Abstract Tropospheric delay is a crucial factor that limits precise point positioning (PPP) performance, especially at low altitude angles. Here, a remote sensing (RS)‐augmented method was developed to improve PPP performance with high‐quality zenith tropospheric delay (ZTD) derived from water vapor products of satellite GOES‐18. The GOES‐18 precipitable water vapor (PWV) was evaluated against the European Center for Medium‐Range Weather Forecasts Reanalysis 5 (ERA5) PWV, with a root mean square error (RMSE) of 2.50 mm. The derived ZTD was validated using International GNSS Service (IGS) ZTD showing RMSE of 16.20 mm. Data from 42 GPS and GLONASS observed IGS stations were collected. The results show that the RS‐augmented PPP improves convergence time and short‐term precision in the vertical component for both GPS + GLONASS (G + R) and GPS‐only compared to traditional PPP. For the G + R vertical component, the convergence time was shortened by 18.9% and the short‐term positioning accuracy improved by 17.4%. For the GPS‐only systems, the convergence time was shortened by 12.2% for the vertical components, while vertical component positioning accuracy increased by 19.5%. The 42 stations were categorized through different geographic conditions and atmospheric water vapor structures (ocean, coastline, and land) to analyze their convergence times and positioning accuracy. The results show that stations in ocean regions exhibited the greatest improvement in both convergence time and positioning accuracy. The improvement in convergence time was mainly related to the accuracy of the ZTD RMSE; the improvement in positioning accuracy was primarily influenced by the geographic conditions of the stations, such as station latitude.

Wave–sea-ice interactions shape the transition zone between open ocean and pack ice in the polar regions. Most theoretical paradigms, implemented in coupled wave–sea-ice models, predict exponential decay of the wave energy but some recent observations deviate from this behaviour. Expanding on a framework based on wave energy dissipation due to ice–water drag, we account for drifting sea ice to derive an improved model for wave energy attenuation. Analytical solutions replicate the observed non-exponential wave energy decay and the spatial evolution of the effective attenuation rate in Antarctic sea ice.

Marine litter sampling across the Western Mediterranean: Critical bibliographic review and dataset compilation.

HAB species of the Bohai Sea detected through metabarcoding in three large-scale seasonal expeditions.

Abstract This study introduces ARCMH25, a high-resolution hybrid Moho model that combines gravimetric and seismic data to estimate two key constituents of the Mohorovičić discontinuity (Moho): Moho Depth (MD), Moho Density Contrast (MDC), along with their associated uncertainties. The model provides 1° × 1° resolution across the Arctic region, including both the Arctic Plate and adjacent oceanic zones, covering latitudes from 60°N to 90°N and longitudes from 180°W to 180°E. ARCMH25 employs a weighted least-squares inversion that integrates multiple observational constraints, including Vening Meinesz–Moritz (VMM) isostatic estimates such as the gravimetric MD-MDC product, gravimetric-seismic MDC, and seismic MDs from the Earth Crustal Model 1 (ECM1). This integrated approach enables simultaneous estimation of MD and MDC, while also providing spatially variable uncertainty fields. Model results show significant lateral variation in MD, ranging from 10 to 20 km beneath the central Arctic Ocean to 50–60 km under continental interiors and Greenland. Similarly, MDC values vary from 100 to 200 kg/m 3 in the oceanic regions to 500–600 kg/m 3 over continents and Greenland. The model also quantifies uncertainty, with MD errors below 2 km in oceanic areas and up to 6 km on land, while MDC uncertainties remain under 50 kg/m 3 offshore and increase to approximately 90 kg/m 3 in continental regions. Comparisons with existing models demonstrate ARCMH25’s enhanced sensitivity and resolution, especially in tectonically transitional zones. The model effectively captures lithospheric variability across ocean basins, continental shields, and rifted margins, providing new insights into Arctic geodynamics. Moreover, the ARCMH25 framework is adaptable and can be applied to other seismically under-sampled regions for crustal and tectonic studies.

The increasing demand for continuous and reliable air traffic surveillance over remote and oceanic regions has prompted the exploration of innovative solutions beyond traditional radar and satellite-based systems. In this context, High-Altitude Pseudo-Satellites (HAPSs) have emerged as a promising technology capable of extending surveillance and communication coverage within the stratosphere at significantly lower cost and greater operational flexibility. This paper presents the results of Research and Development (R&D) efforts focused on the conceptualization and development of a HAPS prototype serving as a proof of concept to enhance Air Traffic Management (ATM) surveillance capabilities. The study quantitatively examines the HAPS operational environment by classifying and evaluating the geometric, physical, environmental, thermal and atmospheric factors influencing prototype performance. The developed prototype establishes a scalable foundation for future multi-platform HAPS networks, and forthcoming research will focus on experimental validation under real-world conditions and performance optimization to enable integration into next-generation ATM systems.

AGE DATING OF PALEOGENE BIOSTRATIGRAPHIC DIATOM LEVELS FROM THE MARINE CENOZOIC STRATIGRAPHIC KEY SECTION OF WEST KAMCHATKA AT THE KVACHINA BAY BASED ON MAGNETOSTRATIGRAPHIC DATA

For Central Asia, sandwiched between two great powers – Russia and China – because of geography’s tyranny, access to the Indian Ocean region offers one more, albeit potentially very powerful, avenue of engagement with the rest of the world. While a strategic pivot to the South provides economic advancement, the article contends that the synergy of the terrestrial and maritime realms through interconnectivity initiatives such as Beijing’s China–Pakistan Economic Corridor or New Delhi’s International North–South Transport Corridor adds a layer of complexity to the great power rivalry and multi-threat environment that Central Asian leaders have traditionally ignored but can no longer avoid. Therefore, the article offers a critical inside-out view of the economic, geopolitical and security calibrations by Central Asian states as they engage with the Indian Ocean region. The article contributes to the scholarship on Eurasian geopolitics by emphasising the overlooked maritime dimensions of the Indian Ocean in relation to Central Asia, shifting the focus beyond economic gains to geopolitical implications of interconnectivity initiatives, and emphasising the agency of Central Asian states amidst great power rivalry.

Over the last few years India has been progressively attempting to establish itself as a ‘preferred security partner’ in the Indian Ocean Region (IOR). This transformation represents a fundamental shift from India’s historically passive maritime posture described by strategic thinkers as a manifestation of its ‘sea blindness’ to a robust maritime-oriented outlook characterised by proactive regional leadership, enhanced naval capabilities, multilateral security arrangements and comprehensive engagement with littoral states. This essay examines the evolution, mechanisms and implications of India’s emergence as a preferred security partner in the IOR.

Summary Given the scarcity of seismometers in marine environments, traditional seismology has limited effectiveness in oceanic regions. Submarine Distributed Acoustic Sensing (DAS) systems offer a promising alternative for seismic monitoring in these areas. However, the existing machine learning model trained on land-based DAS data does not perform well with submarine DAS due to differences in noise characteristics, deployment conditions, and environmental factors. This study presents a machine learning approach tailored specifically to submarine DAS data to enable automated seismic event detection and P and S wave identification. Leveraging DeepLab v3, a neural network architecture optimized for semantic segmentation, we developed a specialized model to handle the unique challenges of submarine DAS data. Our model was trained and validated on a dataset comprising nearly 57 million manually and semi-automatically labeled seismic records from multiple globally distributed submarine sites, providing a robust basis for accurate seismic detection. The model adapts to a variety of deployment scenarios and can process DAS data from cables with different lengths, configurations, and channel spacings, making it versatile for various ocean environments. We thus provide an adaptable and efficient tool for automated earthquake analysis of DAS data, which has the potential to enhance real-time earthquake monitoring and tsunami early warning in submarine environments.

Monomethylmercury (MMHg) is a potent neurotoxin to which humans are exposed via fish consumption. However, the relative importance of planktonic and benthic biomagnification pathways to fish MMHg concentrations in marine food webs is challenging to quantify. Here, we apply compound-specific isotope analysis (CSIA) of Hg to identify fish MMHg biomagnification pathways across nearshore bay (NB), marine continental shelf (MCS), and pelagic ocean (PO) regions. We observe significant differences in Δ199Hg between MMHg and total mercury (THg), highlighting the limitations of using THg isotopes to resolve MMHg dynamics in the environment. In NB fish, Δ199Hg of MMHg closely matches that of benthic invertebrates, while in MCS and PO fish, it aligns with phytoplankton. According to the MMHg isotope binary mixing model, about 85% of MMHg in NB fish derives from the benthic biomagnification pathway, whereas over 90% of MMHg in MCS and PO fish originates from seawater-phytoplankton trophic transfer. These findings reveal that the benthic biomagnification pathway in near-shore regions has been underestimated in previous models, leading to potential uncertainties in evaluating marine Hg cycling and human exposure risks. This study highlights the importance of the benthic biomagnification pathway in coastal environments and demonstrates the potential of the CSIA of Hg for investigating MMHg biomagnification pathways in marine food webs, which provides new insights for global Hg pollution management under the Minamata Convention.

Astrobiology seeks to understand the origin, evolution, distribution, and future of life in the Universe, focusing on habitability beyond Earth. Due to the high cost and complexity of space missions, studying planetary analog sites on Earth is essential for supporting and de-risking future exploration. These analog sites are extreme terrestrial environments that mirror environmental, geological, geochemical, or biological conditions on other planetary bodies. Investigating how life persists in these settings advances knowledge of extraterrestrial habitability and enables realistic testing of life-detection instruments. This review presents the first comprehensive synthesis of more than 50 planetary analog field sites across the Indian subcontinent and Indian Ocean region. We identify 2 geological regions with active astrobiological research, 4 requiring targeted geochemical and geomicrobiological surveys, and 5 with high planetary relevance but minimal study. We assess how these sites fill gaps in global astrobiological research and evaluate their readiness for future investigations. The sites include high-altitude cryospheric settings such as Himalayan glaciers and permafrost, analogues to Martian and lunar environments; saline-alkaline lakes like Sambhar Lake, comparable to Martian paleolakes; intrabasaltic bole beds in the Deccan Traps, relevant to phyllosilicate formation on Mars; subsurface caves and mines, analogous to lunar lava tubes; and hydrothermal vent systems along the Central and Southwest Indian Ridges, relevant to icy ocean worlds. Comparing these sites to global analogues reveals that, although most are not yet fully characterized, several offer unique environmental combinations. As deep-space missions prepare to search for life beyond Earth, a geographically broader set of analog sites is critical. Highlighting the diversity and scientific value of these under-characterized regions in South Asia and their marine periphery, this review provides a foundation for characterizing previously overlooked planetary analog sites. These sites expand the global analogue parameter space and offer underutilized natural laboratories for planetary habitability and biosignature research.

Offshore oil exploration and the volume of imported crude oil shipping have increased steadily, elevating the risk of oil spills. An advanced offshore oil film identification method is proposed to realize the accurate and robust recognition and segmentation of oil films from marine radar images in offshore oil spill detection. This method integrates feature engineering with an improved Beetle Antennae Search (BAS) optimization algorithm, aiming to address the key issues of low discrimination between oil films and complex marine backgrounds and insufficient spill boundary localization accuracy in radar image analysis. First, the raw radar image was transformed into the Cartesian coordinate system, and a filtering procedure was applied to attenuate interference. Subsequently, the gray distribution and local contrast of the denoised image was further improved. Afterwards, the complexity of the grayscale distribution within each feature map was quantified using Shannon entropy. The Top-K feature maps with the highest entropy values were subsequently used to construct an information-rich subset. The subset was then processed through a pixel-wise averaging strategy to generate a coupled feature image. Then, Otsu threshold was used to refine ocean wave regions. Finally, the oil films were segmented with an improved BAS optimization algorithm. The fitness function of the improved BAS algorithm was augmented through the integration of edge fitting accuracy, and a target-proximity penalization scheme. Through an adaptive step-length modulation paradigm and Perceptual Mechanism, it can achieve a marked improvement in search accuracy and achieving precise segmentation of oil slicks. The detection accuracy of the proposed method is significantly enhanced relative to the traditional BAS algorithm and existing marine radar oil spill detection methods. The IOU, Dice, recall and F1-score reached 81.2%, 89.6%, 85.2%, and 90.1% respectively. This method not only advances the methodological rigor of spill detection but also provides critical data support for the development of more effective control and remediation practices.

Abstract It remains unclear how changes in moisture supply drive droughts in the Agro‐Pastoral Ecotone of Northern China (APENC), where ecological restoration and food security are increasingly vulnerable under warming. Using a moisture‐tracking model, we quantify the moisture sources of APENC's precipitation and its trends, and reveal mechanisms linking anomalous upwind moisture transport to droughts. Terrestrial moisture sources (67.60%) dominate APENC's precipitation. Over 2000–2023, moisture sources from high‐latitude Eurasia and the Tibetan Plateau have increased, whereas those from oceanic sources have decreased significantly. During recent drought events, reductions in moisture inflow from key terrestrial source regions, especially East Asia and the South Asia–Indian Ocean region, primarily triggered rainfall deficits in the APENC. The combination of weakened moisture inflows and reduced local humidity amplified moisture scarcity, sustaining drought severity. These findings highlight the coupled roles of remote transport and land–atmosphere feedbacks in APENC droughts, providing new evidence for understanding semi‐arid hydroclimate risks.

The present paper is an exploration of the deepening of the geopolitical rivalry between China and India in the strategically important Indian Ocean Region. The most important sea lines of communication and significant energy and trade flows define the IOR, making it a significant nexus in the power relations within the world. The competition between them, driven by the strategic interests of each state, naval buildups, and by infrastructural projects, such as the String of Pearls strategy of China, and the counter-measures of India, such as the Chabahar Port, goes beyond bilateralism and reflects a broader superpower rivalry and its consequences to global security. Through qualitative evaluation of the interactions of superpowers, regional blocs, and non-state actors, this investigation provides information to scholars, investors, and policymakers on the complex nature of the dynamics that will make up the direction the IOR takes.

Abstract. The partial pressure of carbon dioxide (pCO2) on the surface of the ocean is crucial for quantifying and evaluating the ocean carbon budget. Insufficient consideration of the effects at the sea area scale makes it difficult to comprehensively evaluate the spatiotemporal distribution characteristics and variation patterns of pCO2. This study constructed a pCO2 evaluation dataset based on LDEO measurement data and multi-source data. After conducting correlation testing on a global, far sea, and near sea scale, an ocean surface pCO2 evaluation model was constructed using multiple linear regression, convolutional neural network, gated recurrent unit, long short-term memory network, generalized additive model, extreme gradient boosting, least squares boosting, and random forest. Performance evaluation indicates that the random-forest model consistently achieves the best accuracy across all spatial scales, yielding a global RMSE of 6.123 µatm and an R2 of 0.986. In the open ocean, RMSE decreases to 4.699 µatm and R2 rises to 0.988, whereas in coastal waters RMSE increases to 8.044 µatm and R2 declines to 0.972. Based on this, the annual sea surface pCO2 distribution of 0.25° × 0.25° from 2000 to 2019 was reconstructed. The reconstructed field shows a typical equatorial high/polar low pattern, as well as an overall upward trend consistent with independent observations, with acceleration particularly evident in specific regions of subtropical coastal oceans.

Abstract Recent studies have analyzed the Madden-Julian oscillation (MJO) as a moisture mode over the Indian Ocean region where MJO convection is driven by moisture anomalies. Specifically, the distribution of moist entropy (ME) tendency with negative anomalies to the west of the convective center and positive anomalies to the east is an important factor in MJO propagation. Nonetheless, some MJO events terminate despite being associated with a downstream environment that is becoming more favorable based on ME tendency. This study builds and investigates a climatology of counterintuitive MJOs, i.e., events that behave differently from expectation, based on classifications stemming from the moisture mode framework. The ME tendency east of the convective center and associated budget revealed that counterintuitive continuing events have downstream environments that become more hostile due to negative contributions from longwave radiation and latent heat fluxes that nearly balance positive contributions from the advective terms. Meanwhile, counterintuitive terminating events have environments that become more favorable due to lower magnitude negative contributions from the same terms despite similar positive contributions from advection. The RMM index amplitude and total anomalous ME were used to observe connections between MJO strength and counterintuitive events. Both metrics were unable to discriminate between events that behave similarly given different evolving downstream environments or events with different outcomes but similarly evolving environments. Tropical wave activity was also analyzed using multiple variables and higher local power in westward wave activity was observed for events that terminate with higher power in eastward wave modes for continuing events.

Technetium-99: Sources, transport, bioaccumulation, and trophic transfer in marine ecosystem.

Vertical zonation and interaction patterns of heterotrophic protists in the Bay of Bengal and Eastern Indian Ocean.

Organic and inorganic carbon stocks in seagrass sediments of Mauritius.