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 (DOM_H), 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 DOM_H (r² > 0.72). These results suggest that all these trace elements are tightly combined with DOM_H, 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 (A_T) and total inorganic carbon (C_T) 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.

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 (E_a) 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 (t_1/2 between 2.3 and 33.4 min, inversely), while theoretical calculations were of 0.048 min^-1 (t_1/2=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.