Geneviève W. Elsworth, Nicole S. Lovenduski, Kristen M. Krumhardt, Thomas M. Marchitto, Sarah Schlunegger
Abstract. Earth system models suggest that anthropogenic climate change will influence marine phytoplankton over the coming century with light-limited regions becoming more productive and nutrient-limited regions less productive. Anthropogenic climate change can influence not only the mean state but also the internal variability around the mean state, yet little is known about how internal variability in marine phytoplankton will change with time. Here, we quantify the influence of anthropogenic climate change on internal variability in marine phytoplankton biomass from 1920 to 2100 using the Community Earth System Model 1 Large Ensemble (CESM1-LE). We find a significant decrease in the internal variability of global phytoplankton carbon biomass under a high emission (RCP8.5) scenario and heterogeneous regional trends. Decreasing internal variability in biomass is most apparent in the subpolar North Atlantic and North Pacific. In these high-latitude regions, bottom-up controls (e.g., nutrient supply, temperature) influence changes in biomass internal variability. In the biogeochemically critical regions of the Southern Ocean and the equatorial Pacific, bottom-up controls (e.g., light, nutrients) and top-down controls (e.g., grazer biomass) affect changes in phytoplankton carbon internal variability, respectively. Our results suggest that climate mitigation and adaptation efforts that account for marine phytoplankton changes (e.g., fisheries, marine carbon cycling) should also consider changes in phytoplankton internal variability driven by anthropogenic warming, particularly on regional scales.
{"title":"Anthropogenic climate change drives non-stationary phytoplankton internal variability","authors":"Geneviève W. Elsworth, Nicole S. Lovenduski, Kristen M. Krumhardt, Thomas M. Marchitto, Sarah Schlunegger","doi":"10.5194/bg-20-4477-2023","DOIUrl":"https://doi.org/10.5194/bg-20-4477-2023","url":null,"abstract":"Abstract. Earth system models suggest that anthropogenic climate change will influence marine phytoplankton over the coming century with light-limited regions becoming more productive and nutrient-limited regions less productive. Anthropogenic climate change can influence not only the mean state but also the internal variability around the mean state, yet little is known about how internal variability in marine phytoplankton will change with time. Here, we quantify the influence of anthropogenic climate change on internal variability in marine phytoplankton biomass from 1920 to 2100 using the Community Earth System Model 1 Large Ensemble (CESM1-LE). We find a significant decrease in the internal variability of global phytoplankton carbon biomass under a high emission (RCP8.5) scenario and heterogeneous regional trends. Decreasing internal variability in biomass is most apparent in the subpolar North Atlantic and North Pacific. In these high-latitude regions, bottom-up controls (e.g., nutrient supply, temperature) influence changes in biomass internal variability. In the biogeochemically critical regions of the Southern Ocean and the equatorial Pacific, bottom-up controls (e.g., light, nutrients) and top-down controls (e.g., grazer biomass) affect changes in phytoplankton carbon internal variability, respectively. Our results suggest that climate mitigation and adaptation efforts that account for marine phytoplankton changes (e.g., fisheries, marine carbon cycling) should also consider changes in phytoplankton internal variability driven by anthropogenic warming, particularly on regional scales.","PeriodicalId":8899,"journal":{"name":"Biogeosciences","volume":" 1291","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-11-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135186699","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}
Joyson Ahongshangbam, Liisa Kulmala, Jesse Soininen, Yasmin Frühauf, Esko Karvinen, Yann Salmon, Anna Lintunen, Anni Karvonen, Leena Järvi
Abstract. Urban vegetation plays a role in offsetting urban CO2 emissions, mitigating heat through tree transpiration and shading, and acting as deposition surfaces for pollutants. The frequent occurrence of heatwaves and of concurrent drought conditions significantly disrupts the processes of urban trees, particularly their photosynthesis and transpiration rates. Despite the pivotal role of urban tree functioning in delivering essential ecosystem services, the precise nature of their response remains uncertain. We conducted sap flux density (Js) and leaf gas exchange measurements of four tree species (Tilia cordata, Tilia × europaea, Betula pendula, and Malus spp.) located in different urban green areas (Park, Street, Forest, and Orchard) in Helsinki, Finland. Measurements were made over two contrasting summers 2020 and 2021. Summer 2021 experienced a local heatwave and drought, whereas summer 2020 was more typical of Helsinki. In this study, we aimed to understand the responses of urban tree transpiration (measured with sap flux density) and leaf gas exchange to heatwave and drought conditions, and we examined the main environmental drivers controlling the tree transpiration rate during these periods. We observed varying responses of Js during the heatwave period at the four urban sites. When comparing the heatwave and no heatwave periods, a 35 %–67 % increase in Js was observed at the Park, Forest, and Orchard locations, whereas no significant change was seen at the Street site. Our results also showed that Js was higher (31 %–63 %) at all sites under drought conditions compared with non-dry periods. The higher Js values during the heatwave and dry periods were mainly driven by the high atmospheric demand for evapotranspiration, represented by the high vapor pressure deficit (VPD), suggesting that the trees were not experiencing severe enough heat or drought stress that stomatal control would have decreased transpiration. Accordingly, photosynthetic potential (Amax), stomatal conductance (gs), and transpiration (E) at the leaf level did not change during heatwave and drought periods, excluding the Park site where a significant reduction in gs was seen. VPD explained 55 %–69 % of the variation in the daily mean Js during heatwave and drought periods at all sites. At the Forest site, the increase in Js saturated after a certain VPD level, likely due to low soil water availability during these hot and dry periods. Overall, the heat and drought conditions were untypical of the region but not excessive enough to restrict stomatal control and transpiration, indicating that ecosystem services such as cooling were not at risk.
{"title":"Sap flow and leaf gas exchange response to a drought and heatwave in urban green spaces in a Nordic city","authors":"Joyson Ahongshangbam, Liisa Kulmala, Jesse Soininen, Yasmin Frühauf, Esko Karvinen, Yann Salmon, Anna Lintunen, Anni Karvonen, Leena Järvi","doi":"10.5194/bg-20-4455-2023","DOIUrl":"https://doi.org/10.5194/bg-20-4455-2023","url":null,"abstract":"Abstract. Urban vegetation plays a role in offsetting urban CO2 emissions, mitigating heat through tree transpiration and shading, and acting as deposition surfaces for pollutants. The frequent occurrence of heatwaves and of concurrent drought conditions significantly disrupts the processes of urban trees, particularly their photosynthesis and transpiration rates. Despite the pivotal role of urban tree functioning in delivering essential ecosystem services, the precise nature of their response remains uncertain. We conducted sap flux density (Js) and leaf gas exchange measurements of four tree species (Tilia cordata, Tilia × europaea, Betula pendula, and Malus spp.) located in different urban green areas (Park, Street, Forest, and Orchard) in Helsinki, Finland. Measurements were made over two contrasting summers 2020 and 2021. Summer 2021 experienced a local heatwave and drought, whereas summer 2020 was more typical of Helsinki. In this study, we aimed to understand the responses of urban tree transpiration (measured with sap flux density) and leaf gas exchange to heatwave and drought conditions, and we examined the main environmental drivers controlling the tree transpiration rate during these periods. We observed varying responses of Js during the heatwave period at the four urban sites. When comparing the heatwave and no heatwave periods, a 35 %–67 % increase in Js was observed at the Park, Forest, and Orchard locations, whereas no significant change was seen at the Street site. Our results also showed that Js was higher (31 %–63 %) at all sites under drought conditions compared with non-dry periods. The higher Js values during the heatwave and dry periods were mainly driven by the high atmospheric demand for evapotranspiration, represented by the high vapor pressure deficit (VPD), suggesting that the trees were not experiencing severe enough heat or drought stress that stomatal control would have decreased transpiration. Accordingly, photosynthetic potential (Amax), stomatal conductance (gs), and transpiration (E) at the leaf level did not change during heatwave and drought periods, excluding the Park site where a significant reduction in gs was seen. VPD explained 55 %–69 % of the variation in the daily mean Js during heatwave and drought periods at all sites. At the Forest site, the increase in Js saturated after a certain VPD level, likely due to low soil water availability during these hot and dry periods. Overall, the heat and drought conditions were untypical of the region but not excessive enough to restrict stomatal control and transpiration, indicating that ecosystem services such as cooling were not at risk.","PeriodicalId":8899,"journal":{"name":"Biogeosciences","volume":"78 3","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-11-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135342544","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}
Nestor Gaviria-Lugo, Charlotte Läuchli, Hella Wittmann, Anne Bernhard, Patrick Frings, Mahyar Mohtadi, Oliver Rach, Dirk Sachse
Abstract. The hydrogen isotope composition of leaf wax biomarkers (δ2Hwax) is a valuable tool for reconstructing continental paleohydrology, since it serves as a proxy for the hydrogen isotope composition of precipitation (δ2Hpre). To yield robust palaeohydrological reconstructions using δ2Hwax in marine archives, it is necessary to examine the impacts of regional climate on δ2Hwax and assess the similarity between marine sedimentary δ2Hwax and the source of continental δ2Hwax. Here, we examined an aridity gradient from hyperarid to humid along the Chilean coast. We sampled sediments at the outlets of rivers draining into the Pacific as well as soils within catchments and marine surface sediments adjacent to the outlets of the studied rivers and analyzed the relationship between climatic variables and δ2Hwax values. We found that apparent fractionation between leaf waxes and source water is relatively constant in humid and semiarid regions (average: −121 ‰). However, it becomes less negative in hyperarid regions (average: −86 ‰) as a result of evapotranspirative processes affecting soil and leaf water 2H enrichment. We also observed that along strong aridity gradients, the 2H enrichment of δ2Hwax follows a non-linear relationship with water content and water flux variables, driven by strong soil evaporation and plant transpiration. Furthermore, our results indicate that δ2Hwax values in marine surface sediments largely reflect δ2Hwax values from the continent, confirming the robustness of marine δ2Hwax records for paleohydrological reconstructions along the Chilean margin. These findings also highlight the importance of considering the effects of hyperaridity in the interpretation of δ2Hwax values and pave the way for more quantitative paleohydrological reconstructions using δ2Hwax.
{"title":"Climatic controls on leaf wax hydrogen isotope ratios in terrestrial and marine sediments along a hyperarid-to-humid gradient","authors":"Nestor Gaviria-Lugo, Charlotte Läuchli, Hella Wittmann, Anne Bernhard, Patrick Frings, Mahyar Mohtadi, Oliver Rach, Dirk Sachse","doi":"10.5194/bg-20-4433-2023","DOIUrl":"https://doi.org/10.5194/bg-20-4433-2023","url":null,"abstract":"Abstract. The hydrogen isotope composition of leaf wax biomarkers (δ2Hwax) is a valuable tool for reconstructing continental paleohydrology, since it serves as a proxy for the hydrogen isotope composition of precipitation (δ2Hpre). To yield robust palaeohydrological reconstructions using δ2Hwax in marine archives, it is necessary to examine the impacts of regional climate on δ2Hwax and assess the similarity between marine sedimentary δ2Hwax and the source of continental δ2Hwax. Here, we examined an aridity gradient from hyperarid to humid along the Chilean coast. We sampled sediments at the outlets of rivers draining into the Pacific as well as soils within catchments and marine surface sediments adjacent to the outlets of the studied rivers and analyzed the relationship between climatic variables and δ2Hwax values. We found that apparent fractionation between leaf waxes and source water is relatively constant in humid and semiarid regions (average: −121 ‰). However, it becomes less negative in hyperarid regions (average: −86 ‰) as a result of evapotranspirative processes affecting soil and leaf water 2H enrichment. We also observed that along strong aridity gradients, the 2H enrichment of δ2Hwax follows a non-linear relationship with water content and water flux variables, driven by strong soil evaporation and plant transpiration. Furthermore, our results indicate that δ2Hwax values in marine surface sediments largely reflect δ2Hwax values from the continent, confirming the robustness of marine δ2Hwax records for paleohydrological reconstructions along the Chilean margin. These findings also highlight the importance of considering the effects of hyperaridity in the interpretation of δ2Hwax values and pave the way for more quantitative paleohydrological reconstructions using δ2Hwax.","PeriodicalId":8899,"journal":{"name":"Biogeosciences","volume":"221 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-11-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135476377","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}
Laurie C. Menviel, Paul Spence, Andrew E. Kiss, Matthew A. Chamberlain, Hakase Hayashida, Matthew H. England, Darryn Waugh
Abstract. While the Southern Ocean (SO) provides the largest oceanic sink of carbon, some observational studies have suggested that the SO total CO2 (tCO2) uptake exhibited large (∼ 0.3 GtC yr−1) decadal-scale variability over the last 30 years, with a similar SO tCO2 uptake in 2016 as in the early 1990s. Here, using an eddy-rich ocean, sea-ice, carbon cycle model, with a nominal resolution of 0.1∘, we explore the changes in total, natural and anthropogenic SO CO2 fluxes over the period 1980–2021 and the processes leading to the CO2 flux variability. The simulated tCO2 flux exhibits decadal-scale variability with an amplitude of ∼ 0.1 GtC yr−1 globally in phase with observations. Notably, two stagnations in tCO2 uptake are simulated: between 1982 and 2000, and between 2003 and 2011, while re-invigorations are simulated between 2000 and 2003, as well as since 2012. This decadal-scale variability is primarily due to changes in natural CO2 (nCO2) fluxes south of the polar front associated with variability in the Southern Annular Mode (SAM). Positive phases of the SAM, i.e. stronger and poleward shifted southern hemispheric (SH) westerlies, lead to enhanced SO nCO2 outgassing due to higher surface natural dissolved inorganic carbon (DIC) brought about by a combination of Ekman-driven vertical advection and DIC diffusion at the base of the mixed layer. The pattern of the CO2 flux anomalies indicate a dominant control of the interaction between the mean flow south of the polar front and the main topographic features. While positive phases of the SAM also lead to enhanced anthropogenic CO2 (aCO2) uptake south of the polar front, the amplitude of the changes in aCO2 fluxes is only 25 % of the changes in nCO2 fluxes. Due to the larger nCO2 outgassing compared to aCO2 uptake as the SH westerlies strengthen and shift poleward, the SO tCO2 uptake capability thus reduced since 1980 in response to the shift towards positive phases of the SAM. Our results indicate that, even in an eddy-rich ocean model, a strengthening and/or poleward shift of the SH westerlies enhance CO2 outgassing. The projected poleward strengthening of the SH westerlies over the coming century will, thus, reduce the capability of the SO to mitigate the increase in atmospheric CO2.
{"title":"Enhanced Southern Ocean CO<sub>2</sub> outgassing as a result of stronger and poleward shifted southern hemispheric westerlies","authors":"Laurie C. Menviel, Paul Spence, Andrew E. Kiss, Matthew A. Chamberlain, Hakase Hayashida, Matthew H. England, Darryn Waugh","doi":"10.5194/bg-20-4413-2023","DOIUrl":"https://doi.org/10.5194/bg-20-4413-2023","url":null,"abstract":"Abstract. While the Southern Ocean (SO) provides the largest oceanic sink of carbon, some observational studies have suggested that the SO total CO2 (tCO2) uptake exhibited large (∼ 0.3 GtC yr−1) decadal-scale variability over the last 30 years, with a similar SO tCO2 uptake in 2016 as in the early 1990s. Here, using an eddy-rich ocean, sea-ice, carbon cycle model, with a nominal resolution of 0.1∘, we explore the changes in total, natural and anthropogenic SO CO2 fluxes over the period 1980–2021 and the processes leading to the CO2 flux variability. The simulated tCO2 flux exhibits decadal-scale variability with an amplitude of ∼ 0.1 GtC yr−1 globally in phase with observations. Notably, two stagnations in tCO2 uptake are simulated: between 1982 and 2000, and between 2003 and 2011, while re-invigorations are simulated between 2000 and 2003, as well as since 2012. This decadal-scale variability is primarily due to changes in natural CO2 (nCO2) fluxes south of the polar front associated with variability in the Southern Annular Mode (SAM). Positive phases of the SAM, i.e. stronger and poleward shifted southern hemispheric (SH) westerlies, lead to enhanced SO nCO2 outgassing due to higher surface natural dissolved inorganic carbon (DIC) brought about by a combination of Ekman-driven vertical advection and DIC diffusion at the base of the mixed layer. The pattern of the CO2 flux anomalies indicate a dominant control of the interaction between the mean flow south of the polar front and the main topographic features. While positive phases of the SAM also lead to enhanced anthropogenic CO2 (aCO2) uptake south of the polar front, the amplitude of the changes in aCO2 fluxes is only 25 % of the changes in nCO2 fluxes. Due to the larger nCO2 outgassing compared to aCO2 uptake as the SH westerlies strengthen and shift poleward, the SO tCO2 uptake capability thus reduced since 1980 in response to the shift towards positive phases of the SAM. Our results indicate that, even in an eddy-rich ocean model, a strengthening and/or poleward shift of the SH westerlies enhance CO2 outgassing. The projected poleward strengthening of the SH westerlies over the coming century will, thus, reduce the capability of the SO to mitigate the increase in atmospheric CO2.","PeriodicalId":8899,"journal":{"name":"Biogeosciences","volume":"30 8","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-11-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135679489","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}
Ryan Vella, Andrea Pozzer, Matthew Forrest, Jos Lelieveld, Thomas Hickler, Holger Tost
Abstract. Emissions of biogenic volatile organic compounds (BVOCs) from the terrestrial biosphere play a significant role in major atmospheric processes. BVOCs are highly reactive compounds that influence the atmosphere's oxidation capacity and also serve as precursors for the formation of aerosols that influence global radiation budgets. Emissions depend on the response of vegetation to atmospheric conditions (primarily temperature and light), as well as other stresses, e.g. from droughts and herbivory. The El Niño–Southern Oscillation (ENSO) is a naturally occurring cycle arising from anomalies in the sea surface temperature (SST) in the tropical Pacific. ENSO perturbs the natural seasonality of weather systems on both global and regional scales and is considered the most significant driver of climate variability. Several studies have evaluated the sensitivity of BVOC fluxes during ENSO events using historical transient simulations. While this approach employs realistic scenarios, it is difficult to assess the impact of ENSO alone given the multiple types of climate forcing, e.g. from anthropogenic emissions of CO2 and aerosol. In this study, a global atmospheric chemistry–climate model with enabled interactive vegetation was used to conduct two sets of simulations: (1) isolated ENSO event simulations, in which a single ENSO event is used to perturb otherwise baseline conditions, and (2) sustained ENSO simulations, in which the same ENSO conditions are reproduced for an extended period of time. From the isolated ENSO events, we present global and regional BVOC emission changes resulting from the immediate response of vegetation to atmospheric states. More focus is given to the sustained ENSO simulations, which have the benefit of reducing the internal variability for more robust statistics when linking atmospheric and vegetation variables with BVOC flux anomalies. Additionally, these simulations explore long-term changes in the biosphere with potential shifts in vegetation in this possible climate mode, accounting for the prospect of increased intensity and frequency of ENSO with climate change. Our results show that strong El Niño events increase global isoprene emission fluxes by 2.9 % and that one single ENSO event perturbs the Earth system so markedly that BVOC emission fluxes do not return to baseline emissions within several years after the event. We show that persistent ENSO conditions shift the vegetation to a new quasi-equilibrium state, leading to an amplification of BVOC emission changes with up to a 19 % increase in isoprene fluxes over the Amazon. We provide evidence that BVOC-induced changes in plant phenology, such as the leaf area index (LAI), have a significant influence on BVOC emissions in the sustained ENSO climate mode.
{"title":"Changes in biogenic volatile organic compound emissions in response to the El Niño–Southern Oscillation","authors":"Ryan Vella, Andrea Pozzer, Matthew Forrest, Jos Lelieveld, Thomas Hickler, Holger Tost","doi":"10.5194/bg-20-4391-2023","DOIUrl":"https://doi.org/10.5194/bg-20-4391-2023","url":null,"abstract":"Abstract. Emissions of biogenic volatile organic compounds (BVOCs) from the terrestrial biosphere play a significant role in major atmospheric processes. BVOCs are highly reactive compounds that influence the atmosphere's oxidation capacity and also serve as precursors for the formation of aerosols that influence global radiation budgets. Emissions depend on the response of vegetation to atmospheric conditions (primarily temperature and light), as well as other stresses, e.g. from droughts and herbivory. The El Niño–Southern Oscillation (ENSO) is a naturally occurring cycle arising from anomalies in the sea surface temperature (SST) in the tropical Pacific. ENSO perturbs the natural seasonality of weather systems on both global and regional scales and is considered the most significant driver of climate variability. Several studies have evaluated the sensitivity of BVOC fluxes during ENSO events using historical transient simulations. While this approach employs realistic scenarios, it is difficult to assess the impact of ENSO alone given the multiple types of climate forcing, e.g. from anthropogenic emissions of CO2 and aerosol. In this study, a global atmospheric chemistry–climate model with enabled interactive vegetation was used to conduct two sets of simulations: (1) isolated ENSO event simulations, in which a single ENSO event is used to perturb otherwise baseline conditions, and (2) sustained ENSO simulations, in which the same ENSO conditions are reproduced for an extended period of time. From the isolated ENSO events, we present global and regional BVOC emission changes resulting from the immediate response of vegetation to atmospheric states. More focus is given to the sustained ENSO simulations, which have the benefit of reducing the internal variability for more robust statistics when linking atmospheric and vegetation variables with BVOC flux anomalies. Additionally, these simulations explore long-term changes in the biosphere with potential shifts in vegetation in this possible climate mode, accounting for the prospect of increased intensity and frequency of ENSO with climate change. Our results show that strong El Niño events increase global isoprene emission fluxes by 2.9 % and that one single ENSO event perturbs the Earth system so markedly that BVOC emission fluxes do not return to baseline emissions within several years after the event. We show that persistent ENSO conditions shift the vegetation to a new quasi-equilibrium state, leading to an amplification of BVOC emission changes with up to a 19 % increase in isoprene fluxes over the Amazon. We provide evidence that BVOC-induced changes in plant phenology, such as the leaf area index (LAI), have a significant influence on BVOC emissions in the sustained ENSO climate mode.","PeriodicalId":8899,"journal":{"name":"Biogeosciences","volume":"86 2","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136317172","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}
Sebastian J. E. Krause, Jiarui Liu, David J. Yousavich, DeMarcus Robinson, David W. Hoyt, Qianhui Qin, Frank Wenzhöfer, Felix Janssen, David L. Valentine, Tina Treude
Abstract. The recently discovered cryptic methane cycle in the sulfate-reducing zone of marine and wetland sediment couples methylotrophic methanogenesis to anaerobic oxidation of methane (AOM). Here we present evidence of cryptic methane cycling activity within the upper regions of the sulfate-reducing zone, along a depth transect within the Santa Barbara Basin, off the coast of California, USA. The top 0–20 cm of sediment from each station was subjected to geochemical analyses and radiotracer incubations using 35S–SO42-, 14C–mono-methylamine, and 14C–CH4 to find evidence of cryptic methane cycling. Methane concentrations were consistently low (3 to 16 µM) across the depth transect, despite AOM rates increasing with decreasing water depth (from max 0.05 nmol cm−3 d−1 at the deepest station to max 1.8 nmol cm−3 d−1 at the shallowest station). Porewater sulfate concentrations remained high (23 to 29 mM), despite the detection of sulfate reduction activity from 35S–SO42- incubations with rates up to 134 nmol cm−3 d−1. Metabolomic analysis showed that substrates for methanogenesis (i.e., acetate, methanol and methylamines) were mostly below the detection limit in the porewater, but some samples from the 1–2 cm depth section showed non-quantifiable evidence of these substrates, indicating their rapid turnover. Estimated methanogenesis from mono-methylamine ranged from 0.2 to 0.5 nmol cm−3 d−1. Discrepancies between the rate constants (k) of methanogenesis (from 14C–mono-methylamine) and AOM (from either 14C–mono-methylamine-derived 14C–CH4 or from directly injected 14C–CH4) suggest the activity of a separate, concurrent metabolic process directly metabolizing mono-methylamine to inorganic carbon. We conclude that the results presented in this work show strong evidence of cryptic methane cycling occurring within the top 20 cm of sediment in the Santa Barbara Basin. The rapid cycling of carbon between methanogenesis and methanotropy likely prevents major build-up of methane in the sulfate-reducing zone. Furthermore, our data suggest that methylamine is utilized by both methanogenic archaea capable of methylotrophic methanogenesis and non-methanogenic microbial groups. We hypothesize that sulfate reduction is responsible for the additional methylamine turnover, but further investigation is needed to elucidate this metabolic activity.
{"title":"Evidence of cryptic methane cycling and non-methanogenic methylamine consumption in the sulfate-reducing zone of sediment in the Santa Barbara Basin, California","authors":"Sebastian J. E. Krause, Jiarui Liu, David J. Yousavich, DeMarcus Robinson, David W. Hoyt, Qianhui Qin, Frank Wenzhöfer, Felix Janssen, David L. Valentine, Tina Treude","doi":"10.5194/bg-20-4377-2023","DOIUrl":"https://doi.org/10.5194/bg-20-4377-2023","url":null,"abstract":"Abstract. The recently discovered cryptic methane cycle in the sulfate-reducing zone of marine and wetland sediment couples methylotrophic methanogenesis to anaerobic oxidation of methane (AOM). Here we present evidence of cryptic methane cycling activity within the upper regions of the sulfate-reducing zone, along a depth transect within the Santa Barbara Basin, off the coast of California, USA. The top 0–20 cm of sediment from each station was subjected to geochemical analyses and radiotracer incubations using 35S–SO42-, 14C–mono-methylamine, and 14C–CH4 to find evidence of cryptic methane cycling. Methane concentrations were consistently low (3 to 16 µM) across the depth transect, despite AOM rates increasing with decreasing water depth (from max 0.05 nmol cm−3 d−1 at the deepest station to max 1.8 nmol cm−3 d−1 at the shallowest station). Porewater sulfate concentrations remained high (23 to 29 mM), despite the detection of sulfate reduction activity from 35S–SO42- incubations with rates up to 134 nmol cm−3 d−1. Metabolomic analysis showed that substrates for methanogenesis (i.e., acetate, methanol and methylamines) were mostly below the detection limit in the porewater, but some samples from the 1–2 cm depth section showed non-quantifiable evidence of these substrates, indicating their rapid turnover. Estimated methanogenesis from mono-methylamine ranged from 0.2 to 0.5 nmol cm−3 d−1. Discrepancies between the rate constants (k) of methanogenesis (from 14C–mono-methylamine) and AOM (from either 14C–mono-methylamine-derived 14C–CH4 or from directly injected 14C–CH4) suggest the activity of a separate, concurrent metabolic process directly metabolizing mono-methylamine to inorganic carbon. We conclude that the results presented in this work show strong evidence of cryptic methane cycling occurring within the top 20 cm of sediment in the Santa Barbara Basin. The rapid cycling of carbon between methanogenesis and methanotropy likely prevents major build-up of methane in the sulfate-reducing zone. Furthermore, our data suggest that methylamine is utilized by both methanogenic archaea capable of methylotrophic methanogenesis and non-methanogenic microbial groups. We hypothesize that sulfate reduction is responsible for the additional methylamine turnover, but further investigation is needed to elucidate this metabolic activity.","PeriodicalId":8899,"journal":{"name":"Biogeosciences","volume":"23 3","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134907383","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}
Abstract. Extreme climates affect the seasonal and interannual patterns of carbon (C) distribution in lentic ecosystems due to the regimes of river inflow and thermal stratification. Typhoons rapidly load substantial amounts of terrestrial C into smaller subtropical lakes (i.e., Yuan-Yang Lake in Taiwan, hereafter referred to as YYL), renewing and mixing the water column. We developed a conceptual dissolved C model and hypothesized that allochthonous C loading and river inflow intrusion may affect the dissolved inorganic C (DIC) and dissolved organic C (DOC) distributions in a small subtropical lake under these extreme climates. A two-layer conceptual C model was developed to explore how the DIC and DOC fluxes respond to typhoon disturbances on seasonal and interannual timescales in YYL while simultaneously considering autochthonous processes such as algal photosynthesis, remineralization, and vertical transformation. To compare the temporal patterns of fluxes between typhoon years (2015–2016) and non-typhoon years (2017–2018), monthly field samples were obtained and their DIC, DOC, and chlorophyll a (Chl a) concentrations measured. The results demonstrated that net ecosystem production was 3.14 times higher in typhoon years than in non-typhoon years. These results suggested that a loading of allochthonous C was the most crucial driver of the temporal variation in C fluxes in typhoon years because of changes in physical and biochemical processes, such as photosynthesis, mineralization, and vertical transportation. However, the lowered vertical transportation rate shaped the seasonal C in non-typhoon years due to thermal stratification within this small subtropical lake.
{"title":"Conceptual models of dissolved carbon fluxes in a two-layer stratified lake: interannual typhoon responses under extreme climates","authors":"Hao-Chi Lin, Keisuke Nakayama, Jeng-Wei Tsai, Chih-Yu Chiu","doi":"10.5194/bg-20-4359-2023","DOIUrl":"https://doi.org/10.5194/bg-20-4359-2023","url":null,"abstract":"Abstract. Extreme climates affect the seasonal and interannual patterns of carbon (C) distribution in lentic ecosystems due to the regimes of river inflow and thermal stratification. Typhoons rapidly load substantial amounts of terrestrial C into smaller subtropical lakes (i.e., Yuan-Yang Lake in Taiwan, hereafter referred to as YYL), renewing and mixing the water column. We developed a conceptual dissolved C model and hypothesized that allochthonous C loading and river inflow intrusion may affect the dissolved inorganic C (DIC) and dissolved organic C (DOC) distributions in a small subtropical lake under these extreme climates. A two-layer conceptual C model was developed to explore how the DIC and DOC fluxes respond to typhoon disturbances on seasonal and interannual timescales in YYL while simultaneously considering autochthonous processes such as algal photosynthesis, remineralization, and vertical transformation. To compare the temporal patterns of fluxes between typhoon years (2015–2016) and non-typhoon years (2017–2018), monthly field samples were obtained and their DIC, DOC, and chlorophyll a (Chl a) concentrations measured. The results demonstrated that net ecosystem production was 3.14 times higher in typhoon years than in non-typhoon years. These results suggested that a loading of allochthonous C was the most crucial driver of the temporal variation in C fluxes in typhoon years because of changes in physical and biochemical processes, such as photosynthesis, mineralization, and vertical transportation. However, the lowered vertical transportation rate shaped the seasonal C in non-typhoon years due to thermal stratification within this small subtropical lake.","PeriodicalId":8899,"journal":{"name":"Biogeosciences","volume":"54 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135217155","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}
Tania M. Kenyon, Daniel Harris, Tom Baldock, David Callaghan, Christopher Doropoulos, Gregory Webb, Steven P. Newman, Peter J. Mumby
Abstract. The proportional cover of rubble on reefs is predicted to increase as disturbances increase in intensity and frequency. Unstable rubble can kill coral recruits and impair binding processes that transform rubble into a stable substrate for coral recruitment. A clearer understanding of the mechanisms of inhibited coral recovery on rubble requires characterisation of the hydrodynamic conditions that trigger rubble mobilisation. Here, we investigated rubble mobilisation under regular wave conditions in a wave flume and irregular wave conditions in situ on a coral reef in the Maldives. We examined how changes in near-bed wave orbital velocity influenced the likelihood of rubble motion (e.g. rocking) and transport (by walking, sliding or flipping). Rubble mobilisation was considered as a function of rubble length, branchiness (branched vs. unbranched) and underlying substrate (rubble vs. sand). The effect of near-bed wave orbital velocity on rubble mobilisation was comparable between flume and reef observations. As near-bed wave orbital velocity increased, rubble was more likely to rock, be transported and travel greater distances. Averaged across length, branchiness and substrate, loose rubble had a 50 % chance of transport when near-bed wave orbital velocities reached 0.30 m s−1 in both the wave flume and on the reef. However, small and/or unbranched rubble pieces were generally mobilised more and at lower velocities than larger, branched rubble. Rubble also travelled further distances per day (∼2 cm) on substrates composed of sand than rubble. Importantly, if rubble was interlocked, it was very unlikely to move (< 7 % chance) even at the highest velocity tested (0.4 m s−1). Furthermore, the probability of rubble transport declined over 3 d deployments in the field, suggesting rubble had snagged or settled into more hydrodynamically stable positions within the first days of deployment. We expect that snagged or settled rubble is transported more commonly in locations with higher-energy events and more variable wave environments. At our field site in the Maldives, we expect recovery windows for binding (when rubble is stable) to predominantly occur during the calmer north-eastern monsoon when wave energy impacting the atoll is less and wave heights are smaller. Our results show that rubble beds comprised of small rubble pieces and/or pieces with fewer branches are more likely to have shorter windows of recovery (stability) between mobilisation events, and thus be good candidates for rubble stabilisation interventions to enhance coral recruitment and binding.
摘要据预测，随着扰动强度和频率的增加，礁石上的碎石覆盖比例也会增加。不稳定的碎石会杀死新招募的珊瑚，并破坏将碎石转化为珊瑚招募的稳定基质的结合过程。要更清楚地了解珊瑚在碎石上被抑制的恢复机制，就需要描述触发碎石动员的水动力条件。在这里，我们调查了马尔代夫珊瑚礁在波浪水槽和不规则波浪条件下的正常波浪条件下的碎石动员。我们研究了近床波轨道速度的变化如何影响碎石运动(例如摇晃)和运输(通过行走，滑动或翻转)的可能性。碎石的动员被认为是碎石长度、分枝性(分枝与未分枝)和底层基质(碎石与沙子)的函数。近床波轨道速度对碎石动员的影响在水槽和珊瑚礁观测之间是相当的。随着近床波轨道速度的增加，碎石更有可能形成岩石，被运输并传播更远的距离。在长度、分枝和基材上平均，当近床波轨道速度在波浪水槽和礁石上达到0.30 m s - 1时，松散的碎石有50%的机会被搬运。然而，小的和/或未分叉的碎石块通常比大的、分叉的碎石块移动得更多，速度也更低。在由沙子组成的基质上，碎石比碎石每天移动的距离更远(约2厘米)。重要的是，如果碎石是环环相扣的，它就不太可能移动。即使在测试的最高速度(0.4 m s - 1)下，也有7%的机会。此外，在现场的3d部署中，碎石运输的可能性下降了，这表明在部署的头几天内，碎石已经堵塞或固定在更流体动力学稳定的位置。我们预计，在具有更高能量事件和更多变的波浪环境的地方，受阻或沉降的碎石更常被运输。在我们在马尔代夫的现场，我们预计绑定的恢复窗口(当碎石稳定时)主要发生在较平静的东北季风期间，当时影响环礁的波浪能量较小，波浪高度较小。我们的研究结果表明，碎石床由小碎石块和/或具有较少分支的碎石块组成，在动员事件之间更有可能具有较短的恢复(稳定性)窗口，因此是碎石稳定干预措施的良好候选者，以增强珊瑚的招募和结合。
{"title":"Mobilisation thresholds for coral rubble and consequences for windows of reef recovery","authors":"Tania M. Kenyon, Daniel Harris, Tom Baldock, David Callaghan, Christopher Doropoulos, Gregory Webb, Steven P. Newman, Peter J. Mumby","doi":"10.5194/bg-20-4339-2023","DOIUrl":"https://doi.org/10.5194/bg-20-4339-2023","url":null,"abstract":"Abstract. The proportional cover of rubble on reefs is predicted to increase as disturbances increase in intensity and frequency. Unstable rubble can kill coral recruits and impair binding processes that transform rubble into a stable substrate for coral recruitment. A clearer understanding of the mechanisms of inhibited coral recovery on rubble requires characterisation of the hydrodynamic conditions that trigger rubble mobilisation. Here, we investigated rubble mobilisation under regular wave conditions in a wave flume and irregular wave conditions in situ on a coral reef in the Maldives. We examined how changes in near-bed wave orbital velocity influenced the likelihood of rubble motion (e.g. rocking) and transport (by walking, sliding or flipping). Rubble mobilisation was considered as a function of rubble length, branchiness (branched vs. unbranched) and underlying substrate (rubble vs. sand). The effect of near-bed wave orbital velocity on rubble mobilisation was comparable between flume and reef observations. As near-bed wave orbital velocity increased, rubble was more likely to rock, be transported and travel greater distances. Averaged across length, branchiness and substrate, loose rubble had a 50 % chance of transport when near-bed wave orbital velocities reached 0.30 m s−1 in both the wave flume and on the reef. However, small and/or unbranched rubble pieces were generally mobilised more and at lower velocities than larger, branched rubble. Rubble also travelled further distances per day (∼2 cm) on substrates composed of sand than rubble. Importantly, if rubble was interlocked, it was very unlikely to move (< 7 % chance) even at the highest velocity tested (0.4 m s−1). Furthermore, the probability of rubble transport declined over 3 d deployments in the field, suggesting rubble had snagged or settled into more hydrodynamically stable positions within the first days of deployment. We expect that snagged or settled rubble is transported more commonly in locations with higher-energy events and more variable wave environments. At our field site in the Maldives, we expect recovery windows for binding (when rubble is stable) to predominantly occur during the calmer north-eastern monsoon when wave energy impacting the atoll is less and wave heights are smaller. Our results show that rubble beds comprised of small rubble pieces and/or pieces with fewer branches are more likely to have shorter windows of recovery (stability) between mobilisation events, and thus be good candidates for rubble stabilisation interventions to enhance coral recruitment and binding.","PeriodicalId":8899,"journal":{"name":"Biogeosciences","volume":"28 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135322566","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}
Abstract. The semi-enclosed coastal seas serve as a transition zone between land and the open ocean, and their environments are therefore affected by both. The influences of land were noticed but that of the open ocean were usually neglected. The Seto Inland Sea (SIS), which is connected to the Pacific Ocean, is a typical representative of semi-enclosed seas. To quantitatively assess the inventory of nutrients originating from land and the open ocean, as well as their supported phytoplankton in the SIS, we developed a three-dimensional coupled hydrodynamic–biogeochemical model and embedded a tracking technique in it. Model results showed that the open ocean contributes 61 % and 46 % to the annual inventory of dissolved inorganic nitrogen (DIN) and phytoplankton in the SIS, respectively. This proportion has apparent spatial variations, being highest near the boundary with the open ocean, decreasing from there towards the interior area of the SIS, and being lowest in the nearshore areas. The open ocean imports 799 mol s−1 of DIN to the SIS, 25 % of which is consumed by biogeochemical processes and 75 % of which is delivered again to the open ocean. Such a large amount of oceanic nutrient input and its large contribution to the inventory of DIN and phytoplankton suggest the necessity of considering the impact of open-ocean variabilities in the management of the land loading of nutrients for the semi-enclosed seas.
{"title":"Contribution of the open ocean to the nutrient and phytoplankton inventory in a semi-enclosed coastal sea","authors":"Qian Leng, Xinyu Guo, Junying Zhu, Akihiko Morimoto","doi":"10.5194/bg-20-4323-2023","DOIUrl":"https://doi.org/10.5194/bg-20-4323-2023","url":null,"abstract":"Abstract. The semi-enclosed coastal seas serve as a transition zone between land and the open ocean, and their environments are therefore affected by both. The influences of land were noticed but that of the open ocean were usually neglected. The Seto Inland Sea (SIS), which is connected to the Pacific Ocean, is a typical representative of semi-enclosed seas. To quantitatively assess the inventory of nutrients originating from land and the open ocean, as well as their supported phytoplankton in the SIS, we developed a three-dimensional coupled hydrodynamic–biogeochemical model and embedded a tracking technique in it. Model results showed that the open ocean contributes 61 % and 46 % to the annual inventory of dissolved inorganic nitrogen (DIN) and phytoplankton in the SIS, respectively. This proportion has apparent spatial variations, being highest near the boundary with the open ocean, decreasing from there towards the interior area of the SIS, and being lowest in the nearshore areas. The open ocean imports 799 mol s−1 of DIN to the SIS, 25 % of which is consumed by biogeochemical processes and 75 % of which is delivered again to the open ocean. Such a large amount of oceanic nutrient input and its large contribution to the inventory of DIN and phytoplankton suggest the necessity of considering the impact of open-ocean variabilities in the management of the land loading of nutrients for the semi-enclosed seas.","PeriodicalId":8899,"journal":{"name":"Biogeosciences","volume":"12 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135322564","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}
Mona Norbisrath, Andreas Neumann, Kirstin Dähnke, Tina Sanders, Andreas Schöl, Justus E. E. van Beusekom, Helmuth Thomas
Abstract. Total alkalinity (TA) regulates the oceanic storage capacity of atmospheric CO2. In heterotrophic temperate estuaries, anaerobic respiration of organic matter, e.g., by denitrification, can be an important source of TA. Denitrification is the anaerobic reduction of nitrate (NO3-) to elemental nitrogen (N2). By contrast, anammox yields N2 as its terminal product via comproportionation of ammonium (NH4+) and nitrite (NO2-); however, this occurs without release of TA as a byproduct. In order to investigate these two nitrate and nitrite respiration pathways and their resulting impact on TA generation, we sampled the highly turbid estuary of the Ems River, discharging into the North Sea in June 2020. During ebb tide, a transect was sampled from the Wadden Sea to the upper tidal estuary, where we additionally sampled fluid mud for incubation experiments and five vertical profiles in the hyper-turbid tidal river. The data reveal a strong increase of TA and dissolved inorganic carbon (DIC) in the tidal river, where stable nitrate isotopes indicate water column denitrification as the dominant pathway. However, in the fluid mud of the tidal river, the measured TA and the N2 incubation experiments imply only low denitrification rates, with the majority of the N2 being produced by anammox (>90 %). The relative abundances of anammox and denitrification, respectively, thus exert a major control on the CO2 storage capacity of adjacent coastal waters.
{"title":"Alkalinity and nitrate dynamics reveal dominance of anammox in a hyper-turbid estuary","authors":"Mona Norbisrath, Andreas Neumann, Kirstin Dähnke, Tina Sanders, Andreas Schöl, Justus E. E. van Beusekom, Helmuth Thomas","doi":"10.5194/bg-20-4307-2023","DOIUrl":"https://doi.org/10.5194/bg-20-4307-2023","url":null,"abstract":"Abstract. Total alkalinity (TA) regulates the oceanic storage capacity of atmospheric CO2. In heterotrophic temperate estuaries, anaerobic respiration of organic matter, e.g., by denitrification, can be an important source of TA. Denitrification is the anaerobic reduction of nitrate (NO3-) to elemental nitrogen (N2). By contrast, anammox yields N2 as its terminal product via comproportionation of ammonium (NH4+) and nitrite (NO2-); however, this occurs without release of TA as a byproduct. In order to investigate these two nitrate and nitrite respiration pathways and their resulting impact on TA generation, we sampled the highly turbid estuary of the Ems River, discharging into the North Sea in June 2020. During ebb tide, a transect was sampled from the Wadden Sea to the upper tidal estuary, where we additionally sampled fluid mud for incubation experiments and five vertical profiles in the hyper-turbid tidal river. The data reveal a strong increase of TA and dissolved inorganic carbon (DIC) in the tidal river, where stable nitrate isotopes indicate water column denitrification as the dominant pathway. However, in the fluid mud of the tidal river, the measured TA and the N2 incubation experiments imply only low denitrification rates, with the majority of the N2 being produced by anammox (>90 %). The relative abundances of anammox and denitrification, respectively, thus exert a major control on the CO2 storage capacity of adjacent coastal waters.","PeriodicalId":8899,"journal":{"name":"Biogeosciences","volume":"1998 11","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135413577","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}
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