vertical crustal motions from the doris space geodesy system five years 1993 1997 of doris data on the spot and topex poseidon satellites have been analyzed to estimate vertical motions at 33 sites of the permanent doris network rates have been determined assuming constant velocity over the 5 year time span except for a few stations vertical rates are lower than 5 mm yr comparison with solutions provided by gps slr or vlbi at colocated sites shows good agreement for most stations some space geodesy vertical rates however disagree significantly this may result from interannual to decadal fluctuations affecting the vertical motions giving rise to different apparent linear trends if estimated over different time spans except for six high latitude stations post glacial rebound produces negligible signal and cannot explain the observed motions other local or regional phenomena from geophysical or anthropogenic origin may be responsible for the estimated vertical motions

ice sheet retreat and glacio isostatic adjustment in lutzow holm bay east antarctica the east antarctic ice sheet has relatively few field data to constrain its past volume and contribution to global sea level change since the last glacial maximum we provide new data on deglaciation history and develop new relative sea level rsl curves along an 80 km transect from skallen to skarsvnes langhovde and the ongul islands in lutzow holm bay east antarctica the geological constraints were compared with output from two glacial isostatic adjustment gia models the minimum radiocarbon age for regional deglaciation is c 11 240 cal yr bp on west ongul island with progressively younger deglaciation ages approaching the main regional ice outflow at shirase glacier marked regional differences in the magnitude and timing of rsl change were observed more in particular in skarvsnes a minimum marine limit of 32 7 m was inferred which is c 12 7 m higher than previously published evidence and at least 15 m higher than that reported in the other three ice free areas current gia model predictions slightly underestimate the rate of late holocene rsl fall at skallen langhovde and west ongul but provide a reasonable fit to the reconstructed minimum marine limit at these sites gia model predictions are unable to provide an explanation for the shape of the reconstructed rsl curve at skarvsnes we consider a range of possible explanations for the skarvsnes rsl data and favour an interpretation where the anomalously high marine limit and rate of rsl fall is due to reactivation of a local fault

subsidence compaction and gravity sliding implications for 3d geometry dynamic rupture and seismic hazard of active basin bounding faults in southern california in southern california high rates of measured geodetic shortening occur where active basin bounding faults thrust early cenozoic rocks over young uncon solidated sediments this implies that compaction subsidence and other nonelastic processes of footwall deformation may play an important role in contributing to the high rates of observed crustal strain even in the absence of active tectonic short ening sediment compaction alone can produce surficial motions that mimic deep fault slip or elastic strain accumulation differential compaction and subsidence of footwall sediments relative to hanging wall rocks can lead to increased vertical sep aration basinward collapse and fault rotation about horizontal axes such effects contribute to net horizontal and vertical motions in both geologic and geodetic data and if not properly accounted for result in incorrect estimates of the inferred seismic hazard subsidence and compaction also increase the potential for gravity sliding toward the basin and the development of significant nonplanar 3d fault geometry a prime example occurs along the san cayetano fault that bounds the eastern ventura basin at shallow levels a large thrust sheet the modelo lobe with low dip extends out in front of the more steeply dipping planar fault segment by over 4 km is nearly 2 km thick and occupies over 60 cubic km this geometry is strongly indicative of gravity driven failure resulting from hanging wall uplift basinward tilt and collapse enhanced by footwall subsidence and compaction failure of this mega slide off the hanging wall block most likely occurred within the rincon formation a thick ductile shale sequence that often accommodates detachment slip this 3d geometry has significant implications for how the fault may behave during dynamic rupture and implies that additional care should be taken in extrapolating near surface measure ments or estimates of fault slip and dip to seismogenic depths

a diatom based palaeosalinity history of ace lake vestfold hills antarctica a comprehensive diatom stratigraphy is used to calculate a palaeosalinity history for an antarctic lake via an established diatom salinity transfer function for the vestfold hills antarctica a sediment core taken from ace lake in 1995 shows three distinct changes in diatom assemblage constituents initial benthic hyposaline freshwater taxa are replaced by marine planktonic and sea ice taxa with these taxa in turn replaced by the benthic hypersaline taxa dominant in the lake today these changes in assemblage composition enable the lakewater salinity of each stage to be determined and the holocene evolution of the lake to be refined deglaciation of the vestfold hills at the beginning of the holocene exposed ace lake basin following this fresh lacustrine diatoms were deposited from 11 380 to 8110 corrected 14c yr bp relative sea level rise after this time led to the progressive marine inundation of the lake and the deposition of marine diatom taxa marine taxa were dominant in the sediment for mo

holocene lake development and glacial isostatic uplift at lake skallen and lake oyako lutzow holm bay east antarctica based on biogeochemical facies and molecular signatures abstract the paleolimnology of two lakes which were isolated as a result of the crustal uplift during the late holocene along the soya coast lutzow holm bay east antarctica were studied the focus was on temporal variations in the biogeochemical composition of sediment cores recovered from lake skallen at skallen and lake oyako at skarvsnes both sets of lake sediments record environmental changes associated with a transition from marine to lacustrine settings as indicated by analyses of c and n contents nitrogen isotopic compositions 15 n and major element concentrations changes in the dominant primary producers during the marine lacustrine transition marine diatom to cyanobacteria at l skallen was clearly revealed by biogenic opal a diatom assemblages and molecular signature from denaturing gradient gel electrophoresis dgge with 16s ribosomal rna rrna gene analysis radiocarbon dating of acid insoluble organic c suggested that the environmental transition from marine to fresh water occurred at 2940 100 cal yr bp at l skallen and 1060 90 cal yr bp at l oyako based on these data a mean crustal uplift rate of 3 2 mm yr 1 is inferred for the history of marine lacustrine transition via brackish conditions the geological setting causing glacio isostatic uplift was the primary factor in controlling the transition event in sedimentary and biological facies

detection of aquifer system compaction and land subsidence using interferometric synthetic aperture radar antelope valley mojave desert california interferometric synthetic aperture radar insar has great potential to detect and quantify land subsidence caused by aquifer system compaction insar maps with high spatial detail and resolution of range displacement 10 mm in change of land surface elevation were developed for a groundwater basin 103 km2 in antelope valley california using radar data collected from the ers 1 satellite these data allow comprehensive comparison between recent 1993 1995 subsidence patterns and those detected historically 1926 1992 by more traditional methods the changed subsidence patterns are generally compatible with recent shifts in land and water use the insar detected patterns are generally consistent with predictions based on a coupled model of groundwater flow and aquifer system compaction the minor inconsistencies may reflect our imperfect knowledge of the distribution and properties of compressible sediments when used in conjunction with coincident measurements of groundwater levels and other geologic information insar data may be useful for constraining parameter estimates in simulations of aquifer system compaction

monitoring and modeling land subsidence at the cerro prieto geothermal field baja california mexico using sar interferometry images derived from repeat pass spaceborne interferometric synthetic aperture radar insar systems offer the possibility of mapping surface deformation of small spatial extent and monitoring its spatio temporal evolution a slow local subsidence has been detected at the cerro prieto geothermal field from images acquired by the european space agency remote sensing satellites ers 1 2 between 1993 and 1997 although agricultural activity in the area limited the investigation interferometric monitoring revealed that the ground deformation is associated with the withdrawal of geothermal fluid and agreed with the leveling data modeling of the subsidence was carried out assuming elastic deformation in a half space from simple point sources of which five were necessary to reproduce the fringe patterns observed on the interferograms the depths and locations of three of the sources are compatible with the location of the known reservoir the study improves prior knowledge of the displacement field and of the mecanisms involved in the subsidence phenomenon

impact of antarctic climate during the late quaternary records from zub lake sedimentary archives from schirmacher hills east antarctica abstract the antarctic continental margin is marked with ice free areas which are host to numerous freshwater lakes these lacustrine systems are rich in sedimentary deposits which archive in them the regional and general climatic variations these lakes respond to the seasonal variations in climate over glacial interglacial timescales and can be inferred from the sedimentary proxies in this study a 79 cm long radiocarbon dated sediment core retrieved from a peri glacial lake is analysed for elementary corg norg isotopic 13com 15nom and particle size sand silt clay the radiocarbon dated sections 0 65 cm extends up to 43 kyr bp the time series of sedimentary organic matter om proxies corg 3 5 3 c natomic ratio 11 3 and 13com 14 4 indicate that the om in this lake sedimentary record is an admixture of terrestrial and lacustrine biomass distinctly higher lower values during the holocene lgm suggests presence of terrestrial and aquatic aquatic biomass indicating ice free ice cover and warm cold holocene glacial conditions which would result in an increased decreased lake productivity and fluvial wind input of sand and clay silt higher sand content 30 24 and 15 kyr bp silt content 24 kyr bp corg and norg 24 kyr bp within the last glacial stage lgs indicates intermittent warming period in coherence with the antarctic isotope maximum aim the transition in values corg norg c n ratio 13com sand content starting at 16 6 kyr bp closely following antarctic deglaciation to reach holocene optimum values at 11 3 kyr bp documents the influence of antarctic climate on regional areas

opal sedimentation shifts in the world ocean over the last 15 myr biogenic silica opal accumulation records were used to trace mechanisms consequence and geographic pattern of shifts in the main locus of opal deposition of the world ocean over the last 15 myr over this time interval the main opal sink seems to have moved from the north atlantic to the pacific equatorial pacific eastern equatorial pacific eastern boundary current upwelling systems california namibia peru and finally to the southern ocean the interplay between opal deposition and a series of climatic tectonic oceanographic and biologic events has been analyzed and discussed these events include the cenozoic global cooling trend intensified glaciation in antarctica late miocene early pliocene biogenic bloom development of northern hemisphere glaciation nhg closing of the panama seaway transition of the climate system from a monopolarto a bipolar glaciated world mid pleistocene revolution mpr nutrient availability evolution of diatoms and c4 plants and changes in continental weathering rates while the observed shifts are mostly traceable to oceanic reorganizations and global climatic evolution conditions favorable to opal deposition involve the above mentioned complex mix of processes for this reason the interpretation of opal deposition records might not always be straightforward we however believe that it can still provide clear indications of large scale oceanographic reorganizations in the geological past d 2004 elsevier b v all rights reserved

the last deglacial history of lutzow holm bay east antarctica past fluctuations of the antarctic ice sheet are poorly understood because of a lack of datable materials radiocarbon reservoir ages and severe environments direct evidence of the timing of ice retreat is important in order to understand the antarctic contribution to global sea level rise since the last glacial maximum here we report the first exposure ages constraining the timing of the last deglaciation from lutzow holm bay east antarctica our data suggest that the final retreat of the ice sheet in the region occurred rapidly in the early holocene and the reduction of the ice thickness in the region was at least 350 m this occurred after the major northern hemisphere deglaciation copyright 2011 john wiley sons ltd

predictions of antarctic crustal motions driven by present day ice sheet evolution and by isostatic memory of the last glacial maximum detectable crustal motion and secular rate of change of solid surface gravity may be produced by the earth s response to present day and past ice mass changes in antarctica scenarios of present day ice mass balance previously utilized to explore the global geodetic signatures of the antarctic ice sheet produce elastic crustal responses that are typically bounded by uplift rates 5 mm yr horizontal motion 1 mm yr and solid surface gravity change rates 1 gal yr in a restricted locality one scenario produces uplift rates slightly in excess of 10 mm yr and correspondingly enhanced horizontal and gravity rates in contrast the viscoelastic response to ice mass changes occurring since last glacial maximum lgm exceeds 5 mm yr uplift over substantial portions of west antarctica for a wide range of plausible choices of timing and magnitude of deglaciation and mantle viscosity similarly viscoelastic gravity rate predictions exceed 1 gal yr decrease over large regions confirming suggestions that a global positioning system gps and absolute gravity based program of crustal monitoring in antarctica could potentially detect postglacial rebound a published revision to the climap model of the antarctic ice sheet at lgm herein called the d91 model features a substantially altered west antarctic ice sheet reconstruction this revision predicts a spatial pattern of present day crustal motion and surface gravity change that diverges strikingly from climap based models peak d91 crustal rates assuming deglaciation begins at 12 kyr and ends at 5 kyr are around 16 mm yr uplift 2 mm yr horizontal and 2 5 gal yr gravity tabulated crustal response predictions for selected antarctic bedrock sites indicate critical localities in the interior of west antarctica where expected responses are large and d91 predictions differ from climap based models by a factor of 2 or more observations of the postglacial rebound signal in antarctica might help constrain antarctic mass balance and contribution to sea level rise over the past 20 000 years

relative sea level history from the lambert glacier region east antarctica and its relation to deglaciation and holocene glacier readvance we present a relative sea level rsl history constrained by ams radiocarbon dated marine freshwater transitions in isolation basins from a site adjacent to the lambert glacier east antarctica the rsl data suggest an initial ice retreat between c 15 370 and 12 660 cal yr b p within this period meltwater pulse ia mwp ia between c 14 600 14 200 and 14 100 13 700 cal yr b p occurred an exceptionally large ice melting event inferred from far field sea level records the rsl curve shows a pronounced highstand of approximately 8 m between c 7570 7270 and 7250 6950 cal yr b p that is consistent with the timing of the rsl highstand in the nearby vestfold hills this is followed by a fall in rsl to the present in contrast to previous findings the isolation of the lakes in the larsemann hills postdates the isolation of lakes with similar sill heights in the vestfold hills an increase in rsl fall during the late holocene may record a decline in the rate of isostatic uplift in the larsemann hills between c 7250 6950 and 2847 2509 cal yr b p that occurred in response to a documented mid holocene glacier readvance followed by a late holocene retreat

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

the antarctic ice sheet during the last glacial maximum and its subsequent retreat history a review abstract an emerging body of evidence from studies of the last glacial interglacial cycle suggests that the east and west antarctic ice sheets have not advanced and retreated in concert the west antarctic ice sheet advanced to the outer shelf in most regions during the last glacial maximum lgm the retreat from the shelf commenced shortly after the lgm and continued into the late holocene the west antarctic ice sheet in ross and amundsen seas slid across a deforming bed at least during the final phases of extended glaciation this implies that at this time the ice sheet had a low profile differences in the number and locations of grounding zone wedges and smaller grounding zone features from trough to trough imply that individual west antarctic ice sheet ice streams retreated episodically details concerning the expansion retreat and behavior of the east antarctic ice sheet eais are more sparse the picture emerging is that the eais did not expand to the continental shelf edge during the lgm rather it achieved a maximum extent of a mid shelf position in some locations while in other areas the ice terminus was situated near its present location the timing of retreat along sectors within the eais appears diachronous and in places occurred prior to the lgm the antarctic peninsula shelf contained considerably more ice during the lgm than previously proposed the results presented in this paper support more recent published ice sheet models that call for greater contributions of melting ice from west antarctica including the antarctic peninsula to the post glacial rise in sea level

ten years of seismic monitoring over a gas field abstract ten years of seismic recording allows us to locate more than 800 tremors with magnitudes ranging from 1 0 to 4 2 in a small 10 by 10 by 5 km volume near a major gas field lacq france the seismic activity began 10 yr after gas extraction began nearly all of the epicenters are located within the lateral extent of the gas field the only perturbation of the stress or strain fields which has the same spatial and temporal scale as the seismicity is the 500 bar drop in gas pressure due to 20 yr of gas exploitation demonstrating that these events are induced the network established to monitor this activity consists of eight telemetered stations including a well bottom geophone located at 3200 m depth using three dimensional relocation techniques we computed new hypocenter positions for more than 280 events these better located hypocenters form a diffuse zone that mimics the local dome structure taking the regional tectonic stresses into account we suggest that these ruptures may be the result of unfolding of the dome structure

land subsidence in the cerro prieto geothermal field baja california mexico from 1994 to 2005 an integrated analysis of dinsar leveling and geological data abstract cerro prieto is the oldest and largest mexican geothermal field in operation and has been producing electricity since 1973 the large amount of geothermal fluids extracted to supply steam to the power plants has resulted in considerable deformation in and around the field the deformation includes land subsidence and related ground fissuring and faulting these phenomena have produced severe damages to the local infrastructure such as roads irrigation canals and other facilities in this paper the technique of differential synthetic aperture radar interferometry dinsar is applied using c band envisar asar data acquired between 2003 and 2006 to determine the extent and amount of land subsidence in the mexicali valley near cerro prieto geothermal field the dinsar results were compared with published data from precise leveling surveys 1994 1997 and 1997 2006 and detailed geological information in order to improve understanding of the temporal and spatial distributions of anthropogenic subsidence in the mexicali valley the leveling and dinsar data were modeled to characterize the observed deformation in terms of fluid extraction the results confirm that the tectonic faults control the spatial extent of the observed subsidence these faults likely act as groundwater flow barriers for aquifers and reservoirs the shape of the subsiding area coincides with the cerro prieto pull apart basin in addition the changes in spatial pattern and rate of the subsidence are correlated with the development of the cerro prieto geothermal field

fluctuations of the east antarctic ice sheet margin since the last glaciation from the stratigraphy of raised beach deposits along the soya coast

energy evolution characteristics of hard rock during triaxial failure with different loading and unloading paths abstract triaxial compression tests were conducted on fine to medium grained granite specimens with initial confining pressures of 10 20 40 and 60 mpa under various loading and unloading stress paths the energy evolution characteristics of granite specimens from a quarry in miluo city china were studied in the triaxial deformation and failure process of the rocks the results show that the time history curves of the total strain energy elastic strain energy and dissipative strain energy exhibit significant stage features in particular the ratio of the dissipative strain energy to the total strain energy can be used to describe the deformation and degree of damage to rock specimens during the triaxial loading and unloading processes under the same initial confining pressure the maximum values of the total strain energy elastic strain energy and dissipative strain energy occur in the conventional triaxial compressive testing of group i and the minimum values occur in test group ii with constant axial stress and decreasing confining pressure the total strain energy elastic strain energy and circumferential strain energy all increase as the initial confining pressure increases whereas the dissipative strain energy does not during the process of unloading the confining pressure the increase of the circumferential strain is considerably larger than that of the axial strain under unloading conditions rock bursts may occur more easily for hard rocks than under conventional triaxial loading conditions especially under the conditions of test group iii with increasing axial stress and decreasing confining pressure the micro difference in the granite micro cracks was identified using a scanning electron microscope sem combined with an energy dispersive spectrometer eds shear failure characteristics were observed in a conventional triaxial test and the combined tension and shear failure was identified through unloading confining pressure tests the tensile failure characteristics of the granite in group iii are more pronounced than those of group ii this indicates that the triaxial failure of rock results from the development of micro extension cracks and volumetric expansion in the granite specimen under unloading confining pressure tests

combined dna and lipid analyses of sediments reveal changes in holocene haptophyte and diatom populations in an antarctic lake preserved ribosomal dna of planktonic phototrophic algae was recovered from holocene anoxic sediments of ace lake antarctica and the ancient community members were identified based on comparative sequence analysis the similar concentration profiles of dna of haptophytes and their traditional lipid biomarkers alkenones and alkenoates revealed that fossil rdna also served as quantitative biomarkers in this environment the dna data clearly revealed the presence of six novel phylotypes related to known alkenone and alkenoate biosynthesizing haptophytes with isochrysis galbana uio 102 as their closest relative the relative abundance of these phylotypes changed as the lake chemistry particularly salinity evolved over time changes in the alkenone distributions reflect these population changes rather than a physiological response to salinity by a single haptophyte using this novel paleo ecological approach of combining data from lipid biomarkers and preserved dna we showed that the post glacial development of ace lake from freshwater basin to marine inlet and the present day lacustrine saline system caused major qualitative and quantitative changes in the biodiversity of the planktonic populations over time

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

plate tectonics and basin subsidence history tectonic setting exerts fi rst order control on basin formation as refl ected in basin subsidence history while our approach ignores the effects of fl exural loading and eustatic sea level change consistency of backstripped subsidence histories i e with local loading effects of sediment removed suggests consistent tectonic driving mechanisms in each tectonic setting with the possible exception of forearc basins based on published subsidence curves and open fi le stratigraphic data we show the subsidence characteristics of passive margins strike slip basins intracontinental basins foreland basins and forearc basins passive margin subsidence is characterized by two stages rapid initial synrift subsidence and slow post rift thermal subsidence with increasing subsidence rates toward the adjacent ocean basin subsidence of intracontinental basins is similar in magnitude to that seen in passive margin settings but the former is generally slower longer lived and lacks initial subsidence long lived subsidence for many intracontinental basins is consistent with cooling following thermal perturbation of thick lithosphere found beneath old parts of continents basins associated with strike slip faults are usually short lived with very rapid subsidence changes in local stress regimes as strike slip faults evolve and migrate over time coupled with three dimensional heat loss in these small basins likely explain this subsidence pattern foreland basin subsidence rates refl ect the fl exural response to episodic thrust loading resultant subsidence curves are punctuated by convex up accelerating segments forearc basins have the least consistent subsidence patterns subsidence histories of these basins are complex and may refl ect multiple driving mechanisms of subsidence in forearc settings second order deviations in subsidence suggest reactivation or superimposed tectonic events in many basin settings the effects of eustatic sea level change may also explain some deviations in curves for many of these settings subsidence histories are suffi ciently distinctive to be used to help determine tectonic setting of ancient basin deposits

abrupt holocene ice sheet thinning along the southern soya coast lutzow holm bay east antarctica revealed by glacial geomorphology and surface exposure dating abstract geological reconstruction of the retreat history of the east antarctic ice sheet eais since the last glacial maximum lgm is essential for understanding the response of the ice sheet to global climatic change and the mechanisms of retreat including a possible abrupt melting event such information is key for constraining climatic and ice sheet models that are used to predict future antarctic ice sheet ais melting however data required to make a detailed reconstruction of the history of the eais involving changes in its thickness and lateral extent since the lgm remain sparse here we present a new detailed ice sheet history for the southern soya coast lutzow holm bay east antarctica based on geomorphological observations and surface exposure ages our results demonstrate that the ice sheet completely covered the highest peak of skarvsnes 400 m a s l prior to 9 ka and retreated eastward by at least 10 km during the early to mid holocene ca 9 to 5 ka the timing of the abrupt ice sheet thinning and retreat is consistent with the intrusion of modified circumpolar deep water mcdw into deep submarine valleys in lutzow holm bay as inferred from fossil foraminifera records of marine sediment cores thus we propose that the mechanism of the abrupt thinning and retreat of the eais along the southern soya coast was marine ice sheet instability caused by mcdw intrusion into deep submarine valleys such abrupt ice sheet thinning and retreat with similar magnitude and timing have also been reported from enderby land east antarctica our findings suggest that abrupt thinning and retreat as a consequence of marine ice sheet instability and intrusion of mcdw during the early to mid holocene may have led to rapid ice surface lowering of hundreds of meters in east antarctica

groundwater pumping and land subsidence in the emilia romagna coastland italy modeling the past occurrence and the future trend 1 the emilia romagna coastland south of the po river delta italy has experienced a dramatic land settlement mainly due to the large groundwater withdrawal related to the local economic and tourist development started in the early 1950s although the use of surface water has reduced the settlement rate over the last three decades anthropogenic land subsidence still continues in a few kilometer wide coastal strip at a rate larger than the natural one the occurrence is reconstructed since 1946 with the aid of advanced finite element flow and poromechanical models implemented with a realistically detailed geology of the regional shallow multiaquifer system the models have been calibrated against the piezometric leveling and extensometer records observed over the last 50 years and a land subsidence prediction in 2016 is performed the results show that the extensive groundwater pumping that occurred in the past is most likely the main cause of the recent land settlement as well because of the delayed compaction of the clay aquitards comprised between the depleted aquifers however the available pumping data do not allow for a thorough understanding of the current local settlement process along the coastline which is the most vulnerable area of the emilia romagna region from an environmental viewpoint if the planned scenario of groundwater resource management will be implemented anthropogenic land subsidence is bound to become a marginal problem for the central and northern portion of the emilia romagna coastland

injection induced microseismicity in colorado shales imperial oil resources limited uses cyclic steam stimulation to recover oil from their cold lake oil field in alberta this operation in particular situations can be associated with the failure of well casings in the colorado shales above the oil bearing formation a number of fluid injection operations was undertaken at this site and the associated microseismicity was detected using two three component geophones and fifteen hydrophones the purpose of this experiment was to simulate the occurrence of a casing failure determine the feasibility of monitoring in a shallow environment and characterize the microseismic activity a calibration survey provided values of 1786 108 m s for p wave velocity 643 56 mks for s wave velocity and 0 428 0 017 for poisson s ratio in the shale formation estimates of the quality factor q p were 15 for the horizontal direction and 38 for the vertical direction corroborating the evidence of velocity anisotropy calibration shots were located to within 10 m of the actual shot points using triangulation and polarization techniques several hundred microseismic events were recorded and 135 events were located the results showed that microseismic activity was confined to depths within 10 meters of the injection depth the experiment clearly established the feasibility of detecting microseismicity induced by fluid injection rates typical of casing failures in shales at distances over 100 m

properties of seismic wave scattering around water injection well at fenton hill hot dry rock geothermal site to determine the scattering properties of microcracks created by water injection in hot dry rock a method for analyzing trajectory ellipsoids of seismic particle motions has been applied lengths and directions of three principal axes of trajectory ellipsoids were calculated and a distribution of the shape of these ellipsoids suggests existence of a strong scattering region around the injection point this strong scattering has an anisotropic property presumably due to microcrack orientation in the original rock

holocene sea level change and ice sheet history in the vestfold hills east antarctica abstract a new holocene sea level record from the vestfold hills antarctica has been obtained by dating the lacustrine marine and marine lacustrine transitions that occur in sediment cores from lakes which were formerly connected to the sea from an elevation of 7 5 m 8000 yr ago relative sea level rose to a maximum 9 m above present sea level 6200 yr ago since then sea level has fallen monotonically until the present the precision of the new record makes it suitable for constraining the recent history of the ice sheet in that region using numerical models of glacio hydro isostasy simplified regional models suggest that the ice sheet margin has retreated 30 40 km since the last glacial maximum with 600 700 m of thinning occurring at the present coastline

coastal oceanographic conditions in the prydz bay region east antarctica during the holocene recorded in an isolation basin information on east antarctic coastal environments during the holocene is relatively sparse this is surprising as sedimentary records from the interface between land and sea can provide chronologies of climatic change isostatic uplift relative sea level and the colonization of newly formed biomes here we examine a sediment core from pup lagoon a coastal lake in the larsemann hills east antarctica sediment stratigraphy fossil pigments and diatoms were used to infer the sequence of holocene environmental and climatic change results show that between 5800 and 5500 cal yr bp the marine coast of prydz bay was characterized by stratified open water conditions during spring and summer and seasonally warm conditions from 5500 to 2750 cal yr bp sea ice duration in prydz bay increased with the coast being ice free for 2 3 months each year conditions which are similar to the present day a return to stratified open water conditions and a reduction in winter sea ice extent between 2750 and 2200 cal yr bp is signalled by enhanced biogenic production and more open water diatom taxa this is consistent with evidence for the mid holocene hypsithermal detected in other records in east antarctica isostatic isolation of the pup lagoon basin from the sea between 2200 and 2000 cal yr bp slightly precedes the emergence of lakes with comparable sill heights from the nearby vestfold hills the colonization of pup lagoon after its isolation as a freshwater lake was initiated by a siliceous flora dominated by stomatocysts with microbial mat development being prevented by mechanical or physical stress a brief period of marine incursion following the mid holocene hypsithermal may be related to local events such as iceberg calving or to minor sea level change weighted averaging regression used to infer salinity in the lacustrine zone shows that from 1500 cal yr bp pup lagoon is a freshwater lake where the flora is dominated by stratified cyanobacterial mats with green algae and diatoms as co dominants comparable to modem pup lagoon and other lakes in the larsemann hills

processes controlling the distribution of ti and al in weathering profiles siliciclastic sediments and sedimentary rocks abstract the ratio of ti to al varies greatly in primary igneous source rocks these elements are considered to be relatively immobile in most weathering regimes so that tio2 al2o3 ratios have been used to investigate the provenance of sediments and sedimentary rocks in modern weathering profiles that have undergone moderate weathering ti al ratios remain fairly constant so that siliciclastic sediments derived from them should have ti al ratios like that of the source materials under extreme weathering conditions however the upper most weathered parts of profiles commonly show a marked increase in ti al ratio that is thought to be due to preferential translocation of al rich phases under steady state weathering conditions one particular level of the profile may act as the main source of detrital material and may thus control the ti al ratio of sediments produced from it in a glacio fluvial setting minimum weathering moderate sorting there is considerable variation in ti content but al is nearly constant this is due to concentration of ti bearing mafic minerals such as biotite in the fine fraction in modern sediments derived from moderately weathered and sorted material the ti al distribution reflects mixing of al and ti enriched fine grained materials with sands that are depleted in these elements when a plot of tio2 vs al2o3 is constructed for a suite of such sands and muds the resultant trend differs significantly from that shown by a similar suite of unweathered glacio fluvial sediments comparison of these results with data from sedimentary rock suites suggests that trends shown by plots of tio2 vs al2o3 may provide insight into weathering and depositional history in addition to their use as provenance indicators

pre bomb radiocarbon and the reservoir correction for calcareous marine species in the southern ocean four antarctic marine mollusc shells which were collected alive between 1917 and 1940 were analyzed by accelerator mass spectrometry to provide the first pre bomb radiocarbon measurements of biogenic carbonates from the southern ocean after correcting for the impact of fossil fuel combustion suess effect radiocarbon activities of the pre bomb shells averaged 149 8 10 4 in contrast the 14c values for post bomb molluscs echinoderms brachiopods and foraminifera averaged 96 1 25 2 these biogenic carbonate 14c values are nearly identical to pre bomb estimates 148 to 152 and post bomb measurements 98 4 22 0 of the surface waters in the southern ocean average radiocarbon ages of the biogenic carbonates before and after 1950 1303 84 years and 811 205 years respectively along with those from seals and penguins indicate that the antarctic marine radiocarbon reservoir has decreased in age by nearly 500 years during the second half of the 20th century marine species and seawater measurements firmly place the radiocarbon reservoir correction at 1300 100 years for calcareous marine fossils which are widespread abundant and well preserved organic materials for interpreting ice sheet climate and sea level impacts on the antarctic marine ecosystem during the holocene

differential compaction and subsidence in sedimentary basins due to silica diagenesis a case study the conversion of opal a to opal ct is a thermochemical diagenetic process that can cause kilometer scale differential compaction and differential subsidence within clastic sedimentary basins this is demonstrated for an opal a to opal ct conversion imaged by three dimensional seismic data on the northeastern atlantic margin this diagenetic front has a circular to polygonal ridge depression morphology the ridges have a relief of 10 50 m and separate circular to polygonal depressions that have diameters of 1 2 km some of which link up to form interconnected networks this morphology initially developed because the host sediments mantled an underlying polygonal fault system and the front tracked deformed stratigraphy ridges formed above the tips of the underlying faults and depressions formed between them ridge relief and width then progressively increased due to earlier opal a to opal ct conversion above ridges as well as conversion laterally along beds or bed sets this caused compaction and concomitant subsidence in the overburden and the development of a circular to polygonal network of overburden troughs aligned with the ridge system a positive feedback loop was established where additional overburden sediment above the growing ridges reached the depth of conversion ahead of adjacent areas driving more compaction and differential subsidence this paper provides the first insights into the large scale morphological characteristics of opal a to opal ct diagenetic fronts it demonstrates the potential for a local stratigraphic control on diagenetic front development and morphology and lastly highlights the potential utility of seismic reflection data for understanding diagenetic processes

a diatom inferred record of lake variability during the last 900 years in lutzow holm bay east antarctica decadal centennial scale climate variability in coastal antarctica remains poorly understood due to the limited number of highly resolved well dated records we present a 900 year decadal scale reconstruction based on sedimentary diatoms from lake abi in lutzow holm bay east antarctica hydrological change is inferred from diatom ecological preferences in conjunction with an existing regional training set and implies that lake water specific conductivity depth and nitrogen availability are the key drivers of diatom assemblage change lake abi underwent a series of subtle environmental changes related to these environmental variables possibly driven by changes in catchment snow melt and the duration of seasonal ice cover ordination is used to trace the major patterns of change in the diatom community with notable shifts identified between 470 and 400 and at 350 cal a bp where present ce 1950 the frequency of environmental variability at lake abi is broadly consistent with a record of the interdecadal pacific oscillation during the last millennium but contrasts with the apparent climate stability elsewhere in eastern antarctica further research is required to constrain the limnological and ecological responses of lakes in coastal antarctica to obtain more rigorous palaeoclimate reconstructions from these sites of immense potential

holocene antarctic melting and lithospheric uplift history of the southern okinawa trough inferred from mid to late holocene sea level in iriomote island ryukyu japan abstract relative sea level deduced from fossil oysters and mangroves are reported for iriomote island ryukyus southwestern japan radiocarbon dated fossil oysters as well as previously analyzed mangrove muds are compared to geophysical and glacio hydro isostatic adjustment gia models that describe earth deformation due to changing surface loading the holocene high stand hhs inferred from oyster fossils saccostrea echinata and saccostrea malaboensis is 2 7 m at ca 3500 years ago after which sea level gradually fell to present level the hhs magnitude attributed to gia for the last ca 4000 is between 1 and 1 5 m above present day sea level and the residual indicates the long term lithospheric uplift rate of the island the timing of peak hhs also indicates that late holocene melting mainly from antarctica ceased by approximately 4000 years ago

gps observation of the sea level variation in lutzow holm bay antarctica differential gps observations were conducted on the fast ice in lutzow holm bay antarctica the observations were carried out intermittently from april to december in 1998 the vertical displacement which is a combination of oceanic tidal variation and high frequency variations of 3 6 minutes period was clearly detected eight hours comparison of the height variation derived from gps with that from a video monitoring system showed good agreement with a standard deviation of 2 2 cm the high frequency fluctuations of about 1 cm were obvious in both observations and had significant correlation with each other the low pass filtered variations agreed well with a standard deviation of 1 7 cm tidal constituents derived from the gps observations for the entire period showed good agreement with those from the seven years of pressure gauge observations thus gps has demonstrated the ability to observe 2 cm accuracy sea level variations

combining scanning electron microscopy and compressibility measurement to understand subsurface processes leading to subsidence at tauhara geothermal field new zealand abstract the tauhara geothermal field is located within the taupo volcanic zone new zealand and has undergone subsidence in three localized areas referred to as the crown rakaunui and spa sights bowls with measured subsidences of 0 9 2 4 and 2 9 m respectively these subsidence bowls are situated close to taupo township and are of concern to the public and for geothermal developers therefore an intensive subsidence study at the tauhara field was undertaken to better understand and mitigate further subsidence tauhara and wairakei are often referred to as one system as a shallow low resistivity anomaly extends continuously across both fields however they are two individual fields with separate up flows tauhara is located in the south of the system while wairakei is located in the northern area the wairakei field also has subsidence bowls that reach up to 15 m in localized areas extraction of fluids from the wairakei field began in 1958 currently 171 mwe but did not begin at tauhara until 2010 currently 23 mwe at wairakei initial fluid withdrawal was from the waiora formation which extends under both the wairakei and tauhara fields since 1958 fluid pressure in the waiora formation has dropped and this pressure decline extends under both the wairakei and tauhara fields a pressure drop has also been detected in the mid huka falls formation which is a permeable stratigraphic unit present at shallower depth relative to the waiora formation in both fields the tauhara subsidence investigation included drilling with continuous core recovery at selected sites located inside thm 16 outside thm 13 thm 14 and on the periphery thm 12 of known subsidence bowls cored samples representative of the seven formations encountered were analyzed to establish their stiffness by determining their constrained modulus cm value on the same samples the effect of hydrothermal alteration was established using scanning electron microscopy sem electron dispersive spectroscopy eds petrography and x ray diffraction xrd key findings include the following 1 cm values ranged from 20 to 1800 mpa 2 thm 16 revealed the lowest cm values of the study

timing of the last glacial maximum from observed sea level minima during the last glacial maximum ice sheets covered large areas in northern latitudes and global temperatures were significantly lower than today but few direct estimates exist of the volume of the ice sheets or the timing and rates of change during their advance and retreat here we analyze four distinct sediment facies in the shallow tectonically stable bonaparte gulf australia each of which is characteristic of a distinct range in sea level to estimate the maximum volume of land based ice during the last glaciation and the timing of the initial melting phase we use faunal assemblages and preservation status of the sediments to distinguish open marine shallow marine marginal marine and brackish conditions and estimate the timing and the mass of the ice sheets using radiocarbon dating and glacio hydroisostatic modelling our results indicate that from at least 22 000 to 19 000 calendar years before present land based ice volume was at its maximum exceeding today s grounded ice sheets by 52 5 x 10 exp 6 cu km a rapid decrease in ice volume by about 10 percent within a few hundred years terminated the last glacial maximum at 19 000 250 years

the 26 5 ka oruanui eruption new zealand an introduction and overview abstract the 26 5 ka oruanui eruption from taupo volcano in the central north island of new zealand is the largest known wet eruption generating 430 km3 of fall deposits 320 km3 of pyroclastic density current pdc deposits mostly ignimbrite and 420 km3 of primary intracaldera material equivalent to 530 km3 of magma erupted magma is 99 rhyolite and 90 pdc deposits range from mm to cm thick ultra thin veneers enclosed within fall material to 200 m thick ignimbrite in proximal areas the farthest travelled 90 km most energetic pdcs velocities 100 m s 1 occurred during phase 8 but the most voluminous pdc deposits were emplaced during phase 10 grain size variations in the pdc deposits are complex with changes seen vertically in thick proximal accumulations being greater than those seen laterally from near source to most distal deposits modern lake taupo partly infills the caldera generated during this eruption a 140 km2 structural collapse area is concealed beneath the lake while the lake outline reflects coeval peripheral and volcano tectonic collapse early eruption phases saw shifting vent positions development of the caldera to its maximum extent indicated by lithic lag breccias occurred during phase 10 the oruanui eruption shows many unusual features its episodic nature wide range of depositional conditions in fall deposits of very wide dispersal and complex interplay of fall and pdc activity

the effect of fluid compressibility and elastic rock properties on deformation of geothermal reservoirs a geothermal reservoir deforms when the extraction of pore fluid exceeds reservoir recharge causing a decrease in pore pressure the magnitude of this deformation is related to the amount of pore fluid that is extracted assuming compressible material properties in a homogeneous reservoir we derive an expression for the ratio of reservoir volume change per extracted fluid mass we show that this ratio depends on a number of parameters notably the compressibilities of reservoir rock and pore fluid we apply the obtained relationship to three different geothermal areas hellisheidi reykjanes and the geysers to illustrate under which circumstances the relation between reservoir deformation and the amount of extracted fluid is able to help us learn more about reservoir conditions we find that the fluid compressibility depending on whether the system is single phase or two phase may explain large differences in estimates of reservoir volume changes per mass of extracted fluid

preservation of organic matter and alteration of its carbon and nitrogen isotope composition during simulated and in situ early sedimentary diagenesis abstract the carbon and nitrogen isotope composition of organic matter has been widely used to trace biogeochemical processes in marine and lacustrine environments in order to reconstruct past environmental changes from sedimentary organic matter it is crucial to consider potential alteration of the primary isotopic signal by bacterial degradation in the water column and during early diagenesis in the sediments in a series of oxic and anoxic incubation experiments we examined the fate of organic matter and the alteration of its carbon and nitrogen isotopic composition during microbial degradation the decomposition rates determined with a double exponential decay model show that the more reactive fraction of organic matter degrades at similar rates under oxic and anoxic conditions however under oxic conditions the proportion of organic matter resistent to degradation is much lower than under anoxic conditions within three months of incubation the 13c of bulk organic matter decreased by 1 6 with respect to the initial value the depletion can be attributed to the selective preservation of 13c depleted organic compounds during anoxic decay the 15n values continuously decreased to about 3 below the initial value the decrease probably results from bacterial growth adding 15n depleted biomass to the residual material in the oxic experiment 15n values increased by more then 3 before decreasing to a value indistinguishable from the initial isotopic composition the dissimilarity between oxic and anoxic conditions may be attributed to differences in the type timing and degree of microbial activity and preferential degradation in agreement with the anoxic incubation experiments sediments from eutrophic lake lugano are on average depleted in 13c 1 5 and 15n 1 2 with respect to sinking particulate organic matter collected during a long term sediment trap study

identification of p s wave successions for application in microseismicity interpretation ofp s wave successions is used in induced or passive microseismicity it makes the location of microseismic events possible when the triangulation technique cannot be used to improve the reliability of the method we propose a technique that identifies thep s wave successions among recorded wave successions a polarization software is used to verify the orthogonality between thep ands polarization axes the polarization parameters are computed all along the 3 component acoustic signal then the algorithm detects time windows within which the signal polarization axis is perpendicular to the polarization axis of the wave in the reference time window representative of thep wave the technique is demonstrated for a synthetic event and three application cases are presented the first one corresponds to a calibration shot within which the arrivals of perpendicularly polarized waves are correctly detected in spite of their moderate amplitude the second example presents a microseismic event recorded during gas withdrawal from an underground gas storage reservoir the last example is chosen as a counter example concerning a microseismic event recorded during a hydraulic fracturing job the detection algorithm reveals that in this case the wave succession does not correspond to ap s one this implies that such an event must not be located by the method based on the interpretation of ap s wave succession as no such a succession is confirmed

glacial rebound and sea level change an example of a relationship between mantle and surface processes lambeck k 1993 glacial rebound and sea level change an example of a relationship between mantle and surface processes in r wortel u hansen and r sabadini editors relationships between mantle processes and geological processes at or near the earth s surface tectonophysics 223 15 37 the problem of glacial rebound provides an outstanding example of the relationship between surface and mantle processes on time scales of 103 to 105 years changes in surface loading of ice and melt water associated with the growth and decay of the great ice sheets deform the surface of the planet and induces flow in the mantle a measure of the earth s response to the changing surface loads and internal deformation is provided by observations of past sea levels relative to the present level and inversion of these observations provides constraints on both the models of the rheological response of the earth to loading and on models of the ice sheets constraints on ice sheet models include the total volume of the grounded ice at the time of maximum glaciation the global rates of melting of the ice sheets the thickness of the ice at maximum glaciation the extent of ice cover over shallow seas such as the north sea and the barents sea and the role of antarctica in the global ice balance constraints on mantle parameters include the effective lithospheric thickness and the effective viscosity of the mantle some recent results for both sets of parameters are discussed

subsidence at the geysers geothermal field n california from a comparison of gps and leveling surveys between 1994 and 1996 three gps surveys were conducted in the geysers region of northern california our aim was to constrain models of the stresses and strains induced by geothermal power production in that region each survey spanned the geysers geothermal field and consisted of typically 40 monuments these monuments had been previously employed in a series of first order leveling surveys during the 1970 s this earlier study had determined that the geysers region was subsiding with a maximum rate of 0 048 0 0055 m yr between 1973 and 1977 in order to be able to directly compare the leveling and gps surveys we transform them to the same reference frame using the geoid 96 geoid model for the period 1977 1996 we determine a maximum susbsidence rate of 0 047 0 002 m yr we then model this subsidence using a series of point sources of contraction and find their optimal configuration by applying the random cost method and the f test the minimum volume strain that we find consistent with this subsidence is approximately 5 10 4 such a strain cannot be explained by a thermoelastic mechanism but does seem to be consistent with poroelastic deformation and a quasi static reservoir bulk modulus k of 3 6 109 pa