precise analysis of icesat altimetry data and assessment of the hydrostatic equilibrium for subglacial lake vostok east antarctica summary based on the ice cloud and land elevation satellite icesat laser altimetry data the hydrostatic equilibrium he condition for the subglacial lake vostok east antarctica is evaluated a digital elevation model dem of the ice surface is derived by a regional crossover adjustment the analysis of the dem and its comparison with gps derived ice surface elevations and an ice surface dem based on radar altimetry data reveal an overall accuracy of better than 0 7 m for the lake area the dem is combined with an ice thickness model and a regional geoid model to determine the deviation of the local ice surface height from he for large parts of the lake the ice sheet fulfils the he our results reveal a strong positive deviation of about 10 m along the lake shoreline in addition positive deviations are found in the northern part of the lake which coincide with ice rumples detected by radio echo sounding in the southern part of the lake we find a linear negative deviation 4 0 m which coincides with the convoy route from vostok station to mirny base in addition to the dem relative biases for the icesat laser operational periods are determined in the regional crossover adjustment

facies analysis of a pliocene river dominated deltaic succession siena basin italy implications for the formation and infilling of terminal distributary channels the recent recognition and description of terminal distributary channels in ancient delta front deposits have led to important progress when it comes to understanding delta construction processes the plan view shapes of both modern and ancient river dominated deltas and sediment dispersal within deltas deltaic deposits fed by terminal distributary channels can be observed in the extensive outcrops approximately up to 300 m wide and 50 to 70 m thick in the central sector of the pliocene siena basin in tuscany italy stratigraphic constraints indicate that the deposition occurred in relatively shallow marine settings was not affected by tidal effects and was influenced only locally by wave action as a consequence these rock exposures provide an opportunity to investigate the facies assemblage of an ancient delta complex which was built up almost exclusively as the result of river related processes the studied deltaic succession is composed of vertically stacked parasequence like units which are invariably characterized by the lack of coarse grained distributary channel deposits at the top and an extensive network of terminal distributary channels that controlled the deltaic deposition these deposits were interpreted previously as deep water turbidites this study provides new elements for the correct distinction between hyperpycnal dominated delta fronts and basinal turbidite deposits the terminal distributary channel facies documented in this study are more complex than those investigated in previous research the channels are often passively filled during abandonment phases and not just due to the aggradation and lateral upstream migration of mouth bars as classically proposed moreover the frequent occurrence of mudstone beds just above the basal channel scours may be indicative of an abandonment phase after the channel incision and before its infilling with subsequent implications for the formational and infilling mechanisms of terminal distributary channels furthermore the channel fills are often the result of alternating depositional and erosional phases leading to a complex stratigraphic arrangement

tectono sedimentary characteristics of late miocene quaternary extensional basins of the northern apennines italy abstract extensional and compressional regimes exist at the same time in adjacent parts of the northern apennines italy and the former regime succeeded the latter at the same place as the thrust mountain front moved eastward since miocene times numerous extensional basins have developed west of the present mountain divide the westernmost ones formed over attenuated continental crust since late miocene and have been subjected to several subsidence and uplift events with rates of subsidence generally faster than rates of sedimentation they contain continental deposits overlain by gypsum bearing upper miocene marine sequences and siliciclastic marine pliocene deposits these basins were affected by shallow magmatism and are still experiencing high geothermal gradient and late to post magmatic activities such as in the renowned thermal region of larderello to the east closer to the present mountain divide the extensional basins formed later from pliocene to quaternary contain continental fluvial and lacustrine deposits and have not experienced near surface magmatic activities the sedimentary fill architecture of the apennine extensional basins is similar to that of other european american and african extensional or transtensional systems for instance a common characteristic is the prevalence of large alluvial fan deposits at the hanging wall shoulder of half grabens coarser smaller alluvial fans at the footwall shoulder and some fluvial deposits introduced longitudinally unlike the african rifts though the sedimentary facies distribution of extensional basins which developed in active orogenic zones such as in the apennines may be strongly affected by uplifting steep mountain slopes and can have large thick coarse alluvial fans also on the footwall side of the half grabens

assessing aeolian beach surface dynamics using a remote sensing approach a remote sensing technique for assessing beach surface moisture was used to provide insight into beach surface evolution during an aeolian event an experiment was carried out on october 21 2007 at greenwich dunes prince edward island national park canada during which cameras were mounted on a mast on the foredune crest at a height of about 14 m above the beach maps of beach surface moisture were created based on a calibrated relationship between surface brightness from the photographs and surface moisture content measured in situ at points spaced every 2 5 metres along a transect using a delta t moisture probe a time sequence of maps of surface moisture content captured beach surface evolution through the transport event at a spatial and temporal resolution that would be difficult to achieve with other sampling techniques such as impedance probes erosion of the foreshore and berm crest resulted in an increase in surface moisture content in these areas as the wetter underlying sediments were exposed flow expansion downwind of the berm crest led to sand deposition and a consequent decrease in surface moisture content remote sensing systems such as the one presented here allow observations of the combined evolution of beach surface moisture shoreline position and fetch distances during short term experiments and hence provide a comprehensive rendering of sediment erosion and transport processes

a terrestrial validation of icesat elevation measurements and implications for global reanalyses the primary goal of nasa s ice cloud and land elevation satellite icesat mission was to detect centimeter level changes in global ice sheet elevations at the spatial scale of individual ice streams confidence in detecting these small signals requires careful validation over time to characterize the uncertainty and stability of measured elevations a common validation approach compares altimeter elevations to an independently characterized and stable reference surface using a digital elevation model dem from geodetic surveys of one such surface the salar de uyuni in bolivia we show that icesat elevations at this location have a 0 0 cm bias relative to the wgs84 ellipsoid 4 0 cm 1 sigma uncertainty overall and 1 8 cm uncertainty under ideal conditions over short 50 km profiles we observe no elevation bias between ascending and descending orbits but we do find that elevations measured immediately after transitions from low to high surface albedo may be negatively biased previous studies have reported intercampaign biases icbs between various icesat observation campaigns but we find no statistically significant icbs or icb trends in our data we do find a previously unreported 3 1 cm bias between icesat s laser 2 and laser 3 and we find even larger interlaser biases in reanalyzed data from other studies for an altimeter with an exact repeat orbit like icesat we also demonstrate that validation results with respect to averaged elevation profiles along a single ground track are comparable to results obtained using reference elevations from an in situ survey

formal ratification of the quaternary system period and the pleistocene series epoch with a base at 2 58 ma in june 2009 the executive committee of the international union of geological sciences iugs formally ratified a proposal by the international commission on stratigraphy to lower the base of the quaternary system period to the global stratotype section and point gssp of the gelasian stage age at monte san nicola sicily italy the gelasian until then had been the uppermost stage of the pliocene series epoch the base of the gelasian corresponds to marine isotope stage 103 and has an astronomically tuned age of 2 58 ma a proposal that the base of the pleistocene series epoch be lowered to coincide with that of the quaternary the gelasian gssp was also accepted by the iugs executive committee the gssp at vrica calabria italy which had hitherto defined the basal boundary of both the quaternary and the pleistocene remains available as the base of the calabrian stage age now the second stage of the revised pleistocene in ratifying these proposals the iugs has acknowledged the distinctive qualities of the quaternary by reaffirming it as a full system period correctly complied with the hierarchical requirements of the geological timescale by lowering the base of the pleistocene to that of the quaternary and fully respected the historical and widespread current usage of both the terms quaternary and pleistocene copyright 2009 john wiley sons ltd

wave ravinement surfaces classification and key characteristics abstract the wave ravinement surface wrs is a surface of sequence stratigraphic significance that forms in shallow water settings during transgression it develops progressively landward during shoreface retreat due to wave action which erodes the substrate and leads to sediment bypass in the offshore direction the wrs may rework previously formed surfaces such as the maximum regressive surface also known as the transgressive surface and the subaerial unconformity becoming a systems tract and or sequence boundary due to the associated lithological contrast between underlying and overlying deposits and the presence of lags and or shell pavements the wrs has a very good appearance in both outcrop and cores and is often used as the boundary of shallow marine stratigraphic sequences the wrs therefore represents an important lithological and paleo environmental break and its recognition is significant for reconstructing stratigraphic architectures and the history of relative sea level change as well as for reservoir characterization several controlling factors govern the development of the wrs and of the associated deposits they include the accommodation to sedimentation a s ratio environmental energy topographic gradient roughness and lithology of the substrate relatively low rates of relative sea level rise and sediment supply high wave energy steep topographies and easily erodible substrates favor the development of the wrs these factors interact leading to a high variability in the amount of erosion shape length along depositional dip and deposits associated with these surfaces wrss may be classified based on either underlying or overlying deposits or a combination of both a classification based on the deposits that underlie the wrs helps to determine the location of the studied outcrop along depositional dip whereas a classification based on the deposits that overlie the wrs afford insights into the physical conditions that accompanied its formation however the best description of the wrs in terms of location of a considered outcrop physical conditions under which the wrs developed and their lateral variability type of substrate as well as its practical significance for reservoir modeling is achieved with a combination of the two criteria

arctic ocean gravity field derived from icesat and ers 2 altimetry tectonic implications a new detailed marine gravity field for the persistently ice covered arctic ocean derived entirely from satellite data reveals important new tectonic features in both the amerasian and eurasian basins reprocessed geoscience laser altimeter system glas data collected by nasa s ice cloud and land elevation satellite icesat between 2003 and 2005 have been combined with 8 years worth of retracked radar altimeter data from esa s ers 2 satellite to produce the highest available resolution gravity mapping of the entire arctic ocean complete to 86 degrees n this arctic satellite only arcs marine gravity field uniformly and confidently resolves marine gravity to wavelengths as short as 35 km arcs relies on a gravity recovery and climate experiment grace only satellite gravity model at long 580 km wavelengths and plainly shows tectonic fabric and numerous details imprinted in the arctic seafloor in particular in the enigmatic amerasian basin ab for example in the makarov basin portion of the ab two north south trending lineations are likely clues to the highly uncertain seafloor spreading history which formed the ab

ice shelf grounding zone structure from icesat laser altimetry 1 we present a technique for investigating the grounding zone gz of antarctic ice shelves using laser altimetry from the ice cloud and land elevation satellite icesat most surface height variability in the gz is easily resolved by the icesat laser s 65 m footprint and 172 m along track spacing comparisons of repeated tracks sampled at different phases of the ocean tide identify the landward and seaward limits of tide forced ice flexure providing gz location and width information for each track using icesat data in the institute ice stream region of southern ronne ice shelf we demonstrate that the location of the gz based on feature identification in satellite imagery or digital elevation models may be in error by several km our results show that icesat will contribute significantly to improving knowledge of gz structure and to studies requiring accurate gz locations e g ice mass balance calculations and ice sheet ocean modeling

a comparison of greenland ice sheet volume changes derived from altimetry measurements we compare rates of surface elevation change on the greenland ice sheet derived from european remote sensing satellite 2 ers 2 radar altimeter data with those obtained from laser altimeter data collected over nearly the same time periods radar altimeter data show more rapid thickening 9 1 cm a 1 above 1500 m elevation in the north and 3 1 cm a 1 above 2000 m in the south than the laser estimates possibly caused by a lifting of the radar reflection horizon associated with changes in the snowpack such as those caused by progressively increased surface melting as summer temperatures rise over all the ice sheet above 2000m this results in an ers derived volume balance 75 15 km 3 a 1 more positive than that from laser data this bias between laser and radar estimates of elevation change varies spatially and temporally so cannot at present be corrected without independent surveys such as those presented here at lower elevations comparison of detailed repeat laser surveys over jakobshavn isbrae with ers results over the same time interval shows substantial ers underestimation of ice thinning rates this results partly from missing data because of bad radar waveforms over the very rough surface topography and partly from the tendency for large radar footprints to sample preferentially local high points in the topography thus missing regions of most rapid thinning along glacier depressions

stable isotope evidence for rapid uplift of the central apennines since the late pliocene abstract the central apennines an accretionary wedge overlying an area of slab detachment are characterized by prominent topography active normal faulting and high uplift rates however previous studies have failed to resolve the surface uplift history complicating efforts to link the topographic evolution with underlying geodynamic processes we aim to better quantify orographic changes by using stable oxygen isotope paleoaltimetry modern surface water 18 o are 5 lower at high elevation than at sea level reflecting orographic rainout over the apennines we present 262 new lacustrine and paleosol carbonate 18 o measurements collected from ten extensional intermontane basins spanning both high and low elevations and combine these with 1 166 published 18 o data permitting us to constrain changes in 18 o both spatially and temporally since the pliocene 18 o in present day high elevation basins has continuously decreased even as 18 o in lowland basins has remained constant over time we attribute this continuous 5 shift to increased orographic rainout as the central apennines were uplifted we estimate an increase in mean elevation of approximately 1 2 km since the late pliocene and these estimates match the suggested timing and expected amplitude of slab break off related uplift this supports the hypothesis that the opening of the adriatic slab window and associated mantle flow contributed significantly to building topography in the central apennines

basin physiography and tectonic influence on sequence architecture and stacking pattern pleistocene succession of the canoa basin central ecuador facies shell bed features and sequence stratigraphic framework for the shallow marine pleistocene upper canoa and tablazo formations are presented based on outcrop data from the southern coast of cabo san lorenzo ecuador sediments of this succession exhibit a distinct cyclic pattern consisting of a stack of eight depositional sequences cyclothems likely developed under the main control of orbitally induced sea level changes as a rule within the studied interval an idealized cyclothem is composed of a transgressive systems tract tst and a highstand systems tract hst whereas deposits attributable to the lowstand and falling stage systems tracts are not present transgressive lithosomes may be defined by estuarine deposits interposed between the sequence boundary and the ravinement surface back barrier wedge and by upward fining shoreface to inner shelf facies successions above the ravinement backstepping shelf wedge separated by an expanded siliciclastic core hiatal shell concentrations occur at the base onlap shell beds and the top backlap shell beds of the transgressive shelf wedges and some occur at the base of highstand systems tracts downlap shell beds on the basis of sedimentary facies geometry taphonomy and paleoecology of shell beds and the nature of the transition between siliciclastic and mollusk bearing sediments cyclothems were classified into two main types that show dependence upon paleoshoreline morphological configuration sheltered in the upper canoa formation and exposed in the tablazo formation notwithstanding the different synsedimentary tectonic and climatic regimes the ecuadorian cyclothems share basic patterns of condensation and facies assemblages with other roughly coeval cyclothemic successions around the world this suggests that 1 hiatal shell bed development is not just a temperate latitude phenomenon 2 a global process such as glacio eustatic sea level change is the primary mechanism of control for the general architecture of sequences and 3 specific paleogeographic settings play an important role by determining the taphonomic and paleoecologic characteristics of key shell beds the nature of their contacts with the encasing sediments and the type of the component set of facies at a multicycle time scale tectonics influenced the long term trend of the relative sea level changes and consequently the large scale stratigraphic organization owing to the continued tectonic uplift of the area successive high frequency depositional sequences are nested to form a longer order falling stage sequence set

recurring dynamically induced thinning during 1985 to 2010 on upernavik isstrom west greenland this is the publisher s version also available electronically from http onlinelibrary wiley com

ice elevations and surface change on the malaspina glacier alaska 1 here we use ice cloud and land elevation satellite icesat derived elevations and surface characteristics to investigate the malaspina glacier of southern alaska although there is significant elevation variability between icesat tracks on this glacier we were able to discern general patterns in surface elevation change by using a regional digital elevation model dem as a reference surface specifically we report elevation differences between icesat laser 1 3 observations february 2003 november 2004 and a shuttle radar topography mission srtm derived dem from february 2000 elevation decreases of up to 20 25 m over a 3 4 year time period were observed across the folded loop moraine on the southern portion of the malaspina glacier

major controls on architecture sequence stratigraphy and paleosols of middle pleistocene continental sediments qc unit eastern central italy abstract middle pleistocene continental sediments in central italy qc unit record the oldest fluvial accumulation along the uplifting margin of the peri adriatic basin the architecture of the sediment body can be divided into two unconformity bounded fining upward cycles interpreted as genetically related depositional sequences these sequences highlight the systematic adjustment of the fluvial system to changes in the ratio between accommodation space and sediment supply a s ratio and from base to top comprise the following surfaces and stratal components i a regionally correlative sequence boundary resulting from an a s ratio 0 ii a low accommodation systems tract characterized by conglomerate rich amalgamated channel fills and recording an a s ratio 1 and v a mature red argillic paleosol to constrain the climatic signal for paleosols formation the two sequence capping mature paleosols have been investigated the results of these studies suggest that they were developed under humid and warm climatic conditions associated with interglacial phases which have been correlatively attributed to marine oxygen isotope stages 11 and 9

sequence development during uplift palaeogene stratigraphy and relative sea level history of the outer moray firth uk north sea abstract published models of sequence stratigraphy have been derived from studies of the depositional history of subsiding basins during the palaeogene sediment accumulation in the outer moray firth basin of the north sea coincided with episodes of basin uplift palaeogene trends in coastal onlap and relative sea level in this basin have been estimated directly from seismic data and reveal two long duration cycles of relative sea level fall and rise the first cycle comprising over 800 m fall followed by 500 m rise was initiated in the earliest palaeocene and lasted approximately 9 my the second cycle began in the early eocene and resulted in approximately 70 m fall and 150 m rise in relative sea level over 13 my the duration of both of these cycles can be defined as second order superimposed on both of these long term second order cycles are higher frequency variations in relative sea level with periodicities of around 1 5 my and amplitudes of up to 150 m these shorter cycles are associated with the deposition of sequences identified on the seismic data one of the effects of this superimposition was to either subdue or enhance the development of systems tracts within the sequences enhancement took place where the sea level trends were similar on both the long and the short duration curves e g both rising systems tracts were subdued where sea level trends were opposed in general lowstands and transgressive systems tracts showed significant enhancement within a sequence when the sequence coincided with the steeply falling and steeply rising portions respectively of the long duration relative sea level cycle groups of these skewed sequences are stacked in certain distinct patterns termed sequence sets the pattern type is again dependent on the coincidence of the group of sequences with the second order cycle in general downstepping sequence sets are associated with the steeply falling part of the second order cycle progradational sequence sets with the gently falling to gently rising portion and retrogradational sequence sets with the steeply rising portion these stacking patterns reflect large scale changes in accommodation volume the multi sequence depositional record of a tectonically driven long duration cycle of relative sea level can be considered as a composite sequence where its systems tracts are composed of sequence sets

the ice cloud and land elevation satellite 2 mission a global geolocated photon product derived from the advanced topographic laser altimeter system abstract the ice cloud and land elevation satellite 2 icesat 2 observatory was launched on 15 september 2018 to measure ice sheet and glacier elevation change sea ice freeboard and enable the determination of the heights of earth s forests icesat 2 s laser altimeter the advanced topographic laser altimeter system atlas uses green 532 nm laser light and single photon sensitive detection to measure time of flight and subsequently surface height along each of its six beams in this paper we describe the major components of atlas including the transmitter the receiver and the components of the timing system we present the major components of the icesat 2 observatory including the global positioning system star trackers and inertial measurement unit the icesat 2 level 1b data product atl02 provides the precise photon round trip time of flight among other data the icesat 2 level 2a data product atl03 combines the photon times of flight with the observatory position and attitude to determine the geodetic location i e the latitude longitude and height of the ground bounce point of photons detected by atlas the atl03 data product is used by higher level level 3a surface specific data products to determine glacier and ice sheet height sea ice freeboard vegetation canopy height ocean surface topography and inland water body height

understanding wind blown sand six vexations abstract the study of aeolian geomorphological systems over the last half century has advanced along several important fronts supported by developments in technologies and analytic methods and the evolution of modeling approaches remote sensing has led to a wealth of knowledge concerning the distribution and dynamics of dunes on earth and elsewhere and wind tunnels have elucidated the roles of aeolian processes in reshaping surfaces improvements in laboratory and field instrumentation allow measurement of aeolian sand transport systems at levels of detail unimaginable when the binghamton geomorphology symposium began we have seen for example the advent of large sophisticated field campaigns and advanced modeling approaches using cellular automata and computational fluid dynamics methods select avenues of development especially concerned with depositional environments are briefly summarized advances in many fields have not been matched with proportional advances in our ability to predict rates of sand transport in natural environments one of the most fundamental challenges at least eight commonly cited sand transport rate models do not agree with each other and do not replicate field observations even under near ideal conditions this review focuses on select reasons why that might be so and categorizes those reasons into six principal theoretical and empirical vexations that have made sand transport an intractable problem predicting rates of transport characterizing grain size characterizing fluid and sand densities estimating shear velocity predicting the threshold of motion including the effects of sand moisture content and understanding granular electrification the examination of potential sources of error in the rate of transport and threshold of motion models leads to a point by point consideration of our current assumptions and protocols or lack thereof the objective is to help us identify the hard targets and the soft targets for future research

reduction of icesat systematic geolocation errors and the impact on ice sheet elevation change detection 1 the ice cloud and land elevation satellite icesat has been acquiring unprecedented observations of our planet s varied surfaces with impressive precision however systematic errors remain in the data including orbital variation and long term bias trend pointing errors these errors are particularly troublesome because they cannot be separated from true surface elevation change and confound instrument range bias determination we present a method to correct these systematic pointing errors to the sub arcsecond level we demonstrate the impact of these errors and their corrections on greenland and antarctica ice sheet surface elevation change observations and sea surface anomaly observations as well as instrument range bias determination while further improvements in the icesat data will certainly be made the analysis presented here demonstrates a major error source can be significantly reduced resulting in improved surface elevation accuracies for ice sheet elevation change detection

ice velocity mapping of ross ice shelf antarctica by matching surface undulations measured by icesat laser altimetry abstract we present a novel method for estimating the surface horizontal velocity on ice shelves using laser altimetry data from the ice cloud and land elevation satellite icesat 2003 2009 the method matches undulations measured at crossover points between successive campaigns elevation measurements are first relocated into a time varying moving coordinate system using an initial velocity e g from velmap and then crossover height differences are minimized with an adjustment vector errors in geolocation of the icesat tracks result in some error in the adjustment vectors but these are small relative to the velocity adjustment for fast moving ice shelves we use the algorithm to estimate changes in the ice velocity of ross ice shelf between an earlier mapping from velmap and the icesat period the new velocity field is compared with velocities from in situ measurements and satellite radar interferometry the slowdown of 98 34 m yr 1 23 is observed in the ice shelf downstream of whillans ice stream and the deceleration rate is 3 1 1 1 m yr 2 during last three decades the method can be expanded to the simultaneous mapping of ice horizontal velocity ice thickness change and surface deformation for antarctic ice shelves as well as a more accurate mapping using future icesat 2 measurements

contributions to sequence stratigraphy from analogue and numerical experiments the sequence stratigraphic model although no longer focused on eustasy and accommodation has been until recently based largely on observation and interpretation of outcrop and subsurface data this approach may be restrictive if the current model places limits on what is observed and how observations are interpreted to make progress in our understanding of strata the sequence stratigraphic model and method should be tested against and fully incorporate theoretical and experimental results that provide new knowledge of 1 autogenesis 2 intrinsic stratigraphic responses 3 alluvial grade and 4 scales appropriate to single depositional systems evolving with relative sea level changes more extensive inclusion of analogue and numerical experimental results could lead to significant modification and refinement of existing sequence stratigraphic models

precision and accuracy of satellite radar and laser altimeter data over the continental ice sheets the unprecedented accuracy of elevations retrieved from the ice cloud and land elevation satellite icesat laser altimeter is investigated and used to characterize the range errors in the environmental satellite envisat and european remote sensing 2 satellite ers 2 radar altimeters over the continental ice sheets cross mission crossover analysis between time coincident ers 2 envisat and icesat retrieved elevations and comparisons to an icesat derived digital elevation map are used to quantify the radar elevation error budget as a function of surface slope and to investigate the effectiveness of a method to account for the radar altimeter slope induced error the precision and accuracy of the elevations retrieved from the icesat geoscience laser altimeter system and the european space agency radar altimeters on ers 2 and envisat are calculated over the greenland and antarctic ice sheets using a crossover analysis as a result of this work the laser precision is found to vary as a function of surface slope from 14 to 59 cm and the radar precision varies from 59 cm to 3 7 m for ers 2 and from 28 cm to 2 06 m for envisat envisat elevation retrievals when compared with icesat results over regions with less than 0 1deg surface slopes show a mean difference of 9plusmn5 cm for greenland and 40plusmn98 cm over antarctica ers 2 elevation retrievals over these same low surface slope regions differ from icesat results by 56plusmn72 cm over greenland and 1 12plusmn1 16 m over antarctica at higher surface slopes of 0 7deg to 0 8deg the envisat icesat differences increase to 2 27plusmn23 m over greenland and to 0 05plusmn26 m over antarctica

gsfc00 mean sea surface gravity anomaly and vertical gravity gradient from satellite altimeter data a mean sea surface gsfc00 and its derivatives the altimetry gravity anomaly and vertical gravity gradient fields were computed using sea surface heights of topex ers and geosat satellite altimeter missions provided by the nasa ocean altimeter pathfinder project koblinsky et al 1998 a new estimation method distinct from the gsfc98 mean sea surface computation wang 2000a was explored and used to reduce ocean variability in the mean sea surface heights the gravity anomaly and vertical gravity gradient fields were then computed from the mean sea surface height implied geoid undulations validation of the gsfc00 mean sea surface and gravity anomaly was also performed

the mid pliocene sea level conundrum glacial isostasy eustasy and dynamic topography abstract determining eustatic sea level during the mid pliocene warm period 3 3 to 2 9 ma has been a central but elusive goal in the study of past warm climates estimates of eustatic sea level based on geologic data span a broad range variation that we now recognize is due in part to geographically varying post depositional displacement caused by glacial isostatic adjustment and dynamic topography in this study we combine field observations and glacial isostatic adjustment modeling to estimate the dynamic topography signal in three areas that are important to paleo sea level studies of the mid pliocene warm period south africa west australia and southeastern united states we show that dynamic topography played a significant role in the post depositional displacement of pliocene and even younger pleistocene shorelines in this regard we provide a robust paleo sea level elevation data set corrected for glacial isostatic adjustment that can be used to evaluate predictions from mantle flow models of dynamic topography

facies and sequence stratigraphic modeling of a upper pliocene lower pleistocene fluvial succession valdelsa basin central italy abstract this paper illustrates the results of sedimentologic and stratigraphic analyses of the upper piacenzian gelasian fluvial succession exposed in the neogene quaternary valdelsa basin central italy the succession shows a cyclothemic stacking of gravelly sandy and muddy lithofacies organized into four monogenic facies associations a d these record depositional environments ranging from braided to low sinuosity river channels to flood basins associations a d attest to lowstand a b transgressive and high stand c d depositions in a full cycle of base level variations in each association internal erosional surfaces separate early transgressive association c from the late lowstand association b the systematic b c channel scouring is interpreted as the result of a high water sediment discharge ratio determined by a decrease of coarse grained sediment supply to the fluvial systems during rise of base level this erosive surface is conceptually analogous to the ravinement surface sculpted by wave erosion during the transgressive landward migration of a shoreface the late transgressive and highstand mud dominated association d records the flood basin a depositional environment indicative of a high base level which transformed a former channel belt in a plain dominated by fine grained sediment settling bio and pedoturbation the studied succession records rhythmic variations of base level and sediment supply to the fluvial systems in turn regulated by different rank relative fluctuations of piacenzian sea level in this perspective concepts of sequence stratigraphy and facies analysis are exploited for producing a reliable fluvial sequence stratigraphic model

carbonate deposition in restricted basins a pliocene case study from the central mediterranean northwestern apennines italy abstract carbonate depositional models are often informed by the study of platforms of good lateral continuity and sizable thickness because of their significance in petroleum geology however spatially restricted and more ephemeral carbonate accumulations can be an important but frequently overlooked component of otherwise siliciclastic dominated or mixed carbonate siliciclastic systems pliocene successions of tuscany and the tyrrhenian shelf northern apennines italy record a regional pulse of nontropical carbonate deposition across several restricted basins that has not yet been precisely constrained in its genesis and correlation this study investigates the stratigraphic expression of these carbonates to extract general aspects applicable to carbonate sedimentation across tectonically structured and physiographically complex shelves analyses of the extension composition facies and sequence stratigraphic architecture of the studied piacenzian carbonate units are complemented by new biostratigraphic and magnetostratigraphic data which document the slightly diachronous development of the carbonates within mediterranean planktonic foraminifera subzones mpl4b and mpl5a and magnetic polarity chron c2an the carbonate units are part of a regionally defined tectonically controlled sequence and represent the first transgressive unit overlying the basal sequence boundary but are also found in the regressive portion of the sequence collectively the units document the establishment of a shallow marine carbonate factory dominated by calcareous red algae the larger benthic foraminifer amphistegina and heterozoan skeletal components along the margins of a complex archipelago like coastal domain a review of the studied successions and other examples from the literature indicates that carbonate accumulations in settings with varied coastal physiography and active partitioning of depocenters are generally characterized by a spatial discontinuity b an overall skeletal association consistent across separate basins but with local variability in dominant skeletal components c preferential accumulation along basin margins or over isolated structural highs not in direct proximity to a hinterland with major drainage systems d predominance of low to moderate energy facies e preferential onset of deposition during transgression with possible development of mixed carbonate siliciclastic facies and f differing internal stratigraphic architecture tied to the specific subsidence and uplift history of coeval individual basins these observations built upon the study of mid piacenzian carbonate units from the central mediterranean contribute to the refinement of carbonate facies models and their application in the fields of sequence stratigraphy and basin analysis

pliocene stratigraphic paleobiology in tuscany and the fossil record of marine megafauna abstract tuscany has a rich pliocene record of marine megafauna mm including mysticetes odontocetes sirenians and seals among the mammals and six orders of sharks among the elasmobranchs this is reviewed with respect to paleogeography and sequence stratigraphy in six different basins conditions at the ancient seafloor are explored by means of sedimentary facies analysis taphonomy and multivariate techniques applied to a large quantitative dataset of benthic molluscs mm is rare or absent in most basins during the zanclean except in one basin and most abundant in piacenzian deposits in all six basins mm occurs preferentially in fine grained shelfal highstand deposits of small scale depositional sequences or at condensed horizons of the maximum flooding interval it is rare in shallow marine paleonvironments and nearly absent in bathyal paleosettings paleogeographic and paleoecological evidence and a comparison with modern patterns of marine upwelling suggest that a wedge of nutrient rich waters sustained in the offshore during the pliocene a high biomass of primary producers and a community of apex consumers and mesopredators similarly to the modern northwestern mediterranean sea with a species richness higher than the modern and a more complex trophic structure the highest mm diversity coincides with the mid piacenzian warm period suggesting that facies control does not obscure a link between climate and diversity we underline however that not all marine environments were suitable for marine mammal preservation buoyant carcasses were preferentially dismembered and destroyed in high energy shallow waters with the possible exception of delta front deposits where sudden sediment input occasionally buried pristine carcasses we hypothesise that carcasses sunken on the seafloor below the shelf break underwent destruction through the activity of a whale fall biota of modern type specialised in the consumption of decomposing tissues both soft and mineralised a taphonomic window was left between storm wave base and the shelf break here water pressure is high enough to prevent the formation of decomposing gases and the resurfacing of carcasses while the lack of a specialised whale fall biota slows down bone degradation with respect to deeper settings sedimentation rate was high enough to cover skeletal material before its complete destruction an estimate of paleobathymetries based on multivariate techniques suggests that the preferential depth for the inclusion of mm in the fossil record was 30 300 m the results are compared with major mesozoic and cenozoic mm records worldwide available evidence suggests that the late neogene radiation of large whales true ecosystem engineers and their size increase triggered the radiation of a bone eating fauna that hampered and hampers mm preservation in the deep sea stratigraphic paleobiology and an ecosystem level approach deliver useful insights to the nature of the fossil record

icesat antarctic elevation data preliminary precision and accuracy assessment 1 since first light on february 20th 2003 nasa s ice cloud and land elevation satellite icesat has derived surface elevations from 86 n to 86 s latitude these unique altimetry data have been acquired in a series of observation periods in repeated track patterns using all three geoscience laser altimeter system glas lasers here we focus on antarctic ice sheet elevation data that were obtained in 2003 2004 we present preliminary precision and accuracy assessments of selected elevation data and discuss factors impacting elevation change detection we show that for low slope and clear sky conditions the precision of gla12 laser 2a release 21 data is 2 1 cm and the relative accuracy of icesat elevations is 14 cm based on crossover differences

shoal water deltas in high accommodation settings insights from the lacustrine valimi formation gulf of corinth greece the stratigraphic architecture of shoal water deltaic systems developed in low accommodation settings is relatively well known in contrast the features of shoal water deltas developed in high accommodation settings remain relatively poorly documented especially when compared with the available data sets for gilbert type deltaic systems developed in the same settings the lacustrine valimi formation gulf of corinth greece provides an opportunity to investigate the facies assemblage and architectural style of shoal water deltaic systems developed in high accommodation settings the studied interval accumulated during the pliocene and pleistocene and represents part of the early syn rift gulf of corinth succession six facies associations each described in terms of depositional processes and geometries have been identified and interpreted to represent a range of proximal to distal deltaic sub environments delta plain distributary channel mouth bar delta front prodelta and open lake the facies associations and their architectural elements reveal characteristics which are not common in traditionally described shoal water deltas of note different facies arrangements are observed in the distributary channels in different sectors of the delta passing from thick single storey channel fills embedded within delta plain fines in landward positions to thin amalgamated and multi storey channels closer to the river mouth this study proposes a new depositional model for shoal water deltas in high accommodation settings documenting for the first time that shoal water delta deposits can form a substantial part of stratigraphic successions that accumulate in these settings the proposed depositional model provides new criteria for the recognition and interpretation of these deposits the results of this study have applied significance for reservoir characterization

improving the geometry of kaguya extended mission data through refined orbit determination using laser altimetry abstract the japan aerospace exploration agency s jaxa kaguya spacecraft carried a suite of instruments to map the moon and its environment globally during its extended mission the average altitude was 50 km or lower and kaguya science products using these data hence have an increased spatial resolution however the geodetic position quality of these products is much worse than that of those acquired during the primary mission at an altitude of 100 km because of reduced radiometric tracking and frequent thrusting to maintain spacecraft attitude after the loss of momentum wheels we have analyzed the kaguya tracking data using gravity models based on the gravity recovery and interior laboratory grail mission and by making use of a new data type based on laser altimeter data collected by kaguya we adjust the spacecraft orbit such that the altimetry tracks fit a precise topographic basemap based on the lunar reconnaissance orbiter s lro lunar orbiter laser altimeter lola data this results in geodetically accurate orbits tied to the precise lola lro frame whereas previously archived orbits show errors at the level of several kilometers the inclusion of altimetry greatly improves the orbit precision to a level of several tens of meters when altimetry data are not available the combination of grail gravity and radio tracking results in an orbit precision of around several hundreds of meters for the low altitude phase of the extended mission our greatly improved orbits result in better geolocation of the kaguya extended mission data set

okhotsk sea intermediate water formation deduced from oxygen isotope systematics to clarify the mechanisms of the okhotsk sea intermediate water formation water samples collected in the okhotsk sea and neighboring western north pacific were analyzed for 18o as well as salinity and other routinely measured components the 18o salinity relation in the okhotsk sea was markedly different from that in the western subarctic pacific feeding the okhotsk sea the intermediate water of the okhotsk sea was less saline than that of the western subarctic water at the same density but was more saline at the same 18o value especially in the density range 26 5 27 0 this could be due to mixing of dense shelf water formed during sea ice formation with neighboring water the amount of fresh water removed by the sea ice formation was estimated from the salinity anomaly of the okhotsk sea intermediate water the calculated amounts of fresh water removed from the okhotsk sea intermediate water corresponded to the amount of sea ice formed for 0 6 3 8 years in the okhotsk sea this suggests that the residence time of the okhotsk sea intermediate water is a few years

high resolution ground based gps measurements show intercampaign bias in icesat elevation data near summit greenland the geoscience laser altimeter system glas aboard the national aeronautics and space administration s ice cloud and land elevation satellite icesat collected data from early 2003 to late 2009 with the specific goal of measuring ice surface elevation changes while the precision of glas instrumentation has been studied over its intended target ice its accuracy has only been robustly estimated using independent terrestrial nonlaser methods over salt flats here we perform repeat high precision global positioning system gps surveys under four passes of icesat track 0412 campaigns l3i l3j l2d and l2e to compare directly glas elevation data footprints to a coincident gps ground truth near summit greenland analysis and comparison of glas data with gps data show a campaign dependent elevation bias ranging from 0 112 0 030 m l3j to 0 121 0 071 m l2e although uncorrected reflectance values and field observations both indicate that forward scattering of the laser signal through the atmosphere accounts for the anomalously negative l3j bias the biases of all campaigns studied are within the instrument s goal accuracy of 0 15 m however our analysis shows a campaign dependence in the bias which may propagate through estimates of mass balance the error introduced from intercampaign biases illustrates the importance of long term independent validation experiments of satellite altimetry data over ice sheets

analysis of icesat data using kalman filter and kriging to study height changes in east antarctica 1 we analyze icesat derived heights collected between feb 03 nov 04 using a kriging kalman filtering approach to investigate height changes in east antarctica the model s parameters are height change to an a priori static digital height model seasonal signal expressed as an amplitude b and phase and height change rate dh dt for each 100 km 2 block from the kalman filter results dh dt has a mean of 0 06 m yr in the flat interior of east antarctica spatially correlated pointing errors in the current data releases give uncertainties in the range 0 06 m yr making height change detection unreliable at this time our test shows that when using all available data with pointing knowledge equivalent to that of laser 2a height change detection with an accuracy level 0 02 m yr can be achieved over flat terrains in east antarctica

correlation of carboniferous strata using a hierarchy of transgressive regressive units carboniferous strata can be described interpreted and correlated using six scales of allocyclic transgressive regressive t r units these t r units are inferred to be the net result of deposition during cycles of sea level change all pennsylvanian and lower permian strata constitute one second order t r unit or synthem the pennsylvanian system contains third fourth fifth and sixth order t r units that can be correlated across both marine and nonmarine facies in the appalachian basin this permits differentiation of allocyclic t r units from autocyclic t r units or fluvial autocyclic units the hierarchical approach is also useful for predicting the location of marine horizons coals claystones and various types of stratigraphic breaks a hierarchical scheme of allocyclic t r units could be combined with biostratigraphic radiometric and magnetostratigraphic data to form a practical chronostratigraphic framework for the carboniferous

high tide of the warm pliocene implications of global sea level for antarctic deglaciation we obtained global sea level eustatic estimates with a peak of 22 m higher than present for the pliocene interval 2 7 3 2 ma from backstripping in virginia united states new zealand and enewetak atoll north pacifi c ocean benthic foraminiferal 18 o values and mg ca 18 o estimates statistical analysis indicates that it is likely 68 confi dence interval that peak sea level was 22 5 m higher than modern and extremely likely 95 that it was 22 10 m higher than modern benthic foraminiferal 18 o values appear to require that the peak was 20 21 m our estimates imply loss of the equivalent of the greenland and west antarctic ice sheets and some volume loss from the east antarctic ice sheet and address the longstanding controversy concerning the pliocene stability of the east antarctic ice sheet

composite sequence stratigraphic patterns in alluvial to shallow marine successions examples from the piacenzian of the valdelsa basin central italy abstract the sequence stratigraphic analysis of continental and shallow marine successions is a helpful tool for investigating the cyclicity of the sedimentary record a similar approach is adopted in the present study to illustrate the composite cyclothemic facies architecture that characterizes the piacenzian strata of the southern valdelsa basin central italy specifically we integrated facies analysis paleopedology paleobiology of marine mollusk assemblages and biostratigraphy to assess the response of geomorphic sedimentary and biotic systems to piacenzian multifrequency relative sea level fluctuations this integrated approach resulted in the definition of a composite sequence stratigraphic framework that includes a hierarchy of units ranging from the elementary to the composite depositional sequences referred to the 5th to 3rd order cycles of sea level fluctuations respectively a correlation with the piacenzian oxygen isotopic signature of glacial and interglacial stages and related sea level fluctuations associates the cyclic development of fluvial coastal and shallow marine depositional systems to the mid piacenzian warm period and to the subsequent transition to the gelasian thus the glacio eustatic control prevailed on the development of the described multi scale cyclical pattern of sedimentation compared to the role played by the deformation of the northern apennines orogen

the ice cloud and land elevation satellite 2 icesat 2 science requirements concept and implementation abstract the ice cloud and land elevation satellite icesat mission used laser altimetry measurements to determine changes in elevations of glaciers and ice sheets as well as sea ice thickness distribution these measurements have provided important information on the response of the cryopshere earth s frozen surfaces to changes in atmosphere and ocean condition icesat operated from 2003 to 2009 and provided repeat altimetry measurements not only to the cryosphere scientific community but also to the ocean terrestrial and atmospheric scientific communities the conclusive assessment of significant ongoing rapid changes in the earth s ice cover in part supported by icesat observations has strengthened the need for sustained high accuracy repeat observations similar to what was provided by the icesat mission following recommendations from the national research council for an icesat follow on mission the icesat 2 mission is now under development for planned launch in 2018 the primary scientific aims of the icesat 2 mission are to continue measurements of sea ice freeboard and ice sheet elevation to determine their changes at scales from outlet glaciers to the entire ice sheet and from 10s of meters to the entire polar oceans for sea ice freeboard icesat carried a single beam profiling laser altimeter that produced 70 m diameter footprints on the surface of the earth at 150 m along track intervals in contrast icesat 2 will operate with three pairs of beams each pair separated by about 3 km cross track with a pair spacing of 90 m each of the beams will have a nominal 17 m diameter footprint with an along track sampling interval of 0 7 m the differences in the icesat 2 measurement concept are a result of overcoming some limitations associated with the approach used in the icesat mission the beam pair configuration of icesat 2 allows for the determination of local cross track slope a significant factor in measuring elevation change for the outlet glaciers surrounding the greenland and antarctica coasts the multiple beam pairs also provide improved spatial coverage the dense spatial sampling eliminates along track measurement gaps and the small footprint diameter is especially useful for sea surface height measurements in the often narrow leads needed for sea ice freeboard and ice thickness retrievals the icesat 2 instrumentation concept uses a low energy 532 nm green laser in conjunction with single photon sensitive detectors to measure range combining icesat 2 data with altimetry data collected since the start of the icesat mission in 2003 such as operation icebridge and esa s cryosat 2 will yield a 15 year record of changes in ice sheet elevation and sea ice thickness icesat 2 will also provide information of mountain glacier and ice cap elevations changes land and vegetation heights inland water elevations sea surface heights and cloud layering and optical thickness

the sequence stratigraphy of fluvial depositional systems the role of floodplain sediment storage abstract the currently used model for alluvial sequence stratigraphy has been criticised miall 1991 and an alternative model is offered here in this model alluviation mainly takes place during transgressive and not highstand phases when accommodation space allows sediment storage the high capacity for some river systems to store floodplain sediments is a critical consideration the effects of climatic and intrinsic geomorphic changes during fluvial deposition are likely to greatly complicate simple base level controlled sequence models and recognising higher order fourth and fifth order cycles will be particularly difficult

bored pebbles and ravinement surface clusters in a transgressive systems tract sant llorenc del munt fan delta complex se ebro basin spain abstract a 25 m thick transgressive systems tract in the sant llorenc del munt wave influenced fan delta system eocene se ebro basin has an internal framework consisting of a cluster of transgressive erosion surfaces each of which has minor relief and which are collectively stacked vertically no more than two metres apart each erosion surface bounds a cycle containing a conglomeratic lag up to 0 5 m thick followed by a coarsening upward sandstone to conglomeratic unit the uppermost levels of which can be nonmarine individual cycles become entirely nonmarine landwards of the termination of the basal bounding erosion surface whereas they thin and eventually become entirely marine basinwards the individual erosion surfaces within the transgressive tract some 16 of them within a 20 m thick lithosome are interpreted as wave ravinement surfaces that repeatedly eroded into the conglomeratic shoreface during transgression this interpretation rather than one invoking nonmarine flooding or other marine erosion surface types is consistent with the arrangement of bivalve and sponge borings on the top surfaces of clasts and with the associated lag pavements multiphase boring around the entire surface of clasts as well as erosion of the clasts at some horizons particularly in reaches of the tract where the ravinement trajectory is sub horizontal suggest repeated reworking of previously generated lag pavements in zones of minimal aggradation during transgression where the transgressive shoreline trajectory rises more steeply and there has been more rapid aggradation during transgression the lag pavements show only single phase borings with the borings on the upper surface of the pebble pavement only the close spacing of erosion surfaces within the transgressive systems tract together with estimates of time span in the tract suggest that transgressive erosion occurred with a frequency of less than 500 years

registering imagery to icesat data for measuring elevation changes on byrd glacier antarctica 1 we present a new approach to derive control information from icesat data that enables rigorous registration of aerial and satellite imagery the technique based on matching terrain features identified from icesat measurements and aerial imagery opens the door to transform results of previous studies to a global reference frame we demonstrate the proposed methodology with historical aerial photographs to determine surface changes between 1979 and 2004 over byrd glacier this is important because there is no satellite radar altimetry coverage south of 81 5 s which limits mass balance knowledge of outlet glaciers draining the east antarctic ice sheet through the southern transantarctic mountains our study indicates that the grounded part of byrd glacier is close to being in balance however we observe large thinning on the floating part of the glacier probably induced by increased basal melting citation schenk t b csatho c j van der veen h brecher y ahn and t yoon 2005 registering imagery to icesat data for measuring elevation changes on byrd glacier antarctica geophys res lett 32 l23s05 doi 10 1029 2005gl024328

departures from eustasy in pliocene sea level records estimates for sea level three million years ago a period with similar atmospheric co2 levels to today vary from 10 to 40 m above present glacial isostatic adjustment modelling suggests that variations in the height of palaeoshorelines result from the residual adjustment of continental flexure following recent glaciations

an integrated numerical model for the stability of artificial submarine slope under wave load abstract the stability evaluation of artificial submarine slope under wave load is a primary concern in the construction of offshore structures such as submarine pipelines and immersed tunnels aiming at this issue an integrated finite element method fem model of wave seabed interaction is proposed to investigate the effects of wave action on the wave induced slope stability of the temporary trench the reynolds averaged navier stokes rans equations are adopted to describe the wave motion in the fluid domain while the seabed domain is described using the mohr coulomb constitutive model the wave induced seepage pressure near the slope is determined by darcy s law and considered as an external load in the analysis the stability of the temporary slope is evaluated by the means of shear strength reduction the present numerical model is firstly validated through the comparison with the analytical solution and the experimental data available in the literature the integrated numerical model is then applied to a practical engineering application including a new evaluation method of stability for the trench slope excavated temporarily for the fully buried submarine pipelines at an actual site the results indicate that the stability of submarine slope is closely related to the dynamic wave pressure from the upper seawater the minimum of fos factor of safety corresponding to the most dangerous situation is introduced as the stability index for the slope with specific slope ratio in the whole process of dynamic wave loading additionally the wave induced seepage pressure should be considered as external load in the design for the seabed with large permeability such as sandy soils

anatomy of a transgressive lag panther tongue sandstone star point formation central utah the panther tongue of the star point formation in central utah contains a variety of transgressive lag deposits that when mapped regionally show a sensitive dependence upon pre existing topography of the palaeoshoreline the panther tongue consists of a coarsening upward sandstone wedge that prograded into the western interior seaway during late cretaceous santonian time high resolution sequence stratigraphic analysis revealed that this member was deposited during the long distance 50 km regression and transgression of a delta into shallow marine environments containing basal highstand forced regression lowstand and transgressive systems tracts based on grain size clast composition lateral extent and stratigraphic position the coarse sandstones on top of the panther tongue were classified into four types 1 simple 2 dispersed 3 oxidized and 4 local lags the simple lag is composed of dark grey coarse sandstone with oyster fragments and shark teeth this lag is typically extensively bioturbated and massive laminated and cross bedded units are also common this type of coarse sandstone is interpreted as a typical transgressive lag the dispersed lag differs in that it contains abundant mud and commonly occurs as multiple beds in thick intervals of muddy sandstone mixing of bay estuarine and shallow marine mud with simple lag sand may be responsible for deposition of this type of coarse sandstone the oxidized lag is distinctive in its reddish colour with extensive bioturbation and is commonly overlain by a simple lag the local lag is composed of thin bedded dark grey coarse sandstone occurring locally between the mouth bar and distributary channel the variation in types grain size and bed thickness of the coarse grained lags was mainly controlled by antecedent topography as suggested by immediately underlying lithofacies relatively thick 30 cm simple lags are present on top of mouth bar sandstones whereas dispersed lags are common on top of the distributary channel sandstone and in bay estuarine and shallow marine mudstones erosion of topographic highs mouth bar resulted in relatively thick accumulation of simple lags in topographic low areas such as distributary channel estuary bay and shallow marine environments fine grained muddy sands that were eroded from the nearby topographic highs were redeposited intermittent storm waves transported coarse sands both landward and seaward forming a dispersed lag the net effect was reworking of local topographic relief during overall transgression forming an apparently planar transgressive surface of erosion

surface height determination of crevassed glaciers mathematical principles of an autoadaptive density dimension algorithm and validation using icesat 2 simulator simpl data glacial acceleration is a main source of uncertainty in sea level change assessment measurement of ice surface heights with a spatial and temporal resolution that not only allows elevation change calculation but also captures ice surface morphology and its changes is required to aid in investigations of the geophysical processes associated with glacial acceleration the advanced topographic laser altimeter system aboard nasa s future icesat 2 mission launch 2017 will implement multibeam micropulse photon counting lidar altimetry aimed at measuring ice surface heights at 0 7 m along track spacing the instrument is designed to resolve spatial and temporal variability of rapidly changing glaciers and ice sheets and the arctic sea ice the new technology requires the development of a new mathematical algorithm for the retrieval of height information we introduce the density dimension algorithm dda that utilizes the radial basis function to calculate a weighted density as a form of data aggregation in the photon cloud and considers density an additional dimension as an aid in autoadaptive threshold determination the autoadaptive capability of the algorithm is necessary to separate returns from noise and signal photons under changing environmental conditions the algorithm is evaluated using data collected with an icesat 2 simulator instrument the slope imaging multi polarization photon counting lidar over the heavily crevassed giesecke braer in northwestern greenland in summer 2015 results demonstrate that icesat 2 may be expected to provide ice surface height measurements over crevassed glaciers and other complex ice surfaces the dda is generally applicable for the analysis of airborne and spaceborne micropulse photon counting lidar data over complex and simple surfaces

icesat measurements reveal complex pattern of elevation changes on siple coast ice streams antarctica 1 we compare icesat data 2003 2004 to airborne laser altimetry data 1997 98 and 1999 2000 to monitor surface changes over portions of van der veen vdvis whillans wis and kamb ice streams kis in the ross embayment of the west antarctic ice sheet the spatial pattern of detected surface changes is generally consistent with earlier observations however important changes have occurred during the past decade for example areas on the vdvis and wis where large thinning was detected by the airborne surveys are now closer to being in balance the upper trunk of kis continues to build up with thickening rates reaching 0 4 m year our results provide new evidence that the overall mass balance of the region is becoming more positive but a significant spatial variability exists they also demonstrate the potential of icesat data for detecting spatial patterns of surface elevation change in antarctica

perspectives on the sequence stratigraphy of continental strata this report is the result of a working group on continental sequence stratigraphy that was set up at the 1991 nuna conference in banff canada to date sequence stratigraphic concepts have been applied mainly to the marine realm but unconformity bounded units have long been recognized in nonmarine strata successful application of sequence stratigraphic concepts to continental strata requires careful consideration of controls on base level and sediment supply as with shallow marine environments relative sea level can be considered as the stratigraphic as well as the geomorphic base level for coastal nonmarine settings farther inland stratigraphic base level which determines accommodation space is more complex and takes various forms such as the graded profile for fluvial strata groundwater tables for some eolian strata and lake level for some intermontane sediments sediment supply is also generally a more complex variable for nonmarine environments than in the marine realm because of the proximity to the source area the influence of climate and tectonism on sediment supply can clearly be seen in many continental sediments the fact that the major controls of climate tectonism and eustasy are somewhat interdependent and that a change in one parameter will most likely be reflected in others is also more readily apparent in continental strata although in its infancy sequence stratigraphic concepts have been applied to a wide variety of continental settings in attempts to explain variations in facies architecture of particular interest are studies that have linked fluvial architecture on coastal plains to variations in relative sea level as indicated by coeval marine strata and studies of lacustrine environments that show marked variation in facies between highstand and lowstand deposits the application of sequence stratigraphy to continental strata will likely result in the development of better correlation techniques and models that better predict the location and nature of fluvial and eolian reservoirs

the use of laser altimetry in the orbit and attitude determination of mars global surveyor altimetry from the mars observer laser altimeter mola an instrument on board the mars global surveyor mgs spacecraft has been analyzed for the period of the mgs science phasing orbit 1 spo 1 mission phase altimeter ranges have been used to improve significantly the orbit and attitude knowledge of the spacecraft by the use of crossover constraint equations derived from short passes of the mola data these constraint equations differ from traditional crossover constraints and exploit the small footprint associated with laser altimetry the rationale for using this technique with laser altimetry over sloping terrain is laid out and evidence of the resulting benefit is presented

icesat validation of srtm c band digital elevation models 1 the geoscience laser altimeter system glas on the ice cloud and land elevation satellite icesat provides a globally distributed data set well suited for evaluating the vertical accuracy of shuttle radar topography mission srtm digital elevation models dems the horizontal error 2 4 7 3 m and vertical error 0 04 0 13 m per degree of incidence angle for the icesat data used are small compared to those for srtm using glas echo waveforms we document differences between the srtm c band phase center and the highest centroid and lowest elevations within icesat laser footprints in the western united states in areas of low relief and sparse tree cover the mean and standard deviation of elevation differences between the icesat centroid and srtm are 0 60 3 46 m the differences are 5 61 15 68 m in high relief sparse tree cover areas and 3 53 8 04 m in flat areas with dense tree cover the largest differences occur in rugged densely vegetated regions

a preliminary tidal analysis of icesat laser altimetry southern ross ice shelf 1 satellite laser altimetry could soon play a key role in mapping poorly known ocean tides underneath antarctic ice shelves the amount of icesat data now collected over the southernmost part of the ross ice shelf is sufficient to warrant direct tidal analysis tides are estimated here from ten operational icesat periods totaling 363 days a response analysis helps overcome unfavorable tidal sampling especially an s2 correlation with the annual cycle comparisons of tidal estimates against independent station data show rms constituent differences around 3 cm still somewhat large but an encouraging result for such a challenging region

recent elevation changes on the ice streams and ridges of the ross embayment from icesat crossovers 1 we analyze differences in icesat elevation estimates at orbital crossover locations to determine short term rates of elevation change for small regions within the ross embayment of the west antarctic ice sheet a linear regression of crossover elevation difference against time difference gives an estimate of the mean elevation change rate during the icesat mission to date we observe prevalent elevation change in the south with uplift in the upstream end of kamb ice stream at 0 24 0 30 m a 1 and thinning in the parts of whillans ice stream mercer ice stream and the adjacent conway and engelhardt ice ridges at 0 05 0 18 m a 1 these rates of elevation change are too large to be explained by the 0 02 0 03 m a 1 formal regression error by seasonal height variations or by accumulation or densification rate variability suggesting that they reflect real variations stemming from ice dynamics of the region