The shoreline is defined as the boundary between land and water, and most predictive and observational techniques are based on this definition. From a process perspective, shoreline evolution is primarily driven by external forcings, particularly waves propagating from the open sea. In this study, the shoreline is defined based on its distance from the wave diffraction point, which may help reduce cross-shore variability. Polynomial regression is then applied to long-term shoreline observations to account for temporal shoreline variability across multiple shoreline profiles. Application of different polynomial orders to the Narrabeen-Collaroy Beach observations indicated that the fourth-order polynomial provided the most reasonable representation of the observed temporal variability. The proposed methodology can be implemented within existing shoreline evolution models driven by wave forcing. The methodology is further evaluated using independent validation with prediction horizons ranging from 2 to 48 months. The results show reasonable predictive agreement for shorter prediction horizons, whereas predictive performance began to deteriorate noticeably beyond approximately 24 months. The proposed methodology provides a practical extension for representing temporal shoreline variability across multiple shoreline profiles while retaining the basic structure of the underlying shoreline evolution model.
Marine ecosystems along China's coastal and shelf seas are increasingly affected by intensifying climate change and large-scale human activities such as commercial fishing, mariculture, maritime tourism, and offshore energy extraction, all operating across multiple overlapping spatial scales. To support long-term sustainable management, ecosystem-based management (EBM) depends on ecological indicators that effectively link scientific understanding with policy objectives within the framework of China's Blue Economy development agenda. However, the reliability of these indicators often depends on the spatial and temporal resolution of the available monitoring data. This study evaluates the spatial and temporal behaviours of a suite of ecological indicators across nested spatial scales in China's coastal and shelf seas—encompassing the Bohai Sea, Yellow Sea, East China Sea, and South China Sea—to determine whether the scale at which an indicator is calculated changes the conclusions drawn from it. Three central questions are addressed: (i) whether the current spatial and temporal resolution of survey data is adequate to detect meaningful changes in ecological indicators at the monitoring zone level, (ii) the extent to which trends between indicators at the zone level are similar to those found at coarser spatial scales, and (iii) the extent of spatial consistency across survey zones and across indicators. Using a suite of 20 ecological indicators derived from China's National Fisheries-Independent Research Vessel Survey data (1980–2022) and employing Generalized Additive Models with Dynamic Time Warping clustering, we demonstrate that spatial scale significantly influences indicator behaviours. Model performance and the number of statistically significant trends increased with both spatial extent and survey-set density; trends at finer (zone) scales were frequently asynchronous with those at broader scales, driven mainly by local propagation and, to a lesser extent, local masking. DTW clustering revealed broad swaths of spatial coherence that did not align with existing maritime management and jurisdictional boundaries. These results provide strong support for the importance of spatial scale in interpreting indicator behaviours and for the development of scale-sensitive monitoring systems aligned with China's Blue Economy resilience goals. A framework is proposed to assess the robustness of ecological indicators at macroscale spatial levels, thereby validating information critical for ecosystem-based management decisions supporting sustainable Blue Economy governance.
This study evaluated the performance of 15 CMIP6 models, using ORAS5 and GLORYS12V1 as reference datasets, in simulating current velocity, seawater temperature, salinity, as well as the associated volume transport, ocean heat transport, and freshwater transport in the Bering Strait region. Based on the evaluation results, it then projected future changes in water transports. ORAS5 and GLORYS12V1 show broadly similar spatial patterns in current velocity, seawater temperature, and salinity, while the CMIP6 models exhibit notable inter-model spread. The comprehensive evaluation revealed considerable variability in model performance for current velocity, temperature, and salinity. Estimates of volume transport, ocean heat transport, and freshwater transport aligned with two reanalysis datasets in their seasonal variations, while most models underestimated those transports. The analysis identified differences in the well-performing models for each transport. Ensemble experiments with different numbers of well-performing models determined reasonable schemes for projections of future inflow transports. Under SSP2–4.5 and SSP5–8.5 scenarios, volume and freshwater transport showed declining trends, while ocean heat transport increased, with trends being more pronounced under SSP5–8.5. The multi-model mean based on well-performing models exhibited differences in trend values compared with the ensemble of all unassessed models. The relationship between the horizontal and vertical resolutions of the models and their estimates of volume transport, ocean heat transport, and freshwater transport was also examined. This study deepens the understanding of the ability of CMIP6 models to simulate ocean dynamics in the Bering Strait region and provides new insights into potential future changes in Pacific inflow.
The ocean and climate systems are closely linked, yet public and policymakers frequently view them as separate. This review synthesises recent research and key policy documents to propose ‘ocean-climate literacy’ as an interdisciplinary framework for illuminating informed decision-making and advancing equitable climate action. The present research first demonstrates the imperative for the scientific justification of the ocean-climate system and the necessity to propose an integrated approach to addressing interconnected environmental risks and social disparities. In wake of this clarification, we then develop an interdisciplinary framework combining social-ecological systems theory with constructivist and place-based pedagogy. Collectively, the current study is dedicated to exploring how this literacy can be promoted to overcome persistent barriers through innovative education and engagement strategies. Aligning with global initiatives, notably the UN Ocean Decade, we outline future directions for policy integration, international cooperation, research, capacity building, and citizen science. Building on existing efforts in ocean literacy, this review provides educators, researchers, policymakers, and practitioners with an actionable roadmap aimed at fostering justice-oriented and ocean-aware citizens capable of addressing the intertwined environmental and social challenges at the land-sea interface.
Low-trophic aquaculture species, including seaweeds and shellfish, receive increasing interest. These species can exert reciprocal effects on each other and their surrounding environment through the uptake and recycling of nutrients and the regulation of phytoplankton. This study explores potential benefits or disadvantages of co-cultivating sugar kelp (Saccharina latissima) and the blue mussel (Mytilus edulis), in a mesocosm experiment during the production cycle of kelp (November to April). The experimental setup comprised 4 treatments divided over 24 tanks: either kelp or mussels, both in co-cultivation, and a control with neither. Overall, the results showed no detectable effect of treatment on kelp or mussel biomass growth throughout the experiment, although kelp frond length elongation did show a significant effect of treatment. Filter feeding by mussels was determined by assessing the retention efficiency (RE) of different particle sizes, which showed that RE was high for all particle sizes counted, and in particular for particle sizes between 3 and 20 μm. Although particle counts were generally lower in tanks with mussels, no effect was detected on water turbidity and light conditions. The C:N ratio in kelp tissue was not affected by the presence of mussels, nor by the supplementation of extra nitrogen. On the whole, no statistically detectable differences were found between monoculture and co-cultivation treatments during winter-spring in this flow-through mesocosm experiment.
Spawning habitats are critical for population persistence, yet they remain poorly resolved for many endangered and data-poor marine species. Developing effective and non-invasive approaches to identify these habitats is therefore essential for conservation and management. Here, we integrated bottom trawl surveys with environmental DNA (eDNA) metabarcoding and droplet digital PCR (ddPCR) to investigate the spawning-season distribution of an endangered marine fish, the large yellow croaker (Larimichthys crocea), in the South China Sea. Reproductive activity was suggested during autumn, with a potential aggregation hotspot identified in a narrow depth range (20–41 m), whereas no clear spawning signals were observed during the sampled spring period. This pattern suggests a seasonally aggregated potential spawning habitat, potentially associated with local hydrodynamic conditions. Across methods, eDNA approaches showed higher detection sensitivity than conventional trawl surveys, while ddPCR provided clearer spatial differentiation than metabarcoding. The consistency between molecular and fishery data suggests that eDNA captures major spatial patterns and indicates additional potential distribution areas beyond those detected by trawl surveys. Our results demonstrate that integrating eDNA with traditional surveys improves the reliability of habitat identification, while providing a practical, non-invasive approach for delineating potential critical habitats. This approach supports habitat-based management of endangered marine species, particularly where direct observation or destructive sampling is limited.
This study examined thermal extremes and multi-stressor environmental variability across reef-habitat site clusters in the Belize Barrier Reef System (BBRS) by integrating NOAA Coral Reef Watch CoralTemp SST and bleaching heat-stress metrics, Copernicus Marine and NASA ocean-color products, surface-current and wind products, climate indices, and reconstructed carbonate-system fields. Daily sea surface temperature, Degree Heating Weeks (DHW), marine heatwave (MHW) metrics, optical water-quality indicators, surface circulation, wind forcing, climate indices, and carbonate-system proxies were integrated across reef-habitat site clusters to characterize spatial and temporal differences in reef-associated environmental exposure. Thermal stress intensified markedly across the BBRS during 1985–2025. MHWs became more frequent, longer lasting, and more severe after approximately 2015, while DHW exceedances became increasingly frequent and intense during the most recent decade. Within the 1985–2025 BBRS record, 1998 was the first year in which all site clusters experienced bleaching-level DHW exposure, whereas the highest site-level DHW values occurred in 2023 and 2024, with several sites exceeding 16 °C-weeks, corresponding to NOAA Bleaching Alert Level 4 but not Alert Level 5. DHW and MHW weighted severity captured complementary dimensions of thermal exposure. DHW identified recurrent cumulative bleaching-level heat stress, whereas MHW weighted days characterized acute, category-weighted thermal extremes. Site-level results further showed distinct environmental regimes. Site A represented the strongest acute multi-stressor regime, combining the highest mean event-year DHW, the highest MHW weighted severity, and degraded optical conditions. Site I represented a chronic multi-stressor regime, with the highest DHW recurrence, weak current speed, and persistently elevated optical water-quality indicators. Site J represented an episodically severe thermal-stress regime, while Site K represented a comparatively well-flushed and optically clear setting. Carbonate-system proxies during 1985–2024 showed a shift toward higher surface-ocean pCO₂, lower pH, and reduced aragonite and calcite saturation states, although the magnitude of change varied among sites. Site B showed the strongest carbonate-system stress, whereas Sites E, G, and J remained comparatively more favorable. Overall, the results show that environmental exposure across the BBRS is spatially heterogeneous and shaped by the co-occurrence of cumulative heat stress, acute MHW severity, optical water-quality gradients, hydrodynamic exchange, climate variability, and carbonate-system change. This integrated framework improves the interpretation of reef-system environmental variability beyond temperature-only assessments.
Marine protected areas (MPAs) are central to biodiversity conservation, but modelled corridor connectivity in densely used coastal waters can be constrained by dynamic maritime pressure. This study develops a social–ecological connectivity framework that integrates automatic identification system (AIS)-derived maritime activity as social resistance and a budget-based indicator of management-resource availability as governance response. Using the Pearl River estuary, China, and a fixed set of 35 Chinese white dolphin (Sousa chinensis) habitat-use hotspots, we constructed annual least-cost-path corridor networks for 2017–2021 and estimated temporal exponential random graph models. Annual corridor-cost summaries were highest in 2019 and partially eased in 2020. Social resistance was negatively associated with corridor-tie formation, whereas budget-based governance response showed a positive conditional association. A complementary node-level analysis identified recurrent structural–ecological mismatch at PID16, PID14, PID03, and PID07, among other candidate sites for monitoring and management review. These mismatches do not by themselves demonstrate ecological underperformance or governance failure, because low local habitat-use intensity may also occur at transit locations and may be affected by survey effort. The integrated edge- and node-level framework is therefore best used as a diagnostic and hypothesis-generating tool for linking AIS monitoring with targeted ecological verification in human-dominated coastal seascapes
Eddy–eddy interactions, ubiquitous across the global ocean, play a significant role in eddy evolution. Utilizing satellite altimetry data from 1993 to 2023, coupled with the angular momentum eddy detection and tracking algorithm (AMEDA), this study investigates eddy–eddy interactions east of the Drake Passage. These interactions are predominantly concentrated within the western and southern Argentine Basin and the Scotia Sea. In the region, the number of eddy–eddy interactions is higher during summer and lower during winter in the Southern Hemisphere. On seasonal timescales, both eddy intensity and the eddy Rossby number are negatively correlated with eddy number and the number of eddy–eddy interactions. This indicates that when the eddy intensity is greater, the likelihood of interaction is lower, which may be related to eddy stability. Quantitatively, merged eddies attain 193.7% of the mean area and 134.1% of the mean azimuthal velocity of their pre-merger counterparts; conversely, pre-split eddies reach 207.0% of the area and 137.7% of the azimuthal velocity averaged over the two post-split eddies. Spatially, regions with a high number of eddy–eddy interactions coincide with areas characterized by high topographic roughness and are also characterized by frequent eddy generation and dissipation. Notably, in the western Argentine Basin, interacting eddies propagate at larger angles relative to the local isobaths, whereas non-interacting eddies primarily propagate along the isobaths. These findings highlight the significant roles of both eddy intensity and topographic roughness in modulating eddy–eddy interactions.
The Marine Protected Area of the Sylt Outer Reef – Eastern German Bight (SOR), located in the German Exclusive Economic Zone of the North Sea, is an ecologically important region that provides essential habitats for numerous species and supports high benthic faunal diversity. In this study, we developed the first mass-balanced food web model for the SOR covering the period 2010–2020, using Ecopath with Ecosim (EwE), in order to understand ecosystem functioning, structure, and energy flows prior to the implementation of management measures. The model included 44 functional groups and 8 fishing gear types. We found that the SOR is dominated by low trophic levels and strong benthic recycling, with detritus and primary producers contributing 33.43% and 20.41% of total system throughput (TST), respectively. Ecosystem indicators highlight that the system is detritus-driven with high internal recycling. It has multiple alternative pathways for energy and biomass flow, supporting a complex trophic structure and potentially being resilient to disturbance. Keystone groups and species included surface-feeding birds and harbour porpoise, whereas key structuring groups included carnivorous polychaetes, phytoplankton, herbivorous zooplankton, and sandeels. Fishing gears in the SOR target both pelagic and demersal groups, primarily forage fish such as sandeels and sprat. The static food web model of the SOR is a baseline for evaluating the effect of the implemented management measures on the ecosystem as the next step, supporting ecosystem-based management decisions for the Sylt Outer Reef such as the exclusion of bottom trawling from many areas of the SOR in March 2023.
Cold seeps host chemosynthesis-based ecosystems that play an important role in shaping deep-sea benthic biodiversity. Benthic foraminifera are widely used as indicators of environmental change, yet their molecular ecological responses to cold seep activity and their long-term dynamics remain poorly understood. In this study, environmental DNA (eDNA) metabarcoding was applied to investigate foraminiferal communities in surface sediments along a seepage gradient and in a radiocarbon-dated sediment core (SY186–3) from the “Haima” cold seeps in the South China Sea. Surface sediments reveal a distinct distribution pattern of foraminiferal assemblages. Read abundance declines toward the seep center, whereas Shannon–Wiener and Margalef diversity indices increase, producing a characteristic high-diversity but low-abundance community in seep-influenced sediments. Functional annotation of bacterial communities shows an enrichment of sulfur-metabolizing microorganisms near the seep core, suggesting intensified sulfur cycling and close interactions between microbial activity and benthic microfauna. The sediment core further documents two phases in Holocene ecosystem development. An earlier stage is marked by a gradual increase in foraminiferal abundance and diversity, indicating the establishment of seep-influenced benthic habitats. In contrast, the later stage shows pronounced millennial-scale fluctuations in community composition. Overall, these findings demonstrate that sedimentary eDNA records can link microbial activity, sedimentary geochemical conditions, and benthic microfaunal communities, offering a powerful approach for investigating ecological dynamics in deep-sea methane-seep environments.
Concern about how climate change affects marine ecosystems is growing, despite international commitments to reduce CO2 emissions. Predicting amphipod species responses to ocean warming is critical due to their high abundance and key ecological role in marine ecosystems. We selected 35 widespread benthic amphipod species with at least 30 unique occurrence records after thinning from two or more biogeographical regions and classified them according to depth and feeding strategy. Following spatial thinning, 17 species retained sufficient occurrence records for Maximum Entropy (MaxEnt) modeling, of which 15 met the model evaluation criteria by having a Partial ROC value below 1 or a 5% omission rate exceeding 0.2. We projected species distributions under the low emission RCP 2.6 and high emission RCP 8.5 scenarios for 2050 and 2100. To compare species responses among feeding groups, we used linear mixed effects models with feeding type, scenario_time combination, and their interaction as fixed effects and species identity as a random effect. Species were also classified by depth, but statistical comparisons among depth groups were not performed because of limited species representation. Projected distributions showed substantial species-specific distribution shifts, including both gains and losses of suitable habitat and changes in areas of high species richness. Linear mixed effects models showed that potential future changes in suitable habitat area did not differ significantly among feeding groups, whereas centroid shifts were significantly influenced by the interaction between feeding type and scenario–time combinations. This indicates that trophic strategy influences the spatial response of amphipods to future climate change. These findings highlight that climate change may dramatically alter the functional composition of benthic communities and their ecological roles, beyond simple changes in species distributions. Incorporating trophic identity and functional roles into climate impact assessments will be essential for predicting ecosystem responses and informing conservation strategies that safeguard marine ecosystems functioning under future climate change. This approach will improve predictions of ecosystem responses and strengthen conservation and management strategies aimed at maintaining ecosystem functioning in a rapidly changing ocean.
Biomonitoring using Biomarkers is essential for evaluating the environmental contamination, especially if combined with chemical analysis. This study aims to provide an integrated assessment of environmental quality at 8 sites along the northwestern Atlantic coast of Morocco by analyzing 10 trace metal concentrations in Mytilus galloprovincialis and evaluating their biological effects through a multibiomarker approach, pollution indices, and human health risk assessment, thereby highlighting early biological effects that may not be detectable through chemical data alone. Biomarkers of neurotoxicity, oxidative stress, and detoxification were assessed alongside pollution indices and condition indices to determine site-specific variations in mussel health, while measured metal concentrations were compared with international background and guideline values (WMW, NS&T, RNO) to contextualize contamination levels. The results showed that trace metal concentrations decreased in the order: Fe > Zn > Mn > As>Cu > Ni > Pb > Cd > Co > Hg but were within regulatory safety limits for most of the study sites. Biomarker responses revealed localized environmental stress, particularly at sites influenced by urban-industrial activities (notably S3, S5, and S6), where elevated bioaccumulation of Ni, Zn, Cd, and Pb coincided with increased enzymatic and stress responses. The integration of chemical and biological data provided a comprehensive assessment of contamination, demonstrating that multibiomarker approaches provide sensitive early-warning signals of environmental stress in coastal ecosystems, even when trace metal concentrations remain largely within regulatory limits, thereby confirming that biomonitoring is essential for detecting early signs of pollution before metal levels reach critical thresholds and emphasizing their relevance for environmental management and marine biosurveillance programs.
In recent years, more and more satellite SSS products become available for improving salinity simulation in ocean models. This study introduces the implementation of satellite SSS as Dirichlet surface haline boundary condition (SHBC) in general ocean model. Using the Hybrid Coordinate Ocean Model, three numerical experiments covering the period 2019 on a quasi-global domain were performed with Dirichlet SHBC, Nudging and virtual salt flux, respectively. The effectiveness of the different SHBCs was assessed by comparisons with Argo observations and intercomparisons with the GLORYS12 reanalysis. The results demonstrate that the novel Dirichlet SHBC is able to constrain the modelled salinity in the upper 100 m depth better than other SHBCs. In particular, with respect to the Argo salinity, the Dirichlet SHBC is comparable to the GLORYS12 reanalysis in the upper 30 m depth in the Pacific Ocean. The sensitivity analysis on the observation error of the satellite SSS suggests that the proposed Dirichlet SHBC is optimal where the actual error of the satellite SSS relative to Argo is less than 0.8 PSU which can be reached by most SSS products. Furthermore, the novel Dirichlet SHBC has positive effects on mixed layer depth but is helpless for seawater temperature. This study offers a new perspective on the integration of high-accuracy satellite observations and ocean numerical models.
Fishing pressure can affect marine fish species differently according to their biological traits. This study investigates how the trait composition of fish landed in the Azores changed over four decades of exploitation. Using landings data spanning 42 years (1980–2021), 103 fish species landed in the Azores were analysed. Archetypal analysis was used to summarize ecological and life-history traits into three strategy endpoints: periodic, opportunistic, and equilibrium. Interannual variability and long-term temporal patterns in richness, landings, and intrinsic vulnerability were analysed using the coefficient of variation, standard Generalized Additive Models, and Generalized Additive Mixed Models with AR(1) correlation structure. The results showed that richness of periodic-type species increased through time, indicating a greater contribution of periodic-type species to the landed catch. Landings of opportunistic-type species showed no robust long-term directional pattern, whereas their intrinsic vulnerability declined through most of the time series and stabilized in recent years. Landings of periodic-type species showed marked interannual variability, but this temporal pattern was not statistically significant after accounting for AR(1) autocorrelation. Landings of equilibrium-type species and intrinsic vulnerability declined over time, indicating a shift in the landed biomass and vulnerability composition associated with slow-turnover species. These findings suggest that long-term changes in Azorean landings reflect shifts in the representation of life-history trait composition rather than simple changes in species counts or total landing alone. Integrating the life-history strategies framework into fisheries management is essential for aligning exploitation with biodiversity conservation and ecosystem functions.
The absolute geostrophic currents in the South Indian Ocean were estimated using gridded Argo profiling float data from 2004 to 2023, and the P-vector method. These currents were subsequently used to investigate the spatial patterns and seasonal variability of meridional salt transport (MST) and meridional heat transport (MHT). On an annual basis, the geostrophic components of MST and MHT are directed southward north of 16°S, and reverse to a northward direction south of 16°S. The reversal is primarily attributed to variations in wind stress curl. In contrast, the Ekman components of MST and MHT remain southward throughout the basin. The total interior MST and MHT exhibit southward transport north of 20°S and northward transport south of 20°S, with pronounced maxima near 5°S, 13°S, and 24°S. These maxima are predominantly controlled by the geostrophic component. Meanwhile, the western boundary currents (WBCs), located near 14°S and 24°S. There are display extreme values opposite in sign to those of MST and MHT. This results from the Ekman suction effect and is consistent with Sverdrup balance theory. The seasonal variability of total interior MST and MHT is primarily driven by the Ekman component, exhibits strong agreement with variations in zonal wind stress.
Transplantation of bioindicator organisms, a widely used method in monitoring of chemical pollution, was tested to be used for the monitoring of concentrations of microplastics (MP) and their potential biological effects. Previous data on chemical contaminants and selected biomarker responses measured in mussels (Mytilus spp.) were combined with new MP observations in mussel soft tissues after a two-month caging period along the coastline of Finland (Baltic Sea). The number of MP observed in the tissues was on average 20.0 ± 41.1 per mussel and 168.9 ± 236.8 per g mussel dry weight. Polyethylene terephthalate and polyethylene were the two main polymer types observed. The Integrated Biomarker Index was elevated in mussels at the caging site with the highest tissue concentrations of MP. However, the relationship between tissue concentrations of MP and biomarker responses was not clear at all sites. Further, variability in tissue concentrations of MP between the sites was high without a clear link to local contamination, suggesting that the mussel caging approach should be studied more before accepting it as a monitoring method for detecting spatial variability in concentrations of MP.
Coastal eutrophication driven by increasing nutrient inputs is a major threat to seagrass ecosystems, often acting in synergy with opportunistic macroalgae proliferation. This study investigated the short-term combined effects of sediment nutrient enrichment and varying loads of the green macroalgae Chaetomorpha linum on the structural, morphological, and physiological traits of the seagrass Cymodoce nodosa. A 90-day in situ factorial experiment was conducted in Bekalta, Tunisia, combining three nutrient enrichment levels and four macroalgal levels treatments. Seagrass structural, morphometric and physiological traits were monitored. Nutrient enrichment significantly increased porewater nutrient concentrations and initially stimulated leaf growth, shoot surface area, and chlorophyll content, indicating an initially nutrient-limited system. However, macroalgae load had a stronger negative impact on plant performance, causing marked reductions in shoot density, aboveground biomass, and growth rates, primarily through light limitation. Physiological analyses revealed that nutrient enrichment and algal shading induced metabolic adjustments, including decreased soluble proteins, sugars, and phenolic compounds, alongside enhanced antioxidant enzyme activity. These responses indicate a shift in carbon allocation toward nitrogen assimilation and oxidative stress regulation. With increased nutrient availability, epiphyte biomass also rose significantly, potentially exacerbating light stress. Overall, the results demonstrate that C. nodosa exhibits short-term physiological plasticity under nutrient enrichment, but macroalgal overgrowth remains the dominant stressor affecting meadow structure. While nutrient inputs did not immediately impair plant integrity, they induced metabolic costs that may compromise long-term resilience. These findings highlight the importance of managing both nutrient loading and macroalgal proliferation to preserve Mediterranean seagrass ecosystems and their associated ecological functions.
Pacific water serves as the main source of heat and freshwater to the Arctic Ocean and strongly influences upper-ocean stratification and sea ice melting. However, long-term hydrographic observations over the northern Chukchi slope remain limited. Here, we investigate the hydrographic variability and transport of Pacific Water using a two-year mooring record from Station C1 on the northern Chukchi slope (2018-2020), together with upstream temperature records from Bering Strait moorings A2, A3, and A4, satellite sea-ice concentration, atmospheric reanalysis, and ocean reanalysis data. The mooring observations reveal pronounced seasonal and vertical hydrographic variability at C1. The upper layer exhibits the strongest seasonal warming and freshest conditions, whereas deeper layers remain colder, saltier, and more stable. Pacific Summer Water, mainly expressed as Bering Summer Water, is most common from August to December, while Remnant Winter Water and Newly-Ventilated Winter Water dominate in winter and spring. Current measurements indicate a persistent poleward to northwestward flow, with most speeds ranging from 5 to 20 cm/s and stronger flow in summer-autumn than in winter-spring. A mixed-layer heat budget analysis shows that upper-ocean warming near C1 was controlled primarily by oceanic advection, especially geostrophic advection, with Ekman advection providing a secondary and intermittent contribution, while Ekman pumping and net surface heat flux were comparatively weak. Lag-correlation analysis between upstream and downstream temperature records indicates that the summer Pacific-origin warm signal reaches the upper layer at C1 after about two months, with peak lags of 59-65 days. In addition, the anomalously strong warm event observed at C1 in 2018 was likely associated with a more favorable regional advective background. These results highlight the importance of seasonal water-mass transformation, poleward advection, and regional circulation variability in shaping hydrographic conditions over the northern Chukchi slope.
Offshore wind farms are rapidly expanding across shallow shelf seas, yet their cumulative impacts on tidal hydrodynamics and transport pathways remain poorly constrained. Here, we quantify the hydrodynamic response of the southeastern North Sea to large offshore wind farm (OWF) arrays using the coastal circulation model FESOM-C with explicit resolution of individual turbine foundations. Two barotropic simulations were conducted: a reference case without turbines and a wind-farm scenario in which 700 monopile foundations, grouped into twelve wind-farm polygons, were directly represented in the computational mesh. An unstructured grid enabled sub-metre resolution ( 1.4 m) around individual monopiles while maintaining basin-scale coverage ( 2.34 & times; 10 10 m 2 ), allowing turbine-scale processes and regional responses to be resolved simultaneously. Comparative analysis reveals physically meaningful differences between the two scenarios, both within OWF areas and across the wider shelf. The presence of wind farms redistributes tidal kinetic and potential energy, with domain-averaged changes of approximately 1-2.5%, systematically attenuates current speeds within turbine clusters, and localises flow acceleration along farm peripheries. At the turbine scale, near-stagnant zones ( 1-10 m) and enhanced shear develop adjacent to monopiles and persist throughout the tidal cycle. Passive Lagrangian drifter simulations indicate that these flow modifications may reduce horizontal dispersion and enhance particle retention within and around wind farms, with implications for larval transport, sediment dynamics, and ecological connectivity. Our results suggest that offshore wind farms may act not only as local perturbations but also as regional modifiers of tidal circulation and transport pathways extending over several kilometres. The magnitude and spatial coherence of the response depend on turbine density and array configuration, indicating that wind-farm layout can influence the strength of cumulative hydrodynamic effects. These findings highlight the necessity of high-resolution, turbine-resolving models to assess and manage the large-scale environmental impacts of offshore wind development in shelf seas.
