Late Quaternary vegetation and climate dynamics in central-eastern Brazil: insights from a ~35k cal a bp peat record in the Cerrado biome     

Ingrid Horák-Terra  Antonio Martínez Cortizas  Cynthia Fernandes Pinto Da Luz  Alexandre Christófaro Silva  Tim Mighall  Plínio Barbosa De Camargo  Carlos Victor Mendonça-Filho  Paulo Eduardo De Oliveira  Francisco Willian Cruz  Pablo Vidal-Torrado 《第四纪科学杂志》2020,35(5):664-676

The late Quaternary evolution of central-eastern Brazil has been under-researched. Questions remain as to the origin of the Cerrado, a highly endangered biome, and other types of vegetation, such as the Capões – small vegetation islands of semi-deciduous and mountain forests. We investigated the factors that influenced the expansion and contraction of the Cerrado and Capões during the late Quaternary (last ~35 ka), using a multi-proxy approach: stable isotopes (δ¹³C, δ¹⁵N), geochemistry, pollen and multivariate statistics derived from a peat core (Pinheiro mire, Serra do Espinhaço Meridional). Five major shifts in precipitation, temperature, vegetation and landscape stability occurred at different timescales. Our study revealed that changes in the South Atlantic Convergence Zone (SACZ) seem to have been coeval with these shifts: from the Late Glacial Maximum to mid-Holocene the SACZ remained near (~29.6 to ~16.5k cal a bp ) and over (~16.5 to ~6.1 k cal a bp ) the study area, providing humidity to the region. This challenges previous research which suggested that climate was drier for this time period. At present, the Capões are likely to be a remnant of a more humid climate; meanwhile, the Cerrado biome seems to have stablished in the late Holocene, after ~3.1 k cal a bp .  相似文献   

An extreme wave event in eastern Yucatán,Mexico: Evidence of a palaeotsunami event during the Mayan times     

Javier Lario  Chris Spencer  Teresa Bardají  Ángel Marchante  Victor H. Garduño-monroy  Jorge Macias  Sergio Ortega 《Sedimentology》2020,67(3):1481-1504

The Yucatán Peninsula, Mexico, has typically been considered a tectonically stable region with little significant seismic activity. The region though, is one that is regularly affected by hurricanes. A detailed survey of ca 100 km of the eastern Yucatán and Cozumel coast identified the presence of ridges containing individual boulders measuring >1 m in length. The boulder ridges reach 5 m in height and their origin is associated with extreme wave event activity. Previously modelled tsunami waves from known seismically active zones in the region (Muertos Thrust Belt and South Caribbean Deformed Belt) are not of sufficient scale in the area of the Yucatán Peninsula to have produced the boulder ridges recorded in this study. The occurrence of hurricanes in this region is more common, but two of the most destructive (Hurricane Gilbert 1988 and Hurricane Wilma 2005) produced coastal waves too small to have created the ridges recorded here. In this paper, a new tsunami model with a source area located on the Motagua/Swan Island Fault System has been generated that indicates a tsunami event may have caused the extreme wave events that resulted in the deposition of the boulder ridges.  相似文献   

Icefish Adaptations to Climate Change on the South Georgia Island Shelf (Sub-Antarctic)     

Ryszard Traczyk  Victor Benno Meyer-Rochow  Robert M. Hughes 《Ocean Science Journal》2020,55(2):303-319

Icefish populations continue to decline. Historical as well as current over-exploitations of stocks aggravated by climate change are frequently seen as res  相似文献   

Dissolved organic carbon in permafrost regions: A review     

Qiang MA  Huijun JIN  Congrong YU  Victor F.BENSE 《中国科学:地球科学(英文版)》2019,(2)

A large quantity of organic carbon(C) is stored in northern and elevational permafrost regions. A portion of this large terrestrial organic C pool will be transferred by water into soil solution(～0.4 Pg C yr~(-1))(1 Pg=10~(15) g), rivers (～0.06 Pg C yr~(-1)),wetlands, lakes, and oceans. The lateral transport of dissolved organic carbon(DOC) is the primary pathway, impacting river biogeochemistry and ecosystems. However, climate warming will substantially alter the lateral C shifts in permafrost regions.Vegetation, permafrost, precipitation, soil humidity and temperature, and microbial activities, among many other environmental factors, will shift substantially under a warming climate. It remains uncertain as to what extent the lateral C cycle is responding,and will respond, to climate change. This paper reviews recent studies on terrestrial origins of DOC, biodegradability, transfer pathways, and modelling, and on how to forecast of DOC fluxes in permafrost regions under a warming climate, as well as the potential anthropogenic impacts on DOC in permafrost regions. It is concluded that:(1) surface organic layer, permafrost soils,and vegetation leachates are the main DOC sources, with about 4.72 Pg C DOC stored in the topsoil at depths of 0–1 m in permafrost regions;(2) in-stream DOC concentrations vary spatially and temporally to a relatively small extent (1–60 mg C L~(-1)) and annual export varies from 0.1–10 g C m~(-2) yr~(-1);(3) biodegradability of DOC from the thawing permafrost can be as high as 71%, with a median at 52%;(4) DOC flux is controlled by multiple factors, mainly including vegetation, soil properties,permafrost occurrence, river discharge and other related environmental factors, and(5) many statistical and process-based models have been developed, but model predictions are inconsistent with observational results largely dependent on the individual watershed characteristics and future discharge trends. Thus, it is still difficult to predict how future lateral C flux will respond to climate change, but changes in the DOC regimes in individual catchments can be predicted with a reasonable reliability. It is advised that sampling protocols and preservation and analysis methods should be standardized, and analytical techniques at molecular scales and numerical modeling on thermokarsting processes should be prioritized.  相似文献   

Development,urban planning and political decisions. A triad that built territories at risk     

Lara  Alejandro  Bucci  Felipe  Palma  Cristobal  Munizaga  Juan  Montre-Águila  Victor 《Natural Hazards》2021,109(2):1935-1957

Natural Hazards - Chilean geography exposes the country to high-level risks such as earthquakes and tsunamis. The disasters of 1930, 1960, 2010, and 2014 testify to the continuous link between...  相似文献   

Quantitative assessment of landslide hazard along transportation lines using historical records   总被引：2，自引：1，他引：1  

Pankaj Jaiswal  Cees J. van Westen  Victor Jetten 《Landslides》2011,8(3):279-291

In this paper, a quantitative landslide hazard model is presented for transportation lines, with an example for a road and railroad alignment, in parts of Nilgiri hills in southern India. The data required for the hazard assessment were obtained from historical records available for a 21-year period from 1987 to 2007. A total of 901 landslides from cut slopes along the railroad and road alignment were included in the inventory. The landslides were grouped into three magnitude classes based on the landslide type, volume, scar depth, and run-out distance. To calculate landslide hazard, we estimated the total number of individual landslides per kilometer of the (rail) road for different return periods, based on the relationship between past landslides (recorded in our database) and triggering events. These were multiplied by the probability that the landslides belong to a given magnitude class. This gives the hazard for a given return period expressed as the number of landslides of a given magnitude class per kilometer of (rail) road. The relationship between the total number of landslides and the return period was established using a Gumbel distribution model, and the probability of landslide magnitude was obtained from frequency–volume statistics. The results of the analysis indicate that the total number of landslides, from 1- to 50-year return period, varies from 56 to 197 along the railroad and from 14 to 82 along the road. In total, 18 hazard scenarios were generated using the three magnitude classes and six return periods (1, 3, 5, 15, 25, and 50 years). The hazard scenarios derived from the model form the basis for future direct and indirect landslide risk analysis along the transportation lines. The model was validated with landslides that occurred in the year 2009.  相似文献   

Preliminary Evidence for Iodate Reduction in Bottom Waters of the Gulf of Mexico During an Hypoxic Event     

Piers Chapman  Victor W. Truesdale 《Aquatic Geochemistry》2011,17(4-5):671-695

The distributions of iodate and total inorganic iodine concentrations in the waters on the Texas?CLouisiana shelf in April, June, and August 2004 are described. Iodine?Csalinity graphs show three-end-member mixing involving onshore and offshore surface waters and deep offshore water. The April survey showed simple mixing on the surface, but in the later surveys, iodate concentrations were often much lower than predicted by the mixing curve while those for total inorganic iodine were higher. This demonstrated both iodate reduction in the water and iodide addition, although individual samples did not show equivalent speciation changes. Hydrographically, the system consists of the estuaries of the Mississippi and Atchafalaya rivers as they spill onto the shelf. The waters are stratified seasonally by a robust halocline, leading to hypoxia in the bottom waters from the combined effect of restricted downward diffusion of oxygen and the sinking of the luxuriant growth of phytoplankton induced by riverine nutrient supply. The distributions of iodate and total inorganic iodine are, therefore, interpreted in terms of water?Csediment interaction as the shelf shoals to the north.  相似文献   

The study of metal contamination in urban topsoils of Mexico City using GIS   总被引：1，自引：0，他引：1  

María Teresa Rodríguez-Salazar  Ofelia Morton-Bermea  Elizabeth Hernández-Álvarez  Rufino Lozano  Victor Tapia-Cruz 《Environmental Earth Sciences》2011,62(5):899-905

This research presents and discusses information concerning the spatial distribution of heavy metals (Pb, Cu, Zn, Ba, Co, Cr, Ni and V) in the urban environments of Mexico City using geographical information system and statistical analysis. Superficial soil samples (n = 146) were analyzed. The highest contamination indices were found in the north and center zone of the metropolitan area. In contrast, the surrounding rural fields show a lower impact grade. The higher concentrations of Pb, Cu, Zn and Ba were observed as being related to high vehicular traffic, nevertheless other elements such as Co, Cr, Ni and V do not show anthropogenic influence and their content can be attributed to the parental rock. The results are compared with previous surveys carried out in 2003 in order to evaluate temporal deposition trends. No changes were found on reported concentrations except for Cu and Zn, whose concentration has increased in later years. The results suggest that spatial distribution analysis and results in comparison with previous studies could be useful for the management and sustainable development of the metropolitan area of Mexico City.  相似文献   

http://www.sciencedirect.com/science/article/pii/S1674987111000594     

Victor D. Mats  Tatiana I. Perepelova 《地学前缘(英文版)》2011,2(3):349-365

A new model is suggested for the history of the Baikal Rift,in deviation from the classic two-stage evolution scenario,based on a synthesis of the available data from the Baikal Basin and revised correlation between tectonic-lithological-stratigraphic complexes(TLSC) in sedimentary sections around Lake Baikal and seismic stratigraphic sequences(SSS) in the lake sediments.Unlike the previous models,the revised model places the onset of rifting during Late Cretaceous and comprises three major stages which are subdivided into several substages.The stages and the substages are separated by events of tectonic activity and stress reversal when additional compression produced folds and shear structures.The events that mark the stage boundaries show up as gaps,unconformities,and deformation features in the deposition patterns. The earliest Late Cretaceous-Oligocene stage began long before the India-Eurasia collision in a setting of diffuse extension that acted over a large territory of Asia.The NW-SE far-field pure extension produced an NE-striking half-graben oriented along an old zone of weakness at the edge of the Siberian craton.That was already the onset of rift evolution recorded in weathered lacustrine deposits on the Baikal shore and in a wedge-shaped acoustically transparent seismic unit in the lake sediments.The second stage spanning Late Oligocene-Early Pliocene time began with a stress change when the effect from the Eocene India-Eurasia collision had reached the region and became a major control of its geodynamics.The EW and NE transpression and shear from the collisional front transformed the Late Cretaceous half-graben into a U-shaped one which accumulated a deformed layered sequence of sediments.Rifting at the latest stage was driven by extension from a local source associated with hot mantle material rising to the base of the rifted crust.The asthenospheric upwarp first induced the growth of the Baikal dome and the related change from finer to coarser molasse deposition.With time,the upwarp became a more powerful stress source than the collision,and the stress vector returned to the previous NW-SE extension that changed the rift geometry back to a half-graben. The layered Late Pliocene-Quaternary subaerial tectonic-lithological-stratigraphic and the Quaternary submarine seismic stratigraphic units filling the latest half-graben remained almost undeformed.The rifting mechanisms were thus passive during two earlier stages and active during the third stage. The three-stage model of the rift history does not rule out the previous division into two major stages but rather extends its limits back into time as far as the Maastrichtian.Our model is consistent with geological, stratigraphic,structural,and geophysical data and provides further insights into the understanding of rifting in the Baikal region in particular and continental rifting in general.  相似文献   

Surficial geophysical deduction of the geomaterial and aquifer distributions at Ngor-Okpala local government area of Imo State, South Eastern Nigeria     

Obianwu I. Victor  Chimezie C. Innocent  Akpan E. Anthony  George N. Jimmy 《Central European Journal of Geosciences》2011,3(4):368-374

Twenty seven vertical electrical sounding (VES) profiles surrounding four known traverses were obtained in Ngor-Okpala local government area of Imo state to examine the subsurface geomaterials and the associated groundwater potential. The VES data, constrained by borehole data, provided useful information about the subsurface hydrogeologic and lithologic conditions. From the validated interpretation, the area assessed has loamy soil, medium grained sands, well-sorted medium-grained/gravelly sands and river sand as the lithologic succession from top to the bottom of the depth penetrated. The aquifers in the area were found in the medium-grained sands and well-sorted medium-coarse-grained sands. The aquifer depth for all-season groundwater that would be devoid of draw-down can be found at a depth range of 42–50 m. The resistivity maps of selected depths exhibit sharp resistivity changes at depth due mainly to undulating subsurface topography. A map of the distribution of the kσ-values shows that good quality groundwater can be found in most parts of the area.  相似文献