The subtidal seabed sedimentary habitats in the UK’s English waters contain between 80 and 100 Mt of organic carbon (OC) and so have a significant climate change mitigation potential (as Blue Carbon). Although it is known that OC input (amount and rate) and composition (source and reactivity), sediment type and environmental setting (e.g., temperature, oxygen) control both amount of OC stock and OC burial rates, the regional understanding of the links between these controls, their spatial variability remains poorly understood.
Much of the UK’s shelf seabed organic carbon stock is under pressure from physical disturbances by various human activities, significantly trawling as well as climate forcing processes and temperature increases. These pressures promote changes in OC status and climate regulation service provision (storage and burial), although the net direction of change is highly uncertain. Management of human activities, including protection or restoration of seabed areas containing OC, may therefore provide a significant Nature-based Solution (NbS) to climate change itself.
We present an exemplar case study in the North Sea which aimed to identify and explore regions of OC climate regulation service provision and draw together evidence strands to support management decisions and measures to allow optimisation of sedimentary OC (‘Blue Carbon’) to mitigate climate change.
Three key aspects and related questions are addressed:
- Organic carbon storage and burial in space across the shelf: what drives variability, and what is the role of OC composition, source and reactivity?
- Present pressures on seabed carbon: Where is OC storage under pressure? By how much? What is the potential impact?
- Policy and management: How can this evidence base inform management interventions and measures, including protection and recovery measures which promote the potential of the seabed climate change regulation service (blue carbon)?
Within each element insights into the developing underpinning datasets, future approaches needed, and remaining knowledge gaps and priorities will be presented.
How to cite: Parker, R., Aldridge, J., Brown, L., Clare, D., Dal Molin, F., Garcia, C., Hughes, D., Hynes, C., Mason, C., Martinez, R., McEwan, R., Powell, C., Proctor, W., and Graves, C.: Assessing seabed carbon storage and sequestration (Blue Carbon): response to pressures and management interventions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9573, https://doi.org/10.5194/egusphere-egu25-9573, 2025.
The North and Celtic Seas are influenced by both natural and anthropogenic inputs of organic carbon. Allochthonous sources include terrestrial carbon, delivered via riverine and atmospheric pathways, while autochthonous sources include in-situ production of marine phytoplankton and other primary producers. Ultimately the sediment acts as sink and storage for deposited organic carbon. However, gaps remain around our knowledge of the provenance of this carbon, which is important for accurate carbon budgets and the move towards Net Zero, and for understanding how carbon may behave in the environment. Carbon composition differs with source, whether marine, terrestrial or anthropogenic, and this can influence the reactivity of that carbon. Labile, fresh carbon will be more easily degraded whilst refractory carbon will be more stable and long lasting. We used a molecular marker approach employing n-alkanes as carbon tracers to help unravel the complex sources of sedimentary organic carbon. Sediment cores were taken between 2021 - 2024 over numerous surveys encompassing different regions of the North and Celtic Seas, including nearshore, coastal and offshore locations, with differing sediment types ranging from sandy through to muddy. We analysed a suite of organic compounds, including n-alkanes and other biomarkers, polycyclic aromatic hydrocarbons (PAHs), and black carbon, to probe natural and anthropogenic carbon sources. Our results showed that organic carbon provenance varied in both space and time (depth). Nearshore and coastal sites generally had higher levels of terrestrial rather than marine carbon, however appreciable terrestrial inputs were also observed at various offshore locations, including at depth. Elsewhere offshore sites were dominated by marine and/or mixed sources, whilst anthropogenic inputs were observed at nearshore sites, and at coastal sites with finer sediment, but also offshore especially in the vicinity human oil and gas activity. Our study provides insights into different carbon sources, areas of accumulation and storage, as well as post depositional changes. This work moves us towards a classification of marine-terrestrial-anthropogenic sites in the North and Celtic Seas, which informs and supports marine management strategies including the climate mitigation potential of the English seabed.
How to cite: Hynes, C., Powell, C., Dal Molin, F., Mason, C., and Parker, R.: How ‘blue’ is your carbon? Sources of sedimentary shelf carbon in the North and Celtic Seas using n-alkane lipid tracers and geochemical tools, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21148, https://doi.org/10.5194/egusphere-egu25-21148, 2025.
Continental shelf sediments contain some of the largest stocks of organic carbon (OC) on Earth and critically influence the global carbon cycle. Quantifying how much OC continental shelves store and determining its residence time is key to assess how the ocean carbon cycle will be altered by climate change and anthropogenic perturbations of the seabed. Spatial variations in terrestrial carbon stocks are well studied and mapped at high resolution, but our knowledge of the distribution of marine OC in different seafloor settings is still very limited, particularly in dynamic and spatially variable shelf environments. This lack of knowledge reduces our ability to understand and predict how much and for how long the ocean sequesters CO2.
In this study, we use high-resolution multibeam echosounder (MBES) data from the Eastern Shore Islands offshore Nova Scotia (Canada), combined with OC measurements from discrete samples, to assess the distribution of OC content in seafloor sediments. We derive four different spatial estimates of organic carbon stock: (i) OC density estimates scaled to the entire study region assuming a homogenous seafloor, (ii) interpolation of OC density estimates using empirical Bayesian kriging, (iii) OC density estimates scaled to areas of soft substrate estimated using a high-resolution classified substrate map, and (iv) empirical Bayesian regression kriging of OC density within areas of estimated soft sediment only. These four distinct spatial models yielded dramatically different estimates of standing stock of OC in our study area of 223 km2: 80,901, 58,406, 16,437 and 6,475 t of OC, respectively. Our study demonstrates that high-resolution mapping is critically important for improved estimates of OC stocks on continental shelves and for the identification of carbon hotspots that need to be considered in seabed management and climate mitigation strategies. These results will be discussed in the larger context of OC storage on the Atlantic Canadian Shelf.
How to cite: Kienast, M., Brenan, C., Maselli, V., Algar, C., Misiuk, B., and Brown, C.: Not all continental shelf seafloor is the same: detailed sediment characterization dramatically reduces estimates of organic carbon standing stock, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13070, https://doi.org/10.5194/egusphere-egu25-13070, 2025.
Coastal sediments act as a huge reservoir of sedimentary organic carbon (SOC). Yet, the processes governing the long-term burial and preservation of this type of coastal organic carbon are complex and depend on the interplay between several factors, such as sedimentation rates, regional climatic conditions, post-depositional biological activity, and degradation. All these factors can significantly vary spatio-temporally within local micro-environmental conditions. The present study aims to understand the preservation of organic matter from two distinct climate zones of tropical India, the humid eastern lower Gangetic floodplain containing mangroves (average annual precipitation ranging ~1200–1600 mm) and the dry western Kachchh basin, which is essentially a salt flat (average annual precipitation ranging ~ 200–400 mm). At both places, sedimentation rates, total organic carbon (TOC), separated labile and refractory fractions of SOC (through chemical oxidation method), and their stable carbon isotopic (δ13C) compositions have been compared. The available data, along with the results from the present study, show that the sedimentation rate patterns through the Holocene are comparable at both study sites, showing higher rates (~0.4–0.6 cm/yr) up till Mid-Holocene which decreases to <0.05 cm/yr during the Late Holocene. The TOC ranges from 0.1 to 1.0% in Kachchh (average ~0.4%) and 0.2 to 2.1% in the lower Ganges floodplain (average ~0.6%). However, when the bulk and refractory fractions of SOC are compared, they reveal distinct patterns. The Gangetic floodplain exhibits a difference in the bulk and refractory δ13C values as it contains more labile and partially decomposed organic matter. In contrast, the Kachchh sediment shows consistent δ13C values in both the bulk and refractory fractions, indicating negligible presence of labile or decomposed organic matter. These findings suggest that in arid climates, the SOC is predominantly deposited in oxidized conditions, thus comprising mainly the refractory fraction of organic matter. At the same time, in humid environments, the SOC includes a mixture of labile and partially decomposed organic matter. This comparative study provides an example of how climatic variability plays a critical role in shaping SOC characteristics in otherwise similar depositional settings and emphasizes the importance of studying both labile and refractory fractions of SOC for reconstructing past climates.
How to cite: Ram, F.: Nature of organic matter preservation in coastal sediments: Insights from humid to arid climatic regimes of India., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5189, https://doi.org/10.5194/egusphere-egu25-5189, 2025.
Bioturbation by benthic and sediment-dwelling species significantly influences organic carbon preservation, accounting for 4% of the variation in sediment mixing depth. Yet our understanding of how different species, communities or functional bioturbation roles influence water-sediment carbon fluxes or contribute to long-term carbon burial is poorly understood. This is a key knowledge gap for assessing the impacts that seabed disturbance, such as bottom trawling, may have on carbon processes or for determining the potential carbon benefits of better seabed protection.
As part of the Convex Seascape Survey, we have been investigating the effect of faunally mediated sediment mixing and burrow ventilation on water-sediment carbon processes and associated nutrient fluxes. In a series of mesocosm experiments, we assembled 17 macrofaunal invertebrate species in monoculture and in a three-species mixture. In all experiments, individuals were collected using a van veen grab from the Firth of Clyde or Loch Etive, Scotland, and were placed in sediment-filled mesocosm aquaria (6 x 6 x 23 cm) with overlying seawater. Fluorescent sediment particles were added after 24 hours to quantify sediment reworking, and experiments were maintained for up to 10 days. Using Carbon-13 labelled algae, we quantified the movement of particulate organic carbon into the sediment. Overlying water parameters (e.g., pH, DIC, oxygen consumption) and sediment mixing and burrow ventilation activities were measured to assess inter- and intra-species contributions to nutrient cycling and carbon flux.
Our data reveal that different groups of sediment mixers (predominantly deep burrowers versus surficial modifiers) perform distinct functional roles in the cycling of nutrients and carbon. We find, for example, that deep burrowers and active bioturbators promote higher levels of nitrite (NO₂⁻) and nitrate (NO₃⁻) release into the overlying water. This suggests that their burrow formation and ventilation enhance microbial nitrification, converting ammonium into nitrite and then nitrate. In contrast, surficial modifiers were associated with elevated levels of phosphorus and ammonium in the overlying water. This pattern likely reflects the dominance of ammonification, where organic matter decomposition releases ammonium and remineralisation releases phosphorous in surface layers with moderate oxygenation. Dissolved inorganic carbon release and concomitant alkalinity changes produced by individuals in our studies are species-specific and can be quite pronounced in relation to bioturbation function. The amount of particulate organic carbon redistributed by bioturbation is also species-specific and our labelled algae both help understand this redistribution of carbon in the surface sediments beyond more traditional methods of measuring bioturbation but also call into scrutiny categorical methods of grouping bioturbating organisms.
These findings highlight that functional traits of bioturbating animals matter more than taxonomic species identity in regulating carbon fluxes and burial at the water-sediment interface. They reveal a divergence of roles across sediment depths, emphasising the potential for functional loss and ecosystem degradation from depth-specific disturbances like bottom trawling.
How to cite: Porter, A., Godbold, J., Kitidis, V., Solan, M., and Lewis, C.: From Sediment to Sequestration: Linking Bioturbation to Carbon Cycling, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20490, https://doi.org/10.5194/egusphere-egu25-20490, 2025.
Physical disturbance of the seafloor related to bottom trawling has led to widespread concern within the scientific community, as it may cause long-lasting impacts to benthic ecosystems, sediment composition, and biogeochemical cycling. Although trawling-induced effects on benthic habitats have been widely studied, the effects on sediment carbon mineralization and carbon stocks on the seabed remain unclear. Most of the catch obtained by bottom trawling is harvested from productive continental shelves, which play an important role in carbon sequestration and burial. Parts of the Baltic Sea have been trawled between one to ten times annually and thus provide a prime locality to study trawling related effects on benthic ecosystems and on the geochemical system. This study investigates the effects of trawling on carbon mineralization within the Bornholm Basin of the southern Baltic Sea, which has been consistently trawled until 2019. This was achieved through on-site sampling and analysis of porewater geochemistry, solid-phase sediment profiles, benthic fluxes and macrofaunal abundances sampled in the summer of 2023.
Comparisons between 4 study sites, paired into high-and low-trawled pairs based on fishing intensity data, revealed greater differences in measured physical and chemical properties than those between high- and low-trawled locality pairs, suggesting that environmental variability significantly influences carbon mineralization. However, high-trawled areas generally exhibited higher concentrations of TOC (total organic carbon) in their sediments as well as higher DIC (dissolved inorganic carbon) and nutrients in their porewaters. The higher porewater concentrations are likely a result of reduced advective transport and macrofaunal-related mixing, as a consequence of lower bioturbation and bioirrigation, whereby mineralization end-products (NH4+, PO43- and DIC) accumulate in porewaters due to slow upward diffusive transport to the sediment surface in comparison to low-trawled localities. Chlorophyll concentrations at the sediment surface from recently settled organic material from the spring phytoplankton bloom were higher at high-trawled localities and likely associated with the decreased macrofauna biomass and grazing activity. It is concluded that biogeochemical ecosystem functions in once-trawled sediment biotopes are only partially reconstituted after 4 years, with lasting differences in macrofaunal benthic community structure and bioturbation potential.
How to cite: Golda, C., Brüchert, V., and Bradshaw, C.: Impact of benthic trawling on carbon mineralization in continental shelf sediments of the Bornholm Basin, southern Baltic Sea, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4432, https://doi.org/10.5194/egusphere-egu25-4432, 2025.
Recent reviews have highlighted that the effect of bottom trawling on sediment carbon content and biogeochemistry varies depending on environmental conditions, the type of sediment (e.g. mud vs sand) and the chemical nature of the organic carbon. However, most data are from analyses of total carbon or organic matter and from bulk surface sediments (top 2 cm) rather than deeper sediment profiles, limiting our ability to interpret these results in terms of the biogeochemical processes involved in carbon degradation and burial.
The Kattegat is one of the most heavily trawled seas in the world with some parts being swept by fishing gear up to 15 times per year. However, fishing effort is patchy and there is also a marine protected area where bottom trawling is forbidden; the resulting large range in trawling disturbance makes the Kattegat an ideal site for studying potential impacts on the seafloor.
We analysed sediments across the trawling gradient, in 1cm-layers downcore, and determined the relative effect of trawling intensity and environmental variables (e.g. bottom water oxygen, sediment grain size) and biological variables (e.g. bioturbation) on sediment carbon content, reactivity and degradation rates. In general, environmental factors and physical properties of the sediment appeared to be the strongest explanatory variables, with trawling intensity being less important. The best explanatory variables also varied depending on the sediment depth analysed, potentially due to the relative importance of seasonal inputs of fresh organic carbon at the sediment surface, mixing depth and type of bioturbation and penetration depth of the trawls.
How to cite: Bradshaw, C., Blomqvist, M., Sköld, M., Ennas, C., Seidel, L., Maciute, A., and Pusceddu, A.: Relative effects of bottom trawling and environmental factors on sedimentary carbon properties and degradation in the heavily trawled Kattegat, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10289, https://doi.org/10.5194/egusphere-egu25-10289, 2025.
Continental margin sediments are a major hotspot for organic carbon burial and play a vital role in the carbon cycle. Disturbance of sedimentary organic carbon by human activities such as mobile bottom fishing might lead to (i) reductions of the organic carbon stocks, (ii) impacts on carbon cycling, primary productivity and biodiversity and (iii) ocean acidification and atmospheric CO2 emissions. Spatially explicit studies that have been conducted to inform marine management have so far looked at organic carbon stocks that have already been affected by mobile bottom fishing. Here, we focus instead on areas on the Norwegian continental margin that have not been fished previously, based on fishing data covering the years 2009 – 2020. We estimate that the surface sediment layer (0 – 2 cm) in unfished areas covering 765,600 km2 contains 139.2 Tg of organic carbon. Based on data from a meta-analysis of demersal fishing impacts on organic carbon density, we estimate that 16.4 Tg (1.8 – 29.6 Tg) of organic carbon might be vulnerable to mobile bottom fishing. Of this, approximately one third is currently located in existing area-based protection measures. Additional protection could be guided by hotspots of vulnerable organic carbon, which are found in the Barents Sea. We argue that the protection of vulnerable organic carbon that is at high risk of being lost in areas becoming accessible to fishing due to sea ice retreat in the northern Barents Sea should be prioritised over easing pressure on already impacted organic carbon stocks.
How to cite: Diesing, M., Sciberras, M., Thorsnes, T., Bjarnadóttir, L. R., and Moe, Ø. G.: Mapping vulnerable organic carbon in Norway’s continental margin sediments, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3024, https://doi.org/10.5194/egusphere-egu25-3024, 2025.
Coastal seas play a critical role in removing carbon from the atmosphere and sequestering it in marine sediments, partially offsetting anthropogenic greenhouse gas emissions. The North Sea, despite its shallow depth, intense tidal mixing, and increasing anthropogenic pressures, stores over a million tonnes of organic carbon (OC) annually in the deep Norwegian Trench, and exports OC to the Skagerrak Strait. However, the rapid pace of global climate change is disrupting biogeochemical cycles, including carbon dynamics in coastal seas.
In recent decades, the North Sea has become a hotspot for offshore wind farm (OWF) construction. Their hard substrates are colonized by filter feeders (e.g., blue mussels), which filter OC particles from the water column and biodeposit them onto the seabed, creating localized areas of carbon-enriched sediments near OWFs.
As part of the JPI Climate & Oceans project CE2COAST, which aims to evaluate pressures on coastal seas and their ecosystem services under a changing climate, we developed a high-resolution coupled hydrodynamic-wave-sediment-biogeochemical-diagenetic model. This model covers the North Sea, utilizing a 5x5 km resolution horizontal grid and a vertical grid comprising 30 water column layers and 26 sediment layers. It integrates pelagic and benthic biogeochemical processes, simulating sedimentary fluxes and solute diffusion at the sediment-water interface. OWFs are represented in the model as surface areas suitable for bivalve colonization, based on their location and turbine density. Changes to sediment properties that affect OC resuspension are incorporated to represent the retention of deposited OC by local ecosystems. The model has been calibrated and validated using available physical and biogeochemical data for both pelagic and sedimentary environments.
The model is used to assess the combined effects of climate change and OWFs on biogeochemical cycling, with a focus on carbon cycling and sequestration. Simulations were conducted for both current (1993–2023) and future climates (up to 2100) under the IPCC SSP370 “upper-middle” scenario. Scenarios for OWF construction were based on plans for 2035 and assumed constant until the end of the century. The model was forced by a regional atmospheric model (MAR), driven by outputs from the MPI climate model and at the lateral open boundaries by outputs from the NorESM2 Earth System model.
Key findings from comparisons between present conditions and projections include higher remineralization rates of organic carbon in both the water column and upper sediment layers, along with enhanced conditions for phytoplankton carbon fixation via photosynthesis. While increased primary production offsets higher remineralization rates in the water column, OWF construction along the European coast significantly alters traditional carbon transport pathways. Instead of being transported to the Skagerrak Strait and the Norwegian Trench, more organic carbon is retained in the shallow European shelf. This enhances the North Sea’s capacity to sequester OC in the medium term but raises concerns about its fate following the OWF decommissioning and the removal of hard substrates.
This study highlights the complex interplay of physical and biogeochemical processes in the North Sea and emphasizes the importance of coupled modeling approaches to predict future changes in carbon storage under a changing climate and increasing anthropogenic influence.
How to cite: Ivanov, E., Grailet, J.-F., and Grégoire, M.: Carbon Storage in North Sea Sediments: Impacts of Climate Change and Offshore Wind Farms Revealed by Coupled Modeling, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18790, https://doi.org/10.5194/egusphere-egu25-18790, 2025.
As global warming progresses, sedimentary carbon sinks are becoming increasingly important in climate change mitigation measures. Thus, there is a need for in-depth knowledge of both the dynamics and vulnerabilities of the sedimentary carbon sinks, as well as the legal and political options to protect and restore their natural carbon sequestration efficiency. Here, we report on the transdisciplinary research project APOC, which addressed the Anthropogenic impacts on the cycling of Particulate Organic Carbon in the North Sea. Important results of the project include the quantification of sedimentation rates in the accumulation areas of the German Bight and the Skagerrak, assessing the factors that enhance organic carbon burial/storage and the determination of the sources and reactivity of deposited carbon. As major anthropogenic disturbances, the effects of bottom trawling and wind farm construction on benthic carbon storage were investigated and assessed. Bottom trawling in particular was significantly decreasing the benthic carbon storage due to a multitude of coupled physical and ecological effects. However, at the environmental policy level, it became clear that sedimentary deposits are not sufficiently recognized and protected as valuable natural carbon sinks, although their storage capacity is believed to be much higher than that of blue carbon ecosystems at similar latitudes. While the project was staffed mainly with natural scientists, important expertise in environmental policies was provided by the marine conservation office of the BUND, one of the largest environmental NGOs in Germany. As a fully-fledged project partner, BUND made it possible to recognize the relevance of the various project focal points for the environmental policy arena throughout the entire project. In turn, the policy experts were able to distribute the latest scientific findings to the environmental policy committees. In effect, the transdisciplinary cooperation within the project not only produced valuable scientific results, but also numerous expert briefings on environmental policy at all levels, from local authorities to the EU Parliament, emphasizing the importance of protecting natural fine-grained sedimentary carbon sinks for climate change mitigation measures. Key to this outcome was the continuous exchange of scientific findings and practical environmental policy knowledge, which kept all participants focused on the societal relevant objectives that were originally pursued with the project funding. The results of the project APOC can contribute directly to the new EU Nature Restoration Law adopted in June 2024. To this end, measures to strengthen and protect ecosystems both on land and in national coastal waters are to be introduced on 20 % of land and marine areas across the EU, including restoration of at least 30 % of important habitat types in poor condition by 2030.
How to cite: Kasten, S., Holtappels, M., Müller, D., Wallmann, K., Porz, L., Daewel, U., Zhang, W., Kuhlmann, J., Taylor, B., and Zeibarth, N.: Assessing, protecting and restoring the natural carbon storage capacity of marine sediments – the need for enhanced transdisciplinary dialogue and cooperation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21441, https://doi.org/10.5194/egusphere-egu25-21441, 2025.
Continental margin sediments are key long-term sinks for atmospheric carbon dioxide (CO₂). Despite their global significance, the magnitude and spatial distribution of organic carbon (OC) burial in this environment remains poorly quantified mainly due to the exceptional heterogeneity of the coastal ocean. Yet, this knowledge is critical not only for closing the global carbon budget but also for guiding policy decisions. Here, we integrate the rapidly growing observational data set with spatial machine learning and inverse as well as forward reaction-transport modelling, capturing the spatial heterogeneity of global continental margins to deliver robust OC flux estimates.
We estimate a global continental margin OC burial flux of 441 Tg C yr⁻¹ through the base of the mixed layer, decreasing to 293 Tg C yr⁻¹ at the 1 kyr age horizon (<1–33 m sediment depth). Approximately 70% of this burial occurs in the northern hemisphere, and >50% is concentrated within the latitudinal band 10°S–30°N. Using the MARgins and CATchments Segmentation framework, tropical regions show the highest OC flux densities and total long-term burial flux globally (5.4 tC km-2 yr⁻¹ and 64 Tg C yr⁻¹). In addition, polar regions and marginal seas also reveal high total long-term burial fluxes (42 Tg C yr⁻1 and 35 Tg C yr⁻¹). In polar regions, high burial is driven by modest OC flux densities over vast areas, while marginal seas exhibit high flux densities but limited spatial extent. Each of the other MARCAT regions contributes less than 15% to global OC burial. We thus find the highest OC burial rates in the Exclusive Economic Zones (EEZs) of Indonesia (27 Tg C yr⁻¹) and Russia (20 Tg C yr⁻¹), followed by the EEZs of the Philipines, Antarctica, the United States, Japan, Papua New Guinea, Canada, New Zealand, Brazil, Yemen, and Mexico (each accounting for 2-5% of global OC burial). The EU EEZs collectively bury approximately as much OC as the Russian EEZ.
When combined with global radiocarbon data for organic carbon (OC), our global estimates reveal several hotspots of young, marine-derived OC burial that actively remove contemporary atmospheric CO₂. These regions include tropical margins such as the Sunda Shelf, the Caribbean coastal zones, the western coast of Mexico, and the South China Sea, as well as marginal seas. In contrast, other burial hotspots—such as tropical margins adjacent to large river deltas or the Arctic shelf—predominantly sequester older, pre-aged terrestrial OC and petrogenic OC. While OC burial in these areas has a limited direct impact on contemporary CO₂ levels, it plays a crucial role in the modern carbon cycle by preventing the release of this geological carbon through microbial degradation.
How to cite: Arndt, S., Diesing, M., Hülse, D., Paradis, S., and Smeaton, C.: Organic Carbon Burial in Global Continental Margin Sediments, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10839, https://doi.org/10.5194/egusphere-egu25-10839, 2025.
Quantifying the various pools of marine carbon is a fundamental initial step towards establishing the potential value of ocean carbon storage in climate change mitigation. While subtidal sediments hold less carbon per unit area than the coastal ‘traditional blue carbon habitats’ (mangrove, saltmarsh, seagrass), their large extent makes them an important component of the UK’s blue carbon inventory. Global and regional maps of seabed organic carbon have been published, but they do not provide a consensus view of northwest European Shelf subtidal sediment carbon storage. Improved seabed carbon maps, using predictive mapping approaches, require high confidence measurements of sediment organic carbon content with appropriate good spatial coverage as well and overall sampling of predictor ‘parameter space’. They also rely on availability and selection of appropriate high-resolution predictor variables. Our efforts to map seabed organic carbon have two, sometimes complimentary sometimes conflicting, objectives: (i) to generate the most accurate map possible, and (ii) to provide our process-focused understanding of how and why carbon content varies and which parameters control that variability in the context of seabed biogeochemical cycling.
We initially applied a Gradient Boosting Machine Learning method to generate a new predicted seabed carbon map for the northwest European Shelf using more than 2,000 observations of near-surface sediment (0-2 to 0-10 cm below seafloor) organic carbon content. We explored the importance of various methodological decisions on the importance of different predictors (e.g., mud content) and the predictive power and accuracy of the model. We discuss the differences and similarities of our data product and mapping approach with previous seabed carbon maps, highlighting the impact of knowledge gaps on potential use by policymakers.
How to cite: Graves, C., Barry, J., Mason, C., Garcia, C., Claire, D., Brown, L., and Parker, R.: Organic carbon storage in northwest European shelf subtidal sediments: towards a consensus map, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21089, https://doi.org/10.5194/egusphere-egu25-21089, 2025.
Sediment echo sounder data are routinely collected during research cruises with a geophysical or geological programme. This has resulted in the accumulation of huge amounts of sub-bottom data over the last decades (more than 30,000 survey lines of variable length in the Baltic Sea for the IOW alone), which are often not further interpreted. On the other hand, the value of these datasets for research and industry is increasing, as new regulations (e.g. related to the establishment of marine protected areas) and offshore infrastructure (e.g. wind farms) often prohibit the collection of new survey data. Current topics of interest in the Baltic Sea include the reconstruction of the Late Pleistocene to Holocene palaeogeography of the Baltic Sea and the identification of fluid flow and free methane in the subsurface. The latter can be used to assess the potential release of methane from carbon-rich sediments accumulating in the Baltic Sea basins by identifying the extent, depth and temporal variation of free gas surfaces (e.g. due to seasonal effects and changing wind conditions) in sediment echosounder data. Free gas in the subsurface and water column is readily identified in sediment echosounder and low-frequency multibeam echosounder data due to the increase in acoustic impedance between water-saturated sediments and gas. Information on methane release is needed to assess the suitability of natural sediments in the Baltic Sea basins as a long-term carbon sink. The methane reservoirs in the southern Baltic Sea are related to various sedimentary and tectonic situations. The frequent generation of methane due to organic carbon accumulation, which is released into the water column and potentially the atmosphere, would have an antagonistic effect on carbon burial. Due to the large amount of data available, a deep learning model (U-Net) is trained on sediment echo sounder data from the Arkona Basin in the southern Baltic Sea to identify free gas surfaces and their depth below the surface. The parameters of the free gas surfaces are related to the thickness of the Late Pleistocene and Holocene sedimentary units (Baltic Ice Lake, Ancylus Lake and Littorina Sea). Repeated lines of sediment echo sounder data allow assessment of changes in spatial extent and depth of free gas through time.
How to cite: Feldens, P. and Seidel, E.: Mapping free gas surfaces in Baltic Sea sediments, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10366, https://doi.org/10.5194/egusphere-egu25-10366, 2025.
Mapping and understanding the distribution of seabed sediments in shelf seas is crucial for sustainable coastal management, offshore activities, and assessing and conserving Blue Carbon stocks. Fine-grained sediments, such as mud, play a vital role in long-term organic carbon storage, and so it is essential to map and measure the extent of these carbon-rich deposits across shelf seas. However, despite their importance in the global carbon cycle, many regional shelf seas, such as the Patagonian Shelf, remain poorly studied. We present a novel high-resolution palaeotidal model for the Patagonian Shelf and consider how changing tidal dynamics since the Last Glacial Maximum have contributed to the development and preservation of mud deposits across the shelf. The simulations are compared with existing seabed substrate data to identify correlations between spatial and temporal changes in tidally driven parameters with the locations of muddy, often carbon-rich, deposits. We utilise observational data gathered through an extensive data mining exercise of the region, which includes grain size data and total organic carbon data. This work both enhances understanding of the region's palaeoenvironmental dynamics and highlights opportunities for future research, including synthetic mapping approaches and carbon stock analyses.
How to cite: Ward, S., Roseby, Z., Bradley, S., and Scourse, J.: Reconstructing past tidal dynamics and sediment transport on the Patagonian Shelf: implications for Blue Carbon, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5947, https://doi.org/10.5194/egusphere-egu25-5947, 2025.
Muddy sediments across continental shelves serve as a reserve for blue carbon and act as a natural carbon sink, supporting the buffering ability of shelf seas against the global rise in carbon dioxide and associated climate warming. However, these areas are also exposed to anthropogenic activities, mainly fishing and bottom trawling, increasing the probability of additional carbon loss by remineralisation. For the successful management of shelf sea carbon stocks, it is thus important to understand the amount of carbon stored, the reactivity of the organic carbon (labile or refractory), and the transfer efficiency of the organic carbon. The transfer efficiency reflects the balance between the sediment accumulation rate and the degradation rate before the material ultimately gets buried. In areas of fast sediment accumulation, carbon will be sequestered quickly, protecting it from natural and anthropogenic disturbances. In areas with very slow sedimentation rates, the carbon will be exposed to disturbances for a longer period. Thus, different areas of the continental shelf with different depositional settings require specific marine management strategies. This study aims to understand the quantity, quality, and transfer efficiency of carbon within the muddy depocenter of the Fladen Ground, North Sea, which provides a case study for investigating the vulnerability of carbon in a relict mud deposit with very low active sedimentation. We present new age-depth models, dry bulk density, and total organic carbon (TOC) measurements from multiple sediment cores and use them to calculate organic carbon accumulation rates for the Fladen Ground. This area has been exposed to historic and ongoing trawling, offering an opportunity to understand the fate of carbon in relict mud deposits under anthropogenic disturbances.
How to cite: Sengupta, T., Roseby, Z., Ward, S., Vosper, D., Blaauw, M., and Scourse, J. D.: Evolution and vulnerability of blue carbon stocks in a continental shelf mud depocenter: Fladen Ground, North Sea, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17437, https://doi.org/10.5194/egusphere-egu25-17437, 2025.
In recent years, the lead-210 (210Pb) geochronological tool has been extensively utilised to determine the burial rate of Blue Carbon in various marine environments. Numerous physical disturbances, originating from both anthropogenic and natural sources, can influence its applications. Additionally, many non-nuclear industries discharge waste containing elevated levels of naturally occurring radioactive materials, known as NORM industries, which presents another challenge if sediment cores are collected near such industrial activities.
The presence of anthropogenically derived 210Pb and radium-226 (226Ra) is often associated with high concentrations of heavy elements such as aluminium, barium, iron, manganese, strontium, zinc, and lead. These elements can significantly impact the direct measurement of 210Pb via gamma spectrometry and, subsequently, the application of various 210Pb-based dating techniques, making estimates of accumulation rates particularly challenging.
In this study, several sediment cores were collected in proximity to a decommissioned oil and gas platform located offshore in the UK North Sea (North West Hutton (NWH), 61.11N, 1.31E). Elemental and radioelemental signatures from legacy NORM discharges were observed in the sediment cores collected within 200 metres north and south of the former NWH platform and were thoroughly characterised using ICP-MS and gamma spectrometry, respectively. This enabled the forensic differentiation of the NORM-derived 226Ra fraction from the natural background and the generation of relative factors based on bulk elemental composition analysis to correct 210Pb results obtained from initial gamma spectrometric analysis. This corrective approach was validated by measuring polonium-210, a decay product of 210Pb, via alpha spectrometry, and allowed the estimation for the first time of carbon accumulation rates in sediment cores using different modelling approaches (CIC, CFCS, CRS, and RPLUM).
How to cite: Dal Molin, F., Woodward-Rowe, H., Davis, T., Jervis, J., Parker, R., and Hicks, N.: Corrected Pb-210 based estimations of accumulation rates in marine sediments contaminated by legacy NORM discharges, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11525, https://doi.org/10.5194/egusphere-egu25-11525, 2025.
In recent years, seagrass has been presented as a solution to sequester excess carbon emissions from the atmosphere, with studies reporting that seagrass meadows are responsible for burying as much as 10% of anthropogenic carbon per year (Fourqurean et al. 2012). However, this estimate has started to seem improbable as more recent research, specifically from North American study sites, are reporting carbon stock estimates much lower than the global average. Here, we present estimates of organic carbon (OC) stock in an eelgrass meadow on the Eastern Shore of Nova Scotia, Canada. To quantify sediment OC stock, we combined sediment geochemical analysis with geospatial mapping based on high-resolution optical aerial imagery collected by drone flights. Three sediment cores, plus a control, were extracted from the meadow in regions with differing levels of vegetative cover. The control core was used to establish a background signal for sediment OC, which we assume to be representative of nearshore unvegetated sediments in the region.
Despite the health and anecdotally reported longevity of this eelgrass meadow measuring 4.7 Ha in size, the carbon stock is estimated to be less than 10 Mg OC/Ha. This is significantly lower than the global average estimates of ~163.3-660 Mg/Ha (Fourqurean et al. 2012) but is comparable to other reports emerging from the North American east coast (eg. 3.7 Mg/Ha from coastal Virginia, US: Greiner et al. 2013). From the individual core slices, the maximum sediment OC did not exceed 2.5 weight % even in the densest, healthiest part of the meadow. There was also a notable correlation between presence of coarse biomass and higher sediment OC in the bulk sample, suggesting that the carbon is mostly associated with living biomass rather than being buried and stored in sediments. Further, radiocarbon ages of the bulk OC of up to 1140 years in the topmost sediment layer imply a significant admixture of pre-aged, likely terrestrial, OC to the bulk OC, rendering the stock estimates absolute maximum estimates. Overall, this study adds to the growing body of evidence that suggests that global estimates of OC storage in eelgrass beds need to be carefully reevaluated.
How to cite: Taniguchi, E., Mui, A., Boerder, K., Kienast, M., and Brown, C.: Combining sediment analysis with geospatial mapping to quantify carbon sequestration by an eelgrass bed on the Nova Scotian coast, eastern Canada. , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12515, https://doi.org/10.5194/egusphere-egu25-12515, 2025.
The management of coastal blue carbon ecosystems can contribute to mitigate anthropogenic greenhouse gas emissions. However, limited information on soil organic carbon (OC) decay rates in tidal marsh, mangrove and seagrass soils hinders their inclusion in climate strategies and carbon-crediting schemes. Here, we analyzed downcore OC trends in 3,733 soil cores from blue carbon ecosystems worldwide. A decrease in OC content with soil depth was measured in 63% of the cores, whereas stable and increasing trends were observed in 23% and 14% of the cores, respectively. Based on 75 profiles where OC decay could be modelled, the OC decay rate in blue carbon ecosystems was 0.024±0.002 yr-1 over the last 100 years and 0.007±0.0007 yr-1 over the last 1,000 years. This results in the stabilization of 9% and 0.1% of the soil OC inputs 100 and 1,000 yr after burial, respectively, showcasing the long residence time of OC in the sinks associated to blue carbon ecosystems. The models provided can inform baseline scenarios towards the implementation of carbon-crediting schemes.
How to cite: Piñeiro-Juncal, N., Mateo, M. Á., Leiva-Dueñas, C., Serrano, E., Inostroza, K., Soler, M., Apostolaki, E., Lavery, P., Duarte, C., Lafratta, A., and Serrano, O.: Soil organic carbon preservation and decay trends in tidal marsh, mangrove and seagrass blue carbon ecosystems, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15835, https://doi.org/10.5194/egusphere-egu25-15835, 2025.
Bottom trawling is a widespread fishing practice that has consistently been established to result in harmful, enduring effects including physical modification of the seafloor, and impacts on biogeochemical cycling as well as benthic ecosystems. The mechanisms of the equipment used, such as trawl doors, penetrate the seafloor and disturb the sediment structure, resuspending particulate matter and altering the seafloor's organic matter composition and morphology.
Previous studies have assessed the impacts of trawling on carbon storage in marine sediments, utilising sediment samples obtained from the seafloor and the water column to analyse the volume of sediment disturbed physically and geochemically. Additionally, Vessel Monitoring System (VMS) data has been employed to track fishing vessels and determine fishing intensity. These datasets are then widely used to determine the sedimentological and geochemical response to the trawl activity to demonstrate the potential global implications for disturbances in Blue Carbon environments regarding carbon remineralisation. However, post-trawl sampling intervals are irregular, differing in frequency and sampling methodology across studies.
The Celtic Sea is an area of significant trawling activity, with a region known as “The Smalls”, a particular area of focus as a Nephrops fishing ground. The area comprises a predominantly muddy substrate and is intensely trawled using Otter trawl gear. A field experiment was conducted at two sites in the Celtic Sea in 2024 investigating the sediment and organic matter recovery following a trawl event. To do so, a benthic lander was deployed to measure seafloor community oxygen consumption rates. Sediment cores (30 cm) were recovered to calculate and qualify organic carbon stocks in addition to particle size analysis. Similarly, water samples were gathered near the seafloor to measure suspended sediment concentrations. Geophysical data was also gathered to measure seafloor sediment volumetric changes, persistence of trawl scars and sediment plume dynamics. The two sites examined in this study differed in their substrate type, with one site comprising muddy sediment and another slightly coarser silty sediment. A coordinated effort with the Irish Groundfish Survey (IGFS) allowed researchers to survey the two sites 12-24 hours in advance of a trawl occurring, establishing a baseline of environmental conditions. A geophysical survey was conducted in unison with the IGFS during trawling events and the area was then resurveyed over a time series of 1 hour to a week post trawl. Establishing pre-, during and post-trawl conditions at the two trawl sites and offering a thorough understanding of how the sedimentary carbon properties change following anthropogenic disturbance.
Results indicate that oxygen consumption increased three times the original pre-trawled levels following a trawl event, with implications for carbon release. The use of ramped pyrolysis oxidation on core samples will elucidate changes in sedimentary organic carbon quality through carbon transformation/remineralisation. Different substrates at the two sites will allow for the analysis of differing sediment plume dynamics, with the finer substrate remaining in suspension for longer, potentially increasing transformation in the water column. The results of this study have implications for marine management in the area in the context of anthropogenic sediment disturbance.
How to cite: Walsh, P., Grey, A., Ní Mhaoldomhnaigh, C., Hunter, W., Kelleher, B., Stokes, D., and Coughlan, M.: Assessing marine sedimentary carbon disturbance and seabed recovery in response to benthic trawling: a case study in the Celtic Sea, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17000, https://doi.org/10.5194/egusphere-egu25-17000, 2025.
Continental shelf sediments are vast areas, some regions of which accumulate and store organic carbon. However, these regions are increasingly impacted by anthropogenic pressures, particularly from infrastructure related to energy extraction. While determining the standing stock of carbon within sediment provides a useful snapshot for current carbon budgets, directly measuring the accumulation potential allows for assessments of how inputs which drive carbon stocks will vary temporally and defines the climate regulation service (aka ‘blue carbon’) in space. However, estimating carbon accumulation potential of sediments can be confounded by anthropogenic activity, particularly around oil and gas extraction activities.
This study describes carbon stocks, sediment type and carbon accumulation rates (CARs) in sediment surrounding the North West Hutton decommissioned platform in the northern North Sea. By accounting for heavy metals derived from ICP-MS to create correction factors, previous estimates of CARs from gamma spectrometry have been corrected and CARs close to North West Hutton, which were previously undetermined, have been calculated. Results show that CARs determined by gamma spectrometry alone are consistently lower than those corrected by heavy metal attenuation factors and also using polonium-210 measurements from alpha spectrometry analysis. This work indicated that CARs could be underestimated in regions directly impacted by heavy metals associated with the extraction activity.
This novel method provides an opportunity to determine CARs in other marine areas impacted by similar chemical pollution pressures. Many coastal regions across Europe are directly affected by legacy or operational industrial discharges of waste containing enhanced levels of heavy metals and natural radioactivity, also known as NORM, in particular from mineral mining, extraction and processing activities. This work highlights the potential underestimation in the offshore environment, but if this approach is applied to coastal sites where accumulation rates are generally considerably higher, and impacted by industry, this could have widespread implications for service assessments and blue carbon accounting.
How to cite: Woodward-Rowe, H., Dal Molin, F., Jervis, J., Parker, R., Davis, T., and Hicks, N.: Determination of Blue Carbon accumulation rates in sediments impacted by legacy oil and gas extraction activities , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10160, https://doi.org/10.5194/egusphere-egu25-10160, 2025.
Continental shelf mud deposits off large rivers are substantial repositories for organic carbon; however, many of these rivers and the deltas they build have been extensively modified to support the development of growing coastal populations. While such modification is dramatic for most large Asian rivers (e.g., the Chang Jiang, Huang He, and Ganges-Brahmaputra), the Ayeyarwady-Thanlwin rivers remain an exception because of the absence of dams on the mainstems. Despite this, increased deforestation and associated land use change over the last 50 years has begun to alter fluvial sediment loads for this system, likely impacting the flux of sediment-bound terrestrial organic carbon to the global ocean. Together the Ayeyarwady- Thanlwin rivers transport a globally significant ~ 485 Mt yr-1 of sediment and as much as 7.7 Mt yr-1 of particulate organic carbon to the Northern Andaman Sea, where extreme tides in the Gulf of Martaban cause extensive resuspension of material prior to accumulation as a muddy, mid-shelf clinoform. Based on bulk stable isotope analyses, frequent resuspension of the seabed in the Gulf of Martaban creates a low-pass filter for geochemical signatures, effectively limiting signals of land use change during the past century. Whereas previous bulk analyses have indicated that terrestrial organic carbon may be remineralized during across-shelf transport, ramped pyrolysis/oxidation and radiocarbon methods show consistent terrestrial organic carbon character and content across the shelf, indicating that refractory terrestrial organic carbon dominates shelf deposits. Comparing these findings with organic signatures of the rivers’ sediments, we suggest that significant remineralization of labile terrestrial material may occur prior to reaching the open shelf. Our findings also suggest that bulk sediment analyses have generally underestimated offshore terrestrial organic carbon content, which substantially impacts the derivation of carbon budgets for the Ayeyarwady-Thanlwin and other systems. While terrestrial organic carbon content in the offshore delta is currently high, with little indication of modern human impacts in the sediment record, organic carbon accumulation has the potential to be drastically impacted by future planned mainstem dam installation as well as changing climate (e.g., monsoon patterns and cyclone frequency and strength). Anticipated mainstem damming will likely alter the nature and magnitude of terrestrial organic carbon on the shelf due to increased reservoir retention and reduced sediment load. The consequent reduction in sediment supply may also drive the erosion of the clinoform, re-exposing and redistributing previously sequestered material on the shelf. The frequency of cyclonic activity and monsoon strength are also likely important climatic controls on offshore carbon delivery and sequestration. While the offshore Ayeyarwady delta currently exhibits minimal impacts from human activity, we predict that future damming and changes in climate will substantially alter terrestrial organic carbon sequestration in the offshore Ayeyarwady Delta, impacting both regional and global carbon budgets.
How to cite: Flynn, E., Kuehl, S., Galy, V., Colombo, M., and Harris, C.: Decoding impacts of modern human development on terrestrial organic carbon sequestration seaward of the Ayeyarwady-Thanlwin rivers, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7278, https://doi.org/10.5194/egusphere-egu25-7278, 2025.
Posters virtual: Wed, 30 Apr, 14:00–15:45 | vPoster spot A
EGU25-19205 | ECS | Posters virtual | VPS4
Carbon accumulation, storage and provenance in the Portuguese continental shelfWed, 30 Apr, 14:00–15:45 (CEST) | vPA.25
The field of Blue Carbon research has traditionally focused on the carbon sequestration capacity of coastal vegetated habitats, despite these habitats comprising only a small fraction of oceanic sediment. However, continental shelf sediments also play a significant role in carbon sequestration and represent a significantly larger surface area. While the majority of organic carbon deposited in the shelf sediment is initially fixated by phytoplankton, and then potentially cycled through other marine organisms, some of it is originated from coastal and terrestrial producers, such as marine macroalgae, then transported, deposited and sequestered into shelf sedimentary basins. In this study, we investigated the sedimentary organic carbon (OC) stocks and sequestration rates at two sites of the continental shelf of Portugal, each adjacent to major wetland systems dominated by saltmash and seagrasses: the northern site is located off the Sado estuary at the Arrábida coast where macroalgae forests are also present, and the southern site off the Ria Formosa coastal lagoon. We also assessed the contributions of marine and terrestrial primary producers to sedimentary OC using various proxies such as C/N ratios, carbon isotopic signature (δ13 C), magnetic susceptibility, lipid contents and sedimentary DNA metabarcoding. Our findings revealed similar OC sequestration rates at both sites (23.3 ± 7.1 g OC m⁻² yr⁻¹ and 20.9 ± 5.7 g OC m⁻² yr⁻¹ for the northern and southern sites, respectively) and comparable OC stocks in the top 25 cm of sediment (29.5 ± 2.33 g OC cm⁻² and 21.1 ± 3.01 g OC cm⁻², respectively). Clear differences were observed on the contributions of terrestrial versus marine sources to the sediment organic matter, with the northern site showing lower terrestrial contribution as opposed to the southern site. This conclusion is supported by the different proxies used. For example, the northern site consistently exhibited higher OC contents at comparable particle sizes, indicative of a greater deposition rate of organic carbon not adhered to sediment particles, typical of oceanic primary productivity. Sedimentary DNA metabarcoding detected seagrass and saltmarsh genetic material in sedimentary organic matter from both sites, indicating that detritus from the two wetlands are being exported to the continental shelf. Further investigation is needed to quantify the relative magnitude of this export. Understanding this process is essential to accurately assess the role of coastal vegetated habitats in the global carbon cycle, as current estimates focus solely on in-situ sequestration and often overlook the potential contribution of exported organic matter. Our study highlights the need to expand our perspective on the interconnectedness of coastal and oceanic carbon dynamics.
How to cite: Martins, M., Magalhães, V., Salgueiro, E., Cordeiro, L. G., Abrantes, F., Masqué, P., de los Santos, C. B., and Santos, R.: Carbon accumulation, storage and provenance in the Portuguese continental shelf , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19205, https://doi.org/10.5194/egusphere-egu25-19205, 2025.
EGU25-21501 | Posters virtual | VPS4
Temporal variability in organic carbon fixation, export, sedimentation and utilisation in the Clarion Clipperton ZoneWed, 30 Apr, 14:00–15:45 (CEST) | vPA.34
There is interest in biogeochemical cycling and ecosystem functioning in the Clarion Clipperton Zone (CCZ, equatorial Pacific) due to the possibility in the near future of deep sea mining of polymetallic nodules. A set of important processes and ecosystem services relate to the fixation, export and deposition in sediment of organic carbon (C). This is important to understand both as a mechanism for C sequestration, and also as a set of processes which feeds deep sea biological communities. However, due to the remote nature of the CCZ, and the considerable resource required, it has rarely been possible to directly observe the coupling between processes from the sea surface all the way through the water column to the fate of organic C in sediments, nor how those linked processes vary over time or in response to mining disturbance.
Here we present data on C fixation, export, sediment composition and relationships with benthic community biomass. We show clear coupling between surface productivity, export and sinking flux, but that sediment organic C concentrations are not always closely coupled to water column processes. Repeated measurements over a period of ~18 months show inter-annual variability at the seafloor, rather than a stable seasonal pattern. Organic C delivery to the sediment is reflected in the biomass of faunal groups, with different temporal responses in the different groups (macrofauna, metazoan meiofauna and foraminifera) linked to factors such as competition, predation pressure and life cycle differences. Changes in sediment total organic carbon following a mining vehicle test will also be considered.
How to cite: Woulds, C., Lough, A., and Homoky, W. and the Carbon fixation, export, sedimentation and utilisation Team: Temporal variability in organic carbon fixation, export, sedimentation and utilisation in the Clarion Clipperton Zone, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21501, https://doi.org/10.5194/egusphere-egu25-21501, 2025.
