evolution of a surge type glacier in its quiescent phase kongsvegen spitsbergen 1964 95 kongsyegen is a 102 km 2 sub polar polythermal surge type glacier in northwest spitsbergen svalbard it surged just before 1948 and is currently in its quiescent phase measurements of surface geometry since 1966 show a retreat of the front and strong thinning of up to 75 m in the ablation area and a build up of up to 32 m in the accumulation area present day annual velocities along the glacier are low from 1 4 up to 3 6 m a 1 the measured mean net balance for the period 1987 94 and the balance reconstructed back to 1967 show a weak positive balance of about 0 1 m w e the measured actual ice flux is low and the mass transfer down glacier at the ela is only about 3 20 of that required for steady state thus the glacier is building up towards a new surge the total thickening rate on kongsvegen is somewhat higher than in other cases from svalbard but it is small compared with other well studied surge type glaciers in alaska and he pamirs this relatively low rate of change is a function of the low accumulation rate and the relatively cold climate compared to other areas and is common for surge type glaciers in svalbard

activation volume of si diffusion in san carlos olivine implications for upper mantle rheology the effect of pressure on silicon diffusion in san carlos olivine has been determined using a uniaxial split sphere apparatus ussa 2000 and the nuclear reaction analysis technique nra on the 30si isotope experiments were performed at high temperature t 1763 k and pressures between 4 and 9 gpa the specimens were inserted into a pure fe capsule which is very effective in maintaining the oxygen fugacity within the stability field of olivine as well as providing a soft medium to mechanically protect the crystals diffusion profiles along the b crystallographic axis and of characteristic length of the order of 50 nm were obtained after annealing the olivine samples between 1 and 4 hours we find the activation volume for silicon diffusion in san carlos olivine to be vsi 0 7 2 3 10 6 m3 mol after a correction for oxygen fugacity which is pressure dependent this result demonstrates that pressure has practically no effect upon silicon diffusion under our temperature and pressure conditions extrapolation of our high pressure measurements to 1 atm gives a si diffusion coefficient log dsi 18 9 1 0 with dsi in m2 s finally our experiments show that according to the point defect model of jaoul 1990 the activation volume for creep of olivine at high temperature is dominated by the effect of pressure on the mg defect concentration and has an activation volume close to 6 10 6 m3 mol

halogen chemistry and hydrogen isotopes of apatite from the 3 7 ga isua supracrustal belt sw greenland abstract the origin and evolution of volatiles particularly water in the abiotic early earth environment have been intensively studied and this is a topic of high relevance when considering the timing and conditions of life s emergence investigation of hydrogen isotopes in the oldest crystals of minerals from the apatite group ca10 po4 6 f cl oh 2 should bring new insight to this topic as the d h ratio of apatite has proved useful for establishing the evolution of volatiles in other solar system bodies apatite crystals from metasedimentary and metavolcanic rocks collected from a low strain domain of the eoarchean isua supracrustal belt have been investigated for their d h signatures using secondary ion mass spectrometry and for major and trace element abundances using epma and laser ablation icp ms apatite crystals from isua have a broad range in volatile compositions both within samples from the same lithology e g banded iron formation bif and between different lithologies bif metacarbonate mafic dyke most of the crystals are chlorine rich which is in contrast to typical modern sedimentary apatite that is predominantly carbonate fluorapatite we have used the ree distribution patterns from isua apatite to distinguish those crystals having sedimentary metasomatic and magmatic origins the d h ratios for all samples were determined to be very low with dvsmow values falling within the range from 93 to 56 d values of isua apatite do not correlate with ree signatures of crystals nor could we relate d to the host lithologies we conclude that this geochemical system has been reset during long and multi phase geologic history making it difficult if not impossible to use hydrogen isotopes for assessment of the primary signatures of the archean hydrosphere

hydrological characteristics of the drainage system beneath a surging glacier a rare combination of natural circumstances permits assessment of current theories on water flow beneath glaciers outburst floods from the subglacial lake grimsvotn in iceland took place before during and after surging of skei ararjokull the glacier beneath which the outburst floods drain the observable drainage patterns associated with these floods show the different nature of the basal water conduit system of the glacier during surge and non surge phases during surge conditions basal water is dispersed slowly across the bed in a distributed drainage system but when the glacier is not surging water is transported rapidly through a system of tunnels

surface velocity and mass balance of ice streams d and e west antarctica over 75 000 surface velocity measurements are extracted from sequential satellite imagery of ice streams d and e to reveal a complex pattern of flow not apparent from previous measurements horizontal and vertical strain rates calculated from surface velocity indicate that the bed experiences larger basal shear where the surface of these ice streams is rougher ten airborne radar profiles and one surface based radar profile of ice thickness make possible the calculation of mass balance for longitudinal sections of each ice stream improved data collection methods increase data density substantially reducing random errors in velocity however systematic errors continue to limit the ability of the flux differencing technique used here to resolve local variations in mass balance nevertheless significant local variations in mass balance are revealed while overall ice streams d and e are in approximate equilibrium an earlier estimate of the net mass balance for ice stream d is improved

ice front variations and speed changes of calving glaciers in the southern patagonia icefield from 1984 to 2011 patagonian icefields are losing volume and their loss is due partly to rapid changes in their outlet glaciers that terminate in lakes or the ocean despite this key influence from outlet glaciers relatively few of these calving glaciers have had high frequency measurements on their frontal variations and ice speed changes we describe here recent frontal variations and ice speed changes of all 28 major calving glaciers in the southern patagonia icefield spi including ice speed maps covering approximately half of the entire icefield the analysis is based on satellite data from 1984 to 2011 over this period only the two termini of glaciar pio xi advanced of the remaining glacial fronts 12 changed less than 0 5 km but 17 retreated at least 0 5 km in the latter group three glacial fronts glaciar jorge montt hps12 and upsala retreated over 6 km averaged over all 31 glacial fronts of the calving glaciers the front positions retreated 1 56 km median is 0 71 km along the flowline within 20 km of the front the ice speeds up to 5900 200 m a 1 except for regions showing large acceleration or deceleration the mean speed over the measured area decreased by 30 m a 1 from 1984 to 2011 the three most rapidly retreating glaciers showed much larger acceleration near the calving front suggesting that ice dynamics drive their rapid retreat thus we see retreat as a long term trend for the calving glaciers in the spi with behavior that implies a dynamically controlled rapid recession that may explain the recently reported volume change of the spi

the olivine spinel transformation and the rheology of subducting lithosphere during subduction relatively hot lithospheric slabs are expected to deform in a superplastic flow regime below a depth of 300 km if olivine reacts to fine grained spinel this process reduces the flow strength of such slabs below the phase boundary so that they become aseismic at about this depth in colder slabs temperatures are too low for superplastic deformation and a high flow strength and seismic activity are maintained to a depth of 600 700 km

volume and velocity changes at mittivakkat gletscher southeast greenland we document changes for mittivakkat gletscher the peripheral glacier in greenland with the longest field based observed mass balance and surface velocity time series between 1986 and 2011 this glacier changed by 15 in mean ice thickness and 30 in volume we attribute these changes to summer warming and lower winter snow accumulation vertical strain compensated for 60 of the elevation change due to surface mass balance smb in the lower part and 25 in the upper part the annual mean ice surface velocity changed by 30 which can be fully explained by the dynamic effect of ice thinning within uncertainty mittivakkat gletscher summer surface velocities were on average 50 60 above winter background values and up to 160 higher during peak velocity events peak velocity events were accompanied by uplift of a few centimeters

accelerating shrinkage of patagonian glaciers from the little ice age ad 1870 to 2011 davies b j glasser n f 2012 accelerating shrinkage of patagonian glaciers from the little ice age similar to ad 1870 to 2011 journal of glaciology 58 212 1063 1084

high temperature elasticity of iron bearing olivines the first high temperature data on the nine adiabatic elastic moduli for iron bearing olivine are reported these measurements are on two single crystal specimens of natural olivine at ambient pressure and from room temperature to a maximum of 1500 k the two specimens contain 8 and 9 modal percent fayalite which required the oxygen fugacity be controlled at high temperature to preserve their chemical stability the rectangular parallelepiped resonance apparatus was adapted to buffer the specimens from the atmosphere with a mixture of co and co2 gas a small increase 1 2 gpa in the adiabatic bulk modulus of each specimen over that of end member forsterite was found the data are high quality to extreme temperatures with good agreement found when comparing the temperature derivatives of the elastic moduli of the two specimens neither specimen exhibits measurable nonlinear temperature dependence in the computed isotropic bulk and shear moduli which is in contrast to published forsterite data the temperature derivatives of the isotropic bulk modulus ks are 1 69 1 80 10 2 gpa k 1 for the two olivine specimens and the shear modulus g derivatives are 1 38 1 36 10 2 gpa k 1 these derivatives are only slightly larger in magnitude than ks t p 1 56 10 2 and g t p 1 30 10 2 gpa k 1 found previously for iron bearing olivine over a very small temperature range there are also no significant differences between the temperature derivatives found here and the average derivatives of end member forsterite from data retrieved over a slightly larger temperature range several dimensionless parameters have been calculated from these results and are discussed in view of systematics which bear on high pressure phases in earth s transition zone one result from these systematics related to the seismic velocities in the earth and especially the shear wave velocities is that an olivine content of less than 50 is implied at the 400 km discontinuity if earth s upper mantle is isochemical furthermore the substitution of almost 10 iron for magnesium at the forsterite end of the olivine solid solution series has little effect on the dimensionless parameters or on the temperature derivatives of the elastic moduli at high temperature

hasty retreat of glaciers in northern patagonia from 1985 to 2011 mapping changes in glacier extent from repeat optical satellite data has revealed widespread glacier decline in nearly all regions of the world over the past few decades while numerous studies have documented the changes of the outlet glaciers of the northern and southern patagonia icefields npi spi information about glacier changes in the patagonian andes to the north of the npi is much scarcer here we present an assessment of area changes for glaciers mainly located in the palena district of chile based on glacier inventories for 1985 2000 and 2011 that were derived from two consecutive landsat scenes and a digital elevation model the analysis revealed a dramatic area decline for the largest glaciers and total area loss of 25 from 1985 to 2011 the lower parts of several larger glaciers 10 km 2 melted completely area loss below 1000 m elevation was 50 100 in both periods and 374 glaciers out of 1664 disappeared the number of proglacial lakes increased from 223 to 327 and their area expanded by 11 6 km 2 59 between 1985 and 2011 seasonal snow persisting at high elevations in the 2011 scene was a major obstacle to glacier delineation so the obtained area change rate of 1 a 1 over the entire period is a lower bound estimate the observed climate trends e g cooling in puerto montt are in contrast to the observed shrinkage

surface velocities and ice front positions of eight major glaciers in the southern patagonian ice field south america from 2002 to 2011 abstract the patagonian ice fields are known to have undergone rapid retreat of frontal positions and significant thinning of its glaciers over the past decades however surface velocities have been measured at only a few of these glaciers thus it remains uncertain if and to what extent the glacier dynamics has changed over time and contributed to ice loss in these ice fields in this study we examine the temporal evolution of flow velocities and ice front positions at eight major glaciers in the southern patagonian ice field spi hielo patagonico sur by using advanced synthetic aperture radar asar images from the environmental satellite envisat launched in 2002 by the european space agency and advanced land observation satellite phased array type l band synthetic aperture radar alos palsar data recorded from 2002 to 2011 the examined eight glaciers include glaciar jorge montt occidental pio xi or bruggen o higgins viedma upsala perito moreno and grey not all the glaciers revealed significant changes in frontal positions and flow velocities in the study period we detected significant temporal velocity changes at glaciar upsala jorge montt occidental and pio xi among these four glaciers glaciars upsala jorge montt and occidental revealed significant acceleration and terminus retreat and were undergoing dynamic thinning the markedly different absolute velocities but equally large longitudinal near terminus stretching at the three glaciers support a calving model based on crevasse depth criteria which predict a calving position where crevasse depths are equal to ice thickness crevasse depths are controlled by the longitudinal stretching rate meanwhile glaciar pio xi revealed complex spatial and temporal evolution in surface velocities without significant retreat and its dynamics remains enigmatic

accuracy assessment for mapping glacier flow velocity and detecting flow dynamics from aster satellite imagery tasman glacier new zealand abstract image matching via correlation of remotely sensed imagery is an increasingly popular technique for measuring glacier flow because it can provide spatially distributed measurements while mitigating many of the challenges accompanying in situ measurements of glacier velocity despite the increasing use of such techniques and the requirement for well understood uncertainties where analysis of temporal variability is sought studies that incorporate an assessment of accuracy based on in situ data remain rare this study presents a rigorous methodology to quantify the uncertainties that apply to glacier flow velocities derived from optical satellite imagery this method is applied on three successive aster images of tasman glacier new zealand evaluation of the quality of co registration between image pair constituents allows unique uncertainties to be calculated for individual velocity measurements these uncertainties have magnitudes that correspond to sub pixel co registration errors and account for anisotropic co registration variance compared to estimated velocities uncertainties on the order of 2 30 are achieved flow fields for the 2009 2010 and 2010 2011 periods were derived using various spectral bands and validated with in situ data obtained by gps survey over a nearly coincident period this revealed the importance of considering the spectral characteristics of the target surface when selecting bands for image correlation while validation demonstrated the success of the implemented methodology uncertainties derived for the flow fields permitted statistical significance of velocity change between measurement periods to be assessed significant velocity changes observed across the glacier surface suggest that the tasman glacier behaves in a more dynamic way than previously recognised highlighting the advantages of the methodology described here

calving processes and the dynamics of calving glaciers abstract calving of icebergs is an important component of mass loss from the polar ice sheets and glaciers in many parts of the world calving rates can increase dramatically in response to increases in velocity and or retreat of the glacier margin with important implications for sea level change despite their importance calving and related dynamic processes are poorly represented in the current generation of ice sheet models this is largely because understanding the calving problem involves several other long standing problems in glaciology combined with the difficulties and dangers of field data collection in this paper we systematically review different aspects of the calving problem and outline a new framework for representing calving processes in ice sheet models we define a hierarchy of calving processes to distinguish those that exert a fundamental control on the position of the ice margin from more localised processes responsible for individual calving events the first order control on calving is the strain rate arising from spatial variations in velocity particularly sliding speed which determines the location and depth of surface crevasses superimposed on this first order process are second order processes that can further erode the ice margin these include fracture propagation in response to local stress imbalances in the immediate vicinity of the glacier front undercutting of the glacier terminus by melting at or below the waterline and bending at the junction between grounded and buoyant parts of an ice tongue calving of projecting submerged ice feet can be regarded as a third order process because it is paced by first or second order calving above the waterline first order calving can be represented in glacier models using a calving criterion based on crevasse depth which is a function of longitudinal strain rate modelling changes in terminus position and calving rates thus reduces to the problem of determining the ice geometry and velocity distribution realistic solutions to the problem of modelling ice flow therefore depend critically on an appropriate choice of sliding law models that assume that basal velocities are controlled by basal drag can replicate much of the observed behaviour of calving glaciers with grounded termini but an important limitation is that they cannot be used to model floating glacier termini or ice shelves alternative sliding laws that parameterise drag from the glacier margins provide more flexible and robust ways of representing calving in ice sheet models such models can explain a remarkable range of observed phenomena within a simple unifying framework including downglacier increases in velocity and strain rates where basal and or lateral drag diminishes flow acceleration in response to thinning through time the tendency for glaciers to stabilise at pinning points in relatively shallow water or fjord narrowings the constraints on ice shelf stability and the contrasts in calving rates between tidewater and freshwater calving glaciers many unresolved issues remain however including the role played by the removal of backstress in the acceleration of retreating calving glaciers and the controls on melting at and below the waterline

native nickel in the tag hydrothermal field sediments mid atlantic ridge 26 n space trotter guest from mantle or a widespread mineral connected with serpentinization 1 tiny metallic particles have been found in the sediments of the trans atlantic geotraverse tag hydrothermal field mid atlantic ridge mar the metallic grains are almost pure ni and have compositional and structural characteristics similar to those of other terrestrial metallic ni0 occurrences native nickel grains documented here for the first time in oceanic sediments appear in calcareous oozes intercalated with metalliferous layers layers with bedrock rubble and sporadically scattered cosmic microspherules there are three possibilities for the metallic ni0 genesis 1 cosmic 2 lower mantle at the core mantle boundary or 3 upper mantle lower crust the flake like appearance of the ni0 grains rules out cosmic ablation origin no unequivocal evidence was found that the ni0 particles could have formed under high pressure conditions similar to those at the core mantle boundary ni0 formation through seawater serpentinization of the upper mantle lower crust is the most plausible mechanism at the slow spreading mar seawater penetrates down through highly fractured crest zone and serpentinizes the olivine and pyroxene of the upper mantle lower crust ultramafics mafics serpentinization results in the generation of highly reduced volatile species h2 and hydrocarbons in such an extremely reduced environment fe and other transition metals co ni cu zn released from olivines and pyroxenes tend to appear as native metals if fs2 approaches 0 the lightened serpentinized blocks uplift and expose the serpentinized ultramafics mafics at the rift valley s walls i speculate that tectonic movements and weathering could liberate the native metallic grains scattered in the serpentinized rocks which may then have been dispersed in the proximate sediments by near bottom currents

contribution of the patagonia icefields of south america to sea level rise digital elevation models of the northern and southern patagonia icefields of south america generated from the 2000 shuttle radar topography mission were compared with earlier cartography to estimate the volume change of the largest 63 glaciers during the period 1968 1975 2000 these glaciers lost ice at a rate equivalent to a sea level rise of 0 042 0 002 millimeters per year in the more recent years 1995 2000 average ice thinning rates have more than doubled to an equivalent sea level rise of 0 105 0 011 millimeters per year the glaciers are thinning more quickly than can be explained by warmer air temperatures and decreased precipitation and their contribution to sea level per unit area is larger than that of alaska glaciers

high temperature creep of olivine crystals from four localities to compare the rheologies of olivine samples from various tectonic settings an experimental investigation of the high temperature creep behavior of crystals from china fo89 91 norway fo93 and the red sea fo90 was carried out the results were examined in the context of the well documented flow data for olivine from the usa fo89 93 both the major element and the minor element compositions differed depending on locality creep experiments were performed in an 1 atm deformation rig at temperatures from 1200 to 1500 c and compressive stresses from 15 to 175 mpa oxygen fugacity was varied over the full stability field of olivine during deformation along three orientations the samples remained in contact with orthopyroxene the mechanical results for samples from all three localities can be summarized as follows for the 110 c orientation three rate controlling creep mechanisms were observed each can be described by a power law relationship activation energies of 160 kj mol 1 1100 kj mol 1 and 380 kj mol 1 and oxygen fugacity exponents of 0 37 0 04 and 0 13 were obtained for the low intermediate and high temperature creep regimes respectively for the 101 c orientation activation energies of 270 kj mol 1 and 660 kj mol 1 and oxygen fugacity exponents of 0 30 and 0 05 were measured for the low and high oxygen fugacity creep regimes respectively for the 011 c orientation an activation energy of 510 kj mol 1 was obtained over the full range of oxygen fugacity however oxygen fugacity exponents of 0 02 and 0 31 were determined for the low and high oxygen fugacity creep regimes respectively the stress exponent is approximately 3 5 for all creep regimes within experimental error the creep results for olivine from all three localities are the same as those reported for san carlos olivine single crystals therefore moderate differences in forsterite content from fo89 to fo93 and in the concentrations of minor elements such as ni cr and mn do not significantly affect the creep behavior of olivine consequently rheological data obtained for olivine samples from specific localities can be reasonably applied to model plastic deformation processes in the upper mantle

rheology of olivine and the strength of the lithosphere in order to throw some light on the rheological behavior of the upper mantle of the earth a detailed series of high temperature deformation experiments has been performed on olivine single crystals at 1 atm pressure under highly controlled thermodynamic conditions the effects of stress temperature oxygen fugacity and orthopyroxene activity on the deformation rate of olivine have been carefully measured for the major high temperature slip systems these experimental results have been extrapolated to the pressures and strain rates of the upper mantle to provide new insight into the mechanical behavior of the mantle and a better constrained approach to extrapolation of laboratory deformation data to the conditions present in the upper mantle the authors suggest that extrapolations in stress provide the most reliable means for extending laboratory creep data to upper mantle strain rates they also predict that in the dislocation creep field the bulk of the strain in olivine in the upper mantle is accommodated by the 010 100 slip system in addition true mantle strengths are probably most accurately modeled using the experimental data for samples oriented favoring the 010 001 slip system however the reliable prediction of mantle strengths requires highly accurate temperature versus depth relationships and good indicationsmore of the local oxygen fugacity in the mantle less

formation of band ogives and associated structures at bas glacier d arolla valais switzerland hambrey m j glasser n f goodsell becky 2002 formation of band ogives and associated structures at bas glacier d arolla valais switzerland journal of glaciology 48 161 pp 287 300 keywords europe switzerland geometrical structure three dimensional structure radar observation glacier crevasse models debris interface basal ice glacial tongue stratification glacier

an electron microscope study of the stability field and degree of nonstoichiometry in olivine the stability of san carlos olivine fo 90 5 relative to changes in oxygen fugacity at 1300 sup 0 c has been determined by studying the microstructural changes in single crystals using transmission and analytical electron microscopy the first detectable metallic phase heterogeneously nucleated along dislocations within 100 and 001 subboundaries had a composition ni sub 65 fe sub 35 equilibrated with a co co sub 2 gas mixture having an oxygen fugacity f sub 02 of 10 sup 5 6 pa although the 100 subboundaries contained a high density of dislocations with burgers vector 100 the nucleation sites were restricted to 010 and 001 dislocations a result consistent with the theory of heterogeneous nucleation along dislocations under the reducing conditions of an f2 of 10 sup 12 pa a forsteritic olivine is produced at the gas mineral interface with a high density of metallic precipitates fe sub 96 ni sub 4 homogeneously nucleated in the olivine nonstoichiometry of the olivine was inferred from the absence of any additional silica rich phases the nonstoichiometry was analyzed in terms of possible crystalline defect structures especially vacancies assuming no evaporative losses from the surface except an oxygen exchange reaction on the basis of the model proposed the highly reduced olivine would contain an excess of sio sub 2 x2more 0 355 compared with a stoichiometric value of 0 333 from the surface to a depth of several micrometers less

ice motion of the patagonian icefields of south america 1984 2014 2015 american geophysical union all rights reserved we present the first comprehensive high resolution mosaic of ice velocity of the northern npi and southern patagonian icefields spi from multiple synthetic aperture radar and optical data collected between 1984 and 2014 the results reveal that many of the outlet glaciers extend far into the central ice plateaus which implies that changes in ice dynamics propagate far inside the accumulation area we report pronounced seasonal to interannual variability of ice motion on pio xi and jorge montt a doubling in speed of jorge montt a major slow down of o higgins significant fluctuations of upsala and a deceleration of san rafael which illustrate the need for sustained continuous time series of ice motion to understand the long term evolution of the rapidly thinning icefields the velocity product also resolves major ambiguities in glacier drainage in areas of relatively flat topography illustrating the need to combine topography and flow direction to map drainage basins

the earth as a planet paradigms and paradoxes the independent growth of the various branches of the earth sciences in the past two decades has led to a divergence of geophysical geochemical geological and planetological models for the composition and evolution of a terrestrial planet evidence for differentiation and volcanism on small planets and a magma ocean on the moon contrasts with hypotheses for a mostly primitive still undifferentiated and homogeneous terrestrial mantle in comparison with the moon the earth has an extraordinarily thin crust the geoid which should reflect convection in the mantle is apparently unrelated to the current distribution of continents and oceanic ridges if the earth is deformable the whole mantle should wander relative to the axis of rotation but the implications of this are seldom discussed the proposal of a mantle rich in olivine violates expectations based on evidence from extraterrestrial sources these and other paradoxes force a reexamination of some long held assumptions

evolution of glacial flow and drainage during the ablation season proglacial discharge is controlled by the geometry of the glacial drainage network and by meltwater processes the glacial drainage systems of some alpine glaciers have been characterised using a model based on a proglacial discharge analysis in this paper we apply high frequency systemic analysis to data collected from the baounet glacier french alps during two successive ablation seasons our approach is based on an analysis of the evolution of daily recession curves during the ablation period the observed data are fitted by a single coefficient dependant recession law changes in are compared to variations in the daily discharge amplitude and the time lag between air temperature and proglacial discharge the changes in the values do not appear to be related to changes in the time lag and the amplitude of the daily discharge there were significant variations in the coefficient during the two ablation periods studied here even if there was no time lag or the daily discharge amplitude change high values of correspond to high drainage velocities therefore increases in values can be used as an indicator of the evolution of the glacier s internal drainage network

how do glaciers surge a review the quasi periodic oscillations between normal and fast motion exhibited by surge type glaciers provide the best observational opportunity to determine limiting conditions that allow fast motion the measurements from variegated glacier prove that its surge motion is caused by rapid sliding induced by high water pressure this arises from a major restructuring of the basal hydraulic system which impedes water discharge prior to and during surge although the evolving glacier geometry and stress distribution play a principal enabling role the seasonal timing of two distinct surge pulses each initiated in winter and terminated in summer indicates a major influence from variable external water inputs this influence is not considered in existing surge models and should promote caution in the use of data from temperate and subpolar surge type glaciers to deduce surge potential in polar ice masses the spatial spreading of surge motion from a zone of local initiation occurs by stress redistribution which may spread the surging zone rapidly upglacier or downglacier inside a region of active ice and by mass redistribution with compressional thickening at the surge front which enables down glacier propagation into less active ice the data from other surge type glaciers including the extensive data from medvezhiy glacier are not inconsistent with the above processes but are inadequate to establish whether completely different mechanisms operate in some surges the way by which water accumulates and produces fast sliding is not established in detail for any surge type glacier and may be different on different glaciers depending for example on the presence or absence of unconsolidated debris between the ice and rock

a reconciled estimate of glacier contributions to sea level rise 2003 to 2009 glaciers distinct from the greenland and antarctic ice sheets are losing large amounts of water to the world s oceans however estimates of their contribution to sea level rise disagree we provide a consensus estimate by standardizing existing and creating new mass budget estimates from satellite gravimetry and altimetry and from local glaciological records in many regions local measurements are more negative than satellite based estimates all regions lost mass during 2003 2009 with the largest losses from arctic canada alaska coastal greenland the southern andes and high mountain asia but there was little loss from glaciers in antarctica over this period the global mass budget was 259 28 gigatons per year equivalent to the combined loss from both ice sheets and accounting for 29 13 of the observed sea level rise

computer simulations of water interactions with low coordinated forsterite surface sites implications for the origin of water in the inner solar system abstract adsorption of water to fractal dust grains during accretion has been proposed as a possible source of water for rocky planets we have used computer simulations to study the feasibility of chemisorption onto forsterite dust grains by investigating the adsorption of dissociated water to stoichiometric and defective surfaces defects were modeled using steps corner sites and vacancies on different forsterite surfaces our results show that water dissociation is expected on the stoichiometric 100 surface but not on the stoichiometric 010 surface however the energies released by dissociative adsorption at steps and corners indicate that the energetic barrier to chemisorption on the 010 surface would be favorable if these features were present steps and corners on all surfaces studied produced mg sites that have low coordination and thus were highly reactive favoring the dissociation of water terrace size between the steps was shown to have a limited effect on the final energies although smaller terraces created more reactive mg sites at corners a simple langmuir model was used with the energetic data from our simulations to examine the effectiveness of water adsorption at temperature and pressure conditions applicable to the accretion disk the findings of this study suggest that water would be strongly chemisorbed at fractal forsterite surfaces even at low partial pressures suggesting that water could be retained during planetary accretion

large strain deformation and strain partitioning in polyphase rocks dislocation creep of olivine magnesiowustite aggregates aggregates composed of olivine and magnesiowustite have been deformed to large strains at high pressure and temperature to investigate stress and strain partitioning phase segregation and possible localization of deformation in a polyphase material samples with 20 vol of natural olivine and 80 vol of mg0 7fe0 3 o were synthesized and deformed in a gas medium torsion apparatus at temperatures of 1127 c and 1250 c a confining pressure of 300 mpa and constant angular displacement rates equivalent to constant shear strain rates of 1 3 3 10 4 s 1 the samples deformed homogeneously to total shear strains of up to 15 during constant strain rate measurements the flow stress remained approximately stable at 1250 c while it progressively decreased after the initial yield stress at the lower temperature mechanical data microstructures and textures indicate that both phases were deforming in the dislocation creep regime the weaker component magnesiowustite controlled the rheological behavior of the bulk material and accommodated most of the strain deformation and dynamic recrystallization lead to grain refinement and to textures that were not previously observed in pure magnesiowustite and may have developed due to the presence of the second phase at 1127 c olivine grains behaved as semi rigid inclusions rotating in a viscous matrix at 1250 c some olivine grains remained largely undeformed while deformation and recrystallization of other grains oriented for a slip on 010 resulted in a weak foliation and a texture typical for pure dry olivine aggregates both a slip and c slip on 010 were activated in olivine even though the nominal stresses were up to 2 orders of magnitude lower than those needed to activate these slip systems in pure olivine at the same conditions

thermal structure of svalbard glaciers and implications for thermal switch models of glacier surging switches between cold and warm based conditions have long been invoked to explain surges of high arctic glaciers here we compile existing and new data on the thermal regime of six glaciers in svalbard to test the applicability of thermal switch models two of the large glaciers of our sample are water terminating while one is land terminating all three have a well known surge history they have a thick basal layer of temperate ice superimposed by cold ice a cold terminus forms during quiescence but is mechanically removed by calving on tidewater glaciers the other three glaciers are relatively small and are either entirely cold or have a diminishing warm core all three bear evidence of former warm based thermal regimes and in two cases surge like behavior during the little ice age in svalbard therefore three types of glaciers have switched from slow to fast flow 1 small glaciers that underwent thermal cycles during and following the lia switches between cold and warm based conditions 2 large terrestrial glaciers which remain warm based throughout the entire surge cycle but develop cold termini during quiescence and 3 large tidewater glaciers that remain warm based throughout the surge cycle our results demonstrate that thermal switching cannot explain the surges of large glaciers in svalbard we apply the concept of enthalpy cycling to the spectrum of surge and surge like behavior displayed by these glaciers and demonstrate that all svalbard surge type glaciers can be understood within a single conceptual framework

rheology of the lithosphere selected topics we review recent results concerning the rheology of the lithosphere with special attention to the following topics 1 the flexure of the oceanic lithosphere 2 deformation of the continental lithosphere resulting from vertical surface loads and forces applied at plate margins 3 the rheological stratification of the continents 4 strain localization and shear zone development and 5 strain induced crystallographic preferred orientations and anisotropies in body wave velocities we conclude with a section citing the 1983 1986 rock mechanics literature by category

glacier area changes in the central chilean and argentinean andes 1955 2013 14 to improve our knowledge of glacier area changes in the central chilean and argentinean andes 32 9 s 33 4 s two new glacier inventories from 1989 to 2013 14 are compared with a reinterpreted inventory from 1955 comparisons show glacier area retreat of 30 3 since 1955 decreasing from 134 to 94 km2 in 2013 14 whilst the annual rate of area loss showed a small increase insignificant between the periods of 1955 1989 and 1989 2013 14 separate analysis of the 1989 and 2013 14 inventories including a larger sample revealed a higher rate of glacier change compared with the smaller samples of these inventories additionally an analysis at 5 year intervals for six major glaciers 1955 2013 indicates large variability in response times and area loss magnitudes glacier olivares alfa for example lost 63 of its ice area while the juncal norte glacier lost only 10 1955 2013 the findings from this study improve our current knowledge base concerning widespread glacier decline in the southern andes and furthers monitoring efforts in this poorly described region of the world a region containing vital water resources for populated areas in south america

regional cooling in a warming world recent temperature trends in the southeast pacific and along the west coast of subtropical south america 1979 2006 1 while it is widely accepted that the global mean atmospheric temperature has increased in recent decades the spatial distribution of global warming has been complex in this study we comprehensively characterize the spatial pattern including vertical structure of temperature trends along the subtropical west coast of south america continental chile for the period 1979 2006 and examine their consistency with expectations based on the cmip 3 ensemble of coupled ocean atmosphere simulations for the late 20th century in central and northern chile 17 37 s the most notable feature is a strong contrast between surface cooling at coastal stations 0 2 c decade and warming in the andes 0 25 c decade only 100 200 km further inland coastal radiosonde data imply that the coast andes variation is largely due to strong vertical stratification of temperature trends in the atmosphere west of the andes the coastal cooling appears to form part of a larger scale la nina like pattern and may extend below the ocean mixed layer to depths of at least 500 m over continental chile the cmip 3 gcm ensemble predicts temperature trends similar to those observed in the andes the cooling along the chilean coast is not reproduced by the models but the mean sst warming is weaker there than any other part of the world except the southern ocean it is proposed that the intensification of the south pacific anticyclone during recent decades which is also a simulated consequence of global warming is likely to play a major role in maintaining cooler temperatures off the coast of chile

relationships between organics water and early stages of aqueous alteration in the pristine cr3 0 chondrite met 00426 abstract in order to investigate the nature of organics at the time of their accretion into chondrite parent bodies as well as their subsequent evolution with aqueous alteration we have conducted a study of the morphologies spatial distribution and relationships between organic particles and the surrounding matrix phases in one of the most pristine carbonaceous chondrites currently known met 00426 cr which is therefore likely to contain the best preserved record of pre accretion features focused ion beam sections were extracted for transmission electron microscope observations from its matrix organic matter om shows a heterogeneous population of grains most of them smaller than 1 m diverse morphologies are observed such as compact rounded aggregates individual and aggregated nanoglobules and micron to nanometer sized veins a common feature is the systematic presence of cracks connected to the grains and filled with om the surrounding matrix groundmass consists of amorphous iron rich silicate particles intimately mixed with phyllosilicates sulfides and occasional tochilinite with sizes ranging from several hundreds of nanometers to below 10 nm a close spatial relationship is commonly observed between some of the organic matter particles and alteration phases such as tochilinite and phyllosilicates phyllosilicates sometimes occur intimately intercalated with organic matter at a scale below 10 nm we used tem eds techniques to quantify the water concentration in the matrix amorphous silicate material and the phyllosilicates the water contents of both materials are identical at 10 6 wt h 2 o and demonstrate that the amorphous silicate material in this meteorite is hydrated therefore even though these cr3 0 chondrites are the least altered objects from a mineralogical point of view their matrices contain significant amounts of water in the amorphous silicate this coupled in situ study of organics and aqueous alteration suggests that a significant population of the om accreted as a mixture of soluble and insoluble molecules together with water ice grains and that the om was mobile at the micrometer scale the spatial distribution of the om grains can therefore in part be attributed to parent body processes we suggest that as accreted ice melted hydration of the amorphous silicates and formation of tochilinite and phyllosilicates occurred in the immediate vicinity of the composite water ice organic matter grains the water soluble component of the organics was likely transported and redistributed in the surrounding porosity cracks grain boundaries as water circulated the textural settings suggest that some of the om material could have been polymerized during aqueous alteration and transformed into insoluble molecules perhaps during the last stages of alteration as water was consumed by silicate hydration reactions

experimental study and tem characterization of dusty olivines in chondrites evidence for formation by in situ reduction an analytical transmission electron microscopy atem study was undertaken in order to better understand the formation conditions of dusty olivines i e olivines containing abundant tiny inclusions of fe ni metal in primitive meteorites dusty olivines from type i chondrules in the bishunpur chondrite ll3 1 and from synthetic samples obtained by reduction of san carlos olivines were examined in both natural and experimental samples micron size metal blebs observed in the dusty region often show preferential alignments along crystallographic directions of the olivine grains have low ni contents typically 2 wt and are frequently surrounded by a silica rich glass layer these features suggest that dusty olivines are formed by a sub solidus reduction of initially fayalitic olivines according to the following reaction fe2sio4 in olivine 2fe metal xsio2 in melt 1 x sioin gas 3 x 2o2 in gas some volatilization of siogas may account for the apparent excess of metal relative to silica rich glass observed in both experimental and natural samples comparison with experimentally produced dusty olivines suggests that time scales of the order of minutes usually inferred for chondrule formation are also adequate for the formation of dusty olivines these observations are in agreement with the hypothesis that at least part of the metal phase in chondrites originated from reduction during chondrule formation

the dynamics of ice sheet outlets a comparison of data from aircraft altimetry landsat imagery and radia echo sounding has shown characteristic surface topographies associated with sheet and stream flow the transition between the two is abrupt and occurs at a step in the subglacial topography this marks the onset of basal sliding and high velocities caused by subglacial water it results in crevassed amphitheatre like basins round the head of outlet glaciers it is also the zone of maximum driving stress beyond which values decline rapidly as velocities increase this abrupt transition appears to be topographically controlled since basal temperatures are at the pressure melting point well inland of the change in regime the marie byrd land ice streams exhibit qualitative differences from other ice sheet outlets however the change to lower driving stresses is much more gradual and occurs several hundred kilometres inland such ice streams have particularly low surface slopes and appear in form and flow regime to resemble confined ice shelves rather than grounded ice the repeated association of the transition to rapid sliding with a distinct subglacial feature implies a stabilizing effect on discharge through outlet glaciers acceleration of the ice is pinned to a subglacial step and propagation of high velocities inland of this feature seems improbable rapid ice flow through subglacial trenches may also ensure a relatively permanent trough through accentuation of the feature by erosion this is concentrated towards the heads of outlet glaciers up stream of the region where significant basal decoupling occurs this may be a mechanism for the overdeepening of fjords at their inland ends and the development of very steep fjord headwalls

melt induced speed up of greenland ice sheet offset by efficient subglacial drainage fluctuations in surface melting are known to affect the speed of glaciers and ice sheets but their impact on the greenland ice sheet in a warming climate remains uncertain although some studies suggest that greater melting produces greater ice sheet acceleration others have identified a long term decrease in greenland s flow despite increased melting here we use satellite observations of ice motion recorded in a land terminating sector of southwest greenland to investigate the manner in which ice flow develops during years of markedly different melting although peak rates of ice speed up are positively correlated with the degree of melting mean summer flow rates are not because glacier slowdown occurs on average when a critical run off threshold of about 1 4 centimetres a day is exceeded in contrast to the first half of summer when flow is similar in all years speed up during the latter half is 62 16 per cent less in warmer years consequently in warmer years the period of fast ice flow is three times shorter and overall summer ice flow is slower this behaviour is at odds with that expected from basal lubrication alone instead it mirrors that of mountain glaciers where melt induced acceleration of flow ceases during years of high melting once subglacial drainage becomes efficient a model of ice sheet flow that captures switching between cavity and channel drainage modes is consistent with the run off threshold fast flow periods and later summer speeds we have observed simulations of the greenland ice sheet flow under climate warming scenarios should account for the dynamic evolution of subglacial drainage a simple model of basal lubrication alone misses key aspects of the ice sheet s response to climate warming

glacier thickening and decay analysis from 50 years of glaciological observations performed on glacier d argentiere mont blanc area france numerous glaciological data have been obtained from measurements carried out on glacier d argentiere mont blanc area france since the beginning of the 20th century moreover data on annual mass balance ice flow velocity thickness variation and length fluctuation have been obtained from yearly measurements performed since 1975 this dataset provides an excellent opportunity to analyze the relationships between surface mass balance and dynamic response over time periods during which net mass balance changed from positive to negative following a positive specific net balance period between 1960 and 1981 the ablation zone experienced a large increase in thickness and ice flow velocities conversely the highly negative specific net balance period since 1982 has led to strong thinning deceleration and retreat of the tongue the response of these observed dynamics to surface mass balance is analyzed from ice flux calculations performed on three transverse cross sections our results reveal that the ice fluxes are largely accommodated by ice flow velocities velocity fluctuations are synchronous over the entire area studied in the largest part of the glacier no compressing extending flow change has been observed over the last 30 years and thickness changes are solely driven by surface mass balance changes however on the tongue of the glacier thickness changes do not depend on surface mass balance but are mainly driven by changes in the longitudinal strain rate

microstructural investigations on strongly stained olivines of the chassignite nwa 2737 and implications for its shock history abstract olivines from the meteorite northwest africa 2737 nwa 2737 show unique characteristics such as strong brownish staining the occurrence of perpendicular sets of bright lamellae and the exsolution of metallic nanoparticles these features were investigated by transmission electron microscopy and spectroscopic techniques to understand their formation and consequent implications for the shock history of nwa 2737 areas showing optically an intense brown staining are characterised by the occurrence of finely dispersed metallic nanoparticles an extreme high density 10 16 m 2 of polygonised dislocations with burgers vector 001 and a high abundance of trivalent iron 16 as determined by electron energy loss spectroscopy in contrast the bright lamellae contain individual dislocation lines with burgers vector 001 of a slightly lower density 10 14 m 2 almost no metallic nanoparticles and significantly lower trivalent iron content model mass balance calculations suggest that the high content of trivalent iron can be incorporated as a laihunite component into the cores of polygonised dislocations this is charge balanced by the formation of metallic nanoparticles trivalent iron is likely responsible for the intense brown colour whereas nanoparticles darken these areas considerably and cause an intense red slope in the infrared range the proposed diffusion of trivalent iron into the cores of polygonised dislocations and the associated exsolution of metallic iron nanoparticles are likely fundamental processes for intense olivine staining during meteoritic impacts in general detailed analyses of variously stained regions suggest that the bright lamellae have experienced slightly higher shock induced strain causing a recrystallisation of olivine which occurred simultaneously with the polygonisation and exsolution processes resulting in the olivine staining of adjacent areas the existence of individual dislocations can be interpreted as the result of a two stage shock history for nwa 2737 after a first impact the material of nwa 2737 was likely embedded in a hot ejecta blanket this would ensure sufficient time at elevated temperatures for the polygonisation of dislocations and the recrystallisation of bright lamellae a second impact resulted in the emission of individual dislocations into recrystallised olivine and the ejection of that meteorite from mars

ice velocity changes on penny ice cap baffin island since the 1950s predicting the velocity response of glaciers to increased surface melt is a major topic of ongoing research with significant implications for accurate sea level rise forecasting in this study we u

comparison of satellite derived with ground based measurements of the fluctuations of the margins of vatnajokull iceland 1973 92 vatnajokull iceland is the earth s most studied ice cap and represents a classical glaciological field site on the basis of s palsson s seminal glaciological field research in the late 18th century since the 19th century vatnajokull has been the focus of an array of glaciological studies by scientists from many nations including many remote sensing investigations since 1951 landsat derived positions of the termini of 11 outlet glaciers of vatnajokull were compared with frontal positions of six of these 11 outlet glaciers determined by field observations during the period 1973 92 the largest changes during the 19 year period 1973 92 occurred in the large lobate surge type outlet glaciers along the southwestern western and northern margins of vatnajokull tungnaarjokull receded 1413 112 m 1380 1 m from ground observations and bruarjokull receded 1975 191 m 2096 5 m from extrapolated ground observations between 1973 and 1992 satellite images can be used to delineate glacier margin changes on a time lapse basis if the glacier margin can be spectrally discriminated from terminal moraines and sandur deposits and if the advance recession is larger than maximum image pixel size local knowledge of glaciers is critically important however in the accurate delineation of glacier margins on landsat images

consideration of the errors inherent in mapping historical glacier positions in austria from the ground and space 1893 2001 the historical record of in situ measurements of the terminus positions of the pasterze and kleines fleiskees glaciers in the eastern alps of austria is used to assess uncertainties in the measurement of decadal scale changes using satellite data topographic maps beginning in 1893 and satellite data from 1976 to 2001 were studied in concert with ground measurements to measure glacier changes ground measurements show that the tongue of the pasterze glacier receded f1150 m from 1893 to 2001 while satellite derived measurements using august 2001 landsat enhanced thematic mapper plus etm data registered to an 1893 topographic map show a recession of 1300 1800 m with an unknown error the measurement accuracy depends on the registration technique and the pixel resolution of the sensor when two satellite images are used when using topographic maps an additional source of error is the accuracy of the glacier position shown on the map between 1976 and 2001 landsat derived measurements show a recession of the terminus of the pasterze glacier of 479f136 m at an average rate of 19 1 m a 1 while measurements from the ground showed a recession of 428 m at an average rate of 17 1 ma 1 four meter resolution ikonos satellite images from 2000 and 2001 reveal a shrinkage of 22 096f46 m 2 in the pasterze tongue the nearby kleines fleiskees glacier lost 30 of its area between 1984 and 2001 and the area of exposed ice increased by 0 44f0 0023 km 2 according to landsat satellite measurements as more recent satellite images are utilized especially data that are geocoded the uncertainty associated with measuring glacier changes has decreased it is not possible to assess the uncertainty when an old topographic map and a satellite image are coregistered

the electrical conductivity of lherzolite between 700oc and 1200oc and time over a period of 1700 hours are reported for a lherzolite nodule from mount porndon australia analysis of complex impedance collected at 100 hz 1 khz and 10 khz indicates that there is significant frequency dispersion in this rock at temperatures below 900oc 1000oc by choosing the resistance of an equivalent parallel rc network at the frequency having minimum phase the effect of dispersion is largely avoided conductivity as a function of time collected following changes in fo2 at 1010 and 1200oc has been analyzed to determine the diffusivity of defects relating fo2 to the electrical conduction mechanism in olivine the diffusivities so obtained are in remarkably good agreement with those determined from strain measurements during creep tests which implies that magnesium vacancies are the rate limiting step for conductivity reequilibration after fo2 changes a longer term process is observed in this rock in which the conductivity drifts upward or downward with a time constant of hundreds of hours after initial reequilibration to gas mix fo2 changes we speculate that this long term drift could be related to equilibration of the iron distribution between coexisting olivine and pyroxene as a function of fo2 the sense is an increase in conductivity olivine gains iron at low fo2 and vice versa the lherzolite conductivity data are not significantly different from measurements made on olivine single crystals and polycrystals even though the rock contains about 34 modal pyroxene this consistency of laboratory measurements of electrical conductivity of olivines from many localities and geological settings supports the use of recent models relating mantle temperature with electrical conductivity in the interpretation of mantle geo electromagnetic soundings

ice loss rates at the northern patagonian icefield derived using a decade of satellite remote sensing abstract we use a satellite based survey of glacier surface elevation changes speeds and surface melt conditions between 2000 and 2011 to quantify mass loss from the northern patagonian icefield npi chile a history of ice elevation change is found by differencing aster digital elevation models dems relative to a void filled version of the dem collected by the shuttle radar topography mission srtm in february 2000 thinning rates have accelerated at lower elevations while above the equilibrium line altitude ela recent thinning rates are not significantly different from those observed in previous studies a volumetric change of 4 06 0 11 km 3 yr is found by summing surface elevation changes over all glaciers in the npi this is regarded as a lower bound because volume loss due to frontal retreat and sub aqueous melting is not included this volume change is converted to a mass loss of 3 40 0 07 gt yr taking into account density differences above and below the equilibrium line we find that the npi is providing at least 0 009 0 0002 mm yr to ongoing sea level change in agreement with previous estimates sub pixel offset tracking of aster image pairs is used to produce glacier displacements over intervals typically ranging from 6 days to 18 months the first whole icefield composite velocity map is presented the terminus of the san rafael glacier on the western side of the npi sustained a peak calving front speed of 19 7 1 2 m day for 7 days in the austral fall of 2007 passive microwave observations indicate that the surface of the accumulation basin of the glacier was wet during this period of rapid motion suggesting that the fast speed may be a consequence of a rise in sub glacial water pressure sourced from melt or rainwater making its way to the glacier bed and reducing basal friction several other outlet glaciers including the benito and hpn1 glaciers on the isolated western side of the icefield accelerated while thinning between 2007 and 2011 marked acceleration also occurred after 2007 at the front of the san quintin glacier the largest outlet glacier of the npi the paucity of thickness measurements at the outlet glaciers means it is impossible to accurately gauge the mass flux of the icefield and thus give a full estimate of the mass balance

incorporation of water into olivine during nebular condensation insights from density functional theory and thermodynamics and implications for phyllosilicate formation and terrestrial water inventory using density functional theory we have examined the hydration mechanism of olivine with the objective of understanding the reaction pathways toward the formation of crystalline serpentine and brucite it is found that further supply of water beyond saturation of the adsorption sites on olivine surfaces leads to the formation of amorphous brucite and serpentine molecules with the latter forming in the subsurface domain the calculated activation energy for this process is 25 kj mol 1 which permits formation of the amorphous materials well within the life span of the solar nebula in addition molecular dynamic simulations show that the adsorbed water in olivine is stable at least up to 900 k a finding that is in accord with independent experimental studies thus adsorption plus subsurface reaction of h2o in olivine could have taken place at temperatures considerably higher than the stability limit of hydrous minerals in the nebular condition using the dft derived enthalpy of adsorption data and reasonable approximation for the entropy of adsorption we have calculated the fractional coverage of the reactive surface sites of olivine grains of spherical geometry by adsorbed water and the corresponding ocean equivalent water oew that could have been accreted into the earth these results suggest that adsorption and the associated subsurface hydroxylation of olivine grains might have been responsible for a significant fraction of the earth s water budget the adsorption of water into olivine crystals in the solar nebula might also have led to the delivery of water to other planetary bodies

mapping the nebular condensates and the chemical composition of the terrestrial planets abstract we demonstrate that the condensation theory of planet formation yields solids of suitable compositions in the solar nebula that accrete to form the terrestrial planetary bodies the mineral chemistry of the condensed objects provides definite criteria to establish the pressure and temperature of their formation the solids condensing at a high nebular pressure of 0 01 to 0 001 bar and temperature of 1530 k had the best chemical composition and density to form mercury 64 wt iron and 36 wt oxides density 5 32 g cm 3 solids that condensed around a pressure of 0 0001 bar or less and a temperature of 700 k formed earth and venus 31 wt iron ni and s and 69 wt oxides density 4 g cm 3 and mars 33 6 wt fe and s and 66 4 wt oxides density 3 7 g cm 3 iron sulfide provided s 3 wt for the core hydrous minerals forming in the lower temperature region provided water to the mantle these results are highly significant because we have used only the chemical composition of the solar nebula thermochemistry and astrophysical data on densities of the planets

glacier fluctuations in extratropical south america during the past 1000 years article i nfo this paper presents an updated extensive review of glacier fluctuations during the past 1000 years in the extratropical andes of south america between ca 17 and 55 s given the variety of environmental conditions and evidence available for glacier fluctuations across this wide latitudinal range regional accounts are given for the desert andes 17 31 s the andes of central chile and argentina 31 36 s and the north 36 45 s and south 45 55 s patagonian andes the techniques dating limitations and interpretations of the glacier records along this transect are also discussed information on glacier fluctuations in the desert andes is limited to the 20th century documentation on past glacier variations is more abundant in the central chilean argentinean andes but the number of chronologies dealing with glacier fluctuations prior to the 1900s is also limited most records indicate that glaciers were generally more extensive prior to the 20th century with dates of maximum expansion ranging from the 16th to the 19th centuries the number and extent of glaciers increase significantly in the patagonian region where the evidence available for dating glacier variations during the past centuries is more abundant and the dating control for glacier events is generally better than in the northern parts of the study area for some patagonian glaciers maximum little ice age lia or post lia advances have been precisely dated by dendro geomorphological determinations or in situ measurements however for most sites the evidence available is still preliminary and there is considerable variability in the extent and timing of events related to the maximum lia expansion identified in most areas between the 16th and 19th centuries evidence is starting to appear at a growing number of sites for glacier advances during the first half of the past millennium these events were generally less extensive than the lia maximum pulses despite the occurrence of several post lia readvances over the past 100 110 years most areas in the andes of extratropical south america have experienced a general pattern of glacier recession and significant ice mass losses the differences in the glacier histories observed at local and regional scales probably reflect the inherent limitations associated with the glacier records and or the dating techniques used in each case together with the varying dominance of precipitation temperature and other climatic and non climatic factors on glacier mass balance and glacier dynamics these differences indicate that the late holocene glacier history of southern south america is more complex than commonly assumed the evidence discussed in this study highlights not only the immense potential for glaciological studies of this region but also a significant need for an increased number of detailed well dated records of glacier fluctuations

recent glacier variations at the aconcagua basin central chilean andes the majority of glaciers in central chile have receded in recent decades from 50 m to only a few meters per year mainly in response to an increase in the 08c isotherm altitude the aconcagua river basin 338 s is one of the major glaciated basins in central chile with 121 km 2 of ice in 2003 an earlier inventory using 1955 aerial photographs yielded a total surface area of 151 km 2 implying a reduction in glacier area of 20 0 63 km 2 a 1 over the 48 years photographic stereo models high resolution satellite images landsat aster and srtm data have been used to delineate glacier basins a focus on glaciar juncal norte one of the largest glaciers in the basin allows a more detailed analysis of changes the glacier has exhibited a smaller reduction 14 between 1955 and 2006 and the resulting elevation changes over this smaller period are not significant the above reduction rates are lower than in other glaciers of central chile and argentina this trend emphasizes water runoff availability in a river where most of the water in the dry summers is generated by glaciers and snowpack and where most of the superficial water rights are already allocated ongoing hydrological research including modelling of future water runoff will improve our understanding

electrical conductivity of san carlos olivine along 100 under oxygen and pyroxene buffered conditions and implications for defect equilibria the electrical conductivity along 100 of single crystal san carlos olivine was measured as a function of temperature between 1100 and 1200 c and oxygen fugacity between 10 6 and 10 0 5 pa at 1200 c and either with pyroxene buffered or without self buffered an added natural pyroxene buffer from a san carlos lherzolite under these temperature and o2 conditions electrical conduction in the self buffered sample is attributed to polarons fe and electrons e and in the pyroxene buffered sample is attributed to polarons fe and magnesium vacancies v mg over the range of temperature and o2 investigated the electrical conductivity of the self buffered sample is given by sb 100 2 27 s m e 0 55 ev kt o20 18 306 3 s m e 2 25 ev kt o2 0 18 and for the pyroxene buffered sample by pb 100 0 18 s m e 0 34 ev kt o20 17 15 2 s m e 1 3 ev kt where k is boltzmann s constant t is in kelvin and o2 is in atmospheres the conductivity of the pyroxene buffered sample is lower than that of the self buffered sample primarily as a result of a decrease in the polaron concentration the electrical conductivity of both samples was found to decrease irreversibly once the samples experienced an oxygen fugacity more reducing than approximately the wustite magnetite buffer electron microprobe analyses indicate that this effect results from loss of iron from the olivine samples to the iridium electrodes a series conduction model based on the observed compositional gradient adequately accounts for the magnitude of the irreversible conductivity decrease and limits the thickness of any surficial pyroxene phase to 0 1 m mantle temperature profiles based on laboratory measurements of self buffered samples predict temperatures of the order of between 25 and 150 c colder depending on the ambient oxygen fugacity than those based on measurements of pyroxene buffered samples

an analytical electron microscopy aem investigation of opaque inclusions in some type 6 ordinary chondrites abstract a large number of ordinary chondrites contains micron sized particles of metal and or troilite dispersed in their silicate grains such metallic phases are responsible for the so called darkening of the silicate grains and might be either precipitates which formed during reduction of the silicates or inclusions injected as a melt during a shock event we have investigated these tiny foreign phases by analytical transmission electron microscopy in three unweathered metamorphosed ordinary chondrites saint severin ll6 tsarev l6 and kernouve h6 we also looked for remnant shock indices our tem observations suggest the following sequence of events in the three meteorites first a number of relatively strong shock events occurred on the parent body bodies producing an fe fes melt that was injected into silicate grains along a dense network of open fractures most of these shock defects were subsequently erased by high temperature 700 900 c thermal metamorphism some remnants of the shock events are the observed trails of tiny metal and or sulfide inclusions that formed as a result of fracture healing chemical homogenization of the silicates and limited oxidation of the metallic blebs also occurred during this high temperature annealing event resulting in ni rich inclusions this effect was especially pronounced in the l and ll chondrites studied during subsequent cooling of the body bodies inclusions of chromite and phosphate precipitated nucleating preferentially on lattice defects dislocations subgrain boundaries and on the metal and sulfide inclusions a later shock event of moderate intensity probably corresponding to the separation of the meteorite from its parent body produced new shock features in the silicate grains of the saint severin meteorite including mechanical twins in diopside and straight free screw dislocations in olivine