Multidisciplinary approach of the hyperarid desert of Pampas de La Joya in southern Peru as a new Mars-like soil analog     

Julio E. Valdivia-Silva  Rafael Navarro-González  Lauren E. Fletcher  Reneé Condori-Apaza 《Geochimica et cosmochimica acta》2011,75(7):1975-1991

The distribution of living organisms, organic matter, and chemical properties in Mars-like environments on Earth can be used as a model to guide the investigation of possible habitable environments on Mars. This work aims to demonstrate that the place known informally as the “Mar de Cuarzo” (Sea of Quartz) in the Pampas de La Joya desert southern Peru (between 16°S and 17°S latitude), contains soils with characteristics similar to those found on the Martian surface. Using a multidisciplinary approach, we studied the environmental data, geology, organic matter content, oxidant activity, and microbiology of this area. Our data show that (1) Mar de Cuarzo is a hyper arid area with a lower concentration of organic matter than those found in the Mars-like soils from Yungay area (Atacama Desert in Chile), while at the same time having, comparable extreme environmental conditions, and very low levels of microorganisms. (2) The detrital components of the soils come essentially from the Andean volcanic chain and local outcrops of Precambrian gneisses and Cretaceous granitic batholiths. (3) The presence of microclimates, geomorphological features, and the high influence of the “El Niño Southern Oscillation (ENSO)” allowed the formation of exotic and heterogeneous chemical deposits in these soils, including iron oxides, sulfates, and other evaporites. (4) Thermal volatilization in these soils (using methods similar to the Viking and Phoenix instruments) shows high oxidant activity. (5) Labeled release experiment (similar to the Viking instrument) shows high degradation of nutrients added in these soils.Altogether, the Mar de Cuarzo area in the Pampas de La Joya is an interesting place for astrobiological studies as a new analog to Mars, and for comparative analyses with other hyperarid analogs as Yungay.  相似文献   

Recurrent spring‐fed rivers in a Middle to Late Pleistocene semi‐arid grassland: Implications for environments of early humans in the Lake Victoria Basin,Kenya          下载免费PDF全文

Emily J. Beverly  Steven G. Driese  Daniel J. Peppe  Cara R. Johnson  Lauren A. Michel  J. Tyler Faith  Christian A. Tryon  Warren D. Sharp 《Sedimentology》2015,62(6):1611-1635

The effect of changing palaeoclimate and palaeoenvironment on human evolution during the Pleistocene is debated, but hampered by few East African records directly associated with archaeological sites prior to the Last Glacial Maximum. Middle to Late Pleistocene deposits on the shoreline of eastern Lake Victoria preserve abundant vertebrate fossils and Middle Stone Age arte‐facts associated with riverine tufas at the base of the deposits, which are ideal for palaeoenvironmental reconstructions. New data from tufas identified on Rusinga Island and on the mainland near Karungu, Kenya are provided from outcrop, thin sections, mineralogical, stable isotopic and U‐series dating analyses. Tufa is identified in four sites: Nyamita (94·0 ± 3·3 and 111·4 ± 4·2 ka); Kisaaka, Aringo (455 ± 45 ka); and Obware. The age ranges of these tufa deposits demonstrate that spring‐fed rivers were a recurrent, variably preserved feature on the Pleistocene landscape for ca 360 kyr. Poor sorting of clastic facies from all sites indicates flashy, ephemeral discharge, but these facies are commonly associated with barrage tufas, paludal environments with δ¹³C values of ca 10‰ indicative of C₃ plants and fossil Hippopotamus, all of which indicate a perennial water source. Other tufa deposits from Nyamita, Obware and Aringo have a mixed C₃/C₄ signature consistent with a semi‐arid C₄ grassland surrounding these spring‐fed rivers. The δ¹⁸O values of tufa from Nyamita are on average ca 1‰ more negative than calcite precipitated from modern rainfall in the region, suggesting greater contribution of depleted monsoonal input, similar to the Last Glacial Maximum. Microdebitage and surface‐collected artefacts indicate that early modern humans were utilizing these spring‐fed rivers. The presence of spring?fed rivers would have afforded animals a reliable water source, sustaining a diverse plant and animal community in an otherwise arid environment.  相似文献   

Influence of human pressure on forest resources and productivity at stand and tree scales: The case study of Yunnan pine in SW China     

Thomas M.HINCKLEY  Phillip CHI  Keala HAGMANN  Stevan HARRELL  Amanda Henck SCHMIDT  Lauren URGENSON  Zong-yong ZENG 《山地科学学报》2013,10(5):824-832

This paper examines human impact on stands and individual trees of Pinus yunnanensis growing near the small mountain villages of Pianshui and Yangjuan in southwestern Sichuan Province,China.In an effort to assess whether use of these forests was sustainable,we examined the effects of human use in two ways.First,we directly measured the effect of cutting branches,for fuel and fodder,on tree growth.We hypothesized that branch cutting would negatively impact tree growth.We established 12 plots on four hills and compared 14 pairs of trees,one tree in each pair with an apparently full crown and the other with a considerable portion of the crown removed.Second,we assessed stand and tree properties over a 500 m elevation gradient above the villages where we hypothesized that as elevation increases,stand and tree properties should show fewer human impacts.Although extensive branch cutting reduced the live crown,tree height and diameter,compensatory processes likely enabled trees to recover and to add basal area increments(BAIs) similar to those added by trees with full crowns.Trees and stands close to villages showed less growth and lower basal areas,respectively,than stands and trees at intermediate or distant elevations from villages.Areas relatively close to the villages showed considerable effects of human-related disturbances such as branch cutting,grazing,tree and shrub removal,losses of litter,and human and animal trails.Such areas had increased soil erosion and often loss of the ‘A’ horizon.Stands close to villages had younger trees,lower stand basal areas,smaller basal area increments,and more stumps.Our results suggest an increasingly vulnerable interface between occupants of these two villages and their surrounding forests.  相似文献   

Influence of Alluvial Morphology on Upscaled Hydraulic Conductivity          下载免费PDF全文

Sanjeev Kumar Jha  Gregoire Mariethoz  George Mathews  John Vial  Bryce F.J. Kelly 《Ground water》2016,54(3):384-393

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Reverse Water‐Level Fluctuations Associated with Fracture Connectivity     

Christopher A. Gellasch  Herbert F. Wang  Kenneth R. Bradbury  Jean M. Bahr  Lauren L. Lande 《Ground water》2014,52(1):105-117

Reverse water‐level fluctuations (RWFs), a phenomenon in which water levels rise briefly in response to pumping, were detected in monitoring wells in a fractured siliciclastic aquifer system near a deep public supply well. The magnitude and timing of RWFs provide important information that can help interpret aquifer hydraulics near pumping wells. A RWF in a well is normally attributed to poroelastic coupling between the solid and fluid components in an aquifer system. In addition to revealing classical pumping‐induced poroelastic RWFs, data from pressure transducers located at varying depths and distances from the public supply well suggest that the RWFs propagate rapidly through fractures to influence wells hundreds of meters from the pumping well. The rate and cycling frequency of pumping is an important factor in the magnitude of RWFs. The pattern of RWF propagation can be used to better define fracture connectivity in an aquifer system. Rapid, cyclic head changes due to RWFs may also serve as a mechanism for contaminant transport.  相似文献   

Change and variability in sea ice during the 2007–2008 Canadian International Polar Year program     

David G. Barber  Matthew G. Asplin  Richard L. Raddatz  Lauren M. Candlish  Scot Nickels  Stephanie Meakin  Klaus P. Hochheim  Jennifer V. Lukovich  Ryan J. Galley  Simon J. Prinsenberg 《Climatic change》2012,115(1):115-133

In this paper we describe sea ice change and variability during the Canadian International Polar Year (IPY) program and examine several regional and hemispheric causes of this change. In a companion paper (Barber et al., Climate Change 2012) we present an overview of the consequences of this observed change and variability on ecosystem function, climatically relevant gas exchange, habitats of primary and apex predators, and impacts on northern peoples. Sea ice-themed research projects within the fourth IPY were designed to be among the most diverse international science programs. They greatly enhanced the exchange of Inuit knowledge and scientific ideas across nations and disciplines. This interdisciplinary and cultural exchange helped to explain and communicate the impacts of a transition of the Arctic Ocean and ecosystem to a seasonally ice-free state, the commensurate replacement of perennial with annual sea ice types and the causes and consequences of this globally significant metamorphosis. This paper presents a synthesis of scientific sea ice research and traditional knowledge results from Canadian-led IPY projects between 2007 and 2009. In particular, a summary of sea ice trends, basin-wide and regional, is presented in conjunction with Inuit knowledge of sea ice, gathered from communities in northern Canada. We focus on the recent observed changes in sea ice and discuss some of the causes of this change including atmospheric and oceanic forcing of both dynamic and thermodynamic forcing on the ice. Pertinent results include: 1) In the Amundsen Gulf, at the western end of the Northwest Passage, open water persists longer than normal and winter sea ice is thinner and more mobile. 2) Large areas of summer sea ice are becoming heavily decayed during summer and can be broken up by long-period waves being generated in the now extensive open water areas of the Chukchi Sea. 3) Cyclones play an important role in flaw leads??regions of open water between pack ice and land-fast ice. They delay the formation of new ice and the growth of multi-year ice. 4) Feedbacks involving the increased period of open water, long-period wave generation, increased open-ocean roughness, and the precipitation of autumn snow are all partially responsible for the observed reduction in multiyear sea ice. 5) The atmosphere is observed as remaining generally stable throughout the winter, preventing vertical entrainment of moisture above the surface.  相似文献   

Geochemistry and mineral chemistry of pyroxenite xenoliths and host volcanic alkaline rocks from north west of Marand (NW Iran)     

Khezerlou  Ali Akbar  Amel  Nasir  Gregoire  Michel  Moayyed  Mohsen  Jahangiri  Ahmad 《Mineralogy and Petrology》2017,111(6):865-885

Mineralogy and Petrology - The Plio-Quaternary alkaline volcanic rocks from the northwest of Marand (NW Iran) consist of trachy-andesites, trachy-basaltic andesites, leucite-tephrites and...  相似文献   

Author's reply to discussion on: probabilistic risk analysis of structural impact in seismic events for linear and nonlinear systems          下载免费PDF全文

J. Geoffrey Chase  Florent Boyer  Geoffrey W. Rodgers  Gregoire Labrosse  Gregory A. MacRae 《地震工程与结构动力学》2015,44(3):495-498

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Constraints on the anhydrous precursor mineralogy of fine-grained materials in CM carbonaceous chondrites     

Lauren BROWNING  William BOURCIER 《Meteoritics & planetary science》1998,33(6):1213-1220

Abstract— Mass balance calculations were performed to constrain the precursor mineralogy of fine-grained, aqueously altered materials in CM carbonaceous chondrites. The bulk composition of unaltered fine-grained CM materials was estimated and then used to calculate phase proportions for several different initial assemblages. All starting assemblages contain relic, unaltered Fe-poor phases observed in CM chondrites, plus iron sulfides. The original sources of Fe are uncertain, because most primary Fe-rich phases were aqueously altered. Four endmember assemblages are considered by adding Fe metal, Fa₅₀, Fa₁₀₀, or FeO-rich amorphous materials to the Fe-poor phases. These represent the Fe-bearing phases in CM and/or other chondritic classes. Results indicate that the precursor CM assemblage may have contained a maximum of either ～10 vol% Fe metal, 57 vol% Fa₅₀, ～28 vol% Fa₁₀₀, or 37.0 vol% FeO-rich amorphous materials. Additional calculations were performed in which Fe metal was added to the various FeO-bearing assemblages. These reveal a strong positive correlation between the forsterite/(forsterite + enstatite) ratio and the amount of FeO-bearing phases that coexist with metal. If forsterite was more abundant than low-Ca pyroxene in the accreted CM materials, then these materials must have also contained significant amounts of FeO-rich phases (e.g., at least 36 vol% Fa₅₀, 10 vol% Fa₁₀₀, or 17 vol% FeO-bearing glasses). Calculated mineral proportions suggest that intact calcium-aluminum-rich inclusions (CAIs) represent only about one-half of the original CAI budget, which is consistent with previous hypotheses that the initial CAI contents of CM and CO chondrites were similar. Some similarities exist between the primary CM assemblages calculated here and the mineralogies of other chondrite classes, but the initial CM materials do not appear to be represented in our meteorite inventory.  相似文献   

Conduit properties and karstification in the unconfined Floridan aquifer   总被引：3，自引：0，他引：3  

Screaton E  Martin JB  Ginn B  Smith L 《Ground water》2004,42(3):338-346

Exchange of water between conduits and matrix is an important control on regional chemical compositions, karstification, and quality of ground water resources in karst aquifers. A sinking stream (Santa Fe River Sink) and its resurgence (River Rise) in the unconfined portion of the Floridan Aquifer provide the opportunity to monitor conduit inflow and outflow. The use of temperature as a tracer allows determination of residence times and velocities through the conduit system. Based on temperature records from two high water events, flow is reasonably represented as pipe flow with a cross-sectional area of 380 m2, although this model may be complicated by losses of water from the conduit system at higher discharge rates. Over the course of the study year, the River Rise discharged a total of 1.9 x 10(7) m3 more water than entered the River Sink, reflecting net contribution of ground water from the matrix into the conduit system. However, as River Sink discharge rates peaked following three rainfall events during the study period, the conduit system lost water, presumably into the matrix. Surface water in high flow events is typically undersaturated with respect to calcite and thus may lead to dissolution, depending on its residence time in the matrix. A calculation of local denudation is larger than other regional estimates, perhaps reflecting return of water to conduits before calcite equilibrium is reached. The exchange of matrix and conduit water is an important variable in karst hydrology that should be considered in management of these water resources.  相似文献