rapid disintegration of the wordie ice shelf in response to atmospheric warming the breaking up of ice shelves around the antarctic peninsula has been cited1 as a sign that a dangerous warming is beginning in antarctica here we present satellite images showing the disintegration of the wordie ice shelf which lies off the west coast of the antarctic peninsula fig 1 fracture either in the form of surface crevasses or rifts extending to the bottom of the ice shelf has been responsible for iceberg calving and weakening the central region of the ice shelf these fracture processes which led to retreat of the ice front were apparently enhanced by the presence of increased amounts of melt water resulting from a warming trend recorded in mean annual air temperatures in marguerite bay if this warming trend continues other nearby ice shelves on the antarctic peninsula may be at risk but substantial additional warming would be required before similar processes could initiate breakup of the ross and filchner ronne ice shelves which help stabilize the west antarctic ice sheet

internal waves across the pacific 1 the long range propagation of the semidiurnal internal tide northward from the hawaiian ridge and its susceptibility to parametric subharmonic instability psi at the critical latitude c 28 8 n were examined in spring 2006 with intensive shipboard and moored observations spanning 25 37 n along a tidal beam velocity and shear at c were dominated by intense vertically standing inertially rotating bands of several hundred meters vertical wavelength these occurred in bursts following spring tide contrasting sharply with the downward propagating wind generated features seen at other latitudes these marginally stable layers which have inverse 16 meter richardson number ri16 1 0 7 are interpreted as the inertial waves resulting from psi of the internal tide elevated near inertial energy and parameterized diapycnal diffusivity and reduced asymmetry in upgoing downgoing energy were also observed at and equatorward of c yet simultaneous moored measurements of semidiurnal energy flux and 1 km deep velocity sections measured from the ship indicate that the internal tide propagates at least to 37 n with no detectable energy loss or phase discontinuity at c our observations indicate that psi occurs in the ocean with sufficient intensity to substantially alter the inertial shear field at and equatorward of c but that it does not appreciably disrupt the propagation of the tide at our location

ice dammed lateral lake and epishelf lake insights into holocene dynamics of marguerite trough ice stream and george vi ice shelf alexander island antarctic peninsula abstract we present new data regarding the past dynamics of marguerite trough ice stream george vi ice shelf and valley glaciers from ablation point massif on alexander island antarctic peninsula this ice free oasis preserves a geological record of ice stream lateral moraines ice dammed lakes ice shelf moraines and valley glacier moraines which we dated using cosmogenic nuclide ages we provide one of the first detailed sediment landform assemblage descriptions of epishelf lake shorelines marguerite trough ice stream imprinted lateral moraines against eastern alexander island at 120 m at ablation point massif during deglaciation lateral lakes formed in the ablation and moutonnee valleys dammed against the ice stream in george vi sound exposure ages from boulders on these shorelines yielded ages of 13 9 to 9 7 ka following recession of the ice stream george vi ice shelf formed in george vi sound an epishelf lake formed at 15 20 m asl in ablation and moutonnee valleys dated from 9 4 to 4 6 ka suggesting that the lake was stable and persistent for some 5000 years lake level lowering occurred after this with the lake level at 12 m at 3 1 0 4 ka and at 5 m asl today a readvance of the valley glaciers on alexander island at 4 4 0 7 ka is recorded by valley glacier moraines overlying epishelf lake sediments we speculate that the glacier readvance which occurred during a period of warmth may have been caused by a dynamic response of the glaciers to a lowering in surface elevation of george vi ice shelf

retreat of northern margins of george vi and wilkins ice shelves antarctic peninsula the george vi and wilkins ice shelves are considered at risk of disinteg ration due to a regional atmospheric warming trend on the antarctic peninsula retreat of the northern margin of the george vi ice shelf has been observed previously but the wilkins ice shelf was thought to be stable we investigated the positions of the northern fronts of these shelves from the literature and looked for changes on 1974 landsat and 1992 and 1995 european remote sensing satellite ers synthetic aperture radar images our investigation shows that the northern george vi ice shelf lost a total of 906 km 2 between 1974 and 1992 and an additional 87 km2 by 1995 the northern margin of the wilkins ice shelf lost 796 km2 between 1990 and 1992 and another 564 km2 between 1992 and 1995 armadas of tabular icebergs were visible in front of this shelf in the ers images these two ice shelves mark the southern most documented conspicuous retreat of ice shelf margins

honeycomb development on alexander island glacial history of george vi sound and palaeoclimatic implications two step cliffs mars oasis w antarctica abstract analysis of three generations of glacial deposits and of a range of geomorphic features including widespread honeycombs and tafonis at two step cliffs mars oasis 71 52 s 68 15 w provides new insights into the geomorphological evolution of west antarctica with special respect to alveolar weathering at two step terrace indicators of the inherited character of cavernous weathering were found such as 97 non flaking and varnished backwalls and 80 tafoni floors that are till covered and or sealed by lithobiontic coatings based on the ne predominant aspect of the alveolized boulder faces tafoni initiation is attributed to coastal salt spray weathering by halite coming from the george vi sound during the 6 5 ka bp open water period the present day activity of these inherited cavities is restricted to roof flaking attributed to a combination of processes involving thermal stresses this 6 5 ka bp phase of coastal alveolization is the first step of a six stage holocene geomorphological scenario that includes alternatively phases of glacial advance or stationing and phases of vegetal colonization and or rock weathering and aeolian abrasion on the deglaciated outcrops this geomorphic scenario is tentatively correlated with the available palaeoenvironmental record in the antarctic peninsula region with two potential geomorphic indicators of the holocene optimum being identified 1 clusters of centimetric honeycombs facing the sound marine optimum at 6 5 ka bp 2 salmon pink lithobiontic coatings preserved inside cavities and at the boulder surface terrestrial optimum at 4 3 ka bp

climatic impacts of parameterized local and remote tidal mixing abstractturbulent mixing driven by breaking internal tides plays a primary role in the meridional overturning and oceanic heat budget most current climate models explicitly parameterize only the local dissipation of internal tides at the generation sites representing the remote dissipation of low mode internal tides that propagate away through a uniform background diffusivity in this study a simple energetically consistent parameterization of the low mode internal tide dissipation is derived and implemented in the geophysical fluid dynamics laboratory earth system model with gold component gfdl esm2g the impact of remote and local internal tide dissipation on the ocean state is examined using a series of simulations with the same total amount of energy input for mixing but with different scalings of the vertical profile of dissipation with the stratification and with different idealized scenarios for the distribution of the low mode internal tide energy dissipation uniformly over ocean basins co

deformation and failure of the ice bridge on the wilkins ice shelf antarctica a narrow bridge of floating ice that connected the wilkins ice shelf antarctica to two confining islands eventually collapsed in early april 2009 in the month preceding the collapse we observed deformation of the ice bridge by means of satellite imagery and from an in situ gps station terrasar x images acquired in stripmap mode were used to compile a time series the ice bridge bent most strongly in its narrowest part westerly while the northern end near charcot island shifted in a northeasterly direction in the south the ice bridge experienced compressive strain parallel to its long axis gps position data were acquired a little south of the narrowest part of the ice bridge from 19 january 2009 analysis of these data showed both cyclic and monotonic components of motion meteorological data and re analysis of the output of weather prediction models indicated that easterly winds were responsible for the cyclic motion component in particular wind stress on the rough ice melange that occupied the area to the east exerted significant pressure on the ice bridge the collapse of the ice bridge began with crack formation in the southern section parallel to the long axis of the ice bridge and led to shattering of the southern part ultimately the narrowest part only 900 m wide ruptured the formation of many small icebergs released energy of 125 106 j

a recent sea ice retreat west of the antarctic peninsula satellite passive microwave data show a record decrease in sea ice extent in the bellingshausen sea from mid 1988 through early 1991 the change coincides with more southerly surface winds increased cyclonic activity and rising surface air temperatures which reached historic highs along the west coast of the antarctic peninsula in 1989 preceded by high ice cover in 1986 87 the retreat was most evident during summer in the formerly perennial sea ice field over the continental shelf ocean heat storage probably contributed to the persistence and coastal propagation of this anomaly

overturning circulation driven by breaking internal waves in the deep ocean a global estimate of the water mass transformation by internal wave driven mixing in the deep ocean is presented the estimate is based on the energy conversion from tidal and geostrophic motions into internal waves combined with a turbulent mixing parameterization we show that internal wave driven mixing in the deep ocean can sustain 20 30 sv of water mass transformation one third or more of this transformation is attributed to lee waves generated by geostrophic motions flowing over rough topography primarily in the southern ocean while these results are uncertain due to many assumptions poorly constrained parameters and data noise that enter in the calculation the result that lee wave driven mixing plays an important role in the abyssal ocean circulation is likely robust the implication is that lee wave driven mixing should be represented in ocean and climate models but currently it is not citation nikurashin m and r ferrari 2013 overturning circulation driven by breaking internal waves in the deep ocean geophys res lett 40 doi 10 1002 grl 50542

surface melting on antarctic peninsula ice shelves detected by passive microwave sensors a 13 year time series of spaceborne passive microwave radiance measurements over the antarctic peninsula ice shelves reveals a systematic increase in the duration of the summer melt season combined with data from meteorological stations on the antarctic peninsula the annual motion and long term trends of the 0 c isotherm can be monitored

the retreat of jones ice shelf antarctic peninsula in recent decades several ice shelves along the antarctic peninsula have diminished in size as a result of climate warming using aerial photographic satellite and survey data we document a similar retreat of jones ice shelf which was another small ice shelf on the west coast of the antarctic peninsula this ice shelf was roughly stable between 1947 and 1969 but in the early 1970s it began to retreat and had completely disappeared by early 2003 jones ice shelf has two ice fronts only a few kilometres apart and its retreat provides a unique opportunity to examine how different ice fronts retreat when subjected to similar climate forcing we mapped the retreat of both the east and west ice fronts of jones ice shelf and found that although individual episodes of retreat may be related to particularly warm summers the overall progress of retreat of the two ice fronts has been rather different this suggests that in this case the course of retreat is controlled by the geometry of the embayment and location of pinning points as well as climatic events

numerical simulations of the ice flow dynamics of george vi ice shelf antarctica a diagnostic dynamic thermodynamic ice shelf model is applied to the george vi ice shelf situated in the bellinghausen sea antarctica the george vi ice shelf has a peculiar flow geometry which sets it apart from other ice shelves inflow occurs along the two longest and almost parallel sides whereas outflow occurs on the two ice fronts that are relatively short and situated at opposite ends of the ice shelf two data sources were used to derive the ice thickness distribution conventional radio echo sounding from the british antarctic survey was combined with thickness inferred from surface elevation obtained by the nasa glas satellite system assuming hydrostatic equilibrium we simulate the present ice flow over the ice shelf that results from the ice thickness distribution the inflow at the grounding line and the flow rate factor the high spatial resolution of the ice thickness distribution leads to very detailed simulations the flow field has some extraordinary elements e g the stagnation point characteristics resulting from the unusual ice shelf geometry

saturation of the internal tides and induced mixing in the abyssal ocean as part of an ongoing effort to develop a parameterization of wave induced abyssal mixing the authors derive an heuristic model for nonlinear wave breaking and energy dissipation associated with internal tides then the saturation and dissipation of internal tides for idealized and observed topography samples are investigated one of the main results is that the wave induced mixing could be more intense and more confined to the bottom than previously assumed in numerical models furthermore in this model wave breaking and mixing clearly depend on the small scales of the topography below 10 km or so which is below the current resolution of global bathymetry this motivates the use of a statistical approach to represent the unresolved topography when addressing the role of internal tides in mixing the deep ocean

ice shelf disintegration by plate bending and hydro fracture satellite observations and model results of the 2008 wilkins ice shelf break ups abstract satellite remote sensing observations of three break up events in 2008 for the wilkins ice shelf 28 february to 6 march 27 may to 31 may and 28 june to mid july provide unprecedented detail of ice shelf calving during rapid break up the observations reveal that the wilkins break ups occur through a distinctive type of shelf calving which we term disintegration as well as more typical rifting and calving here we focus on the disintegration process which is characterized by repeated rapid fracturing that creates narrow ice edge parallel blocks with subsequent block toppling and fragmentation forming an expanding iceberg and ice rubble mass we use these data to develop and test a model of floating ice plate disintegration in which ice plate bending stresses at the ice front arising from buoyancy forces can lead to runaway calving when free mobile water is available high resolution satellite images and laser altimetry of the first break up event provide details of fracture spacings ice thicknesses and plate bending profiles that agree well with our model predictions we suggest that surface or near surface meltwater is the main pre condition for disintegration and that hydro fracture is the main mechanism brine layers from near waterline brine infiltration can support a similar process but this is less effective unless regional ice stress patterns contribute to the net stress available at the crack tip for fracturing a combination of brine enhanced fracturing and changing internal net extensional stresses was the likely mechanism behind the latter two wilkins events

forcing of oceanic mean flows by dissipating internal tides we present a theoretical and numerical study of the effective mean force exerted on an oceanic mean flow due to the presence of small amplitude internal waves that are forced by the oscillatory flow of a barotropic tide over undulating topography and are also subject to dissipation this extends the classic lee wave drag problem of atmospheric wave mean interaction theory to a more complicated oceanographic setting because now the steady lee waves are replaced by oscillatory internal tides and most importantly because now the three dimensional oceanic mean flow is defined by time averaging over the fast tidal cycles rather than by the zonal averaging familiar from atmospheric theory although the details of our computation are quite different we recover the main action at a distance result from the atmospheric setting namely that the effective mean force that is felt by the mean flow is located in regions of wave dissipation and not necessarily near the topographic wave source specifically we derive an explicit expression for the effective mean force at leading order using a perturbation series in small wave amplitude within the framework of generalized lagrangian mean theory discuss in detail the range of situations in which a strong secularly growing mean flow response can be expected and then compute the effective mean force numerically in a number of idealized examples with simple topographies

circulation and melting beneath george vi ice shelf antarctica introduction george vi ice shelf sandwiched between the western coast of palmer land and the eastern coast of alexander island is the largest and most studied of the west antarctic peninsula ice shelves it covers an area of approximately 25 000 km2 and is underlain by circumpolar deep water cdw with temperatures in excess of 1oc giving rise to rapid basal melting bishop and walton 1981 lennon et al 1982 the maximum ice thickness of about 500 m occurs about 70 km from the southern ice front where a ridge of thick ice extends across george vi sound near 70ow see figure 1 effectively dividing the upper water column into northern and southern regions the northern ice front which faces marguerite bay appears to be near the geographical limit of ice shelf viability and has undergone a gradual retreat in recent decades lucchitta and rosanova 1998 a timeframe over which much of the nearby wordie ice shelf disintegrated doake and vaughan 1991 there is extensive surface melting over the northern parts of the ice shelf and much of the ice column near the northern ice front appears to be temperate paren and cooper 1986 conditions in the south where the ice front faces into ronne entrance are colder and the ice front position appears to be steady the vast majority of the flow into the ice shelf comes from palmer land but basal melting is sufficient to remove most of this so that the ice is derived almost exclusively from local accumulation by the time it reaches the ice fronts potter et al 1984 there is some evidence at the margins of the ice shelf to suggest that it may have disappeared completely during the early holocene before reforming sugden and clapperton 1981 bentley et al 2005

climate since ad 1510 on dyer plateau antarctic peninsula evidence for recent climate change a 480 year record of the oxygen isotope ratios dust content chemical species and net accumulation from ice cores drilled in 1989 90 on dyer plateau in the antarctic peninsula is presented the continuous analyses of small sub annual samples reveal well preserved annual variations in both sulfate content and 18o thus allowing an excellent time scale to be established this history reveals a recent pronounced warming in which the last two decades have been among the warmest in the last five centuries furthermore unlike in east antarctica on dyer plateau conditions appear to have been fairly normal from ad 1500 to 1850 with cooler conditions from 1850 to 1930 and a warming trend dominating since 1930 reconstructed annual layer thicknesses suggest an increase in net accumulation beginning early in the 19th century and continuing to the present this intuitive conflict between increasing net accumulation and depleted 18o cooler climate in the 19th century appears widespread in the peninsula region and challenges our understanding of the physical relationships among moisture sources air temperatures and snow accumulation the complex meteorological regime in the antarctic peninsula region complicates meaningful interpretation of proxy indicators and results in a strong imprint of local high frequency processes upon the larger scale climate picture

retreating glacier fronts on the antarctic peninsula over the past half century the continued retreat of ice shelves on the antarctic peninsula has been widely attributed to recent atmospheric warming but there is little published work describing changes in glacier margin positions we present trends in 244 marine glacier fronts on the peninsula and associated islands over the past 61 years of these glaciers 87 have retreated and a clear boundary between mean advance and retreat has migrated progressively southward the pattern is broadly compatible with retreat driven by atmospheric warming but the rapidity of the migration suggests that this may not be the sole driver of glacier retreat in this region

rapid collapse of northern larsen ice shelf antarctica in january 1995 4200 square kilometers of the northern larsen ice shelf antarctic peninsula broke away radar images from the ers 1 satellite complemented by field observations showed that the two northernmost sections of the ice shelf fractured and disintegrated almost completely within a few days this breakup followed a period of steady retreat that coincided with a regional trend of atmospheric warming the observations imply that after an ice shelf retreats beyond a critical limit it may collapse rapidly as a result of perturbated mass balance

parametric subharmonic instability of the internal tide at 29 n observational evidence is presented for transfer of energy from the internal tide to near inertial motions near 298n in the pacific ocean the transfer is accomplished via parametric subharmonic instability psi which involvesinteractionbetweena primarywave the internaltide in this case andtwo smaller scale waves of nearly half the frequency the internal tide at this location is a complex superposition of a low mode waves propagating north from hawaii and higher mode waves generated at local seamounts making application of psi theory challenging nevertheless a statistically significant phase locking is documented between the internal tide and upward and downward propagating near inertial waves the phase between those three waves is consistent with that expected from psi theory calculated energy transfer rates from the tide to nearinertial motions are modest consistent with local dissipation rate estimates the conclusion is that while psi does befall the tide near a critical latitude of 298n it does not do so catastrophically

a mechanism for local dissipation of internal tides generated at rough topography abstract fine and micro structure observations indicate that turbulent mixing is enhanced within o 1 km above rough topography enhanced mixing is associated with internal wave breaking and in many regions of the ocean has been linked to the breaking and dissipation of internal tides the generation and dissipation of internal tides are explored in this study using a high resolution two dimensional nonhydrostatic numerical model which explicitly resolves the instabilities leading to wave breaking configured in an idealized domain with a realistic multiscale topography and flow characteristics the control simulation chosen to represent the brazil basin region produces a vertical profile of energy dissipation and temporal characteristics of finescale motions that are consistent with observations results suggest that a significant fraction of mixing in the bottom o 1 km of the ocean is sustained by the transfer of energy from the large scale internal tides to smaller scale internal waves by nonlin

glaciological and oceanographic calculations of the mass balance and oxygen isotope ratio of a melting ice shelf on a etudie l alimentation du george vi ice shelf en relation avec l accumulation le velage et la fonte on releve la relation temperature taux d isotope de l oxygene ces donnees sont couplees a des donnees oceanologiques sur les eaux chaudes et son interaction avec le shelf

interannual caribbean salinity in satellite data and model simulations aquarius sea surface salinity sss reveals the presence of interannual variations in the caribbean with about 0 5 psu change between salty and fresh events which propagate westward across that basin at an average speed of 11 cm s and are preceded by corresponding sss anomalies east of the lesser antilles these upstream sss anomalies are produced by interannual changes in the amazon plume their presence is verified using in situ measurements from the northwest tropical atlantic station in contrast to sss which displays westward propagation sst changes almost immediately across the caribbean suggesting large scale atmospheric processes have a primary role in regulating interannual sst in contrast to sss a global 1 10 mesoscale ocean model is used to quantify possible origination mechanisms of the caribbean salinity anomalies and their fate simulations confirm that they are produced by anomalous horizontal salt advection which conveys these salinity anomalies from an area east of the lesser antilles across the caribbean anomalous horizontal advection is dominated by mean currents acting on anomalous salinity the model suggests that interannual caribbean salinity anomalies eventually enter the florida current and reach the gulf stream 6 12 months after crossing the central caribbean previous studies link the origin of salinity anomalies in the amazon plume to variations in the annual freshwater discharge from the continent in this model interannual discharge variations are absent while simulated sss variability is in line with observations this suggests that interannually forced ocean dynamics plays a key role in river plume variability and its spatial dispersion

oceanic controls on the mass balance of wilkins ice shelf antarctica 0 8 m a 1 driven by a mean basal melt rate of wb 1 3 0 4 m a 1 interannual variability was large associated with changes in both surface mass accumulation and wb basal melt rate declined significantly around 2000 from 1 8 0 4 m a 1 for 1992 2000 to 0 75 0 55 m a 1 for 2001 2008 the latter value corresponding to approximately steady state ice shelf mass observations of ocean temperature t obtained during 2007 2009 by instrumented seals reveal a cold deep halo of winter water ww t 1 6 c surrounding wis the base of the ww in the halo is 170 m approximately the mean ice draft for wis we hypothesize that the transition in wb in 2000 was caused by a small perturbation 10 20 m in the relative depths of the ice base and the bottom of the ww layer in the halo we conclude that basal melting of thin ice shelves like wis is very sensitive to upper ocean and coastal processes that act on shorter time and space scales than those affecting basal melting of thicker west antarctic ice shelves such as george vi and pine island glacier

extreme sediment and ice discharge from marine based ice streams new evidence from the north sea a major problem for understanding the dynamics of ice streams has been a lack of precise data on ice streaming longevity and sediment transport efficacy here we present the first well constrained data on sediment flux from a paleoice stream this has been achieved by computing the volume of sediment deposited as debris flows on the fan located at the outlet of the norwegian channel ice stream and converting to a flux measurement by accounting for the duration of streaming in this episode between 20 and 19 ka during the last glacial stage in this period the ice stream delivered an average 1 1 gt of sediment per year equivalent to 8000 m 3 yr 1 per meter width of ice stream front the calculated flux is an order of magnitude higher than most previous estimates for other paleoice streams and is comparable to the present sediment flux from the world9s largest rivers the short period of debris flow deposition suggests that the norwegian channel ice stream underwent rapid on off switching with punctuated iceberg delivery to the north atlantic as a consequence

subtropical catastrophe significant loss of low mode tidal energy at 28 9 1 an idealized numerical study of a northward propagating internal tide reveals a dramatic loss of energy to small scale subharmonic instabilities near 28 9 n inspired by observations of the internal tide radiating northward from the hawaiian ridge a three dimensional numerical model is initialized with a northward baroclinic tidal flux of approximately 1 7 kw m after an initial spinup period energy is quickly transferred from the baroclinic tide to subharmonic motions with half the horizontal tidal wavenumber and small vertical scales through nonlinear advection of horizontal tidal velocity gradients potential oceanic implications are twofold first once a steady state has been reached the instability acts as a partial filter of northward tidal flux between 27 5 and 29 5 n in rough agreement with some altimetric tidal observations second elevated shear of the subharmonic motions suggests the potential for elevated near surface dissipation rates near the critical latitude that may be important for upper ocean mixing

recent atmospheric warming and retreat of ice shelves on the antarctic peninsula in 1978 mercer1 discussed the probable effects of climate warming on the antarctic ice sheet predicting that one sign of a warming trend in this region would be the retreat of ice shelves on the antarctic peninsula analyses of 50 year meteorological records have since revealed atmospheric warming on the antarctic peninsula2 3 and a number of ice shelves have retreated4 8 here we present time series of observations of the areal extent of nine ice shelves on the antarctic peninsula showing that five northerly ones have retreated dramatically in the past fifty years while those further south show no clear trend comparison with airtemperature data shows that the pattern and magnitude of ice shelf retreat is consistent with the existence of an abrupt thermal limit on iceshelf viability the isotherm associated with this limit having been driven south by the atmospheric warming ice shelves therefore appear to be sensitive indicators of climate change

pattern of retreat and disintegration of larsen b ice shelf antarctic peninsula the retreat of the larsen b ice shelf antarctic peninsula and the collapse of its northern section are analyzed using satellite images acquired between january 1995 and may 2003 over 1 week during march 2002 after a period of steady retreat since 1995 2300 km 2 of the ice shelf broke up into many small icebergs this rapid collapse occurred at the end of an exceptionally warm summer and after a multi year period of decreasing surface net mass balance ice thinning flow acceleration and widening of rifts the ice shelf area decreased from 11 512 km 2 in january 1995 to 3463 km 2 in march 2002 and 2667 km 2 in april 2003 ers synthetic aperture radar sar images were used to identify ice shelf zones with different surface morphology which generated icebergs of different sizes and shapes the pattern of retreat and break up similar to that of larsen a in 1995 suggests that fracturing enhanced by abundant surface melt played a key role in addition the recent changes of grounded and residual floating ice north of larsen b are analyzed by means of envisat advanced synthetic aperture radar asar images up to summer 2003 showing significant loss of grounded ice upstream of those ice shelf sections which disintegrated in 1995 and 2002

a synthesis of remote sensing data on wilkins ice shelf antarctica wilkins ice shelf has an area of 16000 km2 and lies off the west coast of the antarctic peninsula bounded by alexander latady charcot and rothschild islands several ice shelves including wilkins exist close to a climatic limit of viability the recent disintegration of the neighbouring wordie ice shelf has been linked to atmopsheric warming observed on the antarctic peninsula the limit of ice shelf viability thus appears to have migrated south should this continue the question arises how long will wilkins ice shelf survive compared with the other ice shelves on the antarctic peninsula few surface glaciological data have been collected on wilkins ice shelf we compare contrast and combine a variety of remotely sensed data the recently declassified geosat geodetic mission altimetry landsat mss and tm imagery and radio echo sounding data res to study its structure and mass balance regime we find that this shelf has an unusual mass balance regime and relies heavily for sustenance on in situ accumulation its response to a continued atmospheric warming may be significantly different from that of wordie ice shelf wordie ice shelf was fed by several dynamic outlet glaciers which accelerated the disintegration process when the ice shelf fractured wilkins ice shelf by contrast is almost stagnant and is expected to respond by normal calving at the ice front changes in the accumulation rate or basal melt rate may however dominate any dynamic effect over the last two decades the ice front positions have remained stable

structure of southeastern antarctic peninsula ice shelves and ice tongues from synthetic aperture radar imagery examination of synthetic aperture radar data collected over the southeastern antarctic peninsula shows that features sometimes mapped as ice shelves are more likely composed of numerous ice tongues interspersed within a matrix of fast ice and icebergs the tongues are formed by the seaward extension of numerous small mountain glaciers that drain from the antarctic peninsula once afloat the tongues intermingle with a matrix of fast ice and brash examination of 1997 radarsat 1 image mosaics shows that southeastern antarctic peninsula composite ice shelves covered an area of about 3500 km 2 like ice tongues around the rest of antarctica these features are highly fragmented and likely to be susceptible to mechanical failure one such composite shelf located between new bedford and wright inlets was observed to decrease in area by 1200km 2 between 1997 and 2000

turning ocean mixing upside down abstractit is generally understood that small scale mixing such as is caused by breaking internal waves drives upwelling of the densest ocean waters that sink to the ocean bottom at high latitudes however the observational evidence that the strong turbulent fluxes generated by small scale mixing in the stratified ocean interior are more vigorous close to the ocean bottom boundary than above implies that small scale mixing converts light waters into denser ones thus driving a net sinking of abyssal waters using a combination of theoretical ideas and numerical models it is argued that abyssal waters upwell along weakly stratified boundary layers where small scale mixing of density decreases to zero to satisfy the no density flux condition at the ocean bottom the abyssal ocean meridional overturning circulation is the small residual of a large net sinking of waters driven by small scale mixing in the stratified interior above the bottom boundary layers and a slightly larger net upwelling driven b

eruptive environment of volcanism on brabant island evidence for thin wet based ice in northern antarctic peninsula during the late quaternary terrestrial volcanism occurred extensively on brabant island northern antarctic peninsula during the late quaternary 200 ka probably entirely late pleistocene two compositionally distinct volcanic sequences formed three large shield volcanoes the volcanoes were constructed in association with a 150 m thick non ice stream glacial cover although it was likely to be thicker few hundred metres where it extended onto the continental shelf the glacial cover on the volcanoes was probably mainly permeable snow firn and fractured crevassed ice it was wet based erosive and sediment forming indicating either a temperate or perhaps more likely sub polar thermal regime and would have been more extensive than that present today such a thin ice sheet would have had a low surface gradient during periods of extension across the continental shelf this is the first direct evidence for the thickness and thermal regime of the terrestrial ice sheet in the antarctic peninsula during any quaternary period prior to the last glacial maximum