Pub Date : 2026-01-01Epub Date: 2025-12-12DOI: 10.1016/j.marchem.2025.104598
R.M. Lawrence , A. Shrikumar , E. Le Roy , J. Swift , P.J. Lam , G.A. Cutter , K.L. Casciotti
The GEOTRACES GP15 Pacific Meridional Transect sampled several biogeochemical provinces in the central Pacific Ocean between 56°N and 20°S. This transect was designed to study processes driving the distributions of nutrients, trace elements, and isotopes (TEIs) in the Pacific, including their inputs, losses, and internal cycling. In this study, we report the nutrients (nitrate, nitrite, phosphate, silicate), hydrography (temperature, salinity), and oxygen data for GP15 and quantify how water mass mixing underlies their distributions along GP15 using a modified Optimum Multiparameter Analysis (PYOMPA). By imposing ’soft’ penalties on water mass distributions and using archetype analysis to define endmember properties, results from PYOMPA not only aligned with expectations but yielded lower residuals and allowed us to quantify water mass contributions at regional boundaries with more confidence. The use of flexible regeneration stoichiometry in PYOMPA also highlighted the impacts of regional regeneration and biogeochemical cycling on nutrient distributions along GP15. This analysis informs a better understanding of nutrient transport and regeneration patterns in the central Pacific Ocean, which captures key features of the meridional overturning circulation.
{"title":"Analysis of nutrient and hydrographic patterns on the GEOTRACES Pacific Meridional Section (GP15) using PYOMPA, a new framework for water mass analysis","authors":"R.M. Lawrence , A. Shrikumar , E. Le Roy , J. Swift , P.J. Lam , G.A. Cutter , K.L. Casciotti","doi":"10.1016/j.marchem.2025.104598","DOIUrl":"10.1016/j.marchem.2025.104598","url":null,"abstract":"<div><div>The GEOTRACES GP15 Pacific Meridional Transect sampled several biogeochemical provinces in the central Pacific Ocean between 56°N and 20°S. This transect was designed to study processes driving the distributions of nutrients, trace elements, and isotopes (TEIs) in the Pacific, including their inputs, losses, and internal cycling. In this study, we report the nutrients (nitrate, nitrite, phosphate, silicate), hydrography (temperature, salinity), and oxygen data for GP15 and quantify how water mass mixing underlies their distributions along GP15 using a modified Optimum Multiparameter Analysis (PYOMPA). By imposing ’soft’ penalties on water mass distributions and using archetype analysis to define endmember properties, results from PYOMPA not only aligned with expectations but yielded lower residuals and allowed us to quantify water mass contributions at regional boundaries with more confidence. The use of flexible regeneration stoichiometry in PYOMPA also highlighted the impacts of regional regeneration and biogeochemical cycling on nutrient distributions along GP15. This analysis informs a better understanding of nutrient transport and regeneration patterns in the central Pacific Ocean, which captures key features of the meridional overturning circulation.</div></div>","PeriodicalId":18219,"journal":{"name":"Marine Chemistry","volume":"274 ","pages":"Article 104598"},"PeriodicalIF":2.5,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145797427","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 : 2026-01-01Epub Date: 2025-12-16DOI: 10.1016/j.marchem.2025.104600
Yu Meng , Meng Lv , Xiao-Tong Zhang , Xiao-Yan Cao , Rong Chen , Gui-Peng Yang
The runoff input of mineral particles in coastal areas affects the migration and transformation of nutrients. Organic phosphorus (OP) has attracted much attention due to coastal eutrophication, while the migration under the influence of mineral inputs has not been understood deeply. This study investigated the sorption behavior of an OP compound (Adenosine 5’-monophosphate, AMP) on goethite, kaolin, and two mixtures of the minerals with natural sediment. Fourier transform infrared spectroscopy (FTIR) spectra and surface acid-base characteristics revealed interactions presented within the mixtures. Sorption kinetics and thermodynamics experiments were carried out through batch methods. The kinetic data were described using a two-compartment first-order equation, and the sorption isotherms were well-fitted by both the Freundlich and Langmuir models. Goethite exhibited a higher sorption ability than kaolin, and the sorption was more sensitive to salinity. The sorption capacity of mineral-added sediments was significantly lower than predicted, particularly for sediments mixed with kaolin, which decreased by 57.4 %. The analysis of OP fractions during sorption revealed an obvious increase in exchangeable or loosely sorbed organic phosphorus (Ex-Po) and iron/aluminium-bound organic phosphorus (NaOH-Po), with NaOH-Po dominating. The sum of Ex-Po and NaOH-Po, as the bioavailable OP, in goethite and kaolin was estimated to be around half of the total sorption amount. Compared to the discrete original ones, the Ex-Po in the sediment with the mineral addition increased while NaOH-Po decreased after sorption, suggesting that the presence of interactions between the minerals and sediment matrix reduced their ability to retain AMP. These findings highlight the significant role of mineral-sediment interactions in altering OP sorption characteristics, with important implications for their biogeochemical fate.
{"title":"Effects of mineral inputs on organic phosphorus (Adenosine 5′-monophosphate) sorption and implications for its biogeochemical behavior on marine sediments","authors":"Yu Meng , Meng Lv , Xiao-Tong Zhang , Xiao-Yan Cao , Rong Chen , Gui-Peng Yang","doi":"10.1016/j.marchem.2025.104600","DOIUrl":"10.1016/j.marchem.2025.104600","url":null,"abstract":"<div><div>The runoff input of mineral particles in coastal areas affects the migration and transformation of nutrients. Organic phosphorus (OP) has attracted much attention due to coastal eutrophication, while the migration under the influence of mineral inputs has not been understood deeply. This study investigated the sorption behavior of an OP compound (Adenosine 5’-monophosphate, AMP) on goethite, kaolin, and two mixtures of the minerals with natural sediment. Fourier transform infrared spectroscopy (FTIR) spectra and surface acid-base characteristics revealed interactions presented within the mixtures. Sorption kinetics and thermodynamics experiments were carried out through batch methods. The kinetic data were described using a two-compartment first-order equation, and the sorption isotherms were well-fitted by both the Freundlich and Langmuir models. Goethite exhibited a higher sorption ability than kaolin, and the sorption was more sensitive to salinity. The sorption capacity of mineral-added sediments was significantly lower than predicted, particularly for sediments mixed with kaolin, which decreased by 57.4 %. The analysis of OP fractions during sorption revealed an obvious increase in exchangeable or loosely sorbed organic phosphorus (Ex-Po) and iron/aluminium-bound organic phosphorus (NaOH-Po), with NaOH-Po dominating. The sum of Ex-Po and NaOH-Po, as the bioavailable OP, in goethite and kaolin was estimated to be around half of the total sorption amount. Compared to the discrete original ones, the Ex-Po in the sediment with the mineral addition increased while NaOH-Po decreased after sorption, suggesting that the presence of interactions between the minerals and sediment matrix reduced their ability to retain AMP. These findings highlight the significant role of mineral-sediment interactions in altering OP sorption characteristics, with important implications for their biogeochemical fate.</div></div>","PeriodicalId":18219,"journal":{"name":"Marine Chemistry","volume":"274 ","pages":"Article 104600"},"PeriodicalIF":2.5,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145840687","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 : 2026-01-01Epub Date: 2025-11-20DOI: 10.1016/j.marchem.2025.104580
Sandra Poehle, Imelda B. Velasquez , Andrea Koschinsky
Molybdenum (Mo) and uranium (U) are usually considered as conservative metals in the oceanic water column though deviations have been observed in e.g. surface waters. The key objective was to study the impact of dust input and pronounced oxygen minimum zones (OMZs) on dissolved Mo and U in comparison with the truly conservative element rubidium (Rb) in seawater samples from two GEOTRACES research cruises: GA11 - NE-Atlantic affected by Saharan dust and the Mauritanian upwelling and GA08 - SE-Atlantic affected by Namibian dust and the Benguela upwelling.
We observed slightly higher Mo and U concentrations, 114.8 nmol/kg and 14.5 nmol/kg, respectively, under the Saharan dust plume trajectory (NE-Atlantic) compared to their average seawater concentrations (107 nmol/kg and 13.9 nmol/kg) leading to the assumption of Saharan dust being a source. Slightly lower than average Mo and U concentrations, 102.8 nmol/kg and 11.9 nmol/kg, respectively, above the suboxic Namibian shelf (SE-Atlantic) can be attributed to the formation of reduced solid Mo and U smaller than 0.015 μm. A first hint to a link between sediment-released organic matter and colloidal U requires more research.
In contrast, Rb concentrations remained constant with depth, unaffected by regional influences in the NE and SE Atlantic, with approx. 1.3 μmol/kg showing truly conservative characteristics.
Our study implies that the expansion of less oxygenated waters with a potential shift towards euxinic conditions and more extensive dust events in the future due to e.g. climate change may affect the distribution and potentially isotopic signatures of Mo and U.
{"title":"Do desert dust input and pronounced oxygen minimum zones act as sources or sinks for dissolved molybdenum and uranium? A GEOTRACES study in the eastern Atlantic Ocean","authors":"Sandra Poehle, Imelda B. Velasquez , Andrea Koschinsky","doi":"10.1016/j.marchem.2025.104580","DOIUrl":"10.1016/j.marchem.2025.104580","url":null,"abstract":"<div><div>Molybdenum (Mo) and uranium (U) are usually considered as conservative metals in the oceanic water column though deviations have been observed in e.g. surface waters. The key objective was to study the impact of dust input and pronounced oxygen minimum zones (OMZs) on dissolved Mo and U in comparison with the truly conservative element rubidium (Rb) in seawater samples from two GEOTRACES research cruises: GA11 - NE-Atlantic affected by Saharan dust and the Mauritanian upwelling and GA08 - SE-Atlantic affected by Namibian dust and the Benguela upwelling.</div><div>We observed slightly higher Mo and U concentrations, 114.8 nmol/kg and 14.5 nmol/kg, respectively, under the Saharan dust plume trajectory (NE-Atlantic) compared to their average seawater concentrations (107 nmol/kg and 13.9 nmol/kg) leading to the assumption of Saharan dust being a source. Slightly lower than average Mo and U concentrations, 102.8 nmol/kg and 11.9 nmol/kg, respectively, above the suboxic Namibian shelf (SE-Atlantic) can be attributed to the formation of reduced solid Mo and U smaller than 0.015 μm. A first hint to a link between sediment-released organic matter and colloidal U requires more research.</div><div>In contrast, Rb concentrations remained constant with depth, unaffected by regional influences in the NE and SE Atlantic, with approx. 1.3 μmol/kg showing truly conservative characteristics.</div><div>Our study implies that the expansion of less oxygenated waters with a potential shift towards euxinic conditions and more extensive dust events in the future due to e.g. climate change may affect the distribution and potentially isotopic signatures of Mo and U.</div></div>","PeriodicalId":18219,"journal":{"name":"Marine Chemistry","volume":"274 ","pages":"Article 104580"},"PeriodicalIF":2.5,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145692281","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 : 2026-01-01Epub Date: 2026-01-09DOI: 10.1016/j.marchem.2026.104604
Fernando Aguado Gonzalo, Katarzyna Koziorowska, Beata Szymczycha, Karol Kuliński
The Arctic Ocean plays a crucial role in anthropogenic carbon sequestration, while also being among the regions most susceptible to Ocean Acidification (OA). To understand, quantify, and monitor the rapid biogeochemical changes in the Arctic shelves and coastal waters, it is necessary to accurately determine the complete marine carbonate system. However, the uncertainty range in the calculated values is still unclear, fogging our ability to properly estimate carbon inventory and OA. In this study, we collected samples in the Arctic open and coastal waters to estimate the internal consistency of total alkalinity (TA), pH, partial pressure of CO2 (pCO2) and dissolved inorganic carbon (DIC) when only two of them are measured and the other two calculated. In open ocean waters, calculated values generally show good consistency with observations, whereas in coastal areas, it was only possible to accurately calculate two variables: 1) pH using as input parameters pCO2 together with either TA or DIC, and 2) pCO2 using DIC and pH. Furthermore, we found that, in this dataset, using the TA estimated from its correlation with salinity together with pCO2 also allowed obtaining accurate pH values in both coastal and ocean waters. This opens a new possibility of monitoring changes in the carbon cycle by measuring only salinity and pCO2 in areas where its consistency has been evaluated. Finally, in this study, we provide guidelines for obtaining and reporting good-quality carbonate system data in Arctic coastal areas.
{"title":"The internal consistency between calculated and measured variables of the marine carbonate system in Arctic open and coastal waters, case study: Atlantic Arctic","authors":"Fernando Aguado Gonzalo, Katarzyna Koziorowska, Beata Szymczycha, Karol Kuliński","doi":"10.1016/j.marchem.2026.104604","DOIUrl":"10.1016/j.marchem.2026.104604","url":null,"abstract":"<div><div>The Arctic Ocean plays a crucial role in anthropogenic carbon sequestration, while also being among the regions most susceptible to Ocean Acidification (OA). To understand, quantify, and monitor the rapid biogeochemical changes in the Arctic shelves and coastal waters, it is necessary to accurately determine the complete marine carbonate system. However, the uncertainty range in the calculated values is still unclear, fogging our ability to properly estimate carbon inventory and OA. In this study, we collected samples in the Arctic open and coastal waters to estimate the internal consistency of total alkalinity (TA), pH, partial pressure of CO<sub>2</sub> (pCO<sub>2</sub>) and dissolved inorganic carbon (DIC) when only two of them are measured and the other two calculated. In open ocean waters, calculated values generally show good consistency with observations, whereas in coastal areas, it was only possible to accurately calculate two variables: 1) pH using as input parameters pCO<sub>2</sub> together with either TA or DIC, and 2) pCO<sub>2</sub> using DIC and pH. Furthermore, we found that, in this dataset, using the TA estimated from its correlation with salinity together with pCO<sub>2</sub> also allowed obtaining accurate pH values in both coastal and ocean waters. This opens a new possibility of monitoring changes in the carbon cycle by measuring only salinity and pCO<sub>2</sub> in areas where its consistency has been evaluated. Finally, in this study, we provide guidelines for obtaining and reporting good-quality carbonate system data in Arctic coastal areas.</div></div>","PeriodicalId":18219,"journal":{"name":"Marine Chemistry","volume":"274 ","pages":"Article 104604"},"PeriodicalIF":2.5,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145976560","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 : 2026-01-01Epub Date: 2025-12-01DOI: 10.1016/j.marchem.2025.104588
K.S. Arya , T.R. Gireeshkumar , Mary Sandra D'cunha , Mohammad Nishad T , K.R. Muraleedharan , V.B. Adarsh , Anjana Jayaprakash
The production pathways and sea-to-air fluxes of climate-relevant trace gases, including methane (CH4), in the southeastern Arabian Sea (SEAS), are poorly addressed and suffer significant uncertainties due to their spatial and seasonal heterogeneity. We measured CH4 in five coastal-oceanic transects along the SEAS during the southwest (SWM) and northeast monsoon (NEM) seasons to understand the distribution and sea-to-air fluxes.CH4 concentrations ranged from 3 to 151 nM (13 ± 16 nM) in SWM and from 1 to 140 nM (16 ± 38 nM) in NEM, decreasing in a gradient towards the offshore, which indicated that freshwater influx and stratification were key processes controlling the CH4 distribution. CH4 concentrations were positively correlated with chlorophyll-a and turbidity during the SWM, indicating anaerobic methanogenesis via micro-niches. Although globally hypoxic zones are considered a significant source of CH4, the SEAS exhibited relatively low CH4 levels under hypoxia, possibly due to the low organic carbon (<5 %) in sediments. The sea-to-air CH4 fluxes in the SEAS ranged from 0.1 to 278 μM m−2 day−1, and the estimated annual CH4 emissions from the SEAS (∼0.006 Tg yr−1) align with previous estimates. The global warming potential during SWM and NEM was 0.21 ± 0.45 and 0.6 ± 1.7 g CO2 eq m−2 day−1, with net annual emissions of 0.18 Tg CO2 yr−1. The present study highlights the significance of SEAS's role as a hotspot for CH4 release, emphasising that accurate and high-resolution measurements of climate-relevant trace gases from the marine environment are essential for improving future climate projections, global greenhouse gas budgets, and the development of mitigation strategies to achieve future climate goals.
阿拉伯海东南部与气候相关的微量气体，包括甲烷（CH4）的产生途径和海气通量，由于其空间和季节异质性，尚未得到充分解决，并且存在很大的不确定性。为了了解CH4在西南和东北季风季节的分布和海气通量，我们对沿南海的5个沿海-海洋样带进行了测量。CH4浓度在SWM为3 ~ 151 nM(13±16 nM)， NEM为1 ~ 140 nM(16±38 nM)，呈梯度递减趋势，表明淡水流入和分层是控制CH4分布的关键过程。在SWM过程中，CH4浓度与叶绿素-a和浊度呈正相关，表明厌氧甲烷是通过微生态位发生的。尽管全球缺氧带被认为是CH4的重要来源，但在缺氧条件下，SEAS的CH4水平相对较低，可能是由于沉积物中的有机碳含量较低（< 5%）。海洋对空气CH4通量的范围为0.1 ~ 278 μM−2 day−1，海洋CH4年排放量的估计值（~ 0.006 Tg yr−1）与以前的估计值一致。SWM和NEM期间的全球变暖潜势分别为0.21±0.45和0.6±1.7 g CO2 eq m−2 day−1，年净排放量为0.18 Tg CO2 yr−1。本研究强调了SEAS作为CH4释放热点的重要性，强调海洋环境中与气候相关的痕量气体的精确和高分辨率测量对于改善未来气候预测、全球温室气体预算以及制定缓解战略以实现未来气候目标至关重要。
{"title":"Methane dynamics in the southeastern Arabian Sea: Patterns of distribution and annual emission estimates","authors":"K.S. Arya , T.R. Gireeshkumar , Mary Sandra D'cunha , Mohammad Nishad T , K.R. Muraleedharan , V.B. Adarsh , Anjana Jayaprakash","doi":"10.1016/j.marchem.2025.104588","DOIUrl":"10.1016/j.marchem.2025.104588","url":null,"abstract":"<div><div>The production pathways and sea-to-air fluxes of climate-relevant trace gases, including methane (CH<sub>4</sub>), in the southeastern Arabian Sea (SEAS), are poorly addressed and suffer significant uncertainties due to their spatial and seasonal heterogeneity. We measured CH<sub>4</sub> in five coastal-oceanic transects along the SEAS during the southwest (SWM) and northeast monsoon (NEM) seasons to understand the distribution and sea-to-air fluxes.CH<sub>4</sub> concentrations ranged from 3 to 151 nM (13 ± 16 nM) in SWM and from 1 to 140 nM (16 ± 38 nM) in NEM, decreasing in a gradient towards the offshore, which indicated that freshwater influx and stratification were key processes controlling the CH<sub>4</sub> distribution. CH<sub>4</sub> concentrations were positively correlated with chlorophyll-<em>a</em> and turbidity during the SWM, indicating anaerobic methanogenesis <em>via</em> micro-niches. Although globally hypoxic zones are considered a significant source of CH<sub>4</sub>, the SEAS exhibited relatively low CH<sub>4</sub> levels under hypoxia, possibly due to the low organic carbon (<5 %) in sediments. The sea-to-air CH<sub>4</sub> fluxes in the SEAS ranged from 0.1 to 278 μM m<sup>−2</sup> day<sup>−1</sup>, and the estimated annual CH<sub>4</sub> emissions from the SEAS (∼0.006 Tg yr<sup>−1</sup>) align with previous estimates. The global warming potential during SWM and NEM was 0.21 ± 0.45 and 0.6 ± 1.7 g CO<sub>2</sub> eq m<sup>−2</sup> day<sup>−1</sup>, with net annual emissions of 0.18 Tg CO<sub>2</sub> yr<sup>−1</sup>. The present study highlights the significance of SEAS's role as a hotspot for CH<sub>4</sub> release, emphasising that accurate and high-resolution measurements of climate-relevant trace gases from the marine environment are essential for improving future climate projections, global greenhouse gas budgets, and the development of mitigation strategies to achieve future climate goals.</div></div>","PeriodicalId":18219,"journal":{"name":"Marine Chemistry","volume":"274 ","pages":"Article 104588"},"PeriodicalIF":2.5,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145692279","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}
Radiocarbon (14C) in seawater is a key tracer for investigating carbon cycling and air–sea exchange. This study quantified 14C concentrations in coastal seawater from 18 sites around the Korean Peninsula using accelerator mass spectrometry (AMS). A CO₂ extraction system optimized for 100 mL seawater samples was developed, achieving 85.5 ± 0.9 % recovery efficiency validated by certified reference materials. AMS results showed fraction modern carbon (fMC) values between 0.98 and 1.03, reflecting equilibrium with atmospheric 14CO₂. The East Sea exhibited relatively high fMC and Δ14C, likely due to open-ocean circulation. The West and South Seas showed lower fMC and negative Δ14C values, influenced by restricted mixing and terrestrial inputs. Average 14C concentrations were 4.99 × 10−3 Bq/L (East Sea), 5.22 × 10−3 Bq/L (West Sea), and 4.84 × 10−3 Bq/L (South Sea). These findings provide a regional baseline for coastal 14C and highlight the need for depth-resolved studies to better understand carbon dynamics.
{"title":"Determination of 14C concentration in coastal seawater of the Korean Peninsula using accelerator mass spectrometry","authors":"Min-Seok Oh , Gwan-Ho Lee , Weon Cheol Lim, Byung-Yong Yu","doi":"10.1016/j.marchem.2025.104602","DOIUrl":"10.1016/j.marchem.2025.104602","url":null,"abstract":"<div><div>Radiocarbon (<sup>14</sup>C) in seawater is a key tracer for investigating carbon cycling and air–sea exchange. This study quantified <sup>14</sup>C concentrations in coastal seawater from 18 sites around the Korean Peninsula using accelerator mass spectrometry (AMS). A CO₂ extraction system optimized for 100 mL seawater samples was developed, achieving 85.5 ± 0.9 % recovery efficiency validated by certified reference materials. AMS results showed fraction modern carbon (fMC) values between 0.98 and 1.03, reflecting equilibrium with atmospheric <sup>14</sup>CO₂. The East Sea exhibited relatively high fMC and Δ<sup>14</sup>C, likely due to open-ocean circulation. The West and South Seas showed lower fMC and negative Δ<sup>14</sup>C values, influenced by restricted mixing and terrestrial inputs. Average <sup>14</sup>C concentrations were 4.99 × 10<sup>−3</sup> Bq/L (East Sea), 5.22 × 10<sup>−3</sup> Bq/L (West Sea), and 4.84 × 10<sup>−3</sup> Bq/L (South Sea). These findings provide a regional baseline for coastal <sup>14</sup>C and highlight the need for depth-resolved studies to better understand carbon dynamics.</div></div>","PeriodicalId":18219,"journal":{"name":"Marine Chemistry","volume":"274 ","pages":"Article 104602"},"PeriodicalIF":2.5,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145925686","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 : 2026-01-01Epub Date: 2025-12-18DOI: 10.1016/j.marchem.2025.104601
Chihyun Oh, Taehee Na, Jeomshik Hwang
Particulate phosphorus (P) can exist in several species, particularly in marginal seas, where sediment resuspension can affect particle fluxes. The effect of P speciation on the C:N:P stoichiometry of particulate organic matter is poorly constrained. We investigated the C:N:P stoichiometry in the East Sea (Japan Sea), which is a marginal sea in the Northwest Pacific, by analyzing sinking particles collected at water depths of 500, 1000, and 2250 m (i.e., 50 m above the seafloor), along with suspended particles in the surface waters and the underlying sediments. We measured particulate organic carbon (POC), particulate nitrogen (PN), and particulate P. The P was separated into total P (TP), organic P (OP), inorganic P (IP), non-apatite inorganic P (NAIP), and apatite P (AP) following the Standards, Measurements, and Testing (SMT) protocol of the European Commission. In addition, Al, Si, and Ca were analyzed to estimate the contents of lithogenic material, opal, and CaCO3 in the sinking particles. The POC:PN ratio increased from 8.2 at 500 m water depth to 8.9 in the surface sediment, whereas the POC:TP and PN:TP ratios decreased from 229 and 28 at 500 m to 68 and 7.6 in the surface sediment, respectively. The IP flux exhibited a strong positive correlation with the Al flux (R2 = 0.92), which is a proxy for material derived by sediment resuspension. After correction based on the content of Al, to eliminate the contribution from sediment resuspension, nearly all of the IP was accounted for by the resuspension-derived fraction, implying that sediment resuspension could be the dominant source of IP in sinking particles in a marginal sea environment. The mean biogenic (i.e., resuspension-corrected) C:N:P ratios were 238:36:1 in suspended particles in the surface water, 444:56:1, 359:45:1, 329:37:1 in sinking particles at water depths of 500, 1000, and 2250 m, respectively, and 109:12:1 in the surface sediment. The biogenic C:N:P stoichiometry suggests that surface IP is labile and subject to rapid recycling in the upper 500 m of the sea. We suggest that C:TP is an appropriate measure of the stoichiometry of biogenic particles in the upper layer, whereas C:OP is more appropriate for sinking particles affected by resuspension in the deeper interior of the sea.
{"title":"Phosphorus speciation and C:N:P stoichiometry in particles in the East Sea (Japan Sea), Northwest Pacific","authors":"Chihyun Oh, Taehee Na, Jeomshik Hwang","doi":"10.1016/j.marchem.2025.104601","DOIUrl":"10.1016/j.marchem.2025.104601","url":null,"abstract":"<div><div>Particulate phosphorus (P) can exist in several species, particularly in marginal seas, where sediment resuspension can affect particle fluxes. The effect of P speciation on the C:N:P stoichiometry of particulate organic matter is poorly constrained. We investigated the C:N:P stoichiometry in the East Sea (Japan Sea), which is a marginal sea in the Northwest Pacific, by analyzing sinking particles collected at water depths of 500, 1000, and 2250 m (i.e., 50 m above the seafloor), along with suspended particles in the surface waters and the underlying sediments. We measured particulate organic carbon (POC), particulate nitrogen (PN), and particulate P. The P was separated into total P (TP), organic P (OP), inorganic P (IP), non-apatite inorganic P (NAIP), and apatite P (AP) following the Standards, Measurements, and Testing (SMT) protocol of the European Commission. In addition, Al, Si, and Ca were analyzed to estimate the contents of lithogenic material, opal, and CaCO<sub>3</sub> in the sinking particles. The POC:PN ratio increased from 8.2 at 500 m water depth to 8.9 in the surface sediment, whereas the POC:TP and PN:TP ratios decreased from 229 and 28 at 500 m to 68 and 7.6 in the surface sediment, respectively. The IP flux exhibited a strong positive correlation with the Al flux (R<sup>2</sup> = 0.92), which is a proxy for material derived by sediment resuspension. After correction based on the content of Al, to eliminate the contribution from sediment resuspension, nearly all of the IP was accounted for by the resuspension-derived fraction, implying that sediment resuspension could be the dominant source of IP in sinking particles in a marginal sea environment. The mean biogenic (i.e., resuspension-corrected) C:N:P ratios were 238:36:1 in suspended particles in the surface water, 444:56:1, 359:45:1, 329:37:1 in sinking particles at water depths of 500, 1000, and 2250 m, respectively, and 109:12:1 in the surface sediment. The biogenic C:N:P stoichiometry suggests that surface IP is labile and subject to rapid recycling in the upper 500 m of the sea. We suggest that C:TP is an appropriate measure of the stoichiometry of biogenic particles in the upper layer, whereas C:OP is more appropriate for sinking particles affected by resuspension in the deeper interior of the sea.</div></div>","PeriodicalId":18219,"journal":{"name":"Marine Chemistry","volume":"274 ","pages":"Article 104601"},"PeriodicalIF":2.5,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145840237","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 : 2026-01-01Epub Date: 2025-11-30DOI: 10.1016/j.marchem.2025.104587
Xintong Jiang , Mengyu Wang , Yue Ming , Ailin Yao , Xianye Wang , Lei Gao
The high-intensity human activities have had a strong impact on the flux and composition of nutrients and organic matter exported from major rivers to the sea worldwide. The goal of this study was to identify the mechanisms that control the distributions and variations of terrestrial nutrients and organic matter transported from the eight major Chinese rivers to the oceans. The continuous construction of reservoirs and dams in river basins causes them to resemble reservoirs, which results in intensified fragmentation of water channels, more transparent water bodies, longer water retention times, greater retention of nutrients, and enhanced biomass and production of phytoplankton. Herein we provide a preliminary definition of “reservoir degree” (i.e., the extent to which a river channel resembles a reservoir or a lake) and offer an empirical equation to roughly quantify the reservoir degree of rivers. We collected surface water samples at the river mouths of China's eight major rivers from different seasons and measured concentrations and compositions of nutrients and organic matter in these samples. Rotated principal component analysis of our data showed that reservoir degree and pollution degree are the two most important factors determining the distributions and variations of nutrients and organic matter in these rivers. We found that the reservoir degrees were often higher in small rivers than in large rivers and in plain rivers versus mountainous rivers. As reservoirs and dams are still being constructed in all the eight river basins, the reservoir degrees of the rivers will continue to increase. Under the implementation of environmental protection projects, however, their pollution degrees would decrease. Therefore, the different biogeochemical parameters will show divergent variation trends in the future. The results of this study help clarify the control mechanisms and the future evolution trends of nutrients and organic matter transported by rivers worldwide.
{"title":"Dynamics of nutrients and organic matter and their control mechanisms at the river mouths of major Chinese rivers","authors":"Xintong Jiang , Mengyu Wang , Yue Ming , Ailin Yao , Xianye Wang , Lei Gao","doi":"10.1016/j.marchem.2025.104587","DOIUrl":"10.1016/j.marchem.2025.104587","url":null,"abstract":"<div><div>The high-intensity human activities have had a strong impact on the flux and composition of nutrients and organic matter exported from major rivers to the sea worldwide. The goal of this study was to identify the mechanisms that control the distributions and variations of terrestrial nutrients and organic matter transported from the eight major Chinese rivers to the oceans. The continuous construction of reservoirs and dams in river basins causes them to resemble reservoirs, which results in intensified fragmentation of water channels, more transparent water bodies, longer water retention times, greater retention of nutrients, and enhanced biomass and production of phytoplankton. Herein we provide a preliminary definition of “reservoir degree” (i.e., the extent to which a river channel resembles a reservoir or a lake) and offer an empirical equation to roughly quantify the reservoir degree of rivers. We collected surface water samples at the river mouths of China's eight major rivers from different seasons and measured concentrations and compositions of nutrients and organic matter in these samples. Rotated principal component analysis of our data showed that reservoir degree and pollution degree are the two most important factors determining the distributions and variations of nutrients and organic matter in these rivers. We found that the reservoir degrees were often higher in small rivers than in large rivers and in plain rivers versus mountainous rivers. As reservoirs and dams are still being constructed in all the eight river basins, the reservoir degrees of the rivers will continue to increase. Under the implementation of environmental protection projects, however, their pollution degrees would decrease. Therefore, the different biogeochemical parameters will show divergent variation trends in the future. The results of this study help clarify the control mechanisms and the future evolution trends of nutrients and organic matter transported by rivers worldwide.</div></div>","PeriodicalId":18219,"journal":{"name":"Marine Chemistry","volume":"274 ","pages":"Article 104587"},"PeriodicalIF":2.5,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145692280","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 : 2026-01-01Epub Date: 2025-11-24DOI: 10.1016/j.marchem.2025.104577
Paco Quintana , Eunice Machado , Rodrigo Kerr
Coastal ecosystems exhibit a wide range of pH trends, from −0.023 to 0.023 pH units yr−1, making them particularly susceptible to acidification or basification. These variations are primarily driven by ecosystem metabolism and the influence of oceanic and riverine endmembers, as observed in the subtropical system of the Patos Lagoon Estuary (PLE, southern Brazil), where biogeochemical variability is largely governed by mixing of water masses with different properties. This study provides the first quantification of the seasonal variability of pH buffering capacity in the inner and outer zones of PLE. From May 2017 to September 2023, we assessed temporal variability using multiple approaches: (i) carbonate system parameters, (ii) sensitivity factors, (iii) buffering capacity of pH to fractional change of dissolved inorganic carbon (βDIC), (iv) metabolic effects on pH, and (v) environmental drivers of pH. The results revealed a distinct seasonal pH pattern, especially between summer with winter and spring, with consistently higher values at the outer station compared to the inner station, though spatial differences were not statistically significant. In winter and particularly in early spring, calcium carbonate (CaCO3) dissolution prevailed due to riverine input characterized by low buffering capacity. Along the salinity gradient, pH exhibited a pronounced difference, particularly between low and high salinity conditions. However, the persistent negative deviation of the metabolic effect on pH throughout the year and in salinity ranges, even under seawater conditions, supports the characterization of this coastal ecosystem as a net CO2 source, with especially high variability at mid-salinity conditions. Although the salinity gradient was comparable between stations, they exhibited differences in the magnitude of pH sensitivity to seasonal biogeochemical changes. These findings indicate that PLE functions as a system with moderate to low buffering capacity, with the outer zone showing greater resilience to pH fluctuations.
{"title":"Resilience of pH to seasonal change in a large subtropical lagoonal estuary","authors":"Paco Quintana , Eunice Machado , Rodrigo Kerr","doi":"10.1016/j.marchem.2025.104577","DOIUrl":"10.1016/j.marchem.2025.104577","url":null,"abstract":"<div><div>Coastal ecosystems exhibit a wide range of pH trends, from −0<em>.</em>023 to 0<em>.</em>023 pH units <em>yr</em><sup>−1</sup>, making them particularly susceptible to acidification or basification. These variations are primarily driven by ecosystem metabolism and the influence of oceanic and riverine endmembers, as observed in the subtropical system of the Patos Lagoon Estuary (PLE, southern Brazil), where biogeochemical variability is largely governed by mixing of water masses with different properties. This study provides the first quantification of the seasonal variability of pH buffering capacity in the inner and outer zones of PLE. From May 2017 to September 2023, we assessed temporal variability using multiple approaches: (i) carbonate system parameters, (ii) sensitivity factors, (iii) buffering capacity of pH to fractional change of dissolved inorganic carbon (<em>β</em>DIC), (iv) metabolic effects on pH, and (v) environmental drivers of pH. The results revealed a distinct seasonal pH pattern, especially between summer with winter and spring, with consistently higher values at the outer station compared to the inner station, though spatial differences were not statistically significant. In winter and particularly in early spring, calcium carbonate (<em>CaCO</em><sub>3</sub>) dissolution prevailed due to riverine input characterized by low buffering capacity. Along the salinity gradient, pH exhibited a pronounced difference, particularly between low and high salinity conditions. However, the persistent negative deviation of the metabolic effect on pH throughout the year and in salinity ranges, even under seawater conditions, supports the characterization of this coastal ecosystem as a net <em>CO</em><sub>2</sub> source, with especially high variability at mid-salinity conditions. Although the salinity gradient was comparable between stations, they exhibited differences in the magnitude of pH sensitivity to seasonal biogeochemical changes. These findings indicate that PLE functions as a system with moderate to low buffering capacity, with the outer zone showing greater resilience to pH fluctuations.</div></div>","PeriodicalId":18219,"journal":{"name":"Marine Chemistry","volume":"274 ","pages":"Article 104577"},"PeriodicalIF":2.5,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145622899","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 : 2026-01-01Epub Date: 2025-12-17DOI: 10.1016/j.marchem.2025.104599
Victor W. Truesdale , Jim Greenwood , Tim Southern
As a prelude to further understanding the dissolution kinetics of CaCO3 in the oceanic water-column, the principles of Chemical Kinetics are applied generally to what recently was defined as the solution-oriented approach to CaCO3 dissolution kinetics. The ultimate objective of the study is to probe what is known commonly as, the ‘mixed-kinetics model’ for dissolution; a sequence of molecular and diffusion reactions derived, historically, from the use of the spinning-disc reactor. As a first step, the paper shows how carbonate chemistry can be introduced into the molecular component, to generate the ions that subsequently diffuse across the hydrodynamic boundary layer surrounding the solid, into the bulk solution. The intention is to discover how control of the whole reaction shifts between molecular and diffusion components with change in stirring conditions, as that condition is a significant barrier to linking laboratory and field studies. In the interim, however, the study presents four archetypal, [Ca2+] versus time plots (geometric templates) that cover reactors either open or closed to CO2, and in which pH is either fixed or variable. These plots provide a better alternative to the more common one of rate versus reaction extent, Ω, favoured in oceanography, but which has proved to be unsatisfactory. In turn, these new templates are compared with existing standard kinetics curves, for example, one from the analytic solution for a non-hydrolysing AB-salt, e.g., gypsum.
{"title":"A new sub-routine for the molecular component of the mixed-kinetics dissolution model of CaCO3 in seawater-like solutions","authors":"Victor W. Truesdale , Jim Greenwood , Tim Southern","doi":"10.1016/j.marchem.2025.104599","DOIUrl":"10.1016/j.marchem.2025.104599","url":null,"abstract":"<div><div>As a prelude to further understanding the dissolution kinetics of CaCO<sub>3</sub> in the oceanic water-column, the principles of Chemical Kinetics are applied generally to what recently was defined as the <em>solution-oriented approach</em> to CaCO<sub>3</sub> dissolution kinetics. The ultimate objective of the study is to probe what is known commonly as, the ‘mixed-kinetics model’ for dissolution; a sequence of molecular and diffusion reactions derived, historically, from the use of the spinning-disc reactor. As a first step, the paper shows how carbonate chemistry can be introduced into the molecular component, to generate the ions that subsequently diffuse across the hydrodynamic boundary layer surrounding the solid, into the bulk solution. The intention is to discover how control of the whole reaction shifts between molecular and diffusion components with change in stirring conditions, as that condition is a significant barrier to linking laboratory and field studies. In the interim, however, the study presents four archetypal, [Ca<sup>2+</sup>] versus time plots (geometric templates) that cover reactors either open or closed to CO<sub>2</sub>, and in which pH is either fixed or variable. These plots provide a better alternative to the more common one of rate versus reaction extent, Ω, favoured in oceanography, but which has proved to be unsatisfactory. In turn, these new templates are compared with existing standard kinetics curves, for example, one from the analytic solution for a non-hydrolysing AB-salt, e.g., gypsum.</div></div>","PeriodicalId":18219,"journal":{"name":"Marine Chemistry","volume":"274 ","pages":"Article 104599"},"PeriodicalIF":2.5,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145840236","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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