Uppermost Part (uppermost + part)

Distribution by Scientific Domains

Selected Abstracts

Shifting altitudinal distribution of outbreak zones of winter moth Operophtera brumata in sub-arctic birch forest: a response to recent climate warming?

ECOGRAPHY, Issue 2 2007
Snorre B. Hagen
Climatic change is expected to affect the extent and severity of geometrid moth outbreaks, a major disturbance factor in sub-arctic birch forests. Previous studies have reported that the two geometrid species involved, autumnal moth and winter moth, differ in their temperature requirements and, consequently, in their altitudinal and latitudinal distribution patterns. In this study, we document the altitudinal distribution of winter moth outbreaks in a large coastal area in northern Norway. We show that, in the present winter moth outbreak, defoliated birch stands were seen as distinct zones with a rather constant width in the uppermost part of the forest and where the upper limit coincided with the forest line. The outbreak zone closely followed the spatially variable forest line as an undulating belt, although some of the variation in outbreak zone width was also related to variation in topographical variables, such as distance from the coast, forest line altitude, and slope of the terrain. A distinct outbreak zone at the altitudinal forest line is the typical picture that has been depicted in more qualitative historical records on previous outbreaks of autumnal moth rather than winter moth. We suggest that the recent documented climate warming in this region may have induced a shift in distribution of the winter moth both relative to topography and geography. Further investigation is, however, required to substantiate these suspicions. [source]

Signals of range expansions and contractions of vascular plants in the high Alps: observations (1994,2004) at the GLORIA, master site Schrankogel, Tyrol, Austria

Abstract High mountain ecosystems are defined by low temperatures and are therefore considered to react sensitively to climate warming. Responding to observed changes in plant species richness on high peaks of the European Alps, an extensive setup of 1 m × 1 m permanent plots was established at the alpine-nival ecotone (between 2900 and 3450 m) on Mount Schrankogel, a GLORIA master site in the central Tyrolean Alps, Austria, in 1994. Recording was repeated in a representative selection of 362 quadrats in 2004. Ten years after the first recording, we observed an average change in vascular plant species richness from 11.4 to 12.7 species per plot, an increase of 11.8% (or of at least 10.6% at a 95% confidence level). The increase in species richness involved 23 species (about 43% of all taxa found at the ecotone), comprising both alpine and nival species and was pronouncedly higher in plots with subnival/nival vegetation than in plots with alpine grassland vegetation. Only three species showed a decrease in plot occupancy: one was an annual species, one was rare, and one a common nival plant that decreased in one part of the area but increased in the uppermost part. Species cover changed in relation to altitudinal preferences of species, showing significant declines of all subnival to nival plants, whereas alpine pioneer species increased in cover. Recent climate warming in the Alps, which has been twice as high as the global average, is considered to be the primary driver of the observed differential changes in species cover. Our results indicate an ongoing range contraction of subnival to nival species at their rear (i.e. lower) edge and a concurrent expansion of alpine pioneer species at their leading edge. Although this was expected from predictive distribution models and different temperature-related habitat preferences of alpine and nival species, we provide first evidence on , most likely , warming-induced species declines in the high European Alps. The projected acceleration of climate warming raises concerns that this phenomenon could become the major threat to biodiversity in high mountains. [source]

Hydrological importance of an unusual hazard in a mountainous basin: flood and landslide

Umesh K. Haritashya
Abstract The Bhagirathi River, a proglacial melt water stream of the Gangotri Glacier, is the principal source of the Ganges river system. The upper part of the basin lies in the high altitude region of the Garhwal Himalayas and is extensively covered by glaciers. We provide hydro-meteorological insight into a severe storm that produced unusual high rains in June 2000 in the uppermost part of the Bhagirathi River. This storm was concentrated upstream of Gangotri town and triggered landslides/rockslides at several locations between the glacier snout and Gangotri town. One of the major rockslides blocked the Bhagirathi River at Bhujbas, about 3 km downstream of the Gangotri Glacier snout, creating an artificial lake at this location. High stream flow in the river, generated by rapid runoff response from mountain slopes along with melt runoff from the glacier, quickly increased the level of water stored in the artificial lake. Daily rainfall in this region rarely exceeds 10 mm, while total rainfall during this 6-day storm was 131·5 mm. This unusual rain event occurred during the tourist season in June, consequently trapping a large number of tourists and vendors in this area. Sudden release of stored water generated floods that created havoc downstream of the artificially created lake. This paper presents the hydrological and meteorological information related to such an unusual and devastating event observed in the high altitude region of the Himalayas. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Understanding Late Quaternary extinctions: the case of Myotragus balearicus (Bate, 1909)

Pere Bover
Abstract Aim, In this study we present a new view on the extinction of Myotragus balearicus, an extinct highly modified dwarf caprine from the Gymnesic Islands (or eastern Balearic Islands), as a methodological case study for interpretation of Late Quaternary extinctions (LQEs). Methods, We analyse all available 14C ages obtained from M. balearicus bones from the uppermost part of the Pleistocene and the Holocene, together with the available chronological data of the putative causes of Myotragus extinction. Results, It has been possible to define two critical dates that allow us to establish an ,uncertainty period for the Myotragus extinction' (UPME) in each analysed island (Mallorca, Menorca and Cabrera). For Mallorca, the UPME corresponds to the interval c. 3700 to 2030 calbc (i.e. c. 1670 years of uncertainty). In the case of Menorca, the UPME spans from 10,000 to 1930 calbc (8070 years of uncertainity). In Cabrera the UPME is placed between 3650 and 300 calbc (3350 years of uncertainty). These periods, together with a review of the available information on the chronology of human arrival and the chronology of Holocene climatic change, shed light on the possible causes of the extinction of this species. Main conclusions, Extinction of Myotragus because of climatic change can be definitively rejected. The Myotragus extinction must be attributed to the rapid effects of the first human occupation. The use of uncertainity periods for the disappearance of species represents a useful tool for the analysis of LQEs. [source]

Predatory boreholes in Tournaisian (Lower Carboniferous) spiriferid brachiopods

LETHAIA, Issue 3 2009
A brachiopod fauna from the uppermost part of the Tournaisian Tournai Formation (Belgium) contains an undetermined species of Crurithyris (Spiriferida, Ambocoeliidae), which displays numerous bored shells. About 8% of the 432 specimens with conjoined valves display single, small (, 1 mm) boreholes, which are smooth-sided, cylindrical or weakly conical, circular to slightly elliptical in plan view, perpendicular to the shell surface and generally complete. Of the 35 bored articulated specimens, 27 were drilled on the ventral valve. Most of the boreholes are located in the posterior half of the shell, and no case of edge-drilling has been observed. The boreholes were drilled by a predator, or possibly a parasite, which selected individuals greater than 2.5 mm long. Crurithyris sp. may have represented an attractive (in terms of energy cost) and easy target for a small-sized predator because of its thin shell and ornament of minute spines. [source]

Characterisation of Diesel Engine Cylinder Liner Deposits by Surface Measurements

Øyvind Buhaug
Abstract This paper briefly reviews cylinder liner deposits and describes their effect on lubricating oil consumption and surface topography. Cylinder liner deposits may be invisible to the naked eye, but can be identified by surface topography measurement. A simulation of a cylinder liner with deposits is used to identify which of the available surface characteristics is best suited as a measure of deposit severity. Surface measurements are used to detect deposits in a case study. The deposits are found to be concentrated in a belt around the mid-stroke region of the cylinder liner. The comparatively low position of the deposit may explain the slow response of a fuel additive treatment in restoring oil consumption control, as the additive treatment in this case is seen to be most effective in the uppermost part of the cylinder liner. [source]

An international and multidisciplinary drilling project into a young complex impact structure: The 2004 ICDP Bosumtwi Crater Drilling Project,An overview

Christian KOEBERL
It is the source crater of the Ivory Coast tektites. The structure was excavated in 2.1,2.2 Gyr old metasediments and metavolcanics of the Birimian Supergroup. A drilling project was conceived that would combine two major scientific interests in this crater: 1) to obtain a complete paleoenvironmental record from the time of crater formation about one million years ago, at a near-equatorial location in Africa for which very few data are available so far, and 2) to obtain a complete record of impactites at the central uplift and in the crater moat, for ground truthing and comparison with other structures. Within the framework of an international and multidisciplinary drilling project led by the International Continental Scientific Drilling Program (ICDP), 16 drill cores were obtained from June to October 2004 at six locations within Lake Bosumtwi, which is 8.5 km in diameter. The 14 sediment cores are currently being investigated for paleoenvironmental indicators. The two impactite cores LB-07A and LB-08A were drilled into the deepest section of the annular moat (540 m) and the flank of the central uplift (450 m), respectively. They are the main subject of this special issue of Meteoritics & Planetary Science, which represents the first detailed presentations of results from the deep drilling into the Bosumtwi impactite sequence. Drilling progressed in both cases through the impact breccia layer into fractured bedrock. LB-07A comprises lithic (in the uppermost part) and suevitic impact breccias with appreciable amounts of impact melt fragments. The lithic clast content is dominated by graywacke, besides various metapelites, quartzite, and a carbonate target component. Shock deformation in the form of quartz grains with planar microdeformations is abundant. First chemical results indicate a number of suevite samples that are strongly enriched in siderophile elements and Mg, but the presence of a definite meteoritic component in these samples cannot be confirmed due to high indigenous values. Core LB-08A comprises suevitic breccia in the uppermost part, followed with depth by a thick sequence of graywacke-dominated metasediment with suevite and a few granitoid dike intercalations. It is assumed that the metasediment package represents bedrock intersected in the flank of the central uplift. Both 7A and 8A suevite intersections differ from suevites outside of the northern crater rim. Deep drilling results confirmed the gross structure of the crater as imaged by the pre-drilling seismic surveys. Borehole geophysical studies conducted in the two boreholes confirmed the low seismic velocities for the post-impact sediments (less than 1800 m/s) and the impactites (2600,3300 m/s). The impactites exhibit very high porosities (up to 30 vol%), which has important implications for mechanical rock stability. The statistical analysis of the velocities and densities reveals a seismically transparent impactite sequence (free of prominent internal reflections). Petrophysical core analyses provide no support for the presence of a homogeneous magnetic unit (= melt breccia) within the center of the structure. Borehole vector magnetic data point to a patchy distribution of highly magnetic rocks within the impactite sequence. The lack of a coherent melt sheet, or indeed of any significant amounts of melt rock in the crater fill, is in contrast to expectations from modeling and pre-drilling geophysics, and presents an interesting problem for comparative studies and requires re-evaluation of existing data from other terrestrial impact craters, as well as modeling parameters. [source]

Uppermost impact fallback layer in the Bosumtwi crater (Ghana): Mineralogy, geochemistry, and comparison with Ivory Coast tektites

Christian KOEBERL
In one (LB-05) of 16 cores drilled into the lake sediments, the zone between the impact breccias and the post-impact sediments was penetrated, preserving the final, fine-grained impact fallback layer. This ,30 cm thick layer contains in the top 10 cm "accretionary" lapilli, microtektite-like glass spherules, and shocked quartz grains. Glass particles,mostly of splash form less than 1 mm size,make up the bulk of the grains (,70,78% by number) in the coarser size fraction (>125 ,m) of the top of the fallback layer. About one-third of all quartz grains in the uppermost part of the layer are shocked, with planar deformation features (PDFs); almost half of these grains are highly shocked, with 3 or more sets of PDFs. K-feldspar grains also occur and some show shock deformation. The abundance of shocked quartz grains and the average shock level as indicated by the number of sets of PDFs, for both quartz and K-feldspar, decrease with depth into the layer. The well-preserved glass spherules and fragments are chemically rather homogeneous within each particle, and also show relatively small variations between the various particles. On average, the composition of the fallback spherules from core LB-5B is very similar to the composition of Ivory Coast tektites and microtektites, with the exception of CaO contents, which are about 1.5 to 2 times higher in the fallback spherules. This is a rare case in which the uppermost fallback layer and the transition to the post-impact sediments has been preserved in an impact structure; its presence indicates that the impactite sequence at Bosumtwi is complete and that Bosumtwi is a very well-preserved impact crater. [source]

Presence of an iron-rich nanophase material in the upper layer of the Cretaceous-Tertiary boundary clay

Mössbauer spectroscopic data reveals that a ubiquitous iron-rich nanophase material exists at the uppermost part of the K-T boundary layer in the Western Hemisphere and in Europe in marine and continental fine-grained sedimentary rock. The high surface-to-volume ratio of nanophase material suggests that it may be the carrier of the iridium abundance enhancement that marks the K-T boundary. Even more provocative is the possibility that the discovered nanophase material is, for the most part, composed of the vaporized impactor after the impact-generated high-temperature vapor plume rose and cooled above the atmosphere. [source]

The transient layer: implications for geocryology and climate-change science

Yuri Shur
Abstract Research treating permafrost-climate interactions is traditionally based on a two-layer conceptual model involving a seasonally frozen active layer and underlying perennially frozen materials. This conceptualization is inadequate to explain the behaviour of the active-layer/permafrost system over long periods, particularly in ice-rich terrain. Recent research in North America supports earlier Russian conclusions about the existence of a transition zone that alternates in status between seasonally frozen ground and permafrost over sub-decadal to centennial time scales. The transition zone is ice-enriched, and functions as a buffer between the active layer and long-term permafrost by increasing the latent heat required for thaw. The existence of the transition zone has an impact on the formation of a cryogenic soil structure, and imparts stability to permafrost under low-amplitude or random climatic fluctuations. Despite its importance, the transition zone has been the focus of relatively little research. The impacts of possible global warming in permafrost regions cannot be understood fully without consideration of a more realistic three-layer model. The extensive data set under development within the Circumpolar Active Layer Monitoring (CALM) program will provide a significant source of information about the development, characteristics, behaviour, and extent of the transition zone. This paper is focused on the uppermost part of the transition zone, which joins the active layer at sub-decadal to multi-centennial time scales. This upper part of the transition zone is known as the transient layer. Copyright © 2005 John Wiley & Sons, Ltd. [source]

The role of glacitectonic rafting and comminution in the production of subglacial tills: examples from southwest Ireland and Antarctica

BOREAS, Issue 4 2007
John F. Hiemstra
Sedimentological and structural geological data from two sites in southwest Ireland and Antarctica provide evidence for the formation of subglacial till by the brecciation and crushing of bedrock rafts. Up-sequence transitions, from undisturbed bedrock, to deformed bedrock, to crushed and brecciated bedrock, to massive matrix-supported till with far-travelled erratics, represent a process-form continuum of till production. Initially, bedrock fragments and rafts up to several metres in length are liberated from the substrate by glacitectonic thrusting and plucking. These rafts are then crushed to produce the matrix of a till. Such products are commonly referred to as comminution tills, although the original definition focused primarily on the second phase of the process (crushing of bedrock rafts and fragments) as well as abrasion of bedrock. Data from Ireland and Antarctica indicate that rafting of bedrock is an essential part of the process of till formation. This process is facilitated by weak sedimentary bedrock, which can be displaced along joints and bedding planes to form rafts that are then incorporated into the ,proto-till' prior to being crushed subglacially. Our field data suggest that bedrock failure and displacement of such rafts can occur to depths of 3 m. The occurrence of erratics in the uppermost part of the till demonstrates that the glacier effectively mixes far-travelled and local materials. [source]

The geomorphic work of George Leslie Adkin (1888,1964) and glaciation in the Tararua Range, North Island, New Zealand

M. S. Brook
Abstract:, Research initiated in 1909 by G. Leslie Adkin (1888,1964) suggested Park Valley in the Tararua Range was glaciated during the Late Quaternary, based on the ,U-shaped' cross-profiles in the uppermost parts of several valleys. Findings were published, but were not met with universal acceptance. Adkin's work remained the only glacial research undertaken on the North Island's axial ranges until the latter part of the 20th century. Adkin holds a special position in New Zealand, because although he worked full-time as a farmer he published nearly 40 articles in scientific journals on topics as varied as M,ori archaeology and geomorphology. [source]

Provenance of siliciclastic and hybrid turbiditic arenites of the Eocene Hecho Group, Spanish Pyrenees: implications for the tectonic evolution of a foreland basin

BASIN RESEARCH, Issue 2 2010
M. A. Caja
ABSTRACT The Eocene Hecho Group turbidite system of the Aínsa-Jaca foreland Basin (southcentral Pyrenees) provides an excellent opportunity to constrain compositional variations within the context of spatial and temporal distribution of source rocks during tectonostratigraphic evolution of foreland basins. The complex tectonic setting necessitated the use of petrographic, geochemical and multivariate statistical techniques to achieve this goal. The turbidite deposits comprise four unconformity-bounded tectonostratigraphic units (TSU), consisting of quartz-rich and feldspar-poor sandstones, calclithites rich in extrabasinal carbonates and hybrid arenites dominated by intrabasinal carbonates. The sandstones occur exclusively in TSU-2, whereas calclithites and hybrid arenites occur in the overlying TSU-3, TSU-4 and TSU-5. The calclithites were deposited at the base of each TSU and hybrid arenites in the uppermost parts. Extrabasinal carbonate sources were derived from the fold-and-thrust belt (mainly Cretaceous and Palaeocene limestones). Conversely, intrabasinal carbonate grains were sourced from foramol shelf carbonate factories. This compositional trend is attributed to alternating episodes of uplift and thrust propagation (siliciclastic and extrabasinal carbonates supplies) and subsequent episodes of development of carbonate platforms supplying intrabasinal detrital grains. The quartz-rich and feldspar-poor composition of the sandstones suggests derivation from intensely weathered cratonic basement rocks during the initial fill of the foreland basin. Successive sediments (calclithites and hybrid arenites) were derived from older uplifted basement rocks (feldspar-rich and, to some extent, rock fragments-rich sandstones), thrust-and-fold belt deposits and from coeval carbonate platforms developed at the basin margins. This study demonstrates that the integration of tectono-stratigraphy, petrology and geochemistry of arenites provides a powerful tool to constrain the spatial and temporal variation in provenance during the tectonic evolution of foreland basins. [source]