Impacts of tectonic and orbital forcing on East African climate: a comparison based on global climate model simulations

A global atmosphere–ocean model has been forced with topographic and orbital scenarios in order to evaluate the relative role of both factors for the past climate of East Africa. Forcing the model with a significantly reduced topography in Eastern and Southern Africa leads to a distinct increase in moisture transport from the Indian Ocean into the eastern part of the continent and increased precipitation in Eastern Africa. Simulations with step-wise reduced height show that this climate change occurs continuously with the change in topography, i.e., an abrupt change of local climatic features with a critical height is not found. Simulations of the last interglacial (at 125,000 years before present, i.e., the Eemian interglacial) and the last glacial inception (at 115,000 years before present) are used as examples for the role of orbital-induced changes in insolation. Here, changes in meridional temperature gradients lead to modifications in moisture transport of similar order of magnitude, but with different spatial and seasonal structure. For the Eemian interglacial, a distinct increase in summer moisture transport from the Atlantic deep into the continent at around 20°N is simulated.     

Time-domain demodulation of RHESSI light curves

This paper presents an algorithm to decompose the modulated RHESSI light curves into periodic functions and a smooth function, representing the true (demodulated) time profile of an impulsive source. The decomposition is achieved by optimizing a trade-off between the Poisson likelihood, a smoothness constraint, and conditions on the average grid transmission and the (modulating or non-modulating) background. The algorithm, which operates on the level of count rates and does not require imaging information, is verified by numerical simulations and applied to some early RHESSI data, where – as a preliminary result – several impulsive features on time scales < 4 s may have been identified.     

From nappe stacking to exhumation: Cretaceous tectonics in the Apuseni Mountains (Romania)

International Journal of Earth Sciences - New Ar–Ar muscovite and Rb–Sr biotite age data in combination with structural analyses from the Apuseni Mountains provide new constraints on...     

Microbial nitrogen transformations in sediments and inorganic nitrogen fluxes across the sediment/water interface on the South Island West Coast,New Zealand

In January 1982, sediment microbial N transformations and inorganic N fluxes across the sediment/water interface were studied at nine sites off the South Island West Coast, New Zealand. The sediments showed a great variety in physical, chemical and biological properties. The sediment organic matter had a molar $\text{C}\text{N}$ ratio of 5.9–10.9, and the total $\text{N}\text{P}$ ratio was 1.2–4.0. The denitrification capacity in the top 7.5 cm of sediment was 0.1–77.2 mmol N m^?2 day^?1 and generally declined with increasing sediment depth. The in situ denitrification rate was 0.02–1.84 mmol N m^?2 day^?1 and highest activities were generally found in surface sediments and at 6–7.5 cm depth. Denitrification accounted for 82–100% of total nitrate reduction. Net N mineralization was indirectly estimated at 0.6–2.4 mmol N m^?2 day^?1, and the experimental determination of this N transformation gave 0.6–3.2 mmol N m^?2 day^?1. Denitrification accounted for 3–75% of net N mineralization. The diffusive flux of ammonium and nitrate across the sediment/water interface was 0.1–0.7 and 0.1–0.6 mmol N m^?2 day^?1, respectively.     

A contribution to the migration of gold in the biosphere of the humid mild zone

The content of gold in plants has been used as an indicator in the prospecting for gold. For this purpose non-destructive analytical methods have been developed. In the humid mild zone — where the process of weathering is of a kaolinitic character — there is practically no migration of gold, and consequently its increased content indicates the presence of a gold deposit.     

Reducing landscape heterogeneity for improved land use and land cover (LULC) classification across the large and complex Ethiopian highlands

This paper presents a land use and land cover (LULC) classification approach that accounts landscape heterogeneity. We addressed this challenge by subdividing the study area into more homogeneous segments using several biophysical and socio-economic factors as well as spectral information. This was followed by unsupervised clustering within each homogeneous segment and supervised class assignment. Two classification schemes differing in their level of detail were successfully applied to four landscape types of distinct LULC composition. The resulting LULC map fulfills two major requirements: (1) differentiation and identification of several LULC classes that are of interest at the local, regional, and national scales, and (2) high accuracy of classification. The approach overcomes commonly encountered difficulties of classifying second-level classes in large and heterogeneous landscapes. The output of the study responds to the need for comprehensive LULC data to support ecosystem assessment, policy formulation, and decision-making towards sustainable land resources management.     

An automated method for mapping physical soil and water conservation structures on cultivated land using GIS and remote sensing techniques

An efficient and reliable automated model that can map physical Soil and Water Conservation (SWC) structures on cultivated land was developed using very high spatial resolution imagery obtained from Google Earth and ArcGIS®, ERDAS IMAGINE®, and SDC Morphology Toolbox for MATLAB and statistical techniques. The model was developed using the following procedures: (1) a high-pass spatial filter algorithm was applied to detect linear features, (2) morphological processing was used to remove unwanted linear features, (3) the raster format was vectorized, (4) the vectorized linear features were split per hectare (ha) and each line was then classified according to its compass direction, and (5) the sum of all vector lengths per class of direction per ha was calculated. Finally, the direction class with the greatest length was selected from each ha to predict the physical SWC structures. The model was calibrated and validated on the Ethiopian Highlands. The model correctly mapped 80% of the existing structures. The developed model was then tested at different sites with different topography. The results show that the developed model is feasible for automated mapping of physical SWC structures. Therefore, the model is useful for predicting and mapping physical SWC structures areas across diverse areas.     

Estimating the Impact of Global Change on Flood and Drought Risks in Europe: A Continental, Integrated Analysis

Most studies on the impact of climate change on regional water resources focus on long-term average flows or mean water availability, and they rarely take the effects of altered human water use into account. When analyzing extreme events such as floods and droughts, the assessments are typically confined to smaller areas and case studies. At the same time it is acknowledged that climate change may severely alter the risk of hydrological extremes over large regional scales, and that human water use will put additional pressure on future water resources. In an attempt to bridge these various aspects, this paper presents a first-time continental, integrated analysis of possible impacts of global change (here defined as climate and water use change) on future flood and drought frequencies for the selected study area of Europe. The global integrated water model WaterGAP is evaluated regarding its capability to simulate high and low-flow regimes and is then applied to calculate relative changes in flood and drought frequencies. The results indicate large ‘critical regions’ for which significant changes in flood or drought risks are expected under the proposed global change scenarios. The regions most prone to a rise in flood frequencies are northern to northeastern Europe, while southern and southeastern Europe show significant increases in drought frequencies. In the critical regions, events with an intensity of today's 100-year floods and droughts may recur every 10–50 years by the 2070s. Though interim and preliminary, and despite the inherent uncertainties in the presented approach, the results underpin the importance of developing mitigation and adaptation strategies for global change impacts on a continental scale.     

A Jurassic-Cretaceous island arc in the Ladakh-Himalayas

The Ladakh Mesozoic ophiolite belt (western Himalaya) contains a pile of volcanic thrust sheets (Dras unit) which differ significantly in structure and composition from the ophiolitic mélange zones. The Dras unit is composed of pillow lavas, doleritic sills, very irregular basaltic (?basaltic andesites) and dacitic flows intercalated with pyroclastics, volcanoclastic sediments and radiolarian cherts. According to fossil evidence, this volcanism must have been active between Upper Jurassic and Upper Cretaceous.The presence of relict primary minerals, such as magnesiochromite, clinopyroxene, hastingsitic hornblende and Ti-magnetite as well as distinctive bulk chemistries, suggests that the volcanics belong to island arc tholeiite and to calc-alkaline rock series, typical of present island arcs in the Caribbean and Pacific.Model calculations incorporating probed phenocryst phases indicate that in addition to olivine, clinopyroxene and plagioclase, amphibole and titanomagnetite are crucial fractionating phases in the development of the dacites from a primitive tholeiitic melt. The latter process must have taken place at about 1000°C and at moderate depth of 5–15 km within or underneath the island arc. Today, hornblende-bearing mafic cumulates appear in the vicinity of Kargil within and close to the Dras volcanics.In a Sr-evolution diagram, the Dras volcanics have yielded a “pseudo-isochron” with a low initial ratio of 0.7035 ± 0.0003, which is in the same range as the mean of modern island arc volcanics. However, a geologically unrealistic age of 263 m.y., is obtained from the slope of this isochron.The upper mantle is regarded as the source material for the island arc tholeiitic magmas. Enrichment in K, Ba, Sr and LREE supports the involvement of components derived from dehydration or incipient melting of subducted Tethyan oceanic crust in the mantle.     

The effect of migratory shorebirds on the benthic species of three southwestern Atlantic Argentinean estuaries

We experimentally evaluate the effect of migratory shorebirds on the benthic fauna of three southwestern Atlantic Argentinean stop-over and wintering sites: Bahía Samborombon (35°30′–36°22′S, 57°23′W), Mar Chiquita coastal lagoon (37°40′S, 57°26′W), and Bahía Blanca (38°48′–39°25′S, 50°–62°25′W). The experiments consisted of exclusion ceilings and controls (both 1 m²), with 10 replicates each and aligned at the same tidal level. During December 1994–May 1995 these experiments were done, twice in Bahía Samborombon, twice at two sites (Sotelo and Celpa) 4 km apart in Mar Chiquita coastal lagoon, and three times in Bahía Blanca. Three polychaete species (Laeonereis acuta, Nephtys fluviatilis, andHeteromastus similis) were found in similar densities in both areas of the Mar Chiquita lagoon.L. acuta andN. fluviatilis were affected in Sotelo, but there was no treatment effect in Celpa. In Sotelo the most abundant shorebirds were Hudsonian godwit (Limosa haemastica), American golden plover (Pluvialis dominica), and White-rumped sandpiper (Calidris fuscicollis), and in Celpa the most abundant shorebirds were White-rumped sandpiper, two-banded plower (Charadrius falklandicus), and lesser yellowlegs (Tringa flavipes). The largest polychaete densities were in the upper sediment layer (0–6 cm), which was also the most affected layer. Three polychaete species were found in Bahía Samborombon (L. acuta, H. similis, andNeanthes succinea), but onlyH. similis showed a treatment effect. The most abundant shorebirds in Samborombon were white-rumped sandpiper and two-banded plover. No effect was detected in Bahía Blanca, where the most abundant shorebirds were white-rumped sandpiper and American golden plover. In all cases, the species affected by shorebirds were the most abundant species. From the two sites of Mar Chiquita, there was a treatment effect only in Sotelo, which was also the area with higher shorebirds counts. However, much lower densities observed in Samborombon (similar to the unaffected area of Mar Chiquita) also produced a significant decrease in infaunal abundance. These evidences also suggest that just selection of study sites may produce different views of the interaction between shorebirds and benthic species.