high frequency oscillations and their correlation with the wind forcing during the first sequal year two arrays of inverted echo sounders one along the equator and the other across the north equatorial countercurrent are analysed together with a wind record from st peter and st paul rocks the dominant high frequency feature along the equator is an energetic oscillation with a period of 5 8 days that shows strong coherence with the meridional component of the wind the sounder at 3 n 28 w on the other hand shows a high degree of coherence with the zonal component of the wind at a period of 4 5 days comparison of these measurements in 1983 with measurements made in 1979 suggest considerable non stationarity

sea ice models for climate study retrospective and new directions scientific observations of sea ice began more than a century ago but detailed sea ice models appeared only in the latter half of the last century the high albedo of sea ice is critical for the earth s heat balance and ice motion across the ocean s surface transports fresh water and salt the basic components in a complete sea ice model must include vertical thermodynamics and horizontal dynamics including a constitutive relation for the ice advection and deformational processes this overview surveys topics in sea ice modeling from the global climate modeling perspective emphasizing work that significantly advanced the state of the art and highlighting promising new developments

influence of snow depth and surface flooding on light transmission through antarctic pack ice snow on sea ice alters the properties of the underlying ice cover as well as associated physical and biological processes at the interfaces between atmosphere sea ice and ocean the antarctic snow cover persists during most of the year and contributes significantly to the sea ice mass due to the widespread surface flooding and related snow ice formation snow also enhances the sea ice surface reflectivity of incoming shortwave radiation and determines therefore the amount of light being reflected absorbed and transmitted to the upper ocean here we present results of a case study of spectral solar radiation measurements under antarctic pack ice with an instrumented remotely operated vehicle in the weddell sea in 2013 in order to identify the key variables controlling the spatial distribution of the under ice light regime we exploit under ice optical measurements in combination with simultaneous characterization of surface properties such as sea ice thickness and snow depth our results reveal that the distribution of flooded and nonflooded sea ice areas dominates the spatial scales of under ice light variability for areas smaller than 100 m by 100 m however the heterogeneous and highly metamorphous snow on antarctic pack ice obscures a direct correlation between the under ice light field and snow depth compared to the arctic light levels under antarctic pack ice are extremely low during spring 0 1 this is mostly a result of the distinctly different dominant sea ice and snow properties with seasonal snow cover including strong surface melt and summer melt ponds in the arctic and a year round snow cover and widespread surface flooding in the southern ocean

origin of chromite in mafic ultramafic hosted hydrothermal massive sulfides from the main uralian fault south urals russia abstract mafic ultramafic hosted hydrothermal fe cu ni co sulfide ores from the main uralian fault zone mufz south urals ivanovka and ishkinino ore fields contain a relatively large up to 3 proportion of chromite this association is common for magmatic fe ni cu sulfides but definitely unusual for hydrothermal sulfides textural morphological and compositional data are used here to gain an insight into the origin and significance of this unusual chromite sulfide association the studied chromites occur both as broken fragments and as euhedral or subhedral crystals which are included in the sulfides or scattered in their talc chlorite saponite quartz carbonate matrix they are characterized by high cr cr al ratios 0 58 0 85 and range in composition from magnesiochromite to chromite sensu stricto textural morphological and compositional features as well as the occurrence of relatively high silica low ti low k melt inclusions in some of the crystals indicate that the ore associated chromites i are a mixed population of grains derived from mafic ultramafic mantle and crustal magmatic rocks and mantle peridotite melting residua ii have no genetic relation with the host sulfides and iii represent relicts derived from the hydrothermally altered country rocks the compositions of the chromites and of the melt inclusions denote a clear supra subduction zone signature the melts parent to the cumulitic chromites had an arc tholeiitic to possibly boninitic affinity these data suggest that the host mafic ultramafic complexes formed in an early arc or forearc setting and do not represent obducted portions of morb oceanic lithosphere hence contrary to previous interpretations the associated massive sulfides could not originate on a mid ocean ridge but rather in an early arc or forearc environment given the relatively short life of the western uralian arc system the most probable time window for sulfide ore deposition is confined to early to middle devonian time

heat flux through sea ice in the western weddell sea convective and conductive transfer processes the heat flux through the snow and sea ice cover and at the ice ocean interface were calculated at five sites in the western weddell sea during autumn and early winter 1992 the ocean heat flux averaged 7 2 w m2 from late february to early june and average ice air heat flux in the second year floes depended on the depth of the snow cover and ranged from 9 to 17 0 8 w m2 in late february three of the five sites had an ice surface which was depressed below sea level resulting at two of the sites in a partially flooded snow cover and a slush layer at the snow ice interface as this slush layer froze to form snow ice the dense brine which was rejected flowed out through brine drainage channels and was replaced by lower salinity nutrient rich seawater from the ocean upper layer we estimate that about half of the second year ice in the region was covered with this slush layer early in the winter as the slush layer froze over a 2 to 3 week period the convection within the ice transported salt from the ice to the upper ocean and increased total heat flux through the overlying ice and snow cover on an area wide basis approximately 10 cm of snow ice growth occurred within second year pack ice primarily during a 2 to 3 week period in february and march this ice growth near the surface of the ice provides a salt flux to the upper ocean equivalent to 5 cm of ice growth despite the thick about 1 m ice cover in addition to the ice growth in the small area less than 5 open water regions

physical structural and isotopic characteristics and growth processes of fast sea ice in lutzow holm bay antarctica a sea ice ocean study was conducted off queen maud land and enderby land antarctica from 1990 to 1991 by the japanese antarctic research expedition observations of multiyear land fast sea ice were made in lutzow holm bay over a period of 2 years to determine the snow and ice characteristics and ice growth processes the snow depth in the bay reached large values of 1 0 to 1 5 m during the winter season at offshore locations from the analysis of ice thickness measurements it is confirmed that the fast ice with deep snow cover grew little in winter but substantially thickened during the summer months on the basis of ice core structure salinity and stable isotopic composition we conclude that the summer growth was caused by upward growth at the top of the ice to which snow ice and superimposed ice formation contribute these processes were the primary contributors to sea ice growth and characteristics only where the snow accumulation was large in areas of low snow accumulation there was no surface growth superimposed ice formation on sea ice in antarctica has not been reported previously evidence for snow cover melting which is a prerequisite for superimposed ice formation was also found

temporal evolution of decaying summer first year sea ice in the western weddell sea antarctica abstract the evolution of the main physico chemical properties of the unflooded 90 cm thick first year sea ice cover at the ice station polarstern ispol clean site is described ispol was an international experiment of the german research icebreaker r v polarstern the vessel was anchored to an ice floe for an observation period of 5 weeks during the early summer melt onset in the western weddell sea the clean site was specially designed and accessed so as to prevent any trace metal contamination of the sampling area observations were made at 5 day intervals during december 2004 in the central part of the main floe results show the succession of two contrasting phases in the behavior of the brine network brine channels pockets and tubes initially brine salinity was higher than that of sea water leading to brine migration and a decrease in the mean bulk salinity of the ice cover this process is highly favored by the already high bulk porosity 14 which ensures full connectivity of the brine network gravity drainage rather than convection seems to be the dominant brine transfer process half way through the observation period the brine salinity became lower than that of the sea water throughout the ice column the brine network therefore switched to a stratified regime in which exchange with sea water was limited to molecular diffusion strongly stabilizing the bulk mean sea ice salinity during the transition between the two regimes and in areas closer to ridges slush water resulting from a mixture of snow meltwater and sea water accumulated at the snow ice interface penetrated through the growing honeycomb like structure and replaced the downward draining brines this resulted in a slight local replenishment of nutrients as indicated by dissolved silicic acid however as a whole the described decaying regime in this globally unflooded location with limited snow cover should be unfavorable to the development of healthy and active surface and internal microbial communities the switch from gravity to diffusion controlled transport mechanisms within the ice column also should affect the efficiency of gas exchange across the sea ice cover the observed late build up of a continuous impermeable superimposed ice layer should further significantly hamper gas exchange statistical estimates of the evolution of the ice thickness during the observation period and salinity trends of the under ice water salinity down to 30 m corroborate model predictions of a moderate bottom melting 5 10 cm from ocean heat fluxes

microstructure and lattice preferred orientation of calcite mylonites at the base of the southern urals accretionary prism emplacement of the southern urals accretionary complex onto the east european craton involved off scraping of shallow marine limestones from the continental margin and their underplating to the base of the accretionary complex during the final stages of arc continent collision these limestones underwent localized ductile to semi brittle deformation at upper crustal levels at temperatures close to 200 c field observations macroscopic fabric elements and crystallographic preferred orientations indicate a heterogeneous distribution of the deformation measurements from twinned calcite grains indicate that peak differential stress conditions during deformation attained c 230 40 mpa these differential stress conditions are further supported by the small size of both recrystallized and twinned calcite grains twinning and intracrystalline slip were the major contributors to the bulk deformation and lattice preferred orientation lpo formation lpo evolved with progressive strain from an initial constrictional fabric that is consistent with the macroscopic mineral lineation as the dominant macroscopic fabric element to a c axis maximum normal to foliation as the rock underwent dynamic recrystallization and grain refinement during progressive simple shear

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

winter snow cover on sea ice in the weddell sea measurements of snow thickness temperature salinity density and stratigraphy acquired during the 1992 winter weddell gyre study are presented results indicate that the winter snow cover on sea ice in the weddell sea is extremely variable extreme fluctuations in antarctic synoptic conditions air temperature precipitation humidity and wind speed occur during the austral winter they result in unique modifications and additions to the snow layer during the aging process and act to stabilize an otherwise easily wind redistributed shallow snow cover and develop well packed drift features the latter occur even over relatively undeformed areas of sea ice and have a significant localized effect on the snow thickness distribution significant variability in snow grain size mean 2 73 3 12 mm and density 0 32 0 09 g cm 3 is observed as a result of cyclical switches between high and low temperature gradient metamorphism multiple icy layers indicate multiple thaw freeze events one such event occurred during a 3 day station during which the air temperature rose by 22 c in 12 hours to approximately 0 c this paper also examines mechanisms for flooding of the snow ice interface including snow loading even where the latter is not a factor the layer of snow immediately above the snow ice interface is commonly damp and saline 10 limitations in the data set are discussed and comparisons are drawn with other experiments

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

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

evolution of first year and second year snow properties on sea ice in the weddell sea during spring summer transition observations of snow properties superimposed ice and atmospheric heat fluxes have been performed on first year and second year sea ice in the western weddell sea antarctica snow in this region is particular as it does usually survive summer ablation measurements were performed during ice station polarstern ispol a 5 week drift station of the german icebreaker rv polarstern net heat flux to the snowpack was 8 w m 2 causing only 0 1 to 0 2 m of thinning of both snow cover types thinner first year and thicker second year snow snow thinning was dominated by compaction and evaporation whereas melt was of minor importance and occurred only internally at or close to the surface characteristic differences between snow on first year and second year ice were found in snow thickness temperature and stratigraphy snow on second year ice was thicker colder denser and more layered than on first year ice metamorphism and ablation and thus mass balance were similar between both regimes because they depend more on surface heat fluxes and less on underground properties ice freeboard was mostly negative but flooding occurred mainly on first year ice snow and ice interface temperature did not reach the melting point during the observation period nevertheless formation of discontinuous superimposed ice was observed color tracer experiments suggest considerable meltwater percolation within the snow despite below melting temperatures of lower layers strong meridional gradients of snow and sea ice properties were found in this region they suggest similar gradients in atmospheric and oceanographic conditions and implicate their importance for melt processes and the location of the summer ice edge

forced oscillations on the equatorial atlantic basin during the seasonal response of the equatorial atlantic program 1983 1984 a subset of data from an array of eight inverted echo sounders and a meteorological station deployed and maintained for 15 months in the equatorial atlantic as part of the seasonal response of the equatorial atlantic program are analyzed to determine the variability of forced oscillations of the basin the analysis is done to study both low and high frequency variability at low frequencies the equatorial basin responds as a whole to the seasonally varying winds the dominant signal is the annual cycle of the equatorial system as a composite of the response to the strong seasonal wind curl that is maximum in the western basin and the part of the zonal transfer to mass associated with the seasonal equatorial upwelling and downwelling system three bands of energy appear as dominant in the combined spectrum of the ocean and the atmosphere at higher frequencies 20 30 days 13 16 days and the inertial gravity wave band each one of the bands is analyzed and discussed instability waves are detected on the echo sounder records the waves have periods centered at 30 2 days and propagate westward with a wavelength of 1000 km and a phase speed of 0 35 m s the most energetic oscillation in the analyzed wind records is at periods centered around 14 days the response of the ocean to this oscillation has a meridional distribution with maximum amplitude at 3 n the most significant oceanic oscillations in the inertial gravity band are centered at 5 2 and 3 5 days from the study of their meridional structure it is concluded that those oscillations correspond to forced inertial gravity waves with meridional structures corresponding to the meridional numbers n 1 and n 3 respectively

seasonal variation of the gulf of guinea thermal structure data from 6 temperature sections are combined with other sequal focal data along 4 w from the coast 5 n to 3 s to study the seasonal variation of the temperature field in the gulf of guinea during 1983 the equatorial upwelling begins during mid april approximately 1 1 2 months before the climatic mean but has a normal amplitude and duration the upwelling on the coast at abidjan occurs approximately 1 1 2 months after the equatorial upwelling and precedes its climatic mean by 2 weeks at the equator vertical displacements of isotherms within the thermostad are complicated by an anomalous warming of the thermostad in may between the thermostad and the deeper thermocline at 230 m the seasonal isotherm displacement amplitude has a minimum at greater depths it increases again in all respects the fluctuation of the thermal field at the equator is similar to the climatic mean but displaced forward in time by 1 1 2 months

equations for determining the gas and brine volumes in sea ice samples on a etabli des equations utilisables pour determiner le taux de gaz inclus dans la glace de mer a partir de mesures de densite de salinite et de temperature dans des gammes de temperatures entre 2 c et 30 c inversement ces relations peuvent etre utilisees pour calculer la densite de la glace de mer en fonction de la temperature et de la salinite en prenant en compte a la fois la presence de gaz et de cristaux de sel dans la glace on donne aussi des equations qui permettent le calcul du volume de gaz et d eau salee dans la glace a des temperatures autres que celle pour laquelle la densite a ete determinee

a one dimensional percolation model of flooding and snow ice formation on antarctic sea ice a one dimensional thermodynamic sea ice growth model is developed with emphasis on seawater flooding and snow ice formation on antarctic sea ice to examine the possibility that flooding is the result of brine percolation through a porous ice matrix and the consequences of this percolation on the salinity structure and mass balance of the ice flooding is modeled in a semiheuristic fashion by examining two possible regimes for seawater and brine infiltration through the porous ice into the snowpack a standard model assumes that the upward flow of brine is horizontally homogeneous and brine flow is modeled using a darcian scheme a simple model assumes that the infiltrating brine does not interact with the internal ice brine network but instead percolates upward through cracks or is restricted in spatial extent results of simulations are shown for the climatology in the ross sea and compared to field data from one autumn and one winter cruise aboard the r v nathaniel b palmer in 1995 sensitivity studies are performed to show the effects of variations in climate forcing the dependence of brine percolation and snow ice formation on key thermophysical parameters is investigated results indicate that the mass balance depends very strongly on the brine flow regime in the standard model ice salinities and brine volumes are greatly affected by brine percolation creating a strong feedback between flooding and future snow ice production snow ice formation for the simple model was much more predictable and depended primarily on snow load comparison of results with field data indicate that if brine percolation is the major mechanism for flooding and snow ice formation then there must be either substantial convective redistribution of salt to maintain ice porosity or the flow must be spatially inhomogeneous

validation of an equatorial atlantic simulation model using inverted echo sounder data changes in the vertically averaged temperature of the water column observed over a 12 month period at eight locations in the tropical atlantic with inverted echo sounders are described in terms of empirical orthogonal functions these modes are compared with those from a similar analysis for data from a general circulation model of the tropical atlantic the method proves to be useful for the validation of models

seasonal variations in the properties and structural composition of sea ice and snow cover in the bellingshausen and amundsen seas antarctica sixty three ice cores were collected in the bellingshausen and amundsen seas in august and september 1993 during a cruise of the r v nathaniel b palmer the structure and stable isotopic composition 18 o 16 o of the cores were investigated in order to understand the growth conditions and to identify the key growth processes particularly the contribution of snow to sea ice formation the structure and isotopic composition of a set of 12 cores that was collected for the same purpose in the bellingshausen sea in march 1992 are reassessed frazil ice and congelation ice contribute 44 and 26 respectively to the composition of both the winter and summer ice core sets evidence that the relatively calm conditions that favour congelation ice formation are neither as common nor as prolonged as the more turbulent conditions that favour frazil ice growth and pancake ice formation both frazil and congelation ice layers have an av erage thickness of 0 12 m in winter evidence that congelation ice and pancake ice thicken primarily by dynamic processes the thermodynamic development of the ice cover relies heavily on the formation of snow ice at the surface of floes after sea water has flooded the snow cover snow ice layers have a mean thickness of 0 20 and 0 28 m in the winter and summer cores respectively and the contribution of snow ice to the winter 24 and summer 16 core sets exceeds most quantities that have been reported previously in other antarctic pack ice zones the thickness and quantity of snow ice may be due to a combination of high snow accumulation rates and snow loads environmental conditions that favour a warm ice cover in which brine convection between the bottom and top of the ice introduces sea water to the snow ice interface and bottom melting losses being compensated by snow ice formation layers of superimposed ice at the top of each of the summer cores make up 4 6 of the ice that was examined and they increase by a factor of 3 the quantity of snow entrained in the ice the accumulation of superimposed ice is evidence that melting in the snow cover on antarctic sea ice floes ran reach an advanced stage and contribute a significant amount of snow to the total ice mass

geochemical investigation of the igneous rocks from the nurali ophiolite melange zone southern urals abstract the nurali massif is a small ophiolite located along the main uralian fault in the southern urals it includes a mantle sequence a transition zone and a melange zone with an intrusive gabbro to oxide diorite unit interposed between the transition zone and the melange various igneous rocks occur as exotic blocks within the nurali melange including tholeiitic gabbro to diorite and calc alkaline diorite tonalite granodiorite and granite intrusives tholeiitic basalt and calc alkaline basaltic andesite to dacite the poljakovka complex basalts of silurian age are similar to the tholeiitic effusives and are also intruded by gabbros similar to those in the melange zone calc alkaline intrusives the rocks of tholeiitic affinity in the tectonic melange are the remnants of an oceanic stage both intrusive and effusive calc alkaline products can likely represent a subduction related magmatism developed in an arc environment intra oceanic arc or continental margin they are analogous to those from the kraka massif which occur west of the main uralian fault

18o concentrations in sea ice of the weddell sea antarctica we present data on ice texture salinity and delta o 18 obtained from identical sections of ice cores during the winter weddell sea project 1986 on rv polarstern from july through august 1986 in the longitude range between 5 degrees w and 7 degrees e we find no uniquely definable relationship between delta o 18 values and ice texture in a particular section however most of the snow ice as well as some sections of frazil ice ar found to have negative delta o 18 concentrations this is due to varying degrees of admixtures of meteoric ice snow and sea water during formation of snow ice in contrast to common assumptions our results seem to indicate that a snow cover contributes positively to sea ice growth rather than slowing down the overall growth rate based on a simple model we have estimated the contributions of meteoric ice mean of 3 3 and the combined meteoric ice sea water fraction a minimum of 7 6 to the total ice thickness for the majority of the sampled floes although this is only a moderate contribution to the overall mass balance in the absence of congelation growth it nevertheless enhances ice growth in general this hypothesis is dependently supported by our snow and ice thickness data wadhams and others 1987 which demonstrate that the depression of the snow ice interface below the water line i e a negative freeboard and the formation of snow ice is a common occurrence in the weddell sea therefore we hypothesize that the major part of the observed apparent increase in ice thickness between our inbound and outbound tracks of wwsp 86 may not be derived from regular thermodynamically driven congelation growth but rather from the snow ice component in floes of the weddell sea

the importance of diurnal processes for the seasonal cycle of sea ice microwave brightness temperatures during early summer in the weddell sea antarctica over the perennial sea ice in the western and central weddell sea antarctica the onset of summer is accompanied by a significant decrease of sea ice brightness temperatures tb as observed by passive microwave radiometers such as the special sensor microwave imager ssm i the summer specific tb drop is the dominant feature in the seasonal cycle of tb data and represents a conspicuous difference to most arctic sea ice regions where the onset of summer is mostly marked by a rise in tb data from a 5 week drift station through the western weddell sea in the 2004 05 austral summer ice station polarstern ispol helped with identifying the characteristic processes for antarctic sea ice in situ glaciological and meteorological data in combination with ssm i swath satellite data indicate that the cycle of repeated diurnal thawing and refreezing of snow freeze thaw cycles is the dominant process in the summer season with the absence of complete snow wetting the resulting metamorphous snow with increased grain size as well as the formation of ice layers leads to decreasing emissivity enhanced volume scattering and increased backscatter this causes the summer tb drop

modes of variability of the 1983 thermocline signal acoustic travel time series from an array of nine inverted echo sounders deployed along the equator and in the north equatorial countercurrent necc are decomposed into empirical orthogonal functions eof to analyze the dominant frequencies of oscillations in the thermocline field at low frequencies the first eof mode describes the seasonal signal shows the reversal of the necc and separates the behavior of the gulf of guinea from the rest of the basin the second eof mode shows rapid changes in the depth of the thermocline in short periods of time on the equator at 10 w and at 3 n 38 30 w comparison with a simulation model by philander and pacanowski shows that the theoretical time series behave in a similar way at these two locations at high frequencies the modes show oscillations in the inertia gravity wave band

the forced annual reversal of the atlantic north equatorial countercurrent abstract we analyze the variability of the thermal structure associated with the atlantic north equatorial countercurrent necc and its relation to the seasonally varying winds the analysis performed allows us to establish the period of time and the region where the necc reverses direction west of 25 w the depth of the thermocline in the southern side of the necc 4 to 7 n annually oscillates 180 out of phase to the oscillations on the northern side 7 to 10 n east of 25 w the thermocline rises and falls nearly in phase across the countercurrent if the flow can be uniquely presumed from the thermal structure the necc disappears during the boreal spring in the western basin the reversal of phase from north to south over one part of the ocean but no the other is shown to be mirrored in the annual variation of the curl of the stress induced at the surface by the winds in order to quantify this result the different terms of the vorticity equation are calculated from the data we conclude that t

development and properties of sea ice in the coastal regime of the southeastern weddell sea from october to december 1986 a program consisting of sea ice core analysis in combination with sea ice observations was carried out from the icebreaker r v polarstern as part of the winter weddell sea project the ship operated in the central and southeastern weddell sea with interests focusing on the ice shelf front between 70 s and 77 s where a system of coastal polynyas extended for several tens to hundreds of kilometers opened and maintained despite temperatures well below freezing by offshore wind forcing three wind controlled ice formation regimes may be distinguished 1 for wind speeds 10 m s the ice cover is heavily ridged and rafted 50 and formation of granular ice predominates of the total length of cores sampled in the coastal regime 32 consisted of columnar and 35 of granular ice in addition we observed two unique ice classes along the coast platelet ice formed through consolidation of underwater ice platelets underneath the solid ice cover contributed 11 to our core samples another 22 consisted of intermediate columnar granular ice which originates under the dynamic hydrographic conditions of the near ice shelf region

erroneous sea ice concentration retrieval in the east antarctic large discrepancies have been observed between satellite derived sea ice concentrations ic from passive microwave remote sensing and those derived from optical images at several locations in the east antarctic between february and april 2014 these artefacts that resemble polynyas in the ic maps appear in areas where optical satellite data show that there is landfast sea ice the ic datasets and the corresponding retrieval algorithms are investigated together with microwave brightness temperature air temperature snowfall and bathymetry to understand the failure of the ic retrieval the artefacts are the result of the application of weather filters in retrieval algorithms these filters use the 37 and 19 ghz channels to correct for atmospheric effects on the retrieval these channels show significant departures from typical ranges when the artefacts occur a melt refreeze cycle with associated snow metamorphism is proposed as the most likely cause together the areas of the artefacts account for up to 0 5 of the antarctic sea ice area and thus cause a bias in sea ic time series in addition erroneous sea ics can adversely affect shipping operations

sea ice growth in ongul strait antarctica a two year study was conducted on the growth processes of sea ice in ongul strait antarctica routine measurements of snow depth and ice thickness were made and sea ice cores were collected to assess their structure temperature and salinity the snow depth varied from 0 to about 1 m in the winter months the growth rate is higher in bare ice regions than in snow covered regions however over the year the ice thickness itself is lower in the bare ice regions than in the snow covered regions sea ice in the snow covered regions increased in thickness in spring rather than in winter due to the formation of snow ice and by ice formation related to the melting of snow cover

comparison of sea ice thickness measurements under summer and winter conditions in the arctic using a small electromagnetic induction device drillhole determined sea ice thickness was compared with values derived remotely using a portable smalloffset loop loop steady state electromagnetic em induction device during expeditions to fram strait and the siberian arctic under typical winter and summer conditions simple empirical transformation equations are derived to convert measured apparent conductivity into ice thickness despite the extreme seasonal differences in sea ice properties as revealed by ice core analysis the transformation equations vary little for winter and summer thus the em induction technique operated on the ice surface in the horizontal dipole mode yields accurate results within 5 to 10 of the drillhole determined thickness over level ice in both seasons the robustness of the induction method with respect to seasonal extremes is attributed to the low salinity of brine or meltwater filling the extensive pore space in summer thus the average bulk ice conductivity for summer multiyear sea ice derived according to archie s law amounts to 23 ms m compared to 3 ms m for winter conditions these mean conductivities cause only minor differences in the em response as is shown by means of 1 d modeling however under summer conditions the range of ice conductivities is wider along with the widespread occurrence of surface melt ponds and freshwater lenses underneath the ice this causes greater scatter in the apparent conductivity ice thickness relation this can result in higher deviations between em derived and drillhole determined thicknesses in summer than in winter

the north equatorial countercurrent observed during the programme francais ocean climat dans l atlantique equatorial experiment in the atlantic ocean july 1982 to august 1984 observations from programme francais ocean climat dans l atlantique equatorial focal cruises in 1982 and 1984 have confirmed that in the central atlantic ocean the north equatorial countercurrent necc has a well defined seasonal regime with a very reduced flux during spring the main core of the necc always lies between 4 n and 6 n focal observations have also shown that a long term change of necc may occur and contribute to the development of an el nino type event in the eastern atlantic ocean

quantifying vulnerability of antarctic ice shelves to hydrofracture using microwave scattering properties abstract recent ice shelf disintegrations on the antarctic peninsula and subsequent increases in ice sheet mass loss have highlighted the importance of tracking ice shelf stability with respect to surface melt ponding and hydrofracture in this study we use active microwave scatterometry in time series to estimate melt season duration and winter backscatter levels as a proxy for relative concentration of refrozen ice lenses in antarctic ice shelf firn we demonstrate a physical relationship between melt days and firn ice backscatter using scatterometry and field data from greenland and apply the observed relationship to derive and map a vulnerability index for antarctica s ice shelves the index reveals that some remaining antarctic peninsula ice shelves have already reached a firn state that is vulnerable to hydrofracture we also show that the progression of an ice shelf towards vulnerability is affected by many factors such as surface mass balance internal stresses and ice shelf geometry

origin and emplacement of ophiolites ever since their recognition ophiolites have been a source of controversy although all workers have agreed upon their importance a number of conflicting schools of thought have become unified in the interpretation of ophiolite complexes as fragments of oceanic crust and mantle formed at spreading centers an expanded version of the penrose ophiolite definition is proposed herein called the ophiolite association taking into account rocks which bear upon the origin and significance of ophiolite complexes an ideal ophiolite association includes the following units from bottom to top 1 a crystalline basement and shallow water sedimentary sequence 2 a tectonic unit of thrust slices of continental margin and rise and abyssal sediments and or melange 3 a metamorphic unit as much as a few hundred meters thick generally with higher grade rocks over lower grade ones 4 ultramafic tectonite unit composed dominantly of multiply deformed peridotite dunite and minor chromitite 5 a cumulate complex ultramafic at the base grading to mafic or intermediate at the top 6 a noncumulus unit of varitextured gabbro and minor trondhjemite 7 a sheeted dike complex 8 an extrusive section of massive and pillowed flows and intercalated sediments 9 an abyssal or bathyal sediment sequence which may include radiolarian chert red pelagic limestone metalliferous sediments breccias and or pyroclastic deposits and 10 postemplacement deposits of laterite reef limestone or shallow marine or subaerial sediments this expanded ophiolite association allows greater precision in inferring original origin and emplacement some ophiolite complexes particularly in the tethys herein designated tethyan type exhibit units 1 2 3 and 4 whereas others particularly in the cordilleran belt herein termed cordilleran type lack units 1 2 3 and in places 4 the emplacement of the former probably occurred during collision of a passive margin with a subduction zone or incipient subduction zone emplacement of the cordilleran type generally is not clear cut the nature of the spreading center which produced a given ophiolite is indicated more clearly by the presence or absence of units 5 9 than by chemistry or mineralogy some ophiolite complexes lack complete sections and may have formed along transform faults others contain volcanic pyroclastic deposits instead of pelagic sedimentary sequence and probably formed within or near an arc several ophiolite complexes may have originated by conversion of a transform fault into a subduction zone such conversion may result from normal plate evolution or from major plate reorganization major times of ophiolite emplacements appear to correspond with global plate reorganizations

snow crystal growth with varying surface temperatures and radiation penetration the temperature field is derived for a sinusoidally varying surface temperature with varying solar radiation penetration the growth rates of snow crystals are calculated to explain the rapidly growing layers of faceted crystals i e depth hoar that form just below the surface at high altitudes and in polar snow the solutions also show that a layer of wet snow can exist just below the surface even on days when the surface temperature remains sub freezing

geology and geodynamic evolution of the high p low t maksyutov complex southern urals russia the high pressure low temperature maksyutov complex is situated in the southern urals between the silurian devonian magnitogorsk island arc and the east european platform the elongated n s trending complex is made up of two contrasting tectono metamorphic units unit 1 consists of a thick pile of proterozoic clastic sediments suggested to represent the passive margin of the east european platform the overlying unit 2 composed of paleozoic sediments volcanic rocks and a serpentinite melange with rodingites is interpreted as a remnant of the uralian paleo ocean devonian eastward subduction of oceanic crust beneath the magnitogorsk island arc resulted in an incipient blueschist facies metamorphism of unit 2 indicated by lawsonite pseudomorphs in the rodingites while unit 2 was accreted to the upper plate subduction of the continental passive margin caused the high pressure metamorphism of unit 1 buoyancy driven exhumation of unit 1 into the forearc region led to its juxtaposition with unit 2 along a retrograde top to the ene shear zone further exhumation of the maksyutov complex into its present tectonic position was accomplished by later shear zones that were active as normal faults and are exposed along the margins of the complex at the western margin a top to the west shear zone juxtaposed a low grade remnant of a paleozoic accretionary prism suvanyak complex above the maksyutov complex along the eastern margin a top to the east shear zone and the brittle main uralian normal fault emplaced the maksyutov complex against the magnitogorsk island arc in the hanging wall

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

investigations on physical and textural properties of arctic first year sea ice in the amundsen gulf canada november 2007 june 2008 ipy cfl system study we report sea ice temperature and bulk salinity measurements as well as textural analysis from 33 first year drift and fast ice stations sampled between november 2007 and june 2008 in the southern beaufort sea amundsen gulf canadian arctic during the international polar year circumpolar flaw lead ipy cfl system study we use this significant dataset to investigate the halo thermodynamic evolution of sea ice from growth to melt a strong desalination phase is observed over a small time window in the spring using calculated proxies of sea ice permeability brine volume fraction and of the intensity of brine convection rayleigh number we demonstrate that this phase corresponds to full depth gravity drainage initiated by a restored connectivity of the brine network with warming in the spring most stations had a textural sequence typical of arctic first year ice with granular ice overlying columnar ice unusual textural features were observed sporadically sandwiched granular ice platelet ice and draped platelet ice we suggest that turbulence in leads and double diffusion in strong brine plumes following the refreeze of cracks are plausible mechanisms for the formation of these textures

kinematics of oceanic thrusting and subduction from basal sections of ophiolites the structural analysis of high stress deformation at the base of the peridotite section in many ophiolites in suture zones enables the kinematics of oceanic convergence responsible for the suture to be defined this deformation results from the thrusting over oceanic crust of a young lithosphere involved in a subduction process flow plane flow line sense of shear related to the thrusting are geometrically deduced from the study of mineral preferred orientations in the basal peridotite and in the quartzites belonging to the amphibolite sole

crystal structure stable isotopes δ18o and development of sea ice in the ross amundsen and bellingshausen seas antarctica the crystal structure and oxygen isotopic composition of ice cores obtained from floes at the end of summer in the eastern ross sea the amundsen sea and the western bellingshausen sea were investigated to determine the ice growth processes and conditions that contribute to sea ice development in the eastern pacific sector of the southern ocean the isotope data indicate that a moderate amount of snow contributes to the development of the sea ice however even the combined use of isotopes and crystal structure analysis does not unambiguously explain the means by which all of the snow is entrained in the ice nevertheless it seems clear that much of the snow is contained in granular snow ice that results from seawater flooding of floes and the base of the snow cover the snow cover in the ross amundsen region was as much as 2 m deep and supported by 7 to 8 m thick floes primarily composed of frazil ice in the bellingshausen region the snow cover and the floes were thinner than in the ross amundsen region the bellingshausen cores were composed primarily of multiple layers of frazil and congelation ice in addition in both regions there were numerous tipped or inclined blocks of congelation ice and layers of rafted nilas in the cores the data indicate that the sea ice develops by multiple mechanisms in a turbulent environment

development of sea ice in the weddell sea we report on the development and physical properties of sea ice in the central and eastern weddell sea the investigations were part of the winter weddell sea project 1986 which extended over the months of july through december major elements of the glaciological part of this study included continuous shipborne observations of sea ice conditions and occasional helicopter reconnaissance flights extensive measurements of snow and ice thicknesses at daily ice stations and detailed analyses of sampled ice cores from each ice station textural investigations of the sampled ice revealed the dominance of frazil ice in the central weddell sea and the occurrence of an additional ice class called platelet ice together with the commonly known frazil and congelation ice in the coastal region of the eastern weddell sea these results in combination with the visual ice observations reveal two major mechanisms for sea ice generation in the antarctic which were not sufficiently well accounted for in previous investigations in the central weddell sea a cycle of pancake ice formation and its growth into consolidated floes seems to be the dominant process of the advancing sea ice edge in the coastal waters the growing sea ice cover consists to a considerable degree of ice platelets which are formed in the underlying water column in front of the ice shelf edges thus congelation ice growth which is mainly controlled by atmospheric thermodynamic forcing seems to be of less importance in the central and south eastern weddell sea than for example in the arctic basin

crustal scale structure and evolution of an arc continent collision zone in the southern urals russia the outcropping geology of the southern urals contains a well preserved accretionary complex related to the paleozoic collision that took place between the magnitogorsk arc and the former east european craton the crustal scale structure of the accretionary complex has been determined from outcropping field geology that is integrated with three reflection seismic profiles the reflection profiles show the accretionary complex to be highly reflective allowing direct comparison of many reflections with surface geological features we interpret the accretionary complex to be a thrust stack that is composed of shallowly subducted continental shelf and rise material syncollisional sediments derived from the arc deeply subducted high pressure gneisses that are intercalated with eclogites and blueschist and at the highest structural level ophiolite complexes it is bound at the base by a thrust and at the rear by a highly deformed zone the main uralian fault adjacent to the backstop the magnitogorsk arc deposition of the late devonian volcaniclastic sediments of the zilair formation appears to be related to collision uplift and erosion of the arc possibly following the arrival of the full thickness of the east european craton continental crust at the subduction zone with the arrival of the continental crust at the subduction zone offscraping and underplating of paleozoic slope and platform material took place at the base of the accretionary complex uplift of the arc was followed by its collapse and the unconformable deposition of lower carboniferous shallow water carbonates on top of it a time lag of 10 15 myr occurred between the high pressure metamorphism and the subsequent arrival of the east european craton at the subduction zone

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

north brazil current retroflection and transports 1 a subset of data collected as a part of a larger program the north brazil current rings nbcr experiment is analyzed to study the variability of the transport of the north brazil current nbc and its relation with the shedding of rings it is concluded that there is a direct relation between the latitude of penetration the number of rings shed and the intensity of the nbc the data set consists of dynamic height time series derived from three inverted echo sounders and a shallow pressure gauge deployed along a section perpendicular to the south american coast between the continent and 7 n and between 48 and 45 w velocity and hydrographic data collected during the nbcr cruises are also analyzed and used to validate the results the 15 month mean transport of the nbc is 16 2 sv the 18 month mean of the retroflected southeastward flow is 22 2 sv both flows display considerable variability the retroflected southeast flow reaches its maximum value during september 1999 near the time when the climatological north equatorial countercurrent necc reaches its maximum strength and it is minimum when the climatological necc reverses or is not present in the basin the mean difference between the nbc flow and the retroflected flow during august december 1999 when the necc is fully established is 7 sv the excess in the retroflected flow is due to north atlantic water joining the retroflected flow from the south atlantic the combination of both flows constitutes the necc

timing and regional patterns of snowmelt on antarctic sea ice from passive microwave satellite observations an improved understanding of the temporal variability and the spatial distribution of snowmelt on antarctic sea ice is crucial to better quantify atmosphere ice ocean interactions in particular sea ice mass and energy budgets it is therefore important to understand the mechanisms that drive snowmelt both at different times of the year and in different regions around antarctica in this study we combine diurnal brightness temperature differences dtb 37ghz and ratios tb 19ghz tb 37ghz to detect and classify snowmelt processes we distinguish temporary snowmelt from continuous snowmelt to characterize dominant melt patterns for different antarctic sea ice regions from 1988 89 to 2014 15 our results indicate four characteristic melt types on average 38 9 6 0 of all detected melt events are diurnal freeze thaw cycles in the surface snow layer characteristic of temporary melt type a less than 2 reveal immediate continuous snowmelt throughout the snowpack i e strong melt over a period of several days type b in 11 7 4 0 type a and b take place consecutively type c and for 47 8 6 8 no surface melt is observed at all type d continuous snowmelt is primarily observed in the outflow of the weddell gyre and in the northern ross sea usually 17 days after the onset of temporary melt comparisons with snow buoy data suggest that also the onset of continuous snowmelt does not translate into changes in snow depth for a longer period but might rather affect the internal stratigraphy and density structure of the snowpack considering the entire data set the timing of snowmelt processes does not show significant temporal trends

upper mantle beneath a young oceanic rift peridotites from the island of zabargad red sea information on the nature of the upper mantle in a young rift zone with lithosphere transitional from continental to oceanic was obtained from the island of zabargad probably an uplifted fragment of red sea lithosphere the island exposes exceptionally fresh mantle derived peridotite spinel iherzolite bodies the mineralogy and major element rare earth element and mineral chemistry of the spinel iherzolites suggest that they equilibrated last at depth 30 km in the mantle and that they have oceanic rather than continental affinity it is unlikely that the zabargad ultramafics are part of a late precambrian early paleozoic ophiolite as found elsewhere in circum red sea regions rather they were uplifted probably in connection with the development of the red sea rift the zabargad peridotites are in tectonic contact with continental metamorphic basement rocks it appears therefore that regions of an embryonic rift such as the red sea can be covered with continental type crust but be underlain by an upper mantle having already oceanic affinities

the seasonal cycle of ers scatterometer signatures over perennial antarctic sea ice and associated surface ice properties and processes time series of satellite radar backscatter coefficients of the ers 1 2 scatterometer are presented for perennial ice regions in the antarctic from june 1991 to june 1999 there is a pronounced seasonal cycle with higher backscatter in summer than in winter on average backscatter increases from spring values of 16 3 db to summer values of 10 7 db within 96 days this rapid rise and the summer maximum are occasionally interrupted by sudden strong signal drops after late summer early fall backscatter decreases again and slowly approaches winter values the seasonal cycle is interpreted in terms of processes at the ice surface the spring backscatter rise is associated with internal snow melt and the formation of superimposed ice this process commences once the surface energy balance becomes positive sudden backscatter drops are caused by temporary melt water saturation of the snow during episodic events of warm air advection in fall when superimposed ice formation ceases due to surface cooling gradual surface flooding with seawater becomes the dominating process this causes the observed decreasing backscatter the re occurrence of the seasonal backscatter cycle in most regions points to the widespread formation of superimposed ice on perennial antarctic sea ice

low frequency meandering of the atlantic north equatorial countercurrent four 19 month time series of indirect measurements of dynamic height were obtained in the tropical atlantic along 28 w at 0 3 6 and 9 n with three inverted echo sounders and one current meter mooring the series were analyzed to study the time latitude variability of the north equatorial countercurrent necc the eastward flow associated with the necc was present at 28 w from 3 to 9 n during most of the observed period except in march april 1983 and april may 1984 periods that coincided with the onset of the wind at the equator the amplitude of the necc s annual cycle was maximum at 6 n and was larger in 1983 than in 1984 the analysis of the time latitude variability of differences in dynamic height shows a long period meridional shift of the necc the core of the current attains its northernmost location during august september in both years and its southernmost location during march april in 1983 and march in 1984 the location of the core is directly related to the position of the intertropical convergence zone from the time series of dynamic height obtained from the indirect measurements geostrophic velocities and transports were estimated and compared with direct observations of currents and values obtained from hydrographic casts

growth properties and relation to radar backscatter coefficient of sea ice in lutzow holm bay antarctica based on studies in the antarctic oceans the contribution of the snow cover to sea ice growth has become of major interest snow can result in upward ice growth in contrast with ordinary downward congelation growth at the bottom a sea ice study was conducted to verify the upward ice growth found in a previous study and to investigate the relation between sea ice growth and radar backscattering signature sea ice samples collected at four points in lutzow holm bay antarctica from 1998 to 2003 are analyzed analyses of snow ice gauge measurements snow depth and ice structure reveal an extremely large amount of upward ice growth of up to 1 0 m during one full year compared with a slight amount of downward growth the upward growth was caused mostly by snow ice and to a lesser extent by superimposed ice the salinity profile remained unchanged although the ice survived the summer melt season characteristics of superimposed ice such as salinity d 18 o values and structure were obliterated during the summer implying complete melting or dissolution of the superimposed layer the ers 2 backscatter showed a remarkable annual variation it had a minimum value in midsummer and increased abruptly to a maximum value in late summer then decreasing gradually in wintertime the relation of the backscatter coefficient to the growth and properties of the snow cover and sea ice are discussed

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

thermocline displacement across the atlantic north equatorial countercurrent during 1983 two time series of thermocline displacement across the north equatorial countercurrent are derived from pairs of inverted echo sounders which straddle the countercurrent along the 28 w and 38 30 w meridians the observations reported are from february to september 1983 from mid may to the end of the record the thermocline deepens to the south and shallows to the north of the countercurrent suggesting a continual strengthening of the countercurrent the rate of increase of the thermocline slope at the western meridian is about twice that at 28 w as expected from historical data an empirical orthogonal functions eof analysis of the four sounders finds the dominant mode accounting for 64 of the variance this is compared to an eof analysis of model results by philander and pacanowski where the forcing is provided by the historical average wind field with the model the dominant mode is almost the entire response 92 of the variance the time dependence of the observed mode tracks that derived from the model during the overlapping seasons

high resolution dimethyl sulfide and dimethylsulfoniopropionate time series profiles in decaying summer first year sea ice at ice station polarstern western weddell sea antarctica high resolution profiles of ice dimethyl sulfide dms and dimethylsulfoniopropionate dmsp concentrations were measured together with a suite of ancillary physical and biological properties during a time series of decaying summer level first year sea ice throughout december 2004 during the ice station polarstern drift experiment western weddell sea antarctica ice dmsp and dms concentrations were always maximum at the bottom of the ice sheet 636 2627 and 292 1430 nm respectively where the highest chlorophyll a levels were also found 15 30 g l 1 throughout the observation period the autotrophic surface community 32 205 g c l 1 was dominated by phaeocystis sp while the bottom community 1622 3830 g c l 1 mainly consisted of pennate diatoms this illustrates that although being known for lower dmsp to chlorophyll a ratios than phaeocystis sp diatoms dominated the overall dmsp production because of their much larger biomass decreasing dmsp concentrations and increasing dms to dmsp ratios in the bottom layers with time suggested active dmsp to dms conversion in a slowly degrading environment drastic temporal brine volume and brine salinity changes associated with the decaying sea ice cover are shown to directly impact 1 the migration of dmsp and dms through the brine network 2 the dmsp to dms conversion processes within the ice interior and 3 the physiological response of the ice algae first order flux estimates show that decaying summer level first year sea ice alone can significantly contribute to the regional sulfur budget of the weddell sea with an estimated average loss rate of 5 7 mol dms p m 2 d 1 toward the atmosphere and the ocean copyright 2010 by the american geophysical union

seasonal development of the properties and composition of landfast sea ice in the gulf of finland the baltic sea 1 the seasonal development of the structure salinity and stable oxygen isotopic composition 18o of landfast sea ice was studied during the winter seasons 1999 2001 in the gulf of finland in the baltic sea the main focuses were on the seasonal and the interannual variability in ice properties and composition and on the contribution of meteoric ice to sea ice mass balance results provide a first statistical description of the seasonal evolution of sea ice in mild ice climate conditions the ice has a characteristic structure with an upper granular ice layer composed almost exclusively of superimposed ice and snow ice averaging at 20 35 of the total ice thickness the remaining is composed of columnar or intermediate granular columnar ice depending on growth conditions while salinity shows a uniform profile through the ice 18o shows lower values in the surface because of meteoric ice formation the thin ice cover is susceptible to changes in atmospheric conditions and rapid changes in ice salinity are connected to changes in the ice thermal regime and flooding the contribution of meteoric ice varied from 0 to 35 by mass depending on season and year superimposed ice formation is a recurring process and significantly contributed to ice growth up to 20 by mass especially late in the season during snowmelt freeze cycles liquid precipitation also cause formation of intermittent superimposed ice layers at these latitudes the contribution of meteoric ice to sea ice mass balance is largely dependent on the amount and timing of snow accumulation and timing of snowmelt freeze processes which all showed large year to year variation the conditions presented here may start to occur at higher latitudes if global warming continues

a model study of differences of snow thinning on arctic and antarctic first year sea ice during spring and summer the one dimensional snow model sntherm is validated using field measurements of snow and superimposed ice thickness and surface energy fluxes these were performed during the spring to summer transition in svalbard and in the weddell sea antarctica both the seasonal snow thickness decrease and the formation of superimposed ice are well reproduced by the model during the three observation periods observed and modeled snow thickness differ only by 13 1 27 1 mm on average in regional studies the model is forced with atmospheric re analysis data european centre for medium range weather forecasts and applied to several meridional transects across the arctic and southern ocean these show fundamental regional differences in the onset duration and magnitude of snow thinning in summer in the central arctic snowmelt onset occurs within a narrow time range of 11 days and without significant regional differences in contrast the snow cover on antarctic sea ice begins to melt about 25 days earlier and the length of the antarctic snow thinning season increases with increasing latitude the importance of melting and evaporation for the modeled snow thickness decrease is very different in the two hemispheres the ratio of evaporated snow mass to melted snow mass per unit area is derived from the model and amounts to approximately 4 2 in the antarctic and only 0 75 in the arctic this agrees with observations and model results of the surface energy balance and illustrates the dominance of surface cooling by upward turbulent fluxes in the antarctic

contrasting tectonic history of the arc continent suture in the southern and middle urals implications for the evolution of the orogen the main uralian fault has been considered the original arc continent suture for 2000 km along the uralide orogen the symmetry of the tectonic units across it suggested a consistent east dipping polarity for the palaeosubduction zone which together with its topographic and aeromagnetic signature supported the idea of a single suture however several characteristics vary at different latitudes in the middle urals it is a strike slip fault zone with moderately deformed and metamorphosed volcanic arc fragments in its hanging wall and low grade metamorphic rocks of the east european craton in its footwall here it has a prominent nnw trending magnetic signature which cross cuts north trending anomalies in its hanging wall and a pronounced reflection seismic signature that can be traced to the top of the middle crust at c 5 s twt in the southern urals it is a serpentinite melange zone of ambiguous kinematics with a weakly deformed and metamorphosed volcanic arc in its hanging wall and moderately metamorphosed to high pressure rocks of the east european craton in its footwall in this part of the orogen it has a weak reflection seismic character and a magnetic signature that parallels that of its hanging wall on the basis of an integrated analysis of these different data sets we suggest that the main uralian fault as it is currently defined is not a single entity but rather the original arc continent suture in the south and the western strand of a strike slip fault system that reworked the original suture in the middle urals

conodont biostratigraphy and faunal assemblages in radiolarian ribbon banded cherts of the burubaital formation west balkhash region kazakhstan biostratigraphical study of the early to mid ordovician conodont fauna from ribbon banded radiolarian cherts of the middle burubaital formation in central kazakhstan reveals an almost complete succession of conodont biozones from the late tremadocian to the early darriwilian during this interval biosiliceous sediments were deposited in basinal environments inhabited by lingulate brachiopods sponges pterobranchs and caryocaridids in conditions of high fertility and primary productivity of surface water the community structure of taxonomically diverse conodont assemblages typifying open oceanic environments is not significantly different from that of epicratonic basins of the north atlantic conodont province the regional increase of oxygenated bottom waters at the base of the oepikodus evae biozone is possibly related to considerable changes in palaeo oceanographical circulation patterns the finds of three natural clusters of prioniodus oepiki mctavish enable us to propose an emended diagnosis of this species

processes and imagery of first year fast sea ice during the melt season an analysis of first year fast sea ice during the melt season has been made by using surface measurements and aircraft radar and photographic imagery obtained during a field study near prince patrick island in the canadian archipelago from june 13 to july 13 1982 and satellite imagery from landsat and seasat distinct changes observed in the properties of the snow layer and the sea ice were a temporary increase in small scale surface roughness caused by formation of nodules of ice at the snow ice interface extensive snow melt and surface flooding development of surface water drainage networks and low topography around fractures and seal breathing holes and a rapid draining of much of the surface water from the extensive salinity profiles obtained two zones of rapid desalination in the first year ice were observed one zone extending from the air ice interface downward toward the center of the ice sheet that resulted from surface warming and drainage of the surface melt water through the ice and the other zone extending from the sea ice interface upward toward the center of the ice sheet that resulted from heating and separation of seawater and ice caused by a layer of low salinity meltwater beneath the ice formed from surface meltwater runoff aircraft radar imagery detected changes in the amount of surface water and in the development of topography surrounding drainage features similar changes were detected in coincident landsat multispectral scanner mss imagery of the study area and in seasat radar imagery and landsat mss imagery of the prince of wales strait from july 1978

thermodynamics of slush and snow ice formation in the antarctic sea ice zone snow over antarctic sea ice is often flooded by brine or seawater particularly in spring forming slush and snow ice here we evaluate the representation of the thermodynamics of slush and snow ice formation in large scale sea ice models using laboratory experiments nacl solutions poured into grated ice in an isolated container scaling analysis highlights latent heat as the main term of the energy budget the temperature of the new sea ice immediately after flooding is found very close to the saltwater freezing point whereas its bulk salinity is typically 20 g kg large scale sea ice models faithfully represent such physics yet the uncertainty on the origin of flooding saltwater impacts the calculated new ice temperature because of the different salinities of seawater and brine the laboratory experiments also suggest a potential limitation to the existing physical representations of flooding for brine fractions 60 ice crystals start floating upon saltwater natural sea ice observations suggest that the isolated system assumption holds for a few hours at most after which rapid heat and salt exchanges mostly destroy the initial flooding signature on temperature and salinity a small footprint on ice salinity remains however natural snow ice is found 3 5 g kg more saline than other forms of sea ice

surface properties and processes of perennial antarctic sea ice in summer ice core and snow data from the amundsen bellingshausen and weddell seas antarctica show that the formation of superimposed ice and the development of seawater filled gap layers with high algal standing stocks is typical of the perennial sea ice in summer the coarse grained and dense snow had salinities mostly below 0 1 per mil a layer of fresh superimposed ice had a mean thickness ranging from 0 04 0 12 m 0 04 to 0 08 m thick gap layers extended downwards from 0 02 to 0 14 m below the water level these gaps were populated by diatom standing stocks up to 439 g l chlorophyll a we propose a comprehensive heuristic model of summer processes where warming and the reversal of temperature gradients cause major transformations in snow and ice properties the warming also causes the re opening of incompletely frozen slush layers caused by flood freeze cycles during winter alternatively superimposed ice forms at the cold interface between snow and slush in the case of flooding with negative freeboard combined these explain the initial formation of gap layers by abiotic means alone the upward growth of superimposed ice above the water level competes with a steady submergence of floes due to bottom and internal melting and accumulation of snow

salinity profiles of antarctic sea ice field data and model results in order to describe and compare sea ice salinity distributions which are of interest in the study of physical and biological ice characteristics as well as ice ocean interaction we have computed composite profiles and fitted third degree polynomials to salinity data of 129 cores from the weddell sea four characteristic profile shapes have been recognized and described through the polynomial coefficients c s i and type profiles the field data have been compared with ideal salinity profiles generated by a simulation scheme based on thermodynamic growth under climatological conditions representative of the weddell sea composite salinity profiles agree well with simulations irrespective of the growth mechanism i e frazil or congelation suggesting that ice properties which depend on salinity or porosity may evolve independent of ice growth conditions analysis of salinity and 18o data in conjunction with the simulations demonstrates that apart from meteorological conditions controlling growth velocity and temperature distribution within the ice flooding and upward brine expulsion are important in raising top salinities as frequently observed low top salinities are typical of ice that has undergone retexturing and differential desalination salinity decreases towards the bottom of a floe are a result of high oceanic heat fluxes and snow cover effects as a consequence of these processes the bulk salinity of weddell sea ice cannot be described by a simple linear age thickness relationship as characteristic of arctic first year ice

petrochemistry and origin of sub ophiolitic metamorphic and related rocks in the oman mountains the semail ophiolite complex of the northern oman mountains was obducted during cenomanian to campanian upper cretaceous times onto the arabian continental margin during this time span schistose metamorphic rocks of amphibolite and greenschist facies exhibiting polyphase deformation were formed and accreted below the ophiolite slice whole rock and mineral analyses confirm that the amphibolites were originally tholeiitic basalts comparable to present day occurrences at mid ocean ridges a comparison of trace element geochemistries however suggests that the protoliths were not equivalent to the haybi alkaline and transitional tholeiites found in the underlying structural slice or to the semail ophiolite volcanic rocks which lie structurally higher in the sequence it is therefore suggested that the amphibolites may have been derived from jurassic or lower cretaceous oceanic basalts not recognized elsewhere in the oman mountains structurally beneath the amphibolites within the metamorphic sheet greenschist facies metasedimentary rocks including quartzites and marbles are interbanded with metabasite horizons containing actinolite and less commonly blue crossitic amphiboles it is suggested that the sedimentary and volcanic protoliths were metamorphosed in a subduction zone environment during initial ophiolite displacement and were accreted to the base of the ophiolite during progressive underthrusting