four decades of winter mass balance of vernagtferner and hintereisferner austria methodology and results in this study long term series of winter mass balances from two neighbouring glaciers in the southern oetztal alps austria i e hintereisferner and vernagtferner are analyzed with respect to the methods used in their determination for this purpose 1 some basic data of field surveys are presented 2 the influence of different temporal systems is discussed and 3 the profile contour and a model method based on energy balance ablation modelling and measured net mass balance are discussed with respect to the reliability of the resulting series the main findings of the investigations are 1 the winter mass balance series for hintereisferner and vernagtferner as determined with all applied methods result in a reliable climatologic average of 1000 100 mm w e 2 when using the profile method different spatial integration approaches are quite sensitive to the altitudinal coverage and the spatial pattern of observations 3 the error of the model method occurs randomly whereas contour as well as profile method errors are more systematic 4 filtered time series from the two glaciers show similar tendencies for the last three decades

spatially integrated geodetic glacier mass balance and its uncertainty based on geostatistical analysis application to the western svartisen ice cap norway estimates of glacier mass balance using geodetic methods can differ significantly from estimates using direct glaciological field based measurements to determine if such differences are real or methodological there is a need to improve uncertainty estimates in both methods in this paper we focus on the uncertainty of geodetic methods and describe a geostatistical technique that takes into account the spatial correlation of the elevation differences when calculating spatially averaged elevation changes we apply this method to the western svartisen ice cap norway using elevation differences from the surrounding bedrock derived from stereophotogrammetry we show that the uncertainty is not only dependent on the standard error of the individual elevation differences but is also dependent on the size of the averaging area and the scale of the spatial correlation to assess if the geostatistical analysis made over bedrock is applicable to glacier surfaces we use concurrent photogrammetrical and laser scanning data from bedrock and a range of glacier surfaces to evaluate the dependency of the geostatistical analysis on the surface type the estimated geodetic mass balance and its uncertainty is 2 6 0 9 m w e for the period 1968 85 and 2 0 2 2 m w e for 1985 2002

automatic measurement of glacier ice ablation using thermistor strings in this work we tested the suitability of thermistor strings as automatic tools for the continuous measurement of glacier ice ablation experimental data collected in summer 2017 over an italian glacier provided ice ablation readings with accuracy similar to manual measurements with ablation stakes and other automatic systems like the draw wire method and the boggild ablatometer thermistor strings have potential for future applications in remote glacier monitoring thanks to their flexibility simple construction and robustness

the transfer of mass balance profiles to unmeasured glaciers for estimation of the mass balance of an unmeasured glacier its area distribution with altitude s h generally is the only available quantitative information the appropriate specific balance profile b h needs to be transferred from a measured glacier where transfer means modification and adaptation to the topographic and climatic situation of the unmeasured glacier such as altitude exposure to sun and wind or temperature this study proposes the area median elevation m a s a parameter of prime importance for the transfer using as an example ten alpine glaciers the similarity of m and equilibrium line altitude is quantified and the effect of aspect and surrounding topography is qualitatively suggested the transfer of b h between well measured glaciers yielded differences in the mean specific balance of 150 mm in the mean of a 10 year period which corresponds to a change in median altitude by 30 m transfer of b h with a shift according to median glacier elevation to a basin with 27 glaciers and 23 km 2 ice cover agreed to within 10 with elevation changes converted from digital elevation models of 1969 and 1997

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

iron isotope constraints on fe cycling and mass balance in oxygenated earth oceans the fe isotope composition of proterozoic to modern clastic sedimentary rocks and aerosols defines a range ind 56 fe values that is only slightly more variable than the range of fe isotope com positions measured in terrestrial igneous rocks indicating that chemical weathering sedimentary transport and diagenesis play only a minor role in producing fe isotope variations in environ ments where fe redox conditions have been controlled by current levels of atmospheric oxygen in contrast the fe isotope composi tions of hot fluids 300 8c from mid ocean ridge mor spread ing centers define a narrow range that is shifted to lower d 56 fe values by 0 2 0 5 as compared to igneous rocks these new data allow a conceptual model for the fe isotope composition of the oxic oceans that predicts large ranges in fe isotope composition under conditions of changing aerosol and mor fe fluxes such as during periods of major worldwide glaciation

could bacteria have formed the precambrian banded iron formations banded iron formations bifs are prominent sedimentary deposits of the precambrian but despite a century of endeavor the mechanisms of their deposition are still unresolved interactions between microorganisms and dissolved ferrous iron in the ancient oceans offer one plausible means of mineral precipitation in which bacteria directly generate ferric iron either by chemolithoautotrophic iron oxidation or by photoferrotrophy on the basis of chemical analyses from bif units of the 2 5 ga hamersley group western australia we show here that even during periods of maximum iron precipitation most if not all of the iron in bifs could be precipitated by iron oxidizing bacteria in cell densities considerably less than those found in modern fe rich aqueous environments those ancient microorganisms would also have been easily supported by the concentrations of nutrients p and trace metals v mn co zn and mo found within the same iron rich bands these calculations highlight the potential importance of early microbial activity on ancient metal cycling

iron isotope fractionation during oceanic crust alteration abstract the purpose of this work is to study the mobility and budget of fe isotopes in the oceanic crust and in particular during low temperature interaction of seawater with oceanic basalt we carried out this investigation using samples from ocean drilling program odp site 801c drilled during leg 129 and leg 185 in jurassic pacific oceanic crust seaward of the mariana trench the site comprises approximately 450 m of sediment overlying a section of 500 m of basalt which includes intercalated pelagic and chemical sediments in the upper basaltic units and two low temperature 10 30 c ocherous si fe hydrothermal deposits fe was chemically separated from 70 selected samples and 57fe 54fe ratios were measured by mc icp ms isoprobe the isotopic ratios were measured relative to an internal standard solution and are reported relative to the international fe standard irmm 14 based on duplicate measurements of natural samples an external precision of 0 2 2 has been obtained the results indicate that the deep sea sediment section has a restricted range of 57fe which is close to the igneous rock value in contrast large variations are observed in the basaltic section with positive 57fe values up to 2 05 for highly altered basalts and negative values down to 2 49 for the associated alteration products and hydrothermal deposits secondary fe minerals such as fe oxyhydroxides or fe bearing clays celadonite and saponite have highly variable 57fe values that have been interpreted as resulting from the partial oxidation of fe2 leached during basalt alteration and precipitated as fe3 rich minerals in contrast altered basalts at site 801c which are depleted in fe up to 80 display an increase in 57fe values relative to fresh values which suggest a preferential leaching of light iron during alteration the apparent fractionation factor between dissolved fe2 and fe remaining in the mineral is from 0 5 to 1 3 and may be consistent with a kinetic isotope fractionation where light fe is stripped from the minerals alternatively the formation of secondary clays minerals such as celadonite during basalt alteration may incorporate preferentially the heavy fe isotopes resulting in the loss of light fe isotopes in the fluids because microbial processes within the oceanic crust are of potential importance in controlling rates of chemical reactions fe redox state and fe isotope fractionation we evaluated the possible effect of this deep biosphere on fe isotope signatures the fe isotope systematics presented in this study suggest that even though iron behavior during seafloor weathering may be mediated by microbes such as iron oxidizers 57fe variations of more than 4 may also be explained by abiotic processes further laboratory experiments are now required to distinguish between various processes of fe isotope fractionation during seafloor weathering

internal accumulation on storglaciaren sweden in a multi layer snow model coupled to a distributed energy and mass balance model to investigate the internal accumulation on storglaciaren sweden we couple a multilayer snow model to a distributed energy and mass balance model the snow model describes the temperature density and water content evolution of the snow ice pack and includes the processes of percolation and refreezing of water the model is run for the period 9 may 2 september 1999 and validated against weather station and mass balance observations on the glacier the model performs reasonably well with an average summer mass balance for the location of stake observations of 1 56 m w e compared to 1 59 m w e observed however the amount of melt is overestimated in the higher parts of the accumulation area and underestimated in the lower parts of the ablation area the modelled mass balance is most sensitive to the albedo parameterization the chosen momentum and scalar roughness lengths and all parameters related to snowfall the modelled internal accumulation is 0 25 m w e which amounts to about 20 of the winter accumulation and results in a positive net balance for 1999 of 0 23 m w e the modelled internal accumulation is most sensitive to the initial subsurface temperature profile and the irreducible water content

diminishing high frequency directivity due to a source effect empirical evidence from small earthquakes in the abruzzo region italy the aim of this study is to investigate the directivity effects of 250 aftershocks magnitudes 3 5 5 of the mw 6 1 2009 l aquila earthquake central italy to this end we estimate the apparent source spectra at each station removing path and site effects inferred by standard generalized inversion technique then we evaluate the residuals between the apparent source spectra and the event mean source spectrum at selected frequencies we investigate azimuthal and frequency dependence of the residuals for 40 events with the best station coverage for most of events with the strongest directivity effect mw 3 4 4 0 we observe a remarkable decrease of the directivity amplification at high frequencies which has not yet been documented for such relatively small magnitude events since there is negligible distance dependence we ascribe this observation to a source phenomenon such as significant small scale rupture propagation complexity

homogenization of long term mass balance time series the re analysis of long term mass balance time series is important to provide bias corrected mass balance data for climate change impact studies a method to homogenize time series of compre hensive mass balance monitoring programmes is presented and applied to the nearly 50 year mass balance records of griesgletscher and silvrettagletscher switzerland using a distributed mass balance model in daily resolution we correct the mass balance data for varying observation dates direct point measurements are combined with independent geodetic mass changes a prerequisite for a thorough homogenization of mass balance records differences between mass balance evaluated in the hydro logical year or according to the measurement period and the stratigraphic system are analyzed and may be up to 0 5 m w e a 1 cumulative mass balance of both glaciers based on the glaciological method generally agrees well with geodetic mass change on the investigated glaciers however for silvretta gletscher a significant bias of 0 37 m w e a 1 has been detected and corrected for since 1994

recent evolution of marmolada glacier dolomites italy by means of ground and airborne gpr surveys abstract a 10 year long evolution of ice thickness and volume of the marmolada glacier is presented quantitative measurements have been performed by using two different ground penetrating radar gpr datasets a ground based survey using two different ground coupled systems equipped with 100 mhz and 35 mhz antennas was performed in 2004 in 2015 the dataset was collected by using a helicopter borne step frequency gpr equipped with a 100 mhz antenna through a critical discussion of the two different methodologies we show how both approaches are useful to estimate the ice volume within a glacier as well as its morphological characteristics and changes with time even if datasets are acquired in different periods of the year the observed 2004 2014 ice volume reduction of the marmolada glacier is equal to about 30 while the area covered by ice decreased by about 22 the glacier is now splitted in several separated units it is very likely that the fragmentation of the marmolada glacier observed in the period 2004 2014 was accelerated due to irregular karst topography by applying the observed 2004 2014 ice melting trend for the future although the marmolada glacier might behave slightly differently compared to glaciers on non karstic terrains owing to dominant vertical subglacial drainage it will likely disappear by the year 2050 only few isolated very small and thin ice patches will eventually survive due to avalanche feeding and shading at the foot of the north facing cliffs

iron isotopes constrain biologic and abiologic processes in banded iron formation genesis abstract the voluminous 2 5 ga banded iron formations bifs from the hamersley basin australia and transvaal craton south africa record an extensive period of fe redox cycling the major fe bearing minerals in the hamersley transvaal bifs magnetite and siderite did not form in fe isotope equilibrium but instead reflect distinct formation pathways the near zero average 56fe values for magnetite record a strong inheritance from fe3 oxide hydroxide precursors that formed in the upper water column through complete or near complete oxidation transformation of the fe3 oxide hydroxide precursors to magnetite occurred through several diagenetic processes that produced a range of 56fe values 1 addition of marine hydrothermal fe 2 aq 2 complete reduction by bacterial dissimilatory iron reduction dir and 3 interaction with excess fe 2 aq that had low 56fe values and was produced by dir most siderite has slightly negative 56fe values of 0 5 that indicate equilibrium with late archean seawater although some very negative 56fe values may record dir support for an important role of dir in siderite formation in bifs comes from previously published c isotope data on siderite which may be explained as a mixture of c from bacterial and seawater sources several factors likely contributed to the important role that dir played in bif formation including high rates of ferric oxide hydroxide formation in the upper water column delivery of organic carbon produced by photosynthesis and low clastic input we infer that dir driven fe redox cycling was much more important at this time than in modern marine systems the low pyrite contents of magnetite and siderite facies bifs suggests that bacterial sulfate reduction was minor at least in the environments of bif formation and the absence of sulfide was important in preserving magnetite and siderite in the bifs minerals that are poorly preserved in the modern marine record the paucity of negative 56fe values in older early archean and younger early proterozoic bifs suggests that the extensive 2 5 ga hamersley transvaal bifs may record a period of maximum expansion of dir in earth s history

40ar 39ar geochronological constraints on the evolution of lateritic iron deposits in the quadrilatero ferrifero minas gerais brazil weathering profiles overlying the sapecado pico and andaime iron ore deposits quadrilatero ferrifero qf minas gerais brazil reach depths of 150 400 m and host world class supergene iron orebodies in addition to hosting supergene ore bodies of global economic significance weathered banded iron formations at the quadrilatero ferrifero and elsewhere e g carajas hamersley are postulated to underlie some of the most ancient continuously exposed weathering profiles on earth laser incremental heating 40ar 39ar results for 69 grains of hollandite group manganese oxides extracted from 23 samples collected at depths ranging from 5 to 150 m at the sapecado pico and andaime deposits reveal ages ranging from ca 62 to 14 ma older mn oxides occur near the surface while younger mn oxides occur at depth however many samples collected at the weathering bedrock interface yield ages in the 51 41 ma range suggesting that the weathering profiles in the quadrilatero ferrifero had already reached their present depth in the paleogene the antiquity of the weathering profiles in the quadrilatero ferrifero is comparable to the antiquity of dated weathering profiles on banded iron formations in the carajas region brazil and the hamersley province western australia the age versus depth distributions obtained in this study but not available for other regions containing similar supergene iron deposits suggest that little further advance of the weathering front has occurred in the quadrilatero ferrifero lateritic profiles during the neogene the results suggest that weathering in some of these ancient landscapes is not controlled by the steady state advance of weathering fronts through time but may reflect climatic and geomorphological conditions prevailing in a remote past the geochronological results also confirm that the ancient landsurfaces in the quadrilatero ferrifero probably remained immune to erosion for tens of millions of years deep weathering mostly in the paleogene combined with low erosion rates account for the abundance and widespread distribution of supergene iron manganese and aluminum orebodies in this region

iron isotope composition of some archean and proterozoic iron formations abstract fe isotopes can provide new insight into redox dependent biogeochemical processes precambrian iron formations if are deserving targets for fe isotope studies because they are composed predominantly of authigenic fe phases and record a period of unprecedented iron deposition in earth s history we present fe isotope data for bulk samples from 24 archean and proterozoic if and eight phanerozoic fe oxide rich deposits these data reveal that many archean and early paleoproterozoic iron formations were a sink for isotopically heavy fe in contrast to later proterozoic and phanerozoic fe oxide rich rocks the positive 56 fe values in if are best explained by delivery of particulate ferric oxides formed in the water column to the sediment water interface because if are a net sink for isotopically heavy fe there must be a corresponding pool of isotopically light fe in the sedimentary record earlier work suggested that archean pyritic black shales were an important part of this light sink before 2 35 billion years ago ga it is therefore likely that the persistently and anomalously low 56 fe values in shales are linked with the deposition of isotopically heavy fe in if in the deeper parts of basins if deposition produced a residual isotopically light dissolved fe pool that was captured by pyritic fe in shales local dissimilatory fe reduction in porewater and associated diagenetic reactions resulting in pyrite and carbonate precipitation may have further enhanced fe isotope heterogeneity in marine sediments and an iron shuttle may have transported isotopically light fe from shelf sediments to the basin nevertheless water column processing of hydrothermally delivered fe likely had the strongest influence on the bulk iron isotope composition of archean and paleoproterozoic iron formations and other marine sediments

interannual persistence of the seasonal snow cover in a glacierized catchment knowledge of the spatial snow distribution and its interannual persistence is of interest for a broad spectrum of issues in cryospheric sciences in this study snow depths derived from airborne laser scanning are analyzed for interannual persistence of the seasonal snow cover in a partly glacierized mountain area 36 km2 at the end of five accumulation periods the snow covered area varied by 16 of its temporal mean mean snow depth of the total area ranged by a factor of two 1 31 2 58 m with a standard deviation of 0 42 m interannual correlation coefficients of snow depth distribution were in the range 0 68 0 84 of the investigated area 75 was found to be interannually persistent the remaining area showed variable snow cover from year to year caused by occasional avalanches and changes in surface topography as a result of glacier retreat snow cover underwent a change from a homogeneous distribution on the former glacier surface to a more heterogeneous snow cover in the recently deglaciated terrain a geostatistical analysis shows interannual persistence in scaling behavior of snow depth in ice free terrain with scale break distances at 20 m scale invariant behavior of snow depth is indicated over 100 m on smooth glacier surfaces

iron isotope fractionation during supergene weathering process and its application to constrain ore genesis in gaosong deposit gejiu district sw china abstract fe isotope compositions of bulk samples from gaosong ore deposit in gejiu district sw china were investigated and an overall variation in 56 fe values from 0 33 to 0 20 has been observed in this study the 56 fe values of primary sulfide ores are lower than the oxidized ores while the iron isotope compositions of gossan samples which represent highest oxidation degree are heavier than the oxidized ore samples these data indicate that iron isotopes experienced fractionation during supergene weathering process furthermore heavier iron isotopes enriched in more oxidized products another highlight is the fe isotope compositions that are affected by mineralogy which is considered as the primary mechanism of the large fe isotopic variations in the primary ores enrichment of light iron isotopes in primary sulfide ores suggests that iron isotopes fractionated during fluid exsolution from its parental magma and the fe source of skarn ores is mainly the magmatic source this observation that significant fe isotope fractionation occurs in supergene weathering process and fluid exsolution process provides an example in using fe isotopes to trace supergene geochemical cycling and ore deposit formation evolution processes

application of inventory data for estimating characteristics of and regional climate change effects on mountain glaciers a pilot study with the european alps a parameterization scheme using simple algorithms for unmeasured glaciers is being applied to glacier inventory data to estimate the basic glaciological characteristics of the inventoried ice bodies and simulate potential climate change effects on mountain glaciers for past and potential climate scenarios glacier changes for assumed mass balance changes are calculated as step functions between steady state conditions for time intervals that approximately correspond to the characteristic dynamic response time a few decades of the glaciers in order to test the procedure a pilot study was carried out in the european alps where detailed glacier inventories had been compiled around the mid 1970s total glacier volume in the alps is estimated at about 130 km3 for the mid 1970s strongly negative mass balances are likely to have caused a loss of about 10 20 of this total volume during the decade 1980 90 backward calculation of glacier length changes using a mean annual mass balance of 0 25m w e a 1 since the end of the little ice age around 1850 ad gives considerable scatter but satisfactory overall results as compared with long term observations the total loss of alpine surface ice mass since 1850 can be estimated at about half the original value an acceleration of this development with annual mass losses of around 1 m a 1 or more as anticipated from ipcc scenario a for the coming century could eliminate major parts of the presently existing alpine ice volume within decades

transamazonian orogeny in the southern sao francisco craton region minas gerais brazil evidence for paleoproterozoic collision and collapse in the quadrilatero ferrifero abstract the paleoproterozoic transamazonian orogeny yielded a series of discrete orogens in brazil the present field study in the quadrilatero ferrifero qf indicates that the southern sao francisco craton region of the brazilian highlands preserves a portion of one of these orogens two sets of transamazonian structures occur in this region the first consists of northwest verging folds and thrusts affecting supracrustal sequences it is suggested that this set formed in a fold thrust belt setting shortly after 2 125 ga during the closure of a passive margin basin that had initiated along the margins of a preexisting continental mass at ca 2 5 ga the second set consists of structures defining the prominent dome and keel architecture of the qf this set a consequence of the emplacement of basement domes against supracrustal rocks at 2 095 ga may reflect the consequences of orogenic collapse narrow conglomerate filled intermontane basins may have formed coevally with dome emplacement formation of an ocean basin east of the present day sao francisco craton eventually occurred in late mesoproterozoic in effect the transamazonian orogen of the qf represents the collision and collapse stages of a paleoproterozoic wilson cycle the contractional phase of the transamazonian orogeny probably represents accretion of an offshore arc to the eastern and southeastern margin of the present day sao francisco craton region the arc and an associated suture may be traced in the brasiliano pan african orogen east of the sao francisco craton northwards into the northeastern lobe of the sao francisco craton clearly initial assembly of crustal blocks to form a larger continent involving south america occurred during the paleoproterozoic 2 1 ga post transamazonian rifting of this continent created the basins which were later inverted during the brasiliano assembly of gondwana

enhanced estimation of glacier mass balance in unsampled areas by means of topographic data a new method was developed to estimate the mass balance in unsampled areas from existing datasets three years of mass balance data from two glaciers in the central italian alps were used to develop and test a multiple regression method based exclusively on a 10 m resolution digital terrain model the introduction of a relative elevation attribute which expresses the degree of wind exposure of the gridcells notably increased the amount of explainable variance in winter balance with respect to altitude itself the summer balance is highly correlated with elevation but in order to obtain reliable extrapolations the clear sky shortwave radiation and the diurnal cloud cover cycle had to be taken into account the net annual mass balance on a glacier system comprising the two monitored glaciers was calculated by applying both a single regression of winter and summer balance with altitude and the new regression method the consistency of results was assessed against measured net balances and snow cover maps drawn in the ablation season the results of the new method were in close agreement with observations and proved to be less sensitive to the spatial representation of the sampled areas

influence of weathering and hydrothermal alteration on the ree and δ56fe composition of iron formation caue formation iron quadrangle brazil abstract continental margin superior type iron formation of the caue formation iron quadrangle brazil is composed of a laminated magnetite rich chemical meta mudstone that was altered during hydrothermal circulation of basinal fluids greenschist to amphibolite facies metamorphism and subsequent supergene enrichment of fe the absence of traction current deposits and storm generated structures suggests that deposition occurred on the distal shelf possibly as deep as the continental slope paragenesis based lithogeochemical analyses of two drill cores with contrasting alteration styles highlight the importance of hydrothermal metamorphic and supergene processes on the rare earth element plus yttrium ree y and 56fe compositions of iron formation the first drill core penetrates to a depth of 540 m in the ouro fino syncline ofs where lithofacies have experienced intense hydrothermal and supergene alteration the second core is from the gandarela syncline gs and contains 450 m of metamorphosed iron formation that has undergone later supergene enrichment of fe petrographically euhedral to subhedral magnetite in the ofs and gs is fabric destructive and depending on the style and degree of alteration can co occur with dolomite siderite goethite and or martite synsedimentary magnetite and other primary fe oxide phases are absent the effect of supergene enrichment and weathering is best captured along the depth profile of each core by the inverse relationship between sio2 and fe2o3 sio2 values are lowest and fe2o3 values highest near the surface the presence of goethite to 500 m records the maximum depth of these processes in the subsurface the ree y and y anomalies from the deepest and least altered lithofacies in both cores are typical of deposition in a redox stratified water column the weathered lithofacies show several changes in the ree y patterns ce anomalies and absence of y anomalies caused mainly by fluid percolation the change in fe isotopic composition with depth is more complex in drill core from the ofs negative 56fe values shift from 0 91 at depth to less negative values of 0 6 near the surface the most altered samples do not lie on this trend because they are characterized by positive values of 0 30 and 1 33 the 56fe values from the gs increase linearly from 0 11 to 1 23 towards the surface with the most negative values 0 7 and 1 16 near the top the most negative values from the ofs could reflect synsedimentary microbial dissimilatory fe reduction and the positive values from the gs may be related to partial fe2 oxidation between the hydrothermal fe source and fe oxyhydr oxides however when interpreted together with mineralogical and ree data these data likely record the various alteration processes that affected the caue iron formation such findings highlight the importance of coupling sedimentologic analysis with elemental and isotopic chemistry to understand iron formation deposition and fe ore forming processes

the role of sedimentology oceanography and alteration on the δ56fe value of the sokoman iron formation labrador trough canada abstract the sokoman formation is a ca 100 m thick succession of interbedded iron formation and fine grained siliciclastics deposited at 1 88 ga accumulation occurred on a dynamic paleoshelf where oxygen stratification coastal upwelling of hydrothermally derived fe and si microbial processes tide and storm currents diagenesis and low grade prehnite pumpellyite metamorphism controlled lithofacies character and produced complex associations of multigenerational chert hematite magnetite greenalite stilpnomelane and fe carbonate hematite rich facies were deposited along suboxic segments of the coastline where photosynthetic oxygen oases impinged on the seafloor hematitic cross stratified grainstones were formed by winnowing and reworking of freshly precipitated fe oxyhydr oxide and opal a by waves and currents into subaqueous dunes magnetite rich facies contain varying proportions of greenalite and stilpnomelane and record deposition in anoxic middle shelf environments beneath an oxygen chemocline minor negative ce anomalies in hematitic facies but prominent positive ce and eu anomalies and high lree hree ratios in magnetite rich facies imply the existence of a weakly oxygenated surface ocean above anoxic bottom waters the fe isotopic composition of 31 whole rock 0 46 56 fe 0 47 and 21 magnetite samples 0 29 56 fe 0 22 from suboxic and anoxic lithofacies was controlled primarily by the physical oceanography of the paleoshelf despite low grade metamorphism recorded by the 18 o values of paragenetically related quartz and magnetite the sokoman formation preserves a robust primary fe isotopic signal coastal upwelling is interpreted to have affected the isotopic equilibria between fe 2 aq and fe oxyhydr oxide in open marine versus coastal environments which controlled the fe isotopic composition of lithofacies unlike previous work that focuses on microbial and abiotic fractionation processes with little regard for paleoenvironment our work demonstrates that depositional setting is paramount in governing the fe isotopic composition of iron formations irrespective of what fe bearing minerals precipitated

new long term mass balance series for the swiss alps in this study we present 19 new or re analysed series of glacier wide seasonal mass balance for the swiss alps based on direct measurements the records partly start around 1920 and continue until today previously unpublished and unevaluated observations of point winter and annual balance are compiled from various sources and archives these highly valuable datasets have not yet been consistently evaluated and were thus unavailable to the scientific community using distributed modelling for spatial interpolation and extrapolation and homogenization of the point measurements we infer continuous series of area averaged mass balance the results are validated against independent decadal ice volume changes from photogrammetric surveys six of the new seasonal series cover 60 years and more and add a substantial amount of information on the variations of regional glacier mass change this will strengthen the worldwide collection of glacier monitoring data especially for the data sparse period before the 1980s we compare our results to existing long term series and present an updated assessment of mass balance variability and glacier sensitivity throughout the european alps

biologically recycled continental iron is a major component in banded iron formations banded iron formations bifs record a time of extensive fe deposition in the precambrian oceans but the sources and pathways for metals in bifs remain controversial here we present fe and nd isotope data that indicate two sources of fe for the large bif units deposited 2 5 billion y ago high end and 56fe signatures in some bif samples record a hydrothermal component but correlated decreases in end and 56fe values reflect contributions from a continental component the continental fe source is best explained by fe mobilization on the continental margin by microbial dissimilatory iron reduction dir and confirms for the first time to our knowledge a microbially driven fe shuttle for the largest bifs on earth detailed sampling at various scales shows that the proportions of hydrothermal and continental fe sources were invariant over periods of 100 103 y indicating that there was no seasonal control although fe sources varied on longer timescales of 105 106 y suggesting a control by marine basin circulation these results show that fe sources and pathways for bifs reflect the interplay between abiologic hydrothermal and biologic processes where the latter reflects dir that operated on a basin wide scale in the archean

dating the itabira iron formation quadrilatero ferrifero of minas gerais brazil at 2 65 ga depositional u pb age of zircon from a metavolcanic layer abstract uranium pb dating of zircon from a metavolcanic layer within the itabira iron formation or caue itabirite quadrilatero ferrifero of minas gerais brazil indicates that its deposition occurred at 2 65 ga i e considerably earlier than proposed by previous geochronological studies which suggested deposition between 2 58 ga detrital zircon age from the underlying moeda formation and 2 42 ga pb pb isochron age from dolomitic rocks of the immediately overlying gandarela formation the new age has major implications for the geology of the quadrilatero ferrifero and connects it with the neoarchaean iron formation of the carajas mineral province

topographic influences on recent changes of very small glaciers in the monashee mountains british columbia canada an analysis of the local topographic setting of very small 0 4 km 2 glaciers within a small region of the monashee mountains british columbia was conducted to investigate its influence on recent changes in the extent of these glaciers net changes in glacier extent were determined from a detailed manual comparison of remotely sensed imagery acquired in 1951 2001 and 2004 most of the 86 glaciers included in the study showed no observable net change in area over the study period while six glaciers retreated four disappeared entirely and only one advanced indices derived to characterize elements of the local topographic setting that might affect the local mass balance suggest that most of the glaciers are situated in locations that favor ice preservation by enhancing mass input and or reducing ablation rates glaciers situated in less favorable settings generally either decreased in area or disappeared the results suggest that most of the glaciers studied have retreated as far as they are likely to under the climatic conditions of the late 20th century