Global Biogeochemical Cycles最新文献_第6页

Linking Surface Phytoplankton Dynamics to Small-Particle Fluxes in the Mesopelagic Zone: Insights From High Latitude Bioregions Using BGC-Argo Floats 将表层浮游植物动力学与中远洋区的小颗粒通量联系起来：来自高纬度生物区的BGC-Argo浮标的见解

IF 5.5 2区地球科学

Global Biogeochemical Cycles Pub Date : 2025-07-09 DOI: 10.1029/2024GB008447

Elsa Simon, Léo Lacour, Hervé Claustre, Nicholas Bock, Marin Cornec, Raphaëlle Sauzède, Catherine Schmechtig, Laurent Coppola

{"title":"Linking Surface Phytoplankton Dynamics to Small-Particle Fluxes in the Mesopelagic Zone: Insights From High Latitude Bioregions Using BGC-Argo Floats","authors":"Elsa Simon, Léo Lacour, Hervé Claustre, Nicholas Bock, Marin Cornec, Raphaëlle Sauzède, Catherine Schmechtig, Laurent Coppola","doi":"10.1029/2024GB008447","DOIUrl":"10.1029/2024GB008447","url":null,"abstract":"Understanding factors controlling the biological carbon pump (BCP) at the regional scale is of major interest for better characterizing carbon sequestration into the deep ocean and, therefore, the ocean's role in climate regulation. This study focuses on high-latitude marine regions, which are responsible for the majority of marine CO2 absorption. Using data from Biogeochemical-Argo floats, a bioregionalization method was performed on 335 annual time series of chlorophyll a concentration and particulate backscattering coefficient, variables from which particulate organic carbon (POC) could be estimated. This analysis highlighted six regimes characterized by distinct seasonality in productivity, export, and transfer of small POC (<100 μm). Both hemispheres exhibited regimes with strong summer blooms and others with deep chlorophyll maxima. Across these regimes, variations in phytoplankton phenology and particle assemblages drove three distinct systems of BCP strength and efficiency for small particles. Despite these differences, processes such as gravitational sinking, the mixed layer pump, or particle fragmentation facilitated the export of small particles down to ∼1,000 m across all regions. This resulted in an average annual contribution of ∼10% of small particles to total organic carbon fluxes at depth, highlighting the role of small particles in long-term carbon sequestration. These findings emphasize the need for future investigations into processes driving small-particle carbon export and transfer in the mesopelagic zone at annual and seasonal scales.","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":"39 7","pages":""},"PeriodicalIF":5.5,"publicationDate":"2025-07-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GB008447","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144581848","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Diatom and Dinoflagellate Cyst Fluxes Over Four Annual Cycles in a High Arctic Fjord, Northeast Greenland 格陵兰东北部高北极峡湾四个年周期的硅藻和鞭毛藻囊通量

IF 5.5 2区地球科学

Global Biogeochemical Cycles Pub Date : 2025-07-05 DOI: 10.1029/2024GB008478

M. Mäkelä, T. Luostarinen, S. Ribeiro, K. Weckström, M. Sejr, M. Winding, M. Heikkilä

{"title":"Diatom and Dinoflagellate Cyst Fluxes Over Four Annual Cycles in a High Arctic Fjord, Northeast Greenland","authors":"M. Mäkelä, T. Luostarinen, S. Ribeiro, K. Weckström, M. Sejr, M. Winding, M. Heikkilä","doi":"10.1029/2024GB008478","DOIUrl":"10.1029/2024GB008478","url":null,"abstract":"Retreating sea ice and freshening surface waters are rapidly changing Arctic coastal environments. To predict the impacts of cryosphere change, it is essential to understand ecosystem variability beyond the instrumental era. Diatoms and dinoflagellate resting cysts have been abundantly used to reconstruct past marine conditions. Our understanding of microfossil species' ecologies is predominantly based on ecophysiological studies, the spatial distribution of species in surface sediments in relation to surface-ocean conditions and sediment-core studies. However, little is known about their seasonal ecologies and how biotic interactions impact species abundances. Here, we present sediment trap records of diatom and dinocyst succession over 4 years in a seasonally ice-covered Northeast Greenland fjord. We found highly seasonal diatom blooms and dinocyst production, but no clear separation in the timing between sea-ice indicating and open-water species fluxes. The interannual variation was not linked with the timing of sea-ice breakup. Instead, we linked higher production of heterotrophic dinocysts with high river discharge, while the highest diatom fluxes were often recorded during relatively low river discharge, suggesting that land-derived meltwaters controlled the blooms through stratification and light limitation. Thus, while we were not able to detect detailed species-environment dynamics due to the resolution of the trap data, our results indicate that the limitation of light and nutrients due to river discharge may override the impacts of sea-surface temperature and sea-ice cycle. We highlight that land-derived inputs should be considered alongside other parameters of sea-surface conditions when using diatoms and dinocysts as paleoecological proxies in Arctic fjord settings.","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":"39 7","pages":""},"PeriodicalIF":5.5,"publicationDate":"2025-07-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GB008478","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144558325","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Contrasting Impacts of Acclimation and Adaptation of Photosynthetic Capacity to Temperature and CO2 Across Biomes 不同生物群系光合能力对温度和CO2的驯化和适应的对比影响

IF 5.5 2区地球科学

Global Biogeochemical Cycles Pub Date : 2025-07-03 DOI: 10.1029/2024GB008398

Rebecca J. Oliver, Lina M. Mercado, Belinda E. Medlyn, Phil P. Harris, Douglas B. Clark

{"title":"Contrasting Impacts of Acclimation and Adaptation of Photosynthetic Capacity to Temperature and CO2 Across Biomes","authors":"Rebecca J. Oliver, Lina M. Mercado, Belinda E. Medlyn, Phil P. Harris, Douglas B. Clark","doi":"10.1029/2024GB008398","DOIUrl":"10.1029/2024GB008398","url":null,"abstract":"The response of photosynthesis to temperature and CO2 is poorly represented in land surface models, contributing uncertainty to estimates of the land carbon sink. We assess the sensitivity of carbon uptake to temperature adaptation and acclimation of photosynthetic capacity and CO2 acclimation of photosynthesis in the JULES model forced with an RCP8.5 climate scenario. Simulations show enhanced global gross primary productivity (GPP) when these processes are included, but over time the enhancement of GPP is weakened. In extratropical regions, temperature acclimation enhances GPP by aligning the photosynthetic temperature optimum with seasonal temperatures, allowing higher rates of carbon assimilation. In the tropics, temperature adaptation weakens the rate of global carbon uptake by reducing the CO2 sensitivity of photosynthesis and limiting the CO2 fertilization response, while acclimation sustains higher rates of photosynthesis as temperatures rise. Combined, our results suggest enhanced thermal resilience of modeled global GPP to warming. Downregulation of photosynthetic capacity in response to elevated CO2 could substantially affect future GPP. However, this response remains uncertain, highlighting the need for improved understanding and representation of CO2 acclimation across biomes, especially in tropical ecosystems where field data are scarce. Results suggest models omitting these processes may underestimate global carbon uptake and ignore important spatial variability in response to climate change.","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":"39 7","pages":""},"PeriodicalIF":5.5,"publicationDate":"2025-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GB008398","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144536863","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Organic Matter Availability and the Production of Methane-Derived Dissolved Organic Carbon at Methane Seeps 甲烷渗漏处有机质有效性和甲烷衍生溶解有机碳的产生

IF 5.5 2区地球科学

Global Biogeochemical Cycles Pub Date : 2025-07-03 DOI: 10.1029/2025GB008535

Ellen Lalk, John W. Pohlman, Laura L. Lapham

{"title":"Organic Matter Availability and the Production of Methane-Derived Dissolved Organic Carbon at Methane Seeps","authors":"Ellen Lalk, John W. Pohlman, Laura L. Lapham","doi":"10.1029/2025GB008535","DOIUrl":"10.1029/2025GB008535","url":null,"abstract":"Methane seeps located along continental margins and slopes export sedimentary methane and dissolved organic carbon (DOC) into the ocean. The flux of these reduced carbon molecules from the seafloor into the ocean impacts ocean chemistry and supports deep-sea life. While significant effort has been made to understand how the anaerobic oxidation of methane (AOM) regulates the release of methane from the seafloor, little is known about the production of DOC in association with AOM or its flux and fate in the ocean. We hypothesize a mechanism for methane incorporation into DOC at seeps and investigate the relationship between sediment total organic carbon (TOC) availability and the incorporation of methane-derived carbon into DOC at four methane seep regions along the Cascadia margin, with a range of microbial and thermogenic methane sources. At sites with <2.0 wt.% TOC (Hydrate Ridge and Bullseye Vent), up to 60%–80% of carbon in DOC is methane-carbon, much more than sites with >2.0 wt.% TOC (Astoria Canyon and Barkley Canyon). We attribute the greater methane contribution at the more TOC-limited sites to a greater role of AOM in the carbon cycle, whereas at the organic matter-rich sites, microbial competition for sulfate as an electron acceptor for organic matter decomposition limits AOM and hence the transfer of carbon from methane to DOC. We estimate that the global diffusive flux of methane-derived DOC from the seafloor is 0.07–10.1 Tg C/yr, contributing to the stock of DOC present in the deep ocean and/or fueling the deep-sea microbial loop.","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":"39 7","pages":""},"PeriodicalIF":5.5,"publicationDate":"2025-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144551028","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

The Imprint of Southern Ocean Storms on Modeled Surface Chlorophyll, Their Drivers and Satellite Biases 南大洋风暴对模拟地表叶绿素的影响及其驱动因素和卫星偏差

IF 5.5 2区地球科学

Global Biogeochemical Cycles Pub Date : 2025-07-01 DOI: 10.1029/2025GB008550

Cara Nissen, Genevieve L. Clow, Nicole S. Lovenduski, Katherine E. Turner, Magdalena M. Carranza, Kristen M. Krumhardt

{"title":"The Imprint of Southern Ocean Storms on Modeled Surface Chlorophyll, Their Drivers and Satellite Biases","authors":"Cara Nissen, Genevieve L. Clow, Nicole S. Lovenduski, Katherine E. Turner, Magdalena M. Carranza, Kristen M. Krumhardt","doi":"10.1029/2025GB008550","DOIUrl":"10.1029/2025GB008550","url":null,"abstract":"Southern Ocean (SO) phytoplankton chlorophyll is highly variable on sub-seasonal time scales. Although the SO is the windiest ocean basin globally, it is not conclusively understood how storms impact SO phytoplankton dynamics. Much of our existing knowledge stems from satellites, but biases due to data gaps from cloud cover and low solar angles remain unquantified. Here, we use ocean–sea-ice simulations with the Community Earth System Model to quantify the climatological 1997–2018 imprint of storms on chlorophyll and phytoplankton dynamics in the ice-free SO. Additionally, by comparing the full-field model output to synthetic satellite observations, we quantify sampling biases in satellite-derived estimates. We find that both the sign and the magnitude of the average surface chlorophyll imprint vary substantially across storms but last for at least 4 days after the storm passing. Based on our analysis, more than one third of the storms explain the majority of local non-seasonal chlorophyll variability, but satellite-derived storm imprints are often too large in magnitude. On the day of the storm passing, changes in vertical mixing predominantly cause surface chlorophyll anomalies, and reduced light availability due to enhanced cloud cover outweighs the enhanced nutrient availability due to entrainment. Interestingly, storms imprint differently on total net primary production than on surface chlorophyll, demonstrating the difficulty to derive carbon-cycle impacts from a surface-chlorophyll assessment. With SO future storm activity projected to increase, complementing satellite observations with other observing technologies, for example, profiling floats, is necessary to better constrain how storms impact biological carbon cycling in the SO.","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":"39 7","pages":""},"PeriodicalIF":5.5,"publicationDate":"2025-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2025GB008550","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144524664","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Zooplankton and Picocyanobacteria Contribute Characteristic Size Ranges of Organic Particles to Different Layers of the Anoxic Water Column 浮游动物和花青菌为缺氧水柱的不同层贡献了有机颗粒的特征尺寸范围

IF 5.5 2区地球科学

Global Biogeochemical Cycles Pub Date : 2025-06-30 DOI: 10.1029/2024GB008397

Clara A. Fuchsman, Jacob A. Cram

{"title":"Zooplankton and Picocyanobacteria Contribute Characteristic Size Ranges of Organic Particles to Different Layers of the Anoxic Water Column","authors":"Clara A. Fuchsman, Jacob A. Cram","doi":"10.1029/2024GB008397","DOIUrl":"10.1029/2024GB008397","url":null,"abstract":"Oxygen deficient zones (ODZs) are key areas of nitrogen loss, a process dependent on organic matter. Understanding the sources of organic matter in the ODZ is necessary to predict how biogeochemical cycles will respond to ocean changes. Size fractionated (5–20, 20–53, 53–180, 180–500, >500 μm) particulate organic C and N (POM) concentration and isotopic composition depth profiles from three stations in the offshore Eastern Tropical North Pacific (ETNP) ODZ were used to gain insights into the origins of POM in the ODZ. Since the within-ODZ Prochlorococcus cells assimilate nitrite, we used the resulting highly depleted δ15N signal to trace organic matter of cyanobacterial origin to medium sized particles at the secondary chlorophyll maximum, and to >500 μm particles directly below the secondary chlorophyll maximum. This organic nitrogen was consumed in the upper ODZ. Other POM maxima were seen at the depths of the zooplankton vertical migration maxima with the increase in POM marked in the 5–20 μm fraction. In the deep ODZ, below the zooplankton migration depth, POM concentrations in the 5–20 μm fraction were unusually small, the C:N ratios were extremely high (>20), and δ15N was enriched (8–12‰), indicating degraded material. In deep samples, δ13C was more depleted in larger particles and correlated with enriched δ15N, indicating increased degradation in 53–500 μm particles. This trend suggests an additional source of small particles, such as from in situ production, rather than just the fragmentation of large particles.","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":"39 7","pages":""},"PeriodicalIF":5.5,"publicationDate":"2025-06-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GB008397","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144515076","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Wave Glider-Based Measurements and Corrections of Near-Surface pCO2 Gradients in the Coastal Ocean 基于波浪滑翔机的近海近地表co2梯度测量与校正

IF 5.5 2区地球科学

Global Biogeochemical Cycles Pub Date : 2025-06-28 DOI: 10.1029/2024GB008396

Sean Morgan, Sara Wong, Tyler Byrne, Adam Comeau, Brian Ward, Mark Barry, Dariia Atamanchuk

{"title":"Wave Glider-Based Measurements and Corrections of Near-Surface pCO2 Gradients in the Coastal Ocean","authors":"Sean Morgan, Sara Wong, Tyler Byrne, Adam Comeau, Brian Ward, Mark Barry, Dariia Atamanchuk","doi":"10.1029/2024GB008396","DOIUrl":"10.1029/2024GB008396","url":null,"abstract":"Carbonate system dynamics are highly variable in coastal and shelf regions, and poor spatiotemporal measurement resolution leads to inadequate constraints for global carbon sequestration estimates. Additionally, conventional pCO2 measurement-based flux calculations require an assumption of homogeneity in near-surface waters, excluding effects such as biological drivers and air-sea disequilibrium. To quantify the effect of these drivers by capturing high resolution measurements during short-term events, we present the deployment of a Liquid Robotics Wave Glider equipped with mirrored gas sensor suites at the surface and sub-surface during the 2022 spring bloom on the Scotian Shelf in eastern Canada. The temporal variability in the data reveals biologically driven diurnal pCO2 behavior that conventional low-resolution methods may overlook. Additionally, through direct measurement of surface and sub-surface pCO2 levels, we demonstrate that conventional underway measurement methods systematically underestimate surface pCO2 values in this region by 1–10 μatm, leading to flux estimation errors of up to 7%. These findings emphasize the value of high-resolution data for determining drivers of spatial variability and question the capacity of underway lines to measure true surface pCO2 values. By employing vehicle-based measurement techniques, we can improve our understanding of carbon dynamics in coastal environments and refine flux estimates for accurate climate modeling and management strategies.","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":"39 7","pages":""},"PeriodicalIF":5.5,"publicationDate":"2025-06-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GB008396","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144503026","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

The Role of Water Masses, Biological Processes, Remineralization and Reversible Scavenging in Controlling the Distribution of Dissolved Nickel in the Arabian Sea 水团、生物过程、再矿化和可逆清除在控制阿拉伯海溶解镍分布中的作用

IF 5.5 2区地球科学

Global Biogeochemical Cycles Pub Date : 2025-06-28 DOI: 10.1029/2024GB008441

Nirmalya Malla, Sunil Kumar Singh, Naman Deep Singh, Arvind Shukla, Venkatesh Chinni, Vineet Goswami, Robin John

{"title":"The Role of Water Masses, Biological Processes, Remineralization and Reversible Scavenging in Controlling the Distribution of Dissolved Nickel in the Arabian Sea","authors":"Nirmalya Malla, Sunil Kumar Singh, Naman Deep Singh, Arvind Shukla, Venkatesh Chinni, Vineet Goswami, Robin John","doi":"10.1029/2024GB008441","DOIUrl":"10.1029/2024GB008441","url":null,"abstract":"The present study describes the distribution of dissolved nickel (dNi) by sampling and analyzing seawater in the Arabian Sea. It aims to understand how different biogeochemical processes impact the distribution of dNi. The concentration of dNi ranges from 1.4–4.6 nM in surface waters to 6.8–12 nM in the deeper waters (>1,000 m) of the Arabian Sea. The distribution of dNi in the Arabian Sea is modulated by sources such as dust, riverine and submarine groundwater discharge, sinks such as biological uptake and adsorption processes, as well as internal cycling such as remineralization, reversible scavenging, and consumption in intense oxygen deficient zone in the water column influence the distribution of dNi in the Arabian Sea. Dissolved nickel has a higher concentration in the surface waters of the Arabian Sea, unlike other micronutrients such as Fe, Cd, Zn, Co, etc., potentially due to its unavailability for biological uptake. A significant portion of dNi (30%–50%) in the intermediate and deeper waters of the Arabian Sea is derived from the remineralization of organic matter, and the reversible scavenging process, similar to that in the Pacific Ocean. This is confirmed by the presence of additional dNi in excess of the preformed dNi supplied by water mass mixing in the Arabian Sea. The results of this study indicate significant depletion of dNi over Phosphate in the intense oxygen minimum zone of the Arabian Sea, implying a complex interplay of factors such as its loss as sulphides or Fe oxides or POC and due to varying ecosystem composition.","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":"39 7","pages":""},"PeriodicalIF":5.5,"publicationDate":"2025-06-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144503027","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Origins of the Nitrate 15N Depletion in the Mediterranean Sea 地中海硝酸盐15N耗竭的起源

IF 5.5 2区地球科学

Global Biogeochemical Cycles Pub Date : 2025-06-25 DOI: 10.1029/2023GB008035

T. Wald, F. Fripiat, A. D. Foreman, Y. Ryu, D. Marconi, T. Tanhua, G. Sisma-Ventura, D. M. Sigman, G. H. Haug, A. Martínez-García

{"title":"Origins of the Nitrate 15N Depletion in the Mediterranean Sea","authors":"T. Wald, F. Fripiat, A. D. Foreman, Y. Ryu, D. Marconi, T. Tanhua, G. Sisma-Ventura, D. M. Sigman, G. H. Haug, A. Martínez-García","doi":"10.1029/2023GB008035","DOIUrl":"10.1029/2023GB008035","url":null,"abstract":"Previous studies have reported a nitrate 15N depletion in the Mediterranean Sea compared to the global ocean, attributed to either N2 fixation or atmospheric deposition of anthropogenic N. In this study, we report basin-wide full-depth profiles of nitrate δ15N (vs. Air) and δ18O (vs. Vienna Standard Mean Ocean Water, VSMOW) in the Mediterranean Sea. Our results confirm a consistent 15N depletion across the entire Mediterranean Sea, with significantly lower nitrate δ15N values in the eastern basin (2.2 ± 0.2‰) than in the western basin (2.9 ± 0.1‰). In contrast, there is no significant difference in nitrate δ18O between the two basins (2.2 ± 0.3‰ and 2.1 ± 0.2‰, respectively). These observations point to a supply of low-δ15N N to the Mediterranean Sea, accumulating as regenerated nitrate, which is diluted by the nitrate in the Atlantic inflow, creating an west-to-east gradient in nitrate δ15N. A four-box model reveals that, given a water residence time of 120–170 years in the Mediterranean, a modest input rate of 1–3 Tg N yr−1—originating from N2 fixation, atmospheric deposition, or their combination—is adequate to produce the observed low δ15N of Mediterranean nitrate. Additionally, partial degradation of dissolved organic nitrogen imported from the Atlantic may add low-δ15N nitrate to the Mediterranean, but it alone cannot explain the full isotopic signal. Distinguishing among these sources will be aided by the reconstruction of Mediterranean nitrate δ15N through time using either time-series data of nitrate δ15N or calcareous fossil-bound organic nitrogen isotope ratios.","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":"39 6","pages":""},"PeriodicalIF":5.5,"publicationDate":"2025-06-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2023GB008035","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144473069","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Tracing Cation Exchange Processes at Earth's Surface Using Mg Isotopes 利用Mg同位素追踪地球表面阳离子交换过程

IF 5.5 2区地球科学

Global Biogeochemical Cycles Pub Date : 2025-06-23 DOI: 10.1029/2024GB008411

Di Cai, Shouye Yang

{"title":"Tracing Cation Exchange Processes at Earth's Surface Using Mg Isotopes","authors":"Di Cai, Shouye Yang","doi":"10.1029/2024GB008411","DOIUrl":"10.1029/2024GB008411","url":null,"abstract":"Investigations into the interaction between rock (sediment) and water at Earth's surface have primarily focused on mineral dissolution/precipitation processes. While the presence of exchangeable cations on mineral surfaces has long been recognized, the coupled chemical evolution of this labile pool with surface water remains less understood. In this study, we demonstrate that Mg isotopes (expressed as δ value-δ26Mg) serve as an effective proxy for tracing cation exchange processes, as our batch exchange experiments and field investigations showed marginal Mg isotope fractionation (<0.2‰) between concomitant dissolved Mg and exchangeable Mg. This finding suggests that Mg isotope exchange follows a simple mixing process, resulting in nearly identical δ26Mg values between dissolved and exchangeable phases once equilibrium is achieved. Thus, the potential for exchangeable Mg to alter the δ26Mg of water—or vice versa—depends on the relative masses of Mg in these two phases. We further investigated the relative proportions of dissolved and exchangeable Mg across the surface sediment cycling pathway, from regolith to rivers and ultimately to estuaries. Our compiled data suggest that the exchangeable Mg pools in regolith from various geological settings are substantial enough to buffer the concentration and isotopic composition of Mg in infiltrating water, reducing their variations in runoff under changing hydrological conditions. In river channels, however, exchangeable Mg in suspended sediments accounts for a small fraction (∼6 ± 1.5%) of total dissolved Mg globally, meaning that exchange reactions are expected to have little impact on water chemistry as suspended particulate matter enter the river channels or the ocean.","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":"39 6","pages":""},"PeriodicalIF":5.5,"publicationDate":"2025-06-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144339314","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0