Marine Chemistry最新文献

{"title":"In situ measurement of trace sulfide concentrations in marine coastal waters using diffusive gradient in thin film passive samplers","authors":"Kevin Diaz ,&nbsp;David Point ,&nbsp;Wilson Carhuapoma ,&nbsp;Astrid Avellan ,&nbsp;Maricarmen Igarza ,&nbsp;Jesús Ledesma ,&nbsp;Fanny Rioual ,&nbsp;Michelle Graco","doi":"10.1016/j.marchem.2025.104521","DOIUrl":"10.1016/j.marchem.2025.104521","url":null,"abstract":"<div><div>The diffusive gradient in thin film technique (DGT) represents an <em>in situ</em> passive sampling method designed to preconcentrate various compounds, including sulfides, for detection at low concentrations. While DGT applications for sulfides have been studied in freshwater, this research extends its use to marine environments. A detailed methodology is presented for synthesizing, assembling, calibrating, and field-deploying DGT samplers to measure sulfides in the low micromolar range in marine waters. The in-house DGT samplers developed in this study demonstrated improved performance, with more homogeneous binding gels and smaller silver iodide particles (0.51 ± 0.34 μm) compared to commercial alternatives. Grayscale imaging enabled accurate quantification of sulfide accumulation in the gels, confirming the method's reliability for detecting trace-level sulfides in marine environments. Comparative analysis showed in-house and commercial samplers performed similarly in estimating sulfide concentrations. Field deployments along the Peruvian coast revealed significant vertical and spatial sulfide gradients. In the Callao coastal area (12°S) (July–August 2022), concentrations ranged from 0.03 to 0.45 μM across a 35 m depth profile. In Paracas bay (13.8°S) (March–April 2023), a shallower coastal station, concentrations ranged from 1.17 to 6.46 μM, reflecting increased benthic production. These results highlight the utility of DGT samplers as cost-effective tools for biogeochemical monitoring, enabling studies of the ocean sulfur cycle. The findings emphasize the growing application of DGTs in marine and coastal water column research.</div></div>","PeriodicalId":18219,"journal":{"name":"Marine Chemistry","volume":"271 ","pages":"Article 104521"},"PeriodicalIF":3.0,"publicationDate":"2025-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143917536","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The role of tidal creeks in carbon processing and export to the freshwater tidal zone at the land-estuary boundary of tropical mangrove estuaries","authors":"Claris N. Sunjo ,&nbsp;Eliot A. Atekwana ,&nbsp;Hendratta N. Ali ,&nbsp;Henry M. Agbogun ,&nbsp;Isaac K. Njilah","doi":"10.1016/j.marchem.2025.104520","DOIUrl":"10.1016/j.marchem.2025.104520","url":null,"abstract":"<div><div>Tidal creeks are conduits for tide-driven processing and exchange of water and dissolved inorganic carbon (DIC) between the open estuary and mangrove forests. Yet, the sources of DIC, and the role of tidal creeks in the cycling of DIC and its transport to the open water of mangrove estuaries is poorly understood. This study was conducted in a tidal creek in the freshwater tidal zone at the land-estuary boundary of a tropical mangrove estuary. We made 177 measurements of salinity and 80 measurements of geogenic solutes (silica, Ca, Mg), DIC components (partial pressure of CO₂ (pCO₂), alkalinity and total DIC) and stable isotopes of water (δ¹⁸O and δD) and DIC (δ¹³C_DIC). We aimed to determine the sources and the timing of water input into the tidal creek, how the different water sources control input of DIC, and how DIC is cycled through semidiurnal mixed tides and over a diel cycle. The salinity-δ¹⁸O relationship indicates two sources of water, while the relationships for salinity-DO, salinity-solute, and salinity-DIC implicated submarine groundwater discharge (SGD) as the source providing the DIC processed and transported to the open estuary. Normalized water level vs. salinity reveals that SGD sourced DIC dominates the water column during tidal ebbing and halfway through tidal flooding. In contrast, freshwater from the open estuary mainly dilutes the solutes and DIC from halfway during tidal flooding to peak high tide. The photocycle, heterotrophic and autotrophic processes are unable to explain the more than 5 times greater than atmospheric pCO₂ recorded during the daytime and at low tide. These findings demonstrate that SGD is a significant DIC source in tidal creeks at the land-estuary transition zone which indicate the important role of SGD in the cycling of carbon in the freshwater tidal zones of mangrove estuaries.</div></div>","PeriodicalId":18219,"journal":{"name":"Marine Chemistry","volume":"270 ","pages":"Article 104520"},"PeriodicalIF":3.0,"publicationDate":"2025-04-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143863748","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Drivers of dissolved organic matter transport in the Guadalquivir estuary (SW, Spain)","authors":"J. Sánchez-Rodríguez ,&nbsp;V. Amaral ,&nbsp;S. Sirviente ,&nbsp;A. Sierra ,&nbsp;M. Bruno ,&nbsp;J. Forja ,&nbsp;T. Ortega","doi":"10.1016/j.marchem.2025.104518","DOIUrl":"10.1016/j.marchem.2025.104518","url":null,"abstract":"<div><div>The Guadalquivir Estuary is the largest in the southwest Iberian Peninsula and is influenced by various anthropic activities, such as damming and rice farming, which regulate river flow and provide lateral inputs to the system. Despite its role as a major source of freshwater and dissolved organic matter (DOM) to the Gulf of Cadiz, there has been limited research on the seasonal distribution of DOM and dissolved organic carbon (DOC) export. This study chemically characterizes DOM using its optical properties along the salinity gradient and during tidal sampling cycles conducted from 2018 to 2022, improving the understanding of DOM dynamics in the estuary. Results show that the DOM in the estuary is predominantly allochthonous, with humic-like components accounting for 85.8 ± 5.8 % of fluorescent DOM (FDOM), while protein-like components, associated with autochthonous processes, account for only 14.2 ± 5.9 %. Mixing and biogeochemical reactivity are the main processes controlling DOM distribution, with mixing being the most significant. Lateral inputs from marshes and rice crops play an important role, particularly in the intermediate zone. Autochthonous DOM is more prominent during the dry season, especially in Summer. The estuary exports 5.8 g C m⁻² yr⁻¹ of DOC, along with substantial amounts of humic-like and protein-like FDOM, especially during extreme rainfall events that increase river flow, and therefore, discharge. DOC transport from the Guadalquivir Estuary is low if we consider the dimensions of its watershed area, highlighting the impact of damming on DOC transport.</div></div>","PeriodicalId":18219,"journal":{"name":"Marine Chemistry","volume":"270 ","pages":"Article 104518"},"PeriodicalIF":3.0,"publicationDate":"2025-04-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143828860","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Dynamics of dissolved trace metals, rare earth elements and Pb isotopes across the eastern margins of the Mediterranean Sea","authors":"Tal Benaltabet ,&nbsp;Gil Lapid ,&nbsp;Ronen Alkalay ,&nbsp;Yishai Weinstein ,&nbsp;Tim Steffens ,&nbsp;Eric P. Achterberg ,&nbsp;Adi Torfstein","doi":"10.1016/j.marchem.2025.104519","DOIUrl":"10.1016/j.marchem.2025.104519","url":null,"abstract":"<div><div>Continental margins support marine primary productivity by transferring nutrients and micro-nutrients (trace metals) from the coast to the oceans. Yet, the mechanisms governing the delivery of trace metals across the land-sea continuum, and how they vary temporally, are still poorly constrained. Here, we report high spatial resolution depth profiles of dissolved trace metals (Al, Mn, Fe, Co, Ni, Cu, Zn, Cd, and Pb), rare earth elements (REEs), nutrients (PO₄, TON, and SiOH₄) and Pb isotopes from two transect cruises in the oligotrophic eastern Mediterranean Sea.</div><div>Varying anthropogenic inputs resulted in inter-cruise variations in Zn and Pb concentrations and Pb isotopes. In contrast, low temporal variability was registered for PO₄, SiOH₄, Cu, and Co. The isotopic composition of Pb in the eastern Mediterranean Sea (²⁰⁶Pb/²⁰⁷Pb = 1.161–1.173 and ²⁰⁸Pb/²⁰⁶Pb = 2.085–2.101) is controlled by advected Atlantic surface water and anthropogenic inputs delivered via continental runoff (terrestrial) or atmospheric shuttles. The deep-water inventory of Pb is partially controlled by historical anthropogenic sources. An enrichment in Zn and Cd (81 and 17 %, respectively) and a 50 % depletion in Pb relative to open-waters was observed in Intermediate Levantine Waters, in tandem with terrestrial Pb isotopic signatures, light REE depletion (shale-normalized Nd/Yb &lt; 0.22) and a strong Ce anomaly (Ce/Ce* &lt; 0.20). These are driven by intermediate nepheloid layers from the margins, which act as both a source and a sink for trace metals through release and scavenging, evident 300–500 km away from the shore. This study highlights the dynamic role of continental margins in modulating terrestrial and anthropogenic inputs to the oceans.</div></div>","PeriodicalId":18219,"journal":{"name":"Marine Chemistry","volume":"270 ","pages":"Article 104519"},"PeriodicalIF":3.0,"publicationDate":"2025-04-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143851335","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Comparative analysis of HPLC methods for measuring phytoplankton pigments in the Western Mediterranean Sea: A contribution to the satellite Cal/Val activities","authors":"Elisabetta Canuti ,&nbsp;F. Artuso ,&nbsp;A. Di Cicco","doi":"10.1016/j.marchem.2025.104516","DOIUrl":"10.1016/j.marchem.2025.104516","url":null,"abstract":"<div><div>High-performance liquid chromatography (HPLC) is the gold standard for calibrating and validating satellite-derived Chlorophyll <em>a</em> (TChl <em>a</em>) concentration. Other phytoplankton pigments quantified by HPLC can provide taxonomic and functional insights into the composition and abundance of phytoplankton communities. This study assesses the uncertainties associated with HPLC measurements by comparing results from two analytical laboratories, one from the Joint Research Centre (JRC) and the other from the Italian National Agency for New Technologies, Energy, and Sustainable Economic Development (ENEA). These laboratories employed different analytical methods to examine natural water samples from the oligotrophic waters of the Western Mediterranean Sea, collected during the Sentinel 2017 campaign. Chlorophyll <em>a</em> concentrations in these samples ranged from 0.048 to 0.653 mg m⁻³ in the JRC dataset. The present study evaluated phytoplankton community composition using multiple techniques, including chemotaxonomic methods based on the analysis of biomarker pigments and CHEMTAX method (<span><span>Mackey et al., 1996</span></span>), alongside unsupervised machine learning approaches such as Hierarchical Clustering Analysis (HCA), Principal Components Analysis (PCA), and Network-Community Analysis (NCA). Significant differences in pigment quantification were observed between the two laboratories, particularly for chlorophylls <em>c</em> (85.5 % difference) and peridinin (56.6 % difference). However, differences in total TChl <em>a</em> quantification were within 6.1 %, indicating that both laboratories are capable of supporting satellite data validation and algorithm development (Hooker et al., 2000). The results highlighted both limitations and advantages of this comparative approach, related to different methods for estimating uncertainties, providing insights into the consistency and reliability of HPLC measurements in a challenging low concentration matrix.</div></div>","PeriodicalId":18219,"journal":{"name":"Marine Chemistry","volume":"270 ","pages":"Article 104516"},"PeriodicalIF":3.0,"publicationDate":"2025-04-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143851334","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Variation in chemical composition of dissolved organic matter during the winter to spring transition in the northern Barents Sea","authors":"Maria G. Digernes ,&nbsp;Jeffrey A. Hawkes ,&nbsp;Oliver Müller ,&nbsp;Stephen G. Kohler ,&nbsp;Murat V. Ardelan","doi":"10.1016/j.marchem.2025.104517","DOIUrl":"10.1016/j.marchem.2025.104517","url":null,"abstract":"<div><div>Molecular characterization of dissolved organic matter (DOM) from the Arctic Ocean is scarce, especially during the winter, which is a crucial period for water mass mixing and carbon cycling. The northern Barents Sea extending into the Arctic Ocean is experiencing global warming at a rate 5–7 times faster than the global average, leading to drastic chemical, physical and ecosystem changes. We sampled a transect along this region during early winter (December), late winter (March) and spring (May) and analyzed seawater samples using high-resolution mass spectrometry. Our results show significant changes in DOM composition driven by biological seasonality and water circulation such as lateral and vertical water transport, whereas water masses did not exhibit significant correlations with DOM composition. Our mass spectrometry-based results indicate that ionizable DOM compounds in early winter contained a greater proportion of unsaturated compounds relative to late winter and spring, as shown by weighted average hydrogen to carbon atomic ratios (H/C_wa) (−0.029, Mann-Whitney <em>U</em> test, <em>p</em> &lt; 0.001). Higher DOM lability in late winter was associated with higher nitrogen containing formulas which could be a result of DOM products from viral processes. Deep waters in the Arctic Basin and on the Barents Sea shelf break show greater lability in spring suggesting an influence of water circulation from the biologically active shelf regions. In early winter, higher weighted average aromaticity index (AI_mod), double-bond equivalents (DBE) and relative intensities of CHO formulas over heteroatom (N, S)-containing formulas were observed, thus supporting the presence of DOM with higher recalcitrance. Early winter also exhibited a significantly higher number of terrigenous peaks (t-Peaks) (<em>p</em> &lt; 0.001), suggesting seasonal removal of these riverine markers. This DOC may be transported to deeper ocean layers during winter water mixing. Our findings bridge the gap in winter DOM molecular characterization, which allows for future assessments of potential changes in the Arctic DOM reactivity.</div></div>","PeriodicalId":18219,"journal":{"name":"Marine Chemistry","volume":"270 ","pages":"Article 104517"},"PeriodicalIF":3.0,"publicationDate":"2025-04-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143834757","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Benthic biogeochemical processes and fluxes in the hypoxic and acidified northern Gulf of Mexico (nGoM), part I: Carbonate dissolution from in situ microprofiles","authors":"Eva Ferreira ,&nbsp;Bruno Lansard ,&nbsp;Gaël Monvoisin ,&nbsp;Evan Magette ,&nbsp;Anthony Boever ,&nbsp;Hanna Bridgham ,&nbsp;Bruno Bombled ,&nbsp;Jordon Scott Beckler ,&nbsp;Martial Taillefert ,&nbsp;Christophe Rabouille","doi":"10.1016/j.marchem.2025.104515","DOIUrl":"10.1016/j.marchem.2025.104515","url":null,"abstract":"<div><div>The northern Gulf of Mexico (nGoM) experiences seasonal coastal hypoxia due to nutrient enrichment from the Mississippi-Atchafalaya River basin, leading to one of the world's largest hypoxic zones. In these shallow zones, benthic processes play an essential role in driving/maintaining deoxygenation and acidification of bottom waters. In this regard, this paper investigates carbonate dissolution processes in surface sediment of the nGoM during hypoxic conditions in summer 2022, as the main acidification feedback mechanism, with a specific focus on the effects of bottom water acidification. A strong linear relationship is observed between oxygen and pH, with a pH difference of 0.37 between the most oxygenated and the nearly anoxic station, reaching a value of 7.63. Using high-resolution techniques, this study combines pH and O₂ microprofiling (200 μm) with benthic measurements of carbonate system parameters (pH, DIC, TA, Ca²⁺) to assess carbonate dissolution at millimeter-scale resolution. The pH microprofiles reveal a significant decrease in the first 3 cm, with pore water pH reaching values of 6.90 at the most hypoxic station. Despite undersaturation with respect to aragonite and occasionally calcite, Ca²⁺ profiles indicate no significant carbonate dissolution, suggesting stability of calcium carbonate in these sediments during the summer. This lack of dissolution, likely influenced by the absence of aragonite, and possible inhibitory effects of dissolved organic carbon and orthophosphate, points to a limited buffering capacity in these sediments. These insights are essential for refining models predicting coastal acidification and hypoxia responses to environmental stressors in the nGoM and similar eutrophic systems.</div></div>","PeriodicalId":18219,"journal":{"name":"Marine Chemistry","volume":"270 ","pages":"Article 104515"},"PeriodicalIF":3.0,"publicationDate":"2025-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143808676","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Samarium (Sm3+) and copper (Cu2+) complexation property with dissolved organic matter","authors":"Nabila Abbad ,&nbsp;Roland Redon ,&nbsp;Benjamin Oursel ,&nbsp;Christophe Lepoupon ,&nbsp;Gaël Durrieu ,&nbsp;Houssam Hajjoul ,&nbsp;Stéphane Mounier","doi":"10.1016/j.marchem.2025.104514","DOIUrl":"10.1016/j.marchem.2025.104514","url":null,"abstract":"<div><div>This study investigates the speciation of Samarium (III) in the presence of natural organic matter, standard humic and fulvic acids from the Suwannee River. Fluorescence quenching and Time-Resolved Laser Fluorescence Spectroscopy (TRLFS) were employed to analyze various samples, using logarithmic additions of Sm³⁺ and Cu²⁺. The 1 L:1 M and 1 L:1 M:H models were applied to account for pH effects, yielding pH-independent complexant parameters K_Sm and K_Cu as well as <span><math><msub><mi>C</mi><msub><mi>L</mi><mi>Sm</mi></msub></msub><mspace></mspace><mi>and</mi><mspace></mspace><msub><mi>C</mi><msub><mi>L</mi><mi>Cu</mi></msub></msub></math></span>that revealed specific binding sites. A notably higher affinity was observed for humic acids with Sm³⁺ compared to Cu²⁺. The logarithms of the complexation constant for the Sm³⁺ were 5.4, 5.2 and 4.7 for SRNOM, SRHA and SRFA, respectively. Fluorescence quenching analyses identified two distinct fluorescent components related to dissolved organic matter, showing different affinities for Sm³⁺ and Cu²⁺ that varied with pH. Humic acids exhibited the highest complexation capacity for Sm³⁺, attributed to their structural properties, with complexation capacities of 4.77 10⁻⁴, 0.82 and 4.46 10⁻³ mol of Sm per g of SRNOM, SRHA and SRFA, respectively. Temporal deconvolution of fluorescence responses revealed a tri-exponential decay with three lifetimes (τ₁, τ₂ and τ₃) remaining relatively constant during Sm³⁺ or Cu²⁺ titrations, confirming that the fluorescence quenching is primarily a static mechanism. Speciation modeling demonstrated a shift from humic-associated complexes in freshwater to carbonate complexes in seawater as salinity increases. These findings highlight the importance of accurately characterizing DOM complexation properties to understand the environmental behavior of trace metals, particularly in response to salinity and carbon concentration gradients in estuarine systems.</div></div>","PeriodicalId":18219,"journal":{"name":"Marine Chemistry","volume":"270 ","pages":"Article 104514"},"PeriodicalIF":3.0,"publicationDate":"2025-03-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143738842","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Influence of seasonal changes in organic matter pool on copper bioavailability in a stratified estuary","authors":"Saša Marcinek,&nbsp;Ana-Marija Cindrić,&nbsp;Dario Omanović","doi":"10.1016/j.marchem.2025.104513","DOIUrl":"10.1016/j.marchem.2025.104513","url":null,"abstract":"<div><div>This work presents a detailed analysis of seasonal changes in copper (Cu) organic speciation and its bioavailability in the Krka River estuary, a highly stratified microtidal system characterized by low riverine input of dissolved organic matter (DOM) and trace metals but experiencing heightened anthropogenic Cu pressures during summer as a result of increased touristic activities. Total dissolved Cu concentrations ranged from 3.4 nmol L⁻¹ in winter up to 25.8 nmol L⁻¹ in summer, with substantial summer increase limited to water layer above the halocline. Two distinct ligand classes were identified in all samples, with conditional stability constants of log<em>K</em>’₁ = 13.2 ± 0.5 and log<em>K</em>’₂ = 11.2 ± 0.4. Dissolved organic carbon (DOC) and concentrations of both ligand classes were higher in summer than in winter, with strong indications of their in situ production driven by enhanced primary production and/or intensified microbial activity. In winter, despite the low DOC levels (avg 63.3 μmol L⁻¹), DOM above the halocline showed pronounced terrestrial signature with higher density of Cu-binding sites compared to DOM in summer with nearly twice as high DOC levels (avg 113.5 μmol L⁻¹). The results suggest that terrestrial humic substances (HS) dominated the ligand pool in these waters during winter (estimated 80 % of total ligand pool), possibly contributing to both ligand classes. While HS remained an important fraction of the ligand pool in the summer (estimated 30 % of total ligand pool), the terrestrial signature of DOM in this season was minimal, pointing to their production within the estuary. The summer increase in ligand concentrations above the halocline was accompanied by a reduction in their binding strengths (by approximately 0.5 log units) compared to winter, along with a decrease in DOM molecular weight, possibly influenced by solar irradiation. Seasonal anthropogenic Cu input was successfully buffered by the ambient ligand pool, keeping the concentration of free Cu-ions, its most bioavailable specie, well below documented toxicity levels for Cu (maximum of 2.54 pmol L⁻¹). The seasonal DOM variations resulted in a ∼ two-fold increase in the Cu-binding capacity in summer (33 nmol L⁻¹) compared to winter (17 nmol L⁻¹). Despite the increased buffering capacity in summer, Cu levels are approaching this safety limit, which may increase its bioavailability to a concerning level, a risk much lower in winter when Cu inputs are minimal. These results underscore the critical role of DOM in mitigating seasonal anthropogenic Cu inputs, while also highlighting the need for further investigation into the long-term resilience of estuarine systems under shifting environmental and anthropogenic pressures.</div></div>","PeriodicalId":18219,"journal":{"name":"Marine Chemistry","volume":"270 ","pages":"Article 104513"},"PeriodicalIF":3.0,"publicationDate":"2025-03-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143682117","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Diatom-driven processes lead to the assimilation of elements from silicate minerals into their frustules","authors":"Tasuku Akagi,&nbsp;Sophia Welti,&nbsp;Rei Tajiri,&nbsp;Kazuhiko Shimada","doi":"10.1016/j.marchem.2025.104512","DOIUrl":"10.1016/j.marchem.2025.104512","url":null,"abstract":"<div><div>To examine whether diatoms dissolve silicate minerals and incorporate foreign metals into their frustules, culture experiments were performed using <em>Achnanthes kuwaitensis</em> Hendey, <em>Eucampia</em> sp. and <em>Coscinodiscus wailesii</em>. These comprised two comparative experiments: (i) an analysis of diatom activities (population, transparent exopolymer particles (TEP) secretion and the Al/Si of frustules) in the presence/absence of feldspar particles, and (ii) an examination of mineral surfaces in the presence/absence of diatoms. Although the presence/absence of silicate minerals did not incur marked differences in diatom population, TEP secretion increased in the presence of silicate particles. Further, it was observed that the girdles of <em>Coscinodiscus</em> frustules showed double Si peaks and the outer layers of the girdles had significantly higher Al/Si ratios than the inner layers when feldspar particles were present. In the diatom cultures, feldspar particles largely disappeared in extended cultivation, and those still present showed rounded or fractured edges, features that were not seen in the absence of diatoms. The presence of diatoms appeared to have more influence on silicate minerals than the presence of silicate minerals on diatom activities. The C/Si ratios of the rounded feldspar grain edges in the <em>Coscinodiscus</em> cultures were significantly higher than those of stepwise edges, that we interpret to indicate that diatoms secrete TEP to dissolve silicate minerals. Two observations substantiated this hypothesis: pH decreases around diatoms, and incorporation of the mineral particles in TEP coatings.</div><div>Nevertheless, the physiological advantage for diatoms to dissolve silicate minerals remains unclear. Given the difference in TEP secretion between two different feldspar minerals, we believe that diatoms actively dissolve silicates in order to incorporate silica. We thus propose a mechanism by which diatoms dissolve silicate minerals. This may explain the inclusion of foreign elements at levels, whose relative concentrations are similar to those in terrigenous matter, in diatom frustules.</div></div>","PeriodicalId":18219,"journal":{"name":"Marine Chemistry","volume":"270 ","pages":"Article 104512"},"PeriodicalIF":3.0,"publicationDate":"2025-03-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143760083","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}