Pub Date : 2025-10-04DOI: 10.1016/j.marchem.2025.104569
Louis C. Bondurant , Megan L. Baker , Sophie Hage , Peter J. Talling , Patrick G. Hatcher
The deposition of terrigenous organic carbon (tOC) in offshore deep-marine settings has traditionally been viewed as inconsequential for organic carbon burial. However, it has been shown that deep-sea sediment flows, turbidity currents, can contribute significantly to the burial of tOC. Elemental, isotopic, and molecular data were obtained on sediment samples from three areas within and adjacent to the Congo Deep-Sea Fan. The elemental, organic geochemical, and isotopic data agree well with previous studies from the Congo Fan, which show that terrigenous organic matter from the Congo River extends seaward in the axis of the submarine canyon to abyssal depths. Using advanced solid-state 13C NMR and TMAH thermochemolysis data we verify that a significant amount of lignin is exported to the canyon (∼14 % wt. lignin) and the distal lobe (∼16 % wt. lignin) sediments. The basin plain contains no detectable lignin but does show the presence of terrigenous long-chain fatty acids having an even carbon number predominance. Following a laboratory oxidation experiment on sediments from the distal lobe for 6 d there was an organic carbon mass loss of 59.8 % and the solid-state 13C NMR spectrum shows a major reduction in peaks associated with carbohydrate-like and lignin molecules and a relative increase in aliphatic molecules. This shows that terrigenous lignin molecules can be remineralized to CO2 and/or altered to structures that no longer resemble that of lignin through oxidative degradation processes. This would have a potentially significant implication on what is traditionally viewed as autochthonous marine organic matter.
{"title":"Variations in lignin content deposited in the Congo fan and its potential for oxidative degradation","authors":"Louis C. Bondurant , Megan L. Baker , Sophie Hage , Peter J. Talling , Patrick G. Hatcher","doi":"10.1016/j.marchem.2025.104569","DOIUrl":"10.1016/j.marchem.2025.104569","url":null,"abstract":"<div><div>The deposition of terrigenous organic carbon (tOC) in offshore deep-marine settings has traditionally been viewed as inconsequential for organic carbon burial. However, it has been shown that deep-sea sediment flows, turbidity currents, can contribute significantly to the burial of tOC. Elemental, isotopic, and molecular data were obtained on sediment samples from three areas within and adjacent to the Congo Deep-Sea Fan. The elemental, organic geochemical, and isotopic data agree well with previous studies from the Congo Fan, which show that terrigenous organic matter from the Congo River extends seaward in the axis of the submarine canyon to abyssal depths. Using advanced solid-state <sup>13</sup>C NMR and TMAH thermochemolysis data we verify that a significant amount of lignin is exported to the canyon (∼14 % wt. lignin) and the distal lobe (∼16 % wt. lignin) sediments. The basin plain contains no detectable lignin but does show the presence of terrigenous long-chain fatty acids having an even carbon number predominance. Following a laboratory oxidation experiment on sediments from the distal lobe for 6 d there was an organic carbon mass loss of 59.8 % and the solid-state <sup>13</sup>C NMR spectrum shows a major reduction in peaks associated with carbohydrate-like and lignin molecules and a relative increase in aliphatic molecules. This shows that terrigenous lignin molecules can be remineralized to CO<sub>2</sub> and/or altered to structures that no longer resemble that of lignin through oxidative degradation processes. This would have a potentially significant implication on what is traditionally viewed as autochthonous marine organic matter.</div></div>","PeriodicalId":18219,"journal":{"name":"Marine Chemistry","volume":"273 ","pages":"Article 104569"},"PeriodicalIF":2.5,"publicationDate":"2025-10-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145266921","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}
Pub Date : 2025-10-01DOI: 10.1016/j.marchem.2025.104568
Nina Davtian , Nuria Penalva , Oriol Teruel , Pau Comes , Antoni Rosell-Melé , Joan Villanueva
Oceanic dissolved black carbon (DBC) is the subject of a conundrum between the dominant riverine inputs in terms of mass flux and its stable and radiogenic carbon isotope composition inconsistent with a predominant riverine origin. Here, we analyzed seawater samples within specific and contrasting water masses along several latitudinal and longitudinal transects across the Atlantic Ocean to quantify DBC and map its latitudinal and water depth changes in this ocean. After comparing latitudinal changes in surface water DBC properties with those in atmospheric pyrogenic carbon inputs from seasonal, massive grass burning events in the African Savanna, we could not demonstrate the significance of atmospheric deposition as a non-riverine source of DBC in the Atlantic Ocean, likely due to the balance by DBC photo-bleaching. We found constant DBC concentrations and increasing trends in the condensation degree of DBC (i.e., B6CA:B5CA molar ratio) from surface to deep Atlantic waters and from the South Atlantic to the North Atlantic within individual shallow to deep water masses. Overall, our mapping of DBC in the Atlantic Ocean highlights the need to explore the following alternative hypotheses in the future to better understand the cycling of oceanic DBC: 1) enhanced regional atmospheric BC deposition from African savanna grassland fires impact particulate rather than dissolved BC in the Atlantic Ocean, 2) oceanic DBC has a predominantly non-pyrogenic origin, and 3) exports of terrigenous DBC across the Atlantic Ocean accompany those of terrigenous humic-like compounds from the North Atlantic via meridional circulation.
{"title":"Mapping of dissolved black carbon in the Atlantic Ocean","authors":"Nina Davtian , Nuria Penalva , Oriol Teruel , Pau Comes , Antoni Rosell-Melé , Joan Villanueva","doi":"10.1016/j.marchem.2025.104568","DOIUrl":"10.1016/j.marchem.2025.104568","url":null,"abstract":"<div><div>Oceanic dissolved black carbon (DBC) is the subject of a conundrum between the dominant riverine inputs in terms of mass flux and its stable and radiogenic carbon isotope composition inconsistent with a predominant riverine origin. Here, we analyzed seawater samples within specific and contrasting water masses along several latitudinal and longitudinal transects across the Atlantic Ocean to quantify DBC and map its latitudinal and water depth changes in this ocean. After comparing latitudinal changes in surface water DBC properties with those in atmospheric pyrogenic carbon inputs from seasonal, massive grass burning events in the African Savanna, we could not demonstrate the significance of atmospheric deposition as a non-riverine source of DBC in the Atlantic Ocean, likely due to the balance by DBC photo-bleaching. We found constant DBC concentrations and increasing trends in the condensation degree of DBC (i.e., B6CA:B5CA molar ratio) from surface to deep Atlantic waters and from the South Atlantic to the North Atlantic within individual shallow to deep water masses. Overall, our mapping of DBC in the Atlantic Ocean highlights the need to explore the following alternative hypotheses in the future to better understand the cycling of oceanic DBC: 1) enhanced regional atmospheric BC deposition from African savanna grassland fires impact particulate rather than dissolved BC in the Atlantic Ocean, 2) oceanic DBC has a predominantly non-pyrogenic origin, and 3) exports of terrigenous DBC across the Atlantic Ocean accompany those of terrigenous humic-like compounds from the North Atlantic via meridional circulation.</div></div>","PeriodicalId":18219,"journal":{"name":"Marine Chemistry","volume":"273 ","pages":"Article 104568"},"PeriodicalIF":2.5,"publicationDate":"2025-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145266920","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}
Pub Date : 2025-09-29DOI: 10.1016/j.marchem.2025.104567
Géraldine Sarthou , Eva Bucciarelli , Fabien Quéroué , François Lacan , Hélène Planquette , Viet Q. Pham , Maxime Grand , Catherine Pradoux , Martine Rodier , Sophie Bonnet , Gérard Eldin , Sophie Cravatte , Catherine Jeandel , Alexandre Ganachaud
As part of the PANDORA cruise (GEOTRACES GP12), concentrations of dissolved iron (dFe) were measured at 11 stations inside and outside the Solomon Sea, a semi-enclosed sea in the western tropical Pacific, with complex topography and straits, and strong western boundary currents supplying the equatorial current system. These measurements aimed to better assess the various sources of dFe in our study area and the Solomon Sea's potential as a source of dFe for the Equatorial Undercurrent (EUC). A simple box model allows calculating and discussing the fate of the dFe in the different water layers flowing through the Solomon Sea and suggests that the amount of dFe enrichment within the enclosed sea was not significant for the lower thermocline and intermediate waters, indicating that most of the dFe was acquired prior to reaching the Solomon Sea at the entrance and/or that inputs are approximately balanced by scavenging within the basin for these two layers. In contrast, dFe enrichment was significant for the upper thermocline layer and the deep waters, highlighting enrichments from external sources, as well as combination of internal processes, such as scavenging and/or organic complexation. The relative dFe contribution of the Solomon Sea to EUC was 20 %, on average. Other sources might thus provide dFe to the EUC, along the water transport downstream of the Solomon Sea (e.g. Bismarck Sea) or from the northern hemisphere. Diazotrophs such as Trichodesmium might also contribute to the dFe enrichment of the EUC after export and remineralization at depth outside the Solomon Sea.
{"title":"Dissolved iron distribution and budget in the Solomon Sea","authors":"Géraldine Sarthou , Eva Bucciarelli , Fabien Quéroué , François Lacan , Hélène Planquette , Viet Q. Pham , Maxime Grand , Catherine Pradoux , Martine Rodier , Sophie Bonnet , Gérard Eldin , Sophie Cravatte , Catherine Jeandel , Alexandre Ganachaud","doi":"10.1016/j.marchem.2025.104567","DOIUrl":"10.1016/j.marchem.2025.104567","url":null,"abstract":"<div><div>As part of the PANDORA cruise (GEOTRACES GP12), concentrations of dissolved iron (dFe) were measured at 11 stations inside and outside the Solomon Sea, a semi-enclosed sea in the western tropical Pacific, with complex topography and straits, and strong western boundary currents supplying the equatorial current system. These measurements aimed to better assess the various sources of dFe in our study area and the Solomon Sea's potential as a source of dFe for the Equatorial Undercurrent (EUC). A simple box model allows calculating and discussing the fate of the dFe in the different water layers flowing through the Solomon Sea and suggests that the amount of dFe enrichment within the enclosed sea was not significant for the lower thermocline and intermediate waters, indicating that most of the dFe was acquired prior to reaching the Solomon Sea at the entrance and/or that inputs are approximately balanced by scavenging within the basin for these two layers. In contrast, dFe enrichment was significant for the upper thermocline layer and the deep waters, highlighting enrichments from external sources, as well as combination of internal processes, such as scavenging and/or organic complexation. The relative dFe contribution of the Solomon Sea to EUC was 20 %, on average. Other sources might thus provide dFe to the EUC, along the water transport downstream of the Solomon Sea (e.g. Bismarck Sea) or from the northern hemisphere. Diazotrophs such as <em>Trichodesmium</em> might also contribute to the dFe enrichment of the EUC after export and remineralization at depth outside the Solomon Sea.</div></div>","PeriodicalId":18219,"journal":{"name":"Marine Chemistry","volume":"273 ","pages":"Article 104567"},"PeriodicalIF":2.5,"publicationDate":"2025-09-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145220621","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}
Pub Date : 2025-09-27DOI: 10.1016/j.marchem.2025.104566
Jianan Liu , Xueqing Yu , Tong Peng , Xinyi Lin , Jinzhou Du
Saltmarsh tidal creeks play a critical role in coastal nutrient cycling, yet submarine groundwater discharge (SGD), as a key driver, remains poorly understood. Research on SGD-derived outwelling of multiple nutrient species is notably scarce in low-salinity estuarine saltmarshes influenced by large rivers. Utilizing long-lived radium isotopes (226Ra and 228Ra) combined with high-frequency monitoring encompassing the most comprehensive species of dissolved nutrient to date during both spring and neap tides, we quantified SGD fluxes and their contribution to nutrient outwelling in a low-salinity saltmarsh tidal creek system of the Yangtze River Estuary. Results showed that driven by tidal pumping, SGD flux during spring tides (12 ± 5.9 cm d−1) was significantly greater than during neap tides (0.77 ± 0.42 cm d−1), along with corresponding differences in nutrient transport fluxes. SGD served as a source of dissolved inorganic nitrogen (DIN) and dissolved silicate (DSi) to the tidal creek system. Specifically, NH4-N contributed approximately 93 % of the outwelling flux, while SGD-derived DSi accounted for 31–36 % of the DSi outwelling. Conversely, SGD functioned as a sink for dissolved phosphorus (inorganic + organic), capable of removing phosphorus in the tidal creek waters. More importantly, due to nitrogen input via SGD and its retention of phosphorus, both groundwater and ebbing tidal creek waters exhibited nitrogen-to‑phosphorus (N/P) ratios significantly exceeding the Redfield ratio. Although the saltmarshes partially mitigated the elevated N/P ratio during the outwelling process, the imbalanced N/P ratio in SGD-driven outwelling still poses risks of inducing coastal eutrophication and harmful algal blooms. This study unveils the crucial regulatory role of SGD in nutrient dynamics within low-salinity saltmarshes, emphasizing the necessity to incorporate groundwater-surface water interactions into coastal nutrient management and ecological conservation.
盐沼潮汐溪在沿海养分循环中起着关键作用，但作为关键驱动因素的海底地下水排放（SGD）仍然知之甚少。在受大河影响的低盐度河口盐沼中，对sgd衍生的多种营养物质外溢的研究尤其缺乏。利用长寿命镭同位素（226Ra和228Ra），结合迄今为止春潮和小潮期间最全面的溶解营养物种类的高频监测，我们量化了长江口低盐度盐沼潮汐溪系统的SGD通量及其对营养物外移的贡献。结果表明，在潮汐泵送的驱动下，春潮期间的SGD通量（12±5.9 cm d - 1）显著大于小潮期间的SGD通量（0.77±0.42 cm d - 1），同时营养物运输通量也存在相应差异。SGD是潮汐溪系统中溶解无机氮（DIN）和溶解硅酸盐（DSi）的来源。具体而言，NH4-N贡献了约93%的外溢通量，而sgd衍生的DSi占DSi外溢的31 - 36%。相反，SGD作为溶解磷（无机+有机）的汇，能够去除潮溪水体中的磷。更重要的是，由于SGD的氮输入及其对磷的滞留，地下水和退潮溪水的氮磷比（N/P）显著超过Redfield比。尽管盐沼在外溢过程中部分缓解了氮磷比的升高，但sgd驱动的外溢中氮磷比的不平衡仍然存在诱发沿海富营养化和有害藻华的风险。本研究揭示了SGD在低盐度盐沼营养动态中的重要调节作用，强调了将地下水-地表水相互作用纳入沿海营养管理和生态保护的必要性。
{"title":"Groundwater modulates nutrient dynamics in a freshened saltmarsh tidal creek","authors":"Jianan Liu , Xueqing Yu , Tong Peng , Xinyi Lin , Jinzhou Du","doi":"10.1016/j.marchem.2025.104566","DOIUrl":"10.1016/j.marchem.2025.104566","url":null,"abstract":"<div><div>Saltmarsh tidal creeks play a critical role in coastal nutrient cycling, yet submarine groundwater discharge (SGD), as a key driver, remains poorly understood. Research on SGD-derived outwelling of multiple nutrient species is notably scarce in low-salinity estuarine saltmarshes influenced by large rivers. Utilizing long-lived radium isotopes (<sup>226</sup>Ra and <sup>228</sup>Ra) combined with high-frequency monitoring encompassing the most comprehensive species of dissolved nutrient to date during both spring and neap tides, we quantified SGD fluxes and their contribution to nutrient outwelling in a low-salinity saltmarsh tidal creek system of the Yangtze River Estuary. Results showed that driven by tidal pumping, SGD flux during spring tides (12 ± 5.9 cm d<sup>−1</sup>) was significantly greater than during neap tides (0.77 ± 0.42 cm d<sup>−1</sup>), along with corresponding differences in nutrient transport fluxes. SGD served as a source of dissolved inorganic nitrogen (DIN) and dissolved silicate (DSi) to the tidal creek system. Specifically, NH<sub>4</sub>-N contributed approximately 93 % of the outwelling flux, while SGD-derived DSi accounted for 31–36 % of the DSi outwelling. Conversely, SGD functioned as a sink for dissolved phosphorus (inorganic + organic), capable of removing phosphorus in the tidal creek waters. More importantly, due to nitrogen input via SGD and its retention of phosphorus, both groundwater and ebbing tidal creek waters exhibited nitrogen-to‑phosphorus (N/P) ratios significantly exceeding the Redfield ratio. Although the saltmarshes partially mitigated the elevated N/P ratio during the outwelling process, the imbalanced N/P ratio in SGD-driven outwelling still poses risks of inducing coastal eutrophication and harmful algal blooms. This study unveils the crucial regulatory role of SGD in nutrient dynamics within low-salinity saltmarshes, emphasizing the necessity to incorporate groundwater-surface water interactions into coastal nutrient management and ecological conservation.</div></div>","PeriodicalId":18219,"journal":{"name":"Marine Chemistry","volume":"273 ","pages":"Article 104566"},"PeriodicalIF":2.5,"publicationDate":"2025-09-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145220622","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}
Pub Date : 2025-09-15DOI: 10.1016/j.marchem.2025.104565
Yasmym Schütz de Vincenzi Weirich , Carlos Eduardo de Rezende , Fernanda Maria de Souza , Valdenira Ferreira dos Santos , César C. Martins
The Oiapoque River estuary, located on the border between Brazil and French Guiana, is an understudied Amazon region characterized by intense discharge of fluvial sediment and terrestrial organic matter (OM). Influenced by environmental factors such as temperature, salinity, tides, and currents, the sedimentary OM composition reflects both autochthonous production and adjacent land biomass. This study aimed to identify and differentiate primary sources of sedimentary OM in the Amazon coastal zone using geochemical parameters such as total organic carbon (TOC), total nitrogen (TN), their relative atomic ratio (expressed as C/N), and carbon and nitrogen isotopic ratios (δ13C and δ15N). Two surface sediment sampling campaigns were conducted in 2018 during the wet and dry seasons. The sediments showed a strong correlation between TOC and TN across both campaigns (R2 = 0.98 and 0.94); however, results suggested the contribution of inorganic nitrogen forms (e.g., NH₄+). The C/N ratio indicated predominant OM from terrigenous input (∼24) at upstream sites and marine input (∼5 and ∼ 9) at downstream ones. The δ13C analysis revealed low variability along the estuary, with values around −27 ‰ upstream and near the mouth (typical of land or C3 plant contributions), intermediate values around −24 ‰ in the central portion (mixed sources), and higher values around −22 ‰ near the mouth (marine inputs). The δ15N values (∼3 ‰) were primarily found in the inner region, at the center of the estuary, and near the mouth where river discharges occur, associated with terrestrial plants. The elemental and isotopic composition of the sedimentary OM indicates a predominance of terrigenous OM, particularly near areas influenced by the Uáça and Ouanary rivers, reflecting land use and human occupation. Estuarine dynamics, influenced by rainfall and tidal currents, affect the distribution of marine inputs and the mixture of allochthonous and autochthonous sources throughout the estuary.
{"title":"Unraveling sedimentary organic matter in the Oiapoque estuarine-marine ecosystem: Insights from elemental composition and isotopic fingerprints on the Amazon coast","authors":"Yasmym Schütz de Vincenzi Weirich , Carlos Eduardo de Rezende , Fernanda Maria de Souza , Valdenira Ferreira dos Santos , César C. Martins","doi":"10.1016/j.marchem.2025.104565","DOIUrl":"10.1016/j.marchem.2025.104565","url":null,"abstract":"<div><div>The Oiapoque River estuary, located on the border between Brazil and French Guiana, is an understudied Amazon region characterized by intense discharge of fluvial sediment and terrestrial organic matter (OM). Influenced by environmental factors such as temperature, salinity, tides, and currents, the sedimentary OM composition reflects both autochthonous production and adjacent land biomass. This study aimed to identify and differentiate primary sources of sedimentary OM in the Amazon coastal zone using geochemical parameters such as total organic carbon (TOC), total nitrogen (TN), their relative atomic ratio (expressed as C/N), and carbon and nitrogen isotopic ratios (δ<sup>13</sup>C and δ<sup>15</sup>N). Two surface sediment sampling campaigns were conducted in 2018 during the wet and dry seasons. The sediments showed a strong correlation between TOC and TN across both campaigns (R<sup>2</sup> = 0.98 and 0.94); however, results suggested the contribution of inorganic nitrogen forms (e.g., NH₄<sup>+</sup>). The C/N ratio indicated predominant OM from terrigenous input (∼24) at upstream sites and marine input (∼5 and ∼ 9) at downstream ones. The δ<sup>13</sup>C analysis revealed low variability along the estuary, with values around −27 ‰ upstream and near the mouth (typical of land or C3 plant contributions), intermediate values around −24 ‰ in the central portion (mixed sources), and higher values around −22 ‰ near the mouth (marine inputs). The δ<sup>15</sup>N values (∼3 ‰) were primarily found in the inner region, at the center of the estuary, and near the mouth where river discharges occur, associated with terrestrial plants. The elemental and isotopic composition of the sedimentary OM indicates a predominance of terrigenous OM, particularly near areas influenced by the Uáça and Ouanary rivers, reflecting land use and human occupation. Estuarine dynamics, influenced by rainfall and tidal currents, affect the distribution of marine inputs and the mixture of allochthonous and autochthonous sources throughout the estuary.</div></div>","PeriodicalId":18219,"journal":{"name":"Marine Chemistry","volume":"273 ","pages":"Article 104565"},"PeriodicalIF":2.5,"publicationDate":"2025-09-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145096881","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}
This study examines benthic macrofauna from Admiralty Bay, maritime Antarctic, using triple stable isotope approach (δ13C, δ15N, and δ34S) to assess the impact of melting glaciers and human activity on trophic interactions in this unique ecosystem. Four species – the limpet Nacella concinna, the sea urchin Sterechinus neumayeri, the starfish Odontaster validus, and the brittle star Ophionotus victoriae – were analyzed to characterize their isotopic composition and trophic niches. The results indicate that diet and feeding strategies were the main drivers of δ13C, δ15N, and δ34S variability, demonstrating the utility of a multi-isotope approach for revealing diet composition, trophic plasticity, and benthic–pelagic coupling in polar benthic communities. Elevated δ13C values, typical of benthic primary producers, and depleted δ34S values, indicative of sulfur derived from sediments, confirmed a strong reliance of benthic macrofauna on benthic food sources. In contrast, decrease in δ13C together with higher and typically marine δ34S, can indicate higher contribution of pelagic diet sources. Spatial isotopic patterns further revealed areas influenced by glacial melt and shifting ice conditions, where consumers were relatively enriched in δ13C and δ15N compared to sites with rather open-ocean conditions. Notably, δ34S emerged as a possible early indicator of human-related disturbance, with depletion reflecting increased anthropogenic sulfur inputs and reduced oxygen conditions in benthic habitats linked to nutrient enrichment. Concurrent to 34S-depletion enrichment in 15N supports the role of nitrogen inputs from human activities. These findings demonstrate that stable isotopic tracers, particularly when incorporating sulfur alongside carbon and nitrogen, provide a powerful tool to detect and interpret ecological responses to both natural and anthropogenic drivers, offering insights into local ecosystem shifts and their broader implications for Antarctic food webs under climate change and growing human pressure.
{"title":"Factors influencing the variability of stable isotopes of carbon, nitrogen, and sulfur in benthic macrofauna from Admiralty Bay, maritime Antarctic","authors":"Agnieszka Jędruch , Marcelina Ziółkowska , Natalia Bulik , Piotr Paneth , Ewa Korejwo , Dominika Saniewska","doi":"10.1016/j.marchem.2025.104564","DOIUrl":"10.1016/j.marchem.2025.104564","url":null,"abstract":"<div><div>This study examines benthic macrofauna from Admiralty Bay, maritime Antarctic, using triple stable isotope approach (<em>δ</em><sup>13</sup>C, <em>δ</em><sup>15</sup>N, and <em>δ</em><sup>34</sup>S) to assess the impact of melting glaciers and human activity on trophic interactions in this unique ecosystem. Four species – the limpet <em>Nacella concinna</em>, the sea urchin <em>Sterechinus neumayeri</em>, the starfish <em>Odontaster validus</em>, and the brittle star <em>Ophionotus victoriae</em> – were analyzed to characterize their isotopic composition and trophic niches. The results indicate that diet and feeding strategies were the main drivers of <em>δ</em><sup>13</sup>C, <em>δ</em><sup>15</sup>N, and <em>δ</em><sup>34</sup>S variability, demonstrating the utility of a multi-isotope approach for revealing diet composition, trophic plasticity, and benthic–pelagic coupling in polar benthic communities. Elevated <em>δ</em><sup>13</sup>C values, typical of benthic primary producers, and depleted <em>δ</em><sup>34</sup>S values, indicative of sulfur derived from sediments, confirmed a strong reliance of benthic macrofauna on benthic food sources. In contrast, decrease in <em>δ</em><sup>13</sup>C together with higher and typically marine <em>δ</em><sup>34</sup>S, can indicate higher contribution of pelagic diet sources. Spatial isotopic patterns further revealed areas influenced by glacial melt and shifting ice conditions, where consumers were relatively enriched in <em>δ</em><sup>13</sup>C and <em>δ</em><sup>15</sup>N compared to sites with rather open-ocean conditions. Notably, <em>δ</em><sup>34</sup>S emerged as a possible early indicator of human-related disturbance, with depletion reflecting increased anthropogenic sulfur inputs and reduced oxygen conditions in benthic habitats linked to nutrient enrichment. Concurrent to <sup>34</sup>S-depletion enrichment in <sup>15</sup>N supports the role of nitrogen inputs from human activities. These findings demonstrate that stable isotopic tracers, particularly when incorporating sulfur alongside carbon and nitrogen, provide a powerful tool to detect and interpret ecological responses to both natural and anthropogenic drivers, offering insights into local ecosystem shifts and their broader implications for Antarctic food webs under climate change and growing human pressure.</div></div>","PeriodicalId":18219,"journal":{"name":"Marine Chemistry","volume":"273 ","pages":"Article 104564"},"PeriodicalIF":2.5,"publicationDate":"2025-09-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145096873","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}
The low iron concentrations in the Equatorial Indian Ocean (EIO) create a challenging environment for microbial life, requiring microorganisms to adapt. One strategy involves the production of siderophores, organic compounds that bind to Fe3+ ions and facilitate their uptake through specific receptors. Multiple siderophores may improve the bioavailability of iron due to the varied structures of siderophores and receptors. Since a single receptor may bind multiple siderophores, it is imperative to understand the molecular mechanisms underlying the interaction between siderophores and their receptors. This study used an in silico approach to explore these interactions. Pseudomonas stutzeri ATCC 17588, isolated from the EIO, was optimized for siderophore production under various growth conditions and analyzed using LC-qTOF-MS. The tertiary structure of the FoxA receptor and its interaction with the ferrioxamine X1-Fe3+ complex were examined through molecular docking. P. stutzeri ATCC 17588 produced multiple siderophores, including ferrioxamine X1, with optimal production at 10 nM iron concentration, pH 8.5, and 25 °C. The interaction energies between ferrioxamine X1-Fe3+ and the FoxA receptor were − 40.81 kcal/mol and − 9.3 kJ/mol, respectively, suggesting stable complexes. The predicted FoxA structure, validated through various analyses, revealed helices interspersed with strands. Hydrophobic interactions, involving residues such as Gln287, Arg792, and Glu180, were primarily responsible for the binding of ferrioxamine X1-Fe3+ to the FoxA receptor. This study sheds light on the role of ferrioxamine X1 in iron acquisition by P. stutzeri in the iron-limited EIO and enhances our understanding of microbial metal-ligand interactions in marine ecosystems.
{"title":"Ferrioxamine X1 mediated iron interaction with FoxA receptor in marine Pseudomonas stutzeri: An in silico approach","authors":"Pratika Singh , Parli Venkateswaran Bhaskar , Alok Kumar Sinha , Vitthal T. Barvkar , Sarat Chandra Tripathy","doi":"10.1016/j.marchem.2025.104563","DOIUrl":"10.1016/j.marchem.2025.104563","url":null,"abstract":"<div><div>The low iron concentrations in the Equatorial Indian Ocean (EIO) create a challenging environment for microbial life, requiring microorganisms to adapt. One strategy involves the production of siderophores, organic compounds that bind to Fe<sup>3+</sup> ions and facilitate their uptake through specific receptors. Multiple siderophores may improve the bioavailability of iron due to the varied structures of siderophores and receptors. Since a single receptor may bind multiple siderophores, it is imperative to understand the molecular mechanisms underlying the interaction between siderophores and their receptors. This study used an <em>in silico</em> approach to explore these interactions. <em>Pseudomonas stutzeri</em> ATCC 17588, isolated from the EIO, was optimized for siderophore production under various growth conditions and analyzed using LC-qTOF-MS. The tertiary structure of the FoxA receptor and its interaction with the ferrioxamine X<sub>1</sub>-Fe<sup>3+</sup> complex were examined through molecular docking. <em>P. stutzeri</em> ATCC 17588 produced multiple siderophores, including ferrioxamine X<sub>1</sub>, with optimal production at 10 nM iron concentration, pH 8.5, and 25 °C. The interaction energies between ferrioxamine X<sub>1</sub>-Fe<sup>3+</sup> and the FoxA receptor were − 40.81 kcal/mol and − 9.3 kJ/mol, respectively, suggesting stable complexes. The predicted FoxA structure, validated through various analyses, revealed helices interspersed with strands. Hydrophobic interactions, involving residues such as Gln287, Arg792, and Glu180, were primarily responsible for the binding of ferrioxamine X<sub>1</sub>-Fe<sup>3+</sup> to the FoxA receptor. This study sheds light on the role of ferrioxamine X<sub>1</sub> in iron acquisition by <em>P. stutzeri</em> in the iron-limited EIO and enhances our understanding of microbial metal-ligand interactions in marine ecosystems.</div></div>","PeriodicalId":18219,"journal":{"name":"Marine Chemistry","volume":"273 ","pages":"Article 104563"},"PeriodicalIF":2.5,"publicationDate":"2025-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145096872","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}
Pub Date : 2025-09-11DOI: 10.1016/j.marchem.2025.104562
Nawal Bouchachi , Hélène Lavanant , Carlos Afonso , Isabelle Schmitz , Barbara Marie , Ingrid Obernosterer , Eva Ortega-Retuerta
In the Mediterranean Sea, an accumulation of dissolved organic matter (DOM) is observed during the stratified summer period, which is decoupled from the spring phytoplankton maxima. This has been classically explained by nutrient limitation, that hampers prokaryotic DOM uptake of the labile DOM released by phytoplankton. However, relatively high heterotrophic prokaryotic activity in summer led us to hypothesize that the accumulated DOM might be recalcitrant and derived from these microorganisms. To test this, we tracked the seasonality of DOM molecular composition and chemical diversity using FT-ICR MS from 2019 to 2021 in the NW Mediterranean Sea, and framed it using a broad suite of environmental and biological parameters. Our results reveal a clear seasonal variation in DOM molecular composition and diversity in the surface mixed layer. Changes in composition reflected a higher proportion of molecular formulae containing CHO in spring and a higher proportion of molecular formulae containing CHOS and CHONS in summer. Proxies of DOM recalcitrance, such as aromaticity, unsaturation, and molecular size, were higher in summer, confirming our hypothesis of an accumulation of recalcitrant DOM in summer. In parallel, an increase in DOM diversity (as number of total molecular formulae, their relative intensity, their average distance (Dist) in the van Krevelen space and their functional diversity) was observed, suggesting that the accumulated DOM in summer is likely the result of the interplay between different processes including dissolved primary production, photodegradation and prokaryotic activity. Our results may have significant implications for carbon sequestration through the microbial carbon pump in the Mediterranean Sea as this DOM accumulated in the surface is likely to be stored once exported into deep layers.
{"title":"Seasonal dynamics of DOM diversity and molecular composition in the NW Mediterranean Sea","authors":"Nawal Bouchachi , Hélène Lavanant , Carlos Afonso , Isabelle Schmitz , Barbara Marie , Ingrid Obernosterer , Eva Ortega-Retuerta","doi":"10.1016/j.marchem.2025.104562","DOIUrl":"10.1016/j.marchem.2025.104562","url":null,"abstract":"<div><div>In the Mediterranean Sea, an accumulation of dissolved organic matter (DOM) is observed during the stratified summer period, which is decoupled from the spring phytoplankton maxima. This has been classically explained by nutrient limitation, that hampers prokaryotic DOM uptake of the labile DOM released by phytoplankton. However, relatively high heterotrophic prokaryotic activity in summer led us to hypothesize that the accumulated DOM might be recalcitrant and derived from these microorganisms. To test this, we tracked the seasonality of DOM molecular composition and chemical diversity using FT-ICR MS from 2019 to 2021 in the NW Mediterranean Sea, and framed it using a broad suite of environmental and biological parameters. Our results reveal a clear seasonal variation in DOM molecular composition and diversity in the surface mixed layer. Changes in composition reflected a higher proportion of molecular formulae containing CHO in spring and a higher proportion of molecular formulae containing CHOS and CHONS in summer. Proxies of DOM recalcitrance, such as aromaticity, unsaturation, and molecular size, were higher in summer, confirming our hypothesis of an accumulation of recalcitrant DOM in summer. In parallel, an increase in DOM diversity (as number of total molecular formulae, their relative intensity, their average distance (Dist) in the van Krevelen space and their functional diversity) was observed, suggesting that the accumulated DOM in summer is likely the result of the interplay between different processes including dissolved primary production, photodegradation and prokaryotic activity. Our results may have significant implications for carbon sequestration through the microbial carbon pump in the Mediterranean Sea as this DOM accumulated in the surface is likely to be stored once exported into deep layers.</div></div>","PeriodicalId":18219,"journal":{"name":"Marine Chemistry","volume":"273 ","pages":"Article 104562"},"PeriodicalIF":2.5,"publicationDate":"2025-09-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145096880","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}
Pub Date : 2025-09-04DOI: 10.1016/j.marchem.2025.104555
Sarah M. Benson , Robert T. Letscher
Marine microbes are vital to oceanic ecosystems and influence the global climate through their paramount role in Earth's biogeochemical cycles. With this intricate role in ecosystems, it is important to understand the effect of increasing ocean temperatures on the cycling of organic matter (OM), which is hypothesized to contribute a positive feedback to future warming via an acceleration in microbial respiration of OM to CO2. We experimentally investigated the temperature sensitivity of microbial consumption of marine particulate OM (POM) focused in the rapidly warming Gulf of Maine during the 2019 and 2020 fall phytoplankton bloom. The overall rate and quantity of microbial POM (C, N, and P pools) consumption at in situ versus elevated temperatures were quantified within bottle incubations over the course of two weeks. POM incubated at warmer temperatures (+5 to 6 °C) was generally consumed at a faster rate with an overall larger quantity consumed compared to cooler temperatures (12 to 14 °C). Significant interannual variability in consumption rates and temperature sensitivity (Q10 parameter) across elemental pools was found and linked to the initial POM C:N:P stoichiometry. More nitrogen-rich POM was preferentially consumed at in situ temperatures, whereas carbon-rich POM, likely containing a terrigenous component, was preferentially consumed at warmer experimental temperatures. The empirically estimated temperature sensitivity (Q10) ranged from 2.7 to 3.4 in 2019 versus 1.0–1.2 in 2020, variable between and amongst POM elemental pools, suggesting both temperature and organic matter substrate stoichiometry (composition) play an important role in dictating the microbial POM remineralization response to warming ocean temperatures.
{"title":"Enhanced microbial consumption of carbon-rich marine organic matter at experimentally elevated temperatures dictated by substrate C:N:P stoichiometry","authors":"Sarah M. Benson , Robert T. Letscher","doi":"10.1016/j.marchem.2025.104555","DOIUrl":"10.1016/j.marchem.2025.104555","url":null,"abstract":"<div><div>Marine microbes are vital to oceanic ecosystems and influence the global climate through their paramount role in Earth's biogeochemical cycles. With this intricate role in ecosystems, it is important to understand the effect of increasing ocean temperatures on the cycling of organic matter (OM), which is hypothesized to contribute a positive feedback to future warming via an acceleration in microbial respiration of OM to CO<sub>2</sub>. We experimentally investigated the temperature sensitivity of microbial consumption of marine particulate OM (POM) focused in the rapidly warming Gulf of Maine during the 2019 and 2020 fall phytoplankton bloom. The overall rate and quantity of microbial POM (C, N, and P pools) consumption at in situ versus elevated temperatures were quantified within bottle incubations over the course of two weeks. POM incubated at warmer temperatures (+5 to 6 °C) was generally consumed at a faster rate with an overall larger quantity consumed compared to cooler temperatures (12 to 14 °C). Significant interannual variability in consumption rates and temperature sensitivity (Q<sub>10</sub> parameter) across elemental pools was found and linked to the initial POM C:N:P stoichiometry. More nitrogen-rich POM was preferentially consumed at in situ temperatures, whereas carbon-rich POM, likely containing a terrigenous component, was preferentially consumed at warmer experimental temperatures. The empirically estimated temperature sensitivity (Q<sub>10</sub>) ranged from 2.7 to 3.4 in 2019 versus 1.0–1.2 in 2020, variable between and amongst POM elemental pools, suggesting both temperature and organic matter substrate stoichiometry (composition) play an important role in dictating the microbial POM remineralization response to warming ocean temperatures.</div></div>","PeriodicalId":18219,"journal":{"name":"Marine Chemistry","volume":"273 ","pages":"Article 104555"},"PeriodicalIF":2.5,"publicationDate":"2025-09-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145019275","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}
Pub Date : 2025-08-31DOI: 10.1016/j.marchem.2025.104554
Hengchao Xu , Xiaotong Peng , Shui-Jiong Wang , Shuangquan Liu , Jiwei Li , Hao Yang
Nickel (Ni) is a biologically essential element in marine systems, yet its oceanic sources and sinks remain incompletely quantified. Micro manganese nodules (MMNs) and particles (MMPs) in marine sediment are major authigenic phase that scavenge critical metals though adsorption or incorporation. The accumulation of these minerals depends strongly on the seawater conditions and diagenetic processes within the sediments. Despite their significance, the influence of different manganese phase on the cycling of polymetallic elements-particularly Ni and its isotopes-has received little attention. This study analyzed MMPs bearing sediments, MMNs, and MMN bearing sediments from the Northwest Pacific Ocean to characterize their geochemical and Ni isotopic signatures. In core JL190, MMNs display Mn/Fe ratio and trace element patterns typical of suboxic-oxic diagenesis. Across all three cores, Ni concentrations track Mn accumulation closely, as shown by strong Mn/Al–Ni/Al correlations. However, core TS01-B10 from the Mariana Trench, which contains diatom-rich clay, yields weaker correlations than the two Philippine Sea cores. Despite these differences, bulk sediment δ60Ni values remain light (0.01–0.79 ‰, median 0.27 ‰), consistent with most pelagic sediments. In core B10, declining δ60Ni alongside rising Mn/Al ratios imply preferential adsorption of lighter Ni isotopes. In contrast, JL189 show simultaneous increase in Mn/Al and δ60Ni, suggesting porewater exchange and isotope fractionation on existing Mn oxides. The heavier Ni isotopic signature in diagenetic MMNs relative to bulk sediments likely reflects prolonged porewater interaction, preserving the porwater's isotopic signature. These results provide the first δ60Ni data for MMNs and elucidate their role as Ni carriers. These findings highlight the importance of authigenic Mn oxides in influencing the benthic flux of heavier Ni isotopes, which contributes to balancing the oceanic Ni budget.
{"title":"Nickel and its isotope in response to differential manganese minerals accumulation in Northwest Pacific sediments","authors":"Hengchao Xu , Xiaotong Peng , Shui-Jiong Wang , Shuangquan Liu , Jiwei Li , Hao Yang","doi":"10.1016/j.marchem.2025.104554","DOIUrl":"10.1016/j.marchem.2025.104554","url":null,"abstract":"<div><div>Nickel (Ni) is a biologically essential element in marine systems, yet its oceanic sources and sinks remain incompletely quantified. Micro manganese nodules (MMNs) and particles (MMPs) in marine sediment are major authigenic phase that scavenge critical metals though adsorption or incorporation. The accumulation of these minerals depends strongly on the seawater conditions and diagenetic processes within the sediments. Despite their significance, the influence of different manganese phase on the cycling of polymetallic elements-particularly Ni and its isotopes-has received little attention. This study analyzed MMPs bearing sediments, MMNs, and MMN bearing sediments from the Northwest Pacific Ocean to characterize their geochemical and Ni isotopic signatures. In core JL190, MMNs display Mn/Fe ratio and trace element patterns typical of suboxic-oxic diagenesis. Across all three cores, Ni concentrations track Mn accumulation closely, as shown by strong Mn/Al–Ni/Al correlations. However, core TS01-B10 from the Mariana Trench, which contains diatom-rich clay, yields weaker correlations than the two Philippine Sea cores. Despite these differences, bulk sediment δ<sup>60</sup>Ni values remain light (0.01–0.79 ‰, median 0.27 ‰), consistent with most pelagic sediments. In core B10, declining δ<sup>60</sup>Ni alongside rising Mn/Al ratios imply preferential adsorption of lighter Ni isotopes. In contrast, JL189 show simultaneous increase in Mn/Al and δ<sup>60</sup>Ni, suggesting porewater exchange and isotope fractionation on existing Mn oxides. The heavier Ni isotopic signature in diagenetic MMNs relative to bulk sediments likely reflects prolonged porewater interaction, preserving the porwater's isotopic signature. These results provide the first δ<sup>60</sup>Ni data for MMNs and elucidate their role as Ni carriers. These findings highlight the importance of authigenic Mn oxides in influencing the benthic flux of heavier Ni isotopes, which contributes to balancing the oceanic Ni budget.</div></div>","PeriodicalId":18219,"journal":{"name":"Marine Chemistry","volume":"273 ","pages":"Article 104554"},"PeriodicalIF":2.5,"publicationDate":"2025-08-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145010744","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}
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