Global Biogeochemical Cycles最新文献

{"title":"Climate Change and Urbanization Decouple Dissolved Organic Carbon Quantity and Composition in Streams","authors":"James D. Kelley,&nbsp;Sandra Klemet-N'Guessan,&nbsp;Nolan J. T. Pearce,&nbsp;Claire M. Stevens,&nbsp;Anthony J. Arsenault,&nbsp;Miracle Denga,&nbsp;P. V. Sasindu L. Gunawardana,&nbsp;Sarah S. E. King,&nbsp;Carolina N. Koebel,&nbsp;Sherryann A. Prowell,&nbsp;Most Shirina Begum,&nbsp;Marguerite A. Xenopoulos","doi":"10.1029/2025GB008534","DOIUrl":"10.1029/2025GB008534","url":null,"abstract":"<p>Dissolved organic carbon (DOC) is a ubiquitous component of freshwater ecosystems that is sensitive to global change. In turn, DOC controls fundamental biogeochemical processes and functions. These controls depend on both the amount and composition of organic molecules comprising the dissolved organic matter (DOM) pool, which reflects the relative contributions of catchment-derived terrestrial inputs and in situ production. Stream DOM fluctuates with land use, soil mobility, and hydrology; however, few studies have monitored long-term changes in DOM composition to investigate links with climate. Here, we characterized 17-year trends in DOC and DOM in 48 streams across a land use gradient and modeled patterns therein with climatic and hydrological conditions. Across streams, Mann-Kendall trend analyses showed that DOC decreased through time, while DOM became fresher, more aromatic, and contained an increased proportion of urban-derived DOM from the terrestrial catchment. Using generalized additive models, we observed significant linear, unimodal, and multimodal patterns in DOM composition with precipitation and soil temperature. Generally, precipitation increased terrestrial DOM, whereas soil temperature increased urban-derived DOM, particularly in catchments characterized by increasing levels of urbanization. Our study highlights the importance of long-term monitoring in understanding dynamic interactions between terrestrial—fluvial carbon transfer and biogeochemical effects of global climate change and urbanization. Altogether, our results show that interactions between climate change and urbanization will shape future DOM dynamics in streams.</p>","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":"39 8","pages":""},"PeriodicalIF":5.5,"publicationDate":"2025-08-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2025GB008534","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144897385","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 Arctic Ocean CO2 Sink: Trends, Uncertainties, and the Impact of Sea Ice","authors":"Victoria R. Dutch,&nbsp;Dorothee C. E. Bakker,&nbsp;Alizée Roobaert,&nbsp;Peter Landschützer,&nbsp;Nicholas P. Roden,&nbsp;Mario Hoppema,&nbsp;Jan Kaiser","doi":"10.1029/2025GB008576","DOIUrl":"10.1029/2025GB008576","url":null,"abstract":"<p>The Arctic Ocean covers 3 % of the Earth's surface but is estimated to contribute 5–14 % to the global ocean carbon sink. Sparse and unevenly distributed observations complicate our understanding of the size and the controlling mechanisms of this carbon sink. We adopt and advance the two-step neural network approach of Landschützer et al. (2016, https://doi.org/10.1002/2015gb005359; Self Organizing Map—Feed Forward Network) to improve region-specific reconstructions of the surface ocean partial pressure of carbon dioxide (<span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mi>p</mi>\u0000 </mrow>\u0000 <annotation> $p$</annotation>\u0000 </semantics></math>(<span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <msub>\u0000 <mtext>CO</mtext>\u0000 <mn>2</mn>\u0000 </msub>\u0000 </mrow>\u0000 <annotation> ${text{CO}}_{2}$</annotation>\u0000 </semantics></math>)) in the Arctic Ocean and subsequently estimate the air-sea <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <msub>\u0000 <mtext>CO</mtext>\u0000 <mn>2</mn>\u0000 </msub>\u0000 </mrow>\u0000 <annotation> ${text{CO}}_{2}$</annotation>\u0000 </semantics></math> flux. Our study shows that biogeochemical properties previously selected as predictor variables for <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mi>p</mi>\u0000 </mrow>\u0000 <annotation> $p$</annotation>\u0000 </semantics></math>(<span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <msub>\u0000 <mtext>CO</mtext>\u0000 <mn>2</mn>\u0000 </msub>\u0000 </mrow>\u0000 <annotation> ${text{CO}}_{2}$</annotation>\u0000 </semantics></math>) at the global scale are not well suited to the Arctic Ocean and a sensitivity study reveals large differences in the size of the Arctic Ocean carbon sink depending on the choice of air-sea <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <msub>\u0000 <mtext>CO</mtext>\u0000 <mn>2</mn>\u0000 </msub>\u0000 </mrow>\u0000 <annotation> ${text{CO}}_{2}$</annotation>\u0000 </semantics></math> flux parameterization. This is most acute for those relating to sea ice cover, leading to a difference of up to 25 % (9.2–13.3 Pg C) in the total size of the Arctic Ocean carbon sink over the 32-year duration of the study.</p>","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":"39 8","pages":""},"PeriodicalIF":5.5,"publicationDate":"2025-08-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2025GB008576","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144894280","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":"Stochastic Dynamics of Gross Soil Nitrogen Transformations in Amazon Forests—High Local Variation but Lack of Basin-Wide Patterns","authors":"T. Rütting,&nbsp;V. Figueiredo,&nbsp;A. Enrich-Prast","doi":"10.1029/2024GB008454","DOIUrl":"10.1029/2024GB008454","url":null,"abstract":"<p>Tropical forests play a critical role in global climate regulation by taking up and storing significant amounts of carbon. Soil nitrogen (N) dynamics is the key to understanding forest productivity. However, we have only a very rudimentary understanding of in situ soil N transformations in the Amazon Basin, the largest intact tropical forest. This study investigated gross soil N dynamics across 12 locations in the Brazilian Amazon Basin using ¹⁵N labeling to quantify gross N transformations in situ. Our results revealed significant variation in both gross N mineralization and nitrification at the local and basin-scales. Unexpectedly, no spatial patterns were observed across locations, nor were gross N rates correlated with any measured soil properties. Our results suggest a stochastic and unpredictable nature of gross N transformation rates in the rainforests of the Amazon basin. These findings highlight the need for a more nuanced understanding of N cycling in tropical forests, which could improve ecological models and inform strategies for managing these ecosystems in the face of climate change and deforestation.</p>","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":"39 8","pages":""},"PeriodicalIF":5.5,"publicationDate":"2025-08-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2024GB008454","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144894388","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 Submarine Groundwater Discharge Drives Coastal Carbon Cycling and Modulates Buffering Capacity","authors":"Wei Wang,&nbsp;Qianqian Wang,&nbsp;Holly A. Michael,&nbsp;Zhaoxi Liu,&nbsp;Zhenyan Wang,&nbsp;Tianwei Wang,&nbsp;Yufei Gao,&nbsp;Manhua Luo,&nbsp;Hailong Li","doi":"10.1029/2025GB008629","DOIUrl":"10.1029/2025GB008629","url":null,"abstract":"<p>Submarine groundwater discharge (SGD) serves as a crucial pathway for terrestrial carbon transport to the ocean. However, our understanding of SGD's contribution to carbon dynamics and biogeochemical processes remains limited. Here, we used the radium quartet to estimate SGD in Daya Bay (China) across seasons and then applied dissolved carbon budget models for dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) to assess carbon sources and sinks and quantify SGD-derived carbon fluxes. The buffering capacity against ocean acidification and associated biogeochemical processes within the carbonate system was analyzed. SGD-derived DIC flux was 19–39 times that of local riverine input in autumn, and 27–66 times that of local riverine input in spring. SGD-derived DOC flux ranged from 2 to 6 times that of local riverine input in autumn and from 2 to 8 times in spring. Further, the biogeochemical processes regulating carbon components in seawater exhibited significant seasonal characteristics. Primary production and CO₂ outgassing were predominant in spring, associated with higher biological activity and calmer wind conditions. With lower primary productivity and enhanced remineralization in autumn, 37.5% of seawater samples might have undergone organic matter degradation and carbonate dissolution. Moreover, groundwater exhibited a buffering capacity across different seasons, with higher values observed in nearshore seawater during autumn and offshore seawater during spring. The buffering capacity of nearshore seawater was affected by coastal groundwater, exhibiting significant deviations relative to offshore seawater. This study emphasizes the essential role of SGD in coastal carbonate systems and reveals the seasonal characteristics in biogeochemical processes, buffering capacity, and environmental implications.</p>","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":"39 8","pages":""},"PeriodicalIF":5.5,"publicationDate":"2025-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144891701","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":"Chemoautotrophy Enhances Iron and Phosphorus Recycling From Sediments at Deep-Sea Methane Seeps","authors":"Yuxuan Lin,&nbsp;Jing Sun,&nbsp;Xiaotian Zhou,&nbsp;Cheng Zhong,&nbsp;Xingyu Yang,&nbsp;Liuqian Yu,&nbsp;Jin Sun,&nbsp;Pei-Yuan Qian,&nbsp;Jiying Li","doi":"10.1029/2025GB008735","DOIUrl":"10.1029/2025GB008735","url":null,"abstract":"<p>Methane-rich cold seeps are oases of life in the deep sea, where microbial chemosynthesis of organic matter sustains thriving ecosystems independent of sunlight-derived energy. Here, we reveal a previously overlooked role of chemoautotrophy at seeps as powerful recyclers of scarce nutrients iron (Fe) and phosphorus (P). Investigations of sediments at Haima cold seeps (1,300–1,500 m deep) across varying methane seepage intensities showed that seep sediments released orders of magnitude more dissolved Fe and phosphate than background sediments, despite comparable organic matter remineralization rates. At Haima seeps with high methane, sediment phosphate effluxes reached 2.00–15.8 µmol m⁻² d⁻¹and dissolved Fe effluxes reached 2.24–47.4 µmol m⁻² d⁻¹, compared to background phosphate efflux of 1.21 µmol m⁻² d⁻¹ and dissolved Fe efflux of 0.412 µmol m⁻² d⁻¹. This enhancement in nutrient recycling stems from a cascade of coupled biogeochemical processes driven by the anaerobic oxidation of methane (AOM). Methane oxidation reduces Fe oxides, releasing both dissolved Fe and Fe-bound P. AOM also reduces sulfate to sulfide, precipitates dissolved Fe and suppresses the regeneration of P-binding Fe oxides, further promoting P release. These mechanisms maintained the disproportionately high benthic Fe and P recycling at seeps, which may significantly impact regional and global nutrient budgets, given the thousands of documented seeps and potentially orders of magnitude more undiscovered in the global ocean.</p>","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":"39 8","pages":""},"PeriodicalIF":5.5,"publicationDate":"2025-08-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144888331","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":"Heterogenous Si Isotopic Composition in Coastal Groundwater: Controls on Dissolved Silicon and Groundwater Discharge Along Indian Coastline","authors":"Sarath Pullyottum Kavil,&nbsp;Jean Riotte,&nbsp;Ramananda Chakrabarti,&nbsp;V. V. S. S. Sarma,&nbsp;B. S. K. Kumar,&nbsp;J. Prunier,&nbsp;Arnaud Dapoigny,&nbsp;Damien Cardinal","doi":"10.1029/2025GB008706","DOIUrl":"10.1029/2025GB008706","url":null,"abstract":"<p>We report stable silicon isotope ratio (δ³⁰Si) of over 80 groundwater samples collected along the Indian coast, spanning a wide range of aquifer lithologies (alluvial, basalt, metamorphic, laterite and limestone), climate (semi-arid to tropical wet) and land use settings. Indian coastal groundwater exhibits large spatial variability in dissolved silicon (DSi) (80–1350 μM) and δ³⁰Si values (−1.1‰ to 4.5‰). On average, the δ³⁰Si value of the Indian coastal groundwater (0.8 ± 1.1‰, 1SD, <i>n</i> = 85) is comparable to published groundwater globally (0.8 ± 0.8‰, <i>n</i> = 117), and significantly lower than Indian riverine δ³⁰Si composition. The coastal groundwater δ³⁰Si values do not show any dependence on regional aquifer lithology. However, the permeable coastal alluvial groundwaters exhibit the highest variability in DSi and δ³⁰Si, likely acquiring signatures of shallow surface/subsurface processes through mixing. A broad negative correlation between δ³⁰Si values and the Ge/Si ratio is best explained by the partitioning of Si into secondary minerals phases within the weathering zone. The majority of coastal groundwater follows a steady-state model evolution, indicating a dynamic equilibrium between Si supply and the formation of secondary phases. In regions of low annual rainfall, groundwater irrigation can lead to infiltration of return flow water to aquifer systems, leading to their heavy δ³⁰Si values. The fresh submarine groundwater discharge along the Indian coast is estimated to be 2.1 GmolSi yr⁻¹, which is less than 1% of the riverine Si flux to the North Indian Ocean and 0.3% of the global fresh groundwater Si flux.</p>","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":"39 8","pages":""},"PeriodicalIF":5.5,"publicationDate":"2025-08-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2025GB008706","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144881384","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":"Composition and Plume Gas Interaction Control Iron Fractional Solubility More Than Particle Size in Volcanic Ash: Implications for Fertilization of the North Atlantic","authors":"H. E. Elliott,&nbsp;E. Blades,&nbsp;H. M. Royer,&nbsp;C. Buck,&nbsp;C. Kollman,&nbsp;R. Kukkadapu,&nbsp;S. China,&nbsp;Z. Cheng,&nbsp;N. N. Lata,&nbsp;M. Engelhard,&nbsp;M. Bowden,&nbsp;N. Lahiri,&nbsp;R. L. Parham,&nbsp;L. Meagher,&nbsp;B. Angstman,&nbsp;A. P. Ault,&nbsp;A. Hornby,&nbsp;K. Dayton,&nbsp;E. Gazel,&nbsp;C. J. Gaston","doi":"10.1029/2025GB008560","DOIUrl":"10.1029/2025GB008560","url":null,"abstract":"<p>Deposition of volcanic ash is thought to impact marine biogeochemical cycling by adding soluble iron (Fe) to the surface ocean. The magnitude of this input is a function of the amount of ash deposited, the total Fe content in the ash, and ash-derived Fe's fractional solubility. However, the relative importance of chemical composition, acidic processing by the volcanic plume, and ash particle size in determining solubility is unclear. We paired an aerosol leach meant to provide an upper limit for fractional Fe solubility with chemical analyses of ash from the Cumbre Vieja (CV) and La Soufrière eruptions, which both impacted the North Atlantic in 2021. Fe in the ash samples is &lt;6% soluble, but Fe fractional solubility in CV ash is approximately triple that of La Soufrière ash. Compared to La Soufrière, a larger proportion of the Fe in CV ash is in silicate rather than oxide minerals, which release more soluble Fe. Elevated levels of surficial fluorine (F) also suggest that CV ash was subjected to a more fluorine-rich eruption plume and underwent more acidic processing. Particle size does not appear to be a primary control on Fe release. We estimate that the CV eruption had a much larger impact on dissolved Fe (DFe) concentration in the surface ocean than the La Soufrière eruption because of differences in soluble Fe content and particle deposition velocity. These differences may help explain why some eruptions elicit a biological response in the ocean while others do not.</p>","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":"39 8","pages":""},"PeriodicalIF":5.5,"publicationDate":"2025-08-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2025GB008560","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144881385","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":"Upper Ocean Carbon Export Flux Estimation in the East Indian Ocean Using 234Th","authors":"S. Subha Anand,&nbsp;R. Rengarajan,&nbsp;A. K. Sudheer,&nbsp;V. V. S. S. Sarma","doi":"10.1029/2024GB008374","DOIUrl":"10.1029/2024GB008374","url":null,"abstract":"<p>The strength of the Biological Carbon Pump (BCP) to sequester atmospheric CO₂ in the East Indian Ocean is unclear due to lack of studies. Here, we estimated Particulate Organic Carbon (POC) export flux by using ²³⁴Th as a flux proxy in the upper Indian Ocean (0–300 m depth), including the East Indian Ocean. In seawater, the soluble parent radionuclide, ²³⁸U (<i>t</i>_1/2 = 4.47 × 10⁹ yr) decays to produce a particle-reactive daughter, ²³⁴Th (<i>t</i>_1/2 = 24.1 d), which surface adsorbs onto particles, and sinks from the euphotic zone to the sea bottom. Disequilibrium between ²³⁸U and ²³⁴Th in seawater and POC/²³⁴Th ratio in sinking particles is used to estimate POC export flux. In this study, euphotic depth integrated ²³⁴Th deficit fluxes and the estimated POC export flux varied from negligible to 2,025 ± 87 dpm m⁻² d⁻¹ and negligible to 6.6 ± 0.6 mmol C m⁻² d⁻¹, respectively. The BCP efficiency varied from negligible (in coastal Arabian Sea) to 14% (near equator), except for the Andaman Sea (0%–80%). Temporal decoupling of primary productivity and POC export flux in the Andaman Sea resulted in a high export ratio. Compilation of spring intermonsoon ²³⁴Th based POC export flux and export efficiency from JGOFS and GEOTRACES showed high export flux and efficiency in the open Arabian Sea and in the Equatorial Indian Ocean but low POC export flux and efficiency in the Bay of Bengal, Andaman Sea, East Indian Ocean, and South Indian Ocean. Although low in magnitude, the Equatorial Indian Ocean sequesters atmospheric CO₂ like the equatorial- Atlantic and Pacific Oceans.</p>","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":"39 8","pages":""},"PeriodicalIF":5.5,"publicationDate":"2025-08-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144869907","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":"Dissolved Oxygen Variability on the Canadian Pacific Shelf: Trends, Drivers, and Projections in the Context of Emerging Hypoxia in Queen Charlotte Sound","authors":"S. W. Stevens,&nbsp;C. Hannah,&nbsp;W. Evans,&nbsp;J. Klymak,&nbsp;S. Waterman,&nbsp;T. Ross","doi":"10.1029/2025GB008608","DOIUrl":"10.1029/2025GB008608","url":null,"abstract":"&lt;p&gt;Hypoxia is an increasing concern along the Northeast Pacific continental margin, driven by dissolved oxygen (&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;) declines related to a warming climate. Although the North Pacific &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; inventory has declined for decades, hypoxia was rarely observed on the central coast of British Columbia, Canada, before 2020. Recent observations from Queen Charlotte Sound (QCS)—the largest shelf sea in the Canadian Pacific—indicate that hypoxia is now an emerging issue in this region. This study synthesizes measurements from numerous platforms to describe regional &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; distributions during 2022 and 2023. These observations reveal persistent shelf-wide hypoxia during summer months, including periods of statistically defined extreme hypoxia. Comparisons with the hydrographic record from 2003 to 2021 show that &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 were lower and hypoxia more common in 2022 and 2023 than in previous years. This recent hypoxia is caused by long-term deoxygenation trends of approximately 5–10 &lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\u0000 &lt;mi&gt;μ&lt;/mi&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; ${upmu }$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt;mol &lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\u0000 &lt;msup&gt;\u0000 &lt;mtext&gt;kg&lt;/mtext&gt;\u0000 &lt;mrow&gt;\u0000 &lt;mo&gt;−&lt;/mo&gt;\u0000 &lt;mn&gt;1&lt;/mn&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;/msup&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; ${text{kg}}^{-1}$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt; per decade at isopycnals representing QCS deep waters, combined with seasonal and intera","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":"https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2025GB008608","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144832555","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":"Long-Term Changes of Surface Total Alkalinity and Its Driving Mechanisms in the North Indian Ocean","authors":"A. P. Joshi,&nbsp;Prasanna Kanti Ghoshal,&nbsp;Kunal Chakraborty,&nbsp;Rajdeep Roy,&nbsp;Chiranjivi Jayaram,&nbsp;B. Sridevi,&nbsp;V. V. S. S. Sarma","doi":"10.1029/2024GB008344","DOIUrl":"10.1029/2024GB008344","url":null,"abstract":"&lt;p&gt;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&lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\u0000 &lt;mo&gt;±&lt;/mo&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; $pm $&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt;0.38 &lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\u0000 &lt;mi&gt;μ&lt;/mi&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; ${upmu }$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt;mol &lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\u0000 &lt;msup&gt;\u0000 &lt;mtext&gt;kg&lt;/mtext&gt;\u0000 &lt;mrow&gt;\u0000 &lt;mo&gt;−&lt;/mo&gt;\u0000 &lt;mn&gt;1&lt;/mn&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;/msup&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; ${text{kg}}^{-1}$&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;mtext&gt;yr&lt;/mtext&gt;\u0000 &lt;mrow&gt;\u0000 &lt;mo&gt;−&lt;/mo&gt;\u0000 &lt;mn&gt;1&lt;/mn&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;/msup&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; ${text{yr}}^{-1}$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt;), southeastern coast of the Arabian Sea (AS) (1.16&lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\u0000 &lt;mo&gt;±&lt;/mo&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; $pm $&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt;0.42 &lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\u0000 &lt;mi&gt;μ&lt;/mi&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; ${upmu }$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt;mol &lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\u0000 &lt;msup&gt;\u0000 &lt;mtext&gt;kg&lt;/mtext&gt;\u0000 &lt;mrow&gt;\u0000 &lt;mo&gt;−&lt;/mo&gt;\u0000 &lt;mn&gt;1&lt;/mn&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;/msup&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; ${text{kg}}^{-1}$&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;mtext&gt;yr&lt;/mtext&gt;\u0000 &lt;mrow&gt;\u0000 &lt;mo&gt;−&lt;/mo&gt;\u0000 &lt;mn&gt;1&lt;/mn&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;/msup&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; ${text{yr}}^{-1}$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt;), and the southwestern region of the Bay of Bengal (BoB) (0.47&lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\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}