Healthy oceans and sustainable development are the core contents of the "Ocean Decade" plan put forward after the United Nations Ocean Conference. Maintaining the health of marine ecosystem is an effective guarantee for the realization of marine service and output functions, an important support for sustainable economic and social development, and a major issue of global concern. In many cases, we manage the ocean without understanding the ocean, because we do not really understand the past, present and future of the ocean, and the most important thing is that we lack the knowledge and hands to perceive, recognize and master the ocean. The health of the oceans depends largely on the state and safety of the organisms in the oceans. So, the theme of how to evaluate the health of the ocean should also be biology. We are concerned about marine eutrophication, because eutrophication can cause red tides and the increase of many harmful algae, which in turn will lead to the accumulation of algae toxins in shellfish that feed on algae, which will have a serious impact on human health and life when humans eat these shellfish. For a long time, our monitoring of the ocean emphasis on the environment, not the ecosystem, and the monitoring content is mainly chemical factors, with emphasis on pollutants, but the monitoring of organisms in the ocean is relatively weak, and the criteria we have long used to classify the state of the ocean are expressed by "several types of seawater", which is far from enough for the healthy ocean and sustainable development. Unable to meet the requirements of marine health assessment, we need to establish a marine health assessment system with marine organisms as the main body to monitor the ocean from the marine ecosystem The goal of measurement should be biological change and the environmental factors that lead to biological change.

How to cite: Sun, S.: A new observation and assessment system is needed to maintain the ocean health and achieve sustainable development, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14482, https://doi.org/10.5194/egusphere-egu25-14482, 2025.

Microplastics (MPs) are widely distributed in the ocean and can be ingested by fish. Despite fish being a major source of aquatic protein for humans, no study has yet addressed how to reduce the risk of human exposure to MPs when consuming fish. This study investigated 1,075 fish from 37 species across representative fishing areas, analyzing MP presence in various tissues, including gills, intestines, and muscles, to assess fish food safety comprehensively. MPs were found in 36.28% of gills and 39.63% of guts, but none were detected in muscle tissues. Fish from upper layers had higher MP abundances and smaller average sizes compared to those from deeper waters. A significant negative correlation was observed between the MP abundance in fish and their length and weight. The global per capita MP consumption from captured fish, including all tissues and muscles, is approximately 5.60 × 10⁴ items/year. Hence, to minimize MP exposure, humans should prioritize consuming only fish muscle and selecting fish from deeper waters and larger sizes whenever possible. Optimizing fish consumption patterns could reduce human exposure to MPs and associated health risks.

How to cite: Meng, L. and Sun, X.: How to reduce human microplastic exposure risks through optimized consumption choices of fish from seawater?, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7626, https://doi.org/10.5194/egusphere-egu25-7626, 2025.

Tidal flats, a vital coastal wetland habitat in the land-sea transition zone, serve as breeding grounds, nurseries, and habitats for numerous estuarine and offshore fish species. Moreover, they play an indispensable role in maintaining fish biodiversity. Regrettably, the cumulative impacts of intensive human activities and climate change have significantly disrupted the landscape structure and functionality of tidal flats. This has led to the degradation of fish habitats and an even more severe loss of suitable living environments for fish populations. Despite the importance of understanding these dynamics, in-depth research into the changing ecological patterns within the coastal zone and their implications for fish communities remains limited. Jiangsu Province, a pivotal development hub within China's Yangtze River Delta region, is endowed with rich tidal flat resources and a densely populated area. To address the knowledge gap, this study aimed to leverage remote sensing imagery of Jiangsu’s coastal zone to extract landscape distribution data. By constructing an ecological security evaluation framework, we comprehensively analyzed the landscape ecological patterns of tidal flats. Additionally, we employed advanced techniques such as ultra-high resolution mass spectrometry and high-throughput sequencing to explore fish diversity characteristics. Integrating these with multi-source data analysis and model simulations, we sought to uncover the intricate relationships between landscape ecological patterns and fish biodiversity characteristics in the coastal zone. The findings were consistent with previous research on the thermophilic ratio of fish communities in the southern Yellow Sea and the offshore areas of Jiangsu. In different landscape ecological pattern groups, spatial heterogeneity was evident in the composition and relative abundance of fish species. When it comes to the protection of tidal flats, it is essential to consider not only the area changes in a specific region but also the structure and function of these areas. Integrating the results of the analysis on tidal flat ecological patterns and fish diversity, preventive, proactive restoration, and rehabilitative measures should be implemented to safeguard and manage coastal areas. Ultimately, this research endeavors to deepen our scientific understanding of the role of fishery resources in the sustainable development of the coastal zone. Based on our findings, we proposed targeted recommendations for the conservation and management of the coastal zone's spatial pattern, thereby contributing to the long-term health and resilience of this critical ecosystem.

How to cite: Cheng, S. and Cao, L.: The influence of landscape ecological pattern changes of tidal flat on fish community in the coastal area, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21737, https://doi.org/10.5194/egusphere-egu25-21737, 2025.

High-resolution carbon isotopic records from organic and carbonate carbon reveal an unprecedented multi-decade decline in stable isotopic compositions over the past millennium. These records were obtained from laminated cores collected in the San Lázaro Basin (SLB), a semi-closed basin off the Baja California Peninsula, Mexico. The SLB is influenced by suboxic waters at depth and lies beneath the southern boundary of the California Current System. Isotopic analyses of two planktic foraminifera species, N. dutertrei and G. ruber, show a decreasing trend in carbon isotopic compositions over the past 80 years, mirroring the trend seen in atmospheric CO₂, albeit with slightly lower slopes. These trends are likely driven by the influx of anthropogenic CO₂ into surface waters of the California Current, a manifestation of the Suess effect in the upper ocean. The differences in slope are likely due to the combined influence of vertical mixing driven by dominant northwest winds, which bring nutrient- and inorganic carbon-rich waters with relatively heavier isotopic values, and the equatorial advection of northern waters carrying anthropogenic CO₂ in this highly productive eastern boundary current.

How to cite: Contreras-Pacheco, Y. V., Abella-Gutierrez, J. L., Vallejo-Espinosa, G., and Herguera, J. C.: The Onset of Anthropogenic Carbon Invasion in the Surface Waters of the Southern California Current, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-757, https://doi.org/10.5194/egusphere-egu25-757, 2025.

As climate change progresses, increasing attention is being devoted to potential impacts on ecosystems and resources under sustained warming. For models that resolve climate impacts on global marine animal biomass, however, most work to date including model intercomparisons have largely focused on the period up to 2100. Here we consider projections to 2300 using a collection of five Marine Ecosystem Models (BOATS, FEISTY, DBPM, MArcroecological, and ZooMSS) driven by output from a collection of CMIP6 Earth system models (including CESM2-WACCM and IPSL-CM6A, as well as UKESM1, MIROC-ES2L, and ACCESS-ESM1.5). Initial results from ESMs with online coupled biogeochemical models suggest that although they exhibit a degree of diversity in their ocean warming response, their disagreements about projected primary production are even more pronounced, with the disagreements being not only in amplitude but also in sign.

We explore the long-term impacts of climate mitigation on marine animal biomass, by comparing Marine Ecosystem Model results under high emissions with low mitigation (SSP5-8.5) and low emissions with high mitigation (SSP1-2.6) forcing. If thermal forcing were to dominate the fish biomass through its effect on mortality with a linear response, one might expect an approximately factor of five difference between SSP1-2.6 and SSP5-8.5 projections of marine animal biomass change to 2300. Both regional and global aspects will be considered, with a focus on identifying potential tipping points under SSP5-8.5 forcing that may be avoided through mitigation.

How to cite: Rodgers, K., Bianchi, D., Aumont, O., Blanchard, J., Bopp, L., Buechner, M., Everett, J., Guiet, J., Heneghan, R., Hill, S., Kawamiya, M., Murphy, K., Petrik, C., Richardson, A., Sharma, S., and Yamaguchi, R.: The high value of climate mitigation for global fish biomass to 2300, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14914, https://doi.org/10.5194/egusphere-egu25-14914, 2025.

Oceanic transport and environmental variability are key for structuring marine populations and designing protection and management plans. While previous regionalizations of the Mediterranean Sea have provided valuable insights into objectively discretizing the marine seascape, they only suggest impacts on biogeography without explicitly testing them. Additionally, these studies often overlooked small-scale, high-frequency processes and focused predominantly on near-surface layers, neglecting deeper biomes.

To address these limitations, (i) we utilize a data-assimilative model and remote-sensing observations at high resolution, and (ii) we focus on two Mediterranean species with contrasting ecological traits, including adult phases exploiting both epi- and meso-pelagic layers as well as highly dispersive early-life stages. Our target species are the red mullet (Mullus barbatus), a demersal fish mainly distributed in the continental shelf, and the deep-water red shrimp (Aristeus antennatus), a pelagic marine decapod. Using passive Lagrangian particles advected within two-dimensional flow fields at several depths, we construct networks of connected areas and cluster them to identify hydrodynamic provinces. The average of these provinces reveals recurrent spatial patterns aligned with multiscale oceanographic features. In parallel, we use seawater temperature gridded data and a community detection algorithm to look for regions based on geographical proximity and temperature similarity. It produces clusters that we then average to mean abiotic regionalizations. Finally, we integrate independent observed biogeographies of the target species, and employ statistical modeling to explain these biogeographies as a combined effect of ocean circulation and abiotic clusters. This approach advances our understanding of biogeographical patterns, by deciphering two regimes depending on spatial scales, teasing apart the respective role of oceanic circulation and abiotic variability and how the latter are modulated by the target species’ ecological traits.

This robust framework helps exploring the controls of the spatial organization of marine life and could be used to predict future biodiversity reorganization in the ocean.

How to cite: Rwawi, C., Moltó, V., Berline, L., Nérini, D., and Rossi, V.: Explaining biogeography through ocean circulation and abiotic variability, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17616, https://doi.org/10.5194/egusphere-egu25-17616, 2025.

Better understanding of the carbon dynamics in coastal areas is essential to develop metrics to evaluate the efficiency of policies regarding carbon neutrality (i.e. whether the coastal environment, more specifically the Belgian part of the North Sea, acts as a source or sink of carbon to the atmosphere). Over the last 8 years data has been collected from discrete samples (pH, DIC, TA) and data produced by the ICOS coastal stations BE-SOOP-Simon Stevin and the BE-FOS-Thornton Buoy (seawater CO₂ concentration). These data are an invaluable source to identify how the carbonate chemistry and air-sea carbon fluxes can be used to determine whether the coastal environment acts as a source or sink of CO₂ and assess the acidification state. More specifically, we will present the temporal evolution of pH, DIC, TA, seawater CO₂ concentration and air-sea CO₂ fluxes from the gathered data. The data show the expected seasonality of carbon dynamics and the link with biogeochemical processes (e.g. phytoplankton blooms) but also trends in the capacity of these areas to absorb or release CO₂. Furthermore, the results show a pH stability of these coastal waters, uncorrelated with the increase in DIC. This suggests the influence of biogeochemical processes, such as riverine inputs, nutrient dynamics, and the organic matter remineralisation within the coastal zone. This work will also investigate whether it is feasible to connect such information directly or indirectly to policies relevant to carbon neutrality.

How to cite: Leseurre, C., Theetaert, H., T'Jampens, M., Van Engeland, T., Verbrugge, S., and Gkritzalis, T.: Using the VLIZ ICOS station measurements and discrete samples to assess the carbonate chemistry trends (since 2017) and carbon neutrality of the Belgian part of the North Sea, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6653, https://doi.org/10.5194/egusphere-egu25-6653, 2025.

The North Sea, a highly productive shelf sea, may play an important role in the local carbon cycle by exchanging carbon and nutrients with the Atlantic Ocean and facilitating carbon burial in its sediments. However, understanding the response of carbon burial rates to natural and anthropogenic forcings remains limited in this setting. To address this gap, this study examines long-term trends in carbon burial and their natural and anthropogenic drivers at North Sea-North Atlantic gateway over the past 14,000 years. Sediment cores – both piston core and multi-core (61.5687 °N, 3.0465 °E) – were analysed using a multi-proxy approach including X-ray fluorescence (XRF), lipid biomarkers, (compound specific) isotopes, and dinoflagellate cysts to reconstruct climate change, patterns of primary productivity and origin of the carbon. Chronology was established using radiocarbon dating. Carbon burial rates were reconstructed by calibrating the Br/Ti log ratio with TOC measurements, while the productivity of calcium-bearing organisms was inferred from the Ca/Fe log ratio. The highest carbon burial rates of 8 gC/m²/yr are during the Younger Dryas and coincides with cold bottom water temperatures/high global ice volume and reduced productivity. In the Early Holocene, productivity increased, followed by a gradual transgression, reducing sedimentation rates and thereby carbon burial rates to 2 gC/m²/yr. At around 500 years BP, carbon accumulation rates increased again to approximately 5 gC/m²/yr, likely caused by anthropogenic factors such as deforestation and changes in land use.

How to cite: Hilgen, C., Hennekam, R., van der Meer, M., Reichart, G.-J., and Sangiorgi, F.: Carbon burial at the North Sea-North Atlantic gateway over the past 14,000 years, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16678, https://doi.org/10.5194/egusphere-egu25-16678, 2025.

The North Sea is a very productive and heavily exploited continental shelf sea that acts as a sink for atmospheric CO₂. The balance between carbon buried in North Sea sediments and exported off the northwest European shelf into the North Atlantic is highly uncertain, rendering carbon budgets difficult to make and future changes of the system hard to predict. As part of the NoSE (North Sea-Atlantic Exchange) project, this study evaluates the uncertainty and variability in the exchange (with the North Atlantic) and burial of carbon in the North Sea as simulated by global Earth System Models (ESMs).  

From six state-of-the-art ESMs (ACCESS-ESM1-5, CanESM5, CMCC-ESM2, CESM2-WACCM, IPSL-CM6A-LR, NorESM2-LM), the years matching the observational period were selected from the CMIP6 historical experiment (1850 to 2014) and the ScenarioMIP of CMIP6 ssp245 experiment (2015 to 2100).

Here, we compare simulated values for sea surface temperature, salinity, phosphate, alkalinity and dissolved inorganic carbon (DIC) to an internally consistent data product for the northwest European shelf (NWESDAP; 347 datapoints). The models show good agreement for temperature (r² > 0.8), but weak simulation of salinity (r² < 0.4). The weak fit is mainly caused by a bad representation of low salinity, whereas in the higher salinity range, the comparison between the models and the observations is better. The model simulation of phosphate shows a weak fit with the observations (r² < 0.5), mainly caused by a bad model representation of higher phosphate concentrations in the observational dataset. Although the model representation of total alkalinity and surface DIC is weak (r² < 0.3), the mean observed DIC values are reasonably well represented by the models. As the horizontal flux of DIC is a product of horizontal water transport and DIC concentration, the representation of the variability in DIC might not be as important for calculating lateral fluxes as an adequate simulation of its spatial mean value.

The model ensemble representation of the main in- and outflow areas, as well as representation of the spatial variability of the variables is considered good enough to compare the present-day and the future North Sea carbon cycle.

Using the model ensemble, we will present the spatial and temporal variability in carbon burial, carbon concentrations, horizontal carbon transport and the balance between these components, both for present-day and future climate conditions.

How to cite: Koek, A. C. (., Humphreys, M., Poll, van de, W., and Bintanja, R.: North Sea carbon burial and transport off the northwest European shelf in global Earth system models (ESMs) – validation and variability , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16030, https://doi.org/10.5194/egusphere-egu25-16030, 2025.

Coastal seas are vital players in the global carbon cycle, acting as both sinks and sources of atmospheric carbon dioxide (CO₂). However, their carbon dynamics remain poorly quantified at the spatial and temporal resolutions necessary for regional carbon budget assessments. Enhanced insights are critical for detecting anthropogenic impacts on the carbon cycle and for monitoring the effectiveness of CO₂ removal strategies. The Belgian Part of the North Sea (BPNS), equipped with advanced monitoring infrastructure, offers a unique platform to address these gaps through in-situ CO₂ measurements collected via buoys, research vessels, and other sources. This data collection provides high spatial and temporal coverage, enabling near-real-time estimation of the exchange of CO₂ with the atmosphere in the region.

To estimate the baseline carbon budget for the BPNS at an unprecedented local scale, we applied a feedforward neural network approach capable of achieving a spatial resolution of 1 km and a temporal resolution of 1 day. This analysis spans the period from 2014 to 2024 and incorporates an extensive dataset of sea surface partial pressure of CO₂ (pCO₂) measurements. These in-situ observations were sourced from the Surface Ocean CO₂ Atlas (SOCAT) and the Integrated Carbon Observation System (ICOS) databases. Additionally, we integrated a suite of predictor variables derived from satellite data and oceanographic reanalysis products, including sea surface temperature, salinity, chlorophyll-a concentrations, and suspended particulate matter, all of which are recognized as key factors influencing pCO₂ variability in the BPNS. By combining this calculated sea surface pCO₂ with atmospheric CO₂, we also estimated the air-sea CO₂ flux.

Initial findings reveal that the sea surface pCO₂ reconstruction achieves strong predictive ability for coastal zones, with an R² exceeding 0.80, successfully capturing both local spatial heterogeneity and seasonal variations. Sensitivity analyses highlight sea surface temperature as the dominant predictor, followed by chlorophyll-a and suspended particulate matter, emphasizing the interplay of thermal and non-thermal processes in shaping pCO₂ variability across the BPNS. The seasonal cycle of pCO₂ decreases after winter primarily due to increased CO₂ solubility in cold water and biological spring uptake, and peaks after summer, mainly driven by warming of the seawater and reduced biological activity, leading to an increased release of CO₂. While sea surface salinity exerts a relatively minor influence overall, its localized impact near the Scheldt estuary plume is significant, underscoring the critical role of riverine inputs in modulating regional carbon dynamics. Overall, our findings indicate that the region functions as a net CO₂ sink for the atmosphere.

How to cite: Keppens, M., Roobaert, A., van Langen Rosón, A., Neukermans, G., and Landschützer, P.: High-Resolution Coastal Carbon Dynamics in the Belgian Part of the North Sea Using Machine Learning, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15600, https://doi.org/10.5194/egusphere-egu25-15600, 2025.

Consistent and quality-controlled data products of marine carbonate system parameters, such as the Global Ocean Data Analysis Product (GLODAP), are needed to investigate the marine carbon cycle and its variability through space and time. However, GLODAP focuses on the open ocean, limiting its utility for understanding the marine carbonate system in shelf seas. While representing only  ̴7% of the global ocean area, these areas play an important role in the global carbon cycle. The northwest European shelf (NWES) seas are of particular interest because of their high heterogeneity and expected capacity to absorb, export and bury carbon. Here, we present a new internally consistent data product for this region, the Northwest European Shelf Data Analysis Product (NWESDAP). NWESDAP includes directly measured marine carbonate system parameters (total alkalinity, dissolved inorganic carbon and pH) as well as physical and nutrient variables focusing on the NWES above 1000 m and between 43°N and 70°N. NWESDAP gathers datasets of discrete measurements from research cruises and time-series stations from throughout the water column. Data from estuaries, deltas and fjords are also included. So far, NWESDAP consists of about 18,000 inorganic carbon data points (of which c. 5,000 were already in GLODAPv2.2023) from around 500 research cruise and station datasets, merged into a consistent format. Data quality flags corresponding to quantified systematic and random uncertainties have been assigned to each dataset depending on the measurement method used and other available metadata. As GLODAP-style quality control (QC) based on deep ocean cross-over analysis is not possible in this shallow region, a secondary QC based on parameter distributions and covariances has been conducted to identify suspected erroneous data points and systematic biases in specific datasets, aiming to ensure the internal consistency of the entire product so it can be used to investigate the highly variable marine carbon cycle in the NWES seas.

How to cite: Brandon, M., Humphreys, M. P., Becker, M., and Bittig, H. C.: The marine carbonate system in the northwest European shelf seas: an internally consistent data product (NWESDAP), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3276, https://doi.org/10.5194/egusphere-egu25-3276, 2025.

Shelf seas filter terrestrial inputs of important macronutrients and bio-essential trace metals such as iron (Fe) and manganese (Mn), which support primary productivity and long-term carbon dioxide (CO₂) storage in the sediments and the deep ocean. The North Sea is a biologically productive shelf sea and a net sink of atmospheric CO₂, yet the exchange of essential (trace) nutrients between the North Sea and the North Atlantic Ocean as well as the role of trace elements in the carbon cycle are poorly constrained. This limits our ability to accurately model biogeochemical interactions and calculate CO₂ fluxes in this region. Within the NoSE (North Sea-Atlantic Exchange) project, we investigate the North Sea's role in the Atlantic Ocean's biogeochemical system, focussing on the Norwegian trench for its pivotal role in the nutrient and inorganic carbon outflow to the Atlantic and sediment accumulation. Here, we present an observational dataset of trace metals, nutrients, and marine carbonate system parameters from the first NoSE expedition in May-June 2023. We analyse the spatial distributions, sources and sinks of (trace) nutrients in the water column and discuss their relationships with carbonate system and other hydrographic parameters. We found clear latitudinal differences as well as differences between shallower (< 200 m) waters above the shelf proper and the deeper waters of the trench. Linear correlations between salinity and certain trace nutrients in the surface waters indicated a fresh water source either from the Baltic Sea or the Norwegian rivers and fjords while correlations between turbidity and Fe and Mn concentrations close to the seafloor suggested sedimentary inputs.

How to cite: Adler, M. A., Humphreys, M., Middag, R., and Brandon, M.: Processes driving trace metal, nutrient, and dissolved inorganic carbon distributions in the Norwegian Trench, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10231, https://doi.org/10.5194/egusphere-egu25-10231, 2025.

In aquatic ecosystems, plankton communities generally form the base of trophic webs, and environmental changes are often reflected, or even amplified, in these communities. In the context of anthropogenic climate change, plankton communities could be drastically impacted by rising temperatures and the increase of extreme climate events. The Belgian Part of the North Sea (BPNS) is already heavily influenced by human activity, and extreme climate events could greatly alter the dynamics of the ecosystem. Recent years have seen an uptick in marine heatwaves in the BPNS, which have been associated with unusually prominent Bellerochea sp. blooms and temporary copepod die-offs. As the frequency of these marine heatwaves is projected to increase, it is necessary to gain an understanding of how phytoplankton and zooplankton communities may respond not only to stable temperature change, but also to rapid change. This research therefore aimed first to characterize BPNS marine heatwaves, and second to analyze the corresponding plankton community dynamics. Initially, 30 years of satellite data were used from the National Oceanic and Atmospheric Administration Optimum Interpolation Sea Surface Temperature dataset (NOAA OI SST V2 High Resolution Dataset). Temperature data was used to establish a 90^th percentile threshold for marine heatwave detection. Marine heatwaves were then characterized based on intensity relative to the 90^th percentile threshold, cumulative intensity (deg. C x days), duration, peak temperature reached, and timing of peak temperature. These results were compared with those from underway temperature measurements at ~3 m depth as well as with CTD temperature measurements, all collected on the RV Simon Stevin. Additionally, we defined and analyzed temperature regions based on both geographical and biological zones. For plankton data, samples were collected monthly (nine coastal stations) and seasonally (with eight additional offshore stations) on board the RV Simon Stevin, with zooplankton data from 2014 onwards and phytoplankton data from 2017 onwards. ZooScan and FlowCam automated imaging sensors were used to quantify zooplankton and phytoplankton, respectively. Plankton dynamics were then analyzed in terms of bloom timings and abundances (dominant groups, diversity indices). Overall temperature data from the BPNS showed similar marine heatwave trends using NOAA satellite data and RV Simon Stevin underway data, and highest temperatures were reached in the summers of 2018 and 2022. At several nearshore stations, the key plankton group Appendicularia had a delayed bloom during the 2022 marine heatwave compared to the 2018 marine heatwave. Ultimately, this parallel characterization of marine heatwaves and plankton dynamics offers insight into the health of the BPNS ecosystem. Furthermore, it offers potential for predicting the responses of phytoplankton and zooplankton to future marine heatwave events.

How to cite: Eske, A., Semmouri, I., Mortelmans, J., Muñiz, C., Hablützel, P., and Janssen, C.: Characterization of Belgian Marine Heatwaves and Their Impacts on Plankton Dynamics, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15734, https://doi.org/10.5194/egusphere-egu25-15734, 2025.

The shallow North Sea is characterized by complex hydrography and environmental variability, which affects the air-sea interactions and the skin layer (< 1mm). The skin layer plays a crucial role in air-sea interactions, and understanding its physical dynamics is essential for advancing knowledge in this field. Ocean fronts are predominantly narrow horizontal gradients of oceanic properties separating water masses and can be hotspots for marine biodiversity. Satellites have been used to observe large scale fronts however frontal features exist even on the sub-mesoscale. By leveraging seasonal data from an autonomous surface vehicle, we investigate the spatial and temporal variability of the skin layer at these small scales, with a focus on the role of oceanic fronts in shaping surface-layer dynamics. We use high-resolution measurements (0.1 Hz) of temperature, salinity, GPS data and weather-related variables at discrete depths in the air and water. These measurements are from our self-designed autonomous surface vehicle known as HALOBATES, which is equipped with multiple sensors and rotating glass discs to sample and measure the skin layer. Primarily, we applied a gradient-based algorithm to identify oceanic fronts, characterized by sharp horizontal gradients in temperature and salinity within the skin layer and bulk water (1-meter depth). To ensure that frontal features are accurately isolated, the effect of diurnal warming or cooling were taken into account. We isolated fronts solely on temperature or salinity, and by both parameters to understand the nature and origin of the fronts. Secondarily, we provide results of front detection from a Machine Learning perspective, showing results of deep learning models like Convolutional Neural Networks and an unsupervised clustering algorithm. We also present the results of the underlying bulk water (1-meter depth) to understand the pre-eminence of the observed front. We also investigate possible forcing factors due to sudden changes in the wind speed and direction as well as heat flux components such as solar radiation, precipitation and evaporation. By using continuous data from an autonomous platform over an extended period, our findings will highlight the dynamics of sub-mesoscale fronts in the North Sea and their role in shaping the physical characteristics of the skin layer. The insights from this study are relevant for ongoing research on topics such as heat and gas exchange at the ocean-atmosphere boundary layer which is a good indicator of the climate dynamics of the North Sea.

How to cite: Ayim, S. M., Jaeger, L., Gassen, L., and Wurl, O.: Detecting and Investigating Frontal Dynamics in the Skin Layer of the North Sea Using Autonomous Surface Vehicle Observations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3158, https://doi.org/10.5194/egusphere-egu25-3158, 2025.

How to cite: Musimwa, R., Standaert, W., Stevens, M., Jesus Fernández Bejarano, S., Muñiz, C., Debusschere, E., Pint, S., and Everaert, G.: Navigating Climate and Policy Shifts: Habitat Suitability Modelling for North Sea Pelagic Fisheries in a Changing World , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21325, https://doi.org/10.5194/egusphere-egu25-21325, 2025.

Marine renewable energies are part of the current energy transition strategy in Europe. Offshore wind farms (OWFs) in the North Sea currently supply around 25.8 GW of power and are aimed to reach at least 117 GW by 2030. Yet, on its own, wind energy supply remains partially unreliable for a consistent energy generation. Offshore photovoltaic (PV) installations are increasingly considered a suitable technology to complement the intermittent energy supply of OWF.  In the North Sea, installation of offshore photovoltaics within OWFs offers two significant advantages: (1) space optimization in an already busy North Sea, and (2) the possibility of utilizing and integrating an existing power network.

However, the installation of such systems comes with significant environmental challenges. In particular, solar technologies currently involve more submerged structures per produced energy unit. These floating structures induce hydrographic changes, particularly in terms of current velocity slowdown and turbulence production. Also, the floaters act as artificial hard substrates that are quickly colonized by organisms, potentially altering the biogeochemical dynamics of the water column and, ultimately, affecting the sediments.

This study provides a first assessment of the impact of PV structures on key hydrodynamic variables (e.g. current velocity fields, bottom shear stress, turbulence production), both in the near-field and far-field around an OWF using the 3D hydrodynamic model COHERENS (https://doi.org/10.5281/zenodo.11654795). A 3D computational grid around the Mermaid OWF in the Belgian part of the North Sea was implemented, with a grid resolution of 50m x 50m. We first present the impact of floating solar panels on the surrounding circulation and turbulence field,  assessed using a sub-grid scale parameterization. Results from different scenarios will be presented and compared.

Second, we present a first estimate of the enrichment of organic carbon flux to the sediments due to the presence of colonizing organisms (mainly Mytilus edulis) on the submerged parts of PV structures. Our aim is to assess the areas of the seabed impacted by the deposition of faecal pellets due to the installation of PV structures within the OWF, considering the hydrodynamic perturbations presented above. This part uses a 3D Lagrangian particle tracking model (OSERIT; Dulière et al., 2012), faecal pellet characteristics gathered from laboratory experiments (e.g. sinking velocity, production rate and carbon content) and literature data on colonization of wind turbine foundations (Mavraki et al., 2020). In this model, each numerical particle represents a certain quantity of faecal pellets and, consequently, organic carbon.

Maps of faecal pellet deposition patterns will be presented for several scenarios of PV structures distribution in the Mermaid OWF. Our simulations show that the footprint affected by faecal pellet depositions could reach up to 18 times the surface area of the OWF and that the amount of carbon deposited could reach up to 1454 gC.km^-² per day (worst-case scenario). These maps illustrate the causal relationship between PV farm design and the surface area of sediment affected by the faecal pellet deposition and thus exposed to organic carbon enrichment.

How to cite: Denis, P., Capet, A., Vanaverbeke, J., Ong, E. Z., Kerkhove, T., and Legrand, S.: Modelling the impacts of floating solar structures in a Belgian offshore wind farm, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16328, https://doi.org/10.5194/egusphere-egu25-16328, 2025.

Due to its geographical location, the North Sea is one of the busiest seas worldwide, undergoing increasing pressure due to continuous developments of offshore human activities. These activities affect the North Sea ecosystem, for example by introducing new habitats/species or infrastructure into previously unobstructed environments. At the same time, climate change has already been affecting the North Sea ecosystem, leading to observed changes in species distribution. These changes may also affect physical processes such as stratification. Stratification is one of the main factors influencing primary production, which constitutes the foundation of the marine food web. To be able to mitigate these effects, it is crucial to understand the bottom-up, cumulative impacts of anthropogenic climate change and offshore activities on marine ecosystems. With this goal, we adapted and nested a 3D process-based hydrodynamics and water quality model of the North Sea (3D DCSM-FM) within a global Earth System Model (CMCC-ESM2). We simulated two contrasting future climate change scenarios: one representing the situation of a society focused on global sustainability, with low carbon emissions (SSP1-RCP2.6), and one of a society focused on global markets, with abundant exploitation of fossil-fuels and high carbon emissions (SSP5-RCP8.5). We investigated how the two different scenarios impact important abiotic and water quality variables, up to the end of the century.

As expected, our model results show clear surface water temperature increases for both scenarios, above 3°C by 2100. The Northern part of the North Sea is mainly driven by exchange with the Atlantic ocean. In the Northern and Eastern North Sea and in the Dogger Bank, our model simulates an increase in temperature stratification, leading to decreases in near-surface dissolved inorganic nutrient concentrations, chlorophyll-a and growing-season primary production (~-20-30% by 2100 on average in the Northern North Sea). The Southern part of the North Sea, especially along the coast, is driven by an along-coast current from the English channel and large, nutrient-rich freshwater inputs. The Southern North Sea shows a more spatially-variable response to the simulated scenarios in terms of nutrient concentrations, chlorophyll-a and primary production, with areas of increase and areas of decrease. Overall, the Southern North Sea shows a small increase in growing-season primary production for scenario SSP1-RCP2.6 by 2100 (+6%), while it shows a decrease for SSP5-RCP8.5 (-14%).

Our model offers the resolution to understand the effects of local pressures within a globally changing climate. Such tools are crucial to support the management of future offshore activities, ensure their long-term effectiveness and minimize their impacts on the ecosystem.

How to cite: Vilmin, L., Schneider, L., Heye, S., Zijl, F., Zijlker, T., Butenschön, M., Kristiansen, T., and van Duren, L.: Modelling bottom-up effects of climate change on primary production in the North Sea, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16984, https://doi.org/10.5194/egusphere-egu25-16984, 2025.