surface geostrophic currents across the antarctic circumpolar current in drake passage from 1992 to 2004 the southern ocean plays an important role in the global overturning circulation as a significant proportion of deep water is converted into intermediate and deeper water masses in this region recently a secular trend has been reported in wind stress around the southern ocean and it is thought theoretically that the strength of the acc is closely related to wind stress so one consequence should be a corresponding increase in acc transport and hence changes in the rate of the global overturning there are no long term data sets of acc transport and so we must examine other data that may also respond to changing wind stress here we calculate surface currents in drake passage every seven days over 11 25 years from 1992 to 2004 we combine surface velocity anomalies calculated from satellite altimeter sea surface heights with measured surface currents since 1992 the uk has regularly occupied woce hydrographic section sr1b across the acc in drake passage from seven hydrographic sections surface currents are estimated by referencing relative geostrophic velocities from ctd sections with current measurements made by shipboard and lowered acoustic doppler current profilers combining the seven estimates of surface currents with the altimeter data reduces bias in the estimates of average currents over time through drake passage and we show that surface current anomalies estimated by satellite and in situ observations are in good agreement the strongest surface currents are found in the subantarctic and polar fronts with average speeds of 50 cm s and 35 cm s respectively and are inversely correlated so that maximum westward flow in one corresponds to minimum westward flow in the other the average cross sectional weighted surface velocity from 1992 to 2004 is 16 7 0 2 cm s a spectral analysis of the average surface current has only weakly increasing energy at higher frequencies and there is no dominant mode of variability the standard deviation of the seven day currents is 0 68 cm s and a running 12 month average has only a slightly smaller standard deviation of 0 52 0 16 cm s the southern annular mode sam measures the circumpolar average of wind stress and like the surface currents its spectrum has slightly increased energy at frequencies greater than 1 cpy a cospectral analysis of these averaging cospectra of five slightly overlapping 36 month segments improve statistical reliability suggests that there is coherence between them at 1 cpy with the currents leading changes in the southern annular mode we conclude that the sam and average drake passage surface currents are weakly correlated with no dominant co varying modes and hence predicting southern ocean transport variability from the sam is not likely to give significant results and that secular trends in surface currents are likely to be masked by weekly and interannual variability

mapping error in southern ocean transport computed from satellite altimetry and argo in an effort to better estimate transport dynamics in response to wind forcing primarily the southern annual mode this study quantifies the uncertainty in mapping zonal geostrophic transport of the antarctic circumpolar current from sparse temperature salinity and sea surface height observations to do this we sampled an ocean state estimate at the locations of both argo floats and the jason 1 altimeter groundtrack these sampled values were then optimally interpolated to create ssh and temperature salinity grids with 1 resolution the temperature salinity and ssh grids were then combined to compute the zonal geostrophic transport and compared to that estimated from the full state estimate there are significant correlations between the baroclinic and barotropic error contributions to the total transport error the increase in argo floats in the southern ocean is effective in reducing mapping error however that error improvement is not uniform by analyzing systematic errors in transport time series we find the transects that are most appropriate for analyzing the dynamics of acc transport using argo and altimetric gridded fields based on our analysis we conclude region south of tasmania is most appropriate with lowest uncertainty using real world data we calculated zonal transport variability at a transect south of tasmania there is an insignificant trend 0 3 0 4 sv yr 1 90 confidence but significant low frequency variability correlated with the southern annular mode 0 53 p 0 05 the barotropic component is most responsible for the low frequency variability and this would be unobservable from ship casts without velocity measurements at depth this article is protected by copyright all rights reserved

variability in southern hemisphere ocean circulation from the 1980s to the 2000s abstractinterannual to decadal variability of ocean circulation in the southern hemisphere was examined using data from the 1980s to the 2000s in a box inverse model to estimate transport across hydrographic sections and three ocean general circulation models ogcms the westerly wind stress over the ogcm southern ocean showed a steady increase of 5 8 decade 1 the meridional overturning circulation was quantified by the transport across 30 s the ogcms suggested a slight strengthening from 0 2 1 0 to 0 8 1 3 sv decade 1 1 sv 106 m3 s 1 of the upper meridional cell deacon cell and two ogcms showed a weakening 0 8 0 6 and 1 0 0 3 sv decade 1 of the lower meridional antarctic bottom water aabw cell partly explained by contraction of the aabw volume the box inverse estimates did not contradict these two findings for antarctic circumpolar current transport quantified by zonal transport across four key sections the box inverse model estimated a decrease of 5 21 sv decomposition

the effect of rock strength on weathering rates of sandstone used for angkor temples in cambodia abstract this study determined the weathering rates from the depths of hollows formed by the deterioration of sandstone blocks used to build angkor temples in the 7th 12th centuries due to capillary processes these hollows generally develop at the bases of building components such as doorframes false doorframes window frames and pillars in this study 55 locations in 29 temples were selected to measure maximum hollow depth based on the ages of the temples the weathering rate was calculated to be in the range 7 92 mm ka 1 the weathering rate was found to be independent of building component type and aspect the calculated weathering rate corresponds to the physical weathering rate of sandstone caused by the wetting drying cycles that result from the tropical environment along with the dry season an equation that can estimate the maximum depth of a hollow in a sandstone block was proposed based on temple age and the coefficient obtained from two types of rock hardness values the equation coefficient is an effective index that can help predict the deterioration of stone cultural artifacts such as the angkor temples

use of grace data to detect the present land uplift rate in fennoscandia after more than 13 years of grace monthly data the determined secular trend of gravity field variation can be used to study the regions of glacial isostatic adjustment gia here we focus on fenn

deterioration of stone materials in the angkor monuments cambodia the angkor monuments in cambodia are built mainly of sandstone and laterite this paper mainly describes the deterioration of sandstone blocks the sandstone in the monuments can be classified into three types based on the colour texture chemical composition and constituent mineral grey to yellowish brown sandstone red sandstone and greenish greywacke the deterioration is distinct in grey to yellowish brown sandstone because of its low compressive strength high porosity well developed bedding and constituent minerals susceptible to alteration such as feldspar and biotite the main causes of deterioration identified are chemical weathering efflorescence related to bat guano and biodeterioration by the growth of trees algae and lichens an water supply is also indispensable for deterioration

a comparison of in situ bottom pressure array measurements with grace estimates in the kuroshio extension 1 ocean bottom pressure estimates from gravity recovery and climate experiment grace have been validated by comparisons with an array of in situ bottom pressure measurements the 600 km by 600 km array comprised 46 bottom pressure sensors that were part of the kuroshio extension system study kess validations in other ocean regions have been limited by available data to pointwise bottom pressure measurements spatially averaged monthly mean bottom pressure over the kess array is highly correlated with grace bottom pressure estimated at the center of the array the correlations are nearly equally high for three standard choices of spatial smoothing radius applied to grace estimates 300 500 and 750 km in contrast pointwise comparisons between grace and individual bottom pressures are high or low in sub regions of kess depending partially upon the local variance of deep mesoscale eddies whose energetic length scales are shorter than 300 km kess is a suitable validation experiment for the grace estimates at monthly scales with 300 to 750 km spatial radius of smoothing

salt weathering of sandstone at the angkor monuments cambodia identification of the origins of salts using sulfur and strontium isotopes abstract the angkor monuments in northwestern cambodia which are primarily made of sandstone are suffering from deterioration due to salt weathering in order to elucidate the sources of the salts and salt weathering process this paper analyzed bulk chemical compositions and s sulfur and sr strontium isotopic ratios for the salts and surrounding environmental materials at places where bats inhabit the structures various kinds of sulfate and phosphate salts are formed on the surface of the sandstone the results of the analysis demonstrate that the s and p phosphorus components in the salts are primarily derived from bat guano moreover ca calcium which is the major element in the salts is suggested to be derived from both bat guano and the sandstone the isotopic data strongly suggests that bat guano is related to salt weathering removal of these animal excrements is essential for future conservation of these monuments on the other hand exfoliation of sandstone commonly occurs due to crystallization of calcite caco 3 on platform surfaces of pyramid type monuments a large amount of ca in calcite is suggested to be derived from calcite cement of the building sandstone

revisiting grace antarctic ice mass trends and accelerations considering autocorrelation previous grace derived ice mass trends and accelerations have almost entirely been based on an assumption that the residuals to a regression model including also semi annual annual and tidal aliasing terms are not serially correlated we consider ice mass change time series for antarctica and show that significant autocorrelation is in fact present we examine power law and autoregressive models and compare them to those that assume white uncorrelated noise the data do not let us separate autoregressive and power law models but both indicate that white noise uncertainties need to be scaled up by a factor of up to 4 for accelerations and 6 for linear rates depending on length of observations and location for the whole of antarctica east antarctica and west antarctica the scale factors are 1 5 1 5 and 2 2 respectively for the trends and for the accelerations 1 5 1 5 and 2 1 substantially lower scale factors are required for offshore time series suggesting much of the time correlation is related to continental mass changes despite the higher uncertainties we find significant 2 sigma accelerations over much of west antarctica overall increasing mass loss and dronning maud land increasing mass gain as well as a marginally significant acceleration for the ice sheet as a whole increasing mass loss

antarctic circumpolar current transport variability during 2003 05 from grace abstract gravity recovery and climate experiment grace gravity data spanning january 2003 november 2005 are used as proxies for ocean bottom pressure bp averaged over 1 month spherical gaussian caps 500 km in radius and along paths bracketing the antarctic circumpolar current s various fronts the grace bp signals are compared with those derived from the estimating the circulation and climate of the ocean ecco ocean modeling assimilation system and to a non boussinesq version of the regional ocean model system roms the discrepancy found between grace and the models is 1 7 cmh2o 1 cmh2o 1 hpa slightly lower than the 1 9 cmh2o estimated by the authors independently from propagation of grace errors the northern signals are weak and uncorrelated among basins the southern signals are strong with a common seasonality the seasonal cycle grace data observed in the pacific and indian ocean sectors of the acc are consistent with annual and semiannual amplitudes of 3 6 and 0 6 cmh2o 1 1 and 0

new insights on intraplate volcanism in french polynesia from wavelet analysis of grace champ and sea surface data in this paper we discuss the origin of superswell volcanism on the basis of representation and analysis of recent gravity and magnetic satellite data with wavelets in spherical geometry we computed a refined gravity field in the south central pacific based on the grace satellite ggm02s global gravity field and the kms02 altimetric grid and a magnetic anomaly field based on champ data the magnetic anomalies are marked by the magnetic lineation of the seafloor spreading and by a strong anomaly in the tuamotu region which we interpret as evidence for crustal thickening we interpret our gravity field through a continuous wavelet analysis that allows to get a first idea of the internal density distribution we also compute the continuous wavelet analysis of the bathymetric contribution to discriminate between deep and superficial sources according to the gravity signature of the different chains as revealed by our analysis various processes are at the origin of the volcanism in french polynesia as evidence we show a large scale anomaly over the society islands that we interpret as the gravity signature of a deeply anchored mantle plume the gravity signature of the cook austral chain indicates a complex origin which may involve deep processes finally we discuss the particular location of the marquesas chain as suggesting that the origin of the volcanism may interfere with secondary convection rolls or may be controlled by lithospheric weakness due to the regional stress field or else related to the presence of the nearby tuamotu plateau

southern ocean velocity and geostrophic transport fields estimated by combining jason altimetry and argo data zonal geostrophic velocity fields above 1975 dbar have been estimated for the southern ocean from 2004 into 2011 based on sea surface topography observed by jason altimetry and temperature salinity measured by argo autonomous floats the velocity at 1000 dbar estimated with the method has been compared to argo drift trajectory at the same pressure level available from the asia pacific data research center apdrc the inferred velocities agree with those from the argo drift within the estimated sampling error of the latter but have fewer gaps in space and time the velocity has also been integrated from depth to surface to determine the mean and time variable zonal geostrophic transport in the southern ocean between 29 5 s and 58 5 s primarily in the south atlantic and south indian ocean basins due to limitations in coverage of argo analysis shows errors can be reduced by 70 by averaging gridded results over wide areas zonal transport averaged over the entire indian ocean basin shows a significant correlation with the antarctic oscillation aao at low frequencies transport is higher than normal during a positive phase of the aao and lower during the negative phase

time variability of the earth s gravity field hydrological and oceanic effects and their possible detection using grace the grace satellite mission scheduled for launch in 2001 is designed to map out the earth s gravity field to high accuracy every 2 4 weeks over a nominal lifetime of 5 years changes in the gravity field are caused by the redistribution of mass within the earth and on or above its surface grace will thus be able to constrain processes that involve mass redistribution in this paper we use output from hydrological oceanographic and atmospheric models to estimate the variability in the gravity field i e in the geoid due to those sources we develop a method for constructing surface mass estimates from the grace gravity coefficients we show the results of simulations where we use synthetic grace gravity data constructed by combining estimated geophysical signals and simulated grace measurement errors to attempt to recover hydrological and oceanographic signals we show that grace may be able to recover changes in continental water storage and in seafloor pressure at scales of a few hundred kilometers and larger and at timescales of a few weeks and longer with accuracies approaching 2 mm in water thickness over land and 0 1 mbar or better in seafloor pressure

annular modes in the extratropical circulation part i month to month variability the leading modes of variability of the extratropical circulation in both hemispheres are characterized by deep zonally symmetric or annular structures with geopotential height perturbations of opposing signs in the polar cap region and in the surrounding zonal ring centered near 458 latitude the structure and dynamics of the southern hemisphere sh annular mode have been extensively documented whereas the existence of a northern hemisphere nh mode herein referred to as the arctic oscillation ao has only recently been recognized like the sh mode the ao can be defined as the leading empirical orthogonal function of the sea level pressure field or of the zonally symmetric geopotential height or zonal wind fields in this paper the structure and seasonality of the nh and sh modes are compared based on data from the national centers for environmental prediction national center for atmospheric research reanalysis and supplementary datasets the structures of the nh and sh annular modes are shown to be remarkably similar not only in the zonally averaged geopotential height and zonal wind fields but in the mean meridional circulations as well both exist year round in the troposphere but they amplify with height upward into the stratosphere during those seasons in which the strength of the zonal flow is conducive to strong planetary wave mean flow interaction midwinter in the nh and late spring in the sh during these active seasons the annular modes modulate the strength of the lagrangian mean circulation in the lower stratosphere total column ozone and tropopause height over mid and high latitudes and the strength of the trade winds of their respective hemispheres the nh mode also contains an embedded planetary wave signature with expressions in surface air temperature precipitation total column ozone and tropopause height it is argued that the horizontal temperature advection by the perturbed zonal mean zonal wind field in the lower troposphere is instrumental in forcing this pattern a companion paper documents the striking resemblance between the structure of the annular modes and observed climate trends over the past few decades

weathering of coastal defensive structures in southwest england a 500 year stone durability trial historic structures can be viewed as exposure trials of the stone of which they are constructed as such they represent a geomorphological weathering experiment several structures of henrician sixteenth century and greater age on the coast of southwest england have been exposed to coastal salt weathering for 500 600 years long term weathering rates on five different rock groups are derived from careful study of weathering depths and forms there is significant variation in weathering rate between five major rock groups rank ordering of weathering rate values reveals a durability order of these rock groups which is confirmed by local juxtapositions controls on rock durability in the coastal weathering environment include both mechanical and mineralogical characteristics specific density and combined quartz and muscovite content are positively related to durability high feldspar and chlorite content are associated with low durability copyright 2000 john wiley sons ltd

coherence of antarctic sea levels southern hemisphere annular mode and flow through drake passage 1 it is known from small sets of tide gauges that sub surface pressure sea level corrected for the inverse barometer effect around antarctica varies coherently around about half of the continent and that this coherent signal is related to atmospheric forcing in the form of the antarctic oscillation or southern hemisphere annular mode we here confirm that this coherence extends to a more extensive network of tide gauges and to parts of the continental shelf far from the shore as measured by bottom pressure gauges we use time series from an eddy permitting ocean model with realistic forcing to relate the coherent mode to fluctuations in transport through drake passage and confirm using a 1 resolution barotropic model that the fluctuations are predominantly due to barotropic dynamics although baroclinic dynamics are expected to play an increasing role at interannual timescales

circumpolar structure and distribution of the antarctic circumpolar current fronts 2 variability and relationship to sea surface height 1 in part 1 of this study we showed that the antarctic circumpolar current acc consisted of multiple fronts each of which was consistently associated with a particular contour of sea surface height ssh or approximate streamline in part 2 we have used maps of ssh to examine the variability of the acc fronts between 1992 and 2007 the ssh label associated with each frontal branch is nearly constant around the circumpolar belt the front labels are also nearly constant in time the bands of enhanced ssh gradient i e fronts occur along the same streamlines throughout the 15 year period of observations both short and long period changes of the ssh frontal labels of the acc are small based on a tight relationship between dynamic height and cumulative baroclinic transport of the acc the baroclinic transport variability of the individual branches of the acc is also expected to be small the major change in the total acc baroclinic transport occurs in the drake passage the streamline associated with the northern branch of the saf saf n does not pass through drake passage and the waters carried by this branch are not observed there instead the transport of the saf n turns north in the pacific to supply the export of water to the indian ocean north and south of australia strong eddy activity in the southeast pacific acts to dissipate the hydrographic signature of the saf n there in the atlantic the saf n reappears as the same streamline is again associated with enhanced ssh gradients to the east of the brazil malvinas confluence zone while the large changes in ssh have occurred in the southern ocean between 1992 and 2007 there are strong regional differences because the acc fronts are robustly associated with particular ssh contours the changes in ssh reflect shifts in the position of the acc fronts in the circumpolar average each of the acc fronts has shifted to the south by about 60 km the changes in ssh in the southern ocean are largely due to changes in ocean circulation rather than warming and freshening by atmospheric fluxes much larger changes in ssh are observed in some locations of the southern ocean particularly where the fronts interact with large scale topography the northern branch of the pf pf n near the kerguelen plateau is an extreme example where the pf n followed a path around the northern end of kerguelen plateau between 1992 and 1997 passed through the fawn trough after 2003 and oscillated between the two paths between 1997 and 2003

temporal variations of the marine geoid the effects of temporal changes in the marine geoid on estimates of the ocean dynamic topography is being investigated influences from changes of land hydrology ice sheets post glacial rebound

comparison of in situ bottom pressure data with grace gravimetry in the crozet kerguelen region two time series of deep ocean bottom pressure records bprs in between the crozet islands and kerguelen are compared with grace gravity recovery and climate experiment equivalent water heights an analysis of the correlation is performed for four time series 1 monthly averages of the equivalent water height at the crozet islands 2 the same near the kerguelen islands 3 the mean of the two preceding series and 4 the difference between the two locations expressed in terms of geostrophic transport we find that smoothed grace solutions are strongly correlated with the bpr data with correlation coefficients in the order of 0 7 0 8 consequently grace measures real oceanic mass variations in this region

insolation weathering and hygric dilatation two competitive factors in stone degradation in the natural environment temperature and moisture are very important parameters in stone degradation therefore on 28 samples from different lithologies magmatic metamorphic and sedimentary rocks thermal and hygric expansion measurements were performed in order to constrain their behaviour related to environmental changes it was shown that marbles even those that are dolomitic are sensitive to temperature impacts for rocks with clay minerals the effect of temperature may be responsible for shrinking finally the amount of residual strain i e the formation of microcracks due to temperature action controls the rate of stone degradation for most sedimentary rocks no residual strain after heating was observed in contrast to most magmatic and metamorphic low porosity rocks sedimentary rocks contain swelling minerals like smectite and even phyllosilicates which are very sensitive to hygric attacks the cycles of wetting and drying i e the natural environmental effects may significantly control the deterioration velocity caused by hygric expansion

durability of carbonate rock as building stone with comments on its preservation carbonate rocks have been extensively used as building stones because of their availability workability and attractiveness unfortunately however some stones suffer from chemical attack or freeze thaw activity the environmental affects especially those due to pollution of the atmosphere are discussed in terms of weathering processes salt crystallization and acid deposition a review of some recent research in relation to deterioration of stone in urban environments is given and carbonate rocks are classified in relation to position within a building geographical location and degree of pollution some comments on stone preservation are provided especially in terms of the properties a preservative should possess

simulation of the direct runoff hydrograph at basin outlet a simple model describing the transformation of effective rainfall to direct runoff through the overland flow mechanism is presented the model is based on the classical representation of a watershed by a combination of planes and channels the dynamics of overland flow in each plane is simulated by the non linear kinematic wave but the outflow from a given plane is concentrated in the middle of the corresponding drainage channel the water routing in the channels is carried out by a piece wise linearized formulation in space of the kinematic wave approximation using synthetic events on 10 watersheds the model was tested by comparing it with results obtained by applying the non linear kinematic wave to all the elements of the watershed the model was found to be adequate even in a form that simplifies the geometric features of the planes through an averaging procedure based on the horton strahler ordering scheme of the watershed 1998 john wiley sons ltd

salt and ice crystallisation in porous sandstones salt and ice crystallisation in the pore spaces causes major physical damage to natural building stones the damaging effect of these processes can be traced back to physically induced stress inside of the rock while crystallizing the increasing scientific research done during the past century has shown that there are numerous parameters that have an influence on the weathering resulting from these processes however the working mechanisms of the stress development within the rock and its material dependency are still subject to discussion this article gives an overview of salt and ice weathering additionally laboratory results of various sandstones examined are presented salt crystallisation tests and freeze thaw tests were done to obtain information about how crystallisation weathering depends on material characteristics such as pore space water transportation and mechanical features simultaneous measuring of the length alternating during the salt and ice crystallisation has revealed detailed information on the development of crystal in the pore spaces as well as the development of stress these findings can help to understand the damaging mechanisms

on the temporal variability of the transport through drake passage a recently obtained series of bottom pressure measurements from various positions in the drake passage dp has been used to estimate the transport variability of the antarctic circumpolar current acc under the assumption that the variability is predominantly barotropic and thus proportional to the north minus south pressure difference the standard deviations in derived transport range from 5 3 sv in 1993 to 8 9 sv in 1990 10 day filter 1 sv 106 m3 s 1 all values are less than the 10 sv 10 day filter obtained during the international southern ocean studies isos program at dp between the mid 1970s and early 1980s whitworth and peterson 1985 although some of this discrepancy is due to differences in procedure in dealing with gaps in the data our data suggest that the acc transport can be persistently less variable over several years than was previously thought in particular the isos data set contains two large amplitude changes in pressure difference over timescales less than 2 weeks while no similar events were observed in the more recent data although the more recent pressure gauges were deployed at different positions to those used in isos their reliability as indicators of acc transport changes has been established by examination of simultaneous pressure measurements within dp

damage phenomenon and petrophysical properties of sandstones at the phnom bakheng temple angkor cambodia first investigations and possible conservation measures sandstones clay in the form of bricks and laterite are the building materials used by the khmer to construct the imposing and magnificent temples in southeast asia many of these monuments suffer from fracturing sanding contour scaling crust formation and salt weathering the affinity to weathering is closely connected to the type of material two sandstone types classified as feldspathic arenite and quartz arenite of angkor as well as two arkosic sandstones from thailand are described and investigated in this study important petrophysical properties determined for the different sandstones consist of hydric expansion thermal expansion pore radii distribution and ultrasonic velocity different investigations such as capillary water uptake surface hardness hygroscopic water sorption and salt resistance tests were undertaken in the laboratory to characterize the various rock types observations and quantified damage mapping were done onsite at the phnom bakheng temple contour scaling in the form of weathering crusts is one of the main deterioration features observable at the angkor monuments comparisons are made between the building stone the crust material from the phnom bakheng temple and fresh stone material used for restoration significant differences in hydric and especially in thermal expansion of the crust and sandstone have been determined the results seem to indicate that extensional processes occur which can be considered a force for detachment i e contour scaling flaking in an experimental trial the hydric and thermal expansion of the weathering crust and the building stone was significantly reduced by using a weak acid for the crust and a swelling inhibitor for the original building stone

consideration of ocean tides in an ogcm and impacts on subseasonal to decadal polar motion excitation ocean induced changes of earth s rotation are attributed either to tides or to variations of the general circulation analogously numerical world ocean models can still be divided into ocean general circulation and tidal models although a neglect of nonlinear interactions in favor of a linear superimposition of both components of motion is questionable by means of a simultaneous simulation of the ocean s circulation and tides we estimate the importance of two oceanic effects with respect to excitation of polar motion nonlinearities between circulation and long period tides and the circulation induced potential due to loading and self attraction of a baroclinic ocean comparing the linear superimposition of separate model simulations with the simultaneous calculation of circulation and tides it turns out that these second order effects contribute about 8 to ocean induced changes in earth s orientation

comparative investigation of the spatial distribution of past weathering impacts on sandstone masonry abstract inspection of the deterioration of both natural outcrops and historical built stone facades reveals that patterns of disruption are not uniform indicating the influence of material and environmental properties sandstones have a spatial variability in weathering response for this reason geostatistical techniques have been applied to studies of sandstone properties mineralogical and structural that influence susceptibility to decay for this study a comparative analysis of permeability data acquired from a quarry fresh stone and a weathered sample is undertaken the depositional processes that resulted in the formation of sandstone also create structures of spatial variation such as laminations or larger bedding planes within the material using geostatistical techniques the permeability variance observed within quarry fresh blocks of sandstone indicates the subsampling of larger geological structures when cut from the quarry face once blocks have been emplaced within a building they will be subjected to the increased stress of the urban environment these conditions result in exacerbated weathering through processes such as salt and chemical weathering weathering can alter material properties such as permeability with the creation of a secondary permeability produced by the opening pores and alteration of pore connectivity through the application of geostatistics in the analysis of permeability data observed from the weathered block variography reveals the presence of smaller scale structures this suggests that alteration of the sandstone s permeability has led to the creation of new weathering structures within the stone overwriting the initial sedimentary structures these weathering related structures will affect both the magnitude and spatial distribution of permeability within the weathered block the interconnected pathways of permeability created by past weathering facilitate the migration of moisture and salts in solution through the substrate this work has demonstrated that through a geostatistical approach with the application of co kriging these potential moisture pathways can be identified and visualised

adjustment of the southern ocean to wind forcing on synoptic time scales abstract this study addresses the response of the southern ocean to high frequency wind forcing focusing on the impact of several barotropic modes on the circumpolar transport a suite of experiments is performed with an unstratified model of the southern ocean forced with a stochastic wind stress that contains a large range of frequencies with synoptic time scales the southern ocean adjustment displays a different character for frequencies below and above 0 2 cpd the low frequency range is dominated by an almost free mode response in the region where contours of f h are obstructed by only a few bathymetric features the truly free mode only plays a minor role topographic form stress rather than friction is the dominant decay mechanism of the southern mode it leads to a spindown time scale on the order of 3 days for the high frequency range the circumpolar transport is dominated by the resonant excitation of oscillatory modes the active response of the ocean leads to strong changes and eve

preliminary observations on the impact of complex stress histories on sandstone response to salt weathering laboratory simulations of process combinations historic sandstone structures carry an inheritance or a memory of past stresses that the stone has undergone since its placement in a facade this inheritance which conditions present day performance may be made up of long term exposure to a combination of low magnitude background environmental factors for example salt weathering temperature and moisture cycling and superimposed upon these less frequent but potentially high magnitude events or exceptional factors for example lime rendering severe frost events fire the impact of complex histories on the decay pathways of historic sandstone is not clearly understood but this paper seeks to improve that understanding through the use of a laboratory process combination study blocks of quartz sandstone peakmoor from nw england were divided into subsets that experienced different histories lime rendering and removal fire and freeze thaw cycles in isolation and combination that reflected the event timeline of a real medieval sandstone monument in ne ireland bonamargy friary mccabe et al 2006b these subsets were then subject to salt weathering cycles using a 10 salt solution of nacl and mgso4 that represents the every day stress environment of for example sandstone structures in coastal or polluted urban location block response to salt weathering was monitored by collecting drying and weighing the debris that was released as blocks were immersed in the salt solution at the beginning of each cycle the results illustrate the complexity of the stone decay system showing that seemingly small variations in stress history can produce divergent response to salt weathering cycles applied to real world historic sandstone structures this concept may help to explain the spatial and temporal variability of sandstone response to background environmental factors on a single facade and encourage conservators to include the role of stress inheritance when selecting and implementing conservation strategies

assessment of flooding in urbanized ungauged basins a case study in the upper tiber area italy the reliability of a procedure for investigation of flooding into an ungauged river reach close to an urban area is investigated the approach is based on the application of a semi distributed rainfall runoff model for a gauged basin including the flood prone area and that furnishes the inlet flow conditions for a two dimensional hydraulic model whose computational domain is the urban area the flood event which occurred in october 1998 in the upper tiber river basin and caused significant damage in the town of pieve s stefano was used to test the approach the built up area often inundated is included in the gauged basin of the montedoglio dam 275 km2 for which the rainfall runoff model was adapted and calibrated through three flood events without over bank flow with the selected set of parameters the hydrological model was found reasonably accurate in simulating the discharge hydrograph of the three events whereas the flood event of october 1998 was simulated poorly with an error in peak discharge and time to peak of 58 and 20 respectively this discrepancy was ascribed to the combined effect of the rainfall spatial variability and a partial obstruction of the bridge located in pieve s stefano in fact taking account of the last hypothesis the hydraulic model reproduced with a fair accuracy the observed flooded urban area moreover incorporating into the hydrological model the flow resulting from a sudden cleaning of the obstruction which was simulated by a shock capturing one dimensional hydraulic model the discharge hydrograph at the basin outlet was well represented if the rainfall was supposed to have occurred in the region near the main channel this was simulated by reducing considerably the dynamic parameter the lag time of the instantaneous unit hydrograph for each homogeneous element into which the basin is divided the error in peak discharge and time to peak decreased by a few percent a sensitivity analysis of both the flooding volume involved in the shock wave and the lag time showed that this latter parameter requires a careful evaluation moreover the analysis of the hydrograph peak prediction due to error in rainfall input showed that the error in peak discharge was lower than that of the same input error quantity therefore the obtained results allowed us to support the hypothesis on the causes which triggered the complex event occurring in october 1998 and pointed out that the proposed procedure can be conveniently adopted for flood risk evaluation in ungauged river basins where a built up area is located the need for a more detailed analysis regarding the processes of runoff generation and flood routing is also highlighted copyright 2005 john wiley sons ltd

the sustainability of water resources in high mountain asia in the context of recent and future glacier change high mountain asia contains the largest volume of glacier ice outside the polar regions and contain the headwaters of some of the largest rivers in central asia these glaciers are losing mass at a mean rate of between 0 18 and 0 5 m water equivalent per year while glaciers in the himalaya are generally shrinking those in the karakoram have experienced a slight mass gain both changes have occurred in response to rising air temperatures due to northern hemisphere climate change in the westerly influenced indus catchment glacier meltwater makes up a large proportion of the hydrological budget and loss of glacier mass will ultimately lead to a decrease in water supplies in the monsoon influenced ganges and brahmaputra catchments the contribution of glacial meltwater is relatively small compared to the indus and the decrease in annual water supplies will be less dramatic therefore enhanced glacier melt will increase river flows until the middle of the twenty first century but in the longer term into the latter part of this century river flows will decline as glaciers shrink declining meltwater supplies may be compensated by increases in precipitation but this could exacerbate the risk of flooding

inscription legibility method for estimating rock weathering rates abstract relative legibility of dated inscription is closely associated with measured surface recessions for 3895 vermont marble tombstones and the resulting ordinal to ratio transfer function allows weathering rates to be computed for many exposed rock surfaces that cannot be measured by more accurate methods case studies demonstrate applications of the technique 1 surfaces of horizontal ground level marble plaques have dissolved at steady rates of 1 3 mm 100 yr in providence ri and 1 1 mm 100 yr in richmond va despite reports of increasing acid rain 2 vertical faces of century old marble tombstones in upper midwestern united states small towns have receded 10 times faster 1 4 mm 100 yr than have stones in less polluted environments 3 vertical faces of limestone monuments have receded at half the rate 0 5 mm 100 yr of vermont marble tombstones 0 9 mm 100 yr in louisville ky 4 aspect differences have not affected recession rates of marble pillar surfaces near philadelphia pa 5 aspect is important to sandstone granular weathering rates at inscription rock nm where north facing cliffs recede 3 times faster 0 9 mm 100 yr than do southeast facing cliffs 6 horizontal pre weathered quartizite surfaces at a scenic overlook in maryland recede at 0 6 mm 100 yr

the gravity recovery and climate experiment mission overview and early results 1 the grace mission is designed to track changes in the earth s gravity field for a period of five years launched in march 2002 the two grace satellites have collected nearly two years of data a span of data available during the commissioning phase was used to obtain initial gravity models the gravity models developed with this data are more than an order of magnitude better at the long and mid wavelengths than previous models the error estimates indicate a 2 cm accuracy uniformly over the land and ocean regions a consequence of the highly accurate global and homogenous nature of the grace data these early results are a strong affirmation of the grace mission concept

assessment of sandstone deterioration at ta keo temple angkor first results and future prospects a first application of geomorphological methods to the assessment of sandstone deterioration at angkor is presented damage diagnosis was carried out on the first eastern tier of the central pyramid of the 1 000 year old ta keo temple methods combine field observations and measurements at 230 sampling points high resolution lasergrammetry and stereophotogrammetry on a 2 m2 test zone and sem observations the first results indicate that decay operates through a synergistic combination of weathering phenomena dominated by scaling and solution and exhibits a high spatial variability percentages of deteriorated surfaces vary from 17 6 to 93 8 and average stone recession values from 0 00 to 2 71 cm minimum and 0 34 to 5 49 cm maximum on the test zone stereophotogrammetry and 3d mapping of the present and reconstructed initial states using lasergrammetry indicate that erosion scars up to 6 cm deep have formed since 1963 on the whole the amount of deteriorated surfaces more than tripled between 1963 and 2008 the degree of implication of salts in stone decay remains unclear for most efflorescences are composed of calcite caco3 with secondary importance of barite baso4 and gypsum caso4 2h2o future prospects aim to evaluate the impact on stone decay of the clearing out of the temple from the forest in the 1920s

weathering of sandstone lotus petals at the angkor site a 1 000 year stone durability trial this article is based on field investigations carried out at ta keo and banteay srei temples angkor cambodia which have similar environmental histories and display the same recurrent decorative pattern lotus petal in three different sandstone lithotypes based on two original scales of mechanical and chemical weathering the degree of deterioration of c 2000 sandstone petals was visually assessed resulting in the proposal of a durability scale an explanatory scheme was provided based on laboratory analyses of stone materials icp aes xrd sem eds polarizing microscopy and mercury injection the key drivers of sandstone durability are both mineralogical and petrophysical the remarkable preservation of the pink sandstone is due to the quartzose nature of its clasts the non swelling clay content of its abundant matrix kaolinite and its porosity structure large connected pores and probable non connected porosity the overall good preservation of the green sandstone is due to its extremely low porosity and specific surface area associated with its strong cementation the severe deterioration of the grey sandstone is due to its laminated structure oriented biotites the susceptibility to hygric swelling and solution of its binding agents chlorite smectite and calcite and its porosity structure which evolves during a two stage weathering sequence the first stage is characterized by a bimodal porosity due to the partial clogging of macropores by swelling clays and the second stage by a substantial increase in porosity and the penetration of salts barite and anhydrite conversely oxidation phenomena associated with weathering can lead to a drastic reduction of porosity

large scale ocean circulation from the grace ggm01 geoid 1 the grace gravity model 01 ggm01 computed from 111 days of grace k band ranging kbr data is differenced from a global mean sea surface mss computed from a decade of satellite altimetry to determine a mean dynamic ocean topography dot as a test of the ggm01 gravity model large scale zonal and meridional surface geostrophic currents are computed from the topography and are compared with those derived from a mean hydrographic surface reduction in residual rms between the two by 30 60 and increased correlation indicates that the ggm01 geoid represents a dramatic improvement over older geoid models which were developed from multiple satellite tracking data altimetry and surface gravity measurements for the first time all major current systems are clearly observed in the dot from space based measurements

short term transport variability of the antarctic circumpolar current from satellite gravity observations 1 ocean bottom pressure gradients deduced from the satellite gravity mission gravity recovery and climate experiment grace were previously shown to provide barotropic transport variations of the antarctic circumpolar current acc with up to monthly resolution here bottom pressure distributions from grace with monthly gfz rl04 and higher temporal resolution cnes grgs with 10 days itg grace2010 with daily resolution are evaluated over the acc area even on time scales shorter than 10 days correlations with in situ bottom pressure records frequently exceed 0 6 with positive explained variances giving evidence that high frequency nontidal ocean mass variability is captured by the daily itg grace2010 solutions not already included in the applied background models bottom pressure is subsequently taken to calculate the barotropic component of the acc transport variability across drake passage for periods longer than 30 days transport shows high correlations between 0 4 and 0 5 with several tide gauge records along the coast of antarctica still significant correlations around 0 25 are obtained even for variability with periods shorter than 10 days since transport variations are predominantly affected by time variable surface winds grace based transports are contrasted against an atmospheric index of the southern annular mode sam which represents the southern hemispheric wind variability correlations between the sam and grace based transports are consistently higher than correlations between any of the available sea level records in all frequency bands considered indicating that grace is indeed able to accurately observe a hemispherically consistent pattern of bottom pressure and hence acc transport variability that is otherwise at least partially masked in tide gauge records due to local weather effects sea ice presence and steric signals

space borne gravimetric satellite constellations and ocean tides aliasing effects summary ocean tides redistribute mass at high temporal frequencies satellite missions that aim to observe medium to low frequency mass variations need to take into account this rapidly varying mass signal correcting for the effects of ocean tides by means of imperfect models might hamper the observation of other temporal gravity field signals of interest this paper explores different methods for mitigating aliasing errors for the specific example of observing mass variations due to land hydrology including temporal filtering of time series of gravity solutions spatial smoothing and the use of satellite constellations for this purpose an earth system model esm was constructed which included state of the art time varying components for ocean atmosphere solid earth hydrology ice sheets and ocean tides using the esm we simulated the retrieval of the hydrologically driven gravity field changes using a number of different satellite constellations we find that 1 the ocean tide aliasing strongly depends on the satellite constellation the choice of orbital parameters and the length of the data span 2 the aliasing effect manifests itself differently for different geographical regions 3 the aliasing causes a peculiar striping pattern along the ground track of the satellite orbits 4 optimizing the choice of orbital parameters of a single grace type tandem can be more effective at reducing the aliasing of ocean tide model errors than flying more tandems finally we corroborate the experiences with grace data analysis that appropriate post processing techniques can significantly improve the quality of the retrieved gravity changes

contrasting weathering and climate regimes in forested and cleared sandstone temples of the angkor region comparative assessment of stone weathering intensities and bioclimatic conditions was conducted at four temples located in cleared and forested sites of the angkor park based on similar protocols four thousand sculpted lotus petals carved in the same grey sandstone were categorized by using two customized scales of weathering intensity and climate monitoring was conducted from december 2008 to november 2009 whereas 70 of the sandstone lotus petals are almost completely destroyed by mechanical weathering in cleared areas 74 of petals located in forested environments appear to be totally free of mechanical weathering and are only affected by superficial biochemical weathering ambient conditions are also contrasting with the magnitude of the diurnal surface temperature and relative humidity ranges being three times higher at cleared sites than in wooded areas as wetting drying cycles are the driving force of sandstone decay at angkor causal links are suggested between weathering and climate regimes in wooded areas the microclimate is buffered by the forest and the associated lithobionts which maintain constant humidity levels reduce thermal stresses at the stone surface and induce a slow biochemical weathering regime in cleared areas direct exposure to sunshine and monsoon rains induces pronounced wetting drying cycles conducive to swelling shrinking movements and other potential processes provoking the rapid mechanical decay of the sandstone even if local damage can be caused by tree roots the forest cover and the associated lithobionts obviously play an overall protective role additionally microtopographical factors related to architectural designs and post building events probably explain intra site and between site minor differences in the amount of sandstone decay by influencing key factors such as the water residence time at the stone surface last the contrasting weathering regimes in forested and cleared sites are but a trend for besides overwhelming mechanical weathering chemical weathering is also operative at cleared sites as indicated by salt efflorescences and ferric oxidation copyright 2012 john wiley sons ltd

the role of saline solution properties on porous limestone salt weathering by magnesium and sodium sulfates saline solution properties viscosity in particular are shown to be critical in salt weathering associated with sodium and magnesium sulfate crystallization in porous limestone the crystallization of sodium and magnesium sulfate within a porous limestone has been studied at a macro and microscale using different techniques including mercury intrusion porosimetry environmental scanning microscopy and x ray computed tomography such analysis enabled the visualization of the crystallization process in situ and at high magnification yielding critical information as to where and how salts crystallize sodium sulfate decahydrate mirabilite tends to crystallize in large pores as euhedral micron sized crystals formed at low supersaturation near to the surface of the stone in contrast magnesium sulfate heptahydrate epsomite tends to precipitate as anhedral wax like aggregates formed at high supersaturation and distributed homogeneously throughout the stone pore system filling large and small pores while the former crystallization behavior resulted in scale formation the latter led to crack development throughout the bulk stone ultimately the contrasting weathering behavior of the two sulfates is explained by considering differences in flow dynamics of solutions within porous materials that are mainly connected with the higher viscosity of magnesium sulfate saturated solution 7 27 cp when compared with sodium sulfate saturated solution 1 83 cp on the basis of such results new ways to tackle salt weathering particularly in the field of cultural heritage conservation are discussed

bottom pressure changes around antarctica and wind driven meridional flows 1 spatially averaged bottom pressure anomalies near antarctica south of 60 s calculated from grace data are well correlated with those produced by the ecco project using least squares optimization methods to fit an ocean model to most available data both grace and ecco results indicate mass exchange primarily between the southern ocean and the pacific and the importance of zonal wind stress to this exchange the ecco flow fields show that the near surface meridional ekman transport directly driven by the zonal wind stress is nearly balanced by return flows below the shallowest topography at 60 s 1300 m at this drake passage latitude with the return transport being slightly lagged in time relative to the ekman transport such time lags which may result from geostrophic adjustment at depth cause the small associated net transport across 60 s to be 90 out of phase with the wind this in turn can explain why zonal wind stress and bottom pressure anomalies around antarctica tend to be anticorrelated in both grace and ecco results

lag prediction in ungauged basins an investigation through actual data of the upper tiber river valley a comparative analysis of a variety of relationships for prediction of basin lag is performed by applying them to 23 basins located in the same geographical area and characterized by a rather similar vegetative cover the results of computations indicate that a lag area relationship with two constant parameters is the best predictor for most basins under different vegetative covers in the same basin only one parameter should be variable for a few other basins characterized by an anomalous drainage channel network of low density such a relationship can lead to unacceptable errors thus there is a need for an additional relationship to overcome this difficulty but a larger number of anomalous basins would be required for its determination an alternative procedure based on the use of the non linear kinematic wave which at least allows singling out the cases where a specific lag area relationship is not reliable is proposed this procedure therefore represents a partial but very useful solution to avoid considerable errors in hydrological practice copyright 2002 john wiley sons ltd

changes in the ocean transport through drake passage during the 1980s and 1990s forced by changes in the southern annular mode 1 we present the first direct evidence that interannual changes in ocean transport through drake passage are forced by variability in the southern annular mode sam this evidence is derived from two decades 1980s and 1990s of subsurface pressure measurements from the tide gauge at faraday station western antarctic peninsula combined with the output of an ocean general circulation model in recent decades the sam has moved toward a higher index state stronger circumpolar winds this trend is not simply monotonic but is the product of a long term change in the seasonality of the sam whilst we cannot address directly the effect of the long term trend on circumpolar transport bottom pressure data from drake passage during the 1990s demonstrate that ocean transport showed the same changes in seasonality as did the sam this offers a mechanism for atmospheric climate change to influence directly the largescale ocean circulation indexterms 4207 oceanography general arctic and antarctic oceanography 4215 oceanography general climate and interannual variability 3309 4532 oceanography physical general circulation 1635 global change oceans 4203 4556 oceanography physical sea level variations citation meredith m p p l woodworth c w hughes and v stepanov 2004 changes in the ocean transport through drake passage during the 1980s and 1990s forced by changes in the southern annular mode geophys res lett 31 l21305 doi 10 1029 2004gl021169

hydraulic modelling calibration in small rivers by using coarse resolution synthetic aperture radar imagery this study investigates the potential of the low resolution images 150m derived by the advanced synthetic aperture radar onboard theenvisat satellite to calibrate a hydraulicmodel coupledwith a semidistributed hydrologicmodel applied to a subcatchment of the upper middletiberriver gennabasin 100 km in central italy wherein afloodevent occurredon28november2010causinghigh damages specifically for thisflood event anadvancedsyntheticapertureradar image is available for the peak regionof the discharge hydrograph different image processing techniques are used for the assessment of the flooded areas by using both a single image and a change detection image based on an additional dry reference image the satellite derived flooded areas are adopted for the calibration of the channel and floodplain manning s roughness coefficients of a quasi two dimensional hydraulic model applied to the study basin which allows to distinguish the main channel from the floodplain the inflows for the hydraulic model corresponding to each tributary of the main channel are determined by a semidistributed hydrologic model calibrated by using a set of historical flood events the hydraulic model calibration is also carried out by using the same set of historical flood events for the event of november 2010 the modelled discharge and water level hydrographs obtained with the two sets of manning roughness via satellite and historical calibration are compared with in situ observations at the outlet of the basin this application on a small catchment contributes to strengthen the value of remote sensing data confirming the potential of synthetic aperture radar imagery to reduce uncertainties in hydraulic modelling calibration copyright 2012 john wiley sons ltd

regional analysis of storm hydrographs in the rescaled width function framework summary the kinematic parameters of the width function based instantaneous unit hydrograph wfiuh are estimated for a variety of italian basins different gauged catchments located within the upper tiber valley some major tributaries of the tiber river itself and the amaseno river central italy were selected to perform a regional analysis of hillslope and channel velocities for catchments with different morphology and lithology the analytical expressions adopted to determine the first and second moment of the wfiuh are revised taking into account the statistical dependence between hillslope and channel lengths velocities are estimated through a moment fitting procedure based on rainfall records runoff data and on the metrics of the catchment larger lag times and travel time variances and smaller hillslope velocities are observed for catchments underlain by carbonaceous formations when compared to other basins the values obtained for both hillslope and channel velocities appear always to maintain a physical meaning finally the capability of the wfiuh as a tool for transferring hydrologic information and obtain the prediction of flow hydrographs in ungauged basins is evaluated two equations relating the kinematic parameters to some easily available characteristics of the catchment namely the average slope and the fraction of basin underlain by carbonaceous formations are proposed

low frequency ocean bottom pressure variations in the north pacific in response to time variable surface winds one decade of time variable gravity field observations from the grace satellite mission reveals low frequency ocean bottom pressure obp variability of up to 2 5 hpa centered at the northern flank of the subtropical gyre in the north pacific from a 145 year long simulation with a coupled chemistry climate model obp variability is found to be related to the prevailing atmospheric sea level pressure and surface wind conditions in the larger north pacific area the dominating atmospheric pressure patterns obtained from the climate model run allow in combination with era interim sea level pressure and surface winds a reconstruction of the obp variability in the north pacific from atmospheric model data only which correlates favorably r 0 7 with grace ocean bottom pressure observations the regression results indicate that grace based obp observations are indeed sensitive to changes in the prevailing sea level pressure and thus surface wind conditions in the north pacific thereby opening opportunities to constrain atmospheric models from satellite gravity observations over the oceans

modifications of the porous network of sandstone accompanying the formation of black varnish black varnish commonly develops on rain washed fine grained monument sandstone stone modifications are to the naked eye limited to 10 m thick black film and underlying modified zone about 1 mm thick transfer properties absorption and drying kinetics and permeability are however modified several centimetres under the surface the present study investigates the modifications of black varnish covered siliceous sandstones taken from alsatian monuments east of france and of fresh sandstone undergoing wetting drying cycles in the laboratory double coloured thin sections revealed gradual changes in the porous network up to 3 cm under the black varnish sem observations showed that the film was mainly composed of iron and phosphorus while the modified zone was rich in calcium and sulphur fifty capillary absorption drying cycles were carried out on fresh sandstone absorption kinetics was measured at each cycle a continuous decrease of sandstone absorption kinetics over the fifty cycles was interpreted as a reorganisation of the porous network reducing the connectivity of the porous network although total porosity remained unchanged wetting drying cycles carried out under an environmental microscope esem showed a displacement of the finest particles clay clusters filling the macroporosity and decreasing the connectivity

antarctic regional ice loss rates from grace abstract using recent improved time variable gravity solutions from the gravity recovery and climate experiment grace we estimate rates of antarctic ice mass change for the period january 2003 through september 2006 combined improvements in data and filtering techniques allow observation of ice loss in the northern antarctic peninsula ap and along the coast of the west and central amundsen sea embayment ase in west antarctica there is also evidence of ice loss along the coast near the stancomb wills sta and jutulstraumen jut glaciers in queen maud land apparent rates are adjusted for influences of limited spatial resolution filtering and estimated postglacial rebound pgr to obtain ice loss rates for the northern ap coastal ase and sta jut of 28 8 7 9 81 17 and 16 7 9 7 km3 yr respectively this is the first estimate for the northern ap from satellite gravity data the ase estimate 81 17 km3 yr is consistent with a previous value 77 14 km3 yr using an earlier grace data release these results indicate significant improvement in grace data quality increased spatial resolution and applicability of grace data to a wider class of problems than previously possible

response of the antarctic circumpolar current to atmospheric variability abstract historical hydrographic profiles combined with recent argo profiles are used to obtain an estimate of the mean geostrophic circulation in the southern ocean thirteen years of altimetric sea level anomaly data are then added to reconstruct the time variable sea level and this new dataset is analyzed to identify and monitor the position of the two main fronts of the antarctic circumpolar current acc during the period 1993 2005 the authors relate their movements to the two main atmospheric climate modes of the southern hemisphere the southern annular mode sam and the el nino southern oscillation enso the study finds that although the fronts are steered by the bathymetry which sets their mean pathway on first order in flat bottom areas the fronts are subject to large meandering because of mesoscale activity and atmospheric forcing while the dominant mode of atmospheric variability in the southern hemisphere sam is relatively symmetric the oceanic response of the fronts is not show

transport and variability of the antarctic circumpolar current in drake passage the baroclinic transport of the antarctic circumpolar current acc above 3000 m through drake passage is 107 3 10 4 sv and has been steady between 1975 and 2000 for six hydrographic sections 1993 2000 along the world ocean circulation experiment woce line sr1b the baroclinic transport relative to the deepest common level is 136 7 7 8 sv the acc transport is carried in two jets the subantarctic front 53 10 sv and the polar front pf 57 5 5 7 sv southward of the acc the southern antarctic circumpolar current transports 9 3 2 4 sv we observe the pf at two latitudes separated by 90 km this bimodal distribution is related to changes in the circulation and properties of antarctic bottom water three realizations of the instantaneous velocity field were obtained with lowered adcps from these observations we obtain near bottom reference velocities for transport calculations net transport due to these reference velocities ranges from 28 to 43 sv consistent with previous estimates of variability the transport in density layers shows systematic variations due to seasonal heating in near surface layers volume transport weighted mean temperatures vary by 0 40 c from spring to summer a seasonal variation in heat flux of about 0 22 pw finally we review a series of papers from the international southern ocean studies program the average yearlong absolute transport is 134 sv and the standard deviation of the average is 11 2 sv the error of the average transport is 15 to 27 sv we emphasize that baroclinic variability is an important contribution to net variability in the acc

sandstone weathering a century of research and innovation abstract a review of sandstone weathering research particularly in the past 100 years reveals a trajectory of enquiry from early description and classification of features to development of process based explanations to decreasing scales of investigation and a disparity between understanding of process es and explanations of the genesis of sandstone weathering features developments in expositions on mesoscale weathering features on sandstone surfaces are discussed demonstrating a range of approaches to weathering phenomena field based and laboratory based that must be linked to provide an explanation of observed features on a landform scale throughout the twentieth century a thematic chronology highlights certain trends in research description of forms often in arid and semi arid environments single process form models an emphasis on experimentation difficulties in measuring weathering rates and a persistent emphasis on physical causes of breakdown a new research agenda is promoted in which biodeterioration and chemical processes gain parity a holistic approach based on conceptual modeling of weathering systems gains prominence and scale issues are addressed more rigorously

sandstone weathering in tropical climate results of low destructive investigations at the temple of angkor wat cambodia abstract investigations at the temple of angkor wat aimed at the explanation of the major weathering processes of building sandstone as well as at the role of both intrinsic factors i e sandstone petrography and properties and extrinsic factors i e climatic and environmental influences since material sampling at the temple was limited to a few boreholes because of the high artistic rank of the building non destructive and low destructive in situ investigation methods like ultrasonic wave and drilling resistance measurements had to be applied to obtain information about the material properties of sandstone and their changes due to weathering moreover hydric swelling behaviour of the sandstone was determined on undecorated pieces of fallen blocks from the walls additional random test stable isotopic investigations of environmental influences and salts and thorough investigations of the spatial distribution of salts in the ashlars at two selected places with typical weathering patterns completed the set of data the results demonstrate that the weathering process is mainly triggered by rain dry cycles salt load found in the stone is composed of gypsum and nitrate compounds sulphur stable isotope investigations of potential sources of gypsum lead to the conclusion that soluble components of bat droppings are the major source of salts influences of environmental factors like sulphate in rainwater or so2 from the air on salt formation are unlikely gypsum may reinforce the surface deterioration due to high swelling shrinking movements of the sandstone 1 mm m during intensive wetting drying cycles

role of clay minerals in the physicomechanical deterioration of sandstone 1 extensive weathering suffered by sandstone in natural outcrops as well as in historical buildings could be attributed among other mechanisms to the action of wetting and drying cycles we have recently shown how to quantify the stresses generated during such cycles to determine whether damage can take place this procedure is further developed in this paper and applied to the tarifa sandstone a sandstone with a 7 wt content of clay minerals and used in the main facade of the church of san mateo in tarifa cadiz spain for which the relevant material properties are measured it is shown that tensile stresses during drying can cause cracking of thin elements and that shear forces can cause buckling of wetted surfaces more generally eventually resulting in scaling and or contour scaling these predictions are supported by visual observations on the monument showing degradation patterns characteristic of those types of damage similar weathering forms have been observed in natural sandstone landscapes application of swelling inhibitors e g cationic surfactants that selectively adsorb on the clay basal planes results in a substantial swelling reduction this confirms that the swelling clays typically present in sandstone are pivotal for its weathering and indicates that swelling inhibitors are a potentially valuable treatment to prevent or minimize damage to stone the circumstances that would lead to weathering are discussed in relation to sandstone material properties in the wet and dry state clay bearing stones are shown to exhibit softening during wetting as well as viscoelastic stress relaxation which is expected to limit the extent of damage these results may aid in the better understanding of sandstone weathering both in nature and in urban environment and may help develop conservation methods to mitigate wetting drying damage in ornamental sandstone or to prevent pore plugging in reservoir sandstones

application of avhrr imagery and grace measurements for calculation of actual evapotranspiration over the quaternary aquifer lake chad basin and validation of groundwater models the paper presents an application of noaa avhrr and grace data for studying the regional hydrogeology of the quaternary aquifer in the lake chad basin the actual evapotranspiration et over the phreatic aquifer is computed using the s sebi algorithm and then compared to the et estimates derived from the grace land water solutions both the grace solutions and the s sebi results are similar in description of the actual et over the lake chad basin avhrr data helped to overcome non uniqueness in the modelling of the piezometry anomalies particularly in regional groundwater models the harr piezometric dome appeared to be an area of relatively high effective recharge while the chari baguirmi and the kadzell piezometric depressions and bahr el gahzal were probably areas of excess et over recharge

volume transport of the antarctic circumpolar current from bottom pressure measurements abstract meausrements from bottom pressure gauges located at the north and south sides of drake passage are used to extend the one year time series of volume transport of the antarctic circumpolar current acc given previously by whitworth a small error in that paper is corrected and a revised transport time series is presented which shows the importance of including the transport in the northern and southern margins of drake passage direct measurements of vertical shear averaged across the passage are in good agreement with geostrophic shear and suggest that the acc is in geostrophic balance although most of the acc transport is in the baroclinic field transport fluctuations are mainly barotropic transport estimates based on pressure difference alone differ from the estimates of whitworth by less than 10 106 m3 s 1 fluctuations in transport of almost half of the mean value occur over periods as short as two weeks