular waves are simulated using the modified Jonswap spectrum, while the irregular boundary deformations are described by superimposing a series of cosine functions that follow a Gaussian distribution. The dynamic responses of a flexible net are solved numerically. The proposed model is validated by comparison with experimental results. When the boundaries of the net irregularly deformed in the vertical direction, the vibrations of the net in the vertical direction are significantly affected, while the vibrations in the horizontal direction are slightly affected, which are mainly dominated by irregular waves.

Three-Water Differential Parallel Conductivity Saturation Model of Low-Permeability Tight Oil and Gas Reservoirs

Addressing the poor performance of existing logging saturation models in low-permeability tight sandstone reservoirs and the challenges in determining model parameters, this study investigates the pore structure and fluid occurrence state of such reservoirs through petrophysical experiments and digital rock visualization simulations. The aim is to uncover new insights into fluid occurrence state and electrical conduction properties and subsequently develop a low-permeability tight sandstone reservoir saturation model with easily determinable parameters. This model is suitable for practical oilfield exploration and development applications with high evaluation accuracy. The research findings reveal that such reservoirs comprise three types of formation water: strongly bound water, weakly bound water, and free water. These types are found in non-connected micropores, poorly connected mesopores where fluid flow occurs when the pressure differential exceeds the critical value, and well-connected macropores. Furthermore, the three types of formation water demonstrate variations in their electrical conduction contributions. By inversely solving rock electrical experiment data, it was determined that for a single sample, the overall cementation index is the highest, followed by the cementation index of pore throats containing strongly bound water, and the lowest for the pore throats with free water. Building on the aforementioned insights, this study develops a parallel electrical pore cementation index term, ϕm′, to account for the differences among the three types of water and introduces a parallel electrical saturation model suitable for logging evaluation of low-permeability tight oil and gas reservoirs. This model demonstrated positive application effects in the logging evaluation of low-permeability tight gas reservoirs in a specific basin in the Chinese offshore area, thereby confirming the advantages of its application.

Is the Yermak Plateau a continental fragment from North America? Constraints from Cretaceous and early Eocene magmatic events

The Yermak Plateau (YP) north of Svalbard is a prominent bathymetric feature in the Eurasia Basin of the Arctic Ocean, forming the northwesternmost margin of the Eurasian plate. Seismic data indicate that the YP comprises continental basement; however, little is known about its geology. New petrographic, geochemical, Sr–Nd isotopic, and Ar–Ar geochronological data were obtained on rock fragments, which were previously recovered from basement highs of the northeastern and southwestern YP and are dominantly of magmatic origin. These new data combined with available literature data, and comparisons with volcanic and sedimentary rocks from onshore and offshore areas adjacent to the YP indicate that the northeastern YP and the southwestern YP are different regarding their geological evolution. The southwestern YP comprises an alkaline basaltic suite for which an Ar–Ar biotite age of 51 Ma was previously reported. The suite was formed in a continental extensional regime offshore northern Svalbard. Associated sedimentary rocks (sandstone, several limestones) show petrographic similarity with rocks of the Devonian Old Red Sandstone on Svalbard. From the northeastern YP, in contrast, we recovered mildly alkaline basaltic rocks with mid-Cretaceous Ar–Ar ages (102 ± 3 and 98 ± 3 Ma). The rocks show certain geochemical characteristics (partial enrichments of P, Ba, and Eu), which overlap with similar-aged Cretaceous basaltic rocks from northern Ellesmere Island of Canada and North Greenland. We suggest that the northeastern YP is a continental fragment derived from the North American plate, which was separated from the conjugate Morris Jesup Rise and juxtaposed to the geologically distinct southwestern YP by the propagation of the Gakkel Ridge spreading center since the early Oligocene.Graphical

Recent Declining Trends in Pelagic Fish Catches in the Indian Ocean off Sri Lanka: Is Gill Oxygen Limitation Theory (GOLT) a Possible Explanation?

Recent trends in the pelagic fish landings of multi-day fishing fleets operated from Sri Lanka indicated significant declines in many fish species. Therefore, the present preliminary analysis investigates the perceptions of fishers on recent declining trends of pelagic fish landings from offshore areas of the Indian Ocean and further investigates whether the most common pelagic species landed in Sri Lanka conform to the gill oxygen limitation theory (GOLT) and to speculate GOLT as a possible explanation to such trends. According to the perceptions of 457 skippers of fishing vessels interviewed, such declines were possibly attributed to shifting of the areas of occurrence of pelagic fish species, making them less vulnerable to multi-day fishing vessels. As climate change and deoxygenation are major stressors affecting fish stocks, there is a challenging need for disentangling the impacts of these stressors from the effects of overfishing. The 18 most common pelagic fish species harvested from the Indian Ocean confirmed to the predictions from the GOLT, suggesting that shifting of these stocks could be due to deoxygenation which may have been triggered by increased sea surface and sub-surface temperatures. Therefore, fishery-independent surveys are needed to investigate the shifting of areas of occurrence of pelagic fishes in the Indian Ocean to understand their areas of occurrence the further investigate the relevance of GOLT for defining regional fisheries management plans.

A short review of marine renewable energy: Generation, storage, and applications

Renewable energy is a sustainable and green energy converted from renewable energy resources in the nature. There is a huge amount of renewable energy resources in the ocean that can be changed into useful energy like electricity, store for long time use, or apply in the daily energy consumption. These marine renewable energies (MRE) include wave energy, ocean thermal energy, tidal energy, ocean current energy, salinity gradient energy, and offshore energy. With a big area, the oceans have been prospected that it brings endless renewable energy sources for social development and human demand. The renewable ocean energy shows many advantages of sustainable energy, clean energy, and non-carbon dioxide emissions by generating from wave and water in the ocean with an enormous amount of natural energy resources. The MRE can service at many areas of off-shore, on-shore, and remote areas where need energy to drive daily living demands. The MRE reveals some disadvantages such as the influence of daily, monthly, season, and period of time. The solutions have been developed to solve the limitations of the MRE such as developing the storage method to store energy for long time use or making the balance of the output performance to improve quality of the renewable energy. The MRE has also received many concerns from countries by promulgating policies, strategies, and plans to develop the renewable ocean energy such as green economy development, blue economy strategy, carbon dioxide emission reduction, and encouragement of using marine renewable energy. This paper reviews current marine renewable energy with its generation, storage, and application. The work also mentioned some advantages, disadvantage, policies, strategies, and solutions to encourage the development of the renewable ocean energy in over the world. The results hope that it will be spread development, exploitation, and application of marine renewable energy in the near future. Keywords: Marine renewable energy, energy storage, generation, application, sustainable energy

Insights into sulfur and hydrogen sulfide induced corrosion of sintered nanocopper paste: A combined experimental and ab initio study

The power semiconductor joining technology through sintering of copper nanoparticles is well-suited for die attachment in wide bandgap (WBG) semiconductors, offering high electrical, thermal, and mechanical performances. However, sintered nanocopper will be prone to degradation resulting from corrosion in sulfur-containing corrosive environments such as offshore areas. In this study, experiments, including aging test and corrosion characterization, and simulations based on density functional theory (DFT) studies were conducted to explore the corrosion behavior and mechanism of elemental sulfur (S8) and hydrogen sulfide (H2S) on sintered nanocopper. The experimental results indicated that loose corrosion products were observed on the sintered nanocopper during the ageing process involving S8, and compact layered corrosion products formed during the ageing process involving H2S. Furthermore, similar corrosion product compositions (Cu2O, Cu2S, CuO, CuS, and potentially Cu2SO4 or CuSO4) were observed in both the S8- and H2S-ageing processes. However, the S8-ageing process exhibited more noticeable corrosion penetration. This was explained in simulations results: the unsaturated Cu sites on the oxide layer [Cu2O(111)] of the sintered nanocopper could adsorb both H2S and S8, while the saturated Cu sites only exhibited the potential to adsorb S8.

Особенности геологического строения и перспективы нефтегазоносности неогеновых отложений южного сегмента Курильской островодужной системы

The article reviews the current state of knowledge about the geological structure and oil and gas bearing of the Southern Kurils, supplemented by the results of the authors’ own observations. Expansion of the mineral resource base of remote regions plays an important role for its economic development. The oil and gas content of the Southern Kurils is a subject of debate. Based on the analysis of the data accumulated and obtained by the authors, the geological structure of the southern islands of the Greater Kuril Ridge has been clarified. The Upper Miocene-Pliocene complex has been identified in potentially oil and gas bearing Neogene sediments on the basis of direct and indirect signs, in which lithological and structural traps may be formed. As a result of comparative analysis of prospective deposits of onshore, offshore areas of the Mid-Kurilsk Trough and adjacent objects of the North-West Pacific, rocks of the basement of the island arc are assumed to be oil and gas bearing. The most perspective areas from the point of view of oil and gas potential onshore and offshore have been identified, which are the Kuibyshev Block, Iturup Island, and Kasatka Bay, respectively.

Petrography and stratigraphic Os isotopic ages of ferromanganese nodules from the Northwest Pacific east of Minamitorishima Island

The area offshore of Minamitorishima Island, Northwestern Pacific Ocean, contains large amounts of seafloor mineral resources such as ferromanganese (Fe–Mn) nodules, Fe–Mn crusts, and rare-earth element and yttrium (REY)-rich muds. In this study, we applied stratigraphic Os isotopic dating to a Fe–Mn nodule for the first time to date its formation/depositional age, and mineralogical and texturally characterized a complementary nodule. Based on macroscopic and microscopic observations, the studied Fe–Mn nodules can be divided into three layers: Layers L2, L1, and L0 from core to rim. Under the microscope, the Fe–Mn nodules are dominated by vernadite and Fe-oxyhydroxide. In particular, Layer L1 is dominated by banded-columnar vernadite and contains lower amounts of clay minerals derived from the detrital component than Layers L2 and L0. The bulk major and trace element geochemical compositions of sampled layers in the Fe–Mn nodules all plotted in the hydrogenous field in several discrimination diagrams. The Os isotopic ages determined by fitting to the paleo-seawater 187Os/188Os curve can be divided into three clusters (35.7–31.0, 19.0–9.0, and 4.0–1.0 Ma, corresponding to Layers L2, L1, and L0, respectively). These Os isotopic ages indicate that two periods of very slow growth or growth hiatuses occurred during the formation of the Fe–Mn nodule; these age gaps are related to the intermittent (discontinuous) timings of the beginning of Fe–Mn nodule formation offshore Minamitorishima Island.

Utilizing residual networks for remote sensing estimation of total nitrogen concentration in Shandong offshore areas

Nitrogen is one of the critical factors in water pollution and eutrophication, so applying the deep learning method in remote sensing inversion of nitrogen can provide basic information for environmental management. This paper proposes a two-step feature extraction method to solve the problem that the number of bands in water quality inversion is insufficient and the deep learning method cannot be fully exploited. Firstly, manual feature extraction is completed through the fusion between bands to obtain a set of high-latitude shallow factors, which make the features rich and diverse. Then, a one-dimensional convolutional residual network (ResNet-1D) is constructed, and the deep features are automatically extracted through convolution operations of the model, where the residual learning is used to reduce the training difficulty. The full connection is established through depth features. The comparison of models shows that the Mean Relative Error (MRE) is decreased by at least 10% in both test and validation datasets. Finally, the spatiotemporal distribution of total nitrogen concentration (TNC) in the coastal waters of Shandong is explored. In general, the spatial distribution is that the concentration near the coast is higher than the far. The temporal variation is that the monthly mean of the TNC is low in March, moderate in May and August, and high in October; the annual average value of TNC is 0.3mg/L, which has decreased slightly year by year since 2014.

Analytical solution for the seismic response of a nearly saturated sloping seabed: Weak interlayer

Sloping seabeds often exist in offshore areas with complex structures. It is difficult to accurately analyze the seismic response characteristics of sloping seabeds based on the assumptions used for horizontal seabeds. The degree of saturation in nearly saturated soil notably affects the seismic response of seabeds. Therefore, we developed an analytical solution for the seismic response of a sloping, nearly saturated multilayer seabed. Using this solution, we analyzed the effects of the slope angle and soil saturation degree on the seismic response of the seabed. The results show that the seafloor inclination may has a minor impact on the seismic motion at a specific point, but it has a very significant effect on the overall site. A weak interlayer refers to a layer of material that has lower strength and/or permeability compared to the surrounding soil or rock. This layer can reduce the natural frequency of the seabed and increase the amplitude of long-period seismic components. In addition, the presence of a weak interlayer can lead to increased pore water pressure, decreased effective stress, and increased susceptibility to shear failure. These factors combine to reduce the stability of submarine slopes, highlighting the importance of understanding and managing the effects of weak interlayers in geotechnical engineering and coastal defense projects.

Particle Size Distribution Slope Changes along the Yellow River Delta Observed from Sentinel 3A/B OLCI Images

Quantitative estimates of particle size in estuaries and shelf areas are important to understand ocean ecology and biogeochemistry. Particle size can be characterized qualitatively from satellite observations of ocean color. As a typical marginal sea, the Yellow River Delta (YRD) with the Bohai Sea experiences a complex hydrodynamic environment. Here, we attempt to quantify the particle size distribution (PSD) slope (ξ) based on its relationship with the particle backscattering exponent from Sentinel-3A/B OLCI. The PSD slope, ξ displays temporal and spatial variability in the YRD with the Bohai Sea. Its value varies between 3 and 4, and typically exceeds 5 in offshore areas. The lowest value of ξ occurs in the winter, indicating the presence of fine inorganic particles in the water, while high values are attained in the spring, when phytoplankton blooms increase the particle size. ξ decreases near the river mouth because of the large sediment-laden discharge debouching into the sea. We detected a slight increase in ξ when turbid waters were present in the period 2016–2022. Environmental factors, such as sea surface temperature, sea surface wave height, and wind, may control particle size and ξ in the long term. Inorganic suspended particle matter is derived along the YRD using the magnitude of ξ. The mean inorganic suspended particle matter area in winter approaches 23,900 km2 when ξ < 4.6. This study thoroughly characterizes variations in ξ in the YRD with the Bohai Sea and clarifies the contributions of driving factors from human activities and climate change.