Cryptophyta Flagellates of Meromictic Lakes Shira and Shunet(Khakassia,Russia):Mechanisms of Vertical Distribution and Trophic Role

正1 Introduction Many of the stratified lakes are characterized by the presence of large populations of cryptomonads in their chemocline zones(Reynolds,1992;Gervais et al,2003;Pedro's-Alio'et al.,1995).These populations are adapted to low light intensity and high sulfide concentration;they have a mixotrophic ability and form the so-called"deep chlorophyll maxima"(Gervais,1998;Marsha"and Laybourn-Parry,2002).A similar Cryptomonas sp.     

A gridded monthly upper-air data set from 1918 to 1957

Significant efforts have been devoted in recent years towards extending observation-based three-dimensional atmospheric data sets back in time. Such data sets form an important basis for a better understanding of the climate system. Here we present a new monthly three-dimensional global data set that is based on historical upper-air data and surface data. We use statistical reconstruction techniques, calibrated using ERA-40 data, to obtain gridded data from the numerous, but scattered and heterogeneous historical upper-air observations. In contrast to previous work, in which we used hemispheric principal components on both the predictor and the predictand side to reconstruct spatially complete fields back to 1880, we restrict the procedure to places and times where upper-air observations are available. Each grid column (consisting of four variables at six levels) is then reconstructed independently using only predictor variables in the vicinity (i.e., only local stationarity is required rather than stationary large-scale patterns). The product, termed REC2, is a gridded, global monthly data set of geopotential height, temperature, and u and v wind from 850 to 100?hPa back to 1918. The data set is sparse (i.e., many grid cells are empty), but provides an alternative to large-scale reconstructions as it allows for non-stationary teleconnections. We show the results of several validation experiments, compare our new data set with a number of existing data sets, and demonstrate that it is suitable for analysing large-scale climate variability on interannual time-scales.     

Directed blasts and blast-generated pyroclastic density currents: a comparison of the Bezymianny 1956, Mount St Helens 1980, and Soufrière Hills,Montserrat 1997 eruptions and deposits

We compare eruptive dynamics, effects and deposits of the Bezymianny 1956 (BZ), Mount St Helens 1980 (MSH), and Soufrière Hills volcano, Montserrat 1997 (SHV) eruptions, the key events of which included powerful directed blasts. Each blast subsequently generated a high-energy stratified pyroclastic density current (PDC) with a high speed at onset. The blasts were triggered by rapid unloading of an extruding or intruding shallow magma body (lava dome and/or cryptodome) of andesitic or dacitic composition. The unloading was caused by sector failures of the volcanic edifices, with respective volumes for BZ, MSH, and SHV c. 0.5, 2.5, and 0.05 km³. The blasts devastated approximately elliptical areas, axial directions of which coincided with the directions of sector failures. We separate the transient directed blast phenomenon into three main parts, the burst phase, the collapse phase, and the PDC phase. In the burst phase the pressurized mixture is driven by initial kinetic energy and expands rapidly into the atmosphere, with much of the expansion having an initially lateral component. The erupted material fails to mix with sufficient air to form a buoyant column, but in the collapse phase, falls beyond the source as an inclined fountain, and thereafter generates a PDC moving parallel to the ground surface. It is possible for the burst phase to comprise an overpressured jet, which requires injection of momentum from an orifice; however some exploding sources may have different geometry and a jet is not necessarily formed. A major unresolved question is whether the preponderance of strong damage observed in the volcanic blasts should be attributed to shock waves within an overpressured jet, or alternatively to dynamic pressures and shocks within the energetic collapse and PDC phases. Internal shock structures related to unsteady flow and compressibility effects can occur in each phase. We withhold judgment about published shock models as a primary explanation for the damage sustained at MSH until modern 3D numerical modeling is accomplished, but argue that much of the damage observed in directed blasts can be reasonably interpreted to have been caused by high dynamic pressures and clast impact loading by an inclined collapsing fountain and stratified PDC. This view is reinforced by recent modeling cited for SHV. In distal and peripheral regions, solids concentration, maximum particle size, current speed, and dynamic pressure are diminished, resulting in lesser damage and enhanced influence by local topography on the PDC. Despite the different scales of the blasts (devastated areas were respectively 500, 600, and >10 km² for BZ, MSH, and SHV), and some complexity involving retrogressive slide blocks and clusters of explosions, their pyroclastic deposits demonstrate strong similarity. Juvenile material composes >50% of the deposits, implying for the blasts a dominantly magmatic mechanism although hydrothermal explosions also occurred. The character of the magma fragmented by explosions (highly viscous, phenocryst-rich, variable microlite content) determined the bimodal distributions of juvenile clast density and vesicularity. Thickness of the deposits fluctuates in proximal areas but in general decreases with distance from the crater, and laterally from the axial region. The proximal stratigraphy of the blast deposits comprises four layers named A, B, C, D from bottom to top. Layer A is represented by very poorly sorted debris with admixtures of vegetation and soil, with a strongly erosive ground contact; its appearance varies at different sites due to different ground conditions at the time of the blasts. The layer reflects intense turbulent boundary shear between the basal part of the energetic head of the PDC and the substrate. Layer B exhibits relatively well-sorted fines-depleted debris with some charred plant fragments; its deposition occurred by rapid suspension sedimentation in rapidly waning, high-concentration conditions. Layer C is mainly a poorly sorted massive layer enriched by fines with its uppermost part laminated, created by rapid sedimentation under moderate-concentration, weakly tractive conditions, with the uppermost laminated part reflecting a dilute depositional regime with grain-by-grain traction deposition. By analogy to laboratory experiments, mixing at the flow head of the PDC created a turbulent dilute wake above the body of a gravity current, with layer B deposited by the flow body and layer C by the wake. The uppermost layer D of fines and accretionary lapilli is an ash fallout deposit of the finest particles from the high-rising buoyant thermal plume derived from the sediment-depleted pyroclastic density current. The strong similarity among these eruptions and their deposits suggests that these cases represent similar source, transport and depositional phenomena.     

Energy Decay of the 2004 Sumatra Tsunami in the World Ocean

The catastrophic Indian Ocean tsunami generated off the coast of Sumatra on 26 December 2004 was recorded by a large number of tide gauges throughout the World Ocean. This study uses gauge records from 173 sites to examine the characteristics and energy decay of the tsunami waves from this event in the Indian, Atlantic and Pacific oceans. Findings reveal that the decay (e-folding) time of the tsunami wave energy within a given oceanic basin is not uniform, as previously reported, but depends on the absorption characteristics of the shelf adjacent to the coastal observation site and the time for the waves to reach the site from the source region. In general, the decay times for island and open-ocean bottom stations are found to be shorter than for coastal mainland stations. Decay times for the 2004 Sumatra tsunami ranged from about 13 h for islands in the Indian Ocean to 40–45 h for mainland stations in the North Pacific.     

Formation of basins and mountain ranges in Attica (Greece): The role of Miocene to Recent low-angle normal detachment faults

In seismically active regions, active low-angle detachment faults are probably more frequent as is commonly thought and may play an important but still underestimated role in the evolution of landforms and basins. We investigate the tectonically active region of Attica (Greece) in the Aegean back arc as a model region to show how basins and mountain ranges commonly thought to be formed by movements on high-angle normal faults in fact reflect the surface expression of displacements on yet undetected, deep-seated, active low-angle normal detachment faults. Inferences are made based on an integrated study of Attica linking the petrology of clastic sediments with geomorphology and structures, and including few new palynological data. From the Miocene to Recent, three sets of normal detachment fault systems were successively active. Shear zones of the 1st (Early Miocene) stage emplaced rocks of the Attic Cycladic high-P metamorphic belt (AC-HP-belt) from depth corresponding to greeschist facies conditions in the brittle, upper crust. In the 2nd stage the WNW dipping Attica low-angle normal detachment fault system between the AC-HP-belt and the un- or weakly metamorphosed rocks of the sub-Pelagonian Zone (SPZ) was active. Clastic sedimentation started in the Late Miocene, during the 2nd stage. Late Miocene and Early Pliocene clastic sediments reveal that during the 2nd stage many areas that presently expose the AC-HP-belt were still covered by the overlying SPZ. Also, now uplifted areas such as the Parnitha mountain range that currently undergo strong erosion were then the sites of sedimentary sinks. The 3rd stage (Late Pliocene through Recent) is associated with dramatic changes in the morphology and recurring steepening of the relief. Reversal of the Parnitha area from the site of deposition into the site of erosion is associated with deposition of coarse conglomerates to the SE of the Parnitha Mt. and S of the Penteli Mt. Sediments of the 3rd stage reflect activity of the here newly described, SSE-dipping Penteli—Athens low-angle detachment fault (PADF) system formed at a high angle to the Attica detachment fault. The outcome of this study is that the present-day geomorphology is to a high degree related to the operation of the PADF system. Steep fault bounding the Athens and Mesogea basins as well as the mountain ranges (Parnitha, Penteli, Hymittos mounts) belongs to its breakaway zone or root into the PADF. Ongoing tectonic movements related to this fault system were responsible for the 1999 Athens (Mw = 6.0) earthquake. We particularly discuss how the PADF may continue into greater depth, the translation magnitude, and how the PADF fits into the wider kinematic framework of the Aegean region.     

Expansion dynamics of deciduous rubber plantations in Xishuangbanna,China during 2000–2010

Monoculture rubber plantations have been replacing tropical rain forests substantially in Southern China and Southeast Asia over the past several decades, which have affected human wellbeing and ecosystem services. However, to the best of our knowledge on the extent of rubber plantation expansion and their stand ages is limited. We tracked the spatiotemporal dynamics of deciduous rubber plantations in Xishuangbanna, the second largest natural rubber production region in China, from 2000 to 2010 using time-series data from the Phased Array type L-band Synthetic Aperture Radar (PALSAR), Landsat, and Moderate Resolution Imaging Spectroradiometer (MODIS). We found that rubber plantations have been expanding across a gradient from the low-elevation plains to the high elevation mountains. The areas of deciduous rubber plantations with stand ages ≤5, 6–10, and ≥11-year old were ~1.2 × 10⁵ ha, ~0.8 × 10⁵ ha, and ~2.9 × 10⁵ ha, respectively. Older rubber plantations were mainly located in low-elevation and species-rich regions (500–900 m) and younger rubber trees were distributed in areas of relative high-elevation with fragile ecosystems. Economic and market factors have driven the expansion of rubber plantations, which is not only a threat to biodiversity and environmental sustainability, but also a trigger for climatic disasters. This study illustrates that the integration of microwave, optical, and thermal data is an effective method for mapping deciduous rubber plantations in tropical mountainous regions and determining their stand ages. Our results demonstrate the spatiotemporal pattern of rubber expansions over the first decade of this century.     

Deriving incline values for street networks from voluntarily collected GPS traces

ABSTRACT

When producing optimal routes through an environment, considering the incline of surfaces can be of great benefit in a number of use cases. For instance, steep segments need to be avoided for energy-efficient routes and for routes that are suitable for mobility-restricted people. Such incline information may be derived from digital elevation models (DEMs). However, the corresponding data capturing methods (e.g. airborne LiDAR, photogrammetry, and terrestrial surveying) are expensive. Current low-cost and open-licensed DEM (e.g. Shuttle Radar Topography Mission [SRTM] and Advanced Spaceborne Thermal Emission and Reflection Radiometer [ASTER]) generally do not have sufficient horizontal resolution or vertical accuracy, and lack a global coverage. Therefore, we have investigated an alternative low-cost approach which derives street incline values from GPS traces that have been voluntarily collected by the OpenStreetMap contributors. Despite the poor absolute accuracy of this data, the relative accuracy of traces seems to be sufficient enough to compute incline values with reasonable accuracy. A validation shows that the accuracy of incline values calculated from GPS traces slightly outperforms incline values derived from SRTM-1 DEM, though results depend on how many traces per street segment are used for computation.