internal tide coherence and decay over a wide shelf sea 1 a quasi synoptic hydrography and velocity section is used to determine the structure and the decay rate of the internal tide it across the broad continental shelf of the celtic sea in these observations the it is coherent over more than 170 km about five wavelengths with an estimated shoreward energy decay scale of 42 km the inferred it wavelength averaged dissipation rate near the shelf edge is estimated as 2 08 10 7 wkg 1 in close agreement with tidally and vertically averaged measurements from the region these results provide the firstin situ evidence of it coherence over many wavelengths in a shelf sea

baroclinic energy flux at the continental shelf edge modified by wind mixing temperature and current measurements from two moorings onshore of the celtic sea shelf break a well known hot spot for tidal energy conversion show the impact of passing summer storms on the baroclinic wavefield wind driven vertical mixing changed stratification to permit an increased on shelf energy transport and baroclinic energy in the semidiurnal band appeared at the moorings 1 4 days after the storm mixed the upper 50 m of the water column the timing of the maximum in the baroclinic energy flux is consistent with the propagation of the semidiurnal internal tide from generation sites at the shelf break to the moorings 40 km away also the 3 day duration of the peak in m2 baroclinic energy flux at the moorings corresponds to the restratification time scale following the first storm

a decade of progress in observing and modelling antarctic subglacial water systems in the decade since the discovery of active antarctic subglacial water systems by detection of subtle surface displacements much progress has been made in our understanding of these dynamic systems here we present some of the key results of observations derived from icesat laser altimetry cryosat 2 radar altimetry operation icebridge airborne laser altimetry satellite image differencing and ground based continuous global positioning system gps experiments deployed in hydrologically active regions these observations provide us with an increased understanding of various lake systems in antarctica whillans mercer ice streams crane glacier recovery ice stream byrd glacier and eastern wilkes land in several cases subglacial water systems are shown to control ice flux through the glacier system for some lake systems we have been able to construct more than a decade of continuous lake activity revealing internal variability on time scales ranging from days to years this variability indicates that continuous accurate time series of altimetry data are critical to understanding these systems on whillans ice stream our results from a 5 year continuous gps record demonstrate that subglacial lake flood events significantly change the regional ice dynamics we also show how models for subglacial water flow have evolved since the availability of observations of lake volume change from regional scale models of water routeing to process models of channels carved into the subglacial sediment instead of the overlying ice we show that progress in understanding the processes governing lake drainage now allows us to create simulated lake volume time series that reproduce time series from satellite observations this transformational decade in antarctic subglacial water research has moved us significantly closer to understanding the processes of water transfer sufficiently for inclusion in continental scale ice sheet models

the ellsworth subglacial highlands inception and retreat of the west antarctic ice sheet antarctic subglacial highlands are where the antarctic ice sheets first developed and the pinning points where retreat phases of the marine based sectors of the ice sheet are impeded due to low ice velocities and limited present day change in the ice sheet interior west antarctic subglacial highlands have been overlooked for detailed study these regions have considerable potential however for establishing the locations from which the west antarctic ice sheet originated and grew and its likely response to warming climates here we characterize the subglacial morphology of the ellsworth subglacial highlands west antarctica from ground based and aerogeophysical radio echo sounding res surveys and the moderate resolution imaging spectroradiometer modis mosaic of antarctica we document well preserved classic landforms associated with restricted dynamic marine proximal alpine glaciation with hanging tributary valleys feeding a significant overdeepened trough the ellsworth trough cut by valley tidewater glaciers fjord mouth threshold bars down ice of two overdeepenings define both the northwest and southeast termini of paleo outlet glaciers which cut and occupied the ellsworth trough satellite imagery reveals numerous other glaciated valleys terminating at the edge of deep former marine basins e g bentley subglacial trench throughout the ellsworth subglacial highlands these geomorphic data can be used to reconstruct the glaciology of the ice masses that formed the proto west antarctic ice sheet the landscape predates the present ice sheet and was formed by a small dynamic ice field s similar to those of the present day antarctic peninsula at times when the marine sections of the west antarctic ice sheet were absent the ellsworth subglacial highlands represent a major seeding center of the paleo west antarctic ice sheet and its margins represent the pinning point at which future retreat of the marine based west antarctic ice sheet would be arrested

a large deep freshwater lake beneath the ice of central east antarctica in 1974 75 an airborne radio echo survey of ice depths over central east antarctica led to the discovery of a sub ice lake of unknown depth and composition with an area of about 10 000km2 and lying beneath 4km of ice1 in 1993 altimetric data from satellite measurements2 provided independent evidence of the lake s areal extent thus confirming it to be the largest known sub ice lake by an order of magnitude here we analyse new altimetric and radio echo data along with existing seismic data3 to show that the lake is deep mean depth of 125 m or more and fresh and that it has an area that exceeds previous estimates by about 50 dimensions comparable with those of lake ontario we estimate that the residence time of the water in the lake is of the order of tens of thousands of years and that the mean age of water in the lake since deposition as surface ice is about one million years regional ice dynamics can be explained in terms of steady state ice flow along and over the lake

identification of subglacial lakes using ers 1 radar altimeter radar altimeter data from ers 1 allow detailed topographic mapping of antarctica to 82 degrees s to be carried out revealing several notable surface features among these is the large subglacial lake near vostok which is mapped here in detail the central part of the lake is found to have an exceptionally smooth surface with r m s elevation variations of less than 0 2 m a search for other large antarctic lakes in the data is made based on the smoothness and low gradient of the surface a number of other flat areas are identified with lake locations previously determined from radio echo sounding observations however radar altimeter observations show that a minimum lake size of 20 km is required for a surface above a lake to become flat numerous bowl like features can be seen in the surface topography and these may be associated with intermediate sized subglacial lakes it is determined that high spatial resolution radar altimetery could be used to identify subglacial lakes greater than 10 km in lateral extent flat regions of the ice sheet are particularly useful as they may be used as height reference surfaces to help fix the orbits of radar altimeter satellites

storms modify baroclinic energy fluxes in a seasonally stratified shelf sea inertial tidal interaction observations made near the celtic sea shelf edge are used to investigate the interaction between wind generated near inertial oscillations and the semidiurnal internal tide linear baroclinic energy fluxes within the near inertial f and semidiurnal m2 wave bands are calculated from measurements of velocity and density structure at two moorings located 40 km from the internal tidal generation zone over the 2 week deployment period the semidiurnal tide drove 28 48 w m 1 of energy directly on shelf little spring neap variability could be detected horizontal near inertial energy fluxes were an order of magnitude weaker but nonlinear interaction between the vertical shear of inertial oscillations and the vertical velocity associated with the semidiurnal internal tide led to a 25 43 increase in positive on shelf energy flux the phase relationship between f and m2 determines whether this nonlinear interaction enhances or dampens the linear tidal component of the flux and introduces a 2 day counter clockwise beating to the energy transport two very clear contrasting regimes of a tidally and b inertially driven shear and energy flux are captured in the observations

ice cover landscape setting and geological framework of lake vostok east antarctica abstract lake vostok located beneath more than 4 km of ice in the middle of east antarctica is a unique subglacial habitat and may contain microorganisms with distinct adaptations to such an extreme environment melting and freezing at the base of the ice sheet which slowly flows across the lake controls the flux of water biota and sediment particles through the lake the influx of thermal energy however is limited to contributions from below thus the geological origin of lake vostok is a critical boundary condition for the subglacial ecosystem we present the first comprehensive maps of ice surface ice thickness and subglacial topography around lake vostok the ice flow across the lake and the landscape setting are closely linked to the geological origin of lake vostok our data show that lake vostok is located along a major geological boundary magnetic and gravity data are distinct east and west of the lake as is the roughness of the subglacial topography the physiographic setting of the lake has important consequences for the ice flow and thus the melting and freezing pattern and the lake s circulation lake vostok is a tectonically controlled subglacial lake the tectonic processes provided the space for a unique habitat and recent minor tectonic activity could have the potential to introduce small but significant amounts of thermal energy into the lake

a microbial ecosystem beneath the west antarctic ice sheet liquid water has been known to occur beneath the antarctic ice sheet for more than 40 years but only recently have these subglacial aqueous environments been recognized as microbial ecosystems that may influence biogeochemical transformations on a global scale here we present the first geomicrobiological description of water and surficial sediments obtained from direct sampling of a subglacial antarctic lake subglacial lake whillans slw lies beneath approximately 800 m of ice on the lower portion of the whillans ice stream wis in west antarctica and is part of an extensive and evolving subglacial drainage network the water column of slw contained metabolically active microorganisms and was derived primarily from glacial ice melt with solute sources from lithogenic weathering and a minor seawater component heterotrophic and autotrophic production data together with small subunit ribosomal rna gene sequencing and biogeochemical data indicate that slw is a chemosynthetically driven ecosystem inhabited by a diverse assemblage of bacteria and archaea our results confirm that aquatic environments beneath the antarctic ice sheet support viable microbial ecosystems corroborating previous reports suggesting that they contain globally relevant pools of carbon and microbes that can mobilize elements from the lithosphere and influence southern ocean geochemical and biological systems

evidence for subglacial water transport in the west antarctic ice sheet through three dimensional satellite radar interferometry 1 radarsat data from the 1997 antarctic mapping mission are used interferometrically to solve for the 3 dimensional surface ice motion in the interior of the west antarctic ice sheet wais an area of 125 km2 in a tributary of the kamb ice stream slumped vertically downwards by up to 50 cm between september 26 and october 18 1997 areas in the bindschadler ice stream also exhibited comparable upward and downward surface displacements as the uplift and subsidence features correspond to sites at which the basal water apparently experiences a hydraulic potential well we suggest transient movement of pockets of subglacial water as the most likely cause for the vertical surface displacements these results and related lidar observations imply that imaging the change in ice surface elevation can help reveal the key role of water in the difficult to observe subglacial environment and its important influence on ice dynamics

rapid discharge connects antarctic subglacial lakes a hidden subglacial world consisting of more than 140 lakes lies beneath the antarctic ice sheet it is widely assumed that these lakes are a static ecosystem cut off from each other and the rest of the world far from it according to a 16 month study of surface elevation changes in the region changes indicating a rapid discharge of water from one lake to another were detected and it is possible that the entire subglacial drainage basin is flushed through periodically by massive water transfers observation of surface elevation changes over 16 months in an area of the east antarctic ice sheet overlying subglacial lakes suggests a rapid discharge of one lake to at least two other lakes involving a water volume of 1 8 km3 in conflict with previous expectations that subglacial lakes have long residence times and slow circulations the existence of many subglacial lakes1 provides clear evidence for the widespread presence of water beneath the east antarctic ice sheet but the hydrology beneath this ice mass is poorly understood2 such knowledge is critical to understanding ice flow basal water transfer to the ice margin glacial landform development and subglacial lake habitats here we present ice sheet surface elevation changes in central east antarctica that we interpret to represent rapid discharge from a subglacial lake our observations indicate that during a period of 16 months 1 8 km3 of water was transferred over 290 km to at least two other subglacial lakes while viscous deformation of the ice roof above may moderate discharge the intrinsic instability of such a system3 suggests that discharge events are a common mode of basal drainage4 if large lakes such as lake vostok or lake concordia1 are pressurizing it is possible that substantial discharges could reach the coast5 6 our observations conflict with expectations that subglacial lakes have long residence times and slow circulations2 7 8 and we suggest that entire subglacial drainage basins may be flushed periodically the rapid transfer of water between lakes would result in large scale solute and microbe relocation and drainage system contamination from in situ exploration is therefore a distinct risk

an inventory of active subglacial lakes in antarctica detected by icesat 2003 2008 through the detection of surface deformation in response to water movement recent satellite studies have demonstrated the existence of subglacial lakes in antarctica that fill and drain on timescales of months to years these studies however were confined to specific regions of the ice sheet here we present the first comprehensive study of these active lakes for the antarctic ice sheet north of 868 s based on 4 5 years 2003 08 of nasa s ice cloud and land elevation satellite icesat laser altimeter data our analysis has detected 124 lakes that were active during this period and we estimate volume changes for each lake the icesat detected lakes are prevalent in coastal antarctica and are present under most of the largest ice stream catchments lakes sometimes appear to transfer water from one to another but also often exchange water with distributed sources undetectable by icesat suggesting that the lakes may provide water to or withdraw water from the hydrologic systems that lubricate glacier flow thus these reservoirs may contribute pulses of water to produce rapid temporal changes in glacier speeds but also may withdraw water at other times to slow flow

significant groundwater contribution to antarctic ice streams hydrologic budget satellite observations have revealed active hydrologic systems beneath antarctic ice streams but sources and sinks of water within these systems are uncertain here we use numerical simulations of ice streams to estimate the generation flux and budget of water beneath five ice streams on the siple coast we estimate that 47 of the total hydrologic input 0 98 km3 yr 1 to whillans wis mercer mis and kamb kis ice streams comes from the ice sheet interior and that only 8 forms by local basal melting the remaining 45 comes from a groundwater reservoir an overlooked source in which depletion significantly exceeds recharge of the total input to bindschadler bis and macayeal macis ice streams 0 56 km3 yr 1 72 comes from the interior 19 from groundwater and 9 from local melting this contrasting hydrologic setting modulates the ice streams flow and has important implications for the search for life in subglacial lakes

salinity impact on water flow and lake ice in lake vostok antarctica 1 lake vostok isolated from direct exchange with the atmosphere for millions of years provides a unique so far inaccessible habitat by using a numerical model and recent geometry information the lake circulation was investigated for different salinites for freshwater thermally driven circulation occurs resulting from pressure dependent melting point differences at the inclined ice ceiling north to south ice pumping provides a steady supply of glacial water the weak circulation is driven by very small density contrasts but requires no unusual geothermal input for low salinity conditions however circulation intensifies occupying the entire lake the maximum amplitudes of melting freezing increase by about 50 and melting extends further south for both conditions approximately 200 m of refrozen ice accumulates beneath vostok station the lake habitat will be affected clearly by salinity it is essential to establish the specific chemistry for comprehending this unique environment and planning in situ experiments

an active subglacial water system in west antarctica mapped from space satellite laser altimeter elevation profiles from 2003 to 2006 collected over the lower parts of whillans and mercer ice streams west antarctica reveal 14 regions of temporally varying elevation which we interpret as the surface expression of subglacial water movement vertical motion and spatial extent of two of the largest regions are confirmed by satellite image differencing a major previously unknown subglacial lake near the grounding line of whillans ice stream is observed to drain 2 0 cubic kilometers of water into the ocean over 3 years while elsewhere a similar volume of water is being stored subglacially these observations reveal a wide spread dynamic subglacial water system that may exert an important control on ice flow and mass balance

tectonically controlled subglacial lakes on the flanks of the gamburtsev subglacial mountains east antarctica 1 the morphology of surface lakes strongly influences their ecology and limnology wetzel 2001 this morphology is a result of both the geologic processes that produce topographic basins and the regional climatic and local hydrologic processes that control water depth and sediment infilling carroll and bohacs 1999 although basin forming processes range from glacial scour to meteorite impacts cohen 2003 the deepest oldest surface lakes are tectonically controlled meybeck 1995 and contain diverse exotic ecosystems rossiterm and kawanabe 2000 subglacial lakes are also thought to be ancient systems that may contain exotic biota bulat et al 2004 karl et al 1999 priscu et al 1999 here we present evidence for the scale and configuration of 2 large subglacial lakes in east antarctica that together with lake vostok define a province of major lakes on the flanks of the gamburtsev subglacial mountains spatially defined in the new moderate resolution imaging spectroradiometer modis imagery of antarctica t scambos et al a modis based mosaic of antarctica moa submitted to remote sensing of environment 2005 hereinafter referred to as scambos et al submitted manuscript 2005 these lakes are aligned parallel to lake vostok other data shows that they are distinguished by distinct gravity lows flat ice surface slopes and have estimated water depths of at least 900 m surface elevation data indicates that large deep subglacial lakes have a profound influence on the regional ice sheet topography and probably ice sheet flow these deep subglacial lakes with elongate rectilinear morphology are tectonically controlled features unlike the shallow lakes in west antarctica and beneath dome concordia these deep subglacial lakes remained stable environments through many glacial cycles since their origin 10 35 ma enabling the development of novel ecosystems

solute sources and geochemical processes in subglacial lake whillans west antarctica national science foundation nsf grants opp 0838933 1346250 and 1439774 italian national antarctic program barbante graduate fellowships from the nsf integrative graduate education and research traineeship program 0654336 and nsf center for dark energy biosphere investigations dissertation grant from the american association of university women

energy of nonlinear internal waves in the south china sea 1 four sets of adcp measurements were taken in the south china sea scs these results were combined with previous satellite observations and internal tide numerical model results analysis suggests that strong internal tides are generated in luzon strait propagate as a narrow tidal beam into the scs are amplified by the shoaling continental slope near tungsha island become nonlinear and evolve into high frequency nonlinear internal waves niw internal waves in the scs have geographically distinct characteristics 1 west of luzon strait the total internal wave energy eiw is 10 that predicted by garrett munk spectra egm levine 2002 there is no sign of niw 2 near tungsha island eiw 13 egm strong nonlinear and high harmonic tides are present repetitive trains of large amplitude niw appear primarily at a semidiurnal periodicity with their amplitudes modulated at a fortnightly tidal cycle the rms vertical velocity of niw shows a clear spring neap tidal cycle and is linearly proportional to the barotropic tidal height in luzon strait with a 1 85 day time lag consistent with the travel time of internal tides from luzon strait to tungsha island 3 at the northern scs shelfbreak eiw 4 egm single depression waves are found but no multiple waves packets are evident 4 on the continental shelf eiw 2 egm both depression and elevation niw exist

recent advances in understanding antarctic subglacial lakes and hydrology it is now well documented that over 400 subglacial lakes exist across the bed of the antarctic ice sheet they comprise a variety of sizes and volumes from the approx 250 km long lake vostok to bodies of water less than 1 km in length relate to a number of discrete topographic settings from those contained within valleys to lakes that reside in broad flat terrain and exhibit a range of dynamic behaviours from active lakes that periodically outburst some or all of their water to those isolated hydrologically for millions of years here we critique recent advances in our understanding of subglacial lakes in particular since the last inventory in 2012 we show that within 3 years our knowledge of the hydrological processes at the ice sheet base has advanced considerably we describe evidence for further active subglacial lakes based on satellite observation of ice surface changes and discuss why detection of many active lakes is not resolved in traditional radio echo sounding methods we go on to review evidence for large scale subglacial water flow in antarctica including the discovery of ancient channels developed by former hydrological processes we end by predicting areas where future discoveries may be possible including the detection measurement and significance of groundwater i e water held beneath the ice bed interface

an extensive subglacial lake and canyon system in princess elizabeth land east antarctica the subglacial landscape of princess elizabeth land pel in east antarctica is poorly known due to a paucity of ice thickness measurements this is problematic given its importance for understanding ice sheet dynamics and landscape and climate evolution to address this issue we describe the topography beneath the ice sheet by assuming that ice surface expressions in satellite imagery relate to large scale subglacial features we find evidence that a large previously undiscovered subglacial drainage network is hidden beneath the ice sheet in pel we interpret a discrete feature that is 140 20 km in plan form and multiple narrow sinuous features that extend over a distance of 1100 km we hypothesize that these are tectonically controlled and relate to a large subglacial basin containing a deep water lake in the interior of pel linked to a series of long deep canyons the presence of 1 km deep canyons is confirmed at a few localities by radio echo sounding data and drainage analysis suggests that these canyons will direct subglacial meltwater to the coast between the vestfold hills and the west ice shelf

airborne radar survey above vostok region east central antarctica ice thickness and lake vostok geometry during the 1999 2000 italian expedition an airborne radar survey was performed along 12 transects across lake vostok antarctica and its western and eastern margins ice thickness subglacial elevation and the precise location of lake boundaries were determined radar data confirm the geometry derived from previous surveys but with some slight differences we measured a length of up to 260 km a maximum width of 81 km and an area of roughly 14 000 km 2 along the major axis from north to south the ice thickness varies from 3800 to 4250 m with a decreasing gradient from west to east the ice thickness is fairly constant except for two narrow strips located on the western and eastern margins where it increases with high thickening rate over the lake the surface elevation increases from 3476 m a s l south to 3525 north with a decreasing gradient while the lake surface elevation decreases from 315 to 750 m a s l with a decreasing gradient absolute value the ice surface and lake ceiling slopes suggest that the lake is in a state of hydrostatic equilibrium

application of a three dimensional numerical model to lake vostok an antarctic subglacial lake the circulation in two water column thickness scenarios for lake vostok a subglacial lake in central east antarctica is investigated using a three dimensional numerical model in a scenario with a constant water column thickness the distance between the sloping ice sheet which caps the lake and the lake bed the circulation is barotropic but with a more realistic water column thickness the flow is baroclinic the different circulations result from the geothermal heat flux warming shallow regions of the realistic lake more efficiently thus forming a different horizontal density structure the differences and uncertainties between the two scenarios highlight the importance that the largely unknown water column thickness and geothermal heat flux have in determining the circulation in the lake

subglacial lake ellsworth a candidate for in situ exploration in west antarctica radio echo sounding reveals a 10 km long lake beneath 3 4 km of ice near the ellsworth mountains in west antarctica 20 km from the ice divide subglacial lake ellsworth is located within a distinct topographic hollow which is 1 5 km deeper than the surrounding bed judging by bed slopes flanking the lake the water depth is at least 10s of metres calculations of basal temperature reveal the ice base to be warm both now and during full glacial periods as the environments of subglacial lakes are broadly similar life may be expected in lake ellsworth as in any other given this its physical characteristics and the fact that the west antarctic ice sheet has been accessed on several occasions lake ellsworth is an excellent candidate for in situ examination

an assessment of deep hot water drilling as a means to undertake direct measurement and sampling of antarctic subglacial lakes experience and lessons learned from the lake ellsworth field season 2012 13 in the early hours of 25 december 2012 an attempt to explore subglacial lake ellsworth west antarctica using a specially designed hot water drill was halted this uk project involving several universities the british antarctic survey and the national oceanography centre had been in planning for 10 years the project developed a full blueprint for subglacial lakes research involving access to the subglacial environment through deep drilling direct measurement and sampling of water and sediment by the construction of a probe and sediment corer and environmental protocols to ensurecleanliness in line with international agreements on stewardship and protection of subglacial systems drilling was ceased after the main borehole failed to link with a subsurface cavity of water built up over 40 hours without this link insufficient water was available to continue drilling downwards to the lake 3000m beneath the surface on return to the uk an external review of the programme was undertaken to formally assess the reasons for the fieldwork failure and to make recommendations on the modifications necessary for success from this review the lake ellsworth programme formulated a pathway along which a second attempt to explore the lake can be developed here details of the lake ellsworth field experiment the circumstances that led to its failure and the corrections required are presented hot water drilling is still regarded as the only feasible scheme for assuring clean access to the subglacial environment the lessons learned from the lake ellsworth experience are substantial however and demonstrate that considerable technological and methodological advances are necessary for successful future research on subglacial lakes beneath thick 2 km ice

a connection between the neoproterozoic dom feliciano brazil uruguay and gariep namibia south africa orogenic belts evidence from a reconnaissance provenance study abstract a provenance study of neoproterozoic siliciclastic successions in the stratigraphically and tectonically lowermost and uppermost parts of the pan african gariep belt stinkfontein subgroup and oranjemund group respectively in southwestern africa as well as in the rocha group of the punta del este terrane dom feliciano belt in uruguay revealed that the oranjemund and rocha groups can be correlated and most likely formed in the same basin thus the rocha group is considered to represent the fill of the westernmost part of a re activated ediacaran gariep basin the lower parts of the oranjemund and rocha groups reflect erosion of mafic rocks whereas the upper parts are derived from a predominantly felsic source area first major and trace element geochemical data are consistent with oceanic islands of within plate geochemistry in the immediate vicinity as the most likely source of the mafic input into the lower part of the oranjemund group whereas a combination of continental margin and island arc is indicated as source for the bulk of the younger sediments in the upper oranjemund group age spectra obtained by shrimp u pb analyses of detrital zircon grains from the stinkfontein subgroup port nolloth group the oranjemund group and the rocha group are very similar except for a lack of the youngest age group around 600 ma in the stinkfontein subgroup in all three units zircon grains of 1000 1200 ma dominate with a further peak in the age distribution between 1700 and 2000 ma these ages compare well with the pre gariep basement geology in southwestern africa where the former age range corresponds to magmatic and high grade metamorphic activity in the mesoproterozoic namaqua natal belt and the latter to an extensive palaeoproterozoic andean type volcanic arc richtersveld terrane comparable ages are conspicuously absent in the basement of the rio de la plata craton in south america derivation of the rocha group sediments from a similar source as the contemporaneous oranjemund group sediments is therefore suggested the most likely source of the youngest detrital zircon grains in these two stratigraphic units is the 640 590 ma magmatic arc of the dom feliciano belt this interpretation explains the continental island arc component in the sediment provenance and takes into account the absence of comparable magmatism in the gariep belt two stages of basin evolution are distinguished for the gariep basin an early failed continental rift that subsequently became re activated as back arc basin related to the cryogenian dom feliciano arc consequently the gariep basin does not represent the main suture between the rio de la plata and the kalahari cratons this suture is now suspected to be west of the dom feliciano volcanic arc and might be connected with the sierra ballena major gercino lineament