Global Biogeochemical Cycles最新文献

{"title":"Long-Term Changes of Surface Total Alkalinity and Its Driving Mechanisms in the North Indian Ocean","authors":"A. P. Joshi, Prasanna Kanti Ghoshal, Kunal Chakraborty, Rajdeep Roy, Chiranjivi Jayaram, B. Sridevi, V. V. S. S. Sarma","doi":"10.1029/2024GB008344","DOIUrl":"10.1029/2024GB008344","url":null,"abstract":"<p>This study examines long-term changes in surface total alkalinity (TA) in the North Indian Ocean (NIO) by developing a machine learning-based data product (INCOIS_TA) using ship-based observations collected from different sources during the period 1978–2019 and a reanalysis data product. We identify three sub-regions within the NIO exhibiting significantly increasing TA trends, which are south of 7°N (0.81<span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mo>±</mo>\u0000 </mrow>\u0000 <annotation> $pm $</annotation>\u0000 </semantics></math>0.38 <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mi>μ</mi>\u0000 </mrow>\u0000 <annotation> ${upmu }$</annotation>\u0000 </semantics></math>mol <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <msup>\u0000 <mtext>kg</mtext>\u0000 <mrow>\u0000 <mo>−</mo>\u0000 <mn>1</mn>\u0000 </mrow>\u0000 </msup>\u0000 </mrow>\u0000 <annotation> ${text{kg}}^{-1}$</annotation>\u0000 </semantics></math> <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <msup>\u0000 <mtext>yr</mtext>\u0000 <mrow>\u0000 <mo>−</mo>\u0000 <mn>1</mn>\u0000 </mrow>\u0000 </msup>\u0000 </mrow>\u0000 <annotation> ${text{yr}}^{-1}$</annotation>\u0000 </semantics></math>), southeastern coast of the Arabian Sea (AS) (1.16<span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mo>±</mo>\u0000 </mrow>\u0000 <annotation> $pm $</annotation>\u0000 </semantics></math>0.42 <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mi>μ</mi>\u0000 </mrow>\u0000 <annotation> ${upmu }$</annotation>\u0000 </semantics></math>mol <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <msup>\u0000 <mtext>kg</mtext>\u0000 <mrow>\u0000 <mo>−</mo>\u0000 <mn>1</mn>\u0000 </mrow>\u0000 </msup>\u0000 </mrow>\u0000 <annotation> ${text{kg}}^{-1}$</annotation>\u0000 </semantics></math> <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <msup>\u0000 <mtext>yr</mtext>\u0000 <mrow>\u0000 <mo>−</mo>\u0000 <mn>1</mn>\u0000 </mrow>\u0000 </msup>\u0000 </mrow>\u0000 <annotation> ${text{yr}}^{-1}$</annotation>\u0000 </semantics></math>), and the southwestern region of the Bay of Bengal (BoB) (0.47<span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 ","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":"39 8","pages":""},"PeriodicalIF":5.5,"publicationDate":"2025-08-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144832556","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}

{"title":"Regulation of Particulate Organic Carbon by Cascade Mega-Reservoirs in the Changjiang Basin: Enhanced Sequestration and Altered Downstream Composition","authors":"Yutian Ke,&nbsp;Damien Calmels,&nbsp;Julien Bouchez,&nbsp;Aurélie Noret,&nbsp;Marc Massault,&nbsp;Benjamin Chetelat,&nbsp;Hongming Cai,&nbsp;Jiubin Chen,&nbsp;Cécile Quantin,&nbsp;Jérôme Gaillardet","doi":"10.1029/2024GB008479","DOIUrl":"10.1029/2024GB008479","url":null,"abstract":"<p>Artificial reservoirs significantly alter the natural transport of suspended particulate matter (SPM) from rivers to oceans, thereby reshaping the global carbon cycle through changes in particulate organic carbon (POC) dynamics over decadal to millennial timescales. Here, we investigate dam-induced perturbation of POC composition, transport, and fate within the Changjiang (CJ) River basin in response to the operation of cascade mega-reservoirs (CMRs) along the Jinshajiang (JSJ) in the upper CJ. The CMRs have introduced new perturbations to SPM and POC delivery, compounding the effects of the Three Gorges Dam (TGD). We analyzed elemental, stable, and radiogenic isotopic compositions of POC, as well as the inorganic chemistry of SPM collected from both the upper and lower CJ. Since the construction of CMRs, POC sequestration in artificial reservoirs reaches approximately 6.6 megatons carbon per year (MtC yr⁻¹), 3.8 MtC yr⁻¹ of which being POC of biospheric origin (POC_bio). Notably, the flux of POC trapped in the TGD declined from 1.6 to 0.4 MtC yr⁻¹, while CMRs sequestered 0.7 MtC yr⁻¹. This shift highlights the relocation of POC burial sites from the TGD and estuary to upstream reservoirs. The rapid burial of terrestrial POC in large mountainous river reservoirs is expected to enhance POC preservation by minimizing mineralization caused by prolonged transport to estuaries. The significant reduction in sediment load and the increased proportion of POC_bio due to reservoir retention have substantially altered the composition and flux of exported POC, impacting downstream and estuarine carbon cycles.</p>","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":"39 8","pages":""},"PeriodicalIF":5.5,"publicationDate":"2025-08-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2024GB008479","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144811083","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}

{"title":"Two Decades of Increase in Southern Ocean Net Community Production Revealed by BGC-Argo Floats","authors":"Guillaume Liniger,&nbsp;Jonathan D. Sharp,&nbsp;Yuichiro Takeshita,&nbsp;Kenneth S. Johnson","doi":"10.1029/2024GB008371","DOIUrl":"10.1029/2024GB008371","url":null,"abstract":"<p>Nitrate is an essential nutrient for phytoplankton growth and is a primary component of ocean carbon cycling. In this study, we developed a neural network constrained by the high spatial and temporal coverage of BGC-Argo floats to predict nitrate in a consistent way throughout space and time in the Southern Ocean, a key area for ocean carbon uptake and controlling global ocean nutrient distributions. After correcting for physical and sampling biases using the Biogeochemical Southern Ocean State Estimate model, we show that annual net community production (ANCP), originally calculated from seasonal nitrate drawdown, reveals the greatest production around the 45–55°S meridional band, and an average basin-wide ANCP of 3.91 ± 0.13 PgC y⁻¹ with a significant increase of 0.67% y⁻¹ from 2004 to 2022. We also highlight that using the common nitrate seasonal drawdown method to derive ANCP might underestimate the true carbon export at depth by about one third. Our findings align with previous studies, which indicate an increase in surface satellite chlorophyll-<i>a</i> and model export fluxes. Our results demonstrate the potential of leveraging machine learning constrained by BGC-Argo observations to study long-term changes of biogeochemical processes in the ocean.</p>","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":"39 8","pages":""},"PeriodicalIF":5.5,"publicationDate":"2025-08-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2024GB008371","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145128952","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}

{"title":"The Role of Sediments in Modulating Nitrous Oxide Production in the Southern Benguela Upwelling System: Insights From Stable Isotopic Tracers","authors":"Sina Wallschuss,&nbsp;Julie Granger,&nbsp;Annie Bourbonnais,&nbsp;Raquel Flynn,&nbsp;Jessica Burger,&nbsp;Keshnee Pillay,&nbsp;Sarah Fawcett","doi":"10.1029/2024GB008463","DOIUrl":"10.1029/2024GB008463","url":null,"abstract":"<p>The ocean accounts for ∼20%–30% of global nitrous oxide (N₂O) emissions, with coastal upwelling systems estimated to contribute disproportionately to the sea-air flux of this potent greenhouse gas. To investigate the mechanisms of and controls on N₂O production in coastal upwelling systems, we measured the concentration and nitrogen and oxygen isotopic composition of N₂O (δ¹⁵N-N₂O and δ¹⁸O-N₂O) along a cross-shelf transect in the Southern Benguela Upwelling System (SBUS). At the shelf bottom, N₂O concentrations increased from the outer shelf toward the shore (11–32 nM) inversely to dissolved oxygen (182 ± 17 to &lt;1 μM) and in concert with the remineralization tracers, apparent oxygen utilization (108 ± 21 to 221 ± 33 μM) and nitrogen (N)-deficit (up to 20.4 μM). These observations suggest that both nitrification and denitrification may be involved in N₂O production on the SBUS shelf. The δ¹⁵N-N₂O implicates both processes as potential N₂O sources on the shelf, with high δ¹⁸O-N₂O values (≤57.2‰) specifically incriminating sediments as the primary N₂O source to the water column. Isotopic changes across the shelf delineate three discrete domains with distinct N₂O sources. Sedimentary nitrification and/or denitrification dominate N₂O production on the <i>midshelf</i>, while coupled nitrification-denitrification explains N₂O production on the <i>inner-shelf</i>. At the <i>shallow inner-shelf</i> where oxygen is depleted, both water column and sedimentary denitrification account for the production and partial consumption of N₂O. This study illuminates the disproportionate contribution of sedimentary N cycling to N₂O production on the SBUS shelf.</p>","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":"39 8","pages":""},"PeriodicalIF":5.5,"publicationDate":"2025-08-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GB008463","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144773641","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}

{"title":"Seasonal and Diurnal Patterns of Methane Emissions From a Northern Pristine Peatland in the Last Decade","authors":"Wenzhuo Duan,&nbsp;Mousong Wu,&nbsp;Matthias Peichl,&nbsp;Hongxing He,&nbsp;Nigel Roulet,&nbsp;Koffi Dodji Noumonvi,&nbsp;Joshua L. Ratcliffe,&nbsp;Mats B. Nilsson,&nbsp;Per-Erik Jansson","doi":"10.1029/2025GB008518","DOIUrl":"10.1029/2025GB008518","url":null,"abstract":"<p>Northern peatlands are key carbon reservoirs and natural sources of methane (CH₄). However, the environmental controls of CH₄-related processes remain unclear, making modeling the emissions a challenge. In this study, we first evaluated the process-based CoupModel with unique long-term (2001–2023) in situ measurements from a pristine sedge-dominated peatland in northern Sweden. Results show that the calibrated model can reproduce the hourly CH₄ fluxes (<i>r</i>² = 0.63) and CO₂ flux, and the abiotic variations well. The CH₄ flux showed significant sensitivity (66% relative importance) to parameters related to CH₄ transport, followed by production and oxidation. We further showed that CH₄ fluxes respond to temperature and water table depth (WTD) with a seasonal hysteresis, suggesting a 35% higher temperature sensitivity during below-average WTD compared to above-average WTD, and a two times higher sensitivity of CH₄ to lowering WTD than to elevating WTD. The hourly growing-season CH₄ fluxes response to temperature also displayed a hysteresis in the diurnal cycle, with nighttime CH₄ fluxes being 14%–23% higher than the daytime fluxes. We presented a CH₄ budget for the site and estimated the annual mean methane emissions from 2014 to 2023 to be 12.2 ± 1.2 gC/m²/yr, identifying the emissions predominantly contributed by diffusion. We conclude that CoupModel can effectively simulate the CH₄ emission and its controls for the northern pristine peatland. Our study reveals the importance of hysteresis in the response of methane fluxes to environmental changes and highlights the need for considering the temporal and hydrologic variability in CH₄-temperature dependencies in peatland management.</p>","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":"39 8","pages":""},"PeriodicalIF":5.5,"publicationDate":"2025-08-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144773834","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}

{"title":"Biological, Biogeochemical, Bio-Optical, and Physical Variability of the Southern Ocean Along 150°W and Its Relevance to the Great Calcite Belt","authors":"W. M. Balch,&nbsp;D. J. McGillicuddy Jr.,&nbsp;N. R. Bates,&nbsp;P. L. Morton,&nbsp;D. Drapeau,&nbsp;B. Bowler,&nbsp;S. Pinkham,&nbsp;M. Enright,&nbsp;R. Garley,&nbsp;H. Oliver","doi":"10.1029/2024GB008457","DOIUrl":"10.1029/2024GB008457","url":null,"abstract":"<p>We report hydrographic and biogeochemical measurements from a meridional transect performed along 150°W, 30°S to 60°S in the Southern Ocean, plus Polar waters to the east. Both of these areas are sites of annual high-reflectance features in ocean color remote sensing, which were heretofore never confirmed with in situ measurements. This study aimed to document factors driving phytoplankton productivity and coccolithophore calcification within the circumpolar coccolithophore-rich band known as the Great Calcite Belt (GCB). We measured concentrations of particulate inorganic carbon (PIC) and biogenic silica (BSi), two common biominerals, sources of ballast for organic matter, and contributors to optical reflectance. Results demonstrated that integrated euphotic standing stocks of PIC were highest in the GCB and at the Polar Front south of 54°S. BSi concentrations were highest south of 54°S. Integrated calcification rates were highest near the Polar and Subantarctic Fronts, whereas peak photosynthesis rates were observed in Subantarctic waters of the GCB, near the site of Subantarctic Mode Water formation. South of ∼54°S, optical particulate backscattering (<i>b</i>_bp) of BSi dominated over PIC <i>b</i>_bp by 10×, while in the GCB, PIC <i>b</i>_bp dominated over BSi <i>b</i>_bp by a similar magnitude. The slope of the particle size distribution function became less negative with depth, a trend that reflects larger particles becoming more abundant relative to smaller particles. Moreover, typical relationships between the particle size distribution slope and beam attenuation were only observed in the top 50 m depth, suggesting a fundamental difference in particle composition and size for deeper suspensions in this region.</p>","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":"39 8","pages":""},"PeriodicalIF":5.5,"publicationDate":"2025-08-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GB008457","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144767882","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}

{"title":"Environmental Drivers and Spatial-Temporal Estimation of Precipitation Change Effects on Soil Respiration at the Global Scale","authors":"Yifan Wu,&nbsp;Xiaobo Li,&nbsp;Xiaoyang Li,&nbsp;Chen Huang,&nbsp;Eli Argaman,&nbsp;Jun Liu,&nbsp;Yan Xiao","doi":"10.1029/2024GB008415","DOIUrl":"10.1029/2024GB008415","url":null,"abstract":"<p>Soil respiration (Rs) is defined as the emission of carbon dioxide from soil into the atmosphere, which represents a critical carbon flux within terrestrial ecosystems. Precipitation change significantly influences Rs, generating feedback mechanisms pertinent to global climate change. Nevertheless, the global distribution and environmental determinants of precipitation's effects on Rs remain uncertain. We compiled a database encompassing 570 Rs observations from field experiments that manipulated precipitation, derived from 221 published studies. Utilizing this comprehensive data set, we conducted a meta-analysis to elucidate Rs responses to precipitation alterations. Subsequently, we employed a machine learning approach to provide a globally spatially explicit quantification of precipitation change effects on Rs under future climate scenarios. Our findings revealed that increased experimental precipitation markedly enhances Rs, while decreased precipitation inhibits it. Furthermore, Rs responses to precipitation change exhibited variability across ecosystems and climatic regions. This study also confirmed that the Rs responses vary based on the intensity and duration of precipitation change, with short-term or heavy precipitation fluctuations exerting the strongest effects. Environmental conditions influenced the reaction of Rs to precipitation change, as factors such as soil type, vegetation, and climate worked together to mediate spatial differences. Projections based on bioclimatic predictors suggest that future climate scenarios significantly amplify Rs responses to precipitation change, potentially increasing uncertainties in greenhouse gas emissions estimates. Overall, our analysis emphasizes the significance of context dependencies and offers a spatially explicit assessment of precipitation change impacts on Rs on a global level, providing a comprehensive reference for comprehending ecosystem carbon dynamics.</p>","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":"39 8","pages":""},"PeriodicalIF":5.5,"publicationDate":"2025-07-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144725374","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}

{"title":"New Deoxygenation Threshold for N2 and N2O Production in Coastal Waters and Sediments","authors":"Ludovic Pascal,&nbsp;Félix Cloutier-Artiwat,&nbsp;Arturo Zanon,&nbsp;Douglas W. R. Wallace,&nbsp;Gwénaëlle Chaillou","doi":"10.1029/2024GB008218","DOIUrl":"10.1029/2024GB008218","url":null,"abstract":"&lt;p&gt;Bioavailable nitrogen governs ocean productivity and carbon fixation by regulating phytoplankton growth and community composition. Nitrogen input primarily results from &lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\u0000 &lt;msub&gt;\u0000 &lt;mi&gt;N&lt;/mi&gt;\u0000 &lt;mn&gt;2&lt;/mn&gt;\u0000 &lt;/msub&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; ${mathrm{N}}_{2}$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt; fixation, while denitrification and anammox remove bioavailable nitrogen in oxygen-depleted conditions. Traditionally considered limited to highly suboxic (i.e., &lt;5 μM) waters, recent studies suggest that fixed-nitrogen removal processes may extend beyond, elevating global nitrogen loss estimates. This study directly quantifies fixed-nitrogen loss across oxygen gradients (from 140 to 32 μM) along the Estuary and Gulf of St. Lawrence using N cycle tracers (&lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\u0000 &lt;msub&gt;\u0000 &lt;mi&gt;N&lt;/mi&gt;\u0000 &lt;mn&gt;2&lt;/mn&gt;\u0000 &lt;/msub&gt;\u0000 &lt;mo&gt;/&lt;/mo&gt;\u0000 &lt;mtext&gt;Ar&lt;/mtext&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; ${mathrm{N}}_{2}/text{Ar}$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt;, &lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\u0000 &lt;msup&gt;\u0000 &lt;mi&gt;N&lt;/mi&gt;\u0000 &lt;mo&gt;∗&lt;/mo&gt;\u0000 &lt;/msup&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; ${mathrm{N}}^{ast }$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt;, and &lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\u0000 &lt;msub&gt;\u0000 &lt;mi&gt;N&lt;/mi&gt;\u0000 &lt;mn&gt;2&lt;/mn&gt;\u0000 &lt;/msub&gt;\u0000 &lt;mi&gt;O&lt;/mi&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; ${mathrm{N}}_{2}mathrm{O}$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt;). Notably, we observe significant &lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\u0000 &lt;msub&gt;\u0000 &lt;mi&gt;N&lt;/mi&gt;\u0000 &lt;mn&gt;2&lt;/mn&gt;\u0000 &lt;/msub&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; ${mathrm{N}}_{2}$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt; production when ambient &lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\u0000 &lt;msub&gt;\u0000 &lt;mi&gt;O&lt;/mi&gt;\u0000 &lt;mn&gt;2&lt;/mn&gt;\u0000 &lt;/msub&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; ${mathrm{O}}_{2}$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt; concentrations fall below a threshold value of 58.9 ± 1.1 μM, including potential water column fixed-nitrogen removal processes above suboxia. We hypothesis that ambient deoxygenation eases the formation of suboxic microareas in suspended organi","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":"39 8","pages":""},"PeriodicalIF":5.5,"publicationDate":"2025-07-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GB008218","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144716492","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}

{"title":"Mechanisms Underlying Near-Universal Export Patterns of Dissolved Carbon From Land to Rivers","authors":"Bryn Stewart,&nbsp;Li Li","doi":"10.1029/2024GB008361","DOIUrl":"10.1029/2024GB008361","url":null,"abstract":"<p>Land-to-river exports of dissolved carbon, characterized through concentration-discharge (CQ) relationships, follow strikingly consistent, near-universal patterns: dissolved organic carbon (DOC) typically exhibits a flushing pattern (<i>C</i> increases with <i>Q</i>), while dissolved inorganic carbon (DIC) exhibits a dilution pattern (<i>C</i> decreases with <i>Q</i>). Another, albeit sparsely documented, universal pattern is their contrasting vertical distributions in subsurface water—DOC concentrations generally decrease with subsurface depth, whereas DIC concentrations increase. These observations prompt intriguing questions: <i>What mechanisms underlie these near-universal patterns, and how are they interconnected?</i> Here, we address these questions by carrying out numerical experiments across a wide range of conditions using a data-grounded, catchment-scale reactive transport model (BioRT-HBV). Results reveal that biogeochemical reactions governing the production and consumption of dissolved carbon dictate the direction of export patterns (flushing or dilution) by establishing vertical concentration gradients—quantified as the concentration ratios between shallow and deep waters (<i>C</i>_ratio). When biogeochemical reactions lead to higher concentrations in shallow soil waters than in deep waters (<i>C</i>_ratio &gt; 1), solutes exhibit flushing patterns, and vice versa. Meanwhile, the relative contributions of shallow and deep flow regulate stream concentration variability, where greater deep flow inputs dampen fluctuations and push CQ relationships toward near-zero slopes. These distinct roles of depth-dependent flow paths and biogeochemical processes indicate the importance of subsurface physical and biogeochemical structures in shaping export patterns of dissolved carbon from land to rivers. As climate extremes and human activities intensify, subsurface structure and processes can change, reshaping the future of carbon cycling, water quality, and ecosystem health.</p>","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":"39 8","pages":""},"PeriodicalIF":5.5,"publicationDate":"2025-07-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GB008361","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144717024","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}

{"title":"Evidence for Vegetation Acclimation to Atmospheric Dryness During European Droughts From a Land Surface Model","authors":"Camille Abadie,&nbsp;Fabienne Maignan,&nbsp;Cédric Bacour,&nbsp;Philippe Peylin","doi":"10.1029/2024GB008362","DOIUrl":"10.1029/2024GB008362","url":null,"abstract":"<p>Accurately characterizing the response of Gross Primary Production (GPP) and plant transpiration to soil moisture stress is crucial for reliable climate simulations as we expect an increase in drought events. In this study, we used the ORCHIDEE land surface model to investigate how the physiological response of vegetation to soil moisture stress can be refined, focusing on Europe, which has experienced significant droughts. We used in situ GPP and latent heat flux (LE) data from more than 40 sites across various biomes, along with data assimilation techniques, to improve GPP and plant transpiration representations. This work shows that the speed of stomatal closure under soil moisture stress can be refined by incorporating vegetation acclimation to long-term vapor pressure deficit (VPD) conditions. This new drought response results in a greater reduction in GPP root mean square deviation than a response based solely on biome type, achieving an 18% improvement at the site scale, whereas the biome-type-only version shows no improvement. Then, the two model versions show similar performance in simulating LE, with an 8%–9% improvement at the site scale. Projections up to 2100 show that, over Europe, incorporating VPD acclimation results in a vegetation sensitivity to drought with stomatal closure that is 22% lower than a response that only depends on the vegetation type. This study underscores the importance of better understanding and accounting for potential acclimation mechanisms in vegetation response to climate change and extreme events.</p>","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":"39 7","pages":""},"PeriodicalIF":5.5,"publicationDate":"2025-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GB008362","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144705556","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}