Global Biogeochemical Cycles最新文献

{"title":"Temperature and Water Levels Collectively Regulate Methane Emissions From Subtropical Freshwater Wetlands","authors":"Keqi He,&nbsp;Wenhong Li,&nbsp;Yu Zhang,&nbsp;Angela Zeng,&nbsp;Inge E. M. de Graaf,&nbsp;Maricar Aguilos,&nbsp;Ge Sun,&nbsp;Steven G. McNulty,&nbsp;John S. King,&nbsp;Neal E. Flanagan,&nbsp;Curtis J. Richardson","doi":"10.1029/2024GB008372","DOIUrl":"https://doi.org/10.1029/2024GB008372","url":null,"abstract":"<p>Wetlands are the largest and most climate-sensitive natural sources of methane. Accurately estimating wetland methane emissions involves reconciling inversion (“top-down”) and process-based (“bottom-up”) models within the global methane budget. However, estimates from these two model types are inherently interdependent and often reveal substantial discrepancies. To enhance the reliability of both approaches, we need a comprehensive understanding of wetland methane emissions and an independent high-resolution long-term flux data set. Here, we employed a data-driven random forest approach to identify key variables influencing methane emissions from subtropical freshwater wetlands in the Southeastern United States. The model-estimated monthly mean methane fluxes fit well with measured methane fluxes (<i>R</i>² = 0.67) at four representative FLUXNET-CH4 wetland sites across the region. Variable importance analysis highlighted the sensitivity of subtropical freshwater wetland methane emissions to variations in both temperature and water levels. High temperatures facilitate methanogenesis by enhancing microbial activities, while elevated water levels maintain anaerobic conditions necessary for methane production. Notably, the response of methane emissions to water level fluctuations is contingent on temperature conditions, and vice versa. Moreover, we constructed the first high-spatial-resolution (∼1 km × 1 km) and long-term (1982–2010) gridded regional wetland methane flux product for the Southeastern United States, estimating annual methane emissions from subtropical freshwater wetlands in the region at 4.93 ± 0.11 Tg CH₄ yr⁻¹ for 1982–2010. This new benchmark product holds promise for validating and parameterizing uncertain wetland methane emission processes in bottom-up models and provides improved prior information for top-down models.</p>","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":"39 3","pages":""},"PeriodicalIF":5.4,"publicationDate":"2025-03-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143533405","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":"Divergent Responses of CH4 Emissions and Uptake to Global Change Drivers","authors":"Tingting Zhu,&nbsp;Yanlian Zhou,&nbsp;Jing M. Chen,&nbsp;Weimin Ju,&nbsp;Ran Yan,&nbsp;Rui Xie,&nbsp;Yu Mao","doi":"10.1029/2024GB008183","DOIUrl":"https://doi.org/10.1029/2024GB008183","url":null,"abstract":"<p>Global changes strongly affect methane (CH₄) emissions and uptake. However, it is unclear how CH₄ emissions and uptake across rice paddy fields, uplands, and natural wetlands are affected by global change drivers, including nitrogen (N) addition, elevated carbon dioxide (eCO₂), warming (W), and precipitation (P). Here, we collected 1,250 observations of manipulated experiments from 303 publications during 1980–2020, encompassing 1,154 observations of single-factor experiments and 96 observations of two-paired experiments, and analyzed the effects of global change drivers on CH₄ emissions and uptake. Results showed CH₄ emissions were stimulated by eCO₂, W, and increased P (IP). CH₄ uptake was inhibited by N and IP but significantly enhanced by W and decreased P. The combined effects of the four global change drivers significantly inhibited CH₄ uptake (−9[−12, −6] %) and stimulated CH₄ emissions (13[7, 19] %). Two-factor interactions significantly reduced CH₄ emissions (−15[−27, −1] %) and insignificantly reduced uptake (−10[−19, 0] %). The interactive effects of any two global change drivers were mostly antagonistic. Random forest analysis indicated that the important factors affecting the responses of CH₄ emissions or uptake to different global change drivers varied. The structural equation model confirmed that climate, soil properties, and wetness index consistently played a remarkable role in regulating the responses of CH₄ emissions and uptake to global change drivers. This synthesis highlights an urgent need to consider the individual and interactive effects of multiple global change drivers on CH₄ emissions and uptake for a better understanding of the methane-climate feedback.</p>","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":"39 3","pages":""},"PeriodicalIF":5.4,"publicationDate":"2025-03-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143554780","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":"Greenhouse Gas Budgets of Central and West Asia (2000–2020): A Significant Net Source to the Atmosphere","authors":"Xiaoyu Qin,&nbsp;Hanqin Tian,&nbsp;Josep G. Canadell,&nbsp;Yu Shi,&nbsp;Shufen Pan,&nbsp;Ana Bastos,&nbsp;Philippe Ciais,&nbsp;Monica Crippa,&nbsp;Naiqing Pan,&nbsp;Prabir K. Patra,&nbsp;Benjamin Poulter,&nbsp;Marielle Saunois,&nbsp;Stephen Sitch","doi":"10.1029/2024GB008370","DOIUrl":"https://doi.org/10.1029/2024GB008370","url":null,"abstract":"<p>This study provides the first comprehensive quantification of three major greenhouse gases (GHGs, including CO₂, CH₄, and N₂O) budgets for Central and West Asia (CWA) from 2000 to 2020, including contributions from fossil fuels, industry, and managed and unmanaged terrestrial ecosystems. We use bottom-up (BU: inventories and process-based models) and top-down approaches (TD: atmospheric inversions) to elucidate CWA's GHG budget and its changes. BU and TD budgets consistently show that CWA was a significant and growing GHG source during the 2010s: average net emissions were 4,175 (range: 4,055–4,301) Tg CO₂eq yr⁻¹ based on BU and using global warming potentials over a 100-year period (GWP100), and slightly higher net emissions of 4,293 (3,760–4,826) Tg CO₂eq yr⁻¹ based on TD. BU estimates show that CO₂ emissions from fossil fuel combustion and fugitive releases were the dominant source, accounting for 61% of the total budget in the 2010s, with 2,554 (2,526–2,582) Tg CO₂eq yr⁻¹. Terrestrial natural ecosystems were a weak CO₂ sink and sources of CH₄ and N₂O, which together resulted in a decadal mean net GHG emission of 220.5 (114.5–332.8) Tg CO₂eq yr⁻¹. Non-CO₂ gases, primarily CH₄, contributed significantly to the region's GHG emissions, accounting for 32% (BU) and 24% (TD) of CWA's total GHG budget under GWP100, and increasing to 57% (BU) and 49% (TD) with GWP20, highlighting CH₄ stronger warming impact over shorter timescales. Overall, CWA contributed about 8% of global net GHG emissions in the 2010s, with about 10% of global CO₂, 7% of CH₄, and 3% of N₂O.</p>","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":"39 3","pages":""},"PeriodicalIF":5.4,"publicationDate":"2025-02-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GB008370","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143521911","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":"Observations and Biogeochemical Modeling Reveal Chlorophyll Diel Cycle With Near-Sunset Maxima in the Red Sea","authors":"Yixin Wang,&nbsp;Matthew R. Mazloff,&nbsp;Ariane Verdy,&nbsp;Ivana Cerovecki,&nbsp;Malika Kheireddine,&nbsp;Patrick Naylor,&nbsp;George Krokos,&nbsp;Ibrahim Hoteit","doi":"10.1029/2024GB008226","DOIUrl":"https://doi.org/10.1029/2024GB008226","url":null,"abstract":"<p>The Red Sea is an extremely warm tropical sea hosting diverse ecosystems, with marine organisms operating at the high end of their thermal tolerance. Therefore, in the context of global warming, it is increasingly important to understand the Red Sea ecosystem, including the variability of chlorophyll at different spatiotemporal scales. Using a coupled physical–biogeochemical model and in situ data, we investigate and quantify the diel cycle in Red Sea chlorophyll concentration for the first time, revealing near-sunset chlorophyll maxima at 17 ± 1 hr local time over the entire basin. This chlorophyll peak time is considerably later than those reported in most other oceans, reflecting the previously reported high irradiance and further suggesting potentially low grazing rates in the Red Sea. Model-based analyses reveal that chlorophyll diel cycle is predominantly controlled by light-driven circadian rhythm (i.e., irradiance), whereas longer-timescale (e.g., seasonal) chlorophyll variability is regulated by nutrient availability, suggesting a light-limited biological production on a diel timescale and a nutrient-limited production on a seasonal scale. The identified chlorophyll diel cycle comprises a fundamental component of the Red Sea ecology and has implications for chlorophyll remote sensing and in situ measurements. Our findings indicate that future field studies investigating phytoplankton growth and zooplankton grazing dynamics—such as phytoplankton community composition and zooplankton diel vertical migration—are still needed to further elucidate the revealed chlorophyll diel cycle in this potentially unique tropical sea.</p>","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":"39 2","pages":""},"PeriodicalIF":5.4,"publicationDate":"2025-02-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GB008226","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143466287","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":"Carbon and Nitrogen Isoscapes of Particulate Organic Matter in the Pacific Ocean","authors":"Sachiko Horii,&nbsp;Taketoshi Kodama,&nbsp;Takuhei Shiozaki,&nbsp;Iwao Tanita,&nbsp;Hiroaki Kurogi,&nbsp;Hiroomi Miyamoto,&nbsp;Satoshi Suyama,&nbsp;Taiki Fuji,&nbsp;Yoshiki Kato,&nbsp;Daisuke Ambe,&nbsp;Takuya Sato,&nbsp;Tadafumi Ichikawa,&nbsp;Ken Furuya,&nbsp;Kazutaka Takahashi","doi":"10.1029/2024GB008336","DOIUrl":"https://doi.org/10.1029/2024GB008336","url":null,"abstract":"<p>Large-scale geographical distributions in nitrogen and carbon stable isotope ratios (δ¹⁵N and δ¹³C) of particulate organic matter (POM) are essential to understand the variation in the baseline of pelagic food webs in the Pacific Ocean, where phytoplankton production and biological N₂ fixation are highly variable because of heterogeneity of nitrate and iron supply. Here, we determined their isoscapes during summer and discussed potential factors characterizing regional ecosystems from the viewpoint of nitrogen cycling. We collected a total of 2,289 and 2,278 isotope values for δ¹³C and δ¹⁵N, respectively, by synthesizing previously published data with our newly measured data, and analyzed their relationships with temperature, concentrations of nitrate and chlorophyll-<i>a</i>, and N₂ fixation activity, obtained from databases. POM δ¹³C and δ¹⁵N regionally varied in ranges of −30 to −18‰ and −4 to 14‰, respectively. POM δ¹³C was correlated positively with temperature throughout the ocean. In contrast, POM δ¹⁵N was negatively correlated with nitrate concentration at high latitudes and with N₂ fixation activity at low latitudes. High values (&gt;8‰) of POM δ¹⁵N were identified mainly in the marginal area of equatorial upwelling; the highest values (10–14‰) were in the subtropical Southeastern Pacific. Using the isotopic values and nitrate concentration, we classified the ecosystems into 10 groups. Our data demonstrated the distribution patterns of ecosystems with different degrees of nitrate utilization, which are presumably associated with iron supply, and ecosystems sustained by different nitrogen sources: diazotrophic nitrogen and nitrate supplied below the nitracline and/or horizontally advected.</p>","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":"39 2","pages":""},"PeriodicalIF":5.4,"publicationDate":"2025-02-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143404421","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":"Anthropogenic Disturbances Superimpose Climate Effects on Soil Organic Carbon in Savanna Woodlands of Sub-Saharan Africa","authors":"F. Jorge,&nbsp;N. Mutwale-Mutale,&nbsp;A. Sandhage-Hofmann,&nbsp;M. Braun,&nbsp;A. Cambule,&nbsp;A. Nhantumbo,&nbsp;L. M. Chabala,&nbsp;C. Shepande,&nbsp;B. Chishala,&nbsp;S. Lisboa,&nbsp;M. Matangue,&nbsp;M. Schmidt,&nbsp;W. Amelung","doi":"10.1029/2023GB008086","DOIUrl":"https://doi.org/10.1029/2023GB008086","url":null,"abstract":"<p>Savanna ecosystems in sub-Saharan Africa harbor substantial yet relatively unexplored reserves of soil organic carbon (SOC). Our study unravels for the first time the interplay between climate, reference soil groups, and anthropogenic disturbances in shaping SOC dynamics in these ecosystems. We analyzed SOC along climosequences in natural woodlands in Mozambique and Zambia, with mean annual temperature (MAT) of 20–24°C, and mean annual precipitation (MAP) of 365–1,227 mm. Anthropogenic disturbances were assessed through comprehensive field surveys and remote sensing of vegetation and indices change. MAT and evapotranspiration (PET) had no discernible effect on SOC. Bulk SOC, particulate organic matter, and mineral-associated organic matter stocks in the topsoil (0–10 cm) increased with MAP, though this relationship was not significant for the subsoil. MAP explained only 35% of topsoil SOC variability, limited by anthropogenic disturbances, which raised SOC stocks in the dry savanna but resulted in SOC losses at &gt;600 mm MAP, which even extended into subsoil. For sites with little disturbance in the past decades, there were soil group-specific effects of MAP on SOC, explaining up to 85% of data variability. In disturbed sites, human presence altered the carbon (C) balance to an extent that, as rough estimate, could account for up to 2.6 Gt CO₂-C loss over 20 years in wetter sites, with another 2.4 Gt CO₂-C at risk as populations spread into these otherwise pristine environments. Accurate modeling of climate-change effects on the C cycle must therefore include the transformative impacts of current human activities, such as wood harvesting and grazing.</p>","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":"39 2","pages":""},"PeriodicalIF":5.4,"publicationDate":"2025-02-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2023GB008086","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143397131","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":"Trends in Sea-Air CO2 Fluxes and Sensitivities to Atmospheric Forcing Using an Extremely Randomized Trees Machine Learning Approach","authors":"Rik Wanninkhof,&nbsp;Joaquin Triñanes,&nbsp;Denis Pierrot,&nbsp;David R. Munro,&nbsp;Colm Sweeney,&nbsp;Amanda R. Fay","doi":"10.1029/2024GB008315","DOIUrl":"https://doi.org/10.1029/2024GB008315","url":null,"abstract":"<p>Monthly global sea-air CO₂ flux maps are created on a 1° by 1° grid from surface water fugacity of CO₂ (fCO_2w) observations using an extremely randomized trees (ET) machine learning technique (AOML-ET) over the period 1998–2020. Global patterns and magnitudes of fCO_2w from AOML-ET are consistent with other machine learning methods and with the updated climatology of Takahashi et al. (2009, https://doi.org/10.1016/j.dsr2.2008.12.009). However, the magnitude and trends of sea-air CO₂ fluxes are sensitive to the treatment of atmospheric forcing. In the default configuration of AOML-ET, the average global sea-air CO₂ flux is −1.70 PgC yr⁻¹ with a negative trend of −0.89 ± 0.19 PgC yr⁻¹ decade⁻¹. The large negative trend is driven by a small uptake at the beginning of the record. This leads to increasing sea-air fCO₂ gradients over time, particularly at high latitudes. However, changing the target variable in AOML-ET from fCO_2w to sea-air CO₂ fugacity difference, ∆fCO₂, results in a lower negative trend of −0.51 PgC yr⁻¹ decade⁻¹, though the average flux remains similar at −1.65 PgC yr⁻¹. This trend is close to the consensus trend of ocean uptake from machine learning and models in the Global Carbon Budget of −0.46 ± 0.11 PgC yr⁻¹ decade⁻¹ switching to a gas transfer parameterization with weaker wind speed dependence reduces uptake by 60% but does not affect the trend. Substituting a spatially resolved marine air CO₂ mole fraction product for the zonally invariant marine boundary layer CO₂ product yields greater influx by up to 20% in the industrialized continental outflow regions.</p>","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":"39 2","pages":""},"PeriodicalIF":5.4,"publicationDate":"2025-02-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GB008315","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143362970","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":"A New Framework for the Attribution of Air-Sea CO2 Exchange","authors":"Takamitsu Ito,&nbsp;Christopher T. Reinhard","doi":"10.1029/2024GB008346","DOIUrl":"https://doi.org/10.1029/2024GB008346","url":null,"abstract":"<p>The air-sea transfer of carbon dioxide can be viewed as a dynamic system through which atmospheric and oceanic processes push surface waters away from thermodynamic equilibrium, while diffusive gas transfer pulls them back toward local equilibrium. These push/pull processes drive significant sub-seasonal, seasonal, and interannual variability in air-sea carbon fluxes, the quantification of which is critical both for diagnosing the ocean response to fossil fuel emissions and for attempts to mitigate anthropogenic climate disruption through intentional modification of surface ocean biogeochemistry. In this study, we present a new approach for attributing air-sea carbon fluxes to specific mechanisms. The new framework is first applied to a two-box ocean nutrient and carbon cycle model as an illustrative example. Next, outputs from a regional eddy-resolving model of the Southern Ocean are analyzed. The roles of multiple physical and biogeochemical processes are identified. The decomposition of the seasonal air-sea carbon flux shows the dominant role of biological carbon pumps that are partially compensated by the transport convergence. Finally, the framework is used to diagnose the response to mesoscale iron and alkalinity release, explicitly quantifying transport feedback and eventual impacts on net air-sea carbon flux. Ocean carbon transport has divergent influences between iron and alkalinity release, due to opposing near-surface gradients of dissolved inorganic carbon. We suggest that our attribution framework may be a useful analytical technique for monitoring natural ocean carbon fluxes and quantifying the impacts of human intervention on the ocean carbon cycle.</p>","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":"39 2","pages":""},"PeriodicalIF":5.4,"publicationDate":"2025-02-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143248848","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":"The Riparian Zone Controls Headwater Hydrology and Biogeochemistry, Doesn't It? Reassessing Linkages Across European Ecoregions","authors":"José L. J. Ledesma,&nbsp;Andreas Musolff,&nbsp;Ryan A. Sponseller,&nbsp;Anna Lupon,&nbsp;Xavier Peñarroya,&nbsp;Carolina Jativa,&nbsp;Susana Bernal","doi":"10.1029/2024GB008250","DOIUrl":"https://doi.org/10.1029/2024GB008250","url":null,"abstract":"<p>Riparian zones are known to control the hydrology and biogeochemistry of forest headwater catchments. Some evidence suggests that these riparian-stream connections are shaped by a relatively small volume of soil, or <i>dominant source layer</i> (DSL), through which most water and solutes are routed laterally. However, the hydrological and biogeochemical significance of the DSL has not been broadly evaluated. We compiled data from four forest headwaters, each from different European sites (boreal, temperate, subhumid Mediterranean, semiarid Mediterranean) to test whether DSL dimensions and biogeochemical characteristics vary predictably across ecoregions based on differences in hydroclimate, topography, and soil features. Boreal DSLs were shallow and thin, whereas small-scale topographic heterogeneity shaped DSL dimensions at the temperate site. In the Mediterranean sites, DSLs were deeper and thicker, but upper riparian layers that seldomly connected to the streams had a large influence on the overall lateral flux. Contrasting hydroclimates and soils led to high dissolved organic carbon concentrations in riparian solutions in both boreal and Mediterranean sites. By contrast, nitrate concentrations were driven by differences in soil saturation, being orders of magnitude higher in dry Mediterranean than in wet temperate and boreal riparian soils. Notably, stream chemistry did not consistently reflect riparian DSL chemistry across flow conditions and ecoregions. We hypothesize that ecoregion-specific water sources bypassing the riparian zone, as well as ecoregion-specific in-stream biogeochemical processes could explain these discrepancies. Overall, conceptualizing the varied roles of the DSL across diverse systems can aid in both scientific assessments and management of land-water connectivity in river networks.</p>","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":"39 2","pages":""},"PeriodicalIF":5.4,"publicationDate":"2025-02-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GB008250","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143111660","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":"Nitrogen Biogeochemistry of Adjacent Mesoscale Eddies in the North Pacific Subtropical Gyre","authors":"Mengyang Zhou,&nbsp;Julie Granger,&nbsp;Cesar B. Rocha,&nbsp;Samantha A. Siedlecki,&nbsp;Benedetto Barone,&nbsp;Angelicque E. White","doi":"10.1029/2024GB008206","DOIUrl":"https://doi.org/10.1029/2024GB008206","url":null,"abstract":"<p>We examined the nitrogen (N) biogeochemistry of adjacent cyclonic and anticyclonic eddies near Hawai'i in the North Pacific Subtropical Gyre (NPSG) and explored mechanisms that sustain productivity in the cyclone after the initial intensification stage. The top of the nutricline was uplifted into the euphotic zone in the cyclone and depressed in the anticyclone. Subsurface nutrient concentrations and apparent oxygen utilization at the cyclone's inner periphery were higher than expected from isopycnal displacement, suggesting that shallow remineralization of organic material generated excess nutrients in the subsurface. The excess nutrients may provide a supply of subsurface nutrients to sustain productivity in maturing eddies. The shallow remineralization also raises questions regarding the extent to which cyclonic eddies promote deep carbon sequestration in subtropical gyres such as the NPSG. An upward increase in nitrate ¹⁵N/¹⁴N isotope ratios below the euphotic zone, indicative of partial nitrate assimilation, coincided with negative preformed nutrients—potentially signaling heterotrophic bacterial consumption of carbon-rich (nitrogen-poor) organic material. The ¹⁵N/¹⁴N of material collected in shallow sediment traps was significantly higher in the cyclone than in the anticyclone and showed correspondence to the ¹⁵N/¹⁴N ratio of the nitrate supply, which is acutely sensitive to sea level anomaly in the region. A number of approaches were applied to estimate the contribution of N₂ fixation to export production. Results among approaches were inconsistent, which we attribute to non-steady state conditions during our observation period.</p>","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":"39 2","pages":""},"PeriodicalIF":5.4,"publicationDate":"2025-02-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143111569","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}