101 research outputs found
Area selection for diamonds using magnetotellurics : examples from southern Africa
Author Posting. © Elsevier B.V., 2009. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Lithos 112 (2009): 83-92, doi:10.1016/j.lithos.2009.06.011.Southern Africa, particularly the Kaapvaal Craton, is one of the world’s best natural
laboratories for studying the lithospheric mantle given the wealth of xenolith and seismic data
that exist for it. The Southern African Magnetotelluric Experiment (SAMTEX) was launched
to complement these databases and provide further constraints on physical parameters and
conditions by obtaining information about electrical conductivity variations laterally and with
depth. Initially it was planned to acquire magnetotelluric data on profiles spatially coincident
with the Kaapvaal Seismic Experiment, however with the addition of seven more partners to
the original four through the course of the experiment, SAMTEX was enlarged from two to
four phases of acquisition, and extended to cover much of Botswana and Namibia. The
complete SAMTEX dataset now comprises MT data from over 675 distinct locations in an
area of over one million square kilometres, making SAMTEX the largest regional-scale MT
experiment conducted to date.
Preliminary images of electrical resistivity and electrical resistivity anisotropy at 100
km and 200 km, constructed through approximate one-dimensional methods, map resistive
regions spatially correlated with the Kaapvaal, Zimbabwe and Angola Cratons, and more
conductive regions spatially associated with the neighbouring mobile belts and the Rehoboth
Terrain. Known diamondiferous kimberlites occur primarily on the boundaries between the
resistive or isotropic regions and conductive or anisotropic regions.
Comparisons between the resistivity image maps and seismic velocities from models
constructed through surface wave and body wave tomography show spatial correlations
between high velocity regions that are resistive, and low velocity regions that are conductive.
In particular, the electrical resistivity of the sub-continental lithospheric mantle of the
Kaapvaal Craton is determined by its bulk parameters, so is controlled by a bulk matrix
property, namely temperature, and to a lesser degree by iron content and composition, and is
not controlled by contributions from interconnected conducting minor phases, such as
graphite, sulphides, iron oxides, hydrous minerals, etc. This makes quantitative correlations
between velocity and resistivity valid, and a robust regression between the two gives an
approximate relationship of Vs [m/s] = 0.045*log(resistivity [ohm.m]).We especially thank our
academic funding sponsors; the Continental Dynamics programme of the U.S. National
Science Foundation, the South African Department of Science and Technology, and Science
Foundation Ireland
Soil temperature effects on the structure and diversity of plant and invertebrate communities in a natural warming experiment
1. Global warming is predicted to significantly alter species physiology, biotic interactions and thus ecosystem functioning, as a consequence of coexisting species exhibiting a wide range of thermal sensitivities. There is, however, a dearth of research examining warming impacts on natural communities. 2. Here, we used a natural warming experiment in Iceland to investigate the changes in above-ground terrestrial plant and invertebrate communities along a soil temperature gradient (10 degrees C-30 degrees C). 3. The alpha-diversity of plants and invertebrates decreased with increasing soil temperature, driven by decreasing plant species richness and increasing dominance of certain invertebrate species in warmer habitats. There was also greater species turnover in both plant and invertebrate communities with increasing pairwise temperature difference between sites. There was no effect of temperature on percentage cover of vegetation at the community level, driven by contrasting effects at the population level. 4. There was a reduction in the mean body mass and an increase in the total abundance of the invertebrate community, resulting in no overall change in community biomass. There were contrasting effects of temperature on the population abundance of various invertebrate species, which could be explained by differential thermal tolerances and metabolic requirements, or may have been mediated by changes in plant community composition. 5. Our study provides an important baseline from which the effect of changing environmental conditions on terrestrial communities can be tracked. It also contributes to our understanding of why community-level studies of warming impacts are imperative if we are to disentangle the contrasting thermal responses of individual populations.Peer reviewe
Characterisation of chemosensory trigeminal receptors in the rainbow trout, Oncorhynchus mykiss
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