first results from the radio plasma imager on image the radio plasma imager rpi is a 3 khz to 3 mhz radio sounder incorporating modern digital processing techniques and long electronically tuned antennas that is flown to large radial distances into the high latitude magnetosphere on the imager for magnetopause to aurora global exploration image satellite clear echoes similar to those observed by ionospheric topside sounders are routinely observed from the polar cap ionosphere by rpi even when image is located at geocentric distances up to approximately 5 earth radii using an inversion technique these echoes have been used to determine electron density distributions from the polar cap ionosphere to the location of the image satellite typical echoes from the plasmapause boundary observed from outside the plasmasphere are of a diffuse nature indicating persistently irregular structure echoes attributed to the cusp and the magnetopause have also been identified those from the cusp have been identified more often and with greater confidence

facies architecture seismic stratigraphy and development of a high latitude basin the powell basin antarctica abstract ten seismic facies assemblages organized into architectural elements have been identified on the basis of multichannel seismic profiles in the powell basin these facies include sheet drapes with parallel high amplitude reflectors sheet drapes with cyclic reflectors sheet drapes with chaotic and moderate amplitude reflectors broad lenses with central channel slope front fills with hummocky reflectors sheet drapes with wavy reflectors sigmoid wedges irregular bodies with contorted reflectors lenses with chaotic reflections and trough fills with divergent reflectors the vertical and horizontal distribution of these architectural elements define the syn rift syn drift and three post drift sequences whose boundaries are characterized by unconformities indicating significant changes in the factors controlling sedimentation on the margins and basin plain the allogenic factors that appear to be more influential on the margin growth patterns are the evolution of subsidence mechanisms the tectonic regime on each of the margins and the distribution of bottom currents related to the weddell sea gyre subsidence controls the evolution of the accommodation space thus causing a trend in the sequence external geometry from wedges during the syn rift phase to sigmoids during the drifting followed by flat downward convex lenses at the beginning of the post drift phase and finally sheet like geometries tectonics has a considerable influence on the extension of the source areas and margin geometry and also modifies the depositional cycles associated to climatic changes processes of ice sheet advance and retreat sea level fluctuations and isostatic adjustments bottom currents influence the distribution of depositional bodies controlling the development of sediment drifts that constitute an important proportion of the sequences on the northern margin and in the basin plain the evolution of the depositional sequences of the powell basin clearly depicts the influence of global processes linked to glacio eustatic changes and the tectonics controlling the different phases in the development of a rifted basin this high latitude basin may be considered as a good example of a semi isolated basin which serves as a model for the stratigraphic reconstruction of margins and basins of high latitudes

niveo aeolian sand deposition in subarctic dunes eastern coast of hudson bay quebec canada aeolian sand transport during winter and the snow free season was assessed quantitatively by direct year round field measurements along transects on the lee side of parabolic dunes in subarctic quebec in 1987 1988 niveo aeolian deposition was more important than aeolian sedimentation in three of the four study sites and contributed 75 of the total annual accumulation in exposed sites and 25 in protected forest sites the maximum depth of interstratified snow and sand deposits 3 5 m was recorded in march semi permanent snow lenses may persist longer than 2 years in the aeolian sediments after dissipation of snow 22 cm of sand as a maximum accumulated on the slipface of the most active dunes whereas only minor sand accumulation occurred in distant areas from active sand erosion wind driven sand was dispersed over 7 4 km2 in the whapmagoostui kuujjuarapik area the acumulation of snow and sand during the snow season together with spring thaw and collapse of the niveo aeolian deposit caused different types of injuries to trees especially in 1985 and 1987 when a maximum of torn branches was recorded over the last 10 year period

small ocean basin development along the scotia antarctica plate boundary and in the northern weddell sea abstract the oceanic crust of the northern weddell sea and scotia sea contains the following principal morphostructural elements 1 the south scotia ridge and the south orkney microcontinent both with continental crust 2 the oceanic powell and jane basins and 3 jane bank which belongs to an island arc the analysis of mcs profiles and of gravimetric and magnetic data from russian italian and spanish cruises supplemented with satellite gravimetric data has enabled us to determine the relationship between these elements and to propose a model for the main stages of cenozoic evolution in the area during the early cenozoic the weddell sea oceanic crust was subducted under the southern margin of the south orkney microcontinent the subduction probably ended westwards at the south powell ridge a submarine extension of the antarctic peninsula a major transcurrent fault zone is identified in the northwestern weddell sea bounding oceanic crust of mesozoic and cenozoic ages this fault zone was probably active at least to the miocene the drifting of the south orkney microcontinent from the antarctic peninsula during the late eocene to early miocene originated the powell basin jane basin developed as a backarc related to the subduction of the weddell sea oceanic crust below jane bank the seismic stratigraphy of the depositional sequences in these two basins indicates that spreading in jane basin started simultaneously with the end of the opening in powell basin the active spreading ridge of the weddell sea collided with the trench and was subducted below jane bank at 15 20 ma drifting in jane basin and subduction below jane bank ended shortly thereafter in the middle miocene and the boundary between the antarctic scotia plates migrated north of the south orkney microcontinent along the south scotia ridge present tectonic activity in the region is minor

the crary fan a trough mouth fan on the weddell sea continental margin antarctica abstract multichannel seismic investigations show the presence of a large trough mouth fan deposit on the continental margin in the southern weddell sea a characteristic feature of the fan is relatively few but large canyons and or channels which appear to have been stable for long periods levees associated with the channels may reach thicknesses of more than 1 km drilling during odp leg 113 recorded the presence of glaciers in east antarctica since early oligocene time and the seismic stratigraphic evidence suggests that the submarine fan is largely composed of glacigenic sediments the channel levee systems and complexes indicate several growth phases apparently controlled by glacial interglacial climate fluctuations with maximum fan growth during glacial periods the present interglacial period is characterized by strong and erosive flow of ice shelf water running down the western slope of the fan and carrying only minor amounts of suspended matter the fan is essentially sediment starved during interglacial periods the dimensions of the channel levee complexes and the persistent loci of sediment supply suggest that turbidite sedimentation resulted from melting of wet based glaciers at or near the shelf edge which has consequently prograded 70 80 km seaward

physical conditions at the base of a fast moving antarctic ice stream boreholes drilled to the bottom of ice stream b in the west antarctic ice sheet reveal that the base of the ice stream is at the melting point and the basal water pressure is within about 1 6 bars of the ice overburden pressure these conditions allow the rapid ice streaming motion to occur by basal sliding or by shear deformation of unconsolidated sediments that underlie the ice in a layer at least 2 meters thick the mechanics of ice streaming plays a role in the response of the ice sheet to climatic change

the scotia antarctica plate boundary from 35 w to 45 w abstract a compilation of available multichannel seismic profiles acquired along the southern margin of the scotia sea east of the south orkney microcontinent has allowed identifying and mapping the main morphological and structural features of the central segment of the scotia antarctica plate boundary this margin is composed by several bathymetric highs of variable size and uncertain crustal nature separated by deep troughs and restricted oceanic basins some of these troughs represent pull apart basins three main segments oriented wnw ese the western sector ene wsw the central sector here named bruce deep and ne sw the eastern sector have been described these segments are separated by nnw sse trending release zones disposed in an en echelon geometry which represent mostly strike slip faults the western segment corresponds to the northern margin of the south orkney microcontinent where a subduction zone seems to be present even if its present day activity is unclear the segment further to the east corresponds to an ene oriented basin bruce deep which separates the bruce bank from the eastern promontory of the south orkney continental platform to the south of the bruce deep a wide deformation zone with n verging folds and thrusts here named jane thrust belt has been identified from seismic data the eastern segment of the plate boundary is structurally the less constrained and may be composed by a series of tectonic lineaments of different lengths from the bruce bank to the east focal mechanisms maintain a prevalent left lateral strike slip motion combined with an extensional component in this sector earthquakes are located in a 150 km wide area and on a local scale are difficult to follow unambiguously at the plate boundary lithologic analyses on dredged material recovered along a flank of one of the morphological relieves present south of the discovery bank to 35 w here collectively named irizar highs yielded a dominant granitic composition a similar composition characterizes the rocks collected in the southern flank of the south easternmost jane bank this suggests a continental crust nature for these bathymetric highs now dispersed along this sector of the scotia antarctica plate boundary we propose here a tectonic evolution for this margin dominated since the early miocene by the northward subduction of the weddell sea oceanic crust the development of a dextral en echelon transform fault system facilitated the process of fragmentation and dispersion of the crustal blocks dismembered the subduction zone and possibly inverted the direction of convergence therefore the scotia plate would subduct beneath the antarctic plate in the western sector and weddell sea would subduct beneath scotia plate in the eastern sector finally the activation of left lateral transtensional strike slip lineaments generated narrow pull apart basins in the fore arc sectors of the convergent zones

seismic stratigraphy of the antarctic peninsula pacific margin a record of pliocene pleistocene ice volume and paleoclimate multichannel seismic profiles across the pacific margin of the antarctic peninsula show a series of oblique progradational sequences these sequences exhibit a variety of unusual characteristics that suggest they were produced by the action of ice sheets grounded out to the shelf edge at times of glacial maximum reflection events from deeper stratigraphic levels followed down the continental slope and onto the rise overlie ocean crust of known age showing that at least eight such glacial sequences have been deposited within the past 6 m y similar groundings have probably occurred on most antarctic margins but the depositional record is particularly well preserved at this margin because of pliocene pleistocene thermal subsidence neogene global sea level fluctuations have been attributed to changes in volume of continental ice sheets the depositional sequences on the pacific margin of the antarctic peninsula are thought to record west antarctic ice sheet fluctuations directly further investigation of these sequences would assess the relation between fluctuations in ice volume and the low latitude record of global sea level change

the antarctic margin and its possible hydrocarbon potential abstract geological and geophysical data over the antarctic margin are reviewed to define those areas where thick sedimentary sequences occur which may have potential to source hydrocarbons where possible the waples lopatin model has been used to calculate whether the degree of maturation of the sediments is sufficient for hydrocarbons to have been generated significant sedimentary sequences occur along the continental margins of wilkes land western dronning maud land antarctic peninsula and ellsworth land and as basins or troughs on the continental shelf of prydz bay weddell sea and ross sea maturation assessments are possible for western dronning maud land eastern weddell sea western antarctic peninsula ellsworth land and ross sea regions within the great limitations of the data only western weddell sea and ross sea basins have maturation values sufficient for the generation of hydrocarbons

tectonics of the scotia antarctica plate boundary constrained from seismic and seismological data abstract the plate boundary between the scotia and antarctic plates runs along the broadly e w trending south scotia ridge it is a mainly transcurrent margin that juxtaposes thinned continental and transitional crust elements with restricted oceanic basins and deep troughs seismic profiles and regional scale seismological constraints are used to define the peculiarities of the crustal structures in and around the southern scotia sea and focal solutions from recent earthquakes help to understand the present day geodynamic setting the northern edge of the western south scotia ridge is marked by a sub vertical left lateral master fault locally a narrow wedge of accreted sediments is present at the base of the slope this segment represents the boundary between the scotia plate and the independent south shetland continental block along the northern margin of the south orkney microcontinent the largest fragment of the south scotia ridge an accretionary prism is present at the base of the slope which was possibly created by the eastward drift of the south orkney microcontinent and the consequent subduction of the transitional crust present to the north east of the south orkney microcontinent the physiography and structure of the plate boundary are less constrained here the tectonic regime exhibits mainly strike slip behavior with some grade of extensional component and the plate boundary is segmented by a series of nnw sse trending release zones which favored the fragmentation and dispersion of the crustal blocks seismic data have also identified along the north western edge of the south scotia ridge an elevated region the ona platform which can be considered along with the terror rise as the conjugate margin of the tierra del fuego before the drake passage opening we propose here an evolutionary sketch for the plate boundary from the late oligocene to the present encompassing the segment from the elephant island platform to the herdman bank

cenozoic marine sedimentation and ice volume variation on the east antarctic craton recycled cretaceous and cenozoic marine microfossils have been recovered from samples of the pliocene sinus formation samples were collected from outcrops in the reedy beardmore and ferrar glacier areas of the transantarctic mountains between lat 77 and 86 s the glaciogene sediments contained diatoms foraminifera calcareous nannoplankton silicoflagellates radiolarians sponge spicules palynomorphs and ostracodes of late cretaceous paleocene eocene late oligocene late miocene and pliocene age this suggests the presence of open marine basins on the east antarctic craton during late mesozoic and cenozoic time the apparent absence of early oligocene and early through middle and earliest late miocene assemblages suggests either that marine regression exposed the basin floors or that ice filled the basins during these times the high elevation setting of sirius formation outcrops suggests one of two hypotheses for their origin 1 they are in situ pliocene glaciomarine deposits that were uplifted 1 750 2 500 m with the transantarctic mountains to their present elevation 2 the sirius formation deposits are a mixture of derived sediments stripped from sub ice intracratonic basins and subsequently redeposited by ice flowing up the inland slope of the transantarctic mountains we favor the second hypothesis with transport to sites sometime within the past 3 m y

mid cenozoic record of glaciation and sea level change on the margin of the victoria land basin antarctica the mssts 1 drill hole in western mcmurdo sound provides the earliest physical record thus far for antarctic cenozoic glaciation the hole penetrated 227 m of muddy marine glacial sediment containing scattered pebble and cobble size clasts including seven diamictite beds deposited from grounded ice during glacial advances a diatom based chronology refined by paleomagnetic stratigraphy for the interval below 116 m subbottom indicates sediment accumulation from 29 ma to about 24 ma sediment texture and paleoecology of diatoms and foraminifers indicate nearshore sedimentation on a wave dominated shelf the oldest strata record a significant shallowing of water depth culminating in ice grounding at around 28 ma and a deepening at 25 ma that may be glacioeustatic

the antarctic ice sheet its history and response to sea level and climatic changes over the past 100 million years abstract the development surface form flow and erosive activity of the antarctic ice sheet over the past 100 million years is related to geological evidence that indicates long term trends of global climate the glaciological description of the evolution of the ice sheet covers its interactions with the atmosphere and with the ocean discussion focuses on changes of the equilibrium line altitude ela with time of the accumulation rate with global temperature and basal melting of ice shelves by ocean waters the tendency of global climate to change rapidly or to drift slowly between two near equilibrium states involves two types of changes the former that has been widely recognized is reversible a second type involving ice sheets or ice shelves appears to be almost irreversible since they remain in their changed state unless a much larger reversal of factors driving climate occurs we refer to any rapid but reversible changes as climatic jumps and to the latter as climate ice switches variability of climate in response to changing radiation with the earth s orbital parameters and other causes is included in our model extensive glaciation of east antarctica commenced after 40 m y b p with wide fluctuations until shortly after 20 m y b p a climate ice switch then prevented any major deglaciation a further climate ice switch associated with the ela falling below sea level occurred soon after 10 m y b p this led to rapid formation of ice shelves and the marine ice sheet of west antarctica which advanced as grounded ice to the edge of the continental shelf after 5 m y b p the grounded ice started to retreat extensive ice shelves remained and most glacial debris was then deposited beneath the inner regions of ice shelves response to northern hemisphere glaciation since 2 4 m y b p during glacial periods involved extension of the grounded ice area a large decrease of mass input and decreased melting of outer parts of large ice shelves while the melting rate beneath inner regions was probably similar to the present marine core evidence suggests that retreat caused by global cooling has been dominant since 5 m y b p and that changes in extent due to northern hemisphere glaciation since 2 4 m y b p have had different effects on the major and on smaller northerly ice shelves

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

seismic investigations in the weddell sea embayment abstract seismic multi channel data collected during norwegian antarctic research expeditions in 1976 1977 and 1978 1979 outline aspects of the cenozoic depositional environment in the weddell sea embayment acoustic basement probably representing the east antarctic craton is exposed in a 50 100 km wide swath along the ice barrier between 78 s 75 5 s on the eastern side of the crary trough the shelf prograded westward and northward from the craton into a subsiding basin colinear with the transantarctic mountain range measured sediment thicknesses exceed 5 km during middle and late tertiary times a submarine fan complex the crary fan developed on the southeastern margin of the weddell sea embayment the glacially eroded crary trough is located at the contact between the craton and a sedimentary basin to the west the entire sedimentary section is undisturbed by faulting or folding which indicates that any movements related to cenozoic uplift of the trans antarctic mountains and or relative motion of east antarctica had little effect in the area north of the filchner ice shelf east of 41 w

niveo aeolian deposits and denivation forms with special reference to the great kobuk sand dunes northwestern alaska the geomorphology lithology and chronostratigraphy of extensive late pleistocene inland and river dune sands aeolian sand sheets cover sands and loess deposits of periglacial origin in northwestern europe are well known however the idea that some of these aeolian sediments result from niveo aeolian processes is still an open question as no diagnostic sedimentary features have yet been reported moreover actual niveo aeolian sediments and related denivation forms reported from various cold climate regions are not suitable analogues recent observations in active dune fields in northwestern alaska indicate that interstratification of wind driven snow and sand preferentially occurs on slip faces of transverse barchanoid or parabolic dune ridges annual denivation forms develop e g snow ramparts sinkholes snow hummocks snow meltwater fans and tensional cracks the surface consists of a cracked wet sand layer with a dimpled surface and spongy structure although the preservation potential of these features is low in this specific case similar features may be observed in ancient sediments elsewhere and provide useful palaeoclimatic indicators the niveo aeolian concept should therefore not specifically be related to late pleistocene cover sand deposition in northwestern europe as previously assumed

a geological map of the scotia sea area constrained by bathymetry geological data geophysical data and seismic tomography models from the deep mantle abstract the scotia sea is one of the tectonically most complex and least understood back arc basins on earth which partly results from its remote location making the acquisition of data challenging here we provide a review of current publicly available geophysical and geological data in the scotia sea realm including magnetic bouguer gravity anomaly high resolution bathymetric heat flow and reflection seismic data and rock type data from cored and dredged samples with this inter disciplinary data set we performed an offshore geological mapping exercise that allowed us to identify lithologies in the predominantly submerged scotia sea domain cross sections combining crustal structure and mantle tomography enabled us to address some of the still persisting geological challenges in this tectonically complex area the data review revealed that basalt is the dominant lithology in the scotia sea area occupying most of the west and east scotia sea wss and ess andesitic and more felsic lithologies are identified in the central scotia sea css and the northern east scotia sea ess mesozoic palaeozoic metamorphic sedimentary lithologies are reported from the highs along the north and south scotia ridges nsr and ssr these highs originate from a land bridge that until the late mesozoic connected the south american and antarctic continents scarcely available and contradicting data prevent the age determination of several structural units surrounding and located on the scotia plate but our mapping exercise allowed us to confirm the presence of the early oligocene late miocene ancestral south sandwich arc assa in the east of the css setting the minimum age of the older segment of the css crust to eocene earliest oligocene three cross sections cross cutting the scotia sea reveal two high velocity zones indicating cold mantle material one is situated below the structural highs along the ssr which we interpreted as remnant slab material of the assa and another below south georgia and the css which we interpreted as the front of the slab that currently subducts at the south sandwich trench ssat the neutral velocity discontinuity below the wss implies mantle conditions of a recently extinct spreading centre the upper mantle low velocity anomaly below the css is interpreted as warmer toroidal flows around the slab edges of the subducting plate at the ssat we have demonstrated that the geological and geophysical data publicly available today allows us to create offshore geological maps in remote inaccessible offshore domains this is a less time consuming economically advantageous exercise which re uses existing geological and geophysical data for a new purpose it is the most data inclusive study there is today of the scotia sea region and serves as a guideline for future expeditions targeting the css and the structural features along the nsr to identify their age and origin a georeferenced version of the map is provided in the supplementary material

ice sublimation as a geomorphic process a planetary perspective abstract sublimation plays a role in the shaping of landforms of planetary surfaces where ice is present as frost as polar caps or in the subsurface this review is focused primarily on the geomorphologic consequences of sublimation a summary of the suite of landforms that have been observed on the surface of various planetary bodies and whose formation is attributed to sublimation is presented this includes the sublimation of a range of different ices that are found on planetary bodies water ice carbonic ice etc at least four groups of landforms are distinguishable independent of the planetary body i residual lags that are depleted in ice which form after sublimation loss such residual lags isolate deeper ice from sublimation and thus can have an important impact on planetary volatile cycles ii landforms due to differential sublimation resulting from enhanced sublimation in low albedo warmer areas of the planet and preservation of ice in the high albedo regions iii landforms due to differential sublimation initiated by fractures or ground heterogeneities for example sublimation enhanced polygonal cracks iv pitted terrains that occur in a relatively homogeneous ice bearing subsurface or as an effect of local ice enrichment or segregation in the ground

sea level changes an integrated approach sea level changes an integrated approach in october 1985 sepm sponsored a four day conference entitled sea level changes an integrated approach the purpose of the conference was to provide a forum for an interdisciplinary exchange of ideas on sea level changes and to provide an opportunity for integrating various types of evidence in approaching unresolved issues the conference was successful in bringing together scientists from industry academia and government representing all of the major geosciences disciplines presentations of many new papers plus significant releases of data that were previously held proprietary provided fertile ground for discussion this much cited volume represents the best of the material presented at the conference includes the early vail chart

tectonic reconstructions for paleobathymetry in drake passage abstract a minimum complexity tectonic reconstruction based on published and new basin opening models depicts how the scotia sea grew by cenozoic plate divergence dismembering a jurassic sheared margin of gondwana part of the jurassic early cretaceous ocean that accreted to this margin forms the core of the central scotia plate the arc plate above a trench at the eastern end of the scotia sea which migrated east away from the antarctic and south american plates a sequence of extensional basins opened on the western edge of the central scotia plate at 50 30 ma decoupled from the south american plate to the northwest by slow motion on a long transform fault succeeding the basins seafloor spreading started around 30 ma on the west scotia ridge which propagated northwards in the 23 17 ma period and ceased to operate at 6 ma the circuits of plate motions inside and outside the scotia arc are joined via rotations that describe antarctic central scotia plate motion in powell basin until 20 ma and along the south scotia ridge thereafter the modelled relative motion at the northern edge of the scotia sea is thus constrained only by the plate circuit but nonetheless resembles that known coarsely from the geological record of tierra del fuego a paleobathymetric interpretation of nine time slices in the model shows drake passage developing as an intermediate depth oceanographic gateway at 50 30 ma with deep flow possible afterwards initially this deep flow would have been made tortuous by numerous intermediate and shallow barriers a frontal pattern resembling that in the modern scotia sea would have awaited the clearance of significant barriers by continuing seafloor spreading in the scotia sea at 18 5 ma at shag rocks passage and after 10 ma southeast of south georgia

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

niveo aeolian sedimentation of loess and sand an experimental and micromorphological approach the concept of a niveo aeolian influence on the genesis of northwest european pleistocene aeolian sand and loess deposits has been advocated in the past both to explain the presence and the absence of lamination field experiments were carried out on artificially deposited alternating layers of sand and snow and of loess and snow to investigate the role of a niveo aeolian mode of deposition on resulting sedimentary structures field observations of sand plots revealed minor changes in surface morphology typical of denivation surfaces the thin sections showed a characteristic porous structure deformations of the depositional structure and indications for erosion and redeposition were limited however the originally smooth aeolian sedimentary surface of the loess changed considerably the thin sections showed also a porous spongy structure indications were found for disturbances by frost action liquefaction during melting of the snow and ice and redeposition of loess by meltwater the experimental results strongly suggest that sand and loess deposited as niveo aeolian material are characterized both by a porous structure and that the original sedimentary structure of the sand is not affected by snowmelt whereas loess becomes non laminated thus the intercalation of snow during sedimentation of sand and loess does not in itself induce a laminated structure

complementary slip distributions of the august 4 2003 mw 7 6 and november 17 2013 mw 7 8 south scotia ridge earthquakes abstract the south scotia ridge transform ssrt plate boundary between the scotia and antarctic plates experienced large strike slip earthquakes on august 4 2003 m w 7 6 and november 17 2013 m w 7 8 these events have overlapping aftershock zones which is unusual a 36 45 southward dipping fault zone ruptured with left lateral displacements in each event along the northern margin of the south orkney micro continent near 60 s slip distributions for the two events are determined using teleseismic body and surface wave recordings along with constraints from gps ground motion recordings at station borc on laurie island south orkney islands just south of the ssrt the aftershock distributions high frequency back projections and unconstrained body wave finite fault inversions permit significant overlap of the 2003 and 2013 slip zones however the gps static displacements resolve differences in the large slip regions of the two ruptures the 2013 earthquake sequence along the ssrt initiated with m w 6 1 november 13 and m w 6 8 november 16 foreshocks located 50 km west of the mainshock hypocenter and had aftershocks extending 250 km eastward the rupture spread primarily eastward at 2 5 km s with a total rupture duration of about 120 s with two distinct patches of large slip located northwest and northeast of the south orkney islands the rupture swept past borc with high rate gps hrgps ground motion recordings capturing the time varying slip history of the faulting traditional gps data require that the largest slip region of the shorter rupture in 2003 is located in the gap nne of borc between the two patches that ruptured in 2013 there appears to be some overlap of lower slip regions the complementary slip distributions comprise a relatively uniform offset along this portion of the ssrt which is one of the most seismically active regions of the entire antarctic plate boundary

role of the plasmapause in dictating the ground accessibility of elf vlf chorus this study explores the manner in which the plasmapause is responsible for dictating which magnetospheric source regions of elf vlf chorus are able to propagate to and be received by midlatitude stations on the ground first we explore the effects of plasmapause extent on ground based observations of chorus via a 3 month study of ground based measurements of chorus at palmer station antarctica l 2 4 50 s geomagnetic latitude and data on the plasmapause extent from the image euv instrument it is found that chorus normalized occurrence peaks when the plasmapause is at l 2 6 somewhat higher than palmer s l shell and that this occurrence peak persists across a range of observed chorus frequencies next reverse ray tracing is employed to evaluate the portion of the equatorial chorus source region distributed in radial distance and wave normal from which chorus is able to reach palmer station via propagation in a nonducted mode the results of ray tracing are similar to those of observations with a peak of expected occurrence when the plasmapause is at l 3 the exact location of the peak is frequency dependent this supports the conclusion that the ability of chorus to propagate to low altitudes and the ground is a strong function of instantaneous plasmapause extent and that peak occurrence of chorus at a given ground station may occur when the l shell of the plasmapause is somewhat beyond that of the observing station these results also suggest that chorus observed on the ground at midlatitude stations propagates predominantly in the nonducted mode

is climate change affecting rates of dune migration in antarctica antarctica is the coldest driest and windiest continent on earth and contains sand dunes like deserts elsewhere the structure and age of the cold climate dunes found in the victoria valley antarctica are described in the light of changing climate in the ross sea region of antarctica during the late holocene ground penetrating radar gpr was used to image sand dune stratigraphy and optically stimulated luminescence osl was used to determine when the sands were deposited the timing of sand dune accretion identified from the gpr stratigraphy ranges from the present day to ca 1 3 kyr b p the osl ages were used to calculate end point migration rates of 0 05 1 5 m yr lower than migration rates from photogrammetry and field surveys undertaken over the past 50 yr the earliest recorded dune development ca 1 3 kyr b p was probably controlled by intensification of circumpolar westerlies at that time as well as by drier conditions and lower temperatures that promoted dune stabilization the dune reactivation ca 300 yr ago coincides with cooling ca a d 1700 1850 and strengthening of southern circumpolar westerlies the increase in rate of dune migration after this period and especially the past 200 yr may coincide with the modern rise in co 2 and the warmest temperatures in antarctica during the past 800 kyr

the structure and origin of prydz bay and macrobertson shelf east antarctica abstract a marine geophysical survey in early 1982 conducted by the australian bureau of mineral resources indicated that much of prydz bay is underlain by a sedimentary basin severe seismic multiples preclude an accurate estimate of total sediment thickness but interpretation of the seismic and magnetic data suggest that it is probably at least 5 km the trends of the southeast basin margin and of mild faulting and folding in the southwest indicate an overall nne trend roughly orthogonal to the continental margin in the south of prydz bay two series of seismic sequences are evident separated by a mildly erosional unconformity the lower series ranges from poorly to well stratified has minor folding and faulting and probably derives from continental and perhaps shallow marine pre breakup sediments the upper series is generally well stratified and prograded near the shelf edge it probably represents shallow marine post breakup sediments the seabed is distinctly unconformable with the underlying sediments implying both that much of the upper series sediments and some of the lower series sediments have been bulldozed off by advances of the amery ice shelf and that present sedimentation rates are very low possible thin moraines or tillites in the northeast part of the prydz bay are also attributed to these glacial advances the continental slope and rise sedimentary section ranges from at least 3 km thick off prydz bay to thin off the macrobertson shelf to the west reflecting the more prolific sediment source in prydz bay the deep water section includes several seismic sequences the most distinctive being interpreted as sheet volcanics and turbidite fans the deepest visible unconformity is locally strongly faulted and may separate the pre breakup and post breakup sediments indo antarctic breakup has been tentatively dated as early neocomian 130 ma and the e w orientation of the resultant antarctic coast invites interpretation of the lambert glacier prydz bay structure as a possible failed rift arm of a triple junction direct information on the age and nature of the sediments under prydz bay is lacking but permian continental sediments cropping out at beaver lake to the south may correspond to the lower pre breakup series this interpretation gains some support from analogies with fault bounded intracratonic basins in india which contain permian to triassic continental strata and which may have been juxtaposed prior to breakup the upper series probably consists of upper cretaceous and cainozoic sands and shales with moraines or tillites at the top of the section

z mode sounding within propagation cavities and other inner magnetospheric regions by the rpi instrument on the image satellite 1 when the radio plasma imager rpi on the image satellite operates in the inner plasmasphere and at moderate to low altitudes over the poles pulses emitted at the low end of the rpi 3 khz to 3 mhz sounding frequency range can propagate in the z mode as well as the whistler mode at medium altitudes within the plasmasphere discrete z mode echoes with turning points earthward of image are often observed analogous in form to the regular and oblique z mode echoes found on topside sounder records in the polar regions where fpe fce 1 usually obtains the z mode echoes tend to be diffuse and to exhibit properties such as an intensity decrease at the local value of fce where there is a significant change with frequency in the topology of the z mode refractive index surface at altitudes up to a few thousand km in polar or near polar regions z mode soundings regularly provide information on the local value of fpe whereas passive recordings that depend upon indications of the upper hybrid resonance frequency fuh usually fail to do so within the transition region from the auroral zone to the plasmasphere and within the plasmasphere itself at altitudes from 2000 km upward we find evidence of the z mode trapping phenomenon noted previously in connection with natural wave emissions detected at polar latitudes this phenomenon involves echoes returning both from turning points in denser regions earthward of the sounder and from more tenuous regions above within z mode cavities discrete z mode echoes are found to propagate back and forth along geomagnetic field aligned paths between upper and lower altitude reflection points the echoes present unique forms depending upon whether image is located above or below a minimum in the altitude profile of the z mode cutoff frequency through an inversion process such echoes make possible determination of the electron density profile along geomagnetic field lines to distances of thousands of km above the location of image all on the basis of echo delay information within frequency bands only 20 to 30 khz wide the forms of such density profiles are in general agreement with results reported from conventional rpi x mode sounding from higher altitudes as well as with predictions based upon a diffusive equilibrium model of density along plasmasphere field lines

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

mesozoic to recent evolution of intraplate stress fields under multiple remote stresses the case of signy island south orkney microcontinent antarctica abstract palaeostresses inferred from approximately 3200 brittle mesostructures measured at 43 sites in signy island show a stress field characterized by compressional strike slip and extensional stress states there is a dominant nw se horizontal compression direction as well as three nnw sse wnw ese and ene wsw secondary 1 horizontal stress directions orientation of 3 shows a main mode trending nw se together with secondary north south and ne sw extensional stress directions the nnw sse horizontal compression is consistent with the stretching shearing direction defined from the fold axis trend this is owing to a subduction related tectonic regime during early to middle jurassic times in middle jurassic early cretaceous times the tectonic regime changes to extensional with north south extensional stress directions the early processes of subduction of the northern sector of the weddell sea oceanic crust below the south orkney microcontinent from the paleocene until the middle miocene is related to the 1 direction wnw ese to nw se the spreading of powell basin took place from the late eocene to the early miocene and is the cause of east west and ne sw extensional processes in the southern south orkney microcontinent finally the nw se 3 direction is related to the current left lateral strike slip movement between the scotia and antarctic plates

effect of cenozoic ice sheet fluctuations in antarctica on the stratigraphic signature of the neogene stratigraphic successions from the gulf of mexico offshore alabama northeast java indonesia ross sea antarctica and several other continental margins have been examined all are characterized by very similar neogene stratal geometries in seismic profiles and well log cross sections from these areas a large mid oligocene i e latest early oligocene earliest late oligocene basinward shift in coastal onlap is followed by a major early miocene transgression and aggradation which is in turn followed by early middle miocene transgressions and late middle and late miocene progradational episodes the succession culminates in plio pleistocene high frequency progradations and transgressions the interregional character of the neogene stratal signature and its similarity to the stratal geometry found in seismic data from the ross sea continental shelf antarctica suggest that the neogene stratal signature is a manifestation of glacioeustatic fluctuations a review of the literature and an analysis of recently acquired and published data indicate that the first major ice sheet grounding event in the ross sea occurred during middle to late oligoce time the ross sea is the repository for ice flowing from a major portion of the continental interior thus the glacial record of the ross sea should serve as a gage of ice volume changes on the continent that were large enough to influence global eustasy the ice advance onto the ross sea continental shelf during middle to late oligocene time may have been the result of a decrease in the rate of shelf subsidence as rifting in the ross sea slowed or ceased advance of the ice sheet resulted in widespread erosion of the continental shelf and shelf overdeepening it is hypothesized that metastable marine based ice sheets have waxed and waned on the antarctic continental shelf since at least the oligocene and that the these waxing and waning events were responsible for the development of a global neogene stratigraphic signature

seismic stratigraphy and tectonics of the northwestern weddell sea antarctica inferred from marine geophysical surveys abstract marine geophysical studies of the northwestern weddell sea show several interesting stratigraphic and tectonic features synthesis of the odp drilling results on the south orkney microcontinent with the circum antarctic depositional model allows identification of the main reflectors within the cretaceous cenozoic sedimentary cover the age and composition of pre rift syn rift and post rift units probably vary throughout the region the observed seismic pattern of the jane bank suggests a young asymmetric zone of extension a seismic record across the south orkney trough and central scotia basin indicates an association with an accretion zone and spreading centre

grid mapping the northern plains of mars using morphotype and distribution of ice related landforms to understand multiple ice rich deposits in utopia planitia this work in utopia planitia is the first continuous regional mapping of ice related landforms integrated into an effort to study the three main basins arcadia acidalia utopia planitiae in the northern plains the distribution and morphotypes of these landforms sharad detections and crater size frequency distribution measurements 50 m in diameter were used to understand the permafrost cryolithology and its past evolution in relation to climate in utopia planitia three assemblages of landforms were identified based on their spatial correlation and correlation with mola surface roughness along a strip from 30 n to 80 n at 30 38 n the assemblage is formed by km scale polygons high albedo mounds and thumbprint terrains this assemblage is associated with a lobate deposit of 30 m in thickness with a crater retention age of 1 ga at 38 47 n the assemblage is comprised of large scallops 100 m diameter polygons pits and mantled deposits this assemblage is correlated with a deposit of 80 m in thickness containing excess ice 50 85 by volume with a crater retention age of about 10 ma at 47 78 n the assemblage is composed of mantled deposits textured terrains and 30 m diameter polygons this assemblage is related to the ice rich debris covered latitude dependent mantle that has a crater retention age of about 1 5 ma utopia planitia appears to be a region of combined depositions of sediment and continuous cold climatic conditions that leaded to a complex distribution of ground ice

aeolian dune field development in a water table controlled system skeiđararsandur southern iceland aeolian dune fields characterized by partly vegetated bedforms undergoing active construction and with interdune depressions that lie at or close to the water table are widespread on skei ararsandur southern iceland the largest aeolian dune complex on the sandur covers an area of 80 km2 and is characterized by four distinct landform types i spatially isolated aeolian dunes ii extensive areas of damp and wet flooded interdune flat with small fluvial channels iii small aeolian dune fields composed of assemblages of bedforms with simple morphologies and small predominantly damp interdune corridors and iv larger aeolian dune fields composed of assemblages of complex bedforms floored by older aeolian dune deposits that are themselves raised above the level of the surrounding wet sandur plain the morphology of each of these landform areas reflects a range of styles of interaction between aeolian dune interdune and fluvial processes that operate coevally on the sandur surface the geometry scale orientation and facies composition of sets of strata in the cores of the aeolian dunes and their relationship to adjoining interdune strata have been analysed to explain the temporal behaviour of the dunes in terms of their mode of initiation construction pattern of migration style of accumulation and nature of preservation seasonal and longer term flooding induced changes in water table level have caused episodic expansion and contraction of the wet interdune ponds most of the dunes are currently undergoing active construction and migration and although sediment availability is limited because of the high water table substantial aeolian transport must occur especially during winter months when the surface of the wet interdune ponds is frozen and sand can be blown across the sandur without being trapped by surface moisture bedforms within the larger dune fields have grown to a size whereby formerly damp interdune flats have been reduced to dry enclosed depressions and dry aeolian system accumulation via bedform climb is ongoing despite regional uplift of the proximal sandur surface in response to glacial retreat and unloading over the past century sediment compaction induced subsidence of the distal sandur is progressively placing aeolian deposits below the water table and is enabling the accumulation of wet aeolian systems and increasing the likelihood of their long term preservation wet dry and stabilizing aeolian system types all co exist on skei ararsandur and the dunes are variously undergoing coeval construction accumulation bypass stabilization and destruction as a result of interactions between localized factors

debris flows on the great kobuk sand dunes alaska implications for analogous processes on mars abstract we observed niveo aeolian deposits denivation features and small meltwater induced debris flows that had formed at the great kobuk sand dunes northwestern interior alaska in late march 2010 this high latitude cold climate dune field is being studied as a planetary analog to improve our understanding of factors that may trigger debris flows on the lee slopes of martian aeolian dunes debris flows consisted of a sand and liquid water mixture that cascaded down the lee slopes of two barchanoid dunes on days when measured ground surface temperatures were below freezing we hypothesize that relatively dark sand on snow caused local hot spots where solar radiation could be absorbed by the sand and conducted into the underlying snow enabling meltwater to form and sand to be mobilized this investigation provides insights into the interactions between niveo aeolian deposition slope aspect and insolation thawing and initiation of alluvial processes these debris flows are morphologically similar to those associated with seasonal gullies or erosion tracks visible on the slopes of mid to high latitude dune fields in both martian hemispheres localized heating and thawing at scales too small for orbital sensors to identify may yield martian debris flows at current climate conditions

observations of structured optical emissions and particle precipitation equatorward of the traditional auroral oval 1 high sensitivity all sky images from south central alaska show the common occurrence of slow moving faint optical emissions at 557 7 and 427 8 nm well equatorward of the discrete aurora these emissions appear over a continuum of forms ranging from homogenous longitudinal bands to bands with irregular structure on their poleward edge to widely distributed arrays of vortex like curls and widely spaced spots on the order of 10 km in diameter these forms appear to correspond to various stages in the temporal evolution of nearly corotating precipitation regions populated by particles injected from more distant areas of the magnetosphere and may exhibit morphological control by an instability operating on cold plasma near the plasmapause although these phenomena are most common in the evening hours and typically persist for hours at a time one case demonstrates that the features can remain throughout the night on occasion these faint optical features appear to be colocated with regions of enhanced background counts in dmsp particle measurements and to be associated with the ring current outer radiation belt region equatorward of subauroral polarization streams saps the features can occur in conjunction with hf and mf radio frequency absorption at levels which are often too low to show up on routine absorption instruments such as the riometer this has practical implications on the operation and interpretation of ionospheric interaction experiments carried out in the subauroral region

effects of temperature and humidity upon the transport of sedimentary particles by wind aeolian transport of sedimentary particles is a well recognized phenomenon in cold regions but the effect of low temperature t and specific humidity q upon particle entrainment has not previously been investigated this study reports on wind tunnel experiments 12 c t 32 c and 1 g kg 1 q 10 g kg 1 that suggest the aerodynamic drag required to entrain sand sized particles can be 30 lower in cold or high latitude settings as compared to hot deserts for any given regional wind velocity this effect will increase the wind strength index and thereby the proportion of time a surface is active at low temperature

holocene palaeosols and aeolian activities in the umimmalissuaq valley west greenland aeolian sand sheets and active dunefields preserve an ancient holocene land surface represented by palaeosols that occur around the present ice margin in the kangerlussuaq area west greenland to determine the relation between holocene aeolian activities and periods of soil formation both substantially dependent on the deglaciation history palaeosols aeolian sand sheets and dunefields were analysed using field data grain size analyses optically stimulated luminescence dating and ams 14c data in an area of about 15 km2 of the umimmalissuaq valley palaeosols are developed close to the ice margin 60 wt are comparable with aeolian sand sheets currently formed at greater distances 4 5 km from the present ice margin we propose a transport distance for fine aeolian sediments in which the palaeosols are formed of at least 4 km from inboard of the present ice margin soil for

annual to decadal morphodynamics of the foredune system at greenwich dunes prince edward island canada the purpose of this study was to quantify relationships between season sediment availability sediment transport pathways and beach foredune morphology at greenwich dunes pei this was done for periods ranging from a few days to multiple decades using erosion pins bedframe measurements annual surveys and digital photogrammetry using historical aerial photographs the relative significance of seasonal annual processes versus response of the foredune system to broader geomorphic controls e g relative sea level rise storms etc was also assessed the data show that there are clear seasonal differences in the patterns of sand supply from the beach to the foredune at greenwich and that there are differences in sediment supply to the foredune between the east and west reaches of the study area resulting in ongoing differences in foredune morphology they also demonstrate that models that incorporate wind climate alone or even models that include other factors like beach moisture would not be able to predict the amount of sediment movement from the beach to the foredune in this environment unless there were some way to parameterize system morphology especially the presence or absence of a dune ramp finally the data suggest that the foredune can migrate landward while maintaining its form via transfers of sediment from the stoss slope over the crest and onto the lee slope although the rate of foredune development or recovery after disturbance changes over time due to morphological feedback the overall decadal evolution of the foredune system at greenwich is consistent with and supports the davidson arnott 2005 conceptual model of dune transgression under rising sea level copyright 2012 john wiley sons ltd

distribution and provenance of recycled palynomorphs in surficial sediments of the ross sea antarctica abstract quantitative analysis of surficial sediments in the ross sea has shown that the highest densities of recycled palynomorphs occur in a region in the southeast immediately north of the ross ice shelf in the vicinity of roosevelt island there spores and pollen of late cretaceous to early tertiary age predominate eocene dinoflagellates and rare palaeozoic spores are also present in the western half of the ross sea densities of recycled palynomorphs are lower but relative frequencies of palaeozoic types are higher on the continental shelf the palynomorphs have been recovered in equal abundance from sediments identified as basal tills and compound glaci marine sediments comparison of the observed patterns of distribution with patterns of ice flow in the ross ice shelf shows a clear correlation between the high palynomorph densities in the southeastern ross sea and discharge from ice streams d and e geophysical information from aeromagnetic and radio echo sounding surveys in the catchment areas of these ice streams suggests the most likely source for the recycled palynomorphs to be in a region of subdued topography inland of the present grounding line in the marie byrd land sector of the ross ice shelf extending probably not further east than 130 w this region probably represents a continuation of the easternmost ross sea basin the presence of marine eocene sediments there attested to by dinoflagellates in the recycled assemblages accords with suggestions of a late mesozoic cenozoic opening of the ross sea the observed patterns of palynomorph distribution reflect input from ice drainage areas in both east and west antarctica the preservation of sediments of differing provenance in distinct areas on the sea floor probably indicates processes of meltout of debris near the grounding line of the ross ice shelf during past phases of expansion marine bottom currents have not significantly redistributed the recycled microfossils

bathymetry depth to magnetic basement and sediment thickness estimates from aerogeophysical data over the western weddell basin we estimated the bathymetry and sediment thickness of a remote and difficult to access portion of the antarctic continental margin using aerogeophysical surveying techniques the u s argentina chile aerogeophysical survey collected magnetic and gravity data over the basins surrounding the antarctic peninsula thirty seven of these flight lines were used to estimate bathymetry and depth to magnetic basement for the western weddell basin a wavenumber technique was applied to individual magnetic anomaly profiles in an automated fashion to obtain estimates of the depth to magnetic basement the bathymetric estimates were obtained by admittance inversions of the gravity field the results were then gridded at a 40 km interval for the region 64 w 44 w 73 s and 62 s bathymetric estimates and depth to magnetic basement estimates were differenced at each grid point to obtain a regional estimate of the thickness of nonmagnetic overburden assumed to be sediment subsequent spot measurements of topography in the estimated region of the continental margin generally agree to about 52 m the estimated magnetic basement deepens from the antarctic peninsula margin eastward to a maximum of 10 12 km near 54 w we also postulate the existence of two moderately large basins flanking the eastward continuation of the jason peninsula farther east the basement steps upward with a correspondent thinning of the sedimentary layer along the east coast of the peninsula results agree well with seismic studies on james ross island and magnetotelluric studies on marambio island and the larsen nunatak as well as the british antarctic survey basement estimates from aeromagnetic data this study further demonstrates the utility of combined application of airborne and satellite geophysical techniques in the study of structure and tectonic evolution of continental margins and marine basins

sublimation and aeolian sand movement from a frozen surface experimental results from presqu ile beach ontario abstract recent aeolian literature has indicated that sand movement can and does take place on frozen surfaces the winter aeolian process is influenced by the pore ice which binds the sand grains together and increases the surface resistance to wind action sublimation of the frozen moisture provides loose grains of sand which subsequently can be entrained by the wind field experiments carried out on the presqu ile beach ontario in the 1992 1993 winter provide some data on variables which affect sand loss from frozen surfaces because of sublimation sand moisture content determines the resistivity of the surface to sublimation induced sand loss frozen surfaces with higher moisture contents experience less sand loss the existing literature has indicated that temperature plays an important role in the occurrence of sublimation higher temperatures i e temperatures which are closer to 0 c result in higher rates of sublimation however the presqu ile experiments show that wind speed is more strongly correlated with sublimation induced particle loss than temperature or relative humidity higher wind speeds allow sand from the surface and sublimation produced water vapour to be removed from the area thus providing an incentive for further sublimation and sand loss to take place information on the variables which affect sublimation induced sand loss from frozen surfaces can be used to increase understanding of the processes involved in sand movement on frozen surfaces under subzero temperatures

morphology seismic structure and tectonic development of the powell basin antarctica the powell basin located near the scotia antarctica strike slip plate boundary is bounded on three sides by continental crustal blocks and it separates the south orkney microcontinent from the northeastern antarctic peninsula on the basis of the entire geophysical data set available the main structural and geological elements of the basin are identified the northern domain is characterized by an oceanic like environment with a ridge axis in the centre of the basin two conjugate deep restricted sedimentary basins are located at the base of the northeastern and northwestern margins and filled by thick sedimentary sequences the southern domain is mainly floored by transitional crust and presents rift related basement graben the margins surrounding the basin are different with the northern and southern margins mainly transcurrent whereas most of the eastern and western margins show passive margin characteristics the sedimentary sequences filling the basin have been correlated to the main tectonic processes responsible for powell basin opening and partially dated using marine magnetic anomaly identifications three main evolutionary phases are recognized that explain the geological setting of the powell basin an early phase of separation between the antarctic peninsula and the south orkney microcontinent produced stretching and progressive continental lithospheric thinning with the creation of restricted pull apart basins proto powell phase this phase was followed by a northward movement possibly accomplished with a clockwise rotation of the south orkney microcontinent drift phase with consequent oceanic crustal accretion in the northern sector of the basin and development of rift related structures in the southern sector phase spanning 27 18 ma as determined from the marine magnetic anomalies a successive clockwise rotation of the south orkney microcontinent determined the complete development of the northern sector of the basin with spreading and final structuration of the margins encircling the basin plain

meteorological controls on sand transport and dune morphology in a polar desert victoria valley antarctica the hyperarid polar desert of the mcmurdo dry valleys contains an abundance of aeolian sedimentary deposits the largest in antarctica providing a unique setting for studying cold climate aeolian processes and dune morphology meteorological controls on sand transport and changes in dune morphology were monitored for 11 days in november december 2004 on a barchan dune in the victoria valley mcmurdo dry valleys sand transport in this environment was found to be influenced by 1 interparticle cohesion ice bonding 2 diurnal variations in the speed of thermally driven easterly valley winds due to reduced solar heating by night and 3 topographically modified foehn southwesterly winds the threshold entrainment velocity during easterly valleys winds was 5 3 m s at 0 4 m 0 21 m s warm dry and gusty foehn southwesterly winds were found to promote aeolian processes by dislodging surface sediments with dune morphology responding rapidly importantly no diurnal signal in sand transport was observed under these conditions when wind speed and sand transport occurred independently of solar heating measured changes in dune morphology indicate that the dune field of the victoria valley under current environmental conditions is in dynamic equilibrium with frequent up valley sand transport by thermally generated valley winds balanced by less frequent but greater magnitude down valley sand transport by moderate to strong foehn southwesterlies this results in little net movement of dunes and subsequent change in the position of the dune field accordingly we believe that regional scale shifts in climate that cause change in the synoptic circulation patterns of the ross sea region that affect the frequency of either the up valley easterlies or down valley foehn winds will result in a net change in the morphology of the victoria valley s dune field such change in circulation may become apparent early as change in the morphology of the victoria valley sand dunes we therefore suggest this site should be monitored as an indicator site for identifying change in regional weather and climate

kinetic energy transfer through impact and its role in entrainment by wind of particles from frozen surfaces while extensive aeolian deposits are associated with glaciation little is known of the mechanisms which produced them observation of glaciofluvial sediments in pangnirtung pass n w t indicates that peak deflation occurs in the fall and winter months so that the nature of sediment transport involving frozen surfaces greatly differs from warm environments laboratory experiments indicate that such surfaces are mobilized through abrasion and are most susceptible at low volumetric water content less than 20 and low temperature 20 c stable surfaces have volumetric water contents in excess of 30 and temperatures of 15 c surface stability also increases with decreasing particle size density and possibly transport load collisions with frozen surfaces are relatively elastic with significantly greater kinetic energy transfer to ejected surface grains than observed for loose dry surfaces saltation transport in cold environments could therefore be sustained at lower windspeeds than for dry surfaces provided that some loose particles are available initially but do not accumulate at the surface

aeolian sand preserved in silver lake a new signal of holocene high stands of lake michigan aeolian sand within lake sediment from silver lake michigan can be used as a proxy for the timing of high lake levels of lake michigan we demonstrate that the sand record from silver lake plotted as percent weight is in phase with the elevation curve of lake michigan since the mid holocene nipissing phase because fluctuations in lake michigan s lake level are recorded in beach ridges and are a response to climate change the aeolian sand record within silver lake is also a proxy for climate change it appears that increases in dune activity and lake sand are controlled by similar climatic shifts that drive fluctuations in lake level of lake michigan high lake levels destabilize coastal bluffs that drive dune sand instability and along with greater wintertime storminess increase niveo aeolian transport of sand across lake ice the sand is introduced into the lake each spring as the ice cover melts

small scale field aligned plasmaspheric density structures inferred from the radio plasma imager on image 1 among the objectives of the radio plasma imager rpi on image is the observation of the earth s plasmasphere from the satellite s polar orbit with apogee 8 re geocentric distance and perigee near 1200 km altitude this objective is here pursued by 1 remote sounding from high altitude regions outside the main plasmasphere 2 sounding within the plasmasphere and 3 in situ passive measurements of natural wave activity during sounding of the plasmasphere from both outside and inside the plasmapause rpi echoes that follow non field aligned ray paths are usually not the discrete traces on range versus frequency records plasmagrams that are predicted by ray tracing simulations in smooth magnetospheric density models instead such rpi echoes exhibit various amounts of spreading from 0 5 re to 2 re in virtual range range assuming free space speed of light propagation the range spreading is attributed to scattering from partial reflection from and propagation along geomagnetic field aligned electron density irregularities there exists a substantial body of theoretical work on mechanisms that might explain the appearance of such irregularities both within and beyond the plasmasphere that the spread producing irregularities are field aligned is suggested by the efficiency with which rpi excites discrete echoes that propagate along the geomagnetic field sometimes into both hemispheres the spatial distributions and scale sizes of the spread producing irregularities remain to be investigated the rpi echo data however coupled with earlier evidence from topside sounders and whistler mode instruments suggest that they can have cross field scale sizes within a range from 200 m to over 10 km and electron densities within 10 of background rpi is found capable of detecting plasmapause locations from distances of 3 re or more when minimal signal integration is used the location and range of density values of a steep plasmapause can be determined from distances of order 1 re and echoes can at times be returned from points extending inward from the plasmapause to locations where the electron density reaches 3000 cm 3 which is usually at l 3

the margins of the south orkney microcontinent marine geophysical studies of the south orkney microcontinent show two intersecting tectonic fabrics of different age the older fabric is oriented e w and represents the magmatic arc and fore arc created by subduction related processes at the pacific margin during the mesozoic the younger oriented nnw to sse comprises half graben related to e w rifting at both the eastern and western margins of the microcontinent both fabrics provide constraints on a 40 ma reconstruction which shows a highly systematic distribution of arc and fore arc provinces and points to the importance of e w strike slip in regional tectonic evolution the rifting apparently of oligocene age is associated with back arc extension which created the oceanic basins to either side of the microcontinent this strongly supports the existence of subduction with the same orientation as the present south sandwich arc as far back as 35 or 40 ma

glacigenic sediments on a passive continental margin as exemplified by the barents sea abstract reflection seismics data borehole data and gravity cores have been used to map the sedimentary facies of the epicontinental southwestern barents sea its continental margin and adjacent coastal areas an upper unconformity with a glacially eroded morphology extends over most of the continental shelf up to 300 m of stratiform glacigenic sediments overlie this unconformity these sediments can be grouped into seismic units which are separated by smooth or irregular erosional surfaces each sequence may be up to 150 m thick normally with a lateral extent of 100 300 km three dominant seismic signatures may be discerned semi transparent stratified and chaotic reflection patterns these sediments are partly glacifluvial in origin but on the whole they represent more or less tectonized glacimarine deposits the deeper troughs on the continental shelf contain an undeformed postglacial glacimarine marine trough fill the greatest thickness up to 1000 m of glacigenic sediments occurs at the shelf break and below the upper slope the depocentres are situated at trough mouth fans the sediments comprise several prograding sequences with a complex sigmoid oblique character indicating alternating upbuilding and depositional bypass erosion in the topset segment small and large scale slide scars are observed on the upper slope and debris lobes on the lower slope a marked progradation seems to have occurred during the plio pleistocene glacial periods this progradation also resulted in an unstable slope with various types of sediment gravity flows currents flowing along the slope were established during interglacials and gullying by cold dense shelf water and downslope transport occurred maximum net sedimentation rates are 0 2 m ka continental slope 0 4 m ka shelf break 0 1 m ka shelf stratiform diamictons 1 m ka shelf trough fills and 60 m ka fjord trough fills

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

development of hybrid aeolian dunes the william river dune field northwest saskatchewan canada observations have been made on the structure morphology and pattern of sand movement on large scale roughly elongate northwest southeast aligned aeolian sand dunes in a desert area of northern saskatchewan canada transverse profiles show steeper northeast flanks the lower parts of which are covered with psammophilous grasses dune structure is dominated by northeast dipping accretion laminae and 14c dates of organic material trapped between such exposed laminae on the southwest flank indicate migration to the northeast at about 0 5 m year in the last few centuries on the other hand there is a progressive increase in height bulk symmetry and peakedness of the dunes from northwest to southeast suggestive of substantial along dune sand movement the present day wind regime shows a potential resultant sand transport vector to the southeast virtually parallel to the dune axis winds from the north northeast and northeast dominate the first 6 months of the year followed by winds from the west so

scotia sea regional tectonic evolution implications for mantle flow and palaeocirculation abstract the scotia sea and surrounding scotia arc have evolved over the past 40 ma by extension behind an east migrating subduction zone at the boundary between the south american sam and antarctic ant plates the considerable data set now available regional geology and geophysics earthquake seismology satellite altimetry global plate analyses suggest why east migrating subduction began what has been the driving force that has sustained it and what other processes have controlled the mode of back arc extension in the scotia sea a suite of six reconstructions has been developed based on this data set the reconstruction to 40 ma creates a compact cuspate continental connection between south america and the antarctic peninsula at the subducting pacific margin with fragments now dispersed around the scotia arc occupying positions within it compatible with their known geology the driving force has been subduction of south american ocean floor which began as a result of southward migration of the pole of south american antarctic plate rotation and a key modulator of back arc extension has been collision of ridge crest sections of the south american antarctic plate boundary with the east advancing trench cenozoic regional tectonic evolution has two other likely consequences which greatly increase its importance firstly this region saw the tectonic disruption of the final barrier to complete circum antarctic deep water flow that may have had a profound effect on palaeoclimate secondly it is possible that the rapid roll back of the hinge of subduction is related to shallow eastward flow in the sub lithospheric mantle both of these consequences are explored the reconstructions show that rapid roll back of the subduction hinge averaging 50 mm a over the last 40 ma with respect to the south american plate has been a feature of all of scotia sea evolution and provide a history of motion of several oceanic microplates most of which are now welded together within the scotia sea this will guide the location of seismometers and or dredge hauls to test the hypothesis of shallow mantle flow and help interpret the results the reconstructions also allow an assessment of the creation of deep water pathways that would have permitted the development of the present day antarctic circumpolar current acc an early miocene onset within the period 22 17 ma seems likely for the acc depending on the structure and palaeo elevation of davis bank and aurora bank sections of the north scotia ridge however the study shows there was a delay of one or more million years between initial provision of a deep water pathway and the major mid miocene change in global climate involving the general level of antarctic glaciation that may have been related if these changes were related then the delay suggests that other factors possibly rough elevated ocean floor but also non tectonic factors such as atmospheric co2 were important in determining palaeoclimate

ancient and modern cold climate aeolian sand deposition a review although partly active aeolian sand sheets and dunes cover large areas in the zones of dis continuous permafrost little precise information is available about the influence of cold climate conditions on modern aeolian processes this means that palaeoenvironmental reconstructions in the stabilised mainly late pleistocene dune fields and cover sand regions in the sand belts of the european lowlands and the northern great plains of the usa and canada are necessarily still based on ancient evidence cold climate wind deposits are typically derived from areas of abundant sediment supply like unvegetated flood plains glacial outwash plains till plains and lake shores the common parabolic and transverse dune forms resemble those observed in temperate regions although a variety of periglacial features has been identified in late pleistocene dune and cover sands none of them indicate that permafrost is crucial to aeolian activity specific structures in aeolian strata permit tentative interpretation of the moisture content of depositional sand surfaces the nature of annual sedimentation cycles and the processes by which strata were deposited and or contorted but surprisingly little is known about the role of vegetation in the process of sand accumulation dunes are most informative with respect to reconstructions of past wind regimes which offer important data for verification of palaeoclimatic simulations

geology and petroleum potential of adelie coast margin east antarctica the few rock outcrops on adelie coast wilkes land consist mainly of precambrian plutonic rocks and metasediments on the continental margin several multichannel seismic surveys including the 1982 ifp survey reveal the presence of a thick sedimentary basin especially beneath the outer continental shelf and upper slope where it may exceed 6000 m thin basin results from the creation and evolution of a continental margin initiated some 100 ma from the separation of australia and antarctica beneath the outer shelf which is 400 500 m deep the sedimentary series consist of four units separated by three major unconformities 1 a predrift unit including a precambrian basement possible paleozoic and early mesozoic sediments and a mesozoic syn rift sequence 2 an upper eocene to oligocene unit in a shallow marine environment and 3 a neogene glacial prograding unit the predrift and early postrift units are considered to be a promising target with reference to other passive margins although no major hydrocarbon accumulation has been discovered as yet on the australian conjugate margin

winter variability of aeolian sediment transport threshold on a cold climate dune abstract changes in surface conditions on cold climate aeolian dunes are pronounced during winter dunes are wet snow covered and or frozen for extended periods of time it is unknown how the critical wind speed for sediment transport threshold varies and how threshold may influence sediment transport predictions although the impact of surface conditions on threshold has been examined in synthetic experiments wind tunnels complicated feedbacks between threshold sand transport and surface conditions that occur in natural environments suggest that a ground based empirical approach may provide enhanced insight in this study we investigate threshold variability for 73 days during fall winter spring surface conditions from 18 november 2008 to 30 may 2009 in the bigstick sand hills of saskatchewan canada simultaneous measurements of threshold and atmospheric variables air temperature relative humidity solar radiation wind speed and direction were used to examine the extent to which surface erodibility was regulated by meteorology time lapse images of the surface from a co located camera were used for quality control and interpreting changes in the surface affecting threshold results reveal that threshold varied throughout the deployment 25 75 quartiles 6 92 8 28 m s 1 mean 7 79 m s 1 threshold variability was especially evident at two scales i event timescale and ii seasonal timescale event scale variability peaked during mid winter in one event the threshold varied by 6 m s 1 in 2 h with freezing and re freezing of the surface and relatively constant atmospheric conditions the causes of event scale variability are complex though qualitatively related to changes of wind direction antecedent meteorological conditions and vertical variations of grain scale bonding agents such as pore ice and moisture seasonal scale changes manifested as an increase in threshold during fall peaking in mid winter and decreasing in spring increased threshold in mid winter was linked to lower insolation and air temperature suggesting low erodibility due to the presence of pore ice correlation coefficients of threshold versus atmospheric variables yielded relatively weak correlations air temperature r 0 322 relative humidity r 0 388 solar radiation r 0 309 that also varied according to wind direction suggesting that the link between atmospheric conditions and surface erodibility on cold climate dunes is complex this contrasts with results from field based studies in warmer climates and controlled wind tunnel experiments which show a more direct link between atmospheric variables temperature and humidity and surface erodibility nevertheless our results do show a seasonal pattern of threshold that could be important for modeling cold climate aeolian sediment transport

dynamics of extensional basin formation and inversion introduction this volume contains a cohection of papers on the dynamics of extensional basin formation and inversion presented at the 3rd annual workshop of the international lithosphere program task force origin of sedimentary basins in sundvollen norway 18 23 august 1992 previous workshops of the ilp task force had been in rueil malmaison france 1990 and in matrahaza hungary 19911 on the rim of the pannonian basin the task force also organized a number of sessions during the 1992 european geophysical society and the 1993 european union of geosciences conferences reports of these meetings have been published in a number of special volumes and papers cloetingh et al 1993a b stephenson 1993 cloetingh sassi and task force team 1994 the 4th task force meeting focusing on the interplay of extension and compression was held in benevento southern italy in october 1993 a selection of papers presented at that task force workshop will be published in a forthcoming special volume of tectonophysics the emphasis of the 5th workshop of the task force taking place in the dead sea rift israel is on rifting and strike slip tectonics the 1995 workshop will be organized in the southern pyrenean foreland basin with the aim of examining the relationships between tectonics and eustasy in foreland fold and thrust belts the emphasis of the sundvollen workshop was on modelling studies as well as observational approaches to the dynamics of basin extension and inversion important elements of the meeting were the discussion of extensional tectonics rifting in passive margin settings and volcanism and magmatism in rifts and basins following the task force strategy to link subsurface data to field analogues an important part of the meeting was devoted to a thematic excursion in the oslo rift field guides have been published separately larsen et al 1992a

a model of the antarctic ice sheet numerical modelling of ice sheets and glaciers has become a useful tool in glaciological research a model described here deals with the vertical mean ice velocity is time dependent computes bedrock adjustment and uses an empirical diagnostic relationship to derive the distribution of ice thickness in ice shelves the rate of snowfall and ice snow melt depends on the prescribed sea level temperature surface slope elevation and distance to open water the model is able to reproduce the major features of the antarctic ice sheet when it is run to a steady state for present climatic conditions the main difference with the present ice sheet is that the shallow parts of the weddell sea become covered by grounded ice

spread f and the structure of equatorial ionization depletions in the southern anomaly region combined optical and radio sensors provide a unique characterization of the structure of equatorial emission depletion regions connected to rising bubbles over the magnetic equator in chile as part of the miseta campaign in fall 1994 a ccd enhanced all sky imaging photometer provided optical images of the postsunset appearance and motions of the depletion bands at a magnetic dip latitude of 11 s concurrently a digisonde collocated with the photometer monitored the appearance of spread f in between the ionograms the sounder operated as a doppler interferometer identifying the locations of f layer irregularities associated with the spread f they were found to lie inside the emission depletion regions the hf sounder requiring orthogonality with the field aligned f layer irregularities to generate the spread structure tracked these irregularities inside the emission depletion bands as they drifted eastward ray tracing simulations show that the radio waves become trapped within the depletion regions when the depletions are within 300 km of the sounder site model calculations indicate that the sounder rays encounter orthogonality with the earth s magnetic field within the depletion bubble southward from the site consistent with the local dip angle the combination of optical images with hf radio sounding demonstrated that radio imaging in the equatorial ionosphere can be done with a digital ionosonde that operates as a doppler interferometer the digisonde measurements and ray tracing show for the first time that the spread f signatures on ionograms are the result of coherent scatter from irregularities primarily within the walls of the depletion

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