detection and classification of surface roughness in an arctic marginal sea ice zone sea ice dynamic and thermodynamic processes are important and highly variable elements of the marginal ice zone miz this study examines the detection and classification of statistically separable sea ice classes in the miz through a range of temporal and spatial scales a helicopter based laser system was used to obtain large scale and a ship based laser profiler to identify small scale roughness types respectively the analysis of variance of surface height data from helicopter and ship based laser systems active microwave amw c band backscattering data and passive microwave pmw 37 and 89 ghz brightness temperature data reveal different classes that statistically differ from one another we found significant statistical difference in variances in amw data with six classes that differ in vv polarization three classes in vh polarization and five classes in hh polarization in the miz e g snow covered first year ice ice rubble pancake ice frost flowers melt pond flooded ice and ice edge of southeastern beaufort sea the pmw emission was not as effective at discrimination yielding only one statistically separable class the results can potentially be extended to satellite based investigations of the miz at regional scales copyright 2012 john wiley sons ltd

gravel bodies in the kumtagh desert and their geomorphological implications although developed in predominantly arid environments desert geomorphology sometimes bears information about past environmental change china s kumtagh desert has only recently been studied by researchers these investigations revealed the existence of several unique features compared with other chinese deserts including gravel bodies distributed in the northern part of the desert this paper summarizes the results of previous research in the region as well as information obtained from remote sensing and field investigations then discusses the geological background underlying quaternary geomorphology and the types development stages and geomorphological implications of the desert s gravel bodies four main types of gravel bodies and four developmental stages were identified it is suggested that the great elevation difference between the altyn tagh mountains and the kumtagh desert caused by uplift of the qinghai tibetan plateau constitutes the overall background for the development of gravel bodies but subsequent climatic events were the direct causes of their evolution the gravel bodies resulted from alluvial deposits on loose fine sediments mainly of aeolian origin that were subsequently subjected to wind erosion erosion cycles then progressively scattered these gravels to form gravel sheets the gravel bodies have three main geomorphological implications they record anomalous ancient climate events after the dune field formed and have little influence on the development of nearby seif dunes in the northeast demonstrate that the altyn tagh mountains are the main sediment source for the kumtagh desert and suggest that the evolution of the environment and geomorphology of the kumtagh desert have been influenced by neotectonic movements

provenance and transport process for interdune sands in the kumtagh sand sea northwest china abstract interdune areas are an important part of dune systems as they affect dune evolution and sand sea development however there has been little work on the provenance of interdune sediments our lack of knowledge of these sediments prevents a more complete understanding of sand sea formation and evolution in the present study we focused on the provenance of interdune sediments in the kumtagh sand sea based on their granular mineral and geochemical characteristics then further identified the spatial scope of the contribution of these sources to the interdune sediments and the associated transport mechanisms although sediment supply analysis suggested that the interdune sand may derive from the altyn tagh mountains beishan mountains and sanlongsha dune field the provenance signature based on the k rb and k ba ratios revealed that the ultimate sources were the altyn tagh mountains in the south and the beishan mountains in the north by plotting the identified provenance results on a map of the sand sea we found that the spatial scopes of contributions from these sources were separated at around 40 n however the existence of a fluvial load em1 and of reworked coarse particles em3 in the northern sand sea demonstrated that the interdune sands in this region were partly derived from the altyn tagh mountains in the south consequently by combining our results with the transport agents condition we concluded that the altyn tagh mountains supplied sediments to interdune areas by fluvial transport throughout the sand sea but that sediment in the northern sand sea was subsequently reworked and mixed with windblown sand originated from the beishan mountains

strong and highly variable push of ocean waves on southern ocean sea ice sea ice in the southern ocean has expanded over most of the past 20 y but the decline in sea ice since 2016 has taken experts by surprise this recent evolution highlights the poor performance of numerical models for predicting extent and thickness which is due to our poor understanding of ice dynamics ocean waves are known to play an important role in ice break up and formation in addition as ocean waves decay they cause a stress that pushes the ice in the direction of wave propagation this wave stress could not previously be quantified due to insufficient observations at large scales sentinel 1 synthetic aperture radars sars provide high resolution imagery from which wave height is measured year round encompassing antarctica since 2014 our estimates give an average wave stress that is comparable to the average wind stress acting over 50 km of sea ice we further reveal highly variable half decay distances ranging from 400 m to 700 km and wave stresses from 0 01 to 1 pa we expect that this variability is related to ice properties and possibly different floe sizes and ice thicknesses a strong feedback of waves on sea ice via break up and rafting may be the cause of highly variable sea ice properties

raked linear dunes in the kumtagh desert china abstract linear dunes are extensive in sand seas and dune fields around the world but they take a range of forms due to the complex factors that control their development raked linear dunes composed of primary ridges and subsidiary ridges that lie almost perpendicular to the primary ridges were recently identified in the northern part of china s kumtagh desert the primary ridges are typical linear dunes but the subsidiary ridges display vestiges of barchan dunes the subsidiary ridges are sufficiently short that they do not greatly affect the general appearance of the linear dunes however the raked linear dunes in the kumtagh desert have several unique characteristics that distinguish them from typical linear dunes these dunes develop in an environment that is deficient in available sediment and under a wind regime typical of linear dunes an environment with a high wind energy and a directional variability index rdp dp around 0 5 the raked linear dunes appear to have evolved from barchans following a modified form of tsoar s 1984 model barchans formed under a northern wind regime were modified by an eastern wind regime oriented at an oblique angle to the barchans the strengths of the two wind regimes are similar under these conditions the barchans became reoriented with the limbs farthest from the eastern winds extending to form subsidiary ridges and the limbs closest to the eastern winds forming the primary ridges which appear to form mainly from dune collisions

wave attenuation and wave drift in the marginal ice zone abstract surface gravity waves in a viscous rotating ocean are studied theoretically when they penetrate an area covered by highly concentrated brashlike ice the motion is described by a lagrangian formulation and the brash is modeled by a viscous newtonian fluid results for wave attenuation and wave drift are obtained in the asymptotic limit of a thin very viscous upper layer the derived damping rate compares favorably with field data from the marginal ice zone miz the drift velocity in the ocean exhibits a marked maximum in the viscous boundary layer near the ice ocean interface at the outer edge of the boundary layer it exceeds the inviscid stokes drift by a factor of 7 4 computed values for the mean viscous drag on the ice induced by the wave motion show that this effect may compete with the frictional effected of the wind in packing the ice finally it is demonstrated that the integrated horizontal mass transports in the open ocean and under the ice do not match which leads to upwelling in

ocean surface wave evolvement in the arctic basin 1 recent basin scale changes to the compactness and thickness of arctic sea ice foreshadow that encroaching swells and locally generated waves will exert more influence there in the future indeed it is conceivable that waves may have already hastened the adjustments observed by breaking up ice floes yet waves advancing in sea ice attenuate due to being scattered from ice thickness variations and damped by ice inelasticity turbulence and friction while past research focuses on scattering by unnaturally perfect features in the ice the model reported herein assimilates realistic basin scale swathes of heterogeneous ice and parameterizes damping by way of example we show how an ocean wave train evolves during its passage in an 1670 km long arctic sea ice profile obtained from submarine

the effect of the marginal ice zone on the directional wave spectrum of the ocean abstract during the mizex 84 experiment in the greenland sea in june july 1984 a cooperative program was carried out between the scott polar research institute spri and the institute of oceanographic sciences ios to measure the change in the directional character of the ocean wave spectrum in the immediate vicinity of the ice edge the aim was to extend one dimensional spectral measurements made hitherto so as to study in full the processes of reflection and refraction directional spectrum analysis of these records shows that i significant reflection of wave energy occurs at the ice edge detected using long hasselmann analysis ii within the ice the directional spectrum at high frequencies where attenuation is rapid broadens to become almost isotropic whereas iii the directional spectrum at swell frequencies where the attenuation is slower becomes initially narrower before broadening more slowly than the high frequency energy an explanation of these effects is offered in terms of scatte

size distribution and shape properties of relatively small sea ice floes in the antarctic marginal ice zone in late winter in the marginal sea ice zone miz where relatively small ice floes are dominant the floe size distribution is an important parameter affecting melt processes given the larger cumulative perimeter of multiple small floes compared with a single ice floe of the same area smaller ice floes are therefore subject to increased lateral melt however the available data have been very limited so far analysis of sea ice in the sea of okhotsk revealed that while floe size distribution is basically scale invariant a regime shift occurs at a size of about 40 m in order to extend this preliminary result to the antarctic miz and further examine the controlling factors the first concurrent ice floe size and ice thickness measurements were conducted in the northwestern weddell sea and off wilkes land around 64 s 117 e with a heli borne digital video camera in the late winter of 2006 and 2007 respectively the floe sizes ranged from 2 to 100 m our analysis shows 1 the scale invariance and regime shift are confirmed in both regions 2 the floe size at which regime shift occurs slightly increases from 20 to 40 m with ice thickness consistent with the theory of the flexural failure of sea ice and 3 the aspect ratio is 1 6 1 9 on average close to the previous results based on these results the processes affecting the floe size distribution and the subsequent implications on melt processes are discussed by applying a renormalization group method to interpret the scale invariance in floe size distribution the fractal dimension is related to the fragility of sea ice these results indicate the importance of wave ice interaction in determining the floe size distribution

finite floe wave reflection and transmission coefficients from a semi infinite model a model to describe the reflection and transmission of ocean waves by a single ice floe is developed from the semi infinite model of fox and squire 1990 1991 this is done by considering the coefficients for the transition from ice to water in the semi infinite case in terms of those from water to ice finite floe reflection and transmission coefficients r and t respectively are then found as the solution of a set of four simple simultaneous equations the properties of r and t are investigated and examples of their absolute values are given for several geometries r compares well with the predictions of a precise model in the case of deep water these results suggest that the analytical model described has applications to defining the sea state within marginal ice zones given the floe size and ice thickness distributions and the incoming sea wave spectrum

implications of fractured arctic perennial ice cover on thermodynamic and dynamic sea ice processes decline of the arctic summer minimum sea ice extent is characterized by large expanses of open water in the siberian laptev chukchi and beaufort seas and introduces large fetch distances in the arctic ocean long waves can propagate deep into the pack ice thereby causing flexural swell and failure of the sea ice this process shifts the floe size diameter distribution smaller increases floe surface area and thereby affects sea ice dynamic and thermodynamic processes the results of radarsat 2 imagery analysis show that a flexural fracture event which occurred in the beaufort sea region on 6 september 2009 affected 40 000 km2 open water fractional area in the area affected initially decreased from 3 7 to 2 7 but later increased to 20 following wind forced divergence of the ice pack energy available for lateral melting was assessed by estimating the change in energy entrainment from longwave and shortwave radiation in the mixed layer of the ocean following flexural fracture 11 54 mj m 2 of additional energy for lateral melting of ice floes was identified in affected areas the impact of this process in future arctic sea ice melt seasons was assessed using estimations of earlier occurrences of fracture during the melt season and is discussed in context with ocean heat fluxes atmospheric mixing of the ocean mixed layer and declining sea ice cover we conclude that this process is an important positive feedback to arctic sea ice loss and timing of initiation is critical in how it affects sea ice thermodynamic and dynamic processes

gravel deposits on the margins of the qinghai xizang plateau and their environmental significance abstract the thick deposits of quaternary gravels found along the margins of the qinghai xizang tibet plateau have been studied for decades here we concentrate on two sediment series widely developed along the kunlun tian shan and qilian mountains the xiyu formation a molassic series of lower pleistocene age and the middle and upper pleistocene gobi gravels these two series with their contained fossil assemblages throw light on the question of the mean altitudes and uplift rates of the tibetan plateau during the quaternary and on the related problem of the vigour and penetration of advected summer monsoonal moisture into central asia the sedimentary series on the northern piedmonts of the tibetan plateau considered here challege the view that plateau uplift accelerated in the upper pleistocene they indicate that the plateau had reached mean altitudes in the range 4000 5000 m perhaps by the end of the lower pleistocene and certainly by the middle pleistocene this diminished the incursion of southerly monsoonal moisture and so imposed arid and semi arid conditions across much of a vast region north of the plateau which among other effects precluded widespread mountain glaciation in the lower pleistocene and general ice sheet glaciation of the tibetan plateau as a whole

autonomous underwater vehicles auvs and investigations of the ice ocean interface in antarctic and arctic waters limitations of access have long restricted exploration and investigation of the cavities beneath ice shelves to a small number of drillholes studies of sea ice underwater morphology are limited largely to scientific utilization of submarines remotely operated vehicles tethered to a mother ship by umbilical cable have been deployed to investigate tidewater glacier and ice shelf margins but their range is often restricted the development of free flying autonomous underwater vehicles auvs with ranges of tens to hundreds of kilometres enables extensive missions to take place beneath sea ice and floating ice shelves autosub2 is a 3600 kg 6 7 m long auv with a 1600 m operating depth and range of 400 km based on the earlier autosub1 which had a 500 m depth limit a single direct drive d c motor and five bladed propeller produce speeds of 1 2 m s 1 rear mounted rudder and stern plane control yaw pitch and depth the vehicle has three sections the front and rear sections are free flooding built around aluminium extrusion space frames covered with glass fibre reinforced plastic panels the central section has a set of carbon fibre reinforced plastic pressure vessels four tubes contain batteries powering the vehicle the other three house vehicle control systems and sensors the rear section houses subsystems for navigation control actuation and propulsion and scientific sensors e g digital camera upward looking 300 khz acoustic doppler current profiler 200 khz multibeam receiver the front section contains forward looking collision sensor emergency abort the homing systems argos satellite data and location transmitters and flashing lights for relocation as well as science sensors e g twin conductivity temperature depth instruments multibeam transmitter sub bottom profiler aqualab water sampler payload restrictions mean that a subset of scientific instruments is actually in place on any given dive the scientific instruments carried on autosub are described and examples of observational data collected from each sensor in arctic or antarctic waters are given e g of roughness at the underside of floating ice shelves and sea ice

observations and analyses of an intense waves in ice event in the sea of okhotsk 1 ice draft ice velocity ice concentration and current profile data gathered at an array of eight continental shelf monitoring sites east of sakhalin island were analyzed in conjunction with regional meteorological data to document and explain intense wave occurrences several hundred kilometers inside the sea of okhotsk ice pack the studied event was associated with the 19 21 march 1998 passage of an intense cyclone which produced waves with amplitudes in excess of 1 m at the most offshore monitoring location the relatively monochromatic character of the waves allowed extraction of wave intensity time series from ice draft time series data spatial and temporal variations in these data were used to establish directions and speeds of wave energy propagation for comparisons with an earlier interpretation liu and mollo christensen 1988 of an antarctic intense waves in ice event it was concluded that although both events are compatible with a two stage process in which initially slowly advancing wave activity increases subsequent ice cover wave transmissivity the first stage of the sea of okhotsk event was not explicable in terms of the static stress induced changes in the waves in ice dispersion relationship proposed by liu and mollo christensen an alternative explanation is offered that eschews the linkage between wave group velocities and the observed slow rates of wave energy propagation and attributes the subsequent transition to more normal wave propagation behavior to ice pack divergence

a fresh look at how ocean waves and sea ice interact because of their capacity to alter floe size distribution and concentration and consequently to influence atmosphere ocean fluxes there is a compelling justification and demand to include waves in

geomorphology and origin of yardangs in the kumtagh desert northwest china yardangs are typical wind eroded landforms that are found in most of the world s major deserts this paper describes the morphology of yardangs in the kumtagh desert analyzes their control factors and discusses their development processes age and rates of formation yardangs in the kumtagh desert lack the ideal streamlined morphology and the length to width ratio close to 4 1 that have been previously described as being due to their unique controlling factors which include a combination of stratigraphic structures wind erosion and fluvial erosion fluvial erosion plays a particularly important role in the development of the yardangs though wind continuously sculpts their morphology the development of yardangs can be divided into four stages an embryonic stage adolescence maturation and recession most yardangs in the kumtagh desert are in the mature to receding stages we determined an approximate age for the yardangs based on the erosion rates estimated by several researchers on this basis the yardangs in the kumtagh desert appear to have formed during the holocene

marginal ice zone thickness and extent due to wave radiation stress abstractocean surface wave radiation stress represents the flux of momentum due to the waves when waves are dissipated or reflected by sea ice that momentum is absorbed or reflected resulting in

the attenuation rates of ocean waves in the marginal ice zone during field operations in the greenland and bering seas in 1978 1979 and 1983 a number of experiments were carried out in which wave energy was measured along a line of stations running from the open sea deep into an icefield wave buoys in the water and accelerometer packages on floes were the instruments employed with airborne vertical photography to supply information on floe size distribution it was found that the decay of waves is exponential with a decay coefficient which generally increases with frequency except for a roll over at the highest frequencies the observations can be fitted reasonably well to a theory of one dimensional scattering

geomorphological patterns in a linear dune field and ages of the linear dunes in the northern kumtagh desert northwest china the unique linear dunes in the northern kumtagh desert of northwest china have inspired enthusiastic debate among aeolian geomorphologists over their origins and classification their uniqueness lies not only in their morphology but also in their geomorphological patterns in this paper the geomorphological patterns and ages of the linear dunes in the northern kumtagh desert are analyzed using the pattern analysis method that was recently adopted by geomorphologists the analysis suggests that these linear dunes have developed since 13 ka bp during the late part of the most recent deglaciation stage when the region s dry climate was favorable for dune formation the differences in dune construction time within this region result from the complex factors that control their formation and spatial variations in the local environment but these factors were not strong enough to prevent us from estimating the dune age recorded by the geomorphological patterns with acceptable precision it is also suggested that the pattern analysis method can be used to estimate dune ages in the absence of more reliable dating methods

nimbus 7 smmr observations of the bering sea ice cover during march 1979 a method of deriving sea ice concentrations from the 0 81 cm wavelength radiances of the nimbus 7 scanning multichannel microwave radiometer smmr is described and used in a comparative study of the bering sea ice cover during march 1979 case studies during 2 days in march demonstrate the utility of the smmr for studying marginal ice zone processes the first day provides an example of ice divergent conditions with winds from the northeast advecting the ice southwest toward the ice edge comparison of the smmr derived ice concentration maps with surface aircraft and tiros derived ice charts shows that the microwave data give the ice edge position to within 30 km corresponding to the highest spatial resolution of smmr the smmr ice concentrations also give an accurate description of the general morphology of the ice cover including the presence of lee shore polynyas the second day illustrates the effect of a storm passage on the ice cover the smmr ice map for this day correctly describes the retreat of the ice cover and gives the positions of local regions of open water and of high ice concentration within the pack the two examples show that for the bering sea the smmr algorithm provides accurate large scale to mesoscale data on both the ice edge position and the location of low and high ice concentration regions

reflection and transmission characteristics at the edge of shore fast sea ice the reflection and transmission of ocean waves at a sea ice boundary is reconsidered the sea ice is modelled as a continuous thin elastic plate of uniform thickness floating on water of arbitrary constant depth unlike earlier solutions matching of potentials between the free surface domain and the ice covered domain is done at all depths previous solutions were incompletely matched as the potentials in each domain were deficient in the present solution a number of the infinity of evanescent modes which were hitherto ignored are included in the solution and allow matching to be carried out by minimization of an integrated error term from surface to seafloor reflection and transmission are found to be markedly influenced by the inclusion of these modes suggesting that conclusions based on the incomplete potentials may be substantially in error

the use of sar to measure ocean wave dispersion in frazil pancake icefields abstract icefields composed of frazil and pancake ice play important roles in both polar regions in winter during the early to midwinter period pancake ice is a major component of the antarctic sea ice cover while in the arctic the odden ice tongue in the greenland sea associated with deep convection is composed mainly of pancake ice the retrieval of sea ice thickness by remote sensing is in general a very difficult task in this paper the change in dispersion of ocean waves as they penetrate into pancake ice is considered so as to gain insight into its possible relationship with thickness spectral analysis of subscenes from ers 2 second european remote sensing satellite synthetic aperture radar sar images yields the wavelength and direction of the principal spectral component both outside and inside the ice cover there is a decrease of wavelength at the ice edge as well as refraction toward the normal and a loss of amplitude the analysis is complex because the true wave spectrum must be re

a three dimensional model of wave attenuation in the marginal ice zone 1 a three dimensional model of wave scattering by a large array of floating thin elastic plates is used to predict the rate of ocean wave attenuation in the marginal ice zone in terms of the properties of the ice cover and the incoming wavefield this is regarded as a small step toward assimilating interactions of ocean waves with areas of sea ice into oceanic general circulation models numerical results confirm previous findings that attenuation is predominantly affected by wave period and by the average thickness of the ice cover it is found that the shape and distribution of the floes and the inclusion of an archimedean draft has little impact on the attenuation produced the model demonstrates a linear relationship between ice cover concentration and attenuation an additional study is conducted into the directional evolvement of the wavefield where collimation and spreading can both occur depending on the physical circumstances finally the attenuation predicted by the new three dimensional model is compared with an existing two dimensional model and with two sets of experimental data with the latter producing convincing agreement

ross ice shelf vibrations broadband seismic stations were deployed across the ross ice shelf ris in november 2014 to study ocean gravity wave induced vibrations initial data from three stations 100 km from the ris front and within 10 km of each other show both dispersed infragravity ig wave and ocean swell generated signals resulting from waves that originate in the north pacific spectral levels from 0 001 to 10 hz have the highest accelerations in the ig band 0 0025 0 03 hz polarization analyses indicate complex frequency dependent particle motions with energy in several frequency bands having distinctly different propagation characteristics the dominant ig band signals exhibit predominantly horizontal propagation from the north particle motion analyses indicate retrograde elliptical particle motions in the ig band consistent with these signals propagating as rayleigh lamb flexural waves in the ice shelf water cavity system that are excited by ocean wave interactions nearer the shelf front

controls of eolian dune size and spacing data for the namib and gran desierto sand seas suggest that the controls of dune size and spacing are complex the relation between dune height and spacing varies with dune type and location and reflects both dune dynamics vertical accretion vs migration or extension and availability of sand there is no general relation between dune spacing and grain size in the namib sand sea the height of compound and complex dunes draas is inversely proportional to potential sand transport rates whereas the height of dunes superimposed on their flanks varies directly with potential sand transport rates these observations can be combined with data on dune spacing to demonstrate the existence of a hierarchy of eolian dunes each element of which responds to variations in sand transport rates at different temporal and spatial scales whereas the morphology of individual simple dunes and superimposed dunes on draas is related to contemporary rates and directions of sand transport the morphology and development of draas reflects long term and regional patterns of sand transport and deposition

an ice water vortex at the edge of the east greenland current during the y mer 80 cruise in august 1980 we observed an ice feature of 60 km diameter having the shape of a breaking wave it lay at the edge of the east greenland drift ice in fram strait with its center at 79 15 n 00 38 e and the wave was breaking upstream relative to the east greenland current two conductivity temperature and depth sections across the feature in n s and e w directions revealed warm up to 4 3 c water some 60 km inside the polar front in lenses centered at 40 m depth but with an effect to beyond 600 m the temperature anomalies were accompanied by salinity anomalies so that there was little net effect on the density profile the form of the sections together with the ice distribution observed by vertical photography from a helicopter and surface motion observed by tracking four radar transponders all suggest that the feature is a vortex produced by an instability in the polar front it has similar characteristics to vortices investigated experimentally and theoretically by griffiths and linden 1981a b 1982 and observationally by wadhams et al 1979

morphology of the transition from an axial high to a rift valley at the southeast indian ridge and the relation to variations in mantle temperature the southeast indian ridge exhibits a transition in axial morphology from an east pacific rise like axial high near 100 e to a mid atlantic ridge like rift valley near 116 e but spreads at a nearly constant rate of 74 76 mm yr assuming that the source of this transition lies in variations in mantle temperature we use shipboard gravity derived crustal thickness and ridge flank depth to estimate the variations in temperature associated with the changes in morphological style within the transitional region seabeam 2000 bathymetry shows scattered instances of highs valleys and split volcanic ridges at the axis a comparison of axial morphology to abyssal hill shapes and symmetry properties suggests that this unorganized distribution is due to the ridge axis episodically alternating between an axial valley and a volcanic ridge axial morphology can then be divided into three classes with distinct geographic borders axial highs and rifted highs are observed west of a transform fault at 102 45 e rift valleys are observed east of a transform fault at 114 e and an intermediate style morphology which alternates between a volcanic ridge and a shallow axial valley is observed between the two one segment between 107 and 108 30 e forms an exception to the geographical boundaries gravity derived crustal thickness and flank depth generally vary monotonically over the region with the exception of the segment between 107 e and 108 30 e the long wavelength variations in these properties correlate with the above morphological classification gravity derived crustal thickness varies on average 2 km between the axial high and rift valley regions the application of previous models relating crustal thickness and mantle temperature places the corresponding temperature variation at 25 c 50 c depending on the model used the average depth of ridge flanks varies by 550 m over the study area for a variation of 25 50 c thermal models of the mantle predict depth variations of 75 150 m these values are consistent with observations when the combined contributions of crustal thickness and mantle density to ridge flank depth are considered assuming airy isostasy crustal thickness variations differ at the two transitions described above a difference of 750 m in crustal thickness is observed at the rift valley intermediate style transition suggesting small variations in crustal thickness and mantle temperature drive this transition at the axial high rifted high intermediate style transition crustal thickness variations are not resolvable suggesting that this transition is controlled by threshold values of crustal thickness and mantle temperature and is perhaps related to the presence of a steady state magma chamber

ice properties in the greenland and barents seas during summer resultats d analyse de carotte de glace de mer dans l arctique europeen les proprietes de la glace sont mises en rapport avec les conditions generales de la distribution de glace leur epaisseur et leur relief dans la zone exploree interpretation de la salinite sur les glaces de premiere annee et pluri annuelles

pseudo feathery dunes in the kumtagh desert abstract the kumtagh desert is the last explored desert in china the unique patterns on aerial photographs and satellite images have led previous researchers to the conclusion that the kumtagh desert is the only place over the world where typical feathery dunes are developed and that some unique wind regimes are at work recent field investigation reveals that the feathery patterns in fact reflect the albedo contrasts between the seif dunes bright dune like drifts and the dark inter dune lag sediments the wind regime in the area containing the so called feathery dunes is typical of the regime that produces seif dunes that were considered to be shafts of the feathery dunes and the vanes of the feathery dunes are in fact bright dune like drifts with indistinct height from the surroundings rather than true transverse dunes further analysis indicates that the sediments of seif dunes dune like drifts and dark inter dune flats differ in grain size distribution mineralogy reflectance spectrum and particle micro morphology sediments that constitute seif dunes and dune like drifts are finer and poorly rounded contain relatively more quartz and hence have higher albedo while the sediments that constitute the dark inter dune flats are coarser and better rounded contain far less quartz but relatively more andesite and dacite and hence have lower albedo as a result what was originally perceived as unique feathery dunes are in fact only pseudo feathery dunes composed primarily of seif dunes this discovery also demonstrates that blowing sand drifts can form dune like patterns that remain visible for long periods of time it is important to distinguish between the patterns of true dunes and those of dune like drifts pseudo dunes that cause albedo contrasts in interpreting remote sensing images

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

sea ice floes dissipate the energy of steep ocean waves a laboratory experimental model of an incident ocean wave interacting with an ice floe is used to validate the canonical solitary floe version of contemporary theoretical models of wave attenuation in the ice covered ocean amplitudes of waves transmitted by the floe are presented as functions of incident wave steepness for different incident wavelengths the model is shown to predict the transmitted amplitudes accurately for low incident steepness but to overpredict the amplitudes by an increasing amount as the incident wave becomes steeper the proportion of incident wave energy dissipated by the floe in the experiments is shown to correlate with the agreement between the theoretical model and the experimental data thus implying that wave floe interactions increasingly dissipate wave energy as the incident wave becomes steeper

a wave based model for the marginal ice zone including a floe breaking parameterization 1 the marginal ice zone miz is the boundary between the open ocean and ice covered seas where sea ice is significantly affected by the onslaught of ocean waves waves are responsible for the breakup of ice floes and determine the extent of the miz and floe size distribution when the ice cover is highly fragmented its behavior is qualitatively different from that of pack ice with large floes therefore it is important to incorporate wave ice interactions into sea ice ocean models in order to achieve this goal two effects are considered the role of sea ice as a dampener of wave energy and the wave induced breakup of ice floes these two processes act in concert to modify the incident wave spectrum and determine the main properties of the miz a simple but novel parameterization for floe breaking is derived by considering alternatively ice as a flexible and rigid material and by using current estimates of ice critical flexural strain and strength this parameterization is combined with a wave scattering model in a one dimensional numerical framework to evaluate the floe size distribution and the extent of the miz the model predicts a sharp transition between fragmented sea ice and the central pack thus providing a natural definition for the miz reasonable values are found for the extent of the miz given realistic initial and boundary conditions the numerical setting is commensurate with typical ice ocean models with the future implementation into two dimensional sea ice models in mind

late cenozoic geological evolution of the foreland basin bordering the west kunlun range in pulu area constraints on timing of uplift of northern margin of the tibetan plateau 1 with an average elevation of 5000 m the west kunlun range marks northwestern margin of the tibetan plateau and formed as an orogen in response to the collision of india and asia 50 ma ago its history of uplift and erosion in the late cenozoic is recorded in a unique sedimentary sequence exposed through the highest terrace along the southern margin of the tarim basin in pulu area the terrace is composed of coarse grain conglomerate at the bottom alkaline enriched volcanic rocks in the middle and eolian sediments on the top the underlying basement rocks are formed by neogene rocks and paleozoic granite named the xiyu conglomerate the coarse grained conglomerate is assigned a depositional age in the late pliocene and the early pleistocene 3 4 1 6 ma and generally considered to be the products of rapid uplift of the tibetan plateau to reveal the relations between uplift erosion and sedimentation we have collected samples of granite overlain by the xiyu conglomerate for dating the fission track age of apatite the fission track ages date the absolute time of cooling through the track retention temperature of the granite within the west kunlun range to be miocene to early pliocene 20 4 8 ma the cooling event was coeval with the north verging thrusting along the northern boundary fault and the associated foreland basin deposition suggesting that the west kunlun range once underwent significant tectonic uplift in the neogene in contrast to the underlying tertiary foreland basin strata the xiyu conglomerate thins toward the west kunlun range and contains granite pebbles of cooling ages of 93 18 and 12 ma our study suggests that the primary cause for accumulation of the xiyu conglomerate and the correspondent sediments is the increase of erosion and sedimentation rates after the main pulse of tectonic uplift due to quaternary climate change

wave effects on ocean ice interaction in the marginal ice zone the effects of wave train on ice ocean interaction in the marginal ice zone are studied through numerical modeling a coupled two dimensional ice ocean model has been developed to include wave effects and wind stress for the predictions of ice edge dynamics the sea ice model is coupled to the reduced gravity ocean model through interfacial stresses the main dynamic balance in the ice momentum is between water ice stress wind stress and wave radiation stresses by considering the exchange of momentum between waves and ice pack through radiation stress for decaying waves a parametric study of the effects of wave stress and wind stress on ice edge dynamics has been performed the numerical results show significant effects from wave action the ice edge is sharper and ice edge meanders form in the marginal ice zone owing to forcing by wave action and refraction of swell system after a couple of days upwelling at the ice edge and eddy formation can be enhanced by the nonlinear effects of wave action wave action sharpens the ice edge and can produce ice meandering which enhances local ekman pumping and pycnocline anomalies the resulting ice concentration pycnocline changes and flow velocity field are shown to be consistent with previous observations

ocean wave sea ice interactions in the south eastern coastal zone of sakhalin island abstract a long duration set of wave observations is reported conducted in the coastal region of south eastern sakhalin island in the sea of okhotsk using bottom mounted pressure sensors during both ice free conditions and while sea ice was present although one instrument was not able to be recovered the two remaining high precision instruments device located close to the shoreline and situated 7 5 km seaward in the south easterly direction provided time series sampled at 1 s allowing wave periods from 2 s to 20 min to be detected and spectrally analysed the time series reveal intriguing significant differences between open water periods and times when sea ice covered the surface e g preferential resonant frequencies appear in seastate energy density spectra during episodes of sizeable swell when sea ice is present but not when it is absent and what is believed to be a trapped edge wave of approximately 11 min period in open water increases in period to 11 8 min when the sea ice is there although no technical mathematical theory is advanced the authors speculate on potential explanations for these anomalies and invite readers to provide alternative hypotheses