influence of tides on melting and freezing beneath filchner ronne ice shelf antarctica an isopycnic coordinate ocean circulation model is applied to the ocean cavity beneath filchner ronne ice shelf investigating the role of tides on sub ice shelf circulation and ice shelf basal mass balance including tidal forcing causes a significant intensification in the sub ice shelf circulation with an increase in melting 3 fold and refreezing 6 fold the net melt rate and seawater flux through the cavity approximately doubles with tidal forcing the spatial pattern and magnitude of basal melting and freezing generally match observations the 0 22 m a 1 net melt rate is close to satellite derived estimates and at the lower end of oceanographic values the ice shelf water outflow mixes with shelf waters forming a cold 1 9 degrees c dense overflow 0 83 sv that spills down the continental slope these results demonstrate that tidal forcing is fundamental to both ice shelf ocean interactions and deep water formation in the southern weddell sea citation makinson k p r holland a jenkins k w nicholls and d m holland 2011 influence of tides on melting and freezing beneath filchner ronne ice shelf antarctica geophys res lett 38 l06601 doi 10 1029 2010gl046462

an example of 3 d avo for lithology discrimination in widuri field asri basin indonesia abstract drilling offshore southeast sumatra in the area of the widuri field asri basin has demonstrated that the oil producing upper gita sandstones within the lower miocene talang akar formation correlate with bright seismic amplitudes on 3 d stack data seismic amplitude maps at the base upper gita horizon are interpreted as either a network of distributary channels or a meandering fluvial system channel fill lithologies vary considerably and are difficult to interpret from conventional seismic stack data carbonaceous shales likely deposited during the abandonment phase of channeling have acoustic impedances similar to sandstones dipole sonic log measurements of poisson s ratio are significantly higher in carbonaceous shales than sandstones based on raytraced models carbonaceous shale has a strongly decreasing avo while sand has flat avo response no change in amplitude with offset avo attributes p and g or intercept and gradient inverted from 3 d prestack seismic data are used for detection of carbonaceous shale based on mapping good correlation exists between well data and the avo product attribute p g the stratigraphic model of shale abandonment fill in a meandering fluvial system is interpreted to be supported by the 3 d avo data this interpretation will be tested with future drilling

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

a new formation process for calcic pendants from pahranagat valley nevada usa and implication for dating quaternary landforms abstract it has been assumed that soil pendants form in a similar manner as stalactites in which innermost laminae are the oldest and outer laminae are the youngest this study presents a new interpretation for soil pendant development pahranagat valley nevada pendants contain features indicating continued precipitation through time at the clast pendant contact implying that the oldest deposits are not always found at the pendant clast contact as other studies have assumed these features include a void at the clast pendant contact where minerals such as calcium carbonate silica and or fibrous silicate clays precipitate in addition fragments of the parent clast and detrital grains are incorporated into the pendant and are displaced and or dissolved and result in the formation of sepiolite this study indicates that pendants are complex open systems that during and after their formation undergo chemical changes that complicate their usefulness for dating and paleoenvironmental analyses

a model of ice shelf ocean interaction with application to the filcher ronne and ross ice shelves a simple analytical model has been developed to study the formation of ice shelf water isw isw is assumed to flow as a buoyancy driven layer underneath the ice shelf a relation between potential temperature and salinity in the isw layer is calculated from the mass and energy balance this temperature salinity relation is shown to depend only on the temperature and the salinity of the source water mass and to be practically independent of entrainment and melt rates the model results are obtained without making any assumptions about entrainment and melt rates the model is in good agreement with observations under the ronne ice shelf and it indicates that isw in the filchner depression is formed from western shelf water wsw with salinity higher than 34 75 practical salinity units such high salinity water is only observed in the ronne depression in the western part of the continental shelf this implies a circulation of wsw under the filchner ronne ice shelf from the ronne depression into the filchner depression similarly the model shows that the isw observed under j9 at the ross ice shelf has been formed from low salinity shelf water lssw from the eastern parts of the ross sea continental shelf lssw must therefore circulate under the eastern parts of the ross ice shelf

carbonate accumulation and weathering of the granitic substratum of tanecherfi basin northeastern morocco abstract in the tanecherfi basin a granitic body is partly overlain by a calcrete which only seems superimposed morphologically the profiles consist of three horizons the lowest one corresponds to a filling of carbonates into the weathered granitic rocks microscopically the carbonates cut the primary minerals along open cracks and voids in the second horizon the increased carbonation results in calcite septa that gradually isolate rock cells inclosed in a micritic matrix forming a cortex gradually the rock residues vanish and glaebules appear the upper horizon is characterized by a micritic matrix associated with the disappearance of the nodules these morphologic relations are confirmed by chemical data the primary minerals are weathered silica is locally released and precipitates partly around the glaebules magnesium combines into the carbonate structure but locally combines with the silica of the cortex of the glaebules aluminium seems to be totally removed the granite calcrete relationships indicate a weathering process rather to a simple superposition

freshening of the ross sea during the late 20th century ocean measurements in the ross sea over the past four decades one of the longest records near antarctica reveal marked decreases in shelf water salinity and the surface salinity within the ross gyre these changes have been accompanied by atmospheric warming on ross island ocean warming at depths of 300 meters north of the continental shelf a more negative southern oscillation index and thinning of southeast pacific ice shelves the freshening appears to have resulted from a combination of factors including increased precipitation reduced sea ice production and increased melting of the west antarctic ice sheet

properties of a marine ice layer under the amery ice shelf east antarctica the amery ice shelf east antarctica undergoes high basal melt rates near the southern limit of its grounding line where 80 of the ice melts within 240 km of becoming afloat a considerable portion of this later refreezes downstream as marine ice this produces a marine ice layer up to 200 m thick in the northwest sector of the ice shelf concentrated in a pair of longitudinal bands that extend some 200 km all the way to the calving front we drilled through the eastern marine ice band at two locations 70 km apart on the same flowline we determine an average accretion rate of marine ice of 1 1 0 2 m a 1 at a reference density of 920 kg m 3 between borehole sites and infer a similar average rate of 1 3 0 2 m a 1 upstream the deeper marine ice was permeable enough that a hydraulic connection was made whilst the drill was still 70 100 m above the ice shelf base below this marine close off depth borehole video imagery showed permeable ice with water filled cavities and individual ice platelets fused together while the upper marine ice was impermeable with small brine cell inclusions we infer that the uppermost portion of the permeable ice becomes impermeable with the passage of time and as more marine ice is accreted on the base of the shelf we estimate an average closure rate of 0 3 m a 1 between the borehole sites upstream the average closure rate is faster at 0 9 m a 1 we estimate an average porosity of the total marine ice layer of 14 20 such that the deeper ice must have even higher values high permeability implies that sea water can move relatively freely through the material and we propose that where such marine ice exists this renders deep parts of the ice shelf particularly vulnerable to changes in ocean properties

antarctic bottom water production by intense sea ice formation in the cape darnley polynya antarctic bottom water fills much of the global abyssal ocean and is known to form in three main sites in the southern ocean data from instrumented elephant seals and moorings suggest an additional source of bottom water formation in the cape darnley polynya that is driven by sea ice production

separation and characterization of pedogenic barite crystals from petrocalcic horizon materials for future isotopic and geochronological applications abstract although extensive work has been conducted on pedogenic barite in the petrocalcic soil horizons at mormon mesa nv further investigations are required to understand the mode and timing of its precipitation isolation of barite crystals from petrocalcic soil materials is an important first step after which crystal morphology can be examined we sought a method to isolate barite and other heavy minerals to examine their feasibility for future isotopic and geochronological techniques using xrd sem with eds and microprobe analyses barite was analyzed for evidence of chemical or physical alteration after chemical separation procedures with hcl to remove carbonate and methylene iodide to separate minerals with specific gravities greater than and less than 3 3 g ml after separation barite clusters were observed within the heavy mineral separates barite showed no remarkable signs of physical or chemical alteration after separation and small

modeling tidal currents beneath filchner ronne ice shelf and on the adjacent continental shelf their effect on mixing and transport a depth averaged tidal model has been applied to the southern weddell sea the model domain covers the southern continental shelf including the ocean cavity beneath filchner ronne ice shelf reasonable agreement with the available current meter data has been achieved our results confirm that in areas with shallow water and large topographic gradients tidal oscillations with peak velocities up to 1 m s 1 play a significant role in the vertical mixing and transport of water masses the estimated energy dissipation beneath filchner ronne ice shelf due to surface friction is 25 gw approximately 1 of the world s total tidal dissipation tidally induced lagrangian residual currents converging at the ice front an area of strong mixing draw together water masses from the continental shelf and sub ice shelf cavity the model indicates that lagrangian residual currents have fluxes of up to 250 000 m3 s 1 and speeds of over 5 cm s 1 along the ice front with over 350 000 m3 s 1 being exchanged between the sub ice shelf cavity and adjacent continental shelf these currents are particularly efficient in ventilating the sub ice shelf cavity within 150 km of ronne ice front such strong tidal mixing will significantly modify the properties of water masses that flow through this region particularly to the west of berkner island the model predictions indicate that tidal processes strongly influence the oceanographic conditions in the vicinity of ronne ice front shipborne observations along the ice front support many of the model predictions concerning the effect of tides on the hydrography

thermohaline circulation below the ross ice shelf a consequence of tidally induced vertical mixing and basal melting the warmest water below parts of the ross ice shelf resides in the lowest portion of the water column because of its high salinity vertical mixing caused by tidal stirring can thus induce ablation by lifting the warm but dense water into contact with the ice shelf a numerical tidal simulation indicates that vertically well mixed conditions predominate in the southeastern part of the sub ice shelf cavity where the water column thickness is small basal melting in this region is expected to be between 0 05 and 0 5 m yr and will drive a thermohaline circulation having the following characteristics high salinity shelf water at 1 8oc formed by winter sea ice production in the open ross sea flows along the seabed toward the tidal mixing fronts below the ice shelf and meltwater at 2 2oc produced in the wellmixed region flows out of the sub ice shelf cavity along the ice shelf bottom sensitivity of this ablation process to climatic change is expected to be small because high salinity shelf water is constrained to have the sea surface freezing temperature

estimation of the thin ice thickness and heat flux for the chukchi sea alaskan coast polynya from special sensor microwave imager data 1990 2001 1 one of the largest arctic polynyas occurs along the alaskan coast of the chukchi sea between cape lisburne and point barrow for this polynya a new thin ice thickness algorithm is described that uses the ratio of the vertically and horizontally polarized special sensor microwave imager ssm i 37 ghz channels to retrieve the distribution of thicknesses and heat fluxes at a 25 km resolution comparison with clear sky advanced very high resolution radiometer data shows that the ssm i thicknesses and heat fluxes are valid for ice thicknesses less than 10 20 cm and comparison with several synthetic aperture radar sar images shows that the 10 cm ice ssm i ice thickness contour approximately follows the sar polynya edge for the twelve winters of 1990 2001 the ice thicknesses and heat fluxes within the polynya are estimated from daily ssm i data then compared with field data and with estimates from other investigations the results show the following first our calculated heat losses are consistent with 2 years of over winter salinity and temperature field data second comparison with other numerical and satellite estimates of the ice production shows that although our ice production per unit area is smaller our polynya areas are larger so that our ice production estimates are of the same order because our salinity forcing occurs over a larger area than in the other models the oceanic response associated with our forcing will be modified index terms 4540 oceanography physical ice mechanics and air sea ice exchange processes 3360 meteorology and atmospheric dynamics remote sensing 4504 oceanography physical air sea interactions 0312 4572 oceanography physical upper ocean processes 4207 oceanography general arctic and antarctic oceanography keywords chukchi sea coastal polynya remote sensing

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

duripans of idaho u s a in situ alteration of eolian dust loess to an opal a x ray amorphous phase abstract micromorphological techniques were used to study the silicification process in a wide range of duripans from idaho u s a investigations indicated that once loess was incorporated into a carbonaterich pan it was altered in situ to an opal a x ray amorphous phase loess became incorporated by at least two pathways each of which had a distinctive micromorphic signature the first pathway began immediately above the duripan as calcite encapsulated eolian materials to create sand sized loess agglomerates incorporation was completed either as the upward developing duripan enveloped the agglomerates or as they filled fractures in the duripans and were subsequently cemented by calcite after encasement of the loess agglomerates within the duripan aluminosilicate minerals were embayed by reaction with the calcareous soil solution the most altered loess agglomerates consisted of opal a x ray amorphous material and calcite the second pathway was initiated when fractures in the duripan were filled by eolian dust to create pedotubules the tops of pedotubules had a fabric similar to unaltered loess silasepic plasmic however the bottoms of pedotubules were invariably altered to a microgranular array of opal a and calcite impetus for alteration appears to have been high ph created by closed system conditions combined with increased surface free energy of minerals caused by elevated grain to grain pressures which led to enhanced solubility of aluminosilicate minerals the incorporation of loess and its subsequent alteration may be an important process in the silicification of calcareous pans

on the modified circumpolar deep water upwelling over the four ladies bank in prydz bay east antarctica analyses of hydrographic observation data sets revealed that modified circumpolar deep water mcdw tends to flood the western flank 73 78 degrees e 67 68 degrees s of the four ladies bank flb in prydz bay in this study we investigated the mechanism responsible for mcdw upwelling over the flb based on an eddy resolving coupled ocean sea ice ice shelf model in conjunction with the latest high accuracy bathymetry it was found that zonal step like declines in the seabed over the flb are crucial for the mcdw onshore upwelling through topographic dynamic effects on the alongshore antarctic slope current in the presence of meridional cross shelf sigma isopycnals warm mcdw at 500 m depth in the deep sea can make its approach to the shallower continental shelf 200 to 500 m depths characterized as a warm layer 1 8 degrees c bounded by the cross shelf sigma isopycnal surfaces of 27 5 and 27 7kg m 3 the simulated outflow of the prydz bay gyre is concentrated to the eastern flank of the prydz channel these results suggest that in addition to the depressions and troughs around the antarctic smaller topographic features such as step like declines in the seabed near the antarctic slope current are also favorable for onshore mcdw intrusion this study demonstrates that mcdw onshore transport around the antarctic continental shelf might be significantly underestimated by numerical models with coarse spatial representations of the topography plain language summary based the observational data sets warm circumpolar deep water was identified over the four ladies bank in prydz bay east antarctica the warm signals could be delivered into the ocean cavity beneath the downstream ice shelf and result in remarkable influences to the ice shelf basal melting in order to investigate the intrusion of warm circumpolar deep water we used a numerical model to simulate the oceanic circulations in prydz bay by assessing the simulated results we found that the topographic influences of the changes in seabed on the continental shelf break jet play a dominant role in the responsible mechanism for warm water intrusion our findings highlighted that the improvements in the spatial resolution of the numerical model and the accuracy of the topographical representations are very useful in the investigation of warm water intrusion around the antarctic continental shelf

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

temperature and salinity beneath ronne ice shelf antarctica salinity and temperature measurements have been made beneath ronne ice shelf antarctica access to the seawater was gained by hot water drilling through 562 m of ice at a site 300 km from the ice front the ice column is composed of 516 m of meteoric origin ice underlain by 31 m of consolidated saline ice with a further 15 m of unconsolidated slush at the base the 360 m deep water column beneath the ice shelf consists broadly of a 210 m layer of ice shelf water isw at a potential temperature of 2 30 c and salinity 34 53 overlying a 100 m thick layer of modified western shelf water 2 03 c 34 64 the layers are separated by a weak 50 m thick pycnocline isotopic analyses of water samples support this interpretation of the water types comparison of the data with published oceanographic observations from the shore lead indicate that the source of the water is either the western berkner shelf or north of the ice front in the ronne depression the measurements from the drill site broadly match predictions from a simple plume model of the sub ice shelf water circulation in that model the basal slope of the ice shelf plays a central role in determining the properties of the isw plume with the exception of the upper few tens of meters the temperature and salinity of the entire water column vary by about 0 04 c and 0 03 on tidal timescales and there is evidence for a longer term drift presumably connected with shifts in the larger scale circulation there is also much variability from internal wave activity the salinity and deuterium budgets indicate that the meltwater fraction in the isw observed at the drill site was between 5 3 and 6 5 in reasonable agreement with values previously found for isw in the open ocean

the temperature and salinity fine structure of the ocean under the ross ice shelf a series of temperature and salinity profiles was made in the ocean under the ross ice shelf at 82 22 5 s 168 37 5 w where the ice was 420 and the underlying seawater 240 m thick the water structure consisted of a fairly well mixed low salinity layer at the in situ freezing point of the ice water interface about 30 m thick a transition layer characterized by intrusions about 85 m thick a strongly stratified layer with increasing temperature and salinity about 50 m thick another transition layer characterized by intrusions about 45 m thick and an isohaline bottom layer with a nearly abiabatic temperature gradient about 30 m thick the temperature fluctuations in the two transition layers can be attributed mainly to intrusive activity even though internal wave activity was highest in these regions in the central stable layer internal waves probably contribute to the temperature fluctuations equally with intrusions the internal wave dropped displacement spectrum seems to be very similar to those found in the open ocean some profiles showed intrusions in the top transition layer colder than the top boundary layer and some showed intrusions in the bottom transition layer warmer than the bottom boundary layer indicating that horizontal shear must be present internal waves of near inertial frequency excited by the semidiurnal tides combined with shear induced instabilities seem to be the likely causes of the observed fine structure

ice flow variations at polar record glacier east antarctica relatively little is known about the physical mechanisms that drive the dynamics of the east antarctic outlet glaciers here we conduct a remote sensing investigation of the polar record glacier prg east antarctica to analyze its ice flow acceleration ice front variations and ice surface melting ice flow speeds at prg increased by up to 15 from 2005 to 2015 with substantial interannual fluctuations the ice velocities also showed seasonal variations accelerating by up to 9 between september and january multiple mechanisms contribute to the observed seasonal variations the initial acceleration may result from the lost back stress provided by the sea ice in the austral spring and the later speedup relate to the surface meltwater that leads to weakened ice shelf and shear margins the sensitivity of the prg to oceanic forcing is confirmed by comparing the secular ice velocity increases with ocean temperatures these measurements suggest that the dynamics of east antarctic ice shelves are sensitive to melt at both the surface and base at a range of timescales

micromorphology and formation of pedogenic ooids in calcic soils and petrocalcic horizons abstract ooids pisoids nodules concretions and a host of other terms are used to describe concentrically zoned pedogenic carbonate phyllosilicates silica and other minerals in calcic and petrocalcic horizons worldwide the pedogenic and paleoenvironmental significance of such features is not always easy to interpret because variations in size structure composition and soil geomorphic context have been used to infer distinct modes of genesis for features that appear similar using both optical and scanning electron microscopy petrocalcic soil samples from the jornada la mesa geomorphic surface in new mexico and the mormon mesa geomorphic surface in nevada were studied to reconsider the formation of pedogenic ooids in this paper ooids are 2 mm in diameter and have a range of internal morphologies ooids were especially common within features including clast pendant laminae pisoids and laminar horizons or laminar horizon caps we propose a possible new mode of ooid genesis suggesting that crystal growth can move ooids tiny incremental distances over time and that phyllosilicates are an important genetic component ooids are interpreted to form via 1 mineralization during the evaporation of solutions held by surface tension around mineral grains clasts or petrocalcic fragments with or without the presence of organic matter 2 hydration and plastic behavior of pervasive pedogenic fibrous phyllosilicates that co precipitate with pedogenic calcite and 3 tiny successive movements caused by the crystallization pressure of pedogenic carbonate and other minerals during soil solution evaporation spheroidal morphology is initially promoted by chemical precipitation from evaporating solutions around grains next crystallization pressures from the surrounding matrix displace grains non uniformly promoting stochastic contacts or knocking of ooids against one another and against the soil matrix over long time spans this micrometer scale episodic translocation and rotation in tandem with the plastic behavior of fibrous phyllosilicates enhances the spherical shape of ooids the model described here does not preclude possible biological contributions to ooid genesis nor refute the role of other processes in producing similar features in the same soil finally ooid size is limited by physical and hydrological thresholds pisoids as larger features are more complex and are more likely to involve erosion they do not form in the same manner as ooids this study has implications for paleoenvironmental interpretations of calcic and petrocalcic horizons and for the selection of pedogenic features for isotopic analysis

formation of arcs and backarc basins inferred from the tectonic evolution of southeast asia since the late cretaceous abstract results of the geological and geophysical surveys in the daito ridges and basin in the northern west philippine basin suggest that the daito ridge was an arc facing toward the south from the late cretaceous to the early tertiary the late cretaceous and tertiary history of southeast asia is evaluated based on these data in the daito ridges and basins and reconstructed based on overall plate kinematics that have operated in this area during the late cretaceous the daito ridge and the east philippine islands were positioned along the boundary between the indian and pacific plates the western half of the philippines setting on the indian plate approached from the south and collided with the east philippine daito arc either during the latest paleocene or the earliest eocene it is inferred that the bulk of the philippine archipelago rotated clockwise and borneo spun counterclockwise during the tertiary from the reconstruction the formation of backarc basins and their spreading direction are assessed as a result some primary causes and significant characteristics are suggested for the opening of backarc basins in southeast asia first opening of some backarc basins commenced with or was triggered by collisions second backarc basins opened approximately parallel to oceanic plate motion third the formation of some backarc basins was triggered by the approach of a hot spreading center fourth the spreading mode or direction of backarc basins was greatly affected by the configuration of the surrounding continent and was also rearranged to spread approximately parallel to oceanic plate motion the formation of backarc basins and their spreading direction can be reasonably explained by plate kinematics however the generative force responsible for their formation is possibly within the subduction system particularly to form horizontal tensional force in backarc side

circulation of modified circumpolar deep water and basal melt beneath the amery ice shelf east antarctica antarctic ice sheet mass loss has been linked to an increase in oceanic heat supply which enhances basal melt and thinning of ice shelves here we detail the interaction of modified circumpolar deep water mcdw with the amery ice shelf the largest ice shelf in east antarctica and provide the first estimates of basal melting due to mcdw we use subice shelf ocean observations from a borehole site am02 situated 70 km inshore of the ice shelf front together with open ocean observations in prydz bay we find that mcdw transport into the cavity is about 0 22 0 06 sv 1 sv 106 m3 s 1 the inflow of mcdw drives a net basal melt rate of up to 2 0 5 m yr 1 during 2001 23 9 6 52 gt yr 1 from under about 12 800 km2 of the north eastern flank of the ice shelf the heat content flux by mcdw at am02 shows high intra annual variability up to 40 our results suggest two main modes of subice shelf circulation and basal melt regimes 1 the ice pump high salinity shelf water circulation on the western flank and 2 the mcdw meltwater driven circulation in conjunction with the ice pump on the eastern flank these results highlight the sensitivity of the amery s basal melting to changes in mcdw inflow improved understanding of such ice shelf ocean interaction is crucial to refining projections of mass loss and associated sea level rise

remotely induced warming of antarctic bottom water in the eastern weddell gyre 1 four repeat hydrographic sections across the eastern weddell gyre at 30 e reveal a warming by 0 1 c and lightening by 0 02 0 03 kg m 3 of the antarctic bottom water aabw entering the gyre from the indian sector of the southern ocean between the mid 1990s and late 2000s historical hydrographic and altimetric measurements in the region suggest that the most likely explanation for the change is increased entrainment of warmer mid depth circumpolar deep water by cascading shelf water plumes close to cape darnley where the indian sourced aabw entering the weddell gyre from the east is ventilated this change in entrainment is associated with a concurrent southward shift of the antarctic circumpolar current s acc southern boundary in the region this mechanism of aabw warming may affect wherever the acc flows close to antarctica

analysis of velocity field mass balance and basal melt of the lambert glacier amery ice shelf system by incorporating radarsat sar interferometry and icesat laser altimetry measurements 1 by incorporating recently available remote sensing data we investigated the mass balance for all individual tributary glacial basins of the lambert glacier amery ice shelf system east antarctica on the basis of the ice flow information derived from sar interferometry and icesat laser altimetry we have determined the spatial configuration of eight tributary drainage basins of the lambert amery glacial system by combining the coherence information from sar interferometry and the texture information from sar and modis images we have interpreted and refined the grounding line position we calculated ice volume flux of each tributary glacial basin based on the ice velocity field derived from radarsat three pass interferometry together with ice thickness data interpolated from australian and russian airborne radio echo sounding res surveys and inferred from icesat laser altimetry data our analysis reveals that three tributary basins have a significant net positive imbalance while five other subbasins are slightly positive or close to zero balance overall in contrast to previous studies we find that the grounded ice in lambert glacier amery ice shelf system has a positive mass imbalance of 22 9 4 4 gt a 1 the net basal melting for the entire amery ice shelf is estimated to be 27 0 7 0 gt a 1 the melting rate decreases rapidly from the grounding zone to the ice shelf front significant basal refreezing is detected in the downstream section of the ice shelf the mass balance estimates for both the grounded ice sheet and the ice shelf mass differ substantially from other recent estimates

volcanic ash beds recorders of upper cenozoic silicic pyroclastic volcanism in the western united states stratigraphic relationships and tephrochronologic information for volcanic ash beds 4 0 0 1 m y of the western interior allow the recognition of at least 68 different ash falls the average reoccurrence rate based on the succession of the isotopically dated ash beds is near one eruption every 57 000 years the ash beds were grouped into two chemical types rhyolitic and dacitic the main property that distinguishes dacitic from rhyolitic ashes is the larger ca and mg and smaller k content in dacitic ashes dacitic volcanic ashes were defined to have more than 0 55 wt ca rhyolitic ashes were subdivided further into two types w and g type based on the presence of biotite in the w type and its absence in g type w type rhyolitic ashes are chalky white have less than 0 55 wt fe have colorless glass shards of pumiceous habit g type rhyolitic ashes are light to medium gray have from 0 55 to 2 0 wt fe in the glass shards lack biotite have colorless platy bubble wall and bubble junction glass shards dacitic ashes are light gray to grayish brown have more than 0 55 wt fe and ca and have a complex mixture of colorless to light brown shards including pumiceous fibrous chunky and bubble wall and bubble junction types w type rhyolitic ashes possibly formed from magmas that were cooler 695 to 830 c and thus more viscous than the hotter 870 to 1000 c magma progenitors of g type ashes based on fe ti oxide mineral compositions primary microphenocrysts in the ash beds comprise assemblages of the following quartz sanidine plagioclase biotite amphibole clinopyroxene orthopyroxene fayalite zircon apatite allanite chevkinite sphene magnetite and ilmentite fayalite and chevkinite only have been found in g type biotite and sphene only have been found in w type rhyolitic ashes are highly evolved and contain 74 79 wt sio2 dacitic ashes vary from 67 77 wt sio2 al ranges from 10 5 to 14 5 wt al2o3 mg ranges from 0 06 to 1 0 wt mgo and fe as fe3o4 ranges from 0 50 to 4 1 wt dacitic ash beds have the most 0 80 3 8 wt as fe3o4 and rhyolitic ashes have the least 0 50 1 9 wt as fe3o4 ca varies from an unusually low amount 0 25 wt cao in a few rhyolitic ashes to as much as 2 2 in some dacitic ashes rhyolitic glasses show larger eu deficiencies compared to dacitic glasses on rare earth element diagrams w type rhyolitic glasses have moderately large la to sm ratios and have la contents from about 30 to 100 times chondrite values g type rhyolitic glasses also have moderately large la to sm ratios and contain somewhat more la than do the w type rhyolitic ashes generally from 100 to 300 times chondrites amounts

morphology and genesis of carbonate soils on the kyle canyon fan nevada u s a the physical and chemical properties of soils formed in an arid climate on calcareous alluvium of the kyle canyon alluvial fan southern nevada were studied in order to infer the rates and relative importance of various soil forming processes these studies included field and microscopic observations and analyses of thin sections major oxides extractable iron and clay minerals the results are interpreted to reflect five major pedogenic processes 1 the calcic horizons and calcretes of kyle canyon soils form by precipitation of caco3 derived from eolian dust and alluvium as clast coats matrix cement and massive layers 2 the a and uppermost b horizons are essentially dust derived for they contain large amounts of detrital material not present in the alluvial parent material and their major oxide content is similar to that of modern dust 3 clay particles are translocated from a into b horizons 4 iron bearing minerals in the near surface b horizons are slowly oxidized 5 carbonate and aluminosilicate grains are both displaced and replaced by pedogenic caco3 the silica released by replacement of aluminosilicates may be locally precipitated as amorphous or opaline silica and or incorporated into newly formed palygorskite and sepiolite rates of soil development at kyle canyon are approximate due to uncertainties in age estimates some soil field properties change at rates that are similar to rates for soils formed in rhyolitic parent material near mercury nevada the rate of accumulation of caco3 3 5 g m 2 yr 1 at kyle canyon is an order of magnitude faster than that near mercury but is comparable to rates calculated for soils in southern new mexico and utah

clay transformation and pedogenic calcite formation on a lithosequence of igneous rocks in northwestern iran abstract knowledge about the pathways of pedogenic calcite formations and clay transformations on igneous rocks in semiarid regions plays a vital role in the commentary of soil development on these rocks the present study was conducted to explore the weathering stages and pathways for the formation of pedogenic calcite in soils developed on selected plutonic and volcanic rocks in a semiarid climate in north western iran the soils developed on plutonic rocks were found to be in the primary stage of weathering with very few pedogenic calcites except for soil developed on alkali granite which contained few calcitic pedofeatures calcitic crystallitic b fabrics and calcitic pedofeatures were found in all soils developed on volcanic rocks in situ weathering of ca bearing minerals such as plagioclases amphiboles and pyroxenes could be the possible explanation for the accumulation of pedogenic calcite in the absence of calcareous parent rocks in the studied area micritic calcite was observed to be the dominant form in most of the soils developed on volcanic rocks indicating a rapid precipitation of calcium carbonate smectite kaolinite and mica illite were present in the soils developed on plutonic rocks and the clay content in these soils was less than that of the volcanic rocks feldspars plus mica were supposed to be the most likely source minerals for the formation of pedogenic illite which could be consequently transformed into smectite in these semi arid environments smectite mica illite and kaolinite were the most abundant clay minerals in the soils developed on dacite and andesite rocks while a minor quantity of vermiculite occurred only in andesite derived soils smectite as the dominant mineral and some kaolinite with fairly constant variation in content with depth were observed in the soils formed on hornblende andesite and pyroxene andesite this could indicate that the smectite had the authigenic origin and was formed most likely from the weathering of plagioclase hornblende and pyroxene in general in situ crystallization of pedogenic carbonates and high quantities of smectite in the clay fraction confirmed that the soils formed on volcanic rocks were more developed than those on plutonic rocks in the studied semiarid region moreover our results showed that releasing calcium from ca bearing minerals in igneous rocks in conjunction with biological activities resulted in pedogenic calcite formation

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

roles of marine ice rheology and fracture in the flow and stability of the brunt stancomb wills ice shelf marine ice sometimes as part of an ice melange significantly affects ice shelf flow and ice fracture the highly heterogeneous structure of the brunt stancomb wills ice shelf bsw system in the east weddell sea offers a rare setting for uncovering the difference in rheology between meteoric and marine ice here we use data assimilation to infer the rheology of the brunt stancomb wills ice shelf by an inverse control method that combines interferometric synthetic aperture radar measurements with numerical modeling we then apply the inferred rheology to support the hypothesis attributing the observed 1970s ice shelf flow acceleration to a change in the stiffness of the ice melange area connecting brunt proper with stancomb wills and to examine the consequences of frontal rift propagation we conclude that while the brunt stancomb wills system is currently not susceptible to extreme fragmentation similar to that of the larsen b ice shelf in 2002 our inverse and forward modeling results emphasize its vulnerability to destabilization by relatively rapid changes in the ice melange properties resulting from the interaction of its marine ice component with ocean water or by the further propagation of a frontal rift copyright 2009 by the american geophysical union

open ocean convection observations theory and models we review what is known about the convective process in the open ocean in which the properties of large volumes of water are changed by intermittent deep reaching convection triggered by winter storms observational laboratory and modeling studies reveal a fascinating and complex interplay of convective and geostrophic scales the large scale circulation of the ocean and the prevailing meteorology two aspects make ocean convection interesting from a theoretical point of view first the timescales of the convective process in the ocean are sufficiently long that it may be modified by the earth s rotation second the convective process is localized in space so that vertical buoyancy transfer by upright convection can give way to slantwise transfer by baroclinic instability moreover the convective and geostrophic scales are not very disparate from one another detailed observations of the process in the labrador greenland and mediterranean seas are described which were made possible by new observing technology when interpreted in terms of underlying dynamics and theory and the context provided by laboratory and numerical experiments of rotating convection great progress in our description and understanding of the processes at work is being made

thermohaline circulation and interaction between ice shelf cavities and the adjacent open ocean the circulation system in an ice shelf cavity is driven by buoyancy fluxes due to melting and freezing of ice and horizontal pressure gradients at the interface between the cavity and the open ocean hence the inflow and outflow pattern and the hydrography in the open ocean influence the general hydrographic condition in the cavity which at least provides the potential for melting and freezing processes applying a three dimensional ocean general circulation model to an idealized ice shelf cavity geometry coupled with an open ocean at a topographic ice shelf barrier we found an important parameter controlling the interaction between these two systems idealized studies for different ice shelf and sea bottom topographies and forcing mechanisms for the open ocean show that the ice shelf edge represents a natural barrier for barotropic interaction because of the sudden decrease in water column thickness since the water column thickness and the coriolis force determine the characteristics for geostrophic flow separated circulation systems arise for the open ocean and the ice shelf cavity only in areas where constant water column thickness and from the oceanographic point of view constant f h contours can be observed across the barrier an increased barotropic current can surmount the ice edge and ventilate the water mass beneath the ice shelf this is only the case at lateral sloping sidewalls or at deep depressions which can be found for example in the southern weddell sea in all other cases the circulation in the ice shelf cavity is closed and almost unaffected by the hydrography outside the barrier

basal melt seasonal water mass transformation ocean current variability and deep convection processes along the amery ice shelf calving front east antarctica despite the amery ice shelf ais being the third largest ice shelf in antarctica the seasonal variability of the physical processes involved in the ais ocean interaction remains undocumented and a robust observational oceanographic based basal melt rate estimate has been lacking here we use year long time series of water column temperature salinity and horizontal velocities measured along the ice shelf front from 2001 to 2002 our results show strong zonal variations in the distribution of water masses along the ice shelf front modified circumpolar deep water mcdw arrives in the east while in the west ice shelf water isw and dense shelf water dsw formed in the mackenzie polynya dominate the water column baroclinic eddies formed during winter deep convection down to 1100 m drive the inflow of dsw into the ice shelf cavity our net basal melt rate estimate is 57 4 25 3 gt yr 1 1 0 4 m yr 1 larger than previous modeling based and glaciological based estimates and results from the inflow of dsw 0 52 0 38 sv 1 sv 106 m3 s 1 and mcdw 0 22 0 06 sv into the cavity our results highlight the role of the mackenzie polynya in the seasonal exchange of water masses across the ice shelf front and the role of the isw in controlling the formation rate and thermohaline properties of dsw these two processes directly impact on the ice shelf mass balance and on the contribution of dsw isw to the formation of antarctic bottom water

ocean circulation and ice ocean interaction beneath the amery ice shelf antarctica simulations of the ocean dynamics in the cavity under the amery ice shelf antarctica were carried out using a three dimensional numerical ocean model two different boundary conditions were used to describe the open ocean barotropic exchange at the ice front the simulations show that the circulation in the ocean cavity is predominantly barotropic and is generally steered by the cavity topography the circulation is driven by the density gradient in the cavity which is strongly influenced by the heat and salt fluxes from melting and freezing processes at the ice ocean interface and by the horizontal exchange of heat and salt across the open ocean boundary at the ice front the interaction at the ice ocean interface allows the basal component of the mass loss of the amery ice shelf to be estimated in the two simulations the computed losses were 5 8 gt yr 1 and 18 0 gt yr 1 values consistent with observations the bulk of the melting occurred near the southern grounding line of the ice shelf although substantial melting also occurred in areas where heat transport by horizontal circulation was large accretion was restricted to areas where water from upstream melting became supercooled as it ascended the ice shelf base

current measurements near ronne ice shelf implications for circulation and melting we present the first year long current meter records ever obtained near the floating filchner ronne ice shelf in the weddell sea the currents are steered along the ice front but in the lower layer where the bottom topography is descending toward the west the current has a component toward the ice front of about 3 cm s 1 during winter the temperature stayed near the surface freezing point while the salinity increased indicating that ice was formed and brine released the seasonal variation in salinity was 0 15 0 05 psu corresponding to the formation of 1 2 m of ice on a shelf depth of 400 m the transport of high salinity shelf water hssw into the ice shelf cavity was found to be of the order 0 5 106 m3 s 1 the production of this water due to oscillating tides and off shelf winds was found to be of the same order of magnitude in contact with glacial ice at great depths and because of the depression of the freezing point the hssw is transformed to ice shelf water isw by cooling and melting processes the melting rate was estimated to 1 1011 ton yr 1 this corresponds to the melting of 0 2 m ice per year if the melting is evenly distributed over the filchner ronne ice shelf if the melting is concentrated along a path from the berkner shelf around the berkner island to the filchner depression then melting rates up to 7 m yr 1 must be expected a comparison of hssw characteristics in the ronne depression our winter observations on the berkner shelf and the isw flowing out of the filchner depression indicates that very little water passes through the cavity from the ronne to the filchner depression it appears that most of the isw originating from processes on the berkner shelf escapes the cavity in the filchner depression this leaves the berkner shelf as the important source of isw and subsequently of the weddell sea bottom water formed from isw

investigation of limestone and dolomite clast alteration in petrocalcic horizons southern nevada usa abstract petrocalcic horizons formed on quaternary surfaces in southern nevada contain altered limestone and dolomite clasts in the enveloping carbonate matrix three profiles from two geomorphic surfaces contain pebble to cobble clasts with distinct voids and alteration textures at their tops clast and alteration zone characteristics were analyzed with scanning electron microscopy energy dispersive x ray spectroscopy x ray diffraction electron microprobe analysis and with an inductively coupled plasma spectrophotometer limestone and dolomite clasts display considerable top down alteration marked by vertical tubular voids and an increase in neoformed fibrous clay in the altered regions downward percolating soil waters moved through the cemented horizon and contacted the upper clast boundaries as evidenced by selective alteration and void development at the tops of clasts the preservation of voids indicates that alteration and void development began no earlier than initial petrocalcic formation when soil matrix pore spaces were largely filled with pedogenic carbonate undersaturation of soil fluids with respect to primary clast components ca and or mg and or increased pco2 under conditions enhanced during wetter pluvial climates is interpreted to drive dissolution and alteration of clasts in these horizons resulting morphological and mineralogical changes in these petrocalcic horizons may mark past climate and geomorphic influence on their development over time misinterpretation of parent material provenance as a result of selected removal of individual clast lithologies may occur

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

reduced sea ice production due to upwelled oceanic heat flux in prydz bay east antarctica the coastal shelf region of east antarctica is hypothesized to be shielded from the offshore heat of circumpolar deep water cdw due to the dynamic barrier of the antarctic slope front yet modified cdw mcdw intrudes into the coastal environment in key locations with impacts on dense shelf water formation and ocean ice shelf interaction that remain largely unquantified using moored measurements and conductivity temperature depth instrumented seal hydrographic data collected in prydz bay east antarctica we find buoyancy driven upwelling of mcdw into the subsurface 50 m layer of the southeastern embayment wintertime convection extends as deep as 300 m entraining heat of the upwelled mcdw to the surface accumulated sensible heat supply to the surface through deep convection during june july reduces the potential sea ice production by 45 in the davis polynya demonstrating that stronger warmer mcdw intrusions onto the shelf will likely reduce the shelf water density and threaten antarctic bottom water formation

basal melting and freezing under the amery ice shelf east antarctica the basal melting and freezing rates under the amery ice shelf east antarctica are evaluated and their spatial distributions mapped ice velocity surface elevation and accumulation rate datasets are employed in the analysis along with a column averaged ice density model our analysis shows that the total area of basal melting is 34 700 km 2 with a total annual melt of 62 5 9 3 gt and an average melting rate of 1 8 0 3 m a 1 basal freezing mainly occurs in the northwestern part of the ice shelf over a total area of 26 100 km 2 and with a maximum freezing rate of 2 4 0 4 m a 1 the total marine ice that accretes to the ice shelf base is estimated to be 16 2 2 4 gt a 1 using a redefined grounding line and geometry of the amery ice shelf we estimate the net melt over the ice shelf base is about 46 4 6 9 gt a 1 which is higher than previous modeling and oceanographic estimates net basal melting accounts for about half of the total ice shelf mass loss with the rest being from iceberg discharge our basal melting and freezing distribution map provides a scientific basis for quantitative analysis of ice ocean interaction at the ice shelf ocean interface

platelet ice attachment to instrument strings beneath the amery ice shelf east antarctica oceanographic instruments suspended beneath the amery ice shelf east antarctica have recorded sporadic pressure decreases of 10 20 dbar over a few days at three sites where basal marine ice growth is expected we attribute these events to flotation due to platelet ice accretion on the instrument moorings some events were transient rapidly returning to pre event pressures probably through dislodgement of loosely attached crystals driven by these pressure changes temperatures recorded by the shallowest instruments within 20 m of the shelf base tracked in situ freezing temperatures during the events these observations provide indirect evidence for the presence of frazil ice in the sub ice shelf mixed layer and for active marine ice accretion at one site we infer that a dense layer of platelet ice 1 5 m thick was accreted to the ice shelf over a 50 day period following some permanent abrupt pressure decreases which we interpret as due to the lodgement of the uppermost instrument at the ice shelf base altered background trends in pressure suggest compaction rates of 3 4 m a 1 for the accreted basal platelet layer attachment of platelet ice and resulting displacement of moorings has ramifications for project design and instrument deployment and implications for interpretation of oceanographic data from sub ice shelf environments

observations of platelet ice growth and oceanographic conditions during the winter of 2003 in mcmurdo sound antarctica 1 platelet ice is the name given to ice crystals that nucleate in the ocean and grow either at depth or loosely attached to the ice water interface related to the proximity of ice shelves it is known to form in supercooled seawater this study details the conditions for its growth during the austral winter of 2003 in mcmurdo sound antarctica a key finding is that the presence of platelet ice in the sea ice cover is conclusively linked to the time history of the appearance of ice crystals in the water column monitored using the strength of the backscattered signal from an acoustic doppler current profiler as a proxy generally these crystals appeared from mid may as water near the interface became supercooled this near surface supercooling appears to be related to a simultaneous abrupt change in the structure of the upper 250 m of the water column from one that behaved dynamically and contained both the warmest and coolest measured temperatures to one in which the water was essentially isothermal near its surface freezing temperature near surface ocean temperature was also affected by tidal mixing and by an increase in the thickness and density over the course of winter of the surface mixed layer created by salt rejection during ice growth these processes allowed cold water trapped by buoyancy in a band at the base of the mixed layer in early winter to gain access to the ice water interface by midwinter this band of cold water probably had its origin beneath the mcmurdo ice shelf

pedogenic replacement of aluminosilicate grains by caco3 in ustollic haplargids south central montana u s a abstract a chronosequence of calcic soils formed on granitic glaciofluvial terrace deposits of rock creek and the clarks fork in south central montana shows progressive replacement of aluminosilicate parent material grains by calcium magnesium carbonate the terraces range from late pliocene to holocene in age as dated by tephrochronology correlation and stream incision rates replacement is first seen in soils that are as old as 120 000 yr the amount and degree of replacement increase in soils older than 120 000 yr along with the development of calcic horizons under the petrographic microscope carbonate replacement of quartz feldspars and the groundmass of andesite grains in rock creek soils is shown by embayed grains networks of carbonate along cracks and between parts of polycrystalline grains and optically aligned grain fragments within carbonate masses microprobe data suggest that silica is released by replacement because it is absent from carbonate filled spaces and is depleted in corrosion pits little microscopic evidence exists to support displacement of framework grains by carbonate because fragments of a single grain are rarely rotated out of optical alignment in the calcic soils of rock creek k fabric grains floating in a carbonate matrix may form by both replacement and displacement

pedogenesis on talus slopes the buckskin range nevada usa abstract soil development on steep mountainous topography generally leads to thin and undifferentiated pedons on talus slopes of the buckskin mountains a fault blocked range of west central nevada usa thick differentiated pedons occur talus occurs on the western front where block rotation has formed very steep slopes and consists of angular dacite cobbles and boulders the study area is arid averaging less than 20 cm of precipitation per year typical pedons consist of surface talus filled with vesicular non structured sandy loam to loam material this material overlies clay textured prismatic and blocky structured horizons mostly rock free that in places are over 1 m thick pedons are classified as fine mixed mesic xeralfic paleargids soil macro and micromorphological features soil mineralogy and soil chemical and physical attributes suggest the following developmental sequence which began sometime before the middle pleistocene the talus serves as a baffle to collect eolian dust once eolian dust accumulates to a threshold thickness primary minerals are transformed in situ mostly to a smectitic clay as clay content increases a second threshold level is reached at which time the horizon of clay enrichment has sufficient strength and shrink swell potential to support and raft the talus upward the exposed talus can then continue to trap eolian dust the soil profile thickens and the pedon is protected from erosion a variation of this soil cumulation process may be partially responsible for textural b horizon formation in avid and semiarid climates

distribution of marine ice beneath the amery ice shelf we present a map of the marine ice accreted to the base of the amery ice shelf ais east antarctica this map is obtained by converting a digital elevation model dem of the ais generated from satellite radar altimeter data to an ice thickness map assuming hydrostatic equilibrium and subtracting from that a second ice thickness map derived from airborne radio echo sounding res measurements the res signal does not penetrate the marine ice so the measurement is only to the meteoric marine ice boundary and therefore the difference between the two maps is the marine ice thickness the marine ice is up to 190 m thick and accounts for about 9 of the shelf volume it is concentrated in the northwest of the shelf a result of the clockwise ocean circulation in the cavity below

marine ice sheet collapse potentially under way for the thwaites glacier basin west antarctica resting atop a deep marine basin the west antarctic ice sheet has long been considered prone to instability using a numerical model we investigated the sensitivity of thwaites glacier to ocean melt and whether its unstable retreat is already under way our model reproduces observed losses when forced with ocean melt comparable to estimates simulated losses are moderate 1 mm per year of sea level rise collapse in the different simulations within the range of 200 to 900 years

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

antarctic ice sheet loss driven by basal melting of ice shelves accurate prediction of global sea level rise requires that we understand the cause of recent widespread and intensifying glacier acceleration along antarctic ice sheet coastal margins atmospheric and oceanic forcing have the potential to reduce the thickness and extent of floating ice shelves potentially limiting their ability to buttress the flow of grounded tributary glaciers indeed recent ice shelf collapse led to retreat and acceleration of several glaciers on the antarctic peninsula but the extent and magnitude of ice shelf thickness change the underlying causes of such change and its link to glacier flow rate are so poorly understood that its future impact on the ice sheets cannot yet be predicted here we use satellite laser altimetry and modelling of the surface firn layer to reveal the circum antarctic pattern of ice shelf thinning through increased basal melt we deduce that this increased melt is the primary control of antarctic ice sheet loss through a reduction in buttressing of the adjacent ice sheet leading to accelerated glacier flow the highest thinning rates occur where warm water at depth can access thick ice shelves via submarine troughs crossing the continental shelf wind forcing could explain the dominant patterns of both basal melting and the surface melting and collapse of antarctic ice shelves through ocean upwelling in the amundsen and bellingshausen seas and atmospheric warming on the antarctic peninsula this implies that climate forcing through changing winds influences antarctic ice sheet mass balance and hence global sea level on annual to decadal timescales

ice shelf ocean interactions under the amery ice shelf seasonal variability and its effect on marine ice formation 1 marine ice is an important factor in ice shelf stability an extensive marine ice layer is present under the amery ice shelf ais east antarctica this paper documents observations on the seasonal variability of the ais ocean interaction beneath the marine ice layer we focus on data collected during 2002 through a borehole at am01 100 km from the ice shelf calving front and use additional data from two other boreholes to complement the study at am01 the top 20 m of the water column is super cooled almost year round protecting the marine ice layer and promoting frazil ice formation the mixed layer thickness varies from 50 m in february to at least 160 m by june as the water column cools and freshens high salinity shelf water hssw abruptly arrives at am01 in june august as an eddy like flow we suggest that the flow characteristics are a result of baroclinic instabilities in addition the inflow of hssw results in a steepening of the isopycnals that enhances the upwelling of ice shelf water this study documents for the first time a seasonal signal in the formation of marine ice under the ais our results highlight the vulnerability of the marine ice layer to ocean variability with potential consequences for the overall ice shelf mass balance

barotropic tides beneath the amery ice shelf 1 a barotropic tidal model has been applied to the amery ice shelf cavity and prydz bay region of east antarctica the sensitivity of the tidal solution of the model to variation of the water column thickness of the amery ice shelf cavity has been determined a best estimate water column thickness grid is presented which both fits available water column thickness data bed elevation and ice thickness and results in reasonable agreement with available tidal elevation data this is an important result for the amery ice shelf given the severe lack of sub ice shelf bed elevation and limited direct ice thickness measurements using the resulting topography simulated tidal current speeds in the sub amery ice shelf cavity are significantly less than those beneath other major embayed antarctic ice shelves with maximum tidal current speeds of 26 cm s 1 indicated for this cavity similarly the estimated energy dissipation beneath the amery ice shelf due to surface friction of 6 mw is low in comparison with the other ice shelves tidally induced vertical mixing is found to be too weak to destroy the stratification associated with the relatively warm water in the lower part of the cavity and ice shelf meltwater in the upper part of the cavity however it is proposed that buoyancy driven upwelling rather than vertical mixing is sufficient to bring the lower water mass into contact with the ice shelf the depth averaged model suggests that barotropic tidal processes have little influence on the oceanographic properties of the amery ice shelf cavity

carbonatation in palaeosols formed on terraces of the tormes river basin salamanca spain abstract a macro and micromorphological study was made of the carbonate accumulations in a total of 21 relict unburied palaeosols haploxeralfs and palexeralfs of ages corresponding to the late middle and early pleistocene formed on fluvial terraces in the tormes river basin salamanca spain under a present day subhumid continental mediterranean climate the fluvial deposits were predominantly gravels and sands derived from the erosion of granite slate sandstone and quartzite with a notable absence of calcareous materials secondary carbonates commonly filled cracks forming laminae in preferentially horizontal disposition though also tipped and vertical giving rise to distinctive patterns that have long attracted scientific attention in the youngest soils of the lower terraces late pleistocene 300 000 years especially in the upper levels within the calcic horizon in rare cases the pseudomycelia and the coatings were comprised of fine needle fibre calcite the carbonates in these soils are recrystallized even in the some of the youngest soils of these terraces 40 000 years the older soils of the middle terraces and particularly in the upper terraces 300 000 years reflected an intense process of replacement of silicates by carbonates in addition the clays in the micromass and illuvial coatings as well as the detrital grains such as feldspars and quartz were progressively replaced by carbonates the carbonate accumulations as well as the subsequent recrystallization and replacement tended to increase with the age of the soils in addition the secondary carbonatation and dissolution of carbonate observed indicate the genetic complexity of these soils the form of the carbonates present at the micro as well as macroscopic level their distribution within the soil profiles and throughout the region as well as the relationship with other processes subsequent to clay illuviation and associated with hydromorphy imply that vadose water at certain geological stages must have been responsible for the carbonate accumulation in these soils the carbonates were deposited during the coldest periods of the isotope substages 6 2 7 4 10 2 12 2 13 2 and 16 2 the presence of dissolution in the soils corresponding to the isotope substages 7 4 and 13 2 appears to indicate the development of two wetter periods towards 200 000 and 500 000 years b p the absence of carbonates in the soils of the youngest surfaces plains flood and the lowest terraces holocene and late pleistocene

acoustic detection of ice crystals in antarctic waters during the voyage of the rsv aurora australis to the region of prydz bay antarctica in january march 1991 ice crystals were encountered at depths from the surface to 125 m in the western area of the bay on two occasions crystals were retrieved by netting and echo sounder records have been used to infer additional regions of occurrence acoustic target strength estimates made on the ice crystal assemblies encountered show significant spatial variation which may relate to crystal size and or aggregation data from a suite of conductivity temperature depth casts have been used to map regions of the study area where in situ water temperatures fell below the computed freezing point such regions correlate well with those selected on the basis of echogram type and imply that ice crystals occurred at depth over large areas of the bay during the cruise period the ice crystal distribution described is consistent with that expected from a plume of supercooled water emerging from under the amery ice shelf and forming part of the general circulation of the bay the magnitude of the supercooled water plume is greater than those reported previously in the prydz bay region if misinterpreted as biota on echo sounder records ice crystals could significantly bias biomass estimates based on echo integration in this and potentially other areas

dynamic model of the genesis of calcretes replacing silicate rocks in semi arid regions abstract in both pedogenic and groundwater calcretes calcium carbonate precipitates in voids or displacing other grains or replacing underlying parent silicates replacement textures are widespread in pedogenic calcrete many calcretes also contain magnesium layer silicates and minor chert we present a reaction transport model that accounts for the genesis of replacement in calcretes and for their mineralogy replacement is difficult to account for geochemically because it requires simultaneous removal of large amounts of silicates and import of also large amounts of caco 3 in the model the genesis of replacement is directly related to seasonally alternating dry wet climates and to appropriate groundwater or circulating soil water compositions in a dry season water evaporation causes caco 3 and sepiolite or attapulgite to precipitate if groundwater contains enough mg 2 sepiolite precipitation by the chemical divide mechanism depletes sio 2 aq resulting in the dissolution of parent silicates in the following wet season sepiolite dissolves fast and silica and cations are flushed away by rainwater making room for caco 3 precipitation in the next dry season as climate cycles repeat caco 3 is accumulated and silicates are removed the sepiolite or attapulgite or mg smectite serves as a temporary storage of silica between seasons if the groundwater contains too little aqueous mg then the model predicts growth of calcium carbonate without removing silicates thus producing void filling and or displacive textures instead of replacement the model consists of a set of nonlinear partial differential equations taking account of mass conservation dispersion advection rainwater infiltration evaporation and the kinetics of mineral reactions the hydrodynamics of unsaturated media is applied in determining water flow in calcrete profiles wet dry seasonal changes are incorporated by alternating the upper boundary conditions the model successfully produces the mineral and textural zonation observed in many calcretes namely at the bottom of the profile the parent rock is first replaced by sepiolite only part of which is in turn replaced by calcite whereas at the top of the calcrete the sepiolite is itself completely replaced by the calcite which appears to directly replace the parent rock the model can produce calcrete near the earth s surface well above the water table low p co 2 intensive evaporation and long dry seasons all are predicted to produce thicker calcretes calcretes constitute an effective geochemical tool that via replacement removes parent silicate rocks and shapes the landscape of semi arid countries the model herein provides a mechanism that accounts for the efficiency of replacement in removing silicates

a field and laboratory study of wave damping by grease ice in a field and laboratory study we discuss the formation growth and wave absorption properties of grease ice our field observations show that grease ice formation occurs under cold windy conditions in both leads and polynyas in leads grease ice forms in the open water then is herded to the down wind edge of the lead in polynyas a langmuir circulation herds the grease ice into long plumes parallel to the wind in the laboratory we grow grease ice in a wave tank and measure its wave absorption properties for single frequency two dimensional waves on a large scale we find that the thickness of the grease ice which increases away from the paddle is determined by a balance between the wave momentum flux and the free surface tilt on a small scale our photographs show that the crystals which make up the grease ice consist of discs measuring about 1 mm in diameter and 1 10 m thick which at low rates of shear sinter together into larger clumps yielding a viscosity increase to measure this non linear viscosity we study the decay of wave amplitude between two critical distances measured inwards from the leading edge the first occurs when the depth of grease ice exceeds k 1 where k is the wave number the second further distance is a line of transition from liquid to solid behavior which we call the dead zone between these two distances the wave amplitude decays with a linear slope which increases as a 0 k 2 where a0 is the wave amplitude in open water concurrent measurements of ice concentration show that it increases from values of 18 22 at the leading edge to a local maximum of 32 44 at the dead zone while the values at the dead zone increase non linearly with a0k finally comparison of the observed to that calculated from a yield stress viscosity model shows if the yield stress coefficient is proportional to the incident wave momentum flux the model predicts the observed

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

calving fluxes and basal melt rates of antarctic ice shelves iceberg calving has been assumed to be the dominant cause of mass loss for the antarctic ice sheet with previous estimates of the calving flux exceeding 2 000 gigatonnes per year1 2 more recently the importance of melting by the ocean has been demonstrated close to the grounding line and near the calving front3 4 5 so far however no study has reliably quantified the calving flux and the basal mass balance the balance between accretion and ablation at the ice shelf base for the whole of antarctica the distribution of fresh water in the southern ocean and its partitioning between the liquid and solid phases is therefore poorly constrained here we estimate the mass balance components for all ice shelves in antarctica using satellite measurements of calving flux and grounding line flux modelled ice shelf snow accumulation rates6 and a regional scaling that accounts for unsurveyed areas we obtain a total calving flux of 1 321 144 gigatonnes per year and a total basal mass balance of 1 454 174 gigatonnes per year this means that about half of the ice sheet surface mass gain is lost through oceanic erosion before reaching the ice front and the calving flux is about 34 per cent less than previous estimates derived from iceberg tracking1 2 7 in addition the fraction of mass loss due to basal processes varies from about 10 to 90 per cent between ice shelves we find a significant positive correlation between basal mass loss and surface elevation change for ice shelves experiencing surface lowering8 and enhanced discharge9 we suggest that basal mass loss is a valuable metric for predicting future ice shelf vulnerability to oceanic forcing

carbonate and elemental accumulation rates in arid soils of mid to late pleistocene outwash terraces southeastern wind river range wyoming usa an important result of the past few decades of soil geomorphic research is the awareness of the major role of dust and related carbonate precipitates in arid soils the temporal evolution of soils developed on outwash terraces is still a matter of debate particularly regarding the type of evolution progressive evolution and constant rates vs complex and or interval accumulation rates progressive or regressive evolution possible soils on a chronosequence of outwash terraces just outside and downstream of canyon mouths of the wind river range usa were analysed for carbonate accumulation organic carbon and poorly crystalline pedogenetic oxyhydroxides stocks and pathways of chemical weathering the soils and their carbonate stocks in the fine earth fraction 2 mm can be used as a relative dating tool and appear to correlate with regional glacial chronostratigraphy pinedale c 20 ky bull lake with two different units around 160 and 260 ky and sacagawea ridge c 660 ky carbonate stocks of soils on these terraces increase with increasing soil age but at generally decreasing rates a quasi steady state situation however was not reached before 1 my the time split approach showed that caco3 accumulation rates were the highest during marine isotope mis cold stages 2 13 g caco3 m2 y presumably due to a sparse vegetation cover during mis2 pinedale and 8 lower bull lake compared to organic carbon c 8 10 kg corg m2 the inorganic carbon stocks of the fine earth fraction were much higher c 60 kg cinorg m2 although the dominant pedogenic process here appears to be carbonate accumulation chemical weathering and elemental leaching also are significant weathering data were obtained using immobile elements and rare earth elements ree as tracers chemical weathering and related leaching were particularly notable for na originating from plagioclase in addition pedogenetic al and mn oxyhydroxides accumulate 220 and 32 g m2 respectively after 660 ky these form at relatively low rates however when compared to moister and cooler conditions at higher altitudes in the wind river range due to the dry climate under which the terrace soils formed annual precipitation 32 cm yr 1 weakly crystalline and amorphous fe oxyhydroxide is rapidly transformed into crystalline forms hematite over time consequently the stocks of weakly crystalline and amorphous fe oxyhydroxide was significantly lower in the 660 ky soils 50 g m2 than in the holocene soils 1000 g m2 the development of soils on quaternary outwash terraces in this region is controlled through the rates of aeolian influx over time as modified by glacial interglacial climate variations rather than by moisture availability consequently carbonate accumulation rates in these soils are influx limited rather than moisture limited

eddy driven exchange between the open ocean and a sub ice shelf cavity the exchange between the open ocean and sub ice shelf cavities is important to both water mass transformations and ice shelf melting here we use a high resolution 500 m numerical model to investigate to which degree eddies produced by frontal instability at the edge of a polynya are capable of transporting dense high salinity shelf water hssw underneath an ice shelf the applied surface buoyancy flux and ice shelf geometry is based on ronne ice shelf in the southern weddell sea an area of intense wintertime sea ice production where a flow of hssw into the cavity has been observed results show that eddies are able to enter the cavity at the southwestern corner of the polynya where an anticyclonic rim current intersects the ice shelf front the size and time scale of simulated eddies are in agreement with observations close to the ronne ice front the properties and strength of the inflow are sensitive to the prescribed total ice production flushing the ice shelf cavity at a rate of 0 2 0 4 106 m3 s 1 depending on polynya size and magnitude of surface buoyancy flux eddy driven hssw transport into the cavity is reduced by about 50 if the model grid resolution is decreased to 2 5 km and eddies are not properly resolved

significant marine ice accumulation in the ablation zone beneath an antarctic ice shelf high resolution crystallographic salinity and isotopic analyses of a 45 m ice core reveal the presence of a thick layer of marine ice near the grounding line of the nansen ice shelf antarctica the anomalous formation of marine ice in a zone assumed to be the site of active basal melting leads us to propose the hypothesis of large basal crevasses as a favorable environment for important marine ice accretion this hitherto unexplored possibility is supported by the overall field configuration and by the discrepancy in some ice properties between this core and the marine ice sections of previous drilling projects these findings could have important implications for the general stability of ice shelves and their disintegration processes the specific properties of this core reveal that marine ice is post genetically deformed