This paper presents preliminary results of three-dimensional thermomechanical finite-element models of a parameter study to compute the current temperature and stress distribution in the subduction zone of the central...This paper presents preliminary results of three-dimensional thermomechanical finite-element models of a parameter study to compute the current temperature and stress distribution in the subduction zone of the central Andes （16°S-26°S） up to a depth of 400 km, the bottom of the asthenosphere. For this purpose a simulation running over c. 50,000 years will be realized based on the geometry of a generic subduction zone and an elasto-viscoplastic Drucker-Prager rheology. The kinematic and thermal boundary conditions as well as the rheological parameters represent the current state of the study area. In future works the model will be refined using a systematic study of physical parameters in order to estimate the influence of the main parameters （e.g. viscosity, fault friction, velocity, shear heating） on the results of the reference model presented here. The reference model is kept as simple as possible to be able to estimate the influence of the parameters in future studies in the best possible way, whilst minimizing comnutational time.展开更多
The Central Patagonian Andes is a particular segment of the Andean Cordillera that has been subjected to the subduction of two spreading ridges during Eocene and Neogene times. In order to understand the Cenozoic geol...The Central Patagonian Andes is a particular segment of the Andean Cordillera that has been subjected to the subduction of two spreading ridges during Eocene and Neogene times. In order to understand the Cenozoic geologic evolution of the Central Patagonian Andes, we carried out geochronologic(U-Pb and^(40)Ar/^(39)Ar), provenance, stratigraphic, sedimentologic, and geochemical studies on the sedimentary and volcanic Cenozoic deposits that crop out in the Meseta Guadal and Chile Chico areas(～47°S). Our data indicate the presence of a nearly complete Cenozoic record, which refutes previous interpretations of a hiatus during the middle Eocene-late Oligocene in the Central Patagonian Andes. Our study suggests that the fluvial strata of the Ligorio Marquez Formation and the flood basalts of the Basaltos Inferiores de la Meseta Chile Chico Formation were deposited in an extensional setting related to the subduction of the Aluk-Farallon spreading ridge during the late Paleocene-Eocene. Geochemical data on volcanic rocks interbedded with fluvial strata of the San Jose Formation suggest that this unit was deposited in an extensional setting during the middle Eocene to late Oligocene. Progressive crustal thinning allowed the transgression of marine waters of Atlantic origin and deposition of the upper Oligocene-lower Miocene Guadal Formation. The fluvial synorogenic strata of the Santa Cruz Formation were deposited as a consequence of an important phase of compressive deformation and Andean uplift during the early-middle Miocene. Finally, alkali flood basalts of the late middle to late Miocene Basaltos Superiores de la Meseta Chile Chico Formation were extruded in the area in response to the suduction of the Chile Ridge under an extensional regime. Our studies indicate that the tectonic evolution of the Central Patagonian Andes is similar to that of the North Patagonian Andes and appears to differ from that of the Southern Patagonian Andes, which is thought to have been the subject of continuous compressive deformation since the late Early Cretaceous.展开更多
The páramo of the Northern Andes provide critically important ecosystem services to the Northern Andean region in the form of water provisioning and carbon sequestration, both of which are a result of the pá...The páramo of the Northern Andes provide critically important ecosystem services to the Northern Andean region in the form of water provisioning and carbon sequestration, both of which are a result of the páramo?s organic-rich soils. Little is known, however, about the hydro-geomorphic characteristics of the rivers that drain these ecosystems. With impending plans for widespread hydro-development and increasing implementation of carbon-sequestering compensation for ecosystem services programs in the region it is imperative that we develop a thorough understanding of the hydrogeomorphic role that rivers play in this unique ecosystem. The objective of this study was to quantify bank erosion along an Amazonian headwater stream draining a small, relatively undisturbed páramo catchment to gain a better understanding of the natural erosion regime and the resulting sediment contributions from this unique ecosystem. This study implemented a combination of field, laboratory, and Geographic Information Systems techniques to quantify bank erosion rates and determine a bank erosion sediment yield from the Ningar River, a small páramo catchment(22.7 km^2) located in the eastern Andean cordillera of Ecuador. Results show that bank erosion rates range from 3.0 to ≥ 390.0 mm/yr, are highly episodic, and yield at least 487 tons of sediment annually to the Ningar River. These results imply that 1) páramo ecosystems substantially contribute to the sediment load of the Amazon River basin; 2) bank erosion is a potentially significant flux component of basin-scale carbon cycles in páramo ecosystems; and 3) hydrologic alteration campaigns(dam building) will likely critically alter these contributions and concomitantly disconnect a critical source of sediment and nutrients to downstream ecosystems.展开更多
In this article, we review the current knowledge of the glacial recession and related glacial lake development in the Andes of South America. Since the mid-1980 s, hundreds of glacial lakes either expanded or formed, ...In this article, we review the current knowledge of the glacial recession and related glacial lake development in the Andes of South America. Since the mid-1980 s, hundreds of glacial lakes either expanded or formed, and predictions show that additional hundreds of lakes will form throughout the 21 st century. However, studies on glacial lakes in the Andes are still relatively rare. Many glacial lakes pose a potential hazard to local communities, but glacial lake outburst floods(GLOFs) are understudied. We provide an overview on hazards from glacial lakes such as GLOFs and water pollution, and their monitoring approaches. In real-time monitoring, the use of unmanned aerial systems(UASs) and early warning systems(EWSs) is still extremely rare in the Andes, but increasingly authorities plan to install mitigation systems to reduce glacial lake risk and protect local communities. In support, we propose an international remote sensing-based observation initiative following the model of, for example, the Global Land Ice Measurements from Space(GLIMS) one, with the headquarters in one of the Andean nations.展开更多
The most heavily glacierized tropical range in the world– the Peruvian Cordillera Blanca-has been losing ice since the end of the Little Ice Age(LIA).In this study,the decline of the Churup glacier(9°28’18"...The most heavily glacierized tropical range in the world– the Peruvian Cordillera Blanca-has been losing ice since the end of the Little Ice Age(LIA).In this study,the decline of the Churup glacier(9°28’18"S;77°25’02"W)and associated processes were documented employing multi-proxy approach including the analysis of remotely sensed images(1948-2016),the Schmidt hammer rock test and lichenometric dating.It is shown that Churup glacier has lost the vast majority of its estimated LIA extent(1.05±0.1 km^2;45.0×10^6-57.4×10^6 m^3).The rate of glacier retreat is documented to vary in space(SE,SW and NW-facing slopes)and time,with the peak between 1986 and 1995.With an area of 0.045 km^2 in 2016,it is expected that the complete deglaciation of the Churup valley is inevitable in the near future.Recently(post-LIA)exposed bedrock surfaces have shown higher R-values(54.2-66.4,AVG 63.3,STDEV 2.9)compared to pre-LIA exposed surfaces(46.1-59.3,AVG 50.1,STDEV 4.9),confirming the links to the duration of rock weathering.The Lichenometric dating is applied to recently exposed areas and elevations above 4800 m a.s.l.,revealing only limited reliability and agreement with the age of deglaciation estimated from remotely-sensed images in such an environment.展开更多
The rheological behavior of the lithosphere beneath the Northwestern(NW)Andes(Colombian)remains uncertain under a complex geological setting.Here,we analyze the earthquake distribution and the stress drop on the weste...The rheological behavior of the lithosphere beneath the Northwestern(NW)Andes(Colombian)remains uncertain under a complex geological setting.Here,we analyze the earthquake distribution and the stress drop on the western and the eastern of the transition area between the Upper Magdalena Valley(UMV)and the Middle Magdalena Valley(MMV),a zone related to a plate tectonic transition from steeper to flatter subduction style slabs(Nazca and Caribbean plates).Our results consistently explain the tectonic and geodynamic context of the study area supported in two rheological profiles,which reveal the brittle/ductile transition of the lithospheric crust and mantle and allow to constrain the lithospheric rheological thickness.The subduction phenomenon of the Nazca Plate under the South American Plate is observed in the western zone.In the eastern region,we find a remarkable aseismic zone under the Eastern Cordillera below 20-km-deep,which made more difficultan accurate estimation of the crust/mantle boundary.This seismic particularity leads us to support the hypothesis of a delamination process due to the tectonic overload generated by the Eastern Cordillera,and that promotes thermal anomalies.Our results also suggest that the earthquake dataset correlated with rheological estimations may offer a consistent interpretation of the mechanical behavior of the lithosphere.展开更多
One way of deducing vertical shifts in the altitudinal distribution of Colombian high-altitude páramo environments is by inferring fluctuations in the height of the local freezing level.In our research,we are imp...One way of deducing vertical shifts in the altitudinal distribution of Colombian high-altitude páramo environments is by inferring fluctuations in the height of the local freezing level.In our research,we are implementing two complementary approaches to reconstruct Late Pleistocene to Holocene changes in the freezing level height(FLH)in two of the most extensively glacier-covered areas of the northern Andes.We combined remote sensing and field-based geomorphological mapping with time-series reconstruction of changes in the altitude of the 0°C isotherm.Changes in the FLH were based on alreadypublished~30 kyr paleo-reconstructions of sea surface temperatures(SSTs)of the eastern tropical Pacific and the western tropical Atlantic,as well as on reconstructed long-term sea level changes and empirical orthogonal functions of present-day(historical)Indo-Pacific and tropical Atlantic SST anomalies.We also analyzed the probability distribution of air-sea temperature differences and the spatial distribution of grid points with SSTs above the minimum threshold necessary to initiate deep convection.We considered available historical nearsurface and free air temperature data of ERA-Interim reanalysis products,General Circulation Model(GCM)simulations,weather stations,and(deployed by our group)digital sensors,to assess the normal Environmental Lapse Rates(ELRs)at the regional to local scale.The combined maps of glacial landforms and our reconstructed FLHs provided us with a wellfounded inference of potential past glacier advances,narrowing down the coarse resolution of ice margins suggested by previous research efforts.The extent of the areas with temperatures below the freezing point suggested here for the summits of our main study site exceeds in magnitude the corresponding glacier icecaps and front advances proposed by previous studies.Conversely,our average lowest altitudes of the FLH for our comparative site are consistently above the main glacier-front advances previously suggested.Our results indicate that,compared to the maximum upward changes that likely took place over the past ca.20,000 years in our two areas of interest,the observed(present-day)upward shifts of the FLH have occurred at a rate that significantly surpasses our inferred rates.Our study helps fill the gaps in understanding past climatic changes and present trends in the region of interest and provides some insights into analyzing the signals of natural and anthropogenic climate change.展开更多
Tropical alpine ecosystems exhibit outstanding plant diversity and endemism while being particularly sensitive to the impacts of climate change.Although understanding spatiotemporal changes in plant species compositio...Tropical alpine ecosystems exhibit outstanding plant diversity and endemism while being particularly sensitive to the impacts of climate change.Although understanding spatiotemporal changes in plant species composition,richness and community structure along tropical alpine altitudinal gradients is of primary importance,both the functional and historical/biogeographic dimensions of vegetation diversity remain largely unexplored.We used Generalized Linear Models and multivariate analyses to assess changes in species,growth forms,and biogeographic groups richness and abundance,in response to habitat variables along an elevation gradient in seven summits(3800 to 4600 m asl)in the Venezuelan Andes,studied using the standardized approach of the GLORIA-Andes monitoring network.The habitat variables assessed were soil temperature(-10 cm),soil organic matter,slope inclination,and substrate cover.We found 113 species,representing72 genera,32 families,13 growth forms,and seven biogeographic origins,that included 25%of endemic elements.We observed richer vegetation,both in terms of species and growth forms,in summits with higher soil temperatures and higher SOM content,as well as higher biogeographic origin richness with increasing soil temperatures.The presence of holarctic elements increased toward higher elevations,while the occurrence of austral antarctic elements increased toward lower elevations.Our results indicate that biogeographic and functional approaches to vegetation diversity capture well the effect of abiotic filtering on community structuring in these tropical alpine environments.These findings constitute an important baseline for monitoring vegetation dynamics linked to climate change in the Venezuelan Andes by highlighting the functional and historical perspective on vegetation analyses,in contrast with more traditional approaches,based only on taxonomic species diversity.展开更多
Due to their ecological disadvantages, many mountain regions have experienced land-use abandonment and shrub encroachment on former grassland at higher altitudinal zones--especially during recent decades of urbanizati...Due to their ecological disadvantages, many mountain regions have experienced land-use abandonment and shrub encroachment on former grassland at higher altitudinal zones--especially during recent decades of urbanization. But does this trend also apply to the hinterland of urban settlements？ By using the Southern Colombian example of Popay^n, a medium-sized city located in the Northern Andes, we can show that the landscape changes observed between 1989 and 2010 can hardly be related to agricultural abandonment. Hypsometric variations of land-cover change indicate that, until 2001, woods or shrubland expanded faster at the lower altitudinal range adjacent to the city than at the more remote higher zones. In contrast, after 2001 grassland areas increased on former woods or shrnbland at all altitudinal belts. Both periods thus present developments that can be interpreted as the result of land-use expansion below 2000 m asl and land-use persistence in the tierrafrla of the mountain city＇s hinterland.展开更多
Paramo is a term used to describe tropical alpine vegetation between the continuous timberline and the snow line in tbe Northern Andes. Paramo environments provide important species habitat and ecosystem services. Cha...Paramo is a term used to describe tropical alpine vegetation between the continuous timberline and the snow line in tbe Northern Andes. Paramo environments provide important species habitat and ecosystem services. Changes in spatial extent of the paramo ecosystem at Pambamarca in the Central Cordillera of the northern Ecuadorian Andes were analysed using multi-temporal Landsat TM/ETM＋ satellite data. The region suffered a loss of 1826.6 ha or 20% of the total area at a rate of 100 ha/annum during 1988-2007 period. It is found that permanent paramo cover decreased from 8350 ha in 1988 to 5864 ha in 2007 at a fairly constant rate （R^2=0.94）. This loss is attributed to expansion of commercial agriculture and floriculture in the valleys coupled with increased population pressure. Land at higher elevations has been cleared for small scale agriculture. Loss of the paramo ecosystem will exert a number of negative impacts on ecosystem services and livelihoods of the local population at Pambamarca.展开更多
Many Andisols of the Andes have been disturbed by traditional potato-based rotation agriculture disrupting soil structure, water retention capacity and organic matter content. This study was undertaken to investigate ...Many Andisols of the Andes have been disturbed by traditional potato-based rotation agriculture disrupting soil structure, water retention capacity and organic matter content. This study was undertaken to investigate the contribution of conservation farming technology or reduced tillage in potato-based rotations in the Colombian Andes in order to rehabilitate total and aggregated soil organic C in disturbed organic matter-rich Andisols. Soils were sampled from farms with 7-year of reduced tillage and farms with conventional farming practices. Ultrasound energy was applied to samples to disrupt aggregation and total soil C was determined in order to investigate the amount of carbon held inside the aggregates of different soil size classes. Results indicated that reduced tillage in potato-based crop rotations increased the soil C concentration and average C content in the whole profile (≈117 cm depth) by 50 and 33% (1636 t C ha?1 vs. 1224 t C ha?1), respectively, as compared to conventional farming practices. Carbon content increased 177% in the subsoil (A2 horizon, 78 -117 cm depth, from 215 to 596 t?ha?1), although most of the soil C was in the A1 horizon (between 0 -78 cm average thickness, 1097 t?ha?1). These increases show that reduced tillage enhances C stores in Andisols which are already high in organic matter. In addition, C in aggregates represented more than 80% of the total organic matter and it was positively affected by conservation practices. The C increase was preferential in the smaller macroaggregates (展开更多
Global change threatens mountainous plant communities,causing habitat displacement.Phylogenetic studies reveal evolutionary and ecological processes in community assembly.We examined taxonomic and phylogenetic diversi...Global change threatens mountainous plant communities,causing habitat displacement.Phylogenetic studies reveal evolutionary and ecological processes in community assembly.We examined taxonomic and phylogenetic diversity in Andean Páramos across altitudes.Our hypotheses were that increasing altitude is an environmental filter,as altitude is expected to be a stronger variable than soil depth.The Páramos,alpine vegetation in the Andes,range from 3,000 to 4,700 meters,with our plots spanning 3,200 to 4,100 meters.Sampling was conducted at six altitudinal levels,measuring soil depth,taxonomic,and phylogenetic diversity.Data analysis employed multiple linear regressions and mixed-effects models to assess the effects of soil depth and altitude.We sampled 110 angiosperm species from 70 genera,30 families,and 18 orders.Asterales and Poales were prominent.Species richness generally decreased with altitude but increased at the summit.Soil depth affected species richness and taxonomic diversity,while altitude did not.Phylogenetic diversity increased with soil depth and decreased with altitude.Phylogenetic turnover increased with altitude differences.The hypothesis that increasing altitude intensifies environmental filtering in the altitudeadapted Páramos resulting in lower species richness and more clustered phylogenetic structures,was rejected.Although species richness,Shannon diversity,and Simpson diversity decreased initially with increasing altitude,this trend was not linear because the summit presented intermediate species richness.The hypothesis that altitude is a stronger explanatory variable than soil depth was also rejected.Despite expectations,taxonomic results did not support altitude as an environmental filter,but soil depth.Greater altitude differences increased beta phylogenetic dissimilarity,supporting niche conservatism.展开更多
1 It's a sunny afternoon in Juliaca,a city near Lake Titicaca,Peru.Among the thousands of native Quechua people gathering in the town square is a man dressed in black on a black horse.He's dressed in memory of...1 It's a sunny afternoon in Juliaca,a city near Lake Titicaca,Peru.Among the thousands of native Quechua people gathering in the town square is a man dressed in black on a black horse.He's dressed in memory of the country's most respected figure:Túpac AmaruⅡ,a native leader who led a war against the Spanish Empire and became a symbol for the fighting spirits in the Andes.He's also there to rap.From horseback,Cay Sur performs his song about heroes,its hip⁃hop beat pulsing(洋溢)through the crowd.展开更多
The Chilean Pampean flat slab subduction segment is characterized by the nearly horizontal subduction of the Nazca Plate within the depth range of 100-120 km.Numerous seismic tomography studies have been conducted to ...The Chilean Pampean flat slab subduction segment is characterized by the nearly horizontal subduction of the Nazca Plate within the depth range of 100-120 km.Numerous seismic tomography studies have been conducted to investigate its velocity structure;however,they have used only seismic body wave data or surface wave data.As a result,the existing velocity models in the region may have relatively large uncertainties.In this study,we use body wave arrival times from earthquakes occurring in central Chile between 2014 and 2019,as well as Rayleigh wave phase velocity maps at periods of 5-80 s from ambient noise empirical Green’s functions in Chile.By jointly using body wave arrival times and surface wave dispersion data,we refine the VS model and improve earthquake locations in the central Chile subduction zone.Compared with previous velocity models,our velocity model better reveals an eastward-dipping high-velocity plate representing the subducting Nazca Plate,which is 40-50 km thick and is more consistent with the slab thickness estimated by receiver function imaging and thermal modeling.Overall,the intraslab seismicity distribution spatially correlates well with the slab high-velocity anomalies except along the subduction paths of the CopiapóRidge and Juan Fernández Ridge.Additionally,parallel low-velocity stripes are imaged beneath the subducting plate,which are likely associated with the accumulated melts.The joint inversion velocity model also resolves widespread low-velocity anomalies in the crust beneath the Central Volcanic Zone of the central Andes,likely representing crustal magma chambers for various volcanoes.展开更多
Significant changes in the area and snowline altitude of two glacierized mountains - Nevado Champara (Cordillera Blanca,Peru) and Cerro Tilata (Cordillera Real,Bolivia)- in the tropical Andes,before and after the rece...Significant changes in the area and snowline altitude of two glacierized mountains - Nevado Champara (Cordillera Blanca,Peru) and Cerro Tilata (Cordillera Real,Bolivia)- in the tropical Andes,before and after the recent El Nino in 2015/16 period,have been analysed using Sentinel 2A and Landsat data.It is seen that the recent El Nino has been accompanied by higher fluctuation in glacier coverage on Nevado Champara and the loss of glacier coverage on Cerro Tilata was very high during the past 16 years.Rise in snowline altitude of selected glaciers was very high after the 2015/16 El Nino.Increase in the area covered by snow and ice during the La Nina periods were not enough to cover the ice loss occurred during the previous El Nino events and the strongest El Nino in 2015/ 16 was followed by a significant loss of ice-covered areas in the tropical Andes.Freshwater resources in this region will be affected in the near future if the current trends in glacier decline continue.Adaptation strategies needs to be implemented to reduce the impacts of the continuing loss of glacierized on regional communities in the tropical Andean region.展开更多
Aims The importance of quantifying carbon stocks in terrestrial ecosystems is crucial for determining climate change dynamics.However,the present regional assessments of carbon stocks in tropical grasslands are extrap...Aims The importance of quantifying carbon stocks in terrestrial ecosystems is crucial for determining climate change dynamics.However,the present regional assessments of carbon stocks in tropical grasslands are extrapolated to unsampled areas with a high degree of uncertainty and without considering the carbon and nitrogen composition of vegetation and soil along altitudinal ranges.This study aims to assess carbon and nitrogen concentrations in soil and vegetation,aboveground carbon stocks distribution and soil organic carbon stocks along an altitudinal range in the páramo region in the Ecuadorian Andes.Methods The vegetation inventory was conducted using 15×15 m sampling plots distributed in three altitudinal ranges.Based on the patterns exhibited by the dominant vegetation growth forms,biomass and soil were sampled to quantify the corresponding carbon and nitrogen concentrations.Subsequently,the aboveground live biomass along the páramo altitudinal range was estimated using allometric equations.Finally,soil and vegetation carbon stocks were estimated for the entire basin.Important Findings Altitudinal analysis supported a potential distribution of carbon and nitrogen concentrations in soil,litter and live tissues,where higher concentrations were found in the low altitudinal range mainly for tussocks and acaulescent rosettes.Cellulose in litter showed higher concentrations at low altitudinal ranges for acaulescent rosettes and cushions only.For the same growth forms,lignin patterns in litter were higher in high altitudinal ranges.Soil texture provided complementary information:high percentage of silt was highly correlated to high soil nitrogen and carbon concentration.Tussocks were found to be responsive to altitude with their,highest aboveground carbon stocks occurring at the low altitudinal range,but cushions and acaulescent rosettes responded differently.The established relationships among soil,vegetation and altitude shown in this study must be taken into account to estimate both aboveground and soil organic carbon stocks in páramo regions—such estimates will be considerably inaccurate if these relationships are ignored.展开更多
Data gaps and biases are two important issues that affect the quality of biodiversity information and downstream results.Understanding how best to fill existing gaps and account for biases is necessary to improve our ...Data gaps and biases are two important issues that affect the quality of biodiversity information and downstream results.Understanding how best to fill existing gaps and account for biases is necessary to improve our current information most effectively.Two current main approaches for obtaining and improving data include(1)curation of biological collections,and(2)fieldwork.However,the comparative effectiveness of these approaches in improving biodiversity data remains little explored.We used the Flora de Bogota project to study the magnitude of change in species richness,spatial coverage,and sample coverage of plant records based on curation versus fieldwork.The process of curation resulted in a decrease in species richness(synonym and error removal),but it significantly increased the number of records per species.Fieldwork contributed to a slight increase in species richness,via accumulation of new records.Additionally,curation led to increases in spatial coverage,species observed by locality,the number of plant records by species,and localities by species compared to fieldwork.Overall,curationwas more efficient in producing new information compared to fieldwork,mainly because of the large number of records available in herbaria.We recommend intensive curatorial work as the first step in increasing biodiversity data quality and quantity,to identify bias and gaps at the regional scale that can then be targeted with fieldwork.The stepwise strategy would enable fieldwork to be planned more costeffectively given the limited resources for biodiversity exploration and characterization.展开更多
文摘This paper presents preliminary results of three-dimensional thermomechanical finite-element models of a parameter study to compute the current temperature and stress distribution in the subduction zone of the central Andes （16°S-26°S） up to a depth of 400 km, the bottom of the asthenosphere. For this purpose a simulation running over c. 50,000 years will be realized based on the geometry of a generic subduction zone and an elasto-viscoplastic Drucker-Prager rheology. The kinematic and thermal boundary conditions as well as the rheological parameters represent the current state of the study area. In future works the model will be refined using a systematic study of physical parameters in order to estimate the influence of the main parameters （e.g. viscosity, fault friction, velocity, shear heating） on the results of the reference model presented here. The reference model is kept as simple as possible to be able to estimate the influence of the parameters in future studies in the best possible way, whilst minimizing comnutational time.
基金funded by Fondecyt Projects(Nos. 1151146 and 1110914)Programa de Fomento y Transferencia tecnológica en Exploración Minera, código BIP № 30114940-0, PIP CONICET 2015-2017 No. 11220150100426,UBACYT 2015-2017 No. 20020150100166BA, PICT 2016 No. 2252, NSF EAR-165031the Yale Institute for Biospheric Studies
文摘The Central Patagonian Andes is a particular segment of the Andean Cordillera that has been subjected to the subduction of two spreading ridges during Eocene and Neogene times. In order to understand the Cenozoic geologic evolution of the Central Patagonian Andes, we carried out geochronologic(U-Pb and^(40)Ar/^(39)Ar), provenance, stratigraphic, sedimentologic, and geochemical studies on the sedimentary and volcanic Cenozoic deposits that crop out in the Meseta Guadal and Chile Chico areas(～47°S). Our data indicate the presence of a nearly complete Cenozoic record, which refutes previous interpretations of a hiatus during the middle Eocene-late Oligocene in the Central Patagonian Andes. Our study suggests that the fluvial strata of the Ligorio Marquez Formation and the flood basalts of the Basaltos Inferiores de la Meseta Chile Chico Formation were deposited in an extensional setting related to the subduction of the Aluk-Farallon spreading ridge during the late Paleocene-Eocene. Geochemical data on volcanic rocks interbedded with fluvial strata of the San Jose Formation suggest that this unit was deposited in an extensional setting during the middle Eocene to late Oligocene. Progressive crustal thinning allowed the transgression of marine waters of Atlantic origin and deposition of the upper Oligocene-lower Miocene Guadal Formation. The fluvial synorogenic strata of the Santa Cruz Formation were deposited as a consequence of an important phase of compressive deformation and Andean uplift during the early-middle Miocene. Finally, alkali flood basalts of the late middle to late Miocene Basaltos Superiores de la Meseta Chile Chico Formation were extruded in the area in response to the suduction of the Chile Ridge under an extensional regime. Our studies indicate that the tectonic evolution of the Central Patagonian Andes is similar to that of the North Patagonian Andes and appears to differ from that of the Southern Patagonian Andes, which is thought to have been the subject of continuous compressive deformation since the late Early Cretaceous.
基金an Oak Ridge Associated Universities Junior Faculty Enhancement Awardan Appalachian State University Board of Trustees International Research Grant+1 种基金an Appalachian State University Research Council grant awarded to PI Martina Fulbright Foundation Science and Technology grant awarded to PI Wemple
文摘The páramo of the Northern Andes provide critically important ecosystem services to the Northern Andean region in the form of water provisioning and carbon sequestration, both of which are a result of the páramo?s organic-rich soils. Little is known, however, about the hydro-geomorphic characteristics of the rivers that drain these ecosystems. With impending plans for widespread hydro-development and increasing implementation of carbon-sequestering compensation for ecosystem services programs in the region it is imperative that we develop a thorough understanding of the hydrogeomorphic role that rivers play in this unique ecosystem. The objective of this study was to quantify bank erosion along an Amazonian headwater stream draining a small, relatively undisturbed páramo catchment to gain a better understanding of the natural erosion regime and the resulting sediment contributions from this unique ecosystem. This study implemented a combination of field, laboratory, and Geographic Information Systems techniques to quantify bank erosion rates and determine a bank erosion sediment yield from the Ningar River, a small páramo catchment(22.7 km^2) located in the eastern Andean cordillera of Ecuador. Results show that bank erosion rates range from 3.0 to ≥ 390.0 mm/yr, are highly episodic, and yield at least 487 tons of sediment annually to the Ningar River. These results imply that 1) páramo ecosystems substantially contribute to the sediment load of the Amazon River basin; 2) bank erosion is a potentially significant flux component of basin-scale carbon cycles in páramo ecosystems; and 3) hydrologic alteration campaigns(dam building) will likely critically alter these contributions and concomitantly disconnect a critical source of sediment and nutrients to downstream ecosystems.
文摘In this article, we review the current knowledge of the glacial recession and related glacial lake development in the Andes of South America. Since the mid-1980 s, hundreds of glacial lakes either expanded or formed, and predictions show that additional hundreds of lakes will form throughout the 21 st century. However, studies on glacial lakes in the Andes are still relatively rare. Many glacial lakes pose a potential hazard to local communities, but glacial lake outburst floods(GLOFs) are understudied. We provide an overview on hazards from glacial lakes such as GLOFs and water pollution, and their monitoring approaches. In real-time monitoring, the use of unmanned aerial systems(UASs) and early warning systems(EWSs) is still extremely rare in the Andes, but increasingly authorities plan to install mitigation systems to reduce glacial lake risk and protect local communities. In support, we propose an international remote sensing-based observation initiative following the model of, for example, the Global Land Ice Measurements from Space(GLIMS) one, with the headquarters in one of the Andean nations.
基金the Ministry of Education, Youth and Sports of the Czech Republic within the framework of the National Sustainability Programme Ⅰ(NPU Ⅰ), Grant No. LO1415
文摘The most heavily glacierized tropical range in the world– the Peruvian Cordillera Blanca-has been losing ice since the end of the Little Ice Age(LIA).In this study,the decline of the Churup glacier(9°28’18"S;77°25’02"W)and associated processes were documented employing multi-proxy approach including the analysis of remotely sensed images(1948-2016),the Schmidt hammer rock test and lichenometric dating.It is shown that Churup glacier has lost the vast majority of its estimated LIA extent(1.05±0.1 km^2;45.0×10^6-57.4×10^6 m^3).The rate of glacier retreat is documented to vary in space(SE,SW and NW-facing slopes)and time,with the peak between 1986 and 1995.With an area of 0.045 km^2 in 2016,it is expected that the complete deglaciation of the Churup valley is inevitable in the near future.Recently(post-LIA)exposed bedrock surfaces have shown higher R-values(54.2-66.4,AVG 63.3,STDEV 2.9)compared to pre-LIA exposed surfaces(46.1-59.3,AVG 50.1,STDEV 4.9),confirming the links to the duration of rock weathering.The Lichenometric dating is applied to recently exposed areas and elevations above 4800 m a.s.l.,revealing only limited reliability and agreement with the age of deglaciation estimated from remotely-sensed images in such an environment.
基金the Geophysical Research Group and the Geophysical Instrumentation Laboratory(LIG),belonging to the Geosciences Department of the Universidad Nacional de Colombia at Bogota,which support our work with the following grant IDs:Hermes-43777-UNAL
文摘The rheological behavior of the lithosphere beneath the Northwestern(NW)Andes(Colombian)remains uncertain under a complex geological setting.Here,we analyze the earthquake distribution and the stress drop on the western and the eastern of the transition area between the Upper Magdalena Valley(UMV)and the Middle Magdalena Valley(MMV),a zone related to a plate tectonic transition from steeper to flatter subduction style slabs(Nazca and Caribbean plates).Our results consistently explain the tectonic and geodynamic context of the study area supported in two rheological profiles,which reveal the brittle/ductile transition of the lithospheric crust and mantle and allow to constrain the lithospheric rheological thickness.The subduction phenomenon of the Nazca Plate under the South American Plate is observed in the western zone.In the eastern region,we find a remarkable aseismic zone under the Eastern Cordillera below 20-km-deep,which made more difficultan accurate estimation of the crust/mantle boundary.This seismic particularity leads us to support the hypothesis of a delamination process due to the tectonic overload generated by the Eastern Cordillera,and that promotes thermal anomalies.Our results also suggest that the earthquake dataset correlated with rheological estimations may offer a consistent interpretation of the mechanical behavior of the lithosphere.
文摘One way of deducing vertical shifts in the altitudinal distribution of Colombian high-altitude páramo environments is by inferring fluctuations in the height of the local freezing level.In our research,we are implementing two complementary approaches to reconstruct Late Pleistocene to Holocene changes in the freezing level height(FLH)in two of the most extensively glacier-covered areas of the northern Andes.We combined remote sensing and field-based geomorphological mapping with time-series reconstruction of changes in the altitude of the 0°C isotherm.Changes in the FLH were based on alreadypublished~30 kyr paleo-reconstructions of sea surface temperatures(SSTs)of the eastern tropical Pacific and the western tropical Atlantic,as well as on reconstructed long-term sea level changes and empirical orthogonal functions of present-day(historical)Indo-Pacific and tropical Atlantic SST anomalies.We also analyzed the probability distribution of air-sea temperature differences and the spatial distribution of grid points with SSTs above the minimum threshold necessary to initiate deep convection.We considered available historical nearsurface and free air temperature data of ERA-Interim reanalysis products,General Circulation Model(GCM)simulations,weather stations,and(deployed by our group)digital sensors,to assess the normal Environmental Lapse Rates(ELRs)at the regional to local scale.The combined maps of glacial landforms and our reconstructed FLHs provided us with a wellfounded inference of potential past glacier advances,narrowing down the coarse resolution of ice margins suggested by previous research efforts.The extent of the areas with temperatures below the freezing point suggested here for the summits of our main study site exceeds in magnitude the corresponding glacier icecaps and front advances proposed by previous studies.Conversely,our average lowest altitudes of the FLH for our comparative site are consistently above the main glacier-front advances previously suggested.Our results indicate that,compared to the maximum upward changes that likely took place over the past ca.20,000 years in our two areas of interest,the observed(present-day)upward shifts of the FLH have occurred at a rate that significantly surpasses our inferred rates.Our study helps fill the gaps in understanding past climatic changes and present trends in the region of interest and provides some insights into analyzing the signals of natural and anthropogenic climate change.
基金the financial support to the GLORIA-Andes network in Venezuela of CONDESAN and the Swiss Development Agency(SDC)The present synthesis analysis was financed by the Adaptation at Altitude Program(CONDESAN-SDC)。
文摘Tropical alpine ecosystems exhibit outstanding plant diversity and endemism while being particularly sensitive to the impacts of climate change.Although understanding spatiotemporal changes in plant species composition,richness and community structure along tropical alpine altitudinal gradients is of primary importance,both the functional and historical/biogeographic dimensions of vegetation diversity remain largely unexplored.We used Generalized Linear Models and multivariate analyses to assess changes in species,growth forms,and biogeographic groups richness and abundance,in response to habitat variables along an elevation gradient in seven summits(3800 to 4600 m asl)in the Venezuelan Andes,studied using the standardized approach of the GLORIA-Andes monitoring network.The habitat variables assessed were soil temperature(-10 cm),soil organic matter,slope inclination,and substrate cover.We found 113 species,representing72 genera,32 families,13 growth forms,and seven biogeographic origins,that included 25%of endemic elements.We observed richer vegetation,both in terms of species and growth forms,in summits with higher soil temperatures and higher SOM content,as well as higher biogeographic origin richness with increasing soil temperatures.The presence of holarctic elements increased toward higher elevations,while the occurrence of austral antarctic elements increased toward lower elevations.Our results indicate that biogeographic and functional approaches to vegetation diversity capture well the effect of abiotic filtering on community structuring in these tropical alpine environments.These findings constitute an important baseline for monitoring vegetation dynamics linked to climate change in the Venezuelan Andes by highlighting the functional and historical perspective on vegetation analyses,in contrast with more traditional approaches,based only on taxonomic species diversity.
基金funded by the Austrian Science Fund (FWF) [Project No. P24692]
文摘Due to their ecological disadvantages, many mountain regions have experienced land-use abandonment and shrub encroachment on former grassland at higher altitudinal zones--especially during recent decades of urbanization. But does this trend also apply to the hinterland of urban settlements？ By using the Southern Colombian example of Popay^n, a medium-sized city located in the Northern Andes, we can show that the landscape changes observed between 1989 and 2010 can hardly be related to agricultural abandonment. Hypsometric variations of land-cover change indicate that, until 2001, woods or shrubland expanded faster at the lower altitudinal range adjacent to the city than at the more remote higher zones. In contrast, after 2001 grassland areas increased on former woods or shrnbland at all altitudinal belts. Both periods thus present developments that can be interpreted as the result of land-use expansion below 2000 m asl and land-use persistence in the tierrafrla of the mountain city＇s hinterland.
文摘Paramo is a term used to describe tropical alpine vegetation between the continuous timberline and the snow line in tbe Northern Andes. Paramo environments provide important species habitat and ecosystem services. Changes in spatial extent of the paramo ecosystem at Pambamarca in the Central Cordillera of the northern Ecuadorian Andes were analysed using multi-temporal Landsat TM/ETM＋ satellite data. The region suffered a loss of 1826.6 ha or 20% of the total area at a rate of 100 ha/annum during 1988-2007 period. It is found that permanent paramo cover decreased from 8350 ha in 1988 to 5864 ha in 2007 at a fairly constant rate （R^2=0.94）. This loss is attributed to expansion of commercial agriculture and floriculture in the valleys coupled with increased population pressure. Land at higher elevations has been cleared for small scale agriculture. Loss of the paramo ecosystem will exert a number of negative impacts on ecosystem services and livelihoods of the local population at Pambamarca.
文摘Many Andisols of the Andes have been disturbed by traditional potato-based rotation agriculture disrupting soil structure, water retention capacity and organic matter content. This study was undertaken to investigate the contribution of conservation farming technology or reduced tillage in potato-based rotations in the Colombian Andes in order to rehabilitate total and aggregated soil organic C in disturbed organic matter-rich Andisols. Soils were sampled from farms with 7-year of reduced tillage and farms with conventional farming practices. Ultrasound energy was applied to samples to disrupt aggregation and total soil C was determined in order to investigate the amount of carbon held inside the aggregates of different soil size classes. Results indicated that reduced tillage in potato-based crop rotations increased the soil C concentration and average C content in the whole profile (≈117 cm depth) by 50 and 33% (1636 t C ha?1 vs. 1224 t C ha?1), respectively, as compared to conventional farming practices. Carbon content increased 177% in the subsoil (A2 horizon, 78 -117 cm depth, from 215 to 596 t?ha?1), although most of the soil C was in the A1 horizon (between 0 -78 cm average thickness, 1097 t?ha?1). These increases show that reduced tillage enhances C stores in Andisols which are already high in organic matter. In addition, C in aggregates represented more than 80% of the total organic matter and it was positively affected by conservation practices. The C increase was preferential in the smaller macroaggregates (
基金the Botany Graduate Program of Universidade Federal de Vicosa - PPGBot-UFV for the infrastructure and scholarshipsprovided by FAPEMIG (FORTIS/PPGBot-UFV, PPM00584-16, APQ-01309-16)+1 种基金CAPES (PROAP and Pr Int/PPGBot-UFV)CNPq (307591/2016-6, 306335/2020-4)
文摘Global change threatens mountainous plant communities,causing habitat displacement.Phylogenetic studies reveal evolutionary and ecological processes in community assembly.We examined taxonomic and phylogenetic diversity in Andean Páramos across altitudes.Our hypotheses were that increasing altitude is an environmental filter,as altitude is expected to be a stronger variable than soil depth.The Páramos,alpine vegetation in the Andes,range from 3,000 to 4,700 meters,with our plots spanning 3,200 to 4,100 meters.Sampling was conducted at six altitudinal levels,measuring soil depth,taxonomic,and phylogenetic diversity.Data analysis employed multiple linear regressions and mixed-effects models to assess the effects of soil depth and altitude.We sampled 110 angiosperm species from 70 genera,30 families,and 18 orders.Asterales and Poales were prominent.Species richness generally decreased with altitude but increased at the summit.Soil depth affected species richness and taxonomic diversity,while altitude did not.Phylogenetic diversity increased with soil depth and decreased with altitude.Phylogenetic turnover increased with altitude differences.The hypothesis that increasing altitude intensifies environmental filtering in the altitudeadapted Páramos resulting in lower species richness and more clustered phylogenetic structures,was rejected.Although species richness,Shannon diversity,and Simpson diversity decreased initially with increasing altitude,this trend was not linear because the summit presented intermediate species richness.The hypothesis that altitude is a stronger explanatory variable than soil depth was also rejected.Despite expectations,taxonomic results did not support altitude as an environmental filter,but soil depth.Greater altitude differences increased beta phylogenetic dissimilarity,supporting niche conservatism.
文摘1 It's a sunny afternoon in Juliaca,a city near Lake Titicaca,Peru.Among the thousands of native Quechua people gathering in the town square is a man dressed in black on a black horse.He's dressed in memory of the country's most respected figure:Túpac AmaruⅡ,a native leader who led a war against the Spanish Empire and became a symbol for the fighting spirits in the Andes.He's also there to rap.From horseback,Cay Sur performs his song about heroes,its hip⁃hop beat pulsing(洋溢)through the crowd.
基金funded by the National Natural Science Foundation of China under Grant 42230101the National Agency for Research and Development of Chile(ANID)by Projects AFB180004 and AFB220002the ANID Programa de Cooperación Internacional(PCI)Grant PII-180003.
文摘The Chilean Pampean flat slab subduction segment is characterized by the nearly horizontal subduction of the Nazca Plate within the depth range of 100-120 km.Numerous seismic tomography studies have been conducted to investigate its velocity structure;however,they have used only seismic body wave data or surface wave data.As a result,the existing velocity models in the region may have relatively large uncertainties.In this study,we use body wave arrival times from earthquakes occurring in central Chile between 2014 and 2019,as well as Rayleigh wave phase velocity maps at periods of 5-80 s from ambient noise empirical Green’s functions in Chile.By jointly using body wave arrival times and surface wave dispersion data,we refine the VS model and improve earthquake locations in the central Chile subduction zone.Compared with previous velocity models,our velocity model better reveals an eastward-dipping high-velocity plate representing the subducting Nazca Plate,which is 40-50 km thick and is more consistent with the slab thickness estimated by receiver function imaging and thermal modeling.Overall,the intraslab seismicity distribution spatially correlates well with the slab high-velocity anomalies except along the subduction paths of the CopiapóRidge and Juan Fernández Ridge.Additionally,parallel low-velocity stripes are imaged beneath the subducting plate,which are likely associated with the accumulated melts.The joint inversion velocity model also resolves widespread low-velocity anomalies in the crust beneath the Central Volcanic Zone of the central Andes,likely representing crustal magma chambers for various volcanoes.
文摘Significant changes in the area and snowline altitude of two glacierized mountains - Nevado Champara (Cordillera Blanca,Peru) and Cerro Tilata (Cordillera Real,Bolivia)- in the tropical Andes,before and after the recent El Nino in 2015/16 period,have been analysed using Sentinel 2A and Landsat data.It is seen that the recent El Nino has been accompanied by higher fluctuation in glacier coverage on Nevado Champara and the loss of glacier coverage on Cerro Tilata was very high during the past 16 years.Rise in snowline altitude of selected glaciers was very high after the 2015/16 El Nino.Increase in the area covered by snow and ice during the La Nina periods were not enough to cover the ice loss occurred during the previous El Nino events and the strongest El Nino in 2015/ 16 was followed by a significant loss of ice-covered areas in the tropical Andes.Freshwater resources in this region will be affected in the near future if the current trends in glacier decline continue.Adaptation strategies needs to be implemented to reduce the impacts of the continuing loss of glacierized on regional communities in the tropical Andean region.
基金Ecuador’s SENESCYT(Secretaría Nacional de Educación Superior,Ciencia,Tecnología e Innovación)Dutch Ministry of Foreign Affairs(DUPC Program at UNESCO-IHE).
文摘Aims The importance of quantifying carbon stocks in terrestrial ecosystems is crucial for determining climate change dynamics.However,the present regional assessments of carbon stocks in tropical grasslands are extrapolated to unsampled areas with a high degree of uncertainty and without considering the carbon and nitrogen composition of vegetation and soil along altitudinal ranges.This study aims to assess carbon and nitrogen concentrations in soil and vegetation,aboveground carbon stocks distribution and soil organic carbon stocks along an altitudinal range in the páramo region in the Ecuadorian Andes.Methods The vegetation inventory was conducted using 15×15 m sampling plots distributed in three altitudinal ranges.Based on the patterns exhibited by the dominant vegetation growth forms,biomass and soil were sampled to quantify the corresponding carbon and nitrogen concentrations.Subsequently,the aboveground live biomass along the páramo altitudinal range was estimated using allometric equations.Finally,soil and vegetation carbon stocks were estimated for the entire basin.Important Findings Altitudinal analysis supported a potential distribution of carbon and nitrogen concentrations in soil,litter and live tissues,where higher concentrations were found in the low altitudinal range mainly for tussocks and acaulescent rosettes.Cellulose in litter showed higher concentrations at low altitudinal ranges for acaulescent rosettes and cushions only.For the same growth forms,lignin patterns in litter were higher in high altitudinal ranges.Soil texture provided complementary information:high percentage of silt was highly correlated to high soil nitrogen and carbon concentration.Tussocks were found to be responsive to altitude with their,highest aboveground carbon stocks occurring at the low altitudinal range,but cushions and acaulescent rosettes responded differently.The established relationships among soil,vegetation and altitude shown in this study must be taken into account to estimate both aboveground and soil organic carbon stocks in páramo regions—such estimates will be considerably inaccurate if these relationships are ignored.
基金supported by Colciencias Doctoral funding (727-2015)Universidad del Rosario, through a teaching assistantship and a doctoral grant
文摘Data gaps and biases are two important issues that affect the quality of biodiversity information and downstream results.Understanding how best to fill existing gaps and account for biases is necessary to improve our current information most effectively.Two current main approaches for obtaining and improving data include(1)curation of biological collections,and(2)fieldwork.However,the comparative effectiveness of these approaches in improving biodiversity data remains little explored.We used the Flora de Bogota project to study the magnitude of change in species richness,spatial coverage,and sample coverage of plant records based on curation versus fieldwork.The process of curation resulted in a decrease in species richness(synonym and error removal),but it significantly increased the number of records per species.Fieldwork contributed to a slight increase in species richness,via accumulation of new records.Additionally,curation led to increases in spatial coverage,species observed by locality,the number of plant records by species,and localities by species compared to fieldwork.Overall,curationwas more efficient in producing new information compared to fieldwork,mainly because of the large number of records available in herbaria.We recommend intensive curatorial work as the first step in increasing biodiversity data quality and quantity,to identify bias and gaps at the regional scale that can then be targeted with fieldwork.The stepwise strategy would enable fieldwork to be planned more costeffectively given the limited resources for biodiversity exploration and characterization.
