Scott C. Doney, Kayla A. Mitchell, Stephanie A. Henson, Emma Cavan, Tim DeVries, Nicolas Gruber, Judith Hauck, Colleen B. Mouw, Jens D. Müller, Francois W. Primeau
This study characterized ocean biological carbon pump metrics in the second iteration of the REgional Carbon Cycle Assessment and Processes (RECCAP2) project. The analysis here focused on comparisons of global and biome-scale regional patterns in particulate organic carbon (POC) production and sinking flux from the RECCAP2 ocean biogeochemical model ensemble against observational products derived from satellite remote sensing, sediment traps, and geochemical methods. There was generally good model-data agreement in mean large-scale spatial patterns, but with substantial spread across the model ensemble and observational products. The global-integrated, model ensemble-mean export production, taken as the sinking POC flux at 100 m (6.08 ± 1.17 Pg C yr−1), and export ratio defined as sinking flux divided by net primary production (0.154 ± 0.026) both fell at the lower end of observational estimates. Comparison with observational constraints also suggested that the model ensemble may have underestimated regional biological CO2 drawdown and air-sea CO2 flux in high productivity regions. Reasonable model-data agreement was found for global-integrated, ensemble-mean sinking POC flux into the deep ocean at 1,000 m (0.65 ± 0.24 Pg C yr−1) and the transfer efficiency defined as flux at 1,000 m divided by flux at 100 m (0.122 ± 0.041), with both variables exhibiting considerable regional variability. The RECCAP2 analysis presents standard ocean biological carbon pump metrics for assessing biogeochemical model skill, metrics that are crucial for further modeling efforts to resolve remaining uncertainties involving system-level interactions between ocean physics and biogeochemistry.
{"title":"Observational and Numerical Modeling Constraints on the Global Ocean Biological Carbon Pump","authors":"Scott C. Doney, Kayla A. Mitchell, Stephanie A. Henson, Emma Cavan, Tim DeVries, Nicolas Gruber, Judith Hauck, Colleen B. Mouw, Jens D. Müller, Francois W. Primeau","doi":"10.1029/2024GB008156","DOIUrl":"https://doi.org/10.1029/2024GB008156","url":null,"abstract":"<p>This study characterized ocean biological carbon pump metrics in the second iteration of the REgional Carbon Cycle Assessment and Processes (RECCAP2) project. The analysis here focused on comparisons of global and biome-scale regional patterns in particulate organic carbon (POC) production and sinking flux from the RECCAP2 ocean biogeochemical model ensemble against observational products derived from satellite remote sensing, sediment traps, and geochemical methods. There was generally good model-data agreement in mean large-scale spatial patterns, but with substantial spread across the model ensemble and observational products. The global-integrated, model ensemble-mean export production, taken as the sinking POC flux at 100 m (6.08 ± 1.17 Pg C yr<sup>−1</sup>), and export ratio defined as sinking flux divided by net primary production (0.154 ± 0.026) both fell at the lower end of observational estimates. Comparison with observational constraints also suggested that the model ensemble may have underestimated regional biological CO<sub>2</sub> drawdown and air-sea CO<sub>2</sub> flux in high productivity regions. Reasonable model-data agreement was found for global-integrated, ensemble-mean sinking POC flux into the deep ocean at 1,000 m (0.65 ± 0.24 Pg C yr<sup>−1</sup>) and the transfer efficiency defined as flux at 1,000 m divided by flux at 100 m (0.122 ± 0.041), with both variables exhibiting considerable regional variability. The RECCAP2 analysis presents standard ocean biological carbon pump metrics for assessing biogeochemical model skill, metrics that are crucial for further modeling efforts to resolve remaining uncertainties involving system-level interactions between ocean physics and biogeochemistry.</p>","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":null,"pages":null},"PeriodicalIF":5.4,"publicationDate":"2024-07-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GB008156","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141536743","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}
Xiaoyu Cen, Nianpeng He, Mingxu Li, Li Xu, Xueying Yu, Weixiang Cai, Xin Li, Klaus Butterbach-Bahl
Methane (CH4) is the second most important atmospheric greenhouse gas (GHG) and forest soils are a significant sink for atmospheric CH4. Uptake of CH4 by global forest soils is affected by nitrogen (N) deposition; clarifying the effect of N deposition helps to reduce uncertainties of the global CH4 budget. However, it remains an unsolved puzzle why N input stimulates soil CH4 uptake in some forests while suppressing it in others. Combining previous findings and data from N addition experiments conducted in global forests, we proposed and tested a “stimulating-suppressing-weakened effect” (“three stages”) hypothesis on the changing responses of soil CH4 flux (RCH4) to N input. Specifically, we calculated the response factors (f) of RCH4 to N input for N-limited and N-saturated forests across biomes; the phased changes in f values supported our hypothesis. We also estimated the global forest soil CH4 uptake budget to be approximately 11.2 Tg yr−1. CH4 uptake hotspots were predominantly located in temperate forests. Furthermore, we quantified that the current level of N deposition reduced global forest soil CH4 uptake by ∼3%. This suppression effect was more pronounced in temperate forests than in tropical or boreal forests, likely due to differences in N status. The proposed “three stages” hypothesis in this study generalizes the diverse effects of N input on RCH4, which could help improve experimental design. Additionally, our findings imply that by regulating N pollution and reducing N deposition, soil CH4 uptake can be significantly increased in the N-saturated forests in tropical and temperate biomes.
{"title":"Suppression of Nitrogen Deposition on Global Forest Soil CH4 Uptake Depends on Nitrogen Status","authors":"Xiaoyu Cen, Nianpeng He, Mingxu Li, Li Xu, Xueying Yu, Weixiang Cai, Xin Li, Klaus Butterbach-Bahl","doi":"10.1029/2024GB008098","DOIUrl":"https://doi.org/10.1029/2024GB008098","url":null,"abstract":"<p>Methane (CH<sub>4</sub>) is the second most important atmospheric greenhouse gas (GHG) and forest soils are a significant sink for atmospheric CH<sub>4</sub>. Uptake of CH<sub>4</sub> by global forest soils is affected by nitrogen (N) deposition; clarifying the effect of N deposition helps to reduce uncertainties of the global CH<sub>4</sub> budget. However, it remains an unsolved puzzle why N input stimulates soil CH<sub>4</sub> uptake in some forests while suppressing it in others. Combining previous findings and data from N addition experiments conducted in global forests, we proposed and tested a “stimulating-suppressing-weakened effect” (“three stages”) hypothesis on the changing responses of soil CH<sub>4</sub> flux (<i>R</i><sub><i>CH4</i></sub>) to N input. Specifically, we calculated the response factors (<i>f</i>) of <i>R</i><sub><i>CH4</i></sub> to N input for N-limited and N-saturated forests across biomes; the phased changes in <i>f</i> values supported our hypothesis. We also estimated the global forest soil CH<sub>4</sub> uptake budget to be approximately 11.2 Tg yr<sup>−1</sup>. CH<sub>4</sub> uptake hotspots were predominantly located in temperate forests. Furthermore, we quantified that the current level of N deposition reduced global forest soil CH<sub>4</sub> uptake by ∼3%. This suppression effect was more pronounced in temperate forests than in tropical or boreal forests, likely due to differences in N status. The proposed “three stages” hypothesis in this study generalizes the diverse effects of N input on <i>R</i><sub><i>CH4</i></sub>, which could help improve experimental design. Additionally, our findings imply that by regulating N pollution and reducing N deposition, soil CH<sub>4</sub> uptake can be significantly increased in the N-saturated forests in tropical and temperate biomes.</p>","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":null,"pages":null},"PeriodicalIF":5.4,"publicationDate":"2024-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141536865","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}
Daniel Wasner, Rose Abramoff, Marco Griepentrog, Erick Zagal Venegas, Pascal Boeckx, Sebastian Doetterl
Organic matter accumulation in soil is understood as the result of the dynamics between mineral-associated (more decomposed, microbial derived) organic matter and free particulate (less decomposed, plant derived) organic matter. However, from regional to global scales, patterns and drivers behind main soil organic carbon (SOC) fractions are not well understood and remain poorly linked to the pedogenetic variation across soil types. Here, we separated SOC associated with silt- and clay-sized particles (S + C), stable aggregates (>63 μm, SA) and particulate organic matter (POM) from a diverse range of grassland topsoils sampled along a geoclimatic gradient. The relative contribution of the two mineral-associated fractions (S + C & SA) to SOC differed significantly across the gradient, while POM was never the dominant SOC fraction. Stable aggregates (>63 μm) emerged as the major SOC fraction in carbon-rich soils. The degree of decomposition of carbon in stable aggregates (>63 μm) was consistently between that of the S + C and POM fractions and did not change along the investigated gradient. In contrast, carbon associated with the S + C fraction was less microbially decomposed in carbon-rich soils than in carbon-poor soils. The amount of SOC in the S + C fraction was positively correlated to pedogenic oxide contents and texture, whereas the amount of SOC associated with stable aggregates (>63 μm) was positively correlated to pedogenic oxide contents and negatively to temperature. We present a conceptual summary of our findings, which integrates the role of stable aggregates (>63 μm) with other major SOC fractions and illustrates their changing importance across (soil-)environmental gradients.
据了解,土壤中有机物的积累是矿物质相关(分解程度较高、微生物衍生)有机物和游离颗粒(分解程度较低、植物衍生)有机物之间动态变化的结果。然而,从区域到全球范围内,主要土壤有机碳(SOC)组分的模式和驱动因素并不十分清楚,而且与不同土壤类型的成因变化之间的联系也不紧密。在这里,我们从沿地理气候梯度取样的各种草地表层土壤中分离出了与淤泥和粘土大小的颗粒(S + C)、稳定团聚体(>63 μm, SA)和颗粒有机质(POM)相关的有机碳。两种与矿物质相关的组分(S + C & SA)对SOC的相对贡献在梯度上有显著差异,而POM从来都不是SOC的主要组分。在富碳土壤中,稳定团聚体(63 μm)成为主要的 SOC 部分。稳定团聚体(63 μm)中碳的分解程度始终介于 S + C 和 POM 部分之间,并且在调查梯度上没有变化。相比之下,富碳土壤中与 S + C 部分相关的碳被微生物分解的程度低于贫碳土壤。S + C 部分的 SOC 量与氧化皮含量和质地呈正相关,而与稳定团聚体(63 μm)相关的 SOC 量与氧化皮含量呈正相关,与温度呈负相关。我们对研究结果进行了概念性总结,将稳定团聚体(63 μm)的作用与其他主要 SOC 部分结合起来,并说明了它们在不同(土壤-)环境梯度中不断变化的重要性。
{"title":"The Role of Climate, Mineralogy and Stable Aggregates for Soil Organic Carbon Dynamics Along a Geoclimatic Gradient","authors":"Daniel Wasner, Rose Abramoff, Marco Griepentrog, Erick Zagal Venegas, Pascal Boeckx, Sebastian Doetterl","doi":"10.1029/2023GB007934","DOIUrl":"https://doi.org/10.1029/2023GB007934","url":null,"abstract":"<p>Organic matter accumulation in soil is understood as the result of the dynamics between mineral-associated (more decomposed, microbial derived) organic matter and free particulate (less decomposed, plant derived) organic matter. However, from regional to global scales, patterns and drivers behind main soil organic carbon (SOC) fractions are not well understood and remain poorly linked to the pedogenetic variation across soil types. Here, we separated SOC associated with silt- and clay-sized particles (S + C), stable aggregates (>63 μm, SA) and particulate organic matter (POM) from a diverse range of grassland topsoils sampled along a geoclimatic gradient. The relative contribution of the two mineral-associated fractions (S + C & SA) to SOC differed significantly across the gradient, while POM was never the dominant SOC fraction. Stable aggregates (>63 μm) emerged as the major SOC fraction in carbon-rich soils. The degree of decomposition of carbon in stable aggregates (>63 μm) was consistently between that of the S + C and POM fractions and did not change along the investigated gradient. In contrast, carbon associated with the S + C fraction was less microbially decomposed in carbon-rich soils than in carbon-poor soils. The amount of SOC in the S + C fraction was positively correlated to pedogenic oxide contents and texture, whereas the amount of SOC associated with stable aggregates (>63 μm) was positively correlated to pedogenic oxide contents and negatively to temperature. We present a conceptual summary of our findings, which integrates the role of stable aggregates (>63 μm) with other major SOC fractions and illustrates their changing importance across (soil-)environmental gradients.</p>","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":null,"pages":null},"PeriodicalIF":5.4,"publicationDate":"2024-06-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2023GB007934","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141488324","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}
Dongsheng Liu, Qiuwen Chen, Taylor Maavara, Jianyun Zhang, Yuchen Chen
Reservoir drawdown areas (DAs) can be both important nitrogen (N) sources to river networks and hot spots for N removal from freshwater ecosystems. The net effect of DAs on the N availability in reservoirs within a full hydrological cycle remains unclear. In this paper, the N dynamics in the DA of the Three Gorges Reservoir, Yangtze River, China, are investigated through a combination of discrete and continuous in situ observations and sampling over a span of 2 years, complemented by numerical modeling. We show that the DA is a net source of N to the water column, and that about 30% of the total annual N load released from the DA is mitigated by the sediment through denitrification and capture. The annual net load of the total N from the DA to the reservoir is ca. 0.59 kg per meter along the river, which is on the same order of magnitude as the input load from the density current of the Yangtze River to its tributaries, generally considered to be the primary driver of eutrophication in tributaries. N release in the DA mainly occurs during the drying period, whereas denitrification in the sediment mostly takes place during the flooding period when the oxido-reducing potential is low. Our findings quantify and therefore clarify the N source/sink dynamics from the DA to the reservoir, offering a new perspective on the importance of DA nutrient loading in decision-making related to integrated management of inundated lands to alleviate reservoir eutrophication by river damming.
{"title":"Nitrogen Cycling in Reservoir Drawdown Areas and the Impacts on Water Quality","authors":"Dongsheng Liu, Qiuwen Chen, Taylor Maavara, Jianyun Zhang, Yuchen Chen","doi":"10.1029/2024GB008136","DOIUrl":"https://doi.org/10.1029/2024GB008136","url":null,"abstract":"<p>Reservoir drawdown areas (DAs) can be both important nitrogen (N) sources to river networks and hot spots for N removal from freshwater ecosystems. The net effect of DAs on the N availability in reservoirs within a full hydrological cycle remains unclear. In this paper, the N dynamics in the DA of the Three Gorges Reservoir, Yangtze River, China, are investigated through a combination of discrete and continuous in situ observations and sampling over a span of 2 years, complemented by numerical modeling. We show that the DA is a net source of N to the water column, and that about 30% of the total annual N load released from the DA is mitigated by the sediment through denitrification and capture. The annual net load of the total N from the DA to the reservoir is ca. 0.59 kg per meter along the river, which is on the same order of magnitude as the input load from the density current of the Yangtze River to its tributaries, generally considered to be the primary driver of eutrophication in tributaries. N release in the DA mainly occurs during the drying period, whereas denitrification in the sediment mostly takes place during the flooding period when the oxido-reducing potential is low. Our findings quantify and therefore clarify the N source/sink dynamics from the DA to the reservoir, offering a new perspective on the importance of DA nutrient loading in decision-making related to integrated management of inundated lands to alleviate reservoir eutrophication by river damming.</p>","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":null,"pages":null},"PeriodicalIF":5.4,"publicationDate":"2024-06-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141488844","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}
Pyrogenic carbon (PyC) is a significant component of the global soil carbon pool due to its longer environmental persistence than other soil organic matter components. Despite PyC's persistence in soil, recent work has indicated that it is susceptible to loss processes such as mineralization and leaching, with the significance and magnitude of these largely unknown at the hillslope and watershed scales. We present a review of the work concerning dissolved PyC transport in soil and freshwater. Our analysis found that the primary environmental controls on dissolved PyC (dPyC) transport are the formation conditions and quality of the PyC itself, with longer and higher temperature charring conditions leading to less transport of dPyC. While correlations between dPyC and dissolved organic carbon in rivers and other pools are frequently reported, the slope of these correlations was pool-dependent (i.e., soil-water, precipitation, lakes, streams, rivers), suggesting site-specific environmental controls. However, the lack of consistency in analytical techniques and sample preparation remains a major challenge to quantifying environmental controls on dPyC fluxes. We propose that future research should focus on the following: (a) consistency in methodological approaches, (b) more quantitative measures of dPyC in pools and fluxes from soils to streams, (c) turnover times of dPyC in soils and aquatic systems, and (d) improved understanding of how mechanisms controlling the fate of dPyC in dynamic post-fire landscapes interact. With more refined quantitative information about the controls on dPyC transport at the hillslope and landscape scale, we can increase the accuracy and utility of global carbon models.
{"title":"Constraints and Drivers of Dissolved Fluxes of Pyrogenic Carbon in Soil and Freshwater Systems: A Global Review and Meta-Analysis","authors":"R. B. Abney, M. E. Barnes, A. Moss, F. Santos","doi":"10.1029/2023GB008092","DOIUrl":"https://doi.org/10.1029/2023GB008092","url":null,"abstract":"<p>Pyrogenic carbon (PyC) is a significant component of the global soil carbon pool due to its longer environmental persistence than other soil organic matter components. Despite PyC's persistence in soil, recent work has indicated that it is susceptible to loss processes such as mineralization and leaching, with the significance and magnitude of these largely unknown at the hillslope and watershed scales. We present a review of the work concerning dissolved PyC transport in soil and freshwater. Our analysis found that the primary environmental controls on dissolved PyC (dPyC) transport are the formation conditions and quality of the PyC itself, with longer and higher temperature charring conditions leading to less transport of dPyC. While correlations between dPyC and dissolved organic carbon in rivers and other pools are frequently reported, the slope of these correlations was pool-dependent (i.e., soil-water, precipitation, lakes, streams, rivers), suggesting site-specific environmental controls. However, the lack of consistency in analytical techniques and sample preparation remains a major challenge to quantifying environmental controls on dPyC fluxes. We propose that future research should focus on the following: (a) consistency in methodological approaches, (b) more quantitative measures of dPyC in pools and fluxes from soils to streams, (c) turnover times of dPyC in soils and aquatic systems, and (d) improved understanding of how mechanisms controlling the fate of dPyC in dynamic post-fire landscapes interact. With more refined quantitative information about the controls on dPyC transport at the hillslope and landscape scale, we can increase the accuracy and utility of global carbon models.</p>","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":null,"pages":null},"PeriodicalIF":5.4,"publicationDate":"2024-06-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2023GB008092","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141488252","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}
Marine dissolved organic matter (DOM) cycles play a pivotal role in sustaining marine ecosystems and regulating the ocean's carbon sequestration from the atmosphere. However, the response of DOM cycles, including dissolved organic carbon (DOC) and dissolved organic phosphorus (DOP), to future climate change remains highly uncertain. Using the Community Earth System Model version 2 large ensemble simulations, we find that the C:P ratios in DOM are projected to increase by up to two-fold in oligotrophic gyres by 2100. Increased upper ocean stratification reduces surface phosphate availability, thereby elevating phytoplankton C:P ratios and enhancing phytoplankton utilization of DOP, both acting to deprive DOM of P. Moreover, ocean stratification has a direct effect on exporting less DOC to the subsurface while accumulating more DOC at the sea surface. As a result of the strong sensitivity to ocean surface warming, the anthropogenically driven trends in upper ocean DOM concentration and its C:P ratios are estimated to emerge earlier from the simulated natural variability than upper ocean phosphate concentrations and net primary production—two key biogeochemical variables that are frequently monitored. This study suggests that changes in the C:P ratios of DOM could serve as a sensitive fingerprint of anthropogenic ocean warming, potentially exerting broad impacts on marine microbes. Our estimated 4% reduction in the globally integrated DOC export below 100 m is comparable to a 2% reduction in particulate organic carbon (POC) export by 2100, implying that global warming is likely to weaken the biological carbon pump through both DOC and POC.
海洋溶解有机物(DOM)循环在维持海洋生态系统和调节海洋从大气中固碳方面发挥着关键作用。然而,包括溶解有机碳(DOC)和溶解有机磷(DOP)在内的溶解有机物循环对未来气候变化的响应仍具有很大的不确定性。利用群落地球系统模式第二版大型集合模拟,我们发现预计到 2100 年,低营养回旋中 DOM 的 C:P 比率将增加最多两倍。海洋上层分层的增加减少了海面磷酸盐的供应,从而提高了浮游植物的 C:P 比值,并增强了浮游植物对 DOP 的利用,两者都起到了剥夺 DOM 中 P 的作用。由于对海洋表面升温的敏感性很强,估计人类活动引起的上层海洋 DOM 浓度及其碳-钾比例的变化趋势,会比上层海洋磷酸盐浓度和净初级生产力--这两个经常监测的关键生物地球化学变量--更早从模拟的自然变化中显现出来。这项研究表明,DOM 的 C:P 比率的变化可以作为人为海洋变暖的敏感指纹,可能对海洋微生物产生广泛影响。据估计,到 2100 年,100 米以下全球综合 DOC 出口将减少 4%,而颗粒有机碳(POC)出口将减少 2%,这意味着全球变暖可能会削弱通过 DOC 和 POC 产生的生物碳泵。
{"title":"Anthropogenically Driven Changes in the Carbon to Phosphorus Ratio of Marine Dissolved Organic Matter","authors":"Mohanan Geethalekshmi Sreeush, Eun Young Kwon, Sun-Seon Lee, Arjun Babu Nellikkattil","doi":"10.1029/2023GB008069","DOIUrl":"https://doi.org/10.1029/2023GB008069","url":null,"abstract":"<p>Marine dissolved organic matter (DOM) cycles play a pivotal role in sustaining marine ecosystems and regulating the ocean's carbon sequestration from the atmosphere. However, the response of DOM cycles, including dissolved organic carbon (DOC) and dissolved organic phosphorus (DOP), to future climate change remains highly uncertain. Using the Community Earth System Model version 2 large ensemble simulations, we find that the C:P ratios in DOM are projected to increase by up to two-fold in oligotrophic gyres by 2100. Increased upper ocean stratification reduces surface phosphate availability, thereby elevating phytoplankton C:P ratios and enhancing phytoplankton utilization of DOP, both acting to deprive DOM of P. Moreover, ocean stratification has a direct effect on exporting less DOC to the subsurface while accumulating more DOC at the sea surface. As a result of the strong sensitivity to ocean surface warming, the anthropogenically driven trends in upper ocean DOM concentration and its C:P ratios are estimated to emerge earlier from the simulated natural variability than upper ocean phosphate concentrations and net primary production—two key biogeochemical variables that are frequently monitored. This study suggests that changes in the C:P ratios of DOM could serve as a sensitive fingerprint of anthropogenic ocean warming, potentially exerting broad impacts on marine microbes. Our estimated 4% reduction in the globally integrated DOC export below 100 m is comparable to a 2% reduction in particulate organic carbon (POC) export by 2100, implying that global warming is likely to weaken the biological carbon pump through both DOC and POC.</p>","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":null,"pages":null},"PeriodicalIF":5.4,"publicationDate":"2024-06-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2023GB008069","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141439600","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}
V. Hatje, J. Schijf, K. H. Johannesson, R. Andrade, M. Caetano, P. Brito, B. A. Haley, M. Lagarde, C. Jeandel
To improve our understanding and guide future studies and applications, we review the biogeochemistry of the rare earth elements (REE). The REEs, which form a chemically uniform group due to their nearly identical physicochemical properties, include the lanthanide series elements plus scandium (Sc) and yttrium (Y). These elements, in conjunction with the neodymium isotopes, are powerful tools for understanding key oceanic, terrestrial, biological and even anthropogenic processes. Furthermore, their unique properties render them essential for various technological processes and products. Here, we delve into the characteristics of REE biogeochemistry and discuss normalization procedures and REE anomalies. We also examine the aqueous speciation of REEs, contributing to a better understanding of their behavior in aquatic settings, including the role of neodymium isotopes. We then focus on their environmental distribution, fractionation, and controlling processes in different environmental systems across the land-ocean continuum. In addition, we analyze sinks, sources, and the mobility of REEs, providing insights into their behavior in these environments. We further investigate the sources of anthropogenic REEs and their bioavailability, bioaccumulation, and transfer along food webs. We also explore the potential effects of climate change on the cycling, mobility and bioavailability of REEs, underlining the importance of current research in this evolving field. In summary, we provide a comprehensive review of REE behavior in the environment, from their properties and roles to their distribution and anthropogenic impacts, offering valuable insights and pinpointing key knowledge gaps.
{"title":"The Global Biogeochemical Cycle of the Rare Earth Elements","authors":"V. Hatje, J. Schijf, K. H. Johannesson, R. Andrade, M. Caetano, P. Brito, B. A. Haley, M. Lagarde, C. Jeandel","doi":"10.1029/2024GB008125","DOIUrl":"https://doi.org/10.1029/2024GB008125","url":null,"abstract":"<p>To improve our understanding and guide future studies and applications, we review the biogeochemistry of the rare earth elements (REE). The REEs, which form a chemically uniform group due to their nearly identical physicochemical properties, include the lanthanide series elements plus scandium (Sc) and yttrium (Y). These elements, in conjunction with the neodymium isotopes, are powerful tools for understanding key oceanic, terrestrial, biological and even anthropogenic processes. Furthermore, their unique properties render them essential for various technological processes and products. Here, we delve into the characteristics of REE biogeochemistry and discuss normalization procedures and REE anomalies. We also examine the aqueous speciation of REEs, contributing to a better understanding of their behavior in aquatic settings, including the role of neodymium isotopes. We then focus on their environmental distribution, fractionation, and controlling processes in different environmental systems across the land-ocean continuum. In addition, we analyze sinks, sources, and the mobility of REEs, providing insights into their behavior in these environments. We further investigate the sources of anthropogenic REEs and their bioavailability, bioaccumulation, and transfer along food webs. We also explore the potential effects of climate change on the cycling, mobility and bioavailability of REEs, underlining the importance of current research in this evolving field. In summary, we provide a comprehensive review of REE behavior in the environment, from their properties and roles to their distribution and anthropogenic impacts, offering valuable insights and pinpointing key knowledge gaps.</p>","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":null,"pages":null},"PeriodicalIF":5.4,"publicationDate":"2024-06-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GB008125","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141435638","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}
Rachel P. Martineac, Renato M. Castelao, Patricia M. Medeiros
The Amazon River is a large source of terrigenous dissolved organic carbon (tDOC) to the Atlantic Ocean. The fate of this tDOC in the ocean remains unclear despite its importance to the global carbon cycle. Here, we used two decades of satellite ocean color to describe variability in tDOC in the Amazon River plume. Our analyses showed that tDOC distribution has a distinct seasonal pattern, reaching northwest toward the Caribbean during high discharge periods, and moving eastward entrained in the North Brazil Current retroflection during low discharge periods. Elevated tDOC content extended beyond the shelfbreak in all months of the year, suggesting that cross-shelf carbon transport occurs year-round. Maximum variability was found at the plume core, where seasonality accounted for 40% of the total variance, while interannual variability accounted for 15% of the variance. Our results revealed a seasonal pattern in tDOC removal over the shelf with increased consumption in May when river discharge is high. Anomalies in tDOC removal over the shelf with respect to the seasonal cycle were significantly correlated with anomalies in tDOC concentration offshore of the shelfbreak with a lag of 30–40 days, so that anomalously high inshore tDOC removal was associated with anomalously low tDOC content offshore. This suggests that variability in the offshore transport of tDOC in the Amazon River plume is modulated by interannual changes in tDOC removal over the shelf.
{"title":"Seasonal and Interannual Variability in the Distribution and Removal of Terrigenous Dissolved Organic Carbon in the Amazon River Plume","authors":"Rachel P. Martineac, Renato M. Castelao, Patricia M. Medeiros","doi":"10.1029/2023GB007995","DOIUrl":"https://doi.org/10.1029/2023GB007995","url":null,"abstract":"<p>The Amazon River is a large source of terrigenous dissolved organic carbon (tDOC) to the Atlantic Ocean. The fate of this tDOC in the ocean remains unclear despite its importance to the global carbon cycle. Here, we used two decades of satellite ocean color to describe variability in tDOC in the Amazon River plume. Our analyses showed that tDOC distribution has a distinct seasonal pattern, reaching northwest toward the Caribbean during high discharge periods, and moving eastward entrained in the North Brazil Current retroflection during low discharge periods. Elevated tDOC content extended beyond the shelfbreak in all months of the year, suggesting that cross-shelf carbon transport occurs year-round. Maximum variability was found at the plume core, where seasonality accounted for 40% of the total variance, while interannual variability accounted for 15% of the variance. Our results revealed a seasonal pattern in tDOC removal over the shelf with increased consumption in May when river discharge is high. Anomalies in tDOC removal over the shelf with respect to the seasonal cycle were significantly correlated with anomalies in tDOC concentration offshore of the shelfbreak with a lag of 30–40 days, so that anomalously high inshore tDOC removal was associated with anomalously low tDOC content offshore. This suggests that variability in the offshore transport of tDOC in the Amazon River plume is modulated by interannual changes in tDOC removal over the shelf.</p>","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":null,"pages":null},"PeriodicalIF":5.2,"publicationDate":"2024-06-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2023GB007995","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141424885","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}
S. A. Meyjes, C. M. Petrik, T. Rohr, B. B. Cael, A. Mashayek
The biological carbon pump is a key controller of how much carbon is stored within the global ocean. This pathway is influenced by food web interactions between zooplankton and their prey. In global biogeochemical models, Holling Type functional responses are frequently used to represent grazing interactions. How these responses are parameterized greatly influences biomass and subsequent carbon export estimates. The half-saturation constant, or k value, is central to the Holling functional response. Empirical studies show k can vary over three orders of magnitude, however, this variation is poorly represented in global models. This study derives zooplankton grazing dynamics from remote sensing products of phytoplankton biomass, resulting in global distribution maps of the grazing parameter k. The impact of these spatially varying k values on model skill and carbon export flux estimates is then considered. This study finds large spatial variation in k values across the global ocean, with distinct distributions for micro- and mesozooplankton. High half-saturation constants, which drive slower grazing, are generally associated with areas of high productivity. Grazing rate parameterization is found to be critical in reproducing satellite-derived distributions of small phytoplankton biomass, highlighting the importance of top-down drivers for this size class. Spatially varying grazing dynamics decrease mean total carbon export by >17% compared to globally homogeneous dynamics, with increases in fecal pellet export and decreases in export from algal aggregates. This study highlights the importance of grazing dynamics to both community structure and carbon export, with implications for modeling marine carbon sequestration under future climate scenarios.
生物碳泵是全球海洋碳储存量的关键控制因素。这一途径受到浮游动物与其猎物之间食物网相互作用的影响。在全球生物地球化学模型中,霍林式功能响应经常被用来表示放牧相互作用。如何将这些反应参数化会极大地影响生物量和随后的碳输出估计值。半饱和常数或 k 值是霍林功能响应的核心。经验研究表明,k 值的变化可超过三个数量级,但这种变化在全球模型中的表现却很不理想。本研究从浮游植物生物量的遥感数据中推导出浮游动物的摄食动态,从而得到摄食参数 k 的全球分布图。这项研究发现,全球海洋中的 k 值存在很大的空间差异,微型和中型浮游生物的分布各不相同。高半饱和常数通常与高生产力区域相关,而高半饱和常数会减缓放牧速度。研究发现,放牧率参数化对再现小型浮游植物生物量的卫星衍生分布至关重要,这凸显了自上而下的驱动因素对这一大小类别的重要性。与全球均匀的动态相比,空间变化的放牧动态使平均总碳输出量减少了 17%,粪便颗粒输出量增加,藻类聚集体输出量减少。这项研究强调了放牧动力学对群落结构和碳输出的重要性,对模拟未来气候情景下的海洋碳固存具有重要意义。
{"title":"Impact of Spatial Variability in Zooplankton Grazing Rates on Carbon Export Flux","authors":"S. A. Meyjes, C. M. Petrik, T. Rohr, B. B. Cael, A. Mashayek","doi":"10.1029/2023GB008085","DOIUrl":"https://doi.org/10.1029/2023GB008085","url":null,"abstract":"<p>The biological carbon pump is a key controller of how much carbon is stored within the global ocean. This pathway is influenced by food web interactions between zooplankton and their prey. In global biogeochemical models, Holling Type functional responses are frequently used to represent grazing interactions. How these responses are parameterized greatly influences biomass and subsequent carbon export estimates. The half-saturation constant, or <i>k</i> value, is central to the Holling functional response. Empirical studies show <i>k</i> can vary over three orders of magnitude, however, this variation is poorly represented in global models. This study derives zooplankton grazing dynamics from remote sensing products of phytoplankton biomass, resulting in global distribution maps of the grazing parameter <i>k</i>. The impact of these spatially varying <i>k</i> values on model skill and carbon export flux estimates is then considered. This study finds large spatial variation in <i>k</i> values across the global ocean, with distinct distributions for micro- and mesozooplankton. High half-saturation constants, which drive slower grazing, are generally associated with areas of high productivity. Grazing rate parameterization is found to be critical in reproducing satellite-derived distributions of small phytoplankton biomass, highlighting the importance of top-down drivers for this size class. Spatially varying grazing dynamics decrease mean total carbon export by >17% compared to globally homogeneous dynamics, with increases in fecal pellet export and decreases in export from algal aggregates. This study highlights the importance of grazing dynamics to both community structure and carbon export, with implications for modeling marine carbon sequestration under future climate scenarios.</p>","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":null,"pages":null},"PeriodicalIF":5.2,"publicationDate":"2024-06-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2023GB008085","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141326426","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}
The priming effects (PEs) of soil organic carbon (SOC) decomposition is a crucial process affecting the C balance of terrestrial ecosystems. However, there is uncertainty about how PEs will respond to climate warming. In this study, we sampled soils along a subtropical elevation gradient in China and conducted a 126-day lab-incubation experiment with and without the addition of 13C-labeled high-bioavailability glucose or low-bioavailability lignin. Based on the mean annual temperature (MAT) of each elevation (9.3–16.4°C), a temperature increase of 4°C was used to explore how PEs mediate the decomposition of SOC in response to warming. Our results showed that the magnitude of glucose-induced PEs (PEglucose) was higher than lignin-induced PEs (PElignin), with both PEs linearly increasing with MAT. Across the MAT (i.e., elevation) gradient, short-term warming had a constant magnitude of negative effects on PEglucose, whereas rising MAT exacerbated the negative effects of short-term warming on PElignin. Moreover, the temperature sensitivity of SOC decomposition decreased after adding glucose and lignin across the MAT gradient, suggesting that fresh C inputs may prime the microbial breakdown of labile SOC under warming. Taken together, warming alleviated SOC loss due to PEs through varying mechanisms depending on substrate bioavailability. Warming mediated the PEglucose by increasing available nitrogen and weakening microbial nitrogen-mining but inhibited the PElignin by shifting from microbial nitrogen-mining to microbial co-metabolization. Our findings highlight the role of warming in regulating the PEs and suggest that incorporating the suppression effect of warming on PEs can contribute to the accurate prediction of soil C dynamics in a warming world.
土壤有机碳(SOC)分解的启动效应(PEs)是影响陆地生态系统碳平衡的关键过程。然而,土壤有机碳分解对气候变暖的响应尚不确定。在本研究中,我们沿中国亚热带海拔梯度对土壤进行了取样,并在添加和不添加 13C 标记的高生物利用率葡萄糖或低生物利用率木质素的情况下进行了为期 126 天的实验室培养实验。根据每个海拔高度的年平均气温(9.3-16.4°C),我们采用升温 4°C 的方法来探讨 PE 如何在气候变暖时介导 SOC 的分解。我们的结果表明,葡萄糖诱导的 PEs(PEglucose)比木质素诱导的 PEs(PElignin)高,两种 PEs 都随 MAT 线性增加。在 MAT(即海拔高度)梯度上,短期升温对 PEglucose 的负面影响大小不变,而 MAT 升高则加剧了短期升温对 PElignin 的负面影响。此外,加入葡萄糖和木质素后,SOC 分解的温度敏感性在整个 MAT 梯度上都有所下降,这表明在气候变暖的情况下,新鲜 C 输入可能会加速微生物对易变 SOC 的分解。综上所述,升温可通过不同的机制(取决于底物的生物利用率)缓解 PE 导致的 SOC 损失。气候变暖通过增加可利用氮和削弱微生物的采氮作用来介导聚乙烯葡萄糖,但通过从微生物采氮转向微生物协同代谢来抑制聚乙烯木质素。我们的研究结果突显了气候变暖在调节 PEs 方面的作用,并表明将气候变暖对 PEs 的抑制作用纳入其中有助于准确预测气候变暖世界中的土壤碳动态。
{"title":"Warming Reduces Priming Effect of Soil Organic Carbon Decomposition Along a Subtropical Elevation Gradient","authors":"Xiaojie Li, Maokui Lyu, Qiufang Zhang, Jiguang Feng, Xiaofei Liu, Biao Zhu, Xiaohong Wang, Yusheng Yang, Jinsheng Xie","doi":"10.1029/2024GB008113","DOIUrl":"https://doi.org/10.1029/2024GB008113","url":null,"abstract":"<p>The priming effects (PEs) of soil organic carbon (SOC) decomposition is a crucial process affecting the C balance of terrestrial ecosystems. However, there is uncertainty about how PEs will respond to climate warming. In this study, we sampled soils along a subtropical elevation gradient in China and conducted a 126-day lab-incubation experiment with and without the addition of <sup>13</sup>C-labeled high-bioavailability glucose or low-bioavailability lignin. Based on the mean annual temperature (MAT) of each elevation (9.3–16.4°C), a temperature increase of 4°C was used to explore how PEs mediate the decomposition of SOC in response to warming. Our results showed that the magnitude of glucose-induced PEs (PE<sub>glucose</sub>) was higher than lignin-induced PEs (PE<sub>lignin</sub>), with both PEs linearly increasing with MAT. Across the MAT (i.e., elevation) gradient, short-term warming had a constant magnitude of negative effects on PE<sub>glucose</sub>, whereas rising MAT exacerbated the negative effects of short-term warming on PE<sub>lignin</sub>. Moreover, the temperature sensitivity of SOC decomposition decreased after adding glucose and lignin across the MAT gradient, suggesting that fresh C inputs may prime the microbial breakdown of labile SOC under warming. Taken together, warming alleviated SOC loss due to PEs through varying mechanisms depending on substrate bioavailability. Warming mediated the PE<sub>glucose</sub> by increasing available nitrogen and weakening microbial nitrogen-mining but inhibited the PE<sub>lignin</sub> by shifting from microbial nitrogen-mining to microbial co-metabolization. Our findings highlight the role of warming in regulating the PEs and suggest that incorporating the suppression effect of warming on PEs can contribute to the accurate prediction of soil C dynamics in a warming world.</p>","PeriodicalId":12729,"journal":{"name":"Global Biogeochemical Cycles","volume":null,"pages":null},"PeriodicalIF":5.2,"publicationDate":"2024-06-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141304181","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}