This session aims to bring together researchers from diverse fields to discuss the latest findings on the biogeochemical processes occurring in coastal oceans, improve our knowledge, identify impacts, and propose solutions in terms of coastal management and blue economy. We welcome research studies that focus on both natural and anthropogenic processes that are affecting the biogeochemical cycles in coastal waters, trace metal chemistry, CO2 system, ocean acidification, ocean alkalinization, nutrient cycle, organic matter, CO2 sequestration, blue carbon, etc.
Orals: Wed, 6 May, 08:30–10:15 | Room 1.34
The Arabian/Persian Gulf is an extreme marine environment with pronounced and significant changes in temperature, nutrients and oxygen concentrations, and hydrodynamics. It can be used as a model system for studying marine biogeochemistry under changing and extreme environmental conditions. In this study, we studied the distributions and biogeochemical controls of particulate trace metals (pTM) in size-fractionated surface plankton (120 and 50 mm) and suspended particulate matter (SPM) in a transect across the Exclusive Economic Zone (EEZ) of Qatar, in the Central Arabian/Persian Gulf. Samples were collected in two seasons, summer and winter, and analyzed using ICP-MS, along with data collected for chlorophyll, oxygen and hydrography to investigate the factors and controls on pTM. Six bioactive trace metals (Fe, Mn, Co, Cu, Zn and Ni) and two major elements (Al and P) were measured. Our results show that Fe and Zn are enriched in plankton and SPM, which we attribute to enhanced and recurring aerosol depositions through dust events. Metal-to-aluminum (Me/Al) ratios showed that dust and lithogenic influences have a strong effect on the distribution of pTMs, especially at surface waters during the summer. Meanwhile, Mn, Ni, Cu and Co showed that hydrographic parameters, with density in particular, showed significant controls on these metals. Oxygen was shown to have negative correlation with specific metals in SPM including Fe, Mn and Co, which explains their depletion at deeper waters and near sediments, and is explained by their redox sensitivity. Plankton samples showed that biogenic fractions, shown from Me/P ratios, also display strong controls/effects on the distribution of pTMs in surface waters. The results of this study show that the distributions and biogeochemical as well as environmental controls/influences on particulate metals in an extreme environment in the Arabian Gulf.
How to cite: Yigiterhan, O., Al-Thani, J., Tutsak, E., Alagha, D. I. J., Al-Maslamani, I. A., Al-Ansari, E. M. A. S., and Soliman, Y.: Biogeochemistry and Distribution of Bioactive Particulate Trace Metals in a warm and hypersaline environment: The Central Arabian/Persian Gulf , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20025, https://doi.org/10.5194/egusphere-egu26-20025, 2026.
The Benguela Upwelling System (BUS) is one of four major Eastern Boundary Upwelling Systems with significant ecological and economical importance. It sustains high biological productivity and is characterised by a pronounced Oxygen Minimum Zone (OMZ). Despite extensive research, long-term OMZ variability and its biogeochemical impacts remain poorly constrained, particularly between the Northern (NBUS) and Southern (SBUS) subsystems. This study examines OMZ variability and its influence on Redfield stoichiometry (C:N:P = 106:16:1) to elucidate underlying biogeochemical processes.
Data from cruises along the A09 (NBUS) and A10 (SBUS) sections in 1991, 1992, 2003, 2011, 2017, and 2018 were analysed. Dissolved oxygen (DO), dissolved inorganic carbon (DIC), nitrate (N), and phosphate (P) data were obtained from the CLIVAR and Carbon Hydrographic Data Office (CCHDO), supplemented with three datasets from Flohr et al. (2014). Only stations within 200 km of the coastline were included, and OMZ vertical extent was assessed using three DO thresholds (20, 60, and 120 µmol kg-1).
Results reveal contraction of the OMZ core in the NBUS, with the 20 and 60 µmol kg-1 thresholds contracting from 301.4 m to 172.2 m and from 871.4 m to 521.9 m, respectively, between 1991 and 2011, while the 120 µmol kg-1 threshold expanded from 373.0 m in 2008 to 550.7 m in 2018, likely associated with reduced inflow of South Atlantic Central Water (SACW). In the SBUS, the 120 µmol kg-1 threshold expanded slightly from 270.3 m to 295.8 m between 2003 and 2011, while DO concentrations remained above this level, indicating a well-oxygenated water column. In the NBUS, C:N ratios increased from 4.94 to 6.19 in the upper 200 m and from 0.09 to 1.88 in the 200-500 m layer from 1991-2011, while in the SBUS, ratios increased from 5.66 to 5.77 and from 3.75 to 5.33 in the same layers from 1992-2011, indicating enhanced N loss. In the NBUS, C:P ratios decreased from 116.91 to 107.66 in the upper 200 m and ranged from 5.22 to 27.41 in the 200-500 m layer, while N:P ratios decreased from 20.78 to 17.12 and from 9.48 to 8.82, over the same depths from 1991-2011, indicating increased P accumulation. In contrast, in the SBUS, C:P ratios increased from 91.20 to 96.70 in the upper 200 m and from 60.83 to 81.70 in the 200-500 m layer from 1992-2011, indicating reduced P accumulation.
These findings indicate that, despite contraction of the OMZ core (20 and 60 µmol kg-1) and expansion of the 120 µmol kg-1 threshold during 1991-2011, and reduced SACW inflow moderating hypoxia in the upper 500 m, the development of the OMZ with its vertical variability continues intensifying denitrification and/or anammox, resulting in N loss and enhanced P release from sediments in hypoxic waters, leading to P accumulation in the NBUS. OMZ variability exerts a stronger influence on both nitrogen and phosphorus cycling in the NBUS, while nitrogen cycling is more strongly affected than phosphorus cycling in the SBUS. This study highlights long-term oxygen variability as a key bottom-up driver shaping biogeochemical cycling and ecosystem functioning across the BUS.
How to cite: Urala Gamage, S. S., Ruppegoda Gamage, A. I., and Kokuhennadige, H. N.: Influence of Long-Term Oxygen Minimum Zone Variability on Biogeochemical Cycling in the Benguela Upwelling System, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15798, https://doi.org/10.5194/egusphere-egu26-15798, 2026.
Partitioning sedimentary organic carbon (OC) into marine (OCmar) and terrestrial (OCter) components is critical for understanding carbon cycling and sequestration in coastal and marginal seas. Organic-bound bromine (Brorg) has been proposed as a proxy for OCmar due to the enrichment of bromine in marine organic matter. Although bromine has long been considered a conservative element in marine systems, it is now recognized as biogeochemically active. In the water column, hydrogen peroxide reacts with bromide to form reactive bromine species, resulting in phytoplankton and macroalgae to generate a wide range of brominated organic compounds. While volatile brominated compounds have been extensively studied due to their climatic relevance, non-volatile brominated organic compounds remain associated with organic matter and are transferred to the sediments. However, their environmental controls remain poorly constrained. Here, we present a dataset of Brorg from core-top sediments collected in the Baltic Sea, North Sea, Atlantic Ocean, Mediterranean Sea, and Black Sea. We assess relationships between Brorg and key environmental parameters such as sea surface salinity, net primary productivity (NPP), and bottom-water oxygen. NPP shows a stronger correlation with Brorg concentration (R2 = 0.64) than with total organic carbon or carbon isotopic composition, indicating a higher sensitivity to variations in organic matter source, production, and reactivity. The relationship between NPP and Brorg differ between oxic and anoxic basins, highlighting the effect of preservation conditions. This proxy for marine organic carbon and productivity in oxic coastal settings can be used in downcore records to distinguish natural variability in older sediments from anthropogenic effects in more recent sediments.
How to cite: Hilgen, C., Reichart, G.-J., Boer, W., van der Meer, M., Sangiorgi, F., and Hennekam, R.: Sedimentary organic bromine as an indicator of marine organic carbon and primary productivity in coastal and marginal seas, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14126, https://doi.org/10.5194/egusphere-egu26-14126, 2026.
The Marmara Sea has been highly affected by the Black Sea inflow and anthropogenic activities such as overfishing, urban effluents, industrial and agricultural run-off, and shipping. Recent large-scale mucilage outbreaks have accelerated eutrophication and reduced deep-water oxygen levels. Despite this trend, there are only a few studies to understand the consequences of eutrophication and deoxygenation on sediment biogeochemistry, particularly for redox-sensitive elements such as manganese (Mn). Here, we present the most recent findings on manganese in the Marmara Sea's deep-waters and sediments, based on data collected by R/V Bilim-2 in July 2024 and August 2025. Understanding the vertical distribution of Mn, as well as other trace metals, in the Marmara Sea is crucial, as they play essential catalytic roles in many biogeochemical processes. Samples were collected from six stations distributed across the western, central, and eastern sub-regions of the Marmara basin. Mn(II) and Mn(III) concentrations were measured on board using a spectroscopic porphine method. Based on water measurements from the 2024 cruise, Mn(II) ranged from 1.07 μM to 3 μM, while Mn(III) ranged from 0.22 μM to 0.44 μM at two stations. However, during the 2025 cruise, manganese was detected at only one station (45C), where both Mn(II) and Mn(III) were measured at 1.32 μM. According to the manganese sediment profiles from the 2025 cruise, Mn(II) concentrations increased in the upper sediment layers due to the reduction of Mn(III) to Mn(II) and then decreased at greater depths where redox conditions became more stable. At several stations, including Gemlik, West, and the Southern Shelf, Mn(II) concentrations increased again in deeper layers, likely due to the dissolution of Mn-bearing minerals from the sediment. Mn(III) was detected at all six stations. Among all sites, Station 45C exhibited the highest manganese levels, with maximum concentrations of approximately 105 μM Mn(II) and 6 μM Mn(III). Station İzmit Deep followed with 80 μM Mn(II) and 3 μM Mn(III). The other stations showed lower peak values: Gemlik (~43 μM Mn(II), 6 μM Mn(III)), West (~22 μM Mn(II), 6 μM Mn(III)), Northern Shelf (~6 μM Mn(II), 6 μM Mn(III)), and Southern Shelf (~9 μM Mn(II), 6 μM Mn(III)). Our results provide an updated perspective on the vertical distribution of manganese in the Marmara Sea, along with associated flux estimates. They also emphasize the links between manganese dynamics, oxygen availability, and the system’s response to anthropogenic stressors.
How to cite: Cura, H. and Yücel, M.: Seafloor manganese speciation and fluxes in a rapidly deoxygenated coastal sea: The case of Marmara Sea deep-waters and sediments, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-569, https://doi.org/10.5194/egusphere-egu26-569, 2026.
In the oligotrophic Southeastern Mediterranean Sea (SEMS), it has been shown that dissolved inorganic nutrient (DIN) from fresh submarine groundwater discharge (FSGD) enhance primary production in coastal waters. In this study pH, TA and DIN of seawater and fresh water in a sea-cave in the northern part of the Israeli Mediterranean coast and a nearby contact spring, respectively, were measured during October 2018 – March 2020. The results show gradients of measured salinity, TA, pH and DIN along the cave axis year-round, suggesting that they are influenced by FSGD. The seawater near the back of the cave was supersaturated with respect to atmospheric CO2 nearly year-round and there is a strong positive divergence from its regional open-water thermal dependence, which suggests that FSGD is also a source of atmospheric CO2 in this region. Comparison of TA, salinity and pCO2 from the back of the sea cave to their corresponding values from an abrasion platform monitoring site, ca. 3 km south of the cave, suggests that FSGD is occurring along the entire shoreline in this region. Thus, despite the increased productivity due to FSGD mediated nutrient enrichment of adjacent coastal waters of the oligotrophic SEMS, they are still a source of atmospheric CO2 nearly year-round. Finally, the apparent trends of seawater acidification (ΔpH/Δt = -0.006 yr-1) and pCO2 increase (+8 ppmV yr-1) observed at the nearby monitoring site since 2013 are explained by increased groundwater recharge and resulting FSGD total alkalinity compared to dissolved inorganic carbon inputs (ΔTA/ΔDIC=1:1.2).
How to cite: Silverman, J. and Asfur, M.: Submarine groundwater discharge enhances seawater acidification along the northern Mediterranean coast of Israel, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5008, https://doi.org/10.5194/egusphere-egu26-5008, 2026.
How to cite: Bindoni, D., Esposito, F., and Abbà, A.: Alkalinity injection in stratified marine environment to assess the risk of carbonate precipitation: a numerical study, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-521, https://doi.org/10.5194/egusphere-egu26-521, 2026.
Rare earth elements (REEs: La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, and Lu) are increasingly recognized as emerging contaminants in marine environments, yet their bioavailability and bioaccumulation processes remain insufficiently understood. Sediment-bound REEs may be bioaccumulated by benthic organisms, with deposit- and filter-feeders at greatest risk. This study investigates the bioaccumulation of sediment-released REEs in the bivalve Ruditapes philippinarum under controlled laboratory conditions, with a focus on tissue-specific accumulation patterns and the evaluation of Diffusive Gradients in Thin Films (DGT) as a proxy for bioavailable REEs. Sediments were collected from two contrasting coastal environments in SW Spain: the Río San Pedro, a relatively unpolluted site, and the Guadiana estuary, characterized by elevated metal content. Sediment REE concentrations in the Río San Pedro are relatively low (84.8 mg kg-1), whereas the Guadiana estuary exhibits elevated levels (215.8 mg kg-1), potentially influenced by wastewater discharges and the proximity of a hospital. Clams and DGT exposure experiments were conducted in triplicates. Water-type DGTs with Chelex resin were deployed at the sediment-water interface to integrate labile REE fluxes over time. From each tank, three clams and one DGT device were sampled after 0 h, 24 h, 48 h, and 7 days. REE concentrations, along with selected metals (Co, Cu, Zn, Ni, Pb) are determined in different clam tissues (gills, digestive gland, and remaining soft tissues) to assess tissue-specific uptake and internal partitioning, while DGTs are used to characterize time-resolved accumulation dynamics of labile REEs. By comparing REE accumulation in clam tissues with DGT uptake kinetics the aim of the study is to critically assess whether DGT-measured concentrations are representative of biologically available REEs and to assess the suitability of passive sampling techniques for monitoring REE contamination in coastal environments. The results also provide a preliminary assessment of potential exposure of benthic organisms to REEs and other metals, contributing to an initial evaluation of ecological risk in sediment-influenced systems and contribute to the current understanding of REE bioavailability.
How to cite: Marcinek, S., Basallote, M. D., Cobelo-García, A., Blasco, J., Tovar-Sánchez, A., and Rodríguez-Romero, A.: Rare earth elements uptake in bivalves and assessment of DGT as a proxy for bioavailable fractions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14204, https://doi.org/10.5194/egusphere-egu26-14204, 2026.
Essential trace metals (e.g., Fe, Co, Cu) are vital for phytoplankton metabolism and marine biogeochemical cycles, while toxic metals and emerging contaminants (e.g., Cd, Pb, Hg, Li, microplastics) pose ecological risks. Their bioavailability and transfer through marine food webs depend partly on their chemical form (speciation between dissolved, colloidal, particulate) and biological uptake by plankton. These processes – chemical speciation and trophic transfer - can modify phytoplankton community structure and the entire marine food web with potential consequences for ecosystem functioning.
To investigate how metals and contaminants transfer through the water column and plankton, a mesocosm experiment conditions was carried out. Mesocosms with the natural phytoplanktonic assemblage from Villefranche Bay (Mediterranean Sea, France) and copepods collected from the same location were exposed to a gradient of metals, Li and UV-degraded microplastics, ranging from present-day concentration to levels representative of plausible future environmental scenarios.
This experiment was conducted in 9 x 300 L with a 1 m high water column allowing the development of export fluxes. Major nutrients were added in all mesocosm to insure the phytoplanktonic development before metals and contaminants additions of treatment. Treatments were as follow : 1 mesocosm control; 3 mesocosms with x1.5, x2 and x5 of natural metals concentrations (Fe, Mn, Zn, Co, Cd, Cu, Ni and Li); 2 mesocosms with addition of different concentrations of UV-degraded polypropylene (10 and 160 µg/L, size distribution centred at ~50 µm); and 3 mesocosms with different concentrations of both metals and microplastics.
During the 17-day experiment biological parameters (nutrient concentrations, biovolume, particulate organic carbon and nitrogen, pigment concentration and cell abondance) were monitored throughout the experiment and first results indicate an initial exponential growth phase, followed by nutrient limitation and a transition toward heterotrophic conditions. Metals concentrations will be analysed in colloidal (3kDa – 0.22 µm), dissolved (< 0.22 µm) and particulate (> 0.22µm) fractions. The particulate fraction, included microphytoplankton, was rinsed with EDTA/oxalate to quantify intracellular metals. Zooplankton was sampled at the beginning and the end of the experiment to assess potential bioaccumulation. Exported material was collected daily to quantify and characterize export fluxes. These data will allow determination of partition coefficients and bioaccumulation. Daily photophysiological measurements - including the maximum quantum yield (Fv/Fm), absorption cross-section (SigmaPSII) of photosystem II, photosynthesis–irradiance curves and photoprotection capacity - will enable the detection of any potential adverse effects of the treatment on the physiological status of phytoplankton.
This presentation will report on the experiment and present preliminary results on the partition coefficients and bioaccumulation of metals and contaminants, and will explore their potential impact on phytoplankton and zooplankton communities.
How to cite: Heydon, M., Diss, M.-L., Payant, L., Guieu, C., Talec, A., Bailleul, B., Uher, E., Vigier, N., Montanes, M., Leblond, N., Herment, G., Urrutti, P., and Bressac, M.: Transfer of metals and contaminants through the water column and lower trophic levels: a mesocosm experiment, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20541, https://doi.org/10.5194/egusphere-egu26-20541, 2026.
Mariculture represents one of the most significant anthropogenic perturbations to coastal biogeochemical cycles. As the world’s largest producer, China’s mariculture plays a critical role in global food security, yet its long-term impacts on coastal water chemistry and climate remain poorly quantified. This study presents a comprehensive assessment of greenhouse gas (GHG), nitrogen (N), and phosphorus (P) dynamics in China’s mariculture from 1983 to 2024, combined with projections of future trajectories under twelve development scenarios using long-term reconstruction and scenario-based modeling frameworks.
Our results show that China’s mariculture has consistently acted as a net GHG source, with emissions increasing from 0.02–0.10 Mt in 1983 to 61.60–71.60 Mt in 2024. Concurrently, N and P discharges surged approximately 150-fold. Although extractive species provided substantial mitigation, the annual growth rate of emissions exceeded biological removals by approximately 6%, indicating a widening imbalance between anthropogenic inputs and ecosystem assimilation capacity. A pronounced source–sink divergence was identified, driven by climatic suitability and farming structure. Northern provinces, characterized by extensive macroalgal cultivation, function as persistent nutrient sinks, whereas southern provinces dominated by intensive fed aquaculture have emerged as major emission sources. Projections indicate that without structural adjustment, net N discharges could increase four- to ten-fold by 2030, accompanied by an approximately 50% rise in GHG emissions. Conversely, optimizing species composition and adopting clean energy could enable peak GHG emissions by approximately 2050, carbon neutrality by 2075, and net N removal of nearly 39 kilotons by 2100. These findings provide critical benchmarks for managing anthropogenic influences on coastal chemical processes and support the evidence-based sustainable transformation of the global blue economy.
How to cite: Liu, J., Yang, W., Marín Del Valle, T., Zou, Z., and Zhu, B.: Long-term impacts of mariculture on coastal greenhouse gas, nitrogen, and phosphorus dynamics in China, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9140, https://doi.org/10.5194/egusphere-egu26-9140, 2026.
Coastal wetlands, which are vital for global carbon storage, face unprecedented stress due to changing water levels and salinity. Their resilience depends on complex biogeochemical interactions, particularly the cycling of redox-sensitive metals (Fe, Mn, Cu, and Zn), which control nutrient availability and vegetation patterns. This study decouples how these physicochemical factors drive the ecosystem structure in the Nanhui Wetland, Shanghai.
Here, we report physicochemical parameters across a salinity gradient, measuring nutrients, trace metals, pH, and dissolved oxygen. The results demonstrate that hydrological oscillations create distinct redox zones. This fluctuating oxygen availability drives competitive reductive dissolution and re-precipitation reactions of Fe and Mn oxides. Concurrently, these redox shifts modify the ligand environments and sulfide availability, thereby regulating the complexation, solubility, and potential toxicity of Cu and Zn. These dual pathways involve nutrient processing via Fe/Mn cycling and metal toxicity modulation. Geochemical shifts govern nitrogen processing and carbon stabilization at the sediment-water interface. This creates an observable geochemical template that directly filters salt-tolerant plant zonation based on species-specific tolerances to nutrient and metal stress. By quantifying these core interactions, our study establishes a mechanistic foundation required to constrain next-generation biogeochemical models, enabling targeted strategies for managing blue carbon ecosystems to enhance their resilience and sequestration.
How to cite: Vásquez, A. C., Li, Z., Abdul Razak, N. S., and Yang, S.: How physicochemical factors shape coastal vegetation patterns: Redox zonation drives coupled metal-nutrient dynamics in Nanhui Wetland, Shanghai, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2843, https://doi.org/10.5194/egusphere-egu26-2843, 2026.
Posters on site: Tue, 5 May, 08:30–10:15 | Hall X4
This study investigated dissolved and particulate metals (Cu, Zn, Cd, and Pb), together with Pb isotopic compositions, in coastal seawater from the Oehwang River estuary and Onsan Port, which have been reported as severely contaminated areas due to industrial complexes and harbor activities. A total of 53 surface seawater samples were collected during each of four sampling periods (April, July, August, and October 2025). Water quality parameters, including salinity, pH, and turbidity, were measured in situ, and dissolved and particulate metal concentrations as well as Pb isotopic ratios were analyzed.
Overall, metal concentrations within Onsan Port were consistently higher than those in the estuarine zone. Concentrations of Cu, Zn, and Pb in Onsan Port frequently exceeded the chronic toxicity water quality guidelines. In addition, three sites sampled in August, located in front of wharfs B and C, showed Zn concentrations exceeding the acute toxicity guideline.
Pb isotopic compositions plotted against the inverse of Pb concentrations for both dissolved and particulate phases revealed three distinct two–end-member mixing relationships involving four isotopic end members. The ²⁰⁷Pb/²⁰⁶Pb ratios of the dissolved phase (particulate phase in parentheses) were 0.915 (0.942), 0.892 (0.894), 0.888 (0.883), and 0.870 (0.865). These mixing relationships correspond to three zones: the area in front of wharfs B and C within Onsan Port, the inner and outer areas of Onsan Port, and the Oehwang River estuary.
Pb isotopic signatures in the hotspot area indicate that the sources of elevated Pb and Zn concentrations were zinc concentrates imported from Australia and unloaded at wharf B during the sampling period. In contrast, other isotopic end members with distinct Pb isotope ratios represent metal concentrates that were unloaded during previous periods.
The strong linear correlations observed between dissolved and particulate metal concentrations suggest that dissolved Cu, Zn, Cd, and Pb in this area primarily originate from the dissolution of imported metal concentrates during unloading activities at the wharfs, while particulate metals represent residual materials remaining after partial dissolution in seawater.
Temporal variations in both the spatial distribution patterns and concentration ranges of metals were pronounced and were mainly controlled by harbor-related inputs rather than freshwater discharge. Because local metal sources could be clearly identified using spatial distributions of dissolved and particulate metals together with Pb isotopic compositions, key characteristics of the mixing processes—such as source-receptor area, mixing time scale, and spatial extent—could be effectively constrained in this complex coastal environment.
How to cite: Choi, M. S., Choi, S., Joe, D., Yang, D., and Lee, M.: Dissolved and particulate metals, and Pb isotopes in Oehwang River estuary and Onsan port seawaters, Korea , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2068, https://doi.org/10.5194/egusphere-egu26-2068, 2026.
After collecting sediment using a box corer in the northern East China Sea, sub-samples were collected from the sediment chamber and sediment incubation experiments were performed to calculate sediment oxygen consumption rate, hydrogen sulfide flux, methane flux and nutrient flux. Sediment incubation experiments were conducted at a total 5 sites, and the experiments were conducted for approximately 144 hours (6 days). Organic carbon regeneration rate was calculated as the sediment oxygen consumption rate. The sediments at all sites were muddy or muddy sand sediments, and the organic carbon content ranged from 0.25% to 0.94%. The C/N ratio is in the range of 3 to 7, and most of the organic matter in the sediment is assumed to be of marine origin. The sediment oxygen consumption rate ranged from 0.82 to 4.2 mmol/m²/day, a relatively low value compared to the sediment oxygen consumption rate in coastal area. The organic carbon regeneration rate ranged from 0.39 to 1.99 g/m²/year. The fluxes of hydrogen sulfide were 0.86 μmol/m²/day and 0.39 μmol/m²/day at the Z3-A03 site and Z3-D03 site, respectively. The fluxes of methane ranged from 0.022 to 4.838 μmol/m²/day. Methane fluxes showed a good correlation with the sediment oxygen consumption rate. Nitrate concentrations showed tended to little change or increase at sites with low oxygen consumption rates, whereas at sites with high oxygen consumption rates, concentrations tended to sharply decreased during the incubation. Ammonium concentration showed no change during the initial phase of incubation, but increased sharply from the 2 days after. The silicate concentrations continuously increased during the incubation, with the silicate flux being proportional to the oxygen consumption rate.
How to cite: Lee, T., Lee, K., Hong, J., and Kim, H. J.: Methane, hydrogen sulfide and nutrients fluxes in southern Yellow Sea sediments, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6057, https://doi.org/10.5194/egusphere-egu26-6057, 2026.
This study presents and evaluates the distribution patterns and deposition fluxes of both natural and artificial radionuclides, 210Pb and 137Cs, in the sediments of the Yellow Sea region. Higher sediment deposition fluxes of 210Pb were observed in the muddy sediment area compared to the sandy area. In addition, the deposition fluxes of excess 210Pb at the dumping site and surrounding areas showed higher values (663.1 ± 588.6 Bq/m2 yr−1) than those at the non-dumping sites (359.7 ± 373.3 Bq/m2 yr−1) within the muddy area. Thus, although the sedimentation rates in the study area calculated using excess 210Pb showed an average value of 0.35 ± 0.23 cm yr−1, which is comparable with those reported in previous studies of the Yellow Sea, this study indicates the significant influence of anthropogenic waste dumping on the accumulation of 210Pb in the bottom sediments. The 137Cs activities in most stations exhibited an exponential decrease from the surface sediments, similar to the pattern of 210Pb, although one site showed peak values at depths of 9–13 cm. However, unlike the typical 137Cs peaks that correspond to major events, such as the 1963 nuclear tests, the age of the sediments at peak depths in this study ranged widely, from the 1950s to the 1970s. This imprecision in dating is likely attributable to the high sediment turbulence in the Yellow Sea and the weaker particle-reactive nature of 137Cs, which facilitates the remobilization of particulate 137Cs into the dissolved phase. Moreover, our results indicate a much lower deposition flux of 137Cs compared to previous studies, further demonstrating the limitations of using 137Cs as a tracer in high-sediment-surface areas. Overall, this study highlights the impact of waste dumping on the accumulation of 210Pb in marginal seas, even in dynamic sedimentary environments such as the Yellow Sea.
How to cite: Kim, I. and Chen, X.: Behaviours of 210Pb and 137Cs in Yellow Sea Sediments Under the Influence of Waste Dumping, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6179, https://doi.org/10.5194/egusphere-egu26-6179, 2026.
As part of the South Korean government's long-term national objectives for achieving greenhouse gas neutrality, we are developing a project to establish a systematic framework for assessing organic carbon storage in seafloor sediments across the coastal and offshore regions of the South Korean Peninsula's Exclusive Economic Zone (EEZ), utilising sediment core and surface sediment analyses. In Korean waters, existing sedimentary carbon data are mostly limited to the surface layers, which are highly vulnerable to physical and chemical disturbances, resulting in considerable uncertainty in carbon storage evaluations. Through this project, we aim to address these critical limitations.
For this study, we collected sediment core samples from 48 stations in Korean EEZ waters, and sediments were analysed for surface and core sediment properties, water content, total carbon (TC), total inorganic carbon (TIC), and total organic carbon (TOC). Water content was calculated from the weights of wet and dry sediment and used as a proxy for sediment porosity and structural characteristics. Contrary to general expectations, our results show that samples characterised by lower mean surface grain size values (φ) exhibit relatively high-water content (R2 = 0.4658) and a weak negative relationship to TOC (R2 = 0.3061), resulting in elevated TOC values in sediments that are texturally classified as sandy. Furthermore, TOC concentrations show a weak positive relationship with increasing water content (R² = 0.2326), suggesting possible mechanisms such as poorly sorted sands containing interstitial fine particles, enhanced intragranular porosity associated with biogenic or carbonate-rich sands, and rapid burial of organic matter under energetic depositional conditions that limit early diagenetic degradation.
Our findings highlight the limitations of using mean surface grain size as a key predictor of surface sedimentary organic carbon and emphasise the importance of incorporating water content and sediment physical properties when assessing carbon storage potential. Understanding these physical and biogeochemical controls is crucial for enhancing estimates of marine carbon burial and for the development of robust frameworks to assess the role of seafloor sediments in climate mitigation strategies.
How to cite: Kaluthotage, P. and Kim, H. J.: Assessment of Carbon Storage in Marine Sediments of the South Korean EEZ: An Insight into Surface Sediment Grain Size in the Retention of Organic Carbon, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6229, https://doi.org/10.5194/egusphere-egu26-6229, 2026.
Coastal mangrove habitats are among the most efficient natural carbon sinks on the planet: their upper soil typically contains about 3–5 times more soil organic carbon than the global average and can sequester carbon at rates 2–4 times greater than tropical terrestrial forests. Nevertheless, degradation and hydrological disruption driven by climate change and anthropogenic perturbations jeopardize these carbon reservoirs, potentially transforming mangroves from net carbon sinks into carbon sources. We hypothesized that restoring hydrological connectivity and vegetation would enhance soil organic carbon accumulation and reactivate blue carbon cycling. To test this, we examined the Sundarbans—the largest contiguous mangrove forest in the world, extending across India and Bangladesh. Three sites under distinct ecosystem conditions in the Indian part of the Sundarbans were selected: a degraded mangrove site—where vegetation loss and hydrological disruption have promoted oxidation and loss of soil organic carbon; a restored mangrove forest maintained by a local NGO; and a mature old-growth mangrove. Soil core samples collected up to 35 cm depth at 3–5 cm intervals were analyzed for total organic carbon (TOC) and nitrogen (N), stable carbon isotopes (δ¹³C), n-alkane biomarkers, and radiocarbon abundance. Soils from the degraded mangrove site contained low TOC, high δ¹³C values, a high ratio of aquatic-to-terrestrial n-alkanes (Paq), and a consistent decrease in terrestrial plant wax n-alkanes (Pwax) with depth, along with variably lower C/N ratios, signifying heterogeneous carbon inputs dominated by aquatic sources. In contrast, soils from the restored mangrove site showed TOC and δ¹³C values comparable to mature systems, higher Pwax, longer n-alkane average chain lengths (ACL), and consistently elevated C/N ratios, indicating stable, plant-dominated carbon inputs under restored vegetation and hydrological connectivity. The relationship between C/N ratios and δ¹³C values further confirmed a shift from aquatic-derived carbon in the degraded site to terrestrial C3 plant carbon in the restored site, with the old-growth mangrove site exhibiting mixed-source signatures. Radiocarbon profiles revealed a gradual decrease with depth, reflecting the aging and stabilization of organic matter. Our results highlight the dual role of mangrove restoration in rapidly rebuilding carbon stocks while enhancing carbon turnover, underscoring its importance for climate mitigation strategies and blue carbon credit frameworks.
[Keywords: mangrove restoration, blue carbon, carbon sequestration, n-alkane biomarker, carbon isotopes]
How to cite: Nizam, S., Dutta, S., Sen, I. S., and Sachse, D.: Isotopic and Biomarker Constraints on Soil Carbon Dynamics Across Degraded, Restored, and Old-Growth Mangroves in the Sundarbans, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6454, https://doi.org/10.5194/egusphere-egu26-6454, 2026.
Tropical islands play a significant role in oligotrophic gyres by supplying macro- and micronutrients that support phytoplankton production in otherwise nutrient-poor waters. This so-called island mass effect remains poorly documented and is likely to be highly system-specific. Here, we compare the island mass effects of two contrasting tropical environments: a volcanic island in the Caribbean Sea (Guadeloupe, French West Indies) and an ultramafic island enriched in nickel, iron, and other trace metals within the lagoon system of New Caledonia (Coral Sea).
This study combines oceanic and terrestrial field campaigns, including river surveys, to identify and quantify nutrient sources surrounding each island, together with analyses of phytoplankton community distributions. Complementary laboratory experiments were conducted to assess the role of coastal sediments as a source of trace metals and their effects on phytoplankton.
Our results highlight marked differences in the island mass effect both within and between the two systems. These differences likely result from a combination of environmental and physical drivers, including soil composition, hydrological regime, wind exposure, land use, hydrothermal activity, island-scale circulation, and the presence of a continental shelf. The impacts of these contrasting nutrient sources on natural phytoplankton assemblages are discussed.
How to cite: Boye, M., Moreau, E., Pascal, P.-Y., Juillot, F., Dupouy, C., and Messié, M.: The comparative island mass effect in volcanic and ultramafic tropical islands, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6517, https://doi.org/10.5194/egusphere-egu26-6517, 2026.
Aquaculture plays a crucial role in sustainable food production, but excessive organic matter discharge can lead to environmental issues such as eutrophication and algal blooms. This study investigated the dynamics of organic pollution in a land-based olive flounder (Paralichthys olivaceus) aquafarm on Jeju Island, Korea, comparing water quality during feeding and fasting periods. Two 24-hour monitoring campaigns were conducted to assess changes in chromophoric (CDOM) and fluorescent dissolved organic matter (FDOM), alongside conventional parameters such as chemical oxygen demand (COD), dissolved organic carbon (DOC), and total dissolved nitrogen (TDN). Feed elution experiments were conducted to examine temporal changes in dissolved organic matter following feed addition. Significant differences (p<0.01) were observed between influent and effluent during feeding, with DOC, TDN, and FDOM increasing by 10–200% within one hour. When the peak excretion rate occurred 8–9 hours after feeding, all water quality parameters except specific ultraviolet absorbance (SUVA254) showed increasing trends. A gradual increase was observed 7–8 hours post-feeding for all water quality parameters except SUVA254, and feed elution experiments also showed a similar trend over time, suggesting the influence of excretion and unconsumed feed. Robust correlations between DOC and optical parameters were observed in both influent and effluent (r2 = 0.56–0.91, P<0.001), suggesting that CDOM and FDOM can be used as indicators of aquaculture-derived organic wastewater. A unique fluorescence peak, previously unreported and observed in both effluent and feed elution samples, may serve as a tracer for aquaculture feed. These findings demonstrate that optical analysis is effective for rapid monitoring and can aid in tracing organic pollutants, informing water quality management strategies to support sustainable aquaculture while minimizing environmental impacts.
How to cite: Ji, S., Notter, B. L., and Kim, J.: Assessment of effluent water quality according to aquaculture activities using absorption and fluorescence spectroscopy, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6534, https://doi.org/10.5194/egusphere-egu26-6534, 2026.
Cadmium (Cd) is a highly toxic heavy metal released into marine environments through anthropogenic activities such as mining, smelting, and industrial waste. Tracking these pollution sources requires precise isotope analysis, yet marine sediments present significant challenges due to low Cd concentrations (<0.2 mg/kg) and complex matrix interferences. While conventional methods often utilize desolvation systems to enhance sensitivity, they are frequently limited by instrumental mass bias instability and significant memory effects.
In this study, we optimized a robust Cd stable isotope analytical procedure using multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) equipped with a standard pneumatic nebulizer (SPN). To achieve high-precision data, a two-step ion-exchange chromatography process (AGMP-1M and TRU-SPEC resins) was established, ensuring >90% Cd recovery and effective removal of major matrix elements(Al, Fe, Ca) and isobaric/molecular interferents (Sn, Mo, Nb, Zr) even without the help of a desolvator.
Our results define the optimal analytical thresholds for reliable δ114/110Cd measurements: a minimum Cd concentration of 50 ng/g (approx. 150 ng total) is required, making this protocol applicable to sediments with Cd levels as low as 0.15 mg/kg. Strict interference control limits were established, maintaining matrix-to-Cd ratios (M/Cd ≤ 5) and suppressing molecular interferences from Mo, Nb, and Zr below ratios of 0.01, 0.0005, and 0.0001, respectively.
The data quality of the method was extensively validated through a comprehensive assessment of isotope fractionation and comparison with reference values for standard materials. The entire dataset (n=733), encompassing 12 types of reference materials (RMs) (e.g., NIST SRM 2711a, NRCC PACS-3, USGS NOD-A-1), verification standards (BAM-I012), and the zero-delta standard (NIST 3108), exhibited exceptional mass fractionation linearity. The slope between δ114/110Cd and δ113/110Cd was 0.7544 (R2=0.996) and that between δ114Cd and δ111Cd was 0.2545 (R2=0.944). The slope between δ¹¹⁴/¹¹⁰Cd and δ¹¹³/¹¹⁰Cd was 0.7544 (R² = 0.996), and that between δ¹¹⁴Cd and δ¹¹¹Cd was 0.2545 (R² = 0.944). These slopes agree with predicted values based on mass-dependent fractionation, demonstrating that potential isobaric and molecular interferences were effectively eliminated and ensuring the fundamental reliability of the data. The measured δ114/110Cd values for the 12 RMs showed an average absolute deviation of only 0.079±0.086‰ compared to previously reported literature values. Furthermore, a rigorous inter-laboratory cross-validation was conducted between Chungnam National University (using the SPN and external mass-bias correction with Ag-doping) and Kyoto University (using the conventional desolvator and double-spike mass-bias correction). This comparison, involving 5 RMs and 5 surface sediment samples from Onsan Port collected in April 2025 (OS4, OS5, OS8, OS14, OS35), yielded a high correlation coefficient (R2=0.944) and a small absolute deviation (0.037±0.015).
These findings demonstrate that our optimized analytical framework ensures international-level reliability and precision. This protocol provides a powerful tool for environmental forensics, successfully differentiating natural background levels from anthropogenic inputs—such as zinc smelting and coal—in complex marine ecosystems.
How to cite: Lee, M., Choi, M.-S., Kim, J., Choi, M.-S., and Takano, S.: Optimization of Cadmium Isotope Analysis in Marine Sediments Using a Standard Pneumatic Nebulizer Coupled with MC-ICP-MS, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8538, https://doi.org/10.5194/egusphere-egu26-8538, 2026.
The southern East China Sea (ECS) is influenced by four major water masses—China Coastal Water, Taiwan Warm Current (TWC), upwelling water, and Kuroshio Water—each characterized by distinct hydrographic and biogeochemical properties. Our results show pronounced spatial contrasts in nutrient availability and planktonic processes among these water masses. Nitrate concentrations were highest in China Coastal Water, followed by upwelling water and TWC, and lowest in Kuroshio Water. Correspondingly, chlorophyll a and particulate organic carbon (POC) exhibited decreasing gradients from coastal to offshore waters. Bacterial production and plankton community respiration (CR) closely mirrored these patterns, with the highest rates observed in China Coastal Water, intermediate values in upwelling and TWC regions, and minimal rates in Kuroshio Water. Mean plankton CR integrated over the upper 40 m ranged from ~129 mg C m⁻³ d⁻¹ in coastal waters to ~11 mg C m⁻³ d⁻¹ in Kuroshio waters. Significant positive relationships were identified between plankton CR and chlorophyll a, POC, and bacterial production, indicating tight coupling among phytoplankton biomass, microbial activity, and organic carbon consumption. These findings highlight the dominant role of nutrient-rich coastal and upwelling waters in driving organic carbon remineralization on the southern ECS shelf and underscore the importance of water-mass mixing in regulating carbon cycling and ecosystem functioning across this dynamic marginal sea.
How to cite: Chen, C.-C. and Shiah, F.-K.: Impact of water masses on plankton community respiration in the southern East China Sea, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8568, https://doi.org/10.5194/egusphere-egu26-8568, 2026.
Posters on site: Tue, 5 May, 10:45–12:30 | Hall X4
Nitrogen is one of the key nutrients limiting marine primary productivity and plays a central role in controlling phytoplankton growth and ecosystem structure. In this study, we focus on the Tonegawa River estuary along the Pacific coast of Japan. In addition to direct nutrient inputs from the Tonegawa River, this region is influenced by the interaction between the Kuroshio and Oyashio currents, leading to strong variability in water masses and elevated biological productivity. Owing to these characteristics, the area has long been recognized as one of Japan’s major fishing grounds.
In the estuary and adjacent coastal waters, the sediment–water interface also represents an important site for inorganic nitrogen regeneration. Organic nitrogen deposited on the seafloor can be transformed into dissolved inorganic nitrogen through mineralization and nitrification processes and subsequently released into the overlying water column. Using bottom-water observations together with simulations from a sediment biogeochemical model, we show that sedimentary processes provide a substantial source of inorganic nitrogen to the water column in the study area. More than 80% of the regenerated nitrogen is released as ammonium, while approximately 16% is returned as nitrate, highlighting the dominant role of ammonium regeneration in sustaining nitrogen availability in the estuarine system.
Previous studies using hydrodynamic models (MRI.COM) coupled with ecosystem models (NPZD), without explicitly including sediment processes, have emphasized river inputs as the primary nitrogen source in this region. Furthermore, our results indicate that benthic biogeochemical processes at the sediment–water interface make an important contribution to the nitrogen budget of the Tonegawa estuary. These findings highlight the need to explicitly include sedimentary nitrogen regeneration when studying nitrogen cycling and ecosystem dynamics in marginal seas and estuarine environments.
How to cite: Wang, Y., Nakajima, T., Urakawa, S., Matsumura, Y., and Itoh, S.: Role of Sedimentary Nitrogen Regeneration in the Tonegawa River Estuary, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14179, https://doi.org/10.5194/egusphere-egu26-14179, 2026.
Arctic fjord ecosystems are sensitive to environmental changes such as accelerating warming and ocean acidification. In northwestern Greenland, fjords show strong contrasts in temperature, salinity, and pH due to differences in bathymetric sill depth and ocean circulation. Measurements conducted during the 2019 Ryder expedition onboard I/B Oden revealed a warm (<4 °C) and acidic (pH down to ~7.5) surface ocean from the outer part of Sherard Osborn Fjord. The surface ocean of Petermann Fjord, on the other hand, was colder (~0 °C) and less acidic (pH>8). These hydrographic differences could potentially affect baseline carbonate chemistry and sediment–water interactions. Here, we examine whether natural ocean acidification as a result of meltwater input can be buffered by carbonate weathering on the seafloor of northwestern Greenland, using controlled high-pressure flow-through incubations to simulate in-situ seafloor conditions.
Experiments were conducted at ca. 102 (+/- 1) bar and 6 (+/- 0.5) °C, hypothetical conditions simulating the intrusion of warm water. A custom-built high-pressure system consisting of three incubators, each containing paired upper and lower sand-packs (6 sand-packs in total), was used. The system was equipped with sapphire-window visual cells and fiber-optic pH sensors, enabling continuous monitoring of pH, temperature, pressure, and flow rate. Four sediment sand-packs (incubators 1 and 2) were filled with mixed sediments collected from the Petermann Fjord collected during the 2024 GEOEO North of Greenland Expedition onboard I/B Oden, spanning depths from the surface to 53 cm below seafloor, and incubated with IAPSO standard seawater. Sediment-free IAPSO seawater was incubated under the same conditions in incubator 3 as a control. During the three-month long experiments, inlet seawater was gradually acidified from pH 8.3 to 7.5 using 37% high purity HCl. Fluids were automatically collected six consecutive days per week using an auto-sampler throughout the experiments. Fluids were analyzed for major cations and anions by dual-channel ion chromatography (IC-dual). System performance and integrity were verified prior to the actual experiments by using silica gel and IAPSO seawater.
Preliminary results indicate a systematic increase in the Ca/Cl ratio responding to lower pH values in sediment-containing incubators compared to the controlled incubation, suggesting enhanced carbonate dissolution. Temporal variability in solute concentrations suggests dynamic fluid–sediment interactions and potentially coupled dissolution–precipitation processes during acidification. These findings provide experimental evidence that ongoing ocean acidification may promote carbonate dissolution in northwestern Greenland fjord sediments, with implications for coastal carbon cycling under ongoing ocean acidification.
How to cite: Amiri, N., Hong, W.-L., O'Regan, M., Kirchner, N., and Jakobsson, M.: Can seafloor carbonate weathering buffer ocean acidification in northwestern Greenland?, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14382, https://doi.org/10.5194/egusphere-egu26-14382, 2026.
Coastal regions are recognized as areas of significant biogeochemical activities, primarily due to the influx of nutrients from rivers. However, under the influence of climatic changes, these riverine fluxes are diminishing, significantly altering the biogeochemistry of coastal regions. Such changes could also impact carbon chemistry in these regions, affecting the health of ecosystems. Therefore, it is imperative to conduct long-term studies to monitor the impact of these hydrological changes on the carbon chemistry of coastal systems. In this study, we conducted an analysis of a decadal time series data on dissolved inorganic carbon (DIC) and total alkalinity (TA), along with physicochemical parameters (including pH, Temperature, Salinity), in the Mission-Aransas estuary, located in the northwestern Gulf of Mexico. These samples were collected at five stations from April 2014 to August 2025. Our focus was on characterizing the sources and sinks of DIC and TA and evaluating the hydrological impacts on carbonate parameters. The results show both non-conservative removal and gain of DIC and TA from the mixing line between river water and seawater. Gain of DIC and TA is mainly observed <~25 salinity, whereas removal is observed at higher salinities. Additional supply of DIC and TA can be attributed to the fluxes at the sediment-water interface and the dissolution of carbonates. The most significant increase is observed during periods of high-water flow, which suggests that carbonate dissolution is facilitated by a decrease in pH resulting from the mixing of low pH and high pCO2 water. Additionally, the remineralization of organic matter transported by rivers contributes to this process by lowering the pH. Removal of DIC and TA is due to the biological activities, for example calcification by oysters, which are abundant in this estuary. Although these water samples predominantly exhibit supersaturation with respect to both calcite and aragonite, this suggests the potential for abiotic precipitation of carbonate minerals. Furthermore, the oxidation of reducing agents such as sedimentary sulfide, introduced through the sediment-water interface because of significant resuspension activities, may potentially decrease the TA concentration. This study suggests that DIC and TA cycling in coastal regions is greatly influenced by hydrological changes, and more global studies are needed to predict carbon behaviors in these biogeochemically active regions to accurately quantify the impact on net export fluxes of DIC and TA to the coastal ocean.
How to cite: Danish, M. and Hu, X.: Hydrological controls on the distribution of dissolved inorganic carbon and total alkalinity in a northwestern Gulf of Mexico estuary, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15906, https://doi.org/10.5194/egusphere-egu26-15906, 2026.
Shallow marine hydrothermal systems with natural CO2 emissions generate localized chemical gradients and perturbations in seawater carbonate chemistry, offering opportunities to investigate coastal biogeochemical processes under elevated CO2 conditions. We present a multidisciplinary characterization of the Calent Mound hydrothermal field (Columbretes Islands, Western Mediterranean) based on two oceanographic surveys conducted in 2020 and 2021. Hydrographic measurements revealed pronounced pH anomalies, with reductions of up to 1.12 units relative to reference conditions localized above active venting areas. Water-column temperature and salinity anomalies were minimal, whereas subsurface sediments exhibited thermal anomalies up to +5.7 °C below the seafloor. CO2 emission-frequency analysis revealed heterogeneous degassing patterns, from sporadic to continuous, producing an estimated flux of ~3.3 kt yr-1 over an active area of 17,000 m2. Dissolved inorganic nutrient concentrations in vent fluids were markedly enriched relative to open-water reference values, particularly for phosphate, nitrate + nitrite, and silicate. Sequencing of microbial mats revealed distinct prokaryotic and eukaryotic communities associated with hydrothermal influence, including sulfur-, iron-, and ammonia-oxidizing taxa. Interannual variability was evident, although several key microbial taxa were consistently detected across both surveys. These observations characterize the chemical processes governing natural CO2 venting effects on local and regional biogeochemistry and highlight the influence of hydrothermal inputs on carbonate chemistry, nutrient dynamics, and microbial community structure in a shallow marine environment.
How to cite: Martín-Díaz, J. P., González-Vega, A., Pérez-Barrancos, C., Arrieta, J. M., Palomino, D., Baena, I., Mallol, S., R. de la Ballina, N., Díez, I., Vázquez, J. T., Díaz-Viñolas, D., and Fraile-Nuez, E.: Hydrothermal CO2 venting, pH anomalies, and biogeochemical consequences in a shallow hydrothermal system (Calent Mound, Western Mediterranean), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18905, https://doi.org/10.5194/egusphere-egu26-18905, 2026.
Urbanized and turbid reef environments pose challenges for coral-based paleoclimate reconstructions, highlighting the need to broaden the range of target taxa beyond conventional massive Porites and to develop additional archives suitable for climate proxy applications. In this study, we present monthly-resolved δ¹⁸O and δ¹³C records covering the past 20 years, from two Psammocora digitata corals (SG1, SG2) and one Porites core (SG3) collected from a turbid nearshore reef in Singapore. All three records show clear seasonal cycles, with the Psammocora exhibiting higher intra-coral reproducibility. SG1 and SG2 share nearly identical δ¹⁸O and δ¹³C means, variances, and seasonal amplitudes, consistent with similar hydrographic conditions at ~3 m depth. The shallower Porites core (SG3, ~2 m) is offset toward lower δ¹⁸O and δ¹³C values and displays reduced δ¹⁸O seasonal amplitude, perhaps reflecting species-specific baselines. Seasonal δ¹⁸O variability is primarily driven by salinity changes (~60%), with temperature exerting a smaller influence (~40%). SG1 and SG2 show δ¹⁸O amplitudes of ~1.8‰ and closely matched interannual patterns, while SG3 records a smaller amplitude (~1.2‰) consistent with its lower variance. δ¹³C exhibits larger overall variability (standard deviations 0.65–0.71‰; seasonal amplitudes ~3.0–3.9‰), responding to changes in underwater light, turbidity, colored dissolved organic matter, ambient δ¹³CDIC, and minor colony-level physiological effects. In each coral, δ¹⁸O and δ¹³C show significant positive correlations (r = 0.59–0.68), reflecting shared environmental drivers—such as freshwater input or seasonal hydrological variability—rather than colony-specific metabolic effects. Taken together, these results show that Psammocora can provide robust, high-resolution isotopic records suitable for reconstructing hydroclimate and biogeochemical variability in sediment-rich coastal environments.
How to cite: Lin, K., Zhang, Y. Z., Han, T., Morgan, K., Martin, P., Wu, M.-H., and Wang, X.: Evaluating coral proxy fidelity at monthly resolution in urban reefs: A 20-year δ18O and δ13C comparison of Psammocora and Porites, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20271, https://doi.org/10.5194/egusphere-egu26-20271, 2026.
Since its eruption in 2011, the submarine volcano Tagoro (El Hierro, Canary Islands) has been continuously monitored by the Spanish Institute of Oceanography (IEO-CSIC), as it is one of the few submarine volcanoes studied from the onset of its formation. This study analyzes data from the VULCANA-0421 and VULCANA-0125 cruises, focusing on key inorganic nutrients essential for marine productivity: silicate, phosphate, ammonium, nitrite, and nitrate. The results reveal that, more than a decade after the eruption, intense hydrothermal activity persists, continuing to alter the chemical composition of the water column. Elevated and spatially variable concentrations of all nutrients were observed, with enrichment levels reaching up to 57.00-fold for silicate and 3.96-fold for phosphate in the vicinity of the Tagoro volcano. Nitrogen species exhibited an increasing oxidation gradient with distance, suggesting active nitrification processes. In addition, the effect of sample freezing on silicate measurements was evaluated, showing underestimations at concentrations above 40 μmol/kg. As a methodological improvement, a thermal treatment at 50 °C is proposed to enhance analytical accuracy. This study underscores the importance of long-term monitoring and contributes valuable insights into nutrient dynamics in volcanically disturbed marine environments.
How to cite: Ayuso-Candal, S., González-Vega, A., Martín-Díaz, J. P., Clemente Martín, S., Escánez-Pérez, J., Pereira, C., and Fraile-Nuez, E.: Study of the Distribution of Inorganic Nutrients in the Natural Fertilization Induced by the Submarine Volcano Tagoro (El Hierro) and the Effect of Sample Freezing., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20272, https://doi.org/10.5194/egusphere-egu26-20272, 2026.
Traditionally, Blue Carbon habitats included coastal and intertidal settings such as salt marshes, seagrass meadows and mangrove forests. However, the sub-tidal sediments of continental shelves are now also recognised as a globally significant carbon sink due to the sheer volume and expanse, with increasing focus placed on qualifying organic carbon quality (or reactivity) and quantifying organic carbon stock. The ultimate sink for Blue Carbon in the marine environment is in seafloor sediments, however, once deposited, the fate of this carbon is variable. Many environmental factors are at play in the stabilisation, transformation, and/or liberation of carbon from sediments. Clay minerals and Fe-(hydr)oxides have been shown to play instrumental roles in OC preservation and transformation in marine sediments. Building on previous carbon-stock evaluations performed in the area, an investigation into the role that mineralogy plays in Blue Carbon storage and stability in Irish offshore continental sediments is outlined.
Focus is placed on vibrocores to a depth of >5m below the seafloor from mud-dominant, depositional areas, to assess how carbon storage, source and stability has changed throughout modern sediments and the Holocene. Bulk physical and geochemical characterisation of sediment are determined, including particle size analysis (PSA), % total OC (TOC), total nitrogen (TN) and elemental concentrations generated by X-ray fluorescence (XRF). The relationship between PSA, TOC, and total specific surface area (TSSA) is examined to help elucidate the role of mineralogy in carbon storage. From selected depths, the <2μm sediment fraction is separated from the bulk by centrifugation. Clay mineral identification is conducted by X-ray diffraction (XRD) on the <2μm fraction. Organic matter characterisation through pyrolysis-gas chromatography-mass spectrometry is conducted on the same depths as those selected for clay mineral XRD. Sedimentation rates for the uppermost horizons are estimated using gamma spectrometry (e.g. 210Pb). Radionuclide profiles suggest minimal downcore sediment mixing has occurred at the study site, with sedimentation rates remaining relatively stable in the upper 1m if the sediment column. TOC concentrations range from 0.8-1.4w t%, with values stabilising below 2m and remaining relatively consistent to 5.5m, indicating sustained sediment OC storage throughout the sediment profile. C:N molar ratios suggest organic matter is primarily of marine source, however increased C:N ratios are observed in the upper 30cm of the sediment profile, coinciding with increased heavy metal concentrations (Zn, Pb, Cu). Preliminary Bulk XRD results indicate clay-rich mineral assemblage, consistent with enhanced organic matter preservation in fine-grained sediments.
These results highlight the strong control that sedimentary environment and mineralogical composition exert on the capacity of continental shelf sediments to store and stabilise organic carbon. The predominance of marine-derived organic matter suggests that offshore shelf sediments play a significant role in recycling and preserving oceanic primary production, while the elevated C:N ratios and metal concentrations in surface sediments point to recent anthropogenic influences on carbon inputs and sediment geochemistry. As such, the preservation of mud-dominated shelf environments should be considered in marine spatial planning and climate mitigation strategies, given their potential to function as stable, long-term carbon sinks under future environmental change.
How to cite: Ní Mhaoldomhnaigh, C., Grey, A., Chatting, M., Walsh, P., Smeaton, C., Coughlan, M., and Kelleher, B.: The Influence of Clay Mineralogy on Carbon Stabilisation in Ireland’s Shelf Sediments: Past and Present, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21487, https://doi.org/10.5194/egusphere-egu26-21487, 2026.
Understanding of characteristics and transport of perfluoroalkyl acids (PFAAs) in heterogeneous estuarine en- vironments is limited. Furthermore, the role of suspended particles (SPS) in different layers remains unclear. This study explores the multiphase distribution process and mechanism of PFAAs controlled by SPS across surface and bottom layers in five small estuaries. Peaks in PFAA concentrations are consistently observed at strongly strat- ified sites. Concentrations of the PFAAs in both surface and bottom SPS decreased as the degree of mixing increased from strongly stratified levels to well-mixed levels. The water-SPS partitioning of some short-chain PFAAs (PFBS, PFHxA, and PFHpA) is influenced by environmental factors (pH, depth, temperature, and salinity) due to electrostatic interactions, while the sorption of some long-chain PFAAs (PFOA, PFOS, and PFNA) is controlled by SPS and dissolved organic carbon (OC), driven by hydrophobic interactions. Additionally, SPS dominates OC transport in estuarine systems, except in sandy sediment environments. SPS plays a dominant role in PFAA partitioning in both surface and bottom water-SPS systems (p < 0.05), and salinity only significantly affects PFBS in bottom layer (p < 0.01). These findings are critical for understanding the drivers of PFAA par- titioning and the roles of SPS in different layers, underscoring the necessity of considering particle-associated PFAA fractions in future coastal environmental management.
How to cite: Dong, J., Feng, R., Yao, Z., Wang, J., Wang, Y., Wang, H., Yan, D., Cui, Y., Xie, H., Du, Y., and Xia, X.: Layer-specific mechanisms of perfluoroalkyl acid (PFAA) transport and partition in estuarine environments: Unveiling thedepth-dependent differences, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16572, https://doi.org/10.5194/egusphere-egu26-16572, 2026.
