occurrence of rocky and sedimentary glacier beds in the swiss alps as estimated from glacier inventory data the occurrence of rocky and sedimentary glacier beds in the swiss alps was investigated using two approaches 1 a detailed and systematic classification of glacier forefields in the completely revised swiss glacier inventory and 2 the application of an algorithm for estimating bed characteristics from glacier inventory data the algorithm is based on the assumption that the sediment balance of a glacierized catchment i e the ratio between debris input from the surrounding rock walls and debris evacuation by the meltwater stream determines the occurrence of rocky sedimentary or mixed beds the processes which govern the sediment balance within a glacierized catchment cannot be easily observed or measured in the field however the main factors reflecting them can be organized in the form of an erosion sedimentation index this index discriminates between glaciers eroding into bedrock and those building up thick sediment beds and thus allows for rough assessments concerning bed characteristics sedimentary and mixed sedimentary rocky glacier beds clearly predominate in the swiss alps but more detailed spatial analysis is required for better predictions

evidence for a till layer beneath storglaciaren sweden based on electrical resistivity measurements evidence for a till layer beneath storglaciaren sweden based on electrical resistivity measurements

response of sediment to ice sheet loading in northwestern germany effective stresses and glacier bed stability laboratory tests on sediment over ridden by the last ice sheet in northwestern germany reveal very low ice induced pre consolidation and high palaeo pore water pressures sediment consolidation at the base of the glacier was largely controlled by hydraulic properties of the substratum generally low permeabilities of the bed caused sustained high pore water pressure in over ridden sediments close to the flotation point this implies a serious possibility of hydraulic lifting of the ice sheet it is believed that the reduced basal coupling limited the transformation of glacier shear stress on to the bed sediments which is indicated by a lack of sedimentological evidence for widespread pervasive bed deformation ice motion was probably focused at the glacier sole by some combination of sliding and ploughing however isolated spots with deformation occur so that the subglacial system in the study area can be characterized as a stable deforming mosaic

europe s southernmost glaciers response and adaptation to climate change the southernmost glaciers in europe are located on the iberian apennine and balkan peninsulas in mid latitudes between 41 n and 44 n at altitudes ranging from 2000 to 3000 m a s l all these glaciers are a legacy of the little ice age lia they survive in a relatively warm environment mean annual temperature 0 ct o 1 c due to local topographic controls and high levels of accumulation as a result of avalanche and wind blown snow in the pirin mountains bulgaria snezhnika glacieret has been cored providing an archive of recent climate change small glaciers such as this respond quickly to climatic extremes since the lia maximum during the 19th century all southern european glaciers have retreated losing 30 100 of their volume however despite the trend towards warmer years since the late 1970s some glaciers still survive even after some of the hottest summers on record predicted future warming especially in summer and drier conditions in the mediterranean basin may result in the disappearance of all glacier features at these latitudes in europe within the next few decades

groundwater flow beneath ice sheets part ii its impact on glacier tectonic structures and moraine formation abstract meltwater flowing as groundwater from beneath the margin of an ice sheet determines the distribution of sub surface heads and effective pressures a subglacial groundwater flow model is used together with an ice sheet loading model to compute the magnitudes and directions of the principal effective stresses in the subsurface from which the distribution of different types of sub surface failure in the subglacial and proglacial zones are deduced zones of hydrofracturing shear fracture and pervasive shear failure are distinguished beneath the ice sheet divide area intact rocks of high tensile strength may fail hydrofracturing and liquefaction are two coupled processes which lead to the formation of upward filled and downward filled sediment dykes and till wedges quicksand conditions are developed where strong vertical seepage pressures occur producing sediment diapirism it is suggested that subglacial permeability magnitude may be the product of a self organising process certain types of moraine extrusion moraines are suggested to be a consequence of upward movement and surface extrusion of sediment driven by rising groundwater it is suggested that groundwater over pressure associated with narrow proglacial permafrost plates are conductive to the formation of large push moraines and that many large ancient and modern examples are produced in this setting

an assessment of landform composition and functioning with the first proglacial systems dataset of the central european alps abstract proglacial systems are enlarging as glacier masses decline they are in a transitory state from glacier dominated to hillslope and fluvially dominated geomorphological processes they are a very important meltwater sediment and solute source this study makes the first quantitative systematic and regional assessment of landform composition and functioning within proglacial systems that have developed in the short term since the little ice age lia proglacial system extent was thus defined as the area between the lia moraine ridges and the contemporary glacier we achieved this assessment via a series of topographic analyses of 10 m resolution digital elevation models dems covering the central european alps specifically of austria and switzerland across the 2812 proglacial systems that have a combined area of 933 km2 the mean proportional area of each proglacial system that is directly affected by glacial meltwater is 37 however there are examples where there is no glacial meltwater influence whatsoever due to complete disappearance of glaciers since the lia and there are examples where 90 of the proglacial area is probably affected by glacial meltwater in all of the major drainage basins the inn drava venetian coast po rhine rhone and danube the proportions of the combined land area belonging to each landform class is remarkably similar with 10 fluvial 35 alluvial and debris fans 50 moraine ridges and talus scree and 10 bedrock which will be very helpful for considering estimates of regional sediment yield and denudation rates we find groupings of the relationship between proglacial system hypsometric index and lithology and of a slope threshold discriminating between hillslope and fluvial dominated terrain both of which we interpret to be due to grain size we estimate of contemporary total volume loss from all of these proglacial systems of 44 m m3a 1 which equates to a mean of 0 3 mm a 1 contemporary surface lowering overall these first quantifications of proglacial landform and landscape evolution will be an important basis for inter and intra catchment considerations of climate change effects on proglacial systems such as land stability and changing water sediment and solute source fluxes our datasets are made freely available

internal tides and baroclinicity in the southern weddell sea 1 model description near the continental shelf break in the southern weddell sea warm deep water and western shelf water meet mixing mechanisms such as internal tides have the potential to mix these water masses and form antarctic bottom water a modified version of the princeton ocean model was utilized to investigate the internal tidal fields generated by the interaction of the m 2 barotropic tide with topography for transects across the continental shelf and slope in the southern weddell sea internal tides were generated over the upper continental slope as predicted by linear internal wave theory although the essentially two dimensional domain resulted in differences between the model elevations and the observations exceeding the observational uncertainties the cross slope velocities agreed well with differences less than the uncertainties for 78 of the existing observations

on estimating length fluctuations of glaciers caused by changes in climatic forcing the reaction of alpine glaciers to shifts in the equilibrium line altitude ela is calculated by using a two dimensional numerical model to solve the full equations for the velocity and stress fields full system model in the absence of basal motion rates of advance and retreat of the snout of typically sized alpine glaciers are found to be insensitive to the details of the flow at the snout even when the glaciers are far from steady state a comparison of results obtained with a full system model and a shallow ice approximation sia model yields no significant differences in advance or retreat rates this assumption has been implicitly made in numerous previous climatic studies and is here shown to be well justified using a realistic mass balance altitude feedback only slight model dependent changes in steady state lengths are found the relative importance of mass balance and glacier dynamics for the transient response of alpine glaciers to changes in the ela is given a precise meaning by determining the model dependent additional shifts in ela needed for the sia and the full system models to produce identical changes in length for alpine glaciers these additional shifts in ela are on the order of 10 m which is within the error range of ela estimates it follows that at least in the absence of significant basal motion there is no need to include the effects of horizontal stresses when calculating the reaction of alpine glaciers to climatic changes attention should focus on accurate determination of the mass balance distribution and model tuning to give realistic ice thickness distributions

reduced mixing from the breaking of internal waves in equatorial waters in the oceans heat salt and nutrients are redistributed much more easily within water masses of uniform density than across surfaces separating waters of different densities but the magnitude and distribution of mixing across density surfaces are also important for the earth s climate as well as the concentrations of organisms most of this mixing occurs where internal waves break overturning the density stratification of the ocean and creating patches of turbulence predictions of the rate at which internal waves dissipate were confirmed earlier at mid latitudes here we present observations of temperature and velocity fluctuations in the pacific and atlantic oceans between 42 degrees n and 2 degrees s to extend that result to equatorial regions we find a strong latitude dependence of dissipation in accordance with the predictions in our observations dissipation rates and accompanying mixing across density surfaces near the equator are less than 10 of those at mid latitudes for a similar background of internal waves reduced mixing close to the equator will have to be taken into account in numerical simulations of ocean dynamics for example in climate change experiments

multivariate geostatistical modeling of the spatial sediment distribution in a large scale drainage basin upper rhone switzerland abstract there is a notable discrepancy between detailed sediment budget studies in small headwater catchments 103 km2 in higher order catchments applying modeling and or remote sensing based approaches for major sediment storage delineation to bridge the gap between these scales we compiled an inventory of sediment and bedrock coverage from field mapping remote sensing analysis and published data for five key sites in the upper rhone basin val d illiez val de la liene turtmanntal lotschental goms 360 3 km2 equivalent to 6 7 of the upper rhone basin this inventory was used as training and testing data for the classification of sediment and bedrock cover from a digital elevation model 2 2 m ground resolution and landsat imagery we derived 22 parameters characterizing local morphometry topography and position contributing area and climatic and biotic factors on different spatial scales which were used as inputs for different statistical models logistic regression principal component logistic regression generalized additive model best prediction results with an excellent performance mean auroc 0 8721 0 0012 and both a high spatial and non spatial transferability were achieved applying a generalized additive model since the model has a high thematic consistency the independent input variables chosen based on their geomorphic relevance are suitable to model the spatial distribution of sediment our high resolution classification shows that 53 5 21 7 of the upper rhone basin are covered with sediment these are by no means evenly distributed small headwaters

mixing on the continental slope of the southern weddell sea shipboard hydrography and current profiles collected in 2003 and time series from moored current meters deployed in late 1990s are analyzed to study the variability of mixing in the southeastern weddell sea profiles of eddy diffusivity k are inferred from finescale shear vertical derivative of horizontal velocity and strain vertical derivative of isopycnal displacement variance using parameterizations which relate the internal wave energy to the dissipation rate at small scales the highest mixing rates are seen near the bottom where the eddy diffusivities are elevated by one order of magnitude from those in the interior and exceed 10 4 m 2 s 1 the observations show latitudinal variability in k particularly near the bottom where k significantly increases near 74 28 s the critical latitude for lunar semi diurnal m2 tides in this region the critical latitude coincides with near critical topography on the upper continental slope a situation which favors generation of m2 internal waves consistent with the results from finescale shear and strain parameterizations which indicate highest bottom diffusivities near the critical latitude independent analysis of current time series from moored instruments shows a thickening of the frictional bottom boundary layer near the critical latitude semidiurnal tidal dynamics at the upper continental slope together with the critical latitude effects lead to mixing that might significantly affect the regional heat budget and the circulation in the study area

clast collision frequency as an indicator of glacier sliding rate the mechanical interaction between a glacier and subglacial sediment can be observed using an instrumented rod that we refer to as the ubc ploughmeter for clast rich sediments the rate of collision between clasts and a rod dragged through these sediments should be related to the glacier sliding rate by assuming that proglacial measurements of sediment granulometry represent the subglacial granulometry of trapridge glacier yukon territory canada we have used ploughmeter results to obtain an estimated sliding rate of 45 mm d 1 in good agreement with known rates in addition for a subglacial material treated as a solid liquid dispersion having a linear viscous rheology the force of collision experienced by the rod should be proportional to the effective sediment viscosity our estimate of 2 0 x 10 10 pa s agrees well with previously derived values

application of inventory data for estimating characteristics of and regional climate change effects on mountain glaciers a pilot study with the european alps a parameterization scheme using simple algorithms for unmeasured glaciers is being applied to glacier inventory data to estimate the basic glaciological characteristics of the inventoried ice bodies and simulate potential climate change effects on mountain glaciers for past and potential climate scenarios glacier changes for assumed mass balance changes are calculated as step functions between steady state conditions for time intervals that approximately correspond to the characteristic dynamic response time a few decades of the glaciers in order to test the procedure a pilot study was carried out in the european alps where detailed glacier inventories had been compiled around the mid 1970s total glacier volume in the alps is estimated at about 130 km3 for the mid 1970s strongly negative mass balances are likely to have caused a loss of about 10 20 of this total volume during the decade 1980 90 backward calculation of glacier length changes using a mean annual mass balance of 0 25m w e a 1 since the end of the little ice age around 1850 ad gives considerable scatter but satisfactory overall results as compared with long term observations the total loss of alpine surface ice mass since 1850 can be estimated at about half the original value an acceleration of this development with annual mass losses of around 1 m a 1 or more as anticipated from ipcc scenario a for the coming century could eliminate major parts of the presently existing alpine ice volume within decades

constant denudation rates in a high alpine catchment for the last 6 kyrs terrestrial cosmogenic nuclides tcn have widely been used as proxies in determining denudation rates in catchments most studies were limited to samples from modern active streams thus little is known about the magnitude and causes of tcn variability on millennial time scales in this work we present a 6 kyrs long high resolution record of 10be concentrations n 18 which were measured in sediment cores from an alluvial fan delta at the outlet of the fedoz valley in the swiss alps this record is paired with a three year time series n 4 of 10be measured in sediment from the active stream currently feeding this fan delta the temporal trend in the 10be concentrations after correction for postdepositional production of 10be was found to be overall constant and in good agreement with the modern river 10be concentration the calculated mean catchment wide denudation rate amounts to 0 73 0 18 mm yr this fairly constant level of 10be concentrations can be caused by a constant denudation rate over time within the catchment or alternatively by a buffered signal in this contribution we suggest that the large alluvial floodplain in the fedoz valley may act as an efficient buffer on holocene time scales in which sediments with different 10be signatures are mixed therefore presumable variations in the 10be signals derived from changes in denudation under a fluctuating holocene climate are only poorly transferred to the catchment outlet and not recorded in the 10be record however despite the absence of high frequency signals we propose that the buffered and averaged 10be signal could be meaningfully and faithfully interpreted in terms of long term catchment averaged denudation rate our study suggests that alluvial buffers play an important role in regulating the 10be signal exported by some alpine settings that needs to be taken into account and further investigated this article is protected by copyright all rights reserved

prevention of outburst floods from periglacial lakes at grubengletscher valais swiss alps flood and debris flow hazards at grubengletscher near saas balen in the saas valley valais swiss alps result from the formation and growth of several lakes at the glacier margin and within the surrounding permafrost in order to prevent damage related to such hazards systematic investigations were carried out and practical measures taken the evolution of the polythermal glacier the creeping permafrost within the large adjacent rock glacier and the development of the various periglacial lakes were monitored and documented for the last 25 years by photogrammetric analysis of annually flown high resolution aerial photographs seismic refraction d c resistivity and gravimetry soundings were performed together with hydrological tracer experiments to determine the structure and stability of a moraine dam at a proglacial lake the results indicate a maximum moraine thickness of 100 m extremely high porosity and even ground caverns near the surface may have resulted from degradation of sub and periglacial permafrost following 19th 20th century retreat of the partially cold glacier tongue the safety and retention capacity of the proglacial lake were enhanced by deepening and reinforcing the outlet structure on top of the moraine complex the water level of an ice dammed lake was lowered and a thermokarst lake artficially drained

instruments and methods direct measurement of sliding at the glacier bed sliding at the base of trapridge glacier yukon territory canada was measured using a drag spool we describe this simple and inexpensive instrument as well as its installation and operation from 1990 to 1992 seven sites were instrumented with drag spools at six of the sites basal sliding during the period of observation accounted for 50 70 of the total flow observed at the glacier surface the contribution from ice creep is known to be small so most of the remaining surface motion must be attributed to subglacial sediment deformation for the seventh site the observed sliding rate was 90 of the total flow an indication that the sliding contribution varies spatially across the bed diurnal variations in the response of one of our instruments appear to be correlated to subglacial water pressure fluctuations and are interpreted in terms of changes in sliding velocity rather than the opening and closing of basal cavities

in situ la mc icp ms u pb geochronology of igneous rocks in the ashele basin altay orogenic belt northwest china constraints on the timing of polymetallic copper mineralization abstract the altay orogenic belt of kazakhstan hosts a world class polymetallic copper volcanogenic massive sulfide vms metallogenic belt and the eastern margin of this belt extends into the southern chinese altay the ashele basin is located at the western end of the chinese altay and borders kazakhstan the basin hosts the large ashele copper zinc deposit which is a typical vms deposit and the largest deposit in the ashele basin and it hosts the subvolcanic hosted medium sized sarsuk polymetallic gold deposit both of these deposits are hosted in the ashele formation volcanic sequence the ashele copper zinc orebodies are stratabound orebodies located between basalt and tuff units and were formed during exhalative sediment deposition in comparison the sarsuk gold copper lead zinc orebodies are hosted by rhyolite porphyry that contains disseminated veinlet and veinlet stockwork ore that formed during intrusion of the rhyolite porphyry this study presents new zircon la mc icp ms u pb analyses of six volcanic and subvolcanic units and dikes associated with the sarsuk and ashele deposits the ore bearing rhyolite porphyry diabase dike basalt tuff and dacite porphyry samples analyzed during this study yielded ages of 382 0 382 8 381 7 388 2 387 0 and 379 4 ma respectively these data indicate that the ashele formation formed during the early mid devonian 375 402 ma whereas the ashele copper zinc deposit formed during the middle devonian 388 387 ma and the sarsuk polymetallic copper gold deposit formed during the latest middle devonian 382 ma inherited zircons within the six samples analyzed during this study yielded u pb ages of 618 2294 ma suggesting the presence of precambrian crystalline basement within the altay orogenic belt

internal tides and baroclinicity in the southern weddell sea 2 effects of the critical latitude and stratification tidal dynamics affect antarctic bottom water and ice shelf water production in the southern weddell sea and the general circulation and mixing in this region tidal dynamics were found to be extremely sensitive both to the proximity of the continental shelf slope break to the critical latitude crit and to the existence of a shelf break front if the continental slope was not in the vicinity of crit or a shelf break front was absent generation of internal tides was negligible generation of internal tides was greatest when both a shelf break front was present and the continental slope was near and equatorward of crit when a shelf break front was present and the continental slope was near but poleward of crit a strong benthic response occurred this response included development of benthic inertial oscillations at the continental shelf slope break increased benthic shear a thicker benthic boundary layer and increased benthic dissipation a shelf break front with even a slight horizontal density gradient was found to significantly enhance internal tide generation and or the benthic effects

river loads and modern denudation of the alps a review this paper presents the first comprehensive analysis of sediment and dissolved load across an entire mountain range we investigate patterns and rates of modern denudation of the european alps based on a compilation of data about river loads and reservoir sedimentation from 202 drainage basins that are between ca 1 to 10 000 km2 large the study basins cover about 50 of the total area of the alps modern glaciated basins have the highest sediment yields of up to 7000 t km 2 a 1 which are on average 5 to 10 times higher than in non glaciated basins likewise sediment yield and glacial cover are positively correlated instead relief is a relatively weak predictor of sediment yield the strong glacial impact in the correlations is due to glacier recession since the 19th century as well as due to glacial conditioning during repeated quaternary glaciations which have produced the strong transient state of the alpine landscape we suggest that this is the major cause for ca 3 fold enhanced denudation of the western compared to the eastern alps chemical denudation rates are highest in the external alps dominated by carbonate sedimentary rocks where they make up about one third of total denudation the high rates cannot be explained without anhydrite dissolution we estimated that only 45 of the sediments mobilized in headwaters are exported out off the alps most sediments being trapped in artificial reservoirs the total amount of sediment annually trapped within the alps equates to 43 mt when corrected for sediment storage we obtain an area weighted mean total denudation rate for the alps of about 0 32 mm a 1 the pre dam rate might be as high as 0 42 mm a 1 in total ca 35 plus 23 mt of mass are exported each year out of the alps as solids and solutes respectively these rates are not enough to out pace modern rock uplift nevertheless pattern of sediment yield across the alps coincides roughly with the intensity of glacial conditioning and modern rock uplift supporting the hypothesis of an erosion driven uplift of the alps

evidence for enhanced mixing over rough topography in the abyssal ocean the overturning circulation of the ocean plays an important role in modulating the earth s climate but whereas the mechanisms for the vertical transport of water into the deep ocean deep water formation at high latitudes and horizontal transport in ocean currents have been largely identified it is not clear how the compensating vertical transport of water from the depths to the surface is accomplished turbulent mixing across surfaces of constant density is the only viable mechanism for reducing the density of the water and enabling it to rise however measurements of the internal wave field the main source of energy for mixing and of turbulent dissipation rates have typically implied diffusivities across surfaces of equal density of only approximately 0 1 cm2 s 1 too small to account for the return flow here we report measurements of tracer dispersion and turbulent energy dissipation in the brazil basin that reveal diffusivities of 2 4 cm2 s 1 at a depth of 500 m above abyssal hills on the flank of the mid atlantic ridge and approximately 10 cm2 s 1 nearer the bottom this amount of mixing probably driven by breaking internal waves that are generated by tidal currents flowing over the rough bathymetry may be large enough to close the buoyancy budget for the brazil basin and suggests a mechanism for closing the global overturning circulation

combining satellite multispectral image data and a digital elevation model for mapping debris covered glaciers automated glacier mapping from satellite multispectral image data is hampered by debris cover on glacier surfaces supraglacial debris exhibits the same spectral properties as lateral and terminal moraines fluvioglacial deposits and bedrock outside the glacier margin and is thus not detectable by means of multispectral classification alone based on the observation of low slope angles for debris covered glacier tongues we developed a multisource method for mapping supraglacial debris the method combines the advantages of automated multispectral classification for clean glacier ice and vegetation with slope information derived from a digital elevation model dem neighbourhood analysis and change detection is applied for further improvement of the resulting glacier debris map a significant percentage of the processing can be done automatically in order to test the sensitivity of our method against different dem qualities it was also applied to a dem obtained from aster stereo data additionally we compared our multisource approach to an artificial neural network ann classification of debris using only multispectral data while the combination with an aster derived dem revealed promising results the ann classification without dem data does not

theory of glacial erosion transport and deposition as a consequence of subglacial sediment deformation a theory of erosion transport and deposition of unlithified sediments by glaciers is presented it predicts the large scale areal distribution of zones and rates of erosion and deposition in time and space through a complete glacial cycle together with the resultant intensity of large scale lincations drumlins which will be incised in the landscape the theory also predicts the dispersal patterns of subglacial lithologies together with the form of dispersal trains derived from distinctive sources and the vertical and horizontal distribution of lithologies within a till it predicts major erosional discontinuities within tills and the formation of boulder pavements it suggests that the dominant proportion of the lowland tills produced by pleistocene mid latitude ice sheets was generated by subglacial deformation and explains why they are predominantly fine grained the theory is based on an analysis of glacier dynamic processes and therefore can be used to infer the dynamic behaviour of former ice sheets from the distribution of tills and their lithologic composition

determination of the internal structure of alpine talus deposits using different geophysical methods lechtaler alps austria abstract the total thickness and structure of alpine talus accumulations were investigated in a study area in the northern alps using ground penetrating radar gpr completed by 2d geoelectric ert and seismic refraction soundings the loose steep talus cones of the parzinn cirque are situated at an elevation of 2100 2300 m a s l and end downslope at late glacial protalus ramparts the surrounding rockwalls consist of hauptdolomit a brittle dolostone in most of the gpr profiles the bedrock surface was clearly recognizable from the radargrams total talus thicknesses of up to 45 m were estimated the uppermost talus layer is characterized by surface parallel radar reflection patterns intermediate resistivities 4 10 k m and low seismic velocities 400 500 m s these deposits are interpreted as stratified debris built up during the holocene by rockfall deposits occasionally resorted by debris flows below this unit a zone of more irregular radar reflection patterns and enhanced electrical resistivities follows the combined results lead to the assumption of very coarse grained paraglacial rockfall deposits or to a core of basal moraine beneath the talus some zones of especially high resistivity 25 k m may be related to sporadic permafrost occurrence in the depressions between the talus and the moraine ridges striped radar structures are also recognizable in the moraine bodies the stratified sediments give evidence for glaciofluvial transport or debris flows as an agent of protalus rampart formation however these features probably result from a combination of different processes including periglacial creep gpr turned out to be a powerful tool for the determination of debris volumes and internal structures however supporting geoelectric and seismic investigations are advisable to validate the results and to facilitate and improve the interpretation the results point to an average holocene rockwall retreat of 500 to 800 mm ka which is roughly three times higher than recent backweathering rates

mixing of a tracer in the pycnocline a patch of sulfur hexafluoride was released in may 1992 in the eastern north atlantic on an isopycnal surface near 300 m depth and was surveyed over a period of 30 months as it dispersed across and along isopycnal surfaces the diapycnal eddy diffusivity k estimated for the first 6 months was 0 12 0 02 cm2 s while for the subsequent 24 months it was 0 17 0 02 cm2 s the vertical tracer distribution remained very close to gaussian for the full 30 months as the root mean square rms dispersion grew from 5 to 50 m lateral dispersion was measured on several scales the growth of the rms width of the tracer streaks from less than 100 m to approximately 300 m within 2 weeks implies an isopycnal diffusivity of 0 07 m2 s at scales of 0 1 to 1 km larger than expected from the interaction between vertical shear of the internal waves and diapycnal mixing teasing of the overall patch initially about 25 km across into streaks with an overall length of 1800 km within 6 months supports predictions of exponential growth by the mesoscale strain field at a rate of 3 0 5 10 7 s 1 the rms width of these streaks estimated as 3 km and maintained in the face of the streak growth indicates an isopycnal diffusivity of 2 m2 s at scales of 1 to 10 km much greater than expected from internal wave shear dispersion the patch was painted in albeit streakily by 12 months confirming expectations from analytical and numerical models homogenization of the patch continued during the subsequent 18 months while the patch continued to spread with an effective isopycnal eddy diffusivity on the order of 1000 m2 s acting at scales of 30 to 300 km

spatial variability of mixing in the southern ocean 1 strain variance from standard hydrographic profiles in the southern hemisphere oceans shows that turbulent mixing is vertically and spatially non uniform in the south atlantic indian and south pacific oceans enhanced diffusivities are found over rough topography consistent with internal tide generated mixing the water column diffusivity returns to background levels 500 m to 1000 m off the sea floor in the southern ocean enhanced diffusivities throughout the entire water column below 1500 m are found in the antarctic circumpolar current over complex topography differences in the vertical extent of enhanced diffusivity profiles in the antarctic circumpolar current between the parameterizations based on tidal models and topography and of the present estimate of strain variance imply that elevated vertical diffusivity profiles in the southern ocean are due to the interaction between the mean geostrophic current and bottom topography

the impact of supraglacial debris on proglacial runoff and water chemistry debris is known to influence the ablation topography and hydrological systems of glaciers this paper determines for the first time how these influences impact on bulk water routing and the proglacial runoff signal using analyses of supraglacial and proglacial water chemistry and proglacial discharge at miage glacier italian alps debris does influence the supraglacial water chemistry but the inefficient subglacial system beneath the debris covered zone also plays a role in increasing the ion contribution to the proglacial stream daily hydrographs had a lower amplitude and later discharge peak compared to clean glaciers and fewer diurnal hydrographs were found compared to similar analysis for haut glacier d arolla we attribute these observations to the attenuating effect of the debris on ablation smaller input streams on the debris covered area a less efficient subglacial system and possible leakage into a raised sediment bed beneath the glacier strongly diurnal hydrographs are constrained to periods with warmer than average conditions average weather conditions result in a hydrograph with reverse asymmetry conductivity and discharge commonly show anti clockwise hysteresis suggesting the more dilute rapidly routed melt component from the mid glacier peaks before the discharge peak with components from higher up glacier and the debris covered areas arriving later at the proglacial stream the results of this study could lead to a greater understanding of the hydrological structure of other debris covered glaciers with findings highlighting the need to include the influence of the debris cover within future models of debris covered glacier runoff