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71.
In Lutzito catchment on Barro Colorado Island, Panama, extraordinarily high suspended‐sediment yields of 1–2 Mg ha?1 year?1 were generated despite the dense forest cover coinciding with erosion‐resistant soils. We hypothesized that ant mounding activity is an important zoogeomorphological mechanism in this area, providing relevant quantities of easily transportable material at the soil surface. To test this hypothesis, all ant mound material was collected collected for dry mass determination from thirty 4 m2 plots installed in the study area every 1–3 days during the 39‐day sampling period. Additionally, three ground‐nesting ant species responsible for mounds in the study area, Ectatomma ruidum, Trachymyrmex cornetzi and Strumigenys marginiventris, were identified. On the basis of the total of 1.38 kg of material collected in the wet season of 2011, the estimate for the whole 8 months wet season amounts to 725 kg ha?1. As this value is in the same order of magnitude as sediment output, it shows that ants may act as important ecosystem engineers and contribute to sediment production here by providing large quantities of fine‐grained, readily erodible material at the soil surface for subsequent transport to the streambed. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
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We used thermochemical equilibrium calculations to predict stabilities of pure rock-forming hydrous silicates on Venus' surface as a function of elevation, atmospheric H2O and SO2concentrations, and oxygen fugacity (fO2). About 50 different hydrous silicates were included in our calculations. We find that many of these are unstable on Venus's surface because of the low atmospheric H2O content of 30–45 parts per million by volume (ppmv) and the high surface temperatures (660 K on Maxwell Montes to 740 K in the plains). Hydrous Fe2+-bearing silicates are unstable due to oxidation to magnetite and/or hematite at the fO2of the near-surface atmosphere. Ca-bearing hydrous silicates are unstable because of sulfatization to anhydrite. Some Fe-free micas (e.g., eastonite, eastonite–phlogopite micas), and some alkali amphiboles might be stable on Venus' surface, especially in the lower temperature highlands. We discuss hydrous mineral formation in the interior and on the surface of Venus. We review the literature on mica and amphibole thermal decomposition and find that dehydration of phlogopitic micas and fibrous amphiboles produces (metastable) dehydroxylated anhydrides that decompose to more stable minerals at temperatures hundreds of degrees higher than the onset of dehydroxylation. These observations raise the possibility that anhydrides formed from hydrous silicates, which may have been present during a wetter period in Venus' history, may persist somewhere on Venus' present surface. We discuss experiments that could be used on future spacecraft missions to detect hydroxyl in rocks and hydrous silicates on Venus. Finally, we review estimates of the amount of water and OH (hydroxyl) in the Earth's mantle. Based on this review, we suggest that even if no hydrous silicates are stable on Venus, significant amounts of water are plausibly present in surface rocks as OH in nominally anhydrous minerals. 相似文献
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Matthias Jonas Katharina Fleischmann Andrey V. Ganopolski Jaroslav Krabec Uta Sauer Krzysztof Olendrzyński Vladimir K. Petoukhov Roderick W. Shaw 《Climatic change》1996,34(3-4):479-512
This paper describes a methodology that combines the outputs of (1) the Integrated Model to Assess the Greenhouse Effect (IMAGE Version 1.0) of the Netherlands National Institute of Public Health and Environmental Protection (RIVM) (given a greenhouse gas emission policy, this model can estimate the effects such as global mean surface air temperature change for a wide variety of policies) and (2) ECHAM-1/LSG, the Global Circulation Model (GCM) of the Max-Planck Institute for Meteorology in Hamburg, Germany. The combination enables one to calculate grid point surface air temperature changes for different scenarios with a turnaround time that is much quicker than that for a GCM. The methodology is based upon a geographical pattern of the ratio of grid point temperature change to global mean values during a certain period of the simulation, as calculated by ECHAM-1/LSG for the 1990 Scenarios A and D of the Intergovernmental Panel on Climate Change (IPCC). A procedure, based upon signal-to noise ratios in the outputs, enabled us to estimate where we have confidence in the methodology; this is at about 23% to 83% of the total of 2,048 grid points, depending upon the scenario and the decade in the simulation. It was found that the methodology enabled IMAGE to provide useful estimates of the GCM-predicted grid point temperature changes. These estimates were within 0.5K (0.25K) throughout the 100 years of a given simulation for at least 79% (74%) of the grid points where we are confident in applying the methodology. The temperature ratio pattern from Scenario A enabled IMAGE to provide useful estimates of temperature change within 0.5K (0.25K) in Scenario D for at least 88% (68%) of the grid points where we have confidence; indicating that the methodology is transferable to other scenarios. Tests with the Geophysical Fluid Dynamics Laboratory GCM indicated, however, that a temperature ratio pattern may have to be developed for each GCM. The methodology, using a temperature ratio pattern from the 1990 IPCC Scenario A and involving IMAGE, gave gridded surface air temperature patterns for the 1992 IPCC radiative-forcing Scenarios C and E and the RIVM emission Scenario B; none of these scenarios has been simulated by ECHAM-1/LSG. The simulations reflect the uncertainty range of a future warming.The work reported by the authors was carried out during their stay at the project Forestry and Climate Change of the International Institute for Applied Systems Analysis, Laxenburg, Austria. 相似文献
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Photo-acclimatisation by the algal endosymbionts of scleractinian corals to changes in environmental conditions may influence their density and/or the concentration of photosynthetic pigments, and hence coral brightness, on short time-scales. To examine coral pigmentation as a bioindicator of water quality, the brightness of massive corals was quantified using colour charts, concentrations of the pigment chlorophyll a and reflectance spectrometry in the field and with manipulative experiments. Along a water quality gradient, massive Porites became progressively lighter as nutrients decreased and irradiance increased. A laboratory experiment showed that Porites nubbins darkened within 25 days following exposure to reduced water quality. The results of a transplantation experiment of Porites nubbins in a manipulation incorporating multiple depths and zones of water quality confirmed colony brightness as a simple tool to monitor changes in marine water quality, provided effects due to other influences on pigmentation, e.g. seawater temperatures, are taken into consideration. 相似文献
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Abstract— The origin of the aubrite parent body (APB) and its relation to the enstatite chondrites is still unclear. Therefore we began a detailed chemical study of the aubrite Peña Blanca Spring. Bulk samples and mineral separates (oldhamite, troilite, alabandite, pyroxene) of Peña Blanca Spring were analyzed for major and trace elements by instrumental neutron activation analysis (INAA). In addition, a leaching experiment was performed on a powdered bulk sample to study the distribution of trace elements in aubrite minerals. The elemental abundances in Peña Blanca Spring are compared to abundances in EH-chondrites and EL-chondrites in an attempt to distinguish volatility related fractionations (evaporation, condensation) from planetary differentiation (melting and core formation). Low abundances of siderophile (e.g., Ir) and chalcophile (e.g., V) elements in bulk samples indicate that 25% (by mass) metal and about 6% (by mass) sulfide separated from an enstatite chondrite like-parent body to form a core and a residual mantle with aubrite composition. We argue that the high observed rare earth element (REE) abundances in oldhamite (>100 × EH-chondrite normalized) reflect REE incorporation into oldhamite during nebular condensation. Thus, oldhamite in aubrites is, at least in part, a relict phase as originally proposed by Lodders and Palme (1990). Some re-equilibration of CaS with silicates has, however, occurred, leading to partial redistribution of REE, as exemplified by the uptake of Eu by plagioclase. The distribution of the REE among aubritic minerals cannot be the result of fractional crystallization, which would occur if high degrees of partial melting took place on the APB. Instead, the REE distributions indicate incomplete equilibrium of oldhamite and other phases. Therefore, a short non-equlibrium melting episode led to segregation of metal and sulfides. 相似文献
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This review provides an introduction to presolar grains - preserved stardust from the interstellar molecular cloud from which our solar system formed - found in primitive meteorites. We describe the search for the presolar components, the currently known presolar mineral populations, and the chemical and isotopic characteristics of the grains and dust-forming stars to identify the grains’ most probable stellar sources. 相似文献
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Validation of official erosion modelling based on high‐resolution radar rain data by aerial photo erosion classification 
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下载免费PDF全文 Franziska Katharina Fischer Michael Kistler Robert Brandhuber Harald Maier Melanie Treisch Karl Auerswald 《地球表面变化过程与地形》2018,43(1):187-194
The universal soil loss equation (USLE) is the most frequently applied erosion prediction model and it is also implemented as an official decision‐making instrument for agricultural regulations. The USLE itself has been already validated using different approaches. Additional errors, however, arise from input data and interpolation procedures that become necessary for field‐specific predictions on a national scale for administrative purposes. In this study, predicted event soil loss using the official prediction system in Bavaria (Germany) was validated by comparison with aerial photo erosion classifications of 8100 fields. Values for the USLE factors were mainly taken from the official Bavarian high‐resolution (5 × 5 m2) erosion cadastre. As series of erosion events were examined, the cover and management factor was replaced by the soil loss ratio. The event erosivity factor was calculated from high‐resolution (1 × 1 km2, 5 min), rain gauge‐adjusted radar rain data (RADOLAN). Aerial photo erosion interpretation worked sufficiently well and average erosion predictions and visual classifications correlated closely. This was also true for data broken down to individual factors and different crops. There was no reason to assume a general invalidity of the USLE and the official parametrization procedures. Event predictions mainly suffered from errors in the assumed crop stage period and tillage practices, which do not reflect interannual and farm‐specific variation. In addition, the resolution of radar data (1 km2) did not seem to be sufficient to predict short‐term erosion on individual fields given the strong spatial gradients within individual rains. The quality of the input data clearly determined prediction quality. Differences between USLE predictions and observations are most likely caused by parametrization weaknesses but not by a failure of the model itself. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献