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. We welcome research studies that focus on both natural and anthropogenic processes that are affecting the trace metal chemistry, CO2 system, ocean acidification, nutrient cycle, organic matter, CO2 sequestration and their impacts on the chemical processes, etc.
Orals: Fri, 2 May | Room L2
Nutrient pollution along the California coast poses a growing environmental and ecological challenge, driven by anthropogenic inputs and regional oceanographic dynamics. Using a combination of observational data, biogeochemical modeling, and satellite-derived measurements, this presentation of 10 years of research explores the sources, transport pathways, and ecological impacts of nutrient enrichment in California’s coastal waters. Coastal upwelling, a defining feature of the California Current System, plays a dual role—providing natural nutrient inputs that fuel primary productivity while also exacerbating anthropogenic nutrient overloading in nearshore ecosystems.
Results reveal hotspots of eutrophication associated with urban runoff and wastewater discharges, particularly in areas of limited water circulation. Elevated levels of nitrogen in these regions could trigger harmful algal blooms and lead to hypoxic and acidic conditions, threatening marine biodiversity and fisheries. The research highlights the interplay between physical drivers, such as wind stress and stratification, and nutrient dynamics, offering insights into the temporal variability of nutrient-driven impacts and the mechanistic pathways to carbon and oxygen cycles.
Uncertainties and scenarios of future nutrient management strategies are also underway, emphasizing the need for integrated land-sea management approaches to mitigate eutrophication and enhance ecosystem resilience in a changing climate. This work underscores the importance of continued monitoring and interdisciplinary approaches to safeguard California’s coastal ecosystems from the adverse effects of nutrient pollution.
How to cite: Kessouri, F., Sutula, M., Bianchi, D., and McWilliams, J.: Coastal eutrophication and nutrient management along the California Coast: Processes, Impacts and Pathways, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19888, https://doi.org/10.5194/egusphere-egu25-19888, 2025.
The maritime industry's transition to ammonia as a low-carbon fuel calls for a reassessment of environmental criteria, particularly in Southeast Asia's biodiverse yet data-deficient seas. This study addresses the knowledge gap by proposing updated ammonia criterion values tailored to Southeast Asian region. Using species sensitivity distributions (SSDs) and toxicity data from over 50 regionally relevant species. The study estimates thresholds of 1.0 μM, 2.4 μM, and 4.3 μM of total ammonia nitrogen, which corresponds to protecting 99%, 95%, and 90% of species based on 96hr no observed effect concentration. These proposed concentrations are lower than those for non-tropical regions due to the inclusion of tropical reef-building corals, which are highly sensitive to ammonia. The study also compares these criteria with ammonia release scenarios from bunkering activities, underscoring the importance of situating such operations away from sensitive marine habitats. By providing a region-specific framework, this study offers new insights to guide policy development, ensuring a balance between environmental conservation and the maritime industry's sustainability objectives.
How to cite: Chen, M., Low, K. S. B., Chee, K. J., Yang, M., Lee, B. Y., Zhao, H., Christy, E., Liu, M., and Wang, Z.: Towards Sustainable maritime Management: a re-visit of ammonia criterion values in Southeast Asian tropical seas, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-818, https://doi.org/10.5194/egusphere-egu25-818, 2025.
During the past decades, large enrichments of 226Ra in coastal waters have been reported worldwide. By means of elimination, these 226Ra enrichments were used to infer large submarine groundwater discharge from a hypothetical “subterranean estuary”. A critical assumption thereof is that regeneration of 226Ra on marine sediments contributes little to enrichments of this nuclide in the coastal ocean. In this study, we have measured 226Ra and 230Th activities in two ~ 30-meter-long sediment cores collected from the subaqueous delta of the Pearl River, China. Using this novel 226Ra/230Th tracer approach, we show that regeneration of 226Ra from surface sediments between 0 and 5 m dominated the total 226Ra flux out of the seabed. We have further demonstrated that the replenishing rate of the subterranean estuary must be < 0.01 yr-1. As a consequence, the total groundwater flux is at least 2 orders of magnitude lower than the river-water flux. More importantly, the fluxes of associated dissolved constituents are also orders of magnitude lower than the regenerated fluxes from the surface sediments. Thus, to acquire an unbiased understanding of coastal ocean chemistry, future studies should focus on solute exchange occurring at the sediment-water interface.
How to cite: Cai, P., Yuan, L., Sheng, C., Cheng, Y., Chen, Y., Luo, X., and Jiao, J. J.: Is submarine groundwater discharge a major pathway of carbon and nutrients into the coastal ocean?, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5558, https://doi.org/10.5194/egusphere-egu25-5558, 2025.
Since the pace and scale of geological CO2 storage deployment have fallen short of expectations, there is a growing interest in ocean-based CO2 storage options, such as the storage in the form of bicarbonates ions in seawater. Limenet technology stores CO2 in the form of bicarbonate ions (HCO3-) by seawater alkalinization through the addition of calcium hydroxide (Ca(OH)2) at pH-equilibrated conditions, i.e., increasing seawater alkalinity without pH alteration.
Calcium hydroxide, generated from the calcination of calcium carbonate (CaCO3), reacts with captured CO2 and seawater in reactors to form stable bicarbonate ions that is then released in the sea, ensuring carbon sequestration and neutralizing ocean acidification.
This study investigated the ecological impact of bicarbonate-enriched seawater released from Limenet pilot plant on the recruitment of benthic communities in the Gulf of La Spezia (western Mediterranean Sea, northern Italy). A controlled mesocosm experiment, conducted from March to the end of May 2024, assessed the responses of benthic organisms to different concentrations of bicarbonate-enriched seawater.
Land mesocosms were housed within a purpose-built shelter, designed to simulate natural marine conditions while allowing for precise experimental control. Seawater was sourced directly from the gulf, ensuring natural baseline conditions. Important parameters such as pH, alkalinity, temperature, dissolved oxygen, and salinity were continuously monitored.
Five treatments were tested, representing different concentrations of bicarbonate-enriched seawater as a proportion of the total mesocosm volume (1,000 liters): control (no treated seawater), low (3.3% treated water), medium (6.7% treated water), high (13.3% treated water), very high (26.3% treated water). In this experiment, the “very high” treatment represented oversaturated seawater (Ωaragonite7.1), specifically designed to investigate the potential adverse effects of operating above the saturation limit.
Six calcareous plates (10×10 cm) were placed in each mesocosm to serve as substrates for benthic organisms. Sampling was conducted at two intervals: after 50 days to assess early recruitment and after 85 days to evaluate survival indices and the long-term community structure.
Benthic communities were analyzed using a combination of stereomicroscopy, advanced imaging, and software tools.
Serpulid worms (Serpulidae) were the dominant group across all treatments, with no significant differences in their abundance between natural and treated water conditions, except, as expected, for the very high treatment. In this case, serpulids abundance was lower, likely due to high saturation levels and extensive precipitation of bicarbonates into calcium carbonate, which may have created less favorable conditions for recruitment and survival.
These findings represent an important first step in safely deploying Limenet and other seawater alkalinization solutions without causing alteration to benthic communities, when they are applied within established thresholds.
How to cite: Calvi, D., Groppelli, S., Azzellino, A., Campo, F., Comazzi, F., Basso, D., and Cappello, S.: Assessing the Ecological Impacts of Bicarbonate-Enriched Seawater on Benthic Communities: A Mesocosm Experiment in the Gulf of La Spezia, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6785, https://doi.org/10.5194/egusphere-egu25-6785, 2025.
The Baltic Sea is a semi-enclosed, shallow, brackish sea under persistent anthropogenic pressure, receiving thermogenic organic compounds as products of incomplete combustion via riverine input and atmospheric deposition. We assessed the distribution, sources, and composition of thermogenic organic matter in the Baltic Sea water column via the quantification of polycyclic aromatic hydrocarbons (PAH) and dissolved black carbon (DBC). The overall imprint of combustion processes on dissolved organic matter (DOM) molecular composition was evaluated via ultra-high resolution mass spectrometry. By combining PAH and DBC with DOM characterization, we aimed to contribute to a better understanding of the distribution and behavior of combustion products in coastal environments. Water samples were taken in the southern Baltic Sea in a salinity gradient (~6 to ~21). PAH were homogeneously distributed (average: 16.05 ± 4.44 ng L-1) likely due to balanced sources and sinks and a long lifetime. In contrast, DBC concentrations showed significant spatial variability (average: 14.2 ± 2.8 µM), with a strong negative correlation to salinity, highlighting the input of thermogenic organic compounds from land via riverine transport to the Baltic Sea. In addition, the abundance of polycyclic aromatic compounds detected on a molecular formula level in DOM correlated with PAH diagnostic ratios. Although PAH were evenly distributed throughout the water PAH concentrations in the sea-surface microlayer increased with the contribution of biomass combustion, likely due to the use of coal during the heating season. Our study emphasizes the sources and distribution of thermogenic organic matter to the Baltic Sea, where PAH and DBC serve as proxies of different anthropogenic influences, revealing also their strengths and weaknesses. This research provides a comprehensive understanding of the sources of the long-lived portion of the carbon pool, emphasizing the role of the Baltic Sea as a catchment basin for anthropogenic pollutants and a dynamic system for the cycling of DOM.
How to cite: S. G. Serafim, T., Schulz-Bull, D. E., Rüger, C. P., Dittmar, T., Niggemann, J., Zimmermann, R., Waniek, J. J., and Osterholz, H.: Tracing the Products of Combustion Processes in the Baltic Sea Water Column, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8122, https://doi.org/10.5194/egusphere-egu25-8122, 2025.
The dissolution of CO2 in seawater as bicarbonate ions (HCO₃⁻) offers a promising alternative to geological storage, provided the process ensures long-term stability and avoids harming marine ecosystems. Storing CO2 in the form of bicarbonate ions could remain effective for geologic timescales, potentially up to 10,000 years [1–3]. This approach involves treating natural seawater by mixing it with pre-equilibrated seawater solutions produced from the reaction of CO2 with Ca(OH)2, adjusted to maintain the same pH as seawater. Recent research [4] has shown that the resulting bicarbonate-rich solution is stable, but concerns persist regarding its potential environmental impacts. While alkalinity itself does not directly affect marine biology, its increase significantly alters pH and the concentrations of key ions and molecules, such as those in the carbonate system, which can directly influence biological processes. The extent of modifications to seawater carbonate chemistry depends on the amount of alkalinity added per unit volume and the rate at which this volume mixes with surrounding waters. The rate at which perturbed seawater equilibrates with the atmosphere is also a critical factor. Seagrasses, marine angiosperms that evolved from terrestrial plants and returned to the sea during the Cretaceous period (approximately 140 to 100 million years ago), play a vital role in marine ecosystems. Seagrass meadows are among the most productive ecosystems on Earth, with an average primary productivity ranging from 394 to 1200 g C m⁻² y⁻¹. These meadows provide numerous essential ecosystem services. Seagrasses are thought to benefit from ocean acidification, as they can utilize both CO₂ and HCO₃⁻ for photosynthesis, although they have a higher affinity for CO₂ and are often carbon-limited [6–7]. Additionally, evidence from natural volcanic CO₂ vents at Ischia, Panarea Islands, and Basiluzzo Islet—where conditions of natural acidification occur—indicates a correlation between increased dissolved inorganic carbon (DIC) and enhanced net primary production [8]. Building on existing literature, this analysis will explore the potential co-benefits of increased bicarbonate concentrations for seagrasses, aiming to assess how these benefits could enhance seagrass health and growth. It will also evaluate the opportunity to integrate this technology with Nature-Based Solutions, such as seagrass restoration, to maximize ecosystem resilience and climate mitigation efforts.
References
[1] Renforth & Henderson. (2017). Assessing Ocean Alkalinity for Carbon Sequestration. Rev. Geophys.
[2] Middelburg et al. (2020). Ocean Alkalinity, Buffering and Biogeochemical Processes. Rev. Geophys.
[3] Eisaman et al. (2023). Assessing the Technical Aspects of Ocean-Alkalinity-Enhancement Approaches. State Planet, 2-oae2023, 1–29.
[4] Varliero et al. (2024). Assessing the Limit of CO2 Storage in Seawater as Bicarbonate-Enriched Solutions. Molecules. 29, 4069.
[5] Duarte et al. (2005). Major role of marine vegetation on the oceanic carbon cycle. Biogeosciences 2, 1–8.
[6] Invers et al. (2001). Inorganic carbon sources for seagrass photosynthesis: an experimental evaluation of bicarbonate use in species inhabiting temperate waters, J. Exp. Mar. Biol. Ecol., 265, 203–217, 2001.
[7] Koch et al. (2013). Climate change and ocean acidification effects on seagrasses and marine macroalgae, Glob. Change Biol., 19, 103–132.
[8] Guilini et al. (2017). Response of Posidonia oceanica seagrass and its epibiont communities to ocean acidification. PLoS ONE 12 (8): e0181531
How to cite: Azzellino, A., Basso, D., Barbaccia, E., Gabualdi, M., Campo, F. P., Cappello, G., Cappello, S., Caserini, S., Comazzi, F., Varliero, S., Macchi, P., Alamooti, S., and Raos, G.: CO2 Dissolution as Bicarbonate in Seawater: Potential Co-benefits for Net Primary Production, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19618, https://doi.org/10.5194/egusphere-egu25-19618, 2025.
Iron is a critical micronutrient in the ocean, playing a limiting role in primary productivity across vast regions of the global ocean and significantly impacting global CO₂ uptake. Despite its importance, inorganic iron is highly insoluble under the physicochemical conditions of seawater. However, complexation by natural organic ligands prevents precipitation and enables iron concentrations to remain in the nanomolar and subnanomolar range. Identifying and characterizing these ligands remains a challenge. Humic substances (HS), a complex and hydrophobic mix of organic compounds, are considered key candidates for constituting a significant portion of these iron-binding ligands. HS concentrations and Fe-HS complex concentrations can be measured directly in seawater using recent voltammetric protocols.
In this presentation, we will report on Fe, HS, and Fe-HS concentrations measured across the Atlantic sector of the Arctic Ocean and the Northwest Atlantic Ocean. Samples collected during three different cruises reveal the significant variability in the role of HS in iron solubility, ranging from negligible to critical, depending on the biogeochemical and physical characteristics of the water masses encountered. We will discuss the influence of the Transpolar Drift outflow, the East Greenland Current, fjord water outflows, and Icelandic sills on HS distribution and iron solubility in the region.
How to cite: Laglera, L. M., Sukekava, C., Middag, R., and Gerringa, L.: The Role of Humic Substances in Iron Complexation and Solubilization in the Arctic Ocean and Northwest Atlantic Ocean, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17265, https://doi.org/10.5194/egusphere-egu25-17265, 2025.
Coastal marine systems are critical environments that can be affected by harmful algal blooms caused by the diatom Pseudo-nitzschia australis. This species produces a neurotoxin, domoic acid (DA), which poses significant risks to human health and raises societal and environmental concerns. The factors determining the toxigenicity of P. australis strains remain unclear, particularly concerning the effects of copper (Cu) and zinc (Zn). Cu and Zn are essential trace metals that are ubiquitous in coastal environments but can become toxic at nanomolar ionic concentrations. While Cu is known to enhance DA production in some Pseudo-nitzschia species, the effect of Zn on the DA metabolic pathway has not been studied. This study aims to investigate the effects of Cu²⁺ and Zn²⁺ on the metabolism of the toxic diatom P. australis. We examined the physiology, elemental composition, and isotopic composition of a coastal P. australis strain isolated from the North Biscay region (France). We present results from 10-day laboratory-controlled culture experiments, exposing the diatom to pico- to nanomolar concentrations of Cu²⁺ and Zn²⁺. The results reveal direct effects of these metals on DA production by P. australis. We report Cu, Zn, and carbon intracellular quotas, along with the first measurements of Cu isotopic composition (δ⁶⁵Cu) in cultured cells under varying metal exposure conditions. Our findings demonstrate metal-specific physiological responses in P. australis, with distinct δ¹³C and δ⁶⁵Cu isotope fractionation patterns depending on cell metabolism, including the DA production regime.
How to cite: Bassez, M., Araújo, D., Maguer, J.-F., Hégaret, H., and Dulaquais, G.: Metabolism, elemental and isotopic composition of the coastal diatom Pseudo-nitzschia australis under Cu and Zn exposure, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1379, https://doi.org/10.5194/egusphere-egu25-1379, 2025.
To combat global warming and achieve carbon neutrality, carbon storage solutions for Carbon Dioxide Removal (CDR) from the atmosphere are being explored for their potential to sequester atmospheric CO2. This study evaluates the ecological impacts of pH-equilibrated alkalinization, using the Limenet® process, a method that combines CO2, calcium hydroxide (Ca(OH)2), and seawater to generate bicarbonate-enriched solutions. Similar to other marine CDR based on Ocean Alkalinity Enhancement (OAE), this approach addresses not only climate change but also ocean acidification. A mesocosm experiment conducted in La Spezia, Italy, assessed how natural plankton communities respond to varying levels of alkalinization treatments. Fifteen land-based mesocosms were filled with seawater treated with five different levels of alkalinization: untreated, Low, Medium, High and Oversaturated bicarbonate conditions. Over a 15-day period, the physicochemical properties, nutrient dynamics, and plankton community responses were systematically monitored. Results showed effective bicarbonate stabilization in the Low, Medium, and High treatments, while oversaturation and runaway carbonate precipitation were recorded, as expected, in the oversaturated condition. The monitored pH and alkalinity demonstrated that the treated seawater maintained near-natural conditions while enhancing bicarbonate availability. Nutrient analysis revealed a rapid depletion of silica across all treatments, limiting diatom growth and triggering shifts in plankton community composition. Diatoms initially dominated the community in all mesocosms but declined over time as silica became depleted, giving way to a relative increase in dinoflagellates. The diatom-to-dinoflagellate ratio served as a key indicator of community response. In control and oversaturated treatments, the ratio exhibited steep declines, reflecting significant ecological shifts and reduced stability in plankton dynamics. By contrast, Low, Medium, and High treatments showed more gradual changes in the ratio, suggesting that pH-equilibrated alkalinization mitigates sharp shifts in planktonic communities. When compared with diatoms and dinoflagellates, the calcareous plankton component is negligible in mass in the La Spezia harbour, however, a dedicated effort is ongoing to assess the effect of pH-equilibrated alkalinization on nannoplankton dynamics. These findings highlight the dual potential of pH equilibrated alkalinization as a CDR strategy: effectively enhancing marine carbon sequestration while buffering ecosystems against extreme shifts in plankton structure. The experimental results suggest that this approach promotes ecological resilience by supporting balanced carbon uptake processes and mitigating the risks of bicarbonates (HCO3-) precipitation in Calcium Carbonate (CaCO3) and pH destabilization, which are critical challenges in OAE implementation. This study provides valuable insights into the feasibility of pH equilibrated alkalinization as a CDR technology, underscoring the importance of sustainable practices and renewable energy integration to maximize its environmental benefits. While the results are promising, further research is needed to evaluate long-term ecological impacts, trophic-level interactions, and the scalability of this approach in diverse marine environments.
How to cite: Groppelli, S., Calvi, D., Azzellino, A., Campo, F., Comazzi, F., Jamali Alamooti, S., Macchi, P., Raos, G., Basso, D., and Cappello, S.: The response of phytoplankton to pH-Equilibrated Ocean Alkalinization: a mesocosm experiment in the Gulf of La Spezia, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10595, https://doi.org/10.5194/egusphere-egu25-10595, 2025.
With increasing atmospheric concentration of carbon dioxide, more CO2 is dissolved in seawater, resulting in ocean acidification (OA). The consequences of OA can be altered by alkalinity (TA), dissolved inorganic carbon (DIC) and freshwater inputs. Here, we study wheter submarine groundwater discharge (SGD) may impact coastal acidification. The DIC and TA relationship in rivers and SGD across six countries and 16 beaches along the Baltic Sea coastline were resolved. TA was greater in groundwater (average = 2521 µmol/kg) than river (1324 µmol/kg) and surface seawater (1307 µmol/kg) samples. The average concentration of DIC in SGD was more than twice the concentration of river and surface Baltic Sea water. SGD contributes with a TA deficiency relative to DIC. 84% of the groundwater samples were acidifying compared to 74% and 38% for river and surface water respectively. Mixing plots revealed that 7 out of 9 basins experienced non-conservative TA and DIC in the subterranean estuary. The surplus of both DIC and TA indicates diagenetic sources such as sulfate reduction and oxic respiration. Overall, SGD can acidify the Baltic Sea and therefore should be included in regional carbon budgets to assess regional ocean acidification.
How to cite: Börjesson, S., Ljungberg, W., Reithmaier, G., Yau, Y., Majtényi Hill, C., McKenzie, T., Rodriguez-Puig, J., Henriksson, L., Holloway, C., and Santos, I. R.: Effects of alkalinity and carbon in submarine groundwater discharge on coastal acidification in the Baltic Sea, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9696, https://doi.org/10.5194/egusphere-egu25-9696, 2025.
Posters on site: Fri, 2 May, 10:45–12:30 | Hall X4
Dimethylsulfoniopropionate (DMSP) is a plentiful organic sulfur metabolite and the primary precursor for dimethyl sulfide (DMS), which plays a crucial role in global sulfur cycling, the formation of clouds, and cooling the warming earth. The origin and fate of DMSP are intricately linked to marine microorganisms, making the variation of the microorganism community crucial for DMSP dynamics. Nonetheless, the impact of pervasive marine microplastics on microorganisms and processes related to DMSP synthesis and degradation remains insufficiently investigated. To bridge this gap, the present study aimed to investigate the influences of microplastic pollution on microorganic community structure and the synthesis and degradation of DMS and DMSP. A 14-day deck-based microcosm experiment was conducted, revealing that exposure to microplastics led to significant alterations in the diversity and structure of microorganism communities and had detrimental effects on the productions of DMS and DMSP. Furthermore, multivariate analysis indicated that variations both in environmental variables, such as Si, Chl-a, and microorganism communities caused by microplastics were forcing factors influencing the synthesis and degradation of DMS and DMSP. Additionally, the predicted function of the bacterial community showed a significant reduction in the presence of dddP and dmdA genes when exposed to microplastics, which directly disrupted both the demethylation and cleavage pathways of DMSP. These results indicate that the release of DMS and DMSP in marine ecosystems can be significantly affected by microplastics through influencing microorganisms. Under the influence of environmental pollution, the sea-air exchange flux of DMS in coastal areas may undergo substantial modifications, consequently impacting regional and even global climate patterns. Thus, it is imperative to conduct research on controlling the synthesis and degradation of DMSP in the ocean, particularly in response to these environmental pollution issues. Such research can help discern new patterns from specific phenomena and identify crucial processes.
How to cite: Liu, Q., Guo, F., Liu, L., and Yang, G.: Microplastics Stress Alters Microorganism Community Structure and Reduces the Production of Biogenic Dimethylated Sulfur Compounds, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1982, https://doi.org/10.5194/egusphere-egu25-1982, 2025.
210Pb and 137Cs have been widely used as tracers to estimate sediment ages and sedimentation rates, enhancing the understanding of geoscientific processes. The Yellow Sea, located between the western coast of Korea and the northeast coast of China, has an average depth of 50 m and is influenced significant boundary inputs from various sources such as atmospheric deposition, river runoff, and submarine groundwater discharge. In the Yellow Sea sediments, the concentrations of 210Pb and 137Cs were found to be twice and six times higher, respectively, in dumping sites compared to other regions. Based on the 210Pb distributions, the overall sediment rates was found to be 0.30 to 0.49 (avg. 0.35±0.23) cm yr-1 on average, which is much higher than that of the East Sea. This calculated sedimentation rate also agreed well with that estimated by 137Cs in some stations. Overall, our results imply that the substantially high sedimentation rates in the Yellow Sea could be due to the massive inputs from the various sources from surrounding continents, especially the dumping site.
How to cite: Kim, I., Lee, J., and Seo, J.: Sedimentation rates in the Yellow Sea based on 210Pb and 137Cs, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3440, https://doi.org/10.5194/egusphere-egu25-3440, 2025.
The behavior of dissolved trace elements in coastal seawater is influenced by various biogeochemical processes, including particle adsorption, decomposition of organic matter, and organic complexation. In this study, we measured the concentrations of dissolved trace elements (Al, V, Ni, Fe, Mn, Cu, Pb, Co, and Zn), together with dissolved organic matter (DOM), including organic carbon (DOC) and humic DOM (DOMH), and 234Th in the artificial and saline Lake Shihwa, Korea. The concentrations of DOC (117–311 μM) and trace elements were significantly higher than those in other coastal waters, with average Al, Fe, and Mn concentrations of 709 ± 613 nM, 491 ± 452 nM, and 957 ± 657 nM, respectively. The large deficiencies of 234Th relative to 238U suggest an effective removal of 234Th via scavenging, with residence times of 1.4 ± 1.3 days. However, the concentrations of all measured trace elements against salinities showed conservative mixing patterns with significant positive correlations with DOMH (r2 > 0.72). These results suggest that all these trace elements are tightly combined with DOMH, resulting in their conservative behaviors in the dissolved organic-rich coastal waters.
How to cite: Park, J. and Kim, G.: Behaviors of trace elements associated with dissolved organic matter in waters of Lake Shihwa, Korea, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4055, https://doi.org/10.5194/egusphere-egu25-4055, 2025.
The existence of offshore freshened groundwater (OFG) has been well recognised over the globe but studies on the chemistry of OFG are extremely limited due to the scarcity of dedicated drilling investigations. In this study, we integrate offshore hydrogeology, geochemical and isotopic tracers, and transport modelling to quantitatively evaluate the hydrochemical characteristics and persistence of an OFG system in the Pearl River Estuary and its adjacent shelf. Offshore drilling suggests the OFG system comprises a vast low-salinity groundwater body extending up to 180 km offshore, with a chloride concentration as low as only ~2.5% of that in seawater. The integrated analysis of porewater isotopic signals 18O and 2H with sediment radioisotope pair 226Ra/230Th indicates that the OFG in the Pearl River Estuary and its adjacent shelf is fossil groundwater, sequestered since the late Pleistocene during periods of low sea level. Geochemical modelling of conservative tracers further corroborates the system’s persistence, estimating its residence time at approximately 69–82 kyr. The significant reduction of major ions, along with the isolated status and long residence time of porewater in the estuarine-shelf sediment system, suggests distinctive redox conditions in the OFG systems compared to OFG-free sediments. The study underscores the profound role of OFG in influencing sub-seafloor biogeochemical cycles and ecosystems on local and global scales over extended timescales.
How to cite: Jiao, J. J., Sheng, C., Yuan, L., Luo, X., Cai, P., Zuo, J., and Hensen, C.: Hydrochemical characteristics and origin of offshore freshened groundwater in the Pearl River Estuary and its adjacent shelf, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4818, https://doi.org/10.5194/egusphere-egu25-4818, 2025.
Coastal systems host a large amount of biodiversity, play a fundamental role in socio-economic development, and are highly affected by human activities. Canary Islands are a natural laboratory that allow the study of CO2 system in coastal sites with different characteristics, natural and human-pressure. Then, it will help to identify the potential amount of blue carbon as well the relationship with other parameters such as Fe concentration, dissolved organic carbon (DOC), nutrients, etc. However, there are lack of information about these multidisciplinary processes and the implications on blue carbon. In this present work, we present the data related with the CO2 system and the fixed carbon in the biomass.
During one year, two coastal sites in the Canary islands (El Pajar, Gran Canaria island; and Abades, Tenerife island) and three habitats were monitored: seagrass beds, algal covers, and sandy zones. This work provides an overview of project activities and preliminary findings, encompassing monthly measurements of key parameters including sea surface temperature (SST), sea surface salinity (SSS), partial pressure of CO2 (pCO2), pH, and dissolved oxygen (DO). Each parameter was measured for 1 h. Samples to measure total alkalinity (AT) and total inorganic carbon (CT) were collected and measured in the laboratory. Additionally, analyses extend to include the percentage of carbon, hydrogen, and nitrogen (CHN) content.
According to the results, the temperature controls the partial pressure of CO2 (pCO2) in these coastal sites. pCO2 was ranged from 363.1 to 660 ppm in El Pajar, and 343.4 to 541.2 ppm in Abades. The maximum pCO2 level coincided with the higher temperature 25.3 and 25.1ºC, respectively, and resulted in the lower pH value (7.9 in both sites), in September. The minimum values were measured in winter period (February). Measuring the carbon content of the biomass in the area, the sequestered carbon was computed as 2.1± 0.6 gCO2/gbiomass, and the DOC in the two locations and three habitats were practically constant during the whole year, ranked for both sites between 0.70 and 1.24 mg L-1.
The results of this investigation are helping to quantify the amount of carbon transfer from the atmosphere to the seawater and the fixed by the biomass in these two sites. Since the seagrass has been decreasing in the Canary Islands by more than 90% in the last 10 years, the capacity to act as a sink of CO2 is also drastically decreasing and the role of the temperature has to be estimated. The results of this project will be a decision-making tool for regional and national agencies to conserve those ecosystems where there is greater CO2 capture.
Keywords: CO2 observations, coastal waters, blue carbon, Canary Islands
Acknowledgements: Multi-COast Project (TED2021-130892B-I00) has been funded by MCIN/AEI/10.13039/501100011033 and the Europe Union “NextGenerationEU”/PRTR».
How to cite: González, A. G., González-Santana, D., Castro-Álamo, A., Curbelo-Hernández, D., Santana-Casiano, J. M., Bullón-Téllez, A., Coussy, V., Suárez-Betancor, L., and González-Dávila, M.: Multiparametric study to understand the coastal blue carbon in the Canary Islands, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7272, https://doi.org/10.5194/egusphere-egu25-7272, 2025.
We analyzed spatiotemporal variation in the artificial radionuclides 137Cs and 239,240Pu in seawater around Korea Seas (East Sea, Yellow Sea and South Sea of Korea) from 2018 to 2024. The 137Cs activity in surface water of the East Sea range of 0.88 - 1.97 mBq/kg (average: 1.33 ± 0.29 mBq/kg, n=21). Vertically, the highest activities of 137Cs were sub-to surface later (0-100m) and decreased with depths. The 239,240Pu activities range of 1.70 - 5.18 μ㏃/kg (average: 3.83 ± 1.43 μ㏃/kg, n=11) in the surface layer. 239,240Pu activities were lower in the surface layer and also decreased with depths. This trend appears to be result from the adsorption onto particle and resultant sedimentation of Pu in the water column. The surface layer 137Cs activities in the Yellow sea and South Sea of Korea ranged from 0.56 - 1.96 mBq/kg (average: 1.42 ± 0.39 mBq/kg, n= 10), 0.92 to 2.43 mBq/kg (average: 1.65 ± 0.33 mBq/kg, n=29), respectively. In these regions, the spatial and vertical distributions of 137Cs and 239,240Pu were almost consistent. However, a substantial increase in 137Cs was observed at some stations in the southernmost part of South Sea, which seems to be due to the fluvial input of surround region. Overall, the distribution of 137Cs and 239,240Pu seems to be primarily influenced by local boundary inputs, such as freshwater from river, atmospheric deposition, sediment resuspension, and others from the surrounding Far East Asian continents. We quantified the interlinked budget balance of 137Cs between the East Sea, Yellow Sea and South Sea. This study suggests that advection from the open ocean is the dominant source of 137Cs in the Korean Seas and the major sinks for 137Cs in these regions are natural decay and removal via sinking flux.
How to cite: Lee, J., Kim, I., and Lee, H.: The spatialtemporal variation and transport of artificial radionuclides (137Cs and 239,240Pu)around Korea Seas (East Sea, Yellow Sea, South Sea of Korea), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7567, https://doi.org/10.5194/egusphere-egu25-7567, 2025.
Acidification and warming in the ocean and their effect on the biogeochemical cycles of trace metals can be studied from both an anthropogenic climate change perspective or natural perspective. The former is a consequence of anthropogenic CO2 emissions into the atmosphere and their subsequent transfer to the ocean, while the latter is driven by volcanic and hydrothermal gas emissions. Both phenomena occur in the ocean, making it a natural laboratory where the effect of these processes can be investigated.
In the FeRIA project, the behaviour of iron (Fe) under conditions of acidification and warming was studied at different sites affected by volcanic CO2 emissions (Fuencaliente and Tazacorte, La Palma) and anthropogenic CO2 emissions (El Hierro, Gran Canaria). Although both processes lead to ocean acidification, volcanic emissions contribute other chemical components that can modify Fe behaviour. Since each oceanic region has specific properties, Fe(II) oxidation processes are not uniform. These processes are affected by not only the physical-chemical properties (pH, T, S, O2) of the environment but also by the biogeochemical conditions (dissolved and particulate organic matter). Ocean acidification contributes to reducing the rate of Fe(II) oxidation in the ocean, therefore favouring the availability of Fe(II) for longer periods. In contrast, higher temperatures accelerate Fe(II) oxidation. Organic matter, depending on its characteristics and functional groups, can contribute to speed up or slow down the oxidation process.
These studies will make it possible to address two key questions: (1) whether regions affected by volcanic emissions can serve as models for regions where acidification and warming are caused only by anthropogenic climatic effects, and (2) whether the persistence of Fe (II) in the marine environment is controlled by the same factors.
Key words: Iron, kinetics, ocean acidification, warming, volcanic emissions
Acknowledgments: This work has been funded by FeRIA (PID2021-123997NB-I00) project given by the Ministerio de Ciencia e Inovación from Spain. LSB participation was funded by the PhD grant (PRE 2022-101456) associated to FeRIA project. A. Bullón-Téllez participation was funded by the PhD grant (ULPGC2023-2-01).
How to cite: Santana-Casiano, J. M., González-Dávila, M., González, A. G., Bullón-Téllez, A., Castro-Álamo, A., Coussy, V., Suárez-Betancor, L., and González-Santana, D.: Fe RESPONSE IN AN ACIDIFIED OCEAN. FeRIA PROJECT, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8284, https://doi.org/10.5194/egusphere-egu25-8284, 2025.
Volcanic eruptions represent a variable source of trace metals to the ocean. This study focuses on the 2021 Tajogaite volcano eruption in La Palma (Canary Islands, Spain) and its significant impact on coastal iron (Fe) dynamics. Over 85 days of activity, the eruption contributed vast amounts of volcanic ash and lava to the ocean, resulting in elevated Fe concentrations. Measurements revealed that Fe levels in seawater reached over 1900 nmol L⁻¹, with 99% of the Fe in particulate form. Soluble Fe concentrations were approximately ten times higher than typical values in the open Atlantic Ocean, demonstrating the eruption’s role in enhancing bioavailable Fe.
This poster explores Fe size fractionation during the eruption, observing a transition from large particulate dominance to increased colloidal and soluble Fe over time. Lava-seawater interactions produced hydrothermal plumes, characterized by increased temperatures, low pH, and elevated turbidity, significantly altering the local marine environment. Spatial and temporal variability in Fe concentrations highlight the dynamic nature of these coastal systems during volcanic events.
Our findings underscore the potential of volcanic activity as a natural iron fertilization mechanism in nutrient-limited regions, with implications for primary productivity and carbon cycling. The episodic nature of these interactions necessitates refined models to incorporate volcanic contributions to ocean biogeochemistry models.
How to cite: González-Santana, D., González-Dávila, M., G. González, A., Medina-Escuela, A., Fariña, D., and Santana-Casiano, J. M.: Volcanic Eruptions as Drivers of Coastal Iron Fertilization, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9497, https://doi.org/10.5194/egusphere-egu25-9497, 2025.
Zinc (Zn)-containing metalloenzymes facilitate the uptake and fixation of dissolved inorganic carbon and phosphorus (P) in marine phytoplankton, coupling the Zn biogeochemistry with biological cycling in the ocean. Furthermore, dissolved Zn (dZn) distribution in the global ocean is strongly linked with surface biogeochemistry, water mass formation and circulation in the Southern Ocean. However, additional controls of basin-scale biogeochemical processes on Zn cycling outside the Southern Ocean still remain uncertain. We present dZn distribution measured along the GEOTRACES cruise section, GP11, in the Equatorial Pacific Ocean (EPO) and discuss the relative roles of regional biological cycling and large-scale physical circulation in controlling the observed distribution. Dissolved Zn and P in the surface and thermocline waters (< 400m) exhibit an overall positive linear relation, albeit with an apparent kink at ~1μM of P: strong correlation above the kink and uniform, low dZn concentration below the kink. The estimated dZn to P ratio (0.74 ± 0.07) from the linear relation in the thermocline waters is comparable to the observed Zn/P uptake ratio (0.68) for the equatorial Pacific picoplankton, which dominate the phytoplankton biomass in the region, and larger than that reported over similar potential density range in the source region of the thermocline waters (~0.18–0.32). This indicates the important control of organic matter regeneration on observed dZn variations in the upper water column of EPO. Anomalously high dZn concentrations are observed close to the South American margin in the oxygen-deficient sub-surface waters, suggesting Zn sourced from remineralization of Zn-rich biogenic particles and/or authigenic Zn sulfide phases in resuspended reducing margin sediments. However, this signal decreases offshore due to advective mixing with low dZn ambient waters. In the deeper waters (> 500m), we used an extended optimum multiparameter water mass model and end-member composition of water masses to demonstrate that water mass mixing predominantly governs the dZn distribution in the EPO, while the impact of organic matter regeneration and reversible particle scavenging is limited. Overall, our study highlights the influence of local phytoplankton trace metal uptake stoichiometry in the upper waters (< 400m) and water circulation on the dZn distribution in deeper waters (> 500m) of the EPO, and offers new insights into the inter-basin variability in Zn biogeochemical cycling in the Pacific Ocean.
How to cite: Singh, N. D., Achterberg, E. P., Chen, X.-G., Gosnell, K. J., Steiner, Z., O'Sullivan, E. M., Guo, Y., Jasinski, D., Mutzberg, A., and Steffens, T.: Biogeochemical controls on dissolved zinc cycling in the Equatorial Pacific Ocean, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14618, https://doi.org/10.5194/egusphere-egu25-14618, 2025.
We present data on bioactive trace metal concentrations of suspended particulate matter (SPM) samples from the Exclusive Economic Zone (EEZ) of Qatar as part of a broader study examining the distributions of particulate bioactive metals, biogenic and lithogenic influences, and biogeochemical controls on particulate trace metal concentrations in the Arabian Gulf. The influence of dust deposition and hydrography was also investigated as factors controlling on bioactive metal concentrations. In this study, we analyzed the composition of water column SPM (> 1 µm) along a transect across the Gulf during two seasonal periods: late spring (May) and late summer (September) 2019. Eight bioactive trace metals (Fe, V, Mn, Zn, Co, Cu, Ni and Ba) were measured in SPM using ICP-MS. Our results show that Fe and Zn are enriched in SPM, likely due to aerosol depositions, while Mn, Ni, Cu, Co and Ba exhibited trends corresponding to hydrographic parameters such as density. Fe, Mn, Co, Ba demonstrated negative correlations with oxygen, explaining their depletion at depth and near sediment layer.
How to cite: Yigiterhan, O., Al-Thani, J. A., Tutsak, E., Al-Maslamani, I. A., Al-Ansari, E. M. A. S., and Soliman, Y.: Bioactive Particulate Trace Metal Distributions and their Biogeochemical Controls in the Central Arabian Gulf, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15043, https://doi.org/10.5194/egusphere-egu25-15043, 2025.
Suspended particulate organic matter (SPOM) is an essential component of marine environments and plays an integral role in biogeochemical cycles of carbon and nitrogen. Marginal seas, such as the Arabian Gulf (AG), experience pronounced extreme climatic and environmental conditions including extreme temperature, high salinity and oligotrophy/eutrophication which largely affect the dynamics of SPOM. In this study, we quantified particulate organic carbon (POC), particulate nitrogen (PN) and the stable isotopic ratio composition (d13C & d15N) of SPOM in samples collected during summer 2019 and winter 2020 from the Central AG. SPOM exhibited significant variation with seasons, depth and distance from shore (p < 0.05). POC and PN averaged 14.8 mM and 1.6 mM in summer, and 8.4 mM and 0.9 mM in winter, while the C:NSPOM averaged 9.5 during summer and 10.3 in winter. The concentrations of POC, PN were higher in coastal regions and in surface waters at offshore regions in summer, while they were predominantly low overall in winter. The d13CPOC was not significantly different between summer (-18.6 ‰) and winter (-18.7‰) and implied mixed sources including marine allochthonous and some contribution from terrestrial organic matter. The ratios of d15N (average d15N= 1.7 ‰ in summer and 2.0 ‰ in winter). implied that nitrogen fixation and regenerated nitrogen are the main sources in the waters of the Gulf. Principal component analysis showed that POC, PN were strongly correlated with Chl-a, while the d13C and d15N correlated strongly with salinity in the summer. PCA showed that the d15N, Chl-a, NH4, NO3 ,PO4, and PN were negatively correlated with nutrients (NO3, NH4) and Chl-a during winter. This research highlights the first investigation into particulate organic carbon and nitrogen in the Arabian Gulf and utilization of stable isotopes and elemental ratios to identify the sources and characteristics of organic carbon and nitrogen and their cycling under the extreme conditions of the Gulf.
How to cite: Al-Thani, J., Al-Ansari, E., Al-Maslamani, I., Yigiterhan, O., and Soliman, Y.: Sources and Dynamics of Suspended Particulate Organic Matter in the Central Arabian Gulf assessed using C and N stable isotope ratios, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16894, https://doi.org/10.5194/egusphere-egu25-16894, 2025.
River discharge of freshwater and nutrients regulates coastal ecosystems, as it exerts a significant impact on their hydrology, biogeochemistry and productivity. Moreover, rivers act as important sources of carbon dioxide (CO2) to the atmosphere and play an important role in the estuarine carbonate system.
Hydrology, biogeochemistry and productivity of the Gulf of Trieste (GoT), a shallow semi-enclosed basin of the northernmost part of the Mediterranean Sea, are mainly influenced by rivers, which represent the major allochthonous source of freshwater, total alkalinity (TA) and nutrients in the area. The Isonzo River is the main freshwater input into the GoT. It generally shows significant seasonal variations in discharge, with two main flooding periods related to snowmelt and rainfall, developing a turbidity plume strongly influenced by wind. The second freshwater source to the GoT is the Timavo River, which flows underground for about 38 km before re-emerging in proximity of its mouth. The Timavo has particularly complex hydrological characteristics related to its karstic nature, as the flow at the mouth is also influenced by underground circulation within the karst aquifer, moreover several minor springs are scattered along the coastline. Despite the relevance of the input of these rivers to the GoT, data on discharges of TA, dissolved inorganic carbon (DIC) and nutrients are scarce and fragmented. The aim of this study is to fill these knowledge gaps by providing a monthly biogeochemical characterisation of Isonzo and Timavo in terms of nutrients and carbonate system parameters, to shed light on their dynamics at the end of the catchment and estimate the input of nutrients, alkalinity and DIC into the marine system. Here we present the data from monthly sampling carried out during a dry (2022) and a rainy (2023) year at the mouth of Isonzo and Timavo rivers. Considering the karstic nature of Timavo, samples were also collected at one of its underwater springs.
The average annual discharge of AT, DIC and nutrients under different hydrological conditions (2022 vs. 2023) highlighted that riverine nutrients and inorganic carbon load is highly related to the runoff which strongly varies on interannual scale. Moreover, we observed that the Timavo waters generally had lower pH and higher DIC and TA values than Isonzo, likely as a consequence of the different catchment basins and the nature of the rivers’ course (hypogeous vs. surface). The implementation of this study, which is still ongoing, will continue over the next two years. The results will be also useful to assess the real influence of the numerous coastal and underwater springs of the Timavo River, which are often underestimated or neglected, on this coastal ecosystem. As river discharge dynamics are one of the main drivers influencing the biogeochemistry of marine ecosystem, our results will provide a basis for assessing the impact of rivers on the GoT, and support future studies on oligotrophication and acidification.
How to cite: Relitti, F., Bazzaro, M., Covelli, S., Douss, N., Giani, M., Krajnc, B., Kralj, M., Laudicella, V. A., Ogrinc, N., Pavoni, E., Retelletti Brogi, S., Toffanin, L., and De Vittor, C.: Monthly riverine load of inorganic nutrients and carbon into the Gulf of Trieste (north-eastern Mediterranean Sea): insights from flood and drought periods, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19004, https://doi.org/10.5194/egusphere-egu25-19004, 2025.
Ocean liming is a promising marine carbon dioxide removal (mCDR) method with substantial potential for carbon sequestration. This technique involves dispersing CO₂-reactive alkaline minerals onto the ocean surface, increasing the flux of atmospheric CO₂ into the ocean and counteracting ocean acidification by elevating pH levels. Coralline algae of the subfamily Corallinophycidae are vital habitat engineers found in ecosystems ranging from tropical to polar regions. These globally distributed algae inhabit environments extending from intertidal zones to the lower limits of the photic zone. Despite their complex role in the global carbon cycle, the mechanisms governing their cell wall calcification remain poorly understood. Additionally, the potential impacts of ocean liming on these organisms require further investigation.
Mesocosm experiments were conducted in Vigo, Spain, and Crete, Greece, using Ca(OH)₂ treatment at two different concentrations (Low and High) at each site, with three replicates per treatment. The study examined genus-specific factors influencing magnesium (Mg) incorporation into the calcified cell walls of coralline algae as a proxy for growth and active calcification. The tested specimens included three genetically identified species: Phymatolithon calcareum and P. lusitanicum from Vigo, and Lithothamnion corallioides from Crete. SEM-EDS, Raman spectroscopy and XRD techniques were integratedto investigate in detail our coralline thalli mineralogy. The results revealed significant variations in Mg and other ion distributions between primary (PCW) and secondary (SCW) cell walls, emphasizing the role of microanatomical features over the broader temperature-driven trends in Mg concentrations within coralline thalli. Specifically, Phymatolithon species exhibited higher Mg content in SCWs compared to PCWs, whereas L. corallioides showed equal or lower Mg concentrations in SCWs.
High Ca(OH)₂ treatments caused a decrease in Mg content in shallow-water Phymatolithon specimens from Vigo, suggesting inhibited growth due to reduced water circulation and smothering by aragonite precipitation within the mesocosms. In contrast, deep-water L. corallioides in Crete displayed no significant changes in Mg levels under either Low or High treatments. These findings suggest a non-significant impact of ocean liming on the tested coralline species, and underscore the intricate nature and variate response of calcification in coralline algae. The results highlight the importance of microanatomical features, environmental conditions, and species-specific traits in determining the impact of such mCDR interventions on marine calcifiers.
How to cite: Borromeo, L., Basso, D., Varliero, S., Panizzuti, F., Galimberti, L., Gentile, P., González, J., Magiopoulos, I., Romano, F., Pitta, P., Macchi, P., and Azzellino, A.: Genus-specific and microanatomical controls on element incorporation in coralline calcification revealed by Ocean Alkalinity Enhancement experiments, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19226, https://doi.org/10.5194/egusphere-egu25-19226, 2025.
Due to intensive human activity, especially in the second half of the 20th century, a significant amount of chemical elements has been extracted from the Earth's natural deposits. Some of these elements have no beneficial role in living organisms and are toxic. Ideally, such toxic elements would not be present in our natural environment. However, this is not the case, nor will it ever be, as these elements naturally occur on our planet and have been further introduced into the ecosystem through industrial use. There are also chemical elements that are essential or even necessary for the proper development of animal and plant organisms. However, at elevated concentrations, these elements become highly toxic. Thanks to regulations introduced in many European countries at the turn of the 20th and 21st centuries, emissions of toxic elements from anthropogenic sources have significantly decreased. Nevertheless, their concentrations in the natural environment have not declined proportionally. It is therefore crucial to understand their pathways and circulation in the environment, particularly in marine ecosystems, as fish and seafood often serve as key sources of these elements for humans. While numerous scientific studies have examined the concentrations of toxic elements (e.g., Hg, Pb, Cd, Zn, Cu, As, Se) in sediments and commercially significant fish species, there is a notable lack of data on their transfer through individual links in the trophic network, especially among small, non-commercial fish. Moreover, there is limited information in the scientific literature regarding the concentrations of technology-critical elements, some of which are or could potentially be highly toxic to living organisms. The purpose of this research is to investigate the role of small, non-commercial fish in the transfer of toxic elements within the marine trophic network, using the southern Baltic Sea as a case study. The Puck Lagoon has been selected as the research area.
How to cite: Malec, R., Bełdowska, M., Sapota, M., Dziubińska, A., Wilman, B., Woźniczka, A., and Kornijów, R.: The role of non-commercial fish in incorporating toxic elements into the trophic web in the lagoons of the southern Baltic Sea, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20354, https://doi.org/10.5194/egusphere-egu25-20354, 2025.
Iron (Fe) is an essential micronutrient for marine productivity and dissolved Fe can be found as Fe(III) and Fe(II), being the first one the most abundant and the second one the most bioavailable form. Natural organic ligands play a fundamental role in the Fe speciation and redox chemistry. However, there is a lack of information about the impact of individual organic compounds on the Fe(III) reduction to Fe(II) in seawater. Among the amount of organic ligands, the amino acid Tryptophan (Trp) is linked with marine microorganisms, contributing to the ligand pool in aquatic environments. In this current investigation, the Fe(II) production from Fe(III) reduction by Trp has been studied under different conditions of Trp concentration (50 – 500 nM), pH (7.0 – 8.0) and temperature (10 – 25 ºC) in seawater and NaCl solutions (0.7 M NaCl + 2 mM NaHCO3). According to the results, the reaction was pH-dependent, not occurring above pH 7.8 in seawater. The Fe(III) reduction is also dependent of Trp levels, with 6.49 % and 18.10 % reduction observed after 60 minutes at Trp concentration of 50 nM and 500 nM, respectively, at pH 7.8. A relationship between Trp levels and the reduction capacity at different pH values (7.0 and 7.8) was established, showing a more significant effect at lower pH, suggesting that Trp plays a more crucial role in Fe(III) reduction in lower pH environments. This effect can be understood by the competition with major ions in seawater. The impact of these ions (SO₄²⁻, K⁺, F⁻, Ca²⁺, Mg²⁺, and Sr²⁺) showed lower pseudo first-order Fe(III) reduction rate constant (k´Fe(III)-red in s⁻¹) values than the reference solution (0.7 M NaCl + 2 mM NaHCO3).
On the other hand, the Fe(III) reduction by Trp was a temperature-dependent process, leading to higher k´Fe(III)-red values at higher temperatures (25ºC) with respect to lower temperatures (10ºC). The k´Fe(III)-red increased from 0.62∙10-5 to 1.99∙10-5 s-1 when temperatures changed from 10 ºC to 25 ºC, respectively, at pH 7.8. The Energies of Activation (Ea) were 77.80 kJ mol-1 and 53.02 kJ mol-1 at pH 7.0 and 7.8, respectively.
According to the current results, in a situation of global warming and ocean acidification, changes in the physico-chemical conditions enhance the Fe(III) reduction by organic ligands, such as amino acids, and influence the Fe marine biogeochemical cycles promoting the formation of bioavailable Fe(II) in seawater.
How to cite: Suárez-Betancor, L., González, A. G., González-Dávila, M., and Santana-Casiano, J. M.: Fe(II) regeneration by Tryptophan in seawater at nanomolar levels, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4064, https://doi.org/10.5194/egusphere-egu25-4064, 2025.
The eruptive process that took place in La Palma, Canary Islands, Spain, in September 2021 was the longest in the island records. The eruption lasted 85 days, had a major social and environmental impact and gave rise to the Tajogaite volcano. During this time, the lava formed two lava deltas on the west coast of the island (Tazacorte). Lava entered the sea during four different time periods. Previous research by González-Santana et al., (2024) presented the evolution of the iron size fractionation during the Tajogaite eruption, demonstrating a long term fertilization effect. In this work, we expand the research with Fe(II) oxidation kinetics studies after the post-eruptive phase to study the regeneration and the evolution of the zone. For this study, 7 coastal cruises were carried out between January 2023 and December 2024 in the proximities of the formed deltas. During each cruise, seawater samples were collected at 10 surface stations.
Iron is an essential trace metal in the development of life. Its speciation plays a key role in its bioavailability. Monitoring the oxidation of iron(II) in this environment is an opportunity to improve our understanding of its behaviour in coastal and volcanic environments. These environments are characterized by high organic compounds concentrations and variability. Iron can be complexed by organic ligands that affect its speciation. Understanding how iron impacts biogeochemical cycles in marine ecosystems is crucial. These behaviours are still poorly constrained, particularly in relation to factors like organic matter composition, and seasonally influenced variables in surface waters.
The experimental methodology is based on the Direct Flow Injection Analysis by Chemiluminescence (FIA-CL) method (Santana-González et al., 2018). Analysis at fixed temperature, pH and oxygen saturation conditions (T=15ºC, pH=8 and Sat[O2]=100%) were carried out to remove the effects of these factors on the iron speciation. Results show a great variability between sampling points, with sections affected by groundwater discharge. Analysed oxidation rate constants (k ') were between 0.021 and 0.300 min-1 (t1/2 between 2.3 and 33.4 min, inversely), while theoretical calculations were of 0.048 min-1 (t1/2=14.6 min). Colloidal sized particles are thought to slow down oxidation rates. The colloidal-sized effect was demonstrated by performing the analyses using samples collected with different pore-sized filters (unfiltered, 0.2μm and 0.02μm), at different temperatures (T= 5, 10, 15 and 20ºC) and at constant pH=8, which allowed for the calculation of the activation energy (Ea) of each sample, around 120 kJ·mol-1. Analysis at different pH conditions (pH=7.5, 7.8 and 8) and at a fixed temperature (T=15ºC) were performed to characterise pH dependent processes occurring in the colloidal-sized fraction.
Acknowledgments: This work was funded by the FeRIA project (PID2021-123997NB-I00) from the Ministerio de Ciencia e Innovación (Spain). A. Bullón-Téllez participation was funded by the PhD grant (ULPGC2023-2-01).
References:
González-Santana et al., (2024). Hot spot volcano emissions as a source of natural iron fertilization in the ocean. Science of The Total Environment, 957, 177638. https://doi.org/10.1016/j.scitotenv.2024.177638
Santana-González et al., (2018). Fe(II) oxidation kinetics in the North Atlantic along the 59.5° N during 2016. Marine Chemistry, 203, 64-77. https://doi.org/10.1016/j.marchem.2018.05.002
How to cite: Bullón-Téllez, A., Santana-Casiano, J. M., González-Santana, M., González, A. G., and González-Santana, D.: Two years of monitoring the Fe(II) oxidation rate constants in coastal seawater affected by the La Palma eruption, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6045, https://doi.org/10.5194/egusphere-egu25-6045, 2025.
Plastics are an omnipresent contaminant, with the marine environment serving as their largest sink. Their unique properties, including low density, surface charges, and remarkable resilience introduce novel conditions to aquatic ecosystems. The biofilm forming on plastic surfaces - the so-called Plastisphere, is an emerging ecological niche and has been found to harbor a variety of microorganisms, minerals, metals and organic matter. The biotic and abiotic properties of this complex eco-corona facilitate biogeochemical interactions and have wide implications for ecosystem and human health.
Plastisphere composition can drive or hinder biological uptake and gene transfer, alter plastic transport, influence element cycling and promote polymere degradation or prolong plastic stability in the environment. Abiotic minerals such as salts, carbonates, and silicates, along with biominerals and metal deposits, form or attach to plastic surfaces, functioning as attachment and nucleation sites and catalysts for further reactions. Metals such as iron, manganese, and copper further enhance surface reactivity and microbial metabolic activity. The Plastisphere can therefore foster environments conducive to horizontal gene transfer, potentially amplifying the spread of antibiotic resistance genes and enhancing the ability of pathogens to thrive. These interactions modulate marine geochemistry, impacting processes such as silica and carbon cycling, metal fluxes, and microbial metabolism.
Here, we characterize mineral-plastic interactions across scales, employing bioimaging, geochemical and polymer analysis, outlining their significance for biogeochemical cycling of plastics, plastic degradation and environmental and human health. Furthermore we discuss the potential impacts of micro- and nanoplastics on biomineralization processes and the implications within the marine silica and carbon cycles.
How to cite: Schmidt, D., Peydaei, A., Dodhia, M., Neu, T., Krarup Svenninggaard Sand, K., and Posth, N. R. E.: Understanding the role of (bio)minerals and metals on marine plastic biogeochemistry and degradation processes, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19721, https://doi.org/10.5194/egusphere-egu25-19721, 2025.
