geothermobarometry of high grade metapelites simultaneously operating reactions s u m m a r y experimental data on equilibria involving rock forming minerals in highgrade metapelites garnet orthopyroxene cordierite and plagioclase have been used to derive an internally consistent system of mineralogical thermometers and barometers based on component reactions and excess mixing properties of solid solutions application of these data to a granulite facies metapelite sample reveals that compositional inhomogeneity of minerals on a thin section scale is likely to be a result of several reactions opening simultaneously at the retrograde stage of metamorphic evolution the widely accepted practice of estimating pressure and temperature from separate reactions may thus lead to errors and misinterpretation of p t paths

sapphirine bearing orthopyroxene kyanite sillimanite granulites from south harris nw scotland evidence for proterozoic uht metamorphism in the lewisian sapphirine bearing orthopyroxene kyanite opx ky and sillimanite opx sil granulites have been found in the lewisian complex of south harris in northwest scotland in the opx ky granulites orthopyroxene and kyanite are intergrown in a stable mineral assemblage which indicates metamorphic condition at 800 900 c 12 kbar sillimanite inclusions within orthopyroxene suggest that sillimanite formed earlier conditions are estimated at 950 30 c at 10 kbar from orthopyroxene isopleths for aluminous orthopyroxene 8 kbar according to the fmas petrogenetic grid and similar conditions were obtained by using orthopyroxene garnet geothermobarometers the two types of orthopyroxene aluminosilicate granulites indicate that the peak metamorphic conditions were over 900 c compatible with ultra high temperature metamorphism as accessory sapphirine occurs in several assemblages and with different compositions it is interpreted to be formed at different stages of the metamorphism these granulites were formed during early proterozoic high grade metamorphism due to the emplacement of the south harris igneous complex at c 2170 1870 ma and are not related to the major metamorphic episode of the badcallian inverian metamorphism at c 2700 2500 ma in the mainland lewisian

high frequency internal wave observations in the marginal ice zone three thermistor chains extending from 15 to 65 m were deployed from ice floes in the marginal ice zone north of svalbard in a triangle with sides of 500 800 m for a period of 7 days vertical displacement spectra indicate that the internal wave energy level is lower than the garrett and munk spectrum by a factor of 2 3 but higher than other observations in the arctic a group of internal waves a wave train with frequency of 2 3 cph was observed to propagate at 0 05 m s through the triangle in a west southwesterly direction during a 4 to 6 hour period a case study of this wave train where the horizontal phase differences between the three thermistor chains were analyzed showed wavelengths of 100 200 m and phase velocities of 0 10 0 15 m s observation of the density field and the velocity field indicated that stratification dominated over vertical shear consequently the dispersion relation was calculated by solving numerically the vertical mode equation for internal waves in a shearless ocean the estimated wavelengths and phase velocities agree with the dispersion relation for first mode internal waves the generating mechanisms may be tidal oscillations associated with a seamount located east of the triangle or ice keels moving in relation to the water creating lee waves in the pycnocline

origin of freshwater and polynya water in the arctic ocean halocline in summer 2007 extremely low summer sea ice coverage in the arctic ocean in 2007 allowed extensive sampling and a wide quasi synoptic hydrographic and 18o dataset could be collected in the eurasian basin and the makarov basin up to the alpha ridge and the east siberian continental margin with the aim of determining the origin of freshwater in the halocline fractions of river water and sea ice meltwater in the upper 150 m were quantified by a combination of salinity and 18o in the eurasian basin two methods applying the preformed phosphate concentration po and the nitrate to phosphate ratio n p were compared to further differentiate the marine fraction into atlantic and pacific derived contributions while po based assessments systematically underestimate the contribution of pacific derived waters n p based calculations overestimate pacific derived waters within the transpolar drift due to denitrification in bottom sediments at the laptev sea continental margin within the eurasian basin a west to east oriented front between net melting and production of sea ice is observed outside the atlantic regime dominated by net sea ice melting a pronounced layer influenced by brines released during sea ice formation is present at about 30 to 50 m water depth with a maximum over the lomonosov ridge the geographically distinct definition of this maximum demonstrates the rapid release and transport of signals from the shelf regions in discrete pulses within the transpolar drift the ratio of sea ice derived brine influence and river water is roughly constant within each layer of the arctic ocean halocline the correlation between brine influence and river water reveals two clusters that can be assigned to the two main mechanisms of sea ice formation within the arctic ocean over the open ocean or in polynyas at the continental slope where relatively small amounts of river water are found sea ice formation results in a linear correlation between brine influence and river water at salinities of about 32 to 34 in coastal polynyas in the shallow regions of the laptev sea and southern kara sea sea ice formation transports river water into the shelf s bottom layer due to the close proximity to the river mouths this process therefore results in waters that form a second linear correlation between brine influence and river water at salinities of about 30 to 32 our study indicates which layers of the arctic ocean halocline are primarily influenced by sea ice formation in coastal polynyas and which layers are primarily influenced by sea ice formation over the open ocean accordingly we use the ratio of sea ice derived brine influence and river water to link the maximum in brine influence within the transpolar drift with a pulse of shelf waters from the laptev sea that was likely released in summer 2005

the pyrope coesite rocks and their country rocks at parigi dora maira massif western alps detailed petrography mineral chemistry and pt path both the coarse and fine grained varieties of the partly coesite bearing pyrope quartzites their interlayered jadeite kyanite rocks and the biotite phengite gneiss country rock common to all of them were subjected to detailed petrographic and textural studies in order to determine the sequence of crystallisation of their mineral constituents which were also studied analytically by microprobe prior to pyrope and coesite growth the mg rich metapelites were talc kyanite chlorite rutile ellenbergerite schists which upon continued prograde metamorphism developed first pyrope megacrysts in silica deficient local environments at the expense of chlorite talc kyanite and subsequently the smaller pyrope crystals with coesite inclusions from reacting talc kyanite based on geobarometrically useful mineral inclusions as well as on experimentally determined phase relations a prograde pt path simplified for water activity 1 is constructed which passes through the approximate pt conditions 16 kbar and 560 c 29 kbar and 720 c and finally up to 37 kbar at about 800 c where the mg rich metapelite was a pyrope coesite rock with phengite kyanite and talc still present during the retrograde path pyrope was altered metasomatically either into phlogopite kyanite quartz or at a later stage to chlorite muscovite quartz both assemblages yield pt constraints the latter about 7 9 kbar 500 600 c the country rock gneisses have also endured high pressures of at least 15 kbar but they provide mostly constraints on the lowest portion of the uplift conditions within the greenschist facies about 5 kbar 450 c microprobe data are presented for the following minerals pyrope ellenbergerite dumortierite unusually mgti rich jadeite vermiculite formed after na phlogopite paragonite and for several generations of phengite chlorite talc phlogopite dravite and glaucophane in the high pressure rocks as well as for biotite chlorite phengites epidote garnet albite and k feldspar in the country rock gneisses an outstanding open problem identified in this study is the preservation of minerals as inclusions within kyanite and pyrope beyond their pt stability limits

mixing properties of phengitic micas and revised garnet phengite thermobarometers mixing properties for muscovite celadonite ferroceladonite solid solutions are derived from combining available experimental phase equilibrium data with tabulated thermodynamic data for mineral end members when a partially ordered solution model is assumed the enthalpy of mixing among the end members muscovite celadonite ferroceladonite is nearly ideal although the gibbs energies of muscovite celadonite and muscovite ferroceladonite solutions are asymmetric due to an asymmetry in the entropy of mixing thermodynamic consistency is achieved for data on phengite compositions inassemblages with a pyrope kyanite quartz coesite b almandine kyanite quartz coesite c talc kyanite quartz coesite and d garnet phengite pairs equilibrated both experimentally at high temperatures and natural pairs from low grade schists the muscovite paragonite solvus has been reanalysed using the asymmetric van laar model and the effects of the phengite substitution into muscovite have been quantitatively addressed in order to complete the simple thermodynamic mixing model for the solid solution among the mica end members results are applied to a natural pyrope coesite phengite talc rock from the western alps and to investigate the conditions under which biotite bearing mica schists transform to whiteschist like biotite absent assemblages for average pelite bulk compositions

the sea ice thickness distribution in the northwestern weddell sea we present new data on distribution of snow and sea ice thicknesses in the northwestern weddell sea the data were obtained through direct measurements along 19 profiles each approximately 100 m long on 17 different floes located between 54 46 w and 59 64 s the overall probability density functions pdfs for ice thicknesses reflect the complex mixture of first second and multi year ice to be expected in the outflowing branch of the weddell gyre further differentiation of the data reveals four distinct thickness classes which reflect differences in the formation and subsequent histories of the ice encountered these classes i iv represent strongly deformed first year ice less deformed first and second year ice and deformed second or multi year ice respectively each of the classes is characterized by a specific set of quantities related to ice texture and surface snow characteristics and by distinct pdfs for snow and ice thicknesses in addition geometric surface and bottom roughness characteristics differ significantly for each of the floe classes

coesite and pure pyrope in high grade blueschists of the western alps a first record and some consequences a pyrope quartzite originally described by vialon 1966 from the dora maira massif was resampled and reinvestigated garnet up to 25 cm in size phengite kyanite talc and rutile are in textural equilibrium in an undeformed matrix of polygonal quartz the garnet is a pyrope almandine solid solution with 90 to 98 mol mg end member it contains inclusions of coesite which has partially inverted to quartz resulting in a typical radial cracking of the host garnet around the inclusions several lines of evidence show that coesite crystallised under nearly static pressure conditions and that the whole matrix has once been coesite

experimental evidence for diamond facies metamorphism in the dora maira massif the peak metamorphic conditions of subducted continental crust in the dora maira massif western alps have been revised by combining experimental results in the kcmash system with petrologic information from whiteschists textural observations in whiteschists suggest that the peak metamorphic assemblage garnet phengite kyanite coesite talc originates from the reaction kyanite talc garnet coesite liquid in the experimentally determined petrogenetic grid this reaction occurs above 45 kbar at 730 c at lower pressures talc reacts either to orthopyroxene and coesite or together with phengite to biotite coesite and kyanite the liberated liquid contains probably similar amounts of h2o and dissolved granitic components the composition of the liquid in the whiteschists at peak metamorphic conditions a major unknown in earlier studies was probably very similar to the liquid composition produced in the experiments therefore the experimentally determined petrogenetic grid represents a good model for the estimation of the peak metamorphic conditions in whiteschists experimentally determined si isopleths for phengite further constrain peak pressures to 43 kbar for the measured si 3 60 of phengite in the natural whiteschists all these data provide evidence that the whiteschists reached diamond facies conditions the fluid absent equilibrium 4 kyanite 3 celadonite 4 coesite 3 muscovite pyrope has been calibrated on the basis of garnet and phengite compositions in the experiments and serves as a geothermobarometer for ultra high pressure uhp metapelites for graphite bearing metapelites and kyanite phengite eclogites forming the country rocks of the whiteschists peak metamorphic pressures of about 44 3 kbar were calculated from this barometer for temperatures of 750 c estimated from garnet phengite thermometry therefore the whole ultra high pressure unit of the dora maira massif most likely experienced peak metamorphic conditions in the diamond stability field while graphite is common in the metapelites diamond has not been found so far the absence of metamorphic microdiamonds might be explained by the low temperature of metamorphism the absence of a free fluid phase in the metapelites and a short residence time in diamond facies conditions resulting in kinetic problems in the conversion of graphite to diamond

regulation of algal blooms in antarctic shelf waters by the release of iron from melting sea ice during summer 1995 96 we measured iron in the water column and conducted iron enrichment bottle incubation experiments at a station in the central ross sea 76 30 s 170 40 w first in the presence of melting sea ice and 17 days later in ice free conditions we observed a striking temporal change in mixed layer dissolved iron concentrations at this station from 0 72 2 3 nm with sea ice present to 0 16 0 17 nm in ice free conditions these changes were accompanied by a significant drawdown in macronutrients and an approximate doubling of algal diatom biomass our incubation experiments suggest that conditions were iron replete in the presence of sea ice and iron deficient in the absence of sea ice we surmise that bioavailable iron was released into seawater from the melting sea ice stimulating phytoplankton production and the biological removal of dissolved iron from the mixed layer until iron limited conditions developed these observations suggest that the episodic release of bioavailable iron from melting sea ice is an important factor regulating phytoplankton production particularly ice edge blooms in seasonally ice covered antarctic waters

a petrogenetic grid for the system mgo al_ 2 o_ 3 sio_ 2 a comprehensive analysis of phase relations in the system mgo al 2 o 3 sio 2 mas was carried out using primarily the data from phase equilibrium experiments in mas spinel and garnet peridotite systems the resulting phase relations were extended to the whole mas system by maintaining internal consistency and using other relevant experimental data equilibria include cordierite and sapphirine which are usually omitted in the construction of comprehensive petrogenetic grids a larger number of petrologically important equilibria involving these and the other mas phases appear to be stable and have not been enumerated previously the analysis produced an internally consistent set of thermodynamic parameters that closely agree with the measured thermochemical values although some outstanding discrepancies still remain the result provides a simple and practical tool for calculating the phase relations in the mas system and potentially also in more complex chemical systems this is demonstrated with

melting of peridotites through to granites a simple thermodynamic model in the system kncfmashtocr a new set of thermodynamic models is presented for calculating phase relations in bulk compositions extending from peridotite to granite from 0 001 to 70 kbar and from 650 c to peridotite liquidus temperatures in the system k2o na2o cao feo mgo al2o3 sio2 h2o tio2 fe2o3 cr2o3 kncfmashtocr the models may be used to calculate phase equilibria in partial melting of a large range of mantle and crustal compositions they provide a good fit to experimental phase relation topologies and melt compositions across the compositional range of the model compared with the preliminary model of jennings holland 2015 for peridotite basalt melting relations the inclusion of k2o and tio2 allows for better modelling of small melt fractions in peridotite melting and in reproducing rutile bearing eclogite melting at high pressures an improved order disorder model for spinel is now incorporated above 10 kbar pressure wet partial melting relations may be significantly affected by the dissolution of silicates in aqueous fluid so the set of models includes an aqueous low density silicate bearing fluid in addition to a high density h2o bearing silicate melt oxygen fugacity may be readily calculated for the whole range of bulk compositions investigated and the effect of water content on melt fo2 is assessed

fluvial and hydrothermal input of manganese into the arctic ocean abstract a total of 773 samples were analysed for dissolved manganese mn in the arctic ocean aboard r v polarstern during expedition ark xxii 2 from 28 july until 07 october 2007 from tromso norway to bremerhaven concentrations of mn were elevated in the surface layer with concentrations of up to 6 nm over the deep basins and over 20 nm in the laptev sea the general distribution of mn through the water column is consistent with previous studies but there are differences in the absolute concentrations that are most likely related to differences in sample area sampling and filtration the elevated concentrations of mn in the surface layer are related to fresh water input this was visible in the strong negative correlations observed between dissolved mn and salinity the correlation between mn and salinity and the correlation between mn and the quasi conservative trace water mass tracer po4 showed fluvial and melt water input and the pacific and atlantic origin of the surface waters a large portion of the mn delivered by the arctic rivers is removed in the shelf seas and does not pass into the central basins most likely a benthic flux is at the origin of the elevated concentrations of mn near the sediments in the barents and kara seas these elevated concentrations of mn apparently affected the deep basins as well as maxima in the concentrations of mn were observed that corresponded with lowered transmission over the continental slope a maximum in the concentration of mn in the deep basin corresponded with anomalies in light transmission potential temperature and dissolved iron confirming the hydrothermal origin the hydrothermal plume was observed throughout the nansen basin and over the deep gakkel ridge around 2500 m depth and a smaller plume was observed around 3200 m the concentration of mn at the mn maximum around 2500 m depth decreased exponentially consistent with a first order scavenging model the concentrations of mn were extremely low in the deep makarov basin 0 05 nm and slightly higher in the eurasian basin 0 1 nm outside the influence of the hydrothermal activity

boundary layer upper ocean and ice observations in the greenland sea marginal ice zone during the 1984 marginal ice zone experiment a coordinated ocean boundary layer and mixed layer experiment was carried out in concert with a complete heat and mass balance study in the summer marginal ice zone miz of the greenland sea the measurements were made at two drifting ice stations and included observations of ocean boundary layer turbulence profiles of water temperature salinity and velocity ice ablation ice concentration solar radiation and spectral albedos ocean conditions were found to be extremely variable the ice and water velocities were heavily influenced by tidal and inertial motions with amplitudes from 6 to 12 cm s 1 in the course of the drift a 30 km eddy was crossed wherein ice and water velocities exceeded 15 cm s 1 the northern extension of the east greenland polar front was encountered and a northward flow of atlantic water into the arctic basin was observed below the eastern edge of the front but the drift station never moved quite far enough west to be caught in the southward transport of arctic surface water heat from the ocean was a major factor in ice melt and when the ice was over atlantic water it was the dominant factor the events that had the greatest impact on the ice were two outbreaks during which off ice winds blew the ice across warm ice edge ocean fronts once south of these fronts and over surface water as warm as 1 c the ice bottom melted at rates up to 100 kg m 2 d 1 the rapid changes in stratification associated with the outbreaks had a dramatic impact on the drag and heat transfer coefficients the drag coefficient relative to the square of the relative water velocity at 30 m ranged from 0 002 to 0 02 and averaged 0 006 the heat transfer coefficient relative to the friction velocity u and the mixed layer temperature elevation above freezing ranged from 0 0025 to 0 009 and averaged 0 0038 in agreement with the idea that stratification inhibits turbulent exchange the heat transfer coefficient decreased when stratification increased in fact the observed melt rates can be simulated well if molecular heat and salt transfer through a thin near surface laminar boundary layer are accounted for as well as transfer through the turbulent outer boundary layer also in agreement with turbulent boundary layer theory the drag coefficient decreased when stratification increased slightly above neutral however for the large increases in surface stratification the drag coefficient increased this was due to the generation of internal gravity waves by ice bottom roughness because the surface exchange coefficients are so sensitive to surface stratification which is in turn highly variable in the miz accurate simulations of ice motion and ice melt will require realistic estimates of stratification and a good understanding of the relation between the ice ocean interactions and upper ocean conditions

freshwater balance and the sources of deep and bottom waters in the arctic ocean inferred from the distribution of h218o data from sections across the eurasian basin of the arctic ocean occupied in 1987 and 1991 are used to derive information on the freshwater balance of the arctic ocean and on sources of the deep waters of the nansen amundsen and makarov basins using salinity h218o and mass balances we estimate the river runoff and the sea ice melt water fractions contained in the upper waters of the arctic ocean and infer pathways of the river runoff signal from the shelf seas across the central arctic ocean to fram strait the average mean residence time of the river runoff fraction contained in the arctic ocean halocline is determined to be about 11 to 14 years pacific water entering through bering strait is traced using silicate and its influence on the halocline waters of the canadian basin is estimated water column inventories of river runoff and sea ice melt water are calculated for a section just north of fram strait and implications of these inventories for sea ice export through fram strait are discussed comparison of the 18o 16o ratios of shelf water atlantic water and the deep waters of the arctic ocean indicate that the sources of the deep and bottom waters of the eurasian basin are located in the barents and kara seas

thermodynamic modelling of sodic pyroxene solid solution and its application in a garnet omphacite kyanite coesite geothermobarometer for uhp metamorphic rocks a garnet omphacite kyanite coesite geothermobarometer is constructed to estimate the peak metamorphic pressure of ultrahigh pressure uhp eclogites for this we use a quaternary regular solution model for garnet and propose a new model for sodic pyroxene that assumes double site solid solution na ca m2 al fe3 fe2 mg m1si2o6 where cations in the m2 and the m1 sites mix randomly but with inter site interactions not only between nearest neighboring cations but also between next nearest neighboring cations in the new model overall excess interaction parameters are quantitatively deduced from the previous experimental data and critical temperature and the activity of the jadeite component agrees reasonably with that based on the landau theory furthermore the relations of the calculated order parameter to temperature and composition are consistent with other experimental works these facts support the usefulness of the new model application of our geothermobarometer to kyanite eclogite gave metamorphic conditions around 3 4 gpa and 800 c for both samples from the dora maira massif western alps and from rongcheng county in the su lu region of eastern china

water masses and circulation in the eurasian basin results from the oden 91 expedition the oden 91 north pole expedition obtained oceanographic measurements on four sections in the nansen and amundsen basins of the eurasian basin and in the makarov basin of the canadian basin thereby proving the feasibility of carrying out a typical oceanographic program using an icebreaker in the arctic ocean the data show greater spatial variability in water structure and circulation than was apparent from previous data the results show that a clear front exists between the eurasian and canadian basins such that upper halocline water in the canadian basin is almost absent from the eurasian basin the lower halocline water produced in the barents kara sea region permeates much of the eurasian basin and flows along the continental slope into the canadian basin the deeper circulation is strongly influenced by topography three return flows of the atlantic layer are identified one over the nansen gakkel ridge one over the lomonosov ridge and a third flowing from the canadian basin the slight differences observed in salinity and temperature characteristics of the deeper waters of the nansen and amundsen basins do not lead to an obvious explanation of their origin or flow pattern

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

low pressure temperature stability of pyrope quartz relative to orthopyroxene kyanite a new model for aluminous orthopyroxene with vacancies determination of the stability of pyrope with quartz could provide theoretical pressure temperature p t constraints on silica saturated eclogites as well as near end member pyrope bearing terrains the lower p t stability of pyrope in the presence of quartz in the system mgo al2o3 sio2 can be modeled by the reaction 3 enstatite 2 kyanite 2 pyrope 2 quartz reaction reversals were experimentally obtained using a in diameter piston cylinder press and a 1000 t multi anvil press besides natural quartz all other starting materials including orthopyroxene pyrope and kyanite were synthesized the reaction has been bracketed at 1 50 gpa at 1040 1080 c 1 69 1 79 gpa at 1000 c 2 26 gpa at 920 940 c 2 90 gpa at 840 860 c the bracketed boundary is higher in temperature and pressure than that calculated using the newest dataset of holland et al j petrol 59 881 900 https doi org 10 1093 petrology egy048 2018 particularly at higher pressures aluminum is usually thought to be taken into orthopyroxene in the form of mg tschermak s pyroxene mgts mgal2sio6 under these experimental p t conditions in contrast the observed orthopyroxene composition indicated the involvement of a non stoichiometric component mg eskola pyroxene mges mg0 5 0 5alsi2o6 an aluminous orthopyroxene with octahedral vacancies end member thermodynamic properties for mges as well as a mixing model for the ternary enstatite mgts mges solid solution have been derived the thermodynamic calculations employing the mixing model are in good agreement with the experimental brackets the new model has potential applications to constrain p t conditions of tectonic settings such as ultrahigh pressure and ultrahigh temperature metamorphisms

fluids of the lower crust deep is different deep fluids are important for the evolution and properties of the lower continental and arc crust in tectonically active settings they comprise four components h2o nonpolar gases salts and roc

contour mapping of arctic basin ice draft and roughness parameters a data base of ice draft and roughness parameters has been constructed for selected portions of the arctic ocean based upon analysis of under ice draft distribution data acquired by inverted echo sounder systems on submarines from the voyages of 12 submarines which traversed the alaskan canadian and central arctic regions of the arctic ocean during the summer and winter seasons a series of mean ice draft and deep draft keel statistics was calculated for 50 km segments along each submarine track contour maps of the mean ice draft its standard deviation the mean keel draft and the spatial frequency of ice keels were constructed they show that the greatest ice drafts the roughest ice and the greatest number of deep draft keels are found off the north coasts of the canadian archipelago and greenland due to ice convergence on these land barriers

pacific freshwater river water and sea ice meltwater across arctic ocean basins results from the 2005 beringia expedition 1 pacific water sea ice meltwater and river water are the primary sources of freshwater in the arctic ocean we have determined their relative fractions on a transect across the arctic ocean section 2005 expedition onboard ib oden which took place from 21 august to 23 september 2005 the transect began north of alaska continued through the central canada basin to the alpha ridge and into the makarov basin and ended in amundsen basin pacific freshwater and river water were the major sources of freshwater throughout the central canada basin and into makarov basin with river water fractions sometimes considerably higher than pacific water in the top 50 m pacific freshwater extended to depths of about 200 m pacific water found over the alpha ridge and in the amundsen basin is suggested to have been transported there in the transpolar drift the inventories of pacific freshwater and river water were roughly constant along the section through most of the canada and makarov basins river water fractions were greater than those of pacific freshwater in the amundsen basin sea ice meltwater fractions were negative reflecting net ice formation or near zero throughout most of the section a comparison of freshwater inventories with those at stations occupied during expeditions in 1991 1994 and 1996 indicated an increase in river water inventories in the makarov and amundsen basins on the eurasian side of the arctic ocean

distribution of atlantic and pacific waters in the upper arctic ocean implications for circulation the atlantic and pacific oceans provide source waters for the arctic ocean that can be distinguished by their differing nitrate and phosphate concentration relationships using these relationships we estimate the amount of atlantic and pacific waters in the surface layer top 30 m of the arctic ocean atlantic source water is dominant in most of the eurasian basin and is present in significant amounts in the makarov basin north of the east siberian sea pacific source water is dominant in most of the canadian basin and is present in significant amounts in the amundsen basin north of greenland we deduce circulation patterns from the distributions of atlantic and pacific source waters in the surface layer of the arctic ocean and conclude that the flow within the surface layer differs from ice drift along the north american and european boundaries of the polar basin

internal wave generation by ice floes moving in stratified water results from a laboratory study a series of tests has been conducted to investigate the increased ice water drag exhibited by ice floes in two layer salinity stratified water scaled model tests are used to quantify the additional drag due to internal wave creation at the fresh water salt water interface this additional drag is shown to have a peak value five times the drag in similar unstratified conditions and to have a strong dependence on a few well defined nondimensional parameters describing the ice and water characteristics

the al 2 o 3 contents of enstatite in equilibrium with garnet in the system mgo al 2 o 3 sio 2 at 15 40 kbar and 900 1 600 c forty six reversed determinations of the al2o3content of enstatite in equilibrium with garnet were made in the p t range 15 40 kbar 900 1 600 c in the mgo al2o3 sio2 system starting materials were mixtures of synthetic pyrope al free enstatite and pyrope enstatite 5 12 al2o3 al2o3 contents in reversal run pairs closely approached common values from both the high and low al sides most experiments were done in a piston cylinder device using a nacl medium some runs at very high temperatures were made in pyrex nacl or pyrex talc assemblies the measured enstatite compositions expressed as mole fractions of mg2 mgal alsi3 o12 x opy en were fitted by a monte carlo method to the equilibrium condition begin gathered delta h 970 0 970 delta s 970 0 hfill mathop smallint limits 1 p delta v 970 0 dp mathop smallint limits 970 t delta s t 0 dt rt ln x opy en 0 hfill end gathered where the best fit parameters of h s and v 1 bar 970 k for the reaction pyrope opy are 2 040 cal mol 2 12 eu and 9 55 cc mol in addition to the determination of al2o3 contents of enstatite the univariant reaction pyrope forsterite enstatite spinel was reversibly located in the range 1 100 1 400 c a best fit line passes through 22 22 5 and 25 kbar at 1 040 1 255 and 1 415 c respectively our results for the univariant reaction are in agreement with previous studies of macgregor 1974 and haselton 1979 however comparison of the experimentally determined curve with thermochemical calculations suggests that there may be a small error in the tabulated h f 970 1 0 value for enstatite a value of 8 32 rather than 8 81 kcal mole charlu et al 1975 is consistent with the present data application of garnet enstatite spinel forsterite equilibria to natural materials is fraught with difficulties the effects of nonternary components are poorly understood and the low solubilities of al2o3 in enstatite under most geologically reasonable conditions make barometric or thermometric calculations highly sensitive more detailed studies including reversed determinations in low friction assemblies are sorely needed before the effects of important diluents such as fe ca and cr can be fully understood

river runoff sea ice meltwater and pacific water distribution and mean residence times in the arctic ocean hydrographic and tracer data collected during ark iv 3 fs polarstern in 1987 arctic91 ib oden and aos94 ccgs louis s st laurent expeditions reveal the evolution of the near surface waters in the arctic ocean during the late 1980s and early 1990s salinity nutrients dissolved oxygen and 18 o data are used to quantify the components of arctic freshwater river runoff sea ice meltwater and pacific water the calculated river runoff fractions suggest that in 1994 a large portion of water from the pechora ob yenisey kotuy and lena rivers did not flow off the shelf closest to their river deltas but remained on the shelf and traveled via cyclonic circulation into the laptev and east siberian seas river runoff flowed off the shelf at the lomonosov ridge and most left the shelf at the mendeleyev ridge arctic91 and aos94 pacific water fraction estimates of upper halocline water the traditionally defined core of the pacific water mass document a decrease in extent compared to historical data the front between atlantic water and pacific water shifted from the lomonosov ridge location in 1991 to the mendeleyev ridge in 1994 the relative age structure of the upper waters is described by using the 3 h 3 he age the mean 3 h 3 he age measured in the halocline within the salinity surface of 33 1 0 3 is 4 3 1 7 years and that for the 34 2 0 2 salinity surface is 9 6 4 6 years lateral variations in the relative age structure within the halocline and atlantic water support the well known cyclonic boundary current circulation

dehydration of glaucophane in the system na2o mgo al2o3 sio2 h2o and the effects of nacl co2 and silicate bearing aqueous fluids

downward lee wave radiation from tropical instability waves in the central equatorial pacific ocean a possible energy pathway to turbulent mixing turbulent mixing in the equatorial pacific ocean is an important process that controls diapycnal heat transport and hence affects the air sea interactions and global climate it is recently shown that in the eastern equatorial pacific strong mixing is induced in the thermocline by enhanced vertical shear associated with tropical instability waves tiws which propagate westward along the equator at a speed of 0 5 m s 1 with a wavelength of 1000 km in this study using a high resolution ocean general circulation model we show that the tiws can play an important role in inducing turbulent mixing in the thermocline also in the central equatorial pacific although the thermocline is too deep to be directly affected by the vertical shear of the tiws the front of the tiw is clearly manifested as a narrow strip of strong convergence of horizontal surface flow from which area downward and westward propagating internal waves are intermittently emanated these internal waves can be interpreted as lee waves generated by the surface flow convergence zone which acts like an inverted obstacle moving along the stratified ocean surface by inducing downward flow the associated downward energy flux below the surface mixed layer increases as the tiw structure becomes deeper toward the central equatorial pacific so that the energy pathway to turbulent mixing in the thermocline can be created the downward energy flux integrated over the entire equatorial pacific and averaged during january 2011 amounts to 8 1 gw occupying a significant fraction of the energy input to the tiws

effect of h2o on liquidus relationships in mgo al2o3 sio2 at 30 kilobars dehydrated gels with compositions corresponding to mixtures of pyrope enstatite pyrope quartz and pyrope quartz corundum were sealed in platinum capsules and reacted in half inch piston cylinder apparatus at 30 kbar samples were pyrope composition with variable h2o and other compositions with 7 5 wt h2o highly aluminous metastable orthopyroxenes nucleated from and persisted in mixtures with compositions near pyrope there is no univariant fusion curve for pyrope h2o pyrope dissolves incongruently in h2o subsolidus and a trace of liquid is produced near 1000 c a univariant reaction pyrope forsterite vapor spinel liquid was located at 1150 20 c the liquidus for pyrope with excess h2o is at 1310 c orthopyroxenes coexisting with sio2 rich liquids contain 0 8 5 7 excess sio2 compared with mgsio3 al2o3 liquidus diagrams dry with 7 5 h2o and with excess h2o illustrate the effect of h2o on the liquidus relationships with increasing h2o the liquidus volume for opx expands greatly at

excess silica in omphacite and the formation of free silica in eclogite silica lamellae in eclogitic clinopyroxene are widely interpreted as evidence of exsolution during decompression of eclogite however mechanisms other than exsolution might produce free silica and the possible mechanisms depend in part on the nature and definition of excess silica excess silica may occur in both stoichiometric and non stoichiometric pyroxene although the issue has been debated we show that all common definitions of excess silica in non stoichiometric clinopyroxene are internally consistent interchangeable and therefore equivalent the excess silica content of pyroxene is easily illustrated in a three component condensed composition space and may be plotted directly from a structural formula unit or recalculated end members in order to evaluate possible mechanisms for the formation of free silica in eclogite we examined the net transfer reactions in model eclogites using a thompson reaction space we show that there are at least three broad classes of reactions that release free silica in eclogite i vacancy consumption in non stoichiometric pyroxene ii dissolution of ti phases in pyroxene or garnet iii reactions between accessory phases and either pyroxene or garnet we suggest that reliable interpretation of the significance of silica lamellae in natural clinopyroxene will require the evaluation not only of silica solubility but also of titanium solubility and the possible roles of accessory phases and inclusions on the balance of free silica

generation of internal waves by sea ice observations in the greenland sea marginal ice zone suggest that when strong stratification occurs near the surface momentum flux into the internal wave field of the upper ocean can be a major component of the force balance that governs ice drift since energy is radiated away by the internal waves turbulent mixing and heat flux are also affected we investigate the downward flux of momentum and energy by internal waves in an ice covered ocean with an idealized model comprising a mixed layer overlying a deep uniformly stratified layer a buoyancy jump separates the mixed layer from the pycnocline drag from a single wave number component of the under ice roughness spectrum is derived as the product of a drag coefficient based on ice speed under ice roughness wave number and amplitude and uniform stratification to the ice ocean interface times an attenuation factor that depends additionally on mixed layer depth and the buoyancy jump at the base of the mixed layer the model is extended to a plausible spectrum of under ice roughness by integration over wave number space internal wave effects are parameterized in terms of the drag coefficient from the integrated spectrum and incorporated into an upper ocean turbulence model model calculations show that plausible values for the peak wave number of the idealized spectrum and roughness variance can account for 1 decreased ice velocity relative to the wind 2 decreased heat exchange coefficient between the ice and ocean and 3 lack of mixed layer deepening all of which were observed during the last week of the 1984 marginal ice zone experiment

alumina solubility in orthopyroxene coexisting with sapphirine and quartz the solubility of alumina in orthopyroxene coexisting with sapphirine and quartz was determined over the p t interval 1 250 1 350 c and 10 16 kbar in the system mgo al2o3 sio2 five isobaric experiments were reversed at 12 kbar at 25 c intervals between 1 250 and 1 350 c and two isothermal experiments at 1 325 c at 14 and 16 kbar these constrain the p t x relationships of the reaction rm mg tschermak s rm orthopyroxene mg sapphirine rm 221 rm quartz the reaction is strongly temperature dependent and slightly pressure dependent dp dt ca 94 b k 1 and alumina in orthopyroxene increases by ca 1 wt per 26 c over the temperature interval studied no corresponding compositional trend in sapphirine was resolvable an effect attributed to only small changes in alumina solubility with temperature and sluggish kinetics of sapphirine entropy calculations for sapphirine based on a recent dataset and minimum constraints from an oxide sum approach fall within the 90 confidence limits of our data but above a linear best fit of our data the latter discrepancy suggests that disequilibrium in sapphirine and or configurational disorder in orthopyroxene may have been important in the experiments when taken into account these factors bring our data into reasonable agreement with an oxide sum calculation

dissolved iron in the arctic shelf seas and surface waters of the central arctic ocean impact of arctic river water and ice melt key points dfe in the arctic shelves and surface is linked to freshwater and alkalinity fluvial input main contributor to high dfe low alkalinity in central arctic remineralisation and biological depletion determine dfe in the arctic shelf seas abstract concentrations of dissolved 10 nm in the bottom waters of the laptev sea shelf may be attributed to either sediment resuspension sinking of brine or regeneration of dfe in the lower layers a significant correlation r2 0 60 between salinity and dfe is observed using 18o salinity nutrients and total alkalinity data the main source for the high 2 nm dfe concentrations in the amundsen and makarov basins is identified as eurasian river water transported with the transpolar drift tpd on the north american side of the tpd the dfe concentrations are low 4 above the shelf and low 4 off the shelf

first data on trace metal level and behaviour in two major arctic river estuarine systems ob and yenisey and in the adjacent kara sea russia dissolved and colloidal trace element concentrations cd cu fe ni and pb were determined in the ob and yenisey river estuary systems and in the adjacent kara sea in september 1993 the data show a natural low concentration level of dissolved 0 4 m trace metals cd cu fe ni and pb in the two rivers and in the kara sea as compared to world unpolluted rivers and the central arctic ocean suggesting that the region studied is pristine with respect to trace metals the pathway of trace metals transported from rivers to the ocean seems to be complicated and largely influenced by biogeochemical processes taking place in the estuarine mixing zone colloidal material 104 daltons 0 4 m in addition to its significant contribution to the so called dissolved fraction has been shown to play a fundamental role in determining the behaviour of both conservative and non conservative trace metals during estuarine mixing hence colloids may control to a large extent the fate of dissolved trace metals as well as their net input from the rivers to the kara sea

the stability of mg rich garnet in the system cao mgo al 2 o 3 sio 2 at 1000 1300 degrees c and high pressure buffering assemblages are stable in separate divariant p t fields separated by three univariant reactions garnet quartz orthopyroxene anorthite sillimanite garnet quartz clinopyroxene orthopyroxene anorthite clinopyroxene sillimanite garnet quartz anorthite the sequence of mineral assemblages is consistent with natural parageneses modified journal abstract

the reaction forsterite cordierite aluminous orthopyroxene spinel in the system mgo al2o3 sio2 reversal experiments at 1 150 1 300 c on the reaction forsterite cordierite aluminous orthopyroxene spinel in the system mgo al2o3 sio2 show the equilibrium to have a negativedt dp the slope andt p location of this equilibrium have been modelled using available heat capacity data and various structural models which explore the configurational entropy contributions to the total s the experimental data are consistent with the aluminous orthopyroxene model of ganguly and ghose 1979 where limited al disorder occurs between them1 andm2 sites al si mixing occurs on the tetrahedralb site with the aluminum avoidance principle maintained and mg al disorder occurs in spinel with an interchange enthalpy of 9 12 kcal mol 1 additionally al si disordering which occurs in the indialite structure of cordierite is inconsistent with the experimental data and all pyroxene and spinel mixing models consequently si and al in anhydrous cordierites to 1 300 c in the system mgo al2o3 sio2 must be largely ordered