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

circulation mixing and production of antarctic bottom water abstract the antarctic source of bottom water to the abyssal layer of the world ocean is examined as well as its large scale flow pattern and ultimate entrainment rate into the deep water above we make use of the available high quality station data in the southern ocean to construct bottom maps of neutral density and mean property maps including chlorofluorocarbon cfc for the abyssal layer underneath a selected neutral density surface the maximum density at the sill depth of drake passage is used to distinguish between the voluminous deep water mass that is a continuous component of the antarctic circumpolar current from the relatively denser bottom water originated along the antarctic continental margins based on water density antarctic bottom water aabw is defined here generically to include all volumes of non circumpolar water of antarctic origin over the shelf regime multiple localized sources of specific aabw types contribute to the abyssal layer of the adjacent antarctic basins characteristics of these dense bottom waters reflect closely those observed on the parent shelf water mass spreading paths of newly formed deep and bottom waters over the slope regime and their subsequent oceanic circulation patterns are analyzed on the basis of global property maps for the aabw layer interior mixing and interbasin exchanges of aabw are deduced from mean characteristic curves following the southern streamline of the antarctic circumpolar current outflow and mixing of aabw from the weddell sea to the argentine basin is depicted using density and cfc distributions of two zonal hydrographic lines recirculation and mixing of deep and bottom waters within the weddell gyre are also detailed using a meridional section along the greenwich meridian the strength of all localized sources of aabw combined is estimated by two independent approaches an estimate of the total production rate of aabw is calculated based on the oceanic cfc budget for the aabw layer offshore of the 2500 m isobath the sum of all downslope inputs of well ventilated bottom water types underneath the top isopycnal must account for the measured cfc content in the bottom layer the resulting total aabw production rate is about 8 sv which is a conservative figure that neglects the loss of cfc bearing waters across the top isopycnal in recent years whereas about 9 5 sv is calculated assuming a well mixed bottom layer making use of their transient nature cfc distributions at the top of the aabw layer indicate that more direct and rapid entrainment of cfc rich bottom waters below occurs over localized areas with relatively strong upwelling rates and enhanced vertical mixing a second more ad hoc but independent oceanic mass budget of the bottom layer is also constructed a typical basin wide rate of deep upwelling of 3 10 7 m s 1 requires 10 sv 1 sv 106 m3 s 1 of newly formed aabw to sink down the slope around antarctica we have also formulated a spatial distribution of deep upwelling on the isopycnal at the top of the aabw it is expressed as a combination of wind topographic and turbulent components which in turn are functions of the isopycnal depth bottom depth and bottom layer thickness this non uniform upwelling field yields about 12 sv of aabw exported across the top isopycnal fortuitously the overall average of upward speed at the top isopycnal 3 7 10 7 m s 1 compares well with previous estimates of deep upwelling in the northern basins a series of likely sites for strong vertical entrainment of aabw are clearly identified in the modeled distribution of deep upwelling consonant with the observed cfc distributions on the top isopycnal altogether regions with relatively high upwelling rates 5 10 7 m s 1 occupy only a quarter of the total areal extent of the top isopycnal but they account for as much as 45 of the total vertical transport

ice ocean processes over the continental shelf of the southern weddell sea antarctica a review 1 interactions between the southern ocean and the weddell sea ice shelves are important both to the antarctic ice sheet and to the production of globally significant water masses here we review the interaction between the filchner ronne ice shelf and the shelf sea in which it floats the continental shelf processes leading to the production of weddell sea deep and bottom waters from the original off shelf source waters are discussed and a new view is offered of the initial production of high salinity shelf water data from ship based measurements at the ice front from glaciological methods and from measurements made within the sub ice shelf cavity itself are used to describe the pattern of flows beneath the ice shelf we also consider the variability observed within the cavity from tidal to interannual time scales and finish with a discussion of future research priorities in the region

deformation of two phase systems with contrasting rheologies abstract rheological model experiments are used as analogues for foliation development in quartz mica rocks in a regime of pure shear in situ observations involving ice containing varying proportions and distributions of naphthalene and camphor illustrated two contrasting types of behaviour a matrix controlled versus a particle controlled deformation the matrix controlled deformation accommodates shortening predominantly by intracrystalline slip in the ice accompanied by some recrystallization while the more rigid naphthalene plates undergo rotation and mechanical alignment where shortening is normal to an initial platelet preferred orientation the foliation is enhanced and the matrix material aggregates between the rigid plates whereas a conjugate foliation is produced during shortening parallel to an initial platelet preferred orientation during particle controlled deformation strain is localized in particle concentrates the matrix areas and particles isolated in the matrix show little deformation at shortenings 10 dissolution of selected particles is achieved through an artificial fluid transport mechanism to create voids further shortening does not create closure of the fluid filled holes where shape is supported by the rigid matrix

trapped diurnal internal tides propagating semidiurnal internal tides and mixing estimates in the california current system from sustained glider observations 2006 2012 abstract from 2006 2012 along 3 repeated cross shore transects california cooperative oceanic fisheries investigations lines 66 7 80 and 90 in the california current system 33 609 shear and 39 737 strain profiles from 66 glider missions are used to estimate mixing via finescale parameterizations from a dataset containing over 52 000 profiles elevated diffusivity estimates and energetic diurnal d1 and semidiurnal d2 internal tides are found a within 100 km of the coast on lines 66 7 and 80 and b over the santa rosa cortes ridge srcr in the southern california bight scb on line 90 while finding elevated mixing near topography and associated with internal tides is not novel the combination of resolution and extent in this ongoing data collection is unmatched in the coastal ocean to our knowledge both d1 and d2 internal tides are energy sources for mixing at these latitudes the d1 internal tide is subinertial on line 90 d1 and d2 tides are equally energetic over the srcr the main site of elevated mixing within the scb numerous sources of internal tides at the rough topography in the scb produce standing and or partially standing waves on lines 66 7 and 80 the dominant energy source below about 100 m for mixing is the d1 internal tide which has an energy density of the d2 internal tide on line 80 estimated diffusivity estimated dissipation and d1 energy density peak in summer the d1 energy density shows an increasing trend from 2006 to 2012 its amplitude and phase are mostly consistent with topographically trapped d1 internal tides traveling with the topography on their right the observed offshore decay of the diffusivity estimates is consistent with the exponential decay of a trapped wave with a mode 1 rossby radius of 20 30 km despite the variable mesoscale it is remarkable that coherent internal tidal phase is found

spatial variability of turbulent mixing in the abyssal ocean ocean microstructure data show that turbulent mixing in the deep brazil basin of the south atlantic ocean is weak at all depths above smooth abyssal plains and the south american continental rise the diapycnal diffusivity there was estimated to be less than or approximately equal to 0 1 x 10 4 meters squared per second in contrast mixing rates are large throughout the water column above the rough mid atlantic ridge and the diffusivity deduced for the bottom most 150 meters exceeds 5 x 10 4 meters squared per second such patterns in vertical mixing imply that abyssal circulations have complex spatial structures that are linked to the underlying bathymetry

foliation and strain development in ice mica models abstract the behaviour during experimental deformation of composite foliated rock models composed of ice and ice mica is described in order to replicate deformation in quartz mica rocks the deformation involves pure shear and a component of simple shear oblique to the shortening axis a foliation is developed which is defined by an alignment of micas and a preferred orientation of airbubbles that closely parallels the principal plane of the local finite strain ellipsoid the degree of mica re alignment is not purely dependent on a parameter such as strain but is also controlled by the nature of the initial mica fabric and the orientation of layering relative to the shortening direction where there is some obliquity of a primary layering to the bulk shortening direction the deformation is markedly inhomogeneous with non uniform extension parallel to the flow direction over short distances this results in varying local strain and mica distributions values of strain obtained from such mica orientation distributions are always less than the observed finite strain and are therefore incompatible with a march model however deformation of an initial layering parallel to the shortening direction that contains a uniform mica distribution results in a homogeneous finite strain distribution and the mica distribution strengthens parallel to the principal plane of the local strain ellipsoid this mica distribution produces values of strain that correspond to the predictions of the march model in contrast deformation of initial bimodal fabrics or fabrics asymmetric to the shortening direction will develop strong preferred orientations quicker than an initial uniform distribution and characteristics of the initial fabric pattern always persist within the deformed mica preferred orientation shortening perpendicular to a strong initial preferred orientation only strengthens the mica fabric intracrystalline slip in the ductile ice matrix is the main means of accommodating the deformation and also produces a strong c axis preferred orientation grain boundary mobility in the ice is retarded by the dispersed mica phase however grain growth during and post dating deformation does not effect mica orientation distributions these features resemble and are compared with identical structures observed in many quartz mica rocks

circulation and water masses beneath the northern ronne ice shelf antarctica 1 we present oceanographic data from beneath the northern ronne ice shelf the data were collected during the austral summer of 2002 2003 from four sites located near the ice front in the ronne depression they consist of conductivity temperature depth ctd profiles and time series from moored instruments that vary in length from 9 to 20 weeks a strong tidally modulated inflow of relatively fresh water was found at the eastern margin of the ronne depression this low density inflow powers high basal melt rates that are responsible for a substantially thinned area of ice shelf a northward flow of ice shelf water along the western margin of the depression the antarctic peninsula coast was inferred from the ctd data from the new ctd and current meter data and from published results from cruises along the ice front we suggest that the flows at the margins of the ronne depression establish east west density gradients that drive an anticyclonic circulation within the depression the barotropic component of the circulation forms a gyre of strength 5 105 m3 s 1 and occupies a bowl in the field of water column thickness in the northern portion of the depression all water masses sampled had temperatures below the surface freezing point and are therefore classified as ice shelf water the relatively complex nature of the oceanographic regime in the ronne depression is overlain by a seasonal variability that is hinted at by the available time series probably explaining the apparent absence of inflowing hssw at the time of the measurements

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

the origin of kinks in polycrystalline ice abstract in situ observations of events leading to development of kink hands kbs and kink band boundaries kbbs and changes in their morphology are recorded during the deformation of layered polycrystalline ice at temperatures above 10 c slip on 0001 preceeded kb initiation and two different mechanisms a shear mode and a buckling mode are proposed for the development of the observed kbs the shear mode occurs with axial compression parallel to 0001 and is restricted to a band of material with sharply defined kbbs involved with an effective macroscopic simple shear sub perpendicular to the slip plane during deformation these bands progressively reduce their width while maintaining a stable orientation secondary kbs and microfractures are propagated within the kb as a result of increasing shear deformation in the band these phenomena are attributed to a limiting of the shear deformation to a band and the necessity to accommodate the dilatation changes in the buckling mode kb initiation is preceeded by the formation of deformation bands and this type of kb can initiate from inherent heterogeneities within the grain aggregate microstructural sensitivity is put forward to explain the apparent instability of this type of kb which is often curved and capable of migrating through a crystalline lattice the buckling mode occurs in grains where 0001 is oblique to the compression direction

a new tide model for the antarctic ice shelves and seas we describe a new tide model for the seas surrounding antarctica including the ocean cavities under the floating ice shelves the model uses data assimilation to improve its fit to available data typical peak to peak tide ranges on ice shelves are 1 2 m but can exceed 3 m for the filchner ronne and larsen ice shelves in the weddell sea spring tidal ranges are about twice these values model performance is judged relative to the 5 10 cm accuracy that is needed to fully utilize ice shelf height data that will be collected with the geoscience laser altimeter system scheduled to be launched on the ice cloud and land elevation satellite in late 2002 the model does not yet achieve this level of accuracy except very near the few high quality tidal records that have been assimilated into the model some improvement in predictive skill is expected from increased sophistication of model physics but we also require better definition of ice shelf grounding lines and more accurate water column thickness data in shelf seas and under the ice shelves long duration tide measurements bottom pressure gauge or gps in critical data sparse areas particularly near and on the filchner ronne and ross ice shelves and pine island bay are required to improve the performance of the data assimilation model

hydrography and circulation in the filchner depression weddell sea antarctica cold and dense ice shelf water isw emerging from the filchner ronne ice shelf cavity in the southwestern weddell sea flows northward through the filchner depression to eventually descend the continental slope and contribute to the formation of bottom water new ship born observations of hydrography and currents from filchner depression in january 2013 suggest that the northward flow of isw takes place in a middepth jet along the eastern flank of the depression thus questioning the traditional view with outflow along the western flank this interpretation of the data is supported by results from a regional numerical model which shows that isw flowing northward along the eastern coast of berkner island turns eastward and crosses the depression to its eastern side upon reaching the filchner ice front the ice front represents a sudden change in the thickness of the water column and thus a potential vorticity barrier transport estimates of northward isw flux based on observations ranges from 0 2 to 1 0 sv

the development of shear zones in polycrystalline camphor urai j l and humphreys f j 1981 the development of shear zones in polycrystalline camphor in g s lister h j behr k weber and h j zwart editors the effect of deformation on rocks tectonophysics 78 677 685 thin polycrystalline specimens of rhombohedral camphor have been deformed in pure shear in the temperature range 283 343k the deformation processes dynamic recrystallization and the development of microstructure were followed by transmission polarized light microscopy when the stress distribution in the specimens was favourable shear zones were initiated the development of microstructure changed drastically above 310320k the shape of the dynamically recrystallized grains which was equiaxed below this temperature became strongly elongated this change probably due to the development of a marked anisotropy in grain boundary mobilities and the activation of new slip systems made the development of shear zones a more frequently occurring phenomenon above 310 320k

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

observations of thermohaline convection adjacent to brunt ice shelf observations were made of ocean microstructure and horizontal currents adjacent to brunt ice shelf in the southeastern weddell sea periods of in situ supercooled water extending as deep as 65 m were associated with ice nucleation and frazil formation at depth ascending ice crystals due to convection lead to increased dissipation rates the main outflow of potentially supercooled water from deep beneath ice shelf is suggested to be in the deep channel northeast of the measurement site because this water is advected southward along the front it becomes in situ supercooled leading to suspended ice formation thermohaline convection and enhanced dissipation

observations of a diapycnal shortcut to adiabatic upwelling of antarctic circumpolar deep water in the southern ocean small scale turbulence causes diapycnal mixing which influences important water mass transformations in turn impacting large scale ocean transports such as the meridional overturning circulation moc a key controller of earth s climate we present direct observations of mixing over the antarctic continental slope between water masses that are part of the southern ocean moc a 12 h time series of microstructure turbulence measurements hydrography and velocity observations off elephant island north of the antarctic peninsula reveals two concurrent bursts of elevated dissipation of o 10 6 w kg 1 resulting in heat fluxes 10 times higher than basin integrated drake passage estimates this occurs across the boundary between adjacent adiabatic upwelling and downwelling overturning cells ray tracing to nearby topography shows mixing between 300 and 400 m is consistent with the breaking of locally generated internal tidal waves since similar conditions extend to much of the antarctic continental slope where these water masses outcrop diapycnal mixing may contribute significantly to upwelling

shear bands crenulations and differentiated layering in ice mica models abstract thin sheets of composite ice mica have been deformed in order to simulate the development of cleavages in quartz mica rocks a strong initial mica preferred orientation was variably oriented to the shortening direction deformation parallel to the foliation results in a crenulation type cleavage developing from shear bands initiated after a component of pure shear deformation oblique to the foliation produces a differentiated cleavage and involves a large component of shear strain subparallel to the original anisotropy the strain is accommodated by intra and intercrystalline processes that produce extensive grain elongation and rearrangement of the ductile matrix thereby forming ice vs mica rich regions on the other hand there is no drastic morphological change when a sample is shortened perpendicular to an original foliation that is where the micas lie in the plane of no shear strain instead the mica fabric is strengthened and the grains in the ductile matrix are flattened two models are presented for the initiation propagation and evolution of the observed crenulation versus differentiated cleavage types these depend on mica stacking and orientation relative to the transverse properties of the sample and also on the direction of anisotropy to the xy plane of the bulk strain ellipsoid the models invoke shear on planes of high shear strain and rotation of the shear bands and rigid mica grains into a direction approximately parallel to the bulk extension direction

the concept of steady state foliation abstract a steady state foliation is thought of as a foliation with constant orientation and intensity in a rock undergoing steady state flow the problem discussed is whether such straininsensitive foliations exist in rocks and how they might be distinguished from the more familiar strain sensitive foliations steady state foliations would be useful indicators of stress or of strain rate yet misleading if used as indicators of finite strain one requirement for maintenance of steady state foliations is operation of processes that locally weaken grain shape preferred orientation or reduce grain aspect ratios or destroy lithological layering during flow these are the inverses of the processes normally discussed in connection with foliation development many such processes are known though the details of how and when they operate efficiently enough to stabilize a foliation are unknown there is however a tendency for some of them to operate more efficiently at high strains high temperatures and in flow regimes with high vorticity natural and experimental high temperature shear zones are accordingly one environment in which steadystate foliations may be encountered an experiment is described in which a thin specimen of para dichlorobenzene was given a large shearing deformation at 90 of its absolute melting point a steady state foliation was not produced but the technique is a promising one for further microstructural studies where in situ observation of material undergoing large deformations is desirable

boundary mixing in orkney passage outflow one of the most remarkable features of contemporary oceanic climate change is the warming and contraction of antarctic bottom water over much of global ocean abyss these signatures represent changes in ventilation mediated by mixing and entrainment processes that may be location specific here we use available data to document as best possible those mixing processes as weddell sea deep and bottom waters flow along the south orkney plateau exit the weddell sea via orkney passage and fill the abyssal scotia sea first we find that an abrupt transition in topography upstream of orkney passage delimits the extent of the coldest waters along the plateau s flanks and may indicate a region of especially intense mixing second we revisit a control volume budget by heywood et al nature 2002 for waters trapped within the scotia sea after entering through orkney passage this budget requires extremely vigorous water mass transformations with a diapycnal transfer coefficient of 39 10 10 4 m2 s 1 evidence for such intense diapycnal mixing is not found in the abyssal scotia sea interior and while we do find large rates of diapycnal mixing in conjunction with a downwelling ekman layer on the western side of orkney passage it is insufficient to close the budget this leads us to hypothesize that the heywood budget is closed by a boundary mixing process in which the ekman layer associated with the weddell sea deep water boundary current experiences relatively large vertical scale overturning associated with tidal forcing along the southern boundary of the scotia sea this article is protected by copyright all rights reserved

variability and mixing of the filchner overflow plume on the continental slope weddell sea abstracta large fraction of antarctic bottom water is produced in the weddell sea through mixing between the cold and dense shelf water masses and the warm and saline off shelf water we present o

observations of the antarctic slope undercurrent in the southeastern weddell sea 1 the antarctic slope front presents a dynamical barrier between the cold antarctic shelf waters in contact with ice shelves and the warmer subsurface waters offshore two hydrographic sections with full depth current measurements were undertaken in january and february 2009 across the slope and shelf in the southeastern weddell sea southwestward surface intensified currents of 30 cm s 1 and northeastward undercurrents of 6 9 cm s 1 were in thermal wind balance with the sloping isopycnals across the front which migrated offshore by 30 km in the time interval between the two sections a mid depth undercurrent on february 23 was associated with a 130 m uplift of the main pycnocline bringing warm deep water closer to the shelf break this vertical displacement comparable to that caused by seasonal variations in wind speed implies that undercurrents may affect the exchanges between coastal and deep waters near the antarctic continental margins

the antarctic slope current in a changing climate the antarctic slope current asc is a coherent circulation feature that rings the antarctic continental shelf and regulates the flow of water towards the antarctic coastline the structure and variability of the asc influences key processes near the antarctic coastline that have global implications such as the melting of antarctic ice shelves and water mass formation that determines the strength of the global overturning circulation recent theoretical modeling and observational advances have revealed new dynamical properties of the asc making it timely to review earlier reviews of the asc focused largely on local classifications of water properties of the asc s primary front here we instead provide a classification of the current s frontal structure based on the dynamical mechanisms that govern both the along slope and cross slope circulation these two modes of circulation are strongly coupled similar to the antarctic circumpolar current highly variable motions such as dense overflows tides and eddies are shown to be critical components of cross slope and cross shelf exchange but understanding of how the distribution and intensity of these processes will evolve in a changing climate remains poor due to observational and modeling limitations results linking the asc to larger modes of climate variability such as el nino show that the asc is an integral part of global climate an improved dynamical understanding of the asc is still needed to accurately model and predict future antarctic sea ice extent the stability of the antarctic ice sheets and the southern ocean s contribution to the global carbon cycle

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

tidal conversion and dissipation at steep topography in a channel poleward of the critical latitude abstractin high latitude fjords and channels in the canadian arctic archipelago walls support radiating internal tides as kelvin waves such waves allow for significant barotropic to baroclinic ti

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

deep bottom mixed layer drives intrinsic variability of the antarctic slope front the antarctic slope front asf is located along much of the antarctic continental shelf break and helps to maintain a barrier to the movement of circumpolar deep water cdw onto the continental shelf the stability of the asf has a major control on cross shelf heat transport and ocean driven basal melting of antarctic ice shelves here the asf dynamics are investigated for continental shelves with weak dense shelf water dsw formation which are thought to have a stable asf common for regions in east antarctica using an ocean process model this study demonstrates how offshore bottom ekman transport of shelf waters leads to the development of a deep bottom mixed layer at the lower continental slope and subsequently determines an intrinsic variability of the asf the asf variability is characterized by instability events that affect the entire water column and occur every 5 10 years and last for approximately half a year during these instability events the cross shelf density gradient weakens and cdw moves closer to the continent stronger winds increase the formation rate of the bottom mixed layer which causes a subsequent increase of instability events if the observed freshening trend of continental shelf waters leads to weaker dsw formation more regions might be vulnerable for the asf variability to develop in the future

internal tide reflection and turbulent mixing on the continental slope abstract observations of turbulence internal waves and subinertial flow were made over a steep corrugated continental slope off virginia during may june 1998 at semidiurnal frequencies a convergence of low mode onshore energy flux is approximately balanced by a divergence of high wavenumber offshore energy flux this conversion occurs in a region where the continental slope is nearly critical with respect to the semidiurnal tide it is suggested that elevated near bottom mixing k 10 3 m2 s 1 observed offshore of the supercritical continental slope arises from the reflection of a remotely generated low mode m2 internal tide based on the observed turbulent kinetic energy dissipation rate the high wavenumber internal tide decays on time scales o 1 day no evidence for internal lee wave generation by flow over the slope s corrugations or internal tide generation at the shelf break was found at this site

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

idealized solutions for the energy balance of the finescale internal wave field abstract recent fine and microstructure observations indicate enhanced finescale shear and strain in conjunction with bottom intensified turbulent dissipation above rough bathymetry in the brazil basin such observations implicate the bottom boundary as an energy source for the finescale internal wave field simple analytical and numerical solutions to an equation governing the spatial and temporal evolution of the finescale wave field are described here the governing equation implicitly treats the effects of wave breaking on the vertical propagation of internal waves through a flux representation of nonlinear transports associated with internal wave wave interactions these solutions identify the rate of dissipation of turbulent kinetic energy with downscale energy transports at high vertical wavenumber resulting in an estimate of dissipation versus depth the sensitivity of the turbulent dissipation depth profile to various environmental parameters is examined observed dissipation profiles and shear

an estimate of tidal energy lost to turbulence at the hawaiian ridge abstract an integrated analysis of turbulence observations from four unique instrument platforms obtained over the hawaiian ridge leads to an assessment of the vertical cross ridge and along ridge structure of turbulence dissipation rate and diffusivity the diffusivity near the seafloor was on average 15 times that in the midwater column at 1000 m depth the diffusivity atop the ridge was 30 times that 10 km off the ridge decreasing to background oceanic values by 60 km a weak factor of 2 spring neap variation in dissipation was observed the observations also suggest a kinematic relationship between the energy in the semidiurnal internal tide e and the depth integrated dissipation d such that d e1 0 5 at sites along the ridge this kinematic relationship is supported by combining a simple knife edge model to estimate internal tide generation with wave wave interaction time scales to estimate dissipation the along ridge kinematic relationship and the observed vertical and cross ridge st

position of the lhasa terrane prior to india asia collision derived from palaeomagnetic inclinations of 53 ma old dykes of the linzhou basin constraints on the age of collision and post collisional shortening within the tibetan plateau the lhasa terrane comprises the southern eurasian margin since at least mid cretaceous therefore paleomagnetic data from the lhasa terrane are crucial to reconstruct the pre collisional southern margin of eurasia previous paleomagnetic data from the cretaceous takena formation provide a rough constraint on the pre collisional paleolatitudinal position of the southern eurasian margin however paleogene paleomagnetic data from the lhasa terrane which can provide more direct constraints are very limited in addition reliability of the existing data is ambiguous because of a possible later overprint in our new study 17 sites were drilled from mafic dykes intruded in the t1 unit of the linzizong formation of the linzhou basin near lhasa for paleomagnetic studies figure 1 the dykes were ar 40 ar 39 dated to c 53 ma by yue and ding 2006 from ten sites a higher coercivity component demagnetized between 20 and 100 mt could be isolated detailed rockmagnetic analyses reveal ti rich titanomagnetite as the remanence carrier which suggests that the rock is not much altered and the remanent magnetization is likely of primary origin this is supported by a positive fold test the occurrence of normal and reverse polarity directions within single sites the subvolcanic character of the dykes and the within site scatter as well as the scatter between site mean directions indicate that paleosecular variation is recorded within sites tilt correction was performed using the bedding of overlying fluvial lacustrine sediments and tilt angles of ignimbrite columns postdating the dyke emplacement bedding corrected directions give an overall mean direction of d i 12 3 27 2 95 10 6 k 21 7 n 10 corresponding to a paleolatitude of 13 2 5 8 n at a reference location on the suture zone 20 n 90 e comparison with previous cretaceous data mainly from the takena formation yields a stable position of the lhasa terrane during cretaceous and early eocene this indicates that no large north south crustal shortening occurred along the southern eurasian margin between late cretaceous and early eocene the difference between expected paleolatitudes determined from the apwp of eurasia and observed paleolatitudes reveals relative northward movement of the lhasa block of ca 1847 763 km since early eocene this is attributed to indentation of india into asia and implies a considerable amount of north south crustal shortening two models of greater india were used to determine the extended northern margin of india ali and aitchison 2005 proposed a greater india based on bathymetric features in the eastern indian ocean and patzelt and others 1996 determined the paleolatitude of northern india using paleomagnetic investigations on paleocene sediments of the zongpu formation at gamba and duela intersection of the pre collisional southern eurasian margin and the northern margin of india yields a collision age of the indian and eurasian continents of c 5349 ma an initial collision within this time range is in accordance with previous studies based on paleomagnetic or geologic data e g patriat and achache 1984 klootwijk and others 1992 guillot and others 2003 a significantly later collision age at the eocene oligocene boundary as proposed by aitchison and others 2007 is not in agreement with our new and previous paleomagnetic data from the lhasa block