A "critical" climatic evaluation of last interglacial (MIS 5e) records from the Norwegian Sea     

Henning A. Bauch  & Helmut Erlenkeuser 《Polar research》2008,27(2):135-151

Sediment cores from the Norwegian Sea were studied to evaluate interglacial climate conditions of the marine isotope stage 5e (MIS 5e). Using planktic forminiferal assemblages as the core method, a detailed picture of the evolution of surface water conditions was derived. According to our age model, a step-like deglaciation of the Saalian ice sheets is noted between ca. 135 and 124.5 Kya, but the deglaciation shows little response with regard to surface ocean warming. From then on, the rapidly increasing abundance of subpolar forminifers, concomitant with decreasing iceberg indicators, provides evidence for the development of interglacial conditions sensu stricto (5e- ss ), a period that lasted for about 9 Ky. As interpreted from the foraminiferal records, and supported by the other proxies, this interval of 5e- ss was in two parts: showing an early warm phase, but with a fresher, i.e., lower salinity, water mass, and a subsequent cooling phase that lasted until ca. 118.5 Kya. After this time, the climatic optimum with the most intense advection of Atlantic surface water masses occurred until ca. 116 Kya. A rapid transition with two notable climatic perturbations is observed subsequently during the glacial inception. Overall, the peak warmth of the last interglacial period occurred relatively late after deglaciation, and at no time did it reach the high warmth level of the early Holocene. This finding must be considered when using the last interglacial situation as an analogue model for enhanced meridional transfer of ocean heat to the Arctic, with the prospect of a future warmer climate.  相似文献   

Introduction Part II     

Xander Campman  Jean Virieux  Kees Wapenaar  Helmut Jakubowicz 《Geophysical Prospecting》2008,56(4):453-454

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Nitrogen transformation processes in the Elbe River: Distinguishing between assimilation and denitrification by means of stable isotope ratios in nitrate   总被引：3，自引：0，他引：3  

Barbara Deutsch  Maren Voss  Helmut Fischer 《Aquatic Sciences - Research Across Boundaries》2009,71(2):228-237

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Spatio-temporal patterns of throughfall and solute deposition in an open tropical rain forest   总被引：4，自引：0，他引：4  

Alexander Zimmermann  Sonja Germer  Christopher Neill  Alex V. Krusche  Helmut Elsenbeer 《Journal of Hydrology》2008,360(1-4):87-102

The brief interaction of precipitation with a forest canopy can create a high spatial variability of both throughfall and solute deposition. We hypothesized that (i) the variability in natural forest systems is high but depends on system-inherent stability, (ii) the spatial variability of solute deposition shows seasonal dynamics depending on the increase in rainfall frequency, and (iii) spatial patterns persist only in the short-term. The study area in the north-western Brazilian state of Rondônia is subject to a climate with a distinct wet and dry season. We collected rain and throughfall on an event basis during the early wet season (n = 14) and peak of the wet season (n = 14) and analyzed the samples for pH and concentrations of , Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl⁻, , and DOC. The coefficient of variation for throughfall based on both sampling intervals was 29%, which is at the lower end of values reported from other tropical forest sites, but which is higher than in most temperate forests. Coefficients of variation of solute deposition ranged from 29% to 52%. This heterogeneity of solute deposition is neither particularly high nor particularly low compared with a range of tropical and temperate forest ecosystems. We observed an increase in solute deposition variability with the progressing wet season, which was explained by a negative correlation between heterogeneity of solute deposition and antecedent dry period. The temporal stability of throughfall patterns was low during the early wet season, but gained in stability as the wet season progressed. We suggest that rapid plant growth at the beginning of the rainy season is responsible for the lower stability, whereas less vegetative activity during the later rainy season might favor the higher persistence of “hot” and “cold” spots of throughfall quantities. The relatively high stability of throughfall patterns during later stages of the wet season may influence processes at the forest floor and in the soil. Solute deposition patterns showed less clear trends but all patterns displayed a short-term stability only. The weak stability of those patterns is apt to impede the formation of solute deposition-induced biochemical microhabitats in the soil.  相似文献   

Texture analysis of heterogeneous data—a farewell to F-coefficients     

Helmut Schaeben   《Journal of Structural Geology》2000,22(11-12)

This contribution describes the mathematical and numerical possibility to analyse heterogeneous data, e.g. experimental intensity data measured for many crystallographic but few sample directions, adaptively refined high resolution intensity data, or a mixture of diffraction intensity data and individual orientation data from scanning electron microscopy.These possibilities are put forward within the dual approach to texture analysis provided by the differential equation governing pole figures. The general solution of this differential equation is represented both in terms of spherical harmonics or characteristics. The resulting systems of equations are capable of considering such heterogeneous data as mentioned above.The eventual aim of this contribution is to show that (i) the mostly tacit ‘paradigm’ of texture analysis that additional pole figures can be calculated from experimental pole figures only by using a detour via the ODF is not correct, and (ii) any function satisfying the differential equation governing pole figures is the actual pole figure projection, or X-ray transform, of a common function defined in a higher dimensional space.Summarily, it is shown that the two dual approaches to texture analysis provided by the projection formula or the differential equation are equivalent, but put emphasis on different issues of the same problem.  相似文献   

GARSTEC—the Garching Stellar Evolution Code     

Achim Weiss  Helmut Schlattl 《Astrophysics and Space Science》2008,316(1-4):99-106

We describe the Garching Stellar Evolution Code. General features, treatment of the microphysics, details of the numerical solution, handling and particularities are discussed. The standard solar model serves as the most basic benchmark to test the accurateness of the code and is presented, too.  相似文献   

Intra‐event scale bar–bank interactions and their role in channel widening          下载免费PDF全文

Mario Klösch  Bernadette Blamauer  Helmut Habersack 《地球表面变化过程与地形》2015,40(11):1506-1523

Channel bars and banks strongly affect the morphology of both braided and meandering rivers. Accordingly, bar formation and bank erosion processes have been greatly explored. There is, however, a lack of investigations addressing the interactions between bed and bank morphodynamics, especially over short timescales. One major implication of this gap is that the processes leading to the repeated accretion of mid‐channel bars and associated widenings remain unsolved. In a restored section of the Drau River, a gravel‐bed river in Austria, mid‐channel bars have developed in a widening channel. During mean flow conditions, the bars divert the flow towards the banks. One channel section exhibited both an actively retreating bank and an expanding mid‐channel bar, and was selected to investigate the morphodynamic processes involved in bar accretion and channel widening at the intra‐event timescale. We repeatedly surveyed riverbed and riverbank topography, monitored riverbank hydrology and mounted a time‐lapse camera for continuous observation of riverbank erosion processes during four flow events. The mid‐channel bar was shown to accrete when it was submerged during flood events, which at the subsequent flow diversion during lower discharges narrowed the branch along the bank and increased the water surface elevation upstream from the riffle, which constituted the inlet into the branch. These changes of bed topography accelerated the flow along the bank and triggered bank failures up to 20 days after the flood events. Four analysed flow events exhibited a total bar expansion from initially 126 m² to 295 m², while bank retreat was 6 m at the apex of the branch. The results revealed the forcing role of bar accretion in channel widening and highlighted the importance of intra‐event scale bed morphodynamics for bank erosion, which were summarized in a conceptual model of the observed bar–bank interactions. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Changes of the plankton community composition during chemical neutralisation of the Bockwitz pit lake     

Helmut Rönicke  Volker Neumann  Jörg Tittel 《Limnologica》2010,40(2):191-198

Lake Bockwitz, a pit lake in a former lignite open-cast mine south of Leipzig (Germany), was neutralised (from pH 2.65 to pH 7.1) by addition of soda ash (14,620 t) from 2004 to 2007. The additions had to be continued due to ongoing inflows of acid ground and surface water. This paper reports on the changes in the plankton community accompanying the neutralisation.At the beginning, the community composition and biomass was comparable to other acidic pit lakes, i.e. the pigmented flagellates Chlamydomonas and Ochromonas dominated the autotrophs, and ciliates and rotifers were the top predators. The biomass was small (maximum 2 mg fresh weight per litre) and decreased until the end of 2008. With increasing pH, the autotrophic community became more diverse, whereby diatoms, chrysophyceans and blue greens contributed significantly to biomass. Although neutral pH conditions were achieved in autumn 2007, picocyanobacteria were not present until the end of 2008. In addition, crustaceans were under-represented in terms of biomass and diversity. Daphnids were not found. We attributed this to short-term changes of the ionic composition of the water and to the limited time available for non-acido-tolerant organisms to colonise the system.  相似文献   

Human impact on Holocene sediment dynamics in the Eastern Mediterranean – the example of the Roman harbour of Ephesus          下载免费PDF全文

Friederike Stock  Maria Knipping  Anna Pint  Sabine Ladstätter  Hugo Delile  Andreas G. Heiss  Hannes Laermanns  Piers D. Mitchell  René Ployer  Martin Steskal  Ursula Thanheiser  Ralf Urz  Volker Wennrich  Helmut Brückner 《地球表面变化过程与地形》2016,41(7):980-996

During the past millennia, many erosion and accumulation processes have been modified by anthropogenic impact. This holds especially true for the environs of ancient settlements and their harbours along the Mediterranean coasts. Our multi‐proxy investigations in the Roman harbour and the harbour canal of Ephesus (western Turkey) reveals that humans have significantly triggered soil erosion during the last three millennia. Since the eighth century bc , and especially since the Hellenistic period, a high sedimentation rate indicates fast alluviation and delta progradation of the Küçük Menderes. Deforestation, agriculture (especially ploughing) and grazing (especially goats) were the main reasons for erosion of the river catchment area. One consequence was significant siltation of the Hellenistic/Roman harbour basin. This sediment trap archives the human impact, which was strongly enhanced from Hellenistic/Roman to Byzantine times (second/first centuries bc to the sixth/seventh centuries ad ), evidenced by high sedimentation rates, raised values of heavy metal contaminations [lead (Pb), copper (Cu)], the occurrence of fruit tree pollen and of intestinal parasites. From the middle to the end of the first millennium ad , the influence of Ephesus declined, which resulted in a decrease of human impact. Studies of several ancient settlements around the Mediterranean Sea tell a comparable story. They also confirm that during their most flourishing periods the human impact totally overprinted the climatic one. To detect the latter, geo‐bio‐archives of relatively pristine areas have to be investigated in detail. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

The chemical variability at the surface of Mars: Implication for sediment formation and rock weathering     

Christoph Kolb  Josep A. Martín-Fernández  Helmut Lammer 《Icarus》2006,183(1):10-29

Compositional data analysis was performed on chemical compositions of martian surface materials in order to unravel scenarios of past and present weathering and to evaluate the role of meteoritic accumulation. The observed chemical variability is analyzed by means of principal component analysis. Potential reservoirs that may have contributed primary material to soil formation are assessed. Chemical alteration in the course of in situ weathering is described in terms of alteration vectors that link the compositions of fresh rocks and their weathering crusts. The interplay of localized chemical alteration and global scale re-distribution and mixing of fines material is documented through the identification of different soil forming branches. These branches emanate from distinct compositional domains, which comprise basaltic and basalt-andesitic primary materials, and they converge to a global dust composition, which represents the product of chemical and physical disintegration and subsequent global mixing. Mass balance considerations applied to localized weathering phenomena are in line with findings from experimental acid-sulfate weathering on olivine-bearing basalts and the persistence of secondary silica in evaporitic rocks. In addition the composition and oxidation state of involved volcanic gases is deduced. Our findings corroborate the past activity of volcanic exhalation products in combination with liquid water. We conclude that average martian crust is dominated by basaltic materials at its topmost level and that the amount of meteoritic accumulation may contribute about 6 wt% to the martian fines. From the meteoritic contribution minimum soil formation rates of 60±20 cm/Gyr are derived. Sequestration of atmospheric oxygen during weathering of primary materials may account for the oxygen deficiency of the martian atmosphere. A 4-14-m-thick layer of oxidized martian fines may account for the estimated deficit of 1.7×¹⁰¹⁸ mol O₂ in the martian atmosphere depending on the primary oxidation state of volatile volcanic emanations.  相似文献