A Long-Term Ecological Research strategy for polar environmental research     

Langdon B. Quetin  Robin M. Ross 《Marine pollution bulletin》1992,25(9-12):233-238

The Palmer Long-Term Ecological Research site was established in the vicinity of Palmer Station, Antarctica in 1990. It is the eighteenth and most recent addition to the LTER Network funded by the National Science Foundation of the United States. The Palmer LTER expands the geographical and habitat coverage of the LTER Network to southern polar regions and offers unique opportunities for ecological synthesis and the study of long-term ecological phenomena in the Antarctic marine ecosystem. The central hypothesis of the Palmer LTER is that many significant biological processes in the Antarctic marine environment are strongly affected by physical processes, particularly interannual variability in the annual extent and dynamics of pack ice and variations in ocean currents. The Palmer LTER Studies Group is multidisciplinary and seeks to understand and model interactions between key species from different trophic levels and the physical environment. It is recognized that anthropogenic impacts in Antarctica cannot be adequately evaluated without understanding the underlying natural variability in Antarctic ecosystems.  相似文献   

Corrections for near surface effects: Decomposition of the magnetotelluric impedance tensor and scaling corrections for regional resistivities: A tutorial   总被引：1，自引：0，他引：1  

Ross W. Groom  Karsten Bahr 《Surveys in Geophysics》1992,13(4-5):341-379

This paper primarily examines the effects of small-scale or near-surface conductivity inhomogeneities on the magnetotelluric (MT) impedance tensor. These effects cause three different types of distortion results. (1) The well-knownstatic shifts of sounding curves. (2) When the underlying regional setting is two-dimensional then the two regional impedances are mixed in an arbitrary coordinate system. Thus the level and shape of each sounding curve is distorted as are the phases. (3) At sufficiently high frequencies these effects generate anomalous magnetic fields that in turn alter the background phases.This tutorial first explores the usefulness of various MT tensor analysis techniques to overcome the problem of phase mixing and to recover regional information in the presence of local geological noise. Synthetic and experimental data are considered. A sequence ofa priori models of increasing complexity are described. The use of appropriate decompositions of the MT tensor each with an increasing number of parameters is emphasised. In a second part, phase mixing and static shifts are examined from a synoptic view. Some static shift removal techniques that can be used in conjunction with the decomposition are discussed. This paper is not a review but rather an investigation of a few methods that the authors have found useful with field data.  相似文献   

The vourinos ophiolite complex, Greece: The tectonite suite     

J.V. Ross  J-C.C. Mercier  H.G. Ave Lallemant  N.L. Carter  J. Zimmerman   《Tectonophysics》1980,70(1-2)

Classical structural analysis, in combination with new techniques including pyroxene thermobarometry and recrystallized-grain- and subgrain-size paleopiezometry, has been used to deduce the tectonic history of the Vourinos Ophiolite Complex, Greece. Results can be used to infer the variation with depth of differential stress in the upper mantle and indicate that these rocks were subjected to an initial stress level of 10–100 bar over a depth interval from 100 to 40 km, respectively. Subsequently, they underwent mylonitization, associated with stresses of about 2500 bar at 30 km depth. Rocks equilibrated at the deepest levels commonly have the highest structural positions within the ultramafic tectonites and also show appreciable Al depletion. Lack of annealing recrystallization in the mylonitic rocks, together with low stress levels and an abnormally high pyroxene geotherm for the Complex lead to the interpretation of the Complex being the remnant of a mantle diapir, with an overlying magma chamber, located at a spreading ridge.  相似文献   

Rheology of the upper mantle: Inferences from peridotite xenoliths   总被引：1，自引：0，他引：1  

H.G. Ave Lallemant  J-C.C. Mercier  N.L. Carter  J.V. Ross   《Tectonophysics》1980,70(1-2)

Stress estimates as a function of depth are obtained for peridotite xenoliths from the upper mantle of three types of tectonic environments by applying revised recrystallizedgrain-size paleopiezometry and pyroxene thermobarometry. The general increase in grain size with depth and hence decrease in deviatoric stress, observed previously, is confirmed but reversals in these trends are now established and remain enigmatic. Stresses and temperatures obtained are combined with a representative creep-flow law to calculate strainrate and viscosity profiles that appear to be physically reasonable. Profiles for the highthermal-gradient rift/ridge environments show a complexity that is interpreted as.a rheological discontinuity resulting from the emplacement of asthenospheric diapirs during late stages of continental rifting. Profiles for broad continental extension zones (C.E.Z.), believed to be most representative of oceanic upper mantle, fluctuate between 50 and 80 km, with a general small increase in strain rate and decrease in viscosity with depth; deepest samples apparently come from the base of the lithosphere. Profiles for the infracratonic mantle of southern Africa show nearly a uniform increase in strain rate to values greater than 10⁻¹⁴/sec, and a decrease in viscosity to lower than 10²¹ poise, at a depth of 230 km. These profiles may transect the mechanically defined lithosphere—asthenosphere transition at about 200 km and, if so, there is no evidence for a mechanical discontinuity at the boundary. This observation, coupled with evidence that the sense of shear is homogeneous for all mantle profiles constructed, clearly favors a model whereby lithospheric plates are dragged by thermal convection of the asthenosphere below. Sea-floor spreading rates and relative plate-velocity estimates are consistent with this interpretation but do not independently permit a definitive choice between the two favored models advanced to explain the driving force for plate motions.  相似文献   

Ecology of saltcedar—A plea for research     

Benjamin L. Everitt 《Environmental Geology》1980,3(2):77-84

Because of the interdiscriplinary requirements of studies of river-floodplain systems, development of this field in the United States has been slow, and much information needed for watershed and river-basin planning is not available. This is particularly true in the southwestern United States, where study has been further complicated within the last 50 years by the introduction and spread of saltcedar (Tamarix chinensis)which has occurred simultaneously with other independently generated environmental changes. The spread of saltcedar has been aided both by purposeful planding and by a fortuitous combination of events that has weakened the native ecosystem at the time that seeds of the new species have been made available, events that possibly include changes in such environmental parameters as flood frequency, channel stability, the season of the peak annual flood, water temperature and salinity, and sediment grain size. Careful research is needed to unravel and understand the network of relationships involved. Phenomena are arranged in chains of necessary sequence. … If we examine any link of the chain, we find it has more than one antecedent and more than one consequent. … Antecedent and consequent relations are therefore not merely linear, but constitute a plexus; and this plexus pervades nature.  相似文献   

Prediction of Flow and Hydraulic Head Fields for Vertical Circulation Wells     

Ross D. Philip  Gary R. Walter 《Ground water》1992,30(5):765-773

  相似文献   

The construction of extreme compositions     

Ross M. Renner 《Mathematical Geology》1995,27(4):485-497

If a geochemical compositional dataset X (n×p)is a realization of a physical mixing process, then each of its sample (row) vectors will approximately be a convex combination (mixture) of a fixed set of (l×p)extreme compositions termed endmembers. The kpoints in p-space corresponding to a specified set of k (klinearly independent endmember estimates associated with a p-variate (n×p)compositional dataset X,define the vertices of a (k–1)dimensional simplex H.The nestimated mixtures X (n×p)which together account for the systematic variation in the dataset X,should each be convex combinations of the kfixed endmember estimates. Accordingly,the npoints in p-space which represent these mixtures should be interior points of the simplex H.Otherwise, for each sample point which lies outside H,at least one of the mixture coefficients (endmember contributions) will be negative. The purpose of this paper is to describe procedures for expanding H in the situation that its vertices are not a set of extreme points for the set which represents the mixtures.  相似文献   

SOUTH AUSTRALIA FROM THE AIR. By M. Williams (Ed.) A.N.Z.A.A.S.     

G. Ross  Cochrane 《New Zealand geographer》1971,27(1):94-95

  相似文献   

THE CENTRAL BUSINESS DISTRICT OF MEXICO CITY AS INDICATED ON THE SANBORN MAPS OF 1906*     

Stanley H. Ross 《The Professional geographer》1971,23(1):31-39

  相似文献   

New material of Laophis crotaloides,an enigmatic giant snake from Greece,with an overview of the largest fossil European vipers     

Georgios L. Georgalis  Zbigniew Szyndlar  Benjamin P. Kear  Massimo Delfino 《Swiss Journal of Geoscience》2016,109(1):103-116

  相似文献