processes of forearc and accretionary complex formation during arc continent collision in the southern ural mountains the southern ural mountains of russia contain a well preserved well exposed paleozoic accretionary wedge and forearc that can be readily compared to those in active arc continent collision zones the early convergent history in the southern ural mountains is marked by the generation of boninite bearing arc tholeiites in the magnitogorsk forearc followed by arc tholeiite to calc alkaline volcanism with the entry of the east european craton continental crust in the subduction zone volcanism waned and stopped and high pressure metamorphism of its leading edge took place the arrival of the full thickness of the continental crust at the subduction zone is marked by increased sedimentation in the forearc basin and deposition of arc derived volcaniclastic turbidites across the subducting slab these together with offscraped continental material the exhumed high pressure rocks and a lherzolite massif formed an accretionary wedge a broad melange zone containing ultramafic fragments separates the forearc basement from the accretionary wedge and marks the damage zone that developed along the backstop region shallow water carbonates deposited unconformably on top of the mildly deformed arc record the end of the collision and the collapse of the arc

an introduction to wavelet transform tidal analysis methods continuous wavelet transforms cwts provide an approach to understanding the numerous tidal phenomena that deviate markedly from an assumed statistical stationarity or exact periodicity inherent in traditional tidal methods use of wavelets allows determination of the degree of non stationarity present in time series such as estuarine and shelf currents usually treated as stationary wavelets also provide a consistent analysis of tidal and non tidal variance a feature often essential for dynamical analyses of non stationary tides we summarize basic notions of the wavelet transform also known as a perfect reconstruction filter bank or a multire solution analysis contrast them with those of harmonic analysis and fourier transforms construct a continuous wavelet transform basis with a scale selection especially adapted to tidal problems describe possibilities for analysis of scalar and vector quantities define a criterion for knowledge of independence of process between adjoining scales and illustrate use of wavelet tools with several examples in contrast to the nearly periodic barotropic tide typical of coastal stations this paper analyses processes that are in part tidally driven but non stationary e g baroclinic tidal currents river tides continental shelf internal tides and some kinds of biological activity in the coastal ocean in all cases wavelet analysis provides a consistent linear analysis of tidal and non tidal variance and reveals features that harmonic analysis on a fourier transform approach could not elucidate

submarine melting at the terminus of a temperate tidewater glacier leconte glacier alaska u s a heat fresh and sea water balances indicate that the late summer rate of submarine melting at the terminus of tidewater leconte glacier alaska u s a in 2000 was about 12md 1 w e averaged over the submerged face this is 57 of the estimated total ice loss at the terminus calving plus melting at this time submarine melting may thusprovidea significantcontributiontotheoverallablationofatidewaterglacier oceano graphic measurements conductivity temperature depth made 200 500m from the ter minus identified an isohaline 27ppt and isothermal 7 2 c layer extending from 130m depthto the fjord floor capping this is a 40mthick overflow plume distinguishedby high outflow rates low salinity 22 25ppt and lower temperatures 5 6 c mixing models indicate that fresh water comprised about11 of this plume it originates mostly as sub glacial discharge whose buoyancy drives convection at the terminus deep warm saline watersareincorporatedintotheplumeasitascends causingsubstantialmeltingoficealong the submarine face the calving terminus undergoes seasonal changes that coincide with changes in subglacial discharge and fjord water temperatures and we suggest that these fluctuations interminuspositionare directly relatedto changes in submarine melting

the age and emplacement of obducted oceanic crust in the urals from smnd and rbsr systematics the urals contain a 2000 km belt of mafic ultramafic bodies the sm nd and rb sr systematics of two of these bodies the kempersai massif in the south ural mountains and the voykar syninsky ophiolite complex in the polar ural mountains have been examined these data confirm the hypothesis that these bodies represent fragments of pre collision oceanic crust and establish constraints on the nature and timing of events in the uralian orogeny two kempersai gabbros define sm nd internal isochrons of 397 20 my and 396 33 my with e nd t 8 7 0 6 and 8 4 1 3 respectively whole rock samples of pillow basalt diabase gabbros troctolite and a metasediment give sm nd values which lie on this isochron indicating that these rocks are genetically related and have an igneous crystallization age of 397 my whole rock samples of voykar syninsky diabase gabbros and clinopyroxenite give sm nd values which lie on or within 1 e unit of this isochron indicating an age and e nd t virtually identical to those of kempersai e nd t for the kempersai and voykar syninsky mafic samples range from 7 3 to 9 0 with an average value of 8 4 this indicates that the urals ophiolites are derived from an ancient depleted mantle source and are most plausibly pieces of the oceanic crust and lithosphere the fact that a metasediment has the same e nd 397 my as the other samples indicates derivation from an oceanic source with negligible continental input e nd t for the massifs is 1 5 e units lower than the average for modern morbs this may be due to the differential evolution of the morb source over the past 397 my and in conjunction with data for other ophiolites and mesozoic morb suggests that over the past 750 my the source for morb has evolved at a rate less than or equal to its rate of evolution averaged over the age of the earth initial 87 sr 86 sr ratios are highly variable ranging from e sr t 25 2 for a gabbro to 70 3 for a highly serpentinized harzburgite this reflects the effects of seawater alteration which is particularly strong on ultrabasic rocks we conclude that the long belt of mafic ultramafic rocks in the urals which includes the kempersai and voykar syninsky massifs represents segments of siluro devonian oceanic crust our igneous age for kempersai in conjunction with other age constraints suggest that these segments of oceanic crust formed at least 80 my before the collision that produced the urals

growth of greenland ice sheet measurement measurements of ice sheet elevation change by satellite altimetry show that the greenland surface elevation south of 72 degrees north latitude is increasing the vertical velocity of the surface is 0 20 0 06 meters per year from measured changes in surface elevations at 5906 intersections between geosat paths in 1985 and seasat in 1978 and 0 28 0 02 meters per year from 256 694 intersections of geosat paths during a 548 day period of 1985 to 1986

re os isotope systematics of sulfides from felsic igneous rocks application to base metal porphyry mineralization in chile dating sulfides and determining the source of ore forming metals have been limiting factors in our understanding of processes that produce hydrothermal ore deposits here we analyze sulfides from base metal porphyry deposits from chile to demonstrate the potential of the re os system to determine both the age and the source of metals for hydrothermal mineralization cogenetic chalcopyrite bornite pyrite and sphalerite from el teniente ca 5 ma have 187 re 188 os ratios from 0 3 to 21 8 and initial 187 os 188 os ratios from 0 17 to 0 22 a paragenetically late pyrite that has an initial 187 os 188 os of 0 88 indicates that the ore deposit is not isotopically homogeneous in os throughout the formation of the deposit pyrite samples from andacollo ca 100 ma have 187 re 188 os ratios from 15 to 3600 and different isochrons yield ages between 87 and 103 ma consistent with different sericite k ar ages initial 187 os 188 os ratios of 0 2 to 1 1 are similar to those of el teniente the relatively homogeneous 187 os 188 os ratios 0 19 for cogenetic sulfides from el teniente suggest that most of the os in the ore was from the causal intrusive the latestage pyrite probably incorporated os leached from the country rock by meteoric fluids which mixed with magmatic fluids at the periphery of the hydrothermal system we demonstrate that the re os isotope system can be a powerful geochronological tool in hydrothermal ore deposits the large range in re os ratios of sulfides permits the age of mineralization to be well constrained despite isotopic heterogeneities of the hydrothermal fluids

a barotropic inverse tidal model for the arctic ocean 1 we describe high resolution 5 km grid linear dynamics and inverse models of arctic ocean barotropic tides obtained with the osu tidal inversion software otis package the 8 constituent dynamics based model uses the latest ibcao bathymetry and open boundary forcing from the recent tpxo 6 2 global barotropic tidal solution this model performs significantly better than the present benchmark arctic tidal model 14 km grid by z kowalik and a proshutinsky as judged by comparisons with 300 coastal tide gauges the greatest improvements are found in the canadian arctic archipelago nares strait and the baffin bay and labrador sea and can be explained by the higher resolution of the new model in these topographically complex regions the new arctic inverse model assimilates coastal and benthic tide gauges and topex poseidon and ers altimetry for further improvements of the 4 dominant constituents m2 s2 k1 and o1

ophiolites of the southern uralides adjacent to the east european continental margin abstract in the southern urals the allochthonous ophiolite belt at the junction between the uralides and the east european continental margin includes lherzolite kraka nurali mindyak etc and harzburgite or lherzolite harzburgite khabarny kempersay etc massifs over a distance of 300 km all the lherzolite massifs are uniform in their structure and composition they show similar patterns of plastic deformation in the mantle sequence and degree of geochemical depletion growing toward the sharp and steep contact with the transitional olivine clinopyroxene rocks above which the layered gabbro unit is missing the former unit is intruded here by amphibole gabbro and gabbro diorites in contrast the harzburgite massifs display a more complex style of deformation in the mantle sequence and are affected by multistage magmatic depletion and impregnation the contact with olivine clinopyroxene plagioclase rocks is less sharp and the transition zone is gradual the upper sequence includes layered and isotropic gabbros sheeted dykes and morb type lavas the allochthonous lherzolite massifs are associated with clastic units typical of continental slope facies and in the root zone they occur as a chain of tectonic slices cherty sediments intercalated with lavas of harzburgite sequences are of oceanic origin all these differences suggest that the lherzolite ophiolite sequences were formed during the rift events with poorly manifested magmatic activity which affected the passive continental margin whereas harzburgite sequences illustrate spreading events in marginal basins with normal oceanic crust the synchronism of early middle ordovician rifting and spreading stages in the southern urals seems to indicate that basin opening was prograding northward along the continental margin during silurian devonian imbrication ophiolite terranes of both types were intruded by basic magmas according to available u pb age determination this occurred at about 400 ma

different crustal sources for au rich and au poor ores of the grasberg cu au porphyry deposit abstract the grasberg is a porphyry copper deposit that is crosscut by a second stage mineralization which is greatly enriched in gold sulfides from the porphyry type event yield a 2 9 0 3 ma re os isochron that agrees with published geochronology the initial 187os 188os ratio of the isochron is 0 56 0 02 and implies a significant crustal component for the source of os and by inference the other base metals the samples from the crosscutting secondary event do not form an isochron but form a mixing line with the older porphyry style mineralization as one of the end members and a very radiogenic end member possibly shale the initial 187os 188os ratios from samples of the second event range from 0 81 to 1 26 and correlate with gold content the most radiogenic samples have the highest gold the re os isotope data indicate different crustal sources for the ore forming elements at the grasberg cu au deposit and support a model in which gold is derived from sedimentary protoliths that may have been pre enriched by sedimentary processes the gold derived from these sources is concentrated by magmatic hydrothermal systems the requirement of a sedimentary source for gold to produce hydrothermal gold deposits has been debated for decades and this study provides strong support for the model

peculiarities of some mafic ultramafic and ultramafic hosted massive sulfide deposits from the main uralian fault zone southern urals abstract some cu rich mafic ultramafic and ultramafic hosted massive sulfide deposits from the southern segment of the main uralian fault zone ivanovka and ishkinino deposits southern urals show unusual characteristics their major features include i relatively high co ni au very low zn and negligible pb grades ii a pyrrhotite dominated mineralization locally characterized by the presence of open latticework aggregates of lamellar pyrrhotite with mg saponite mg chlorite and carbonate matrix iii hydrothermal alteration of ultramafic host rocks into talc carbonate quartz chlorite and of mafic host rocks into chloritites iv the presence of clastic facies with reworked sulfide and ultramafic or mafic components v the widespread occurrence of sulfide associated chromite vi the specific mineralogy of co ni fe and as including sulfoarsenides mono and diarsenides and co rich pentlandite and pyrite vii the supra subduction zone geochemical signature of the host serpentinites and volcanic rocks although some of these features have been separately reported in certain modern ocean seafloor and ophiolite hosted fossil deposits a true equivalent has yet to be found based on recognized partial analogies with a few modern seafloor examples the arc tholeiitic boninitic geochemical signature of sulfide associated volcanic rocks and the highly refractory compositions of sulfide hosted chromite relicts the studied deposits are believed to have formed by seafloor subseafloor hydrothermal processes in an oceanic island arc setting possible tectonostratigraphic correlation of sulfide associated units with infant non accretionary arc volcanic units of the adjacent magnitogorsk oceanic island arc system suggests formation of the studied deposits during the earliest stages of devonian subduction related volcanism

precise eclogitization ages deduced from rb sr mineral systematics the maksyutov complex southern urals russia abstract the maksyutov complex southern urals russia is a well preserved example of subduction related high pressure metamorphism one of its two litho tectonic units consists of rocks that experienced eclogite facies conditions published 40ar 39ar data on phengite u pb data on rutile and sm nd mineral data define a cluster of ages around 370 to 380 ma nevertheless no consensus exists as to the detailed interpretation of data and the exact age of eclogitization we present new high precision internal mineral rb sr isochrons for eclogite facies metabasites felsic eclogites and eclogite facies quartz veins nine isochrons mainly controlled by omphacite and white mica phases give concordant ages with an average value of 375 2 ma 2 microtextural features such as prograde growth zoning in eclogite facies phases suggest that the assemblages dated formed at a stage of prograde metamorphism sr isotopic equilibria among eclogite facies phases and among eclogite facies fluid veins and the host rocks indicate that our ages reflect crystallization ages related to the prograde metamorphic probably fluid mediated eclogitization reactions this interpretation is reinforced by data from fluid precipitated quartzitic eclogites whose modal composition together with intergrowth relationships conclusively imply closed system behavior after crystallization the possible occurrence of a pre 375 ma event of ultra high pressure metamorphism uhpm in the maksyutov complex is disproved by isotope systematics microtextures and mineral zoning patterns

shelf fjord exchange driven by coastal trapped waves in the arctic in this article we show that the class of low frequency subinertial waves known as coastal trapped waves ctws are a significant agent of water volume exchange in a west svalbard fjord and by extension more widely along the west svalbard and east greenland margins where similar conditions prevail we show that ctws generated by weather systems passing across the sloping topography of the shelf break propagate into the fjord steered by the topography of an across shelf trough the ctws have characteristic periods of 2 days set by the passage time of weather systems phase speeds and wavelengths vary seasonally by a factor of two according to stratification winter summer values are cp 0 25 ms 1 0 5 ms 1 and 40 km 84 km ctw induced flow velocities in excess of 0 2 ms 1 at 100 m water depth are recorded observationally scaled ctw model results allow their explicit role in volume exchange to be quantified of the estimated exchange terms estuarine exchange is weakest qest 0 62 103 m3s 1 followed by barotropic tidal pumping qbt 2 5 103 m3s 1 with intermediary exchange dominating qi 2 4 104 m3s 1 oscillatory flows display greatest activity in the 1 5 day period band and ctw activity is identified as the likely source of variability in the 40 60 h period band within that band intermediary exchange driven by ctws is estimated as qictw ave 0 82 104 m3s 1 an exchange rate exceeding both barotropic and estuarine exchange estimates

envisat derived elevation changes of the greenland ice sheet and a comparison with icesat results in the accumulation area abstract we show for the first time over the greenland ice sheet that an along track method for deriving rates of elevation change can successfully be applied to envisat radar altimetry data 2002 2010 the results provide improved resolution and coverage compared to previous results obtained from cross over methods also we find that temporal changes in the elevation change rate can be derived from envisat data and show clear examples of this by generating five year running means for selected areas of the greenland ice sheet for a period between 2003 and 2009 the elevation of the ice sheets was measured by both the laser altimeter on board icesat and the radar altimeter on board envisat we compare rates of elevation change derived from icesat and envisat for this time span in which both sensors were operating we focus on the area above the equilibrium line altitude in order to specifically derive information on snow parameters a comparison of the elevation changes observed by the two sensors shows a complex pattern which can be explained regionally by model output describing the changes in both firn air content and accumulation rates

diffusion of osmium in pyrrhotite and pyrite implications for closure of the re os isotopic system abstract in order to better constrain the extent to which common sulfide minerals will retain their osmium isotopic composition subsequent to crystallization we have conducted experiments to quantify the diffusion behavior of osmium in pyrite and pyrrhotite experiments consisted of either 1 isothermal soaking of diffusion couples consisting of natural pyrite or pyrrhotite crystals packed against powdered os bearing fe sulfide or 2 relaxation of initially high near surface osmium concentrations produced in the latter experiments pyrite only osmium penetration into samples was characterized by depth profiling using rutherford backscattering spectroscopy rbs pyrite or electron microprobe analyses across sectioned run products pyrrhotite results of the first type of diffusion experiment involving pyrite show only limited osmium penetration into sample surfaces with the extent of penetration uncorrelated with run duration images of pyrite samples using atomic force microscopy show roughening of initially smooth surfaces as a consequence of step formation and suggest that osmium incorporation into the near surface occurred by solute uptake during step growth and not by volume diffusion prolonged 1000 h relaxation experiments revealed no additional osmium penetration into pyrite surfaces and based on the depth resolution for rbs a maximum diffusion coefficient of 2 5 10 23 m2 s at 500 c was calculated experiments involving pyrrhotite over the temperature range of 950 1100 c showed extensive osmium uptake and osmium concentration gradients that conform with fickian diffusion behavior we found that pyrrhotite fe s could be varied by changes in the composition of the starting material and osmium source and over the range of fe s produced in experiments molar fe s 0 83 0 90 we observed no systematic variation in the osmium diffusion coefficient diffusion coefficients measured parallel to the a crystallographic axis were on average 1 4 higher than values measured parallel to c and regression of the c axis data yielded the arrhenius relation d t 1 31 0 16 10 5 m 2 s exp 211 5 14 7 kj mol rt the application of these diffusion data to simple models of diffusive exchange during static or polythermal time temperature histories is used to assess the conditions under which radiogenic osmium will be retained during isothermal annealing calculations indicate that the cores of millimeter sized spherical pyrrhotite crystals undergoing diffusive exchange with an external osmium reservoir will have their initial compositions perturbed in 0 5 ma at temperatures exceeding 400 c pyrite undergoing the same process at 500 c requires in excess of 10 ma before crystal cores are affected the relatively short core retention time scales for pyrrhotite indicates that this mineral may be prone to isotopic resetting following relatively brief crustal thermal events thus possibly accounting for the scatter that commonly occurs in re os isochrons generated from massive sulfide samples calculated closure temperatures tc for osmium exchange in pyrrhotite yielded values of 300 400 c for grain sizes ranging from 10 to 1000 m these values of tc are similar to those calculated for ar retention in biotite and considerably lower than for sr in apatite and plagioclase for example such low closure temperatures for pyrrhotite suggest this mineral will date the final stage in the cooling of a magmatic system and possibly be susceptible to open system osmium exchange in the presence of late stage hydrothermal fluids this latter result infers that caution be applied when interpreting elevated initial osmium isotopic ratios as a product of crustal assimilation at the magmatic stage

25 years of elevation changes of the greenland ice sheet from ers envisat and cryosat 2 radar altimetry abstract the shape of the large ice sheets responds rapidly to climate change making the elevation changes of these ice covered regions an essential climate variable consistent long time series of these elevation changes are of great scientific value here we present a newly developed data product of 25 years of elevation changes of the greenland ice sheet derived from satellite radar altimetry the data product is made publicly available within the greenland ice sheets project as part of the esa climate change initiative programme analyzing repeated elevation measurements from radar altimetry is widely used for monitoring changes of ice covered regions the greenland ice sheet has been mapped by conventional radar altimetry since the launch of ers 1 in 1991 which was followed by ers 2 envisat and currently cryosat 2 the recently launched sentinel 3a will provide a continuation of the radar altimetry time series since 2010 cryosat 2 has for the first time measured the changes in the coastal regions of the ice sheet with radar altimetry with its novel sar interferometric sarin mode which provides improved measurement over regions with steep slopes here we apply a mission specific combination of cross over along track and plane fit elevation change algorithms to radar data from the ers 1 ers 2 envisat and cryosat 2 radar missions resulting in 25 years of nearly continuous elevation change estimates 1992 2016 of the greenland ice sheet this analysis has been made possible through the recent reprocessing in the reaper project of data from the ers 1 and ers 2 radar missions making them consistent with envisat data the 25 years of elevation changes are evaluated as 5 year running means shifted almost continuously by one year a clear acceleration in thinning is evident in the 5 year maps of elevation following 2003 while only small elevation changes observed in the maps from the 1990s

elevation change of the antarctic ice sheet 1995 2000 from ers 2 satellite radar altimetry we analyzed antarctic ice sheet elevation change dh dt from 1995 to 2000 using 123 million elevation change measurements from european remote sensing 2 ice mode satellite radar altimeter data covering an area of about 7 2 million km sup 2 almost all drainage basins in east antarctica had average dh dt values within spl plusmn 3 0 cm year whereas drainage basins in west antarctica had substantial spatial variability with average dh dt values ranging between 11 to 12 cm year the east antarctic ice sheet had a five year trend of 1 spl plusmn 0 6 cm year where 13 out of the 14 basins had either a positive trend or a trend that was not significantly different than zero the west antarctic ice sheet had a five year trend of 3 6 spl plusmn 1 0 cm year due largely to strong negative trends of around 10 cm year for basins in marie byrd land along the pacific sector of the antarctic coast the continent as a whole had a five year dh dt trend of 0 4 spl plusmn 0 4 cm year finally time series constructed for the pine island thwaites de vicq and land glaciers in west antarctic showed five year dh dt trends from 26 to 135 cm year that were significantly more negative than the average dh dt trends in their respective basins the strongly negative dh dt values for these coastal glacier outlets are consistent with recently reported results indicating increased basal melting at these glaciers grounding lines caused by ocean thermal forcing

ice melange dynamics and implications for terminus stability jakobshavn isbrae greenland 1 we used time lapse imagery seismic and audio recordings iceberg and glacier velocities ocean wave measurements and simple theoretical considerations to investigate the interactions between jakobshavn isbrae and its proglacial ice melange the melange behaves as a weak granular ice shelf whose rheology varies seasonally sea ice growth in winter stiffens the melange matrix by binding iceberg clasts together ultimately preventing the calving of full glacier thickness icebergs the dominant style of calving and enabling a several kilometer terminus advance each summer the melange weakens and the terminus retreats the melange remains strong enough however to be largely unaffected by ocean currents except during calving events and to influence the timing and sequence of calving events furthermore motion of the melange is highly episodic between calving events including the entire winter it is pushed down fjord by the advancing terminus at 40 m d 1 whereas during calving events it can move in excess of 50 103 m d 1 for more than 10 min by influencing the timing of calving events the melange contributes to the glacier s several kilometer seasonal advance and retreat the associated geometric changes of the terminus area affect glacier flow furthermore a force balance analysis shows that large scale calving is only possible from a terminus that is near floatation especially in the presence of a resistive ice melange the net annual retreat of the glacier is therefore limited by its proximity to floatation potentially providing a physical mechanism for a previously described near floatation criterion for calving

a reconciled estimate of ice sheet mass balance we combined an ensemble of satellite altimetry interferometry and gravimetry data sets using common geographical regions time intervals and models of surface mass balance and glacial isostatic adjustment to estimate the mass balance of earth s polar ice sheets we find that there is good agreement between different satellite methods especially in greenland and west antarctica and that combining satellite data sets leads to greater certainty between 1992 and 2011 the ice sheets of greenland east antarctica west antarctica and the antarctic peninsula changed in mass by 142 49 14 43 65 26 and 20 14 gigatonnes year 1 respectively since 1992 the polar ice sheets have contributed on average 0 59 0 20 millimeter year 1 to the rate of global sea level rise

does calving matter evidence for significant submarine melt abstract during the summer in the northeast pacific ocean the alaska coastal current sweeps water with temperatures in excess of 12 c past the mouths of glacierized fjords and bays the extent to which these warm waters affect the mass balance of alaskan tidewater glaciers is uncertain here we report hydrographic measurements made within icy bay alaska and calculate rates of submarine melt at yahtse glacier a tidewater glacier terminating in icy bay we find strongly stratified water properties consistent with estuarine circulation and evidence that warm gulf of alaska water reaches the head of 40 km long icy bay largely unaltered a 10 20 m layer of cold fresh glacially modified water overlies warm saline water the saline water is observed to reach up to 10 4 c within 1 5 km of the terminus of yahtse glacier by quantifying the heat and salt deficit within the glacially modified water we place bounds on the rate of submarine melt the submarine melt rate is estimated at 9 m d 1 at least half the rate at which ice flows into the terminus region and can plausibly account for all of the submarine terminus mass loss our measurements suggest that summer and fall subaerial calving is a direct response to thermal undercutting of the terminus further demonstrating the critical role of the ocean in modulating tidewater glacier dynamics

dynamic thinning of antarctic glaciers from along track repeat radar altimetry since 2002 the envisat radar altimeter has measured the elevation of the antarctic ice sheet with a repeat cycle of 35 days this long and regular time series is processed using an along track algorithm to depict in detail the spatial and temporal pattern of elevation change for the whole ice sheet we use this dataset to examine the spatial and temporal pattern of pine island glacier pig thinning and compare it to the neighbouring glaciers we also examine additional areas especially in east antarctica whose mass balance is poorly known one advantage of the finer along track spacing of measurements is that it reveals places of dynamic thinning in regions of rapid ice flow we observe the acceleration of thinning on pig over the entire basin the volume loss increased from 7 km3 a 1 during 2002 06 to 48 km3 a 1 during 2006 10 we also observe accelerated thinning on the lower tens of kilometres of thwaites glacier with a mean thinning of 0 18 m a 1 over its entire basin during our observation period we confirm the dynamic thinning of totten glacier but we do not detect significantly accelerated thinning on any glacier elsewhere than on the coast of the amundsen sea

envisat radar altimeter measurements over continental surfaces and ice caps using the ice 2 retracking algorithm abstract this study presents the first results obtained with the envisat satellite radar altimeter ra 2 over lands and ice caps as radar altimetry was firstly devoted to ocean study this paper starts with a detailed description of the radar altimetry principle over continental surfaces a general formulation of the radar altimeter echoes according to different surface types is given and the retracking procedure ice 2 specially implemented on the envisat satellite ground segment to provide output parameters over continents is clearly presented the envisat ra 2 datasets processed with the ice 2 procedure are then mapped given an overall description of the output parameters over various surfaces the behaviour of these envisat altimetric parameters are analysed and related to main land surface characteristics such as surface volume echo specularity roughness apart from few unexpected signals which will need to be further investigated the new envisat dataset confirms the potential of inland altimetry and provides a new opportunity to monitor continental surfaces the ku band measurements confirm previous results recently obtained with the altimeters on board ers or topex poseidon and offer a temporal continuity the s band altimeter measurements are in accordance with theoretical expected ones and confirm previous topex poseidon observations in c band the s band and the use of the dual frequency thus bring new capabilities for altimetric applications with important deliveries for temporal evolution survey for instance s band will be used over continents to better detect wetlands located under vegetated areas or to better quantify wave penetration in terrestrial snowpack to accurately retrieve snow depth evolution over ice sheets the dual frequency s and ku band waveforms parameters will provide a more accurate height estimation as it will be possible to quantify the error on height measurements induced by snowpack structure change over time this will then provide a more confident survey of the ice sheets surface topography evolution the combination and complementarities with the other altimetry missions such as ers topex poseidon and jason look already promising and offer a 10 year span dataset for continental altimetry applications

types of massive sulphide deposits in the urals massive sulphide deposits in the urals are found within volcanic and volcanic sedimentary sequences of ordovician to middle devonian ages four types of economic sulphide deposits have been recognized cyprus besshi urals and baimak the cyprus type copper sulphide deposits are hosted by mafic volcanites that occur in the basal parts of palaeozoic volcanic sequences the besshi type copper zinc deposits are located within clastic sedimentary rocks intercalated with basalts and andesites zinc copper deposits of the urals type are hosted by bimodal rhyolite basalt assemblages which occur at a higher stratigraphic level than those of cyprus and besshi types the baimak type zinc copper barite deposits are associated with intrusive quartz porphyries which occur in the upper parts of bimodal volcanic successions in addition there are some sulphide deposits of zinc lead barite and zinc copper composition hosted by ordovician terrigenous sequences which occur within depressions in precambrian blocks these types of sulphide deposits have been formed at various stages of divergence and convergence of the earth s crust during the orogenic history of the urals

rapid submarine melting driven by subglacial discharge leconte glacier alaska 1 we show that subglacial freshwater discharge is the principal process driving high rates of submarine melting at tidewater glaciers this buoyant discharge draws in warm seawater entraining it in a turbulent upwelling flow along the submarine face that melts glacier ice to capture the effects of subglacial discharge on submarine melting we conducted 4 days of hydrographic transects during late summer 2012 at leconte glacier alaska a major rainstorm allowed us to document the influence of large changes in subglacial discharge we found strong submarine melt fluxes that increased from 9 1 1 0 to 16 8 1 3 m d 1 ice face equivalent frontal ablation as a result of the rainstorm with projected continued global warming and increased glacial runoff our results highlight the direct impact that increases in subglacial discharge will have on tidewater outlet systems these effects must be considered when modeling glacier response to future warming and increased runoff

oceanic heat delivery via kangerdlugssuaq fjord to the south east greenland ice sheet acceleration of the greenland ice sheet gris tidewater outlet glaciers has increased the ice sheet s contribution to global sea level rise over the last two decades coincident increases in atmospheric temperatures around greenland explain some of the increased ice loss but warm atlantic origin water aw is increasingly recognized as contributing to the accelerating ice mass loss particularly via the outlet glaciers of south east se greenland however there remains a lack of understanding of the variability in heat content of the water masses found to the east of greenland and how this heat is communicated to the outlet glaciers of the gris here a new analysis is presented of ocean gris interaction in which the oceanic heat flux toward the ice sheet in kangerdlugssuaq fjord 0 26 tw is an order of magnitude greater than that reported for the other major outlet glacier of se greenland helheim heat delivered by aw to the calving front of kangerdlugssuaq is equivalent to 10 m d 1 melt i e 30 60 of the ice flow speed and thus is highly significant during the observational campaign in september 2010 warm polar surface water psww melted a substantial volume of ice within the fjord equivalent to 25 of the volume melted by aw alone satellite derived sea surface temperatures show large interannual variability in psww over the 20 year period 1991 2011 anomalously warm psww was observed within the fjord prior to the well documented major ice front retreats of may 2004 and november 2010

elevation change of the southern greenland ice sheet from 1978 to 1988 interpretation the spatial pattern of elevation change estimates derived from satellite radar altimeter data for the period from 1978 to 1988 for the southern greenland ice sheet is examined as reported previously the results from 12 ice cores widely distributed in the study area indicate that much of the spatial variability in the elevation change estimates can be explained by temporal variations in accumulation most notably the areas of largest thickening and thinning east and west of the ice divide around 66 n recently experienced substantial decadal fluctuations in accumulation sufficient to explain the observed elevation change rates that span the range of 24 cm yr 1 elevation change estimates in the nw of the study area around the 2000 m elevation contour were found to be inconsistent with both short and long term changes in accumulation fluctuations examination of stratigraphy in several shallow ice cores in the nw indicates that significant melting took place in 1977 and 1978 and this was followed by many years of very little melt activity this likely resulted in a significant downward bias in the 1978 1988 elevation change estimates in the nw comparison of measured surface velocities with those calculated assuming steady state balance show very good agreement overall but there are many instances in the southeast where the steady state velocities are significantly smaller than measured surface velocities we cannot rule out the possibility that increased ice flow in lower elevation outlet glaciers has migrated farther upstream thereby causing negative long term mass imbalance in southeast greenland

winter sea ice melting in the atlantic water subduction area svalbard norway herein we study a small area along the shelf west of spitsbergen near prins karls forland where warm saline atlantic water of the west spitsbergen current currently first encounters sea ice this sea ice is drifting in a coastal current that carries arctic water originating from the barents sea northward over the shelf our aim was to investigate whether melting of sea ice by atlantic water in this area might be a significant factor that could contribute to the formation of a cold halocline layer that isolates the sea ice from further melting from below observations of temperature and salinity profiles were collected during two winters via ctd srdl instruments deployed on harbor seals phoca vitulina and fed into a heat and freshwater budget box model in order to quantify the importance of melting relative to other processes that could transform the shelf water mass during winter cross frontal exchange of atlantic water from the west spitsbergen current driven by buoyancy forcing rather than ekman upwelling was determined to be the source of the heat that melted drift ice on the shelf some local sea ice formation did take place but its importance in the total heat and freshwater budgets appeared to be minor the data suggest that the production of a cold halocline layer was preceded by southerly winds and rapid drift ice melting

ice sheet elevation change in west antarctica from ka band satellite radar altimetry satellite altimetry has been used to track changes in ice sheet elevation using a series of ku band radars in orbit since the late 1970s here we produce an assessment of higher frequency ka band satellite radar altimetry for the same purpose using saral altika measurements recorded over west antarctica altika elevations are 3 8 0 5 and 2 5 0 1 m higher than those determined from airborne laser altimetry and cryosat 2 respectively likely due to the instruments coarser footprint in the sloping coastal margins however altika rates of elevation change computed between 2013 and 2019 are within 0 6 2 4 and 0 1 0 1 cm year of airborne laser and cryosat 2 respectively indicating that trends in radar penetration are negligible the fast flowing trunks of the pine island and thwaites glaciers thinned by 117 10 and 100 20 cm year respectively amounting to a 9 reduction and a 43 increase relative to the 2000s

metamorphism of volcanogenic massive sulphide deposits in the urals ore geology abstract the urals vms province comprises a broad spectrum of variably metamorphosed deposits from unmetamorphosed to those without any primary ore textures which are the results of high grade metamorphic processes contact metamorphism near large granite and granodiorite plutons caused the most significant changes of ores with coarse grained to pegmatoidal ores with magnetite closest to its contact with the intrusion followed by pyrrhotite enriched copper ores and more distal zinc pb ag mineralisation koktau tarnyer and vesenneye deposits are metamorphosed to the hornblende hornfels and pyroxene hornfels facies t 400 800 c p 1 6 kbar metamorphism of tash yar dzhusinskoe and krasnogvardeiskoe deposits corresponds to the greenschist and albite epidote hornfels facies t 250 450 c p 1 4 kbar the regional metamorphism of vms ores varies from prehnite pumpellyite facies t 150 300 c p 0 5 4 kbar in the south urals to the epidote amphibolite and amphibolite facies t 400 600 c up to 700 c p 1 6 kbar in the karabash area in the middle urals in the magnitogorsk zone the metamorphism of host rocks and vms bodies increases to the north reaching its peak near the ufa promontory of the east european platform with increased metamorphism the morphology of orebodies evolves from gently dipping thick lenses alexandrinskoe and uzelga fields to subvertical and folded uchaly and novo uchaly deposits and pseudomonoclinal steeply dipping vein like bodies karabash district the massive sulphide transformation in ptx gradient fields led to partial redistribution of ore material an enrichment in cu zn ag and au pb occur in the uppermost parts of large steeply dipping massive sulphide lenses in wide tectonic zones e g gai deposit or as gold sulphide disseminated bodies near large metamorphosed vms lenses distal to a granite pluton tarnyer deposit partial melting probably occurred in some highly metamorphosed deposits tarnyer koktau and mauk redeposition of base metals sulphides chalcopyrite tennantite sphalerite bornite galena as well as the presence of visible gold and tellurides took place during retrograde metamorphism which produced a transfer of ore matter towards the low stress areas such as the outer parts of shear zones the uppermost parts of steeply dipping ore lenses pressure shadows hinge zones of small folds and small extension fractures i e alpine type veins in deformed ore body or its immediate surroundings

a gold copper association in ultramafic hosted hydrothermal sulfides from the mid atlantic ridge sulfide samples from the logatchev hydrothermal field 14 degrees 459 n mid atlantic ridge which occurs on an ultramafic substrate show a bimodal distribution of copper and zinc rich mineralogies both of which have elevated gold contents the copper rich vents show an unusual depression hosted morphology with few chimney structures copper rich samples show evidence for a primary gold copper association as well as gold concentration during small scale replacement and reworking processes evidence from vent morphologies au ag ratios and sulfidation state suggest that in the copper rich samples gold was not transported as au hs super 2

a simple shelf circulation model intrusion of atlantic water on the west spitsbergen shelf abstractbarotropic flow along depth contours is found in accordance with standard geostrophic theory a numerical model is developed that studies the deviation from such a flow the model gives a good approximation of the dynamical processes on the west spitsbergen shelf wss and shows that the west spitsbergen current wsc the main gateway of atlantic water aw toward the arctic connects more easily to the isfjorden trough than anywhere else along the shelf the circulation of aw in the troughs along the wss is here named the spitsbergen trough current stc from hydrographical and ocean current observations it is evident that the stc is primarily barotropic and driven by the sea surface height a connection between the along coast wind stress and the stc is established and it is demonstrated how the increased occurrence of winter cyclones in fram strait during january february accelerates and widens the wsc ultimately this results in a strengthened stc and dominance of aw on the wss the stc re

greenland 2012 melt event effects on cryosat 2 radar altimetry cryosat 2 data are used to study elevation changes over an area in the interior part of the greenland ice sheet during the extreme melt event in july 2012 the penetration of the radar signal into dry snow depends heavily on the snow stratigraphy and the rapid formation of refrozen ice layers can bias the surface elevations obtained from radar altimetry we investigate the change in cryosat 2 waveforms and elevation estimates over the melt event and interpret the findings by comparing in situ surface and snow pit observations from the north greenland eemian ice drilling project camp the investigation shows a major transition of scattering properties around the area and an apparent elevation increase of 56 26 cm is observed in reprocessed cryosat 2 data we suggest that this jump in elevation can be explained by the formation of a refrozen melt layer that raised the reflective surface introducing a positive elevation bias

the giant chromite deposits at kempirsai urals constraints from trace element pge ree and isotope data the investigation of stable and radiogenic isotopes and of platinum group pge and rare earth elements ree in chromitites and associated ultramafic rocks of the kempirsai massif southern urals gives strong evidence for a multistage formation of giant ophiolitic podiform chromite deposits present in the southeastern part of the massif the kempirsai ophiolite massif is divided by a shear zone into two parts in the northwestern area small bodies of al rich chromite formed from basaltic melts between 420 to 400 ma according to sm nd mineral isochrons of harzburgite pyroxenite websterite and gabbro harzburgites and pyroxenites in this area are enriched in light ree and have nd 400 6 and sr 400 5 chromitites have scattered pge distributions pd ir 0 4 7 0 being partly enriched in pd and pt os 400 of one chromitite is 4 4 the southeastern part of the kempirsai massif well known for its world class deposits of podiform low al magnesiochromite is characterized by harzburgite and dunite enriched in light ree with very low nd 400 4 3 to 17 1 and positive sr 400 10 values chromitites are strongly enriched in ir os and ru and depleted in pd and pt os 400 of three chromitites is uniform and approaches c1 and dmm compositions in veins and pods postdating crystallization of massive chromite pargasitic amphibole formed in equilibrium with fluid inclusion bearing chromite at temperatures close to 1000 c these amphiboles give 40ar 39ar stepwise heating ages of 365 to 385 ma and are characterized by low nd 400 0 6 to 4 6 and general enrichment in ree the cooling ages correspond to a 379 3 1 6 ma rb sr mineral isochron produced from amphibole and phlogopite of a pyroxenite vein in the western part of the massif from these data it is concluded that parts of the kempirsai massif have been pervasively metasomatized by large amounts of fluids and melts derived from a subducted slab composed of oceanic crust and sediments subduction occurred at least 15 35 ma after a melting event that produced a typical ophiolitic sequence in the paleozoic sakmara zone we conclude that large chromite orebodies formed from second stage high mg melts that interacted with depleted mantle and fluids on their way upward in a suprasubduction zone regime and in a fore arc position to the magnitogorsk island arc

eddy driven recirculation of atlantic water in fram strait eddy resolving regional ocean model results in conjunction with synthetic float trajectories and observations provide new insights into the recirculation of the atlantic water aw in fram strait that significantly impacts the redistribution of oceanic heat between the nordic seas and the arctic ocean the simulations confirm the existence of a cyclonic gyre around the molloy hole near 80 n suggesting that most of the aw within the west spitsbergen current recirculates there while colder aw recirculates in a westward mean flow south of 79 n that primarily relates to the eastern rim of the greenland sea gyre the fraction of waters recirculating in the northern branch roughly doubles during winter coinciding with a seasonal increase of eddy activity along the yermak plateau slope that also facilitates subduction of aw beneath the ice edge in this area

re os geochronology of the iimori besshi type massive sulfide deposit in the sanbagawa metamorphic belt japan abstract besshi type cu deposits are strata bound volcanogenic massive sulfide deposits usually associated with mafic volcanic rocks or their metamorphic equivalents although there are numerous besshi type deposits in the sanbagawa metamorphic belt japan their tectonic settings and depositional environments remain controversial because of a lack of depositional age constraints we report re os data for the iimori deposit one of the largest besshi type deposits in western kii peninsula in order to examine the robustness of the re os isotope system for dating sulfide minerals in the high p t metamorphic belt and to elucidate the primary depositional environment of the iimori sulfide ores an 11 point re os isochron plot yields an age of 156 8 3 6 ma as this re os isochron age is significantly older than the timing of the sanbagawa peak metamorphism 110 120 or 90 ma and a well defined isochron was obtained the re os age determined here is most likely the primary depositional age despite high grade metamorphism at up to 520 25 c and 8 9 5 kbar the re os isotope system of the iimori sulfides was not disturbed hence we consider that the whole rock re os closure temperature for the iimori sulfide ores was probably higher than 500 c as the accretion age of the sanbagawa metamorphic belt is considered to be 120 130 or 65 90 ma on the basis of radiolarian and radiometric ages we estimated the time from the iimori sulfide deposition on the paleo seafloor to its accretion at the convergent plate boundary to be greater than 25 myr consequently the depositional environment of the iimori sulfide ores was not in the marginal sea but was truly pelagic

significance of late devonian lower carboniferous ages of hydrothermal sulphides and sericites from the urals volcanic hosted massive sulphide deposits abstract formation of the urals volcanic hosted massive sulphide vhms deposits is considered to be related with the intra oceanic stage of the island arc s development in late ordovician middle devonian time ca 460 385 ma based on the biostratigraphic record of ore hosting sedimentary rocks however the known radiometric ages of ore hosting volcanics are very limited here we present direct dating results of sulphide mineralisation from the yaman kasy and kul yurt tau vhms deposits using re os isotope systematics showing similar mineralisation ages of 362 9 ma and 363 1 ma these ages coincide with the previous re os dating of the alexandrinskoe 355 15 ma and dergamysh 366 2 ma vhms deposits this late devonian famennian age corresponds to the late stage of the magnitogorsk arc laurussia continent collision event and coincides with a beginning of large scale subduction related granitoid magmatism the younger mineralisation age relative to the biostratigraphic ages of host rocks is interpreted as one of the latest episodes of the multi stage history of vhms deposits development ar ar ages of sericites from metasomatic rocks of barsuchi log and babaryk deposits show even younger ages clustering around 345 ma and testify another late hydrothermal event in the history of the urals vhms deposits

wintertime warming of an arctic shelf in response to large scale atmospheric circulation 1 observations on the west spitsbergen shelf have shown that the dynamic response of the shelf to wind forcing has a profound effect on the heat content of the water hydrographic and atmospheric data have been analysed with respect to the relative importance of surface heat fluxes and advective processes on ocean temperature during the arctic winter of 2005 06 periods of sustained along shelf winds generated upwelling and cross shelf exchange causing extensive flooding of the coastal waters with warm atlantic water from the west spitsbergen current the winter temperature of the west spitsbergen shelf reverted to that typical of fall interrupting the normal cycle of sea ice formation in the region

recent ice sheet growth in the interior of greenland a continuous data set of greenland ice sheet altimeter height from european remote sensing satellites ers 1 and ers 2 1992 to 2003 has been analyzed an increase of 6 4 0 2 centimeters per year cm year is found in the vast interior areas above 1500 meters in contrast to previous reports of high elevation balance below 1500 meters the elevation change rate is 2 0 0 9 cm year in qualitative agreement with reported thinning in the ice sheet margins averaged over the study area the increase is 5 4 0 2 cm year or 60 cm over 11 years or 54 cm when corrected for isostatic uplift winter elevation changes are shown to be linked to the north atlantic oscillation

accretionary complex structure and kinematics during paleozoic arc continent collision in the southern urals abstract the southern urals contain a well preserved accretionary complex that has overthrust the continental margin during arc continent collision between the east european craton eec and the magnitogorsk island arc in the late devonian within the accretionary complex we study three tectonic units that differ in deformation style and each provides a unique geodynamic implication the zilair nappe the largest and best exposed unit consists of 5 6 km of syncollisional arc derived upper devonian to lower carboniferous polymictic and graywacke turbidites that were deposited across the continental margin and incorporated by frontal accretion into the accretionary complex the zilair nappe is a bivergent thrust imbricate where the west vergent thrusts dominate and have associated kilometer scale ramp anticlines with well developed east dipping axial planar cleavage along its eastern contact however the cleavage fans until it dips moderately westward and the folds are east vergent following its emplacement west vergent basement involved thrusting that breached the whole accretionary complex imbricated the zilair nappe the timirovo duplex is structurally beneath the zilair nappe and outcrops for several tens of kilometers along its northwestern margin the duplex forms a west vergent thrust stack composed of a highly deformed and sheared lower and middle devonian reef carbonates of the former eec margin platform these rocks were shallowly underplated at the base of the accretionary complex during emplacement over the margin the suvanyak complex outcrops along the eastern contact of the zilair nappe and consists of polydeformed greenschist facies metasediments of the former eec slope that were offscraped underplated and incorporated at the rear of the accretionary complex

40ar 39ar u pb and sm nd constraints on the timing of metamorphic events in the maksyutov complex southern ural mountains new 40 ar 39 ar u pb and sm nd data from 13 metamorphic samples constrain the formation and exhumation of the high pressure maksyutov complex in the southern uralide orogen the maksyutov complex records the highest pressure metamorphism in the southern uralides and is part of the thrust stack that composes the footwall beneath the main ural fault the new isotopic data from eclogite in the lower unit of the maksyutov complex include 40 ar 39 ar data from phengite u pb data from rutile and apatite and sm nd data from garnet clinopyroxene rutile and apatite these data indicate that eclogite facies metamorphism occurred in the mid devonian epoch c 380 ma corresponding with eastward subduction of the east european craton beneath the magnitogorsk island arc after partial exhumation the lower unit was juxtaposed c 360 ma based on 40 ar 39 ar white mica data with the middle and upper units at mid crustal levels during the development of a d 3 shear zone within the subduction zone by the late carboniferous epoch the maksyutov complex was exhumed to upper crustal levels compatible with sedimentologic evidence that at this time the foreland thrust and fold belt began to form and material was shed off it into the foreland basin

greenland ice sheet high elevation balance and peripheral thinning aircraft laser altimeter surveys over northern greenland in 1994 and 1999 have been coupled with previously reported data from southern greenland to analyze the recent mass balance of the greenland ice sheet above 2000 meters elevation the ice sheet is in balance on average but has some regions of local thickening or thinning thinning predominates at lower elevations with rates exceeding 1 meter per year close to the coast interpolation of our results between flight lines indicates a net loss of about 51 cubic kilometers of ice per year from the entire ice sheet sufficient to raise sea level by 0 13 millimeter per year approximately 7 of the observed rise

a rare phanerozoic amphibolite hosted gold deposit at danba yangtze craton china significance to fluid and metal sources for orogenic gold systems the danba gold deposit is located in a poorly documented gold province on the north western margin of the yangtze craton it is sited in devonian sequences in a high grade metamorphic terrane that includes an extensional metamorphic core complex around the deposit peak metamorphic conditions of 6 0 5 kbar and 650 50 c at ca 193 ma were followed by retrograde sillimanite grade conditions of 4 5 0 5 kbar and 550 50 c the deposit is hosted in a broadly strata bound ductile brittle shear zone with high t proximal alteration assemblages of biotite amphibole plagioclase and ore assemblages dominated by pyrrhotite but with a strong association between gold and bismuth tellurides alteration mineral thermobarometers together with heating freezing studies of low salinity h2o co2 ch4 fluid inclusions indicate p t conditions of early ore deposition of approximately 4 5 kbar and 500 650 c at around 185 9 ma indicated by re os geochronology on ore related molybdenite in conjunction all data demonstrate that danba represents a lower jurassic hypozonal orogenic gold deposit that formed during post peak metamorphic retrogression the primary high p t nature of the deposit combined with its late metamorphic timing negate that the ore fluid was sourced via devolatilization of the hosting supracrustal sequences a deep externally derived ore fluid source is required the most likely source is the k h2o co2 and ore metal fertilized lithospheric mantle that was metasomatized during neoproterozoic subduction it is proposed that transition from lithospheric transpression to extension in the jurassic triggered the devolatilization of this metasomatized lithosphere to cause the formation of this rare phanerozoic amphibolite hosted gold deposit at danba

re os ages for archean molybdenite and pyrite kuittila kivisuo finland and proterozoic molybdenite kabeliai lithuania testing the chronometer in a metamorphic and metasomatic setting seven 187re 187os ages were determined for molybdenite and pyrite samples from two well dated precambrian intrusions in fennoscandia to examine the sustainability of the re os chronometer in a metamorphic and metasomatic setting using a new 187re decay constant 1 666 10 11y 1 with a much improved uncertainty 0 31 we determined replicate re os ages for molybdenite and pyrite from the kuittila and kivisuo prospects in easternmost finland and for molybdenite from the kabeliai prospect in southernmost lithuania these two localities contain some of the oldest and youngest plutonic activity in fennoscandia and are associated with newly discovered economic au mineralization ilomantsi finland and a cu mo prospect kabeliai lithuania two re os ages for vein hosted kabeliai molybdenite average 1486 5 ma in excellent agreement with a 1505 11 ma u pb zircon age for the hosting kabeliai granite pluton the slightly younger age suggests the introduction of cu mo mineralization by a later phase of the kabeliai magmatic system mean re os ages of 2778 8 ma and 2781 8 ma for kuittila and kivisuo molybdenites respectively are in reasonable agreement with a 2753 5 ma weighted mean u pb zircon age for hosting kuittila tonalite these re os ages agree well with less precise ages of 2789 290 ma for a rb sr whole rock isochron and 2771 75 ma for the average of six sm nd tdm model ages for kuittila tonalite three re os analyses of a single pyrite mineral separate from the same sample of kuittila pluton that yielded a molybdenite separate provide individual model ages of 2710 27 2777 28 and 2830 28 ma re 17 4 12 1 and 8 4 ppb respectively with a mean value of 2770 120 ma in agreement with the kuittila molybdenite age the re and 187os abundances in these three pyrite splits are highly correlated r 0 9994 and provide a 187re 187os isochron age of 2607 47 ma with an intercept of 21 ppt 187os mswd 1 1 it appears that the re os isotopic system in pyrite has been reset on the millimeter scale and that the 21 ppt 187os intercept reflects the in situ decay of 187re during the 160 to 170 m y interval from 2778 ma time of molybdenite pyrite deposition to 2607 ma time of pyrite resetting when the re os data for molybdenites from the nearby kivisuo prospect are plotted together with the kuittila molybdenite and pyrite data a well constrained five point isochron with an age of 2780 8 ma and a 187os intercept 2 4 3 8 ppt of essentially zero results mswd 1 5 we suggest that the pyrite isochron age records a regional metamorphic and or hydrothermal event possibly the time of au mineralization a proposed re os age of 2607 ma for au mineralization is in good agreement with radiometric ages by other methods that address the timing of archean au mineralization in deposits worldwide so called late au model molybdenite in contrast provides a robust re os chronometer retaining its original formation age of 2780 ma despite subsequent metamorphic disturbances in archean and proterozoic time

merging and analysis of elevation time series over greenland ice sheet from satellite radar altimetry spatial temporal variability and changes of greenland ice sheet elevation from 1992 to 2008 are analyzed from merged ers 1 ers 2 and envisat satellite radar altimeter data a methodology for determining intersatellite biases was developed and applied in order to merge measurements from these different satellites and to create continuous and consistent time series intersatellite biases of elevation and backscatter coefficient have shown to be significantly affected by the bias between measurements in ascending and descending orbits adjustment of elevation time series for its dependence on backscatter coefficient and other waveform parameters performed in this paper substantially reduced the amplitude of elevation seasonal variations and locally corrected elevation change rate estimates by up to several centimeters per year it was found that the correction depends not only on the variations in the waveform parameters but also on the temporal variations of the correlation gradients which represent the sensitivity of the elevation change to the change in the waveform parameters an elevation change rate of 2 8 0 2 cm year from 1992 to 2008 over 76 of the greenland ice sheet area was found increases in surface elevation from 1995 observed over the high elevation regions of greenland were followed by an elevation decrease from 2006 for the whole period of 1992 2008 the elevation increase is 4 0 0 2 cm year over 87 of the area above 1500 m in contrast over 38 of the low elevation areas below 1500 m the rate of elevation change is 7 0 1 0 cm year and the surface elevation decrease that started from 2000 has continued

osmium isotope distribution within the palaeozoic alexandrinka seafloor hydrothermal system in the southern urals russia abstract the re os distribution and isotopic composition have been studied within different ore facies host rocks and sediments from the alexandrinka volcanogenic hydrothermal massive sulphide deposit southern urals russia the osmium contents increase and the initial 187os 188os isotopic compositions decrease in the ore facial range sulphide chimneys stockwork zone seafloor massive and clastic sulphides metalliferous sediments this range reflects variable degrees of reduced hydrothermal fluid oxidized seawater mixing during the hydrothermal ore forming process the os isotopic composition of the hydrothermal sulphide chimney 187os 188os 1 3 is estimated to be a minimum value of the devonian hydrothermal fluid which is an intermediate between initial os isotopic compositions of island arc volcanics and interlayered sediments the initial os isotopic composition of metalliferous sediments 187os 188os 0 17 0 2 possibly reflects that of the devonian seawater the low rhenium concentrations in metalliferous sediments about 1 2 ppb could indicate oxic formation conditions the re os isotope data define a best fit line corresponding to a late devonian age of 355 15 ma 2 with initial 187os 188os of 0 12 0 19 this age could indicate a late os isotope reequilibration due to ongoing hydrothermal fluid flow from the givetian stratigraphic age 375 ma until the closure of the ural paleoocean in the late devonian the os contents are higher and re os ratio is lower within palaeozoic island arc hosted urals vhms deposits compared with tag deposit in mor setting

cu ni co au bearing massive sulfide deposits associated with mafic ultramafic rocks of the main urals fault south urals geological structures ore textural and mineralogical features comparison with modern analogs abstract cu rich massive sulfide deposits associated with mafic ultramafic rocks in the southern portion of the main urals fault muf are characterized by variable enrichments in ni up to 0 45 wt co up to 10 wt and au up to 16 ppm in individual hand specimens the cu ni co rich composition of muf deposits as opposed to the cu zn rich composition of more eastward massive sulfide deposits of broadly similar age along the western flank of the magnitogorsk arc reflects the abundance of seafloor exposed ni co rich ultramafic rocks in the most external portion of the early devonian magnitogorsk forearc morphological textural and compositional differences between individual deposits are interpreted to be the result of the sulfide deposition style and in part of the original subseafloor lithology one deposit produced by dominantly on seafloor hydrothermal processes is characterized by pyrite marcasite pyrrhotite not so low zn grades occasionally up to 2 wt abundant clastic facies and periodical superficial oxidation deposits produced by dominantly subseafloor hydrothermal processes are characterized by pyrrhotite pyrite very low zn generally

deep water renewal in the upper basin of loch sunart a scottish fjord abstract recording current meters were deployed near the surface and bottom in the upper basin of loch sunart during the summers of 1987 1989 and 1990 the measurements revealed frequent though irregular deep water renewal events when the basin water was replaced by density driven intrusions the data suggested that these events were induced by wind enhanced estuarine circulation during periods of low fresh water runoff a semi implicit laterally integrated estuarine model was modified to allow variable vertical grid spacing and to permit the sea surface to move vertically through the grid both modifications being necessary in order to apply the model to the sea loch environment a turbulence closure scheme was also incorporated the model can simulate the evolution of the salinity field over periods of several weeks and was used to examine the mechanisms that induce deep water renewal model results suggested that very weak stratification in the basin is required for renewal to occur and indicated

implications of changing scattering properties on greenland ice sheet volume change from cryosat 2 altimetry abstract long term observations of surface elevation change of the greenland ice sheet gris is of utmost importance when assessing the state of the ice sheet satellite radar altimetry offers a long time series of data over the gris starting with ers 1 in 1991 esa s cryosat 2 mission launched in 2010 provides an invaluable radar altimetry dataset for monitoring the current changes of the ice sheets due to its dense spatial and temporal coverage of these areas here we investigate the effects of including different parameters which describe the shape of the return radar waveform waveform parameters in the elevation change algorithm to correct for temporal changes in the ratio between surface and volume scatter in cryosat 2 observations we present elevation and volume changes for the greenland ice sheet in the period from 2010 until 2014 the waveform parameters considered here are the backscatter coefficient and the leading edge width which are both available in the esa cryosat 2 level 2i data product investigations into relocation of radar reflection points are also included inter comparison of the cryosat 2 derived elevation changes with those derived from operation icebridge laser data suggests waveform parameters to be applicable for correcting for changes in volume scattering the best results in the synthetic aperture radar interferometric mode area of the gris are found when applying only the backscatter correction whereas the best result in the low resolution mode area is obtained by only applying a leading edge width correction using this approach to correct for the scattering properties a volume loss of 292 38 km 3 yr 1 is found for the gris for the time span november 2010 until november 2014 the inclusion of waveform parameter corrections and improved relocation for the gris helps to reconcile the satellite derived elevation changes with those observed by operation icebridge however the bias of temporal changes in the scattering horizons of cryosat 2 is not entirely removed and suggests that future improvements could be made by including climate data and or additional waveform parameters to make additional corrections in the cryosat 2 radar altimetry

calving of a tidewater glacier driven by melting at the waterline we present a study of the development of a thermo erosional notch at the waterline and its influence on calving of hansbreen a medium sized grounded tidewater glacier in southern svalbard the study is based on the results of undercut notch melt modelling based on measurements of sea water properties repeated terrestrial laser scans and analysis of time lapse camera images there is a strong correlation between observed calving activity and modelled melt rate of the undercut notch measured depths of the undercut reach 4 m and vary greatly over time the calving activity of hansbreen was significantly lower in 2011 than in 2012 due to the persistent presence of the ice pack in hornsund fjord which cooled the sea surface and suppressed the wave action calving on hansbreen is controlled by a local imbalance of forces at the front due to thermo erosional undercutting at the sea waterline calving activity is therefore sensitive to changes in sea water temperature and wave height it may be expected that calving rates will rise with increased advection of warm oceanic water to the arctic

compensating changes in the penetration depth of pulse limited radar altimetry over the greenland ice sheet changes in firn properties affect the shape of pulse limited radar altimeter echoes acquired over the polar ice sheets we apply a waveform deconvolution model to cryosat 2 low resolution mode echoes to determine the depth distribution of radar backscattering across the greenland ice sheet the deconvolution allows us to calculate the relative contributions of surface and volume scattering and the effective penetration depth of the radar echoes into the snowpack the most prominent signal is associated with the extreme surface melting of summer 2012 which resulted in a shift of the dominant radar scattering horizon toward the snow surface in the accumulation zone at locations above 2000 m the average penetration depth in july 2012 prior to the melt event was 3 79 1 12 m following the melt event there was an abrupt reduction in the average penetration depth across the same region to 1 45 0 94 m the average penetration depth then gradually increased to 3 28 1 13 m by the end of 2017 as fresh snow accumulated on the ice sheet surface although the variation in penetration is evident in surface height estimates derived from the cryosat 2 echoes the magnitude of the effect is reduced by waveform retracking using airborne laser altimeter data recorded over the same time period we show that the penetration variation can be compensated effectively by incorporating the deconvolution penetration depth into the surface height retrieval

the melt anomaly of 2002 on the greenland ice sheet from active and passive microwave satellite observations 1 active and passive microwave satellite data are used to map snowmelt extent and duration on the greenland ice sheet the passive microwave pm data reveal the extreme melt extent of 690 000 km2 in 2002 as compared with an average extent of 455 000 km2 from 1979 2003 a statistical analysis of the melt time series affirms an increased melt extent earlier in the melt season the quikscat qscat or am analysis for 1999 to 2004 confirms the extreme melt situation in 2002 qscat data show a significant increase in melt season length over several areas in 2003 ssm i and qscat melt data reveal that the later detects melt earlier and is more sensitive to surface melt qscat detects an earlier stage of melt and ssm i detects a later stage of melt the ssm i xgpr melt extent is approximately confined to the qscat melt areas experiencing 2 weeks or more of melting time

os isotopes as tracers in seafloor hydrothermal systems metalliferous deposits from the tag hydrothermal area 26 n mid atlantic ridge abstract os isotopic analyses of a suite of samples from the tag hydrothermal area 26 n on the mid atlantic ridge reveal evidence of release of ocean crust derived os to seawater and removal of seawater derived os to the seafloor 187 os 186 os ratios of sulfide samples from the active tag mound vary between 8 7 and 1 3 the highest ratios are indistinguishable from the inferred 187 os 186 os ratio of seawater the incorporation of seawater derived os in these samples is interpreted as evidence of both entrainment of seawater into hydrothermal fluids and the addition of seawater os to samples during sulfide oxidation several sulfide samples from the active tag mound have 187 os 186 os ratios lower than the inferred seawater value with the lowest ratio approaching values expected for pristine oceanic crust these low 187 os 186 os ratios indicate that os derived from alteration of the oceanic crust is released to seawater in association with venting of high temperature hydrothermal fluids precipitates from low temperature hydrothermal fluids fe and mn oxide deposits from the east wall of the axial rift valley also have low 187 os 186 os ratios 4 2 6 8 relative to seawater these data suggest os isotopes may be sensitive tracers of low temperature hydrothermal circulation on the seafloor and that supply of ocean crust derived os to seawater is not strictly limited to high temperature hydrothermal vents the os concentration and isotopic composition of metalliferous sediment samples from a push core collected 125 m from the base of the active tag mound are also reported in this core metalliferous sediment horizons derived from mass wasting of altered sulfides exhibit variable 187 os 186 os ratios 4 8 8 7 reflecting mixing of seawater derived and ocean crust derived os in contrast sediments in which the metalliferous component is derived from fall out of hydrothermal material from the neutrally buoyant hydrothermal plume have 187 os 186 os ratios which vary over a narrow range 8 6 8 7 and appear to accurately record the os isotopic composition of seawater

rhenium osmium evidence for regional mineralization in southwestern north america more than 40 base metal porphyry ore deposits in southwestern north america are associated with the laramide orogeny about 90 million to 50 million years ago rhenium osmium dates on molybdenite a rhenium enriched sulfide common in many of the deposits reveal that in individual deposits mineralization occurs near the final stages of magmatic activity irrespective of the time of inception magnitude or duration of magmatism deposits that differ widely in location and in the extent and timing of magmatism have nearly identical ages for mineralization rhenium osmium ages suggest that mineralization occurred during two distinct intervals from about 74 million to 70 million years ago and from 60 million to 55 million years ago most deposits that formed in the oldest interval are within the older precambrian basement of northwestern arizona whereas the younger deposits are restricted to the younger precambrian basement in southern arizona and northern mexico synchronous widespread mineralization indicates that similar crust mantle interaction occurred on a regional scale for ore deposits once thought to be the product of localized processes

continued evolution of jakobshavn isbrae following its rapid speedup 1 several new data sets reveal that thinning and speedup of jakobshavn isbrae continue following its recent rapid increase in speed as its floating ice tongue disintegrated the present speedup rate of 5 a 1 over much of the fast moving region appears to be a diffusive response to the initial much larger speedup near the front there is strong seasonality in speed over much of the fast flowing main trunk that shows a good inverse correlation with the seasonally varying length of a short typically 6 km floating ice tongue this modulation of speed with ice front position supports the hypothesis that the major speedup was caused by loss of the larger floating ice tongue from 1998 to 2003 analysis of image time series suggests that the transient winter ice tongue is formed when sea ice bonds glacier ice in the fjord to produce a nearly rigid mass that almost entirely suppresses calving major calving only resumes in late winter when much of this ice clears from the fjord the collapse of the ice tongue in the late 1990s followed almost immediately after a sharp decline in winter sea ice concentration in disko bay this decline may have extended the length of the calving season for several consecutive years leading to the ice tongue s collapse

uralian magmatism an overview abstract this paper is an attempt to summarize current knowledge of uralian magmatism focusing on those aspects relevant for understanding its geodynamic evolution the urals consist of three tectonomagmatic domains a suture sector in the west and two n s imbricated island arc continental sectors in the east the suture sector comprises lower palaeozoic mafic ultramafic complexes which show eastward impoverishment in lile thus reflecting the transition of the subcontinental lithospheric mantle of the russian plate to the suboceanic lithospheric mantle of the subducted uralian palaeo ocean the two island arc continental sectors represent the transition from oceanic to continental environments in the middle and south urals collisional magmatism started in the silurian and persisted till the permian migrating progressively eastward and increasing in abundance of lile and 87 sr 86 sr initial magmatic polarity is very similar to that of modern subduction zones and indicates that the subducted slab was dipping eastward during that period the northern and southern island arc continental sectors show many similarities regarding the nature and spatial temporal distribution of magmatism but there are also some important differences which probably indicate somewhat different geodynamic regimes in the northern sector carboniferous tonalite granodiorite batholiths have features compatible with an origin by melting of the oceanic crust in the subducted slab in the southern sector however carboniferous tonalite granodiorite batholiths have features more consistent with a melting event within the lower continental crust above the subduction zone than with melting within the subducted slab upper carboniferous permian granites have high 87 sr 86 sr initial in the north e g 0 7120 in the murzinka batholith but very low 87 sr 86 sr initial in the south e g 0 7045 in the dzhabyk batholith in spite of rocks from both batholiths being equally peraluminous and showing evidence of derivation by anatexis of metasediments the low 87 sr 86 sr initial at dzhabyk might indicate that in the southern sector the accretionary prism grew very rapidly thus allowing involvement in upper palaeozoic melting events

rhenium osmium abundance and isotopic compositions of massive sulfides from modern deep sea hydrothermal systems implications for vent associated ore forming processes studies of rhenium re and osmium os concentrations and isotopic compositions in seafloor hydrothermal sulfides are an important tool for understanding the evolution of hydrothermal systems allowing the determination of both metal sources and reconstructing the physicochemical conditions of their deposition the re os concentrations and isotopic compositions of 38 massive sulfide samples have been studied in different hydrothermal fields from the east pacific rise epr mid atlantic ridge mar central indian ridge cir southwest indian ridge swir and back arc basin bab the majority of the sulfides possess os 187 os 188 that span a narrow range 1 004 to 1 209 which is most easily explained as a seawater derived component this may suggest that those initial os 187 os 188 isotope compositions of ancient seafloor hydrothermal sulfide deposits which were formed by the mixing process between seawater and hydrothermal fluid are possible for analysing ancient seawater os components only two of samples mar05 tvg1 10 2 and mar05 tvg1 21 from the logatchev hydrothermal field lhf mar possess moderately less radiogenic os 187 os 188 0 645 to 0 730 which may reflect the lesser extent of hydrothermal fluid seawater mixing during hydrothermal ore forming process

externally forced fluctuations in ocean temperature at greenland glaciers in non summer months the factors that control the submarine melt rate at greenland s glaciers are uncertain and largely inferred from brief summer surveys in the fjords where glaciers terminate continuous records of water properties and velocity for the months september to may from two large greenland fjords reveal strong variability on 3 to 10 day timescales as a result of pulses of water that are propagated from the shelf ocean

re os isotopic constraints on the genesis and evolution of the dergamish and ivanovka cu co au massive sulphide deposits south urals russia abstract rhenium and osmium elemental and isotopic data have been obtained for the two mafic ultramafic hosted volcanogenic massive sulphide vms deposits of dergamish and ivanovka from the south urals the associated ophiolitic blocks belong to the main uralian fault muf melange zone considered to represent obducted early palaeozoic oceanic crust despite their close geographical proximity the two ore bodies are morphologically mineralogically and isotopically quite different sulphides from ivanovka possess higher ni and os and lower re and cu relative to those from dergamish the re and os isotope data for dergamish define a best fit line corresponding to a late devonian age of 366 2 ma 2 with an mswd of 4 6 this age is some 40 my younger than the inferred silurian crystallisation age of the associated mafic ultramafic rocks but in good agreement with the previously published rb sr and ar ar ages of 360 380 ma corresponding to the high pressure metamorphic age of the adjacent maksyutov metamorphic complex these data suggest that re os systematics of the dergamish sulphide deposit were reset either by diffusion or recrystallisation during high pressure metamorphism or subsequent cooling the preservation of unradiogenic os isotopic ratios in some of the ivanovka samples and the near chondritic initial os isotopic composition obtained for the dergamish samples indicates that most of the os in the massive sulphides was ultimately derived from the mantle the corresponding tectonic setting equates to an area with submarine high level mantle rocks in contrast sulphides from ivanovka have experienced continued re equilibration and have been modified by post depositional processes at least some of which occurred relatively recently

wind driven modulation of warm water supply to a proglacial fjord jorge montt glacier patagonia projections of sea level rise due to ice loss from the land to the ocean have been hampered by a lack of understanding of the role the ocean is playing in glacier retreat including the processes that contribute to the supply of warm water to the ice ocean interface here shipboard moored and weather station data collected off jorge montt a rapidly retreating glacier in patagonia are analyzed to understand the influence of wind forcing during summer synoptic scale down fjord wind events enhance an estuarine like two layer flow increasing the inflow of oceanic deep water during up fjord wind events the inflow of deep water is significantly reduced and a three layer exchange flow develops overall along fjord wind forcing is shown to modulate the inflow of warm water to the fjord by a factor of 2 5 the results sug gest that local channelized winds can be an important process modulating warm water supply and melting of tidewater glaciers

mass changes of the greenland and antarctic ice sheets and shelves and contributions to sea level rise 1992 2002 changes in ice mass are estimated from elevation changes derived from 10 5 years greenland and 9 years antarctica of satellite radar altimetry data from the european remote sensing satellites ers 1 and 2 for the first time the dh dt values are adjusted for changes in surface elevation resulting from temperature driven variations in the rate of firn compaction the greenland ice sheet is thinning at the margins 42 2g t a 1 below the equilibrium line altitude ela and growing inland 53 2g t a 1 above the ela with a small overall mass gain 11 3g t a 1 0 03 mm a 1 sle sea level equivalent the ice sheet in west antarctica wa is losing mass 47 4g t a 1 and the ice sheet in east antarctica ea shows a small mass gain 16 11 gt a 1 for a combined net change of 31 12 gt a 1 0 08 mm a 1 sle the contribution of the three ice sheets to sea level is 0 05 0 03 mm a 1 t he antarctic ice shelves show corresponding mass changes of 95 11 gt a 1 in wa and 142 10 gt a 1 in ea thinning at the margins of the greenland ice sheet and growth at higher elevations is an expected response to increasing temperatures and precipitation in a warming climate the marked thinnings in the pine island and thwaites glacier basins of wa and the totten glacier basin in ea are probably ice dynamic responses to long term climate change and perhaps past removal of their adjacent ice shelves the ice growth in the southern antarctic peninsula and parts of ea may be due to increasing precipitation during the last century