1,721,071 research outputs found
Thermal and geochemical investigation of ice wedges in northern Victoria Land (Antarctica)
No full textDuring the 1998-1999, 2000-2001 and 2003-2004 field seasons, geomorphological surveys of permafrost-related polygons were carried out in northern Victoria Land. Widespread diffusion of ice wedges was ascertained. The ice wedges were found at depths ranging from 10 cm to 74 cm from the ground surface. Their size ranged from 5-7 cm to 155 cm in width, with an average of 49 cm at the top, and from 20 cm to over 150 cm in height, with an average of 85 cm. The wedge ice was milky-white in colour and largely free of sediment, with numerous oriented gas inclusions forming vertical foliations. A vertical open fissure, 2-5 mm wide and filled with small loose ice grains, was present at the centre of most ice wedges and extended down to the bottom of the wedge or to the bottom of the excavated section. The study investigated the thermal regime and stable-isotope composition of selected ice wedges. The aim was to establish whether thermal conditions trigger ice-wedge cracking and to define the processes which lead to the formation of wedge ice
THERMAL AND GEOCHEMICAL INVESTIGATIONS ABOUT SOME ICE WEDGES OF NORTHERN VICTORIA LAND (ANTARCTICA)
No full textDuring the XIV, XVI and XIX Italian Antarctic Expeditions geomorphologic surveys of permafrost-related polygons were carried out in the northern Victoria land. Ice wedges were found in sites with different altitudes and climatic conditions in a vast area extending from the Terra Nova Bay up to Freyberg Mountains.
All the samples were measured for their oxygen isotope ratios and in some cases a co-isotopic study was performed. Tritium activity measurements were also carried out.
Ice-wedge thermal regime monitoring at two selected sites showed high temperature gradients between the ground surface and the top of ice wedge
Geochemical, thermal and petrofabric analyses of Antarctic ice wedges: environmental influences
No full textFrom 1998 to 2006, during four summer field seasons, ice wedges were found in 45 sites at depths ranging from 10 to 74 cm beneath the ground surface. The tops of the ice wedges ranged from 5 to 155 cm wide, and their heights varied from 20 to over 150 cm in length.
A co-isotopic study was performed by measuring both the oxygen (Delta 18O) and hydrogen (Delta D) isotope compositions and the tritium activity. Petrofabric analyses were also performed on ice-wedge ice to investigate changes in fabric across wedges in relation to the
growth mechanism. Data loggers were installed at three ice-wedge polygon sites to monitor the ice-wedge thermal regime. The measurements obtained for Delta 18O and Delta D had
extremely negative d- excess values, showing a strong divergence from the snowfalls expected to occur at the elevation of the sites. Sublimation processes were taken into account to define
the origin of the ice-wedge ice. The presence of hoarfrost crystals, observed in the ice-wedge cracks during summer field surveys, corroborate that sublimation processes may control the
formation of ice in the growth processes of ice wedges. Petrofabric analyses indicated the increasing of crystal size from the ice-wedge centre outward, and in c-axis directions they showed a rotation of crystals from the centre towards the sides. The monitoring of the thermal regime of three ice wedges over a five-year period highlighted that, in winter, extreme gradients between the temperatures at the ground surface and those at the tops of the ice wedges may
trigger cracking. Moreover, the presence of open cracks in the ice wedges, in summer, indicates that the growth processes are still active under the present climatic conditions
Isotopic composition and thermal regime of ice wedges in Northern Victoria Land, East Antarctica
No full textIce wedges, with tops located 27 to 55 cm below the ground surface, were studied over several summers between 1998and 2006 at three sites with differing elevations in northern Victoria Land, East Antarctica. The thermal regime, based on data-logger measurements over five years, exhibits very low temperatures, an inferred absence of snow, and high temperature gradients between the ground surface and the top of the ice wedge that may trigger cracking. A co-isotopic study of the wedge-ice oxygen (d18O) and hydrogen (dD) isotopic values shows extremely negative deuterium excess values and a strong divergence from the expected precipitation. These values and observations of hoarfrost crystals in ice-wedge cracks during summer field surveys indicate that sublimation processes control the formation of ice in wedges, especially at high elevations within this region
Thermal regime, isotopic and morphological characteristics of ice wedges in northern Victoria Land, Antarctica.
No full textThe preliminary results of the research carried out on six ice wedges located in the vicinity of Terra Nova Bay, in northern Victoria Land utilized co-isotope analyses to show that sublimation processes contribute to the formation of the ice-wedge ice. Analysis of the thermal regime of one ice wedge over a period of one year shows
that extreme gradients between the ground surface and the top of the ice wedge temperatures may trigger ice-wedge cracking
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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