surface energy balance and melt thresholds over 11 years at taylor glacier antarctica 11 years ablation 18 cm a 1 was dominated by sublimation with very few occurrences of melt 42 days during 11 years results also indicated that above freezing air temperatures did not necessarily result in melt and in turn melt occurred during subfreezing air temperatures under some conditions for air temperatures near freezing low wind speed was critically important for melt initiation according to the model subsurface melt away from rocks and sediment in the ice occurred three times more frequently than surface melt occurs no deeper than 50 cm below the glacier surface and was small never exceeding 8 by mass the magnitude of subsurface melting and the energy balance indicate that taylor glacier ice is intermediate in optical properties between snow and blue ice

birth death and resurrection the life cycle of suprasubduction zone ophiolites 1 suprasubduction zone ssz ophiolites display a consistent sequence of events during their formation and evolution that suggests that they form in response to processes that are common to all such ophiolites this sequence includes the following 1 birth which entails the formation of the ophiolite above a nascent or reconfigured subduction zone this stage is typically characterized by the eruption of arc tholeiite lavas and the formation of layered gabbros and sheeted dike complex 2 youth during which is continued melting of refractory asthenosphere depleted during birth occurs in response to fluid flux from the subducting slab with extensional deformation of the older plutonic suite eruption of refractory lavas and the intrusion of wehrlite pyroxenite 3 maturity with the onset of semistable arc volcanism typically calc alkaline as the subduction zone matures and stabilizes and the intrusion of quartz diorite and eruption of silicic lavas and 4 death which is the sudden demise of active spreading and ophiolite related volcanism which in many cases is linked to collision with an active spreading center and the onset of shallow underthrusting of the buoyant spreading axis expressed as dikes and lavas with oceanic basalt compositions that crosscut or overlie rocks of the older suites 5 resurrection with emplacement by obduction onto a passive margin or accretionary uplift with continued subduction the early stages 1 3 may be diachronous and each stage may overlap in both time and space the existence of this consistent progression implies that ophiolite formation is not a stochastic event but is a natural consequence of the ssz tectonic setting

measurement and parameterization of albedo variations at haut glacier d arolla switzerland spatial and temporal variations of surface albedo on haut glacier d arolla switzerland during the 1993 and 1994 ablation seasons are described correlation and regression analyses are used to explain the albedo variations in terms of independent meteorological and surface property variables parameterizations are developed which allow estimation of albedo variation in surface energy balance models snow albedo is best estimated from accumulated daily maximum temperatures since snowfall on deep snow 0 5 cm w e depth a logarithmic function is used while on shallow snow 0 5 cm w e depth an exponential function is used to enable the albedo to decay to the underlying ice or debris albedo the transition from deep to shallow snow is calculated as a function of decreasing snow depth combined r 2 0 65 this new parameterization performs better than earlier schemes because accumulated daily maximum temperatures since snowfall correlate strongly with snow grain size and impurity concentration the main physical controls on snow albedo ice albedo may be parameterized by its relationship to elevation r 2 0 28 but this approach results in only a small improvement over the assumption of a constant mean ice albedo

multiple tectonic rotations and transform tectonism in an intraoceanic suture zone sw cyprus abstract new palaeomagnetic data from the late cretaceous neotethyan troodos ophiolite and related units in sw cyprus provide compelling evidence that transform tectonism is recorded outside the main outcrop of the fossil southern troodos transform fault zone sttfz high level intrusive and extrusive sequences were sampled along the sw margin of the troodos massif and in ophiolitic slivers preserved along arcuate fault lineaments further to the south and west these units show cross cutting relationships with corresponding differences in remanent magnetisation directions characteristic of syn magmatic rotation in an active transform setting net tectonic rotation analyses allow decomposition of the total rotation at these sites into early and late components early transform related rotations are consistently clockwise in agreement with all other studies of rotations associated with the sttfz further to the east late rotations and the net rotations derived at localities where cross cutting relationships were not present are regarded as composite in origin the composite rotation axes closely relate to the orientation of observed regional structures in these circumstances additional constraints are used to attempt geologically viable interpretations the overall distribution of transform related rotations steeply and shallowly plunging rotation axes and spreading axis related rotations sub horizontal rotation axes is comparable with that along the sttfz and adjacent parts of the troodos massif this is most readily explained by simple along strike extension of the primary spreading axis and transform fabrics into sw cyprus with minor late disruption by high angle dextral shear zones and neotectonic graben systems

evolution of cryoconite holes and their contribution to meltwater runoff from glaciers in the mcmurdo dry valleys antarctica cryoconite holes are water filled holes in the surface of a glacier caused by enhanced ice melt around trapped sediment measurements on the ablation zones of four glaciers intaylorvalley antarctica show that cryoconite holes cover about 4 6 of the ice surface they typically vary in diameter from 5 to 145 cm with depths ranging from 4 to 56 cm in some cases huge holes form with 5 m depths and 30 m diameters un like cryoconite holes elsewhere these have ice lids up to 36 cm thick and melt from within each spring about one half of the holes are connected to the near surface hydrologic system and the remainder are isolated the duration of isolation estimated from the chlor ide accumulation in hole waters commonly shows ages of several years with one hole of 10 years the cryoconite holes in the mcmurdo dryvalleys create a near surface hydro logic system tens of cm below the ice surface the glacier surface itself is generally frozen and dry comparison of water levels between holes a few meters apart shows independent cycles of water storage and release most likely local freeze thaw effects control water passage and therefore temporary storage rough calculations indicate that the holes gen erate at least 13 of the observed runoff on the one glacier measured this hydrologic system represents the transition between a melting ice cover with supraglacial streams and one entirely frozen and absent of water abstract cryoconite holes are water filled holes in the surface of a glacier caused by enhanced ice melt around trapped sediment measurements on the ablation zones of four glaciers intaylorvalley antarctica show that cryoconite holes cover about 4 6 of the ice surface they typically vary in diameter from 5 to 145 cm with depths ranging from 4 to 56 cm in some cases huge holes form with 5 m depths and 30 m diameters un like cryoconite holes elsewhere these have ice lids up to 36 cm thick and melt from within each spring about one half of the holes are connected to the near surface hydrologic system and the remainder are isolated the duration of isolation estimated from the chlor ide accumulation in hole waters commonly shows ages of several years with one hole of 10 years the cryoconite holes in the mcmurdo dryvalleys create a near surface hydro logic system tens of cm below the ice surface the glacier surface itself is generally frozen and dry comparison of water levels between holes a few meters apart shows independent cycles of water storage and release most likely local freeze thaw effects control water passage and therefore temporary storage rough calculations indicate that the holes gen erate at least 13 of the observed runoff on the one glacier measured this hydrologic system represents the transition between a melting ice cover with supraglacial streams and one entirely frozen and absent of water

frequency magnitude and characteristics of aeolian sediment transport mcmurdo dry valleys antarctica 1 due in part to the challenging environment of earth s high latitude regions available information on cold climate effects on aeolian processes in these areas remains limited data from these areas however provide insight into the physics of sediment transport by wind and the controls on erosive winds in proximity to ice caps and topographic influences this study presents a 2 year record of meteorological saltation activity horizontal saltation flux and particle size distribution data from four sites in the mcmurdo dry valleys of antarctica 2008 to 2010 saltation measurements revealed daily and seasonal patterns with spring and summer sediment transport events occurring between 09 00 and 24 00 hours due to thermally generated winds fall and winter events occur at any time of day with the strongest associated with foehn winds threshold wind speed at 4 2 m in all seasons for all locations was 10 m s 1 saltation occurred in the temperature range 40 c to 5 c westerly winds in the fall winter and easterly winds in spring summer are associated with the majority of transport events the sand in transport is mainly 250 to 500 m in diameter and poorly sorted the integrated saltation flux varies over three orders of magnitude among the sites with the lowest mean flux recorded in the taylor valley 2 9 kg m 1 day 1 and the highest in the eastern victoria valley 2271 kg m 1 day 1 for 24 hours of continuous saltation the percentage of time saltation active at these locations annually is 2 4 and 13 respectively for the victoria taylor and wright valleys

deep electrical imaging of the ultraslow spreading mohns ridge more than a third of mid ocean ridges have a spreading rate of less than 20 millimetres a year1 the lack of deep imaging data means that factors controlling melting and mantle upwelling2 3 the depth to the lithosphere asthenosphere boundary lab 4 5 crustal thickness6 9 and hydrothermal venting are not well understood for ultraslow spreading ridges10 11 modern electromagnetic data have greatly improved our understanding of fast spreading ridges12 13 but have not been available for the ultraslow spreading ridges here we present a detailed 120 kilometre deep electromagnetic joint inversion model for the ultraslow spreading mohns ridge combining controlled source electromagnetic and magnetotelluric data inversion images show mantle upwelling focused along a narrow oblique and strongly asymmetric zone coinciding with asymmetric surface uplift although the upwelling pattern shows several of the characteristics of a dynamic system3 12 14 it probably reflects passive upwelling controlled by slow and asymmetric plate movements instead upwelling asthenosphere and melt can be traced to the inferred depth of the mohorovicic discontinuity and are enveloped by the resistivity 100 ohm metres contour denoted the electrical lab elab the elab may represent a rheological boundary defined by a minimum melt content we also find that neither the melt suppression model7 nor the inhibited migration model15 which explain the correlation between spreading rate and crustal thickness6 16 19 can explain the thin crust below the ridge a model in which crustal thickness is directly controlled by the melt producing rock volumes created by the separating plates is more likely active melt emplacement into oceanic crust about three kilometres thick culminates in an inferred crustal magma chamber draped by fluid convection cells emanating at the loki s castle hydrothermal black smoker field fluid convection extends for long lateral distances exploiting high porosity at mid crustal levels the magnitude and long lived nature of such plumbing systems could promote venting at ultraslow spreading ridges an inversion model for the ultraslow spreading mohns ridge combining controlled source electromagnetic and magnetotelluric data reveals passive mantle upwelling controlled by slow and asymmetric plate movements

distributed modeling of ablation 1996 2011 and climate sensitivity on the glaciers of taylor valley antarctica here the mcmurdo dry valleys of antarctica host the coldest and driest ecosystem on earth which is acutely sensitive to the availability of water coming from glacial runoff we modeled the spatial variability in ablation and assessed climate sensitivity of the glacier ablation zones using 16 years of meteorological and surface mass balance observations collected in taylor valley sublimation was the primary form of mass loss over much of the ablation zones except for near the termini where melt primarily below the surface dominated microclimates in 10 m scale topographic basins generated melt rates up to ten times higher than over smooth glacier surfaces in contrast the vertical terminal cliffs on the glaciers can have higher or lower melt rates than the horizontal surfaces due to differences in incoming solar radiation the model systematically underpredicted ablation for the final 5 years studied possibly due to an increase of windblown sediment surface mass balance sensitivity to temperature was 0 02 m w e k 1 which is among the smallest magnitudes observed globally we also identified a high sensitivity to ice albedo with a decrease of 0 02 having similar effects as a 1 k increase in temperature and a complex sensitivity to wind speed

below surface ice melt on the coastal antarctic ice sheet in the jutulgryta area of dronning maud land antarctica subsurface melting of the ice sheet has been observed the melting takes place during the summer months in blue ice areas under conditions of below freezing air and surface temperatures adjacent snow covered regions having the same meteorological and climatic conditions experience little or no subsurface melting to help explain and understand the observed melt rate differences in the blue ice and snow covered areas a physically based numerical model of the coupled atmosphere radiation snow and blue ice system has been developed the model comprises a heat transfer equation which includes a spectrally dependent solar radiation source term the penetration of radiation into the snow and blue ice depends on the solar radiation spectrum the surface albedo and the snow and blue ice grain sizes and densities in addition the model uses a complete surface energy balance to define the surface boundary conditions it is run over the full annual cycle simulating temperature profiles and melting and freezing quantities throughout the summer and winter seasons the model is driven and validated using field observations collected during the norwegian antarctic research expedition nare 1996 97 the simulations suggest that the observed differences between subsurface snow and blue ice melting can be explained largely by radiative and heat transfer interactions resulting from differences in albedo grain size and density between the two mediums

antarctic lakes suggest millennial reorganizations of southern hemisphere atmospheric and oceanic circulation the phasing of millennial scale oscillations in antarctica relative to those elsewhere in the world is important for discriminating among models for abrupt climate change particularly those involving the southern ocean however records of millennial scale variability from antarctica dating to the last glacial maximum are rare and rely heavily on data from widely spaced ice cores some of which show little variability through that time here we present new data from closed basin lakes in the dry valleys region of east antarctica that show high magnitude high frequency oscillations in surface level during the late pleistocene synchronous with climate fluctuations elsewhere in the southern hemisphere these data suggest a coherent southern hemisphere pattern of climate change on millennial time scales at least in the pacific sector and indicate that any hypothesis concerning the origin of these events must account for synchronous changes in both high and temperate latitudes

splitting marine controlled source electromagnetic responses into sea and subseafloor contributions grounding the air wave abstractwe have found how the effects of the air wave in marine controlled source electromagnetic csem methods gradually vanish in the sea for shallow waters and how at the same time they gradually grow below the seafloor in an effort to comprehend existing detectability definitions the transition from sea to land is smooth because the sea becomes a thin conductive layer when the water depth is smaller than the skin depth in the sea we consider the problem of detecting resistive layers at depth associated with hydrocarbon reservoirs particularly in shallow water explorations and specifically on how the air wave affects detection our analysis is based on an integral representation of the electric field in terms of its sensitivity to changes in the electrical conductivity of a 1d profile two dimensional images of the integrands are obtained by plotting the integrand as a function of depth for different offsets results include the expected growth of the inhibiting effect of the sea as the water d

the mcmurdo dry valleys a landscape on the threshold of change abstract field observations of coastal and lowland regions in the mcmurdo dry valleys suggest they are on the threshold of rapid topographic change in contrast to the high elevation upland landscape that represents some of the lowest rates of surface change on earth a number of landscapes have undergone dramatic and unprecedented landscape changes over the past decade including the wright lower glacier wright valley ablated several tens of meters the garwood river garwood valley has incised 3 m into massive ice permafrost smaller streams in taylor valley crescent lawson and lost seal streams have experienced extensive down cutting and or bank undercutting and canada glacier taylor valley has formed sheer 4 meter deep canyons the commonality between all these landscape changes appears to be sediment on ice acting as a catalyst for melting including ice cement permafrost thaw we attribute these changes to increasing solar radiation over the past decade despite no significant trend in summer air temperature to infer possible future landscape changes in the mcmurdo dry valleys due to anticipated climate warming we map at risk landscapes defined as those with buried massive ice in relative warm regions of the valleys results show that large regions of the valley bottoms are at risk changes in surface topography will trigger important responses in hydrology geochemistry and biological community structure and function

marine transient electromagnetic sounding of deep buried hydrocarbon reservoirs principles methodologies and limitations the possibility of a time domain electromagnetic sounding method using excitation and measurement of vertical electric fields to search for and identify deeply buried reservoirs of hydrocarbons offshore is investigated the method operates on source receiver offsets which are several times less than the depth of the reservoir geoelectric information is obtained from the transient responses recorded in the pauses between the pulses of electric current in the absence of the source field the basics of the method as well as its sensitivity resolution and the highest accessible depth of soundings for various geological conditions in a wide range of sea depths are analyzed for the analysis 1d and 3d geoelectric models of hydrocarbon reservoirs are used it is shown that under existing technologies of excitation and measurement of vertical electric fields the highest accessible depth of soundings can be up to 4 km technology for the inversion and interpretation of transient responses is demonstrated on experimental data

ten years of marine csem for hydrocarbon exploration marine controlled source electromagnetic csem surveying has been in commercial use for predrill reservoir appraisalandhydrocarbonexplorationfor10 years althougha recent decrease has occurred in the number of surveys and publications associated with this technique the method has become firmly established as an important geophysical tool intheoffshoreenvironment thisisaconsequenceoftwoimportant aspects associated with the physics of the method first it is sensitive to high electrical resistivity which although not an unambiguous indicator of hydrocarbons is an important property of economically viable reservoirs second although the method lacks the resolution of seismic wave propagation it has a much better intrinsic resolution than potential field methods such as gravity and magnetic surveying which until now have been the primary nonseismicdatasetsusedinoffshoreexploration althoughbymany measures marine csem is still in its infancy the reliability and noise floors of the instrument systems have improved significantly over the last decade and interpretation methodology has progressed from simple anomaly detection to 3d anisotropic inversion of multicomponent data using some of theworld sfastestsupercomputers researchdirectionspresently include tackling the airwave problem in shallow water by applying time domain methodology continuous profiling tools and the use of csem for reservoir monitoring during production

the 3 d geometry of detachment faulting at mid ocean ridges seismic images of cretaceous slow spreading crust from the eastern central atlantic provide new constraints on the process of seafloor spreading and the importance of detachment faulting the seismic depth sections image detachment faults that appear to have exhumed footwall massifs of similar geometry to massifs of plutonic and mantle rocks mapped at the present mid atlantic ridge the detachments are consistent with the structure and microearthquakes of the mid atlantic ridge at 26 n with the footwall rotation inferred from paleomagnetic data and with numerical modeling of oceanic detachments other seismically imaged detachments have similar dimensions and geometry but are covered by a layer of small fault blocks the detachment types differ in whether or not the fault locks up in the subsurface probably controlled by the fault strength the elastic thickness and whether the exhumed footwall is partly covered by basalts toward the segment middle decreasing mantle serpentinization decreasing elastic thickness and thicker median valley basalts all increase the likelihood that the fault locks up and a new fault propagates upwards from the still active root zone transferring a slice of the hanging wall to the footwall to be rafted with the footwall out of the median valley as a result an oceanic detachment fault exhuming the footwall at a segment end to form an oceanic core complex may disappear laterally beneath rafted blocks detachment faulting may be more widespread at slow spreading ridges than interpreted from seafloor mapping

fore arc basalts and subduction initiation in the izu bonin mariana system recent diving with the jamstec shinkai 6500 manned submersible in the mariana fore arc southeast of guam has discovered that morb like tholeiitic basalts crop out over large areas these fore arc basalts fab underlie boninites and overlie diabasic and gabbroic rocks potential origins include eruption at a spreading center before subduction began or eruption during near trench spreading after subduction began fab trace element patterns are similar to those of morb and most izu bonin mariana ibm back arc lavas however ti v and yb v ratios are lower in fab reflecting a stronger prior depletion of their mantle source compared to the source of basalts from mid ocean ridges and back arc basins some fab also have higher concentrations of fluid soluble elements than do spreading center lavas thus the most likely origin of fab is that they were the first lavas to erupt when the pacific plate began sinking beneath the philippine plate at about 51 ma the magmas were generated by mantle decompression during near trench spreading with little or no mass transfer from the subducting plate boninites were generated later when the residual highly depleted mantle melted at shallow levels after fluxing by a water rich fluid derived from the sinking pacific plate this magmatic stratigraphy of fab overlain by transitional lavas and boninites is similar to that found in many ophiolites suggesting that ophiolitic assemblages might commonly originate from near trench volcanism caused by subduction initiation indeed the widely dispersed jurassic and cretaceous tethyan ophiolites could represent two such significant subduction initiation events

constraints on deformation conditions and the origin of oceanic detachments the mid atlantic ridge core complex at 15 45 n 1 deformed rocks sampled from a corrugated detachment fault surface near the mid atlantic ridge 15 45 n constrain the conditions of deformation and strain localization samples recovered in situ record deformation restricted to the cold shallow lithosphere greenschist facies with no evidence for significant high temperature deformation either at the fault zone or in the footwall near it high temperature deformation 720 750 c is observed only at two sites and cannot be directly linked to the detachment detachment faulting was coeval with dyke intrusions that cross cut it as demonstrated by the presence of undeformed and highly deformed diabase found in shear zones and by the presence of chill margins in diabase against fault rock basalts are very scarce and restricted to clasts in breccias with no evidence of pillows or extrusive structures gabbros crop out along mass wasted and fault scarps structurally below the detachment footwall rocks show little or no deformation due to strain localization along a narrow shear zone 200 m with fluid flow as required to form talc and amphibole schists after an ultramafic protolith we speculate that the alteration front in a heterogeneous lithosphere may be a rheological boundary that may localize deformation during long periods of time our observations and other geological evidence elsewhere suggest that this detachment model limited to the cold shallow lithosphere is applicable to other corrugated surfaces along slow and intermediate spreading ridges these observations preclude detachment models rooting in melt rich zones i e atlantis bank southwest indian ridge or recording high temperature deformation we infer that oceanic detachment faults 1 localize strain at t 500 300 c 2 persist during active magmatism and 3 root at shallow rheological boundaries such as a melt rich zone or magma chamber hot detachments or an alteration front cold detachments

dynamics of intraoceanic subduction initiation 1 oceanic detachment fault inversion and the formation of supra subduction zone ophiolites subduction initiation is a critical link in the plate tectonic cycle intraoceanic subduction zones can form along transform faults and fracture zones but how subduction nucleates parallel to mid ocean ridges as in e g the neotethys ocean during the jurassic remains a matter of debate in recent years extensional detachment faults have been widely documented adjacent to slow spreading and ultraslow spreading ridges where they cut across the oceanic lithosphere these structures are extremely weak due to widespread occurrence of serpentine and talc resulting from hydrothermal alteration and can therefore effectively localize deformation here we show geochemical tectonic and paleomagnetic evidence from the jurassic ophiolites of albania and greece for a subduction zone formed in the western neotethys parallel to a spreading ridge along an oceanic detachment fault with 2 d numerical modeling exploring the evolution of a detachment ridge system experiencing compression we show that serpentinized detachments are always weaker than spreading ridges we conclude that owing to their extreme weakness oceanic detachments can effectively localize deformation under perpendicular far field forcing providing ideal conditions to nucleate new subduction zones parallel and close to or at spreading ridges direct implication of this is that resumed magmatic activity in the forearc during subduction initiation can yield widespread accretion of suprasubduction zone ophiolites at or close to the paleoridge our new model casts the enigmatic origin of regionally extensive ophiolite belts in a novel geodynamic context and calls for future research on three dimensional modeling of subduction initiation and how upper plate extension is associated with that

a modeling study of augmenting coarse grid 3d controlled source electromagnetics with data from a towed receiver array abstractwe have considered the simultaneous 3d inversion of controlled source electromagnetic data from a towed receiver array and a coarse grid of stationary seabed receivers our 3d synthetic model demonstrated the sensitivity and effect on imaging of towed and seabed receiver data the short offset data from the towed receivers at 1 3 km offset are effective at resolving a shallow resistor at a 400 m burial depth on the other hand the data from the stationary seabed receivers have less noise and will resolve the 3d geometry of resistive structures buried at the 1 2 km depths typical of a hydrocarbon reservoir we have determined how the complementary sensitivity of data from the two receiver types can be used in simultaneous inversion to recover the shallow and deep resistors

glacier mass balances 1993 2001 taylor valley mcmurdo dry valleys antarctica mass balances were measured on four glaciers in taylor valley antarctica from 1993 to 2001 we used a piecewise linear regression which provided an objective assessment of error to estimate the mass balance with elevation missing measurements were estimated from linear regressions between points and showed a significant improvement over other methods unlike temperate glaciers the accumulation zone of these polar glaciers accumulates mass in summer and winter and the ablation zone loses mass in both seasons a strong spatial trend of smaller mass balance values with distance inland r 2 0 80 reflects a climatic gradient to warmer air temperatures faster wind speeds and less precipitation annual and seasonal mass balance values range only several tens of millimeters in magnitude and no temporal trend is evident the glaciers of taylor valley and probably the entire mcmurdo dry valleys are in equilibrium with the current climate and contrast with glacier trends elsewhere on the antarctic peninsula and in temperate latitudes

seasonal sediment fluxes forcing supraglacial melting on the wright lower glacier mcmurdo dry valleys antarctica cold based glaciers exist in low temperature and low humidity environments in which shortwave radiation is the largest source of energy to the glacier surface and the energy budget is very sensitive to the surface albedo consequently the presence of relatively low volumes of debris on glacier surfaces has a significant impact on the timing magnitude and rate of ablation at the surface the aim of this study is to understand how the presence of sediment on the glacier surface at the start of the melt season can affect meltwater generation and delivery on a cold based glacier a combination of field measurements energy balance modelling and chemical mixing modelling were used on the wright lower glacier mcmurdo dry valleys antarctica between october 2005 and january 2006 to address this aim in this system sediment was transported onto the glacier surface during the winter months march october by foehn winds which reduced surface albedo at the start of the summer melt season the areas of the glacier on which sediment accumulated began to melt earlier than other parts of the glacier and experienced a longer melt season over the study period the total ablation on the dirty surfaces was nine times greater than for clean ice ablation on the dirty surfaces is dominated by melting whereas sublimation dominates the clean ice as the sediment was unevenly distributed over the glacier surface the variation in melt amount and timing drove the development of a cryoconite hole system copyright 2012 john wiley sons ltd

remote sensing of hydrocarbon layers by seabed logging sbl results from a cruise offshore angola detecting and assessing hydrocarbon reservoirs without the need to drill test wells is of major importance to the petroleum industry seismic methods have traditionally been used in this context but the results can be ambiguous another approach is to use electromagnetic sounding methods that exploit the resistivity differences between a reservoir containing highly resistive hydrocarbons and one saturated with conductive saline fluids modeling presented by eidesmo et al 2002 demonstrates that by using seabed logging sbl a special application of frequency domain controlled source electromagnetic csem sounding the existence or otherwise of hydrocarbon bearing layers can be determined and their lateral extent and boundaries can be quantified such information provides valuable complementary constraints on reservoir geometry and characteristics obtained by seismic surveying

model study of the spatial distribution of the energy and mass balance of morteratschgletscher switzerland to investigate the spatial distribution of the energy and mass balance fluxes of a glacier a two dimensional mass balance model was developed and applied to morteratschgletscher switzerland the model is driven by meteorological input from four synoptic weather stations located in the vicinity of morteratschgletscher the model results were compared to observations made on the glacier the calculated mean specific mass balance is 0 47 m w e for 1999 and 0 23 m w e for 2000 net shortwave radiation shows a minimum at around 3350 m a s l due to the effects of shading slope aspect reflection from the slopes and obstruction of the sky ignoring these effects results in a 37 increase in the annual incoming shortwave radiation on the glacier causing 0 34 m w e more ablation a 1 c change in the air temperature results in a shift of 0 67 m w e in the mean specific mass balance while altering the precipitation by 10 causes a change of 0 17 m w e

solar heating rates and temperature profiles in antarctic snow and ice observations of temperature maxima at about 10 cm depth in cold antarctic snow during summer have previously been explained by proposing that solar heating is distributed with depth whereas thermal infrared cooling is localized at the surface the solid state greenhouse an increase in temperature from the surface to 10 cm depth t 4 k found by rusin 1961 on the antarctic plateau was successfully reproduced by schlatter 1972 in a combined radiative transfer and heat transfer model

the feasibility of reservoir monitoring using time lapse marine csem monitoring changes in hydrocarbon reservoir geometry and pore fluid properties that occur during production is a critical part of estimating extraction efficiency and quantifying remaining reserves we examine the applicability of the marine controlled source electromagnetic csem method to the reservoir monitoring problem by analyzing representative 2d models these studies show that csem responses exhibit small but measureable changes that are characteristic of reservoir depletion geometry with lateral flooding producing a concave up depletion anomaly curve and bottom flooding producing a concave down depletion anomaly curve lateral flooding is also revealed by the spatial temporal variation of the csem anomaly where the edge of the response anomaly closely tracks the retreating edge of the flooding reservoir measureable changes in csem responses are observed when 10 of the resistive reservoir is replaced by conductive pore fluids however to avoid corrupting the relatively small signal changes associated with depletion the acquisition geometry must be maintained to a fraction of a percent accuracy additional factors such as unknown nearby seafloor inhomogeneities and variable seawater conductivity can mask depletion anomalies if not accounted for during repeat monitoring measurements although addressing these factors may be challenging using current exploration csem practices straightforward solutions such as permanent monuments for seafloor receivers and transmitters are available and suggest the method could be utilized with present day technology

the origin of channels on lower taylor glacier mcmurdo dry valleys antarctica and their implication for water runoff well developed surface channels on taylor glacier mcmurdo dry valleys antarctica begin as medial moraines incised as shallow narrow surface depressions and retain this geometry for tens of km over a distance of 1100m the channel geometry dramatically changes reaching depths 20m and widths 100m after rapidly enlarging the channels appear to evolve toward a new equilibrium geometry compared to the glacier surface the air temperature in the channels is warmer by 1 78c wind speed is reduced by 2 4m s and net shortwave radiation is greater by 14wm the microclimate in the channel shifts the energy balance towards enhanced melt field evidence and energy balance modeling indicate ablation in the deep channels is 4 5 times greater than the local horizontal glacier surface and that melt accounts for 99 of the summer ablation compared to 75 on the adjacent horizontal glacier surface melt in these channels supplies 65 of the unaccounted water discharge into the neighboring lake in large part the channels generate the water they carry rather than merely route water generated elsewhere

a temperature index model of stream flow at below freezing temperatures in taylor valley antarctica we model runoff from glaciers in the mcmurdo dry valleys antarctica with summer december january average air temperatures from 1990 to 2002 for the purpose of estimating decades to millennial scale glacial runoff into lakes fryxell hoare and bonney the relationship between summer temperatures and melt is found to be exponential near the melting temperature we propose a variety of simple models that are calibrated using measured discharge from a number of streams draining from ten glaciers in taylor valley the surface melting rate is constrained by mass balance measurements from four of the glaciers a model based solely on temperature produced good results coefficient of determination r 2 0 71 for the south facing glaciers but poor results for the north facing glaciers r 2 2 0 73 for the north facing glaciers with little change from the south facing glaciers including a wind index did not improve the correlation between modeled and measured runoff

the vardar zone as a suture for the mirdita ophiolites albania constraints from the structural analysis of the korabi pelagonia zone the dinarides hellenides result from underthrusting of the adriatic margin during africa europe convergence in albania they consist of 1 a western zone of nappes derived from adria 2 a central belt made up of the mirdita ophiolites and 3 an eastern zone the korabi pelagonia zone of variscan basement overlain by permian to mesozoic rift deposits and carbonates some authors interpret the korabi pelagonia zone as a microcontinent between the mirdita pindos oceanic basin to the west and the eastern vardar oceanic basin to the east other regard the korabi pelagonia zone as a tectonic window below a single ophiolitic nappe this contribution argues for a far traveled thrust sheet the mirdita ophiolites are 165 160 ma the metamorphic sole yielded 40ar 39ar ages of 171 to 162 ma the korabi pelagonia zone is subdivided into the korabi and gjegjan subzones the structural analysis of these rocks supports the rooting of the mirdita ophiolites in the western vardar zone the post variscan cover sequence of the korabi subzone records two phases of deformation d1 is associated with a se dipping to flat lying schistosity axial planar to nw verging folds and thrust faults related to ophiolite obduction d2 is a postobduction nne trending crenulation cleavage published zircon fission track analyses yielded 150 125 ma suggesting that regional metamorphism is early cretaceous or older k ar mica ages from correlative rocks of macedonia cluster between 148 and 130 ma indicating that d1 is late jurassic a west directed obduction is favored as is a rooting east of the mirdita ophiolites because of the top to the west structural polarity of obduction related deformation

foehn winds in the mcmurdo dry valleys antarctica the origin of extreme warming events abstract foehn winds resulting from topographic modification of airflow in the lee of mountain barriers are frequently experienced in the mcmurdo dry valleys mdvs of antarctica strong foehn winds in the mdvs cause dramatic warming at onset and have significant effects on landscape forming processes however no detailed scientific investigation of foehn in the mdvs has been conducted as a result they are often misinterpreted as adiabatically warmed katabatic winds draining from the polar plateau herein observations from surface weather stations and numerical model output from the antarctic mesoscale prediction system amps during foehn events in the mdvs are presented results show that foehn winds in the mdvs are caused by topographic modification of south southwesterly airflow which is channeled into the valleys from higher levels modeling of a winter foehn event identifies mountain wave activity similar to that associated with midlatitude foehn winds these events are found to be caused by str

detection and imaging sensitivity of the marine csem method we have developed a formalism to systematically study the sensitivity of the marine controlled source electromagnetic method for hydrocarbon exploration taking into account measurement errors we utilize error propagation to estimate the data uncertainty and find that contributions that scale by the transmitter dipole moment give qualitatively different behavior than noise contributions that are independent of the dipole moment the uncertainty is used in quantitative criteria to determine if a hydrocarbon reservoir can be detected and whether it can be successfully imaged our formalism can be used to make detailed feasibility studies incorporating equipment accuracy limitations and to identify which experimental component that must be improved to ensure overall improvement in sensitivity the criteria can be applied to identify the limiting factors for detection and imaging of targets with increasing burial depth we have defined experimental accuracy conditions for next generation csem equipment to successfully image a large hydrocarbon reservoir at 5 km burial depth

surface mass balance of glaciers in the french alps distributed modeling and sensitivity to climate change a new physically based distributed surface mass balance model is presented for alpine glaciers based on the crocus prognostic snow model it resolves both the temporal 1 hour time step and spatial 200 m grid step variability of the energy and mass balance of glaciers mass balance reconstructions for the period 1981 2004 are produced using meteorological reconstruction from the safran meteorological model for glacier de saint sorlin and glacier d argentiere french alps both glaciers lost mass at an accelerated rate in the last 23 years the spatial distribution of precipitation within the model grid is adjusted using field mass balance measurements this is the only correction made to the safran meteorological input to the glacier model which also includes surface atmospheric temperature moisture wind and all components of downward radiation independent data from satellite imagery and geodetic measurements are used for model validation with this model glacier sensitivity to climate change can be separately evaluated with respect to a full range of meteorological parameters whereas simpler models such as degree day models only account for temperature and precipitation we provide results for both mass balance and equilibrium line altitude ela using a generic alpine glacier the sensitivity of the ela to air temperature alone is found to be 125 m c 1 or 160 m c 1 if concurrent stefan boltzmann longwave radiation change is taken into account

evolving force balance during incipient subduction nearly half of all active subduction zones initiated during the cenozoic all subduction zones associated with active back arc extension have initiated since the eocene hinting that back arc extension may be intimately associated with an interval several tens of myr following subduction initiation that such a large proportion of subduction zones are young indicates that subduction initiation is a continuous process in which the net resisting force associated with forming a new subduction zone can be overcome during the normal evolution of plates subduction initiation is known to have occurred in a variety of tectonic settings old fracture zones transform faults and extinct spreading centers and through polarity reversal behind active subduction zones although occurring within different tectonic settings four known subduction initiation events izu bonin mariana ibm along a fracture zone tonga kermadec along an extinct subduction boundary new hebrides within a back arc and puysegur fiordland along a spreading center were typified by rapid uplift within the forearc followed by sudden subsidence other constraints corroborate the compressive nature of ibm and tonga kermadec during initiation using an explicit finite element method within a two dimensional domain we explore the evolving force balance during initiation in which elastic flexure viscous flow plastic failure and heat transport are all considered in order to tie theory with observation known tectonic settings of subduction initiation are used as initial and boundary conditions we systematically explore incipient compression of a homogeneous plate a former spreading center and a fracture zone the force balance is typified by a rapid growth in resisting force as the plate begins bending reaching a maximum value dependent on plate thickness but typically ranging from 2 to 3 1012 n m for cases that become self sustaining this is followed by a drop in stress once a shear zone extends through the plate the formation of a throughgoing fault is associated with rapid uplift on the hanging wall and subsidence on the footwall cumulative convergence not the rate of convergence is the dominant control on the force balance viscous tractions influence the force balance only if the viscosity of the asthenosphere is 1020 pa s and then only after plate failure following plate failure buoyancy of the oceanic crust leads to a linear increase with crustal thickness in the work required to initiate subduction the total work done is also influenced by the rate of lithospheric failure a self sustaining subduction zone does not form from a homogeneous plate a ridge placed under compression localizes subduction initiation but the resisting ridge push force is not nearly as large as the force required to bend the subducting plate the large initial bending resistance can be entirely eliminated in ridge models explaining the propensity for new subduction zones to form through polarity reversals a fracture zone fz placed in compression leads to subduction initiation with rapid extension of the overriding plate a fz must be underthrust by the older plate for 100 150 km before a transition from forced to self sustaining states is reached in fz models the change in force during transition is reflected by a shift from forearc uplift to subsidence subduction initiation is followed by trench retreat and back arc extension moderate resisting forces associated with modeled subduction initiation are consistent with the observed youth of pacific subduction zones the models provide an explanation for the compressive state of western pacific margins before and during subduction initiation including ibm and tonga kermadec in the eocene and the association of active back arcs with young subduction zones on the basis of our dynamic models and the relative poles of rotation between pacific and australia during the eocene we predict that the northern segment of the tonga kermadec convergent margin would have initiated earlier with a progressive southern migration of the transition between forced and self sustaining states

rapid calculation of terrain parameters for radiation modeling from digital elevation data digital elevation models are widely used to calculate terrain parameters to determine incoming solar and longwave radiation for use in surface climate models interpretation of remote sensing data and parameters in hydrologic models because of the large number of points in an elevation grid fast algorithms are useful to save computation time a description is given of rapid methods for calculating slope and azimuth solar illumination angle horizons and view factors for radiation from sky and terrain calculation time is reduced by fast algorithms and lookup tables

the marine controlled source electromagnetic method in shallow water we analyzed marine controlled source electromagnetic csem acquisition in shallow water by analytic and numerical calculations the problem at hand was the fact that the amplitude of the airwave due to a horizontal electric dipole becomes larger as the water depth is reduced the amplitude of the scattered field from a buried thin resistor would be difficult to extract from the increased total field if the scattered field amplitude were independent of water depth however we identified and explained a compensating effect where the amplitude of the scattered field increases with reduced water depth this amplification effect makes marine csem surveys in shallow water feasible we derived an approximate expression for the total field for a simple but realistic conductivity model this expression explains why the amplitudes of the term that describes the background field contribution and the term that gives the scattered field from the thin resistor increase when the water depth is reduced our results and sensitivity analysis indicated that the sensitivity of marine csem data acquired in a water depth of 40 m is comparable to the sensitivity of marine csem data acquired in a water depth of 300 m

sublimation and surface energy budget of taylor glacier antarctica taylor glacier an outlet of the east antarctic ice sheet flows through the transantarctic mountains and terminates in the dry valleys understanding how this glacier fluctuates is important for studies of glacial geology paleoclimate ice dynamics and ecology sublimation is the primary mass loss process for most of the glacier four years of specific balance measurements from the ablation zone show sublimation rates up to 40 cma 1 we used data from an array of weather stations as inputs to a model for latent heat flux and hence sublimation rate calculated and measured ablation rates agree to within uncertainties indicating that wind speed and vapour pressure gradient a function of temperature and humidity are the governing variables as expected from theory measurements and model results together allowed us to examine the spatial and temporal variations of sublimation on the glacier on average sublimation is about two times faster in summer than winter rapid sublimation occurs during storms and katabatic wind events but such periods contribute less to the annual total than do slow persistent losses spatially sublimation reaches a maximum midway along the glacier where descending surface air currents are focused by the topography of the aptly named tributary windy gully

aeolian flux of biotic and abiotic material in taylor valley antarctica abstract we studied patterns and mechanisms controlling wind driven flux of soils and associated organic matter in taylor valley antarctica over a 10 year period using passive aeolian traps and dynamic mass erosion particle counters deployment of the particle counters near meteorological stations allowed us to compare the magnitude of soil flux with data on prevailing wind particulate organic c n and p measurements on transported sediment allowed us to examine connectivity of wind dispersed organic matter among landscape units most sediment entrainment occurred within 20 cm of the soil surface during saltation bursts that occupied 1 sediment movement was highest in the up valley reaches of taylor valley and transport was down valley towards mcmurdo sound the general paucity of biological organic matter production throughout the mcmurdo dry valleys in concert with low fluvial transport makes aeolian distribution or organic c n and p an important factor in the distribution of organic matter throughout this polar desert ecosystem and increases connectivity among the ecosystem components

protracted construction of gabbroic crust at a slow spreading ridge constraints from 206pb 238u zircon ages from atlantis massif and iodp hole u1309d 30 n mar sensitive high resolution ion microprobe shrimp u pb zircon ages of 24 samples from oceanic crust recovered in integrated ocean drilling program iodp hole u1309d and from the surface of atlantis massif mid atlantic ridge mar 30 n document a protracted history of accretion in the footwall to an oceanic detachment fault ages for 18 samples of evolved fe ti oxide gabbro and felsic dikes collected 40 1415 m below seafloor in u1309d yield a weighted mean of 1 20 0 03 ma mean square of weighted deviates 7 1 however the ages range from 1 08 0 07 ma and 1 28 0 05 ma indicating crustal construction occurred over a minimum of 100 200 ka the zircon ages along with petrologic observations indicate at least 2 major periods of intrusive activity with age peaks separated by 70 ka the oldest ages are observed below 600 mbsf an observation inconsistent with models requiring constant depth melt intrusion beneath a detachment fault the data are most consistent with a multiple sill model whereby sills intrude at random depths below the ridge axis over a length scale greater than 1 4 km zircon ages from broadly spaced samples collected along the southern ridge of atlantis massif yield a detachment fault slip rate of 28 7 6 7 mm a and imply significant asymmetric plate spreading up to 100 on the north american plate for at least 200 ka during core complex formation

spatial and temporal variations in albedo on storglaciaren sweden extensive albedo data from storglaciaren sweden during nine summers are analyzed focusing on the effect of surface slope on measurements and on the influence of clouds on albedo of both snow and ice surfaces on clear sky days albedo continuously dropped throughout the day by 0 3 when derived from measurements in a horizontal plane over the slightly sloping surface when we correct for the tilt effect over frozen surfaces the apparent decrease in albedo largely disappeared while over melting surfaces it became significantly less pronounced this emphasizes the need to correct horizontally measured data for slope when they are used for example as ground truth for satellite derived albedo or in high resolution glacier melt runoff models albedo varied by 0 1 due to cloud fluctuations to quantify cloud effects albedo changes between successive half hourly and daily data were regressed against corresponding changes in cloudiness expressed by the ratio of global radiation to top of atmosphere solar radiation the resulting relationship over snow explains 66 of oberved albedo changes using hourly and 4 using daily time steps over ice the corresponding values arc 28 and 0 hence cloudiness is a dominating factor in determining short term variability of albedo over snow whereas over ice the observed large day to day variability 20 is mainly attributed to changes in the physical characteristics of the weathering crust results suggest that cloud effects should be incorporated into models treating snow and ice surfaces separately

temporal and spatial variation of the surface albedo of the morteratschgletscher switzerland as derived from 12 landsat images this investigation uses landsat images from 12 days in 1999 and 2000 to study the spatial and temporal variation in surface albedo of a glacier with a rugged topography morteratschgletscher switzerland our retrieval method considers all processes that substantially influence the relationship between the satellite signal and the surface albedo the correction for the anisotropy of the reflected radiation field of ice and snow ranges up to 0 10 depending on wavelength band solar zenith angle and surface type we analyzed the uncertainties in the retrieval method and mainly expect errors in satellite derived albedos for areas with large variation in topography and high albedos the latter is due to application of bidirectional reflectance distribution function brdf parameterizations for the anisotropic correction to albedos outside the parameterizations validity on average satellite derived albedos exceed the measured surface albedo by 0 03 the glacier tongue is characterized by bands of low and high albedo relating to ice with higher and lower concentrations of debris the ice albedo shows no dependence on altitude except at 2000 2200 m a s l it increases during summer which is likely associated with rainfall as concluded from a comparison between summer rainfall and measured albedos

effects of bubbles cracks and volcanic tephra on the spectral albedo of bare ice near the transantarctic mountains implications for sea glaciers on snowball earth 1 spectral albedo was measured along a 6 km transect near the allan hills in east antarctica the transect traversed the sequence from new snow through old snow firn and white ice to blue ice showing a systematic progression of decreasing albedo at all wavelengths as well as decreasing specific surface area ssa and increasing density broadband albedos under clear sky range from 0 80 for snow to 0 57 for blue ice and from 0 87 to 0 65 under cloud both air bubbles and cracks scatter sunlight their contributions to ssa were determined by microcomputed tomography on core samples of the ice although albedo is governed primarily by the ssa and secondarily by the shape of bubbles or snow grains albedo also correlates highly with porosity which as a proxy variable would be easier for ice sheet models to predict than bubble sizes albedo parameterizations are therefore developed as a function of density for three broad wavelength bands commonly used in general circulation models visible near infrared and total solar relevance to snowball earth events derives from the likelihood that sublimation of equatorward flowing sea glaciers during those events progressively exposed the same sequence of surface materials that we measured at allan hills with our short 6 km transect representing a transect across many degrees of latitude on the snowball ocean at the equator of snowball earth climate models predict thick ice or thin ice or open water depending largely on their albedo parameterizations our measured albedos appear to be within the range that favors ice hundreds of meters thick

decadal topographic change in the mcmurdo dry valleys of antarctica thermokarst subsidence glacier thinning and transfer of water storage from the cryosphere to the hydrosphere abstract recent local scale observations of glaciers streams and soil surfaces in the mcmurdo dry valleys of antarctica mdv have documented evidence for rapid ice loss glacial thinning and ground surface subsidence associated with melting of ground ice to evaluate the extent magnitude and location of decadal scale landscape change in the mdv we collected airborne lidar elevation data in 2014 2015 and compared these data to a 2001 2002 airborne lidar campaign this regional assessment of elevation change spans the recent acceleration of warming and melting observed by long term meteorological and ecosystem response experiments allowing us to assess the response of mdv surfaces to warming and potential thawing feedbacks we find that locations of thermokarst subsidence are strongly associated with the presence of excess ground ice and with proximity to surface or shallow subsurface active layer water subsidence occurs across soil types and landforms in low lying low slope areas with impeded drainage and also high on steep valley walls glacier thinning is widespread and is associated with the growth of fine scale roughness pond levels are rising in most closed basin lakes in the mdv across all microclimate zones these observations highlight the continued importance of insolation driven melting in the mdv the regional melt pattern is consistent with an overall transition of water storage from the local cryosphere glaciers permafrost to the hydrosphere closed basin lakes and ponds as well as the ross sea we interpret this regional melting pattern to reflect a transition to arctic and alpine style hydrologically mediated permafrost and glacial melt

vertical vertical controlled source electromagnetic instrumentation and acquisition abstract vertical vertical controlled source electromagnetic is an alternative to other techniques for providing three dimensional resistivity images of the subsurface it utilizes a large and powerful vertical dipole transmitter and arrays of e field receivers with vertical and horizontal dipole sensors the necessary instrumentation and acquisition procedures which differ strongly from other controlled source electromagnetic methods are described in the paper

geodynamic models of mature continental collision evolution of an orogen from lithospheric subduction to continental retreat delamination 1 the behavior of deep lithospheric processes in continental collision are frequently speculated on but poorly understood in this study we build on previous work to explore the styles of continental lithosphere deformation during mature collision where 1800 km of convergence has been accommodated by horizontal shortening we conducted a suite of numerical geodynamic experiments that test the sensitivity of mature continent collision to varying mantle lithosphere density mantle lithosphere yield stress lower crustal strength and to the presence of phase change related density changes in the lower crust i e eclogitization of mafic lower crust the models suggest that the early stages of collision are accommodated by subduction of lower crust and mantle lithosphere along a discrete shear zone beneath the overriding plate following this initial stage of subduction the subducting lower crust and mantle lithosphere can retreat from the collision zone permitting the sub lithospheric mantle to upwell and intrude the overriding plate as a result the lower crust and mantle lithosphere of the overriding plate delaminate from the overlying crust with local isostatic adjustment subduction and delamination driven crustal processes plateau like uplift occurs the sub crustal evolution also causes bands of syn convergent crustal extension to develop in models with a rheologically weaker lower crust surface crustal response to the deep lithosphere dynamics becomes more diffuse as an example the numerical experiments satisfy a number of surface observables of the himalayan tibetan orogen namely 1 the current general mantle lithosphere architecture as defined by seismic analyses 2 the long wavelength plateau uplift of the western tibetan plateau 3 the surface heat flow measurements in india the tethyan himalaya qiangtang and in qaidam basin and 4 the anomalous syn convergent extension in the southern portion of the orogen

quantitative constraint on footwall rotations at the 15 45 n oceanic core complex mid atlantic ridge implications for oceanic detachment fault processes the subsurface geometry of detachment faults at slow spreading mid ocean ridges is debated are they planar features that form and slip at low angles as often inferred for their continental equivalents or do they initiate at steep angles and then flatten in response to flexural unloading as displacement proceeds as predicted in rolling hinge conceptual models an essential difference is that significant rotation of the footwall should occur in the rolling hinge but not the planar fault model this can be tested using paleomagnetism previous attempts to address this question have relied upon data from azimuthally unoriented drill cores although results are consistent with large rotations having occurred these interpretations are very nonunique and other solutions that require minimal rotations are equally permissible we here present a rigorous analysis of paleomagnetic and structural data from a unique set of azimuthally oriented cores collected using a seabed rock drill from the 15 45 n oceanic core complex on the mid atlantic ridge by considering the full paleomagnetic remanence vector in combination with kinematic data from the detachment fault shear zone we are able to quantitatively constrain the geometrically permissible axes and magnitudes of rotation of the detachment fault footwall for the first time without having to make a priori assumptions about the orientation of the axis we show that significant rotations 64 16 have indeed occurred about a gently plunging near ridge parallel axis robustly supporting the rolling hinge models we further discuss the geological implications of this result for oceanic detachment fault processes

a distributed surface energy balance model for complex topography and its application to storglaciaren sweden a grid based surface energy balance mass balance model has been developed to simulate snow and ice melt in mountainous regions with an hourly resolution the model is applied to storglaciaren a valley glacier in sweden using a 30 m resolution digital elevation model emphasis is directed towards computing the radiation components these are modelled individually considering the effects of slope angle aspect and effective horizon a new parameterization for snow albedo is suggested modifying the albedo of the preceding hour as a function of time after snowfall air temperature and cloudiness the model is used to provide the meltwater input for discharge modelling and to assess the influence of the individual components on melt results are validated by means of observed melt rates patterns of snow line retreat and proglacial discharge in general simulations are in good agreement with observations in particular the diurnal and seasonal fluctuations of discharge are simulated remarkably well

optimizing em data acquisition for continental shelf exploration the controlled source electromagnetic csem method has been applied to oil and gas exploration and production for more than 10 years during this time most of the focus has been on derisking deep and ultradeep water drilling decisions in this article we will consider how em methods can be optimized for continental shelf applications which represent approximately 80 of offshore discoveries historically applications of em on the continental shelf have been limited for two principal reasons

ground ice recharge via brine transport in frozen soils of victoria valley antarctica insights from modeling δ18o and δd profiles abstract soils in the mcmurdo dry valleys antarctica contain ice and considerable amounts of salt ice often occurs at shallow depth throughout the dry valleys and other areas of hyperarid permafrost notably on mars this common occurrence of shallow ice is enigmatic however since according to published sublimation models it should disappear relatively quickly at rates of order 0 1 mm a 1 due to vapor loss to the atmosphere this loss may be offset by recharge from snowmelt infiltrating and freezing in the soil herein we present a first quantitative estimate of this recharge based on measured vertical profiles of d and 18 o that reveal considerable detail about the sources and sinks of ice we model these profiles taking into account the salt content and a soil temperature record along a 1 6 m depth profile of 10 ka old ice cemented soils in victoria valley antarctica the stable isotopes of ice are enriched in heavy isotopes at the top of the ice cement 20 cm depth both d and 18 o values plotted against depth exhibit a concave upward curve at depth the isotope composition is similar to that of lake victoria and modern meteoric water the concave shape of the isotope profile is suggestive of downward advection dispersion of snowmelt water enriched in heavy isotopes into the ice cement our advection dispersion model coupled with field data enables us to quantify the advective flux and dispersion of melt water into the ice the advective velocity and dispersion coefficient depend on the time since advection began and the ice to brine ratio they are respectively of the order of 10 11 10 10 m s 1 and 10 12 10 11 m 2 s 1 these values suggest that over the 10 ka time period a total of 190 mm water infiltrated into the ice cemented ground the isotope composition and deuterium excess values of the uppermost ice cement can be modeled from snowmelt water enriched in salts using open system rayleigh fractionation to develop the isotopic signature of the upper ice cement requires evaporation of 95 of the snowmelt water based on 190 mm brine infiltrating into the soil requires an initial total of 4 m of snowmelt water this corresponds to 0 4 mm a 1 suggesting that under the current climate condition water from snowmelt is sufficient to compensate modeled sublimation rates and therefore conserve ground ice in victoria valley

sensitivity of mass balance of five swiss glaciers to temperature changes assessed by tuning a degree day model a degree day model is used to assess the sensitivity of the mass balance of five swiss glaciers to temperature changes the model uses temperature data extrapolated from nearby climate stations and is tuned by varying precipitation to make the model fit the observed distribution of mass balance with altitude once the model is tuned the effect of temperature change is simulated by recalculating the mass balance with the same parameters as before but with a temperature increase of 1 c throughout the year the largest mass balance changes involving increased ablation of 1 m w e a 1 c 1 occur at the snout with a progressively smaller increase with altitude the area averaged sensitivities for the five glaciers are 0 7 to 0 9 m w e a 1 c 1 if annual precipitation also increased by 20 it would partly offset the effect of the 1 c higher temperatures but could not compensate for it