change in climate ocean and ice sheet conditions in the ross embayment antarctica at 6 ka evidence from the ross embayment antarctica suggests an abrupt cooling and a concomitant increase in sea ice cover at about 6000 sp 6 ka stable isotope delta d concentrations in the taylor dome ice core at the western edge of the ross embayment decline rapidly after 6 ka and continue to decline through the late holocene methanesulfonic acid concentrations at taylor dome show opposite trends to delta d sediment cores from the western ross sea show a percentage minimum for the sea ice diatom fragilariopsis curta between 9 and 6 ka when taylor dome delta d values are highest followed by an increase through the late holocene radiocarbon dates from raised beach deposits indicate that the retreat of ice shelves in the ross embayment ceased atabout 6 ka coincident with the environmental changes inferred from the sediment and ice core records the similarity in timing suggests an important role for climate in controlling the evolution of ice shelf margins following the end of the last 9 glaciation

organic geochemical proxies of paleoceanographic paleolimnologic and paleoclimatic processes abstract organic matter constitutes a minor fraction of marine and freshwater sediments yet its important contribution to the sedimentary record can be used to reconstruct marine and continental paleoenvironments the organic matter content of sediments is the residue of past biota the amounts and types of organic matter present in sediments consequently reflect environmental conditions that impacted ecosystems at different past times general sources of the organic matter are inferred from bulk properties such as elemental compositions carbon and nitrogen stable isotope ratios rock eval pyrolysis data and organic petrography details of organic matter origins are refined by analyses of biomarker molecular compositions source changes are proxies for fluctuations in sea level oceanic surface currents and continental climates algal paleoproductivity rates are indicated by organic carbon mass accumulation rates and carbon and nitrogen stable isotopic compositions these parameters record past availability of nutrients and therefore are proxies of surface mixing in the oceans and amount of land runoff to lakes sea surface paleotemperatures are recorded by the number of carbon carbon double bonds in lipid biomarkers produced by marine algae larger proportions of the double bonds are proxies for the cooler surface waters that accompanied periods of global glaciation and intervals of enhanced upwelling the 13c and d values of plant organic matter record past concentrations of carbon dioxide in the atmosphere and changes in delivery of atmospheric moisture respectively diagenesis which causes the concentration and composition of organic matter in sedimentary settings to differ from those of the original biologically synthesized materials can bias organic geochemical paleoenvironmental records the magnitude of this potential source of misinformation must always be considered and evaluated comparison of multiple organic geochemical proxies of past conditions helps to compensate for the effects of diagenetic alterations and thereby to improve interpretations of paleoenvironmental change

sedimentological and stable isotope evolution of lakes in the vestfold hills antarctica the sedimentological chemical and isotopic characteristics of sediment cores from three slightly saline to hypersaline lakes highway ace and organic lakes and two marine inlets ellis fjord and taynaya bay in the vestfold hills antarctica have been examined sections of the cores deposited in marine environments are characterized by uniform regularly laminated fine grained organic rich sediments with uniform organic 13c values 18 0 to 19 4 vs pdb and sulfur contents in contrast sediments deposited in lacustrine environments are extremely heterogeneous varying from finely laminated mat like sequences to poorly sorted clastic rich sediments authigenic monohydrocalcite and aragonite occur in some lake sediments the 13c values of organic matter in the lacustrine sediments exhibit an extremely wide range 10 5 to 25 3 that can be related to variations in physico chemical conditions in the lake waters strongly negative organic 13c values coupled with high sulfur contents are indicative of an anoxic zone in the overlying lake waters whereas less negative organic 13c values coupled with low sulfur contents are indicative of well mixed oxic conditions particularly high organic 13c values result during high levels of microbial activity in the lakes due to high rates of photosynthetic co2 fixation the large shifts in organic 13c are not necessarily accompanied by any change in macroscopic sedimentological characteristics illustrating the utility of isotopic investigations in these environments the 13c composition of authigenic carbonate in hypersaline organic lake sediments provides a record of changes in palaeoproductivity while the 18o of the carbonate provides information on rates of meltwater input and evaporation in the lake 14c dating suggests that highway lake was isolated from the sea by isostatic uplift at least 4600 yr before present b p whereas organic lake was isolated at approximately 2700 yr b p apparent emergence rates calculated from the 14c ages range from 1 0 to 2 1 mm yr 1 the reservoir effect in the lacustrine and marine environments is variable but probably does not exceed 1000 yr in any of the lakes examined

late quaternary diatom assemblages from prydz bay eastern antarctica abstract the paleo depositional environment of inner prydz bay east antarctica has been reconstructed for the past 21 320 14c yr b p using diatom assemblages and sediment facies from a short 352 cm long gravity core between 21 320 and 11 650 14c yr b p compact tillite and diamicton are present in the core and diatom frustules are rare to absent these data suggest that an ice sheet grounded over the site during the last glacial maximum following glacial retreat siliceous muddy ooze was deposited from 11 650 to 2600 14c yr b p in an open marine setting during this stage diatom frustules are abundant and well preserved and thalassiosira antarctica resting spores and fragilariopsis curta dominate the assemblage this assemblage suggests open marine deposition in an environment where the spatial and temporal distribution of sea ice is less than today since 2600 14c yr b p sea ice and ice edge diatom species have become more abundant and neoglacial cooling is inferred the assemblage is similar to that forming currently in prydz bay where sea ice is absent

application of tandem accelerator mass spectrometer dating to late pleistocene holocene sediments of the east antarctic continental shelf abstract glacial recession from the antarctic continental shelf is recorded by glacial marine diamictons sands and overlying siliceous oozes in order to clarify the chronology for this sequence use was made of the university of arizona tandem accelerator mass spectrometer tams for 14 c dating small samples of benthic and planktonic foraminifera were selectively removed from diamictons graded sands and surface sediments which were recovered from the wilkes land continental shelf and slope east antarctica organic carbon was also utilized as a source for tams dating of the siliceous oozes and muds uncorrected ages varied from 14 260 140 to 3230 200 yr b p carbon fixed by phytoplankton and foraminifera is strongly influenced by old glacial derived co 2 thus reservoir corrections of up to 5500 yr are needed for the 14 c dates iceberg turbation reworks foraminifera so that dates from resulting deposits diamictons are interpreted as maximum ages the consistency of corrected ages from the shelf along with the sedimentologic interpretation suggests a rather recent recession perhaps mid holocene for this portion of the east antarctic ice sheet further application of the tams method should help clarify other problems concerning the late quaternary glacial history of antarctica

convection in a volatile nitrogen ice rich layer drives pluto s geological vigour the volatile ice filled basin informally named sputnik planum is central to pluto s geological activity this ice layer is organized into cells or polygons and it is now shown that convective overturn in a several kilometre thick layer of solid nitrogen can explain both the presence of the cells and their great width nasa s new horizons spacecraft has revealed fascinating details of the surface of pluto including a vast ice filled basin known as sputnik planum which is central to pluto s geological activity much of the surface of sputnik planum consisting mostly of nitrogen ice is divided into irregular polygons that are tens of kilometres in diameter and whose centres rise tens of metres above their sides two papers in this issue of nature analyse new horizons images of this polygonal terrain both conclude that it is continually being resurfaced by convection but arrive at contrasting models for the process alexander trowbridge et al report a parameterized convection model in which the nitrogen ice is vigorously convecting ten or more kilometres thick and about a million years old william mckinnon et al from the new horizons team show that sluggish lid convective overturn in a several kilometre thick layer of solid nitrogen can explain both the presence of the cells and their great width the vast deep volatile ice filled basin informally named sputnik planum is central to pluto s vigorous geological activity1 2 composed of molecular nitrogen methane and carbon monoxide ices3 but dominated by nitrogen ice this layer is organized into cells or polygons typically about 10 to 40 kilometres across that resemble the surface manifestation of solid state convection1 2 here we report on the basis of available rheological measurements4 that solid layers of nitrogen ice with a thickness in excess of about one kilometre should undergo convection for estimated present day heat flow conditions on pluto more importantly we show numerically that convective overturn in a several kilometre thick layer of solid nitrogen can explain the great lateral width of the cells the temperature dependence of nitrogen ice viscosity implies that the ice layer convects in the so called sluggish lid regime5 a unique convective mode not previously definitively observed in the solar system average surface horizontal velocities of a few centimetres a year imply surface transport or renewal times of about 500 000 years well under the ten million year upper limit crater retention age for sputnik planum2 similar convective surface renewal may also occur on other dwarf planets in the kuiper belt which may help to explain the high albedos shown by some of these bodies

onset of neoglaciation in the southern hemisphere a review of evidence documenting an early neoglacial mid holocene advance of mountain glaciers in south america and new zealand reveals that of 16 glaciers for which radiocarbon age control exists only two have associated dates that may approximate the culmination of an advance advances of the remaining glaciers are controlled only by minimum or maximum limiting ages additional dates for several new zealand glaciers are based on weathering rind measurements having large potential errors twelve of the glaciers now terminate or have terminated in lakes or in tidewater and are subject to instabilities associated with calving termini an extensive debris cover in the ablation zone of nearly half of the glaciers makes their moraine succession potentially suspect as a record of detailed climatic variation the two glaciers with seemingly reliable age control are located in valleys where large rock avalanches could affect glacier mass balance and lead to random advances or where rock avalanche deposits might easily be mistaken for moraines and tills the early neoglacial interval has been defined primarily based on this set of data the ages taken at face value suggest that the early neoglacial advance culminated between ca 5400 and 4900 cal yr ago ca 4600 4400 14c yr bp this chronology however should remain provisional until improved age control is obtained for a large population of glaciers based on closely bracketing radiocarbon dates and or an adequate number of cosmogenic isotope ages data from calving glaciers and those subject to rock avalanche activity should be avoided or assessed critically copyright 2000 john wiley sons ltd

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

a new 27 ky high resolution east antarctic climate record the ice core recently drilled at the dome concordia site on the east antarctic plateau provides a new high resolution isotope record covering part of the last glacial the last transition and the holocene the two step shape of the deglaciation is remarkably similar for all the ice cores now available on the east antarctic plateau the first warming trend ends about 14000 years ago and is followed by the well marked antarctic cold reversal acr with a secondary peak common to all records during the deglaciation there are more similarities between the near coastal site of taylor dome and inland east antarctica than between taylor dome and central greenland however the results for epica do appear to confirm the taylor dome timescale after about 14 ka showing cooling into the acr roughly in phase between greenland and antarctica while the overall deglacial pattern is asynchronous this suggests that the now classical picture of a temperature seesaw between antarctica and greenland may be too simplistic

planetary science pluto s polygons explained the sputnik planum basin of pluto contains a sheet of nitrogen ice the surface of which is divided into irregular polygons tens of kilometres across two studies reveal that vigorous convection causes these polygons see letters p 79 82

abrupt cooling of antarctic surface waters and sea ice expansion in the south atlantic sector of the southern ocean at 5000 cal yr b p antarctic surface waters were warm and ice free between 10 000 and 5000 cal yr b p as judged from ice rafted debris and microfossils in a piston core at 53 s in the south atlantic this evidence shows that about 5000 cal yr b p sea surface temperatures cooled sea ice advanced and the delivery of ice rafted detritus ird to the subantarctic south atlantic increased abruptly these changes mark the end of the hypsithermal and onset of neoglacial conditions they coincide with an early neoglacial advance of mountain glaciers in south america and new zealand between 5400 and 4900 cal yr b p rapid middle holocene climate changes inferred from the taylor dome ice core antarctica cooling and increased ird in the north atlantic and the end of the african humid period the near synchrony and abruptness of all these climate changes suggest links among the tropics and both poles that involved nonlinear response to gradual changes in northern hemisphere insolation sea ice expansion in the southern ocean may have provided positive feedback that hastened the end of the hypsithermal and african humid periods in the middle holocene

vigorous convection as the explanation for pluto s polygonal terrain a parameterized convection model and observations of the puzzling polygons of the sputnik planum region of pluto are used to compute the rayleigh number of its nitrogen ice and show that it is vigorously convecting kilometres thick and about a million years old nasa s new horizons spacecraft has revealed fascinating details of the surface of pluto including a vast ice filled basin known as sputnik planum which is central to pluto s geological activity much of the surface of sputnik planum consisting mostly of nitrogen ice is divided into irregular polygons that are tens of kilometres in diameter and whose centres rise tens of metres above their sides two papers in this issue of nature analyse new horizons images of this polygonal terrain both conclude that it is continually being resurfaced by convection but arrive at contrasting models for the process alexander trowbridge et al report a parameterized convection model in which the nitrogen ice is vigorously convecting ten or more kilometres thick and about a million years old william mckinnon et al from the new horizons team show that sluggish lid convective overturn in a several kilometre thick layer of solid nitrogen can explain both the presence of the cells and their great width pluto s surface is surprisingly young and geologically active1 one of its youngest terrains is the near equatorial region informally named sputnik planum which is a topographic basin filled by nitrogen n2 ice mixed with minor amounts of ch4 and co ices1 nearly the entire surface of the region is divided into irregular polygons about 20 30 kilometres in diameter whose centres rise tens of metres above their sides the edges of this region exhibit bulk flow features without polygons1 both thermal contraction and convection have been proposed to explain this terrain1 but polygons formed from thermal contraction analogous to ice wedges or mud crack networks 2 3 of n2 are inconsistent with the observations on pluto of non brittle deformation within the n2 ice sheet here we report a parameterized convection model to compute the rayleigh number of the n2 ice and show that it is vigorously convecting making rayleigh benard convection the most likely explanation for these polygons the diameter of sputnik planum s polygons and the dimensions of the floating mountains the hills of of water ice along the edges of the polygons suggest that its n2 ice is about ten kilometres thick the estimated convection velocity of 1 5 centimetres a year indicates a surface age of only around a million years

insar mapping and modelling of an active iranian salt extrusion abstract interferometric synthetic aperture radar insar imaging is a powerful technique that is increasingly used to extract detailed 3d information on earth surface structures including exposed diapiric surfaces we have used insar to map for the first time the cumulative surface deformation in a 6 km 6 km region surrounding an active salt diapir syahoo and its associated surface salt flow or namakier exposed in the zagros mountains of southern iran images provided by the european space agency were acquired in 12 increments ranging in length between 35 and 1248 days over a 14 year interval between july 1992 and may 2006 the deformation of the salt surface is non steady with extrapolated rates of displacement varying between surficial uplifts of 1 4 mm day 1 511 mm a 1 and subsidence of 2 2 mm day 1 803 mm a 1 growth of a central topographic dome occurs following short wet intervals to create a salt fountain morphology which then slowly decays during the intervening long dry periods salt associated with dynamic bulging9 of the central dome during wet intervals may flow laterally via gravity spreading into the surrounding salt sheet resulting in deflation and subsidence of the dome which is counteracted by growth and inflation of the adjacent namakiers salt bulges9 that migrate down the namakier resulting in local inflationary and deflationary cycles of the surface may be regarded as episodic pulses of gravity spreading areas of inflation and deflation are also observed to commonly reverse during dry to wet periods as the overall salt system effectively self regulates as it continually strives for dynamic equilibrium as long as the source of salt remains undepleted gravity spreading of the dome ultimately results in more buoyancy driven salt flowing up the diapiric neck to replenish and feed the extrusion and maintain the gross fountain morphology

diatom evidence for late holocene climatic events in granite harbor antarctica downcore diatom data from a deep basin in granite harbor antarctica provide new high resolution information concerning changes in oceanographic and depositional processes that have occurred during approximately the last 1250 years the influence of global scale climatic change during the time of the medieval warm period and possibly the little ice age is revealed by long term changes in floral assemblages as recorded by changes in the relative concentration of nitzschia cylindrus the diatom data suggest that granite harbor experienced less annual ice and pack ice cover during both these periods possibly because of higher temperatures during the medieval warm period and stronger offshore winds during the little ice age the sedimentary record reveals several distinct short lived events in which nearly monospecific blooms of corethron criophilum and chaetoceros spp occurred possibly the result of strong stabilization of the upper water column and were most likely a response to regional rather than global conditions although short lived these events may play a significant role in the delivery of organic carbon and biogenic silica to the seafloor

productivity cycles of 200 300 years in the antarctic peninsula region understanding linkages among the sun atmosphere oceans sea ice and biota compared to the rest of the world9s oceans high resolution late holocene paleoclimatic data from the southern ocean are still rare we present a multiproxy record from a sediment core retrieved from a deep basin on the western side of the antarctic peninsula that reveals a dramatic perspective on paleoclimatic changes over the past 3700 yr analyses completed include measurement of magnetic susceptibility and granulometry bed thickness particle size percent organic carbon bulk density and microscopic evaluation of diatom and benthic foraminiferal assemblages and abundances downcore variability of these parameters demonstrates the significance of both short term cycles which recur approximately every 200 yr and longer term events 2500 yr cycles that are most likely related to global climatic fluctuations in the upper 600 cm of the core lower values of magnetic susceptibility ms are correlated with lower bulk density the presence of thinly laminated units specific diatom assemblages and generally higher total organic carbon content below 600 cm magnetic susceptibility is uniformly low though variability in other parameters continues the magnetic susceptibility signal is controlled primarily by dilution of ferromagnetic phases with biosiliceous material this signal may be enhanced further by dissolution of magnetite in the magnetic susceptibility lows high total organic carbon the role of variable primary productivity and its relationship to paleoclimate is assessed through the diatom data in particular magnetic susceptibility lows are characterized by higher than normal abundances of chaetoceros resting spores corethron criophilum and or rhizosolenia spp also are found as is a higher ratio of the most common species of fragilariopsis versus species of thalassiosira these assemblages are indicative of periods of high primary productivity driven by the presence of a meltwater stabilized water column the 200 yr cyclicity noted in other paleoclimatic records around the world suggests a global forcing mechanism possibly solar variability in addition to the cyclic changes in productivity overall elevated productivity is noted below 600 cm or prior to ca 2500 yr b p this increased productivity may represent the tail end of a holocene climatic optimum which is widely recognized in other parts of the world but as yet is poorly documented in antarctica

the two step shape and timing of the last deglaciation in antarctica the two step character of the last deglaciation is well recognized in western europe in greenland and in the north atlantic for example in greenland a gradual temperature decrease started at the bolling b around 14 5 ky bp spanned through the allerod a and was followed by the cold younger dryas yd event which terminated abruptly around 11 5 ky bp recent results suggest that this ba yd sequence may have extended throughout all the northern hemisphere but the evidence of a late transition cooling is still poor for the southern hemisphere here we present a detailed isotopic record analyzed in a new ice core drilled at dome b in east antarctica that fully demonstrates the existence of an antarctic cold reversal acr these results suggest that the two step shape of the last deglaciation has a worldwide character but they also point to noticeable interhemispheric differences thus the coldest part of the acr which shows a temperature drop about three times weaker than that recorded during the yd in greenland may have preceded the yd antarctica did not experienced abrupt changes and the two warming periods started there before they started in greenland the links between southern and northern hemisphere climates throughout this period are discussed in the light of additional information derived from the antarctic dust record

the recent fault scarps of the western alps france tectonic surface ruptures or gravitational sackung scarps a combined mapping geomorphic levelling and 10be dating approach abstract in the western alps some recent scarps were previously interpreted as surface ruptures of tectonic reverse and normal faults that agree with microseismicity and gps measurements our analysis shows that in fact there are hundreds of recent scarps up to 30 m high and 2 1 km long with only pure normal motions they share the same characteristics as typical sackung scarps the scarps are mainly uphill facing parallel to the ridge crests and the contour lines they are relatively short less than 2 1 km with respect to tectonic fault ruptures and organized in swarms they cut screes and relict rock glaciers with a slow commonly 1 mm year average slip rate in the aiguilles grives massif these sackung scarps clearly express the gravitational toppling of sub vertical bedding planes in hard rocks in contrast the belledonne outer crystalline massif exhibits scarps that stem from the gravitational reactivation of conjugate tectonic faults the recent faults extend to about 1600 m beneath the rognier ridge crest but are always above the valley floor the main scarp swarm is 9 2 km long and constitutes the largest sackung ever described in the western alps 10 be dating of a scarp and offset surfaces shows that 4 m slip may have occurred rapidly in less than 3800 years sometimes between the end of the glaciation and 8800 1900 years ago this dating together with the location of some faults far from the deep glacial valleys suggests that sagging might have been triggered by strong earthquakes during a post glacial period of probably enhanced seismicity the belledonne and synclinal median faults just beneath the rognier sackung could have been the sources of this seismicity

origin of the salt valleys in the canyonlands section of the colorado plateau evaporite dissolution collapse versus tectonic subsidence abstract the salt valleys over the axis of the salt cored anticlines in the paradox fold and fault belt canyonlands utah and colorado are created by subsidence of the anticline crests traditionally the collapse of the anticlinal crests was attributed to dissolution of the salt walls diapirs forming the anticline cores recent studies based on scaled physical models and field observations propose that the salt valleys are a result of regional extension and that salt dissolution had only a minor influence in the development of the axial depressions this paper presents several arguments and lines of evidence that refute the tectonic model and support the salt dissolution subsidence interpretation the development of contractional structures in salt dissolution experiments led the advocates of the tectonic interpretation to reject the dissolution induced subsidence explanation however these salt dissolution models do not reproduce the karstification of salt walls in a realistic way since their analog involves removal of salt from the base of the diapirs during the experiments additionally numerous field examples and laboratory models conducted by other authors indicate that brittle subsidence in karst settings is commonly controlled by subvertical gravity faults field evidence against the regional extension model includes 1 a thick cap rock at the top of the salt walls 2 the concentration of subsidence deformation structures along the crest of the anticlines salt walls 3 deformational structures not consistent with the proposed nne extension like crestal synforms and ne sw grabens 4 dissolution induced subsidence structures controlled by ring faulting revealing deep seated dissolution 5 large blocks foundered several hundred meters into the salt wall 6 evidence of recent and active dissolution subsidence and 7 the aseismic nature of the recently active collapse faults although underground salt dissolution seems to be the main cause for the generation of the salt valleys this phenomenon may have been favored by regional extension tectonics that enhance the circulation of groundwater and salt dissolution

geomorphology and geochronology of sackung features uphill facing scarps in the central spanish pyrenees abstract the paper analyses uphill facing scarps and associated troughs developed in the oversteepened slopes of two neighbouring glacial valleys in the central spanish pyrenees previous studies of sackung landforms in the pyrenees have argued for deglacial unloading as the genetic mechanism but this causal and temporal relationship has not been proved due to the lack of chronological data the antislope scarps in the two studied locations vallibierna and estos are developed in palaeozoic metasedimentary rocks parallel to the contour lines and the structural grain occur in the intermediate sector of the hillslope and are up to 0 5 km long and several meters high a trench was excavated in a sackung trough fill in each of the valleys in order to gain information about their chronology and genesis charcoal from the lowermost unit in vallibierna provided an age of 5 9 cal ka for the sackung and extrapolation of the three dates obtained in estos indicates that the trough formed ca 7 6 7 8 cal ka deglaciation of the studied sectors of the valleys occurred between 16 and 13 ka the time lag of 5 ka suggests that glacial erosion and the subsequent debutressing of the oversteepened valley walls created slopes predisposed to sackung development but did not initiate the movement seismic shaking is proposed as a probable triggering factor this hypothesis although supported by the sudden deformation event recorded by a failure plane exposed in vallibierna trench and by the seismic and neotectonic activity of the area cannot be proved due to the lack of chronological information about paleoearthquakes

magnitude and geographic variation of the radiocarbon content in antarctic marine life implications for reservoir corrections in radiocarbon dating abstract radiocarbon age estimates on marine derined materials from the antarctic appear old in comparison with the terrestrial radiocarbon timescale as a result of significantly depleted 14 c concentrations in antarctic seas we review measurements of 14 c concentrations in modern antarctic marine life from south georgia the shetland islands and antarctic peninsula and suggest correction factors required to relate radiocarbon measurements on fossil marine materials from these areas to the conventional radiocarbon timescale for dates based on shells seaweeds sealbones and penguin bones the minimum correction factor for south georgia is ca 750 years and for the south shetland islands and antarctic peninsula it may be up to 1250 1300 years for whalebones a minimum correction of 1000 years may apply over a wide geographic area for comparison we also review radiocarbon measurements on marine species and seawater from other sectors of the antarctic in high latitudes correction factors of ca 1400 years are generally applicable to shell seal and penguin samples

palaeoclimatic significance of late quaternary diatom assemblages from southern windmill islands east antarctica abstract the late quaternary palaeoenvironmental history of the southern windmill islands east antarctica has been reconstructed using diatom assemblages from two long well dated sediment cores taken in two marine bays the diatom assemblage of the lowest sediment layers suggests a warm climate with mostly open water conditions during the late pleistocene during the following glacial the windmill islands were covered by grounded ice preventing any in situ bioproductivity following deglaciation a sapropel with a well preserved diatom assemblage was deposited from 10 500 cal yr bp between 10 500 and 4000 cal yr bp total organic carbon corg and total diatom valve concentrations as well as the diatom species composition suggest relatively cool summer temperatures hydrological conditions in coastal bays were characterised by combined winter sea ice and open water conditions this extensive period of glacial retreat was followed by the holocene optimum 4000 to 1000 cal yr bp which occurred later in the southern windmill islands than in most other antarctic coastal regions diatom assemblages in this period suggest ice free conditions and meltwater stratified waters in the marine bays during summer which is also reflected in high proportions of freshwater diatoms in the sediments the diatom assemblage in the upper sediments of both cores indicates neoglacial cooling from 1000 cal yr bp which again led to seasonally persistent sea ice on the bays the holocene optimum and cooling trends in the windmill islands did not occur contemporaneously with other antarctic coastal regions showing that the here presented record reflects partly local environmental conditions rather than global climatic trends

insights on the kinematics of deep seated gravitational slope deformations along the 1915 avezzano earthquake fault central italy from time series dinsar abstract among the causes of deep seated gravitational slope deformations dgsd the most important is relief energy which is closely related to the intensity of the active tectonic deformations either at the regional scale or at the scale of a single active fault we analyzed some examples of dgsd from the eastern border of the fucino basin in the central apennines where extensional tectonics has been active since the late pliocene photogeological and field geomorphological analysis was performed to identify landforms typically associated with dgsd such as counterslope scarps double crests trenches and bulging slopes these features are located on a mountain range at less than 1 km from the causative fault of the 1915 avezzano earthquake we used the sbas differential sar interferometry technique to measure the slow movements of the surface and calculated differential vertical and horizontal ground velocities of 2 4 mm yr 1 during the period spanning from 1992 to 2001 the quantitative information on the kinematics of the deformation provided some inferences on the different processes responsible for the evolution of the observed dgsd the displacement time series shows non linear deformation trends at some locations possibly correlated with a strong meteorological event we speculate that dgsd in this area are normally subject to slow deformation and that sudden slip along sliding surfaces observed in excavations may sporadically be triggered off by extreme meteorological or seismic events evidence of catastrophic collapse of previous dgsd along the same mountain slope reinforce this hypothesis

synchronous climate changes in antarctica and the north atlantic central greenland ice cores provide evidence of abrupt changes in climate over the past 100 000 years many of these changes have also been identified in sedimentary and geochemical signatures in deep sea sediment cores from the north atlantic confirming the link between millennial scale climate variability and ocean thermohaline circulation it is shown here that two of the most prominent north atlantic events the rapid warming that marks the end of the last glacial period and the bolling allerod younger dryas oscillation are also recorded in an ice core from taylor dome in the western ross sea sector of antarctica this result contrasts with evidence from ice cores in other regions of antarctica which show an asynchronous response between the northern and southern hemispheres

evidence from diatoms for holocene climate fluctuation along the east antarctic margin diatom assemblages in two holocene sediment cores gc1 and gc2 from the mac robertson shelf east antarctica are compared with modern sedimentary diatom assemblages from the same area open marine deposition commenced in iceberg alley gc1 on the outer continental shelf 10 7 adj 14 c kyr bp

a genetic classification of sinkholes illustrated from evaporite paleokarst exposures in spain this contribution analyses the processes involved in the generation of sinkholes from the study of paleokarst features exposed in four spanish tertiary basins bedrock strata are subhorizontal evaporites and in three of the basins they include halite and glauberite in the subsurface our studies suggest that formation of dolines in these areas results from a wider range of subsidence processes than those included in the most recently published sinkhole classifications a new genetic classification of sinkholes applicable to both carbonate and evaporite karst areas is thus proposed with the exception of solution dolines it defines the main sinkhole types by use of two terms that refer to the material affected by downward gravitational movements cover bedrock or caprock and the main type of process involved collapse suffosion or sagging sinkholes that result from the combination of several subsidence processes and affect more than one type of material are described by combinations of the different terms with the dominant material or process followed by the secondary one e g bedrock sagging and collapse sinkhole the mechanism of collapse includes any brittle gravitational deformation of cover and bedrock material such as upward stoping of cavities by roof failure development of well defined failure planes and rock brecciation suffosion is the downward migration of cover deposits through dissolutional conduits accompanied with ductile settling sagging is the ductile flexure of sediments caused by differential corrosional lowering of the rockhead or interstratal karstification of the soluble bedrock the paleokarsts we analysed suggest that the sagging mechanism not included in previous genetic classifications plays an important role in the generation of sinkholes in evaporites moreover collapse processes are more significant in extent and rate in areas underlain by evaporites than in carbonate karst primarily due to the greater solubility of the evaporites and the lower mechanical strength and ductile rheology of gypsum and salt rocks

cosmogenic 10be dating of a sackung and its faulted rock glaciers in the alps of savoy france sackungs are the largest gravitational deformation observed in mountains they are characterized by the long term slowness of the movements but their mechanism is still not well understood nowadays cosmic ray exposure cre dating methods allow dating the morphologic structures involved in sackung and can contribute at the understanding of their origin in the alps the 5 3 km long arcs sackung initiated during the activity of rock glaciers three samples from these faulted rock glaciers provide their first cre ages and show that at 2000 m elevation these block accumulations moved during the younger dryas and stopped in early holocene six 10be ages of fault scarps show that the arcs sackung lasted only a few thousand years and stopped at about 8462 432 10be yr they also reveal that deformation migrated upslope in agreement with a mechanism of flexural toppling of vertical layers this unique and long gravitational event characterized by migration of the deformation does not support earthquake shaking as triggering mechanism for individual faults it shows that in the upper isere valley slope deformation was delayed of several thousand years after glacial debuttressing and is not anymore active despite its fresh morphology

differentiating between gravitational and tectonic faults by means of geomorphological mapping trenching and geophysical surveys the case of the zenzano fault iberian chain n spain abstract the zenzano fault scarp has been developed on the top of a 475 m high erosional escarpment underlain by an upper brittle sequence and a lower halite bearing evaporitic formation the 1850 m long fault with a maximum displacement of 45 m and parallel to the escarpment has offset the back of a dip slope generating an antislope scarp with prominent triangular facets up to 38 m high and obstructing consequent transverse drainages defeated streams both gravitational and tectonic interpretations were previously proposed for this active surface rupture the fault scarp has been investigated by detailed geological and geomorphological mapping geophysical surveys gpr and ert and two trenches excavated across the fault in disrupted drainages the geophysical profiles clearly imaged the fault helping to site the trenches and roughly estimate the thickness of the deposits accumulated in the downthrown block although the maximum displacement to length ratio dmax l of the fault fall within the range of tectonic faults of similar length according to the world database the geological and geomorphological context together with several parameters reveal that this structure corresponds to a gravitational failure 1 anomalously high vertical displacement per event 1 4 m 2 high apparent vertical slip rate 0 6 mm year and 3 short recurrence interval of faulting events the negligible horizontal displacement component on the dip slip fault as well as the presence of very large caprock collapse sinkholes and saline springs strongly suggest that interstratal karstification of the halite bearing evaporites has played a primary role in the development of the gravitational failure the formation of this morphostructure has been favoured by pre existing tectonic faults erosional unloading related to the removal of an overburden ca 800 m thick and enhanced groundwater recharge due to the blockage of the drainage this work illustrates that the proposed multidisciplinary approach allows the identification of features and calculation of parameters that may help to elucidate whether an active failure has a gravitational or a tectonic origin

mechanics of graben evolution in canyonlands national park utah results of numerical models and field observations of regularly spaced grabens in canyonlands national park utah demonstrate that salt flow beneath a brittle overburden accommodated recent and ongoing westward gravity spreading erosion of the colorado river canyon differentially loaded the underlying viscous salt in our models the overlying brittle strata flexed downward toward the canyon initiating faults near the surface that propagated downward toward the salt contact modeled grabens developed sequentially away from the canyon eastward as salt was expelled from beneath undeformed strata after their eastern boundary faults broke through horst blocks tilted in the opposite direction of initial flexure resulting in increased symmetry of older grabens closer to the canyon continued extension formed a reactive diapir beneath each graben field observations show that multiple faults bound grabens indicating reactive diapirs beneath them topographic profiles and surveyed points along a stratigraphic layer show that horst blocks subsided as salt migrated toward the river canyon and into the diapirs field data from less evolved horsts imply that individual horst blocks responded to differential loading by progressive flexure and tilt similar to the models horst block flexures also vary along strike and localized folds and faults formed where fault displacement changes abruptly

preservation efficiencies and accumulation rates for biogenic silica and organic c n and p in high latitude sediments the ross sea rates of biogenic sediment accumulation biogenic silica and organic c n and p and pore water flux have been established for a variety of depositional environments in the ross sea on the basis of 14c measurements in kasten cores sediment accumulation rates ranged from 250 cm kyr 1 in the coastal basin of granite harbor to 1 2 cm kyr 1 in the shelf and slope environments of the northern and eastern ross sea burial of biogenic material was most rapid in the southwestern ross sea where biogenic silica accumulation rates ranged from 2 to 31 g cm 2 kyr 1 and organic carbon accumulation rates ranged from 0 05 to 1 4 g cm 2 kyr 1 in the northern and eastern ross sea biogenic silica and organic carbon accumulation rates typically equaled 0 02 0 03 g sio2 cm 2 kyr 1 and 0 002 0 004 g c cm 2 kyr 1 flux core measurements were used to estimate seabed regeneration rates for biogenic silica organic carbon and phosphorus pore water fluxes in general showed much less variability across the ross sea than did the biogenic accumulation rates pore water silicate fluxes in the study area ranged from 0 6 to 5 3 g sio2 cm 2 kyr 1 whereas carbon fluxes ranged from 0 1 to 1 2 g c cm 2 kyr 1 and phosphate fluxes varied from 0 006 to 0 012 g p cm 2 kyr 1 seabed preservation efficiencies were calculated for biogenic silica organic carbon and phosphorus by combining the solid phase and pore water data the seabed preservation efficiencies for biogenic silica 1 86 were greater than for organic carbon 1 71 at all nine stations examined the preferential preservation of biogenic silica relative to organic carbon also was apparent in ross sea sediments because the biogenic silica organic carbon ratio in the material buried in the seabed generally was 2 times greater than the ratio in sediment particles arriving at the sediment water interface sediment accumulation rate correlated strongly with both the biogenic silica and the organic carbon preservation efficiency data p preservation efficiencies remained relatively high 24 65 even when the accumulation rates were low 1 2 cm kyr 1 because of the near zero phosphate fluxes out of the seabed of the total p in the seabed 0 04 0 09 wt approximately 25 existed in the form of organic p the total amount of biogenic silica accumulating on the ross sea shelf is 2 3 1012 g sio2 yr 1 which is approximately an order of magnitude less than the ledford hoffman et al 1986 estimate that was based on 210pb chronologies biogenic silica accumulation rates in the southern central and western ross sea increased during the mid and late holocene reaching their maximum values during the past 500 to 1000 years

deglacial paleoclimate of the american sector of the southern ocean late glacial holocene records from the latitude of canal beagle 55 s argentine tierra del fuego abstract paleoclimate at the time of deglaciation 14 000 10 000 14 c yr b p in different sectors of the southern ocean has followed a continuous warming trend but also warming broken by a transitory episode the younger dryas stadial event during which on the order of a millennium colder conditions prevailed evidence is from antarctic ice cores deep sea cores glacier fluctuations and pollen and beetle records reasons for the apparent nonuniformity include differential sensitivity of each sector to climatic change uneven dating control and the variable forcing response nature of biota used as climatic indicators establishing the late glacial paleoclimate of the southern ocean is of significance as it bears on comprehending the character of deglaciation in a global context with the object of investigating further the sequence of deglacial climatic events pollen stratigraphic studies at canal beagle at the southern extremity of south america were extended westward to the vicinity of ushuaia and lapataia supplementing work done previously at caleta robalo puerto harberton and bahia moat at ushuaia pollen frequency and influx records of the late glacial as well as the holocene chronologically controlled by 25 14 c age determinations are from four sphagnum empetrum mires results obtained at sites dating from 12 500 to 12 000 yr b p show late glacial climatic variability most indicative among tundra communities of grass and dwarf shrub heath is a drop both in frequency and influx of the singular arboreal component nothofagus at the time of the younger dryas when estimated summer january temperature was 3 c lower than at present at ushuaia in general terms the late glacial pattern is not unlike the northwestern european sequence sensu walker 1995 which exhibits a late glacial interstadial 13 000 11 000 yr b p followed by a younger dryas stadial 11 000 10 000 yr b p within limits of the chronology in the american sector there is no indication as shown by marine cores from the southern ocean and by antarctic ice cores that deglacial climatic events at higher latitudes of the southern hemisphere exemplified by the younger dryas lead similar events in the northern hemisphere uninterrupted warming evident in the marine and ice cores occurred after 11 600 11 500 yr b p at canal beagle in contrast the trend toward steadily milder climate indicated by continuous expansion of nothofagus frequency followed in the early holocene after 10 000 yr b p early holocene nothofagus woodland containing grass and composites replaced tundra under a warmer and drier set of conditions coupled with burning estimated summer temperature averaged 1 c higher than today and annual precipitation 100 mm less pollen influx remained generally low until about 5000 yr b p when the rate of nothofagus greatly increased together with increase in the rate of empetrum a characteristic mire component the implication is of late holocene spread of both closed forest and mire the result of greater precipitation and lower temperatures while burning abated summer temperatures evidently varied within about 0 5 c and precipitation by 100 mm compared with the present renewed albeit fluctuating glacial activity is recorded after 5000 yr b p under a variable cooler and more humid late holocene climatic regime

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

temporal behavior of deep seated gravitational slope deformations a review abstract deep seated gravitational slope deformations dsgsds are slow moving hillslope scale mass movements featuring characteristic landforms such as double crested ridges and upslope facing scarps that occur in diverse landscapes throughout the world although these deformations have been studied since the 1960s significant insights to the rates of dsgsds have only been gained within the last two decades owing to progress in geochronology remote sensing and instrumental monitoring absolute age and monitoring data indicate that dsgsd movements are observable over long term 102 years and short term future research directions include constraining the lifespan of dsgsds with absolute age dating and precise high resolution monitoring of spatio temporal displacement across dsgsd bodies it is of great importance to include absolute time scales in the numerical models of dsgsds furthermore combining remote sensing techniques such as synthetic aperture radar interferometry with high resolution lidar scanning and near surface geophysics offers a promising toolkit for collecting very detailed and accurate data on the short term deformation rates of dsgsds

late pleistocene holocene sedimentary fluxes of organic carbon and biogenic silica in the northwestern ross sea antarctica eight sediment gravity cores collected from thejoides and drygalski basins were analysed in order to understand late pleistocene holocene biogenic dux changes in the ross sea driven by paleoenvironmental changes core lithologies and magnetic susceptibility depth profiles were used for core logging and stratigraphic corre lation nineteen ams radiocarbon dates of bulk organic matter were used to set chrono logical constraints and calculate sediment accumulation rates these rates which vary from 1 4 38 cm ka i were used to obtain the burial f1uxes of biogenic components the highest f uxes occur in the deepest parts o the basins toc 0 05 0 2 g cm 2 ka i biogenic silica 1 5 5 g cm 2 ka i whereas topographic highs show the lowest values toc 0 010 1 g cm 2 ka i biogenic silica 0 1 1 4 g cm 2 ka i dramatic changes in both physical properties and fluxes record the establishment of open marine sedimentation conditions which occurred first in thejoides basin and then with a delay of ca 6000 years in the drygalski basin both toc and biogenic silica ouxes increase through the holocene though slightly difterently the high f1uxes of both lobe and biogenic ba suggest that sedi ment accumulation at basin sites is strongly influenced by lateral transport

modeling of grabens extending above evaporites in canyonlands national park utah abstract grabens in canyonlands national park utah began extending above a layer of evaporites when the colorado river cut through the overburden two dimensional finite element models simulate the effects of geometry and rock properties on graben configuration and spacing only those models having a progressively increasing slope or no slope mimicked the natural upslope graben propagation typical rock properties produced the most realistic fault patterns an initial friction angle of 31 a cohesion of 1 mpa and strain weakening comprising cohesion loss and decrease of friction angle to 26 a tensile stress limit narrowed the grabens and reproduced the vertical upper portion of the natural faults the viscous salt resisted overburden spreading and controlled its rate modeled grabens spread at typical rates of 1 2 mm a 1 for a salt viscosity of 1 10 18 pa s and the entire system strained at rates from 6 0 10 14 s 1 to 0 5 10 14 s 1 the faults bounding a graben formed nearly simultaneously at the top surface and propagated downward salt rose beneath the grabens as reactive diapirs overburden adjacent to the canyon flexed as salt was expelled and formed an arching horst and graben a corresponding horst has been found in the field the model results scale to larger dimensions except for the steep upper part of the faults reduced dimensions create vertical or no faults

an oceanic cold reversal during the last deglaciation a detailed deuterium excess profile measured along the dome c epica european project for ice coring in antarctica core reveals the timing and strength of the sea surface temperature changes at the source regions for dome c precipitation we infer that an oceanic cold reversal took place in the southern indian ocean 800 years after the antarctic cold reversal the temperature gradient between the oceanic moisture source and antarctica is similar to the dome c sodium profile during the deglaciation illustrating the strong link between this gradient and the strength of the atmospheric circulation

the pluto system initial results from its exploration by new horizons the pluto system was recently explored by nasa s new horizons spacecraft making closest approach on 14 july 2015 pluto s surface displays diverse landforms terrain ages albedos colors and composition gradients evidence is found for a water ice crust geologically young surface units surface ice convection wind streaks volatile transport and glacial flow pluto s atmosphere is highly extended with trace hydrocarbons a global haze layer and a surface pressure near 10 microbars pluto s diverse surface geology and long term activity raise fundamental questions about how small planets remain active many billions of years after formation pluto s large moon charon displays tectonics and evidence for a heterogeneous crustal composition its north pole displays puzzling dark terrain small satellites hydra and nix have higher albedos than expected

active salt tectonics in the needles district canyonlands utah as detected by interferometric synthetic aperture radar and point target analysis 1992 2002 1 the needles district in canyonlands national park utah is known for its well exposed array of extensional faults which are thought to be produced by gravity driven extension and downward flexure of a thin sandstone plate into the colorado river canyon in response to dissolution and flow of underlying evaporites halite and gypsum owing to a lack of precise geodetic data however it remains uncertain if and to what extent those extensional faults are currently deforming in this study we use synthetic aperture radar sar data to search for ongoing decadal ground displacements by applying both a stacking interferometric sar insar analysis and interferometric point target analysis ipta our results show that most of the needles district is indeed undergoing deformation now at a maximum rate of 2 3 mm year away from the satellite looking roughly westward with an incidence angle of about 20 also we identify a localized region along the riverbank that is uplifting at a rate of 2 3 mm year we estimate the measurement precision to be better than 0 8 mm year except along the riverbank where the errors are probably higher than this by analyzing residual signals and carrying out a signal recovery experiment using synthetic two dimensional correlated noise the deforming region is almost totally bounded by the colorado river canyon to the west and north a rapidly subsiding east west trending graben to the south and a relatively sharp to very diffuse deformation gradient to the east we observe deformation patterns that were previously undetected these include an area in the southwestern part of the deforming region that is deforming at higher rates than anywhere else in the needles but that has little surface extensional faulting rates of deformation are lower but still clearly significant further north in a region of spectacularly exposed fault blocks that have been previously studied in considerable detail

chronology of the palmer deep site antarctic peninsula a holocene palaeoenvironmental reference for the circum antarctic palmer deep sediment cores are used to produce the first high resolution continuous late pleistocene to holocene time series from the antarctic marine system the sedimentary record is dated using accelerator mass spectrometer radiocarbon methods on acid insoluble organic matter and foraminiferal calcite fifty four radiocarbon analyses are utilized in the dating which provides a calibrated timescale back to 13 ka bp reliability of resultant ages on organic matter is assured because duplicates produce a standard deviation from the surface age of less than laboratory error i e 50 years in addition surface organic matter ages at the site are in excellent agreement with living calcite ages at the accepted reservoir age of 1260 years for the antarctic peninsula spectral analyses of the magnetic susceptibility record against the age model reveal unusually strong periodicity in the 400 200 and 50 70 year frequency bands similar to other high resolution records from the holocene but so far unique f

the meander anticline canyonlands utah an unloading structure resulting from horizontal gliding on salt the axial trace of the meander anticline which has a cumulative length of 25 5 mi coincides with the colorado river in canyonlands national park on the southeast side of the river eight tributary canyons also contain anticlines in all cases the anticlines occupy canyons that are eroded between 400 and 1 800 ft into the pennsylvanian permian section a system of closely spaced grabens has developed in the pennsylvanian permian rocks which comprise the plateaus adjacent to the deeper canyons the grabens are most extensively developed southeast of the colorado river where they follow the strike of the meander anticline for 17 mi and extend 9 mi into the plateau the pennsylvanian paradox evaporites consisting of 85 salt underlie the entire anticline graben complex principal stress axes can be deduced from the intersections between conjugate thrust faults in the cores of the anticlines and from the downward intersections of normal faults bounding the grabens the maximum principal stresses associated with the anticlines are horizontal and perpendicular to the axial planes regardless of the strikes of the anticlines in contrast the maximum principal stresses associated with the grabens are near vertical and normal to the strikes of the faults the conclusions of this study are that 1 the anticlines are unloading structures and 2 the mechanism which best accounts for the observed stresses is one involving the breakup of the brittle plate above the paradox salts and its simultaneous gliding toward nearby canyons the breakup and motion within the brittle plate involve a three dimensional deformation which is analogous to the deformation that takes place within large unbounded landslides through compaction of the section largely accounted for by the downdropping of grabens the deforming mass expands laterally yet maintains horizontal continuity the result is the establishment of horizontal stress gradients at depth which produce compression within the rocks that bridge the floors of the deep canyons regardless of the orientations of the canyons through a combination of horizontal shortening and arching the compressed rocks fold into the observed anticlines salt flowage into the cores of the anticlines is not the causative mechanism in their development

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

can flexural slip faults related to evaporite dissolution generate hazardous earthquakes the case of the grand hogback monocline of west central colorado a paleoseismological investigation of flexural slip faults related to interstratal evaporite dissolution suggests that such gravitational structures might have the potential to generate earthquakes with damaging magnitude the carbondale collapse center in the southern rocky mountains of colorado is a morpho structural depression of 1200 km 2 where miocene volcanic rocks are downdropped as much as 1200 m due to interstratal dissolution of halite bearing evaporites on the western margin of the collapse center the debuttressing effect related to active evaporite dissolution drives unfolding of the steeply dipping late laramide grand hogback monocline accompanied by displacement on bedding parallel faults these flexural slip faults rupture unconformable miocene basalts and quaternary mantled pediments generating conspicuous half graben depressions bounded by antislope fault scarps parallel to the underlying strata of the monocline two trenches dug across flexural slip fault scarps developed in each stratigraphic marker basalt cap mantled pediment revealed unexpected evidence of multiple late quaternary faulting events e g faulted colluvial wedge sharp unconformities with displacement per event values of 1 m three faulting events were inferred from the trench dug in the pediment w around 6

holocene climate variability in antarctica based on 11 ice core isotopic records a comparison is made of the holocene records obtained from water isotope measurements along 11 ice cores from coastal and central sites in east antarctica vostok dome b plateau remote komsomolskaia dome c taylor dome dominion range d47 km105 and law dome and west antarctica byrd with temporal resolution from 20 to 50 yr the long term trends possibly reflect local ice sheet elevation fluctuations superimposed on common climatic fluctuations all the records confirm the widespread antarctic early holocene optimum between 11 500 and 9000 yr in the ross sea sector a secondary optimum is identified between 7000 and 5000 yr whereas all eastern antarctic sites show a late optimum between 6000 and 3000 yr superimposed on the long time trend all the records exhibit 9 aperiodic millennial scale oscillations climatic optima show a reduced pacing between warm events typically 800 yr whereas cooler periods are associated with less frequent warm events pacing 1200 yr

palaeoproductivity in the ross sea antarctica during the last 15 kyr bp and its link with ice core temperature proxies a detailed study of organic carbon content obtained from two sediment cores collected in the joides basin western ross sea antarctica was carried out the variations observed during the last deglaciation and the holocene were compared to the high resolution climatic records epica dc and taylor dome preserved in the ice the importance of the carbon content as a proxy for palaeoclimatic and palaeoenvironmental changes was investigated a dramatic decrease in the ross sea palaeoproductivity was observed during the antarctic cold reversal 12 5 14 kyr bp another decrease in total organic carbon in the second half of the holocene after 5 6 kyr bp confirms the climate worsening observed in previous studies

glacio isostasy and glacial ice load at law dome wilkes land east antarctica abstract the holocene sea level high stand or marine limit in wilkes land east antarctica reached 30 m above present sea level at a few dispersed sites the most detailed marine limit data have been recorded for the windmill islands and budd coast at the margin of the law dome ice cap a dome of the east antarctic ice sheet eais relative sea level lowering of 30 m and the associated emergence of the windmill islands have occurred since 6900 14c corr yr b p numerical modeling of the earth s rheology is used to determine the glacio isostatic component of the observed relative sea level lowering glaciological evidence suggests that most of eais thickening occurred around its margin with expansion onto the continental shelf consequently a regional ice history for the last glacial maximum lgm was applied in the glacio isostatic modeling to test whether the observed relative sea level lowering was primarily produced by regional ice sheet changes the results of the modeling indicate that the postglacial 13 000 to 8000 14c yr b p removal of an ice load of between 770 and 1000 m from around the margin of the law dome and adjacent eais have produced the observed relative sea level lowering such an additional ice load would have been associated with a 40 to 65 km expansion of the law dome to near the continental shelf break together with a few hundred meters of ice thickening on the adjoining coastal slope of the eais up to 2000 m elevation whereas the observed changes in relative sea level are shown to be strongly influenced by regional ice sheet changes the glacio isostatic response at the windmill islands results from a combination of regional and to a lesser extent antarctic wide effects the correspondence between the holocene relative sea level lowering interpreted at the margin of the law dome and the lowering interpreted along the remainder of the wilkes land and oates land coasts 105 160 e suggests that a similar ice load of up to 1000 m existed along the eais margin between wilkes land and oates land