Abstract. Observations and theory have suggested that ocean fronts are ecological hotspots, associated with higher diversity and biomass across many trophic levels. The hypothesis that these hotspots are driven by frontal nutrient injections is seemingly supported by the frequent observation of opportunistic diatoms at fronts, but the behavior of the rest of the plankton community is largely unknown. Here we investigate the organization of planktonic communities across fronts by analyzing eight high-resolution transects in the California Current Ecosystem containing extensive data for 24 groups of bacteria, phytoplankton, and zooplankton. We find that a distinct frontal plankton community characterized by enhanced biomass of not only diatoms and copepods but many other groups of plankton such as chaetognaths, rhizarians, and appendicularians emerges over most fronts. Importantly, we find spatial variability at a finer scale (typically 1–5 km) than the width of the front itself (typically 10–30 km) with peaks of different plankton taxa at different locations across the width of a front. Our results suggest that multiple processes, including horizontal stirring and biotic interactions, are responsible for creating this fine-scale patchiness.
{"title":"Sub-frontal niches of plankton communities driven by transport and trophic interactions at ocean fronts","authors":"I. Mangolte, M. Lévy, C. Haëck, M. Ohman","doi":"10.5194/bg-20-3273-2023","DOIUrl":"https://doi.org/10.5194/bg-20-3273-2023","url":null,"abstract":"Abstract. Observations and theory have suggested that ocean fronts are ecological hotspots, associated with higher diversity and biomass across many trophic levels. The hypothesis that these hotspots are driven by frontal nutrient injections is seemingly supported by the frequent observation of opportunistic diatoms at fronts, but the behavior of the rest of the plankton community is largely unknown.\u0000Here we investigate the organization of planktonic communities across fronts by analyzing eight high-resolution transects in the California Current Ecosystem containing extensive data for 24 groups of bacteria, phytoplankton, and zooplankton.\u0000We find that a distinct frontal plankton community characterized by enhanced biomass of not only diatoms and copepods but many other groups of plankton such as chaetognaths, rhizarians, and appendicularians emerges over most fronts. Importantly, we find spatial variability at a finer scale (typically 1–5 km) than the width of the front itself (typically 10–30 km) with peaks of different plankton taxa at different locations across the width of a front. Our results suggest that multiple processes, including horizontal stirring and biotic interactions, are responsible for creating this fine-scale patchiness.\u0000","PeriodicalId":8899,"journal":{"name":"Biogeosciences","volume":" ","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-08-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42599049","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}
J. Dorley, J. Singley, T. Covino, K. Singha, M. Gooseff, David Van Horn, R. González‐Pinzón
Abstract. Many studies in ecohydrology focusing on hydrologic transport argue that longer residence times across a stream ecosystem should consistently result in higher biological uptake of carbon, nutrients, and oxygen. This consideration does not incorporate the potential for biologically mediated reactions to be limited by stoichiometric imbalances. Based on the relevance and co-dependences between hydrologic exchange, stoichiometry, and biological uptake and acknowledging the limited amount of field studies available to determine their net effects on the retention and export of resources, we quantified how microbial respiration is controlled by the interactions between and the supply of essential nutrients (C, N, and P) in a headwater stream in Colorado, USA. For this, we conducted two rounds of nutrient experiments, each consisting of four sets of continuous injections of Cl− as a conservative tracer, resazurin as a proxy for aerobic respiration, and one of the following nutrient treatments: (a) N, (b) N+C, (c) N+P, or (d) C+N+P. Nutrient treatments were considered to be known system modifications that alter metabolism, and statistical tests helped identify the relationships between reach-scale hydrologic transport and respiration metrics. We found that as discharge changed significantly between rounds and across stoichiometric treatments, (a) transient storage mainly occurred in pools lateral to the main channel and was proportional to discharge, and (b) microbial respiration remained similar between rounds and across stoichiometric treatments. Our results contradict the notion that hydrologic transport alone is a dominant control on biogeochemical processing and suggest that complex interactions between hydrology, resource supply, and biological community function are responsible for driving in-stream respiration.
{"title":"Physical and stoichiometric controls on stream respiration in a headwater stream","authors":"J. Dorley, J. Singley, T. Covino, K. Singha, M. Gooseff, David Van Horn, R. González‐Pinzón","doi":"10.5194/bg-20-3353-2023","DOIUrl":"https://doi.org/10.5194/bg-20-3353-2023","url":null,"abstract":"Abstract. Many studies in ecohydrology focusing on hydrologic\u0000transport argue that longer residence times across a stream ecosystem should\u0000consistently result in higher biological uptake of carbon, nutrients, and\u0000oxygen. This consideration does not incorporate the potential for\u0000biologically mediated reactions to be limited by stoichiometric imbalances.\u0000Based on the relevance and co-dependences between hydrologic exchange,\u0000stoichiometry, and biological uptake and acknowledging the limited amount\u0000of field studies available to determine their net effects on the retention\u0000and export of resources, we quantified how microbial respiration is\u0000controlled by the interactions between and the supply of essential nutrients (C, N, and P)\u0000in a headwater stream in Colorado, USA. For this, we conducted two rounds of\u0000nutrient experiments, each consisting of four sets of continuous injections\u0000of Cl− as a conservative tracer, resazurin as a proxy for aerobic\u0000respiration, and one of the following nutrient treatments: (a) N, (b) N+C,\u0000(c) N+P, or (d) C+N+P. Nutrient treatments were considered to be known\u0000system modifications that alter metabolism, and statistical tests helped\u0000identify the relationships between reach-scale hydrologic transport and\u0000respiration metrics. We found that as discharge changed significantly\u0000between rounds and across stoichiometric treatments, (a) transient storage\u0000mainly occurred in pools lateral to the main channel and was proportional to\u0000discharge, and (b) microbial respiration remained similar between rounds and\u0000across stoichiometric treatments. Our results contradict the notion that\u0000hydrologic transport alone is a dominant control on biogeochemical\u0000processing and suggest that complex interactions between hydrology, resource\u0000supply, and biological community function are responsible for driving\u0000in-stream respiration.\u0000","PeriodicalId":8899,"journal":{"name":"Biogeosciences","volume":" ","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-08-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47983010","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}
Corentin Guilhermic, M. Nardelli, A. Mouret, Damien Le Moigne, H. Howa
Abstract. A microcosm experiment was designed to describe how benthic foraminifera react to fine-sediment deposits varying in frequency and intensity as they may occur regularly or occasionally in coastal benthic environments, caused by discharges from (e.g.) river flooding, tidewater glacier melting in polar regions, or diverse anthropic activities linked to harbour or watershed management. The influence of seabed burial resulting from these events on the ecology of benthic ecosystems is often overlooked, and the resilience of benthic communities is poorly known. During a 51 d long experiment, a typical northeastern Atlantic intertidal foraminiferal community, mainly represented by Ammonia confertitesta and Haynesina germanica species, was subjected to two kinds of sedimentary disturbance: (1) a one-time high-volume (OHV) deposit, i.e. sediment about 3 cm thick was added at one time at the beginning of the experiment; and (2) frequent low-volume (FLV) deposits, i.e. sediment about 0.5 cm thick was added each week for 4 weeks. The geochemical environment (e.g. dissolved oxygen penetration in the sediment, salinity, temperature, and nutrient content in the supernatant water) was monitored to follow the microcosm steady state before and during the experiment. In both disturbed microcosms, H. germanica showed a significant linear decrease in abundance during the experiment, while the total abundance of foraminifera was significantly affected only by the OHV treatment, suggesting a stronger effect of a single thick deposit on standing stocks and biodiversity compared to frequent low-volume sediment supplies. Concerning the vertical migration of foraminifera after sedimentary disturbances, the two dominant species moved upwards to the water–sediment interface with migration speeds estimated to be 0.41 and 0.47 mm h−1 respectively for A. confertitesta and H. germanica. In the FLV treatment, the resilient state was already reached within 1 d following a low-thickness burial, while in the OHV, it was achieved between 1 and 7 d after the 3 cm thick deposit. These results suggest that foraminifera can migrate rapidly after a sedimentary burial to recover their preferential life position under the new sediment–water interface, but in the case of an abrupt thick burial, several days are needed to reach a resilient state.
{"title":"Short-term response of benthic foraminifera to fine-sediment depositional events simulated in microcosm","authors":"Corentin Guilhermic, M. Nardelli, A. Mouret, Damien Le Moigne, H. Howa","doi":"10.5194/bg-20-3329-2023","DOIUrl":"https://doi.org/10.5194/bg-20-3329-2023","url":null,"abstract":"Abstract. A microcosm experiment was designed to describe how benthic foraminifera\u0000react to fine-sediment deposits varying in frequency and intensity as they\u0000may occur regularly or occasionally in coastal benthic environments, caused\u0000by discharges from (e.g.) river flooding, tidewater glacier melting in polar\u0000regions, or diverse anthropic activities linked to harbour or watershed\u0000management. The influence of seabed burial resulting from these events on\u0000the ecology of benthic ecosystems is often overlooked, and the resilience of\u0000benthic communities is poorly known. During a 51 d long experiment, a\u0000typical northeastern Atlantic intertidal foraminiferal community, mainly\u0000represented by Ammonia confertitesta and Haynesina germanica species, was subjected to two kinds of sedimentary\u0000disturbance: (1) a one-time high-volume (OHV) deposit, i.e. sediment about 3 cm thick was added at one time at the beginning of the experiment; and (2) frequent low-volume (FLV) deposits, i.e. sediment about 0.5 cm thick was added each week for 4 weeks. The geochemical environment (e.g. dissolved oxygen penetration in the\u0000sediment, salinity, temperature, and nutrient content in the supernatant\u0000water) was monitored to follow the microcosm steady state before and during\u0000the experiment. In both disturbed microcosms, H. germanica showed a significant linear\u0000decrease in abundance during the experiment, while the total abundance of\u0000foraminifera was significantly affected only by the OHV treatment,\u0000suggesting a stronger effect of a single thick deposit on standing stocks\u0000and biodiversity compared to frequent low-volume sediment supplies. Concerning the\u0000vertical migration of foraminifera after sedimentary disturbances, the two\u0000dominant species moved upwards to the water–sediment interface with\u0000migration speeds estimated to be 0.41 and 0.47 mm h−1 respectively for A. confertitesta and H. germanica. In\u0000the FLV treatment, the resilient state was already reached within 1 d\u0000following a low-thickness burial, while in the OHV, it was achieved between 1\u0000and 7 d after the 3 cm thick deposit. These results suggest that\u0000foraminifera can migrate rapidly after a sedimentary burial to recover their\u0000preferential life position under the new sediment–water interface, but in the\u0000case of an abrupt thick burial, several days are needed to reach a resilient\u0000state.\u0000","PeriodicalId":8899,"journal":{"name":"Biogeosciences","volume":" ","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-08-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41503352","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. Many terrestrial landscapes are heterogeneous. Mixed land cover and land use generate a complex mosaic of fragmented ecosystems at fine spatial resolutions with contrasting ecosystem stocks, traits, and processes, each differently sensitive to environmental and human factors. Representing spatial complexity within terrestrial ecosystem models is a key challenge for understanding regional carbon dynamics, their sensitivity to environmental gradients, and their resilience in the face of climate change. Heterogeneity underpins this challenge due to the trade-off between the fidelity of ecosystem representation within modelling frameworks and the computational capacity required for fine-scale model calibration and simulation. We directly address this challenge by quantifying the sensitivity of simulated carbon fluxes in a mixed-use landscape in the UK to the spatial resolution of the model analysis. We test two different approaches for combining Earth observation (EO) data into the CARDAMOM model–data fusion (MDF) framework, assimilating time series of satellite-based EO-derived estimates of ecosystem leaf area and biomass stocks to constrain estimates of model parameters and their uncertainty for an intermediate complexity model of the terrestrial C cycle. In the first approach, ecosystems are calibrated and simulated at pixel level, representing a “community average” of the encompassed land cover and management. This represents our baseline approach. In the second, we stratify each pixel based on land cover (e.g. coniferous forest, arable/pasture) and calibrate the model independently using EO data specific to each stratum. We test the scale dependence of these approaches for grid resolutions spanning 1 to 0.05∘ over a mixed-land-use region of the UK. Our analyses indicate that spatial resolution matters for MDF. Under the community average baseline approach biological C fluxes (gross primary productivity, Reco) simulated by CARDAMOM are relatively insensitive to resolution. However, disturbance fluxes exhibit scale variance that increases with greater landscape fragmentation and for coarser model domains. In contrast, stratification of assimilated data based on fine-resolution land use distributions resolved the resolution dependence, leading to disturbance fluxes that were 40 %–100 % higher than the baseline experiments. The differences in the simulated disturbance fluxes result in estimates of the terrestrial carbon balance in the stratified experiment that suggest a weaker C sink compared to the baseline experiment. We also find that stratifying the model domain based on land use leads to differences in the retrieved parameters that reflect variations in ecosystem function between neighbouring areas of contrasting land use. The emergent differences in model parameters between land use strata give rise to divergent responses to future climate change. Accounting for fine-scale structure in heterogeneous landscapes (e.g. stratification)
{"title":"Scale variance in the carbon dynamics of fragmented, mixed-use landscapes estimated using model–data fusion","authors":"D. Milodowski, T. Smallman, M. Williams","doi":"10.5194/bg-20-3301-2023","DOIUrl":"https://doi.org/10.5194/bg-20-3301-2023","url":null,"abstract":"Abstract. Many terrestrial landscapes are heterogeneous. Mixed land cover and land use generate a complex mosaic of fragmented ecosystems at fine spatial resolutions with contrasting ecosystem stocks, traits, and processes, each differently sensitive to environmental and human factors. Representing spatial complexity within terrestrial ecosystem models is a key challenge for understanding regional carbon dynamics, their sensitivity to environmental gradients, and their resilience in the face of climate change. Heterogeneity underpins this challenge due to the trade-off between the fidelity of ecosystem representation within modelling frameworks and the computational capacity required for fine-scale model calibration and simulation. We directly address this challenge by quantifying the sensitivity of simulated carbon fluxes in a mixed-use landscape in the UK to the spatial resolution of the model analysis. We test two different approaches for combining Earth observation (EO) data into the CARDAMOM model–data fusion (MDF) framework, assimilating time series of satellite-based EO-derived estimates of ecosystem leaf area and biomass stocks to constrain estimates of model parameters and their uncertainty for an intermediate complexity model of the terrestrial C cycle. In the first approach, ecosystems are calibrated and simulated at pixel level, representing a “community average” of the encompassed land cover and management. This represents our baseline approach. In the second, we stratify each pixel based on land cover (e.g. coniferous forest, arable/pasture) and calibrate the model independently using EO data specific to each stratum. We test the scale dependence of these approaches for grid resolutions spanning 1 to 0.05∘ over a mixed-land-use region of the UK. Our analyses indicate that spatial resolution matters for MDF. Under the community average baseline approach biological C fluxes (gross primary productivity, Reco) simulated by CARDAMOM are relatively insensitive to resolution. However, disturbance fluxes exhibit scale variance that increases with greater landscape fragmentation and for coarser model domains. In contrast, stratification of assimilated data based on fine-resolution land use distributions resolved the resolution dependence, leading to disturbance fluxes that were 40 %–100 % higher than the baseline experiments. The differences in the simulated disturbance fluxes result in estimates of the terrestrial carbon balance in the stratified experiment that suggest a weaker C sink compared to the baseline experiment. We also find that stratifying the model domain based on land use leads to differences in the retrieved parameters that reflect variations in ecosystem function between neighbouring areas of contrasting land use. The emergent differences in model parameters between land use strata give rise to divergent responses to future climate change. Accounting for fine-scale structure in heterogeneous landscapes (e.g. stratification) ","PeriodicalId":8899,"journal":{"name":"Biogeosciences","volume":" ","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-08-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46197478","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. Headwater streams are important sources of greenhouse gases to the atmosphere. The magnitude of gas emissions originating from such streams, however, is modulated by the characteristic microtopography of the riverbed, which might promote the spatial heterogeneity of turbulence and air entrainment. In particular, recent studies have revealed that step-and-pool configurations, usually found in close sequences along mountain streams, are important hotspots of gas evasion. Yet, the mechanisms that drive gas transfer at the water–air interface in a step-and-pool configuration are not fully understood. Here, we numerically simulated the hydrodynamics of an artificial step-and-pool configuration to evaluate the contribution of turbulence and air entrainment to the total gas evasion induced by the falling jet. The simulation was validated using observed hydraulic features (stage, velocity) and was then utilized to determine the patterns of energy dissipation, turbulence-induced gas exchange and bubble-mediated transport. The results show that gas evasion is led by bubble entrainment and is mostly concentrated in a small and irregular region of a few square decimeters near the cascade, where the local gas transfer velocity (k) peaks at 500 m d−1. The enhanced spatial heterogeneity of k in the pool does not allow one to define a priori the region of the domain where the outgassing takes place and makes the value of the spatial mean of k inevitably scale-dependent. Accordingly, we propose that the average mass transfer velocity should be used with caution to describe the outgassing in spatially heterogeneous flow fields, such as those encountered in step-and-pool rivers.
摘要水源流是大气中温室气体的重要来源。然而，源自这些溪流的气体排放量受到河床特征微观地形的调节，这可能会促进湍流和空气夹带的空间异质性。特别是，最近的研究表明，通常在山间溪流的紧密序列中发现的台阶和水池结构是天然气泄漏的重要热点。然而，在台阶和水池配置中，驱动水-空气界面气体传输的机制尚不完全清楚。在这里，我们对人工台阶和水池配置的流体动力学进行了数值模拟，以评估湍流和空气夹带对下落射流引起的总气体逃逸的贡献。利用观测到的水力特征（阶段、速度）对模拟进行了验证，然后用于确定能量耗散、湍流诱导的气体交换和气泡介导的传输模式。结果表明，气体逃逸是由气泡夹带引起的，主要集中在叶栅附近几平方分米的小而不规则的区域，其中局部气体传输速度（k）峰值为500 m d−1.池中k的空间异质性增强，不允许先验地定义发生脱气的域的区域，并使k的空间平均值不可避免地与尺度相关。因此，我们建议，应谨慎使用平均传质速度来描述空间非均匀流场中的脱气，例如在梯级和水池中遇到的流场。
{"title":"Local processes with a global impact: unraveling the dynamics of gas evasion in a step-and-pool configuration","authors":"P. Peruzzo, M. Cappozzo, N. Durighetto, G. Botter","doi":"10.5194/bg-20-3261-2023","DOIUrl":"https://doi.org/10.5194/bg-20-3261-2023","url":null,"abstract":"Abstract. Headwater streams are important sources of greenhouse gases to the atmosphere. The magnitude of gas emissions originating from such streams, however, is modulated by the characteristic microtopography of the riverbed, which might promote the spatial heterogeneity of turbulence and air entrainment. In particular, recent studies have revealed that step-and-pool configurations, usually found in close sequences along mountain streams, are important hotspots of gas evasion. Yet, the mechanisms that drive gas transfer at the water–air interface in a step-and-pool configuration are not fully understood. Here, we numerically simulated the hydrodynamics of an artificial step-and-pool configuration to evaluate the contribution of turbulence and air entrainment to the total gas evasion induced by the falling jet. The simulation was validated using observed hydraulic features (stage, velocity) and was then utilized to determine the patterns of energy dissipation, turbulence-induced gas exchange and bubble-mediated transport. The results show that gas evasion is led by bubble entrainment and is mostly concentrated in a small and irregular region of a few square decimeters near the cascade, where the local gas transfer velocity (k) peaks at 500 m d−1. The enhanced spatial heterogeneity of k in the pool does not allow one to define a priori the region of the domain where the outgassing takes place and makes the value of the spatial mean of k inevitably scale-dependent. Accordingly, we propose that the average mass transfer velocity should be used with caution to describe the outgassing in spatially heterogeneous flow fields, such as those encountered in step-and-pool rivers.\u0000","PeriodicalId":8899,"journal":{"name":"Biogeosciences","volume":" ","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-08-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49560547","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}
Julia Homann, Niklas Karbach, S. Carolin, Daniel H. James, D. Hodell, S. Breitenbach, O. Kwiecien, M. Brenner, Carlos Peraza Lope, T. Hoffmann
Abstract. Speleothems (cave stalagmites) contain inorganic and organic substances that can be used to infer past changes in local and regional paleoenvironmental conditions. Specific biomarkers can be employed to elucidate the history of past fires, caused by interactions among climate, regional hydrology, vegetation, humans, and fire activity. We conducted a simple solid–liquid extraction on pulverised carbonate samples to prepare them for analysis of 16 polycyclic aromatic hydrocarbons (PAHs) and three monosaccharide anhydrides (MAs). The preparation method requires only small samples (0.5–1.0 g); PAHs and MAs were measured by GC–MS and LC–HILIC–MS, respectively. Detection limits range from 0.05–2.1 ng for PAHs and 0.01–0.1 ng for MAs. We applied the method to 10 samples from a ∼ 400-year-old stalagmite from Cenote Ch'en Mul, at Mayapan (Mexico), the largest Postclassic Maya capital of the Yucatán Peninsula. We found a strong correlation (r = 0.75, p < 0.05) between the major MA (levoglucosan) and non-alkylated PAHs (Σ15). We investigated multiple diagnostic PAH and MA ratios and found that although not all were applicable as paleo-fire proxies, ratios that combine PAHs with MAs are promising tools for identifying different fire regimes and inferring the type of fuel burned. In the 1950s and 1960s, levoglucosan and Σ15 concentrations roughly doubled compared to other times in the last 400 years, suggesting greater fire activity at Mayapan during these two decades. The higher concentrations of fire markers may have been a consequence of land clearance at the site and exploration of the cave by Carnegie Institution archaeologists.
{"title":"Past fire dynamics inferred from polycyclic aromatic hydrocarbons and monosaccharide anhydrides in a stalagmite from the archaeological site of Mayapan, Mexico","authors":"Julia Homann, Niklas Karbach, S. Carolin, Daniel H. James, D. Hodell, S. Breitenbach, O. Kwiecien, M. Brenner, Carlos Peraza Lope, T. Hoffmann","doi":"10.5194/bg-20-3249-2023","DOIUrl":"https://doi.org/10.5194/bg-20-3249-2023","url":null,"abstract":"Abstract. Speleothems (cave stalagmites) contain inorganic and organic substances that can be used to infer past changes in local and regional paleoenvironmental\u0000conditions. Specific biomarkers can be employed to elucidate the history of\u0000past fires, caused by interactions among climate, regional hydrology,\u0000vegetation, humans, and fire activity. We conducted a simple solid–liquid\u0000extraction on pulverised carbonate samples to prepare them for analysis of\u000016 polycyclic aromatic hydrocarbons (PAHs) and three monosaccharide\u0000anhydrides (MAs). The preparation method requires only small samples\u0000(0.5–1.0 g); PAHs and MAs were measured by GC–MS and LC–HILIC–MS,\u0000respectively. Detection limits range from 0.05–2.1 ng for PAHs and\u00000.01–0.1 ng for MAs. We applied the method to 10 samples from a\u0000∼ 400-year-old stalagmite from Cenote Ch'en Mul, at Mayapan\u0000(Mexico), the largest Postclassic Maya capital of the Yucatán Peninsula. We found a strong correlation (r = 0.75, p < 0.05) between the major\u0000MA (levoglucosan) and non-alkylated PAHs (Σ15). We investigated\u0000multiple diagnostic PAH and MA ratios and found that although not all were\u0000applicable as paleo-fire proxies, ratios that combine PAHs with MAs are\u0000promising tools for identifying different fire regimes and inferring the\u0000type of fuel burned. In the 1950s and 1960s, levoglucosan and Σ15\u0000concentrations roughly doubled compared to other times in the last 400 years, suggesting greater fire activity at Mayapan during these two decades.\u0000The higher concentrations of fire markers may have been a consequence of\u0000land clearance at the site and exploration of the cave by Carnegie\u0000Institution archaeologists.\u0000","PeriodicalId":8899,"journal":{"name":"Biogeosciences","volume":" ","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-08-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41505902","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}
Gesa Schulz, Tina Sanders, Y. Voynova, H. Bange, K. Dähnke
Abstract. Nitrous oxide (N2O) is a greenhouse gas, with a global warming potential 298 times that of carbon dioxide. Estuaries can be sources of N2O, but their emission estimates have significant uncertainties due to limited data availability and high spatiotemporal variability. We investigated the spatial and seasonal variability of dissolved N2O and its emissions along the Elbe Estuary (Germany), a well-mixed temperate estuary with high nutrient loading from agriculture. During nine research cruises performed between 2017 and 2022, we measured dissolved N2O concentrations, as well as dissolved nutrient and oxygen concentrations along the estuary, and calculated N2O saturations, flux densities, and emissions. We found that the estuary was a year-round source of N2O, with the highest emissions in winter when dissolved inorganic nitrogen (DIN) loads and wind speeds are high. However, in spring and summer, N2O saturations and emissions did not decrease alongside lower riverine nitrogen loads, suggesting that estuarine in situ N2O production is an important source of N2O. We identified two hotspot areas of N2O production: the Port of Hamburg, a major port region, and the mesohaline estuary near the maximum turbidity zone (MTZ). N2O production was fueled by the decomposition of riverine organic matter in the Hamburg Port and by marine organic matter in the MTZ. A comparison with previous measurements in the Elbe Estuary revealed that N2O saturation did not decrease alongside the decrease in DIN concentrations after a significant improvement of water quality in the 1990s that allowed for phytoplankton growth to re-establish in the river and estuary. The overarching control of phytoplankton growth on organic matter and, subsequently, on N2O production highlights the fact that eutrophication and elevated agricultural nutrient input can increase N2O emissions in estuaries.
{"title":"Seasonal variability of nitrous oxide concentrations and emissions in a temperate estuary","authors":"Gesa Schulz, Tina Sanders, Y. Voynova, H. Bange, K. Dähnke","doi":"10.5194/bg-20-3229-2023","DOIUrl":"https://doi.org/10.5194/bg-20-3229-2023","url":null,"abstract":"Abstract. Nitrous oxide (N2O) is a greenhouse gas, with a global warming potential 298 times that of carbon dioxide. Estuaries can be sources of\u0000N2O, but their emission estimates have significant uncertainties due to limited data availability and high spatiotemporal variability. We\u0000investigated the spatial and seasonal variability of dissolved N2O and its emissions along the Elbe Estuary (Germany), a well-mixed\u0000temperate estuary with high nutrient loading from agriculture. During nine research cruises performed between 2017 and 2022, we measured dissolved\u0000N2O concentrations, as well as dissolved nutrient and oxygen concentrations along the estuary, and calculated N2O saturations,\u0000flux densities, and emissions. We found that the estuary was a year-round source of N2O, with the highest emissions in winter when dissolved\u0000inorganic nitrogen (DIN) loads and wind speeds are high. However, in spring and summer, N2O saturations and emissions did not decrease\u0000alongside lower riverine nitrogen loads, suggesting that estuarine in situ N2O production is an important source of N2O. We\u0000identified two hotspot areas of N2O production: the Port of Hamburg, a major port region, and the mesohaline estuary near the maximum\u0000turbidity zone (MTZ). N2O production was fueled by the decomposition of riverine organic matter in the Hamburg Port and by marine organic\u0000matter in the MTZ. A comparison with previous measurements in the Elbe Estuary revealed that N2O saturation did not decrease alongside the\u0000decrease in DIN concentrations after a significant improvement of water quality in the 1990s that allowed for phytoplankton growth to re-establish in\u0000the river and estuary. The overarching control of phytoplankton growth on organic matter and, subsequently, on N2O production highlights\u0000the fact that eutrophication and elevated agricultural nutrient input can increase N2O emissions in estuaries.\u0000","PeriodicalId":8899,"journal":{"name":"Biogeosciences","volume":" ","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-08-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44480730","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}
A. Nogovitcyn, Ruslan Shakhmatov, Tomoki Morozumi, S. Tei, Yumiko Miyamoto, Nagai Shin, T. Maximov, A. Sugimoto
Abstract. The taiga ecosystem in northeastern Siberia, a nitrogen-limited ecosystem on permafrost with a dry climate, changed during the extreme wet event in 2007. We investigated the normalized difference vegetation index (NDVI) as a satellite-derived proxy for needle production and compared it with ecosystem parameters such as soil moisture water equivalent (SWE), larch foliar C/N ratio, δ13C and δ15N, and ring width index (RWI) at the Spasskaya Pad Experimental Forest Station in Russia for the period from 1999 to 2019. Historical variations in NDVI showed a large difference between typical larch forest (unaffected) and the sites affected by the extreme wet event in 2007 because of high tree mortality at affected sites under extremely high SWE and waterlogging, resulting in a decrease in NDVI, although there was no difference in the NDVI between typical larch forest and affected sites before the wet event. Before 2007, the NDVI in a typical larch forest showed a positive correlation with SWE and a negative correlation with foliar C/N. These results indicate that not only the water availability (high SWE) in the previous summer and current June but also the soil N availability likely increased needle production. NDVI was also positively correlated with RWI, resulting from similar factors controlling them. However, after the wet event, NDVI was negatively correlated with SWE, while NDVI showed a negative correlation with foliar C/N. These results indicate that after the wet event, high soil moisture availability decreased needle production, which may have resulted from lower N availability. Foliar δ15N was positively correlated with NDVI before 2007, but foliar δ15N decreased after the wet event. This result suggests damage to roots and/or changes in soil N dynamics due to extremely high soil moisture. As a dry forest ecosystem, taiga in northeastern Siberia is affected not only by temperature-induced drought but also by high soil moisture (led by extreme wet events) and nitrogen dynamics.
{"title":"Historical variation in the normalized difference vegetation index compared with soil moisture in a taiga forest ecosystem in northeastern Siberia","authors":"A. Nogovitcyn, Ruslan Shakhmatov, Tomoki Morozumi, S. Tei, Yumiko Miyamoto, Nagai Shin, T. Maximov, A. Sugimoto","doi":"10.5194/bg-20-3185-2023","DOIUrl":"https://doi.org/10.5194/bg-20-3185-2023","url":null,"abstract":"Abstract. The taiga ecosystem in northeastern Siberia, a nitrogen-limited\u0000ecosystem on permafrost with a dry climate, changed during the extreme wet\u0000event in 2007. We investigated the normalized difference vegetation index\u0000(NDVI) as a satellite-derived proxy for needle production and compared it\u0000with ecosystem parameters such as soil moisture water equivalent (SWE),\u0000larch foliar C/N ratio, δ13C and δ15N, and ring\u0000width index (RWI) at the Spasskaya Pad Experimental Forest Station in Russia\u0000for the period from 1999 to 2019. Historical variations in NDVI showed a\u0000large difference between typical larch forest (unaffected) and the sites\u0000affected by the extreme wet event in 2007 because of high tree mortality at\u0000affected sites under extremely high SWE and waterlogging, resulting in a\u0000decrease in NDVI, although there was no difference in the NDVI between\u0000typical larch forest and affected sites before the wet event. Before 2007,\u0000the NDVI in a typical larch forest showed a positive correlation with SWE\u0000and a negative correlation with foliar C/N. These results indicate that not only the water availability (high SWE) in the previous summer and current\u0000June but also the soil N availability likely increased needle production.\u0000NDVI was also positively correlated with RWI, resulting from similar factors\u0000controlling them. However, after the wet event, NDVI was negatively\u0000correlated with SWE, while NDVI showed a negative correlation with foliar\u0000C/N. These results indicate that after the wet event, high soil moisture\u0000availability decreased needle production, which may have resulted from lower\u0000N availability. Foliar δ15N was positively correlated with NDVI\u0000before 2007, but foliar δ15N decreased after the wet event.\u0000This result suggests damage to roots and/or changes in soil N dynamics due\u0000to extremely high soil moisture. As a dry forest ecosystem, taiga in\u0000northeastern Siberia is affected not only by temperature-induced drought but\u0000also by high soil moisture (led by extreme wet events) and nitrogen\u0000dynamics.\u0000","PeriodicalId":8899,"journal":{"name":"Biogeosciences","volume":" ","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-08-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41569529","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 Rhodes Gyre is a cyclonic persistent feature of the general circulation of the Levantine Basin in the eastern Mediterranean Sea. Although it is located in the most oligotrophic basin of the Mediterranean Sea, it is a relatively high primary production area due to strong winter nutrient supply associated with the formation of Levantine Intermediate Water. In this study, a 3D coupled hydrodynamic–biogeochemical model (SYMPHONIE/Eco3M-S) was used to characterize the seasonal and interannual variability of the Rhodes Gyre's ecosystem and to estimate an annual organic carbon budget over the 2013–2020 period. Comparisons of model outputs with satellite data and compiled in situ data from cruises and Biogeochemical-Argo floats revealed the ability of the model to reconstruct the main seasonal and spatial biogeochemical dynamics of the Levantine Basin. The model results indicated that during the winter mixing period, phytoplankton first progressively grow sustained by nutrient supply. Then, short episodes of convection driven by heat loss and wind events, favoring nutrient injections, organic carbon export, and inducing light limitation on primary production, alternate with short episodes of phytoplankton growth. The estimate of the annual organic carbon budget indicated that the Rhodes Gyre is an autotrophic area, with a positive net community production in the upper layer (0–150 m) amounting to 31.2 ± 6.9 gCm-2yr-1. Net community production in the upper layer is almost balanced over the 7-year period by physical transfers, (1) via downward export (16.8 ± 6.2 gCm-2yr-1) and (2) through lateral transport towards the surrounding regions (14.1 ± 2.1 gCm-2yr-1). The intermediate layer (150–400 m) also appears to be a source of organic carbon for the surrounding Levantine Sea (7.5 ± 2.8 gCm-2yr-1) mostly through the subduction of Levantine Intermediate Water following winter mixing. The Rhodes Gyre shows high interannual variability with enhanced primary production, net community production, and exports during years marked by intense heat losses and deep mixed layers. However, annual primary production appears to be only partially driven by winter vertical mixing. Based on our results, we can speculate that future increase of temperature and stratification could strongly impact the carbon fluxes in this region.
{"title":"Seasonal and interannual variability of the pelagic ecosystem and of the organic carbon budget in the Rhodes Gyre (eastern Mediterranean): influence of winter mixing","authors":"Joelle Habib, Caroline Ulses, Claude Estournel, Milad Fakhri, Patrick Marsaleix, Mireille Pujo-Pay, Marine Fourrier, Laurent Coppola, Alexandre Mignot, Laurent Mortier, Pascal Conan","doi":"10.5194/bg-20-3203-2023","DOIUrl":"https://doi.org/10.5194/bg-20-3203-2023","url":null,"abstract":"Abstract. The Rhodes Gyre is a cyclonic persistent feature of the general circulation of the Levantine Basin in the eastern Mediterranean Sea. Although it is located in the most oligotrophic basin of the Mediterranean Sea, it is a relatively high primary production area due to strong winter nutrient supply associated with the formation of Levantine Intermediate Water. In this study, a 3D coupled hydrodynamic–biogeochemical model (SYMPHONIE/Eco3M-S) was used to characterize the seasonal and interannual variability of the Rhodes Gyre's ecosystem and to estimate an annual organic carbon budget over the 2013–2020 period. Comparisons of model outputs with satellite data and compiled in situ data from cruises and Biogeochemical-Argo floats revealed the ability of the model to reconstruct the main seasonal and spatial biogeochemical dynamics of the Levantine Basin. The model results indicated that during the winter mixing period, phytoplankton first progressively grow sustained by nutrient supply. Then, short episodes of convection driven by heat loss and wind events, favoring nutrient injections, organic carbon export, and inducing light limitation on primary production, alternate with short episodes of phytoplankton growth. The estimate of the annual organic carbon budget indicated that the Rhodes Gyre is an autotrophic area, with a positive net community production in the upper layer (0–150 m) amounting to 31.2 ± 6.9 gCm-2yr-1. Net community production in the upper layer is almost balanced over the 7-year period by physical transfers, (1) via downward export (16.8 ± 6.2 gCm-2yr-1) and (2) through lateral transport towards the surrounding regions (14.1 ± 2.1 gCm-2yr-1). The intermediate layer (150–400 m) also appears to be a source of organic carbon for the surrounding Levantine Sea (7.5 ± 2.8 gCm-2yr-1) mostly through the subduction of Levantine Intermediate Water following winter mixing. The Rhodes Gyre shows high interannual variability with enhanced primary production, net community production, and exports during years marked by intense heat losses and deep mixed layers. However, annual primary production appears to be only partially driven by winter vertical mixing. Based on our results, we can speculate that future increase of temperature and stratification could strongly impact the carbon fluxes in this region.","PeriodicalId":8899,"journal":{"name":"Biogeosciences","volume":"20 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-08-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136145146","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}
Marlisa Martinho de Brito, I. Bundeleva, F. Marin, E. Vennin, A. Wilmotte, L. Plasseraud, P. Visscher
Abstract. Extracellular polymeric substances (EPSs) are an important organic carbon reservoir in many pelagic and benthic environments. The production of EPS is intimately associated with the growth of phyto- and picoplankton. EPS plays a critical role in carbonate precipitation through the binding of cations and by acting as a nucleation site for minerals. Large-scale episodes of fine-grained calcium carbonate precipitation in the water column (whiting events) have been linked to cyanobacterial blooms, including of Synechococcus spp. The mechanisms that trigger these precipitation events are still debated. We pose that the cyanobacterial EPS, produced during exponential and stationary growth phases, plays a critical role in the formation of whitings. The aim of this study was to investigate the production of EPS during a 2-month cyanobacterial growth, mimicking a bloom. The production and characteristics of EPS were examined in different growth stages of Synechococcus spp. using various techniques such as Fourier transform infrared (FT-IR) spectroscopy as well as colorimetric and sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS–PAGE) assays. We further evaluated the potential role of EPS in carbonate precipitation through in vitro-forced precipitation experiments. EPS produced during the early and late stationary phase contained a larger amount of negatively charged groups than present in EPS produced during the exponential phase. Consequently, a higher Ca2+-binding affinity of the stationary-phase EPS led to the formation of a larger amount of smaller carbonate minerals (< 50 µm) compared to crystals formed in exponential-phase EPS, which were less abundant and larger (> 50 µm). These findings were used to establish a conceptual model for picoplankton-bloom-mediated CaCO3 precipitation that can explain the role of EPS in whitings.
{"title":"Properties of exopolymeric substances (EPSs) produced during cyanobacterial growth: potential role in whiting events","authors":"Marlisa Martinho de Brito, I. Bundeleva, F. Marin, E. Vennin, A. Wilmotte, L. Plasseraud, P. Visscher","doi":"10.5194/bg-20-3165-2023","DOIUrl":"https://doi.org/10.5194/bg-20-3165-2023","url":null,"abstract":"Abstract. Extracellular polymeric substances (EPSs) are an important organic carbon reservoir in many pelagic and benthic environments. The production of EPS\u0000is intimately associated with the growth of phyto- and picoplankton. EPS plays a critical role in carbonate precipitation through the binding of\u0000cations and by acting as a nucleation site for minerals. Large-scale episodes of fine-grained calcium carbonate precipitation in the water column\u0000(whiting events) have been linked to cyanobacterial blooms, including of Synechococcus spp. The mechanisms that trigger these precipitation\u0000events are still debated. We pose that the cyanobacterial EPS, produced during exponential and stationary growth phases, plays a critical role in the\u0000formation of whitings. The aim of this study was to investigate the production of EPS during a 2-month cyanobacterial growth, mimicking a\u0000bloom. The production and characteristics of EPS were examined in different growth stages of Synechococcus spp. using various techniques\u0000such as Fourier transform infrared (FT-IR) spectroscopy as well as colorimetric and sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS–PAGE) assays. We further evaluated the potential role of EPS in carbonate precipitation through\u0000in vitro-forced precipitation experiments. EPS produced during the early and late stationary\u0000phase contained a larger amount of negatively charged groups than present in EPS produced during the exponential phase. Consequently, a higher\u0000Ca2+-binding affinity of the stationary-phase EPS led to the formation of a larger amount of smaller carbonate minerals\u0000(< 50 µm) compared to crystals formed in exponential-phase EPS, which were less abundant and larger (> 50 µm). These\u0000findings were used to establish a conceptual model for picoplankton-bloom-mediated CaCO3 precipitation that can explain the role of EPS in\u0000whitings.\u0000","PeriodicalId":8899,"journal":{"name":"Biogeosciences","volume":" ","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45949851","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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