cosmogenic nuclides constrain surface fluctuations of an east antarctic outlet glacier since the pliocene understanding past changes in the antarctic ice sheets provides insight into how they might respond to future climate warming during the pliocene and pleistocene geological data show that the east antarctic ice sheet responded to glacial and interglacial cycles by remaining relatively stable in its interior but oscillating at its marine based margin it is currently not clear how outlet glaciers which connect the ice sheet interior to its margin responded to these orbitally paced climate cycles here we report new ice surface constraints from skelton glacier an outlet of the east antarctic ice sheet which drains into the ross ice shelf our multiple isotope 10be and 26al cosmogenic nuclide data indicate that currently ice free areas adjacent to the glacier underwent substantial periods of exposure and ice cover in the past we use an exposure burial model driven by orbitally paced glacial interglacial cycles to determine the probable ice surface history implied by our data this analysis shows that 1 the glacier surface has likely fluctuated since at least the pliocene 2 the ice surface was 200 m higher than today during glacial periods and the glacier has been thicker than present for 75 90 of each glacial interglacial cycle and 3 ice cover at higher elevations possibly occurred for a relatively shorter time per pliocene cycle than pleistocene cycle our multiple nuclide approach demonstrates the magnitude of ice surface fluctuations during the pliocene and pleistocene that are linked to marine based ice margin variability

retreat history of the east antarctic ice sheet since the last glacial maximum the east antarctic ice sheet eais is the largest continental ice mass on earth and documenting its evolution since the last glacial maximum lgm is important for understanding its present day and future behaviour as part of a community effort we review geological evidence from east antarctica that constrains the ice sheet history throughout this period 30 000 years ago to present this includes terrestrial cosmogenic nuclide dates from previously glaciated regions 14c chronologies from glacial and post glacial deposits onshore and on the continental shelf and ice sheet thickness changes inferred from ice cores and continental scale ice sheet models we also include new 14c dates from the george v land terre adelie coast shelf we show that the eais advanced to the continental shelf margin in some parts of east antarctica and that the ice sheet characteristically thickened by 300 400 m near the present day coastline at these sites this advance was associated with the formation of low gradient ice streams that grounded at depths of 1 km below sea level on the inner continental shelf the lambert amery system thickened by a greater amount 800 m near its present day grounding zone but did not advance beyond the inner continental shelf at other sites in coastal east antarctica e g bunger hills larsemann hills very little change in the ice sheet margin occurred at the lgm perhaps because ice streams accommodated any excess ice build up leaving adjacent ice free areas relatively unaffected evidence from nunataks indicates that the amount of ice sheet thickening diminished inland at the lgm an observation supported by ice cores which suggest that interior ice sheet domes were 100 m lower than present at this time ice sheet recession may have started 18 000 years ago in the lambert amery glacial system and by 14 000 years ago in mac robertson land these early pulses of deglaciation may have been responses to abrupt sea level rise events such as meltwater pulse 1a destabilising the margins of the ice sheet it is unlikely however that east antarctica contributed more than 1 m of eustatic sea level equivalent to post glacial meltwater pulses the majority of ice sheet recession occurred after meltwater pulse 1a between 12 000 and 6000 years ago during a period when the adjacent ocean warmed significantly large tracts of east antarctica remain poorly studied and further work is required to develop a robust understanding of the lgm ice sheet expansion and its subsequent contraction further work will also allow the contribution of the eais to post glacial sea level rise and present day estimates of glacio isostatic adjustment to be refined

cosmic ray labeling of erosion surfaces in situ nuclide production rates and erosion models a number of in situ cosmogenic radionuclides and stable nuclides have been measured in natural exposed rock surfaces with a view to study their in situ production and rock erosion rates 1 the in situ radionuclides can be used for a high resolution tomography of the erosional history of an exposed surface two stable nuclides 3he 21ne and five radionuclides 10be 26al 36cl 14c 39ar having half lives in the range of 300 1 5 106 yr half life are measurable in many rock types a prerequisite for the application of the in situ nuclides for the study of erosional histories of surfaces is a knowledge of their production rates under different irradiation conditions altitude latitude irradiation geometry and shielding relative nuclide production rates can be determined fairly accurately using the extensive available data on cosmic ray neutrons 2 absolute nuclide production rates cannot generally be predicted with any accuracy because of lack of data on excitation functions of nuclides unless some normalization is possible as was done in the case of several cosmic ray produced isotopes in the atmosphere 3 based on a recent natural calibration experiment in which erosion free surfaces exposed to cosmic radiation for 11 000 yrs were sampled the absolute production rates of 10be and 26al in quartz have been accurately estimated for mountain altitudes in sierra nevada 4 the absolute production rates of 10be and 26al in quartz can therefore be estimated fairly accurately for any given latitude and altitude some measurements of 14c in rocks of low erosion rate 5 similarly allow an estimate of its production rate attempts made to measure the in situ production rates of 3he in rocks have not yet led to a convergent production rate in view of the importance of knowing the production rates of isotopes of he ne and ar i present here theoretical estimates of their production rates based on available cross section data i discuss the information that can be extracted from the study of the in situ nuclides in rocks useful parameters characterizing the exposure history of a rock surface are 1 the effective surface exposure age and 2 the time averaged erosion rate the implications of these parameters for single and multiple nuclide studies are discussed in terms of the erosion models considered

the overdeepening hypothesis how erosional modification of the marine scape during the early pliocene altered glacial dynamics on the antarctic peninsula s pacific margin abstract a new synthesis of diatom assemblage data from ocean drilling program odp leg 178 suggests that the pacific margin of the antarctic peninsula underwent a transition from a shallow shelf to an overdeepened shelf in the early pliocene this modification of the marine scape was due to a relatively brief interval of erosion begun at 5 2 ma the erosion was caused by high frequency advances of a super inflated antarctic peninsula ice sheet apis the frequent advances of the higher elevation ice sheet were a consequence of abundant moisture delivered to the region as the polar front migrated southward by 5 12 ma ice streams incised foredeepened glacial troughs into basement on the inner shelf sediment eroded from the inner shelf was transported through cross shelf troughs and deposited in large trough mouth fan depocenters on the upper slope overdeepened shelf conditions became widespread as troughs widened and intra trough banks beveled by 4 25 ma trough mouth fan construction ceased and subsequent advances of the apis have been infrequent we propose that the reduced frequency of grounding events signaled the transition to a modern foredeepened and overdeepened shelf we hypothesize that a new glacial dynamic emerged in the early pliocene because overdeepening led to accelerated heat exchange between the ocean and apis in two ways firstly the overdeepened shelf required that a larger area of the grounded ice sheet s marine terminus be in contact with the ocean secondly erosional deepening of the outer shelf was equivalent to lowering a shelf edge sill that permitted frequent and voluminous intrusion of warm circumpolar deep waters that upwell in the region the resultant accelerated melting at the apis marine terminus caused the super inflated apis to deflate on the mainland which further decreased the possibility that grounded ice could advance on the overdeepened shelf

ice surface lowering of skelton glacier transantarctic mountains since the last glacial maximum implications for retreat of grounded ice in the western ross sea abstract quantifying the contribution of the east antarctic ice sheet eais to sea level rise during the last deglaciation is complicated by the limited opportunities to constrain ice sheet models the nunatak escalade peak provides a gauge for past ice surface elevation changes and behaviour throughout the last glacial cycle geomorphological mapping geological evidence and 10be cosmogenic nuclide exposure dating at escalade peak provide new constraints on the ice surface history of the skelton neve since the last glacial maximum lgm an elevation transect from the eastern margin of escalade peak indicates that the ice surface of the skelton neve was at least 50 m and perhaps 120 m higher than present during the lgm in contrast surface exposure ages from a suite of inner moraines blue ice moraines adjacent to escalade peak do not provide independent ice surface elevation constraints but may provide an indirect constraint on the timing of thinning due to exhumation ablation processes maximum simple exposure ages from the inner moraines suggest ice surface ablation was initiated by 19 2 ka but the majority of ice surface lowering at escalade peak likely occurred after 15 ka and reached the present day ice level at 6 ka these findings suggest that slow flowing inland sites of eais outlet glaciers such as southern skelton neve experienced minimal ice surface elevation change since the lgm and record an eais outlet glacier and western ross sea retreat signature rather than widespread ross sea retreat the ice surface lowering is likely to have been in response to retreat of the grounded ice in the western ross embayment causing a reduction in buttressing of the skelton glacier and draw down into the ross sea

multiple cosmogenic nuclides document complex pleistocene exposure history of glacial drifts in terra nova bay northern victoria land antarctica geomorphological and glacial geological surveys and multiple cosmogenic nuclide analyses 10be 26al and 21ne allowed us to reconstruct the chronology of variations prior to the last glacial maximum of the east antarctic ice sheet eais and valley glaciers in the terra nova bay region glacially scoured coastal piedmonts with round topped mountains occur below the highest local erosional trimline they represent relict landscape features eroded by extensive ice overriding the whole coastal area before at least 6 ma pre dating the build up of the mt melbourne volcanic field since then summit surfaces were continuously exposed and well preserved under polar condition with negligible erosion rates on the order of 17 cm ma complex older drifts rest on deglaciated areas above the younger late pleistocene glacial drift and below the previously overridden summits the combination of stable and radionuclide isotopes documents complex exposure histories with substantial periods of burial combined with minimal erosion the areas below rounded summits were repeatedly exposed and buried by ice from local and outlet glaciers the exposure ages of the older drift s indicate multiple pleistocene glacial cycles which did not significantly modify the pre existing landscape

constraining landscape history and glacial erosivity using paired cosmogenic nuclides in upernavik northwest greenland high latitude landscape evolution processes have the potential to preserve old relict surfaces through burial by cold based nonerosive glacial ice to investigate landscape history and age in the high arctic we analyzed in situ cosmogenic 10 be and 26 al in 33 rocks from upernavik northwest greenland we sampled adjacent bedrock boulder pairs along a 100 km transect at elevations up to 1000 m above sea level bedrock samples gave significantly older apparent exposure ages than corresponding boulder samples and minimum limiting ages increased with elevation two isotope calculations 26 al 10 be on 20 of the 33 samples yielded minimum limiting exposure durations up to 112 k y minimum limiting burial durations up to 900 k y and minimum limiting total histories up to 990 k y the prevalence of 10 be and 26 al inherited from previous periods of exposure especially in bedrock samples at high elevation indicates that these areas record long and complex surface exposure histories including significant periods of burial with little subglacial erosion the long total histories suggest that these high elevation surfaces were largely preserved beneath cold based nonerosive ice or snowfields for at least the latter half of the quaternary because of high concentrations of inherited nuclides only the six youngest boulder samples appear to record the timing of ice retreat these six samples suggest deglaciation of the upernavik coast at 11 3 0 5 ka average 1 standard deviation there is no difference in deglaciation age along the 100 km sample transect indicating that the ice marginal position retreated rapidly at rates of 120 m yr 1

critical behaviour and the evolution of fault strength during earthquake cycles the problem of how fault rheology and heterogeneity interact to produce the observed scaling of earthquakes such as the power law moment frequency relationship remains largely unsolved rock friction experiments have elucidated the properties of smooth faults1 2 3 but seem insufficient to explain the observed complexity of real fault dynamics4 5 the recognition of a connection between fault related processes and critical phenomena in other physical systems together with numerical models of repeated earthquakes have resulted in significant progress in the theoretical interpretation of earthquake scaling4 5 6 7 8 9 10 11 12 13 14 but fault rheology and heterogeneity have so far been treated separately here i attempt to unify the requirements of fault rheology and heterogeneity using numerical calculations of quantized slip in an elastic continuum i show that cyclical fault strength evolves naturally by means of a statistical selection for high strength fault patches asperities resulting in the accumulation and eventual failure of those asperities the applicability of these results to real fault systems is supported by a recent analysis of time dependent earthquake statistics15 these results imply that self similarity and criticality on a fault emerge during an earthquake cycle and suggest that the character of local seismicity can be useful in earthquake forecasting by revealing how advanced a fault is within its cycle

mechanical analysis of the geometry of forced folds a mechanical model of forced folding comprised of an anisotropic cover overlying displaced rigid basement blocks is used to investigate the influence of various parameters on theoretical fold form shape and dip of basement fault strength of basement cover contact and degree of anisotropy of the cover we show that the degree of anisotropy in the cover largely influences the geometry of the forelimb of the forced fold folds produced in isotropic cover display forelimbs that taper from large dip angles near the basement cover contact to low dip angles at the ground surface in contrast dips in the forelimbs of folds in anisotropic cover are nearly uniform with depth we show that the basement cover contact and the shape of the basement fault largely influence the geometry of the backlimb backlimb rotation occurs in cover welded to the basement and in cover underlying curved basement faults in addition the kinematic features of the theoretical folds are compared with the fold geometry generated by parallel kink and trishear models folds in isotropic cover overlying straight basement faults closely resemble the fold forms produced by the trishear kinematic model while fold forms in anisotropic cover more closely resemble folds produced by parallel kink geometric constructions

controls on subaerial erosion rates in antarctica erosion rates offer insight on landscape development and the relative importance of chemical and physical processes of weathering minimal chemical weathering makes antarctica an ideal location in which to compare the physical weathering of carbonate rocks to other lithologies here we report the first cosmogenic nuclide derived erosion rates for carbonate rocks in antarctica carbonate samples collected in the southernmost ellsworth mountains reflect a 36cl erosion rate of 0 22 0 02 mm ka this erosion rate is consistent with other reported antarctic erosion rates but is lower than 36cl erosion rates derived from other arid regions in the world these results are integrated with a continent wide reanalysis of 28 erosion rate studies 200 measurements which comprise numerous rock types and other cosmogenic nuclides by combining cosmogenic nuclide derived erosion rates across studies the larger trends provide insight into factors e g lithology glacial history and availability of abrasive material affecting subaerial erosion rates in antarctica statistical analysis of the compiled data set shows differences based on lithology with sandstone having the largest range of erosion rates the compiled data also reveals higher erosion rates in areas with a large potential sediment supply like the dry valleys samples collected from boulders yield lower erosion rates than those collected from bedrock likely due to a combination of physical processes that affect boulders and bedrock differently and glacial history which can affect the apparent cosmogenic nuclide derived erosion rate

timing of glaciation during the last glacial cycle evaluating the concept of a global last glacial maximum lgm abstract it has long been known that mountain glaciers and continental ice sheets around the globe reached their respective maximum extent at different times during the last glacial cycle often well before the global last glacial maximum lgm c 23 19 ka which is formally defined by peaks in global sea level and marine oxygen isotope records however there is increasing evidence from around the world that it was not only mountain glaciers which were asynchronous with the global lgm but also some regions of the large continental glaciers the barents kara ice sheet in northern eurasia together with a majority of ice masses throughout asia and australasia reached their maximum early in the last glacial cycle a few thousand years before the global lgm period the east antarctic ice sheet also reached its maximum extent several millennia before the global lgm in numerous mountainous regions at high mid and low latitudes across the world glaciers reached their maximum extent before marine isotope stage mis 2 in mis 5 4 and 3 this is in contrast to most sectors of the laurentide ice sheet the cordilleran ice sheet the se sector of the fennoscandinavian ice sheet and the alpine ice sheet in central europe which appear to have reached their maximum close to the global lgm in mis 2 the diachronous maximum extents of both mountain glaciers and continental ice sheets during the last glacial cycle means that the term and acronym last glacial maximum lgm has limited chronostratigraphical meaning when correlating glacial deposits and landforms

plio pleistocene history of ferrar glacier antarctica implications for climate and ice sheet stability abstract the areal distribution and elevation of glacial drifts in vernier valley southern victoria land are used to reconstruct the plio pleistocene history of upper ferrar glacier 21 ne cosmogenic nuclide analyses of surface cobbles on four moraines ferrar 1 2 3 and 4 provide age control a minimum age estimate for ferrar drifts calculated by assuming zero surface erosion indicates that the oldest moraine ferrar 4 was deposited at least 3400 ka our preferred age model which applies a very conservative erosion rate of 5 cm ma 1 in age calculations suggests that ferrar 4 is 4000 ka ferrar 3 is 1200 ka and ferrar 2 is 700 ka based on glacial geologic data ferrar 1 is modern cosmogenic ages for cobbles on this moraine suggest a value for nuclide inheritance of 50 ka the ferrar drifts are most easily interpreted in terms of a progressive reduction in the ice surface elevation of upper ferrar glacier during plio pleistocene time relative to today the surface of upper ferrar glacier was 100 to 125 m higher during the pliocene climatic optimum and 50 m higher during early to mid quaternary time conversely during mis 2 the ice surface elevation of upper ferrar glacier was likely no larger than today and may have stood below modern levels the texture and sedimentology of all ferrar drifts indicate that during ice recession from vernier valley the upper ferrar glacier lacked surface melting ablation zones even during the pliocene climatic optimum results from a simple 2 d glaciological flow band model demonstrate that upper ferrar glacier also lacked basal melting zones during ice recession we show that the development of weathering pits and desert varnish on cobbles exposed at the surface of ferrar drifts varies in accord with cosmogenic age the mean width and depth of the largest surface pits on boulders from ferrar drifts increases by 10 mm ma 1 and 6 7 mm ma 1 respectively the maximum thickness of desert varnish on surface boulders increases by 1 5 mm ma 1 these rates may be used to help calculate ages for dolerite rich drifts elsewhere in the western dry valleys region the general stability of the ice surface elevation of upper ferrar glacier and of the landscape in vernier valley suggests minimal climatic amelioration in the upland region of the dry valleys during the last 4 ma

the newest developments of load unload response ratio lurr the load unload response ratio lurr method is an intermediate term earthquake prediction approach that has shown considerable promise it is inspiring that its predictions using lurr have been improving since 2004 we have made a major breakthrough in intermediate term earthquake forecasting of the strong earthquakes on the chinese mainland using lurr and successfully predicted the pakistan earthquake with magnitude m 7 6 on october 8 2005 the causes for improving the prediction in terms of lurr have been discussed in the present paper

east antarctic deglaciation and the link to global cooling during the quaternary evidence from glacial geomorphology and 10be surface exposure dating of the sor rondane mountains dronning maud land abstract reconstructing past variability of the antarctic ice sheets is essential to understand their stability and to anticipate their contribution to sea level change as a result of future climate change recent studies have reported a significant decrease in thickness of the east antarctic ice sheet eais during the last several million years however the geographical extent of this decrease and subsequent isostatic rebound remain uncertain in this study we reconstruct the magnitude and timing of ice sheet retreat at the sor rondane mountains in dronning maud land east antarctica based on detailed geomorphological survey cosmogenic exposure dating and glacial isostatic adjustment modeling three distinct deglaciation phases are identified for this sector during the quaternary based on rock weathering and 10 be surface exposure data we estimate that the ice sheet thinned by at least 500 m during the pleistocene this thinning is attributed to the reorganization of southern ocean circulation associated with global cooling into the pleistocene which reduced the transport of moisture from the southern ocean to the interior of eais the data also show that since the last glacial maximum the ice surface has lowered less than ca 50 m and that this lowering probably started after ca 14 ka this suggests that the eais in dronning maud land is unlikely to have been a major contributor to postglacial sea level rise and meltwater pulse 1a

landscape chronology and glacial history in thule northwest greenland abstract constraining past responses of ice sheets to changes in climate enhances our ability to predict future changes in ice extent and sea level here we employ surficial geologic mapping stratigraphic analysis radiocarbon dating of marine mollusks and analysis of cosmogenic 10 be in glacially deposited boulders to make inferences about past ice extents in thule northwest greenland our work shows the existence of two distinct diamict units in the thule area we infer that one diamict was deposited by the main greenland ice sheet while the second was deposited by a subsequent outlet glacier re advance boulders in the two diamicts n 13 and n 15 respectively have similar bimodal distributions of cosmogenic 10 be ages both diamicts have a group of younger 10 be ages as well as a more diffuse group of considerably older 10 be ages 20 30 ka many of the boulders likely contain nuclides inherited from previous periods of exposure suggesting that glacial ice in the thule region has been cold based and non erosive in the past the landscape chronology we develop suggests that deglaciation after the last glacial maximum occurred 10 8 ka and was later followed by a re advance of outlet glaciers possibly in concert with the 9 3 ka or 8 2 ka cold events

the last glaciation of bear peninsula central amundsen sea embayment of antarctica constraints on timing and duration revealed by in situ cosmogenic 14c and 10be dating abstract ice streams in the pine island thwaites region of west antarctica currently dominate contributions to sea level rise from the antarctic ice sheet predictions of future ice mass loss from this area rely on physical models that are validated with geological constraints on past extent thickness and timing of ice cover however terrestrial records of ice sheet history from the region remain sparse resulting in significant model uncertainties we report glacial geological evidence for the duration and timing of the last glaciation of hunt bluff in the central amundsen sea embayment a multi nuclide approach was used measuring cosmogenic 10be and in situ 14c in bedrock surfaces and a perched erratic cobble bedrock 10be ages 118 144 ka reflect multiple periods of exposure and ice cover not continuous exposure since the last interglacial as had previously been hypothesized in situ 14c dating suggests that the last glaciation of hunt bluff did not start until 21 1 5 8 ka probably during the last glacial maximum and finished by 9 6 0 9 ka at the same time as ice sheet retreat from the continental shelf was complete thickening of ice at hunt bluff most likely post dated the maximum extent of grounded ice on the outer continental shelf flow re organisation provides a possible explanation for this with the date for onset of ice cover at hunt bluff providing a minimum age for the timing of convergence of the dotson and getz tributaries to form a single palaeo ice stream this is the first time that timing of onset of ice cover has been constrained in the amundsen sea embayment

timing of the local last glacial maximum in terra nova bay antarctica defined by cosmogenic dating abstract the jangbogo hills are erratic covered landforms consisting of a series of benches that are parallel to the length of campbell glacier northern victoria land antarctica we sampled 41 erratic cobbles from six benches to reveal the exposure times of glacier erratics using in situ 10be and 26al the erratics from the upper three benches yield exposure ages older than marine isotope stage mis 4 with most exposed since mis 5 however the lower three benches exhibit tight clusters of exposure ages that range from mis 3 to the holocene campbell glacier underwent rapid downwasting during mis 5 centered at 98 3 ka from its maximum position at the penultimate glacial maximum pgm this downwasting continued throughout the last glacial period with a potential minor stagnation around a bench 90 m asl between 35 4 and 17 0 ka our cosmogenic nuclides surface exposure dating results highlight three important points concerning the glacial history of terra nova bay since the penultimate glacial maximum pgm in northern victoria land antarctica 1 campbell glacier was thicker at the pgm than at the global last glacial maximum lgm 2 the local lgm occurred during mis 4 and 3 the extent of campbell glacier during the global lgm 90 m was much smaller than previously assumed 300 400 m hence the previous view that the local lgm mis 4 in victoria land antarctica was synchronous with the global lgm mis 2 should be treated with caution

pleistocene dynamics of the interior east antarctic ice sheet current models describing past configurations of the east antarctic ice sheet are poorly constrained by observations exposure dating of bedrock surfaces using in situ produced cosmogenic nuclides provides an ideal tool for directly constraining former changes in ice sheet elevation we present cosmogenic radionuclide 10 be and 26 al measurements in bedrock surfaces and glacially transported cobbles in the grove mountains a group of nunataks within the slow flowing interior ice sheet dome hundreds of kilometers from the coastal ice margin and from ice streams samples were collected in vertical transects over 500 m of relief minimum bedrock and erratic exposure ages show a trend of increasing age with height above the ice sheet spanning a period from 0 3 to 4 0 ma and 50 900 ka respectively no evidence was found for thicker ice at the last glacial maximum compared to modern ice thickness the older bedrock exposure ages of 2 5 4 0 ma require steady state erosion rates of 1 the measured two isotope bedrock exposure ages are successfully modeled when changes in surface elevation of the ice sheet are described by a combination of linear long term ice surface lowering and shorter term high frequency glacial interglacial oscillations the best fit model requires a long term thinning rate of 50 m m y 1 and an elevation change of 100 m over a 100 k y glacial cycle

a 2 million year glacial chronology of the hatherton glacier antarctica and implications for the size of the east antarctic ice sheet at the last glacial maximum abstract a series of distinct glacial deposits flanking the margins of the upper hatherton glacier an outlet glacier in the central transantarctic mountains are used to constrain the behaviour of the antarctic ice sheets cosmogenic exposure ages of 18 erratics from four glacial drifts covering the ice free dubris and bibra valleys range in age from 5 to 1997 ka our results document four glacial advance and retreat events superimposed on an overall long term ice thickness reduction of about 500 m since the mid pleistocene the lack of field evidence and absence of lgm exposure ages in the glacial deposits of the hatherton glacier supports our conclusion that at the lgm the east antarctic ice sheet was of similar size or may have been slightly smaller than present minimum exposure ages from the oldest two glacial events represented by the isca and danum drifts are 1 2 ma and 0 5 ma respectively the britannia ii drift previously assumed to mark the maximum extent of the last glacial maximum advance has a mean 10 be age of 126 3 2 ka n 5 ages from the younger britannia i drift suggest that since the mid holocene 6 5 1 2 ka n 5 approximately 200 m of additional ice has been lost

evolving towards a critical point a review of accelerating seismic moment energy release prior to large and great earthquakes there is growing evidence that some proportion of large and great earthquakes are preceded by a period of accelerating seismic activity of moderate sized earthquakes these moderate earthquakes occur during the years to decades prior to the occurrence of the large or great event and over a region larger than its rupture zone the size of the region in which these moderate earthquakes occur scales with the size of the ensuing mainshock at least in continental regions a number of numerical simulation studies of faults and fault systems also exhibit similar behavior the combined observational and simulation evidence suggests that the period of increased moment release in moderate earthquakes signals the establishment of long wavelength correlations in the regional stress field the central hypothesis in the critical point model for regional seismicity is that it is only during these time periods that a region of the earth s crust is truly in or near a self organized critical soc state such that small earthquakes are capable of cascading into much larger events the occurrence of a large or great earthquake appears to dissipate a sufficient proportion of the accumulated regional strain to destroy these long wavelength stress correlations and bring the region out of a soc state continued tectonic strain accumulation and stress transfer during smaller earthquakes eventually re establishes the long wavelength stress correlations that allow for the occurrence of larger events these increases in activity occur over longer periods and larger regions than quiescence which is usually observed within the rupture zone of a coming large event the two phenomena appear to have different physical bases and are not incompatible with one another

mid late pleistocene glacial evolution in the grove mountains east antarctica constraints from cosmogenic 10be surface exposure dating of glacial erratic cobbles abstract glacial histories from the east antarctic ice sheet eais provide keys to understanding correlations between the eais and global climate they are especially helpful in the assessment of global sea level change and as a means of quantifying the magnitude of past glacial activity and the rate at which ice responded to climate change given the significance of eais glacial histories it is imperative that more glacial chronologic data for this region be obtained especially for the mid to late pleistocene we report cosmogenic 10 be surface exposure dating results from glacially transported cobbles embedded in blue ice moraine material at mount harding the grove mountains eais forty exotic cobbles sampled along two profiles a and b on this blue ice moraine present apparent exposure ages ranging from 7 2 to 542 2 ka we explore this scattered dataset by using principal component analysis pca to identify statistically significant trends in the data we identify a correlation between exposure age and distance of the cobbles from mount harding in profile a cobbles further from mount harding yield older exposure ages than those that are relatively close in profile b cobbles closer to mount harding are found to have relatively older exposure ages in term of glacial history we suggest that the direction of ice flow changed during the period from 60 to 200 ka and that multiple glacial fluctuations occurred in the mid late pleistocene

importance of sampling across an assemblage of glacial landforms for interpreting cosmogenic ages of deglaciation deglaciation chronologies for some sectors of former ice sheets are relatively poorly constrained because of the paucity of features or materials traditionally used to constrain the timing of deglaciation in areas without good deglaciation varve chronologies and or without widespread occurrence of material that indicates the start of earliest organic radiocarbon accumulations suitable for radiocarbon dating typically only general patterns and chronologies of deglaciation have been deduced however mid latitude ice sheets that had warm based conditions close to their margins often produced distinctive deglaciation landform assemblages including eskers deltas meltwater channels and aligned lineation systems because these features were formed or significantly altered during the last glaciation boulder or bedrock samples from them have the potential to yield reliable deglaciation ages using terrestrial cosmogenic nuclides tcn for exposure age dating here we present the results of a methodological study designed to examine the consistency of tcn based deglaciation ages from a range of deglaciation landforms at a site in northern norway the strong coherence between exposure ages across several landforms indicates great potential for using tcn techniques on features such as eskers deltas and meltwater channels to enhance the temporal resolution of ice sheet deglaciation chronologies over a range of spatial scales

characterization of fault zones there are currently three major competing views on the essential geometrical mechanical and mathematical nature of faults the standard view is that faults are possibly segmented and heterogeneous euclidean zones in a continuum solid the continuum euclidean view is supported by seismic gravity and electromagnetic imaging studies by successful modeling of observed seismic radiation geodetic data and changes in seismicity patterns by detailed field studies of earthquake rupture zones and exhumed faults and by recent high resolution hypocenter distributions along several faults the second view focuses on granular aspects of fault structures and deformation fields the granular view is supported by observations of rock particles in fault zone gouge by studies of block rotations and the mosaic structure of the lithosphere which includes the overall geometry of plate tectonics by concentration of deformation signals along block boundaries by correlation of seismicity patterns on scales several times larger than those compatible with a continuum framework and by strongly heterogeneous wave propagation effects on the earth s surface the third view is that faults are fractal objects with rough surfaces and branching geometry the fractal view is supported by some statistical analysis of regional hypocenter locations by long range correlation of various measurements in geophysical boreholes by the fact that observed power law statistics of earthquakes are compatible with an underlying scale invariant geometrical structure by geometrical analysis of fault traces at the earth s surface and by measurements of joint and fault surfaces topography

controls on interior west antarctic ice sheet elevations inferences from geologic constraints and ice sheet modeling abstract knowledge of the west antarctic ice sheet wais response to past sea level and climate forcing is necessary to predict its response to warmer temperatures in the future the timing and extent of past interior wais elevation changes provides insight to wais behavior and constraints for ice sheet models constraints prior to the last glacial maximum lgm however are rare surface exposure ages of glacial erratics near the wais divide at mt waesche in marie byrd land and at the ohio range in the transantarctic mountains range from 10 ka to 500 ka without a dependence on elevation the probability distribution functions pdf of the exposure ages at both locations are remarkably similar during the last glaciation maximum interior ice elevations as recorded by moraines and erratics were reached between 10 ka and 12 ka however most exposure ages are older than the lgm and cluster around 40 ka and 80 ka the peak in the exposure age distributions at 40 ka includes ages of alpine moraine boulders at mercer ridge in the ohio range comparison of the pdf of exposures ages from the ohio range and mt waesche with the temperature record from the fuji dome ice core indicates that the youngest peak in the exposure age distributions corresponds to the abrupt warming during the last glacial termination a prominent peak in the ohio range pdf corresponds to the penultimate termination stage 5e during the intervening glacial period there is not a consistent relationship between the peaks in the pdf at each location and temperature a combined ice sheet ice shelf model with forcing scaled to marine 18 o predicts that interior wais elevations near the ice divide have varied 300 m over the last glacial cycle peaks in the pdf correspond to model highstands over the last 200 ka in the simulated elevation history maximum ice elevations at ohio range 100 m and mt waesche 60 m occur at 10 ka in agreement with observations from these sites during collapse of the marine portion of the wais ice elevations at ohio range and mt waesche are drawn down at least 200 m below the present ice elevation the good correspondence between the model results and observations at both the ohio range and mt waesche supports the conclusion that interior wais highstands do not occur during glacial maximums rather the highstands are controlled primarily by increased accumulation during temperature maximums that occur early in the interglacials interior down draw events follow highstands resulting from the arrival of a wave of thinning triggered by retreat of the wais grounding line coupled with decreasing accumulation rates

late pleistocene and holocene melting history of the antarctic ice sheet derived from sea level variations abstract spatial and temporal variations of the late pleistocene and holocene sea levels provide important constraints on the melting history of the major ice sheets in this study we have examined the sea level variations at eight sites along the coast of antarctica to investigate the melting history of antarctic ice sheet complexes comparisons of sea level variations between observations and predictions due to glacio hydro isostatic adjustment suggest that the ice thicknesses removed from the last glacial maximum lgm around the weddell sea are significantly thicker than those around the ross embayment sea level observations also indicate that climap derived models predict too much relative sea level change and that consequently ice mass change along the coast has to be scaled down improvement of the late pleistocene antarctic ice model is required to evaluate more accurate predictions of present day geophysical observables associated with this history thus these more accurate predictions can then be subtracted from observables and the residual field can be analyzed to constrain ongoing mass changes from the ice sheet we therefore predicted present day geophysical observables such as the rate of change of solid surface gravity and crustal movement these geophysical observables based on the ice models constructed from observed sea level variations are significantly different from those based on previous models on the other hand detailed sea level observations around syowa indicate the existence of a sea level highstand of about 10 m around 40 kyr bp to investigate these sea level observations we have performed preliminary numerical calculations comparisons between these observations and predictions indicate the synchronous melting of the northern and southern ice sheets suggesting a strong link between the melting histories of both polar ice sheets

load unload response ratio and accelerating moment energy release critical region scaling and earthquake prediction the main idea of the load unload response ratio lurr is that when a system is stable its response to loading corresponds to its response to unloading whereas when the system is approaching an unstable state the response to loading and unloading becomes quite different high lurr values and observations of accelerating moment energy release amr aer prior to large earthquakes have led different research groups to suggest intermediate term earthquake prediction is possible and imply that the lurr and amr aer observations may have a similar physical origin to study this possibility we conducted a retrospective examination of several australian and chinese earthquakes with magnitudes ranging from 5 0 to 7 9 including australia s deadly newcastle earthquake and the devastating tangshan earthquake both lurr values and best fit power law time to failure functions were computed using data within a range of distances from the epicenter like the best fit power law fits in amr aer the lurr value was optimal using data within a certain epicentral distance implying a critical region for lurr furthermore lurr critical region size scales with mainshock magnitude and is similar to the amr aer critical region size these results suggest a common physical origin for both the amr aer and lurr observations further research may provide clues that yield an understanding of this mechanism and help lead to a solid foundation for intermediate term earthquake prediction

cosmogenic noble gas studies in the oldest landscape on earth surface exposure ages of the dry valleys antarctica extraordinarily high surface exposure ages have been determined for sirius group tillites of mt fleming and mt feather as well as at localities in the inner dry valleys using cosmogenic helium and neon ages of 10 ma at mt fleming 5 3 ma at mt feather and 6 5 ma at insel mountain are among the highest nominal exposure ages published so far these values are minimal ages as they are based on the assumption of zero erosion and uplift the mt feather sample independently confirms the pre pliocene age of the sirius group sediments in the dry valleys as previously determined at mt fleming the insel mountain samples provide evidence for a landscape formation of the inner dry valleys not later than late miocene time assuming conservatively low values of 2 5 cm ma 1 for erosion rate and 50 m ma 1 for uplift rate we infer that the sirius group tillites at mt fleming were deposited earlier than 20 ma ago this indicates that the overriding of the dry valleys block of the transantarctic mountains by the east antarctic ice sheet occurred not later than the early miocene maximum long term erosion rates in the inner dry valleys must be 15 cm ma 1 down to altitudes 1000 m since such low erosion rates require permanently cold and hyperarid conditions the response of antarctica to the pliocene warm climatic episode must have been small cosmogenic nuclide data from both the inner dry valleys and the sirius group sediment localities support the hypothesis of a stable east antarctic ice sheet since at least late miocene time implying that the climate of antarctica was decoupled from that of lower southern latitudes we present also new elemental 21ne production rates of p21 mg 196 atoms g 1 yr 1 and p21 al 55 atoms g 1 yr 1 at sea level and high geomagnetic latitude these figures are consistent with a 3he production rate of p3 110 atoms g 1 yr 1 similar to previously published values this consistency provides evidence that pyroxene is retentive for both helium and neon over at least 10 ma cosmogenic ne in quartz and pyroxene has a 22ne 21ne cos ratio of 1 266 0 040 and 1 159 0 040 respectively

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

multiple cosmogenic nuclides document the stability of the east antarctic ice sheet in northern victoria land since the late miocene 5 7 ma the timing and amplitude of changes in the antarctic ice level are relevant to understanding past climate fluctuations and ongoing changes in the global climate and sea levels in this study we present surface exposure ages based on in situ produced cosmogenic 10be and 21ne in the bedrock samples of glacially eroded relict surfaces from the deep freeze range northern victoria land the proximity of this region to the east antarctic ice sheet indicates that the area is sensitive to variations in inland ice volume permitting the investigation of the behavioural relationship between the east antarctic ice sheet and the alpine glacial system in northern victoria land dating erosional surfaces provides a precise chronology of northern victoria land paleoclimate evolution and allows us to correlate the east antarctic ice sheet response to global climate events and local ice level variations the 10be and 21ne concentrations from the highest peaks of the deep freeze range strongly indicate that the relict landscape features were continuously exposed for 5 7 ma denudation rates inferred from our data show that the erosion rate of the summits has been extremely low 5 cm ma for at least 5 7 ma along with evidence of persistent climate stability cold and arid conditions from other sectors of the transantarctic mountains our results indicate that the transition from the wet based to the cold based glacial regime in northern victoria land occurred after the creation of the polar east antarctic ice sheet in the middle miocene

retreat of the east antarctic ice sheet during the last glacial termination the east antarctic ice sheet retreated at the end of the last glacial period terrestrial and marine data suggest that the retreat began 14 000 years ago indicating that the east antarctic ice sheet probably did not contribute to meltwater pulse 1a 14 700 years ago

acoustic emission experiments of rock failure under load simulating the hypocenter condition a series of acoustic emission ae experiments of rock failure have been conducted under cyclic load in tri axial stress tests to simulate the hypocenter condition the specimens are loaded by the combined action of a constant stress intended to simulate the tectonic loading and a small sinusoidal disturbance stress analogous to the earth tide induced by the sun and the moon each acoustic emission signal can indicate the occurrence time location and relative magnitude of the damage micro crack in the specimen the experimental results verified some precursors such as lurr load unload response ratio and aer accelerating energy release before macro fracture of the samples a new parameter the correlation between the ae and the load has been proposed to describe the loading history on the eve of some strong earthquakes the correlation between the benioff strain and the coulomb failure stress cfs decreases similar to the variation of lurr prior to strong earthquakes

unglaciated areas in east antarctica during the last glacial marine isotope stage 3 new evidence from rauer group abstract limited information on the east antarctic ice sheet eais geometry during marine isotope stage 3 mis 3 60 25 ka restricts our understanding of its behaviour during periods of climate and sea level change ice sheet models forced by global parameters suggest an expanded eais compared to the holocene during mis 3 but field evidence from east antarctic coastal areas contradicts such modelling and suggests that the ice sheet margins were no more advanced than at present here we present a new lake sediment record and cosmogenic exposure results from bedrock which confirm that rauer group eastern prydz bay was ice free for much of mis 3 we also refine the likely duration of the last glacial maximum lgm glaciation in the region lacustrine and marine sediments from rauer group indicate the penultimate period of ice retreat predates 50 ka the lacustrine record indicates a change from warmer wetter conditions to cooler drier conditions after ca 35 ka substantive ice sheet re advance however may not have occurred until much closer to 20 ka contemporary coastal areas were still connected to the sea during mis 3 restricting the possible extent of grounded ice in prydz bay on the continental shelf in contrast relative sea levels rsl deduced from field evidence indicate an extra ice load averaging several hundred metres thicker ice across the bay between 45 and 32 ka thus ice must either have been thicker immediately inland with a steeper ice profile or there were additional ice domes on the shallow banks of the outer continental shelf further work is required to reconcile the differences between empirical evidence of past ice sheet histories and the history predicted by ice sheet models from far field temperature and sea level records

holocene deglaciation of marie byrd land west antarctica surface exposure ages of glacial deposits in the ford ranges of western marie byrd land indicate continuous thinning of the west antarctic ice sheet by more than 700 meters near the coast throughout the past 10 000 years deglaciation lagged the disappearance of ice sheets in the northern hemisphere by thousands of years and may still be under way these results provide further evidence that parts of the west antarctic ice sheet are on a long term trajectory of decline west antarctic melting contributed water to the oceans in the late holocene and may continue to do so in the future

a deglacial model for antarctica geological constraints and glaciological modelling as a basis for a new model of antarctic glacial isostatic adjustment abstract we present a new reconstruction of the antarctic ice sheets between 20 ka bp and the present day our reconstruction is derived using a numerical model to generate a physically consistent ice surface across the whole of the continent we define the extent of the ice sheet at five time slices 20 15 10 5 and 0 ka bp assuming an equilibrium state for the 20 ka bp time slice and a transient state for the deglacial time slices the evolution of the ice sheet within the numerical model is driven by variations in temperature accumulation rate and relative sea level in order to reconstruct the concave profile of the ice sheet in marine grounded regions such as the ross and weddell seas we force our model to develop channels of faster flow by defining greater basal sliding along the trajectory of former ice streams we find a strong dependence upon the basal sliding parameters and also the position of the grounding line we use an extensive data base of geological and glaciological data to constrain our ice sheet reconstruction grounding line extent is prescribed from marine geological data and we test ice sheet thickness against onshore geological data at 62 sites of the five time slices considered our 20 ka bp reconstruction is the best constrained by data and has an rms misfit of 147 6 m when compared to observations of ice thickness change between 20 ka bp and the present day across all time slices there are large regions of the ice sheet which are poorly constrained especially after 20 ka bp we estimate the spatial distribution of uncertainty in our ice sheet reconstruction and note that the solutions are least reliable in regions of complex topography we predict that the antarctic ice sheets contributed 9 1 5 m of eustatic sea level to the global ocean between 20 ka bp and the present and our reconstruction with minimum misfit contributes 8 m eustatic sea level during this period these values which we argue are an upper bound are lower than many previous estimates the reconstructed pattern of ice unloading can serve as a new input for glacial isostatic models

geometry and dynamics of an east antarctic ice sheet outlet glacier under past and present climates 1 the behavior of east antarctic ice sheet eais outlet glaciers both at present and during the recent geological past is of considerable interest both from the point of view of understanding the mechanics of contemporary glacier dynamics and also with regard to epoch scale ice sheet stability during plio pleistocene climate transitions here we use a glacier flowline model that incorporates the effects of longitudinal stresses to numerically simulate ferrar glacier first under present day environmental conditions and subsequently under both colder and warmer climate regimes representing the last glacial maximum lgm and mid pliocene peak warmth respectively using airborne radar profiles insar derived surface velocities ice core and geological data for empirical constraint we present a diagnostic simulation that uses an iterative method to closely reproduce observed dynamics our model suggests that the glacier is largely cold based under present conditions flows predominantly by way of internal deformation and cascades over bedrock ridges due to the combined action of changes in cross sectional valley geometry local steepening of the glacier surface and the non local effects of longitudinal coupling time dependent evolutionary simulation of a lower profile glacier under a colder drier lgm climate predicts flow velocities lower than present with minimal bedrock erosion or basal till flux conversely the warmer than present mid pliocene climate produces a more dynamic glacier that is warm based and sliding along much of its bed we propose that eais outlet glaciers such as the ferrar respond dynamically along their length in response to changing environmental forcings with most significant changes taking place in their lower reaches adjustment to perturbations in upper catchments is more muted

a new approach to earthquake prediction the load unload response ratio lurr theory the response to loading is different from that to unloading when the focal media is approaching instability the ratio of the response rate during loading to that during unloading called load unload response ratio y lurr could be a measure of the closeness degree to instability and is used in a new approach to earthquake prediction retrospective examination of some one hundred earthquake cases from m 4 to m 8 6 indicates that for more than 80 of the examined ones the value of y is much higher than 1 for a period before the main shock but the y value always fluctuates slightly about 1 during two decades for seven stable regions so that the parameter y could indicate a dangerous degree of an impending earthquake several earthquakes occurring on the chinese mainland in recent years as well as the northridge california u s a earthquake jan 17 1994 m w 6 7 have been predicted beforehand with this method

cosmogenic exposure and erosion history of australian bedrock landforms exceptionally high activities of in situ produced 1 0 be and 2 6 al indicate that australian bedrock surfaces are some of the most stable in the world these cosmogenic nuclides demonstrate that australian granite exposed and sampled at 10 sites along a transect from the eyre peninsula 33 s to the kakadu area in the northern territory 14 s has in some places eroded only decimeters over the past million years however nuclide activities are not saturated in any of the 61 exposed samples we analyzed mandating that the surfaces we sampled are losing mass albeit slowly over time such mass loss indicates that inselbergs are dynamic landforms confounding the assignment of discreet ages to inselberg surfaces nevertheless the differential between slow rates of erosion measured on the very stable uppermost parts of these landforms and the more rapid rates measured below their flanks and below the adjacent grus covered planes suggests that the forms of many large inselbergs which stand meters to tens of meters high must be at least tertiary in age and possibly much older activities of 1 0 be and 2 6 al in 61 exposed australian samples range from 5 1 0 1 10 6 to 5 3 0 6 x 10 5 atoms g 1 and 2 1 0 1 x 10 7 to 3 4 0 5 x 10 6 atoms g 1 respectively normalized to sea level at latitudes of 60 using only neutron scaling activities of 1 0 be and 2 6 al in seven shielded samples 3 5 13 m below the surface are much lower ranging from 3 4 0 2 x 10 4 to 7 0 0 1 x 10 4 atoms g 1 and 1 6 0 1 x 10 5 to 2 8 0 2 x 10 5 atoms g 1 respectively 2 6 al 1 0 be ratios of exposed samples range from 3 89 0 19 to 6 29 0 82 if 2 uncertainty ranges and a nominal sea level high latitude 1 0 be production rate of 5 17 atoms g 1 yr 1 are considered ratio data for all but one surface sample are consistent with continuous surface or near surface exposure and or erosion rock surfaces farther north in australia where the climate is more humid have lower nuclide activities thus we infer that surface stability is inversely related to mean annual precipitation from 61 exposed samples we calculated maximum limiting single nuclide model erosion rates of 0 3 0 1 to 5 7 1 0 m m y and minimum limiting single nuclide model exposure ages of 105 16 to 1310 190 ka by assuming a sea level high latitude 1 0 be production rate of 5 17 atoms g 1 yr 1 seven shielded samples in which the nuclide inventory is muon generated also have nuclide activities consistent with similarly low rates of erosion but over even longer time scales it appears that the eyre peninsula inselbergs have been and are eroding so slowly that they may well be direct descendents of cenozoic and perhaps even mesozoic forms

glacial history and landscape evolution of southern cumberland peninsula baffin island canada constrained by cosmogenic 10be and 26al since the first application of cosmogenic nuclides to the study of glacial history and processes in 1990 increasing numbers of studies have used a variety of cosmogenic isotopes to quantify the exposure age and erosion rate of glaciated landscapes however obtaining chronological data from glaciated landscapes once covered by cold based nonerosive ice is challenging because these surfaces violate assumptions associated with simple cosmogenic exposure dating nonerosive glacial ice fails to completely remove nuclides produced during previous periods of exposure leaving behind rock surfaces with complex multigenetic nuclide inventories here we constrain the glacial history landscape evolution and efficiency of subglacial erosion in the pangnirtung fiord region of southern baffin island using over 300 paired analyses of in situ cosmogenic 10be and 26al simple exposure ages are 6 3 160 ka for 10be n 152 and 4 3 124 ka for 26al n 153 paired bedrock boulder samples have discordant ages simple exposure ages generally increase with elevation 10be and 26al ages for the same sample disagree and both boulders and bedrock yield multimodal age distributions all patterns suggestive of limited subglacial erosion measured 26al 10be ratios indicate that about one third of the samples in the data set experienced at least one period of pre holocene exposure followed by burial with limited erosion modeled two isotope minimum limiting exposure durations are as high as hundreds of thousands of years and minimum limiting burial durations range up to millions of years implying that parts of southern baffin island have been preserved beneath nonerosive glacial ice for much if not all of the quaternary a subset of the samples contains few nuclides inherited from prior periods of exposure and is thus useful for constraining the chronology of the most recent deglaciation using these samples we infer that deglaciation of most of the landscape occurred ca 11 7 ka and that the duval moraines a prominent feature of the last deglaciation formed ca 11 2 ka

volume of antarctic ice at the last glacial maximum and its impact on global sea level change abstract the volume of antarctic ice at the last glacial maximum is a key factor for calculating the past contribution of melting ice sheets to late pleistocene global sea level change at present there are large uncertainties in our knowledge of the extent and thickness of the formerly expanded antarctic ice sheets and in the timing of their release as meltwater into the world s oceans this paper reviews the four main approaches to determining former antarctic ice volume namely glacial geology glacio isostatic studies glaciological modelling and ice core analysis and attempts to reconcile these to give a best estimate for ice volume in the ross sea there was a major expansion of grounded ice at the last glacial maximum accounting for 2 3 3 2 m of global sea level at some time in the weddell sea a large grounded ice sheet corresponding to c 2 7 m of global sea level extended to the shelf break however this ice expansion has not yet been confidently dated and may not relate to the last glacial maximum around east antarctica there was thickening and advance offshore of ice in coastal regions ice core evidence suggests that the interior of east antarctica was either close to its present elevation or thinner during the last glacial so the effect of east antarctica on sea level depends on the net balance between marginal thickening and interior thinning suggested east antarctic contributions vary from a 3 5 5 m lowering to a 0 64 m rise in global sea level the antarctic peninsula ice sheet thickened and extended offshore at the last glacial maximum with a sea level equivalent contribution of c 1 7 m thus the antarctic ice sheets accounted for between 6 1 and 13 1 m of global sea level fall at the last glacial maximum this is substantially less than has been suggested by most previous studies but the maximum figure matches well with one modelling estimate the timing of antarctic deglaciation is not well known in the ross sea terrestrial evidence suggests deglaciation may have begun at c 13 000 yr bp 1 but that grounded ice persisted until c 6 500 yr bp marine evidence suggests the western ross sea was deglaciated by c 11 500 yr bp deglaciation of the weddell sea is poorly constrained grounded ice in the northern antarctic peninsula had retreated by c 13 000 yr bp and further south deglaciation occurred sometime prior to c 6 000 yr bp many parts of coastal east antarctica apparently escaped glaciation at the lgm but in those areas that were ice covered deglaciation was underway by 10 000 yr bp with existing data the timing of deglaciation shows no firm relation to northern hemisphere driven sea level rise this is probably due partly to lack of antarctic dating evidence but also to the combined influence of several forcing mechanisms acting during deglaciation

sea level changes at the lgm from ice dynamic reconstructions of the greenland and antarctic ice sheets during the glacial cycles abstract new experiments were performed with three dimensional thermomechanical models of the greenland and antarctic ice sheets to simulate their behaviour during the glacial cycles to reconstruct their thickness and extent at the last glacial maximum lgm and to estimate their glacio eustatic contribution to the global sea level stand the calculations used improved ice dynamic and isostatic treatments updated datasets on higher grid resolutions and refined climatic treatments based on newly calibrated transfer functions between ice core records and climatic perturbations results are discussed from a reference run with standard parameters that is compared with available glacial geological observations and from a series of sensitivity experiments focusing on isostatic adjustment thermomechanical coupling climatic forcing mass balance changes and basal melting rates and viscosity changes of antarctic ice shelves for the antarctic ice sheet we find that volume changes are closely linked with grounding line changes of the west antarctic ice sheet at the lgm the grounding line extended close to the continental shelf break almost everywhere ice over central east antarctica was generally thinner than today and varied mainly in accordance with accumulation fluctuations for the greenland ice sheet melting is important only during interglacial periods and the most sensitive period concerns the size of the ice sheet during the eemian at the lgm the greenland ice sheet extended beyond the present coastline to cover at least the inner continental shelf and thinned by up to several hundred meters in central areas for a plausible range of parameters the experiments indicate that at the time of maximum sea level depression 21 kyr bp the antarctic ice sheet contributed 14 18 m to the sea level lowering and the greenland ice sheet 2 3 m significantly less than the older climap reconstructions whereas both ice sheets were at 21 kyr bp close to their maximum extent the experiments also indicate that their maximum volumes were reached only by 16 5 kyr bp greenland and 10 kyr bp antarctica equal to an additional sea level lowering of respectively 0 4 and 3 7 m holocene retreat was essentially complete by 5 kyr bp in greenland but is found to still continue today in west antarctica before reversing to growth during the next millenium the models were found to reproduce gross features of the ice sheet s history since the lgm in reasonably good agreement with available glacial geological data although observational control on ice thickness changes remains very limited

global glacier dynamics during 100 ka pleistocene glacial cycles ice volume during the last ten 100 ka glacial cycles was driven by solar radiation flux in the northern hemisphere early minima in solar radiation combined with critical levels of atmospheric co 2 drove initial glacier expansion glacial cycles between marine isotope stage mis 24 and mis 13 whilst at 100 ka periodicity were irregular in amplitude and the shift to the largest amplitude 100 ka glacial cycles occurred after mis 16 mountain glaciers in the mid latitudes and asia reached their maximum extents early in glacial cycles then retreated as global climate became increasingly arid in contrast larger ice masses close to maritime moisture sources continued to build up and dominated global glacial maxima reflected in marine isotope and sea level records the effect of this pattern of glaciation on the state of the global atmosphere is evident in dust records from antarctic ice cores where pronounced double peaks in dust flux occur in all of the last eight glacial cycles glacier growth is strongly modulated by variations in solar radiation especially in glacial inceptions this external control accounts for 50 60 of ice volume change through glacial cycles internal global glacier climate dynamics account for the rest of the change which is controlled by the geographic distributions of glaciers

paired bedrock and boulder 10be concentrations resulting from early holocene ice retreat near jakobshavn isfjord western greenland we measured in situ cosmogenic 10 be in 16 bedrock and 14 boulder samples collected along a 40 km transect outside of and normal to the modern ice margin near sikuijuitsoq fjord in central west

development of a new approach to earthquake prediction load unload response ratio lurr theory the seismogenic process is nonlinear and irreversible so that the response to loading is different from unloading this difference reflects the damage of a loaded material based on this insight a new parameter load unload response ratio lurr was proposed to measure quantitatively the proximity to rock failure and earthquake more than ten years ago in the present paper we review the fundamental concept of lurr the validation of lurr with experimental and numerical simulation the retrospective examination of lurr with new cases in different tectonic settings california usa and kanto region japan the statistics of earthquake prediction in terms of lurr theory and the random distribution of lurr under poisson s model finally we discuss lurr as a parameter to judge the closeness degree to soc state of the system and the measurement of tidal triggering earthquake the load unload response ratio lurr theory was first proposed in 1984 yin 1987 subsequently a series of advances were made yin and dyin 1991 yin 1993 yin et al 1994a b 1995 maruyama 1995 in this paper the new results after 1995 are summarized yin et al 1996 wang et al 1998a zhuang and yin 1999

the magnitude distribution of declustered earthquakes in southern california abstract the binned distribution densities of magnitudes in both the complete and the declustered catalogs of earthquakes in the southern california region have two significantly different branches with crossover magnitude near m 4 8 in the case of declustered earthquakes the b values on the two branches differ significantly from each other by a factor of about two the absence of self similarity across a broad range of magnitudes in the distribution of declustered earthquakes is an argument against the application of an assumption of scale independence to models of main shock earthquake occurrence and in turn to the use of such models to justify the assertion that earthquakes are unpredictable the presumption of scale independence for complete local earthquake catalogs is attributable not to a universal process of self organization leading to future large earthquakes but to the universality of the process that produces aftershocks which dominate complete catalogs

sensitivity of earthquake cycles on the san andreas fault to small changes in regional compression the current pattern of slip1 2 within the san andreas fault system in the san francisco bay area is distinctly different from the long term slip pattern inferred from the geological record3 4 this difference is not surprising because geological data record the accumulated displacements over many earthquake cycles whereas geodetic data reveal the present day slip pattern it is not known however what mechanism triggers the change from the inter seismic slip pattern when the san andreas fault is locked to the co seismic slip pattern when the san andreas fault ruptures in earthquake slip here we use numerical simulations of the entire seismic cycle on this complex fault system to show that the san andreas fault may be in a critical state and sensitive to small perturbations in regional compression in particular we find that small increases in regional compression may lock the san andreas fault whereas small decreases in regional compression may release the locked segment and so permit co seismic slip this sensitivity suggests that cyclic changes in the regional stress field resulting from plate convergence and thrust faulting in the coast ranges could trigger major earthquakes on the san andreas fault

critical sensitivity and trans scale fluctuations in catastrophic rupture rupture in the heterogeneous crust appears to be a catastrophe transition catastrophic rupture sensitively depends on the details of heterogeneity and stress transfer on multiple scales these are difficult to identify and deal with as a result the threshold of earthquake like rupture presents uncertainty this may be the root of the difficulty of earthquake prediction based on a coupled pattern mapping model we represent critical sensitivity and trans scale fluctuations associated with catastrophic rupture critical sensitivity means that a system may become significantly sensitive near catastrophe transition trans scale fluctuations mean that the level of stress fluctuations increases strongly and the spatial scale of stress and damage fluctuations evolves from the mesoscopic heterogeneity scale to the macroscopic scale as the catastrophe regime is approached the underlying mechanism behind critical sensitivity and trans scale fluctuations is the coupling effect between heterogeneity and dynamical nonlinearity such features may provide clues for prediction of catastrophic rupture like material failure and great earthquakes critical sensitivity may be the physical mechanism underlying a promising earthquake forecasting method the load unload response ratio lurr

widespread complex flow in the interior of the antarctic ice sheet it has been suggested that as much as 90 of the discharge from the antarctic ice sheet is drained through a small number of fast moving ice streams and outlet glaciers fed by relatively stable and inactive catchment areas here evidence obtained from balance velocity estimates suggests that each major drainage basin is fed by complex systems of tributaries that penetrate up to 1000 kilometers from the grounding line into the interior of the ice sheet this finding has important consequences for the modeled or estimated dynamic response time of past and present ice sheets to climate forcing

uncertainties in elevation changes and their impact on antarctic temperature records since the end of the last glacial period abstract this study presents a sensitivity analysis considering the influence of elevation changes associated with both ice thickness and land height changes on water stable isotope temperature proxies from antarctic ice cores we compare results from three different ice sheet models and three different earth viscosity models at a 10 ice core sites as expected the ice thinning signal at west antarctic sites is the largest contributor to elevation induced temperature changes the signal predicted by the ice models considered produced 100 200 of the total glacial to interglacial signal in d indicating that the deglacial ice thinning is overestimated by an amount approaching an order of magnitude at some locations this indicates that the total volume loss in these models is considerably overestimated furthermore the predicted rate of this change is not supported by the isotope data and so again most likely reflects inaccuracies in the adopted ice models estimates of contemporary ice mass changes inferred from satellite gravity data corrected using any of these models with therefore be biased as a result the isostatic signal acts to reduce the total elevation change at most sites and has a relatively small magnitude a few to 20 of that due to the ice thickness change so is secondary at most sites and for most of the time however our results indicate that it could be the dominant control on elevation at some west antarctic sites during the holocene resulting in a secular cooling signal of 10 20 in d none of the models capture the holocene isotopic depletion trend present at several sites in east antarctica

quantification of subaerial and episodic subglacial erosion rates on high latitude upland plateaus cumberland peninsula baffin island arctic canada abstract long term rates of subaerial and episodic subglacial erosion by predominately cold based ice cover are determined for tors on weathered plateaus on cumberland peninsula by measuring terrestrial cosmogenic nuclide concentrations in differentially weathered surfaces on a given tor we reconstruct the complex exposure and erosion history involving recurring cold based ice cover the style and rate of subaerial and subglacial erosion at multiple tor sites on cumberland peninsula are assessed with a monte carlo approach that computes plausible exposure histories based on a proxy record of global ice volume constant subaerial erosion rates by weathering are low

exposure ages from mountain dipsticks in mac robertson land east antarctica indicate little change in ice sheet thickness since the last glacial maximum past changes in east antarctic ice sheet eais volume are poorly known and diffi cult to measure yet are critical for predicting the response of the ice sheet to modern climate change in particular it is important to identify the sources of sea level rise since the last glacial maximum lgm and ascertain the present day stability of the world s largest ice sheet we present altitudinal transects of 10 be and 26 al exposure ages across the framnes mountains in mac robertson land that allow the magnitude and timing of eais retreat to be quantifi ed our data show that the coastal eais thinned by at most 350 m in this region during the past 13 k y this reduction in ice sheet volume occurred over a 5 k y period and the present icesheet profi le was attained ca 7 ka in contrast to the west antarctic ice sheet which continues to retreat today combined with regional offshore and terrestrial geologic evidence our data suggest that the reduction in eais volume since the lgm was smaller than that indicated by contemporary ice sheet models and added little meltwater to the global oceans stability of the ice margin since the middle holocene provides support for the hypothesis that eais volume changes are controlled by growth and decay of northern hemisphere ice sheets and associated global sea level changes

late quaternary glacial history constrains glacio isostatic rebound in enderby land east antarctica measurements of the loss or gain of ice mass from large ice sheets are presently achieved through satellite based techniques such as grace gravity recovery and climate experiment the accuracy of these satellite based measurements to changes in modern ice sheet mass depends on our knowledge of present day glacio isostatic crustal uplift rates caused by past ice sheet changes to improve models of glacio isostatic rebound in east antarctica we investigated ice histories along rayner glacier enderby land and a little explored sector of the ice sheet where grace data had suggested significant mass gain during the last decade observations from a recent glacial geomorphic reconnaissance coupled with cosmogenic nuclide dating indicate that in the lower part of the rayner glacier enderby land ice heights lowered by at least 300 m and the calving margin retreated by at least 10 km in the early holocene 6 to 9 ka b p the magnitude and timing of deglaciation are consistent with ice histories used to model the postglacial rebound corrections for present day grace mass trends these observations strengthen the body of evidence that suggests ice mass gain in enderby land is presently partly offsetting mass loss in other parts of antarctica

post lgm dynamic deglaciation along the victoria land coast antarctica abstract the post last glacial maximum lgm deglaciation of antarctica holds important clues for understanding past environmental changes and predicting future changes in the antarctic ice sheet cosmogenic nuclide exposure dating of glacial erratics documents the spatial and temporal glacier changes during the most recent deglaciation we collected 55 erratic cobbles from the eight glaciated benches on inexpressible island which is at the terminal area of priestley glacier terra nova bay victoria land to elucidate its post lgm deglaciation pattern analyses of the 10be ages and 26al 10be ratios suggest that priestley glacier underwent 254 m of lowering during the mid holocene between 8 9 and 5 9 ka this lowering rate 0 09 m a 1 is faster than those observed along other victoria land outlet glaciers to the north tucker and aviator but slower than the one to the south mackay the post lgm lowering of these outlet glaciers was triggered by marine ice sheet instability with their asynchronous onsets of deglaciation derived from their diachronous response times to the southwestward migration of the grounding line retreat until their synchronous termination of deglaciation at 6 ka a post lgm deglaciation model with the southwestward migration of the western ross ice shelf grounding line provides the best match to the terrestrial exposure dating results of the thinning patterns of the outlet glaciers along the victoria land coast

global glacial isostasy and the surface of the ice age earth the ice 5g vm2 model and grace abstract the 100 kyr quasiperiodic variation of continental ice cover which has been a persistent feature of climate system evolution throughout the most recent 900 kyr of earth history has occurred as a consequence of changes in the seasonal insolation regime forced by the influence of gravitational n body effects in the solar system on the geometry of earth s orbit around the sun the impacts of the changing surface ice load upon both earth s shape and gravitational field as well as upon sea level history have come to be measurable using a variety of geological and geophysical techniques these observations are invertible to obtain useful information on both the internal viscoelastic structure of the solid earth and on the detailed spatiotemporal characteristics of glaciation history this review focuses upon the most recent advances that have been achieved in each of these areas advances that have proven to be central to the construction of the refined model of the global process of glacial isos

cosmogenic evidence for limited local lgm glacial expansion denton hills antarctica abstract the geomorphology of the denton hills provides insight into the timing and magnitude of glacial retreats in a region of antarctica isolated from the influence of the east antarctic ice sheet we present 26 beryllium 10 surface exposure ages from a variety of glacial and lacustrine features in the garwood and miers valleys to document the glacial history of the area from 10 to 286 ka our data show that the cold based miers joyce and garwood glaciers retreated little since their maximum positions at 37 2 6 9 1 n 4 35 1 1 5 1 n 3 and 35 6 10 1 1 n 6 ka respectively the similar timing of advance of all three glaciers and the lack of a significant glacial expansion during the global lgm suggests a local lgm for the denton hills between ca 26 and 51 ka with a mean age of 36 0 7 5 1 n 13 ka a second cohort of exposure ages provides constraints to the behaviour of glacial lake trowbridge that formerly occupied miers valley in the late pleistocene these data show active modification of the landscape from 20 ka until the withdrawal of ice from the valley mouths and deposition of ross sea drift at 10 14 ka