Hydrogen peroxide on Mars: evidence for spatial and seasonal variations     

Th Encrenaz  B Bézard  M.J Richter  S.K Atreya  S Lebonnois  F Forget 《Icarus》2004,170(2):424-429

Hydrogen peroxide (H₂O₂) has been suggested as a possible oxidizer of the martian surface. Photochemical models predict a mean column density in the range of 10¹⁵-10¹⁶ cm⁻². However, a stringent upper limit of the H₂O₂ abundance on Mars (9×10¹⁴ cm⁻²) was derived in February 2001 from ground-based infrared spectroscopy, at a time corresponding to a maximum water vapor abundance in the northern summer (30 pr. μm, Ls=112°). Here we report the detection of H₂O₂ on Mars in June 2003, and its mapping over the martian disk using the same technique, during the southern spring (Ls=206°) when the global water vapor abundance was ∼10 pr. μm. The spatial distribution of H₂O₂ shows a maximum in the morning around the sub-solar latitude. The mean H₂O₂ column density (6×10¹⁵ cm⁻²) is significantly greater than our previous upper limit, pointing to seasonal variations. Our new result is globally consistent with the predictions of photochemical models, and also with submillimeter ground-based measurements obtained in September 2003 (Ls=254°), averaged over the martian disk (Clancy et al., 2004, Icarus 168, 116-121).  相似文献   

Spatial patterns of suspended sediment yields in a humid tropical watershed in Costa Rica     

Jagdish Krishnaswamy  Daniel D. Richter  Patrick N. Halpin  Michael S. Hofmockel 《水文研究》2001,15(12):2237-2257

An Erratum has been published for this article in Hydrological Processes 16(5) 2002, 1130–1131. Humid tropical regions are often characterized by extreme variability of fluvial processes. The Rio Terraba drains the largest river basin, covering 4767 km², in Costa Rica. Mean annual rainfall is 3139±419_sd mm and mean annual discharge is 2168±492_sd mm (1971–88). Loss of forest cover, high rainfall erosivity and geomorphologic instability all have led to considerable degradation of soil and water resources at local to basin scales. Parametric and non‐parametric statistical methods were used to estimate sediment yields. In the Terraba basin, sediment yields per unit area increase from the headwaters to the basin mouth, and the trend is generally robust towards choice of methods (parametric and LOESS) used. This is in contrast to a general view that deposition typically exceeds sediment delivery with increase in basin size. The specific sediment yield increases from 112±11·4_sd t km^?2 year^?1 (at 317·9 km² on a major headwater tributary) to 404±141·7_sd t km^?2 year^?1 (at 4766·7 km²) at the basin mouth (1971–92). The analyses of relationships between sediment yields and basin parameters for the Terraba sub‐basins and for a total of 29 basins all over Costa Rica indicate a strong land use effect related to intensive agriculture besides hydro‐climatology. The best explanation for the observed pattern in the Terraba basin is a combined spatial pattern of land use and rainfall erosivity. These were integrated in a soil erosion index that is related to the observed patterns of sediment yield. Estimated sediment delivery ratios increase with basin area. Intensive agriculture in lower‐lying alluvial fans exposed to highly erosive rainfall contributes a large part of the sediment load. The higher elevation regions, although steep in slope, largely remain under forest, pasture, or tree‐crops. High rainfall erosivity (>7400 MJ mm ha^?1 h^?1 year ^?1) is associated with land uses that provide inadequate soil protection. It is also associated with steep, unstable slopes near the basin mouth. Improvements in land use and soil management in the lower‐lying regions exposed to highly erosive rainfall are recommended, and are especially important to basins in which sediment delivery ratio increases downstream with increasing basin area. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

The Younger Dryas and Holocene climate record of a stalagmite from Hölloch Cave (Bavarian Alps,Germany     

Georg Wurth  Stefan Niggemann  Detlev K. Richter  Augusto Mangini 《第四纪科学杂志》2004,19(3):291-298

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Promotion zum Dr. rer. nat. an den Technischen Hochschulen und Bergakademien     

M. Richter 《International Journal of Earth Sciences》1938,29(7-8):596-596

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Knowledge based systems for risk assessment of the subsurface of contaminated sites     

S. Heynisch  A. Pekdeger  B. Richter  M. -Th. Schafmeister  W. Skala 《Mathematical Geology》1994,26(4):505-517

Computer-based risk evaluation methods are practical tools to compare automatically and evaluate contaminated sites. HYDRISK is an example of adequate knowledge-based systems: HYDRISK evaluates hydrogeological properties and chemical criteria relevant to contaminant transport with respect to the necessary remedial actions. It works at a high investigative level and enables geologists and engineers to draw differentiated conclusions for selecting remediation methods for the contaminated site. HYDRISK emphasizes space and time dependent aspects of the contaminant transport. It is supported by a geographic information system (GIS) to display the evaluation results. Some ideas on considering the spatiotemporal variability of relevant parameters by means of geostatistical methods and numerical models will be given.  相似文献   

Infrared spectroscopy of Triassic conodonts: a new tool for assessing conodont diagenesis     

Sheila Nöth  Detlev K. Richter 《地学学报》1992,4(6):668-675

The Fourier transform infrared spectra of individual conodonts with various CAI values indicate definite changes in conodont francolite during diagenesis. Steady decarbonation can be observed in the increasing intensity of the band with the wavenumber 2340 an^-1, which is assigned to trapped molecular CO₂. Carbon dioxide originates from decomposing CO^2-₃-ions occupying the B-site in francolite. Furthermore, the intensity of the water-deformation band at 1644 cm^-1 decreases with higher CAI values. These changes of intensity can be quantified by calculating the maximum extinction (E_max) for the corresponding absorption maxima and correlated with the CAI. Unaltered conodonts have a relative variable water 'content' and very little CO₂. Up to a CAI value of 4 conodont francolite continuously expells water and carbon dioxide is trapped. Conodonts with CAI = 5 have similar water 'contents' to CAI = 4 conodonts, but decarbonation continues to take place during this stage of diagenesis.  相似文献   

Sequestration of a Biologically Labile Organic Carbon in Soils by Humified Organic Matter     

Allessandro Piccolo  Riccardo Spaccini  Rolf Nieder  Joerg Richter 《Climatic change》2004,67(2-3):329-343

In a long-term (one year) experiment, a sandy Podzol and a silty-loamy Loess soil were treated with labile (polysaccharides, AG) and stable (mature compost, CMP, and two humic acids from compost, HAC, and lignite, HAL) organic matter and the organic carbon (OC) lost by mineralization was periodically evaluated. The stable materials alone induced a significant reduction of OC losses in Podzol CMP <, HAL, <, HAC, Control), whereas the same treatments, except for CMP, produced an OC loss larger than control in Loess. This was attributed to the diverse textural and physical status of the two soils. The added stable organic matter became protected in the Podzol soil within the aggregates formed by the interaction with the coarse inorganic phase, while it was more easily decomposed in the Loess soils due to the strength of the native humic-clay complexes. In both soils, when the stable organic materials were mixed with polysaccharides (AG), the OC losses from this labile fraction were significantly reduced, being CMP more OC sequestering than HAC and HAL, in the order. These results confirmed that labile organic matter in soils can be protected from biodegradation by repartition into the hydrophobic domains of the stable, humified organic matter. This study suggests that mature compost and humic acids may usefully integrate management practices aimed to sequester organic carbon in soils.  相似文献   

Towards a better understanding of magnesium-isotope ratios from marine skeletal carbonates   总被引：2，自引：0，他引：2  

Dorothee Hippler  Dieter Buhl  Detlev K. Richter 《Geochimica et cosmochimica acta》2009,73(20):6134-2836

This study presents magnesium stable-isotope compositions of various biogenic carbonates of several marine calcifying organisms and an algae species, seawater samples collected from the western Dutch Wadden Sea, and reference materials. The aim of this study is to explore the influence of mineralogy, taxonomy and environmental factors (e.g., seawater isotopic composition, temperature, salinity) on magnesium-isotopic (δ²⁶Mg) ratios of skeletal carbonates. Using high-precision multi-collector inductively coupled plasma mass spectrometry, we observed that the magnesium-isotopic composition of seawater from the semi-enclosed Dutch Wadden Sea is identical to that of open marine seawater. We further found that a considerable component of the observed variability in δ²⁶Mg values of marine skeletal carbonates can be attributed to differences in mineralogy. Furthermore, magnesium-isotope fractionation is species-dependent, with all skeletal carbonates being isotopically lighter than seawater. While δ²⁶Mg values of skeletal aragonite and high-magnesium calcite of coralline red algae indicate the absence or negligibility of metabolic influences, the δ²⁶Mg values of echinoids, brachiopods and bivalves likely result from a taxon-specific level of control on Mg-isotope incorporation during biocalcification. Moreover, no resolvable salinity and temperature effect were observed for coralline red algae and echinoids. In contrast, Mg-isotope data of bivalves yield ambiguous results, which require further validation. The data presented here, point to a limited use of Mg isotopes as temperature proxy, but highlight the method’s potential as tracer of seawater chemistry through Earth’s history.  相似文献   

Entstehung und Alter der Oberharzer Gänge     

Max Richter 《International Journal of Earth Sciences》1941,32(1-2):93-105

Ohne Zusammenfassung  相似文献   

Protokoll der wissenschaftlichen Sitzung am 4. und 5. Januar 1937     

Max Richter 《International Journal of Earth Sciences》1937,28(1-2):135-136

Ohne Zusammenfassung  相似文献