circulation mixing and production of antarctic bottom water abstract the antarctic source of bottom water to the abyssal layer of the world ocean is examined as well as its large scale flow pattern and ultimate entrainment rate into the deep water above we make use of the available high quality station data in the southern ocean to construct bottom maps of neutral density and mean property maps including chlorofluorocarbon cfc for the abyssal layer underneath a selected neutral density surface the maximum density at the sill depth of drake passage is used to distinguish between the voluminous deep water mass that is a continuous component of the antarctic circumpolar current from the relatively denser bottom water originated along the antarctic continental margins based on water density antarctic bottom water aabw is defined here generically to include all volumes of non circumpolar water of antarctic origin over the shelf regime multiple localized sources of specific aabw types contribute to the abyssal layer of the adjacent antarctic basins characteristics of these dense bottom waters reflect closely those observed on the parent shelf water mass spreading paths of newly formed deep and bottom waters over the slope regime and their subsequent oceanic circulation patterns are analyzed on the basis of global property maps for the aabw layer interior mixing and interbasin exchanges of aabw are deduced from mean characteristic curves following the southern streamline of the antarctic circumpolar current outflow and mixing of aabw from the weddell sea to the argentine basin is depicted using density and cfc distributions of two zonal hydrographic lines recirculation and mixing of deep and bottom waters within the weddell gyre are also detailed using a meridional section along the greenwich meridian the strength of all localized sources of aabw combined is estimated by two independent approaches an estimate of the total production rate of aabw is calculated based on the oceanic cfc budget for the aabw layer offshore of the 2500 m isobath the sum of all downslope inputs of well ventilated bottom water types underneath the top isopycnal must account for the measured cfc content in the bottom layer the resulting total aabw production rate is about 8 sv which is a conservative figure that neglects the loss of cfc bearing waters across the top isopycnal in recent years whereas about 9 5 sv is calculated assuming a well mixed bottom layer making use of their transient nature cfc distributions at the top of the aabw layer indicate that more direct and rapid entrainment of cfc rich bottom waters below occurs over localized areas with relatively strong upwelling rates and enhanced vertical mixing a second more ad hoc but independent oceanic mass budget of the bottom layer is also constructed a typical basin wide rate of deep upwelling of 3 10 7 m s 1 requires 10 sv 1 sv 106 m3 s 1 of newly formed aabw to sink down the slope around antarctica we have also formulated a spatial distribution of deep upwelling on the isopycnal at the top of the aabw it is expressed as a combination of wind topographic and turbulent components which in turn are functions of the isopycnal depth bottom depth and bottom layer thickness this non uniform upwelling field yields about 12 sv of aabw exported across the top isopycnal fortuitously the overall average of upward speed at the top isopycnal 3 7 10 7 m s 1 compares well with previous estimates of deep upwelling in the northern basins a series of likely sites for strong vertical entrainment of aabw are clearly identified in the modeled distribution of deep upwelling consonant with the observed cfc distributions on the top isopycnal altogether regions with relatively high upwelling rates 5 10 7 m s 1 occupy only a quarter of the total areal extent of the top isopycnal but they account for as much as 45 of the total vertical transport

sea ice growth and water mass modification in the mertz glacier polynya east antarctica during winter in july september 1999 an extensive oceanographic survey 87 conductivity temperature and depth measuring stations was conducted in the mertz glacier polynya over the adelie depression off the antarctic coast between 145 and 150 e we identify and describe four key water masses in this polynya highly modified circumpolar deep water hmcdw winter water ww ice shelf water isw and high salinity shelf water hssw combining surface velocity data from an acoustic doppler current profiler with three hydrographic sections we found the hmcdw to be flowing westward along the shelf break 0 7 sv the ww and hssw flowing eastwards underneath mertz glacier 2 0 sv and that there was a westward return flow of isw against the continent 1 2 sv using a simple box model for the exchanges of heat and fresh water between the principal water masses we find that the polynya was primarily a latent heat polynya with 95 of the total heat flux caused by sea ice formation this heat flux results from a fresh water equivalent sea ice growth rate of 4 9 7 7 cm d 1 and a mass exchange between hmcdw and ww of 1 45 sv the inferred ocean heat flux is 8 14 w m 2 and compares well with other indirect estimates

effects of regional fast ice and iceberg distributions on the behaviour of the mertz glacier polynya east antarctica an observational account of research carried out in july august 1999 shows that grounded iceberg and related fast ice distributions and periodic break outs of fast ice in winter as well as at other times have an important impact on the size and behaviour of the mertz glacier polynya east antarctica and a smaller polynya to the east analysis of satellite and in situ data shows that a semi constant stream of thick broken out fast ice and other large floes from the east extends westwards from north of the glacier terminus to form a compact barrier to the net west northwesterly export of ice formed in the polynya an annual fast ice promontory to the west further narrows the outlet path as a result of this and high ice production rates the polynya periodically back fills significantly reducing the open water area present intervening flush outs by synoptic storm events clear the polynya region to some extent before it back fills again this cycle continued from mid march until early october in 1999 when a significant change in the regional ice drift occurred a preliminary comparison with data from 1998 indicates that the timing and magnitude of the processes may vary interannually similar morphological features were also observed in 1963 on a declassified photoreconnaissance satellite image

rbsr and 40ar39ar laser probe dating of high pressure phengites from the sesia zone western alps underscoring of excess argon and new age constraints on the high pressure metamorphism abstract the combined use of the rb sr and 40ar 39ar laser probe methods allows confirmation of the existence of excess argon in phengites from eclogites from the sesia zone western alps despite systematic 40ar 39ar plateau ages 40ar 39ar phengite ages from two different areas show integrated age spreads between 65 4 0 3 ma and 109 5 0 4 ma the youngest 40ar 39ar plateau age 65 9 0 4 ma is concordant with two rb sr phengite whole rock isochron ages from the same outcrop which display a mean age at 64 2 2 5 ma and older than a rb sr biotite whole rock isochron age at 53 0 1 0 ma this age concordance being incompatible with the concept of isotopic closure temperature is probably fortuitous and probably results from an excess argon contamination however the concordance of the rb sr phengite isotopic closure temperature with the temperature reached during the eclogite facies event suggests that the age at 64 2 2 5 ma could be a crystallization age probably contemporaneous with the eclogite facies event in the sesia zone when compared to recent age data from the piemont zone and the dora maira massif the entire data set which needs to be confirmed by extra measurements support diachronous high pressure hp events in the western alps

an ice ocean coupled model an ice model an ocean model and a method of coupling the models are described the ice model is a synthesis with variations and extensions of previous modeling ideas ice thickness concentration velocity and internal energy are prognostic variables the ice thermodynamics are represented by temperatures at the snow surface ice surface the interior and the bottom surface melting and freezing rates are calculated at the ice atmosphere ice ocean and atmosphere ocean interfaces a prescribed portion of summer meltwater can be stored on the surface and refrozen in the fall the ocean model includes a second moment turbulence closure submodel and enables one to solve for oceanic heat flux the interfacial stress and subsurface properties in this paper the model is applied to one dimensional simulations but the equations are cited in a form for implementation by two and three dimensional models in a companion paper kantha and mellor this issue the model is used for two dimensional vertical plane simulations in the bering sea several one dimensional sensitivity studies are performed in the case where the ice model is decoupled from the ocean here the oceanic heat flux and sea surface temperature are prescribed constants the studies reveal the role and sensitivity of surface trapped meltwater ice concentration and ice divergence with the coupled ice ocean model the seasonally varying oceanic heat flux and mixed layer properties are determined by the model some comparisons with observations in the central arctic ocean are possible the role of the molecular sublayer immediately adjacent to the ice is examined frazi ice production is related to the large disparity in the molecular diffusivities for temperature and salinity the mixed layer model contains empirical constants which are known from turbulence data the molecular sublayer parameterization requires one empirical parameter b which is uncertain but from this study is assuredly greater than zero the value implicit in previous models the ice model requires the empirical parameters ci f and ci u to quantitatively account for freezing or melting processes in open leads their values are also uncertain but we present reasoning and sensitivity studies to suggest specific values finally an empirical parameter g is introduced it is the ratio of the value of the ice thickness used to represent average ice volume in the dynamic and thermodynamic equations to the value of the thickness needed in the heat conduction equation estimates of g are made from observed thickness distribution functions sensitivity studies show it to be an important parameter

modeling the basal melting and marine ice accretion of the amery ice shelf the basal mass balance of the amery ice shelf ais in east antarctica is investigated using a numerical ocean model the main improvements of this model over previous studies are the inclusion of frazil formation and dynamics tides and the use of the latest estimate of the sub ice shelf cavity geometry the model produces a net basal melt rate of 45 6 gt year 1 0 74 m ice year 1 which is in good agreement with reviewed observations the melting at the base of the ice shelf is primarily due to interaction with high salinity shelf water created from the surface sea ice formation in winter the temperature difference between the coldest waters created in the open ocean and the in situ freezing point of ocean water in contact with the deepest part of the ais drives a melt rate that can exceed 30 m of ice year 1 the inclusion of frazil dynamics is shown to be important for both melting and marine ice accretion refreezing frazil initially forms in the supercooled water layer adjacent to the base of the ice shelf the net accretion of marine ice is 5 3 gt year 1 comprised of 3 7 gt year 1 of frazil accretion and 1 6 gt year 1 of direct basal refreezing

katabatic wind forcing of the terra nova bay polynya the terra nova bay polynya is a perennial winter feature in the western ross sea antarctica which occupies roughly 1000 km2 it is formed and maintained by the combined influence of persistent katabatic winds which advect newly formed bay ice eastward and the drygalski ice tongue which prevents northward drifting pack ice from entering terra nova bay existence of anomalously strong katabatic drainage along this coast is predicted by parish s 1982 simulation of wintertime airflow which reveals a pronounced confluence of surface winds upslope from the reeves glacier where the winds are further focused by local topography the simulation is strongly supported by regional sastrugi orientations average wintertime atmospheric conditions and ice sheet topography which control surface air drainage are stable on a climatic time scale therefore persistent wintertime katabatic winds should be an annual phenomenon further evidence comes from multi year landsat images which consistently show windswept snowfree areas on the reeves glacier in marked contrast to typical antarctic katabatic winds strong persistent winter winds are observed at sea level 25 km beyond the coastal slope break air probably descends as bora type winds and is likely to be significantly denser than the air at sea level conditions are not favorable for hydraulic jumps apparently typical of other katabatic regimes the horizontal density difference is maintained during airflow across the nansen ice sheet because relatively little air mass modification occurs there in contrast to situations where air moves over an ice laden ocean observations thus suggest that katabatic winds maintain their identity for some distance seaward of the coast qualitative trajectory calculations indicate that for representative geostrophic conditions this distance is on the order of the observed polynya width estimated ice freezing rates are 20 cm day 1 but wind generated waves and currents prevent ice from consolidating the blocking effect of the drygalski ice tongue is a consequence of its orientation with regard to western ross sea ice drift patterns ice tongue length controls polynya width absence of such blocking along other coasts experiencing strong katabatic outflow partly explains why similar polynyas do not form there

dense shelf water spreading from antarctic coastal polynyas to the deep southern ocean a regional circumpolar model study the spreading of dense shelf water dsw from antarctic coastal margins to lower latitudes plays a vital role in the ocean thermohaline circulation and the global climate system through enhanced localized sea ice production in antarctic coastal polynyas cold and saline dsw is formed over the continental shelf regions as a precursor to antarctic bottom water aabw however the detailed fate of coastal dsw over the southern ocean is still unclear here we conduct extensive passive tracer experiments using a circumpolar ocean sea ice ice shelf model to investigate pathways of the regional polynya based dsw from the antarctic margins to the deep southern ocean basins in the numerical experiments the antarctic coastal margin is divided into nine regions and a passive tracer is released from each region at the same rate as the local sea ice production the modeled spatial distribution of the total concentration of the nine tracers is consistent with the observed aabw distribution and clearly demonstrates nine routes of the dsw over the southern ocean along its bottom topography furthermore the model shows that while 50 of the total tracer is distributed northwards from the continental shelf to the deep ocean 7 is transported polewards beneath ice shelf cavities the comprehensive tracer experiments allow us to estimate the contribution of local dsw to the total concentration along each of the pathways

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

response of the global ocean to greenland and antarctic ice melting 1 we investigate the transient response of the global ocean circulation to enhanced freshwater forcing associated with melting of the greenland and antarctic ice sheets increased freshwater runoff from greenland results in a basin wide response of the north atlantic on timescales of a few years communicated via boundary waves equatorial kelvin waves and westward propagating rossby waves in addition modified air sea interaction plays a fundamental role in setting up the basin scale response of the atlantic circulation in its subpolar and subtropical gyres in particular the modified ocean dynamics and thermodynamics lead to a depression in the central north and south atlantic that would not be expected from linear wave dynamics moreover the heat content increases on basin and global scales in response to anomalous freshwater forcing from greenland suggesting that the ocean s response to enhanced freshwater forcing would be a coupled problem other parts of the world ocean experience a much slower adjustment in response to greenland freshwater forcing communicated via planetary waves but also involving advective diffusive processes especially in the southern ocean over the 50 years considered here most of the sea level increase associated with freshwater input from greenland remains in the atlantic ocean in contrast ice melting around antarctica has a much reduced effect on the global ocean in both cases none of the basins came to a stationary state during the 50 year experiment

the response of stratified frictional flow of shelf and slope waters to fluctuating large scale low frequency wind forcing abstract numerical and analytical models are developed to discuss large scale low frequency wind driven fluctuations over the continental shelf and slope in the presence of realistic density stratification and bottom friction the models employ the long wave assumption that frequencies are small relative to the inertial frequency and that alongshore scales are large relative to cross cross shelf scales an attempt is made to make the effect of bottom friction on the flow as realistic as possible by taking into account the influence of surface gravity waves on bottom stress the results were obtained for sinusoidal wind forcing having frequency and alongshore wavenumber l and are described below a general criterion for barotropic shelf water response for wind forcing frequencies in the weather band 2 few weeks to 2 few days can be derived for the purpose of rapid calculation this criterion reduces approximately tohere ns2 is a shelf averaged value of the buoyancy frequency squared is

pliocene and early pleistocene paleoenvironmental conditions in the pannonian basin hungary slovakia stable isotope analyses of fossil proboscidean and perissodactyl teeth abstract stable carbon and oxygen isotope values of structural carbonate 13c 18oco3 and phosphate 18opo4 in bio apatite were measured for fossil mammalian teeth from slovakia and hungary oxygen isotope compositions of enamel provide new quantitative records of the pliocene and early pleistocene paleoclimate in the pannonian basin pb the 18opo4 values were used to study the temporal variations in the oxygen isotope compositions of precipitation and the changes in temperature over the pb the new o isotope data suggest that surface air temperatures between 4 5 and 2 0 ma were 1 to 4 c warmer with about 700 mm yr more precipitation compared to the present c isotope analyses of samples from proboscideans anancus sp mammut sp and perissodactyls stephanorhinus sp tapirus sp from the pliocene mn15 mn16 and early pleistocene mn17 suggest that they were primarily c3 browsers the mean 13c value is high at 4 5 to 3 7 ma mn14 15 during the pliocene warm period and decreases at about 3 5 to 3 0 ma mn16 mid pliocene warm period with the onset of more humid conditions in europe the 13c values return to higher values from 2 5 ma onwards mn17 most likely reflecting more arid conditions as a consequence of the onset of the northern hemisphere glaciation

la mc icpms and shrimp u pb dating of complex zircons from quaternary tephras from the french massif central magma residence time and geochemical implications abstract analyses of zircon grains from the queureuilh quaternary tephras pumice provide new information about their pre eruptive history u pb dating was performed in situ using two methods shrimp and la mc icpms equipped with a multi ion counting system both methods provided reliable 207pb 206pb and 206pb 238u ratios as well as u and th abundances required for u pb concordia intercept age determination after initial 230th disequilibrium correction the new la mc icpms method was validated by dating a reference zircon 61 308b and zircons from a phonolitic lava dated independently with the two techniques a time resolution of about 20 kyr for 1 ma zircon crystals was achieved for both methods the clear euhedral zircon population from queureuilh tephras is quite complex from several points of view 1 some grains are reddish or yellowish while others are colorless 2 the u and th composition changes by more than an order of magnitude and th u is generally high 1 2 3 there are three discrete ages recorded at 2 35 0 04 1 017 0 008 and 0 640 0 010 ma from the previously determined 40ar 39ar age at 0 571 0 060 ma duffell h 1999 contribution geochronologique a la stratigraphie volcanique du massif des monts dore par la methode 40ar 39ar d e a univ clermont ferrand 56 p the discontinuous zircon age populations the color of the grains and their composition we favor the following model as explanation the oldest less numerous group of reddish zircons represents xenocrystic grains resulting from assimilation of the local material during magma ascent a primitive magma chamber perhaps deep in crustal level was formed at 1 0 ma the related magma previously characterized by high th u ratio 2 2 1 1 underwent rejuvenation during ascent to a new chamber at shallow depth and or during injection of more mafic magmas during this stage at 0 64 ma the colorless zircon grains of lower th u ratio 1 3 0 5 crystallized this last stage defined the magma residence time of 70 kyr prior to eruption dated by the 40ar 39ar method however if the primitive magma is considered the magma residence time as a whole from this first stage reached 446 kyr in the light of the complex history of such magmas which commonly involves recycling of zircon grains that precipitated tens to hundreds of kyr earlier than eruptions the use of zr concentration in geochemical modeling of whole rock compositional data can be problematic

antarctic bottom water from the adelie and george v land coast east antarctica 140 149 e 1 we report on observations of dense shelf water overflows and antarctic bottom water aabw formation along the continental margin of the adelie and george v land coast between 140 e and 149 e vertical sections and bottom layer water mass properties sampled during two rvib nathaniel b palmer hydrographic surveys nbp00 08 december 2000 january 2001 and nbp04 08 october 2004 describe the spreading of cold dense shelf water on the continental slope and rise from two independent source regions the primary source region is the adelie depression exporting high salinity dense shelf water through the adelie sill at 143 e an additional eastern source region of lower salinity dense shelf water from the mertz depression is identified for the first time from bottom layer properties northwest of the mertz sill and mertz bank 146 e 148 e that extend as far as the buffon channel 144 75 e in summer regional analysis of satellite derived ice production estimates over the entire region from 1992 to 2005 suggests that up to 40 of the total ice production for the region occurs over the mertz depression and therefore this area is likely to make a significant contribution to the total dense shelf water export concurrent time series from bottom mounted microcats and adcp instruments from the mertz polynya experiment april 1998 to may 1999 near the adelie sill and on the upper continental slope 1150 m and lower continental rise 3250 m to the north describe the seasonal variability in downslope events and their interaction with the ambient water masses the critical density for shelf water to produce aabw is examined and found to be 27 85 kg m 3 from the adelie depression and as low as 27 80 kg m 3 from the mertz depression this study suggests previous dense shelf water export estimates based on the flow through the adelie sill alone are conservative and that other regions around east antarctica with similar ice production to the mertz depression could be contributing to the total aabw in the australian antarctic basin

interannual to multidecadal responses of antarctic ice shelf ocean interaction and coastal water masses during the twentieth century and the early twenty first century to dynamic and thermodynamic forcing abstractmuch attention has been paid to ocean cryosphere interactions over the southern ocean basal melting of antarctic ice shelves has been reported to be the primary ablation process for the an

recurring polynyas over the cosmonaut sea and the maud rise two polynyas over the deep ocean were observed in the antarctic region during the winter of 1980 one near 43 e 66 s cosmonaut polynya and another near 2 e 64 s maud rise polynya the time history of these two polynyas was examined on an alternate day basis using ice concentration maps from the nimbus 7 scanning multichannel microwave radiometer smmr a quantitative analysis of a study area around it shows that the totally enclosed cosmonaut polynya attained a maximum size on july 25 1980 with an open water area of as much as 137 700 km2 this polynya lasted for a few weeks disappeared on august 16 1980 and was not observed for the rest of the winter similar polynyas in the same region have occurred for several years including 1973 1975 1979 1982 and 1986 the maud rise polynya on the other hand was observed as a reduction in ice concentration to about 37 within the smmr resolution of about 900 km2 however the open water area in the region amounted to 92 800 km2 on july 20 and the polynya recurred several times during the same winter period it is proposed that both polynyas are products of deep reaching convection which introduces warmer deep water into the surface layer in this way they are viewed as sensible heat polynyas in that they are maintained by oceanic heat the oceanographic settings of these two polynyas are similar the hydrographic data at both sites indicate the existence of localized doming of the pycnocline this brings warmer saltier deep water closer to the sea surface which has been demonstrated to be an effective preconditioner for deep reaching convection it is probable that the polynyas are terminated by invasion of sea ice from the sides which attenuates convection the capability of a polynya to survive an entire winter period may be related to its size the larger polynyas are better protected from convergence of the surrounding sea ice for example a simple model shows that a polynya with a diameter of about 100 km or greater is much more likely to survive a winter season than a smaller one

the circulation and water masses of the antarctic shelf and continental slope between 30 and 80 e abstract the circulation and water masses from the antarctic continental shelf to 62 s between 30 and 80 e are described using hydrographic data collected on seven hydrographic sections during the baseline research on oceanography krill and the environment west broke west experiment the eastern limb of the weddell gyre dominates circulation between 30 and 40 e and is significantly cooler and fresher than the region to the east the antarctic circumpolar current acc extends from the north into the survey region east of 40 e reaching as far south as 65 5 s at 60 e this results in increasing observed maximum temperature and salinities progressively towards the east peaking at 80 e due to the intrusion of the southern acc front saccf to 63 s this southward extension is steered by the southern end of kerguelen plateau causing a horizontal shear of over 0 15 m s 1 between the eastward acc and westward flowing antarctic slope current asc the asc is observed at all six meridional sections immediately north of the shelf break it is strongly barotropic and transports a total of 15 8 7 4 sv westwards while the bottom referenced baroclinic component only contributes 1 3 0 3 sv at each section this current intensifies to a narrow westward jet with absolute velocities up to 0 3 m s 1 over the steepest shelf slope gradients at 70 e a v shape is observed in the asf this and the nearby presence of denser shelf water and ice shelf water is characteristic of antarctic bottom water aabw formation but no new aabw is found on this section instead significantly warmer saltier and less oxygenated aabw to the east and newly formed aabw high on the continental slope immediately to the west suggest a formation region just west of 70 e this newly formed aabw progressively becomes warmer and saltier west of 60 e and is observed extending offshore and moving westward below eastward flowing water masses acc frontal positions are found to be 1 2 farther north in the survey region than suggested by historical climatology

modeling interannual dense shelf water export in the region of the mertz glacier tongue 1992 2007 ocean observations around the australian antarctic basin show the importance of coastal latent heat polynyas near the mertz glacier tongue mgt to the formation of dense shelf water dsw and associated antarctic bottom water aabw here we use a regional ocean ice shelf model to investigate the interannual variability of the export of dsw from the adelie west of the mgt and the mertz east of the mgt depressions from 1992 to 2007 the variability in the model is driven by changes in observed surface heat and salt fluxes the model simulates an annual mean export of dsw through the adelie sill of about 0 070 06 sv from 1992 to 1998 the export of dsw through the adelie mertz sills peaked at 0 14 sv 0 29 sv during july to november during periods of mean to strong polynya activity defined by the surface ocean heat loss dsw formed in the adelie depression can spread into the mertz depression via the cavity under the mgt an additional simulation where ocean ice shelf thermodynamics have been disabled highlights the fact that models without ocean ice shelf interaction processes will significantly overestimate rates of dsw export the melt rates of the mgt are 1 20 4 m yr 1 during periods of average to strong polynya activity and can increase to 3 81 5 m yr during periods of sustained weak polynya activity due to the increased presence of relatively warmer water interacting with the base of the ice shelf the increased melting of the mgt during a weak polynya state can cause further freshening of the dsw and ultimately limits the production of aabw

late miocene to early pliocene sedimentary environments and climatic changes in the alpine carpathian pannonian junction area a case study from the danube basin northern margin slovakia abstract the danube basin situated at the alpine carpathian pannonian junction represents a region of the central paratethys strongly influenced by orogen building processes and climatic changes the geodynamic development mirrors gentle docking of the carpathians into the european platform margin associated with synrift and later postrift subsidence of the back arc area onset of the basin inversion characterized the pliocene evolution the aquatic environments gradually changed from marine brackish to caspibrackish and to freshwater within the lake pannon due to isolation followed by development of ephemeral lakes and alluvial plains the terrestrial record documents the extinction of the middle miocene fauna and the retreat of vegetation with subtropical floral elements at the beginning of the late miocene due to changes in paleogeography and climate between 11 5 and 7 1 ma the immigration of a new hipparion fauna as well as the replacement of swamp vegetation by coniferous forest of the temperate zone can be interpreted as the first appearance of seasonality with lowered humidity at the pannonian pontian boundary the late pontian to early pliocene fauna and flora as well as sedimentary environments support the increase of humidity in warm temperate climate between 7 1 and 5 4 ma

on mertz and ninnis glaciers east antarctica two large glacier tongues which extend substantially across the coastline of king george v land in east antarctica have been studied by remote sensing synthetic aperture radar jers 1 the tongue of mertz glacier is in a state of advance while the ninnis glacier tongue is retreating some more specific points are the distinctive surface structure and the form of the glacier tongues indicates that they are floating while the tongue of ninnis glacier has lost about two thirds of its area since 1913 the mertz glacier tongue has advanced substantially and has about doubled its areal extent over the same time period the annual movement of the tongue of mertz glacier was determined as about 1 2 km this is close to the value of the advance of the tip of the tongue since 1963 which was determined as 0 9 km year 1

the surface windfield over the antarctic ice sheets the intense radiative cooling of air over the ice slopes of antarctica generates a surface wind regime that is strongly controlled by topography and plays a key role in determining the behaviour of the atmosphere and ocean in high southern latitudes1 7 resultant surface winds are intimately linked to the orientation of the ice terrain fig 1 and display the highest degree of persistence found on earth the close coupling between wind and topography allows estimation of the former if the latter is known with some precision here we report on time averaged near surface airflow over the antarctic continent during winter diagnosed from a recent accurate synthesis of terrain slopes and from estimates of the lower atmospheric temperature structure the simulated drainage pat tern exhibits strong spatial variability with the airflow concentrated into several zones near the coastal margin these confluence regions are responsible for strong persistent katabatic winds over downstream coastal stretches and are indicative of zones of greatest katabatic potential

cosmonaut polynya in the southern ocean structure and variability along the far eastern margin of the weddell gyre is a persistent feature in the middle of the ice pack which we previously reported and called the cosmonaut polynya a study of polynya occurrences from 1973 to 1993 reveals that since 1986 the polynya has become more active with an average size of about 7 2 104 km2 and an average location at 52 e and 65 s satellite observations indicate that the polynya has recurred several times during winter in recent years with intervals ranging from a few days to a few weeks the centroid of the polynya varies only slightly with each formation during the year and from one year to another suggesting a controlling influence of the ocean and bottom topography that may be initially induced by wind the daily time series indicates two primary modes of formation one that is initiated in the early winter during a storm at a site usually preceded by an embayment of the ice edge and another that occurs during midwinter often preceded by a coastal polynya event adjacent to cape ann the cosmonaut polynya region is characterized in this study by compression of the westward flowing coastal current and the eastward flowing southern edge of the antarctic circumpolar current following the principle of conservation of potential vorticity vertical stretching of the water column would ensue enhancing upwelling such a process accelerates the injection of relatively warm salty deep water into the surface layer inhibiting sea ice growth and causing the polynya formation this theory appears to explain the general behavior of the polynya in terms of frequency duration size and location

in situ u pb zircon geochronology of neogene garnet bearing lavas from slovakia carpatho pannonian region central europe abstract zircons armored in garnet from four neogene lavas of slovakia three andesites and one dacite were dated in situ using excimer laser ablation icp ms for the andesites the 66 analytical points yield a lower intercept age of 13 3 0 1 ma mswd 1 2 which is older than the age of 12 4 0 2 ma recorded for the dacite u pb ages obtained in this study are significantly younger than the lower badenian ages k ar and fission track dating coupled with biostratigraphic correlations classically assumed for the garnet bearing lavas of the western carpathians with a minimum discrepancy of 3 ma accessorily a composite zircon with an inherited core reveals that some pan african crustal component is present at depth garnet bearing andesites and dacites potentially bear critical information about melt generation in the lower crust and possible recycling of pre existing crust into igneous rocks practically the problem is to assess the nature of the melt from which the garnet actually grew for this purpose zircon grains included into garnet may help to clarify the beginning of the magma history it seems likely that zircon was not grown from the bulk dacitic or andesitic melt but rather from a specific rhyolitic batch later mixing and consecutive change in magma chemistry explain that free zircons in the melt were almost totally dissolved whereas zircons shielded into garnets were preserved finally owing to their miocene age the zircon grains armored into garnet preclude any restitic origin for their host and definitely demonstrate the magmatic origin of garnet

volcanism and paleoenvironment of the pula maar complex a pliocene terrestrial fossil site in central europe hungary abstract we describe the late pliocene paleoenvironment and paleoclimate of the pula fossil site of the western pannonian basin hungary which occurs within a lacustrine succession deposited in a volcanic crater maar radiometric dating of adjacent volcanic bodies hosting the fossil bearing sedimentary assemblages gives an age of 4 25 0 17 ma k ar to date five articulated rhinoceros skeletons dihoplus sp have been recovered and a few fragmentary remains of artiodactyls and freshwater fishes perca sp leuciscus sp and gobius sp are also present an insect taphocoenosis comprises terrestrial groups that inhabited the former lake margins syrphidae heteroptera chalcidoidea tenebrionidae as well as aquatic insects dytiscidae baetidae and chironomidae deciduous broad leaved woody plants prevailed in and around the pula locality quercus ulmus zelkova acer salicaceae and are associated with some rare floral elements ginkgo sassafras and buxus deposition at the lake bottom seems to have taken place in oxygen depleted layers and taphonomic evidence indicates that fossil material underwent minimal if any weathering 13c values of one rhinoceros tooth suggest that this mammal consumed mixed c3 plants in a wooded environment the climatic conditions inferred from the reconstructed vegetation and stable oxygen isotope data from the tooth enamel support a cf type climate koppen classification with a mean annual temperature of 10 13 c with some dry periods during the year pula is comparable to other maar fossil sites of pliocene age such as camp dels ninots spain and hajnacka i slovakia

a recount of ross sea waters abstract oceanographic observations within the ross sea have grown dramatically in recent years both in number and quality this has prompted a parallel recount of the circulation and structure of all water masses in the southwestern continental margins of the pacific ocean a high resolution set of horizontal property distributions was combined into a new climatology which in turn is the basis of a fine volumetric s census of all ross sea water masses inshore of the shelf break 700 m isobath the ross sea volume 25 10 4 km 3 partitioning into layers of neutral density n is 25 in the top layer n 3 of antarctic surface water aasw 22 in the middle layer 28 00 kg m 3 n 3 of oceanic thermocline water 12 and modified circumpolar deep water mcdw 10 and 53 in the bottom layer n 28 27 kg m 3 of shelf water sw 1 85 c 22 precursor of the antarctic bottom water aabw offshore aasw flows westward along the outer shelf and southward along the eastern coast past cape colbeck oceanic thermocline waters 28 00 kg m 3 n 3 cross the shelf break west of 170 w and follow southward paths along banks shoaling progressively to near the sea surface of the central and western inner shelves winter buoyancy loss converts aasw and oceanic thermocline water into denser types of mcdw and sw which move cyclonically toward the sills of major troughs the census shows a continuous mode of relatively dense mcdw 28 10 kg m 3 n 3 directly linked to the circumpolar deep water cdw offshore effectively ventilating and freshening the deep ocean at levels below the salinity maximum and above aabw mcdw outflows from the ross sea shelf are traced to the antarctic circumpolar current near 155 e into the australian antarctic basin along the northern flank of the southwest pacific ridge and to near 135 w past the eastern end of the ross gyre two sources of salty sw are inferred near the coastal polynyas in the terra nova bay and western ross ice shelf areas the latter contributes to a major outflow of ice sw that reaches the shelf break along 180 vertical mixing of mcdw and sw produce msw over the shelf continuing over the sills as new aabw export of low salinity aabw s

on the influence of coastline orientation on the steady state width of a latent heat polynya this paper investigates under what conditions the steady state shape of a coastal latent heat polynya is influenced by 1 the direction of flow of free drifting frazil ice and the consolidated offshore ice sheet and 2 coastline orientation analytical solutions are obtained for coastal polynyas when the coastline is straight and when a coastline has a single step from the solutions it is shown that the asymptotic polynya width is given by the generalized pease 1987 width l cos where l is the classical pease width and is the angle between the consolidated ice sheet velocity and the normal to the coastline an expression is also obtained for the alongshore length scale l c over which the polynya adjusts toward its asymptotic width and it is shown that l c depends upon the directions of travel of the frazil ice and the consolidated ice sheet when the frazil ice and the consolidated ice sheet both drift offshore normal to the coast l c 0 in agreement with the classical pease theory variations in the coastline which occur on a length scale much smaller than l c are not reproduced in the polynya shape two numerical simulations are presented for terra nova bay antarctica and the st lawrence island polynya in the bering sea both examples employ realistic coastline geometry and information about the direction of drift of the consolidated ice sheet in each example a realistic polynya shape is obtained the examples highlight the versatility of the model because in the former case the ice sheet drifts almost parallel to the coast while in the latter it drifts offshore

rapid freshening of antarctic bottom water formed in the indian and pacific oceans 1 repeat hydrographic sections occupied in 1995 and 2005 reveal a rapid decline in the salinity and density of antarctic bottom water throughout the australian antarctic basin the basin wide shift of the deep potential temperature salinity s relationship reflects freshening of both the indian and pacific sources of antarctic bottom water the s curves diverge for waters cooler than 0 1 c corresponding to a layer up to 1000 m thick over the antarctic continental slope and rise changes over the last decade are in the same direction but more rapid than those observed between the late 1960s and the 1990s when combined with recent observations of similar freshening of north atlantic deep water these results demonstrate that dense water formed in both hemispheres is freshening in response to changes in the high latitude freshwater balance and rapidly transmitting the signature of changes in surface climate into the deep ocean

on the total input of antarctic waters to the deep ocean a preliminary estimate from chlorofluorocarbon measurements 1 deep ocean inventories of dissolved chlorofluorocarbon 11 cfc 11 along representative sections off antarctica provide the first estimate of the overall strength of all dense water sources in the southern ocean their formation rates are reported for three density layers that span the main water masses involved in the lower limb of the thermohaline circulation thc the bottom layer is supplied via sinking of antarctic bottom water aabw produced at a few continental shelves the middle layer receives the offshore injection of ventilated modified circumpolar deep water mcdw produced along much of the lengthy antarctic slope front the top layer is ventilated by northward export of antarctic surface water into the upper circumpolar deep water of the antarctic circumpolar current average southern ocean inputs to the upper two layers of the deep ocean for the 1970 1990 period are derived on the basis of the cfc 11 distributions along meridional sections the mean cfc 11 saturations of all water mass ingredients and the inferred mixing leading to production of dense source waters about 5 4 1 7 sv 1 sv 10 6 m 3 s 1 of near freezing shelf water ventilate the bottom layer and 4 7 1 7 sv and 3 6 1 3 sv of cold antarctic surface water ventilate the middle and top layers therefore the total contribution of ventilated southern ocean waters to the lower limb of the global thc is about 14 sv this is close to the about 17 sv estimated for north atlantic near surface sources from cfc 11 inventories their entrainment of 7 4 2 4 sv of cfc poor subsurface lower circumpolar deep water during the formation and sinking of aabw and mcdw raises the total southern ocean input to the deep ocean to about 21 sv

chronology petrogenesis and heat sources for successive carboniferous magmatic events in the southern central variscan vosges mts ne france plutonic bodies of the central and southern vosges mts can be assigned to two major early carboniferous magmatic events a visean mg k event c 345 and 340 336 ma and a younger s type event 329 322 ma new petrological geochemical and sr nd isotopic data highlight the existence of two groups of mg k intrusions that might be related to the nature of their primary magma sources that is chur like and enriched mantle which interacted with juvenile and mature crustal material respectively the differences between these two groups are explained by a geodynamic scenario involving deep subduction and relamination of the saxothuringian continental crust under the moldanubian continent the relaminated radiogenic saxothuringian material is thought to have been responsible for dehydration melting of both subducted crust and underlying metasomatized mantle thereby generating the mg k magma subsequently emplaced at middle crustal depth during their ascent the mafic magmas interacted with crustally derived felsic melts significantly later c 10 15 myr a widespread mid crustal anatexis occurred generating voluminous granite intrusions from mixed crustal sources paragneisses and or immature felsic intermediate metaigneous rocks mixed with mg k plutons the principal heat source for such a major melting event is related to the presence of mg k plutons rich in heat producing elements which were responsible after the time lag specified for a temperature increase at mid crustal levels by in situ radiogenic heat production the current study underlines the importance of deep continental crust subduction and relamination for the magmatism and development of collisional orogens supplementary material analytical methods and data and supplementary figures are available at http www geolsoc org uk sup18795

uranium mobilization by fluids associated with ca na metasomatism a p t t record of fluid rock interactions during pan african metamorphism western zambian copperbelt abstract a dozen uranium occurrences are known in the western zambian copperbelt domes region zambia the host rocks neoproterozoic kyanite talc micaschists have been interpreted as meta evaporites that formed part of an epicontinental sequence affected by upper amphibolite metamorphism during the pan african orogeny ca na metasomatism expressed by the presence of apatite epidote and scapolite is regionally extensive in the katanga and the pre katanga rocks in the domes region the present study focuses on the solwezi dome in the western zambian copperbelt two distinct uranium mineralization events that took place here mark the transition from crustal thickening by tectonic accretion to exhumation of the metamorphic host rocks u pb dating of uraninite and th pb dating of monazite show that the first u mineralization event took place between 550 ma and 530 ma the event is therefore contemporaneous with crustal thickening and on the basis of fluid inclusion analyses can be related to circulation of hypersaline ca rich metamorphic fluids trapped at minimum p t conditions of 460 mpa and 500 c on a regional scale the event is related to an epidote apatite metasomatic assemblage the second mineralization event dated at between 510 and 500 ma by th pb dating of monazite is related to high salinity ca na rich metamorphic fluids and occurred during exhumation of the high grade metamorphic rocks these fluids were trapped at the ductile brittle transition at 150 to 260 mpa and 200 to 300 c a regional scale scapolitization is attributed to these late fluid circulations these fluid rock interactions described at the regional scale are also characterized at the mineral scale alteration reactions assisted by cacl 2 rich fluids indicate that monazite and allanite hosted by the pre katanga rocks potentially acted as u sources for these pan african synmetamorphic uranium mineralizations

a latent and sensible heat polynya model for the north water northern baffin bay abstract the pease latent heat polynya model is coupled to a reduced gravity coastal upwelling model in order to simulate the formation and maintenance of the north water now the arctic s largest polynya located in northern beffin bay in this region strong northerly winds during winter and spring drive ice southward as fast as it is produced locally the pease mechanism for polynya formation and also produce upwelling of warm subsurface water along the west coast of greenland this upwelling provides an upward heat flux that melts ice near the coast a sensible host mechanism for polynya formation this combined latent and sensible heat polynya model is formulated as an initial boundary value problem with uniform winds its solution gives the tide evolution of the upper layer velocity and depth and also the polynya width as measured southward from the northern boundary of the polynya there are two fundamental time scales in the problem a fast one of the order of days that characterizes the

modeling water mass formation in the mertz glacier polynya and adelie depression east antarctica 1 high rates of sea ice growth and brine rejection in the mertz glacier polynya drive the production of dense continental shelf waters in the adelie depression we consider the rate of outflow of waters having sufficient density to sink into the neighboring abyssal ocean and form adelie land bottom water albw along with weddell and ross sea bottom waters the albw is an important source of antarctic bottom water the relevant processes are modeled using a variant of the max planck institute ocean model mpiom under daily ncep ncar reanalysis forcing for the period 1991 2000 the orthogonal curvilinear horizontal grid allows for the construction of a global domain with high resolution in our region of interest the modeled mertz glacier polynya is realistic in location and extent exhibiting low ice thickness 0 4 m and low ice fraction 50 the net surface ocean to atmosphere heat flux exceeds 200 w m2 and is dominated by sensible heat exchange in wintertime may through september inclusive 7 5 m of sea ice forms over the adelie depression at a rate of 4 9 cm d 1 this results in annual average volumetric production of 99 km3 of sea ice the associated brine release drives dense shelf water formation the off shelf flow of dense water exhibits strong interannual variability in response to variability in both atmospheric forcing and ocean preconditioning averaged over the period 1991 2000 the off shelf flow of dense water is 0 15 sv for a period of strong outflow 1993 1997 this increases to 0 24 sv most of the outflow occurs during july through october at a rate of 0 40 0 63 sv over the period 1991 2000 1993 1997 the peak mean monthly outflow can exceed 1 sv

the distribution and formative processes of latent heat polynyas in east antarctica a study of polynya characteristics in east antarctica was undertaken using ice concentrations derived from special sensor microwave imager data for the period july 1987 august 1994 the areas of polynyas were defined as having an ice concentration 75 the analysis revealed a total of 28 coastal polynyas within the study region the spatial and temporal variability in areal extent was quantified the timing of mean maximum areal extent varied from june to october the bathymetry and wind regime at each polynya site was examined to gauge the relative importance of these parameters in polynya formation and maintenance in 20 locations shallow banks and shoals form grounding zones for icebergs and anchoring sites for fast ice which form barriers to the predominantly westward drift of the pack ice elsewhere north south coastal protrusions or alignments form similar barriers the subsequent removal of newly formed sea ice from the lee of such barriers by katabatic and synoptic winds maintains areas of reduced ice concentration and open water very few coastal polynyas are attributed solely to katabatic outflow the combined influence of bathymetry topography and winds is responsible for the characteristics of the majority of polynyas many were considered to be marginal characterised by occasional periods when the ice concentration falls below 75 an analysis of annual winter totals of areas with ice concentrations 75 shows no trends in total polynya areal extent over the period 1987 94 known locations of emperor penguin aptenodytes forsteri rookeries were also found to be associated with the locations of coastal polynyas

combined u pb and u th he geochronometry of basalt maars in western carpathians implications for age of intraplate volcanism and origin of zircon metasomatism the age of intraplate volcanism in northern pannonian basin of carpathians is revisited using a combination of zircon u pb zircon u th he and apatite u th he dating techniques complemented by electron microprobe emp characterisation of dated minerals a total of six maar structures and diatremes in the south slovakian volcanic field ssvf were dated and the obtained new ages yielded the following key findings two isolated maars in se part indirectly dated by geomorphologic constraints to late pleistocene are actually of pliocene 2 8 0 2 ma and late miocene 5 5 0 6 ma ages in contrast two maars in nw part of the study area are of late pliocene age 4 1 0 4 and 5 2 5 4 ma younger than the late miocene age 6 5 ma inferred previously from k ar data on the proximal basaltic lava flows these maars therefore belong to the second volcanic phase that was previously identified only in se part of the ssvf in the light of the new geochronologic data it seems likely that the pliocene phreatomagmatic eruptions may have occurred along extension related nw and ne trending orthogonal faults emp analyses and imaging revealed an extensive syn and post growth metasomatic replacement by dissolution reprecipitation in the majority of zircons abundant silicate melt inclusions in porous metasomatised parts of the zircons are diagnostic of magmatic rather than hydrothermal metasomatism consistent ages of the metasomatised and non metasomatised zones do not indicate disturbance of the u pb system during the metasomatism enrichment in u and th loss in the metasomatised zircons are diagnostic of an increasing oxygen fugacity triggered by degassing of the volatile residual melt during the final stages of alkali basalt fractionation rare zircon to baddeleyite transformation was probably connected with lowered silica activity in carbonated basaltic magmas in south eastern part of the study area

continental shelf circulation induced by a moving localized wind stress abstract a linear two dimensional model of a rotating stratified fluid is constructed to investigate the circulation induced by a moving localized line of surface stress this model is used to analyze the effect of moving cold fronts on continental shelf circulation the nature of the induced circulation depends on the relative magnitude of the translation speed of the storm and the natural internal wave speed if the surface stress moves slower than the internal wave speed the disturbance is quasi geostrophic and moves with the storm if the storm moves faster than the internal wave speed two sets of internal inertial waves are produced one set of waves is forced by the surface forcing and travels at the speed of the storm another set of waves is produced by reflection of the directly forced waves from the coastal wall we conclude that free surface deflection slope is responsible for the low frequency quasi geostrophic currents due to passing cold fronts the internal response is composed of t

temperature structure and characteristics appearing on ssm i images of the cosmonaut sea antarctica water temperature structure in the cosmonaut sea at 60 68 s 35 65 e in 1987 92 shows that cold water with a temperature below 1 5 c was present in the coastal region the circumpolar deep water with a temperature higher than 1 0 c was found below about 150m depth from northeast to northwest of the cold water area the ssm i images in 1987 91 indicate that polynya activities were intensive in 1988 and the typical cosmonaut polynya was observed due to weaker activities the small and sporadic cosmonaut polynya formed in 1987 1989 1990 and 1991 a coastal polynya was frequently observed every year at about 66 s 50 60 e a train of polynyas to the east of cosmonaut polynya often appeared it is considered that the atmospheric convergence line and antarctic divergence region are responsible for polynya activities in the cosmonaut sea

a comparison of mechanisms generating vertical transport in the brazilian coastal upwelling regions 1 several mechanisms can drive vertical velocities in the coastal ocean including wind forcing and through gradients in the vorticity field generated by flow topography interactions a two layer steady wind driven analytical model is applied to the major upwelling systems of brazil cabo frio cf and cabo de santa marta csm regions comparisons are made between the relative roles of wind and flow topography interaction in inducing upwelling over these regions ekman pumping is the weakest mechanism over the shelf but does influence the along shelf temperature in the cf area away from coastline irregularities wind driven upwelling ekman transport dominates over all mechanisms however in the vicinity of capes and coastal features topographically driven upwelling plays a significant role and its transports may vary from 43 to 94 of wind driven upwelling upstream of capes topographically driven vertical motions are downwelling favorable and act against the wind driven coastal upwelling while downstream of capes they are upwelling favorable where all mechanisms add up to create strong upwelling peaks in total upwelling in the cf region are about twice as large as those in the csm area because the cf region has stronger winds and larger coastline perturbations than in the csm region observed sea surface temperatures sst agree well with variability in the vertical transports where upwelling peaks are in phase with low temperature peaks along the coast results suggest that on larger scales the sst variability along the coast is mainly controlled by wind driven upwelling while upwelling due to flow topography interaction is responsible for the smaller scale sst variability

the effect of alternative real time wind forcing on southern ocean sea ice simulations 1 southern ocean so sea ice simulations are particularly sensitive to wind forcing two real time wind data sets covering the same period are employed to force so sea ice in a sea ice ocean general circulation model both data sets are analysis products featuring the same temporal resolution but differing in their horizontal resolution and their source even in simulations where the upper ocean temperature is constrained by satellite derived sea ice concentration the sea ice simulations and associated surface buoyancy fluxes reveal pronounced differences along the antarctic coastline while the discrepancies cannot unambiguously be related to the different resolution of the wind forcing their concentration along the coastline is indicative of being related to the representation of orography such as coastal steep slopes and mountain ranges including their ruggedness along the coast of the weddell sea the net ice production rate increases by about a factor of 3 with the higher resolution winds on the other hand along east antarctica the lower resolution winds result in higher ice production due to a generally stronger overestimated offshore component presumably related to the smoother orography extending seaward beyond the coastline this regionally opposite behavior leads to a relatively weak difference in total dense water formation around antarctica and thus global deep ocean properties and circulation overall the results indicate that long term climate model projections are likely to be highly sensitive to model resolution in the antarctic coastal zone

observations of a street of cyclonic eddies in the indian ocean sector of the antarctic divergence hydrographic and drifting buoy data from japanese cruises show that the antarctic divergence in the indian ocean sector is composed of a street of cyclonic eddies these eddies measure about 500 km in the zonal direction and 200 km in the meridional part of the eastward flowing antarctic circumpolar current acc meanders southward in the regions between the eddies in the eddy regions warm saline circumpolar deep water is upwelled into the shallow layers while cold dense coastal water advects into the deep layers the advection occurs along the isobaths of ridges which extend north from the coast the combination of the advection with the upwelling produces a water column denser than the surrounding water and leads to the formation and maintenance of the cyclonic eddies presence of the northward extending ridges approximately governs the location of eddy formation the eddy formation recurs year after year although eddy locations can vary somewhat a polynya was observed to persistently occur and corresponded with one of the eddies in location size and form the oceanographic observations also suggest that the primary meridional exchanges of heat and salt in the antarctic are caused through the eddies and acc meanders within the antarctic divergence

late holocene intensification of colds fronts in southern brazil as indicated by dune development and provenance changes in the sao francisco do sul coastal barrier abstract holocene coastal barriers from southern brazil present great geomorphological changes during their late stages of development in this study we investigate the holocene evolution of the sao francisco do sul sfs barrier through geomorphological heavy minerals and grain size analyses constrained by optically stimulated luminescence osl dating the sfs barrier stands out among the southern brazilian barriers due to its well preserved morphology with a parabolic dune belt in the seaward portion the progradation of the sfs barrier started at least 4914 478 years ago and had a pronounced morphodynamic shift around 1891 155 years ago this shift is characterized by episodic development of parabolic dunes migrating to nnw associated with sand coarsening and a marked variation in sediment provenance represented by the input of sands derived from local coastal watersheds southward from the sfs barrier this morphodynamic provenance shift resulted from the strengthening of sse winds and associated wave systems responsible for the northward alongshore drift implying intensification of cold fronts coupled with higher precipitation since 1891 155 years ago osl dating combined with grain size heavy minerals and geomorphological analyses allowed assessing the response of coastal barriers to the impacts of centennial to millenial climate events occurred during the late holocene reconstruction of the late holocene climate variability and associated impacts on coastal sedimentation is a key issue to evaluate the sensitivity of coastal barriers to future climate changes

controls on circulation cross shelf exchange and dense water formation in an antarctic polynya circulation on the antarctic continental shelf influences cross shelf exchange antarctic bottom water formation and ocean heat flux to floating ice shelves the physical processes driving the shelf circulation and its seasonal and interannual variability remain poorly understood we use a unique time series of repeat hydrographic observations from the adelie land continental shelf and a box inverse model to explore the relationship between surface forcing shelf circulation cross shelf exchange and dense water formation a wind driven northwestward coastal current set up by onshore ekman transport dominates the summer circulation during winter strong buoyancy loss creates dense shelf water this dense water flows off the shelf with a compensating on shelf flow that is an order of magnitude larger in winter than in summer the results demonstrate the importance of winter buoyancy loss in driving the shelf circulation and cross shelf exchange as well as dense water mass formation

modeling antarctic ice shelf responses to future climate changes and impacts on the ocean 1 we investigate basal melting of all antarctic ice shelves by a circumpolar ice shelf sea ice ocean coupled model and estimate the total basal melting of 770 944 gt yr under present day climate conditions we present a comparison of the basal melting with previous observational and modeling estimates for each ice shelf heat sources for basal melting are largely different among the ice shelves sensitivities of the basal melting to surface air warming and to enhanced westerly winds over the antarctic circumpolar current are investigated from a series of numerical experiments in this model the total basal melting strongly depends on the surface air warming but is hardly affected by the change of westerly winds the magnitude of the basal melting response to the warming varies widely from one ice shelf to another the largest response is found at ice shelves in the bellingshausen sea followed by those in the eastern weddell sea and the indian sector these increases of basal melting are caused by increases of circumpolar deep water and or antarctic surface water into ice shelf cavities by contrast basal melting of ice shelves in the ross and weddell seas is insensitive to the surface air warming because even in the warming experiments there is high sea ice production at the front of the ice shelves that keeps the water temperature to the surface freezing point weakening of the thermohaline circulation driven by antarctic dense water formation under warming climate conditions is enhanced by basal melting of ice shelves

sea surface temperature and wind stress curl variability near a cape abstractthe coupling between sea surface temperature sst sst gradients and wind stress curl variability near a cape off brazil is investigated using satellite observations and several different sst high resolution analyses the cape is characterized by strong sst fronts year round associated with upwelling and advection of warm water offshore in a western boundary current observations reveal a strong coupling between crosswind sst gradients and wind stress curl variability with the predominantly negative crosswind gradients leading to negative upwelling favorable wind stress curl anomalies the spatial correlation between empirical orthogonal functions eof of those variables is 0 6 while the correlation between the eof amplitude time series of the wind stress curl and crosswind sst gradients is larger than 0 7 the coupling occurs during summer and winter and is strongly modulated by variations in the wind stress directional steadiness the intensity of the coupling is weaker than around capes

inertial oscillations on the continental shelf of the gulf of lions observations and theory abstract observations in the gulf of lions northwestern mediterranean sea in summer have shown that gusts of wind lasting a few days generate transient upwellings and inertial motions oscillations at the inertial frequency were observed in current meter data near the shore and at a frequency 10 greater in the temperature data vertical coherences in current meter data show a strong baroclinic mode at frequencies greater than inertial frequency a simple one dimensional two layer transient model suggests that these motions are associated with two different physical processes the first process describes the local response of the ocean to meteorological forcing the second is associated with the propagation of long internal waves generated in the transient phase of the geostrophic adjustment process as suggested by the model the direction of propagation of the internal waves is computed from current and temperature data measured at one point and it is found that the shore is the source zone

eddy resolving model estimate of the cabbeling effect on the water mass transformation in the southern ocean abstractcabbeling effect on the water mass transformation in the southern ocean is investigated with the use of an eddy resolving southern ocean model a significant amount of water is densified by cabbeling water mass transformation rates are about 4 sv 1 sv 106 m3 s 1 for transformation from surface thermocline water to subantarctic mode water samw about 7 sv for transformation from samw to antarctic intermediate water aaiw and about 5 sv for transformation from aaiw to upper circumpolar deep water these diapycnal volume transports occur around the antarctic circumpolar current acc where mesoscale eddies are active the water mass transformation by cabbeling in this study is also characterized by a large amount of densification of lower circumpolar deep water lcdw into antarctic bottom water aabw about 9 sv large diapycnal velocity is found not only along the acc but also along the coast of antarctica at the boundary between lcdw and aabw it is found that about 3 sv of lcdw is den

high resolution 5 μm u th pb isotope dating of monazite with excimer laser ablation ela icpms abstract monazite lree po 4 a common accessory mineral in magmatic and metamorphic rocks is complementary to zircon in u th pb geochronology because the mineral can record successive growth phases it is useful for unravelling complex geological histories a high spatial resolution is required to identify contrasted age domains that may occur at the crystal scale bulk mineral techniques such as id tims applied to single monazite grains recording multiple overgrowths or isotope resetting can result in partly scattered discordant analytical points that produce inaccurate intercept ages laser ablation la icpms has been demonstrated to be a useful technique for u th pb dating of zircons and this study tests its analytical capabilities for dating monazite a sector field high resolution icpms coupled with a 193 nm arf excimer laser ablation microprobe is capable of achieving a high spatial resolution and producing stable and reliable isotope measurements the u th pb systematic was applied to monazite grains from several samples a lower palaeozoic lens from high grade terrains in southern madagascar neogene hydrothermal crystals from the western alps a palaeoproterozoic very high temperature granulite from central madagascar and a variscan leucogranite from spain directly on a polished thin section the major aim was to compare and or reproduce tims and emp ages of monazite from a variety of settings and ages the three independent 206 pb 238 u 207 pb 235 u and 208 pb 232 th ratios and ages were calculated isotope fractionation effects mass bias laser induced fractionation were corrected using a chemically homogeneous and u pb concordant monazite as external standard this study demonstrates that excimer laser ablation ela icpms allows u th pb dating of monazite with a high level of repeatability accuracy and precision as well as rapidity of analysis a spatial resolution almost comparable to that of emp in terms of crater width 5 m produced precise 208 pb 232 th 206 pb 238 u and 207 pb 235 u ratios for dating palaeozoic to precambrian monazites the advantages of ela icpms isotope dating are precision accuracy and the ability to detect discordance in the case of late miocene hydrothermal monazites from the alps a larger spot size of 25 m diameter is required and precise and accurate ages were obtained only for 208 pb 232 th systematics results from the variscan granite show that in situ u th pb dating of monazites with ela icpms is possible using a 5 m spot directly on thin sections so that age data can be placed in a textural context

origin and provenance of 2 ma 2 ga zircons ejected by phreatomagmatic eruptions of pliocene basalts in southern slovakia u pb ages of zircons recovered from pliocene pyroclastic deposits in northern part of the cenozoic intra carpathian back arc basin pannonian basin span the interval from pliocene 2 2 ma to paleoproterozoic orosirian rhyacian 1850 2115 ma the scattered u pb ages reflect eruption ages of the host basaltic volcanic centres two episodes of post eocene magmatic crustal growth and the possible tectonic affiliation provenance and age of the subjacent basement or the sedimentary basin detritus sampled by the basaltic magma the youngest zircons define the maximum ages of phreatomagmatic eruptions during the late miocene pliocene extension these zircons are distinguished from older zircons by zr hf 40 90 and th u ratios 0 5 4 5 as well as super chondritic ehf t values ranging from 7 to 14 indicating mantle derived parental magmas the locally increased th u ratios up to 8 accompanied by zr hf 60 are diagnostic of evolved phonolite parental melt hence the youngest zircons can be interpreted as antecrysts originating from evolved melts cogenetic with the host alkali basalts in contrast older zircons represent xenocrysts scavenged by the uprising basalt from surrounding rocks subordinate eocene early oligocene 29 38 ma sub group of zircon xenocrysts is coincidental with the magmatism and volcanism along the periadriatic lineament and the middle hungarian zone the early miocene 18 ma cluster is coeval with the deposition of the bukk mountains felsic ignimbrite correlated with the onset of the back arc extension that triggered miocene sedimentation within the pannonian basin the eocene early oligocene zircons have been likely scavenged from pyroclastic and ash fall deposits of the palaeogene retroarc basin subjacent to the miocene basin infilling sub chondritic ehf t values between 2 5 and 8 in the eocene early miocene zircons attest their crystallization from subduction related felsic to intermediate melts containing large amounts of recycled crustal material palaeozoic proterozoic zircons create a heterogeneous population with variable trace element abundances and ehf t values the determined age clusters are reminiscent of some basement units cropping out recently in central western carpathians zircon hf isotope data indicate recycling of up to 3 4 ga old mafic crust and also the presence of 2 ga old juvenile mafic crust these units had either underlain the northern part of the pannonian basin during pliocene or had been exposed during the deposition of miocene clastic sediments the absence of mesoproterozoic grenvillian zircons 0 9 1 8 ga in the pre cenozoic population of zircon xenocrysts is provisionally interpreted as indicating the evolution of the zircon source area within the west african craton

forced shelf circulation by an alongshore wind band abstract the forced circulation over a continental shelf generated by the alongshore wind stress is studied within the frictional regime the model alongshore wind stress has a finite extent in the alongshore direction and oscillates monochromatically resembling a series of anticyclones traveling across the coast line both the shelf wave response and the localized non wavelike response exist within the wind band the numerical results show that the interaction of shelf waves with locally wind forced response generates a large increase in the phase speed within the wind band given an alongshore variation in the alongshore wind stress a right bounded phase propagation is possible even in the absence of continental shelf waves given a reasonable friction currently accepted for the east coast of the united states the resonance mechanism at the cutoff frequency may not be important and lower frequency wind events generate larger amplitude continental shelf circulation by reducing the friction energy a

modeling modified circumpolar deep water intrusions onto the prydz bay continental shelf east antarctica an eddy resolving coupled regional ocean sea ice ice shelf model is employed to locate the hot spots where modified circumpolar deep water mcdw intrudes onto the continental shelf within prydz bay and locate the paths through which mcdw is transported to the amery ice shelf ais calving front evaluation of the model output is with satellite hydrographic and borehole data two critical windows responsible for mcdw intrusions are identified the first is the eastern branch of the cyclonic prydz bay gyre pbg that carries mcdw to the ice front line accounting for an annual mean heat transport of 8 7 1011 j s 1 the second is located to the east of the four ladies bank flb where mcdw is channeled through submarine troughs accounting for an annual mean heat transport of 16 2 1011 j s 1 the eddy induced heat transport accounts for 23 in the path of the pbg and 52 in the path of the eastern coastal current with respect to their total onshore heat transport the seasonal pulsing of mcdw intrusions is greatly dependent on the seasonal cycle of the antarctic slope current asc that peaks with a maximum of 29 3 sv at 75 e in june in austral winter mcdw is allowed to access the eastern flank of the ais calving front with potential consequences for the basal mass balance of the ais the dynamic effects of small scale troughs on the longshore asc play an important role in the onshore mcdw transport

a numerical study of dense water formation and transport on a shallow sloping continental shelf the circulation and transport of dense water generated by an idealized coastal polynya is studied using a three dimensional primitive equation model starting with a homogeneous quiescent ocean a constant negative buoyancy flux is imposed at the surface over a half elliptical region adjacent to the coastal boundary on a gently sloping continental shelf the flow response can be divided into the following three phases geostrophic adjustment instability and offshore eddy transport during geostrophic adjustment the fluid within the forcing region becomes denser and the flow at the edge of the forcing region accelerates in response to the strong density gradient there eventually the flow at the leading edge of the forcing region relative to kelvin wave propagation becomes unstable and a train of counterrotating eddies develops these eddies then form a complex three dimensional flow field and rapidly transport dense water offshore across isobaths the density within the forcing region reaches a maximum which remains fairly constant after the eddies begin to transport the dense fluid offshore the results are qualitatively insensitive to weakening of the negative buoyancy forcing and to changing the bottom slope eddy scales and velocities are consistent with observations in the arctic the results suggest that instability processes and eddy fluxes are important in transporting dense water off continental shelves and into marginal seas

modeling sea ice production and dense shelf water formation in coastal polynyas around east antarctica 1 using an ice ocean coupled model with fine horizontal resolution around east antarctica sea ice production and dense shelf water dsw formation in coastal polynyas are investigated the model reproduces well the locations of coastal polynyas and the high sea ice production there dsw is formed over the continental shelves under a number of coastal polynyas a threshold density beyond which net production of dsw takes place is largely different among coastal polynyas the densest and most vigorous dsw formation occurs in the cape darnley and mertz ninnis glacier polynyas followed by somewhat less but still significant dsw formation in the prydz barrier and vincennes polynyas assuming mixing of the dsw outflowing across the shelf break with typical modified circumpolar deep water over the continental slope the maximum possible formation rate of antarctic bottom water aabw is estimated to be 7 58 sv around east antarctica between 60 e and 150 e with the cape darnley and mertz ninnis glacier polynyas exhibiting the most active formation rates of 2 13 and 1 97 sv respectively from a series of numerical experiments it is found that the treatment of coastline and grounded icebergs has a large impact on both sea ice production and formation of dsw and aabw

simulations of temperature and turbulence structure of the oceanic boundary layer with the improved near surface process an improved model for the oceanic boundary layer is presented in view of the recent observation of the microstructure of the upper ocean including the high dissipation rate near the sea surface in the new model the surface boundary conditions for both the turbulent kinetic energy flux and the roughness length scale are modified the parameterization of stratification effects on turbulence is improved and the convective process is reformulated on the basis of the observation of uniform temperature and velocity profiles within the convective mixed layer evolutions of the profiles of both the dissipation rate and temperature of the observation data patches experiment as well as the time series of the sea surface temperature over the observation days are successfully simulated during a diurnal cycle for the first time it is also shown that the model reproduces various important features of the oceanic boundary layer for example the formation of a diurnal thermocline the profiles of buoyancy flux and the magnitudes of the buoyancy gradients both within the mixed layer and at the diurnal thermocline performance of the model is compared with that of the widely used mellor yamada model

lagrangian drifter dispersion in the southwestern atlantic ocean abstractin the framework of monitoring by ocean drifters mondo project a set of lagrangian drifters were released in proximity of the brazil current the western branch of the subtropical gyre in the south atlantic ocean the experimental strategy of deploying part of the buoys in clusters offers the opportunity to examine relative dispersion on a wide range of scales adopting a dynamical systems approach the authors focus their attention on scale dependent indicators like the finite scale lyapunov exponent fsle and the finite scale mean square relative velocity fsrv between two drifters as a function of their separation and compare them with classic time dependent statistical quantities like the mean square relative displacement between two drifters and the effective diffusivity as functions of the time lag from the release the authors find that dependently on the given observable the quasigeostrophic turbulence scenario is overall compatible with their data analysis with discrepancies fr

carbonate chemistry in the mertz polynya east antarctica biological and physical modification of dense water outflows and the export of anthropogenic co2 1 dense shelf water dsw is formed in east antarctica from enhanced sea ice production driven by air sea interaction in coastal polynyas cross shelf export and downslope mixing of this dsw produces antarctic bottom water contributing to the lower limb of the global overturning circulation we present biogeochemical observations from the mertz polynya region in summer 2007 2008 with additional observations from spring 2001 and winter 1996 the seasonal changes in mixed layer carbonate chemistry are driven by a combination of air sea co2 exchange biological activity and the formation and melt of sea ice the air sea fluxes in 2008 were 15 mmol c m 2 d 1 and net community production estimated from the summertime surface dissolved inorganic carbon dic deficit ranged from 0 9 to 1 2 mol c m 2 yr 1 we show that biological modification of carbonate chemistry over the shelf in summer preconditions the dsw outflows from the adelie depression this process appears to supply both organic material and water depleted in co2 and with enhanced carbonate saturation state relative to inflowing water to coral communities on the slope we combined model based transports of exported dsw with the natural and anthropogenic cant carbon concentrations and estimate that the annual outflows of dic and cant from the mertz polynya range from 320 to 560 tg c yr 1 and from 3 to 6 tg cant yr 1 respectively the formation and export of dense water from this region and by extension all similar polynyas around antarctica is an effective mechanism for the transfer of anthropogenic carbon into the deep ocean

modeling ocean cryosphere interactions off adelie and george v land east antarctica abstractocean cryosphere interactions along the adelie and george v land agvl coast are investigated using a coupled ocean sea ice ice shelf model the dominant feature of the mertz glacier tongue mgt located at approximately 145 e was a highly productive winter coastal polynya system until its calving in february 2010 dramatically changed the regional icescape this study examines the annual mean seasonal and interannual variabilities of sea ice production basal melting of the mgt ice shelves large icebergs and fast ice dense shelf water dsw export and bottom water properties on the continental slope and rise and assesses the impacts of the calving event the interannual variability of the winter coastal polynya regime is dominated by the regional offshore winds and air temperature which are linked to activity of the amundsen sea low pressure system this is the main driver of the interannual variability of dsw exported from the agvl region the calving event led to a decrease in sea

mapping of sea ice production for antarctic coastal polynyas 1 active sea ice production in antarctic coastal polynyas causes dense water formation finally leading to antarctic bottom water aabw formation this study gives the first mapping of sea ice production in the antarctic ocean based on heat flux calculation with ice thickness data derived from satellite data the highest ice production occurs in the ross ice shelf polynya region the ice production there decreased by 30 from the 1990s to the 2000s which can be one candidate for causing the recent freshening of aabw the cape darnley polynya in east antarctica is found to be the second highest production area suggesting a possible aabw formation area according to our estimation around 10 of southern ocean sea ice is produced in the major antarctic coastal polynyas the mapping provides surface heat and salt flux conditions in the ice covered region which have not been well understood

pathways of basal meltwater from antarctic ice shelves a model study we investigate spreading pathways of basal meltwater released from all antarctic ice shelves using a circumpolar coupled ice shelf sea ice ocean model that reproduces major features of the southern ocean circulation including the antarctic circumpolar current acc several independent virtual tracers are used to identify detailed pathways of basal meltwaters the spreading pathways of the meltwater tracers depend on formation sites because the meltwaters are transported by local ambient ocean circulation meltwaters from ice shelves in the weddell and amundsen bellingshausen seas in surface subsurface layers are effectively advected to lower latitudes with the acc although a large portion of the basal meltwaters is present in surface and subsurface layers a part of the basal meltwaters penetrates into the bottom layer through active dense water formation along the antarctic coastal margins the signals at the seafloor extend along the topography showing a horizontal distribution similar to the observed spreading of antarctic bottom water meltwaters originating from ice shelves in the weddell and ross seas and in the indian sector significantly contribute to the bottom signals a series of numerical experiments in which thermodynamic interaction between the ice shelf and ocean is neglected regionally demonstrates that the basal meltwater of each ice shelf impacts sea ice and or ocean thermohaline circulation in the southern ocean

lidar offshore structural mapping and u pb zircon monazite dating of variscan strain in the leon metamorphic domain nw brittany an exceptional structural picture of the immerged variscan basement offshore the leon metamorphic domain is supplied by high resolution lidar and echosounder data recorded in the molene archipelago western brittany france various types of fabrics are identified and from in situ rock sample analyses further combined with field structural data are interpreted on a lineament trajectory map as the trace of magmatic and tectonic structures our onshore offshore study leads us to propose a two phase kinematic model that emphasizes the role of a strike slip duplex in an ew trending relay zone linking the north armorican and pierres noires ductile shear zones nasz pnsz dextral shearing occurred within a transtensional setting synchronously with magmatic intrusions st renan granite and an offshore gabbro diorite complex dated at 314 320 ma by new u th pb ages it post dated an early regional foliation related to top to the ne ductile transpressional shearing our study emphasizes the key role of strike slip tectonics in the nw part of the armorica variscan belt

modelling the antarctic marine cryosphere at the last glacial maximum we estimate the sea ice extent and basal melt of antarctic ice shelves at the last glacial maximum lgm using a coupled ice shelf sea ice ocean model the shape of antarctic ice shelves ocean conditions and atmospheric surface conditions at the lgm are different from those in the present day these are derived from an ice shelf ice sheet model a sea ice ocean model and a climate model for glacial simulations respectively the winter sea ice in the lgm is shown to extend up to 7 of latitude further equatorward than in the present day for the lgm summer the model shows extensive sea ice cover in the atlantic sector and little sea ice in the other sectors these modelled sea ice features are consistent with those reconstructed from sea floor sedimentary records total basal melt of antarctic ice shelves in the lgm was 2147 gt a 1 which is much larger than the present day value more warm waters originating from circumpolar deep water could be easily transported into ice shelf cavities during the lgm because the full glacial grounding line extended to shelf break regions and ice shelves overhung continental slopes this increased transport of warm water masses underneath an ice shelf and into their basal cavities led to the high basal melt of ice shelves in the lgm

on the circulation and water masses over the antarctic continental slope and rise between 80 and 150 e abstract the circulation and water masses in the region between 80 and 150 e and from the antarctic continental shelf to the southern boundary of the antarctic circumpolar current acc 62 s are described from hydrographic and surface drifter data taken as part of the multi disciplinary experiment baseline research oceanography krill and the environment broke two types of bottom water are identified adelie land bottom water formed locally between 140 and 150 e and ross sea bottom water ross sea bottom water is found only at 150 e whereas adelie land bottom water is found throughout the survey region the bottom water mass properties become progressively warmer and saltier to the west suggesting a westward flow all of the eight meridional ctd sections show an antarctic slope front of varying strength and position with respect to the shelf break in the water formation areas between 140 and 150 e and 104 e the antarctic slope front is more v shaped while elsewhere it is one sided the shape of the slope front and the presence or absence of water formation there are consistent with other meridional sections in the weddel sea and simple theories of bottom water formation gill 1973 deep sea research 20 111 140 whitworth et al 1998 in jacobs and weiss eds ocean ice and atmosphere interactions at the antartic continental margin antarctic research series american geophysical union washington pp 1 27 adcp surface velocities and buoy drift tracks show a strong westward flow over the shelf and slope regions in the region 90 100 e there is a strong eastward flow of the waters just south of the southern boundary of the acc suggesting a recirculation of the westward slope current and the presence of a weak cyclonic gyre using the adcp velocities as a reference for the ctd data the average westward transport in this region is 29 4 14 7 sv

the response of the south brazil bight to the passage of wintertime cold fronts on the southeastern continental shelf of brazil the wintertime subtidal variability of the circulation is highly dominated by the passage of cold fronts hydrographic data for the region reveal that during this july august september season only a weak vertical stratification is observed in this paper the response of the region to cold fronts is studied by using a barotropic finite element model forced by a conceptual cold front wind field derived from the analysis of coastal winds and satellite imagery

model studies of the wind driven transient circulation in the middle atlantic bight part 1 adiabatic boundary conditions abstract a numerical model of the wind driven transient ocean circulation in the middle atlantic bight is described the model incorporates realistic topography and covers the continental shelf between the coast and the 200 m isobath from cape hatteras to the southern tip of nova scotia the traditional shallow water dynamics are used i e the vertically integrated and linearized equations for the flow of a homogeneous fluid driven by atmospheric pressure and wind stress fluctuations and damped by a quadratic bottom stress the equations are integrated in time using a simple modification of platzman s 1972 finite difference scheme with a 12 7 km grid spacing at the coast normal flow is required to vanish at non coastal boundaries the equivalent surface elevation is held fixed several classes of initial value experiments are used to study the free and forced modes of this model and the damped flow driven by a spatially uniform and stationary wind stress and by an idealized travelling synoptic sc

u th pb geochronology of zircon and monazite from syenite and pincinite xenoliths in pliocene alkali basalts of the intra carpathian back arc basin abstract phreatomagmatic eruptions in the lucenec basin in slovakia ejected fragments of igneous rocks of unknown age and ranging in composition from gabbro to syenite and orthopyroxene granodiorite pincinite two kinds of syenites with different fe3 contents composed of anorthoclase and interstitial metaluminous trachyte to alkali rhyolite glass represent the final products of alkali basalt differentiation at depths of 10 and 15 18 km pincinite composed of plagioclase quartz orthopyroxene ilmenite and interstitial peraluminous dacite glass is a quenched supersolidus anatectic melt formed at the depth of 17 20 km by high temperature dehydration melting of biotite bearing gneissic protolith zircon from pincinite and syenite and monazite from syenite were dated using excimer laser ablation icp ms the obtained ages cluster at 5 8 0 1 and 5 4 0 1 ma thus corroborating the genetic link between the two rock types and constraining the residence time of at least 300 100 ka of the parental basalt in the deep crustal magma storage zones the inferred ages overlap the upper miocene pliocene boundary and are considerably younger than spatially associated basaltic lava flows dated using the k ar method consequently the fluviolacustrine poltar formation overlying the maar structure must have sedimented during the pliocene and not during the upper miocene pontian as previously assumed

antarctic sea ice mapping using the avhrr abstract a sea ice mapping scheme based on advanced very high resolution radiometer avhrr data from the national oceanic and atmospheric administration noaa polar orbiting satellites has been developed and applied to daylight images taken between november 1989 to january 1990 and november 1990 to january 1991 over the weddell and the ross seas after masking the continent and ice shelves sea ice is discriminated from clouds and open sea using thresholds applied to the multidimensional space formed by avhrr channel 2 3 and 4 radiances sea ice concentrations in cloud free regions are then computed using the tie point method results based on the analysis of more than 70 images show that the proposed scheme is capable of properly discriminating between sea ice open sea and clouds under most conditions thus allowing high resolution sea ice maps to be produced during the austral summer season

surface winds over the antarctic continent a review surface winds over antarctica often classified as katabatic are intimately related to the orientation and steepness of the underlying ice terrain such flows result primarily from the strong radiational cooling of the sloping ice surface which creates a downslope directed horizontal pressure gradient force it is possible to diagnose the time averaged near surface streamline patterns of cold air drainage currents using recently compiled detailed antarctic ice topography maps and appropriate estimates of the strength of the surface temperature inversion the resulting streamlines agree with available observations and illustrate the high degree of nonuniformity of gravity driven flows off the ice sheets in certain interior sections negatively buoyant air from a large catchment area drains through a restricted section of coastline such confluence zones represent regions of enhanced supplies of cold air and are shown to be related to anomalously strong katabatic winds implications for sea ice formation are discussed

cold ocean cavity and weak basal melting of the sorsdal ice shelf revealed by surveys using autonomous platforms basal melting of ice shelves is inherently difficult to quantify through direct observations yet it is a critical factor controlling antarctic mass balance and global sea level rise while much research attention is paid to larger ice shelves and those experiencing the most rapid change many smaller unstudied ice shelves offer valuable insights here we investigate the oceanographic conditions and melting beneath the sorsdal ice shelf east antarctica we present results from the 2018 2019 sorsdal deployment of the university of tasmania s autonomous underwater vehicle nupiri muka oceanography adjacent to and beneath the ice shelf front shows a cold and relatively saline environment dominated by winter water and dense shelf water while bathymetry measurements show a deep 1 200 m trough running into the ice shelf cavity two multiyear deployments of autonomous phase sensitive radar echo sounders on the surface of the ice shelf show weak melt rates average of 1 6 and 2 3 m yr 1 with low temporal variability these observations are supported by numerical ocean model and satellite estimates of melting we speculate that the presence of a 825 m thick 350 m to at least 1 175 m homogeneous layer of cold dense water blocks access from warmer waters that intrude into prydz bay from offshore resulting in weak melt rates however the newly identified trough means that the ice shelf is vulnerable to any decrease in polynya activity that allows warm water to enter the cavity this could lead to increased basal melting and mass loss through this sector of antarctica

the spring transition from horizontal to vertical thermal stratification on a midlatitude continental shelf 1 the spring transition from wintertime horizontal thermal stratification to the summertime vertically stratified state on a wide sloping midlatitude continental shelf is investigated the sigma z level model szm a new three dimensional primitive equation numerical ocean model employing a hybrid sigma coordinate and z level coordinate in the vertical simulates the continental shelf region a simple analytical model to describe the heating rate of a well mixed water column is applied to the problem to illustrate the importance of bottom slope in determining the evolution of the horizontal thermal stratification the applicability of this simple model to continental shelf dynamics forced by realistic surface fluxes is studied with a pseudo two dimensional x z form of the szm forced with daily heat flux and wind stress records from the west florida shelf a term by term analysis of the depth averaged time integrated temperature equation quantifies the contribution of each physical process to the evolution of the horizontal temperature field the simple model used to describe the heating rate of a homogeneous water column appears as the dominant balance in the integrated temperature equation cross shelf temperature advection associated with upwelling and downwelling alters the horizontal depth integrated temperature over the shelf predicted by the simple model two processes describe the spring transition the erosion of the wintertime horizontal thermal gradient occurs on a timescale of a few months when the water column is being heated and mixed periodically the second process is the formation of the seasonal thermocline following the last strong mixing event this occurs on a timescale of less than a week under a stabilizing heat flux and light winds completing the spring transition from horizontal to vertical thermal stratification

formation and export of dense shelf water from the adelie depression east antarctica 1 coastal polynyas in the adelie depression are an important source of antarctic bottom water to the australian antarctic basin we present time series april 1998 to may 1999 and august 1999 to february 2000 of data from temperature salinity sensors in both the adelie depression and the known outflow region of the adelie sill to describe the annual cycle of shelf water densities from april through september salinification beneath the polynya produces dense shelf waters during september october shelf water densities in the depression peak at 27 94 kg m 3 and the cooling and freshening signature of ice shelf water is observed north of buchanan bay in november december shelf water densities decrease as intrusions of warm and relatively fresh modified circumpolar deep water enter east of the adelie sill from january march the surface layer is conditioned by the cooling of the atmosphere which overturns the upper water column at the adelie sill observed daily mean currents were approximately 10 cm s 1 with intense instantaneous currents greater than 50 cm s 1 at the sill depth using an idealized outflow region with a rectangular cross sectional area 6 106 m2 we present the first estimates of shelf water export by potential density class assuming shelf water with a minimum density of 27 88 kg m 3 has sufficient negative buoyancy for downslope mixing and a fourfold volume increase 1 3 mixing ratio from entrainment the dense shelf water export of 0 1 0 5 sv results in an annual average production of bottom water in this region of between 0 4 and 2 0 sv the wide range in bottom water estimate results from data limitations and a narrowing of this range requires further mooring observations

circulation on the western south atlantic continental shelf 2 spring and autumn realistic simulations 1 buoyancy driven currents are here investigated in a complex scenario where two river plumes the la plata river and the patos lagoon plumes occur in the vicinity of two opposing western boundary currents the malvinas and the brazil currents the study addresses the contrasting scenarios found during the austral spring and fall seasons due to variations in river discharge in wind stress and in the boundary current transport the winds blow preferably from the northeast during the spring and from the southwest during the fall the brazil current transport is stronger during the spring when the brazil malvinas confluence is displaced southward and weaker during the fall when the confluence moves northward the study is conducted as a series of numerical simulations which consider the river discharges the tides variable wind stress and thermohaline fields which are realistic in terms of the brazil malvinas confluence our discussion focuses on the riverine water distribution in each season the austral fall scenario shows coastally trapped plumes and the spring scenario shows significant offshore removal but our fall plumes are not too elongated and narrow as other authors found in the presence of constant winds no tides and no boundary currents and our spring offshore removal is not as strong as found by others

platelet ice the southern ocean s hidden ice a review basal melt of ice shelves is not only an important part of antarctica s ice sheet mass budget but it is also the origin of one of the most peculiar types of sea ice found in the polar oceans platelet ice in many regions around coastal antarctica tiny ice crystals form and grow in supercooled plumes of ice shelf water releasing heat into the surrounding ocean they usually rise towards the surface eventually becoming trapped under an ice shelf as marine ice frequently masses of those crystals are advected out of the ice shelf cavity and accumulate below a solid sea ice cover to form a semiconsolidated layer when the overlying sea ice grows into this so called sub ice platelet layer the loose crystals are consolidated adding additional thickness to the sea ice these phenomena are generally referred to as platelet ice although confusion about the terminology is widespread in the literature the presence of platelet ice has a profound impact on sea ice properties and processes in several regions of antarctica with numerous implications for the local polar marine biosphere most notably sub ice platelet layers provide a stable sheltered nutrient and food rich habitat which usually results in a highly productive and uniquely adapted ecosystem it has also been hypothesised that platelet ice may be an indicator of the state of an ice shelf although comprehensive time series are limited to the ross sea this paper clears up the terminology by providing exact definitions of the relevant terms we review platelet ice formation observational methods as well as geographical and seasonal occurrence the physical properties and ecological implications are merged in a way understandable for physicists and biologists alike to lay the foundation for the interdisciplinary research that is necessary to tackle the current knowledge gaps

sea ice motion and open water area at the ronne polynia antarctica synthetic aperture radar observations versus model results 1 this study deals with observations and simulations of the evolution of coastal polynias focusing on the ronne polynia we compare differences in polynia extent and ice drift patterns derived from satellite radar images and from simulations with the finite element sea ice ocean model employing three atmospheric forcing data sets that differ in spatial and temporal resolution two polynia events are analyzed one from austral summer and one from late fall 2008 the open water area in the polynia is of similar size in the satellite images and in the model simulations but its temporal evolution differs depending on katabatic winds being resolved in the atmospheric forcing data sets modeled ice drift is slower than the observed and reveals greater turning angles relative to the wind direction in many cases for the summer event model results obtained with high resolution forcing are closer to the drift field derived from radar imagery than those from coarse resolution forcing for the late fall event none of the forcing data yields outstanding results our study demonstrates that a dense 1 3 km model grid and atmospheric forcing provided at high spatial resolution 50 km are critical to correctly simulate coastal polynias with a coupled sea ice ocean model

u pb geochronology of zircons from fossiliferous sediments of the hajnacka i maar slovakia type locality of the mn 16a biostratigraphic subzone lacustrine sediments of the hajnacka i maar of southern slovakia contain teeth and skeletal remains of a mammal fauna including index early villanyian arvicoline rodents u pb dating of magmatic zircons extracted from the redeposited fossiliferous maar sediments revealed a total of six volcanic events the oldest age of 3 43 ma was interpreted as that corresponding to the initial phreato magmatic eruption that created the maar most zircons grouped around 3 06 0 03 ma the age attributed to the catastrophic eruption that killed the mammal assemblage thriving within and around the maar studied this age coincides with the 3 1 ma boundary between the mn 16a and 16b subzones of the european mammal neogene chronostratigraphic scale estimated from the succession of early villanyian palaeontological localities according to the hypsometry of rodent teeth younger zircon ages overlapped those of the neighbouring basaltic lava flows necks and dykes thus recording superimposed effusions the youngest 1 58 ma old zircon defines the age limit for the final redeposition of the fossiliferous sediments in the maar drainage lake regime