Sediment-laden sea ice plays an important role in Arctic sediment transport and biogeochemical cycles, as well as the shortwave radiation budget and melt onset of ice surface. However, at present, there is a lack of efficient observation approach from both space and in situ for the coverage of Arctic sediment-laden sea ice. Thus, both spatial distribution and long-term changes in area fraction of such ice floes are still unclear. This study proposes a new classification method to extract Arctic sediment-laden sea ice on the basic of the difference in spectral characteristics between sediment-laden sea ice and clean sea ice in the visible band using the MOD09A1 data with the resolution of 500 m, and obtains its area fraction over the pan Arctic Ocean during 2000−2021. Compared with Landsat-8 true color verification images with a resolution of 30 m, the overall accuracy of our classification method is 92.3%, and the Kappa coefficient is 0.84. The impact of clouds on the results of recognition and spatiotemporal changes of sediment-laden sea ice is relatively small from June to July, compared to that in May or August. Spatially, sediment-laden sea ice mostly appears over the marginal seas of the Arctic Ocean, especially the continental shelf of Chukchi Sea and the Siberian seas. Associated with the retreat of Arctic sea ice extent, the total area of sediment-laden sea ice in June–July also shows a significant decreasing trend of 8.99 × 10⁴ km² per year. The occurrence of sediment-laden sea ice over the Arctic Ocean in June–July leads to the reduce of surface albedo over the ice-covered ocean by 14.1%. This study will help thoroughly understanding of the role of sediment-laden sea ice in the evolution of Arctic climate system and marine ecological environment, as well as the heat budget and mass balance of sea ice itself.

In the last 10 years (2012–2021), five hypoxic events have been observed in summer in the central Bohai Sea (CBS). Frequent and persistent hypoxia will have an impact on the ecosystem of the CBS. In this paper, historical sea temperature (ST), salinity (SAL), density (Den), and dissolved oxygen (DO) concentration data from three stations in the CBS are analyzed via the linear regression method, and the correlations between the stratification factors (ST, SAL, and Den) and DO concentration are determined. The thresholds of the stratification factors at the three stations in June in the year in which hypoxia occurred were determined and applied to survey data from 29 stations in late May to early June in 2022 in the CBS; this assessment found that the data from 19 stations indicated that hypoxia was about to occur. In August, the survey data showed that 14 out of the 29 stations indicated hypoxic conditions, of which 12 were from the predicted 19 stations, meaning that the estimation accuracy reached 63%. The same approach was applied to data from June 2023. The data for August from a bottom-type online monitoring system in the CBS verified the occurrence of hypoxic events around Sta. M2. The results show that the strength of the seawater stratification plays a leading role in hypoxic events in the summer in the CBS, and the thresholds of the stratification factors can be used to predict the occurrence of hypoxic events.

During August and September 2023, three giant icebergs, each bigger than Paris, successively grazed Clarence Island in the northeast of the Antarctic Peninsula, a home to a population of over 100 000 penguins. This incident may serve as a clarion call for the increasing iceberg calving due to global warming and its subsequent impact on the Antarctic ecosystem. Here we investigate this unexpected event and employ historical records and probabilistic analyses of iceberg grounding to assess the degree of impact on penguin colonies of Clarence Island. Among the eleven colonies, there is one with low impact, eight with medium impact, and two with high impact. The low-impact colony, Cape Lloyd, is located in the northern part of the island, while the high-impact colonies, False Ridge and Pink Pool, are in the southeast. The eight medium-impact colonies are distributed along both the eastern and western coasts of the island. This study provides essential support for evaluating the impact of iceberg activity on penguin colonies. We argue that penguin colonies located in areas prone to iceberg drift, such as Clarence Island, may become more vulnerable to the heightened risk of iceberg collisions or groundings in the warming future. Therefore, we hope the public will become more aware of the grave impacts of climate change on penguins and underscore the urgent need for effective conservation strategies.

Mangroves are indispensable to coastlines, maintaining biodiversity, and mitigating climate change. Therefore, improving the accuracy of mangrove information identification is crucial for their ecological protection. Aiming at the limited morphological information of synthetic aperture radar (SAR) images, which is greatly interfered by noise, and the susceptibility of optical images to weather and lighting conditions, this paper proposes a pixel-level weighted fusion method for SAR and optical images. Image fusion enhanced the target features and made mangrove monitoring more comprehensive and accurate. To address the problem of high similarity between mangrove forests and other forests, this paper is based on the U-Net convolutional neural network, and an attention mechanism is added in the feature extraction stage to make the model pay more attention to the mangrove vegetation area in the image. In order to accelerate the convergence and normalize the input, batch normalization (BN) layer and Dropout layer are added after each convolutional layer. Since mangroves are a minority class in the image, an improved cross-entropy loss function is introduced in this paper to improve the model’s ability to recognize mangroves. The AttU-Net model for mangrove recognition in high similarity environments is thus constructed based on the fused images. Through comparison experiments, the overall accuracy of the improved U-Net model trained from the fused images to recognize the predicted regions is significantly improved. Based on the fused images, the recognition results of the AttU-Net model proposed in this paper are compared with its benchmark model, U-Net, and the Dense-Net, Res-Net, and Seg-Net methods. The AttU-Net model captured mangroves’ complex structures and textural features in images more effectively. The average OA, F1-score, and Kappa coefficient in the four tested regions were 94.406%, 90.006%, and 84.045%, which were significantly higher than several other methods. This method can provide some technical support for the monitoring and protection of mangrove ecosystems.

The long-term dynamic evolution and underlying mechanisms of coastal landscape pattern stability, driven by strong anthropogenic interference and consequently climate change, are topics of major interest in national and international scientific research. Guangdong Province, located in southeastern China, has been undergoing rapid urbanization over several decades. In this study, we quantitatively determined the scale threshold characteristics of coastal landscape pattern stability in Guangdong Province, from the dual perspective of spatial heterogeneity and spatial autocorrelation. An analysis of the spatiotemporal evolution of the coastal landscape was conducted after the optical scale was determined. Then, we applied the geodetector statistical method to quantitatively explore the mechanisms underlying coastal landscape pattern stability. Based on the inflection point of landscape metrics and the maximum value of the Moran Ⅰ index, the optimal scale for analyzing coastal landscape pattern stability in Guangdong Province was 240 m × 240 m. Within the past several decades, coastal landscape pattern stability increased slightly and then decreased, with a turning point around 2005. The most significant variations in coastal landscape pattern stability were observed in the transition zone of rural-urban expansion. A q-statistics analysis showed that the explanatory power of paired factors was greater than that of a single driving factor; the paired factors with the greatest impact on coastal landscape pattern stability in Guangdong Province were the change in gross industrial output and change in average annual precipitation from 2010 to 2015, based on a q value of 0.604. These results will contribute to future efforts to achieve sustainable coastal development and provide a scientific basis and technical support for the rational planning and utilization of resources in large estuarine areas, including marine disaster prevention and seawall ecological restoration.

Wave information retrieval from videos captured by a single camera has been increasingly applied in marine observation. However, when the camera observes ocean waves at low grazing angles, the accurate extraction of wave information from videos will be affected by the interference of the fine ripples on the sea surface. To solve this problem, this study develops a method for estimating peak wave periods from videos captured at low grazing angles. The method extracts the motion of the sea surface texture from the video and obtains the peak wave period via the spectral analysis. The calculation results captured from real-world videos are compared with those obtained from X-band radar inversion and tracking buoy movement, with maximum deviations of 8% and 14%, respectively. The analysis of the results shows that the peak wave period of the method has good stability. In addition, this paper uses a pinhole camera model to convert the displacement of the texture from pixel height to actual height and performs moving average filtering on the displacement of the texture, thus conducting a preliminary exploration of the inversion of significant wave height. This study helps to extend the application of sea surface videos.

The Caroline Plate is located among the Pacific Plate, the Philippine Sea Plate, and the India Australia Plate, and plays a key role in controlling the spreading direction of the Philippine Sea Plate. The Caroline Submarine Plateau (or Caroline Ridge) and the Eauripik Rise on the south formed a remarkable T-shaped large igneous rock province, which covered the northern boundary between the Caroline Plate and the Pacific Plate. However, relationship between these tectonic units and magma evolution remains unclear. Based on magnetic data from the Earth Magnetic Anomaly Grid (2-arc-minute resolution) (V2), the normalized vertical derivative of the total horizontal derivative (NVDR-THDR) technique was used to study the boundary of the Caroline Plate. Results show that the northern boundary is a transform fault that runs 1400 km long in approximately 28 km wide along the N8° in E-W direction. The eastern boundary is an NNW-SSE trending fault zone and subduction zone with a width of tens to hundreds of kilometers; and the north of N4° is a fracture zone of dense faults. The southeastern boundary may be the Lyra Trough. The area between the southwestern part of the Caroline Plate and the Ayu Trough is occupied by a wide shear zone up to 100 km wide in nearly S-N trending in general. The Eauripik transform fault (ETF) in the center of the Caroline Plate and the fault zones in the east and west basins are mostly semi-parallel sinistral NNW-SSE–trending faults, which together with the eastern boundary Mussau Trench (MT) sinistral fault, the northern Caroline transform fault (CTF), and the southern shear zone of the western boundary, indicates the sinistral characteristics of the Caroline Plate. The Caroline hotspot erupted in the Pacific Plate near the CTF and formed the west Caroline Ridge, and then joined with the Caroline transform fault at the N8°. A large amount of magma erupted along the CTF, by which the east Caroline Ridge was formed. At the same time, a large amount of magma developed southward via the eastern branch of the ETF, forming the northern segment of the Eauripik Rise. Therefore, the magmatic activity of the T-shaped large igneous province is obviously related to the fault structure of the boundary faults between the Caroline Plate and Pacific Plate, and the active faults within the Caroline Plate.

Studies of converted S-wave data recorded on the ocean bottom seismometer (OBS) allow for the estimation of crustal S-wave velocity, from which is further derived the Vp/Vs ratio to constrain the crustal lithology and geophysical properties. Constructing a precise S-wave velocity model is important for deep structural research, and inversion of converted S-waves provides a potential solution. However, the inversion of the converted S-wave remains a weakness because of the complexity of the seismic ray path and the inconsistent conversion interface. In this study, we introduced two travel time correction methods for the S-wave velocity inversion and imaged different S-wave velocity structures in accordance with the corresponding corrected S-wave phases using seismic data of profile EW6 in the northeastern South China Sea (SCS). The two inversion models show a similar trend in velocities, and the velocity difference is <0.15 km/s (mostly in the range of 0–0.1 km/s), indicating the accuracy of the two travel time correction methods and the reliability of the inversion results. According to simulations of seismic ray tracing based on different models, the velocity of sediments is the primary influencing factor in ray tracing for S-wave phases. If the sedimentary layer has high velocities, the near offset crustal S-wave refractions cannot be traced. In contrast, the ray tracing of Moho S-wave reflections was not significantly impacted by the velocity of the sediments. The two travel time correction methods have their own advantages, and the application of different approaches is based on additional requirements. These works provide an important reference for future improvements in converted S-wave research.

The gas sources in the eastern Cote d’Ivoire Basin (Tano Basin) are seldom reported and remain controversial due to multiple sets of potential source rocks and poorly documented geochemical characteristics of natural gases. The marine source rock potential from the Upper Albian to Turonian as well as the molecular composition and the stable carbon isotope composition of natural gases in the eastern Cote d’Ivoire Basin were studied in detail to investigate the origins of natural gases. The total organic carbon (TOC), hydrogen index (HI), and generation potential (S₁ + S₂) of source rocks indicate that both sapropelic source rocks and humic source rocks developed during the late Albian, whereas sapropelic source rocks developed during the Cenomanian and the Turonian. The normal order of δ¹³CH₄ < δ¹³C₂H₆ < δ¹³C₃H₈ (δ¹³C₁ < δ¹³C₂ < δ¹³C₃), the relationship between C₂/C₃ molar ratio and δ¹³C₂-δ¹³C₃, and the plot of δ¹³C₁ versus C₁/(C₂+C₃) collectively show that the natural gases are thermogenic due to the primary cracking of kerogen, including the typical oil-associated gases from Well D-1, the mixed oil-associated gases and coal-derived gases from Well G-1 and Well L-1. Based on the plot of δ¹³C₁ versus δ¹³C₂ and the established relationship between δ¹³C₁ and equivalent vitrinite reflectance (Ro), we proposed that the natural gases are in a mature stage (Ro generally varies from 1.0% to 1.3%). Combined with results of basin modelling and oil-to-source correlation, the transitional to marine source rocks during the late Albian were thought to have made a great contribution to the natural gases. Our study will make a better understanding on petroleum system in the eastern Cote d’Ivoire Basin.

The northern South China Sea, including the Zhujiangkou Basin and the Beibuwan Basin, developed high-quality lacustrine source rocks during the Eocene rifting period. These source rocks are vital for hydrocarbon generation in the northern South China Sea. The Zhu Ⅰ depression in the Zhujiangkou Basin and the Beibuwan Basin typically exhibit high abundance of C₃₀ 4-methyl steranes. However, shales in the Eocene Wenchang Formation in the Zhu Ⅲ depression of the Zhujiangkou Basin contains lower quantities of high-quality lacustrine source rocks with 4-methyl steranes, which often co-elute with some pentacyclic triterpanes in gas chromatography-mass spectrometry (GC-MS). Therefore, the single 4-methylsterane parameter based on GC-MS cannot accurately distinguish organic source in the deep to semi-deep water lacustrine source rocks of the Wenchang Formation from other source rocks, thus impeding the recognition of their contributions to petroleum reservoirs. In this study, GC-MS of aliphatic hydrocarbons, palynofacies and algal identification, as well as stable carbon isotope data of organic matter were used to identify the algal species and construct the paleoclimate during deposition of the Wenchang Formation source rocks in the Zhu Ⅲ depression of the Zhujiangkou Basin. It is suggested that during the Wenchang Formation period, freshwater green algae prevailed in the lake, which is likely account for the relatively low content of 4-methyl steranes in the high-quality lacustrine source rocks. Controlled by the algal species, it is proposed that the content of C₃₀ tetracyclic polyprenoids (TPP) can better indicate the quality of the Wenchang source rocks than C₃₀ 4-methyl steranes. Consequently, a relationship between the TPP index and the quality of the lacustrine source rocks in the Wenchang Formation of the Zhu Ⅲ depression was established. A higher TPP index indicates higher organic matter abundance and hydrogen index of the lacustrine source rocks. When applied to the origin analysis of oils in the Zhu Ⅲ depression, it is believed that the organic-rich deep lacustrine source rocks in the Wenchang Formation made great contribution to the transitional zone crude oils in the Wenchang A and Wenchang B depressions.