the role of the barents sea in the arctic climate system present global warming is amplified in the arctic and accompanied by unprecedented sea ice decline located along the main pathway of atlantic water entering the arctic the barents sea is the site of coupled feedback processes that are important for creating variability in the entire arctic air ice ocean system as warm atlantic water flows through the barents sea it loses heat to the arctic atmosphere warm periods like today are associated with high northward heat transport reduced arctic sea ice cover and high surface air temperatures the cooling of the atlantic inflow creates dense water sinking to great depths in the arctic basins and 60 of the arctic ocean carbon uptake is removed from the carbon saturated surface this way recently anomalously large ocean heat transport has reduced sea ice formation in the barents sea during winter the missing barents sea winter ice makes up a large part of observed winter arctic sea ice loss and in 2050 the barents sea is projected to be largely ice free throughout the year with 4 c summer warming in the formerly ice covered areas the heating of the barents atmosphere plays an important role both in arctic amplification and the arctic heat budget the heating also perturbs the large scale circulation through expansion of the siberian high northward with a possible link to recent continental wintertime cooling large air ice ocean variability is evident in proxy records of past climate conditions suggesting that the barents sea has had an important role in northern hemisphere climate for at least the last 2500 years

the fluid dynamics of a basaltic magma chamber replenished by influx of hot dense ultrabasic magma this paper describes a fluid dynamical investigation of the influx of hot dense ultrabasic magma into a reservoir containing lighter fractionated basaltic magma this situation is compared with that which develops when hot salty water is introduced under cold fresh water theoretical and empirical models for salt water systems are adapted to develop a model for magmatic systems a feature of the model is that the ultrabasic melt does not immediately mix with the basalt but spreads out over the floor of the chamber forming an independent layer a non turbulent interface forms between this layer and the overlying magma layer across which heat and mass are transferred by the process of molecular diffusion both layers convect vigorously as heat is transferred to the upper layer at a rate which greatly exceeds the heat lost to the surrounding country rock the convection continues until the two layers have almost the same temperature the compositions of the layers remain distinct due to the low diffusivity of mass compared to heat the temperatures of the layers as functions of time and their cooling rate depend on their viscosities their thermal properties the density difference between the layers and their thicknesses for a layer of ultrabasic melt 18 mgo a few tens of metres thick at the base of a basaltic 10 mgo magma chamber a few kilometres thick the temperature of the layers will become nearly identical over a period of between a few months and a few years during this time the turbulent convective velocities in the ultrabasic layer are far larger than the settling velocity of olivines which crystallise within the layer during cooling olivines only settle after the two layers have nearly reached thermal equilibrium at this stage residual basaltic melt segregates as the olivines sediment in the lower layer depending on its density the released basalt can either mix convectively with the overlying basalt layer or can continue as a separate layer the model provides an explanation for large scale cyclic layering in basic and ultrabasic intrusions the model also suggests reasons for the restriction of erupted basaltic liquids to compositions with mgo 10 and the formation of some quench textures in layered igneous rocks

the j m platinum palladium reef of the stillwater complex montana ii origin by double diffusive convective magma mixing and implications for the bushveld complex sequences of cumulates form concurrently by downdip accretion from a column of liquid layers that are primarily separated by diffusive interfaces the low cumulates grow in advance of the upper cumulates in accord with their higher crystallization temperatures an important observation is that mixing of the two parent liquids lowers their crystallization temperatures and consequently should produce unsaturated hybrids that could dissolve earlier cumulates the repetition of cyclic units above the j m reef is explained by having periodic additional injections of dense magma beneath the subsiding column of crystallizing liquid layers neither the j m reef nor the bushveld ore zones should ever have been continuous across the floor of their respective magma chambers and for bushveld the circumstances resulted in zones that are actually minable modified journal abstract

thinning and volume loss of the arctic ocean sea ice cover 2003 2008 1 we present our best estimate of the thickness and volume of the arctic ocean ice cover from 10 ice cloud and land elevation satellite icesat campaigns that span a 5 year period between 2003 and 2008 derived ice drafts are consistently within 0 5 m of those from a submarine cruise in mid november of 2005 and 4 years of ice draft profiles from moorings in the chukchi and beaufort seas along with a more than 42 decrease in multiyear my ice coverage since 2005 there was a remarkable thinning of 0 6 m in my ice thickness over 4 years in contrast the average thickness of the seasonal ice in midwinter 2 m which covered more than two thirds of the arctic ocean in 2007 exhibited a negligible trend average winter sea ice volume over the period weighted by a loss of 3000 km3 between 2007 and 2008 was 14 000 km3 the total my ice volume in the winter has experienced a net loss of 6300 km3 40 in the 4 years since 2005 while the first year ice cover gained volume owing to increased overall area coverage the overall decline in volume and thickness are explained almost entirely by changes in the my ice cover combined with a large decline in my ice coverage over this short record there is a reversal in the volumetric and areal contributions of the two ice types to the total volume and area of the arctic ocean ice cover seasonal ice having surpassed that of my ice in winter area coverage and volume became the dominant ice type it seems that the near zero replenishment of the my ice cover after the summers of 2005 and 2007 an imbalance in the cycle of replenishment and ice export has played a significant role in the loss of arctic sea ice volume over the icesat record

contributions of the siberian shelf polynyas to the arctic ocean intermediate and deep water the role of the open water regions or polynyas in the winter ice pack over the siberian continental shelves in the production of arctic ocean intermediate and deep water is examined through use of a combination of passive microwave satellite data coastal weather station data and oceanographic data the satellite data allow us to derive a time series of the open water areas of selected polynyas for the 1978 1982 winters the polynyas which occur north of svalbard around franz josef land along the west coast and north end of novaya zemlya and to the east of severnaya zemlya and the taymyr peninsula are the primary oceanographic contributors the open water time series for these polynyas are used in combination with coastal weather station data to estimate the heat loss from each polynya for the region north of svalbard which is historically known as whalers bay the study shows that the heat loss is sufficient to provide the observed cooling of the west spitsbergen current for the other polynyas the heat loss is used to compute the ice production rates and the oceanic salt flux we then use the historic oceanographic salinities with the salt fluxes to estimate the contribution of each polynya to the arctic ocean water masses if we assume that the salt contributes only to the arctic intermediate water our results show that the shelves are capable of producing about 20 60 of this water alternatively if the salt contributes only to the deep water of the eurasian basin then without consideration of the mixing of the bottom water with the greenland and norwegian sea water the contribution from the shelves yields a renewal time of about 100 years our results imply that there is insufficient water produced in the shelf polynyas to perform all of the roles that have been historically assigned to it

polynya dynamics a review of observations and modeling 1 polynyas are nonlinear shaped openings within the ice cover ranging in size from 10 to 105 km2 polynyas play an important climatic role first winter polynyas tend to warm the atmosphere thus affecting atmospheric mesoscale motions second ocean surface cooling and brine rejection during sea ice growth in polynyas lead to vertical mixing and convection contributing to the transformation of intermediate and deep waters in the global ocean and the maintenance of the oceanic overturning circulation since 1990 there has been an upsurge in polynya observations and theoretical models for polynya formation and their impact on the biogeochemistry of the polar seas this article reviews polynya research carried out in the last 2 decades focusing on presenting a state of the art picture of the physical interactions between polynyas and the atmosphere sea ice ocean system observational and modeling studies the surface heat budget and water mass transformation within these features are addressed

one dimensional evolution of the upper water column in the atlantic sector of the arctic ocean in winter a one dimensional model is employed to reproduce the observed time evolution of hydrographic properties in the upper water column during winter between 26 january and 11 march 2015 in a region north of svalbard in the nansen basin of the arctic ocean from an observed initial state vertical diffusion equations for temperature and salinity give the hydrographic conditions at a later stage observations of microstructure are used to synthesize profiles of vertical diffusivity k representative of varying wind forcing conditions the ice ocean heat and salt fluxes at the ice ocean interface are implemented as external source terms estimated from the salt and enthalpy budgets using friction velocity from the rossby similarity drag relation and the ice core temperature profiles we are able to reproduce the temporal evolution of hydrography satisfactorily for two pairs of measured profiles suggesting that the vertical processes dominated the observed changes sensitivity tests reveal a significant dependence on k variation in other variables such as the temperature gradient of the sea ice the fraction of heat going to ice melt and the turbulent exchange coefficient for heat are relatively less important the increase in salinity as a result of freezing and brine release is approximately 10 significantly less than that due to entrainment 90 from beneath the mixed layer entrainment was elevated during episodic storm events leading to melting the results highlight the contribution of storms to mixing in the upper arctic ocean and its impact on ice melt and mixed layer salt and nutrient budgets

on the parameterisation of oceanic sensible heat loss to the atmosphere and to ice in an ice covered mixed layer in winter abstract in high latitude oceans with seasonal ice cover the ice and the low salinity mixed layer form an interacting barrier for the heat flux from the ocean to the atmosphere the presence of a less dense surface layer allows ice to form and the ice cover reduces the heat loss to the atmosphere the ice formation weakens the stability at the base of the mixed layer leading to stronger entrainment and larger heat flux from below this heat transport retards and perhaps stops the growth of the ice cover as much heat is then entrained from below as is lost to the atmosphere this heat loss further reduces the stability and unless a net ice melt occurs the mixed layer convects two possibilities exist 1 a net ice melt sufficient to retain the stability will always occur and convection will not take place until all ice is removed the deep convection will then be thermal deepening the mixed layer 2 the ice remains until the stability at the base of the mixed layer disappears the mixed layer then convects through haline convection into the deep ocean warm water rises towards the surface and the ice starts to melt and a new mixed layer is reformed the present work discusses the interactions between ice cover and entrainment during winter when heat loss to the atmosphere is present one crucial hypothesis is introduced when ice is present and the ocean loses sensible heat to the atmosphere and to ice melt the buoyancy input at the sea surface due to ice melt is at a minimum using a one dimensional energy balance model applied to the artificial situation where ice melts directly on warmer water it is found that this corresponds to a constant fraction of the heat loss going to ice melt it is postulated that this partitioning holds for the ice cover and the mixed layer in the high latitude ocean when a constant fraction of heat goes to ice melt at least one deep convection event occurs before the ice cover can be removed by heat entrained from below after one or several convection events the ice normally disappears and a deep reaching thermal convection is established conditions appropriate for the weddell sea and the greenland sea are examined and compared with field observations with realistic initial conditions no convection occurs in the warm regime of the weddell sea a balance between entrained heat and atmospheric heat loss is established and the ice cover remains throughout the winter at maud rise convection may occur but late in winter and normally no polynya can form before the summer ice melt in the central greenland sea the mixed layer generally convects early in winter and the ice is removed by melting from below as early as february or march this is in agreement with existing observations

chromite in the platreef bushveld complex south africa occurrence and evolution of its chemical composition the regional distribution and chemical composition of massive and disseminated chromitites through a platreef sequence and along a strike distance of over 20 km were investigated to correlate them both within the framework of the northern limb and to the eastern and western limbs of the bushveld complex the chromitite layers and seams of the platreef form two main chromite bearing zones the upper chromitite that occurs as two to three discontinuous seams in feldspathic pyroxenite at approximately 20 m below the platreef top contact and the lower chromitite that is composed of multiple seams in feldspathic harzburgite pyroxenite and norite close to the bottom contact of the platreef with footwall electron micro probe analyses reveal that the chemical composition of chromite depends on the host rock type norite and pyroxenite host chromite with the highest cr2o3 content while harzburgite hosted chromites are cr and mg poor the wide range in chromite compositions is explained by the influence of late magmatic processes including post cumulus growth and re equilibration interaction with fluid and sulphide saturated magmatic liquid and contact metamorphism each of these processes is characterised by its own distinct geochemical signature but generally they lead to a decrease in mg and al and an increase in both di and tri valent fe in the chromite the occurrence of chromitite locally on the different distance from the contact between the upper platreef sills and the overlying main zone magma suggests erosion of the upper platreef by the main zone as it was emplaced the localisation of chromitites supports an independent development of the northern limb during the critical zone emplacement although the chemical composition of chromite and co existing silicates from ultramafic rocks suggest a critical zone affinity with the eastern and western limbs of the bushveld complex

magmatic unmixing in spinel from late precambrian concentrically zoned mafic ultramafic intrusions eastern desert egypt abstract spinel is widespread in the ultramafic core rocks of zoned late precambrian mafic ultramafic complexes from the eastern desert of egypt these complexes gabbro akarem genina gharbia and abu hamamid are precambrian analogues of alaskan type complexes they are not metamorphosed although weakly altered each intrusion is composed of a predotite core enveloped by pyroxenites and gabbros at the margin silicate mineralogy and chemistry suggest formation by crystal fractionation from a hydrous magma relatively high cr 2 o 3 contents are recorded in pyroxenes up to 1 1 wt and amphiboles up to 1 4 wt from the three plutons the chrome spinel crystallized at different stages of melt evolution as early cumulus inclusions in olivine inclusions in pyroxenes and amphiboles and late magmatic intercumulus phase the intercumulus chrome spinel is homogenous with narrow range of chemical composition mainly fe 3 rich spinel spinel inclusions in clinopyroxene and amphibole reveal a wide range of al 27 44 wt al 2 o 3 and mg 6 13 wt mgo contents and are commonly zoned the different chemistries of those spinels reflect various stages of melt evolution and re equilibration with the host minerals the early cumulus chrome spinel reveals a complex unmixing structures and compositions three types of unmixed spinels are recognized crystallographically oriented irregular and complete separation unmixing products are al rich type i and fe 3 rich type ii spinels with an extensive solid solution between the two end members the compositions of the unmixed spinels define a miscibility gap with respect to cr al fe 3 extending from the fe 3 al join towards the cr corner spinel unmixing occurs in response to cooling and the increase in oxidation state the chemistry and grain size of the initial spinel and the cooling rate control the type of unmixing and the chemistry of the final products causes of spinel unmixing during late magmatic stage are analogous to those in metamorphosed complexes the chemistry of the unmixed spinels is completely different from the initial spinel composition and is not useful in petrogenetic interpretations spinels from oxidized magmas are likely to re equilibrate during cooling and are not good tools for genetic considerations

sondrestrom radar initial results operation of an incoherent scatter radar at sondre stromfjord greenland began in early february 1983 marking the beginning of a new effort in ground based ionospheric research in the vicinity of the polar cusp and polar cap the sondrestrom radar is located north of the arctic circle on the west coast of greenland near the sondrestrom air base at an invariant latitude of 75 the effects of the polar cusp may frequently be observed at local noon the radar measured signature in the f region is an increase of more than a factor of two in electron density additionally the daytime variations in the f1 region electron density are dramatic in contrast to auroral zone measurements enhanced electron density at 150 km altitude has been observed and a marked absence of detectable e region ionization at night has also been noticed

southern hemisphere thermospheric dynamics a review the dynamics of the upper thermosphere in the southern polar cap auroral and mid latitude zones is reviewed information has been drawn from published measurements from the de 2 and ae c spacecraft and from ground based stations and interpreted using the latest thermospheric general circulation models necessarily frequent reference is made to the f region of the ionosphere which permeates the upper thermosphere great emphasis is placed on the coupling and feedback mechanisms which exist between these interpenetrating fluids it is shown that to obtain close approximation to observation a complex model is required which incorporates these mechanisms in a self consistent way published results from general circulation models show that there is a broad measure of agreement at both high and middle latitudes between simulation and observation over a wide range of geomagnetic activity for the sunlit southern middle and high latitudes near solar maximum however there are comparatively few data for a full investigation to be made and present conclusions must be regarded as strictly interim strong driving forces in the auroral zones and polar caps cause a wind regime which is distinctly different from that observed at middle latitudes geomagnetic activity has been shown to have a strong effect on the extent of the high latitude wind field its strength and its penetration to middle latitudes the orientation of the interplanetary magnetic field has also been shown to be important the coupling mechanisms between ions and neutrals heat the thermosphere and drive its circulation using energy from magnetospheric sources but as yet the details of the thermosphere s variation with geomagnetic and solar activity are not clear from observations the strong vertical winds reported in the literature are certainly indications of powerful heating but the connection between observations of vertical winds and the production of gravity wave activity has not been established halley antarctica is a critical station in the evaluation of model simulations of the winds in the upper thermosphere since it is a high latitude station geographically but middle latitude geomagnetically and is subject to an unusual blend of driving forces the observations are modeled surprisingly well considering the incomplete accounting of asymmetry caused by the large offset of the geomagnetic and geographic poles and also of the south atlantic anomaly it is probable that globally there are detailed disagreements between the actual circulation and the simulations which have not yet come to light for the lack of observations in the absence of new spacecraft experiments new ground based stations are required in the antarctic region to enable simultaneous measurements to be made over a wide range of the southern polar cap

sea ice mass balance observations from the north pole environmental observatory in recent years the periphery of the arctic sea ice cover has undergone significant changes with a reduction in summer ice extent a thinning of the ice and a shift from multiyear to first year ice here we examine sea ice conditions during nine summers between 2000 and 2013 in the interior of the ice pack using autonomous measurements of sea ice mass balance deployed near the north pole results exhibit no definitive trends there is large interannual variability with surface melt ranging from 0 02 m to 0 50 m and bottom melt from 0 10 m to 0 57 m the largest amounts of bottom melt have occurred in the past few years for all 9 years the ice at the end of the melt season was at least 1 2 m thick

the origin of chromitites and related pge mineralization in the bushveld complex new mineralogical and petrological constraints this article reports a study of chromitites from the lg 1 to the ug 2 3 from the bushveld complex chromite from massive chromitite follows two compositional trends on the basis of cation ratios trend a decreasing mg mg fe with increasing cr cr al trend b decreasing mg mg fe with decreasing cr cr al the chromitites are divided into five stages on the basis of which trend they follow and the data of eales et al chemical geology 88 261 278 1990 on the behaviour of the mg fe ratio of the pyroxene and whole rock sr isotope composition of the environment in which they occur following eales et al chemical geology 88 261 278 1990 the different characteristics of the stages are attributed to the rate at which new magma entered the chamber and the effect of this on aal2o3 and in the case of stage 5 the appearance of cumulus plagioclase buffering the aal2o3 the similarity of pge profiles across the mg 3 and mg 4 chromitites that are separated laterally by up to 300 km and the variation in v in the ug 2 argue that the chromitites have largely developed in situ modelling using the programme melts shows that increase in pressure mixing of primitive and fractionated magma felsic contamination of primitive magma or addition of h2o do not promote crystallization of spinel before orthopyroxene in general they hinder it and that the cr2o3 content of the magma was of the order of 0 25 wt less than 20 of the chromite in the magma is removed before orthopyroxene joins chromite which implies a 13 km thickness of magma for the critical zone it is suggested that the large excess of magma has escaped up marginal structures such as the platreef the pge profile of chromitites depends on whether sulphide accumulated or not along with chromite modelling shows that contamination of critical zone magma with a felsic melt will induce sulphide immiscibility although not chromite precipitation the lg 1 to lg 4 chromitites developed without sulphide whilst those from the lg 5 upwards had associated liquid sulphide much of the sulphide originally in the lg 5 and above has been destroyed as a result of reaction with the chromite

the halogen geochemistry of the bushveld complex republic of south africa implications for chalcophile element distribution in the lower and critical zones solidification of the interstitial liquid the stratigraphic distribution halogen bearing minerals especially apatite are minor but ubiof s cu and the pge in the critical zone cannot readily be quitous phases throughout the bushveld complex interstitial apatite explained either by precipitation of sulfide as a cotectic phase or as is near end member chlorapatite below the merensky reef lower a function of trapped liquid abundance evidence from potholes and and critical zones and has increasingly fluorian compositions with the pge rich driekop pipe of the bushveld complex imply that increasing structural height above the reef main and upper zones migrating cl rich fluids mobilized the base and precious metal cl f variations in biotite are more limited owing to crystal chemical sulfides we suggest that the distribution of sulfide minerals and controls on halogen substitution but are also consistent with a the chalcophile elements in the lower and critical zones reflects a decrease in the cl f ratio with structural height in the complex general process of vapor refining and chromatographic separation of a detailed section of the upper lower zone to the critical zone is these elements during the evolution and migration of a metalliferous characterized by an upward decrease in sulfide mode from 0 01 cl rich fluid phase 0 1 to trace 0 001 cu tends to correlate with other incompatible elements in most samples whereas the platinum group elements pge can behave independently particularly in the critical zone the decrease in the cl f ratio of apatite in the

field relations and strontium isotope systematics of the marginal rocks of the eastern bushveld complex the well exposed basal contact of the eastern bushveld complex was mapped at scales of 1 10 000 and 1 20 000 along 130 km of strike and through a 9 km vertical section field relations petrography and geochemistry of the marginal rocks and associated sills have aided their subdivision into two main groups a broadly pyroxenitic group rims the complex from its base to the top of the pyroxenitic subzone of the critical zone a gabbroic group occurs above this level each group consists of a number of closely related rock types most of which have sill analogs rocks of the first group b1 include pyroxenites norites and peridotites all of which may have quench textures all contain orthopyroxene en 78 plagioclase an 65 and chromite with subordinate clinopyroxene and biotite rare earth element patterns are mostly strongly fractionated ce n yb n approximately 10 and have 40x chondritic abundances at ce their initial strontium isotope ratios at 2 05 b y fall in the range 0 7032 to 0 7057 and rb sr ratios approximate 0 2 the gabbroic group consists of microcrystalline two pyroxene gabbros b2n and b3n and their coarser grained equivalents b2 and b3 that border the upper critical and main zones respectively mineral assemblages are dominated by plagioclase approximately an 55 clinopyroxene and orthopyroxene approximately en 63 with abundant magnetite and traces of ilmenite and biotite their rare earth element patterns are less fractionated than b1 rocks the b2n and b2 family have ce n yb n approximately 6 and 30x chondritic abundances at ce the b3n and b3 rocks have ce n yb n approximately 3 6x chondritic abundances at ce and pronounced positive eu anomalies strontium isotope initial ratios at 2 05 b y fall in the range 0 706 to 0 708 and the rb sr ratios are approximately 0 02 whole rock and sr isotope compositions of the peridotitc sills can be successfully simulated by a model involving olivine fractionation from a liquid with an initial sr isotope ratio r 0 similar to that of the transition zone 0 7056 a fraction of such liquid enriched in cumulus olivine crystals when mixed with up to 30 percent of a pyroxenitic liquid with low r 0 0 7034 yields a product having the isotopic and compositional characteristics of the peridotite sills a continuum exists in the initial sr ratios through the pyroxenitic and gabbroic marginal rocks suggesting that these represent mixtures of at least two sources with distinct initial sr isotope ratio characteristics it is argued that neither magma aging nor crustal contamination adequately accounts for the sr isotope characteristics of the marginal rocks or their derived cumulates the unusual chemistry of the pyroxenitic early liquids sio 2 approximately 55 mgo approximately 13 coupled with high concentrations of incompatible elements should be considered primary

observations reveal external driver for arctic sea ice retreat 1 the very low summer extent of arctic sea ice that has been observed in recent years is often casually interpreted as an early warning sign of anthropogenic global warming for examining the validity of this claim previously ipcc model simulations have been used here we focus on the available observational record to examine if this record allows us to identify either internal variability self acceleration or a specific external forcing as the main driver for the observed sea ice retreat we find that the available observations are sufficient to virtually exclude internal variability and self acceleration as an explanation for the observed long term trend clustering and magnitude of recent sea ice minima instead the recent retreat is well described by the superposition of an externally forced linear trend and internal variability for the externally forced trend we find a physically plausible strong correlation only with increasing atmospheric co2concentration our results hence show that the observed evolution of arctic sea ice extent is consistent with the claim that virtually certainly the impact of an anthropogenic climate change is observable in arctic sea ice already today

reaction relationships of chrome spinels in igneous rocks further evidence from the layered intrusions of rhum and mull inner hebrides scotland compositions of chrome spinels in peridotites from the layered igneous rocks of rhum and of the ben buie intrusion mull show evidence of post depositional reaction relationships with the cumulus olivine and or the intercumulus liquid some seam forming spinels in the ben buie intrusion are highly aluminous more so than those in the rhum intrusion occasional zoned spinels in both intrusions show enrichment in al towards their rims the evidence suggests that the spinel reaction trend involving cr al exchange proceeds in the direction of al enrichment equilibrium between chrome spinel and cumulus olivine appears to have been attained rarely thus limiting the application of the olivine spinel geothermometer

textural and compositional features of chromite in the lower and critical zones of the bushveld complex south of potgietersrus chromite is developed as an accessory mineral in a 1 700 m thick sequence of lower and lower critical zone cumulates in the area south of potgietersrus and as a major constituent in a number of chromitite layers within this sequence the lower zone consists of a 1 500 m thick sequence of ultramafic rocks characterized by varying proportions of olivine orthopyroxene and chromite which allows the pile of cumulates to be subdivided into 37 cyclic units the critical zone on the other hand is only 350 m thick of which only the lower 150 m contains chromite bearing lithologies electron microprobe analyses of chromite and coexisting silicates indicate a strong positive correlation between the mg mg fe super 2 and cr fe super 2 fe super 3 ratios of chromite and the mg mg fe super 2 ratio of the mafic silicates the composition of the chromite is also strongly influenced by the mineralogical composition of the host rock and probably reflects conditions within the parental magma during crystallization of these rocks the analytical data have also shown the tio 2 content of the disseminated chromite to be the most informative indicator of the degree of differentiation of the magma a detailed investigation of the chromite across the contact of a thin chromitite layer has shown that the chromitite layers crystallized in response to an influx of magma and that chromite crystallization could have been enhanced by an increase in the f sub o 2 and a rise in the cr 2 o 3 content of the liquid thereby causing an increase in the cr 2 o 3 content of the chromite within the chromitite layers postcumulus modification of the chromitite layers is extensive and primary textural features have been obliterated essentially by sintering sintering took place in the presence of a reactive mg rich liquid which resulted in an increase in the mg mg fe super 2 ratio of the chromite this process resulted in a densification of the chromitite layers from an estimated initial porosity of 30 to 45 percent to less than 10 percent

early spring oceanic heat fluxes and mixing observed from drift stations north of svalbard abstract from several drifting ice stations north of svalbard norway observations were made in early spring of the ocean turbulent characteristics in the upper 150 m using a microstructure profiler and close to the under ice surface using eddy correlation instrumentation the dataset is used to obtain average heat fluxes at the ice water interface in the mixed layer across the main pycnocline as well over different water masses in the region the results are contrasted with proximity to the branches of the warm and saline atlantic water current the west spitsbergen current wsc which is the main oceanic heat and salinity source both to the region and to the arctic ocean hydrographic properties show that the surface water mass modification is typically due to atmospheric cooling with relatively less influence of ice melting surface heat fluxes of o 100 w m 2 are found within the branches of the wsc and over shelf areas with elevated levels of mixing due to strong tides away from the shelves and

mean neutral circulation in the winter polar f region direct measurements of the f region neutral wind field in the northern winter hemisphere during late november and december 1981 were obtained by using the dynamics explorer de 2 satellite and the network of ground based fabry perot interferometers sited in the north american and scandinavian sectors all available data for the study period have been collated and averaged according to universal time ut to provide a global scale experimental determination of the mean or average circulation in the northern hemisphere f region the data are organized into ut bins and are presented as a sequence of 12 climate maps depicting the neutral wind system at 2 hour ut intervals during a mean day in december 1981 the data set provides the most comprehensive experimental measure of the global scale high latitude thermospheric circulation yet reported the averaged measurements from the different instruments exhibit a satisfactory degree of internal consistency when viewed in terms of the global scale neutral flow a detailed comparison with the predictions of the ncar thermospheric general circulation model is discussed the model predictions are in good general agreement with the ut dependent mean circulation reproducing the basic control of the high latitude neutral wind system by ion drag forces modulated in ut as a result of the offset between the geomagnetic and geographic poles differences in flow directions and velocities between model predictions and experimental results are ascribed to natural variability in the thermosphere as well as to the use in the model of a less than fully realistic symmetric ion convection geometry and density distribution the two basic conclusions of this study are that 1 instrumentation deployed around the globe and on satellites can provide powerful composite data sets that can be used to monitor global scale mean thermospheric climatology and that 2 the mean thermospheric f region neutral circulation for the given geophysical situation solar maximum near solstice can be modeled reasonably well using a three dimensional time dependent model with appropriate parameterizations for the energy and momentum inputs

postcumulus modification of magnetite grains in the upper zone of the bushveld complex south africa abstract a detailed electron microprobe study has been made of magnetite grains from magnetitite layer 1 of the upper zone of the bushveld complex in order to establish if there is any evidence for postcumulus processes having affected magnetite compositions representative composition profiles obtained from detailed step traverses are presented for touching magnetite grains and where magnetite is in contact with either ilmenite or plagioclase magnetite grains in all textural settings are compositionally heterogeneous touching magnetite grains display systematic compositional zonations the rims of grains show a marked decrease in al and mg towards the grain boundary the cores are characterised by a distinctive peak and trough pattern for these elements these variations can be related to the positions of exsolved phases exsolutions in the cores are either pleonaste or an fe 3 bearing al mg spinel whereas those at the grain boundaries are generally more al rich and include corundum similar exsolution related compositional variations for mg and al were found in magnetites in contact with ilmenite and plagioclase a model has been developed which illustrates the possible sequence of postcumulus events during the interval between accumulation of the magnetite and the cessation of subsolidus reactions the essential feature of the model is the delicate interplay between depletion of the host magnetite by corundum pleonaste and the fe 3 bearing al mg spinel exsolutions and diffusion of al and mg into the depleted areas from the surrounding magnetite data for cr contents in magnetites show that although this particular trace element is apparently resistant to redistribution by exsolution processes it is affected by subsolidus re equilibration between magnetite and ilmenite or magnetite and intercumulus liquid

poleward ocean heat transports sea ice processes and arctic sea ice variability in noresm1 m simulations results from the noresm1 m coupled climate model were used to examine relationships between arctic sea ice area and ocean heat transports through the primary arctic gateways comparisons were made with two other models cnrm cm5 and mri cgm3 that are part of the cmip5 archive which have the required outputs for calculating ocean heat transports based on an evaluation noresm1 m was found to be best suited to study the effects of heat transports on sea ice area and conclusions are based on results from this model the arctic ocean was divided into two regions the barents sea and the central arctic ocean the sea ice area variability was further analyzed in terms of frazil and congelation growth top and bottom melting and heat transports in the barents sea opening bso and the fram strait fs in the barents sea increased heat transport in the bso has a strong influence on sea ice area in terms of reduced congelation growth while bottom melting is important for the variability in the central arctic ocean the negative trend in sea ice area is considerably greater in the barents sea than in the central arctic ocean despite the central arctic ocean area being much larger and reflects the major trend in the bso heat transport the model results in this study suggest that the ocean has stronger direct impact on changes in sea ice mass in terms of freezing and melting than the atmosphere both in the mean and with respect to variability

nighttime thermospheric winds over sondre stromfjord greenland observations of nighttime thermospheric neutral winds made at sondre stromfjord greenland with optical and radar instrumentation showed an occasional abatement in the equatorward meridional wind at a magnetic local time corresponding to the nighttime division between the evening and morning convection cells this abatement appeared primarily in the poleward observations in contrast however the characteristic midnight surge was usually seen in the equatorward set of observations the apparent acceleration of about 250 m s or greater within 4 6 latitude we attribute in part to a merging of neutral jet streams generated by polar cap ion drag adjacent to the auroral zone boundary and in part to the higher electron densities and plasma convection speeds adjacent to the auroral zone comparison of these results with those from ncar tgcm computations that assumed an analytical plasma convection model showed reasonable agreement except for the abatement feature

arctic ocean heat impact on regional ice decay a suggested positive feedback abstractbroad long living ice free areas in midwinter northeast of svalbard between 2011 and 2014 are investigated the formation of these persistent and reemerging anomalies is linked hypothetically with the increased seasonality of arctic sea ice cover enabling an enhanced influence of oceanic heat on sea ice and in particular heat transported by atlantic water the memory of ice depleted conditions in summer is transferred to the fall season through excess heat content in the upper mixed layer which in turn transfers to midwinter via thinner and younger ice this thinner ice is more fragile and mobile thus facilitating the formation of polynyas and leads when openings in ice cover form along the atlantic water pathway weak density stratification at the mixed layer base supports the development of thermohaline convection which further entrains warm and salty water from deeper layers convection induced upward heat flux from the atlantic layer retards ice formation either keeping ice thick

a strontium isotope and trace element profile through the partridge river troctolite duluth complex minnesota initial 87sr 86sr ratios down a 2 315 foot long core ddh 295 through the partridge river troctolite are lower in the depth range 710 1 410 feet 0 70443 22 than in the underlying and overlying rocks 0 70500 18 these initial ratio variations define three zones i ii and iii thought to be three intrusive units within the troctolite the best estimate of the rb sr age of the troctolite is 1 050 105 m y the olivine compositions and the abundances of the incompatible trace elements zr y and rb show identical variations down the core with downward repetitions of olivine iron enrichment and incompatible trace element enrichments discontinuities in the olivine compositions and incompatible trace element abundances match the initial 87sr 86sr ratio discontinuities in the core

thinning of the arctic sea ice cover comparison of sea ice draft data acquired on submarine cruises between 1993 and 1997 with similar data acquired between 1958 and 1976 indicates that the mean ice draft at the end of the melt season has decreased by about 1 3 m in most of the deep water portion of the arctic ocean from 3 1 m in 1958 1976 to 1 8 m in the 1990s the decrease is greater in the central and eastern arctic than in the beaufort and chukchi seas preliminary evidence is that the ice cover has continued to become thinner in some regions during the 1990s

an origin of small scale fluctuations in orthopyroxene composition in the lower and critical zones of the bushveld complex south africa abstract numerous small and apparently haphazard reversals in mg fe ratio of orthopyroxene grains have been reported by e n cameron in the lower and lower critical zones of the bushveld complex a hypothesis for their origin is presented by extending the suggestion of cameron that modal variation in layered complexes may be attributed to pressure fluctuation an increase in pressure will cause the magma to be supercooled thus speeding up crystallization rates this results in a greater proportion of interstitial liquid being trapped in the cumulate pile on crystallization this liquid adds relatively fe rich orthopyroxene to the cumulus of mg rich phase homogenization produces minerals whose compositions are displaced from the cumulus composition towards the low temperature end member by an amount proportional to the percent of interstitial liquid decreases in pressure produce the opposite effect and may explain the origin of pure adcumulate rocks quantitative data are presented from the lower zone critical zone contact and from the duluth complex to demonstrate this effect

the chronology of magma influxes to the eastern compartment of the bushveld complex as exemplified by its marginal border groups the floor contact of the eastern compartment of the bushveld complex has been mapped in detail for 130 km field relations petrographical and geochemical data have enabled 3 important marginal border groups and a possible parent to the lower zone to be demarcated these represent the 4 main magma influxes which formed the malic phase of the bushveld complex and are in chronological order 1 a contaminated magnesian basalt b1 which gave rise to a saucer shaped laminated marginal zone at the base of the complex with diverse related sills 2 a harrisitic peridotite representing quenched lower zone magma 3 a border group to the more evolved probably basaltic critical zone magma which was intruded in two phases an early quenched norite facies n being followed by a chilled bulk critical zone facies b2 which forms a skin to the whole critical zone finally 4 a border group to the main and upper zone b3 which represents an early magnesian pulse of this last immense volume of tholeiitic liquid there is also evidence for minor influxes of magma within the critical zone and main zone

circulation and transformation of atlantic water in the eurasian basin and the contribution of the fram strait inflow branch to the arctic ocean heat budget abstract the inflows of atlantic water from the nordic seas to the arctic ocean through fram strait and over the barents sea are examined and their pathways and transformations in the eurasian basin are described based primarily on hydrographic observations from two cruises with rv polarstern in 2007 and 2011 the contrast between the high salinity atlantic water core in the nansen basin and the lower atlantic water salinity in the amundsen basin combined with a salinity minimum below the atlantic layer suggest that the fram strait branch mainly remains in the nansen basin while the barents sea branch continues along the continental slope enters the amundsen basin and provides most of the atlantic water in the makarov and canada basins to examine the consequences of such a circulation pattern recently published estimates of the in and outflows of volume and liquid freshwater through the barents sea bering strait and the canadian arctic archipelago as well as river runoff net precipitation and ice export are reviewed and added together to achieve volume and freshwater balances net outflows through fram strait of 2 3 sv and 100 msv respectively are required this is reasonably close to the recently reported fram strait transport estimates the net outflows are separated into two parts upper layer transports less dense than the entering atlantic water and lower layer transports as dense as or denser than the atlantic water the largest net volume outflow occurs in the lower layer 1 65 sv while the liquid freshwater is almost exclusively exported in the 0 64 sv net outflow in upper layer leading to unrealistically low salinities in the upper layer compared with observations atlantic water is north of svalbard transformed into less saline surface water through melting of sea ice which can supply the necessary higher salinity halocline water to the upper layer 1 23 sv of halocline water of salinity 34 2 must be added to obtain a more realistic salinity of 33 1 leading to a total export of 1 84 sv upper layer water in the east greenland current existing observations of the net transports into and out of the arctic ocean through fram strait in different temperature classes are used to estimate the heat loss of the atlantic water entering the arctic ocean through fram strait about 10 tw are supplied to the atmosphere in addition to the loss of 24 tw occurring in connection with the formation of the halocline water if the hypothesis that the fram strait branch remains in the nansen basin is true it implies a heat loss between 5 and 15 w m 2 in the nansen basin depending upon how much heat is temporarily stored in the water column this is high compared to the 2 w m 2 commonly cited as the ocean heat flux to the atmosphere in the arctic ocean

chromite from the swartkop chrome mine an estimate of the effects of subsolidus reequilibration chromites from the lg 3 lg 4 and lg 6 chromitite layers at the zwartkop mine are investigated and subsolidus behavior of chromite in olivine and orthopyroxene hosted environments is compared chromitite layers lg 3 and lg 6 are orthopyroxene hosted but layer lg 4 is olivine hosted with abundant orthopyroxene formed by a reaction relation between olivine and liquid chromite has reequilibrated with host silicate to a degree dependent on the nature of the host silicate and the modal amounts of chromite present in an olivine environment reequilibration between chromite and silicate proceeds to lower temperatures with consequently more iron rich chromite than in an orthopyroxene hosted chromite in a given environment the closure temperature for silicate chromite reequilibration decreases systematically as the modal amount of chromite decreases from this systematic relation the solidus temperature can be estimated and some inferences about the original chromite composition can be made in the lg 6 layer chromite compositions can be projected back to solidus compositions along a trajectory of constant activity of the mga1204 component and at the solidus temperature chromite composition within and adjacent to the chromitite layer is essentially the same the activity of mga1204 remained constant because chromite was in equilibrium with the host orthopyroxene throughout the temperature range in which reequilibration took place in layer lg 4 the activity of mga1204 increased during cooling because the solidus chromite was not in equilibrium with orthopyroxene formed by reaction between olivine and liquid because the liquid which reacted with olivine was more aluminous than the liquid from which the olivine originally crystallized subsolidus reequilibration between orthopyroxene and chromite led to an increase in the concentration of alcoa in chromite consequently the decrease in mg content of chromite during cooling is accompanied by an increase in a1 content in contrast to the more common decrease in a1 content observed in layer lg 6 which results from the higher stability of

a paleoproterozoic ultramafic mafic assemblage and associated volcanic rocks of the boromo greenstone belt fractionates originating from island arc volcanic activity in the west african craton abstract the loraboue birimian ultramafic mafic assemblage located in the boromo greenstone belt burkina faso is interpreted as the remains of a magma chamber that crystallized at the base of an island arc the ultramafic rocks exhibit an heteradcumulate texture being generally made up of wehrlites and more rarely dunites the crystallization sequence inferred from the cumulates is olivine chromite followed by clinopyroxene amphibole orthopyroxene biotite the gabbroic rocks are mainly layered and grade into more differentiated facies with sub pegmatitic texture containing up to 70 modal plagioclase including zircon and more commonly apatite crystals textural relationships and mineral phase chemistry are indicative of crystallization at elevated pressures 8 kbar the parental magma being generated by a moderate to high degree of partial melting of a mantle source affected by previous metasomatic events above a subducted oceanic slab the loraboue volcanic formations exhibit a range of geochemical features they consist dominantly of calc alkaline basalts pyroclastites and rhyolite and more rarely of basalt dolerite and gabbro of tholeiitic affinity these different types of basalt as well as the dolerite and the isolated massive gabbro show the classic features of arc magmatic suites namely lile and pb enrichment depleted hfse patterns and high ce nb and th nb ratios thus the calc alkaline plutonic and volcanic assemblages of loraboue could represent the roots of an island arc and the associated coeval volcanic rocks the paleoproterozoic crust of the west african craton was heterogeneous and was not the consequence of a single process of genesis as some modern igneous province the birimian crust was generated by both volcanic arc accretion and oceanic plateau accretion

chrome spinels from the ōura layered igneous complex central japan abstract chrome spinel is disseminated as a minor cumulus phase in olivine rich ultramafic cumulates in the ura igneous complex a series of layered mafic and ultramafic plutonic rocks the al2o3 content of the spinel increased markedly with proceeding crystallization of the magma the al spinel a magma distribution coefficient seems to have increased with the crystallization of chrome spinel in view of experimental results obtained in the system forsterite anorthite diopside quartz with mgcr2o4 spinel the increase in the distribution coefficient may be interpreted in terms of enrichment of plagioclase component in the magma by olivine fractionation the cr cr al ratio of late separated chrome spinel is presumably an indicator of the chemical conditions of parental magma the ratio decreases with increasing the plagioclase component content of magma on the normative mineral diagram plagioclase clinopyroxene orthopyroxene the presence of highly aluminous chrome spinel in the ura igneous complex suggests that the magma was enriched in plagioclase and clinopyroxene components and depleted in orthopyroxene component it was apparently similar to abyssal tholeiite magma and markedly different from the great dyke and bushveld magmas which were rich in orthopyroxene component

the melt freeze cycle of the arctic ocean ice cover and its dependence on ocean stratification 1 a time dependent 1 d coupled ice ocean model is used to quantify the impact of ocean stratification on the arctic ice cover the model results show that the ice growth during winter equals the ice melt in summer for areas with a well developed cold halocline layer chl provided that the initial ice thickness is around 3 m while thinner initial ice thickness results in net growth areas with weak salt stratification can have a negative annual thickness change irrespective of the initial ice thickness and are thus dependent on ice import in order to remain ice covered the model results also show that ocean stratification is mostly important for ice thickness development during the growing season areas with weak stratification have an ocean heat flux up to 8 w m 2 reaching the ice during the growing season while areas with a chl have an average of about 0 7 w m 2 in the extreme area north of svalbard the ocean heat fluxes are typically around 25 w m 2 but can be up to 400 w m 2 during the initial adjustment when the warm atlantic water has direct contact with the ice a general outcome of the study is that depending on ocean stratification the ice cover of arctic ocean can be divided into one part with net ice growth the major part and another part with net ice melt mainly in the nansen basin

chrome spinels in gabbro wehrlite intrusions of the pechenga area kola peninsula russia emphasis on alteration features abstract chrome spinels are common accessory minerals of the pechenga ultramafic rocks in nw russia varying in metamorphic grade from sub greenschist to amphibolite facies magmatic chrome spinels can be grouped into two main types spinel 1 which crystallized first is represented by al ti chromite it occurs mainly as inclusions in olivine and rather less commonly enclosed within interstitial minerals spinel 2 crystallized after spinel 1 and has composition varying from ti rich chromite to ti rich chrome magnetite spinel 2 occurs in the interstitial spaces between olivine crystals and enclosed within intercumulus silicates zoned crystals with spinel 1 in the core overgrown by spinel 2 are also common cr poor titanomagnetite occurring in pyroxenites and gabbro apparently represents further evolution of spinel 2 phases metamorphic chrome spinels are represented by ferritchromit and cr magnetite which are the dominant chrome spinel phases in the amphibolite facies rocks the continuous trend of the magmatic chrome spinels composition is indicative of their intensive post cumulus alteration by reaction with evolving intercumulus liquid this reaction led to depletion of the earlier crystallized chrome spinels in mg cr and al and their enrichment in ti and fe 3 oxidation exsolution of ilmenite from ti rich chrome spinels is another common process of post crystallization alterations serpentinization of olivine led to formation of magnetite which overgrew and cut chrome spinel grains low temperature hydrothermal processes in particular talc carbonate alterations could cause a local loss of ti and further redistribution of mg mn and zn prograde metamorphic reactions led to formation of ferritchromit and magnetite replacing primary chrome spinels another common process affecting ti rich chrome spinels is a prograde metamorphic recrystallization of exsolved ilmenite which changes from submicron lamellae through a regular grid of coarse ilmenite crystals and further to their irregular blebs and rims metamorphism of epidote amphibolite and amphibolite facies has led to the liberation of most of the elements metamorphically liberated cr was captured by antigorite

revised global model of thermosphere winds using satellite and ground based observations thermospheric wind data obtained from the atmosphere explorer e and dynamics explorer 2 satellites have been combined with wind data for the lower and upper thermosphere from ground based incoherent scatter radar and fabry perot optical interferometers to generate a revision hwm90 of the hwm87 empirical model and extend its applicability to 100 km comparison of the various data sets with the aid of the model shows in general remarkable agreement particularly at mid and low latitudes the ground based data allow modeling of seasonal diurnal variations which are most distinct at mid latitudes while solar activity variations are now included they are found to be small and not always very clearly delineated by the current data they are most obvious at the higher latitudes the model describes the transition from predominately diurnal variations in the upper thermosphere to semidiurnal variations in the lower thermosphere and a transition from summer to winter flow above 140 km to winter to summer flow below significant altitude gradients in the wind are found to extend to 300 km at some local times and pose complications for interpretation of fabry perot observations

the west spitsbergen current disposition and water mass transformation recent work suggests that the west spitsbergen current which provides the principal contribution to the arctic ocean of salt and sensible heat as well as of a variety of anthropogenic tracers is a rather complex circulation feature north of 79 n where the isobaths diverge markedly the current contains two separate warm cores that follow different isobaths the western core carried by the offshore branch of the current follows the western flank of the yermak plateau and north of 80 n at least part of this flow detaches from the plateau probably to contribute to the recirculation in fram strait in contrast the inshore branch follows the shelf break into the arctic ocean it is this inshore branch that provides the primary focus in this paper during the transit of the inshore waters past northwestern spitsbergen the core properties change primarily through vertical heat flux which during ice free conditions in winter is estimated to be of the order of 200 w m 2 from the core layer alone together with some freshening within the arctic ocean this process is responsible for fully transforming the original atlantic water into arctic intermediate water within about 600 km of fram strait

auroral zone thermospheric dynamics 1 averages forty four nights of thermospheric neutral wind and temperature measurements were obtained with a ground based fabry perot spectrometer at college alaska 65 invariant latitude mostly during high to moderate levels of solar activity the spectrometer scanned the o i 15 867 k 6300 a emission line yielding line profile measurements that originate from an altitude range between 170 and 280 km the observed average wind direction is to the northwest in the early evening changing to the south near midnight and then to the southeast in the morning the overall wind pattern generally persists but the wind speed increases with increasing geomagnetic activity a change in the zonal wind direction occurs earlier in magnetic local time with increasing magnetic activity the meridional wind pattern also shifts equatorward with the auroral oval during increasing magnetic activity consequently the average wind pattern in the north during low geomagnetic activity is rather similar to the moderate activity average in the south and the moderate geomagnetic activity average wind pattern in the north is similar to the high geomagnetic activity average in the south the observed average thermospheric temperature is found to be governed by geomagnetic activity and the previous day s 10 7 cm solar flux

petrogenesis of the merensky reef in the rustenburg section of the bushveld complex a petrogenetic model for the merensky reef in the rustenburg section of the bushveld complex has been developed based on detailed field and petrographic observations and electron microprobe data the model maintains that the reef formed by reaction of hydrous melt and a partially molten cumulate assemblage the model is devised to account for several key observations 1 although the dominant rock type in the rusterburg sections is pegmatoidal feldspathic pyroxenite there is a continous range of reef lithology from pyroxenite to pegmatoidal harzburgite and dunite and small amounts of olivine are present in nearly all pegmatoids 2 the pegmatoid is usually bounded above and below by chromitite seams and the basal chromitite separated from underlying norite by a centimeter thick layer of anorthosite the thicknesses of the two layers exhibit a well defined positive correlation 3 inclusion of pyroxenite identical to the hanging wall and of leuconorite identical to the footwall are present in the pegmatoid the leuconorite inclusions are surrounded by thin anorthosite and chromitite layers in the same sequence as that at the base of the reef 4 chromite in seams adjacent to plagioclase rich rocks is characterized by higher mg mg fe and al r3 and lower cr r3 than that in seams adjacent to pyroxene rich rocks similar variations in mineral compositions are observed across individual chromitite seams where the underlying and overlying rock types differ the chromite compositional variations cannot be rationalized in terms of either fractional crystallization or reequilibration with surrounding silicates it is proposed that the present reef was originally a melt rich horizon in norite immediately overlain by relatively crystallized pyroxenite magmatic vapor generated by crystallization of intercumulus melt migrated upward through fractures in the cumulate pile below the protoreef the melt rich protoreef became hydrated because fractures were unable to propagate through it and because the melt itself was water undersaturated hydration of the intercumulus melt was accompanied by melting and the hydration melting front migrated downward into the footwall and upward into the hanging wall in the footwall melting resulted first in the dissolution of orthopyroxene and then of plagioclase with continued hydration chromite was stabilized as melt alumina content increased the regular variations in chromite compositions reflect the original gradients in melt composition at the hydration front the stratigraphic sequence downward through the base of the reef or pegmatoid melt chromitite anorthosite norite represents the sequence of stable mineral assemblages across the hydration melting front the sequence is shown to be consistent with knowledge gained from experiments on melting of hydrous mafic systems at crustal pressures with cooling the hydrated mixture from partial melting of norite footwall and more mafic hanging wall crystallized in the sequence chromite olivine pyroxene plagioclase with peritectic loss of some olivine calculations of mass balance indicate that a significant proportion of the melt was lost from the melt rich horizon variations in the development of the pegmatoid and associated lithologies and amount of modal olivine in the pegmatoids along the strike of the merensky reef resulted because the processes of hydration melting and melt loss operated to varying extents

formation and evolution of the surface mixed layer and halocline of the arctic ocean fresh water from summer ice melt and the total freshwater content of the arctic ocean water column above the thermocline are estimated from vertical profiles of temperature and salinity observed on the i b oden 1991 cruise the seasonal ice melt ranges from 0 5 m to slightly above 1 m and is moderately uniform over the observation area regions of lower melting are seen over the morris jesup plateau the freshwater content is calculated relative to the salinity just above the thermocline north of the barents sea the freshwater content increases toward the interior of the arctic ocean showing that fresh water is advected from other regions into the observation area regions of different freshwater content are separated by fronts over the nansen gakkel ridge over the lomonosov ridge and in the western eurasian basin between waters derived from the eurasian and canadian basins denser water homogenized north of the barents sea is recognized by a temperature minimum layer the absence of the temperature minimum near the nansen gakkel ridge indicates that heat is transferred from the atlantic layer over a longer time than the shortest route would allow this observation can be explained if the layer circulates together with the atlantic layer i e toward the east and returns above the nansen gakkel ridge and along the amundsen basin north of the laptev sea this water formed north of the barents sea becomes covered by low salinity shelf water the increased freshwater content limits the winter convection so it no longer reaches the thermocline and an intermediate halocline is formed the halocline in the eurasian basin consists of water originating from winter convection in the arctic ocean north of the barents sea which then circulates around the basin such a formation mechanism also explains the observed distribution of low no water the strong density increase limits vertical exchange and the vertical diffusion coefficient in the halocline is small 1 10 6 m2 s 1 the increased temperature of the halocline shows that the heat lost upward by the atlantic layer mainly by double diffusive convection is trapped below the mixed layer

mechanisms of summertime upper arctic ocean warming and the effect on sea ice melt 1 in this study we use a numerical sea ice ocean model to examine what causes summertime upper ocean warming and sea ice melt during the 21st century in the arctic ocean our first question is what causes the ocean to warm in the pacific sector during the summer we find that about 80 of total heating over this region comes from ocean surface heat flux with the remaining 20 originating in ocean lateral heat flux convergence the latter occurs mostly within a few hundred kilometers of the northwest alaskan coast in the summer of 2007 the ocean gained just over twice the amount of heat it did over the average of the previous 7 years our second question is what causes sea ice to melt in the pacific sector during summer our analysis shows that top melt dominates total melt early in the summer while bottom melt and in particular bottom melt due to ocean heat transport dominates later in the summer as atmospheric heating declines bottom melt rates in summer 2007 were 34 higher relative to the previous 7 year average the modeled partition of top versus bottom melt closely matches observed melt rates obtained by a drifting buoy bottom melting contributes about 2 3 of total volume melt but is geographically confined to the marginal ice zone while top melting contributes a lesser 1 3 of volume melt but occurs over a much broader area of the ice pack

seasonal dependence of northern high latitude upper thermospheric winds a quiet time climatological study based on ground based and space based measurements this paper investigates the large scale seasonal dependence of geomagnetically quiet time northern high latitude f region thermospheric winds by combining extensive observations from eight ground based optical remote sensing and three space based optical remote sensing and in situ instruments to provide a comprehensive picture of the wind morphology data are assimilated into a seasonal empirical vector wind model as a function of season latitude and local time in magnetic coordinates the model accurately represents the behavior of the constituent data sets there is good general agreement among the various data sets but there are some major offsets between goce and the other data sets especially on the duskside the assimilated wind patterns exhibit a strong and large duskside anticyclonic circulation cell sharp latitudinal gradients in the duskside auroral zone strong antisunward winds in the polar cap and a weaker tendency toward a dawnside cyclonic circulation cell the high latitude wind system shows a progressive intensification of wind patterns from winter to equinox to summer the latitudinal extent of the duskside circulation cell does not depend strongly on season zonal winds show a mainly diurnal variation two extrema around polar and middle latitudes and semidiurnal variation four extrema at auroral latitudes meridional winds are primarily diurnal at all high latitudes the strength of zonal winds channeling through the auroral zone on the duskside is strongest in the summer season the vorticity of the wind pattern increases from winter to summer whereas divergence is maximum in equinox in all three seasons divergence is weaker than vorticity

optical interferometric measurements of nighttime equatorial thermospheric winds at arequipa peru we obtained nighttime measurements of equatorial thermospheric wind dynamics at arequipa peru with an automated field widened fabry perot interferometer between april 1983 and august 1983 and reduced data from 62 nights significant seasonal variations in both zonal and meridional components of the thermospheric neutral wind vector were observed near the equinox between 2000 and 2300 lt the zonal wind component is eastward with an amplitude between 100 and 150 m s that gradually ebbs to zero by dawn the meridional component is generally small throughout the night in the winter months may august and at the winter solstice the zonal wind persists eastward throughout the night with speeds between 50 and 150 m s the meridional component is directed poleward southward toward the winter hemisphere with a speed of 50 75 m s that decays to zero by midnight comparison with the predictions of the national center for atmospheric research thermospheric general circulation model for equinoctial and solstice conditions shows good agreement we conclude that the observed seasonal changes are caused by the changing nature of the solar forcing function the arequipa results found the day to day variability in the winter thermospheric winds to be less than that found for the summer equatorial observations obtained at kwajalein interferometric measurements of the 630 0 nm intensity at equinox showed a major reduction of the emission lasting 1 or 2 hours in all directions but south shortly after evening twilight this decrease was not observed during winter