twenty first century warming of a large antarctic ice shelf cavity by a redirected coastal current the redirection of warm water under the filchner ronne ice shelf during the second half of this century could cause the ice shelf base to melt at a rate 20 times higher than at present warm ocean currents are known to erode ice shelves from below but changes in currents can be forced by many different mechanisms leading to uncertain outcomes this study highlights the vulnerability to climate change of a small antarctic coastal region which has potentially severe consequences for the mass balance of a large antarctic ice shelf hellmer et al use climate modelling to show that the projected loss of sea ice in the weddell sea east of the antarctic peninsula leads to an increase in wind stress which in turn accelerates a warm ocean current far underneath the vast filchner ronne ice shelf the authors predict that the increased warmth could increase melt by a factor of 20 with possible consequences for ice stream dynamics in the east antarctic ice sheet the antarctic ice sheet loses mass at its fringes bordering the southern ocean at this boundary warm circumpolar water can override the continental slope front reaching the grounding line1 2 through submarine glacial troughs and causing high rates of melting at the deep ice shelf bases3 4 the interplay between ocean currents and continental bathymetry is therefore likely to influence future rates of ice mass loss here we show that a redirection of the coastal current into the filchner trough and underneath the filchner ronne ice shelf during the second half of the twenty first century would lead to increased movement of warm waters into the deep southern ice shelf cavity water temperatures in the cavity would increase by more than 2 degrees celsius and boost average basal melting from 0 2 metres or 82 billion tonnes per year to almost 4 metres or 1 600 billion tonnes per year our results which are based on the output of a coupled ice ocean model forced by a range of atmospheric outputs from the hadcm35 climate model suggest that the changes would be caused primarily by an increase in ocean surface stress in the southeastern weddell sea due to thinning of the formerly consolidated sea ice cover the projected ice loss at the base of the filchner ronne ice shelf represents 80 per cent of the present antarctic surface mass balance6 thus the quantification of basal mass loss under changing climate conditions is important for projections regarding the dynamics of antarctic ice streams and ice shelves and global sea level rise

do swarms of migrating barchan dunes record paleoenvironmental changes a case study spanning the middle to late holocene in the pampa de jaguay southern peru swarms of barchan dunes are common in arid environments unlike immobile or slowly moving dunes whose stratigraphy can be used to reconstruct paleoenvironmental changes the high migration rate of barchans seems to prohibit their use as geoarchives in this paper a possible use of barchan swarms for paleoenvironmental reconstructions is presented the approach is based on dune migration in a case study based on 500 dunes in the pampa de jaguay aeolian transport corridor in coastal southern peru middle to late holocene changes in the supply of aeolian material are inferred from calculating the time of dune initiation at the coastline limitations posed by the assumptions underlying this approach are discussed

dating methods and geomorphic evidence of palaeoenvironmental changes at the eastern margin of the south peruvian coastal desert 14 30 s before and during the little ice age abstract the atacama desert is known to be one of the driest places on earth however in the study area between ica and nasca south peru 75 76 w 14 15 s palaeoclimate proxies show several semi arid phases during the holocene a more humid period during the early holocene favoured an open grass land which allowed the accumulation of desert loess eitel b hecht s machtle b schukraft g kadereit a wagner g kromer b unkel i reindel m 2005 geoarchaeological evidence from desert loess in the nazca palpa region southern peru palaeoenvironmental changes and their impact on pre columbian cultures archaeometry 47 137 158 the paracas and nasca cultures existing in that region between the 9th century bc and 7th century ad had propitious conditions to evolve and to settle close to the rivers fed by the monsoonal precipitation in the cordillera occidental culminating aridity after 600 ad might have caused the collapse of the nasca civilization the onset of semi arid climate towards the end of the late intermediate period 14th century ad allowed a reoccupation of the area here we present 14c and osl data from sediments of river terraces a debris flow and loess snails scutalus sp indicating appreciable geomorphic activity between 1390 and 1714 cal ad this phase is isochronous to the little ice age period on the northern hemisphere and to an increase in the ice accumulation on the quelccaya glacier in the peruvian altiplano thompson l g mosley thompson e bolzan j f koci b r 1985 a 1500 year record of tropical precipitation in ice cores from the quelccaya ice cap peru science 229 971 973

antarctic thermocline dynamics along a narrow shelf with easterly winds abstractdetermining the role of southern ocean warm intermediate water for driving melting of the antarctic ice sheet is a major challenge in assessing future sea level rise analysis of 2859 ctd p

amundsen sea ice production and transport 1 drift and variability of sea ice in the amundsen sea are investigated with ice buoys deployed in march 2000 and a coupled ice ocean model the bremerhaven regional ice ocean simulations brios model results are compared with in situ ocean atmosphere and sea ice measurements satellite observations and 8 19 months of buoy drift data we identify a zone of coastal westward drift and a band of faster eastward drift separated by a broad transition region characterized by variable ice motions the model represents drift events at scales approaching its resolution but is limited at smaller scales and by deficiencies in the national centers for environmental prediction forcing two thirds of the modeled ice production in the southern amundsen moves westward near the coast its transport modulated by meridional wind strength damping sea ice formation in the eastern ross sea half of the ice exported from the ross moves eastward into the northern amundsen sea a net sea ice sink that also receives more than one third of the ice generated to its south a low rate of exchange occurs with the bellingshausen sea which must have a more independent ice regime snow ice formation resulting from high precipitation accounts for one quarter of the ice volume in the amundsen sea aiding the formation of thick ice in a region with generally divergent ice drift freshwater extraction by sea ice formation is roughly balanced by precipitation and ice shelf melting but a positive trend in the surface flux is consistent with an amundsen source for reported freshening in the ross sea

fragile landscapes fragile civilizations how climate determined societies in the pre columbian south peruvian andes abstract this paper presents alternating periods of geo ecological fragility and stability in a highly sensitive environmental setting the desert margin area of southern peru 14 5 s there we have to state that fragility was dominantly triggered by climatic changes which induced several oscillations of the desert margin during the mid holocene the study area received the holocene maximum of precipitation soil formation occurred and the desert retreated as loess paleosoil formation documents in contrast the titicaca region further south east experienced extreme drought at that time this regional antagonism between humid and dry conditions was a result of meridional shifts in moisture transport across the andes and occurred also during pre columbian times considering a coincidence between environmental and cultural changes we state that success and decline of civilizations were dominated by hydrological oscillations triggering fertility as well as a critical loss of natural resources fragile periods i e periods of geomorphological activity occurred contemporaneous with cultural transitions in response to spatial changing resources cultural foci were shifted so the success of pre columbian civilizations was closely coupled to areas of geo ecological favorability which were directly controlled by distinct regional impacts of large scale circulation mechanisms including el nino southern oscillation enso this spatial view on non uniform environmental and cultural changes has not been thoroughly considered before therefore for the first time this paper offers geomorphological evidence for diachronous andean agri cultural development which was geographically determined

detailed seismic bathymetry beneath ekstrom ice shelf antarctica implications for glacial history and ice ocean interaction the shape of ice shelf cavities are a major source of uncertainty in understanding ice ocean interactions this limits assessments of the response of the antarctic ice sheets to climate change her

on the structure and the transport of the eastern weddell gyre abstract the circulation pattern and volume transports in the eastern weddell gyre are estimated on the basis of hydrographic data collected by r v polarstern between 1989 and 1996 in the northeastern edge of the weddell gyre eastward flowing water masses from the antarctic circumpolar current and the weddell sea converge due to the strong effect of topographic constraints on ocean currents in the weakly stratified waters of high latitudes the wedge like structure of the southwest indian ridge can cause the convergence the increased shear leads to instabilities of the current at the eastern end of the ridge which produce an intense mesoscale eddy field between 15 and 30 e in the eddies water from the weddell cold regime and the antarctic circumpolar current waters mix and form the water masses of the weddell warm regime these waters are advected southward and flow towards the westward southern rim current which is driven by the antarctic eastwind band hence there is not a continous flow from the northern to the southern rim but a decay of the mean flow in the northeast and a reformation in the south volume transports across the greenwich meridian estimated on the basis of a combined ctd adcp data set result in an eastward flow of 61 sv in the northern rim current and a westward return flow of 66 sv in the southern part of the gyre the transport is about twice as high as previous estimates between kapp norvegia and the northern tip of the antarctic pensinsula indicating a significant gyre circulation north of 70 s

eddy overturning of the antarctic slope front controls glacial melting in the eastern weddell sea 1 the eastern weddell sea is characterized by narrow continental shelves and warm deep water wdw is located in close proximity to the ice shelves in this region the exchange of wdw across the antarctic slope front asf determines the rate of basal ice shelf melting here we present a unique data set consisting of 2351 vertical profiles of temperature and salinity collected by southern elephant seals mirounga leonina and a profile beneath the fimbul ice shelf fis obtained via drilling through 395 m of ice this data set reveals variations in salinity and temperature through winter and using a conceptual model of the coastal salt budget we quantify the main exchange processes our data show that modified wdw with temperatures below 1 5 c is advected onto the shelf and into the ice shelf cavities by an eddy overturning of the asf the onshore ekman flux of surface waters during summer is the main source of freshwater that leads to the formation of low salinity shelf waters in the region the modified wdw that reaches beneath the ice shelves is too cold for basal ice shelf melting to create such low salinity water a high resolution model of an idealized asf continental shelf ice shelf system supports the conclusions from the data analysis the inflow of wdw onto the continental shelf and into the ice shelf cavity occurs within a bottom boundary layer where the eddy advection in the model is particularly strong in close agreement with the observed vertical profile of temperature beneath the fis citation nost o a m biuw v tverberg c lydersen t hattermann q zhou l h smedsrud and k m kovacs 2011 eddy overturning of the antarctic slope front controls glacial melting in the eastern weddell sea j geophys res 116 c11014 doi 10 1029 2011jc006965

millennial scale vulnerability of the antarctic ice sheet to regional ice shelf collapse author s martin df cornford sl payne aj abstract 2019 american geophysical union all rights reserved the antarctic ice sheet ais remains the largest uncertainty in projections of future sea level rise a likely climate driven vulnerability of the ais is thinning of floating ice shelves resulting from surface melt driven hydrofracture or incursion of relatively warm water into subshelf ocean cavities the resulting melting weakening and potential ice shelf collapse reduces shelf buttressing effects upstream ice flow accelerates causing thinning grounding line retreat and potential ice sheet collapse while high resolution projections have been performed for localized antarctic regions full continent simulations have typically been limited to low resolution models here we quantify the vulnerability of the entire present day ais to regional ice shelf collapse on millennial timescales treating relevant ice flow dynamics at the necessary 1 km resolution collapse of any of the ice shelves dynamically connected to the west antarctic ice sheet wais is sufficient to trigger ice sheet collapse in marine grounded portions of the wais vulnerability elsewhere appears limited to localized responses

impact of antarctic ice shelf basal melting on sea ice and deep ocean properties 1 an approximation of antarctica s rocky and icy coastline normally forms the southern boundary in global climate models such a configuration neglects extensive ice shelf areas where ocean ice interaction initiates a net freshwater flux to the circumpolar continental shelf equal to 75 of the annual mean net precipitation in coastal seas the results of a numerical model for the southern ocean using two contrasting configurations with and without caverns beneath major antarctic ice shelves are compared they show that the freshwater flux due to deep basal melting significantly stabilizes the shelf water column in front of an ice shelf as well as downstream due to advection by the coastal current if the freshwater from the caverns is absent sea ice is thinner shelf waters are warmer and saltier and the southern ocean deep basins are flushed by denser waters

seasonal outflow of ice shelf water across the front of the filchner ice shelf weddell sea antarctica the ice shelf water isw found in the filchner trough located in the southern weddell sea antarctica is climatically important it descends into the deep weddell sea contributing to bottom water formation and it blocks warm off shelf waters from accessing the filchner ice shelf cavity yet the circulation of isw within the filchner trough and the processes determining its exchange across the ice shelf front are to a large degree unknown here mooring records from the ice shelf front are presented the longest of which is 4 years long they show that the coldest 2 3 c isw which originates from the ronne trough in the west exits the cavity across the western part of the ice shelf front during late austral summer and early autumn the supercooled isw escaping the cavity flows northward with a velocity of about 0 03 m s during the rest of the year there is no outflow at the western site the current is directed eastward parallel to the ice shelf front and the temperatures at the mooring site are slightly higher 2 0 c the eastern records show a more persistent outflow of isw

limited retreat of the wilkes basin ice sheet during the last interglacial the response of the east antarctic ice sheet to global warming represents a major source of uncertainty in sea level projections thinning of the east antarctic george v and sabrina coast ice cover is currently taking place and regional ice sheet instability episodes might have been triggered in past warm climates however the magnitude of ice retreat in the past can not yet be quantitatively derived from paleo proxy records alone we propose that a runaway retreat of the george v coast grounding line and subsequent instability of the wilkes basin ice sheet would either leave a clear imprint on the water isotope composition in the talos dome region or prohibit a talos dome ice core record from the last interglacial altogether testing this hypothesis our ice sheet model simulations suggest that wilkes basin ice sheet retreat remained relatively limited during the last interglacial and provide a constraint on last interglacial east antarctic grounding line stability

how iceberg calving and grounding change the circulation and hydrography in the filchner ice shelf ocean system the formation of bottom water in the southern weddell sea is strongly influenced by the flow of ice shelf water isw out of the filchner ronne ice shelf cavity the breakout of three giant icebergs in 1986 and their grounding on the shallow berkner bank modified the circulation and water mass formation in the filchner trough and the adjacent sea areas hydrographic measurements along the filchner ice shelf front carried out with rv polarstern in 1995 show significant changes in the water mass characteristics and flow patterns in the filchner trough in comparison to measurements from the early 1980s changes in the trough will affect the flow over the sill to the deep weddell abyssal plain we combine a three dimensional ocean circulation model with conductivity temperature depth and stable isotope measurements to investigate the details of the circulation in front of and beneath the filchner ice shelf we assess the impact of stranded icebergs and a more southerly ice shelf front position caused by a 1986 iceberg calving event on the circulation and observed water mass properties results indicate variations of the flow pattern in the filchner trough and on berkner bank where high salinity shelf water the feedstock for isw is produced the calving and grounding impacts illustrate the sensitivity of the ice shelf ocean system to perturbations in local bathymetric settings

propagation and vertical structure of the tidal flow in nares strait the southward freshwater flux through nares strait is an important component of the arctic s freshwater budget on short time scales flow through the strait is dominated by the tides and tidal dynamics may be important for the magnitude of the freshwater flux over longer periods here we build upon our existing knowledge of the tides in the region by exploring their propagation and vertical structure using data from four bottom mounted acoustic doppler current profilers deployed in nares strait between 2003 and 2006 we observe that propagating barotropic semidiurnal tidal waves interact to create a standing wave pattern explaining the abnormally large tidal amplitudes that are observed in this region in the along strait direction semidiurnal tidal currents exhibit strong variations with depth in contrast the diurnal tides propagate northward through the strait as progressive waves and the tidal currents are broadly depth invariant proximity of nares strait to the semidiurnal critical latitude and the topographical restriction imposed by the steep side wall of ellesmere island are primary drivers behind the observed vertical variability in the upper part of the water column baroclinic activity increases the tidal current amplitude by up to 25 in the across strait direction a two layer structure exists in both the diurnal and semidiurnal tidal flow with a phase lag of approximately a quarter of a tidal cycle across the strait for the semidiurnal tide our results suggest that strong vertical motion exists against the side walls of nares strait as the across strait flow interacts with the steeply sloping bathymetry

a numerical model of the weddell sea large scale circulation and water mass distribution a circumpolar model for regional studies of the wind driven and thermohaline circulation of the southern ocean including the major sub ice shelf areas is described a first series of numerical experiments focusing on the weddell sea reveals a pronounced and persistent double cell structure of the weddell gyre with a maximum transport of 60 sv in agreement with observations experiments with artificial passive tracers point to the shallow shelf areas off the filchner ronne ice shelf as main locations for bottom water production the trajectories of lagrangian floats are used to determine the pathways and timescales of water mass spreading in the model in addition the effect of sub ice shelf forcing on the water mass characteristics is evaluated it is shown that water modified in the sub ice cavities contributes significantly to the deep and bottom water formation along the continental slope and affects the water mass characteristics throughout the weddell sea by increasing the stability of the near surface stratification and preventing deep convection

wind driven spreading of fresh surface water beneath ice shelves in the eastern weddell sea solar heated fresh antarctic surface water asw is a permanent feature along the eastern weddell sea ews coast in summer down to a depth of roughly 200 m recently asw has been observed beneath the fimbul ice shelf suggesting that it might play an important role in basal melting we propose that wind driven coastal downwelling is the main mechanism that spreads asw beneath the ice shelf in this sector of antarctica we validate this hypothesis with observations scaling analyses and numerical modeling along three principle lines i data analyses of about 1500 salinity profiles collected by instrumented seals indicate that the observed freshening of the coastal water column is likely explained by the on shore ekman transport and subsequent downwelling of asw ii an analytical model of the coastal momentum balance indicates that wind driven downwelling is capable of depressing the buoyant surface water to a depth similar to the ice shelf draft and iii simulations from both idealized and regional eddy resolving numerical ice shelf ocean models support our proposition our main conclusion is that wind driven spreading of asw beneath the ice shelf occurs when downwelling exceeds the depth of the ice shelf base furthermore our study adds to the understanding of the oceanic processes at the antarctic slope front in the ews with possible implications for other sectors of antarctica

circum antarctic shoreward heat transport derived from an eddy and tide resolving simulation almost all heat reaching the bases of antarctica s ice shelves originates from warm circumpolar deep water in the open southern ocean this study quantifies the roles of mean and transient flows in transporting heat across almost the entire antarctic continental slope and shelf using an ocean sea ice model run at eddy and tide resolving 1 48 horizontal resolution heat transfer by transient flows is approximately attributed to eddies and tides via a decomposition into time scales shorter than and longer than 1 day respectively it is shown that eddies transfer heat across the continental slope ocean depths greater than 1 500 m but tides produce a stronger shoreward heat flux across the shelf break ocean depths between 500 m and 1 000 m however the tidal heat fluxes are approximately compensated by mean flows leaving the eddy heat flux to balance the net shoreward heat transport the eddy driven cross slope overturning circulation is too weak to account for the eddy heat flux this suggests that isopycnal eddy stirring is the principal mechanism of shoreward heat transport around antarctica though likely modulated by tides and surface forcing

oceanographic conditions south of berkner island beneath filchner ronne ice shelf antarctica we have made oceanographic measurements at two sites beneath the southern filchner ronne ice shelf hot water drilled access holes were made during january 1999 allowing conductivity temperature depth ctd profiling and the deployment of instrument moorings the ctd profiles show that the entire water column is below the surface freezing point we estimate the summer flux of water between the two sites to be 2 106 m3 s 1 the summer potential temperature salinity properties of the water column suggest that this flow is part of a recirculation in the deepest part of the subice shelf cavity and the filchner depression the recirculation is driven by a combination of the melting of deep basal ice and the freezing that results from the depressurization of the cold buoyant water as it ascends the ice shelf base the source of the water was high salinity shelf water hssw produced in the ronne depression this is the water that provides the external heat necessary for the strong melting at the deep grounding lines in the vicinity of foundation ice stream instruments moored at the drill sites show that during the winter hssw formed on the berkner shelf flows beneath the ice shelf and largely displaces the recirculating water from the two sites this provides an externally driven through flow that is warmer nearer the surface freezing point and slower than the internal recirculation and which is low enough in density to escape the filchner depression

modeling giant iceberg drift under the influence of sea ice in the weddell sea antarctica the drift trajectory of giant iceberg c 7 traversing the weddell sea antarctica for 2 years was successfully simulated application of the classical driving forces like wind and ocean currents resulted in a significant discrepancy between modeled and observed iceberg velocities in the western weddell sea the most realistic drift pattern in space and time was achieved by adding a sea ice force which represents the ability of a dense sea ice cover 90 to lock in icebergs and collect the momentum of the wind over an area much larger than the area of the iceberg proper this process was parameterized using a sea ice strength p which depends on sea ice concentration and thickness both having highest values in winter and in the western weddell sea which is covered with multi year sea ice as a consequence of the sensitivity to sea ice the timing of the iceberg drift becomes important revealing the region off brunt ice shelf eastern weddell sea as a location where bergs either continue westward with the coastal current or follow a southern branch onto the shallow continental shelf

age determination of petra s engineered landscape optically stimulated luminescence osl and radiocarbon ages of runoff terrace systems in the eastern highlands of jordan abstract the unfavourable mountainous environment of the petra region in southern jordan was modified by ancient engineers to supply the nabataean roman city of petra with food and water the area was reclaimed by installing extended runoff terrace systems and hydraulic structures the agricultural terrace systems have so far been dated based on surface pottery and the chronology of the systems is under debate in this study optically stimulated luminescence osl and radiocarbon dating techniques were successfully applied to date these terrace systems samples were taken from the fills of agricultural terraces and underneath their walls to determine the chronology of the construction use and abandonment of the agricultural terraces the results suggest that runoff farming in the petra region started around the beginning of the common era and construction use and maintenance lasted at least until 800 ad

the role of tides in ocean ice shelf interactions in the southwestern weddell sea near observed weddell sea gyre continental shelf cavity water masses in interactive ocean sea ice tide ice shelf melt simulations tides amplify basal melt refreeze pattern raising net melt by 50 associated with enhanced time varying kinetic energy at the ice base impacts of additional meltwater production on weddell continental shelf sea ice and newly formed bottom water properties are suggested corresponding author u hausmann uhausc at gmail dot com this article has been accepted for publication and undergone full peer review but has not been through the copyediting typesetting pagination and proofreading process which may lead to differences between this version and the version of record please cite this article as

irrigation agriculture and the sedimentary record in the palpa valley southern peru abstract irrigation agriculture is an ancient and widespread feature in regions where allogenic rivers flow through arid landscapes this paper reports the results of sedimentological pedological investigations in the palpa valley in the coastal desert of southern peru where sediment laden river water is used for irrigation an adapted facies classification is used to deduce a generalised stratigraphical sequence of the valley bottom sediments chronological constraints from radiocarbon dating and archaeological finds are used to reconstruct sedimentation rates for fossil to recent irragric anthrosols actualistic case studies are used to quantify present day irrigation sedimentation the investigations result in a clarification of the sedimentological and geomorphic history of this valley and a quantification of irrigation related sedimentation irragric anthrosols date back more than 3500 years and provide direct evidence for the beginning of irrigation agriculture in this region it is concluded that i the up to approximately 4 m thick fine grained sediments in the palpa valley bottom totaling a volume of 21 4 mio m3 are a result of long lasting human impact and have to be considered as artefacts of prehistoric and historic irrigation agriculture in the hyperarid coastal desert ii the fine grained sediments represent a geoarchive which holds information on the history of irrigation agriculture as well as information on possible natural disturbance by extreme fluvial events iii the identification of irragric anthrosols has implications for archaeological and paleoenvironmental reconstructions

eddy mediated transport of warm circumpolar deep water across the antarctic shelf break the antarctic slope front asf modulates ventilation of the abyssal ocean via the export of dense antarctic bottom water aabw and constrains shoreward transport of warm circumpolar deep water cdw toward marine terminating glaciers along certain stretches of the continental shelf particularly where aabw is exported density surfaces connect the shelf waters to the middepth circumpolar deep water offshore offering a pathway for mesoscale eddies to transport cdw directly onto the continental shelf using an eddy resolving process model of the asf the authors show that mesoscale eddies can supply a dynamically significant transport of heat and mass across the continental shelf break the shoreward transport of surface waters is purely wind driven while the shoreward cdw transport is entirely due to mesoscale eddy transfer the cdw flux is sensitive to all aspects of the model s surface forcing and geometry suggesting that shoreward eddy heat transport may be localized to favorable sections of the continental slope

multidecadal warming of antarctic waters decadal trends in the properties of seawater adjacent to antarctica are poorly known and the mechanisms responsible for such changes are uncertain antarctic ice sheet mass loss is largely driven by ice shelf basal melt which is influenced by ocean ice interactions and has been correlated with antarctic continental shelf bottom water asbw temperature we document the spatial distribution of long term large scale trends in temperature salinity and core depth over the antarctic continental shelf and slope warming at the seabed in the bellingshausen and amundsen seas is linked to increased heat content and to a shoaling of the mid depth temperature maximum over the continental slope allowing warmer saltier water greater access to the shelf in recent years regions of asbw warming are those exhibiting increased ice shelf melt

wintertime ocean conditions over the southern weddell sea continental shelf antarctica 1 during the austral winter of 2007 a weddell seal tagged with a miniaturized conductivity temperature depth ctd instrument travelled over the central southern weddell sea continental shelf the instrument yielded 750 ctd profiles 250 of them to the sea floor the data show a full depth flow of water onto the shelf via a sill at the shelf break 74 s 44 w the warmth from the core of the flow was able to maintain the surface mixed layer above the freezing point resulting in a band of reduced ice production an estimate of the on shelf flux suggests that this flow accounts for most of the estimated 3 sv of water draining from the southern weddell sea continental shelf

seasonal cycle of hydrography on the eastern shelf of the filchner trough weddell sea antarctica new two year long records from three moorings located at 76 s along the eastern flank and shelf of the filchner trough give insight in the seasonal cycle of hydrography to a region where modified warm deep water mwdw enters the southern weddell sea continental shelf possibly reaching the filchner ronne ice shelf the biggest ice shelf by volume in antarctica a persistent northward flow of ice shelf water isw is found along the slope of the trough at 600 m depth while the data on the shelf indicate a seasonal cycle characterized by four phases a distinct warm inflow period separated in two phases with maximum temperatures of 1 c appears to be related to the seasonal heaving of the antarctic slope front thermocline along the continental shelf break further north and a seasonal extension of the isw layer onto the eastern shelf the density gradients between the isw in the trough and the mwdw on the adjacent shelf drive the southward flow during these phases a flow reversal is found in winter ceasing the southward flow along the eastern flank of the trough weaker density gradients between the trough and the shelf during winter allow a westward flow partly driven by a n s density gradient existing across the eastern shelf during this time from spring through to summer the isw layer in the trough extends onto the eastern shelf where it occupies the bottom layer at our moorings and it is associated with northward flow

foraging behaviour of weddell seals leptonychotes weddellii in connection to oceanographic conditions in the southern weddell sea the region of the filchner outflow system fos in the southeastern weddell sea is characterized by intensive and complex interactions of different water masses dense ice shelf water isw emerging from beneath the ice shelf cavities on the continental shelf meets modified warm deep water mwdw originating from the antarctic circumpolar current at the sill of the filchner trough these hydrographic features convert the fos into an oceanographic key region which may also show enhanced biological productivity and corresponding aggregations of marine top predators in this context six adult weddell seals leptonychotes weddellii were instrumented with ctd combined satellite relay data loggers in austral summer 2014 by means of these long term data loggers we aimed at investigating the influence of environmental conditions on the seals foraging behaviour throughout seasons focussing on the local oceanographic features weddell seals performed pelagic and demersal dives mainly on the continental shelf where they presumably exploited the abundant bentho pelagic fish fauna diurnal and seasonal variations in light availability affected foraging activities mwdw was associated with increased foraging effort however we observed differences in movements and habitat use between two different groups of weddell seals seals tagged in the pack ice of the fos focussed their foraging activities to the western and partly eastern flank of the filchner trough which coincides with inflow pathways of mwdw in contrast weddell seals tagged on the coastal fast ice exhibited typical central place foraging and utilized resources close to their colony high foraging effort in mwdw and high utilization of areas associated with an inflow of mwdw raise questions on the underlying biological features this emphasizes the importance of further interdisciplinary ecological investigations in the near future as the fos may soon be impacted by predicted climatic changes

on the effect of topography and wind on warm water inflow an idealized study of the southern weddell sea continental shelf system an idealized eddy resolving numerical model with topographic features common to the southern weddell sea is constructed to study mechanisms through which warm deep water enters a wide continental shelf with a trough the open ocean represented by a 1700 m deep channel is connected to a 400 m deep shelf with a continental slope the shelf is narrow 50 km in the east but widens to 300 km at the center of the model domain over the narrow shelf the slope front is balanced by wind driven ekman downwelling and counteracting eddy overturning favoring on shelf transport of warm water in summer scenarios when fresher surface water is present over the wide shelf the ekman downwelling ceases and the mesoscale eddies relax the front inflow of warm water is sensitive to along shelf salinity gradients and is most efficient when denser water over the wide shelf favors up slope eddy transport along isopycnals of the v shaped slope front inflow along the eastern side of the trough cannot penetrate the sill region due to potential vorticity constraints while along the western trough flank eddy induced inflow crosses the sill and reaches the ice front the warm inflow into the trough is sensitive to the density of the outflowing dense shelf water for weaker winds absence of the dense water outflow leads to a reversal of the trough circulation and a strong inflow of warm water while for stronger winds baroclinic effects become less important and the inflow is similar to experiments including dense water outflow this article is protected by copyright all rights reserved

stronger ocean circulation and increased melting under pine island glacier ice shelf the ice shelf buttressing antarctica s pine island glacier has been melting rapidly observations taken between 1994 and 2009 show that meltwater production has increased by about 50 since 1994 as a result of a stronger circulation below the ice shelf

the fate of the southern weddell sea continental shelf in a warming climate abstractwarm water of open ocean origin on the continental shelf of the amundsen and bellingshausen seas causes the highest basal melt rates reported for antarctic ice shelves with severe consequences for the ice shelf ice sheet dynamics ice shelves fringing the broad continental shelf in the weddell and ross seas melt at rates orders of magnitude smaller however simulations using coupled ice ocean models forced with the atmospheric output of the hadcm3 sres a1b scenario run co2 concentration in the atmosphere reaches 700 ppmv by the year 2100 and stays at that level for an additional 100 years show that the circulation in the southern weddell sea changes during the twenty first century derivatives of circumpolar deep water are directed southward underneath the filchner ronne ice shelf warming the cavity and dramatically increasing basal melting to find out whether the open ocean will always continue to power the melting the authors extend their simulations applying twentieth century atmospheric

adsorption of uranium from groundwater by common fracture secondary minerals laboratory studies have been performed on the uptake of uranium by the chief secondary minerals identified on fracture surfaces in groundwater flow systems of the canadian shield the extent of adsorption from prepared solutions onto these materials i e ferric oxyhydroxide uptake chlorite uptake calcite uptake was similar to that previously observed in place on field samples although adsorption on the oxyhydroxide proceeds rapidly to near equilibrium in about 3 weeks slower two stage processes have been postulated for uranium uptake by both chlorite and calcite in some cases the times required to reach equilibrium are greater than 1 year

seasonal inflow of warm water onto the southern weddell sea continental shelf antarctica 1 to capture the austral summer to winter transition in water mass properties over the southern weddell sea continental shelf and slope region 19 weddell seals were tagged with miniaturized conductivity temperature depth sensors in february 2011 during the following 8 months the instruments yielded about 9000 temperature salinity profiles from a previously undersampled area this allows for the first time a description of the seasonality of warm water intrusions onto the shelf as well as its southward extent towards the filchner ice shelf a temperature section across the filchner depression and eastern shelf shows a pronounced decrease in warm water inflow from summer to winter further supported by an almost 3 year long time series from a shelf break mooring the seasonal variability is related to the surface wind stress and an associated deepening of the off shelf core of warm deep water

the role of long term human impact on avulsion and fan development this study aims to understand mainly qualitatively the long term role of human impact on avulsion processes and the development of fluvial mega fans in semi arid environments in this paper we refer to human impact as the direct influences of actions on the river s hydraulics i e flow regulation flow diversion and channel engineering in five case studies drawn from the khuzestan plains in southwest iran we have analysed the setup and triggering conditions of specific avulsions that occurred in the past timescale of millennia and identified the role of human interference in their causation our analysis is based on the integration of historical archaeological geomorphological and geological data through this study we demonstrate that avulsions in the khuzestan plains are the result of long term and complex interplay between multiple human induced and natural causes in similar ways human induced actions may play important roles during different phases of avulsion development the success of an avulsion in the post triggering phase may be defined by human induced setup causes as well as morphodynamic processes we suggest that present day flood events may be partly inherited from long term human alterations of the natural processes these finding could have implications for any fluvial system e g distributive fluvial systems deltas where avulsion plays a major role in their development and research tends to emphasize on natural mechanisms copyright 2016 john wiley sons ltd

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

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

ice shelf water overflow and bottom water formation in the southern weddell sea 1 cold shelf waters flowing out of the filchner depression in the southern weddell sea make a significant contribution to the production of weddell sea bottom water wsbw a precursor to antarctic bottom water aabw we use all available current meter records from the region to calculate the flux of cold water 1 9 c over the sill at the northern end of the filchner depression 1 6 0 5 sv and to determine its fate the estimated fluxes and mixing rates imply a rate of wsbw formation referenced to 0 8 c of 4 3 1 4 sv we identify three pathways for the cold shelf waters to enter the deep weddell sea circulation one path involves flow constrained to follow the shelf break the other two paths are down the continental slope resulting from the cold dense water being steered northward by prominent ridges that cross the continental slope near 36 w and 37 w mooring data indicate that the deep plumes can retain their core characteristics to depths greater than 2000 m probably aided by thermobaricity the plume water at this depth can flow at a speed approaching 1 m s 1 implying that the flow is occasionally supercritical we postulate that such supercriticality acts to limit mixing between the plume and its environment the transition from supercritical to slower more uniform flow is associated with very efficient mixing probably as a result of hydraulic jumps