persistence in intra annual snow depth distribution 1 measurements and topographic control 1 terrestrial and airborne laser scanning tls and als techniques have only recently developed to the point where they allow wide area measurements of snow distribution in varying terrain in this paper we present multiple tls measurements showing the snow depth development for a series of precipitation events we observe that the pattern of maximum accumulation is similar for the two years presented here correlation up to r 0 97 storms arriving from the northwest show persistent snow depth distributions and contribute most to the final accumulation pattern snow depth patterns of maximum accumulation for the two years are more similar than the distribution created by any two pairs of individual storms based on the strong link between accumulation patterns and terrain we investigated the ability of a model based on terrain and wind direction to predict accumulation patterns this approach of winstral et al 2002 which describes wind exposure and shelter was able to predict the general accumulation pattern over scales of slopes but failed to match observed variance furthermore a high sensitivity to the local wind direction was demonstrated we suggest that winstral et al s model could form a useful tool for application from hydrology and avalanche risk assessment to glaciology

complex dielectric permittivity measurements from ground penetrating radar data to estimate snow liquid water content in the pendular regime 1 monitoring the snow water equivalent swe is critical to effective management of water resources in many parts of the world that depend on the mountain snowpack for water storage there are currently no methods to remotely sense swe with accuracy over large lateral distances in the steep and often forested terrain of mountain basins previous studies have shown that measurements of ground penetrating radar gpr velocity can provide accurate estimates of swe in dry snow introduction of liquid water into the snowpack results in a three phase system that cannot be accurately characterized with gpr velocity alone we show that measuring the frequency dependent gpr signal attenuation and velocity provides a direct estimate of the complex dielectric permittivity because the imaginary component is a function only of liquid water content we can utilize both the real and imaginary components of the permittivity to estimate liquid water content snow density and swe using existing empirical relationships that are valid in the pendular regime we tested this new method at two field sites and found that the estimates were accurate to within 12 of gravimetric methods in both a moist and a dry snowpack gpr has the potential to provide swe estimates across large lateral distances over a broad range of snow conditions

six decades of glacier mass balance observations a review of the worldwide monitoring network glacier mass balance is the direct and undelayed response to atmospheric conditions and hence is among the essential variables required for climate system monitoring it has been recognized as the largest non steric contributor to the present rise in sea level six decades of annual mass balance data have been compiled and made easily available by the world glacier monitoring service and its predecessor organizations in total there have been 3480 annual mass balance measurements reported from 228 glaciers around the globe however the present dataset is strongly biased towards the northern hemisphere and europe and there are only 30 reference glaciers that have uninterrupted series going back to 1976 the available data from the six decades indicate a strong ice loss as early as the 1940s and 1950s followed by a moderate mass loss until the end of the 1970s and a subsequent acceleration that has lasted until now culminating in a mean overall ice loss of over 20 m w e for the period 1946 2006 in view of the discrepancy between the relevance of glacier mass balance data and the shortcomings of the available dataset it is strongly recommended to 1 continue the long term measurements 2 resume interrupted long term data series 3 replace vanishing glaciers by early starting replacement observations 4 extend the monitoring network to strategically important regions 5 validate calibrate and accordingly flag field measurements with geodetic methods and 6 make systematic use of remote sensing and geo informatics for assessment of the representativeness of the available data series for their entire mountain range and for the extrapolation to regions without in situ observations and 7 make all these data and related meta information available

seafloor direct current resistivity techniques for deep marine near bottom gas hydrate investigation abstract geophysical investigations of the first 100 m below the seafloor in deep marine environments are done to assess drilling hazards to plan routes for pipelines and cables and to study benthic organism communities the tool of choice for these investigations is subbottom profiling which uses acoustic signals in the range of 1 to 25 khz to image near bottom stratigraphy an existing engineering scale direct current resistivity dcr system for use in deep marine near bottom environments has been adapted it is potentially useful in settings in which the presence of free gas gas hydrates coarse sediment cemented carbonate or highly deformed sediment limits the effectiveness of the subbottom profiling method the adapted dcr system was used to survey woolsey mound mississippi canyon block 118 mc118 gulf of mexico to characterize the shallow gas hydrate system three conventional modes of dcr data acquisition continuous resistivity profiling crp static array and time lapse with a fix

analysis of a grace global mascon solution for gulf of alaska glaciers we present a high resolution gravity recovery and climate experiment grace mascon solution for gulf of alaska goa glaciers and compare this with in situ glaciological climate and other remote sensing observations our grace solution yields a goa glacier mass balance of 65 11 gt a 1 for the period december 2003 to december 2010 with summer balances driving the interannual variability between october november 2003 and october 2009 we obtain a mass balance of 61 11 gt a 1 from grace which compares well with 65 12 gt a 1 from icesat based on hypsometric extrapolation of glacier elevation changes we find that mean summer june august air temperatures derived from both ground and lower troposphere temperature records were good predictors of grace derived summer mass balances capturing 59 and 72 of the summer balance variability respectively large mass losses during 2009 were likely due to low early melt season surface albedos measured by the moderate resolution imaging spectroradiometer modis and likely associated with the 31 march 2009 eruption of mount redoubt southwestern alaska grace data compared well with in situ measurements at wolverine glacier maritime alaska but poorly with those at gulkana glacier interior alaska we conclude that although goa mass estimates from grace are robust over the entire domain further constraints on subregional and seasonal estimates are necessary to improve fidelity to ground observations

spatial and temporal variability of snow accumulation using ground penetrating radar and ice cores on a svalbard glacier a 50 mhz ground penetrating radar was used to detect horizontal layers in the snowpack along a longitudinal profile on nordenskjoldbreen a svalbard glacier the profile passed two shallow and one deep ice core sites two internal radar reflection layers were dated using parameters measured in the deep core radar travel times were converted to water equivalent yielding snow accumulation rates along the profile for three time periods 1986 99 1963 99 and 1963 86 the results show 40 60 spatial variability in snow accumulation over short distances along the profile the average annual accumulation rate for 1986 99 was found to be about 12 higher than for the period 1963 86 which indicates increased accumulation in the late 1980s and 1990s

inverse estimation of snow accumulation along a radar transect on nordenskioldbreen svalbard we present an inverse modeling approach to reconstruct annual accumulation patterns from ground penetrating radar gpr data a coupled surface energy balance snow model simulates surface melt and the evolution of subsurface density temperature and water content the inverse problem consists of iteratively calibrating accumulation serving as input for the model by finding a match between modeled and observed radar travel times the inverse method is applied to a 16 km gpr transect on nordenskioldbreen svalbard yielding annual accumulation patterns for 2007 2012 accumulation patterns with a mean of 0 75 meter water equivalent mwe a 1contain substantial spatial variability with a mean annual standard deviation of 0 17 mwe a 1 and show only partial consistency from year to year in contrast to traditional methods accounting for melt water percolation refreezing and runoff facilitates accurate accumulation reconstruction in areas with substantial melt additionally accounting for horizontal density variability along the transect is shown to reduce spatial variability in reconstructed accumulation whereas incorporating irreducible water storage lowers accumulation estimates correlating accumulation to terrain characteristics in the dominant wind direction indicates a strong preference of snow deposition on leeward slopes whereas weaker correlations are found with terrain curvature sensitivity experiments reveal a nonlinear response of the mass balance to accumulation changes the related negative impact of small scale accumulation variability on the mean net mass balance is quantified yielding a negligible impact in the accumulation zone and a negative impact of 0 09 mwe a 1in the ablation area

a comparison of seismic and radar methods to establish the thickness and density of glacier snow cover we show that geophysical methods offer an effective means of quantifying snow thickness and density opportunistic efficient but non optimized seismic refraction and ground penetrating radar gpr

rising river flows throughout the twenty first century in two himalayan glacierized watersheds greater himalayan glaciers are retreating and losing mass a combination of the latest ensemble of climate models combined with a glacio hydrological model suggests that in two contrasting watersheds in the greater himalaya glaciers will recede but net glacier melt runoff is on a rising limb until at least 2050

methodological approaches to infer end of winter snow distribution on alpine glaciers snow accumulation is an important component of the mass balance of alpine glaciers to improve our understanding of the processes related to accumulation and their representation in state of the art mass balance models extensive field measurements are required we present measurements of snow accumulation distribution on findelengletscher switzerland for april 2010 using 1 in situ snow probings 2 airborne ground penetrating radar gpr and 3 differencing of two airborne light detection and ranging lidar digital elevation models dems calculating high resolution snow depth from dem differencing requires careful correction for vertical ice flow velocity and densification in the accumulation area all three methods reveal a general increase in snow depth with elevation but also a significant small scale spatial variability lidar differencing and in situ snow probings show good agreement for the mean specific winter balance 0 72 and 0 78 m w e respectively the lidar derived distributed snow depth reveals significant zonal correlations with elevation slope and curvature in a multiple linear regression model unlike lidar differencing gpr derived snow depth is not affected by glacier dynamics or firn compaction but to a smaller degree by snow density and liquid water content it is thus a valuable independent data source for validation the simultaneous availability of the three datasets facilitates the comparison of the methods and contributes to a better understanding of processes that govern winter accumulation distribution on alpine glaciers

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

end of winter snow depth variability on glaciers in alaska a quantitative understanding of snow thickness and snow water equivalent swe on glaciers is essential to a wide range of scientific and resource management topics however robust swe estimates are observationally challenging in part because swe can vary abruptly over short distances in complex terrain due to interactions between topography and meteorological processes in spring 2013 we measured snow accumulation on several glaciers around the gulf of alaska using both ground and helicopter based ground penetrating radar surveys complemented by extensive ground truth observations we found that swe can be highly variable 40 difference over short spatial scales tens to hundreds of meters especially in the ablation zone where the underlying ice surfaces are typically rough elevation provides the dominant basin scale influence on swe with gradients ranging from 115 to 400 mm 100 m regionally total accumulation and the accumulation gradient are strongly controlled by a glacier s distance from the coastal moisture source multiple linear regressions used to calculate distributed swe fields show that robust results require adequate sampling of the true distribution of multiple terrain parameters final swe estimates comparable to winter balances show reasonable agreement with both the parameter elevation relationships on independent slopes model climate data set 9 36 difference and the u s geological survey alaska benchmark glaciers 6 36 difference all the glaciers in our study exhibit substantial sensitivity to changing snow rain fractions regardless of their location in a coastal or continental climate while process based swe projections remain elusive the collection of ground penetrating radar gpr derived data sets provides a greatly enhanced perspective on the spatial distribution of swe and will pave the way for future work that may eventually allow such projections

climate variability in west antarctica derived from annual accumulation rate records from itase firn ice cores thirteen annually resolved accumulation rate records covering the last 200 years from the pine island thwaites and ross drainage systems and the south pole are used to examine climate variability over west antarctica accumulation is controlled spatially by the topography of the ice sheet and temporally by changes in moisture transport and cyclonic activity a comparison of mean accumulation since 1970 at each site to the long term mean indicates an increase in accumulation for sites located in the western sector of the pine island thwaites drainage system accumulation is negatively associated with the southern oscillation index soi for sites near the ice divide and periods of sustained negative soi 1940 42 1991 95 correspond to above mean accumulation at most sites correlations of the accumulation rate records with sea level pressure slp and the soi suggest that accumulation near the ice divide and in the ross drainage system may be associated with the mid latitudes the post 1970 increase in accumulation coupled with strong slp accumulation rate correlations near the coast suggests recent intensification of cyclonic activity in the pine island thwaites drainage system

combining binary decision tree and geostatistical methods to estimate snow distribution in a mountain watershed we model the spatial distribution of snow across a mountain basin using an approach that combines binary decision tree and geostatistical techniques in april 1997 and 1998 intensive snow surveys were conducted in the 6 9 km2 loch vale watershed lvws rocky mountain national park colorado binary decision trees were used to model the large scale variations in snow depth while the small scale variations were modeled through kriging interpolation methods binary decision trees related depth to the physically based independent variables of net solar radiation elevation slope and vegetation cover type these decision tree models explained 54 65 of the observed variance in the depth measurements the tree based modeled depths were then subtracted from the measured depths and the resulting residuals were spatially distributed across lvws through kriging techniques the kriged estimates of the residuals were added to the tree based modeled depths to produce a combined depth model the combined depth estimates explained 60 85 of the variance in the measured depths snow densities were mapped across lvws using regression analysis snow covered area was determined from high resolution aerial photographs combining the modeled depths and densities with a snow cover map produced estimates of the spatial distribution of snow water equivalence swe this modeling approach offers improvement over previous methods of estimating swe distribution in mountain basins

valles caldera region new mexico and the emerging continental scientific drilling program valles caldera is best known in recent years as an excellent example of a resurgent caldera smith and bailey 1968 and as the site of a high temperature geothermal system dondanville 1978 however valles caldera and the surrounding jemez mountains volcanic field possess a rich history of geologic research that dates back to the late 1800s through the years the research focus has changed as different economic and scientific factors have exerted their influence early work emphasized mining activity while modern work has stressed volcanology and later geothermal development only in the last 5 years has it been possible to view the region as a dynamic integrated magma hydrothermal system having a complex evolution lasting more than 13 m y gardner et al 1986 goff and nielson 1986 self et al 1986

the randolph glacier inventory a globally complete inventory of glaciers the randolph glacier inventory rgi is a globally complete collection of digital outlines of glaciers excluding the ice sheets developed to meet the needs of the fifth assessment of the intergovernmental panel on climate change for estimates of past and future mass balance the rgi was created with limited resources in a short period priority was given to completeness of coverage but a limited uniform set of attributes is attached to each of the 198 000 glaciers in its latest version 3 2 satellite imagery from 1999 2010 provided most of the outlines their total extent is estimated as 726 800 34 000 km 2 the uncertainty about 5 is derived from careful single glacier and basin scale uncertainty estimates and comparisons with inventories that were not sources for the rgi the main contributors to uncertainty are probably misinterpretation of seasonal snow cover and debris cover these errors appear not to be normally distributed and quantifying them reliably is an unsolved problem combined with digital elevation models the rgi glacier outlines yield hypsometries that can be com bined with atmospheric data or model outputs for analysis of the impacts of climatic change on glaciers the rgi has already proved its value in the generation of significantly improved aggregate estimates of glacier mass changes and total volume and thus actual and potential contributions to sea level rise

geometry mass balance and thinning at eklutna glacier alaska an altitude mass balance feedback with implications for water resources we analyzed glacier surface elevations 1957 2010 and 2015 and surface mass balance measurements 2008 2015 on the 30 km 2 eklutna glacier in the chugach mountains of southcentral alaska the geodetic mass balances from 1957 to 2010 and 2010 to 2015 are 0 52 0 46 and 0 74 0 10 m w e a 1 respectively the glaciological mass balance of 0 73 m w e a 1 from 2010 to 2015 is indistinguishable from the geodetic value even after accounting for loss of firn in the accumulation zone we found most of the mass loss over both time periods was from a broad low slope basin that includes much of the accumulation zone of the main branch ice equivalent surface elevation changes in the basin were 1 0 0 8 m a 1 from 1957 to 2010 and 0 6 0 1 m a 1 from 2010 to 2015 shifting the glacier hypsometry downward and resulting in more negative mass balances an altitude mass balance feedback net mass loss from eklutna glacier accounts for 7 1 of the average inflow to eklutna reservoir which is entirely used for water and power by anchorage alaska s largest city if the altitude mass balance feedback continues this deglaciation discharge dividend is likely to increase over the short term before it eventually decreases due to diminishing glacier area

mountain snow distribution governed by an altitudinal gradient and terrain roughness 1 the heterogeneous mountain snow cover is challenging the eye and the analytical mind of the observer the snow distribution affects water resources natural hazards such as avalanches and ecology while a lot of recent research has helped to better understand this snow distribution and the processes that cause the heterogeneity it has not yet been possible to predict snow distribution satisfactorily on the basis of terrain parameters alone we present a model of the mean snow depth in topographic control units as a function of two terrain parameters the conventional elevation plus a fractal roughness parameter for this we used a unique data set of high resolution measurements of snow depth from an airborne laser scanner the model captures the heterogeneous snow distribution by merely analysing the terrain and the mean precipitation this unusually simple relationship holds for clusters of the snow depths of small topographical units by applying fractal analysis we describe the roughness of the terrain and use this parameter for the prediction of snow deposition rougher terrain holds less snow than smoother terrain this finding is important not only for avalanche warning or eco hydrological applications but also for reliably predicting how snow water storage may change in the light of the pronounced climate change already ongoing in mountain regions

snow depth structure fractal behavior and interannual consistency over haut glacier d arolla switzerland snow depth patterns over glaciers are controlled by precipitation snow redistribution due to wind and avalanches and the exchange of energy with the atmosphere that determines snow ablation while many studies have advanced the understanding of ablation processes less is known about winter snow patterns and their variability over glaciers we analyze snow depth on haut glacier d arolla switzerland in the two winter seasons 2006 2007 and 2010 2011 to 1 understand whether snow depth over an alpine glacier at the end of the accumulation season exhibits a behavior similar to the one observed on single slopes and vegetated areas and 2 investigate the snow pattern consistency over the two accumulation seasons we perform this analysis on a data set of high resolution lidar derived snow depth using variograms and fractal parameters our first main result is that snow depth patterns on the glacier exhibit a multiscale behavior with a scale break around 20 m after which the fractal dimension increases indicating more autocorrelated structure before the scale break than after second this behavior is consistent over the two years with fractal parameters and their spatial variability almost constant in the two seasons we also show that snow depth patterns exhibit a distinct behavior in the glacier tongue and the upper catchment with longer correlation distances on the tongue in the direction of the main winds suggesting spatial distinctions that are likely induced by different processes and that should be taken into account when extrapolating snow depth from limited samples

the challenge of monitoring glaciers with extreme altitudinal range mass balance reconstruction for kahiltna glacier alaska glaciers spanning large altitudinal ranges often experience different climatic regimes with elevation creating challenges in acquiring mass balance and climate observations that represent the entire glacier we use mixed methods to reconstruct the 1991 2014 mass balance of the kahiltna glacier in alaska a large 503 km 2 glacier with one of the greatest elevation ranges globally 264 6108 m a s l we calibrate an enhanced temperature index model to glacier wide mass balances from repeat laser altimetry and point observations finding a mean net mass balance rate of 0 74 mw e a 1 0 04 std dev of the best performing model simulations results are validated against mass changes from nasa s gravity recovery and climate experiment grace satellites a novel approach at the individual glacier scale correlation is strong between the detrended model and grace derived mass change time series r 2 0 58 and p 0 001 and between summer r 2 0 69 and p 0 003 and annual r 2 0 63 and p 0 006 balances lending greater confidence to our modeling results we find poor correlation however between modeled glacier wide balances and recent single stake monitoring finally we make recommendations for monitoring glaciers with extreme altitudinal ranges including characterizing precipitation via snow radar profiling

radar response of firn exposed to seasonal percolation validation using cores and fdtd modeling we use ground penetrating radars gprs firn cores and electromagnetic finite difference time domain fdtd numerical modeling to characterize the gpr response to a frozen high arctic firn pack as a result of extensive summertime percolation the firn pack comprises a high fraction of ice layers lenses and vertical glands we show that the gpr response on the firn pack mainly depends on the following 1 the thickness of the ice layers 2 the distance between layers 3 the layer roughness and 4 the presence or absence of elliptical ice lenses using 3 d fdtd modeling we show that the gpr is not sensitive to typical ice glands which implies that the gpr underestimates firn heterogeneity such that firn stratigraphy in percolation and wet snow zones could be incorrectly interpreted as being better preserved than it actually is we find that thin ice layers 0 05 m or multiple thin ice layers give a strong response thicker ice layers typically give a weaker backscatter per unit area mainly due to the lack of interference of the reflections from the upper and lower interfaces but are due to their continuity easily trackable ice layers with a thickness comparable to the gpr wavelength give 180deg phase shifted upper and lower reflections and are in general separated by a band of low gpr response due to the lack of permittivity contrast within the ice layers despite the ice lenses relatively short horizontal correlation length as inferred from cores bands of high amplitude clutter caused by these features can be traced over several kilometers in gpr profiles

updated estimates of glacier volume changes in the western chugach mountains alaska and a comparison of regional extrapolation methods and 2001 2004 average net balance rates ranged between 3 1 to 0 16 m yr 1 for the tidewater and 1 5 to 0 02 m yr 1 for the nontidewater glaciers we tested several methods for extrapolating these measurements to all the glaciers of the western chugach mountains using a process similar to cross validation predictions of individual glacier changes appear to be difficult probably because of the effects of glacier dynamics which on long multidecadal timescales complicates the response of glaciers to climate in contrast estimates of regional contributions to rising sea level were similar for different methods mainly because the large glaciers whose changes dominated the regional total were among those measured for instance the above sea level net balance rate of columbia glacier 3 1 0 08 km 3 yr 1 water equivalent weq or an equivalent rise in sea level sle of 0 0090 0 0002 mm yr 1 was nearly half of the total regional net balance rate of the western chugach mountain glaciers 7 4 1 1 km 3 yr 1 weq or 0 020 0 003 mm yr 1 sle between 1950 1957 and 2001 2004 columbia glacier is a rapidly retreating tidewater glacier that has lost mass through processes largely independent of climate tidewater glaciers should therefore be treated separately when performing regional extrapolations

snow depth density and swe estimates derived from gps reflection data validation in the western u s geodetic quality gps systems can be used to measure average snow depth in the 1000 m2 area around the gps antenna a sensing footprint size intermediate between in situ and satellite observations swe can be calculated from density estimates modeled on the gps based snow depth time series we assess the accuracy of gps based snow depth density and swe data at 18 gps sites via comparison to manual observations the manual validation survey was completed around the time of peak accumulation at each site daily snow depth derived from gps reflection data is very similar to the mean snow depth measured manually in the 1000 m2 scale area around each antenna this comparison spans site averaged depths from 0 to 150 cm the gps depth data exhibit a small negative bias 6 cm across this range of snow depths errors tend to be smaller at sites with more usable gps ground tracks snow bulk density is modeled using the gps snow depth time series and model parameters are estimated from nearby snotel sites modeled density is within 0 02 g cm 3 of the density measured in a single snow pit at the validation sites for 12 of 18 comparisons gps based depth and modeled density are multiplied to estimate swe swe estimates are very accurate over the range observed at the validation sites from 0 to 60 cm r2 0 97 and bias 2 cm these results show that the near real time gps snow products have errors small enough for monitoring water resources in snow dominated basins

strong spatial variability of snow accumulation observed with helicopter borne gpr on two adjacent alpine glaciers the spatial distribution of snow accumulation plays an essential role for the mass balancedistribution on alpine glaciers traditional point measurements snow pits and probes are labour intensive and interpolation in between the points causes uncertainties airborne radar measurements have already been used for snow mapping innon glacierized terrain but not on alpine glaciers to enhance our understanding ofthe spatial distribution of accumulation and pin down reasons for observed variations we have conducted high resolution helicopter borne radar measurements on the temperatedglacier findel and neighbouring adler glacier in southwestern switzerland the radar sensor was mounted underneath a helicopter and operated at a centre frequencyof 500 mhz with a bandwidth of 400 mhz the results were validated withextensive ground based profiling of the snow cover the radar data allows a clearrecognition of the snow cover 6 of the total profile length of 10 km did not allowinterpretation due to missing or disturbed layering and agreed well with the groundbased measurements r2 0 85 reduced accumulation has been observed in allcrevassed zones statistical analysis of the correlation between observed accumulationand terrain characteristics have been performed in a gis environment revealing differingaccumulation patterns on the lower part of findel glacier accumulation showsa clear altitudinal trend while the upper part is dominated by strongly varying snowdepth without an altitudinal trend the accumulation characteristic on adler glacieris similar to the upper part of findel glacier but despite of their close vicinity accumulationis reduced by 40 compared to the same elevation on findel glacier thisstudy reveals a large potential of helicopter borne snow profiling for measurements ofaccumulation distribution on alpine glaciers

postmagmatic sulphur loss in the skaergaard intrusion implications for the formation of the platinova reef abstract the stratabound platinova au pd reef in the skaergaard intrusion is intimately linked to cu fe sulphide minerals and occurs at a level that shows changes in the sulphur concentration and the cu s ratio these features suggest that the reef is related to silicate sulphide liquid immiscibility in the skaergaard magma however although the evidence is strong present day sulphur concentrations are too low to support such a model the detailed knowledge of the shape volume and compositional relations of the skaergaard lithologies allows for numerical modeling of sulphur and copper concentrations during fractionation of the magma these data can be evaluated with the current models for sulphur saturation in iron rich mafic magmas to assess the original sulphur concentrations the extent of fractionation the composition of sulphide liquids and the extent of postmagmatic sulphur loss mass balance modeling yields initial copper and sulphur concentrations of 250 and 894 ppm for the parental magma to the lower zone a prior to sulphur saturation cu behaves as an incompatible element with a bulk partition coefficient in the cumulus material dcumuluscu of 0 13 indicating some incorporation of cu into mafic silicates probably augite sulphur can be assumed to be perfectly incompatible in the cumulus minerals although it will be included as a component of the interstitial liquid these values yield sulphur saturation at around 635 ppm cu and 2607 ppm s assuming the sulphur to originally be present as a mixture of monosulphide mss and intermediate solid solution sulphide iss the primary sulphides in the cumulates would amount to 0 07 modal through lower and middle zones and 0 53 modal on average through upper zone the expected weight proportion of primary chalcopyrite pyrrhotite evolves from 30 70 at the base of lza through 26 74 at the level of the platinova reef to 18 82 at the sandwich horizon the present day bornite magnetite mineral assemblage is likely to have been derived from a primary pyrrhotite chalcopyrite assemblage through reequilibration and postmagmatic oxidation significant sulphur appears to have been lost from the lower and middle parts of the layered series lower zone a to upper zone b whereas the sulphides of the upper zone c can be explained in the context of a sulphur gain local scale reequilibration of cu from mafic silicates into sulphides may have contributed to the sulphide mineralogy of the lower and middle zones the structure of the platinova reef probably formed from an original single stratabound reef sulphur loss through oxidation in upward migrating deuteric or hydrothermal fluids could have caused dissolution and reprecipitation of pd and au in a cumulate with several stratiform redox barriers this process can thus explain the successive pd peaks of the reef as well as the variable stratigraphic offset of pd and au across the intrusion