evolution of the southern ocean winter mixed layer and sea ice open ocean deepwater formation and ventilation an analytical model has been developed to describe the nature of the winter ocean sea ice interaction in the southern ocean to determine the principal processes responsible for maintaining stability in this marginally stable region and to predict the response to changes in the external forcing and initial conditions the model accurately describes the sparse winter observations and the general temporal evolution of the ice mixed layer depth and salinity for the period following the elimination of the seasonal pycnocline by rapid fall ice growth a scale analysis and sensitivity study reveal the system parameter dependence this indicates that the magnitude of entrainment is proportional to fst h0 s where fs is the external salt flux h0 the depth of the winter mixed layer and s the salinity gradient through the pycnocline thermodynamic ice growth reflects predominantly the competition between the oceanic diffusive heat gain across the base of the mixed layer and the loss to the atmosphere through the ice and leads a strong thermal gradient across the pycnocline leads to a significant diffusive flux which balances most of the heat lost to the atmosphere this limits the amount of ice growth possible and plays the principal role in maintaining the system stability since the ice growth is required for destabilization through haline rejection during the growth process the system is also sensitive to the large ratio of heat to salt in the pycnocline this introduces a negative feedback where increasing ice growth induces entrainment by the associated salt flux which in turn drives an entrainment heat flux which compensates for heat lost to the atmosphere this moderates the ability to grow ice and drive further entrainment the absolute strength of the salinity gradient on the other hand dictates the effectiveness which a same magnitude external salt flux will have in driving entrainment the effectiveness with which changes in these parameters as well as several other external parameters can influence the southern ocean stability is explicitly evaluated through the sensitivity study and analysis

sedimentary record of a fluctuating ice margin from the pennsylvanian of western gondwana parana basin southern brazil abstract the parana basin is a key locality in the context of the late paleozoic ice age lpia because of its location east of the andean proto margin of gondwana and west of contiguous interior basins today found in western africa in this paper we document the sedimentary record associated with an ice margin that reached the eastern border of the parana basin during the pennsylvanian with the aim of interpreting the depositional environments and discussing paleogeographic implications the examined stratigraphic succession is divided in four stacked facies associations that record an upward transition from subglacial to glaciomarine environments deposition took place during deglaciation but was punctuated by minor readvances of the ice margin that deformed the sediment pile tillites well preserved landforms of subglacial erosion and glaciotectonic deformational structures indicate that the ice flowed to the north and northwest and that the ice margin did not advance far throughout the basin during the glacial maximum consequently time equivalent glacial deposits that crop out in other localities of eastern parana basin are better explained by assuming multiple smaller ice lobes instead of one single large glacier these ice lobes flowed from an ice cap covering uplifted lands now located in western namibia where glacial deposits are younger and occur confined within paleovalleys cut onto the precambrian basement this conclusion corroborates the idea of a topographically controlled ice spreading center in southwestern africa and does not support the view of a large polar ice sheet controlling deposition in the parana basin during the lpia

relating wave attenuation to pancake ice thickness using field measurements and model results wave attenuation coefficients m a1 were calculated from in situ data transmitted by custom wave buoys deployed into the advancing pancake ice region of the weddell sea data cover a 12 day period as the buoy array was first compressed and then dilated under the influence of a passing low pressure system attenuation was found to vary over more than 2 orders of magnitude and to be far higher than that observed in broken floe marginal ice zones a clear linear relation between and ice thickness was demonstrated using ice thickness from a novel dynamic thermodynamic model a simple expression for in terms of wave period and ice thickness was derived for application in research and operational models the variation of was further investigated with a two layer viscous model and a linear relation was found between eddy viscosity in the sub ice boundary layer and ice thickness

late paleozoic glacial episodes in gondwanaland reflected in transgressive regressive depositional sequences in euramerica the late paleozoic glaciation of gondwanaland comprised two short episodes in the famennian i and visean ii confined to brazil and adjacent northwest africa and a long episode that started in the namurian iiia of eastern australia and bolivia argentina expanded to cover much of gondwanaland in the stephanian asselian iiib and collapsed in the early sakmarian iiic dropstones in eastern australia indicate that small ice centers lingered to the kazanian across the belt of low latitudes north of gondwanaland short ranging fossils in widespread shallow marine and paralic deposits indicate synchronous deposition of transgressive regressive sequences in different parts of euramerica these sequences correlate with glacial events in gondwanaland at three levels a four major regressions in euramerica in the famennian 1 visean 2 namurian 3 stephanian 4 and the tastubian transgression that preceded the sterlitamakian regression 5 also recorded in gondwanaland correlate with glacial episodes i ii and iiia iiib and iiic b the time interval of cyclothemic deposition in euramerica brigantian or latest visean to sterlitamakian correlates with that of glacial episode iii and c the dominant period of the euramerican cyclothems as estimated from the middle and late pennsylvanian deposits of the mid continent of north america and of the thickest known gondwanaland glacigenic sediment the earliest permian lyons group of western australia is 0 4 ma equivalent in turn to the long orbital eccentricity period of the quaternary ice age and the dominant period of fluctuation of the late miocene antarctic ice cap the three levels of correlations confirm wanless and shepard9s 1936 hypothesis that the late paleozoic cyclothems are controlled largely by sea level fluctuations related to the gondwanaland glaciation

glacial valley cross profile morphology tian shan mountains china abstract the morphology of glacial valley cross sections can be described in terms of power law y ax b or quadratic equations y a bx cx 2 fitted to empirical data the quadratic solution provides a more robust way of describing the morphology of glacial valley cross sections whereas the power law has more potential in understanding the cross sectional shapes and their evolution these two functions are used to study the cross sectional morphology of glacial valleys in the middle and western tian shan mountains and to discuss the comparison with fluvial channels the major conclusions are 1 power law equation parameters a and b are sensitive to the origin selection with larger sensitivity in vertical and a a ln a values conversely c values of the quadratic equation are more stable regardless of different origins selected 2 hirano and aniya earth surf processes landforms 13 1988 707 716 suggested two characteristic patterns in the relationship between the power law exponent b and the valley form ratio fr however glacial valleys in these areas do not fit the rocky mountain model for b fr values described by hirano and aniya for alpine glacial valleys this indicates that this rocky mountain model cannot be applied to all alpine glacial areas 3 the c values of the quadratic equation represent a curvi linear trend with its corresponding fr s at the same time power law parameters a and b fit a closed linear relationship both from these areas and others in the published literature 4 the cross sectional shapes of glacial valleys show clear differences with fluvial channels by comparing a b values of glacial valleys with the hydraulic geometry of fluvial channels this implies that the a b relationship and the variation range of b values commonly with 1 5 2 5 may be helpful to differentiate valleys formed by different processes

sea level changes in a back arc foreland transition the late carboniferous permian karoo basin of south africa abstract the late carboniferous to early permian succession in the karoo basin consists in ascending stratigraphic order of diamictites mudrocks greywackes and immature sandstones the diamictites are interpreted as glacigene deposits laid down by a marine ice sheet on a shelf post glacial suspension settling of predominantly mud occurred on the basin floor during open marine and later brackish conditions basin floor fan deposits accumulated in the foredeep whereas deltaic mud silt and sand finally infilled the basin glacigene sedimentation occurred in a back arc basin during the late carboniferous and early permian the post glacial succession accumulated in a foreland basin in which the rising orogenic belt was the predominant sediment source relative sea levels following the major namurian regression apparently remained low during the extensive gondwana glaciation marine ice sheets are highly sensitive to sea level fluctuations and minor sea level rises probably climatically controlled were recorded as interglacials when parts of the marine ice sheet collapsed final collapse of the marine ice sheet was associated with a major transgression post glacial mudrock deposition was characterised by relatively high sea levels except for the period of basin floor fan deposition when there was a sea level lowstand final infilling of the basin by prograding deltas was accompanied by a major regression the late carboniferous to early permian sea level fluctuations in the karoo basin show correspondence with global eustatic cycles reflecting low tectonic interference with sea level patterns however late permian sea levels were predominantly tectonically controlled as a result of foreland basin evolution possible global eustatic events complemented apparent sea level changes within the basin during this period

on the origin of the itarare group basal nonconformity and its implications for the late paleozoic glaciation in the parana basin brazil abstract outcrop studies of the itarare group in the alfredo wagner area along the eastern margin of the parana basin in brazil reveal a partially exhumed nnw sse oriented glacial paleovalley the carboniferous rio do sul formation represents the basal interval of the glacially influenced itarare group and rests directly on precambrian basement rocks this nonconformity is thought to represent an areal scouring surface as indicated by the series of glacially carved linear depressions that were incised into the glaciated bedrock during glacial advances these large scale erosional landforms differ in their extent by orders of magnitude and include wide deep troughs as well as narrower shallower gouges glacial troughs and gouges usually display smaller scale subglacial erosion landforms such as polished and grooved striations on their walls and floors these indicate the nnw motion of a warm based grounded glacier in addition large scale erosional features represent local topographic lows within the major glacial paleovalley these local lows are large enough to contain part of the succeeding deglacial deposits which thin toward and onlap the wall of these depressions we grouped these deglacial deposits into six genetic facies associations fa 1 to 6 within three fining upward glacial cycles fa 1 is composed of black shale and represents an initial marine flooding event it can be correlated with the regionally widespread lontras shale fa 2 is composed of sandstones and mudstones associated with flood derived hyperpycnal flows and occasionally with surge type turbidites fa 3 is represented by plastered or injected matrix supported conglomerates emplaced as lodgment tills fa 4 comprises matrix and clast supported conglomerates sandstones and mudstones attributed to ice rafting and concentrated flows in grounding line fan facies this unit also contains ice keel dragging features carved into soft substrate fa 5 is composed of dropstone bearing black shale related to a second major marine flooding event within the paleovalley fa 6 comprises sandstones associated with channelized surge type turbidites forming the second turbidite system in the succession as these deposits are confined to a paleovalley we infer that sedimentation was influenced by topographically controlled ice streams instead of non confined widespread ice lobes as previously suggested reconstructing south america and southern africa in their positions during the lpia suggests that the glacial valleys then present in the namibia area may have extended further into the eastern margin of the parana basin in this scenario confined outlet glaciers would have flowed out from the namibian windhoek ice cap and terminated along the eastern margin of the parana basin

heat flux through sea ice in the western weddell sea convective and conductive transfer processes the heat flux through the snow and sea ice cover and at the ice ocean interface were calculated at five sites in the western weddell sea during autumn and early winter 1992 the ocean heat flux averaged 7 2 w m2 from late february to early june and average ice air heat flux in the second year floes depended on the depth of the snow cover and ranged from 9 to 17 0 8 w m2 in late february three of the five sites had an ice surface which was depressed below sea level resulting at two of the sites in a partially flooded snow cover and a slush layer at the snow ice interface as this slush layer froze to form snow ice the dense brine which was rejected flowed out through brine drainage channels and was replaced by lower salinity nutrient rich seawater from the ocean upper layer we estimate that about half of the second year ice in the region was covered with this slush layer early in the winter as the slush layer froze over a 2 to 3 week period the convection within the ice transported salt from the ice to the upper ocean and increased total heat flux through the overlying ice and snow cover on an area wide basis approximately 10 cm of snow ice growth occurred within second year pack ice primarily during a 2 to 3 week period in february and march this ice growth near the surface of the ice provides a salt flux to the upper ocean equivalent to 5 cm of ice growth despite the thick about 1 m ice cover in addition to the ice growth in the small area less than 5 open water regions

characterization of cavities using the gpr lidar and gnss techniques the study of the many types of natural and manmade cavities in different parts of the world is important to the fields of geology geophysics engineering architectures agriculture heritages and landscape ground penetrating radar gpr is a noninvasive geodetection and geolocation technique suitable for accurately determining buried structures this technique requires knowing the propagation velocity of electromagnetic waves em velocity in the medium we propose a method for calibrating the em velocity using the integration of laser imaging detection and ranging lidar and gpr techniques using the global navigation satellite system gnss as support for geolocation once the em velocity is known and the gpr profiles have been properly processed and migrated they will also show the hidden cavities and the old hidden structures from the cellar in this article we present a complete study of the joint use of the gpr lidar and gnss techniques in the characterization of cavities we apply this methodology to study underground cavities in a group of wine cellars located in atauta soria spain the results serve to identify construction elements that form the cavity and group of cavities or cellars the described methodology could be applied to other shallow underground structures with surface connection where lidar and gpr profiles could be joined as for example in archaeological cavities sewerage systems drainpipes etc

valley formation by fluvial and glacial erosion cross valley profiles from the west slope of the olympic peninsula washington are used to investigate the relative effects of fluvial and glacial erosion on valley formation unlike most ranges where glaciers and rivers sequentially occupied the same valleys neighboring valleys in the olympic mountains developed in similar lithologies but were subject to different degrees of glaciation allowing comparison of the net effect of glacial and fluvial processes integrated over many glacial cycles upslope drainage area was used to normalize comparisons of valley width ridge crest to valley bottom relief and valley cross sectional area as measures of net differences in the mass of rock excavated from below ridgelines for 131 valley spanning transects valley width relief and cross sectional areas are similar for glaciated partly glaciated and unglaciated fluvial valleys with drainage areas of 10 km 2 but diverge downslope glaciated valleys draining 50 km 2 reach two to four times the cross sectional area and have to 500 m greater relief than comparable fluvial valleys partly glaciated valleys have intermediate dimensions at distances of 5 km from valley heads the cumulative upstream volume of rock removed to form valleys is two to four times greater in glacially incised valleys than in fluvial valleys the finding of strong differences in the net result of valley excavation by fluvial and glacial erosion supports the interpretation that alpine glaciers are more effective erosional agents than are rivers and implies that large alpine valleys deepened and enlarged in response to pleistocene glaciation

a depositional record of deglaciation in a paleofjord late carboniferous pennsylvanian of san juan province argentina the role of catastrophic sedimentation the combination of high sediment supply rates and ample accommodation within fjords provides high resolution records of deglaciation ancient fjord fills provide the potential for three dimensional views of the evolution of depositional environments in response to changing sediment supply and base level through the deglacial process we describe the fill jejenes formation of a well exposed late carboniferous pennsylvanian glacial valley and its tributaries these deposits record the progressive marine flooding and infilling of topography by glacially derived sediments the geometry of the valley and its tributaries is controlled by the underlying lower paleozoic lithologies a deep valley with steep sides exists where the bedrock is massive limestones and a broader shallower valley exists where the bedrock is generally a fine grained olistostrome the valleys are locally floored with diamictites including both in situ tillites and remobilized diamictites in the trunk valley these are locally overlain by a small shallow water delta the major part of the valley fill consists of a 150 m thick mudstone dominated succession probably generated by plumes of glacial outwash containing numerous dropstones that decrease in abundance down the fjord the mudstones contain numerous thin sandstone and conglomerate turbidites that were supplied laterally via subaqueous gravel fans feeding in from the tributary valleys each of which has a distinctive clast suite related to the local subcrop the entire succession is overlain by 300 m of sandy turbidites of which the upper part includes large mass transport complexes intercalated within the succession in the trunk valley are structureless graded silty mudstones lacking dropstones but with abundant large wood fragments close to the steep western margin of the trunk valley each of these massive mudstones is underlain by a slump or debris flow locally containing meter scale blocks of ordovician limestone from the valley side we interpret these as a consequence of rockfalls from the steeper valley sides triggering debris flows on the subaqueous fjord slopes we suggest that large solitary waves were generated as the rockfalls entered the water traveling along the fjord and stripping vegetation from the shoreline large amounts of mud and silt were thrown into suspension during these events and subsequently settled from suspension to form the structureless graded beds these deposits and other mass flow deposits within the succession emphasize the potential importance of catastrophic sedimentation within deglacial successions

wind and wave influences on sea ice floe size and leads in the beaufort and chukchi seas during the summer fall transition 2014 sea ice floe size distribution and lead properties in the beaufort and chukchi seas are studied in the summer fall transition 2014 to examine the impact on the sea ice cover from storms and surface waves floe size distributions are analyzed from medea landsat8 and radarsat 2 imagery with a resolution span of 1 100 m landsat8 imagery is also used to identify the orientation and spacing of leads the study period centers around three large wave events during august september 2014 identified by swift buoys and wavewatch iii model data the range of floe sizes from different resolutions provides the overall distribution across a wide range of ice properties and estimated thickness all cumulative floe size distribution curves show a gradual bending toward shallower slopes for smaller floe sizes the overall slopes in the cumulative floe size distribution curves from landsat8 images are lower than while those from radarsat 2 are similar to previously reported results in the same region and seasonal period the medea floe size distributions appeared to be sensitive to the passage of storms lead orientations regardless of length correlate slightly better with the peak wave direction than with the mean wave direction their correlation with the geostrophic wind is stronger than with the surface wind the spacing between shorter leads correlates well with the local incoming surface wavelengths obtained from the model peak wave frequency the information derived shows promise for a coordinated multisensor study of storm effects in the arctic marginal ice zone

analysis of a rapid sea ice retreat event in the bellingshausen sea the winter advance of the sea ice edge in the bellingshausen sea is frequently interrupted by periods of rapid retreat lasting a few days the frequency and duration of such events strongly controls the location of the late winter sea ice edge in this sector of the antarctic we examine the dynamics and thermodynamics of a retreat event that occurred in may 2001 using data from a drifting buoy array together with diagnostics from a kinematic thermodynamic ice growth model and a high resolution 11 km regional coupled ocean ice model during the retreat event the ice edge retreated by 250 km over 13 days in response to strong and persistent northerly winds associated with a quasi stationary low pressure system ice motion in the outer part of the pack was convergent and correlated strongly with local wind forcing by contrast in the region closer to the coast ice motion was less well correlated with wind forcing model diagnostics indicate that ice thickening resulting from convergence in the outer pack was largely balanced by basal melting in the outer pack ice was in a state close to free drift while closer to the coast internal ice stresses became significant the ocean ice model simulated the characteristics of the retreat event realistically giving us confidence in the ability of such models to reproduce ice conditions in this sector

application of field geophysics in geomorphology advances and limitations exemplified by case studies abstract during the last decade the use of geophysical techniques has become popular in many geomorphological studies however the correct handling of geophysical instruments and the subsequent processing of the data they yield are difficult tasks furthermore the description and interpretation of geomorphological settings to which they apply can significantly influence the data gathering and subsequent modelling procedure e g achieving a maximum depth of 30 m requires a certain profile length and geophone spacing or a particular frequency of antenna for more than three decades geophysical techniques have been successfully applied for example in permafrost studies however in many cases complex or more heterogeneous subsurface structures could not be adequately interpreted due to limited computer facilities and time consuming calculations as a result of recent technical improvements geophysical techniques have been applied to a wider spectrum of geomorphological and geological settings this paper aims to present some examples of geomorphological studies that demonstrate the powerful integration of geophysical techniques and highlight some of the limitations of these techniques a focus has been given to the three most frequently used techniques in geomorphology to date namely ground penetrating radar seismic refraction and dc resistivity promising applications are reported for a broad range of landforms and environments such as talus slopes block fields landslides complex valley fill deposits karst and loess covered landforms a qualitative assessment highlights suitable landforms and environments the techniques can help to answer yet unsolved questions in geomorphological research regarding for example sediment thickness and internal structures however based on case studies it can be shown that the use of a single geophysical technique or a single interpretation tool is not recommended for many geomorphological surface and subsurface conditions as this may lead to significant errors in interpretation because of changing physical properties of the subsurface material e g sediment water content in many cases only a combination of two or sometimes even three geophysical methods gives sufficient insight to avoid serious misinterpretation a good practice guide has been framed that provides recommendations to enable the successful application of three important geophysical methods in geomorphology and to help users avoid making serious mistakes

simulation of pancake ice dynamics in a wave field from many field observations it has become well known that pancake ice is ubiquitous in a wave dominated sea these strikingly uniform circular floes are consistently found in the antarctic seas during the ice formation season their presence has also been reported in the bering sea the greenland sea and in polynyas and leads within pack ice in one estimate made by p wadhams personal communication 1991 the areal coverage of pancake ice in the southern ocean marginal ice zone is around 6 106 km2 pancake ice forms through a combination of thermodynamic growth and mechanical thickening caused by rafting of floes that is driven by wave motion this complex growth process is much faster than pure thermodynamic growth and hence may be the main factor responsible for ice edge advance in marginal ice zones in this paper we simulate wave ice floe dynamics by combining a new three dimensional discrete element model with wave hydrodynamics in one set of simulations we calculate ice drift speed as a function of wave amplitude and ice collisional dynamics in a second set of simulations we place a non reflecting vertical barrier meant to simulate the fast ice edge the simulation results show the rate of increase of the ice impact force on the barrier and the accompanying thickening of the rafted region in front of the barrier as a function of wave amplitude results from this study will help quantify the formation process for pancake ice covers in a wave field

modeling of the influence of sea ice cycle and langmuir circulation on the upper ocean mixed layer depth and freshwater distribution at the west antarctic peninsula

on the parameterisation of oceanic sensible heat loss to the atmosphere and to ice in an ice covered mixed layer in winter abstract in high latitude oceans with seasonal ice cover the ice and the low salinity mixed layer form an interacting barrier for the heat flux from the ocean to the atmosphere the presence of a less dense surface layer allows ice to form and the ice cover reduces the heat loss to the atmosphere the ice formation weakens the stability at the base of the mixed layer leading to stronger entrainment and larger heat flux from below this heat transport retards and perhaps stops the growth of the ice cover as much heat is then entrained from below as is lost to the atmosphere this heat loss further reduces the stability and unless a net ice melt occurs the mixed layer convects two possibilities exist 1 a net ice melt sufficient to retain the stability will always occur and convection will not take place until all ice is removed the deep convection will then be thermal deepening the mixed layer 2 the ice remains until the stability at the base of the mixed layer disappears the mixed layer then convects through haline convection into the deep ocean warm water rises towards the surface and the ice starts to melt and a new mixed layer is reformed the present work discusses the interactions between ice cover and entrainment during winter when heat loss to the atmosphere is present one crucial hypothesis is introduced when ice is present and the ocean loses sensible heat to the atmosphere and to ice melt the buoyancy input at the sea surface due to ice melt is at a minimum using a one dimensional energy balance model applied to the artificial situation where ice melts directly on warmer water it is found that this corresponds to a constant fraction of the heat loss going to ice melt it is postulated that this partitioning holds for the ice cover and the mixed layer in the high latitude ocean when a constant fraction of heat goes to ice melt at least one deep convection event occurs before the ice cover can be removed by heat entrained from below after one or several convection events the ice normally disappears and a deep reaching thermal convection is established conditions appropriate for the weddell sea and the greenland sea are examined and compared with field observations with realistic initial conditions no convection occurs in the warm regime of the weddell sea a balance between entrained heat and atmospheric heat loss is established and the ice cover remains throughout the winter at maud rise convection may occur but late in winter and normally no polynya can form before the summer ice melt in the central greenland sea the mixed layer generally convects early in winter and the ice is removed by melting from below as early as february or march this is in agreement with existing observations

deglacial and postglacial sedimentary architecture in a deeply incised paleovalley paleofjord the pennsylvanian late carboniferous jejenes formation san juan argentina quebrada de las lajas near san juan argentina preserves an early pennsylvanian deglacial postglacial succession in a highly confined paleofjord setting the sedimentary succession records four distinct stages in the evolution of the valley fill stage 1 is represented by the deposits of subglacial diamictites ice contact deltas and related deep water lacustrine environments including several subaqueous channels stage 2 records a glacio eustatic marine transgression and a slow down of the clastic supply into the paleofjord stage 3 records a sandy confined turbidite environment stage 4 consists of a coarse grained delta which represents a significant rejuvenation of the sedimentary system in the paleofjord the transition from stage 1 to stage 2 was abrupt and basinwide and has proven to be a good regional correlation marker in this paleovalley the glacio eustatic rise probably caused floating and consequent rapid melting of the valley glacier this resulted in a paleovalley wide turbidite event that is up to 5 m thick and indicates an overall waning character the rapid sediment emplacement in this event and resulting loading of the paleovalley sediments may have helped cause widespread mass transport events at the stage 1 2 boundary all stages show evidence of mass transport related deposits but stage 1 records the most widespread mass transport with a large spectrum of processes represented including coherently slumped material rafted blocks and completely mixed debris flow deposits these mass transport deposits range from a few meters to over 50 m thick and up to hundreds of meters wide and long most of the large mass transport deposits in the lower part of the fjord fill occurred at the transition to stage 2 implicating a rise in relative sea level as a possible trigger for the slope failures additionally stage 3 deposits were affected by several thrust sense dislocations that have large offsets relative to the scale of the sedimentary succession tens to over 50 m vertically and hundreds of meters laterally strata associated with the dislocations exhibit growth indicating very early movement and they are interpreted as the frontal ramp zones of mass transport deposits the abundance and size of mass transport deposits in stages 1 and 3 helped control sediment pathways throughout the paleofjord

chlorinity salinity distribution patterns in experimental granular sea ice this work investigates the possibility of brine channel formation and development during the freezing of granular ice from a loose frazil ice suspension in an nacl solution at sea water concentration three experiments were performed at various constant growth rates in a purpose built vessel with computer controlled thermal driving high resolution chlorinity measurements are used as a proxy for the bulk salinity of the samples these show clear brine segregation processes in the ice with very high salinity gradients for the fast 10 mm h 1 to medium 2 mm h 1 freezing rates provided that a suitable sampling scale is adopted weak segregation was found at the low freezing rate 0 5 mm h 1 the spatial distribution of the bulk salinity fits the visual appearance of brine channels in the ice adequately in both horizontal and vertical sections in a similar way to columnar congelation sea ice the number of brine channels significantly decreases with growth rate but the density of channels is systematically lower in the granular ice than that found at equivalent freezing rates in the columnar ice this is attributed to the lower geometrical constraints on brine transport in the granular medium contrasts between brine channel geometry and density at different growth rates are discussed in light of the mushy layer concept adapted to sea ice growth from the solidification of alloys

late quaternary sedimentation in kejser franz joseph fjord and the continental margin of east greenland the marine sedimentary record in kejser franz joseph fjord and on the east greenland continental margin contains a history of late quaternary glaciation and sedimentation evidence suggests that a middle shelf moraine represents the maximum shelfward extent of the greenland ice sheet during the last glacial maximum on the upper slope coarse grained sediments are derived from the release of significant quantities of iceberg rafted debris ird and subsequent remobilization by subaqueous mass flows the middle lower slope is characterized by hemipelagic sedimentation with lower quantities of ird dropstone mud and sandy mud punctuated episodically by deposition of diamicton and graded sand gravel facies by subaqueous debris flows and turbidity currents derived from the mass failure of upper slope sediments the downslope decrease of ird reflects either the action of the east greenland current egc confining icebergs to the upper slope or to the more ice proximal setting of the upper slope relative to the lgm ice margin sediment gravity flows on the slope are likely to have fed into the east greenland channel system contributing to its formation in conjunction with the cascade of dense brines down the slope following sea ice formation across the shelf deglaciation commenced after 15 300 14c years as indicated by meltwater derived light oxygen isotope ratios an abrupt decrease in both ird deposition and delivery of coarse grained debris to the slope at this time supports ice recession with icebergs confined to the shelf by the egc glacier ice had abandoned the middle shelf before 13 000 14c years with ice loss through iceberg calving and deposition of diamicton continued retreat of glacier ice from the inner shelf and through the fjord is marked by a transition from subglacial till bedrock in acoustic records to ice proximal meltwater derived laminated mud to ice distal bioturbated mud ice abandoned the inner shelf before 9100 14c years and probably stabilized in fosters bugt at 10 000 14c years distinct oxygen isotope minima on the inner shelf indicate meltwater production during ice retreat the outer fjord was free of ice before 7440 14c years glacier retreat through the mid outer fjord was punctuated by topographically controlled stillstands where ice proximal sediment was fed into fjord basins the dominance of fine grained commonly laminated facies during deglaciation supports ablation controlled ice mass loss glacimarine sedimentation within the holocene middle outer fjord system is dominated by sediment gravity flow and suspension settling from meltwater plumes suspension sediments comprise mainly mud facies indicating significant meltwater deposition that overwhelms debris release from icebergs in this east greenland fjord system the relatively widespread occurrence of fine grained lithofacies in east greenland fjords suggests that meltwater sedimentation can be significant in polar glacimarine environments the ice distal continental margin is characterized by meltwater sedimentation in the inner shelf deep iceberg scouring over shallow shelf regions winnowing and erosion by the east greenland current on the middle outer shelf and hemipelagic sedimentation on the continental slope

the development of the odden ice tongue in the greenland sea during winter 1993 from remote sensing and field observations the odden ice tongue in the central greenland sea believed to be associated with midgyre convection developed prominently during the winter of 1993 january april during this period it was studied by a succession of cruises which formed part of the european subpolar ocean programme and which included direct sampling and measurement of the frazil and pancake ice which constituted the material of the ice tongue as well as studies of the ocean structure passive microwave imagery was used to determine the evolution of odden through the winter and when combined with ers 1 synthetic aperture radar studies and the field data yielded estimates of ice extent and thickness through the winter from these studies it was possible to estimate the salt flux into the ocean originating from brine release from sea ice during the growth phases of odden

sedimentation in glacial environments and the identification of tills and tillites in ancient sedimentary sequences abstract tills and tillites are defined and subdivided into primary tills comprising lodgement tills melt out tills and sublimation tills and secondary tills comprising flow tills and deformation tills they are defined on the basis of their mode of deposition which endows them with their distinctive properties another category of till that of supra till is defined on the basis of its debris source derived supraglacially from valley sides and nunataks which gives these tills a coarse grained character the processes of till deposition and of outwash sedimentation are associated in several recurrent combinations which allow the definition of three principal glacial sediment associations and land systems which define the character of the sequences within which tills tend to occur the criteria which allow tills of different genesis to be identified and to be distinguished from non till diamictons are reviewed there are several features which are uniquely characteristic of till but unfortunately these are few it has been found generally necessary to employ an array of characteristics which though not individually unique to till when taken together can be strong evidence for particular till types the recognition of several typical and repetitive facies sequences which form in the major glacial sedimentary environments can also be important indicators of till genesis

18o concentrations in sea ice of the weddell sea antarctica we present data on ice texture salinity and delta o 18 obtained from identical sections of ice cores during the winter weddell sea project 1986 on rv polarstern from july through august 1986 in the longitude range between 5 degrees w and 7 degrees e we find no uniquely definable relationship between delta o 18 values and ice texture in a particular section however most of the snow ice as well as some sections of frazil ice ar found to have negative delta o 18 concentrations this is due to varying degrees of admixtures of meteoric ice snow and sea water during formation of snow ice in contrast to common assumptions our results seem to indicate that a snow cover contributes positively to sea ice growth rather than slowing down the overall growth rate based on a simple model we have estimated the contributions of meteoric ice mean of 3 3 and the combined meteoric ice sea water fraction a minimum of 7 6 to the total ice thickness for the majority of the sampled floes although this is only a moderate contribution to the overall mass balance in the absence of congelation growth it nevertheless enhances ice growth in general this hypothesis is dependently supported by our snow and ice thickness data wadhams and others 1987 which demonstrate that the depression of the snow ice interface below the water line i e a negative freeboard and the formation of snow ice is a common occurrence in the weddell sea therefore we hypothesize that the major part of the observed apparent increase in ice thickness between our inbound and outbound tracks of wwsp 86 may not be derived from regular thermodynamically driven congelation growth but rather from the snow ice component in floes of the weddell sea

western norwegian fjord sediments age volume stratigraphy and role as temporary depository during glacial cycles abstract the sediments in the western norwegian fjords are described chronologically qualitatively and quantitatively by means of seismic profiling and correlation with dated terrestrial sediments along the fjords five chronostratigraphic units i v are proposed for the fjord sediments using the well established quaternary stratigraphy in the area sediment volumes of the main fjords are calculated using a dense seismic grid combined with map analyses approximately 150 km 3 of sediments are present in the fjords between 59 63 n ninety percent of this material is considered to be deposited during deglaciation of the last weichselian ice sheet less than ten percent of the fjord sediments in this area is older than the last glacial weichselian maximum both glacial and glaciofluvial processes are active in emptying the fjord basins and transporting the sediments to the continental shelf and slope during glaciations

rollover of apparent wave attenuation in ice covered seas wave attenuation from two field experiments in the ice covered southern ocean is examined instead of monotonically increasing with shorter waves the measured apparent attenuation rate peaks at an intermediate wave period this rollover phenomenon has been postulated as the result of wind input and nonlinear energy transfer between wave frequencies using wavewatch iii we first validate the model results with available buoy data then use the model data to analyze the apparent wave attenuation with the choice of source parameterizations used in this study it is shown that rollover of the apparent attenuation exists when wind input and nonlinear transfer are present independent of the different wave attenuation models used the period of rollover increases with increasing distance between buoys furthermore the apparent attenuation for shorter waves drops with increasing separation between buoys or increasing wind input these phenomena are direct consequences of the wind input and nonlinear energy transfer which offset the damping caused by the intervening ice

weddell sea ice drift kinematics and wind forcing ice drift in the weddell sea was studied on the basis of positional and meteorological data from argos buoys drifting in 1990 1992 and surface pressure analyses from the european centre for medium range weather forecasts ecmwf the drift kinematics showed differences between the eastern and western parts of the weddell sea close to the antarctic peninsula the ice drifted as an almost nonrotating uniform field at a low speed having reduced small scale motions with little meandering compared to regions further to the east inertial motion was detected from the ice drift in areas east of 35 w and in the region of the antarctic circumpolar current on timescales of days wind was the primary forcing factor for the drift a linear model between the wind and ice drift explained 40 80 of the drift velocity variance the degree of explanation was higher in the central weddell sea around 40 w and lower closer to the antarctic peninsula the geostrophic wind was found to provide almost as good a basis for the general drift estimation as the surface wind observed by the buoys although strong cyclones were not well detected by the ecmwf analyses the data suggest a dependency upon atmospheric stability such that stable stratification reduces the wind forcing on the drift for 60 80 of the time the direction of the drift deviated less than 45 from the geostrophic wind and for 45 70 of the time less than 45 from the ocean current ice transport through a transect crossing the weddell sea from the antarctic peninsula tip to kapp norwegia was estimated on the basis of the geostrophic winds the drift s observed response to the wind and literature based information on ice concentration and thickness the estimated annual mean net export in 1992 1994 varied from 8000 to 22 000 m3 s most of the net export took place in winter and spring export prevailing west of 35 w and import east of it

reevaluation of the timing and extent of late paleozoic glaciation in gondwana role of the transantarctic mountains evidence from antarctica indicates that a 2000 km long section of the transantarctic mountains including victoria land the darwin glacier region and the central transantarctic mountains was not located near the center of an enormous car boniferous to early permian ice sheet as depicted in many paleo geographic reconstructions weathering profiles and soft sediment deformation immediately below the preglacial pre permian un conformity suggest an absence of ice cover during the carbonif erous otherwise multiple glacial cycles would have destroyed these features the occurrence of glaciotectonite massive and strat ified diamictite thrust sheets sandstones containing dewatering structures and lonestone bearing shales in southern victoria land and the darwin glacier region indicate that permian sedimenta tion occurred in ice marginal periglacial and or glaciomarine set tings no evidence was found that indicates the transantarctic mountains were near a glacial spreading center during the late paleozoic although these findings do not negate carboniferous glaciation in antarctica they do indicate that gondwanan glacia tion was less widespread and therefore that glacially driven changes to other earth systems i e glacioeustatic fluctuations cli mate were much smaller than previously hypothesized

patterns of late palaeozoic deglaciation in the parana basin brazil abstract the itarare subgroup middle carboniferous early permian of the parana basin of southeastern brazil contains the thickest most extensive and one of the longest records of late palaeozoic glaciation in all of the gondwana supercontinent glacially controlled deposition started as early as the middle carboniferous when lobate termini of ice streams from the windhoek ice sheet wis and rio grande do sul and asuncion ice caps moved into the parana basin lobes reached sea level and advanced grounded at least as far as 200 km into the basin stabilizing as tidal intertidal margins glaciation and glacial sedimentation occurred penecontemporaneously with the transgressive phase of the late palaeozoic tectonic cycle of the parana basin while gondwana was gradually moving away from the south pole evolution involved complex interaction of tectonic palaeogeographic and palaeoclimatic factors initial flooding of the basin by an epicontinental sea in the middle carboniferous may have provided moisture necessary for the growth of glaciers conversely episodes of sea level rise probably affected the stability of marine glaciers the palaeoclimatic setting for the wis and other ice masses at the margins of the parana basin was mostly temperate multiple ice advances are evidenced by subglacial tillites resting on striated and or glaciotectonized basement and deformed glacigenic sediments identified at different stratigraphic levels in the itarare subgroup glaciation reached its maximum expansion sometime between the late carboniferous and early permian gradually diminishing and vanishing in the late early permian the reconstructed palaeogeographic evolution favors a model of irregular melt back of ice masses particularly along the eastern margin of the parana basin in analogy with the deglacial pattern of the pleistocene laurentide ice sheet in north america retreat of marine glaciers was mostly associated with relatively simple accumulations or complex build ups of ice contact proglacial facies associations in glacial estuarine embayments fast retreat was mainly controlled by decoupling associated with sea level rise and intense calving in the terrestrial environment more fragmentary evidence shows that retreat may have involved several mechanisms including downwasting of stagnant inactive ice margins and destabilization by surging of glaciers moving over deformable sediments highstand sea level following ice wastage is often marked by widespread deposition of relatively thin marine beds at least four stratigraphically different basinwide marine horizons are recognized isostatic rebound of deglaciated margins of the parana basin is recorded by transition from deep marine beds to shallowing coarsening upward prograding sequences of littoral fluvio deltaic facies basinwards sourced from raised basin margins eventually upon emersion these constituted platforms for interglacial and postglacial peat development although glaciation lasted for a long time glacial sedimentation alternated with relatively long periods of intense and widespread subaerial and subaquatic submarine reworking of previously deposited glacigenic sediments and deposition of normal non glacial sediments that comprise the bulk of the itarare subgroup sequence thin coal beds which locally rest on fossil soils denote climatic amelioration during these interglacial phases

drift of pancake ice floes in the winter antarctic marginal ice zone during polar cyclones high temporal resolution in situ measurements of pancake ice drift are presented from a pair of buoys deployed on floes in the antarctic marginal ice zone during the winter sea ice expansion over 9 days in which the region was impacted by four polar cyclones concomitant measurements of wave in ice activity from the buoys are used to infer that the ice remained unconsolidated and pancake ice conditions were maintained over at least the first 7 days analysis of the data shows i the fastest reported ice drift speeds in the southern ocean ii high correlation of drift velocities with the surface wind velocities indicating absence of internal ice stresses 100 km from the ice edge where remotely sensed ice concentration is 100 and iii presence of a strong inertial signature with a 13 hr period a lagrangian free drift model is developed including a term for geostrophic currents that reproduce the 13 hr period signature in the ice motion the calibrated model provides accurate predictions of the ice drift for up to 2 days and the calibrated parameters provide estimates of wind and ocean drag for pancake floes under storm conditions

ichnological signatures of shallow freshwater lakes in the glacial itarare group mafra formation upper carboniferous lower permian of parana basin s brazil abstract the upper carboniferous lower permian glacigenic deposits of the itarare group parana basin are widely known and cover an extensive area in the southern brazil these deposits consist of different arrangements of massive shales diamictites rhythmites and fine to medium grained sandstones with trough cross stratification five genetically distinct thickening locally coarsening upward successions of regular rhythmites can be distinguished in the mafra rio negro region santa catarina and parana states southern brazil representing the landward portion of an incised valley filled during deglaciation a low diversity invertebrate ichnofauna composed of a freshwater shallow burrow dominated suite and trackway dominated suite occurs in these rhythmites the freshwater shallow burrow dominated suite is composed of cochlichnus anguineus cruziana cf problematica gordia arcuata gordia marina hormosiroidea meandrica rusophycus cf carbonarius and treptichnus pollardi as well as undichnia consulca and intermittent rusophiciform traces it represents a mermia ichnocoenosis and occurs in the rhythmites of the upper sets commonly overlapped by d gouldi and d biformis in palimpsest preservation d gouldi and d biformis compose the trackway dominated suite which occur in all ichnofossiliferous paired mudstone siltstone of the basal sets of the rhythmite succession and in almost all of the upper sets it represents an atypical scoyenia ichnocoenosis and is generally preserved over microbially induced wrinkle structures the rhythmic deposition suggests distal underwater gravity flow deposits filling shallow lakes or ponds in depressed areas the siltstones deposited by melting currents and the mudstones by sediment fall out after the flux ceased the abundant wrinkle structures suggest quiet waters the overlying deposits bearing a brackish water ichnofauna and marine fossils suggest a coastal setting connected with the sea although atypical the occurrence of a scoyenia ichnocoenosis in almost all ichnofossiliferous rhythmite couplets preserved over wrinkle structures or overlapping mermia ichnocoenosis suggests that these shallow lakes were episodically dried up at least partially the present data allow interpreting the regular ichnofossiliferous rhythmites of the mafra formation as deposited in shallow lakes or ponds developed in outwash plains at the landward side of a fjord embayment during deglaciation

the contribution of alaskan siberian and canadian coastal polynyas to the cold halocline layer of the arctic ocean numerous arctic ocean circulation and geochemical studies suggest that ice growth in polynyas over the alaskan siberian and canadian continental shelves is a source of cold saline water which contributes to the maintenance of the arctic ocean halocline the purpose of this study is to estimate for the 1978 1987 winters the contributions of arctic coastal polynyas to the cold halocline layer of the arctic ocean the study uses a combination of satellite oceanographic and weather data to calculate the brine fluxes from the polynyas then an oceanic box model is used to calculate their contributions to the cold halocline layer of the arctic ocean this study complements and corrects a previous study of dense water production by coastal polynyas in the barents kara and laptev seas recurrent polynyas form on the canadian and alaskan coasts from banks island to the bering strait and on the siberian coast from the bering strait to the new siberian islands in the bering sea polynyas form in norton sound south and west of st lawrence island and in the gulf of anadyr two regions that account for almost 50 of the total dense water production are the siberian coastal polynyas in the adjacent regions of the gulf of anadyr and anadyr strait and the alaskan coastal polynyas which occur along the coast from cape lisburne to point barrow for all of the western arctic coastal regions examined the mean annual total brine flux is 0 5 0 2 sv combination of this flux with the contribution from the barents kara and laptev seas which is recalculated from data in the earlier study shows that over the entire arctic coastal polynyas generate about 0 7 1 2 sv of dense water this compares well with the theoretical estimates of 1 1 5 sv because an unknown fraction of the barents kara and laptev brine flux must go to the eurasian basin deep water the coastal polynyas alone cannot renew the halocline layer other potential brine generation mechanisms include overall freezing on the shelves and the response of the ice to infrequent violent storms for example during february 1982 an intense storm generated a large region of low ice concentration in the eastern chukchi sea over barrow canyon the refreezing of the region was followed by the flow of a dense plume down barrow canyon although the ocean dynamical response to this refreezing needs to be established the possible response of a barrow canyon flow to this refreezing event suggests that the overall refreezing in response to infrequent violent storms may be a potential source of the additional brine needed to maintain the arctic ocean halocline

thermodynamic investigation of an evolving grease to pancake ice field we present results from a laboratory tank study of ice growing from saline water in a wave field focusing on the transition from a predominantly frazil grease ice cover to a pancake ice cover combining surface temperature observations with direct and indirect determinations of ice salinity and solid fraction we describe the evolution of frazil and pancake ice area fraction salinity and solid ice volume fraction over the course of 1 day in the investigated stage of transition frazil ice surrounding the pancakes was found to have rather constant properties a surface temperature 0 4 0 6 k below the freezing point of the underlying sea water a salinity of 24 26 g kg 1 and a solid volume fraction of 0 25 0 29 the average salinity of young pancake ice estimated from heat and salt budgets decreased from 18 to 15 g kg 1 while average solid volume fractions increased from 0 6 to 0 7 the transition from frazil to pancake is estimated to take place when solid fractions reach 0 37 0 40 and surface temperatures are 0 7 0 9 k below the freezing point we find that for proper modelling of the grease pancake system it is important to distinguish between a surface and volumetric fraction of pancakes and grease ice

the ice thickness distribution across the atlantic sector of the antarctic ocean in midwinter during the first leg of the winter weddell sea project antarktis v 2 cruise of f s polarstern the entire width of the antarctic sea ice zone was traversed in the vicinity of 0 longitude in the period july 18 to september 10 1986 ice thicknesses were measured by direct drilling and by helicopter profiling using an exstar 100 mhz impulse radar system in addition aerial photography of the ice cover was done from 100 to 2000 m altitude using a 70 mm aerial camera mounted in the helicopter the results of the point measurements drilling are reported in this paper together with an indication of how the radar and photography data will be used to extend them so as to yield area averaged ice thickness distributions it was found that the main ice type across the entire width of the ice cover was consolidated pancake ice occurring in vast floes this formed out of a 250 km wide band at the advancing ice edge which comprised a concentrated field of individual pancakes in a matrix of frazil ice preferred thicknesses of undeformed floes were 40 60 cm of ice covered with 5 15 cm of snow the individual pancakes attained almost all of this thickness before consolidation subsequent congelation growth was slow estimated at 0 4 cm d 1 the floes contained much small scale roughness on the upper and lower surfaces due to rafting of pancakes at the time of consolidation but pressure ridging was modest except in the far south a few very thick 8 11 m multiyear floes were observed embedded in the pack at latitudes beyond 66 s

numerical simulations of the profile properties of undeformed first year sea ice during the growth season a simulation scheme is developed that estimates salinity profiles for first year sea ice during the growth season as a function of the growth history of the ice the model considers the dependence of the initial ice salinity on ice growth velocity and sea water salinity and also the subsequent drainage of brine from the ice the equation for ice growth assumes a linear temperature profile within the ice and is driven by surface heat balance equations that are based on smoothed climatic data for the central arctic basin the estimated salinity profiles are in good agreement with natural profiles although temperature and salinity profiles depend upon the time of the year when ice growth is initiated the brine volume profiles which they specify are essentially a unique function of ice thickness a conclusion that holds even when the insulative effects of snow are considered the temperature and brine volume profiles are then utilized to calculate the ice strength and elastic modulus profiles which in turn specify the composite mechanical properties of the ice sheets through the application of a theory developed by assur 1967 significant differences which are largest for thin ice sheets are observed between ice sheet properties as calculated using composite plate theory and properties calculated from uniform plate theory and average ice properties these results provide a justification for the practice common within the ice modeling community of parameterizing the mechanical behavior of pack ice on the basis of the ice thickness distribution

pancake ice formation in the weddell sea 1 the ice formation resulting from two low temperature events at the weddell sea ice edge during april 2000 is presented pancake and frazil ice were sampled at seven stations at varying distances from the ice edge the ice cover was further characterized from above using helicopter aerial photography and from below using a remotely operated vehicle previously undescribed two layer pancake types were observed and classified a novel pancake growth mechanism is introduced to account for these involving the washing of frazil ice over the pancake top surface and its subsequent freezing the process was directly observed in ice tank experiments layer thicknesses seen in the field were compared to the ice growth that would occur both under calm conditions and from free surface frazil ice growth classical bottom accretion pancake growth was found to proceed at a rate similar to that of thin congelation ice top layer growth was more rapid at approximately double the congelation rate overall ice volume production was similar to congelation ice for the thin pancakes considered 20 cm though subsequent thickening was expected to be faster as the rapid top layer process continued and the equivalent congelation growth slowed it is suggested that parameterization of this new process is important for models that aim to simulate the rapid advance and thickening of wave influenced ice covers

development of sea ice in the weddell sea we report on the development and physical properties of sea ice in the central and eastern weddell sea the investigations were part of the winter weddell sea project 1986 which extended over the months of july through december major elements of the glaciological part of this study included continuous shipborne observations of sea ice conditions and occasional helicopter reconnaissance flights extensive measurements of snow and ice thicknesses at daily ice stations and detailed analyses of sampled ice cores from each ice station textural investigations of the sampled ice revealed the dominance of frazil ice in the central weddell sea and the occurrence of an additional ice class called platelet ice together with the commonly known frazil and congelation ice in the coastal region of the eastern weddell sea these results in combination with the visual ice observations reveal two major mechanisms for sea ice generation in the antarctic which were not sufficiently well accounted for in previous investigations in the central weddell sea a cycle of pancake ice formation and its growth into consolidated floes seems to be the dominant process of the advancing sea ice edge in the coastal waters the growing sea ice cover consists to a considerable degree of ice platelets which are formed in the underlying water column in front of the ice shelf edges thus congelation ice growth which is mainly controlled by atmospheric thermodynamic forcing seems to be of less importance in the central and south eastern weddell sea than for example in the arctic basin

a dynamic early east antarctic ice sheet suggested by ice covered fjord landscapes the east antarctic ice sheet has played a fundamental part in modulating climate and sea level during the past 30 million years understanding its history is crucial to evaluating its future behaviour and response to global warming airborne ice penetrating radar studies now reveal a fjord like landscape beneath several kilometres of ice in the east antarctic aurora subglacial basin the data confirm and provide a new constraint on the magnitude and dynamics of the oscillations of the east antarctic ice sheet during the late cenozoic which had previously been supported only by marine cores the first cenozoic ice sheets initiated in antarctica from the gamburtsev subglacial mountains1 and other highlands as a result of rapid global cooling 34 million years ago2 in the subsequent 20 million years at a time of declining atmospheric carbon dioxide concentrations2 and an evolving antarctic circumpolar current2 sedimentary sequence interpretation3 and numerical modelling4 suggest that cyclical periods of ice sheet expansion to the continental margin followed by retreat to the subglacial highlands occurred up to thirty times these fluctuations were paced by orbital changes and were a major influence on global sea levels5 ice sheet models show that the nature of such oscillations is critically dependent on the pattern and extent of antarctic topographic lowlands here we show that the basal topography of the aurora subglacial basin of east antarctica at present overlain by 2 4 5 km of ice is characterized by a series of well defined topographic channels within a mountain block landscape the identification of this fjord landscape based on new data from ice penetrating radar provides an improved understanding of the topography of the aurora subglacial basin and its surroundings and reveals a complex surface sculpted by a succession of ice sheet configurations substantially different from today s at different stages during its fluctuations the edge of the east antarctic ice sheet lay pinned along the margins of the aurora subglacial basin the upland boundaries of which are currently above sea level and the deepest parts of which are more than 1 km below sea level although the timing of the channel incision remains uncertain our results suggest that the fjord landscape was carved by at least two iceflow regimes of different scales and directions each of which would have over deepened existing topographic depressions reversing valley floor slopes

tuffs tectonism and glacially related sea level changes carboniferous permian southern namibia abstract the carboniferous permian glacigene dwyka group in southern africa has been widely regarded as amagmatic only in the higher parts of the permian and subsequent younger strata has evidence of magmatism been recognised particularly in the form of pyroclastic fallout ash beds the source of these tuffs has been suggested to be patagonia and west antarctica forming part of an extensive volcanic arc which lay some 1500 to 2000 km to the south and west in their pre break up gondwana positions rhyolitic dacitic and basaltic andesitic tuff beds within the glaciomarine sediments of the dwyka group in namibia reveal new evidence for an early onset of proximal bimodal volcanic activity in southern africa contemporaneous tectonism is recorded by type 1 unconformities and systematic thickness changes across nw se trending extensional normal faults we suggest that this tectonomagmatic period marks initial extensional events in southern namibia and the carboniferous permian volcanic trend appears to coincide with the position of the eventual namibian continental margin significantly the stratigraphic positions of the tuff beds show a distinct association with enclosing marine transgressive depositional sequences most of them coincide with sharply defined flooding surfaces within relatively thick shaly successions reflecting their multiple transgressive nature widening the study context to the latest early permian in southern africa the main karoo basin of southern africa exhibits a similar coincidence of marine transgressions and extrusion of volcanics the relationship between tuff beds and transgressive depositional sequences is not only the result of enhanced preservational potential during transgression but of a genetic coupling between magmatism extensional tectonics and basin subsidence the latter accelerating a rise in relative sea level this interaction is significant not only for understanding potential controls on relative sea level change but also for understanding the early geodynamic evolution of the southern south atlantic continental margin

extreme freshwater release during the late paleozoic gondwana deglaciation and its impact on coastal ecosystems abstractstrata in the paganzo tarija and parana basins of argentina and brazil provideevidence for reconstructing the effects of late paleozoic glacial retreat the depositionalenvironment of the transgressive and early highstand ne grained deposits has been con troversial with interpretations ranging from normal marine shelves to estuaries to lakes whereas their counterparts from shallow marine settings not in uenced by glaciation hostdiverse fully marine ichnofaunas these ne grained postglacial deposits are dominatedby nonspecialized grazing trails simple feeding traces arthropod trackways and shtrails they are typical of freshwater environments and represent examples of the mermia and scoyenia ichnofacies however the local presence of acritarchs indicates sporadicmarine in uence these observations suggest a new interpretation that freshwater con ditions in fjordlike settings across south america were widespread because gondwananbasins were overwhelmed by strong meltwater discharge issuing from melting of the con tinental ice masses keywords

late paleozoic paleofjord in the southernmost parana basin brazil geomorphology and sedimentary fill abstract in the southernmost part of the parana basin records of the late paleozoic glaciation occur in a discontinuous form preserved in paleovalley systems excavated in the crystalline basement this paper addresses one of these paleovalleys the mariana pimentel which extends over 60 km with nw se valley direction and a constant width of 2 5 km with the objective of demonstrating that the paleovalley worked as a fjord during the glaciation period its origin as well as sedimentary fill and morphology were analyzed the paleovalley morphology was obtained through electrical resistivity electrical sounding and lateral mapping and mathematical modeling in four transverse sections the morphology of the paleovalley documented by the u shape steady width and high depth reaching up to 400 m are typical features of modern glacial valleys the sedimentary facies that fill the base of the paleovalley such as rhythmites and dropstones with thickness up to 70 m and diamictites with faceted pebbles up to 5 m thick are signs of its glacial origin during the glaciation period the paleovalley had a connection to the epicontinental sea located to the northwest extended toward namibia and was excavated by glaciers from the highlands of this region thus the evidence attests that the mariana pimentel paleovalley was a fjord during the late paleozoic glaciation the duration of the late paleozoic glaciation which is longer than the quaternary glaciation the apatite fission track that suggests erosion up to 4 km thick in the study area and the lack of preserved hanging valleys in the mariana pimentel indicate that the paleovalley once featured a higher dimension furthermore the existence of paleofjords excavated in the border of the basement corroborates the idea of small ice centers controlled by topography during the late paleozoic glaciation

sea ice structure and biological activity in the antarctic marginal ice zone ice cores obtained during october november 1981 from weddell sea pack ice were analyzed for physical chemical and biological parameters frazil ice which is associated with dynamic turbulent conditions in the water column predominated 70 both floe thickness and salinity indicate ice which is less than 1 year old chemical analyses particularly with regard to the nutrients revealed a complex picture phosphate values are scattered relative to the dilution curve nitrate and silicate values are lower than expected from simple scaling with salinity and suggest diatom growth within the ice nitrite values are higher in the ice than in adjacent waters frazil ice formation which probably concentrates algal cells from the water column into ice floes results in higher initial chlorophyll a concentrations in the ice than in adjacent waters this mechanical concentration is further enhanced by subsequent reproduction within the ice ice core chlorophyll ranged from 0 09 to 3 8 mg m3 comparable to values previously reported for this area but significantly lower than values for antarctic coastal fast ice the dominance of frazil ice in the weddell is one of the major differences between this area and others consequently we believe that ice structural conditions significantly influence the biological communities in the ice

carboniferous glaciotectonized sediments in the southernmost parana basin brazil ice marginal dynamics and paleoclimate indicators abstract carboniferous glaciogenic strata itarare gp in the southernmost parana basin brazil exhibit soft sediment deformation features previously interpreted as glaciotectonism these sediments were studied in detail to confirm that they were deformed by ice and to assess the nature of the glaciation depositional environments and paleoclimate in this region during the carboniferous five outcrops were described along a railroad transect that contains a conglomerate and diamictite facies with striated and faceted clasts a medium sandstone facies a fine grained silt clay rhythmite and mudstone facies with dropstones and diamictite pellets a sandy clinoform facies and a folded sandstone with interbedded mudstone facies the depositional environment for these sediments is interpreted as an outwash fan and fan delta from an ice proximal transitional terrestrial to estuarine setting rb k values from the rhythmites reflect a transition from a freshwater to brackish environment and the chemical index of alteration cia of the rhythmites ranges from 65 to 73 reflecting a relative increase in the degree of chemical weathering through time deformation features include widespread folding thrust faults hydrofractures decollement surfaces and piggyback fold thrust complexes the deformation is interpreted as evidence of a push moraine complex formed by at least two complete ice advance retreat cycles the occurrence of decollement surfaces plastically deformed proglacial sediments and hydrofractures indicate a dynamic warm based or polythermal glacier abundant outwash sediments rhythmites with dropstones and the shift to average cia values all support a temperate paleoclimate deformation structures indicate a nw direction of ice shove that is in agreement with the regional scale hypothesis that a nnw flowing lobe extended out of uruguay during the carboniferous and terminated in the southernmost parana basin this study demonstrates that late paleozoic glaciation in this region was more dynamic than previously understood with high frequency fluctuations in ice marginal positions

lontras shale parana basin brazil insightful analysis and commentaries on paleoenvironment and fossil preservation into a deglaciation pulse of the late paleozoic ice age abstract the lontras shale is a fossil site located in mafra santa catarina south of brazil this late paleozoic pennsilvanian cisularian stratum holds an important place with great potential for the synthesis of knowledge about paradigmatic events that happened on gondwana this marine fossil site preserved into a 1 1 m black shale comprises a combination of different kinds of preservation in broad taphonomical spectra including hard and or soft tissues of aquatic e g fishes poriferans and ammonoids and terrestrial biotas e g insect and woods among other organisms that were well preserved under still unrevealed process and conditions considering the prevailing depositional settings and aiming to present fossil diagenetic aspects that led to some special preservation modes we performed chemical analyses of sponges and insects by means of energy dispersive spectroscopy eds synchrotron micro x ray fluorescence micro xrf and raman spectroscopy to date we have identified the majority of fossils preserved as carbonaceous compressions or phosphatized forms the well preserved fossils have so far permitted new insights into metazoan evolution especially regarding insecta porifera and conodonta our findings not only allow suggestions regarding the chemical remains of soft tissues on these specimens but also can provide background data for future analyses of these groups in similar depositional settings

modern glacimarine processes and potential future behaviour of kronebreen and kongsvegen polythermal tidewater glaciers kongsfjorden svalbard

ocean heat flux in the central weddell sea during winter abstract seasonal sea ice which plays a pivotal role in air sea interaction in the weddell sea a region of large deep water formation with potential impact on climate depends critically on heat flux from the deep ocean during the austral winter of 1994 an intensive process oriented field program named the antarctic zone flux experiment measured upper ocean turbulent fluxes during two short manned ice drift station experiments near the maud rise seamount region of the weddell sea unmanned data buoys left at the site of the first manned drift provided a season long time series of ice motion mixed layer temperature and salinity plus a truncated high resolution record of temperature within the ice column direct turbulence flux measurements made in the ocean boundary layer during the manned drift stations were extended to the ice ocean interface with a mixing length model and were used to evaluate parameters in bulk expressions for interfacial stress a rossby similarity drag law and ocean to

the physical properties of sea ice in the odden ice tongue abstract the odden ice tongue developed prominently during the winter of 1992 1993 but did not appear at all during the two subsequent winters of the esop period during 1992 1993 the in situ sea ice characteristics within odden were studied on four occasions in addition to direct observation and aerial photography the measurement programme included retrieval and on board analysis of frazil and pancake ice samples wave measurements within odden and near surface ctd measurements to examine the effect of melt on the upper ocean reported in brandon and wadhams 1999 the near surface hydrography beneath the odden ice tongue deep sea research in press this paper reports on the characteristics of the frazil and pancake ice observed and sampled during this season expanding on early results reported in wadhams et al 1996 journal of geographical research 101 c8 18 213 18 235 by combining the results of in situ sampling with the analysis of passive microwave and sar data of the sea ice extent through the winter it was possible to estimate the salt flux into the ocean originating from brine release from sea ice during the growth phases of odden

glacial hydrology and erosion patterns a mechanism for carving glacial valleys article i nfo article history most glacial erosion models assume that erosion rates are proportional to ice sliding velocity while recent studies have shown that water plays a major role in modulating sliding velocities the impact it might have on erosion rates is still unclear here we incorporate subglacial hydrology into a glacial erosion model that is based on a sliding rule our results explicitly highlight that adding subglacial hydrology has profound impacts on the temporal and spatial patterns of glacial erosion first it suggests that erosion might mainly occur during melting seasons when subglacial water pressure is large and effective pressure is low i e before the channels fully develop and reduce the water pressure at the ice bedrock interface which promotes sliding and erosion second the distribution of erosion is bimodal with a peak at the equilibrium line altitude and as we demonstrate enhanced erosion at much lower altitudes within the ablation area where water due to melting abounds this has important implications because it explains why glacial erosion can simultaneously

carboniferous permian carbon isotope stratigraphy of successions from china yangtze platform usa kansas and russia moscow basin and urals abstract the pennsylvanian and early permian were times of extreme sea level changes of 100 to perhaps up to 200 m for example glacio eustatic sea level changes are well documented from the us midcontinent moscow basin and yangtze platform where more than 100 stacked subtidal to supratidal sequences have been described in contrast carbonates developed in the ural mountains and south guizhou of the yangtze platform were deposited in ramp and slope settings 13c values of whole rock samples from the us midcontinent and moscow basin were intensively affected by diagenesis only well preserved brachiopod shells maintained their original carbon isotope ratios in contrast limestones deposited in the deeper water slope environments were not affected by meteoric diagenesis and are interpreted to have mainly retained their carbon isotope ratios mean 13c values of slope carbonates of the yangtze platform increase from about 3 during the visean and serpukhovian to 5 at the carboniferous permian boundary and decrease to values around 2 in the early kungurian this positive 13c excursion coincides with low 13c values in the yangtze platform successions which were reset by meteoric diagenesis the highest 13c values recorded in the slope succession coincide with the inferred maximum glaciation that caused pronounced sea level lowstands short lived but significant negative 13c excursions in the chinese slope succession are interpreted to reflect changes in ocean circulation due to sea level rises which caused enhanced production and or preservation of organic matter which influenced the subsequent early diagenetic cementation

a paleoclimatic review of southern south america during the late paleozoic a record from icehouse to extreme greenhouse conditions abstract this paper provides a review of the late mississippian to permian paleoclimatic history for southern south america based on lithologic indicators biostratigraphic information and chronostratigraphic data the region is divided into three major types of basins 1 eastern intraplate basins e g parana basin 2 western retroarc basins e g paganzo basin and 3 western arc related basins e g rio blanco basin four major types of paleoclimatic stages are recognized in these basins 1 glacial late visean early bashkirian 2 terminal glacial bashkirian earliest cisuralian 3 postglacial cisuralian early guadalupian and 4 semiarid arid late guadalupian lopingian the glacial stage began in the late visean and continued until the latest serpukhovian or early bashkirian in almost all of the basins in southern south america during the bashkirian earliest cisuralian terminal glacial stage glacial deposits disappeared almost completely in the western retroarc basins e g paganzo basin but glaciation persisted in the eastern basins e g parana and sauce grande basins a gradual climatic amelioration postglacial stage began to occur during the earliest permian when glacial deposits completely disappeared across all of south america during this interval glacial diamictites were replaced by thick coal beds in the parana basin while north south climatic belts began to be delineated in the western basins which were likely controlled by the distribution of mountain belts along the panthalassan margin of south america towards the late permian climatic belts became less evident and semiarid or arid conditions dominated in the southern south america basins eolian dunes playa lake deposits and mixed eolian fluvial sequences occur in the parana basin and in the western retroarc basins volcanism and volcaniclastic sedimentation dominated along the western margin of south america at that time the stratigraphic record obtained in southern south america supports a long duration transition from icehouse to extreme greenhouse conditions

the role of shortwave radiation in the summer decay of a sea ice cover heat balance models of ice leads and the underlying water column were used to investigate the role of shortwave radiation in the summer decay of a sea ice cover because of the potential importance of positive feedback between decreasing ice concentration and increasing solar input to the ocean particular emphasis was given to the treatment of heat transfer and lateral melting in leads the rate of heat loss to floe edges was calculated from lead temperatures using an empirical boundary layer parameterization coefficients for this parameterization were obtained from field measurements in the dynamically active ice cover of the greenland sea during the 1984 marginal ice zone experiment and in the static ice of mould bay northwest territories field coefficients were found to be considerably larger than those previously obtained in the laboratory suggesting that heat transfer rates near floe edges were controlled more by winds and currents than by local density differences model studies of individual leads indicate that heat losses to the atmosphere cause lateral melt rates to asymptotically approach a constant value as lead size increases thus although very wide leads transmit considerable energy to the underlying ocean they have relatively little effect on lateral melting other results provide information on the relative importance of horizontal heat transfer rates ice thickness floe perimeter atmospheric forcing and oceanic heat flux in general the calculations indicate that much of the shortwave radiation entering the ocean is absorbed below the ice where it contributes to bottom ablation rather than lateral melting this suggests that previous work has seriously overestimated the magnitude of the feedback between ice concentration and incident shortwave radiation

simulating pancake and frazil ice growth in the weddell sea a process model from freezing to consolidation 1 processes controlling the formation and transformation of frazil to pancake ice are examined using data from an array of drifting buoys deployed at the advancing ice edge in the weddell sea a simple thermodynamic model is coupled to the buoy dynamics and to an ice redistribution model to determine the influence of deformation thermodynamics and mechanical scavenging incorporating frazil crystals from the surrounding slick into the pancakes on the partitioning of ice volume between frazil and pancakes ice production was examined from the time the buoys were deployed until the frazil pancake cover consolidated into the more familiar pack ice the model reproduced the expected ice cover thickness at consolidation 60 cm rafting was the dominant contribution to thickening in the region owing to large scale compression of the initial area by northerly winds from passing low pressure weather systems which are rather typical in the region high resolution positional forcing from the buoys 20 min intervals doubled the contribution of mechanical scavenging to final pancake thickness compared to the coarser 2 h result owing to the larger path length that the pancakes traverse through the frazil slick and produced a significantly larger volume of ice in the pancake phase the ice cover generated at consolidation was approximately twice as thick as would have formed by the more familiar congelation ice growth under the same forcing reinforcing the importance of correctly parameterizing the early stages of ice formation in the antarctic the study highlighted uncertainties in the effect of the frazil pancake cover on ocean atmosphere heat exchange both in terms of the area contributing to ice production and the effect on turbulent exchange coefficients further work placing the empirical parameters into a more constrained physical framework and introducing wave properties is suggested

origin of paleovalleys on the rio grande do sul shield brazil implications for the extent of late paleozoic glaciation in west central gondwana abstract the location longevity and geographic extent of late paleozoic ice centers in west central gondwana remain ambiguous paleovalleys on the rio grande do sul shield of southernmost brazil have previously been interpreted as fjords carved by outlet glaciers that originated in africa and emptied into the parana basin brazil in this study the sedimentology stratigraphy and provenance of sediments infilling two such paleovalleys the mariana pimentel and leao paleovalleys were examined in order to test the hypothesis that an ice center over present day namibia drained across southernmost brazil during the carboniferous and permian contrary to previous findings the facies assemblage from within the paleovalleys is inconsistent with a fjord setting and no clear evidence for glaciation was observed the facies show a transition from a non glacial lacustrine estuarine environment to a fluvial dominated setting and finally to a restricted marine estuarine environment detrital zircon results present a single population of neoproterozoic ages c 800 550 ma from the paleovalley fill that matches the ages of underlying igneous and metamorphic basement dom feliciano belt and is incongruent with african sources that contain abundant older mesoproterozoic paleoproterozoic and archean zircons furthermore results suggest that the formation of the paleovalleys and the deposition of their fill were controlled by the reactivation of neoproterozoic basement structures during the carboniferous and permian the lack of evidence for glaciation in these paleovalleys highlights the need for detailed studies of supposed late paleozoic glacial deposits these results are supportive of the hypothesis that well established glacial sediments on the rio grande do sul shield southern margin of the parana basin may be the product of a separate lobe extending north across uruguay rather than a single massive ice sheet draining west from africa

submarine debris flow deposits from the upper carboniferous dwyka tillite formation in the kalahari basin south africa four types of sediment gravity flow deposits occur interbedded with rhythmite shale siltsone mudstone and minor diamictite in a 230 m thick carboniferous glacial sequence shear and plug zones are present in the cohesive debris flow deposits which have a diamictic texture the high density turbidity flow deposits which consist of coarse to medium grained clastics are characterized by both normal and reverse grading the medium to fine grained low density turbidity flow deposits show normal grading and consist of bouma units a b d and e deposition occurred by gravity flow suspension settling and minor basal melt out during ice retreat along the southern margin of the kalahari basin immediately basinwards of the ice grounding line a proximal diamictite facies consisting predominantly of cohesive and high density turbidity flow deposits and minor melt out tills formed a distal sedimentary facies of graded sandstone and siltstone units deposited by low density turbidity flows and suspension settling of muds with ice rafted debris is located basinwards

a field and laboratory study of wave damping by grease ice in a field and laboratory study we discuss the formation growth and wave absorption properties of grease ice our field observations show that grease ice formation occurs under cold windy conditions in both leads and polynyas in leads grease ice forms in the open water then is herded to the down wind edge of the lead in polynyas a langmuir circulation herds the grease ice into long plumes parallel to the wind in the laboratory we grow grease ice in a wave tank and measure its wave absorption properties for single frequency two dimensional waves on a large scale we find that the thickness of the grease ice which increases away from the paddle is determined by a balance between the wave momentum flux and the free surface tilt on a small scale our photographs show that the crystals which make up the grease ice consist of discs measuring about 1 mm in diameter and 1 10 m thick which at low rates of shear sinter together into larger clumps yielding a viscosity increase to measure this non linear viscosity we study the decay of wave amplitude between two critical distances measured inwards from the leading edge the first occurs when the depth of grease ice exceeds k 1 where k is the wave number the second further distance is a line of transition from liquid to solid behavior which we call the dead zone between these two distances the wave amplitude decays with a linear slope which increases as a 0 k 2 where a0 is the wave amplitude in open water concurrent measurements of ice concentration show that it increases from values of 18 22 at the leading edge to a local maximum of 32 44 at the dead zone while the values at the dead zone increase non linearly with a0k finally comparison of the observed to that calculated from a yield stress viscosity model shows if the yield stress coefficient is proportional to the incident wave momentum flux the model predicts the observed

on the importance of leads in sea ice to the energy balance and ice formation in the weddell sea for a considerable coverage the energy balance of and ice formation by leads in sea ice in the weddell sea are evaluated on the basis of data obtained from drifting buoys for the winter periods from 1986 to 1994 and by using a kinematic thermodynamic sea ice model the net heat flux is defined as the sum total of radiative and turbulent fluxes for thin ice the net turbulent flux is 3 4 times the net radiative flux the contribution of the net heat flux through open and refrozen leads to the total net heat flux through sea ice is twice as large as the area contribution of open and refrozen leads to the total area covered with sea ice in the eastern and central parts of the weddell sea leads contribute some 30 to the total energy flux from the ocean to the atmosphere this flux increases from 10 15 mbox w m 2 in the eastern and central weddell sea regions to 30 mbox w m 2 in the western part of the weddell sea where leads contribute more than 80 of the total net energy transfer the increase is mainly due to the colder and windier atmosphere in connection with the higher variability of the ice motion in the diurnal andsemidiurnal band in the western weddell sea the contribution of leads in winter ice formation exceeds 50 in the whole of the weddell sea monthly area weighted ice growth is 10 15 cm in the east and up to 30 mbox cm over the western continental shelf region in the western part of the weddell sea tidal and inertial motions in the diurnal and semidiurnal bands enhance lead formation and thus contribute 7 to total net heat flux 12 to ice formation and 23 to the salt mass released during ice growth the results are used to assess quantitatively the importance of leads to the interaction of the ocean the sea ice and the atmosphere

southern ocean winter mixed layer austral winter 1986 observations from the polarstern along the greenwich meridian from the ice edge to the antarctic margin show the mixed layer beneath the winter sea ice cover to be significantly depressed in oxygen saturation incorporation of weddell deep water wdw into the winter mixed layer responsible for this undersaturation also introduces heat and salinity into the surface layer which strongly influences the mixed layer sea air exchanges and sea ice formation processes the total wdw transfer into the mixed layer averages 45 myr 1 implying a residence time for the surface water of 2 5 years the associated winter heat flux is 41 w m 2 which limits ice thickness to about 0 55 m agreeing quite well with observations the air temperatures during the cruise are just sufficient to remove the wdw heat input in the presence of observed ice thickness and concentration this suggests that the sea ice cover and wdw heat input into the mixed layer are in approximate balance by midwinter the annual heat flux from wdw to the surface layer and hence into the atmosphere is estimated as 16 w m 2 extrapolation of the greenwich meridian wdw entrainment value to the full circumpolar 60 70 s belt yields total up welling of 24 106 m3 s 1 similar extrapolation of the heat flux value gives a circumpolar total of 2 8 1014 w as a consequence of circulation topography interaction the maud rise water column stands out as an anomaly relative to the surrounding region with a significantly more saline and dense mixed layer below the mixed layer the water column over the crest of the rise is identical to that over the flanks if the latter water column is upwelled by 400 m this uplifting is believed to be a response of the upstream flow encountering the rise increased upstream flow would be expected to increase maud rise upwelling and the dependent salinity density of the mixed layer slight increases in the mixed layer density could trigger a convective mode and generation of a polynya it is hypothesized that spin up of the weddell gyre s barotropic circulation induced by an increase of the regional wind stress curl would enhance the probability of polynya development over maud rise

dynamical contrasts between pancake and pack ice investigated with a drifting buoy array 1 the motion of pancake ice was investigated using an array of specialised drifting buoys deployed into the advancing ice edge of the weddell sea in april 2000 the buoys remained in the ice as the pancakes consolidated into a coherent ice sheet and the study examined the contrasts in dynamics for equivalent periods before and after consolidation drift velocities were largely determined by the meridional component perpendicular to the ice edge prior to consolidation these showed significantly elevated magnitudes at high frequencies periods shorter than six hours scalar velocities were higher than previously reported values reducing with time and distance from the ice edge the same trends were not evident from in situ wind data derivation of momentum transfer parameters wind factor turning angle was hampered by a lack of reliable wind directions from the outermost buoys however relative motions between buoys were investigated using differential kinematic parameters these displayed high amplitude high frequency oscillations in unconsolidated ice with rms invariant values up to two orders of magnitude higher than normally reported for weddell sea pack ice the values were found to be strongly dependent on sampling interval increasing further at intervals less than one hour in situ winds did not display an equivalent variation suggesting that wind forcing was not responsible and translation under wave action either internal or surface gravity was postulated as the forcing

grease ice in basin scale sea ice ocean models the first stage of sea ice formation is often grease ice a mixture of sea water and frazil ice crystals over time grease ice typically congeals first to pancake ice floes and then to a solid sea ice cover grease ice is commonly not explicitly simulated in basin scale sea ice ocean models though it affects oceanic heat loss and ice growth and is expected to play a greater role in a more seasonally ice covered arctic ocean we present an approach to simulate the grease ice layer with as basic properties the surface being at the freezing point a frazil ice volume fraction of 25 and a negligible change in the surface heat flux compared to open water the latter governs grease ice production and a gradual transition to solid sea ice follows with 50 of the grease ice solidifying within 24 hours the new parameterization delays lead closing by solid ice formation enhances oceanic heat loss in fall and winter and produces a grease ice layer that is variable in space and time results indicate a 10 30 increase in mean winter arctic ocean heat loss compared to a standard simulation with instant lead closing leading to significantly enhanced ice growth

sar imaging of wave dispersion in antarctic pancake ice and its use in measuring ice thickness 1 a synthetic aperture radar sar image of the advancing winter marginal ice zone miz in the antarctic composed of frazil pancake ice has been analysed in a new way in order to test the predictions of a recently developed theory of wave dispersion in pancake ice which treats the ice as a viscous layer in the image obtained in april 2000 the structure of the wave spectrum in the miz and its change from the open water spectrum are consistent with a pancake layer 24 cm thick intensive in situ measurements of the pancake ice in the miz 280 km w of the image location were made from fs polarstern during a period covering the satellite imaging and also yielded a mean ice thickness of 24 cm we conclude that this technique gives realistic results for ice thickness whereas earlier work based on a different dispersion theory mass loading tended to over estimate thickness after further validation it is therefore possible that the sar wave technique can become an accepted method for monitoring ice thickness in pancake icefields

shrimp u pb zircon dating and palynology of bentonitic layers from the permian irati formation parana basin brazil abstract this paper presents the first shrimp zircon age data from bentonitic ash fall layers intercalated with the irati sedimentary rocks as well as palynofossils retrieved from the petrobras six mine parana state southern brazil the permian irati formation is one the most important oil source horizons within the parana basin and consists mainly of siltstones gray claystones as well as organic rich claystones intercalated with limestones zircon morphology based on cathodoluminescence images includes two different populations a dominant population of euhedral prismatic elongate to acicular grains which are most likely related to an ash fall volcanism and a population of rounded to large prismatic grains that were interpreted as detrital grains shrimp analysis performed on the euhedral and prismatic grains revealed an age of ca 278 4 2 2 ma 7 points with 95 confidence interpreted as the crystallization age of the volcanic eruption based on this new dating the irati formation should be placed on the lower permian cisuralian artinskian in age modifying substantially the traditional ages previously attributed to this unit the palynofossils from this level include key species of the lueckisporites virkkiae zone such as l virkkiae l densicorpus l stenotaeniatus weylandites lucifer alisporites splendens typical species of this zone also occur in african and other south american argentina permian strata allowing stratigraphical correlations the origin of the ash falls is not clearly defined it may be related either to calc alkaline arc magmatism associated to the sanrafaelica orogeny 275 and 250 ma or to bimodal volcanic events associated to an early intracontinental rift developed within southwestern gondwana at ca 278 my the dating of this unit is significative to calibrate biostratigraphic schemes along the parana basin as well as equivalent zones in gondwana areas mainly in its occidental portion

ice production and brine formation in storfjorden svalbard brines which appear as salty and cold bottom water layers on arctic shelves form by salt rejection during sea ice formation high ice production occurs in latent heat polynyas such as the one that appears in storfjorden under northerly winds using ers 2 synthetic aperture radar imagery we observed the ice cover in storfjorden over the winter 1997 1998 revealing an area of over 6000 km 2 of the open water and thin ice that are characteristic of a polynya changes in the polynya extent correlated well with a simple wind driven polynya size algorithm furthermore using a frazil ice formation algorithm and the hypothesis of ice accumulation at the lee side of the polynya we distinguished between open water thin ice and fast pack ice the average polynya width during the 6 winter months was about 30 km with a maximum of 130 km in march thus storfjorden was composed of 5 6 fast and pack ice and 1 6 polynya open water occupied about half of the polynya the other half was composed of brash ice and thin ice involved in ridging and rafting a total ice volume of 40 km 3 was produced in storfjorden between november 15 1997 and may 15 1998 about 57 of it was formed in the open water area 9 in the thin ice area and 34 in the fast pack ice area this ice production released more than 1 gt gigaton of salt able to increase the salinity of the storfjorden waters by 1 4 practical salinity units psu assuming that brine enriched waters are 0 3 psu more saline than the parent waters the above salt release is able to ventilate storfjorden 4 5 times during the course of the productive season

salinity profiles of antarctic sea ice field data and model results in order to describe and compare sea ice salinity distributions which are of interest in the study of physical and biological ice characteristics as well as ice ocean interaction we have computed composite profiles and fitted third degree polynomials to salinity data of 129 cores from the weddell sea four characteristic profile shapes have been recognized and described through the polynomial coefficients c s i and type profiles the field data have been compared with ideal salinity profiles generated by a simulation scheme based on thermodynamic growth under climatological conditions representative of the weddell sea composite salinity profiles agree well with simulations irrespective of the growth mechanism i e frazil or congelation suggesting that ice properties which depend on salinity or porosity may evolve independent of ice growth conditions analysis of salinity and 18o data in conjunction with the simulations demonstrates that apart from meteorological conditions controlling growth velocity and temperature distribution within the ice flooding and upward brine expulsion are important in raising top salinities as frequently observed low top salinities are typical of ice that has undergone retexturing and differential desalination salinity decreases towards the bottom of a floe are a result of high oceanic heat fluxes and snow cover effects as a consequence of these processes the bulk salinity of weddell sea ice cannot be described by a simple linear age thickness relationship as characteristic of arctic first year ice

lagrangian modelling of frazil ice in the ocean a new modelling framework using lagrangian particle tracking has been developed to assess dynamic and thermodynamic effects of underwater frazil ice this frazil ice model treats a lagrangian particle as a bulk cluster of many frazil crystals and calculates the thermodynamic growth of each particle and the corresponding budget of latent heat and fresh water the effective density and viscosity of sea water depend on the mass fraction of underwater frazil ice and hence affect ocean convection an idealized experiment using our model successfully reproduces the formation of underwater frazil ice and its transition to grease ice at the surface because underwater frazil ice does not reduce the atmosphere ocean heat exchange surface heat flux and net sea ice production in the experiment with frazil ice are relatively high compared with the experiment where surface cooling directly leads to columnar growth of a solid ice cover which effectively insulates the heat flux these results suggest that large scale sea ice models which do not take account of the effects of frazil ice might underestimate atmosphere ocean heat exchange particularly at times of active new ice formation