physical volcanology and geological relationships of the jurassic ferrar large igneous province antarctica abstract the ferrar large igneous province forms a linear belt for 3500 km along the transantarctic mountains and as a geochemical province extends into southeastern australasia the principal components of the ferrar are intrusive ferrar dolerite sills and dikes and dufek intrusion pyroclastic the prebble mawson and exposure hill formations effusive the kirkpatrick basalt in terms of the three dimensional architecture of the ferrar a range of facies can be recognized in each of the principal components the ferrar province was initiated with a major episode of phreatomagmatism leading to formation of tephra cones and associated deposits and near surface vent structures activity switched to predominantly quiet effusion of alternating thick flood basalt flows and thin pahoehoe lobes and flows intrusive bodies were emplaced early given the occurrence of dolerite clasts in tuff breccias but most sills were probably intruded after accumulation of extrusive rocks pre existing rift structures played a major role in controlling the transport and distribution of the ferrar magmas and the apparent centers of extrusive activity the associated paleohydrology controlled the eruption styles

a physical theory of snow gliding snow glide slip of the entire snowpack over the ground is not observed unless water reaches the ground interface in this paper snow gliding is approached from the point of view that a perfect s

rapid stepwise onset of antarctic glaciation and deeper calcite compensation in the pacific ocean the ocean depth at which the rate of calcium carbonate input from surface waters equals the rate of dissolution is termed the calcite compensation depth at present this depth is 4 500 m with some variation between and within ocean basins the calcite compensation depth is linked to ocean acidity which is in turn linked to atmospheric carbon dioxide concentrations and hence global climate1 geological records of changes in the calcite compensation depth show a prominent deepening of more than 1 km near the eocene oligocene boundary 34 million years ago 2 when significant permanent ice sheets first appeared on antarctica3 4 5 6 but the relationship between these two events is poorly understood here we present ocean sediment records of calcium carbonate content as well as carbon and oxygen isotopic compositions from the tropical pacific ocean that cover the eocene oligocene boundary we find that the deepening of the calcite compensation depth was more rapid than previously documented and occurred in two jumps of about 40 000 years each synchronous with the stepwise onset of antarctic ice sheet growth the glaciation was initiated after climatic preconditioning7 by an interval when the earth s orbit of the sun favoured cool summers the changes in oxygen isotope composition across the eocene oligocene boundary are too large to be explained by antarctic ice sheet growth alone and must therefore also indicate contemporaneous global cooling and or northern hemisphere glaciation

integrated provenance and detrital thermochronology studies on the andrill and 2a drill core late oligocene early miocene exhumation of the transantarctic mountains southern victoria land antarctica terra nova 22 361 368 2010 abstract detrital apatite fission track data combined with provenance analysis of gravel fraction detritus are used in this study to investigate the neogene exhumation of the west antarctic rift system samples have been collected from the upper 1000 m of the andrill and 2a drill core which documents the miocene history of the victoria land basin most samples have apatites with fission track ages between 23 and 36 ma and gravel clasts derived from the erebus volcanic province and the transantarctic mountains exposed along the southern victoria land coast these results indicate the existence of a so far undetected oligocene early miocene exhumation phase in the region between the blue koettlitz and skelton mulock glaciers suggesting the importance of fluctuation of local glaciers in the royal society range and or expansions into the mcmurdo sound of an ice sheet mainly sourced by larger outlet glaciers located further south

late cenozoic deposits at reedy glacier transantarctic mountains implications for former thickness of the west antarctic ice sheet abstract deposits corresponding to multiple periods of glaciation are preserved in ice free areas adjacent to reedy glacier southern transantarctic mountains glacial geologic mapping supported by 10be surface exposure dating shows that reedy glacier was significantly thicker than today multiple times during the mid to late cenozoic longitudinal surface profiles reconstructed from the upper limits of deposits indicate greater thickening at the glacier mouth than at the head during these episodes indicating that reedy glacier responded primarily to changes in the thickness of the west antarctic ice sheet surface exposure ages suggest this relationship has been in place since at least 5 ma the last period of thickening of reedy glacier occurred during marine isotope stage 2 at which time the glacier surface near its confluence with the west antarctic ice sheet was at least 500 m higher than today

a detrital apatite fission track study of the ciros 2 sedimentary record tracing ice pathways in the ross sea area over the last 5 ma

tectonic and climatic signals from apatite detrital fission track analysis of the cape roberts project core records south victoria land antarctica abstract the cenozoic tectonic reorganization of the west antarctic rift system in the ross sea region occurred concurrently with a major change in the global climate system and a global reorganization of plate motions this region thus provides the opportunity to study in detail a range of geological issues dealing with tectonic and climate feedbacks during the late eocene early oligocene greenhouse icehouse transition at high latitudes with the aim to decipher tectonic vs climatic forcing in the ice sheet drainage evolution a detrital apatite fission track study was carried out throughout the cenozoic drill cored stratigraphic succession of the cape roberts project mcmurdo sound victoria land basin apatite fission track ages of detrital samples with depositional ages between 34 ma and 17 ma were decomposed into statistically significant age populations three age peaks were detected reflecting different bedrock provenance areas i a young peak p1 between 34 ma and 26 ma recording the signal of a source area exhumed with a constant denudation rate but absent in the proximal continental area and ii two peaks older than 40 ma that are instead compatible with thermochronological data available from the onshore bedrock p1 peak testifies a late oligocene early miocene denudation event and traces a southern provenance of a fraction of the sediments filling the cape roberts basin we propose that this denudation event might have been triggered by renewed n s transtensional shearing along the western shoulder of victoria land basin controlling glacial flow pattern and the associated sediment transport

burial and exhumation of the eisenhower range transantarctic mountains based on thermochronological sedimentary rock maturity and petrographic constraints abstract the eisenhower range is a n s trending mountain range in the transantarctic mountains tam adjacent to the nw ross sea embayment new aft and apatite u th sm he ahe data from vertical basement profiles supplemented by paleotemperature and pressure estimates derived from beacon sandstones provide new quantitative results on regional burial evolution and first regional constraints on basin inversion and exhumation processes aft ages between 32 2 and 259 18 ma and ahe ages of 37 3 173 16 ma correlate positively with sample elevations thermal history modeling of these data and complementary thermal indications detect heating of the paleosurface on the eisenhower range to temperatures 80 c subsequent to ferrar magmatism and constrain late eocene rapid cooling regression of modeled paleotemperatures against sample elevations refers to a high jurassic 45 c km and a moderate cretaceous eocene 28 8 c km geothermal gradient the texture of beacon sandstones supports strong mechanical compaction that requires a higher overburden than preserved in the stratigraphic record modeled paleotemperatures and pressures suggest basement burial that increases from late jurassic 0 7 1 1 km to eocene 1 8 2 1 km the overburden comprises 0 7 1 1 km cumulative beacon ferrar rocks and 0 7 1 4 km of post ferrar sediments rapid cooling of the whole sample suite between 35 and 30 ma implies fast erosion of the post ferrar sediments and re exposure of underlying magmatic rocks subsequent differential sample cooling to present day surface temperature infers ongoing exhumation by glacial incision enhanced by isostatic response to basin inversion decreasing amounts of exhumation from the coast 3 km toward the interior 1 5 2 2 km point to backstepping incision along the fault controlled priestley glacier substantial exhumation of the eisenhower range since the late eocene is hence triggered by both tectonic and climatic factors superimposed by considerable lithological influence during the initial exhumation stage

late pleistocene holocene retreat of the west antarctic ice sheet system in the ross sea part 1 geophysical results in the 1994 1995 and 1998 austral field seasons geophysical research efforts in the ross sea focused on acquiring a high resolution database designed to permit 1 reconstruction of the maximum extent and configuration of the ice sheet during the last glacial maximum i e oxygen isotope stage 2 2 reconstruction of conditions at the base of the ice sheet and 3 assessment of the relative retreat history of the ice sheet following the last glacial maximum five seismic facies are distinguished on the basis of external geometry relationships among features bounding surface amplitude intensity of internal acoustic signature and geometry of internal reflectors seismic facies 1 is a transparent draping unit correlated to diatomaceous mud interpreted as being deposited under open marine conditions seismic facies 2 and 3 are comprised of units displaying subdued massive internal signatures with smooth lower bounding surfaces and hummocky upper surfaces characterized by glacial lineations these units are interpreted to be grounding zone proximal deposits overridden by the expanded ice sheet seismic facies 2 may be a deforming till unit seismic facies 4a is characterized by an internally massive to chaotic signature an erosional often flat lower surface and a hummocky upper surface displaying glacial lineations this unit is interpreted to be till and is divided into deposits associated with the most recent glacial expansion 4a and with an earlier pre last glacial maximum expansion 4b seismic facies 5 is an acoustically laminated ponded and draping deposit interpreted to contain proglacial and sub ice shelf materials deposited continuously since the last interglacial period the associations of these units provide context for the interpretation of the ice edge maximum position conditions at the base of the ice sheet and the relative retreat history of the region there is compelling evidence for a much expanded ice sheet in the ross sea during the last glacial maximum in the western ross sea the maximum grounding position is marked by an isolated grounding zone wedge and placed in the vicinity of coulman island approximately 150 km from the continental shelf edge in the central ross sea the maximum grounding position is close to the continental shelf break based primarily on the presence of an extensive 60 m thick sheet like deposit with a fluted upper surface streaming ice may have occupied bathymetric lows on the continental shelf as suggested by 1 the configuration of bathymetry 2 the presence of glacially eroded troughs 3 the concentration of sediment interpreted to be deforming till within the middle to outer shelf reaches of the troughs and 4 the fluted nature of the upper surface absolute rates of streaming ice flow relative to inter ice stream areas are not implied the western ross sea continental shelf deposits record the retreat history of ice derived predominantly from the east antarctic ice sheet and glaciers of the transantarctic mountains ice flow on the continental shelf is interpreted to have remained fixed in position restricted by the walls of the troughs on the inner shelf of the western ross sea the ice flowed over and eroded lithified sedimentary strata slower moving ice occupied flat topped banks a single grounding zone wedge occurs on the western ross sea central shelf no substantial deposits are observed on the inner continental shelf this lack of grounding zone features reflects a restricted sediment supply and a relatively steady rapid retreat of the ice sheet during retreat ice flow acted independently in each major trough and on the bank tops ice retreated from victoria land basin drygalski trough before it retreated from joides basin ice remained on the bank tops shedding material into the abandoned troughs grounded ice in the central ross sea was derived predominantly from an expanded west antarctic ice sheet the ice sheet remained grounded on the continental shelf edge after retreat of ice from the western ross sea expanded ice eroded the inner shelf and deposited sheets of till on the central and outer shelf ice stream drainage shifted laterally as recorded by rounded laterally accreting ridges that separate bathymetric troughs the central ross sea is the repository for larger volumes of sediment derived from ice flow across basins of relatively thick unlithified sedimentary deposits two till sheets mark grounding zone positions in the central ross sea reflecting the higher sediment supply and a stepped deglaciation ice remained grounded on the pennell bank to the west a series of moraines marks the retreat of ice across the bank mega scale glacial lineations and other streamlined subglacial geomorphic features occur across the continental shelf primarily within the troughs the lineations substantiate the maximum reconstruction and support the interpretation of a deforming substrate beneath the outer reaches of the expanded ice sheet this deforming substrate may have contributed to the onset of deglaciation features associated with meltwater are rare or absent suggesting that basal meltwater played a minor role in retreat of the ice sheet

ross sea paleo ice sheet drainage and deglacial history during and since the lgm onshore and offshore studies show that an expanded grounded ice sheet occupied the ross sea embayment during the last glacial maximum lgm results from studies of till provenance and the orienta

hyperconcentrated flows on a forested alluvial fan of eastern canada geomorphic characteristics return period and triggering scenarios the assessment of the dominant flow type on alluvial fans usually refers to two categories debris flow fans i e sediment gravity flows and fluvial fans i e fluid gravity flows here we report the results of combined morphometric stratigraphic and sedimentological approaches which suggest that hyperconcentrated flows a transitional process rheologically distinct from debris flows and floods and sometimes referred to as debris floods mud floods or transitional debris flows are the dominant fan building process in eastern canada these flows produce transitional facies between those of debris flows which consist of a cohesive matrix supported diamicton and those of river flows which display more distinct stratification the size of the blocks in the channels and the abrasion scars at the base of several trees attest to the high transport capacity of these flows the fan channels are routed according to various obstacles comprised primarily of woody debris that impede sediment transit however these conditions of sediment storage are combined with readily available sediment due to the friable nature of the local lithology tree ring analysis allowed the reconstruction of eight hydrogeomorphic events which are characterized by a return period of 9 25 years for the period 1934 2008 although most of the analyzed events occurred after 1970 historical weather data analysis indicates that they were related to rare hydrometeorological events at regional and local scales this evidence led to the elaboration of weather scenarios likely responsible for triggering flows on the fan according to these scenarios two distinct hydrologic regimes emerge the torrential rainfall regime and the nival regime related to snowmelt processes hydrogeomorphic processes occurring in a cold temperate climate and particularly on small forested alluvial fans of north eastern north america should receive more attention from land managers given the hazard they represent as well as because of their sensitivity to various meteorological parameters copyright 2014 john wiley sons ltd

multianalytical provenance analysis of eastern ross sea lgm till sediments antarctica petrography geochronology and thermochronology detrital data in order to reveal provenance of detrital sediments supplied by west antarctic ice sheet wais 19 glaciomarine cores of last glacial maximum age were analyzed from eastern ross sea and sulzberger bay analytical techniques included petrographic analysis of gravel sized clasts geochronology zircon u pb zrn upb and thermochronology apatite fission track aft of sand sized fractions petrographic analysis revealed a similarity with the lithologies presently exposed in western marie byrd land mbl with major roles played by low grade metamorphic rocks and granitoids furthermore zrn upb and aft data allowed to identify the ages of formation and cooling of sedimentary source area consisting of cambrian precambrian basement i e swanson formation in western mbl which underwent at least two episodes of magma intrusion migmatization and cooling during devonian carboniferous and cretaceous paleocene times scarcity of volcanic clasts in the region of ross sea along the front of west antarctica ice streams in association with the occurrence of aft oligocene pliocene dates suggests a localized tectonic exhumation of portions of mbl as already documented for the opposite side of west antarctic rift system in the transantarctic mountains furthermore a zrn upb and aft population of late triassic jurassic age indicates the presence of unexposed rocks that formed or metamorphosed at that time in the sedimentary source area which could be identified in mcayeal ice stream and bindschadler ice stream catchment areas

ross ice shelf response to climate driven by the tectonic imprint on seafloor bathymetry ocean melting has thinned antarctica s ice shelves at an increasing rate over the past two decades leading to loss of grounded ice the ross ice shelf is currently close to steady state but geological records indicate that it can disintegrate rapidly which would accelerate grounded ice loss from catchments equivalent to 11 6 m of global sea level rise here we use data from the rosetta ice airborne survey and ocean simulations to identify the principal threats to ross ice shelf stability we locate the tectonic boundary between east and west antarctica from magnetic anomalies and use gravity data to generate a new high resolution map of sub ice shelf bathymetry the tectonic imprint on the bathymetry constrains sub ice shelf ocean circulation protecting the ice shelf grounding line from moderate changes in global ocean heat content in contrast local seasonal production of warm upper ocean water near the ice front drives rapid ice shelf melting east of ross island where thinning would lead to faster grounded ice loss from both the east and west antarctic ice sheets we confirm high modelled melt rates in this region using rosetta ice radar data our findings highlight the significance of both the tectonic framework and local ocean atmosphere exchange processes near the ice front in determining the future of the antarctic ice sheet the boundary between west and east antarctica is a tectonic feature that bisects the ross ice shelf this boundary constrains ocean circulation under the ice which affects ice stability according to airborne survey data and ocean simulations

development and inversion of the mesozoic victoria basin in the terra nova bay transantarctic mountains derived from thermochronological data abstract the terra nova bay region of the transantarctic mountains hosts three n s to nnw sse extending mountain ranges deep freeze range eisenhower range and northern prince albert mountains all ranges consist of basement rocks locally overlain by permo triassic sediments and jurassic volcanic rocks recent thermochronological studies recognized that the eisenhower range was originally covered by a kilometre thick jurassic eocene sedimentary sequence here we present a comprehensive apatite fission track aft and u th sm he ahe data set of vertical sample profiles from the terra nova bay to reconstruct architecture extension and geometry of this depocentre and place its evolution in the context of supraregional geodynamic processes the study comprises new data and thermal history models from the deep freeze range and new thermal history models of published data from the northern prince albert mountains new aft and ahe ages of 25 275 ma from the deep freeze range correlate tightly with sample elevations thermal history modelling of these data and complementary proxies detects common heating of the jurassic surface and rapid late eocene cooling regression of vertical paleotemperature profiles reveals an increased jurassic and a moderate cretaceous eocene geothermal gradient of 45 and 25 c km respectively paleotemperatures and gradients used in tandem infer basement burial increasing from 2 km in deep freeze and eisenhower ranges to 3 4 km in the prince albert mountains such a varying overburden probably reflects regional differences in the jurassic basement topography subsequently sediment thickness uniformly increased in the order of 1 km until late eocene mid jurassic basin initiation and subsequent sediment accumulation is explained by extension of a mesozoic victoria basin during gondwana breakup between antarctica and australia late eocene early oligocene basin inversion is associated with the formation of the west antarctic rift system while differential final exhumation represents the change from downwearing to backstepping incision

recent antarctic ice mass loss from radar interferometry and regional climate modelling observed estimates of ice losses in antarctica combined with regional modelling of ice accumulation in the interior suggest that east antarctica is close to a balanced mass budget but large losses of ice occur in the narrow outlet channels of west antarctic glaciers and at the northern tip of the antarctic peninsula

glide avalanche response to an extreme rain on snow event snoqualmie pass washington usa rain on snow events trigger immediate and delayed avalanches as liquid water penetrates the snowpack we present results from an extreme rain on snow event that triggered a glide avalanche near snoqualmie pass washington usa snoqualmie pass recorded 463 cm of snowfall from 13 december 2008 to 6 january 2009 this period of snowfall was followed by a strong southwesterly tropical flow that resulted in an extreme rain on snow event sensors at snoqualmie pass recorded 285 mm of precipitation over a 52 hour period flooding slush flows landslides and avalanches resulted from the influx of precipitation snow heights decreased rapidly over the period with settlement rates approaching 80 mm h 1 liquid water infiltrated and flowed through the snowpack within a few hours of the arrival of rain yet many of the major avalanches occurred 12 30 or more hours after the onset of rain and water outflow a glide avalanche occurred 30 hours after the onset of rain and the establishment of drainage through the snowpack increasing glide rates correlate with periods of rapid snow settlement here glide rates approached 670 mm h 1 although glide and settlement rates increased during periods of intense precipitation glide failure occurred 8 hours after peak precipitation and outflow

reconstructions of antarctic topography since the eocene oligocene boundary abstract accurate models of past antarctic ice sheet behaviour require more realistic reconstructions of the evolution of bedrock topography however other than a preliminary attempt to reconstruct antarctic topography at the eocene oligocene boundary the long term evolution of antarctica s subglacial topography throughout its glacial history has not previously been quantified here we derive new reconstructions of antarctic topography for four key time slices in antarctica s climate and glacial history the eocene oligocene boundary ca 34 ma the oligocene miocene boundary ca 23 ma the mid miocene climate transition ca 14 ma and the mid pliocene warm period ca 3 5 ma to reconstruct past topography we consider a series of processes including ice sheet loading volcanism thermal subsidence horizontal plate motion erosion sedimentation and flexural isostatic adjustment and validate our models where possible using onshore and offshore geological constraints our reconstructions show that the land area of antarctica situated above sea level was 25 larger at the eocene oligocene boundary than at the present day offshore sediment records and terrestrial constraints indicate that the incision of deep subglacial topographic troughs around the margin of east antarctica occurred predominantly in the oligocene and early miocene whereas in west antarctica erosion and sedimentation rates accelerated after the mid miocene changes to the topography after the mid pliocene were comparatively minor our new palaeotopography reconstructions provide a critical boundary condition for models seeking to understand past behaviour of the antarctic ice sheet and have implications for estimating changes in global ice volume temperature and sea level across major cenozoic climate transitions

the eisenhower range transantarctic mountains evaluation of qualitative interpretation concepts of thermochronological data abstract the transantarctic mountains tam were one of the first regions where apatite fission track aft thermochronology was applied routinely to study exhumation processes and long term landscape evolution pioneering publications from the region introduced or refined interpretation concepts of thermochronological data such as the break in slope in vertical age profiles as qualitative marker for the onset of accelerated rock cooling new aft data were compiled from vertical profiles in the eisenhower range northern tam and compared with published data samples originally examined by the population technique were re analyzed via the external detector technique aft ages increase from 32 2 ma at an elevation of 220 m to 175 14 ma at 2380 m geological evidence and thermal history modeling of the aft data require jurassic to late eocene reheating of the samples and an onset of cooling at 35 30 ma this requires the deposition of an 3 to 3 5 km thick sedimentary sequence on the granitic basement subsequent to jurassic ferrar magmatism at 180 ma the regression of paleotemperatures against sample altitudes infers a high jurassic geothermal gradient of 60 c km related to rifting processes and ferrar magmatism and a moderate cretaceous eocene geothermal gradient of 30 c km comparison of ages generated with population and external detector technique shows the importance of determining single grain ages for each sample even from granitic rocks of the same intrusion and thus strongly supports previous cases made for the determination of annealing kinetics and grain age evaluation age comparison additionally illustrates that samples above a break in slope record larger deviations between population and external detector ages than samples below a break in slope we demonstrate that the position and shape of a break in slope result from various factors such as the thermal history prior to final cooling maximum paleotemperatures cooling rate and geothermal gradient a break in slope does not straightly date the onset of final cooling and cannot substitute thermal history modeling therefore earlier studies from the tam and similar settings elsewhere need to be validated by combining thermal history modeling of thermochronological data and supplementary geological information

chemical and mineralogical characterisation of weathered historical bricks from the venice lagoonal environment surficial and bulk samples of historical bricks of different age from xii to xviii centuries recovered from a campaign of archaeological excavations recently carried out at the site of a medieval monastery in the s giacomo in paludo island in thevenice lagoon have been characterised by ft ir tga dtg and dta xrd sem eds the samples belong to a particular brick type commonly used in the venice region the altinella brick the bulk relative abundance of primary i e calcite and dolomite and secondary firing minerals i e diopside and wollastonite in the bricks coupled with their relative geometrical dimensions allows placing the samples in a chronological sequence according to known historical changes in brickmaking firing temperatures and practices most of the bricks were used as paving material and have been exposed to the action of seawater salts chlorides and sulphates due to periodical submersion following high tide episodes salt laden gypsum halite mirabilite surficial patinas are indeed present but salt weathering does not appear to have affected the overall structural soundness of the bricks in this now abandoned island as it is the case with brickwork located in other more populated and polluted areas in venice and its lagoon

analysis of rock samples collected from rock hewn churches of lalibela ethiopia using laser induced breakdown spectroscopy abstract with the aim to study alteration processes of the rock hewn churches from lalibela ethiopia we applied laser induced breakdown spectroscopy libs technique to measure the elemental composition both of the bulk rock materials and their external layers exposed to the environmental factors the analytical plasma was generated by nanosecond pulses of an nd yag laser emitting at 1064 nm different major and minor sample constituents were detected including ca mg na fe ti al and k the detected o emission originates both from air surrounding and the sample while the intensity of n lines coming exclusively from air was used for the libs signal normalization by depth profiling of the weathered basalt rock we observed a lower presence of k in the external layers corresponding to the first 5 laser shots the emission from this element is anti correlated with the line intensities from o and this was attributed to the variations in relative abundances of clay minerals and k feldspar the analogue measurements were performed on the tuff rock and compared to the spectra from powder samples containing only the external soft material scratched from the rocks these analyses show an abundance of h in the weathered wetted layers and suggest that cations are lost from the constituent primary minerals and replaced by h this process disrupts the lattice structure and causes a marked loss of strength the studies presented here demonstrate that libs is a useful technique for studying the alteration processes in the rocks caused by environmental factors

age provinces in the antarctic craton evidence from detrital zircons in permian strata from the beardmore glacier region antarctica abstract the antarctic gondwana sequence crops out along the transantarctic mountains permian strata at mt bowers and mt weeks in the central part of the range were mainly derived from the ice covered east antarctic craton for which the geology is inferred from coastal outcrops and the miller range in the transantarctic mountains analysis of detrital zircons from permian sandstones at those two localities demonstrate a slowly changing zircon age probability distribution for four samples from the lower part of the sequence with an abrupt change for the upper buckley formation sandstone the stratigraphically lowest sample from a unit informally designated the mt bowers sandstone is dominated by zircons in the age range 610 540 ma with minor components at 1 0 ga and 2 7 ga upward the pagoda formation sandstone is likewise dominated by zircons of 600 550 ma age together with a significant grenville age cluster 1 3 1 0 ga and a minor 1 5 1 4 ga cluster the fairchild formation sandstone has a preponderance of grains in the range 600 530 ma with a scatter of older ages zircon grains in the lower buckley formation sandstone are principally in the range 575 520 ma with another cluster at 470 450 ma and a scattering of older ages most zircons in the upper buckley formation sandstone are permian in age but with a very small component in the range 650 475 ma and a trace of older ages archean to early mesoproterozoic zircon grains are few in number and may have been recycled from distal outcrops the 1 5 1 4 ga grains suggest an unexposed mesoproterozoic source within the east antarctic craton which could have been linked to laurentian north america the grenville age source is considered to be similarly a sub glacial belt in the interior of east antarctica zircons with a late neoproterozoic to ordovician signature 600 460 ma were derived from a ross orogen foreland sequence and or an early and inland extension of the orogen itself permian zircons in the upper buckley sandstone reflect the development of a magmatic arc on the gondwana pacific margin

full depth avalanche occurrences caused by snow gliding coquihalla british columbia canada snow glide is the translational slip of the entire snowpack over a sloping ground surface and it is thought that rapid rates of snow glide precede full depth avalanches the nature of avalanches that release at the ground makes them difficult to predict and difficult to control using explosives on slope instrumentation comprised of stainless steel glide shoes was used to measure rates of snow glide for two winters on a bedrock slope adjacent to the coquihalla highway cascade mountains british columbia canada climate data and avalanche occurrences were recorded by the british columbia ministry oftransportation and highways our results show that the supply of free water to the snow ground interface by rain or snow melt is the most important influence on full depth avalanche release full depth avalanche release responds to rainfall and snowmelt events within 12 24 hours occasionally full depth avalanches occur unexpectedly during clear cold periods snowmelt by radiation is thought to contribute enough meltwater during these cold periods to induce higher rates of snow glide and full depth avalanche release the results also indicate that snow glide alone is not a reliable indicator for full depth avalanche release

cenozoic range front faulting and development of the transantarctic mountains near cape surprise antarctica thermochronologic and geomorphologic constraints 1 the transantarctic mountains tam define the western flank of the west antarctic rift system cape surprise near the shackleton glacier in the central tam is the only location along the range s 3500 km length where upper paleozoic beacon supergroup strata are down faulted to near sea level previous studies have inferred a range front master normal fault accommodates extension and rock uplift across the tam front in this region the history of rock uplift is debated suggested as early as mesozoic typically cenozoic or even pliocene or younger structural observations apatite fission track aft thermochronology and geomorphologic mapping undertaken within the tam front east of the shackleton glacier indicate extension faulting and denudation was mostly late eocene late oligocene and likely into the early miocene an exhumed aft partial annealing zone is found at the coast and traced 50 km inland the base of that exhumed partial annealing zone indicates denudation accelerated at 40 ma near the coast and at 30 35 ma on the inland side of the tam front vertically offset aft isochrones across the tam front reveal a step faulted architecture rather than a single master fault the cumulative vertical offset of the 55 ma isochrone is 2 3 2 7 km compared to 2 4 2 6 km offset of beacon strata indicating that all significant normal faulting is cenozoic and not related to mesozoic extension within the west antarctic rift system denudation from 26 ma to 14 ma produced a locally preserved erosion surface within the tam front erosion surface remnants indicate the tam front has undergone minimal internal deformation and only 290 790 m of surface uplift along offshore faults since the middle miocene

dynamics of the last glacial maximum antarctic ice sheet and its response to ocean forcing retreat of the last glacial maximum lgm antarctic ice sheet is thought to have been initiated by changes in ocean heat and eustatic sea level propagated from the northern hemisphere nh as northern ice sheets melted under rising atmospheric temperatures the extent to which spatial variability in ice dynamics may have modulated the resultant pattern and timing of decay of the antarctic ice sheet has so far received little attention however despite the growing recognition that dynamic effects account for a sizeable proportion of mass balance changes observed in modern ice sheets here we use a 5 km resolution whole continent numerical ice sheet model to assess whether differences in the mechanisms governing ice sheet flow could account for discrepancies between geochronological studies in different parts of the continent we first simulate the geometry and flow characteristics of an equilibrium lgm ice sheet using pan antarctic terrestrial and marine geological data for constraint then perturb the system with sea level and ocean heat flux increases to investigate ice sheet vulnerability our results identify that fast flowing glaciers in the eastern weddell sea the amundsen sea central ross sea and in the amery trough respond most rapidly to ocean forcings in agreement with empirical data most significantly we find that although ocean warming and sea level rise bring about mainly localized glacier acceleration concomitant drawdown of ice from neighboring areas leads to widespread thinning of entire glacier catchments a discovery that has important ramifications for the dynamic changes presently being observed in modern ice sheets

provenance of lgm glacial till sand fraction across the ross embayment antarctica abstract the provenance of late quaternary ross embayment till was investigated by comparing the coarse sand composition of east and west antarctic source area tills with till samples from across the ross sea the west antarctic samples from beneath the whillans b and kamb c ice streams are petrologically distinct from samples of lateral moraines flanking several east antarctic outlet glaciers the characteristic assemblage of four west antarctic samples includes felsic intrusive and detrital sedimentary lithic fragments plagioclase and abundant quartz in contrast most of the ten east antarctic till samples contains abundant mafic intrusive and detrital sedimentary lithic fragments as well as less abundant quartz the distinctive composition of these source areas can be linked to 33 samples from 20 cores of last glacial maximum lgm age till distributed across the ross sea western ross sea till samples exhibit mineralogic and lithological similarities to east antarctic till samples although these western ross sea tills contain higher percentages of felsic intrusive and extrusive lithic fragments eastern ross sea till samples are compositionally similar to west antarctic till particularly in their abundance of quartz and dearth of mafic and extrusive lithic components central ross sea till exhibits compositional similarities to both east and west antarctic source terranes including a mafic lithic component and marks the confluence of ice draining from east and west antarctica during the lgm thus west antarctic derived ice streams did not advance into the western ross sea this indicates that even if pre lgm equivalents of the present siple coast ice streams existed they did not simply expand allowing west antarctic derived ice to dominate the lgm ross ice sheet

retreat history of the ross ice sheet shelf since the last glacial maximum from deep basin sediment cores around ross island abstract radiocarbon dated sediment cores from deep basins beneath the mcmurdo ice shelf and seasonally open water north of ross island mcmurdo sound display a characteristic succession of sedimentary facies that document the retreat of the ross ice sheet at the last glacial maximum to its present ice shelf configuration the facies succession records a transition from a nearly grounded ice sheet to open marine environments north of ross island that comprises in ascending stratigraphic order 1 slightly consolidated clast rich muddy diamict dominated by basement clasts from the transantarctic mountains and interpreted as melt out from the basal layer debris proximal to a retreating grounding zone 2 sparsely fossiliferous reworked diatom frustules and non bioturbated mud lacking lonestones interpreted as a sub ice shelf facies and 3 diatom mud and diatom ooze indicative of open marine conditions with evidence of iceberg rafting the succession in the open marine lewis basin north of ross island is similar though the diamict is much sandier and sedimentation rates 1 2 orders of magnitude higher we present a radiocarbon chronology from total organic carbon which implies that lift off of grounded ice in the 900 m deep marine basins surrounding ross island occurred by 10 100 14c years bp following lift off an ice shelf was maintained to the north of ross island until 8900 14c years bp we identify a phase of accelerated retreat at that time between the drygalski trough and ross island immediately preceding the timing of meltwater pulse 1b at 8900 14c years bp the calving line became pinned to ross island significantly decoupling from the grounding line and marking the transition from a retreating ice sheet to the development of the present ice shelf

overcoming the stauchwall viscoelastic stress redistribution and the start of full depth gliding snow avalanches 1 when a full depth tensile crack opens in the mountain snowcover internal forces are transferred from the fracture crown to the stauchwall the stauchwall is located at the lower limit of a gliding zone and must carry the weight of the snowcover the stauchwall can fail leading to full depth snow avalanches or it can withstand the stress redistribution the snowcover often finds a new static equilibrium despite the initial crack we present a model describing how the snowcover reacts to the sudden transfer of the forces from the crown to the stauchwall our goal is to find the conditions for failure and the start of full depth avalanches the model balances the inertial forces of the gliding snowcover with the viscoelastic response of the stauchwall we compute stresses strain rates and deformations during the stress redistribution and show that a new equilibrium state is not found directly but depends on the viscoelastic properties of the snow which are density and temperature dependent during the stress redistribution the stauchwall encounters stresses and strain rates that can be much higher than at the final equilibrium state because of the excess strain rates the stauchwall can fail in brittle compression before reaching the new equilibrium snow viscosity and the length of the gliding snow region are the two critical parameters governing the transition from stable snowpack gliding to avalanche flow the model reveals why the formation of gliding snow avalanches is height invariant and how technical measures to prevent snowpack glide can be optimized to improve avalanche mitigation

the layered character of snow covers snow studies have generally ignored the layered nature of snow covers having achieved a good understanding of the properties and processes in homogeneous snow snow scientists should develop more insight into the evolution of the layers and their effects on overall snow response many of the outstanding problems in snow studies can only be solved by dealing with snow as a layered medium the various mechanisms by which layers are generated their effects and some of the outstanding research problems are described here

the mesozoic victoria basin vanished link between antarctica and australia the transantarctic mountains tam are the largest non compressional mountain belt in the world their origin is traditionally related to crustal thickening during the jurassic ferrar magmatic event that was followed by episodic uplift in the early and late cretaceous and since the paleocene this concept of a long lived morphological high constitutes a base of virtually all gondwana reconstructions and global climate models here we demonstrate that crossover age relationships between thermochronological apatite fission track data and stratigraphic information contradict this established interpretation instead these data together with a wealth of independent thermal indicators and geological evidence require the existence of a vast intra gondwana basin between at least late triassic and late cretaceous times including during the ferrar magmatic event referred to here as the mesozoic victoria basin mvb this basin formed during crustal extension across the paleo pacific margin of antarctica and australia uplift of the tam with associated basin inversion commenced only with the development of the west antarctic rift system in paleogene times the recognition of the long lived mvb has primary consequences for the general understanding of the landscape of gondwana and the breakup between antarctica and australia west antarctic rifting and uplift of the tam and global long term climate evolution and faunal radiation

post mid cretaceous tectonic and topographic evolution of western marie byrd land westantarctica insights from apatite fissiontrack and u th sm he data

glacial removal of late cenozoic subglacially emplaced volcanic edifices by the west antarctic ice sheet local maxima of the horizontal gradient of pseudogravity from closely spaced aeromagnetic surveys over the ross sea northwestern ross ice shelf and the west antarctic ice sheet reveal a linear magnetic rift fabric and numerous subcircular high amplitude anomalies most of these anomalies have sources that probably resulted from late cenozoic volcanism some of these volcanic structures penetrate the neogene sediments beneath the deglaciated continental shelf and are present at the base of the present grounded ice sheet and beneath the ice shelf geophysical data indicate two or three youthful volcanic edifices at widely separated areas beneath the sea and ice cover in the west antarctic rift system in contrast we suggest glacial removal of edifices of volcanic sources of many more anomalies magnetic models controlled by marine seismic reflection and radar ice sounding data allow us to infer that glacial removal of the associated late cenozoic volcanic edifices probably debris comprising pillow breccias and hyaloclastites has occurred essentially concomitantly with their subglacial eruption removal of unconsolidated volcanic debris erupted beneath the ice is probably a more appropriate term than erosion given its fragmented ice contact origin the exposed volcanoes may have been protected from erosion by the surrounding ice sheet because of more competent rock or high elevation above the ice sheet glacial removal may be the general case exposed late cenozoic volcanic peaks and outcrops consisting primarily of flows which erupted during antarctic glacial conditions since approx 30 ma may be the exceptions the volume of the exposed volcanoes is small in contrast to the much greater volume 106 km3 of late cenozoic magmatic rock remaining at volcanic centers beneath the continental shelf ross ice shelf and west antarctic ice sheet

retreat signature of a polar ice stream sub glacial geomorphic features and sediments from the ross sea antarctica abstract three research expeditions to the ross sea antarctica resulted in collection of a dataset of more than 270 km of side scan and chirp sonar data more than 330 km of swath bathymetry and 3 5 khz data and 24 cores within a glacially carved trough the former ice stream flow path is divided into six zones covering a distance of approximately 370 km distinguished by unique stratigraphic signatures and geomorphic features an erosional surface with thin patchy lodgement till characterizes zone 1 this region is interpreted as having experienced relatively high basal shear stress conditions zones 2 3 and 4 are characterized by an erosional surface and thin time transgressive subglacial and grounding line proximal deposits that include back stepping moraines flutes transverse moraines and corrugation moraines these zones represent the transition between erosional and depositional regimes under the expanded lgm ice sheet material eroded from the inner shelf was transported toward the outer shelf possibly as a thin deforming till layer the two outer zones are depositional and include maximum grounding line zone 5 and pro glacial deposits that were overridden subsequently by the ice sheet zone 6 surface features include mega scale glacial lineations corrugation moraines and iceberg furrows ice in these zones is interpreted as having experienced relatively lower basal shear stress an extensional regime and faster flow this advance may have destabilized the ice sheet initiating local draw down and production of icebergs that furrowed the sea floor corrugation moraines are thought to represent annual retreat moraines constraining the retreat rate of the ice sheet across the continental shelf to a consistent 40 to 100 m a 1

early stall of west antarctic ice sheet advance on the eastern ross sea middle shelf followed by retreat at 27 50014cyrbp abstract marine geological and geophysical data suggest that the west antarctic ice sheet wais deposited three thick seismically resolvable units in the eastern ross sea since the last glacial maximum lgm but the chronology of these grounding events is debated existing ice retreat chronologies for the eastern ross sea are considered suspect because nearly all have been developed using radiocarbon dating of acid insoluble organics aio from bulk sediment we used a new strategy to isolate in situ forams from diamict sediment deposited at the middle shelf grounding zone wedge gzw a subaqueous ice marginal landform previously interpreted to represent deposition during the third grounding event since the lgm advance to the shelf edge here we present a synthesis of our new radiocarbon dates of foram tests and aio with previously published radiocarbon dates we propose that the wais s lgm advance in the eastern ross sea sector reached the middle shelf circa 27 500 14c yr bp and that open marine sedimentation began shortly thereafter there is as of yet no clear explanation for why wais retreat in this sector of antarctica apparently began prior to the peak of the last glacial cold period a precipitation deficit localized warm water intrusion an ice dynamic response in the absence of climate forcing or another as of yet unknown forcing mechanism could be responsible

kar dates and paleomagnetic evidence for cretaceous alteration of mesozoic basaltic lava flows mesa range northern victoria land antarctica abstract the mesozoic tholeiite basalts in the transantarctic mountains are probably jurassic in age based on a fragmentary fossil record on their stratigraphic relation to the older sedimentary rocks of the beacon supergroup and on a few 40 ar 39 ar and rb sr age determinations however the whole rock k ar dates of these basalts vary widely between 100 and 200 ma and do not constrain the age of these rocks new whole rock a ar dates of flows on the summit of pain mesa in the mesa range of northern victoria range from 103 4 to 174 7 ma and confirm previously published results however chemical analyses indicate that the k2o concentrations of these flows on pain mesa decrease with increasing volatile content loss on ignition and that most of the low k flows in the mesa range yield low k ar dates this evidence suggests that k was lost as a result of alteration of the flows by aqueous solutions and that the alteration was accompanied by even greater losses of radiogenic 40ar accordingly the new k ar dates of these rocks indicate that the age of alteration is 176 8 ma the discordance of k ar dates of the lava flows of the mesa range as well as those at litell rocks reported by other investigators suggests that northern victoria land experienced a geologic event during the cretaceous period that caused low grade thermal metamorphism and hydrothermal alteration of the flows the occurrence of such an event is supported by paleomagnetic evidence indicating that the basalt flows of the mesa range and the litell rocks as well as sedimentary rocks of early paleozoic age of the bowers terrane in northern victoria land have anomalous virtual geomagnetic pole positions caused by remagnetization during the cretaceous period the tectonothermal and hydrothermal activity in northern victoria land during the cretaceous period indicated by these results may have been caused by the reactivation of deep crustal faults in the area during the separation of australia from antarctica

expansion and rapid retreat of the west antarctic ice sheet in eastern ross sea possible consequence of over extended ice streams abstract marine geological data from the eastern ross sea provide compelling evidence that the west antarctic ice sheet extended to the continental shelf break during the last glacial maximum swath bathymetry records show mega scale glacial lineations within each of the four large glacial troughs on the shelf these features extend virtually uninterrupted across the shelf and have sharp lateral boundaries sediment cores that sampled the lineations recovered diamicton that is interpreted as deformation till the combined data indicate streaming ice the great extent of the paleo ice streams up to 1000 km in length is attributed to the fact that they flowed across unconsolidated sedimentary strata geomorphic features that are known to form at the retreating grounding line such as recessional moraines and ridges are restricted to the southeastern portion of the shelf iceberg furrows that occur at depths of up to 650 m overprint mega scale lineations these deep furrows are interpreted as having been formed by icebergs calved from the grounding line of the ice sheet which indicates the absence of a fringing ice shelf sediment cores sampled a thin layer of glaciomarine sediments resting sharply on till sub ice shelf deposits similar to those sampled in the western ross sea were not recovered in the eastern ross sea these combined results imply rapid retreat of the ice sheet from the shelf crosscutting lineations with different orientations indicate changes in flow direction that probably occurred as the ice profile was lowered and the physiography of the sea floor across which the ice sheet was retreating changed grounding zone wedges vary in number and location within individual troughs which indicates diachronous retreat of ice streams due to a lack of carbonate material for radiocarbon dating all radiocarbon ages were derived from acid insoluble organic aio fractions these dates indicate early retreat of the ice sheet relative to the western ross sea and other areas of west antarctica however the older dates must be viewed as suspect due to a paucity of diatomaceous material and contamination from old carbon while we were not successful at constraining the timing of ice sheet retreat from the continental shelf the data do indicate that the ice sheet was grounded on the shelf during the lgm

chronology of late wisconsin ice retreat from the western ross sea antarctica lithologic data from marine sedimentary cores and accelerator mass spectrometer ams radiocarbon dates indicate that grounded ice did not advance to the western ross sea continental shelf edge during the last glacial maximum lgm a chronology of the timing of ice retreat was provided by 26 ams dates obtained from 12 cores dates ranging from 20 to 29 ka suggest that the outer continental shelf beyond ca lat 74 s was not covered by grounded glacial ice prior to and during the early stages of the lgm 14c dates just above transitions from subglacial diamictons to marine muds indicate that the area around the drygalski ice tongue was deglaciated by at least 11 5 ka the ross ice shelf reached its present day position near ross island by about 7 ka a hiatus of about 15 ka is apparent in radiocarbon dates in cores from the outer continental shelf the hiatus is interpreted to represent an absence of sedimentation caused by the presence of an ice shelf

folding of passive layers and forms of minor structures near terminations of blind thrust faults application to the central appalachian blind thrust abstract the existence of detachment surfaces or decollement zones beneath folded rocks of the valley and ridge and plateau provinces of the appalachians has been recognized as an important condition of folding large folds at the border between the two provinces resulted primarily from repetition of strata by thrusting of blocks over ramp faults that connect detachement surfaces at different horizons some investigators have suggested that folds in the plateau province of pennsylvania were produced by splay faults arising from detachment surfaces but field observations and theoretical analyses by sherwin and by wiltschko chapple suggest that the folds are a result of buckling of multilayered rocks above a decollement an exception may be the burning springs anticline in west virginia which appears to have formed at the termination of a detachment surface investigation of the translation of an homogenous viscous material above a flat detachment surface that terminates laterally indicates that the termination produces a broad low amplitude anticline in passive layering as a result of thickening induced by a gradient of shear stresses in the vertical direction this thickening above the termination of a detachment is a mechanism of folding if the viscous fluid contained mechanical layering the fold would become amplified by buckling computations of stresses in the material indicate that minor faults should be generated first near the termination of the flat detachment surface the burning springs anticline probably was initiated by termination of a detachment surface and subsequently amplified by buckling

efficacy of laser cleaning in the removal of biological patina on the volcanic scoria of the rock hewn churches of lalibela ethiopia the lalibela rock hewn churches are one of the most important religious pilgrimage sites in ethiopia these churches are carved from the scoriaceous basalt rock substrate which has been exposed to attack by biological agents with significant loss of surface material particularly the widespread growth of lichens and other microorganisms on the carved surfaces of the churches has proven to represent a substantial threat for the preservation of the site in this study laboratory tests have been conducted to assess the feasibility of using laser technology as an efficient cleaning method of biological patina from polymineralic stone substrates multi analytical techniques were applied for the characterization of the stone samples collected from two of the lalibela churches bete giyorgis and bete amanuel stone samples artificially inoculated with bacteria yeast fungi isolates and lichen encrusted samples were laser cleaned using uv and ir laser wavelengths the high content of fe and ti oxides and the high porosity have made the stone surfaces easily susceptible to low energy laser treatment results indicate that laser cleaning can be applied to polymineralic lithotypes and uv irradiation can successfully remove lichen colonies further studies need to be conducted to optimize the laser procedure in polymineralic high porosity stones

ross sea mylonites and the timing of intracontinental extension within the west antarctic rift system there are few direct constraints on the timing and style of faulting in the ross sea sector of the west antarctic rift system although cretaceous plate reconstructions indicate that ross sea extension between east and west antarctica occurred prior to breakup of the gondwana margin ca 80 ma mylonitic gneisses dredged from the eastern ross sea indicate shear zone deformation considerably earlier at 98 95 ma strain analysis of fab rics indicates 85 100 extension overprinting brittle structures record translation of shear zone gneisses into the upper crust samples yield sensitive high resolution ion microprobe u pb zircon ages of 102 97 ma correlated to byrd coast granite onshore and concordant 40 ar 39 ar biotite and k feldspar ages of 98 95 ma indicating that granites were mylonitized soon after emplacement and cooled rapidly apatite fission track data corroborate this rapid cooling event and reveal a second rapid cooling event ca 80 ma evidence for contemporaneous deformation and a similar thermal evolution at deep sea drilling project site 270 on the ross sea central high and for a migmatite dome on land attests to the regional extent of intracontinental extension extension occurred at a time of complex microplate interactions along the cretaceous active gondwana margin sug gesting that distributed deformation in the overriding antarctic plate may be related to plate boundary dynamics

analysis of antarctic glacigenic sediment provenance through geochemical and petrologic applications abstract the number of provenance studies of glacigenic sediments in antarctica has increased dramatically over the past decade providing an enhanced understanding of ice sheet history and dynamics along with the broader geologic history such data have been used to assess glacial erosion patterns at the catchment scale flow path reconstructions over a wide range of scales and ice sheet fluctuations indicated by iceberg rafted debris in circumantarctic glacial marine sediments it is notable that even though most of the bedrock of the continent is ice covered and inaccessible provenance data can provide such valuable information about antarctic ice and can even be used to infer buried rock types along with their geo and thermochronologic history glacigenic sediments provide a broader array of provenance analysis opportunities than any other sediment type because of their wide range of grain sizes and in this paper we review methods and examples from all size fractions that have been applied to the antarctic glacigenic sedimentary record interpretations of these records must take careful consideration of the choice of analytical methods uneven patterns of erosion and spatial variability in sediment transport and rock types which all may lead to a preferential identification of different elements of sources in the provenance analyses because of this we advocate a multi proxy approach and highlight studies that demonstrate the value of selecting complementary provenance methods

modelling west antarctic ice sheet growth and collapse through the past five million years changes in earth s orbit are known to influence climate shifts from cold glacials to warm interglacials how the vast west antarctic ice sheet responds to these fluctuations is uncertain but because its collapse could raise sea levels by about 5 metres of great interest naish et al have analysed the and 1b ocean sediment core extracted from beneath the ross ice shelf as part of the andrill drilling project and find evidence that the ice sheet collapsed periodically during the early pliocene 3 5 million years ago when atmospheric co2 levels were similar to or slightly higher than today s the pattern of collapse suggests an influence of approximately 40 000 year cycles in the tilt of earth s rotational axis obliquity also in this issue of nature in a numerical modelling study focused on the past 5 million years in antarctica david pollard and robert deconto combine ice sheet land supported and ice shelf water supported modelling approaches to simulate the movement of the grounding line the border between land and sea ice their results show that over the past 5 million years the west antarctic ice sheet transitioned between full intermediate and collapsed states in just a few thousand years this means that the ice sheet is likely to disintegrate if ocean temperatures in the area rise by 5 c if the west antarctic ice sheet wais melted sea levels would rise by about 5 m such changes are thought to have occurred in the past but could not be simulated by models pollard and deconto combine ice sheet with ice shelf modelling and show that over the past 5 million years the wais transitioned among full intermediate and collapsed states in only a few thousand years suggesting possible disintegration of the wais if ocean temperatures in the area rise by 5 c the west antarctic ice sheet wais with ice volume equivalent to 5 m of sea level1 has long been considered capable of past and future catastrophic collapse2 3 4 today the ice sheet is fringed by vulnerable floating ice shelves that buttress the fast flow of inland ice streams grounding lines are several hundred metres below sea level and the bed deepens upstream raising the prospect of runaway retreat3 5 projections of future wais behaviour have been hampered by limited understanding of past variations and their underlying forcing mechanisms6 7 its variation since the last glacial maximum is best known with grounding lines advancing to the continental shelf edges around 15 kyr ago before retreating to near modern locations by 3 kyr ago8 prior collapses during the warmth of the early pliocene epoch9 and some pleistocene interglacials have been suggested indirectly from records of sea level and deep sea core isotopes and by the discovery of open ocean diatoms in subglacial sediments10 until now11 however little direct evidence of such behaviour has been available here we use a combined ice sheet ice shelf model12 capable of high resolution nesting with a new treatment of grounding line dynamics and ice shelf buttressing5 to simulate antarctic ice sheet variations over the past five million years modelled wais variations range from full glacial extents with grounding lines near the continental shelf break intermediate states similar to modern and brief but dramatic retreats leaving only small isolated ice caps on west antarctic islands transitions between glacial intermediate and collapsed states are relatively rapid taking one to several thousand years our simulation is in good agreement with a new sediment record andrill and 1b recovered from the western ross sea11 indicating a long term trend from more frequently collapsed to more glaciated states dominant 40 kyr cyclicity in the pliocene and major retreats at marine isotope stage 31 1 07 myr ago and other super interglacials

distinguishing subglacial till and glacial marine diamictons in the western ross sea antarctica implications for a last glacial maximum grounding line analyses of lithology stratigraphy and tephra from marine sediment cores collected from the western ross sea during cruises eltanin 32 and 52 and deep freeze 80 and 87 indicate that subglacial till does not extend to the continental shelf edge subglacial till occurs as the lowest unit in most cores landward south of approximately 74 s while seaward of approximately 74 s the lowest diamicton units are glacial marine diamictons glacial marine diamictons are distinguished from subglacial tills by the presence of higher and more variable total organic carbon content downcore distinct tephra layers stratification higher diatom and foraminifera abundances higher sand content and radiocarbon dates in chronological order downcore sand sized tephra layers from two cores on the outer continental shelf are interpreted as single eruptive events one likely to have been derived from the mount melbourne volcano and the other from the pleiades volcano radiocarbon dates from sediment above and below the tephra layer in one of these cores df87 32 show that deposition indicative of open water conditions occurred between 22 and 26 ka in the western ross sea

continuous simulations over the last 40 million years with a coupled antarctic ice sheet sediment model abstract much of the knowledge of antarctic ice sheet variations since its inception 34 ma derives from marine sediments on the continental shelf deposited in glacimarine or sub ice environments by advancing and retreating grounded ice and observed today by seismic profiling and coring here we apply a 3 d coupled ice sheet and sediment model from 40 ma to the present with the goal of directly linking ice sheet variations with the sediment record the ice sheet model uses vertically averaged ice dynamics and parameterized grounding line flux the sediment model includes quarrying of bedrock sub ice transport and marine deposition atmospheric and oceanic forcing are determined by uniform shifts to modern climatology in proportion to records of atmospheric co2 deep sea core 18o and orbital insolation variations the model is run continuously over the last 40 myr at coarse resolution 80 or 160 km modeling post eocene ice landscape evolution and off shore sediment packages in a single self consistent simulation strata and unconformities are tracked by recording times of deposition within the model sediment stacks which can be compared directly with observed seismic profiles the initial bedrock topography is initialized to 34 ma geologic reconstructions or an iterative procedure is used that yields independent estimates of paleo bedrock topography preliminary results are compared with recognized cenozoic ice sheet variations modern sediment distributions and seismic profiles and modern and paleo bedrock topographies

the heavy mineral record in the pliocene to quaternary sediments of the ciros 2 drill core mcmurdo sound antarctica the heavy mineral assemblages of the lower pliocene to quaternary glacial sediments of the ciros 2 drill site situated near the mouth of ferrar glacier on the mcmurdo sound shelf antarctica were analysed by optical means in order to reconstruct the source areas and dynamics of the late cenozoic antarctic ice masses the assemblages are dominated by pyroxenes amphiboles altered minerals and opaque minerals within the pyroxene group clinopyroxenes are most abundant within the amphibole group green and brown hornblendes are dominant other important heavy minerals present in minor amounts are zircon titanite epidote garnet and apatite the downcore distribution of the heavy minerals allows a subdivision of the sedimentary sequence into two major units which can both be further subdivided into two subunits the pliocene interval between 166 and 110 mbsf is characterized by relatively high concentrations of apatite zircon titanite garnet epidote and green hornblende this assemblage accounts for some 40 60 of the heavy minerals and points to a source to the west of the drill site in the transantarctic mountains where intrusive metamorphic and sedimentary rocks cover large areas the interval 166 137 mbsf lower pliocene contains additional brown hornblende and palagonite indicative of a volcanic probably hyaloclastitic source which possibly has to be sought beneath the ice of the ferrar glacier in contrast the uppermost pliocene and quaternary interval between 110 mbsf and the top of the core is characterized by high concentrations of clinopyroxenes altered minerals and opaque minerals this record points to a main source area in the south or east where large areas are occupied by basaltic rocks of the mcmurdo volcanic group a slight change in the composition of the pyroxene group occurs within this interval at 48 mbsf thus the heavy minerals in the sediments of core ciros 2 document different source areas and therewith major changes in the ice dynamics during the pliocene the ice discharged through the transantarctic mountains into the mcmurdo sound the source area shifted in the quaternary to the south to the region of the present day ross ice shelf 1999 elsevier science b v all rights reserved

late pleistocene holocene retreat of the west antarctic ice sheet system in the ross sea part 2 sedimentologic and stratigraphic signature sedimentologic geotechnical geochemical and accelerator mass spectrometer ams radiocarbon data from two marine geologic cruises in the ross sea have allowed us to constrain facies relationships and temporal changes in the west antarctic ice sheet the selection of core sites was facilitated by the use of multibeam bottom imagery and a good quality chirp subbottom reflection system a complex but consistent succession of facies documents a number of environments from subglacial to open marine massive mud rich diamictons have low water contents contain in places a calcareous microfossil assemblage show minimal textural variation and contain low and uniform total organic carbon values this reflects a subglacial setting this unit passes upward into a stratified thin granulated facies consisting of pelletized sandy muddy gravel that is loosely compacted and contains a variable water content and concentrated horizons of pebble sized clasts this facies reflects the lift off zone or thin water film between the basal debris and sea floor overlying this unit are silty clays that contain a well sorted very fine grained sand component there are no coarse grains within this unit this facies is in part laminated and reflects deposition beneath an ice shelf near and away from the grounding line zone the ice shelf facies passes upward into a siliceous mud and ooze unit that represents deposition in an open marine setting a sandy volcaniclastic rich subfacies marks the transition from ice shelf to open marine environments found at the calving line the 86 ams radiocarbon dates on organic matter provide an accurate chronology for 19 cores ice shelf conditions were established in the outer drygalski trough by 11 0 25 ka and perhaps earlier this transition took place in the joides basin by 10 8 ka the calving front of the ross ice shelf passed over the drygalski trough at 74 s by 9 5 0 25 ka the timing of deglaciation in the ross sea calls into question current models for the contribution of antarctic glacial ice to holocene sea level rise and suggests that recession was relatively gradual and more closely aligned with northern hemisphere deglaciation and its associated eustatic pulse

characteristics of snow gliding on rock summary discussion our data from gliding on steep rock show the following characteristics i highly fluctuating values of glide speed are found particularly in early winter and late spring those characteristics are however consistent with gliding theory 2 data for two winters showed that glide rates tend to be similar at the same location for winters of similar character 3 our studies of spatial variation show that glide speed is higher below the step in the rock where snow has separated from the rock in the snow cover than above it there are probably two contributing effects i the presence of the free surface at the uphill surface of the snow allows easier downslope motion of the gliding slab and 2 the open crack can help to concentrate melt water at the glide interface by serving as an open reservoir for surface melt water to concentrate 4 we cannot conclusively say whether glide rates are on average faster during the day than at night better scrutiny of meteorological parameters is needed to understand gliding on a diurnal time scale two winters gliding data do not yield a clear answer 5 we have presented simple analytical expressions for the longitudinal force on restraining barriers in deep snow covers mcclung and larsen 1989 and on roofs when gliding is present the character of the problem on a warm smooth roof is obviously of a different character than that of a deep snow cover bu t it may be approached from a similar mechanics formalism in the zero friction limit equation 3b constants from the glide constitutive equation do not appear mcclung and others snow gliding on rocks one aspect of gliding which is not included in our simple analytical formulae for barrier forces is time dependence even though gliding shows highly fluctuat ing time dependence our equations are based on quasi static formulations a complete time dependent solution is not available yet and its implications for engineering problems have not been fully considered our simple analysis of the fluctuations eq uation 8 and physics of snow gliding shows consistency with the proposed gliding constitutive equation

cenozoic erosion of the transantarctic mountains a source to sink thermochronological study abstract the formation of the transantarctic mountains tam is strictly related to the evolution of the west antarctic rift system but the timing of their exhumation is still not fully assessed in this work we provide new apatite fission track data collected on the region between the royal society range and the britannia range cooling ages are late eocene oligocene in the center of the region but they get older both northwards and southwards we infer that exhumation was strictly controlled by tam parallel fault strands that were active after the oligocene the royal society range and the britannia range represent transition zones corresponding to transverse structures probably inherited from early basement crustal discontinuities and reactivated as transfer regions during rift propagation the exhumation of the investigated region has been then modeled and predicted thermochronological ages have been compared with detrital data from the miocene sedimentary succession drilled in the victoria land basin results indicate that this sector of the tam is the most probable candidate for the source of sediments and that during the neogene 3 km but up to 5 km of rocks was exhumed

soiling of limestone in an urban environment characterized by heavy vehicular exhaust emissions the inorganic and organic chemical composition of weathering sulphate patinas on the limestone walls of emmanuel college cambridge uk have been analysed by ft ir spectroscopy pyrolysis gas chromatography mass spectrometry and scanning electron microscopy the college location is characterized by heavy vehicular exhaust emissions including those from diesel powered public transport vehicles due to its proximity to the main cambridge coach station a complex mixture of gaseous and particulate air pollutants are found deposited in the weathering patinas including organic compounds such as pahs which represent markers for present day vehicular pollution slight differences in composition between patinas collected at different heights on the building facades with in particular more evidence for a biogenic overprint in samples collected at roof level as opposed to ground street level are found analytical results confirm how building stones in urban areas acted in the past and still do today as passive repositories for any kind of gaseous and particulate air pollutant present in the surrounding atmosphere accordingly weathering patinas are slowly changing their composition to accommodate new classes of present day air pollutants

change in snow strength caused by rain rain on snow events can cause wet snow avalanches laboratory experiments were carried out to investigate the change in snow strength with increasing water content through rainwater percolation snowpack was artificially prepared consisting of a thin ice layer and fine compacted snow and rainfall 2mmh 1 was artificially applied 22 25 5 and 49 52 hours after the snowpack was formed snow hardness was measured with a push pull force gauge to indicate the snow strength before and after each rain on snow event after the first rainfall the upper half of the snowpack became wet and a rapid decrease in snow hardness was observed after the second rainfall the rainwater penetrated the ice layer high water content was observed above the ice layer but the hardness exceeded that estimated from an empirical relationship between hardness and water content micrographs of the snow particles suggest that the delay in grain coarsening observed near the wetting front induces the harder than estimated snow condition

evidence of a full west antarctic ice sheet back to the early oligocene insight from double dating of detrital apatites in ross sea sediments the west antarctic ice sheet is the most unstable component of the antarctic cryosphere its fluctuations are well documented since the pliocene but its behaviour over the last 35 ma is more controversial particularly during periods of past high global pco2 values similar to those predicted in future global climate scenarios here we present new u pb dating of detrital apatite grains previously dated by the fission track method from cape roberts project oligocene to pliocene marine sediments in the ross sea two past ice flow patterns were identified one formed by outlet glaciers sourcing short travelled apatites and one northerly directed bringing far travelled apatite grains the latter provides the first robust physical evidence for the presence and repeated expansion of an oligocene west antarctic ice sheet

applications of detrital geochronology and thermochronology from glacial deposits to the paleozoic and mesozoic thermal history of the ross embayment antarctica

kaolinisation of granite in an urban environment under natural acid and wet conditions one of the main weathering processes affecting granitic rocks is the kaolinisation of na ca and k feldspar minerals by h2o co2 attack we here report the occurrence of authigenic kaolinite on the surface of an eighteenth century granitic monument covered with sulphate rich weathering patinas we suggest that in humid mesothermic climates anthropogenically derived gaseous so2 from air pollution is responsible for accelerated kaolinisation of feldspars in an urban environment so2 from air pollution thus plays a dual role in the weathering of silicate rocks being responsible for the well known sulphation of ca bearing materials leading to the formation of sulphate salts such as gypsum as well as the weathering of feldspar minerals to kaolinite the kaolinisation reaction weakens the granite microfabric leading to enhanced decay of the building stone

interpretation of u th he single grain ages from slowly cooled crustal terranes a case study from the transantarctic mountains of southern victoria land low temperature thermochronologic techniques e g apatite fission track aft thermochronology and u th he dating constrain near surface t t paths and are often applied to uplift denudation and landscape evolution studies samples collected in vertical profiles from granitic walls on either side of the ferrar glacier southern victoria land antarctica were analyzed using aft thermochronology and apatite u th he dating to further constrain the lowest temperature thermal history of this portion of the transantarctic mountains aft central ages vary systematically with elevation and together with track length information define a multi stage cooling denudation history in the cretaceous and early tertiary apatite u th he single grain age variation with elevation is not as systematic with considerable intra sample age variation although many complicating factors e g u and th rich micro inclusions fluid inclusions variation in crystal size particle ejection correction zonation and particle ejection correction implantation of he into a crystal or impediment of he diffusion out of a crystal and 147sm derived particles may contribute to age dispersion we found that variation in single grain ages correlated with cooling rate samples that cooled relatively quickly have less variation in single grain ages whereas samples that cooled relatively slowly 3 c m y or resided within an u th he partial retention zone heprz prior to more rapid cooling have a comparatively greater variation in ages decay of u and th via particle emission creates a 4he concentration profile dependent upon the initial parent u th within a crystal variation of single grain ages for samples with non homogeneous u th distributions will be enhanced with long residence time in the partial retention zone i e slow cooling because of the relative importance of loss via volume diffusion and loss via particle ejection with respect to the u th zonation and the grain boundary correction of ages for particle ejection ft correction factor typically assumes uniform u and th distribution within the crystal and when applied to a population of crystals with different u and th distributions will enhance the variation in ages most complicating factors listed above for apatite u th he ages result in ages that are too old we propose that if considerable variation in u th he single grain ages exists that a weighted mean age is determined once outlier single crystal ages are excluded using the criterion of chauvenet or a similar approach we suggest that the true age or most representative age for that age population lies between the minimum u th he age and the weighted mean age we apply this approach coupled with composite age profiles to better constrain the t t history of the profiles along the ferrar glacier significant intra sample variation in single crystal apatite u th he ages and other minerals dated by the u th he method should be expected especially when the cooling rate is slow the variation of u th he single crystal ages is therefore another parameter that can be used to constrain low temperature thermal histories