a strategy for coupled 3d imaging of large scale seismic and electromagnetic data sets application to subsalt imaging abstractoffshore seismic and electromagnetic em imaging for hydrocarbons can require up to tens of millions of parameters to describe the 3d distribution of complex seabed geology and relevant geophysical attributes the imaging and data volumes for such problems are enormous descent based methods are the only viable imaging approach where it is often challenging to manage the convergence of stand alone seismic and em inversion experiments when a joint seismic em inversion is implemented convergence problems with descent based methods are further aggravated moreover resolution mismatches between seismic and em pose another challenge for joint inversion to overcome these problems we evaluated a coupled seismic em inversion workflow and applied it to a set of full wave seismic magnetotelluric mt and controlled source electromagnetic csem data for subsalt imaging in our workflow we address disparate resolution properties between seismic and em data by implementing the seismic inversion in th

biogenic silica accumulation in the ross sea and the importance of antarctic continental shelf deposits in the marine silica budget abstract thirty five box cores were collected from the continental shelf in the ross sea during cruises in january and february 1983 pb 210 and pu 239 240 geochronologies coupled with biogenic silica measurements were used to calculate accumulation rates of biogenic silica sediment in the southern ross sea accumulates at rates ranging from 0 6 to 2 7 mm y with the highest values occurring in the southwestern ross sea biogenic silica content in surface sediments ranges from 2 by weight in sulzberger bay and the eastern ross sea to 41 in the southwestern ross sea biogenic silica accumulation in the southwestern ross sea averages 2 7 10 2 g cm2 y and is comparable to accumulation rates in high productivity upwelling environments from low latitude continental margins e g gulf of california coast of peru the total rate of biogenic silica accumulation in the southern ross sea is approximately 0 2 1014 g y with most of the accumulation occurring in basins 500 1000 m water depth if biogenic silica accumulation in the southern ross sea continental shelf is typical of other basins on the antarctic continental shelf as much as 1 2 1014 g y of silica could be accumulating in these deposits biogenic silica accumulation on the antarctic continental shelf may account for as much as a fourth of the dissolved silica supplied to the world ocean by rivers and hydrothermal vents

substrate control on distribution of subglacial and glaciomarine seismic facies based on stochastic models of glacial seismic facies deposition on the ross sea continental margin antarctica abstract a quantitative approach was utilized to establish the nature of spatial and temporal variations of glaciomarine and subglacial seismic facies deposition in the ross sea the ross sea is an excellent area to study antarctic ice sheet volume variations because it receives ice sheet drainage from approximately 25 of the continent and it contains subsiding basins to preserve the stratigraphic record of the ice sheet volume fluctuations this region receives most of the influence on deposition from the marine based west antarctic ice sheet which is believed to have been subject to catastrophic surges hollin j t 1962 on the glacial history of antarctica journal of glaciology 4 173 195 the eastern basin in particular has been subsiding creating accommodation space in which to preserve the plio pleistocene record of ice sheet fluctuations evidence from high resolution seismic data in conjunction with dsdp leg 28 drilling results are used to test hypotheses of paleo ice sheet behavior here we present quantitative evidence for a dynamic polar style of glaciation meaning that the ice sheets have had dynamic or large ice volume change not merely in the plio pleistocene but back to the late oligocene high resolution seismic data correlated to dsdp sites 270 273 shows evidence of multiple ice sheet grounding events in central and eastern ross sea strata a recipient of both west and east antarctic ice sheets from the late oligocene until the present we suggest that the west and east antarctic ice sheets are dynamic and have gone through a full spectrum of thermal states temperate through polar since the late oligocene and not necessarily in any particular preferred temporal order statistical analysis of the spatial distribution of seismic facies within seismic cores indicates that tectonic influence on distribution of basal substrate is a significant contributor to spatial variability of subglacial depositional processes and therefore distribution of subglacial facies

acquisition geometry analysis in complex 3d media increasingly we must deal with complex subsurface structures in seismic exploration often resulting in poor illumination and therefore poor image quality consequently it is desirable to take into consideration the effects of wave propagation in the subsurface structure when designing an acquisition geometry we developed a new model based implementation of the previously introduced focal beam analysis method the method s objective is to provide quantitative insight into the combined influence of acquisition geometry overburden structure and migration operators on image resolution and angle dependent amplitude accuracy this is achieved by simulation of migrated grid point responses using focal beams note that the seismic response of any subsurface can be composed of a linear sum of grid point responses the focal beams have been chosen because any migration process represents double focusing in addition the focal source beam and focal detector beam relate migration quality to illumination properties of the source geometry and sensing properties of the detector geometry respectively wave equation modeling ensures that frequency dependent effects in the seismic frequency range are incorporated we tested our method by application to a 3d salt model in the gulf of mexico investigation of well sampled all azimuth long offset acquisition geometries revealed fundamental illumination and sensing limitations further results exposed the shortcomings of narrow azimuth data acquisition the method also demonstrates how acquisition related amplitude errors affect seismic inversion results

a modeling approach to wide azimuth design for subsalt imaging subsalt image quality in the deepwater gulf of mexico is often very poor with conventional narrow azimuth towed streamer nats surveys even when the most advanced processing and imaging methods available are used with great care the reasons most often cited for the poor image quality are failure to adequately suppress free surface multiples errors in the velocity model and illumination problems

water masses distribution in the southern ocean improvement of an extended omp eomp analysis abstract the southern ocean so is a major part of the global ocean circulation the formation and mixing of water masses in the so cause changes in the northward flow of the meridional overturning circulation and as a consequence in the earth s climate there have been numerous studies of the so but a full understanding is difficult to achieve due to the complexity of the processes of formation and mixing of the different water masses this work aims to clarify some of these aspects through an extended optimum multiparametric analysis using data downloaded from the glodap and carina databases a total of 11 source water masses were selected accurately describe the physical and biochemical properties of the so shelf surface waters were included in order to accommodate the complex shelf processes involved in the formation of antarctic bottom waters the methodology here developed takes into account the remineralisation of organic matter and as an improvement the variability of data related to the processes of dissolution of caco 3 and opal the results from this analysis are accurate and reliable and led to very informative conclusions thus a volumetric census is presented which confirms circumpolar deep water cdw 53 3 of the so volume as the most volumetrically important water mass in the so followed by antarctic bottom water aabw 17 0 9 and north atlantic deep water nadw 13 0 8 aabw properties are the result of the predefined combination of its three major types i e 77 weddell sea bottom water 20 ross sea bottom water and 3 adelie bottom water cdw comprises 65 aabw 30 nadw and 5 antarctic intermediate water according to the relationship between their conservative properties potential temperature and salinity therefore the volume occupied by aabw and nadw in the so rises to 51 2 and 28 0 8 respectively the ratio between aabw and nadw is 1 79 0 03 which is inside the expected range of 1 3 considering the atlantic sector of the so 70 w 80 e which is the more relevant in terms of aabw production aabw represents 60 0 2 of the volume of the sector the estimated ventilation time is approximately 250 years the same period as for the whole so this demonstrates the very important role of shelf processes in the quantity of aabw formed in the so and its crucial role in terms of global climate

landscape modification in response to repeated onset of hyperarid paleoclimate states since 14 ma atacama desert chile the landscape of the hyperarid atacama desert in northern chile records extremely slow change on earth s surface disputed ages for the onset of hyperaridity range from the late paleogene through the pleistocene a long term paleoclimate record is recorded in a nonmarine basin whose fill is primarily alluvial strata for this setting the primary proxies for climate state are the mineralogical and chemical composition of soil which varies across a precipitation gradient and the landforms and deposits of alluvial fans during the most recent 15 million years five climate related landscape stages are resolved for the pampa del tamarugal sedimentary basin with each successively younger stage inset lower in the local topography than its predecessor the earliest landscape stage is expressed as a set of alluvial strata inherited from a time of arid or semi arid climate ca 14 12 ma the younger four landscape stages generated a composite long lasting exposure surface predominantly hyperarid conditions have persisted since ca 12 1 ma during which four intervals of arid to semi arid climate occurred each wet interval was short lived a million years or less whereas some of the hyperarid periods were lengthy 1 5 m y the hyperarid intervals were roughly 11 5 5 ma 4 5 4 ma 3 6 2 6 ma 2 2 1 ma and repeated intervals during the last 1 m y the onset of hyperaridity ca 12 ma likely reflects the growth of the andes mountains above a climate threshold in contrast sea surface temperature variability likely has controlled atacama paleoclimate changes since the late miocene

late pleistocene and holocene sedimentation on the george v continental shelf east antarctica abstract climatically controlled glaciological and oceanographic environmental changes off the george v coast during the late pleistocene and holocene have been reconstructed from changes in sedimentation processes the evolution of a sediment drift deposit mertz drift located in the deep trough on the shelf has been assessed using a sedimentological approach up to 5 5 m long cores have been collected four late pleistocene to holocene sediment units have been distinguished on the basis of their physical properties grain size distributions geochemical characteristics and ages the basal unit 1 is a grey sandy clayey diamicton 27 37 wt sand deposited before 14 000 14 c yr before present 14 c yr bp unit 1 represents a late pleistocene sub ice shelf water lain till overlain by a thin current winnowed sandy sub unit unit 2 is a massive siliceous sandy mud 11 30 wt sand rich in ice rafted debris deposited between about 14 000 and 5000 14 c yr bp it likely represents an open marine setting proximal to a retreating ice front where strong bottom currents were frequent the overlying unit 3 is a laminated siliceous mud and diatomaceous ooze with less terrigenous material 4 5 wt average sand deposited between 5000 and 3000 14 c yr bp the low wet bulk density values 3 and mass specific magnetic susceptibility values 8 m 3 kg of sediments of unit 3 are a consequence of the high content of biogenic material c org content 1 wt biogenic opal averaging 55 wt unit 3 is probably related to a phase of increased sediment accumulation on the drift site and low bottom current activity on the shelf with a stratified upper water column that could have lead to an enhanced primary productivity occurrence of crossed lamination indicates episodes of slightly enhanced bottom currents probably with velocities up to 3 5 cm s the top unit 4 is a bioturbated siliceous sandy mud on average 50 cm thick deposited under an energetic bottom current regime after about 3000 14 c yr bp this regime is probably related to the activation of a brine rejection mechanism and is linked to the formation of high salinity shelf water hssw in a coastal polynya which causes winnowing of the shelf deposits in contrast the mid holocene setting was characterised by weaker bottom currents that together with high inputs of organic material from the photic zone allowed for the deposition of thick fine grained sediments of unit 3 resulting in an anoxic environment

multi azimuth and wide azimuth seismic shallow to deep water exploration to production ten years is a long time in geophysics in the early days of 3d seismic surveys in the 1980s say it might have taken two years to acquire and process a 3d survey and many business decisions simply could not wait that long by the mid 1990s our seismic contractors had done a wonderful job of making 3d seismic faster and cheaper while making it better truly a class act thanks to them the overwhelming technical advantages of 3d are in routine use in almost every possible application today

deglacial ocean and climate seasonality in laminated diatom sediments mac robertson shelf antarctica the palaeoceanography and climate history of the east antarctic margin eam are less well understood than those of west antarctica yet the eam plays an important role in deep ocean circulation and the global ocean system and has likely done so in the past deglacial age marine sediments from the eam provide clues about its past role during this critical period of rapid climate change several deep basins across the eam such as iceberg alley 67 s 63 e on the mac robertson shelf mrs accommodate thick marine sequences that archive the deglaciation in the form of diatom rich continuously laminated varved sediments these laminated sediments are pristinely preserved and contain seasonal and long term information on the cryospheric and palaeoceanographic changes associated with the rapid retreat of the glacial ice sheet across the mrs we present results of microfabric analysis of the lower 2 m of deglacial varves from jumbo piston core jpc43b iceberg alley backscattered electron imagery bsei of polished thin sections and scanning electron microscope secondary electron imagery sei of lamina parallel fracture surfaces are used to analyze the varves one hundred and ninety two laminations are investigated and their nature and temporal significance are discussed in terms of seasonal deposition and cyclicity of diatom species our high resolution palaeodata record exceptionally high diatom production and silica flux associated with the retreat of the east antarctic ice sheet and seasonal sea ice changes along the eam this information is invaluable for assessing cryospheric oceanographic variation and therefore the local and regional response to this period of rapid climate change varves are made up of lamina couplets comprising i thickly laminated to thinly bedded orange orange brown very pure diatom ooze dominated by hyalochaete chaetoceros spp vegetative cells and resting spores and ii brown blue grey terrigenous angular quartz sand silt and clay with an abundant mixed diatom flora the colour variation between these two types of lamination is striking using floristic and textural information we interpret the diatom oozes as spring flux and the terrigenous laminae as summer flux each couplet pair represents one annual cycle and reflects seasonal changes in nutrient availability and stratification associated with the cyclical advance and retreat of seasonal sea ice the diatom oozes can reach up to 7 5 cm in thickness indicating enormous silica flux to the sea floor associated with ice sheet retreat

west antarctic ice streams draining into the ross ice shelf configuration and mass balance extensive airborne radar soundings closely tied to accurately located ground stations made over a portion of the west antarctic inland ice sheet and the ross ice shelf have enabled us to map the boundaries of the ice streams and their flow bands on the ross ice shelf the surfaces of the active ice streams a and b are heavily crevassed but there are no visible crevasses on ice stream c however the existence of numerous crevasses at a depth of about 35 m implies that ice stream c ceased to be active about 250 years ago there is a complex zone at the head of ice stream b that suggests that ice stream b is currently widening and advancing toward the interior of the ice sheet the grounding lines between the inland ice and the ice shelf were mapped from the surface elevations using the requirement of hydrostatic balance and the character of the radar echoes the inland ice is more extensive than previously mapped and includes a large weakly grounded area downstream of ice streams a and b where the surface elevations are barely above hydrostatic equilibrium crary ice rise extends 70 km upstream of the previously mapped position to relate surface elevation data from satellite observations to sea level three geoidal models were tested we conclude that the gem 10c model is the best of the three for this section of antarctica a new map of surface elevation shows deep marginal troughs and longitudinal ridges along ice streams a and b but not on ice stream c whose surface contours show signs of stagnation ice stream c shows a strongly positive and ice stream b a significantly negative net balance rate ice streams a and d also show a significantly negative net flux whereas ice streams e and f do not the overall net balance of this part of the west antarctic inland ice is suggestively negative 23 15 km3 yr 1 from the measured flux into the ross ice shelf and previous measurements we calculate an average basal melt rate from beneath the ice shelf of 0 12 0 03 m yr 1

a threshold in soil formation at earth s arid hyperarid transition the soils of the atacama desert in northern chile have long been known to contain large quantities of unusual salts yet the processes that form these soils are not yet fully understood we examined the morphology and geochemistry of soils on post miocene fans and stream terraces along a south to north 27 to 24 s rainfall transect that spans the arid to hyperarid transition 21 to 2 mm rain y 1 landform ages are 2 my based on cosmogenic radionuclide concentrations in surface boulders and ar isotopes in interbedded volcanic ash deposits near the driest site indicate a maximum age of 2 1 my a chemical mass balance analysis that explicitly accounts for atmospheric additions was used to quantify net changes in mass and volume as a function of rainfall in the arid 21 mm rain y 1 soil total mass loss to weathering of silicate alluvium and dust 1030 kg m 2 is offset by net addition of salts 170 kg m 2 the most hyperarid soil has accumulated 830 kg m 2 of atmospheric salts including 260 kg sulfate m 2 and 90 kg chloride m 2 resulting in unusually high volumetric expansion 120 for a soil of this age the composition of both airborne particles and atmospheric deposition in passive traps indicates that the geochemistry of the driest soil reflects accumulated atmospheric influxes coupled with limited in soil chemical transformation and loss long term rates of atmospheric solute addition were derived from the ion inventories in the driest soil divided by the landform age and compared to measured contemporary rates with decreasing rainfall the soil salt inventories increase and the retained salts are both more soluble and present at shallower depths all soils generally exhibit vertical variation in their chemistry suggesting slow and stochastic downward water movement and greater climate variability over the past 2 my than is reflected in recent 100 y rainfall averages the geochemistry of these soils shows that the transition from arid to hyperarid rainfall levels marks a fundamental geochemical threshold in wetter soils the rate and character of chemical weathering results in net mass loss and associated volumetric collapse after 105 to 106 years while continuous accumulation of atmospheric solutes in hyperarid soils over similar timescales results in dramatic volumetric expansion the specific geochemistry of hyperarid soils is a function of atmospheric sources and is expected to vary accordingly at other hyperarid sites this work identifies key processes in hyperarid soil formation that are likely to be independent of location and suggests that analogous processes may occur on mars

modelling rates of sedimentation from icebergs abstract icebergs transport debris from ice masses into the glacimarine environment but iceberg production debris content and sedimentation rate will vary with glacier dynamics and the nature of marine waters a model incorporating glaciological and oceanographic parameters calculates the flux of debris calved in icebergs iceberg melt rates and sedimentation rates with distance from calving tidewater ice fronts the flux of basal debris calved through a 1 m width of tidewater margin is h d c 100 v c where h d and c are basal debris rich ice thickness and sediment content and v c is iceberg calving rate iceberg basal melting for any horizontal interval d x away from the calving glacier is dy m b d x v b where m b is iceberg melt rate and v b is horizontal iceberg velocity sediment release for any x increment depends on iceberg debris concentration and previous berg melt history model parameters vary with the nature of climatic conditions on a continuum from cold polar environments e g high canadian arctic antarctic peninsula through sub polar environments e g baffin island svalbard to more temperate environments e g se alaska these parameters include glacier flow velocity glacier thermal regime basal debris rich ice thickness and marine water temperature model results suggest that iceberg sedimentation rates are lowest for high polar settings and most rapid in warm maritime and some sub polar areas however icebergs in cold waters transport debris to significantly greater distances from the parent glacier the model provides calculations of order of magnitude rates of iceberg sedimentation in varying glacimarine settings

sedimentation beneath ice shelves the view from ice stream b abstract ice shelf development is favored by rapid flow of cold ice from outlet glaciers or ice streams into protected embayments with localized high spots basal melting of ice shelves is rapid near the ice front and may occur near the grounding line ice from outlet glaciers may contain significant englacial debris that is deposited as a dropstone diamicton in regions of basal melting englacial debris is sparse or absent in ice streams evidence from ice stream b draining into the ross ice shelf of west antarctica suggests that the rapid ice velocity arises from deformation of a several meter thick water saturated basal till layer that is eroding an unconformity on sediments beneath and that has deposited a till delta tens of meters thick and tens of kilometers long at the grounding line sea level fall would cause conveyor belt recycling of this till delta and grounding line advance across the ross sea to the edge of the continental shelf forming an ice sheet with a low ice stream profile resting on a several meter thick deforming till layer eroding an unconformity the modern ross sea is characterized by a regional unconformity overlain by a diamicton of probable latest pliocene pleistocene age measuring several meters to tens of meters thick we hypothesize that this diamicton is a deformed glacial till and that the ross sea sediments record one or more expansions of the till lubricated west antarctic ice sheet to the edge of the continental shelf

exploring for a record of ancient martian life the immediate task facing exopaleontology is to define a strategy to explore mars for a fossil record during the decade long exploration program that lies ahead consideration of the quality of paleontological information preserved under different geological conditions is important if we are to develop a strategy with broad applicability the preservation of microbial fossils is strongly influenced by the physical chemical and biological factors of the environment which acting together determine the types of information that will be captured and retained in the rock record in detrital sedimentary systems preservation is favored by rapid burial in fine grained clay rich sediments in chemical sedimentary systems preservation is enhanced by rapid entombment in fine grained chemical precipitates for long term preservation host rocks must be composed of stable minerals that are resistant to chemical weathering and that form an impermeable matrix and closed chemical system to protect biosignatures from alteration during subsequent diagenesis or metamorphism in this context host rocks composed of highly ordered chemically stable mineral phases like silica e g cherts or phosphate e g phosphorites are especially favored such lithologies tend to have very long crustal residence times and along with carbonates and shales are the most common host rocks for the precambrian microfossil record on earth although we make the defensible assumption that mars was more like the earth early in its history clearly the geological and historical differences between the two planets are many such differences must be carefully considered when adapting an earth based strategy to mars

use of total grain size distributions to define bed erosion and transport for poorly sorted sediment undergoing simulated bioturbation abstract flume experiments were conducted using poorly sorted beds made to resemble those glacial deposits that blanket the antarctic seafloor today flow within the flume was gradually increased over 2 cm s 1 increments up to 20 cm s 1 an initial run was made without altering the bed and two additional runs were made in which the bed was mechanically mixed in order to simulate bioturbation initial and efficient transport of a given size particle was determined using total grain size distribution data for samples taken from the residual bed from trays placed at different elevations above the floor of the flume and from the water column using this method we were able to measure the current velocities at which initial movement occurred as well as relate different modes of transport for given size ranges to current velocity without mixing the bed current velocities greater than 16 cm s 1 were required to initiate particle movement but because the bed became armored this initial movement was not reflected in the total grain size distribution of the bed with mixing a residual bed containing little silt and clay was produced at velocities of only a few centimeters per second once fines were removed from the bed sand sized material began to move by either traction or saltation a curve relating current velocity to sediment transport by bed load traction and saltation intermittent suspension and suspension is presented the results of our flume experiments demonstrate how sorted sediments are presently being derived from cohesive often overcompacted poorly sorted glacial sediments on high latitude continental shelves where measured current velocities are less than 20 cm s 1 the antarctic seafloor for example furthermore we have gained important information about the true meaning of grain size data as it relates to current velocity mean grain size sorting and skewness reflect not only current velocity but also the efficiency with which the bed was mixed therefore attempts to reconstruct paleovelocity using only these parameters may be meaningless

antiquity of aridity in the chilean atacama desert the atacama desert of northern chile and southern peru has one of the longest histories of arid conditions known although most studies have focused on the hyper aridity prevalent since the miocene all terrestrial sediments in the region from the late triassic onwards also record evaporitic and thus arid climates supergene mineralization in the region did not develop under a more humid climate conducive to deep weathering but under arid conditions these processes may have been facilitated by hydrological changes during miocene uplift and drainage incision but were operational prior to the uplift similarly global cooling and changes to oceanic circulation in the post miocene period only accentuated existing conditions a whole regolith perspective is vital to understanding the history of aridity in the atacama desert and its relevance to arid zone morphogenesis regolith formation and supergene mineralization in particular the long history of aridity raises the possibility that supergene mineralisation under the appropriate conditions form in arid environments instead of requiring humid conditions

terrestrial analogs for interpretation of infrared spectra from the martian surface and subsurface sulfate nitrate carbonate and phyllosilicate bearing atacama desert soils 1 hyperarid 6 5 m was not suited for salt and phyllosilicate detection because of overlapping spectra from primary silicates e g feldspar water and carbon dioxide the visible near infrared 0 35 2 5 m region was suited for detecting carbonate nitrate gypsum water of hydration and phyllosilicate hydroxyls without interference from primary silicates however gypsum water of hydration features can obscure phyllosilicate hydroxyl carbonate and nitrate features if gypsum levels are high overtone combination absorption features in the midinfrared were determined to be the best indicators of sulfate 4 48 4 70 m nitrate 4 12 m and carbonate 3 98 m because interferences from overlapping primary silicate and water features are not present in this region interferences from co2 and thermal emission effects in the overtone combination region are possible but may be minimized by corrective techniques infrared analysis of atacama desert soils can provide insight into the spectral search of sulfate nitrate carbonate and phyllosilicate containing soils on mars

distribution of polar membrane lipids in permafrost soils and sediments of a small high arctic catchment the distribution of bacteriohopanepolyols bhps and intact polar membrane lipids ipls was studied in different soil profiles and in fluvial and marine sediments along the pathway of transport in a small catchment in the high arctic at ny alesund svalbard 79 n 12 e both groups of cellular membrane lipids have been used as biomarkers for determining major microbial groups and biogeochemical processes in natural environments little is known about their distribution and usefulness as environmental markers in the arctic in this study we show that both membrane lipid groups are variably distributed in the drainage area of the broggerbreen glacier with highest abundance and diversity in the organic mat overlying the mineral soils as well as in mossy surface soil the bhp and ipl composition and abundance both indicate a larger community of phototrophic bacteria in the organic mats and fluvial sediments the greater diversity and abundance of bhps relative to ipls in sub soils including probable markers for cyanobacteria suggest a greater resistance to degradation in contrast ipl concentration decreased strongly with soil depth pointing to their rapid degradation bacterial ipls are thus thought to reflect more reliably the biomass of viable phototrophic bacteria the high concentrations of proposed soil marker bhps adenosylhopane and related structures vs published results and their relative increase with soil depth suggest better preservation and more effective accumulation of the compounds at low temperature

a recount of ross sea waters abstract oceanographic observations within the ross sea have grown dramatically in recent years both in number and quality this has prompted a parallel recount of the circulation and structure of all water masses in the southwestern continental margins of the pacific ocean a high resolution set of horizontal property distributions was combined into a new climatology which in turn is the basis of a fine volumetric s census of all ross sea water masses inshore of the shelf break 700 m isobath the ross sea volume 25 10 4 km 3 partitioning into layers of neutral density n is 25 in the top layer n 3 of antarctic surface water aasw 22 in the middle layer 28 00 kg m 3 n 3 of oceanic thermocline water 12 and modified circumpolar deep water mcdw 10 and 53 in the bottom layer n 28 27 kg m 3 of shelf water sw 1 85 c 22 precursor of the antarctic bottom water aabw offshore aasw flows westward along the outer shelf and southward along the eastern coast past cape colbeck oceanic thermocline waters 28 00 kg m 3 n 3 cross the shelf break west of 170 w and follow southward paths along banks shoaling progressively to near the sea surface of the central and western inner shelves winter buoyancy loss converts aasw and oceanic thermocline water into denser types of mcdw and sw which move cyclonically toward the sills of major troughs the census shows a continuous mode of relatively dense mcdw 28 10 kg m 3 n 3 directly linked to the circumpolar deep water cdw offshore effectively ventilating and freshening the deep ocean at levels below the salinity maximum and above aabw mcdw outflows from the ross sea shelf are traced to the antarctic circumpolar current near 155 e into the australian antarctic basin along the northern flank of the southwest pacific ridge and to near 135 w past the eastern end of the ross gyre two sources of salty sw are inferred near the coastal polynyas in the terra nova bay and western ross ice shelf areas the latter contributes to a major outflow of ice sw that reaches the shelf break along 180 vertical mixing of mcdw and sw produce msw over the shelf continuing over the sills as new aabw export of low salinity aabw s

enhanced prestack depth imaging of wide azimuth data from the gulf of mexico a case history we present a case study of enhanced imaging of wide azimuth data from the gulf of mexico utilizing recent technologies and we discuss the resulting improvements in image quality especially in subsalt areas relative to previous results the input seismic data sets are taken from many large scale wide azimuth surveys and conventional narrow azimuth surveys located in the mississippi canyon and atwater valley areas in the course of developing the enhanced wide azimuth processing flow the following three key steps are found to have the most impact on improving subsalt imaging 1 3d true azimuth surface related multiple elimination srme to remove multiple energy in particular complex multiples beneath salt 2 reverse time migration rtm based delayed imaging time dit scans to update the complex subsalt velocity model and 3 tilted transverse isotropic tti rtm to improve image quality our research focuses on the depth imaging aspects of the project with particular emphasis on the applicati

glaciomarine sedimentation in disraeli fiord high arctic canada abstract disraeli fiord represents a glaciomarine environment unique to the north coast of ellesmere island featuring floating glacier tongues multi year landfast sea ice and a strongly stratified water body which results from enclosure of the fiord by ward hunt ice shelf it is a very low energy depositional environment even at sites proximal to glaciers sediment enters the fiord by interflow and is deposited through suspension settling ice rafting is precluded by the year round sea ice cover sedimentation rates in the inner fiord since about 7000 yrs b p are estimated to be 5 10 cm ka a reflection of the limited sediment influx from the cold based glaciers which contact the fiord changes in sediment structure through the holocene reflect changes in the rate and process of sediment input as well as changes in fiord circulation all of which relate to regional climate during deglaciation early holocene sedimentation rates were orders of magnitude greater than at present subglacial meltwater was the dominant source of inflow with sediment transported in turbid plumes as over or interflow and deposited through suspension settling this is supportive of other studies indicating that a pronounced climatic amelioration led to warm based glaciers at this time

marine sedimentation at a calving glacier margin a 2 month study at a subpolar tidewater glacier was conducted at anvers island antarctic peninsula lat 64 s to improve understanding of sedimentary processes and associated deposits in glacial marine settings data collected in the ice proximal environment were 1 brash ice size distribution and melt rates to assess sediment source and transport mechanisms 2 conductivity temperature turbidity depth cttd profiles water samples and sediment trap catches to study processes and patterns of sediment dispersal 3 bottom cores and grabs to document recent glacial marine sedimentation and 4 remotely operated vehicle video surveys of the ice terminus and sea bottom to obtain images of physical and biological processes the water column is stratified and a halocline occurs at 20 30 m water temperature ranged from 1 to 1 6 c salinity was 32 34 and suspended solids were 3 5 mg l well above the bottom ephemeral turbid horizons contain 8 15 mg l suspended solids rare surface plumes and a quasipermanent turbid layer produced by resuspension during calving events reach 25 35 mg l meltwater drains from the glacier surface but no subglacial meltwater was detected directly entering the sea the most important sources of sediment appear to be the direct melting of the submerged ice front and melting of calved glacial ice most fragments of floating ice melt within 1 km of the ice front some sediment may be contributed as low density 1 1 g cm 3 algae bound sediment pellets by meltwater streams draining the ablating ice surface sediment enters the stratified water column and is moved by tidal and wind driven circulation marine sedimentation rates are low 3 mm yr relative to depth of bioturbation resulting in unstratified sandy mud with dispersed clasts

quantifying and increasing the value of multi azimuth seismic conventional marine exploration offshore nile delta is challenged by shallow heterogeneities and a deep complex anhydrite layer called the messinian these subsurface complexities cause variable illumination and strong diffracted multiples resulting in imaging challenges below the anhydrite on conventional narrow azimuth towed streamer acquisition because the recording antenna is too small figure 1a additionally it has proved difficult to build the detailed depth migration velocity model required to correctly image below the messinian layer multi azimuth maz acquisition using time domain processing however has been very successful in addressing both the noise and illumination problems in the nile delta the increased azimuthal and crossline offset coverage bigger antenna is achieved by acquiring six conventional marine surveys over the same area at 30 sail line increments figure 1b

cenozoic prograding sequences of the antarctic continental margin a record of glacio eustatic and tectonic events abstract sedimentary sections up to 6 14 km thick lie beneath many areas of the antarctic continental margin the upper parts of the sections contain up to 6 km of cenozoic glacial and possibly non glacial sequences that have prograded the continental shelf up to 85 km we describe the cenozoic sequences using two general categories based on their acoustic geometries type ia sequences which account for most prograding of the antarctic continental shelf have complex sigmoidal geometries and some acoustic characteristics atypical of low latitude margins such as troughs and mounds lying parallel and normal to the shelf edge and high velocities 2 0 2 6 km s for flat layers within 150 m of the seafloor type iia sequences which principally aggrade the paleoshelf lie beneath type ia sequences and have mostly simple geometries and gently dipping reflections the prograding sequences are commonly located near the seaward edges of major mesozoic and older margin structures relatively rapid cenozoic subsidence has occured due to the probable rifting in the ross sea thermal subsidence in the antarctic peninsula and isostatic crustal flexure in wilkes land in prydz bay and the weddell sea prograding sequences cover mesozoic basins that have undergone little apparent cenozoic tectonism grounded ice sheets are viewed by us and others as the principal mechanism for depositing the antarctic prograding sequences during the initial advance of grounded ice the continental shelf is flexurally overdeepened the inner shelf is heavily eroded and gently dipping glacial strata are deposited on the shelf i e type iia sequences the overdeepened shelf profile is preserved a during glacial times by grounded ice sheets episodically crossing the shelf eroding sediments from onshore and inner shelf areas and depositing sediments at the front of the ice sheet as outer shelf topset banks and continental slope foreset aprons i e type ia sequences and b during interglacial times like today by little or no clastic sedimentation on the continental shelf other than beneath retreated ice shelves lying far from the continental sheld edge ice streams carve broad depressions across the shelf and carry abundant basal sediments directly to the continental shelf edge thereby creating troughmouth fans and sheet like prograding sequences i e type ia sequences numerous acoustic unconformities and multiple overcompacted layers within the prograding sequences suggest major fluctuations of the antarctic ice sheet the available drilling and seismic interpretations provide the following history 1 cenozoic ice sheets have existed in places near the continental shelf since middle to late eocene time 2 a grounded antarctic ice sheet first expanded to the continental shelf edge with probable overdeepening of the outer shelf in late eucene to early oligocene time in prydz bay possibly in early miocene time in the ross sea and at least by middle miocene time in the weddell sea 3 the relative amounts of shelf prograding and inferred ice volume variations and related sea level changes have increased since middle to late miocene time in the eastern ross sea prydz bay and possibly weddell sea our analysis is preliminary further acoustic surveys and scientific drilling are needed to resolve the proximal antarctic record of glacio eustatic climatic and tectonic events recorded by the prograding sequences

keel depths of modern antarctic icebergs and implications for sea floor scouring in the geological record abstract icebergs affect the geological record through the scouring or ploughing action of their keels reworking sediments where they contact the sea floor satellite radar altimeter measurements of the surface elevation of the marine margins of the antarctic ice sheet are inverted to produce ice thickness values these data are assumed to represent the keel depths of newly calved icebergs there are three peaks in the frequency distribution of antarctic iceberg keel depths a about 140 200 m in thickness associated with smaller ice shelves fringing antarctica e g wilkins george vi and brunt ice shelves b about 250 300 m from large ice shelves e g ross ronne amery and c approximately 500 600 m from fast flowing ice sheet outlet glaciers e g pine island and dibble glaciers together with the filchner ice shelf controls on iceberg keel depth are ice thickness at the grounding line creep thinning and the rate of melting freezing at the floating ice shelf base with distance to the calving margin the distribution of sea floor scours produced by iceberg grounding is dependent on the changing form and flow of the glaciers and ice sheets from which icebergs are derived and on berg drift tracks and melt rates sea floor evidence for icebergs with particularly deep keels has sometimes been interpreted to indicate the presence of extensive former ice shelves however the largest modern antarctic ice shelves do not produce large numbers of icebergs thicker than about 350 m implying that sea floor scours found in deeper water are unlikely to be an indicator of extensive past ice shelf development iceberg scours found at water depths in excess of about 500 m in the geological record are instead probably indicative of either a the former presence of fast flowing ice sheet outlet glaciers b ice shelves fed from major interior basins where lateral spreading is constrained topographically or c a pulse of large icebergs released during major deglaciation or ice sheet collapse

finely sampled 3d angle gathers from sparse obn data large scale deepwater ocean bottom node obn surveys typically use a node spacing of about 400 m we make 3d angle gathers from obn data by mapping image traces to the reflection azimuth and reflection angle domain large node spacing may coarsely sample the seismic data in these angles this may result in degraded and noisy angle gathers unless we properly account for the sampling during processing we describe a method for making high quality 3d angle gathers on finely sampled angle grids we do this by properly band limiting the mapping operator with sinc functions defined in the angle domain this method allows us to oversample the 3d angle gathers accurately in the angle domain and obtain high quality results we demonstrate our method with deepwater gulf of mexico node data and show that we can produce high quality gathers even with 800 m node spacing the angle gathers derived from these wider node data preserve residual moveout and therefore are suitable for model building our results add confidence that data acquired with nodes spaced farther apart than 400 m can be processed and imaged successfully

glacial interglacial changes in global deepwater circulation variations in the areal extent of the cryosphere appear to exert an important control over glacial interglacial changes in the mode of formation and source areas for deepwater and bottom water masses during interglacials when ice extents are minimal these water masses form by mechanisms which are well documented for the present interglacial climatically related advances and retreats of sea ice in the northern hemisphere during glacials probably resulted in shifting loci of formation for each of the three types of north atlantic deep water nadw probable glacial advances of grounded ice sheets to the continental shelf margins in antarctica precluded formation of antarctic bottom water aabw at the presently active continental shelf sites because these shifts in source areas for aabw and nadw probably involved source waters with salinity temperature oxygen content and nutrient levels that differed from modern values deep and bottom waters are likely to have had different characteristics in glacials than they do during interglacials

the temperature and salinity fine structure of the ocean under the ross ice shelf a series of temperature and salinity profiles was made in the ocean under the ross ice shelf at 82 22 5 s 168 37 5 w where the ice was 420 and the underlying seawater 240 m thick the water structure consisted of a fairly well mixed low salinity layer at the in situ freezing point of the ice water interface about 30 m thick a transition layer characterized by intrusions about 85 m thick a strongly stratified layer with increasing temperature and salinity about 50 m thick another transition layer characterized by intrusions about 45 m thick and an isohaline bottom layer with a nearly abiabatic temperature gradient about 30 m thick the temperature fluctuations in the two transition layers can be attributed mainly to intrusive activity even though internal wave activity was highest in these regions in the central stable layer internal waves probably contribute to the temperature fluctuations equally with intrusions the internal wave dropped displacement spectrum seems to be very similar to those found in the open ocean some profiles showed intrusions in the top transition layer colder than the top boundary layer and some showed intrusions in the bottom transition layer warmer than the bottom boundary layer indicating that horizontal shear must be present internal waves of near inertial frequency excited by the semidiurnal tides combined with shear induced instabilities seem to be the likely causes of the observed fine structure

sea ice and oceanic processes on the ross sea continental shelf we have investigated the spatial and temporal variability of antarctic sea ice concentrations on the ross sea continental shelf in relation to oceanic and atmospheric forcing sea ice data were derived from nimbus 7 scanning multichannel microwave radiometer smmr brightness temperatures from 1979 1986 ice cover over the shelf was persistently lower than above the adjacent deep ocean averaging 86 during winter with little month to month or interannual variability the large spring ross sea polynya on the western shelf results in a longer period of summer insolation greater surface layer heat storage and later ice formation in that region the following autumn newly identified pennell and ross passage polynyas near the continental shelf break appear to be maintained in part by divergence above a submarine bank and by upwelling of warmer water near the slope front warmer subsurface water enters the shelf region year round and will retard ice growth and enhance heat flux to the atmosphere when entrained in the strong winter vertical circulation temperatures at 125 m depth on a mooring near the ross ice shelf during july 1984 averaged 0 15 c above freezing sufficient to support a vertical heat flux above 100 w m2 monthly average subsurface ocean temperatures along the ross ice shelf lag the air temperature cycle and begin to rise several weeks before spring ice breakout the coarse smmr resolution and dynamic ice shelf coastlines can compromise the use of microwave sea ice data near continental boundaries

hypersaline conditions during deposition of the calcare di base revealed from archaeal di and tetraether inventories abstract the calcare di base is a widespread messinian carbonate formation in the mediterranean especially in sicily and calabria italy the environmental conditions under which these limestones were deposited their formation mechanism and the timing of deposition are a matter of debate in order to shed new light on their formation the lipid biomarker inventories of calcare di base from four locations in sicily and calabria were studied following petrographical and mineralogical characterization of the limestone samples the mineralogy is chiefly calcite the microfabric is mostly peloidal and partly laminated or brecciated deposition took place at high salinity as confirmed by numerous pseudomorphs after halite long chain n fatty acids were the most abundant lipid biomarkers in samples from all sites but isoprenoid alcohols were also abundant the most prominent archaeal compounds were diphytanyl glycerol diethers dgds and glycerol dibiphytanyl glycerol tetraethers gdgts among these archaeol and gdgt 0 caldarchaeol predominated respectively other gdgts were virtually absent minor amounts of c 20 25 dgd extended archaeol a biomarker for halophilic archaea were detected in all samples the 13 c values of caldarchaeol avg 20 and archaeol avg 11 varied widely indicating that these compounds derived from distinct archaeal precursor lipids based on lipid biomarker patterns the calcare di base had been previously considered to represent a normal marine deposit in contrast to the evaporitic gypsum and halite deposits in messinian successions the archaeal biomarker inventories from the calcare di base samples reported here in conjunction with the occurrence of pseudomorphs after halite reveal that deposition took place in a hypersaline environment

diatom flux in mcmurdo sound antarctica abstract quantitative floral analyses have been performed on sea ice sediment trap and surface sediment samples collected from six sites in mcmurdo sound antarctica although diatom abundances in the sea ice reach 108 109 cells m 2 maximum diatom fluxes between october december 1984 as measured in the sediment trap samples are only 105 107 individuals m 2 day 1 the cumulative flux of diatoms for this three month period is approximately 107 109 individuals m 2 possibly an order of magnitude less than the sea ice abundances implying that diatom and opal flux must significantly increase when the sea ice melts and releases those particles previously trapped in the ice five species dominate the sea ice assemblage amphiprora sp pleurosigma sp nitzschia stellata pinnularia quadratarea andnitzschia curta these species are also common in the water column along withthalassiosira spp a genus rarely found within the sea ice within the upper 250 m of the water column at a site in granite harbor diatom flux decreases between 47 79 from 34 to 220 m opal flux however decreases by only 13 40 over this same interval indicating that dissolution of thinly silicified diatom frustules has occurred at mid water depths increases in absolute diatom flux of two species in particular nitzschia curta andthalassiosira spp may indicate their transport from other areas at all sites the greatest increase in diatom flux occurs just above the sea floor resuspension of diatom tests and or lateral advection creates a near bottom nepheloid layer in which significant modification of the diatom assemblage occurs a combination of preferential dissolution of those forms which dominate the sea ice and dilution of the assemblage with resuspended and or advected diatoms representative of many year averages of the flora may be responsible for the production of a sediment assemblage primarily made up ofthalassiosira spp nitzschia curta and other robust forms ofnitzschia

comment on hydrocarbon biomarkers thermal maturity and depositional setting of tasmanite oil shales from tasmania australia by a t revill j k volkman t o leary r e summons c j boreham m r banks and k denwer

150 million years of climatic stability evidence from the atacama desert northern chile the sedimentary succession in the atacama desert records deposition under an arid to semiarid climate from the late jurassic 150 ma to the present day palaeomagnetic data indicate no significant latitudinal movement of this area since the late jurassic the present day location of the atacama within the dry subtropical climate belt is the principal cause of aridity this situation is likely to have prevailed since the late jurassic supplemented by 1 the continentality effect enhanced by the gondwanan landmass and 2 the presence offshore of a cold upwelling current from at least the early cenozoic onwards and possibly earlier resulting in conditions promoting climatic stability and desert development rapid and extreme climatic fluctuations during the plio pleistocene were not sufficient to destabilize the climate within the atacama comparison with other long lived deserts e g sw usa namib sahara and australia suggests that the atacama is the oldest extant desert on earth

characterisation of a landslide fissure pattern by integrating seismic azimuth tomography and geotechnical testing in order to characterise the fissure field provoked by the super sauze mudslide south french alps in the surface material we conducted a seismic survey and compared the resulting p wave tomogram to surface observations and cone penetrometer tests the first results show that the distribution of the p wave velocities correlates well with the fissure parameters i e density depth and thickness estimated from digital photographs and field observations in addition one finds good agreement between the p wave velocity distribution and the material resistances interpolated from the penetrometer tests indicating a probable physical relationship the results of our study demonstrate that seismic azimuth tomography is efficient for characterising fissure systems with the main advantage of the method lying in the integration capacity of wave propagation compared to local mechanical tests provided that the correlation between p wave velocity and fissure characteristics are confirmed at other sites this technique could be the basis for future and more systematic studies of high hazard zones related to landslides copyright 2011 john wiley sons ltd

low frequency currents and continental shelf waves in the southern weddell sea abstract the salient features of low frequency current fluctuations obtained from an analysis of eight current meter records from the continental shelf and slope of the southern weddell sea are compared to baroclinic and barotropic theories a simple baroclinic theory of internal waves is used successfully to predict high frequency spectral cutoff values from low frequency velocity ellipse calculations made from the continental slope mooring data the success of this theory indicates that the higher spectral energy levels observed over the slope compared to the shelf are probably due to baroclinic motions a barotropic model of free continental shelf waves probably by saint guily 1976 is adapted for the local topography and the predictions of the model compared to observations coherences and phases between moorings separated by 10 and 160 km in the along shelf direction provide substantial evidence of the existence of shelf waves as predicted by the theory for periods of 3 60 days and for the lowest

new insights into quaternary glacial dynamic changes on the george v land continental margin east antarctica abstract the continental margin of the george v land represents the seaward termination of one of the largest sub glacial basins the wilkes basin of the east antarctic ice sheet eais and hence is a potentially useful site for the investigation of the cenozoic glacial history of antarctica because the seafloor morphology relates strictly to recent glacial marine sedimentary processes we have compiled all available echo soundings data collected until the year 2001 and integrated the data set with satellite altimetry data as a result we have produced a new bathymetric map of the margin covering an area of more than 80 000 km 2 with a spatial resolution of about 1 km the bathymetric data have been integrated with sub bottom profiler data with the purpose of defining sedimentary processes and their variations during the quaternary the continental shelf of the wilkes land margin is characterised by alternating banks and glacial troughs connected to sub marine canyons that cut into the continental slope our study focussed on the continental rise where asymmetrical ridges alternate with large deep sea channels the ridges have a long gentle eastern side and short steep western side with axis elongated approximately in north south direction perpendicular to the margin the channels represent the main sediment drainage pattern feeding the ridge depositional system found along the continental rise the sediment is supplied to the continental shelf edge by ice sheets and sediment gravity flows are considered the main process for sediment supply to the rise the modern sedimentary environment of the deep margin is affected by turbiditic down slope sediment transfer with a minor contribution from along slope contour currents the wega channel is currently affected by transport and settling of sediment through high salinity shelf water hssw originating on the continental shelf we infer that thermohaline circulation has contributed to sediment transport and deposition since the mid pleistocene

pleistocene sediments beneath the ross ice shelf we report here the results of new micropalaeontological studies of sediments collected from beneath the ross ice shelf at risp site j9 82 22 s 168 38 w risp sediments hold the key to understanding the history of the west antarctic ice sheet dynamics of marine based ice sheets sedimentation processes that operate beneath ice shelves and perhaps the early glacial history of antarctica risp sediments were formerly assigned an age of late middle miocene on the basis of their diatom flora our diatom analyses do not support this age assignment diatoms in risp cores are of mixed ages ranging from miocene to late quaternary thus indicating that the sediments record a history of reworking the most recent of which could have occurred no earlier than late pleistocene these results support our previous work with ross sea sediments but throw considerable doubt on a recent hypothesis concerning miocene palaeogeographical evolution of the ross sea region

xeropreservation of functionalized lipid biomarkers in hyperarid soils in the atacama desert our understanding of long term organic matter preservation comes mostly from studies in aquatic systems in contrast taphonomic processes in extremely dry environments are relatively understudied and are poorly understood we investigated the accumulation and preservation of lipid biomarkers in hyperarid soils in the yungay region of the atacama desert lipids from seven soil horizons in a 2 5 m vertical profile were extracted and analyzed using gc ms and lc ms diagnostic functionalized lipids and geolipids were detected and increased in abundance and diversity with depth deeper clay units contain fossil organic matter radiocarbon dead that has been protected from rainwater since the onset of hyperaridity we show that these clay units contain lipids in an excellent state of structural preservation with functional groups and unsaturated bonds in carbon chains this indicates that minimal degradation of lipids has occurred in these soils since the time of their deposition between 40 000 and 2 million years ago the exceptional structural preservation of biomarkers is likely due to the long term hyperaridity that has minimized microbial and enzymatic activity a taphonomic process we term xeropreservation i e preservation by drying the degree of biomarker preservation allowed us to reconstruct major changes in ecology in the yungay region that reflect a shift in hydrological regime from wet to dry since the early quaternary our results suggest that hyperarid environments which comprise 7 5 of the continental landmass could represent a rich and relatively unexplored source of paleobiological information on earth

bottom currents sedimentation and ice sheet retreat facies successions on the mac robertson shelf east antarctica abstract measurements of water turbidity currents seafloor sediment samples and geophysical data document the sedimentary processes and the late quaternary sedimentary history of a continental shelf valley system on the east antarctic continental margin the valley is up to 1200 m in depth and strikes across the shelf it is interpreted as having formed by glacial erosion processes on the outer shelf sill of the valley northwestward offshore currents with speeds of up to 0 47 m s referenced to 100 cm above the seabed were recorded over a 10 month period such currents are competent to initiate bedload transport of medium sand and formation of small ripple sized bedforms which explains the occurrence of ripple cross bedding observed in some x radiographs of cores a nepheloid layer with concentrations of up to 3 5 mg l was noted at two stations and the available evidence suggests that density flows resulting from the sea ice brine rejection mechanism are competent to entrain shelf bottom sediments episodically sediment cores taken from this environment document the succession of facies resulting from retreat of glacial ice from the shelf during the holocene transgression under low sea level glacial conditions the ice sheet is interpreted to have been grounded on the outer shelf where it deposited a grounding line moraine rising sea level and global warming caused the ice shelf to retreat leaving a sub ice shelf glacial marine mud this is overlain by a laminated to massively bedded ice rafted debris rich facies interpreted as being deposited at the glacial calving front above this is a siliceous mud and ooze facies having a basal age of about 10 000 years bp characterising modern open marine conditions two types of iceberg keel marks on the outer part of the shelf valley are recognised from sidescan sonographs one relict arcuate type formed during the retreat of the ice shelf prior to 10 000 years bp and a second modern elongate type that is presently being formed near the shelf break by iceberg grounding processes this facies succession has been described from other antarctic shelf environments and is probably representative of facies deposited during holocene glacial retreat from the antarctic shelf

beryllium 10 concentrations in the hyper arid soils in the atacama desert chile implications for arid soil formation rates and el nino driven changes in pliocene precipitation abstract meteoric 10be concentrations in soil were measured to understand the mechanism timescale and climatic dependence of soil formation in the hyper arid atacama desert the observed systematic decline of soil 10be concentrations with depth has been reproduced using a simple model that assumes soil matrix including 10be builds up as layers over time while 10be decays in situ this suggests a mechanism of soil accumulation via atmospheric deposition which is in agreement with stable isotopic evidence the model estimates an age of 6 6 0 4 ma for the total soil profile small discrepancies between the model and observations are likely mainly due to changes in precipitation rates that can impact 10be delivery rates and 10be movement within the profile interpreted in this way the 10be data suggest drying in the atacama after 4 7 ma and returning to an insignificant wet period at 1 ma which was possibly connected to el nino or la nina like climate change

summer plankton production and nutrient consumption patterns in the mertz glacier region of east antarctica abstract we report on a biological and nutrient survey conducted off the eastern adelie and george v coasts of east antarctica in late december 2000 and january 2001 the region was dominated by the mertz glacier tongue mgt and its associated polynya that controlled the amount of open water through the season and influenced stratification near forming and melting ice as in other regions of the southern ocean large concentrations of nitrate phosphate and silicic acid were found chlorophyll levels varied from 0 3 mg m 3 in pack ice and slope regions to greater than 10 mg m 3 in a phaeocystis bloom encountered among grounded ice northeast of the mgt net utilization rates of nutrients were derived from the deficit between measured concentrations and estimated winter values nitrate n n and silicic acid utilization rates ranged from 2 to 12 and 14 to 30 mmol m 2 d 1 respectively and were greatest in commonwealth bay the ratio of nitrate to phosphate utilization was low 10 lower silicic acid to n n ratios were found in regions with substantial populations of phaeocystis sp in the eastern grounded ice region however there was significant variation in the silicic acid to n n utilization that may be induced by mixed layer iron levels that varied from

glaciomarine sediments along the filchner ronne ice shelf southern weddell sea first results of the 1983 84 antarktis ii 4 expedition abstract sediment sampling with box corer and gravity corer was conducted along a profile parallel to the filchner ronne ice shelf from 48 to 61 w twenty two sampling locations were determined after evaluation of 12 and 3 5 khz sub bottom profiling records the sediment retrievals show a wide diversity varying from very well sorted pure sands in the se of the profile to heavily glacially influenced pebbly muds close to the foot of the antarctic peninsula in the middle part of the profile mainly soft sediments of muddy to sandy muds were found which were partially influenced by glacially derived dropstones or accumulations of pebble sized material the striking changes of surface sediments marine to glacial observed along the profile led to an attempt to investigate the concurrence of marine and glacial depositional processes controlling the accumulation of these recent sediments

phytoplankton biomass and photosynthetic competency in the summertime mertz glacier region of east antarctica abstract vertical profiles of water temperature salinity beam transmission density pressure wind speed wind direction phytoplankton biomass chlorophyll a chl a plus phaeophytin a and photosynthetic competency by fast repetition rate fluorometry are presented for the mertz glacier region east antarctica for a 3 week period during the austral summer 2000 2001 injection of low salinity water from the melting of the ice pack formed a shallow ca 25 m mixed layer offshore two distinct deep mixing features were observed associated to varying degrees with high chlorophyll levels and high photosynthetic competency along the adelie land coast a deep mixing layer 1400 m with chl a concentrations of 386 mg m 2 and elevated fv fm 0 5 was observed at the eastern end of the study area along a seaward extension of fast ice a bloom of phaeocystis antarctica bloom formed within a shallow 24 m mixed layer with surface chl a concentrations of ca 8 mg m 3 and elevated fv fm 0 5 this feature also had high surface salinity 34 and was contiguous with a deep mixing feature 236 m frrf parameters fv fm and psii were strongly suppressed in surface waters

late pliocene age for the atacama desert implications for the desertification of western south america the atacama desert forms one of the major hyperarid deserts of the world previous studies suggest that desertification commenced at 14 ma during global climate desiccation sedimentologic data from middle miocene to upper pliocene successions in the modern atacama desert indicate that a semiarid climate persisted from 8 to 3 ma punctuated by a phase of increased aridity at ca 6 ma as such hyperaridity did not commence until the late pliocene implications are 1 that the rain shadow generated by the andean cordillera has had a minor influence on climate change and 2 that the upwelling north flowing cold humboldt current although important in establishing the generally arid climate of western south america did not control the shift to hyperaridity the formation of the hyperarid atacama desert in the late pliocene accompanied the development of the current phase of aridification in the sahara and namib deserts and is attributed to a phase of global climate cooling

diagenesis of sediments beneath the ross ice shelf and their sedimentary history micropalaeontological studies of sediment cores collected from beneath the ross ice shelf antarctica give conflicting stratigraphical interpretations the diatom flora initially indicated an in situ succession of later middle miocene age1 2 which was supported by the occurrence of benthic foraminifera3 however subsequent diatom analyses record the presence of flora with mixed ages mostly miocene but also pliocene and pleistocene throughout both of the two lithological units present in the cores these flora are taken to indicate repeated reworking which most recently occurred no earlier than the late pleistocene4 these contrasting views have since been re affirmed5 6 our studies of sediment geochemistry show self consistent patterns in organic carbon organic nitrogen and sulphur diagenesis which suggest a recent in situ origin at least for the upper unit

organic amine biomarker detection in the yungay region of the atacama desert with the urey instrument 1 the urey in situ organic compound analysis instrument consisting of a subcritical water extractor scwe and a portable microchip capillary electrophoresis instrument called the mars organic analyzer moa was field tested in the atacama desert chile in june 2005 soil samples from the most arid yungay region were collected biomarkers were extracted by the scwe and organic amine composition and amino acid chirality analysis was performed by the moa samples collected from the top 1 cm of duracrust soil but shielded from the ambient environment by rocks were compared to the exposed duracrust the shielded duracrust yielded amines and amino acids ranging from 50 to 100 ppb while amino acid signals from the exposed duracrust were below blank levels samples from buried gypsum deposits located directly above a water flow channel contained amino acids ranging from 13 to 90 ppb chiral analysis revealed d l ratios of 0 39 0 08 and 0 34 0 07 for alanine serine and 0 78 0 06 for aspartic acid indicating significant racemization of biologically produced amino acids on the basis of the d l ratios we estimate sample ages ranging from 103 to 105 years these results demonstrate the successful field testing of the urey instrument as well as the detection of biomarkers from past terrestrial life in one of the most arid and mars like regions on earth

how many azimuths do you need examples abound of marine seismic quality uplifts due to multi and wide azimuth acquisition geometries figure 1 reflecting the fact that these techniques are rapidly becoming routine and widespread

sedimentation on the ross sea continental shelf antarctica abstract glacial marine sedimentation has prevailed throughout most of the early glacial history of the ross sea region however since late miocene to early pliocene time the west antarctic ice sheet has advanced onto the continental shelf perhaps several times glacial troughs of the western ross sea may also have formed at this time these glacial troughs border outlet glaciers of the east antarctic ice sheet a widespread lodgement till facies was deposited during this glacial advance holocene retreat of this expanded ice sheet left no conspicuous meltwater record so decoupling of the ice sheet from the seafloor rather than rapid melting is implied modern glacial sediment is far less prevalent than biogenic sediment and reworked glacial sediment except in coastal areas adjacent to small ice shelves and ice tongues little or no debris is being transported beyond the calving line of the ross ice shelf siliceous mud and ooze occurs in the western ross sea where surface circulation is most vigorous and warm deep waters up well this siliceous sediment along with terrigenous silt and clay blankets the seafloor below approximately 300 m water depth most of the ross sea continental shelf is deeper than this surface sediments on shallow banks and coastal platforms have clearly been reworked by marine currents the most vigorous bottom current activity occurs in those areas where geostrophic currents impinge onto the shelf debris flows and turbidity currents are also important in eroding and redistributing glacial sediments on the shelf terrigenous silt and clay are more abundant in surface sediment than basal till the source of this silt and clay is problematic the most plausible sources being onshore transport of suspended sediment by impinging currents and subglacial meltwater input

acoustic detection of ice crystals in antarctic waters during the voyage of the rsv aurora australis to the region of prydz bay antarctica in january march 1991 ice crystals were encountered at depths from the surface to 125 m in the western area of the bay on two occasions crystals were retrieved by netting and echo sounder records have been used to infer additional regions of occurrence acoustic target strength estimates made on the ice crystal assemblies encountered show significant spatial variation which may relate to crystal size and or aggregation data from a suite of conductivity temperature depth casts have been used to map regions of the study area where in situ water temperatures fell below the computed freezing point such regions correlate well with those selected on the basis of echogram type and imply that ice crystals occurred at depth over large areas of the bay during the cruise period the ice crystal distribution described is consistent with that expected from a plume of supercooled water emerging from under the amery ice shelf and forming part of the general circulation of the bay the magnitude of the supercooled water plume is greater than those reported previously in the prydz bay region if misinterpreted as biota on echo sounder records ice crystals could significantly bias biomass estimates based on echo integration in this and potentially other areas

marine controls on modern sedimentation on the antarctic continental shelf abstract the extreme depth and rugged topography of the antarctic continental shelf its seasonal to perennial sea ice cover and its large slowly calving ice shelves exert major influences on the adjacent ocean and sediments regionally variable exchanges of heat and momentum between the atmosphere and ocean result in net off shelf transport of sea ice and net downward salt flux this buoyancy partitioning drives a vertical convection that is followed by westward and northward flows of ventilated dense water across the continental shelves shelf waters meet mix with and modify circumpolar deep water at a dynamic slope front near the continental shelf break locally or periodically forming antarctic bottom water nutrient rich deep water upwells along this front regionally intruding onto the continental shelf in long thermally attenuated filaments these intrusions are frequently linked to mass balance processes at the base of ice tongues and ice shelves melting freezing and tidal currents beneath glacial ice are related to the larger scale circulation and to the fate of basal debris in the ice sheet the ocean circulation near ice fronts and decadal variability in ice front positions may account for several features of the sediment record time series 1 yr current measurements in the ross and weddell seas have revealed moderate to strong currents that are seasonally variable vertically coherent and dominated by the diurnal tide and longer term events few long term current measurements exist in the shelf and slope bottom boundary layers that are most important to sediment deposition and erosion icebergs may frequent certain routes e g in association with currents and fronts near the edge of the continental shelf and are capable of scouring and resuspending sediments down to shelf break depths sea ice plays a role in shelf sedimentation by rafting eolian and bottom debris away from the nearshore regions in addition generally offshore winds produce numerous leads and polynyas along the coastline and within the sea ice fields higher biological productivity in these polynyas may be linked to higher local sedimentation rates biogenic marine sediments apparently comprise a major percentage of the regionally variable modern shelf deposits despite the impressive glacial setting and polar environment

sedimentation on the continental rise west of the antarctic peninsula over the last three glacial cycles abstract the continental rise west of the antarctic peninsula includes a number of large sediment mounds interpreted as contourite drifts cores from six sediment drifts spanning some 650 km of the margin and 4 of latitude have been dated using chemical and isotopic tracers of palaeoproductivity and diatom biostratigraphy interglacial sedimentation rates range from 1 1 to 4 3 cm ka glacial sedimentation rates range from 1 8 to 13 5 cm ka and decrease from proximal to distal sites on each drift late quaternary sedimentation was cyclic with brown biogenic burrowed mud containing ice rafted debris ird in interglacials and grey barren laminated mud in glacials foraminiferal intervals occur in interglacial stages 5 and 7 but not in the holocene processes of terrigenous sediment supply during glacial stages differed meltwater plumes were more important in stages 2 4 turbidity currents and ice rafting in stage 6 the terrigenous component shows compositional changes along the margin more marked in glacials the major oxides al2o3 and k2o are higher in the southwest and cao and tio2 higher in the northeast there is more smectite among the clay minerals in the northeast magnetic susceptibility varies along and between drifts these changes reflect source variations along the margin interglacial sediments show less clear trends and their ird was derived from a wider area downslope processes were dominant in glacials but alongslope processes may have attained equal importance in interglacials the area contrasts with the east antarctic continental slope in the se weddell sea where ice rafting is the dominant process and where interglacial sedimentation rates are much higher than glacial the differences in glacial setting and margin physiography can account for these contrasts

microfossil and stable isotope evidence for changes in late holocene palaeoproductivity and palaeoceanographic conditions in the prydz bay region of antarctica microfaunal and microfloral data from two gravity cores and stable isotope results from one of these cores taken on fram bank near prydz bay antarctica indicate changes in sea ice patterns and oceanographic conditions which may have been linked to regional and global climate changes that occurred over the past 8000 yr modern diatom assemblages indicative of ice free conditions 1 2 months of the year and dominated by nitzschia species became prevalent some time around 2000 2700 yr b p the occurrence of chaetoceros spp diatom spore dominated assemblages and increased abundances of benthic and planktonic foraminifera ostracods and diatoms coupled with carbon and oxygen isotope changes around 2700 3400 yr b p strongly suggests that this area of the shelf experienced conditions conducive to increased productivity during this time period based on diatom assemblage associations recognized in modern environments the upper water column of fram bank shelf waters was probably stratified during that time due to the presence of low salinity melt water and a very shallow mixed layer protected from storms with sea ice cover for less than 10 months per year the close correspondence of 13c and 18o values from n pachyderma r2 0 74 throughout one core suggests that whatever oceanographic conditions influenced 18o also influenced 13c changes in prydz bay microfossil abundances and isotopes may result from alterations in circulation patterns upwelling conditions or sea ice patterns which significantly affected benthic and planktonic productivity in the area the environmental conditions indicated by older sediments in the cores are less clear but an ice tongue may have been in place 3200 3800 yr b p and minor fluctuations in productivity are indicated around 6000 and 7000 7500 yr b p the lower 100 cm of both cores may not represent in situ deposition but if the corrected ams dates reflect the actual age of the sediments analyzed microfossil and isotope data indicate that productivity and oceanographic conditions were very variable around 8500 8600 yr b p the chronology adopted herein must be regarded as tentative until further study of the area has been undertaken