acoustic facies on the inner kara sea shelf implications for late weichselian to holocene sediment dynamics abstract we studied the impact of the last glacial late weichselian sea level cycle on sediment architecture in the inner kara sea using high resolution acoustic sub bottom profiling the acoustic lines were ground truthed with dated sediment cores furthermore we refined the location of the eastern lgm ice margin by new sub bottom profiles new model results of post last glacial maximum lgm isostatic rebound for this area allow a well constrained interpretation of acoustic units in terms of sequence stratigraphy the lowstand or regressive system tract sediments are absent but are represented by an unconformity atop of pleistocene sediments on the shelf and by a major incised dendritic paleo river network the subsequent transgressive and highstand system tracts are best preserved in the incised channels and the recent estuaries while only minor sediment accumulation on the adjacent shelf areas is documented the kara sea can be subdivided into three areas estuaries a the shelf b and c deeper lying areas that accumulated a total of 114 1010 t of holocene sediments

past glacial and interglacial conditions in the arctic ocean and marginal seas a review past changes in the arctic ocean and its marginal seas have been profound even during the last 10 000 years understanding these changes such as those occurring during the transition from glacial to interglacial climates are important for research on modern processes because this knowledge provides a framework and unique perspective in which to view the modern physical and biological processes this paper discusses our current understanding of past environmental change and processes relative to those currently in progress special emphasis is placed on the most recent transition from a glacial state to the modern interglacial conditions

genesis of the huangshannan high ni tenor magmatic sulfide deposit in the eastern tianshan northwest china constraints from pge geochemistry and os s isotopes abstract the huangshannan magmatic ni cu sulfide deposit is one of a group of permian magmatic ni cu deposits located in the southern central asian orogenic belt in the eastern tianshan northwest china it is characterized by elevated ni tenor concentrations in recalculated 100 sulfide in sulfide within ultramafic rocks 9 19 wt with values much higher than other deposits in the region sulfides of the huangshannan deposit are composed of pentlandite chalcopyrite and pyrrhotite and the host rock is relatively fresh indicating that the high ni tenor is a primary magmatic feature rather than formed by alteration processes it is shown that sulfides with high ni tenor can be generated by sulfide olivine equilibrium at an oxygen fugacity of qfm 0 5 for magmas containing 450 ppm ni and 20 olivine ores with 10 wt sulfur have relatively low pge and ni tenors compared to other ores r factor mass ratio of silicate to sulfide liquid modeling of ni indicates that they formed at moderate r values 150 600 based on this constraint on r values ores with 4 5 wt as sulfide rich samples are also depleted in cu and as interstitial sulfides in those samples are physically interconnected at a scale of several cms the low pt and pd anomalies are attributed to solid pt and pd phases crystallization and retention with the monosulfide solid solution mss and cu rich sulfide liquid percolation during mss fractionation this finding indicates that pt anomalies in sulfide rich rocks from magmatic ni cu deposits in the eastern tianshan are the result of sulfide fractionation rather than a hydrothermal effect 187 os 188 os 278ma values of the lherzolite samples vary from 0 27 to 0 37 and os 278ma values vary from 110 to 189 indicating significant magma interaction with crustal sulfides rich in radiogenic os well constrained os values and 34 s values 0 4 to 0 8 indicate that crustal contamination occurred at depth before the arrival of the magma in the huangshannan chamber regionally deposits with high ni tenor have not been reported other than the huangshannan deposit however many intrusions with high ni contents in olivine are present in nw china such as the erhongwa poyi and poshi intrusions those intrusions are capable of forming high ni tenor sulfides due to olivine sulfide silicate equilibrium and relative high ni content in parent magma making them attractive exploration targets

multicentury scale records of carbonate hydrographic variability on the northern iceland margin over the last 5000 years the waters off northern iceland are subjected to extreme hydrographic variability on annual to decadal timescales in years when cold low salinity water moves coastward and sea ice is prevalent i e the late 1960s marine productivity of surface waters is low because the water column is well stratified in the opposite oceanographic mode warm salty atlantic water dominates the shelf and vertical mixing results in high productivity we track these two contrasting modes by measuring the carbonate content of marine sediments a proxy for productivity in three cores from northern iceland the fjord record b997 328pc is anchored by eleven 14c ams dates and has a resolution of one sample every 50 yr thirteen oscillations occurred over the last 4800 cal yr with an average length of 370 yr these are superimposed on a long term decrease in net carbonate accumulation the little ice age is marked by the largest decrease in carbonate content and in flux with smaller minima at 2300 and 3000 cal yr b p marked peaks in carbonate optima occurred at 2000 and 3800 cal yr b p the carbonate record from b997 328pc can be correlated with records on the inner shelf b997 330pc and midshelf b997 327pc indicating that significant regional changes in oceanography occurred at the southern margin of the norwegian greenland sea the marine carbonate fluctuations closely track temperature reconstructions from the greenland summit site for the last 2000 cal yr and show similar but slightly offset oscillations between 2000 and ca 4800 cal yr b p

application of high resolution x ray computed tomography to mineral deposit origin evaluation and processing abstract high resolution x ray computed tomography ct is the industrial equivalent of medical cat scanning and provides a mechanism for non destructive studies of the three dimensional nature of geological materials hrxct produces two dimensional images slices that reveal the interior of an object as if it had been sliced open along the image plane for viewing a ct image is generated by differences in x ray attenuation that arise from differences in density and composition within the object by acquiring a contiguous set of slices volumetric data for all or part of a sample can be obtained allowing three dimensional inspection and measurement of features of interest ct is particularly effective in the study of metallic ores that commonly contain minerals spanning the range of densities of natural materials available software can produce grain shape size and orientation data from the scanned volume which can be particularly useful for oriented samples ct is particularly useful for studies of gold and other precious metal bearing minerals that typically have significant contrast even with common metallic mineral phases ct precisely defines the in situ location of mineral grains of interest within a sample which then can be studied in conventional petrographic sections and other forms of data collected e g isotope or trace element geochemistry another area of application is fluid inclusions which can be discerned even in opaque phases and fluid and vapor volumes measured for sufficiently large occurrences we summarize ct principles and review available instrumentation as well as scanning and data reduction protocols that provide unique three dimensional information for diverse ore types and applications in mineral deposits geology ct applications for economic geology and other fields will continue to expand as instruments continue to evolve and as scanning protocols and applications are extended for more precise quantification of three dimensional relationships particularly for fine grained particles and small fluid inclusions in larger volumes and for separation of minerals with limited contrast

arctic palaeo river discharge and environmental change evidence from the holocene kara sea sedimentary record abstract in this paper we summarize data on terrigenous sediment supply in the kara sea and its accumulation and spatial and temporal variability during holocene times sedimentological organic geochemical and micropaleontological proxies determined in surface sediments allow to characterize the modern riverine terrigenous sediment input ams 14c dated sediment cores from the ob and yenisei estuaries and the adjacent inner kara sea were investigated to determine the terrigenous sediment fluxes and their relationship to paleoenvironmental changes the variability of sediment fluxes during holocene times is related to the post glacial sea level rise and changes in river discharge and coastal erosion input whereas during the late middle holocene most of the terrigenous sediments were deposited in the estuaries and the areas directly off the estuaries huge amounts of sediments accumulated on the kara sea shelf farther north during the early holocene before about 9 cal kyr bp the maximum accumulation at that time is related to the lowered sea level increased coastal erosion and increased river discharge based on sediment thickness charts echograph profiles and sediment core data we estimate an average holocene 0 11 cal kyr bp annual accumulation of 194 106 t yr 1 of total sediment for the whole kara sea based on late holocene modern sediment accumulation in the estuaries probably 12 106 t yr 1 of riverine suspended matter i e about 30 of the input may escape the marginal filter on a geological time scale and is transported onto the open kara sea shelf the high resolution magnetic susceptibility record of a yenisei core suggests a short term variability in siberian climate and river discharge on a frequency of 300 700 yr this variability may reflect natural cyclic climate variations to be seen in context with the interannual and interdecadal environmental changes recorded in the high northern latitudes over the last decades such as the nao ao pattern a major decrease in ms values starting near 2 5 cal kyr bp being more pronounced during the last about 2 cal kyr bp correlates with a cooling trend over greenland as indicated in the gisp 2 ice core extended sea ice cover in the north atlantic and advances of glaciers in western norway our still preliminary interpretation of the ms variability has to be proven by further ms records from additional cores as well as other high resolution multi proxy arctic climate records

comparison study of the modern ostracod associations in the kara and laptev seas ecological aspects recent ostracod assemblages were investigated from coretop sediment samples collected in the eastern kara sea from water depths down to 300 m a total of 45 species were identified 27 of them were reported for the kara sea for the first time the kara sea data were compared with our results on the distribution of ostracods in the eastern laptev sea the spatial distribution of recent taxa and the ecological groupings demonstrate a clear relation to dominant environmental factors which range from estuarine to full marine conditions four assemblages related to average summer bottom water salinities were established 1 a freshwater assemblage from the inner estuaries of the ob and yenisei rivers with salinities less than 2 and from thermokarst lagoons of the southern laptev sea coast with strong salinization in winter 2 a brackishwater assemblage of the outer estuaries of the ob and yenisei rivers with salinities up to 26 3 a mixed euryhaline marine assemblage dominated by euryhaline species paracyprideis pseudopunctillata and heterocyprideis sorbyana from the inner shelf river affected zone of the kara and laptev seas where salinities range between 26 and 32 4 a taxonomically diverse marine assemblage dominated by shallow water marine taxa from the northern parts of the kara and laptev shelves and upper continental slope with stable bottom environments and a salinity higher than 32 abundant euryhaline species found at greater water depths are identified as part of an ice rafted assemblage they are possibly entrained into the newly formed fast ice during autumn storms and freeze up period and then transported to the distal open sea areas during summer

is the central arctic ocean a sediment starved basin abstract numerous short sediment cores have been retrieved from the central arctic ocean many of which have been assigned sedimentation rates on the order of mm ka implying that the arctic basin was starved of sediments during plio pleistocene times a review of both shorter term sedimentation rates through analysis of available sediment core data and longer term sedimentation rates through estimates of total sediment thickness and bedrock age suggests that cm ka scale rates are pervasive in the central arctic ocean this is not surprising considering the physiographic setting of the arctic ocean being a small land locked basin since its initial opening during early cretaceous times we thus conclude that the central arctic ocean has not been a sediment starved basin either during plio pleistocene times or during pre pliocene times rigorous chronstratigraphic analysis permits correlation of sediment cores over a distance of 2600 km from the northwestern amerasia basin to the northwestern eurasia basin via the lomonosov ridge using paleomagnetic biostratigraphic and cyclostratigraphic data

modern seasonal variability and deglacial holocene change of central arctic ocean sea ice cover new insights from biomarker proxy records for the reconstruction of sea ice variability a biomarker approach which is based on 1 the determination of sea ice diatom specific highly branched isoprenoid ip25 and 2 the coupling of phytoplankton biomarkers and ip25 has been used for the first time such a data set was obtained from an array of two sediment traps deployed at the southern lomonosov ridge in the central arctic ocean at water depth of 150 m and 1550 m and recording the seasonal variability of sea ice cover in 1995 1996 these data indicate a predominantly permanent sea ice cover at the trap location between november 1995 and june 1996 an ice edge situation with increased phytoplankton productivity and sea ice algae input in july august 1996 and the start of new ice formation in late september the record of modern sea ice variability is then used to better interpret data from sediment core ps2458 4 recovered at the laptev sea continental slope close to the interception with lomonosov ridge and recording the post glacial to holocene change in sea ice cover based on ip25 and phytoplankton biomarker data from core ps2458 4 minimum sea ice cover was reconstructed for the bolling allerod warm interval between about 14 5 and 13 calendar kyr bp followed by a rapid and distinct increase in sea ice cover at about 12 8 calendar kyr bp this sea ice event was directly preceded by a dramatic freshwater event and a collapse of phytoplankton productivity having started about 100 years earlier these data are the first direct evidence that enhanced freshwater flux caused enhanced sea ice formation in the arctic at the beginning of the younger dryas in combination with a contemporaneous abrupt and very prominent freshwater meltwater pulse in the yermak plateau fram strait area these data may furthermore support the hypothesis that strongly enhanced freshwater and ice export from the arctic into the north atlantic could have played an important trigger role for the onset of the younger dryas cold reversal during the early holocene sea ice cover steadily increased again ice edge situation reaching modern sea ice conditions more or less permanent sea ice cover probably

persistent solar influence on north atlantic climate during the holocene surface winds and surface ocean hydrography in the subpolar north atlantic appear to have been influenced by variations in solar output through the entire holocene the evidence comes from a close correlation between inferred changes in production rates of the cosmogenic nuclides carbon 14 and beryllium 10 and centennial to millennial time scale changes in proxies of drift ice measured in deep sea sediment cores a solar forcing mechanism therefore may underlie at least the holocene segment of the north atlantic9s 1500 year cycle the surface hydrographic changes may have affected production of north atlantic deep water potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally

the extent of the barents kara ice sheet during the last glacial maximum it has been a long standing discussion whether the barents kara ice sheet expanded onto mainland russia during the last glacial maximum lgm in this paper we describe many well dated by conventional and ams 14 c methods and optically stimulated luminescence sedimentary sequences in the controversial area of northern russia the sequences discussed are not covered by till and yet all predate the lgm the deposits consist mostly of aeolian or lacustrine easily deformable soft silt and fine sand two sites feature frozen mammoth carcasses and three sites contain palaeolithic artefacts and mammalian bones we emphasise that these formations show no sign of having been overridden by an ice sheet at several sites deposition of aeolian sediments and formation of ice wedges took place during the lgm time span these observations present unambiguous proof that the barents kara ice sheet did not cover mainland russia during lgm with a possible exception for the northern tip of the taimyr peninsula r 2001 elsevier science ltd all rights reserved

experiments and models bearing on the role of chromite as a collector of platinum group minerals by local reduction chromite is widely recognized to act as a collector for platinum group elements pge which tend to be observed as discrete grains of platinum group minerals included within magmatic chromite grains in the course of experiments involving the re equilibration or growth of chromite and cr spinel in molten silicate we observe that platinum group minerals pgm including metal alloys and laurite form at the mineral melt interface the formation of pgm to the extent observed requires a mechanism involving sustained transport of pge from a source within the experiment to the site of deposition we propose that the driving force for this process is a redox gradient developed in response to mineral growth or re equilibration with the surrounding melt the mechanism is local reduction within the mineral melt interfacial region as a consequence of the selective uptake of trivalent cr and fe from the melt by spinel relative to the divalent species we have modeled the transient perturbation of fo2 in a compositional boundary layer melt around spinel for both crystal growth and diffusive re equilibration of mineral and melt we find that metal solubilities decrease by several per cent in the silicate melt at the melt crystal interface during crystal growth providing the driving force for pgm formation in magmas that are saturated with pgm as a result of falling temperature and oxygen fugacity during spinel crystallization nucleation of pgm will be impeded by interfacial tension everywhere except in the reduced boundary layer around spinel crystals the resulting concentration and trapping of alloy particles in the growing chromite crystals can produce apparent bulk chromite melt partition coefficients exceeding 20 even if there is no solid solution of pge in the chromite the introduction of spinel grains initially equilibrated with a mafic magma into a more primitive magma with higher cr al would lead to disequilibrium between chromite and melt the perturbation of fo2 in the compositional boundary layer surrounding a chromite xenocryst would exceed 0 1 log unit leading to local reduction of alloy solubility of the order of 13 18 a small number of spinel xenocrysts could serve as collection sites for all of the excess pge in the magma leading to the eventual observation that a few chromite crystals contain many pgm inclusions whereas the rest of the chromite population may be relatively free of pgm

holocene interdependences of changes in sea surface temperature productivity and fluvial inputs in the iberian continental shelf tagus mud patch 1 sea surface temperature sst marine productivity and fluvial input have been reconstructed for the last 11 5 calendar cal ka b p using a high resolution study of c37 alkenones coccolithophores iron content and higher plant n alkanes and n alkan 1 ols in sedimentary sequences from the inner shelf off the tagus river estuary in the portuguese margin the sst record is marked by a continuous decrease from 19 c at 10 5 and 7 ka to 15 c at present this trend is interrupted by a fall from 18 c during the roman and medieval warm periods to 16 c in the little ice age river input was very low in the early holocene but increased in the last 3 cal ka b p in association with an intensification of agriculture and deforestation and possibly the onset of the north atlantic oscillation atlantic multidecadal oscillation modes of variability river influence must have reinforced the marine cooling trend relative to the lower amplitude in similar latitude sites of the eastern atlantic the total concentration of alkenones reflects river induced productivity being low in the early holocene but increasing as river input became more important rapid cooling of 1 2 c occurring in 250 years is observed at 11 1 10 6 8 2 6 9 and 5 4 cal ka b p the estimated age of these events matches the ages of equivalent episodes common in the ne atlantic mediterranean region this synchronicity reveals a common widespread climate feature which considering the twentieth century analog between colder ssts and negative north atlantic oscillation nao is likely to reflect periods of strong negative nao

a key source area and constraints on entrainment for basin scale sediment transport by arctic sea ice combining field measurements remote sensing and numerical modelling a key site for ice entrainment and basinwide dispersal of sediments by sea ice has been identified near the new siberian islands the total ice bound sediment export of 18 5 x 10 6 t for an entrainment event documented in 1994 95 is of the same order of magnitude as annual sediment supply to the deep sea sector of the eurasian arctic and the greenland sea satellite imagery and ancillary data indicate that ice advection from this source may play an important role in sedimentation downstream in the transpolar drift

a contemporary sediment and organic carbon budget for the kara sea shelf siberia it has recently been realized that the arctic undergoes drastic changes probably resulting from global change induced processes this acts on the cycling of matter and on biogenic elements in the arctic ocean having feedback mechanisms with the global climate for example by interacting with atmospheric trace gas concentration a contemporary budget for biogenic elements as well as suspended matter for the arctic ocean as a baseline for comparison with effects of further global change is thus needed available budgets are based on the late holocene sedimentary record and are therefore quiet different from the present which has already been affected by the intense anthropogenic activity of the last centuries we calculated a contemporary suspended matter and organic carbon budget for the kara sea utilizing the numerous available data from the recent literature as well as our own data from russian german sirro siberian river run off expeditions for calculation of the budgets we used a multi box model to simplify the kara sea shelf and estuary system input was assumed to comprise riverine and eolian input as well as coastal erosion output was assumed to consist of sedimentation and export to the arctic ocean exchange with the adjacent seas was considered in our budget and primary production as well as recycling of organic material was taken into account according to our calculations about 18 510 6 ty r 1 of sediments and 0 3710 6 t yr 1 of organic carbon are buried in the estuaries whereas 20 910 6 ty r 1 sediment and 0 3110 6 ty r 1 organic carbon are buried on the shelf most sources and sinks of our organic carbon budget of the kara sea are in the same order of magnitude making it a region very sensitive to further changes d 2005 elsevier b v all rights reserved

chromite in komatiites 3d morphologies with implications for crystallization mechanisms high resolution x ray computed tomography has been carried out on a suite of komatiite samples representing a range of volcanic facies chromite contents and degrees of alteration and metamorphism to reveal the wide range of sizes shapes and degrees of clustering that chromite grains display as a function of cooling history dendrites are spectacularly skeletal chromite grains formed during very rapid crystallization of supercooled melt in spinifex zones close to flow tops at slower cooling rates in the interiors of thick flows chromite forms predominantly euhedral grains large clusters up to a dozen of grains are characteristic of liquidus chromite whereas fine dustings of mostly individual 20 m grains form by in situ crystallization from trapped intercumulus liquid chromite in coarse grained olivine cumulates from komatiitic dunite bodies occurs in two forms as clusters or chains of euhedral crystals developing into chicken wire texture where chromite is present in supra cotectic proportions and as strongly dendritic semi poikilitic grains these dendritic grains are likely to have formed by rapid crescumulate growth from magma that was close to its liquidus temperature but supersaturated with chromite in some cases this process seems to have been favoured by nucleation of chromite on the margins of sulphide liquid blebs this texture is a good evidence for the predominantly cumulus origin of oikocrysts and in situ origin of heteradcumulate textures our 3d textural analysis confirms that the morphology of chromite crystals is a distinctive indicator of crystallization environment even in highly altered rocks

calibration and application of marine sedimentary physical properties using a multi sensor core logger abstract we examined geophysical data from a multi sensor core logger mscl a logging device providing continuous measurements of gamma ray attenuation p wave travel time and magnetic susceptibility on marine sediment cores in the first part we focused on the gamma ray system and compared two different calibration methods from the gamma ray attenuation we calculated densities and porosities by incorporating mass weighted attenuation coefficients the application of an iteration method reduces the error of the density and porosity estimates compared to grape data in addition we derived equations to calculate water content and dry bulk density from gamma ray attenuation measurements comparison with physical properties determined on discrete samples revealed a very good correlation of both data sets r 0 99 this correlation is valid for sediments from substantially different geological settings e g turbidites hemipelagic muds and opal rich sediments in the second part we applied our data to marine geological questions for sediments from the antarctic polar frontal zone there is indication that the content of biogenic opal can be assessed using a correlation of density and p wave velocity for sediments from the bengal fan the relationship between the mscl acoustic impedance the product of density and p wave velocity and the grain size distribution in discrete samples can be used to predict clay and sand silt ratios for sediment cores from the shelf and upper continental slope

a multiproxy based reconstruction of the mid to late holocene paleoenvironment in the laptev sea off the lena river delta siberian arctic abstract land shelf interactions and related environmental changes were reconstructed for the past 6 cal kyrs interpreting multiproxy records from the two ams14c dated sediment cores from the sites located to the north and northeast of the lena river delta proxies used include terrestrial and aquatic palynomorphs benthic planktic foraminifers and ostracods paired with benthic 18o and 13c records of haynesina orbiculare the study focused on unravelling the relation between river runoff and the regional climate changes on the one hand and its imprint on the shelf sea environment on timescales beyond the instrumental records on the other the palynomorph records show that the lena river outflow largely determined the composition of species associations and the magnitude of terrestrial matter influx from land pollen assemblages of the inner laptev sea shelf reflect complex pollen contribution of the arctic tundra and remote taiga zones drained by the lena river and indicate a vegetation response to warmer than present climatic conditions between 6 0 and 4 5 cal ka and a subsequent gradual cooling fluvial influence in the records is manifested by 1 increases in sedimentation rates 2 high influxes of pollen spores and freshwater chlorophycean algae wood and plant remains 3 negative 13c excursions due to the introduction of dissolved inorganic carbon dic from river water episodes of enhanced freshwater influence in the surface water layers fluvial events correlate with positive benthic 18o excursions and increasing representation of river distal species among benthics altogether this points to an estuarine like reversed north to south bottom current activity along the submarine paleovalleys on the shelf the most pronounced fluvial events are recognized at 5 3 5 9 1 5 and

variability of sea ice cover in the chukchi sea western arctic ocean during the holocene 1 dinocysts from cores collected in the chukchi sea from the shelf edge to the lower slope were used to reconstruct changes in sea surface conditions and sea ice cover using modern analogue techniques holocene sequences have been recovered in a down slope core b15 2135 m 75 44 n sedimentation rate of 1 cm kyr 1 and in a shelf core p1 201 m 73 41 n sedimentation rate of 22 cm kyr 1 the shelf record spanning about 8000 years suggests high frequency centennial oscillations of sea surface conditions and a significant reduction of the sea ice at circa 6000 and 2500 calendar cal years b p the condensed offshore record b15 reveals an early postglacial optimum with minimum sea ice cover prior to 12 000 cal years b p which corresponds to a terrestrial climate optimum in bering sea area dinocyst data indicate extensive sea ice cover 10 months yr 1 from 12 000 to 6000 cal years b p followed by a general trend of decreasing sea ice and increasing sea surface salinity conditions superimposed on large amplitude millennial scale oscillations in contrast 18o data in mesopelagic foraminifers neogloboquadrina pachyderma and benthic foraminifers cibicides wuellerstorfi reveal maximum subsurface temperature and thus maximum inflow of the north atlantic water around 8000 cal years b p followed by a trend toward cooling of the subsurface to bottom water masses sea surface to subsurface conditions estimated from dinocysts and 18o data in foraminifers thus suggest a decoupling between the surface water layer and the intermediate north atlantic water mass with the existence of a sharp halocline and a reverse thermocline especially before 6000 years b p the overall data and sea ice reconstructions from core b15 are consistent with strong sea ice convergence in the western arctic during the early holocene as suggested on the basis of climate model experiments including sea ice dynamics matching a higher inflow rate of north atlantic water

the santa rita nickel sulfide deposit in the fazenda mirabela intrusion bahia brazil geology sulfide geochemistry and genesis the santa rita ore zone within the fazenda mirabela intrusion is an unusual example of high tonnage magmatic ni cu pge sulfide mineralization developed as a stratiform layer within the main cumulus sequence of a layered intrusion the intrusion as a whole is about 4 2 5 km in outcrop dimensions and at least 3 km in original maximum stratigraphic thickness with an original boat shaped morphology the ore zone comprises a 50 to 200 m thick interval containing up to 5 wt percent disseminated sulfides within a sequence of mostly unaltered harzburgites and orthopyroxenites this orthopyroxene dominated sequence lies between the dominantly olivine rich cumulates that comprise the lower half of the intrusion and the gabbroic cumulates that make up the upper half sulfide tenor variations and silicate host rock compositions have been derived from a very large database of continuous assays of more than 500 diamond drill cores consistent patterns of sulfide tenor gradually decreasing ni from over 20 to about 10 wt percent near constant cu and gradually decreasing pges with cyclically varying pt pd ratios are found within the santa rita ore zone across the entire intrusion and display relatively little lateral variability the position of the sulfide mineralization envelope within the harzburgite orthopyroxenite package migrates to higher stratigraphic levels from the northern to the southern margin of the intrusion maximum grades and thicknesses correlate with the maximum thickness of orthopyroxene bearing cumulates asymmetrically disposed toward the southern margin of the intrusion nickel tenors of the sulfides range from 15 to 25 wt percent exceptionally high for rocks with relatively low values of mgo mgo feo and are closer to the typical values observed in komatiite hosted deposits although cu tenors typically 5 8 wt are much higher than komatiite values sulfide pge tenors range from less than 100 ppb to greater than 10 ppm of both pt and pd with maximum values in s poor rocks at the base of the sulfide bearing interval pges become significantly more depleted toward the top of the santa rita zone we attribute these features along with the localization of the sulfide bearing interval at the contact between ultramafic and mafic cumulates to mixing of an initially s undersaturated moderately ni enriched resident magma with a relatively low ni pge depleted significantly lower temperature replenishing magma charged with suspended sulfide liquid droplets

the application of high resolution x ray computed tomography on naturally deformed rock salt multi scale investigations of the structural inventory abstract x ray computed tomography ct represents a useful technique providing new perspectives and insights for the structural investigation of naturally deformed rock salt several samples of permian rock salt from gorleben asse and teutschenthal germany were investigated by exploiting the non destructive nature of ct and nct techniques particularly for salt rocks ct imaging enabled the visualization and quantification of anhydrite impurities pore space and fluid phases located along grain boundaries or trapped as intracrystalline inclusions disseminated grains and aggregates of anhydrite in rock salt of the gorleben salt dome have been visualized and quantified by ct for the first time in order to portray their spatial occurrence the visualization of anhydrite aggregates and pore space shows no correlation between their spatial distributions this independence excludes the anhydrite to be responsible for elevated porosity 0 87 0 07 vol high resolution nct scans 1 m voxel size of single intracrystalline and grain boundary fluid inclusions from gorleben and asse rock salt allowed the visualization and quantification of their various phase components a major achievement is the detailed description of the morphology and shape of the fluid inclusions and of their phase components which has not been conducted in rock salt research by high resolution x ray ct imaging before

organic carbon and nitrogen composition in the sediment of the kara sea arctic ocean during the last glacial maximum to holocene times 1 a sharp decrease in corg ntot ratios and apparently heavier stable isotope ratios of corg and ntot 13corg and 15ntot after deglaciation were observed in sediment cores st 25 and st 34 collected from the saint anna trough in the kara sea exhibiting a change of sediment origin from terrestrial to marine during the lgm and holocene times organic nitrogen norg contributed about 40 to total nitrogen ntot during the holocene but the norg fraction was hardly observed in the lower lgm sediments below 120 cm depth in st 25 and beneath 170 cm in st 34 this may be due to a permanent cover of sea ice in the area during the lgm in addition the 13c values for oclabile and ocresi were remarkably different between lgm and holocene sediment the unexpected lighter 13c values for ocresi for the lgm period might be due to methanotrophic bacteria in the sediment of kara sea

stable carbon and nitrogen isotopes as indicators for organic matter sources in the kara sea abstract stable carbon and nitrogen isotope ratios 13c 15n are frequently used to decipher organic matter sources and transformation processes here we present stable isotope data of suspended matter and sediments from the ob and yenisei estuaries and the kara sea arctic ocean in order to figure out how they are influenced by seasonal and interannual changes in river run off ice coverage and biological activity our study shows a progressive increase of stable carbon and nitrogen isotopic ratios in offshore direction and a positive correlation of salinity with 13c differences among the correlation of individual annual suspended matter data sets reveal a multitude of processes modulating 13c ratios such as sporadic plankton blooms variations in riverine end members and annual river run off despite this variability the correlation of salinity with 13c of suspended matter from the surface water is very similar to that of surface sediments with the average salinity of the ice free period however sediments show a shift to higher 13c values by about 2 2 since sinking particles in deep water are similar to sedimentary 13c ratios the correlation of salinity with 13c of sediments has been taken to reconstruct the paleosalinity of a sediment core off the yenisei river mouth since 10 000 yr bp

holocene climatic instability a prominent widespread event 8200 yr ago the most prominent holocene climatic event in greenland ice core proxies with approximately half the amplitude of the younger dryas occurred 8000 to 8400 yr ago this holocene event affected regions well beyond the north atlantic basin as shown by synchronous increases in windblown chemical indicators together with a significant decrease in methane widespread proxy records from the tropics to the north polar regions show a short lived cool dry or windy event of similar age the spatial pattern of terrestrial and marine changes is similar to that of the younger dryas event suggesting a role for north atlantic thermohaline circulation possible forcings identified thus far for this holocene event are small consistent with recent model results indicating high sensitivity and strong linkages in the climatic system

modeling the merensky reef bushveld complex republic of south africa the merensky pegmatoid normal reef in the western bushveld complex is commonly characterized as a pyroxene rich pegmatoidal unit with a base that is enriched in chromite and platinum group element bearing sulfides overlying a leuconorite footwall models for its formation have ranged from those that view it as entirely a magmatic cumulate succession to those that have suggested that it is a zone of volatile induced remelting the consequences of the latter interpretation are investigated using the numerical modeling program iridium which links diffusive and advective mass and heat transport with a phase equilibration routine based on the melts program the initial system consists of a simple stratigraphic succession of a partially molten leuconorite overlain by a partially molten pyroxenite both initially at 1 190 c and 2 kbar 2 wt of a volatile fluid composed of 75 mol h2o 20 mol co2 and 5 mol h2s is then added to the lower 20 cm of the pyroxenite the system is then allowed to evolve under conditions of chemical diffusion in the liquid the addition of the volatile components results in a modest increase in the amount of melt in the pyroxenite however chemical diffusion across the leuconorite pyroxenite boundary leads to more extensive melting at and below the boundary with preferential loss of opx from the underlying leuconorite preferential re precipitation of sulfide and chromite and concentration of the pge at this boundary these results mimic actual mineral and compositional profiles across the merensky pegmatoid and illustrate that long term diffusion process can effectively produce mineralogical and compositional layering not present in the original assemblage

modern organic carbon deposition in the laptev sea and the adjacent continental slope surface water productivity vs terrigenous input sediment samples from the laptev sea taken during the 1993 rv polarstern expedition ark ix 4 and the rv ivan kireyev expedition transdrift i were investigated for the amount and composition of their organic carbon fractions of major interest was the identification of different processes controlling organic carbon deposition i e terrigenous supply vs surface water productivity long chain unsaturated alkenones derived from prymnesiophytes and fatty acids derived from diatoms and dinoflagellates were analysed by means of gas chromatography and mass spectrometry first results on the distribution of these biomarkers in surface sediments indicate that the surface water productivity signal is well preserved in the sediment data this is shown by the distribution of the 16 1 n 7 and 20 5 n 3 fatty acids indicative for diatoms and the excellent correlation with the chlorophyll a concentrations in the surface water masses and the biogenic opal content and increased hydrogen indices of the sediments the high concentration of these unsaturated fatty acids in shallow water sediments shows the recent deposition of the organic material in deep sea sediments on the other hand the concentrations are low this decreased content is typical for phytoplankton material which has been degraded by microorganisms or autoxidation in general the alkenone concentrations are very low suggesting low production rates by prymnesiophytes only at one station from the lower continental margin influenced by the inflow of atlantic water masses were some higher amounts of alkenones determined long chain n alkanes as well as high c n ratios and low hydrogen indices indicate the importance of fluvial supply of terrigenous organic matter

sediments in arctic sea ice implications for entrainment transport and release despite the arctic sea ice cover s recognized sensitivity to environmental change the role of sediment inclusions in lowering ice albedo and affecting ice ablation is poorly understood sea ice sediment inclusions were studied in the central arctic ocean during the arctic 91 expedition and in the laptev sea east siberian arctic region expedition 1992 results from these investigations are here combined with previous studies performed in major areas of ice ablation and the southern central arctic ocean this study documents the regional distribution and composition of particle laden ice investigates and evaluates processes by which sediment is incorporated into the ice cover and identifies transport paths and probable depositional centers for the released sediment in april 1992 sea ice in the laptev sea was relatively clean the sediment occasionally observed was distributed diffusely over the entire ice column forming turbid ice observations indicate that frazil and anchor ice formation occurring in a large coastal polynya provide a main mechanism for sediment entrainment in the central arctic ocean sediments are concentrated in layers within or at the surface of ice floes due to melting and refreezing processes the surface sediment accumulation in central arctic multi year sea ice exceeds by far the amounts observed in first year ice from the laptev sea in april 1992 sea ice sediments are generally fine grained although coarse sediments and stones up to 5 cm in diameter are observed component analysis indicates that quartz and clay minerals are the main terrigenous sediment particles the biogenous components namely shells of pelecypods and benthic foraminiferal tests point to a shallow benthic marine source area apparently sediment inclusions were resuspended from shelf areas before and incorporated into the sea ice by suspension freezing clay mineralogy of ice rafted sediments provides information on potential source areas a smectite maximum in sea ice sediment samples repeatedly occurred between 81 n and 83 n along the arctic 91 transect indicating a rather stable and narrow smectite rich ice drift stream of the transpolar drift the smectite concentrations are comparable to those found in both laptev sea shelf sediments and anchor ice sediments pointing to this sea as a potential source area for sea ice sediments in the central arctic ocean sea ice clay mineralogy is significantly different from deep sea clay mineral distribution patterns the contribution of sea ice sediments to the deep sea is apparently diluted by sedimentary material provided by other transport mechanisms

freshwater and atlantic water inflows to the deep northern barents and kara seas since ca 13 14 c ka foraminifera and stable isotopes foraminiferal stable isotopes and assemblages from franz victoria and st anna troughs provide a valuable record of freshwater and atlantic water flows to the northern barents and kara seas from deglaciation to present the d 18 o and d 13 c of planktonic neogloboquadrina pachyderma s and benthic elphidium excavatum were up to1 4 lower than present at ca 13 11 5 and 10 14 c ka global sea level corrected mostly reflecting substantial freshwater inputs coincident with glacial marine sediment deposition cassidulina teretis exceeded 40 of benthic foraminifera ca 13 and 10 14 c ka indicating subsurface penetrations of atlantic water the transition to postglacial marine conditions is marked by a 1 rise in foraminiferal d 18 o and a sharp fall in c teretis soon after 10 14 c ka these changes imply reduced inputs of freshwater and atlantic water subsequent isotopic and foraminiferal assemblage variations reflect changing atlantic water conditions upstream in the nordic seas and shifts between the warm fram strait and cold barents sea branches of atlantic water we hypothesize that glacial isostatically induced deepening by up to 150 m influenced atlantic water inflows to the northern barents sea during deglaciation and the holocene thus effects of isostatic recovery have to be factored into paleoceanographic reconstructions 2001 elsevier science ltd all rights reserved

biomarker distributions in surface sediments from the kara and laptev seas arctic ocean indicators for organic carbon sources and sea ice coverage studies of spatial and temporal changes in modern and past sea ice occurrence may help to understand the processes controlling the recent decrease in arctic sea ice cover here we determined concentrations of ip25 a novel biomarker proxy for sea ice developed in recent years phytoplankton derived biomarkers brassicasterol and dinosterol and terrigenous biomarkers campesterol and sitosterol in the surface sediments from the kara and laptev seas to estimate modern spatial seasonal sea ice variability and organic matter sources c25 hbi dienes and trienes were determined as additional palaeoenvironmental proxies in the study area furthermore a combined phytoplankton ip25 biomarker approach pip25 index is used to reconstruct the modern sea ice distribution more quantitatively the terrigenous biomarkers reach maximum concentrations in the coastal zones and estuaries reflecting the huge discharge by the major rivers ob yenisei and lena maxima in phytoplankton biomarkers indicating increased primary productivity were found in the seasonally ice free central part of the kara and laptev seas neither ip25 nor pip25 however shows a clear and simple correlation with satellite sea ice distribution in our study area due to the complex environmental conditions in our study area and the transportation process of sea ice diatom in the water column differences in the diene ip25 and triene ip25 ratios point to different sources of these hbis and different environmental conditions the diene ip25 ratio seems to correlate positively with sea surface temperature while negatively with salinity distributions

modern dirty sea ice characteristics and sources the role of anchor ice extensive dirty ice patches with up to 7 kg m 2 sediment concentrations in layers of up to 10 cm thickness were encountered in 2005 and 2007 in numerous areas across the central arctic the fe grai

comparison of oxygen isotope records from the gisp2 and grip greenland ice cores recent results1 2 from the greenland ice core project grip summit ice core suggest that the climate in greenland has been remarkably stable during the holocene but was extremely unstable for the time period represented by the rest of the core spanning the last two glaciations and the intervening eemian inter glacial here we present the complete oxygen isotope record for the greenland ice sheet project 2 gisp2 core drilled 28 km west of the grip core we observe large rapid climate fluctuations throughout the last glacial period which closely match those reported for the grip core however in the bottom 10 of the cores spanning the eemian interglacial and the previous glacia tion there are significant differences between the two records it is possible that ice flow may have altered the chronological sequences of the stratigraphy for the bottom part of one or both of the cores considerable further work will be necessary to evaluate the likelihood of this and the extent to which it will still be possible to extract meaningful climate information from the lowest sections of the cores

postglacial to holocene history of the laptev sea continental margin palaeoenvironmental implications of benthic assemblages abstract bivalves ostracods and foraminifers were studied in four ams 14 c dated sediment cores from the laptev sea one from the upper continental slope with a date of 15 8 cal ka in its basal part and three from river palaeovalleys on the outer middle shelf aging back to 12 7 11 2 cal ka at the continental margin high relative proportions of cassidulina neoteretis planktic foraminifers and ostracods with north atlantic affinities provide evidence on past inflows of atlantic derived waters whereas freshwater inputs downslope sediment movements and ice rafting are documented by the presence of euryhaline brackish water and freshwater ostracods and low planktic benthic ratio atlantic derived subsurface waters reached the studied site by ca 16 cal ka i e prior to the establishment of the pathway across the barents sea shelf further west the strongest atlantic influence occurred prior to 12 cal ka and after 3 cal ka a cold low nutrient marine environment with a coastal polynya setting is reconstructed for the time 16 14 cal ka whereas between 12 7 and 11 2 cal ka freshwater influence reached its maximum during a time when the outer shelf was flooded and brackish water assemblages inhabited the estuarine parts of palaeovalleys following the temporal and spatial pattern of sea level rise these fluvially affected assemblages rapidly transformed into shallow marine faunas after ca 3 5 3 cal ka well pronounced changes in the benthic communities indicate a general climate cooling characterized by a more intensified surface and bottom water circulation regime

concentration of platinum group elements by magmatic fluids in layered intrusions evidence leading to a model which supports the formation of pt pd reefs in a layered intrusion by the action of magmatic fluids is presented as well as some of the constraints imposed on such a model the stillwater complex is used as an example of this model within the stillwater complex no laterally continuous sulfide enriched cumulates occur above the lowermost parts of the ultramafic series until one reaches the platiniferous j m reef this sulfide poor stratigraphic interval beneath the j m reef is characterized by unusually cl rich apatite although reported sulfide modes and whole rock sulfur contents in the cumulates below the j m reef are approximately an order of magnitude lower than that expected for a sulfide saturated magma sulfide saturation prior to the formation of the j m reef is suggested by relatively high pd and pt concentrations reported in the cumulates below the j m reef as well as by the presence of sulfide as inclusions in silicate and oxide cumulus minerals hence it is suggested that the footwall cumulates to the j m reef were originally sulfide saturated but later lost sulfur to a fluid phase exsolving from inter cumulus liquid sporadic sulfide bearing pegmatoids in some of these rocks are additional evidence for late loss of sulfur these observations as well as the association of the j m reef at the first significant stratigraphic break in the cl cl f ratio of apatite and the relatively high solubility of pt and pd as aqueous cl complexes are consistent with the formation of the j m reef by exsolution of cl and volatile rich fluids from footwall intercumulus liquids which leached and transported ore components both the pge and s upward to the level of the reef using published whole rock platinum group element pge concentrations for the ultramafic and lower banded series the cumulates below the j m reef must have been enriched by a factor of at most 1 24 for pt and 1 75 for pd if these rocks were to be the source for the metals in the j m reef model raleigh fractionation calculations suggest that the cumulates beneath the j m reef could have had the required metal concentrations if during the crystallization of a parent magma containing no more than 15 ppb of either metal the average bulk solid liquid distribution coefficients for pt and pd were no more than 5 these values are consistent with assumption of sulfide saturation prior to the formation of the j m reef during solidification of intercumulus liquid the separation and loss of a cl rich fluid will deplete the residual assemblage of s and pge if 0 1 to 0 5 wt percent fluid containing 5 percent s evolved during solidification of the footwall cumulates the amount of fluid expected to be exsolved by the crystallization of approximately 2 to 10 percent fluid saturated intercumulus liquid the fluid liquid distribution coefficients for pt and pd would need to be almost as large as the sulfide liquid silicate liquid distribution coefficients to remove significant amounts of pt and pd much smaller distribution coefficients are needed if sulfide is completely lost to fluid during degassing the latter possibility is consistent with the low s contents of the footwall cumulates beneath the j m reef numerical models of the degassing of intercumulus liquids suggest that thick cumulus sequences can act as chromatographic columns to separate the pge and s during the degassing of intercumulus silicate liquids the pge being enriched at a sulfide dissolution front as upward migrating sulfide undersaturated fluids resorb cumulus sulfides zones of pge and s enrichment can occur where degassing fronts encounter stratigraphic physical chemical discontinuities such as changes in the fluid saturation temperature of the intercumulus silicate liquids

sea ice transport of riverine particles from the laptev sea to fram strait based on clay mineral studies the aim of this study was to identify pathways and processes of modern sediment transport from the siberian hinterland to the laptev sea and further to the arctic ocean clay mineral analyses were performed on riverine suspended particulate material spm surface sediments of the laptev sea shelf and sea ice sediments sis material collected during seven expeditions was included in this study clay mineral assemblages are used to decipher the distribution of riverine sediments on the shallow laptev sea shelf the entrainment of fine particles into newly forming ice and the transport of sis from the laptev sea towards the ablation areas a cluster analysis of our data set shows that the clay mineral assemblages of laptev sea shelf sediments and sis are controlled mainly by the input of riverine spm supplied by the khatanga lena and yana rivers whereas the western shelf clay mineral province is characterized by enhanced smectite concentrations supplied by the khatanga river the eastern laptev sea is dominated by illite discharged through the lena and yana rivers the sis smectite concentration serves as an indicator for sediment source areas on the circum arctic shelves subsequently the transpolar drift can be distinguished into a siberian branch fed from the eastern kara sea and the western laptev sea and a polar branch originating from the eastern laptev sea

the formation of pt ir alloys and cu pd rich sulfide melts by partial desulfurization of fe ni cu sulfides results of experiments and implications for natural systems abstract we propose a model of high temperature formation of platinum group element pge alloys from base metal sulfides subjected to decreasing sulfur fugacity f s 2 for this purpose we experimentally investigated the effect of partial desulfurization of monosulfide solid solution mss with variable ni and cu contents on the distribution behaviour of pt ir and pd at 1000 c we partially removed sulfur from the pge bearing mss using the tube in tube technique and pyrrhotite as an f s 2 buffer we found that mss undergoing s loss can produce 1 pt and ir exsolution from the mss matrix in the form of pge bearing alloys 2 partial melting of the cu ni bearing mss to form fe rich mss cu ni pd rich sulfide liquid and fe ir pt alloy both of these processes are geologically important the partial melting of the s depleted sulfides could explain the presence of two types of sulfides found in the mantle mss dominated sulfides and s poor sulfides consisting mainly of pentlandite and chalcopyrite we also suggest that the cu ni pd rich liquid formed by partial melting of the sulfides could migrate away from the mss and fe ir pt alloys thus spatially decoupling ir pt and cu pd as observed in reefs and mantle nodules in addition the formation of pge alloys in response to the desulfurization processes potentially could occur 1 after pressure falls during transport of the basalt magma with entrained sulfide droplets 2 after sulfur removal by s undersaturated melts or fluids from pge enriched sulfide proto ore 3 after degassing of the sulfide droplets occurring in a sub volcanic chamber and 4 as a result of sulfide interaction with chromite

primary cumulus platinum minerals in the monts de cristal complex gabon magmatic microenvironments inferred from high definition x ray fluorescence microscopy an unusual occurrence of pt enriched pyroxenites in the monts de cristal igneous complex is characterized by unusually high ratios of pt to other platinum group elements pges and very low cu and sulfide contents synchrotron x ray fluorescence microscopy was used to identify over a hundred discrete grains of platinum minerals and relate their occurrence to textural associations in the host heteradcumulate orthopyroxenites element associations backed up by fib sem and pixe probe observations indicate that most of the pt is associated with either as or trace cu ni rich sulfides or both some of the pt as grains can be identified as sperrylite and most are likely to be pt fe alloy the relative abundances and volumes of pt minerals to sulfide minerals are very large compared with typical magmatic sulfides almost all of the grains observed lie at or within a few tens of m of cumulus orthopyroxene grain boundaries and there is no significant difference between the populations of grains located inside or outside plagioclase oikocrysts these oikocrysts are inferred to have crystallized either at the cumulus stage or very shortly thereafter on the basis of their relationship to ti enrichment in the margins of pyroxene grains not enclosed in oikocrysts this relationship precludes a significant role of trapped intercumulus liquid in pt deposition or mobilization and also allows a confident inference that pt rich and pt as enriched phases precipitated directly from the magma at the cumulus stage these observations lead to the conclusion that fractionation of pt from other pges in this magmatic system is a consequence of a solubility limit for solid pt metal and or pt arsenide

environmental magnetism principles and applications 1 in environmental magnetism rock and mineral magnetic techniques are used to investigate the formation transportation deposition and postdepositional alterations of magnetic minerals under the influences of a wide range of environmental processes all materials respond in some way to an applied magnetic field and iron bearing minerals are sensitive to a range of environmental processes which makes magnetic measurements extremely useful for detecting signals associated with environmental processes environmental magnetism has grown considerably since the mid 1970s and now contributes to research in the geosciences and in branches of physics chemistry and biology and environmental science including research on climate change pollution iron biomineralization and depositional and diagenetic processes in sediments to name a few applications magnetic parameters are used to routinely scan sediments but interpretation is often difficult and requires understanding of the underlying physics and chemistry thorough examination of magnetic properties and of the environmental processes that give rise to the measured magnetic signal is needed to avoid ambiguities complexities and limitations to interpretations in this review we evaluate environmental magnetic parameters based on theory and empirical results we describe how ambiguities can be resolved by use of combined techniques and demonstrate the power of environmental magnetism in enabling quantitative environmental interpretations we also review recent developments that demonstrate the mutual benefit of environmental magnetism from close collaborations with biology chemistry and physics finally we discuss directions in which environmental magnetism is likely to develop in the future

freshwater chlorophycean algae in recent marine sediments of the beaufort laptev and kara seas arctic ocean as indicators of river runoff freshwater chlorophycean algae are characteristic organic walled microfossils in recent coastal and shelf sediments from the beaufort laptev and kara seas arctic ocean the persistent occurrence of the chlorophycean algae pediastrum spp and botryococcus cf braunii in marine palynomorph assemblages is related to the discharge of freshwater and suspended matter from the large siberian and north american rivers into the arctic shelf seas the distribution patterns of these algae in the marine environments reflect the predominant deposition of riverine sediments and organic matter along the salinity gradient from the outer estuaries and prodeltas to the shelf break sedimentary processes overprint the primary distribution of these algae resuspension of sediments by waves and bottom currents may transport sediments in the bottom nepheloid layer along the submarine channels to the shelf break bottom sediments and microfossils may be incorporated into sea ice during freeze up in autumn and winter leading to an export from the shelves into the deep sea the presence of these freshwater algae in sea ice and bottom sediments in the central arctic ocean confirm that transport in sea ice is an important process which leads to a redistribution of shallow water microfossils

post glacial variability of sea ice cover river run off and biological production in the western laptev sea arctic ocean a high resolution biomarker study abstract multi proxy biomarker measurements were applied on two sediment cores ps51 154 ps51 159 to reconstruct sea ice cover ip25 biological production brassicasterol dinosterol and river run off campesterol sitosterol in the western laptev sea over the last 17 ka with unprecedented temporal resolution the absence of ip25 from 17 2 to 15 5 ka in combination with minimum concentration of phytoplankton biomarkers suggests that the western laptev sea shelf was mostly covered with permanent sea ice very minor river run off and restricted biological production occurred during this cold interval from 16 ka until 7 5 ka a long term decrease of terrigenous riverine organic matter and a coeval increase of marine organic matter reflect the gradual establishment of fully marine conditions in the western laptev sea caused by the onset of the post glacial transgression intensified river run off and reduced sea ice cover characterized the time interval between 15 2 and 12 9 ka including the bolling allerod warm period 14 7 12 9 ka prominent peaks of the dip25 index coinciding with maximum abundances of subpolar foraminifers are interpreted as pulses of atlantic water inflow on the western laptev sea shelf after the warm period a sudden return to severe sea ice conditions with strongest ice coverage between 11 9 and 11 ka coincided with the younger dryas 12 9 11 6 ka at the onset of the younger dryas a distinct alteration of the ecosystem reflected in a distinct drop in terrigenous and phytoplankton biomarkers was detected during the last 7 ka the sea ice proxies reflect a cooling of the laptev sea spring summer season this cooling trend was superimposed by a short term variability in sea ice coverage probably representing bond cycles 1500 500 ka that are related to solar activity changes hence atmospheric circulation changes were apparently able to affect the sea ice conditions on the laptev sea shelf under modern sea level conditions

neoglacial change in deep water exchange and increase of sea ice transport through eastern fram strait evidence from radiogenic isotopes sediment core msm5 5 712 from the west spitsbergen continental margin has been investigated at high resolution for its seawater derived neodymium nd and lead pb isotope compositions stored in ferromanganese oxyhydroxide coatings of the sediment particles to reconstruct holocene changes in the sources and mixing of bottom waters passing the site the radiogenic isotope data are used in combination with a multitude of proxy indicators for the climatic and oceanographic development of the eastern fram strait during the past 8500 years to calibrate the downcore data seawater and core top samples from the area were analysed for their radiogenic isotope compositions core top leachates reveal relatively high more radiogenic nd isotope compositions between end 9 7 and 9 1 which are higher than present day seawater end in eastern fram strait 12 6 to 10 5 and indicate that the seawater values have only been established very recently the core top data agree well with the downcore signatures within the uppermost 40 cm of the sediment core end 9 1 to 8 8 indicating a reduced inflow of waters from the nordic seas concurrent with cool conditions and a south eastward shift of the marginal ice zone after ca 2 8 cal ka bp late holocene high sea ice abundances in eastern fram strait are coeval with the well known neoglacial trend in the northern north atlantic region in contrast warmer conditions of the late early to mid holocene were accompanied by lower less radiogenic end signatures of the bottom waters indicating an increased admixture from the nordic seas 10 6 to 10 1 a shift to significantly more radiogenic end signatures of the detrital material also occurred at 3 cal ka bp and was accompanied by a marked increase in supply of fine grained ice rafted material irf from the arctic ocean to the core site the most likely source areas for this radiogenic material are the shallow arctic shelves in particular the kara sea shelf the evolution of the pb isotope compositions of past seawater was dominated by local signatures characterized by high 208 207 206pb 204pb values during the warm early and mid holocene periods related to enhanced chemical weathering on svalbard and high glacial and riverine input derived from young granitic more radiogenic material to the west spitsbergen margin at 3 cal ka bp both detrital and seawater pb isotope data changed towards more kara sea like signatures

image analysis and composition of platinum group minerals in the j m reef stillwater complex detailed imaging bulk geochemical analyses and laser ablation icp ms analyses were conducted on mineralized samples from the platinum group element pge bearing j m reef stillwater complex montana the aims of the study were to determine which phases are the main hosts of the pge to examine the textural relationships of the pge bearing minerals and the associated base metal sulfides silicates and secondary magnetites the platinum group minerals pgm observed in the studied samples consist of pd or pt sulfides pt fe alloy isoferroplatinum pd or pt tellurides and pd cu alloy skaergaardite with minor native pd ru ir os s sub 2 laurite and au pd ag alloy palladian electrum these minerals account for all the pt half the pd ru and ir and a smaller proportion of the os in whole rocks the balance being found in the base metal sulfide most of these pgm are closely associated with base metal sulfides either included in the base metal sulfide or located at the contact between the base metal sulfide and the silicate or oxide minerals the textures of the pgm within and at the margins of the base metal sulfide suggest that they exsolved from the sulfides we suggest that the pge ni cu and te partitioned into a magmatic sulfide liquid that crystallized into base metal sulfide the pt fe alloys and some of the pd sulfides exsolved from the base metal sulfide during desulfurization at fairly high temperatures in contrast the skaergaardite and some pd sulfides are found in association with secondary magnetite and probably formed at relatively low temperatures approximately 250 degrees 465 degrees c during a second fluid migration event the pd pt ratio of the reef approximately 3 3 is higher than most mafic magmas and the pd pt ratio of the footwall is lower 0 3 0 7 it is possible that some of the pd in the reef was leached from the underlying rocks and deposited in the reef as pgm associated with secondary magnetite

late pleistocene changes in terrestrial biomarkers in sediments from the central arctic ocean abstract biomarkers in late pleistocene sediments collected from the integrated ocean drilling program iodp arctic coring expedition acex hole m0004c central arctic ocean were investigated the major biomarkers are long chain n alkanes n fatty acids and n alkan 1 ols indicating fresh organic matter om derived predominantly from higher plants the dominance of terrestrial biomarkers is attributed to severe om degradation caused by slow sedimentation in oxygen rich benthic water and or low primary production due to permanent sea ice coverage hopanes representing thermally altered om tend to be abundant in samples with abundant ice rafted debris ird an om rich dark grey layer deposited during marine isotope stage mis 6 contains a significant amount of branched glycerol dialkyl glycerol tetraethers branched gdgts suggesting ice erosion of organic rich continental soil followed by transportation to the central arctic by drifting ice the labile refractory index i e the abundance ratio of long chain n alkan 1 ols to the sum of long chain n alkanes and long chain n alkan 1 ols decreases above the dark grey layer indicating that the om became more refractory this change suggests that coverage of the source region by om rich soil decreased because of extensive glacial erosion during mis 6

platinum ore in three dimensions insights from high resolution x ray computed tomography platinum group elements referred to as pge comprising pt pd rh ru ir and os are strategic metals with a wide variety of industrial applications most of the world s pge production is mined from large mafic ultramafic intrusions such as the bushveld complex in south africa which currently provides 75 of the world s pt production the pge mineralization is found within distinctive layers tens to hundred of centimeters thick but extending laterally for many tens of kilometers where the pge occur at low parts per million levels as platinum group minerals pgm and in solid solution within disseminated base metal sulfides there is still heated debate at the most fundamental level about the mode of formation of this class of deposit genetic models range from primary magmatic sulfide collection to concentration by migrating halogen rich fluids a crucial line of evidence is the spatial relationship between the pgm which are the most important pge bearing phases and the base metal sulfide aggregates or blebs so far all observations have been carried out using two dimensional mineralogical studies where textural relationships with other minerals are ambiguous and with statistical limitations owing to sampling of trace phases intersecting random surfaces we present the first detailed three dimensional in situ analysis of the pgm at the sample scale using high resolution x ray computed tomography coupled with conventional microscopic and mineralogical study we find a striking and highly consistent relationship of pgm grains with the edges of complex shaped magmatic sulfide blebs and the intersection of these blebs with chromite silicate grain boundaries these new three dimensional observations strongly support an orthomagmatic model coupled with nucleation and growth of pgm at the margins of sulfide liquid droplets

morphology and microstructure of chromite crystals in chromitites from the merensky reef bushveld complex south africa the merensky reef of the bushveld complex consists of two chromitite layers separated by coarse grained melanorite microstructural analysis of the chromitite layers using electron backscatter diffraction analysis ebsd high resolution x ray microtomography and crystal size distribution analyses distinguished two populations of chromite crystals fine grained idiomorphic and large silicate inclusion bearing crystals the lower chromitite layer contains both populations whereas the upper contains only fine idiomorphic grains most of the inclusion bearing chromites have characteristic amoeboidal shapes that have been previously explained as products of sintering of pre existing smaller idiomorphic crystals two possible mechanisms have been proposed for sintering of chromite crystals 1 amalgamation of a cluster of grains with the same original crystallographic orientation and 2 sintering of randomly orientated crystals followed by annealing into a single grain the ebsd data show no evidence for clusters of similarly oriented grains among the idiomorphic population nor for earlier presence of idiomorphic subgrains spatially related to inclusions and therefore are evidence against both of the proposed sintering mechanisms electron backscatter diffraction analysis maps show deformation related misorientations and curved subgrain boundaries within the large amoeboidal crystals and absence of such features in the fine grained population microstructures observed in the lower chromitite layer are interpreted as the result of deformation during compaction of the orthocumulate layers and constitute evidence for the formation of the amoeboid morphologies at an early stage of consolidation an alternative model is proposed whereby silicate inclusions are incorporated during maturation and recrystallisation of initially dendritic chromite crystals formed as a result of supercooling during emplacement of the lower chromite layer against cooler anorthosite during the magma influx that formed the merensky reef the upper chromite layer formed from a subsequent magma influx and hence lacked a mechanism to form dendritic chromite this accounts for the difference between the two layers

variability of river discharge and atlantic water inflow at the laptev sea continental margin during the past 15 000 years implications from maceral and biomarker records in order to reconstruct the depositional environment from the laptev sea continental slope and shelf during the past 15 000 years bp maceral analysis was carried out on two sediment cores ps2458 4 ps2725 5 and compared with organic geochemical parameters during the transition from the last glacial to the holocene the environment of the laptev sea shelf was controlled by the post glacial sea level rise variations in river discharge surface water productivity and atlantic water inflow along the eurasian continental margin based on our results we identify the following significant changes of the environment a at approximately 13 500 years bp the first step of deglaciation termination 1a is documented by the deposition of marine and fresh water organic matter b at approximately 10 400 years bp the first post glacial influence of atlantic water inflow along the eastern laptev sea continental margin is indicated by an increase in marine organic matter c at the beginning of the holocene an increased fluvial supply is documented by an increase in fresh water alginite and d since 9500 8000 years bp modern marine conditions are established at the laptev sea continental margin as documented in increased amounts of marine macerals biomarkers dinosterol brassicasterol short chain fatty acids and dinoflagellate cysts

regional trends in the platinum group mineralogy of the critical zone of the bushveld complex south africa a wealth of quantitative data on the types volume distribution and mode of occurrence of the platinum group minerals residing in the merensky reef the ug 2 chromitite layer and platreef has been obtained over a twelve year period with the result that general platinum group mineral types for unexplored areas can perhaps now be predicted the platinum group minerals of the ug 2 and overlying merensky layers although locally different in composition mode of occurrence and size show close ties when viewed on a regional scale especially with regard to their pt pd sulfide and pt fe alloy contents thus if in one particular area the merensky reef contains pt pd sulfides as the predominant platinum group minerals then it can be safely inferred that pt pd sulfides will be a significant component of the ug 2 layer in that area the occurrence of pt fe alloy also follows this principle the distribution of pt fe alloy is in fact a major factor in differentiating the ores in the vicinity north and south of the pilansberg alkaline complex from those of the same layers farther along the arcuate strike northeastern and southeastern horns of the western bushveld and has led to an overall concept relating platinum group mineral types to postulated centers of increased volatile activity or perhaps feeder sites of the complex the mineralogy of reef disturbances such as potholes is discussed the mode of occurrence of the platinum group minerals varies between base metal sulfide silicate and chromite associations and the size of platinum group minerals in the various reefs is given solid solution or lattice substitutions of platinum group elements in the base metal sulfides account for the very important latent fraction of the total platinum group elements as distinct from platinum group minerals of the bushveld complex rhodium in the merensky reef occurs almost wholly in solid solution within pentlandite whereas rh minerals occur in the ug 2 layer chromite tends to host microscopic to submicroscopic inclusions of laurite and does not appear to take ru into the crystal lattice the probability of solid solution of platinum group elements in silicate and other oxide phases is discussed

the role of sea ice and other fresh water in the arctic circulation salinity stratification is critical to the vertical circulation of the high latitude ocean we here examine the control of the vertical circulation in the northern seas and the potential for altering it by considering the budgets and storage of fresh water in the arctic ocean and in the convective regions to the south we find that the present day greenland and iceland seas and probably also the labrador sea are rather delicately poised with respect to their ability to sustain convection small variations in the fresh water supplied to the convective gyres from the arctic ocean via the east greenland current can alter or stop the convection in what may be a modern analog to the halocline catastrophes proposed for the distant past the north atlantic salinity anomaly of the 1960s and 1970s is a recent example it must have had its origin in an increased fresh water discharge from the arctic ocean similarly the freshening and cooling of the deep north atlantic in recent years is a likely manifestation of the increased transfer of fresh water from the arctic ocean into the convective gyres finally we note that because of the temperature dependence of compressibility a slight salinity stratification in the convective gyres is required to efficiently ventilate the deep ocean

pge tenor and metal ratios within and below the merensky reef bushveld complex implications for its genesis the merensky reef is the consequence of several major influxes of magma into the bushveld magma chamber that gave rise to at least two cyclic units including the pre merensky and merensky cyclic units analysis of the s ni cu platinum group element pge and au contents of 1140 samples from 24 profiles through the rocks forming these units and two profiles extending downward from the reef to close to the ug 2 horizon of the western bushveld complex provide important petrogenetic constraints on the origin of the reef particular attention is paid to variations in the calculated pge tenors and cu pd ratios of sulfides both vertically and laterally all of the profiles show a decrease in pt tenor and concomitant increase in cu pd ratio upward across the pyroxenite of the merensky unit and laterally away from certain centres that are interpreted as feeder zones the data also document that more mafic horizons within the merensky to ug 2 interval of the southwestern bushveld are characterized by much lower cu pd 100 400 than the ambient ratio 4000 this is interpreted as demonstrating that these horizons are the consequence of incursions of magma whose composition has been modified in a staging chamber by reaction with sulfide resident there the favoured interpretation for the merensky reef is that the bushveld chamber s was occupied by a resident magma crystallizing orthopyroxene and plagioclase pre merensky and subsequently merensky magmas entered the chamber s intermittently from localized feeder structures mixing or mingling with the resident magma and giving rise to the more mafic cumulates at specific horizons including the merensky reef the mixing or mingling caused sulfide immiscibility in these cases as the new magma pulses flowed laterally away from the entry zones they deposited sulfide becoming depleted in pge on coming to rest the magma continued to segregate sulfide and crystallize pyroxene so that the sulfides became progressively depleted in pge and acquired a higher cu pd upward through the pyroxenite this model requires that the merensky magmas could dissolve up to two orders of magnitude more pge than current measurements on dry diopside anorthite melts have indicated it is suggested that very pge rich magmas can develop as a result of sulfide unsaturated magma reacting with early formed sulfide in a staging chamber dissolving fes and enriching the remaining sulfide in pge later magmas equilibrating with this enriched sulfide will themselves become highly enriched in pge

late weichselian deglacial history of the svyataya saint anna trough northern kara sea arctic russia abstract marine sediment core and seismic records from the svyataya saint anna trough provide new insight into the distribution of late weichselian glacial coverage ice retreat pattern and post glacial environments in the northern barents and kara seas these records indicate that the saint anna trough was filled with grounded glacier ice which likely reached the shelf edge during the late weichselian maximum several radiocarbon dates suggest early deglaciation of the deep axial part of the trough prior to 13 3 ka two sandy beds in the deglacial section of the cores imply distinct pulses of iceberg calving and or melting which were probably associated with stepwise retreat of the ice margin morainic ridges and glacial sole markings in the western part of the saint anna trough indicate that the northern central barents sea was a site of a large ice mass during deglaciation a smaller ice cap is inferred for the northern kara plateau at later stages ice retreat on the western flank of the trough was directed towards franz josef land and was presumably facilitated by a separation of the barents sea and novaya zemlya ice domes deglaciation of the saint anna trough was completed by ca 10 ka high post glacial sediment fluxes between 10 and 8 ka were probably related to sea floor coastal erosion and or siberian river discharge during the rising sea level

a 210pb sediment budget and granulometric record of sediment fluxes in a subarctic deltaic system the great whale river canada abstract to elucidate how modern river discharge conditions of the great whale river gwr are represented in the marine sedimentary record eight box and gravity cores were examined in terms of 210 pb and 137 cs radiochemistry granulometry and physical sedimentary structures these data were analyzed to provide insights into sedimentary processes and patterns at the study site sediment accumulation in the study area appears to be a relatively steady process over time scales of 50 100 yr allowing biological activity to overprint the primary depositional fabric subtle differences between 137 cs and 210 pb sediment accumulation rates sars suggest an offshore shift in the locus of fine sediment deposition during the past 150 yr which may be a result of ongoing climatic warming leading to decreasing sea ice coverage and a more energetic marine environment under present day conditions 23 40 000 t yr of the discharged sediment appear to accumulate in a 25 km 2 area off the river mouth the remaining 77 136 000 t yr are either deposited further offshore possibly along the northeastern shore as a result of hudson bay s counterclockwise circulation or dispersed into the hudson bay system grain diameter frequency analyses suggest that environmental processes controlling sediment transport and deposition vary over decadal time scales although we cannot define an exact cause for this pattern these shifts may be related to variations in river discharge wave climate possibly due to windier conditions or less sea ice dampening bioturbation or a combination of all this suggests that also longer term river discharge signals are preserved in the marine sedimentary record offshore the great whale river in summary no major change in sediment discharge over the past 150 yr was observed however the offshore shift in the locus of sediment deposition suggests that a warming climate will lead to more energetic marine conditions less sea ice coverage and an increased offshore transport of terrestrial matter

holocene cooling culminates in sea ice oscillations in fram strait a reconstruction of holocene sea ice conditions in the fram strait provides insight into the palaeoenvironmental and palaeoceanographic development of this climate sensitive area during the past 8500 years bp organic geochemical analyses of sediment cores from eastern and western fram strait enable the identification of variations in the ice coverage that can be linked to changes in the oceanic and atmospheric circulation system by means of the sea ice proxy ip25 phytoplankton derived biomarkers and ice rafted detritus ird increasing sea ice occurrences are traced along the western continental margin of spitsbergen throughout the holocene which supports previous palaeoenvironmental reconstructions that document a general cooling a further significant ice advance during the neoglacial is accompanied by distinct sea ice fluctuations which point to short term perturbations in either the atlantic water advection or arctic water outflow at this site at the continental shelf of east greenland the general holocene cooling however seems to be less pronounced and sea ice conditions remained rather stable here a major neoglacial increase in sea ice coverage did not occur before 1000 years bp phytoplankton ip25 indices pip25 index are used for more explicit sea ice estimates and display a mid holocene shift from a minor sea ice coverage to stable ice margin conditions in eastern fram strait while the inner east greenland shelf experienced less severe to marginal sea ice occurrences throughout the entire holocene highlights biomarker and ird data give insight into holocene sea ice conditions in fram strait we find increasing sea ice coverage off west spitsbergen throughout the holocene oceanic atmospheric variability caused neoglacial sea ice fluctuations ice conditions along east greenland shelf remain rather stable until 1000 years bp

fabric shape and the interpretation of sedimentary fabric data abstract the concept of fabric shape provides a powerful means of visualizing and analyzing data on sedimentary fabric the shape of a fabric is defined in terms of the ratios between eigenvalues s1 s2 and s3 derived using the orientation tensor method a continuum of all possible orthorhombic fabric shapes can be clearly represented on equilateral ternary diagrams originally developed for the presentation of particle shape data two indices are of particular value in scaling these diagrams fabric isotropy i s3 s1 and fabric elongation e 1 s2 s1 together these indices uniquely define the shape of any orthorhombic fabric and provide a rational and quantitative basis for reconstructing depositional and de ormational processes equilateral ternary diagrams provide a more versatile and powerful basis for analyzing fabric data than other eigenvalue diagrams now in use use of the diagrams in reconstructing processes of sediment transport and deposition is illustrated using fabric data from subglacial tills and a variety of slope deposits

surface water productivity and sediment transport by bering strait throughflow in the chukchi shelf the western arctic ocean during the holocene diverse paleoceanographic proxies from three sediment cores gc12ex jpc35 and jpc30 collected from the chukchi shelf north of the bering strait elucidate the holocene paleoceanographic changes surface water productivity and sediment transport caused by the bering strait throughflow from the bering sea into the chukchi sea lithology of three sediment cores identified the same three units based on comparison and correlation to adjacent age dated cores as well as ams 14c dates of core gc12ex the boundary between unit 1 and unit 2a is dated about 8500 cal yr bp and the boundary between unit 2a and unit 2b is also dated about 4500 cal yr bp consistent down core profiles of the geochemical and isotopic properties among the three cores differentiate the paleoceanographic conditions corresponding to lithologic units based on the biogenic opal total organic carbon and 13c values unit 1 is characterized by low surface water marine productivity under relatively shallow water with weak transport of b

glacial to postglacial transformation of organic input pathways in arctic ocean basins 1 the arctic ocean is undergoing rapid loss in ice cover with yet unknown consequences for the cycling of organic material here we examine persistent terrigenous land based alkane and polycyclic aromatic hydrocarbons with vascular plant combustion and petrogenic sources in seven cores collected from all major basins of the arctic ocean for insight as to how organic cycling at the last glacial maximum compares to the present day we find only modest changes between the glacial and postglacial sediments for atmospherically transported hydrocarbon biomarkers demonstrating that glacial sea ice was not a barrier to atmospheric inputs in stark contrast particle associated biomarkers were captured strongly at basin edges during the glacial period and much more evenly transported across basins during the postglacial period evidently the capture of organic matter shifted from the slopes to the shelves as the latter flooded during the holocene and the transpolar drift and beaufort gyre evolved from minor carriers of plant detritus from the glacial ocean margins to major modern transporters of shelf sediment to the basins this suggests that changes in organic transport currently accompanying the loss of sea ice are likely to be very different from those that occurred at the end of the last glacial period

the great salinity anomaly in the northern north atlantic 1968 1982 the widespread freshening of the upper 500 800m layer of the northern north atlantic which this paper describes represents one of the most persistent and extreme variations in global ocean climate yet observed in this century though a range of explanations have been advanced to explain this event including in situ changes in the surface moisture flux this paper describes the great salinity anomaly as largely though not entirely an advective event traceable around the atlantic subpolar gyre for over 14 years from its origins north of iceland in the mid to late 1960s until its return to the greenland sea in 1981 1982 the overall propagation speed around this subpolar gyre is estimated at about 3cm s 1 of the total salt deficit associated with the anomaly as it passed south along the labrador coast in 1971 1973 about 72 109 tonnes a deficit equivalent to about two thirds of this figure 47 109 tonnes ultimately passed through the faroe shetland channel to the barents sea arctic ocean and greenland sea during the mid 1970s possible effects on deep water formation and on the representativeness of historical section data are discussed

new constraints on the origin of the skaergaard intrusion cu pd au mineralization insights from high resolution x ray computed tomography abstract this contribution presents the first detailed three dimensional 3d in situ analysis of samples from the platinova reef using high resolution x ray computed tomography hrxct and 3d image processing and quantification coupled with microscopic and mineralogical investigations our hrxct analyses reveal the complex textural relationships between cu rich sulfides bulk composition close to bornite skaergaardite pdcu au rich phases silicates and fe ti oxides and provide unequivocal textural evidences not observed previously the association in 3d between cu rich sulfide globules pdcu alloy and ilmenite is inconsistent with a hydrothermal origin of the cu pd mineralization in contrast our results combined with phase diagrams strongly support a primary magmatic origin for the cu pd mineralization where cu and pd rich fe poor sulfide liquid represents a cumulus phase that forms by in situ nucleation these sulfide droplets and attached skaergaardite grains were trapped during the formation and crystallization of the fe ti oxides subsequent post cumulus processes led to the partial to total dissolution of the sulfide not entirely enclosed by the fe ti oxides i e not protected from reaction leading to the observed variability in cu and pd composition at the aggregate sulfide pdcu scale and to the occurrence of free pdcu alloys in contrast to the pdcu alloy gold bearing minerals are never observed entirely enclosed within the fe ti oxide two hypotheses can be envisaged for the formation of the gold enriched layer in the upper part of the section gold may have either precipitated from high temperature late magmatic cl rich fluids alternatively gold may have been enriched during fractional crystallization after sulfide had been suppressed from the liquidus after the pd layer crystallized and then deposited along redox barriers

pliocene palaeoceanography of the arctic ocean and subarctic seas the pliocene is important in the geological evolution of the high northern latitudes it marks the transition from restricted local to extensive regional scale glaciations on the circum arctic continents between 3 6 and 2 4 ma since the arctic ocean is an almost land locked basin tectonic activity and sea level fluctuations controlled the geometry of ocean gateways and continental drainage systems and exerted a major influence on the formation of continental ice sheets the distribution of river run off and the circulation and water mass characteristics in the arctic ocean the effect of a water mass exchange restricted to the bering and fram straits on the oceanography is unknown but modelling experiments suggest that this must have influenced the atlantic meridional overturning circulation cold conditions associated with perennial sea ice cover might have prevailed in the central arctic ocean throughout the pliocene whereas colder periods alternated with warmer seasonally ice free periods in the marginal areas the most pronounced oceanographic change occurred in the mid pliocene when the circulation through the bering strait reversed and low salinity waters increasingly flowed from the north pacific into the arctic ocean the excess freshwater supply might have facilitated sea ice formation and contributed to a decrease in the atlantic overturning circulation

fractional crystallization induced variations in sulfides from the noril sk talnakh mining district polar siberia russia abstract the distribution of platinum group elements pge within zoned magmatic ore bodies has been extensively studied and appears to be controlled by the partitioning behavior of the pge during fractional crystallization of magmatic sulfide liquids however other chalcophile elements especially tabs te as bi sb and sn have been neglected despite their critical role in forming platinum group minerals pgm tabs are volatile trace elements that are considered to be mobile so investigating their primary distribution may be challenging in magmatic ore bodies that have been somewhat altered magmatic sulfide ore bodies from the noril sk talnakh mining district polar siberia russia offer an exceptional opportunity to investigate the behavior of tabs during fractional crystallization of sulfide liquids and pgm formation as the primary features of the ore bodies have been relatively well preserved in this study new petrographic 2d and 3d and whole rock geochemical data from cu poor to cu rich sulfide ores of the noril sk talnakh mining district are integrated with published data to consider the role of fractional crystallization in generating mineralogical and geochemical variations across the different ore types disseminated to massive despite textural variations in cu rich massive sulfides lenses veins and breccias these sulfides have similar chemical compositions which suggests that cu rich veins and breccias formed from fractionated sulfide liquids that were injected into the surrounding rocks numerical modeling using the median disseminated sulfide composition as the initial sulfide liquid composition and recent dmss liq and diss liq predicts the compositional variations observed in the massive sulfides especially in terms of pt pd and tabs therefore distribution of these elements in the massive sulfides was likely controlled by their partitioning behavior during sulfide liquid fractional crystallization prior to pgm formation our observations indicate that in the cu poor massive sulfides the pgm formed as the result of exsolution from sulfide minerals whereas in the cu rich massive sulfides the pgm formed by crystallization from late stage fractionated sulfide liquids we suggest that the significant amount of sn bearing pgm may be related to crustal contamination from granodiorite whereas as bi te and sb were likely added to the magma along with s from sedimentary rocks large pgm that are scarce and randomly distributed may account for most of the whole rock pt budget based on our results we propose a holistic genetic model for the formation of the magmatic sulfide ore bodies of the noril sk talnakh mining district

platinum group elements in sulphide minerals platinum group minerals and whole rocks of the merensky reef bushveld complex south africa implications for the formation of the reef the concentrations of platinum group elements pge co re au and ag have been determined in the base metal sulphide bms of a section of the merensky reef in addition we performed detailed image analysis of the platinum group minerals pgm the aims of the study were to establish 1 whether the bms are the principal host of these elements 2 whether individual elements preferentially partition into a specific bms 3 whether the concentration of the elements varies with stratigraphy or lithology 4 what is the proportion of pge hosted by pgm 5 whether the pgm and the pge found in bms could account for the complete pge budget of the whole rocks in all lithologies most of the pge 65 up to 85 are hosted by pgm essentially pt fe alloy pt pd sulphide pt pd bismuthotelluride lesser amounts of pge occur in solid solution within the bms in most cases the pgm occur at the contact between the bms and silicates or oxides or are included within the bms pentlandite is the principal bms host of all of the pge except pt and contains up to 600 ppm combined pge it is preferentially enriched in pd rh and co pyrrhotite contains rh os ir and ru but excludes both pt and pd chalcopyrite contains very little of the pge but does concentrate ag and cd platinum and au do not partition into any of the bms instead they occur in the form of pgm and electrum in the chromitite layers the whole rock concentrations of all the pge except pd are enriched by a factor of five relative to s ni cu and au this enrichment could be attributed to bms in these layers being richer in pge than the bms in the silicate layers however the pge content in the bms varies only slightly as a function of the stratigraphy the bms in the chromitites contain twice as much pge as the bms in the silicate rocks but this is not sufficient to explain the strong enrichment of pge in the chromitites in the light of our results we propose that the collection of the pge occurred in two steps in the chromitites some pgm formed before sulphide saturation during chromitite layer formation the remaining pge were collected by an immiscible sulphide liquid that percolated downward until it encountered the chromitite layers in the silicate rocks pge were collected by only the sulphide liquid

methane release from pingo like features across the south kara sea shelf an area of thawing offshore permafrost the holocene marine transgression starting at 19 ka flooded the arctic shelves driving extensive thawing of terrestrial permafrost it thereby promoted methanogenesis within sediments the dissociation of gas hydrates and the release of formerly trapped gas with the accumulation in pressure of released methane eventually triggering blowouts through weakened zones in the overlying and thinned permafrost here we present a range of geophysical and chemical scenarios for the formation of pingo like formations plfs leading to potential blowouts specifically we report on methane anomalies from the south kara sea shelf focusing on two plfs imaged from high resolution seismic records a variety of geochemical methods are applied to study concentrations and types of gas its character and genesis plf 1 demonstrates ubiquitously low methane concentrations 14 2 55 3 ppm that are likely due to partly unfrozen sediments with an ice saturated internal core reaching close to the seafloor in contrast plf 2 reveals anomalously high methane concentrations of 120 000 ppm where frozen sediments are completely absent the methane in all recovered samples is of microbial and not of thermogenic origin from deep hydrocarbon sources however the relatively low organic matter content 0 52 1 69 of seafloor sediments restricts extensive in situ methane production as a consequence we hypothesize that the high methane concentrations at plf 2 are due to microbial methane production and migration from a deeper source

facies system of the eastern barents sea since the last glaciation to present abstract twenty two sediment cores raised from the central and eastern parts of the barents sea have been studied to reconstruct the evolution of the facies system since the late weichselian glaciation multiproxy records reveal four lithostratigraphic units which reflect major development stages of paleoenvironments age control is provided by 23 ams 14 c dates for holocene sections of four cores continental moraine deposits of the last glaciation are overlain by proximal glaciomarine facies of the initial deglaciation phase during this phase the barents sea ice sheet detached from the ground resulting in seawater penetration into troughs iceberg calving deposition of ird and fine grained glacier meltwater load in newly formed marine basins the main deglaciation phase is characterized by pulsed sedimentation from various gravity flows resulting in accumulation of distal glaciomarine facies comprising laminated clay and sand sequences with minor ird redistribution of fine grained suspended matter by bottom currents and brine induced nepheloid flows combined with biogenic processes and minor ice rafting caused facies diversity of the holocene marine sediments the holocene facies of shelf depressions reflect rather high but variable productivity responding to climate changes and variations of atlantic water inflow into the barents sea

branched glycerol dialkyl glycerol tetraethers and crenarchaeol record post glacial sea level rise and shift in source of terrigenous brgdgts in the kara sea arctic ocean this study evaluates the glycerol dialkyl glycerol tetraether gdgt distribution and provenance in sediments spanning a minimum of 13 3 ka from the st anna trough northern kara sea the site has experienced extensive fluctuation in the delivery of river derived organic matter om caused by a eustatic change in sea level this is in line with the record of the concentration of the isoprenoid gdgt crenarchaeol produced by marine thaumarchaota which was low at the bottom of the core increasing gradually in the most shallow unit the concentration of branched br gdgts showed an opposite trend and a marked shift in distribution the deepest sediments 10 ka with a distribution currently encountered in surface sediments in front of the yenisei river are characterized by terrigenous brgdgts whereas the distribution in the shallowest unit 10 ka is strongly influenced by marine in situ brgdgts during the shift from terrigenous to marine sourced brgdgts there was one horizon where a pronounced shift in the brgdgt distribution was observed and the brgdgt concentration significantly decreased as the brgdgts delivered to the current kara sea system are derived from several sources we postulate that a temporary change in the relative importance of the brgdgt sources happened during this interval both in situ production and changing brgdgt provenance have implications for paleoclimate reconstruction using brgdgts in situ production of marine brgdgts results in a higher reconstructed ph however these in situ produced brgdgts did not influence the reconstructed mean annual air temperature mat when the matmrs calibration was used changes in the relative contribution of brgdgt sub pools were shown however to influence both soil ph reconstruction and mat reconstruction

noble metal enrichment processes in the merensky reef bushveld complex we have analysed sulphides silicates and chromites of the merensky introduction reef for platinum group elements pges re and au using laser the enrichment of noble metals in layered gabbroic ablation inductively coupled plasma mass spectrometry and synthetic intrusions to form stratiform merensky type ore horizons pyrrhotite standards annealed with known quantities of noble metals is an extremely efficient yet poorly understood process os ir and ru reside in solid solution in pyrrhotite and pentlandite metal enrichment must be related to the formation of rh and part of the reef s pd in pentlandite whereas pt au re magmatic layering as the ore horizons form an integral and some pd form discrete phases olivine and chromite often part of the magmatic stratigraphies of their host insuspected to carry os ir and ru are pge free all phases analysed trusions metal concentration is also related to the prescontain noble metals as discrete micro inclusions with diameters ence of magmatic sulphides because the noble metals are either dissolved in base metal sulphides or occur as typically 100 nm inclusions in sulphides commonly have the discrete noble mineral phases intergrown with sulphides element combinations os ir pt and pt pd au inclusions in vermaak hendriks 1976 ballhaus ryan 1995 olivine and chromite are dominated by pt au pd few inclusion ballhaus ulmer 1995 spectra can be related to discrete noble metal phases and few there is considerable controversy as to where the inclusions have formed by sub solidus exsolution rather some metals came from and how metal enrichment worked pge inclusions notably those in olivine and chromite are earlyfor a stratiform platinum group element pge deposit magmatic nuggets trapped when their host phases crystallized we inside the magmatic stratigraphy of a layered intrusion suggest that the silicate melt layer that preceded the merensky reef there are two possibilities either the metals were derived was pge oversaturated at early cumulus times experiments from the melt column above the ore horizon or they came combined with available sulphide silicate partition coefficients sugfrom the magma equivalent to the cumulate package gest that a silicate melt in equilibrium with a sulphide melt underlying the ore owing to the large density contrast containing the pge spectrum of the merensky ore would indeed be between silicate and sulphide melt a popular view is that oversaturated with respect to the least soluble noble metals sulphide the metals were enriched by gravitational settling of melt apparently played little role in enriching the noble metals in sulphide melt i e out of the magma column above the the merensky reef rather its role was to immobilize a pre existing ore campbell et al 1983 barnes naldrett 1985 in situ stratiform pge anomaly in the liquid stratified magma naldrett et al 1987 on the other hand it is well chamber established that gravitational crystal settling plays little role in producing magmatic layering and magmatic stratigraphies mcbirney noyes 1979 morse 1986 campbell 1987 and this cannot remain without consequence for stratiform noble metal deposits a third alternative is noble metal enrichment by late

holocene variations in mineral and grain size composition along the east greenland glaciated margin ca 67 70 n local versus long distance sediment transport quantitative x ray diffraction qxrd analysis of the 2 mm sediment fraction from surface sea floor samples and marine sediment cores that span the last 10 12 cal ka bp are used to describe spatial and temporal variations in non clay mineral compositions for an area between kangerlussuaq trough and scoresby sund 67 70 n east greenland bedrock consists primarily of an early tertiary alkaline complex with high weight of pyroxene and plagioclase farther inland and to the north the bedrock is dominantly felsic with a high fraction of quartz and potassium feldspars principal component pc analysis of the non clay sediment compositions indicates the importance of quartz and pyroxene as compositional end members with an abrupt shift from quartz and k feldspar dominated sediments north of scoresby sund to sediments rich in pyroxene and plagioclase feldspars offshore from the early tertiary basaltic outcrop coarse 2 mm or 1 mm ice rafted sediments are largely absent from the trough sediments between 8 and 5 cal ka bp but then increase in the last 4 cal ka bp compositional unmixing of the sediments in grivel basin and kangerlussuaq trough indicate the dominance of local over long distance sediment sources with pulses of sediment from tidewater glaciers in kangerlussuaq and nansen fjords reaching the inner shelf during the neoglaciation the change in ird is more dramatic in the sediment grain size proxies than in the quartz wt forty to seventy percent of the variance in the quartz records from either side of denmark strait is explained by low frequency trends but the data from the grivel basin east greenland are distinctly different with an approximate 2500 yr periodicity

composition and flux of holocene sediments on the eastern laptev sea shelf arctic siberia a 467 cm long core from the inner shelf of the eastern laptev sea provides a depositional history since 9400 cal yr b p the history involves temporal changes in the fluvial runoff as well as postglacial sea level rise and southward retreat of the coastline although the core contains marine fossils back to 8900 cal yr b p abundant pf ant debris in a sandy facies low in the core shows that a river influenced the study site until similar to 8100 cal yr b p as sea level rose and the distance to the coast increased this riverine influence diminished gradually and the sediment type changed by 7400 cal yr b p from sandy silt to clayey silt although total sediment input decreased in a step like fashion from 7600 to 4000 cal yr b p this interval had the highest average sedimentation rates and the greatest fluxes in most sedimentary components while this maximum probably resulted from middle holocene climate warming the low input of sand to the site after 7400 cal yr b p probably resulted from further southward retreat of the coastline and river mouth since about 4000 cat yr b p total sediment flux has remained rather constant in this part of the laptev sea shelf due to a gradual stabilization of the depositional regime after completion of the holocene sea level rise

organic matter deposition along the kara and laptev seas continental margin eastern arctic ocean during last deglaciation and holocene evidence from organic geochemical and petrographical data abstract organic petrologic maceral analysis and bulk organic geochemical studies were performed on five sediment cores from the eurasian continental margin to reconstruct the environmental changes during the last 13 000 yr the core stratigraphy is based on ams 14c dating and correlation by magnetic susceptibility and lithostratigraphic characteristics variations in terrigenous freshwater and marine organic matter deposition document paleoceanographic and paleoclimatic changes during the transition from the last deglaciation to the holocene glacigenic diamictons deposited in the st anna trough northern kara sea during the last glacial maximum lgm are characterized by reworked terrigenous organic matter in contrast the laptev sea shelf was not covered by an ice sheet but was exposed by the lowered sea level increased deposition of marine organic matter mom during deglaciation indicates enhanced surface water productivity possibly related to influence of atlantic waters the occurrence of freshwater alginite gives evidence for river discharge to the kara and laptev seas after the lgm at the eastern laptev sea slope the first influence of atlantic water masses is indicated by an increase in the contents of mom and dinoflagellate cysts with operculodinium centrocarpum prior to 10 000 yr bp high sedimentation rates in the kara and the laptev seas with the adjacent slope at the beginning of the holocene are presumably related to increased freshwater and sediment discharge from the siberian rivers evidence for elevated holocene freshwater discharge to the laptev sea has been found between 9 8 and 9 kyr bp at 5 kyr bp and at 2 5 kyr bp in the kara sea an increased freshwater signal is obvious at 8 5 kyr bp and at 5 kyr bp higher portions of mom were accumulated in the st anna trough and at the eurasian continental margin at several intervals during the holocene increased primary productivity during these intervals is explained by seasonally ice free conditions possibly associated with increased inflow of atlantic waters

distribution patterns of diatom surface sediment assemblages in the laptev sea arctic ocean abstract the modern diatom distribution in the laptev sea arctic ocean was investigated in 89 surface sediment samples diatom concentrations are relatively low showing values between 0 01 10 6 and 6 7 10 6 valves per gram dry sediment based on a factor analysis using seventeen taxa or taxa groups five diatom surface sediment assemblages can be defined the ice diatom assemblage of the central region of the laptev sea the chaetoceros assemblage of the eastern and southeastern shelf the thalassiosira antarctica assemblage of the continental slope and deep sea the freshwater diatom assemblage in the vicinity of river mouths and deltas and the thalassiosira nordenskioeldii assemblage which shows a patchy occurrence on the central laptev sea shelf the distribution pattern of diatom assemblages in surface sediment is significantly related to oceanographic conditions of surface water masses the main factors controlling the distribution of diatoms in the laptev sea are the riverine freshwater input during the summer which strongly affects the salinity conditions and the sea ice extent furthermore the composition of the thalassiosira antarctica assemblage of the continental slope is largely influenced by dissolution and lateral transport processes

the arctic oscillation signature in the wintertime geopotential height and temperature fields the leading empirical orthogonal function of the wintertime sea level pressure field is more strongly coupled to surface air temperature fluctuations over the eurasian continent than the north atlantic oscillation nao it resembles the nao in many respects but its primary center of action covers more of the arctic giving it a more zonally symmetric appearance coupled to strong fluctuations at the 50 hpa level on the intraseasonal interannual and interdecadal time scales this arctic oscillation ao can be interpreted as the surface signature of modulations in the strength of the polar vortex aloft it is proposed that the zonally asymmetric surface air temperature and mid tropospheric circulation anomalies observed in association with the ao may be secondary baroclinic features induced by the land sea contrasts the same modal structure is mirrored in the pronounced trends in winter and springtime surface air temperature sea level pressure and 50 hpa height over the past 30 years parts of eurasia have warmed by as much as several k sea level pressure over parts of the arctic has fallen by 4 hpa and the core of the lower stratospheric polar vortex has cooled by several k these trends can be interpreted as the development of a systematic bias in one of the atmosphere s dominant naturally occurring modes of variability

paragenesis of multiple platinum group mineral populations in shetland ophiolite chromitite 3d x ray tomography and in situ os isotopes abstract chromitite from the harold s grave locality in the mantle section of the shetland ophiolite complex is extremely enriched in ru os and ir at g g concentrations high resolution x ray computed tomography on micro cores from these chromitites was used to determine the location size distribution and morphology of the platinum group minerals pgm there are five generations of pgm in these chromitites small average 5 m in equivalent sphere diameter esd euhedral laurites often with os ir alloys are totally enclosed in the chromite and are likely to have formed first by direct crystallisation from the magma as the chromite crystallised also within the chromitite there are clusters of larger 50 m esd aligned elongate crystals of pt rh ir os and ru bearing pgm that have different orientations in different chromite crystals these may have formed either by exsolution or by preferential nucleation of pgms in boundary layers around particular growing chromite grains thirdly there is a generation of large 100 m esd composite os ir ru rich pgm that are all interstitial to the chromite grains and sometimes form in clusters it is proposed that os ir and ru in this generation were concentrated in base metal sulfide droplets that were then re dissolved into a later sulfide undersaturated magma leaving pgm interstitial to the chromite grains fourthly there is a group of almost spherical large 80 m esd laurites hosting minor os ir ru rich pgm that form on the edge or enclosed in chromite grains occurring in a sheet crosscutting a chromitite layer these may be hosted in an annealed late syn or post magmatic fracture finally a few of the pgm have been deformed in localised shear zones through the chromitites the vast majority of the pgm including small pgm enclosed within chromite larger interstitial pgm and elongate aligned pgm have os isotope compositions that give re depletion model ages approximately equal to the age of the ophiolite at 492 ma a number of other pgm not confined to a single textural group fall to more or less radiogenic values with four pgm giving anomalously unradiogenic os corresponding to an older age of 1050 ma the 187 os 188 os isotopic ratios for pgm from cliff and quoys from the same ophiolite section are somewhat more radiogenic than those at harold s grave this may be due to a distinct mantle source history or possibly the assimilation of radiogenic crustal os

holocene paleoenvironmental implications of diatom and organic carbon records from the southeastern kara sea siberian margin diatom assemblages and organic carbon records from two sediment cores located within an estuarian bay of the inner kara sea trace changes in yenisei river runoff and postglacial depositional environments paleosalinity and sea ice reconstructions are based on modern relationships of local diatom assemblages and summer surface water salinity approximately 15 500 cal yr b p rivers and bogs characterized the study area when sea level reached the 38 to 40 m paleo isobath approximately 9300 cal yr b p the coring site was flooded from 9300 9100 cal yr b p estuarine conditions occurred proximal to the depocenter of fluvially derived material and salinity was 7 8 paleosalinity increased to 11 13 by 7500 cal yr b p following postglacial sea level rise and the southward shift of the siberian coast sharp decreases in diatom accumulation rates total sediment and organic carbon also occurred suggesting the presence of brackish conditions and greater distance between the coast and study site maximum paleosalinity up to 13 was recorded between 7500 and 6000 cal yr b p which was likely caused by the enhanced penetration of atlantic waters to the kara sea stepwise decreases to modern salinity levels happened over the last 6000 cal yr

an introduction to the application of x ray microtomography to the three dimensional study of igneous rocks imaging rocks in three dimensions through x ray microtomography enables routine visualization of structures in samples which can be spatially resolved down to the sub micron scale although x ray tomography has been applied in biomedical research and clinical settings for decades it has only recently been applied to studies of rocks and few geoscientists realize its value and potential this contribution provides an introduction to the principles and techniques of x ray microtomography to the study of igneous rock textures as well as reviewing the current state of the art we hope that this short review will encourage more geoscientists to apply x ray microtomography in their research and that this will lead to new insights into the processes that occur in magmatic as well as other geological systems

microscale data to macroscale processes a review of microcharacterization applied to mineral systems microanalysis can provide rapid quantitative characterization of mineral systems that complements the field and core scale observations traditionally made in ore deposits we review recent innovations in microanalytical procedures and their application to studies of ore deposits case studies are presented examining how microanalysis can provide constraints on macroscopic processes within mineral systems synchrotron x ray fluorescence shows centimetre scale chemical variations associated with proximity to mineralization in samples from sunrise dam gold mine western australia pseudomorphs of igneous plagioclase and chemically driven recrystallization interpreted from electron backscatter diffraction suggest that the system was dominated by fluid driven brecciation with very little shearing both the fluid chemistry and fluid pressure evolved during a protracted sequence of vein formation and alteration accompanying gold mineralization a second case study of sulphide mineralogy at the mt keith nickel sulphide deposit western australia demonstrates how x ray computed tomography combined with trace element mapping can constrain the chemistry and dynamics of magmatic systems large scale interaction between silicate and sulphide melts shown by homogenous palladium enrichment in pentlandite leads to a large proportion of globular ores with a high nickel content increasing use of microanalysis in ore deposit geology is resulting in the constant reassessment of established models for ore genesis though a combination of micro and macroscale datasets

new constraints on arctic ocean mn stratigraphy from radiocarbon dating on planktonic foraminifera abstract variations in the abundance of manganese mn in arctic ocean sediments are used as a tool to identify glacial and interglacial periods this study aims to provide new insight into the applicability of mn as a stratigraphic tool in the topmost sediment and to investigate the occurrence of mn peaks in sediments within the range of radiocarbon dating in combination with variations in ice rafted debris ird radiocarbon dating is used to better constrain the stratigraphic occurrence of mn peaks and the synchroneity between multiple records especially during the late glacial and the holocene we find that a hiatus spanning mis 2 is widely observed in most of our cores resulting in a merging of mn peaks of holocene age and the later part of mis 3 the holocene mn peak is usually high amplitude but short while the mis 3 mn peak has a lower amplitude and is protracted where preserved mis 2 sediments form a 2 3 cm thick layer characterized by a light color low mn content sparse ird and low foraminiferal abundance ird variations provide a powerful tool to identify the boundary of the holocene and late mis 3 in cores with a mis 2 hiatus because the ird content displays a general increment from the start of mis 3 and both the holocene and mis 2 show small ird variations the end of mis 3 can be pinpointed to the point of decrease in ird the hiatus of mis 2 is widely observed in our cores suggesting extensive persistent sea ice coverage during the peak of the last glacial cycle with sharply reduced sedimentation throughout the arctic ocean identifying similar events during previous glacial periods may be an important step towards constructing longer and more accurate chronologies for arctic ocean sediments

solubility of pt in sulphide mattes implications for the genesis of pge rich horizons in layered intrusions the partitioning of pt in sulphide melt matte has been studied as a function of fs2 and fo2 at 1200 and 1300 c the results show that the solubility of pt in mattes increases strongly with increasing fs2 and decreases weakly with increasing fo2 the increase in pt solubility with increasing fs2 is attributed to pt dissolving in the melt as a sulphide species and the weak inverse dependence of pt solubility on fo2 to the diluting effect of increasing o in the melt at high fo2 these results coupled with measurements of pt solubility in silicate melts taken from the literature allow the calculation of pt matte silicate melt partition coefficients d pt matte sil for a range of conditions pertinent to the formation of pt rich horizons in layered intrusions the calculated values range between 107 and 1011 depending on fo2 and fs2 several orders of magnitude higher than previously published values our preferred value for d pt matte sil for conditions appropriate to the merensky reef is 107 and for the stillwater pt rich horizon 108 the new results are consistent with the magmatic hypothesis for pt rich horizons in layered intrusions

holocene glacier fluctuations of flatebreen and winter precipitation changes in the jostedalsbreen region western norvay based on glaciolacustrine sediment records the history of holocene glacier variations of flatebreen an independent glacier close to the sw part of the jostedalsbreen ice cap has been reconstructed from lacustrine sediments in the proglacial lake jarbuvatnet the sedimentary succession shows evidence of three maini episodes of holocene glacier expansion the first is recorded in the basal part of the core up to 370 cm according to the age depth relationship in the sediment core based on 12 ams radiocarbon dates this glacier expansion episode terminated about 10200 cal yr bp the second major glacier phase lasted from 8400 to 8100 cal yr bp while the third was initiated around 4000 cal yr bp and has continued up to the present at 43 cm in the core the medium silt content increases significantly accompanied by a minor increase in the sand content this textural change is interpreted as the first time that the tenninus of flatebreen extended inlto an upstream lake at 1083 m a s l the age model suggests that this event took place around