a microwave technique for mapping thin sea ice a technique is presented for mapping the distribution of new young and first year sea ice in seasonal sea ice zones that utilizes microwave spectral and polarization information from the defense meteorological satellite program special sensor microwave imager the motivation for this work stems from the need for accurate estimates of open water and thin ice within the arctic ice pack the technique utilizes the microwave polarization and spectral characteristics of these three ice types through two microwave radiance ratios the 19 4 ghz polarization and the spectral gradient ratio which is a measure of the spectral difference between the 19 4 ghz and the 37 0 ghz vertically polarized radiance components the combined use of the spectral gradient ratio and polarization reduces the low ice concentration bias generally associated with the presence of thin ice types the microwave polarization which is sensitive to changes in ice thickness and ice surface characteristics is used to classify new young and first year ice types the polarization varies from about 0 3 for calm ice free water to about 0 15 for new ice and to 0 03 for thick first year ice on the basis of this parameterization improved sea ice concentration maps and maps of new young and first year ice type distributions are derived examples from the bering sea are presented and comparisons are made with analyzed noaa avhrr imagery

classification of new ice in the greenland sea using satellite ssm i radiometer and seawinds scatterometer data and comparison with ice model abstract in the ice covered waters of the greenland sea the polarisation ratio of quikscat seawinds ku band 13 4 ghz scatterometer measurements and the polarisation ratio of dmsp ssm i 19 ghz radiometer measurements are used in combination to classify new ice and mature ice in particular the formation of the new frazil pancake ice odden 8 w 75 n march 11th 18th 2001 is used in the study the results of the ice cover classification in the greenland sea are compared to model parameters from a sea ice model the classification of each ice pixel is performed using its backscatter and radiative properties as reflected in the polarisation ratio our results based on these comparisons show that the transformation into older mature sheet ice occurs within 5 10 days during one day the new ice cover increased by 33 000 km 2 the new ice appears in march 2001 as a peninsula maximum extent 56 000 km 2 appended to the belt of older ice drifting along the east coast of greenland these results are consistent with the ice model and with radarsat images furthermore using the ice model it is demonstrated that the new ice mature ice threshold in the classification corresponds to the physical transition of the ice cover from pancake ice to a consolidated young ice sheet the classification of each pixel into ice or water is done using two scatterometer parameters namely the polarisation ratio and the daily standard deviation of the backscatter

a method of detecting change in the ice conditions of the central greenland sea by the whelping locations of harp seals abstract variations in the extent of sea ice within the greenland sea on daily seasonal or longer time scales are well documented while changes in ice conditions are not by combining historical information on the location and timing of the hunt for the whelping harp seal phoca groenlandica with the ice conditions needed for the seals to give birth details of the types concentration and extent of ice within the central greenland sea in winter have been determined for the mid to late nineteenth century these in turn have been compared to ice extent and concentration from the passive microwave era as well as ice types from field work in the region results suggest that the ice conditions in the central greenland sea in the mid to late nineteenth century were significantly different from those witnessed in recent decades these differences manifest themselves not only in the extent of ice but in ice types concentration and longevity of the ice cover it is hypothesized that these changes could

study of the impact of ice formation in leads upon the sea ice pack mass balance using a new frazil and grease ice parameterization abstractleads are cracks in sea ice that often form because of deformation during winter months leads expose the ocean to the cold atmosphere resulting in supercooling and the formation of frazil ice crystals within the mixed layer here the authors investigate the role of frazil ice formation in leads on the mass balance of the sea ice pack through the incorporation of a new module into the los alamos sea ice model cice the frazil ice module considers an initial cooling of leads followed by a steady state formation of uniformly distributed single size frazil ice crystals that precipitate to the ocean surface as grease ice the grease ice is pushed against one of the lead edges by wind and water drag that the authors represent through a variable collection thickness for new sea ice simulations of the sea ice cover in the arctic and antarctic are performed and compared to a model that treats leads the same as the open ocean the processes of ice formation in the new module slow down the refreezing o

a sea ice model for the marginal ice zone with an application to the greenland sea 1 a model is presented that describes the formation transport and desalinization of frazil and pancake ice as it is formed in marginal seas this model uses as input the total ice concentration evaluated from special sensor microwave imager and wind speed and direction the model calculates the areal concentration thickness volume concentration and salinity of frazil ice as well as the areal concentration thickness and salinity of pancakes a simple parameterization for the odden region of the greenland sea is presented the model is run for the winter of 1996 1997 there are direct observations of the thickness and salinity of pancakes and the volume concentration of frazil ice to compare with the model the model results compare very well with the measured data this new ice model can be tuned to work in marginal seas elsewhere to calculate ice thickness motion and brine rejection also the model can be used to determine the location of the ice edge

global adjoint tomography first generation model we present the first generation global tomographic model constructed based on adjoint tomography an iterative full waveform inversion technique synthetic seismograms were calculated using gpu accelerated spectral element simulations of global seismic wave propagation accommodating effects due to 3d anelastic crust mantle structure topography bathymetry the ocean load ellipticity rotation and self gravitation frechet derivatives were calculated in 3d anelastic models based on an adjoint state method the simulations were performed on the cray xk7 named titan a computer with 18 688 gpu accelerators housed at oak ridge national laboratory the transversely isotropic global model is the result of 15 tomographic iterations which systematically reduced differences between observed and simulated three component seismograms our starting model combined 3d mantle model s362ani kustowski et al 2008 with 3d crustal model crust2 0 bassin et al 2000 we simultaneously inverted for structure in the crust and mantle thereby eliminating the need for widely used crustal corrections we used data from 253 earthquakes in the magnitude range 5 8 mw 7 0 for the first 12 iterations we combined 30 s body wave data with 60 s surface wave data the shortest period of the surface waves was gradually decreased and in the last three iterations we combined 17 s body waves with 45 s surface waves we started using 180 min long seismograms after the 12th iteration and assimilated minor and major arc body and surface waves the 15th iteration model features enhancements of well known slabs an enhanced image of the samoa tahiti plume as well as various other plumes and hotspots such as caroline galapagos yellowstone and erebus furthermore we see clear improvements in slab resolution along the hellenic and japan arcs as well as subduction along the east of scotia plate which does not exist in the starting model point spread function tests demonstrate that we are approaching the resolution of continental scale studies in some areas for example underneath yellowstone this is a consequence of our multi scale smoothing strategy in which we define our smoothing operator as a function of the approximate hessian kernel thereby smoothing gradients less wherever we have good ray coverage such as underneath north america

massive recrystallization of low mg calcite at high temperatures in hydrocarbon source rocks implications for organic acids as factors in diagenesis we document massive recrystallization of low mg calcite lime mudstone source rocks at moderately high temperatures in the smackover formation of mississippi this process was driven by organic acids produced during kerogen maturation and holds the implications for studies of primary migration of hydrocarbons secondary porosity generation in reservoirs and global environmental change this interpretation is based on contrasting the following petrographic and bulk rock geochemical characteristics of organic poor vs organic rich lime mudstones

adjoint tomography of the southern california crust using an inversion strategy based on adjoint methods we developed a three dimensional seismological model of the southern california crust the resulting model involved 16 tomographic iterations which required 6800 wavefield simulations and a total of 0 8 million central processing unit hours the new crustal model reveals strong heterogeneity including local changes of 30 with respect to the initial three dimensional model provided by the southern california earthquake center the model illuminates shallow features such as sedimentary basins and compositional contrasts across faults it also reveals crustal features at depth that aid in the tectonic reconstruction of southern california such as subduction captured oceanic crustal fragments the new model enables more realistic and accurate assessments of seismic hazard

impact of high resolution fwi in the western black sea revealing overburden and reservoir complexity the western black sea wbs is now an area of active petroleum exploration and several seismic surveys have been acquired to support the ongoing activity seismic imaging in the wbs is challenging due to the presence of complex overburden such as canyons shallow gas channels and complex shallow stratigraphy such overburden complexities create amplitude dimming and wipeouts in the images and cause structural distortions of the reservoir units conventional velocity model building and seismic migration methods are not optimal for addressing such challenges full wavefield inversion fwi technology was applied to overcome the complex seismic imaging challenges in the wbs and to support the exploration and development program to date a suite of fwi products has been used to identify shallow hazards derisk prospects optimize well placement perform accurate resource estimation and support development planning unlike traditional seismic migration generated fwi products are not simply depictions of

on the role of density and attenuation in three dimensional multiparameter viscoacoustic vti frequency domain fwi an obc case study from the north sea 3 d frequency domain full waveform inversion fwi is applied on north sea wide azimuth ocean bottom cable data at low frequencies 10 hz to jointly update vertical wave speed density and quality factor q in the viscoacoustic vti approximation we assess whether density and q should be viewed as proxy to absorb artefacts resulting from approximate wave physics or are valuable for interpretation in the presence of soft sediments and gas cloud fwi is performed in the frequency domain to account for attenuation easily multiparameter frequency domain fwi is efficiently performed with a few discrete frequencies following a multiscale frequency continuation however grouping a few frequencies during each multiscale step is necessary to mitigate acquisition footprint and match dispersive shallow guided waves q and density absorb a significant part of the acquisition footprint hence cleaning the velocity model from this pollution low q perturbations correlate with low velocity zones associated with soft sediments and gas cloud however the amplitudes of the q perturbations show significant variations when the inversion tuning is modified this dispersion in the q reconstructions is however not passed on the velocity parameter suggesting that cross talks between first order kinematic and second order dynamic parameters are limited the density model shows a good match with a well log at shallow depths moreover the impedance built a posteriori from the fwi velocity and density models shows a well focused image with however local differences with the velocity model near the sea bed where density might have absorbed elastic effects the fwi models are finally assessed against time domain synthetic seismogram modelling performed with the same frequency domain modelling engine used for fwi

increased co2 uptake due to sea ice growth and decay in the nordic seas 1 the uptake rates of atmospheric co2 in the nordic seas are among the highest in the world s oceans this has been ascribed mainly to a strong biological drawdown but chemical processes within the sea ice itself have also been suggested to play a role the importance of sea ice for the carbon uptake in the nordic seas is currently unknown we present evidence from 50 localities in the arctic ocean that dissolved inorganic carbon is rejected together with brine from growing sea ice and that sea ice melting during summer is rich in carbonates model calculations show that melting of sea ice exported from the arctic ocean into the east greenland current and the nordic seas plays an important and overlooked role in regulating the surface water partial pressure of co2 and increases the seasonal co2 uptake in the area by approximately 50

estimating p and s wave inverse quality factors from observed seismic data using an attenuative elastic impedance p and s wave inverse quality factors quantify seismic wave attenuation which are related to several key reservoir parameters porosity saturation viscosity etc estimating the inverse quality factors from observed seismic data provides additional and useful information during gas bearing reservoir prediction we first propose an approximate reflection coefficient and attenuative elastic impedance in terms of the inverse quality factors and then we establish an approach to estimate elastic properties p and s wave impedances and density and attenuation p and s wave inverse quality factors from seismic data at different incidence angles and frequencies the approach is implemented as a two step inversion a model based and damped least squares inversion for attenuative elastic impedance and a bayesian markov chain monte carlo inversion for the inverse quality factors synthetic data tests confirm that p and s wave impedances and inverse quality factors are reasonably estimated in the case of

inversion of the seismic avf ava signatures of highly attenuative targets frequency dependent seismic field data anomalies appearing in association with low q targets have on occasion been attributed to the presence of a strong absorptive reflection coefficient this absorptive reflectivity represents a potent and largely untapped source of information for determining subsurface target properties it would most likely be encountered where a predominantly elastic nonattenuating overburden suddenly is interrupted by a highly attenuative target series expansions of absorptive reflection coefficients about small parameter contrasts and incidence angles can expose these anomalies to analysis either frequency by frequency amplitude variation with frequency avf or angle by angle amplitude variation with angle of incidence ava within this framework variations in p wave velocity and q can be estimated separately through a range of direct formulas both linear and with nonlinear corrections the latter come to the fore when a contrast from an incidence medium q i

meteoric calcitization and incipient lithification of recent high magnesium calcite muds belize high magnesium calcite dominated muddy sediments on subaerially exposed rays in northern belize are being pervasively altered to and lithified by low magnesium calcite in the meteoric environment such diagenesis occurring in sediments less than 1000 1500 years old is indicated by the rapid loss of mg from muds and foraminifera progressively lighter mean isotopic compositions in lmc cemented muds relative to those in unaltered marine muds and concurrent reduction in sr and increase in mn concentrations the fabrics of these lmc deposits are micrites and microspars to pseudospars with pore filling lmc cements of similar crystal size these fabrics are similar to calcitized aragonite dominated precursor micrites except that aragonite relics in microspar or pseudospar are relatively rare in these samples

improved seismic image by q compensated reverse time migration application to crosswell field data west texas abstractto test the effectiveness of the q compensated reverse time migration q rtm method we applied it to crosswell seismic data from western texas this crosswell field survey was aimed at determining the boundaries and even the internal features of the reservoir in this area the reservoir geologic body exhibits strong attenuation that reduces high frequencies more rapidly thus conventional acoustic rtm produces a dimmed image reduced amplitude and low resolution of the reservoir area and structures underneath in contrast q rtm is able to compensate for the attenuation effects during imaging the vp and qp profiles needed for q rtm were produced by joint traveltime and frequency shift tomography preprocessing of the data was carried out to reduce noise remove tube waves and to separate up and downgoing wavefields along with recovered high wavenumbers the final q rtm image provided many details about geologic layers and structures the lateral and vertical extent and internal structures

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

dense water formation in the laptev sea flaw lead 1 two primitive equation based models are used to estimate the formation of total volumes either of arctic cold halocline water chw intermediate water imw or deep water dw through freeze related salt rejection in the siberian laptev sea flaw lead system model a assumes that the rejected salt remixes with surface mixed water smw beyond the leads until salinities allow for contribution to the midlayers of either the chw the imw or the dw model b simulates direct salt rejection to the upper layer of the cold halocline and after remixing here further contribution to the midlayers of chw imw or dw averaging both model estimates laptev leads contribute either 0 161 sv of chw 0 075 sv of imw or 0 065 sv of dw which represents as much as 23 16 or 30 of arctic wide lead derived dense water contribution to the appropriate layer respectively northwestern laptev leads produce the greatest amount of dense water these lead sections show very short buoyancy equilibrium timescales 6 to 13 days and local dense water production may potentially be amplified by lateral brine injection into the cold halocline through bottom eddies central southern and southeastern leads generally produce little salt due to low surface water salinities as definite separation mechanisms and proportion distributions of rejected lead brines into chw iwm and dw are still unidentified in nature a combination of lead salt rejection and remixing model a and direct downward expulsion of brine packages model b is assumed to steer laptev lead dense water production

evolution of electromagnetic signatures of sea ice from initial formation to the establishment of thick first year ice the spatial and temporal distribution of new and young sea ice types are of particular interest because of the influence this can exert on the heat and mass balance of the polar sea ice the objective of the present work is to characterize the temporal evolution of the electromagnetic em signatures of sea ice from initial formation through the development of first year fy ice on the basis of the temporal variations in the physical properties of the ice the time series of young sea ice signatures including microwave emissivity radar backscatter and visible and infrared spectral albedo has been measured at successive stages in the growth and development of sea ice both under laboratory and field conditions these observations have been accompanied by studies of the physical properties that influence the interaction between radiation and the ice this has resulted in a consistent data set of concurrent multispectral observations that covers essentially all phases of the development of the different types of sea ice from initial formation to thick fy ice mutually consistent theoretical models covering the entire wavelength range of the observations are applied to selected cases and successfully match the observations principal component analysis pca of the data set suggests combinations of the set of frequencies to effectively distinguish among different stages in the temporal evolution of the sea ice

ice extent in the greenland sea 1978 1995 abstract during the european subpolar ocean programme esop project from 1993 to 1995 very little ice was formed in the central greenland sea the large scale ice cover in the area during the period october 1978 to june 1995 has been mapped using passive microwave data from the scanning multichannel microwave radiometer smmr and the special sensor microwave imager ssm i special emphasis is put on the last three years of the period the esop years from the summer of 1992 to the summer of 1995 the results for the three winters compared with the average winter of the previous 12 yr show unusually little ice in the greenland sea during the winters of 1993 1995 in particular the winters of 1994 and 1995 saw no ice i e no odden in the central greenland sea at all another result is an observed upper limit of approximately 250 000 km 2 to the seasonal ice cover in the study region the odden area within the central greenland sea over the period 1978 1995

brackish water and evaporitic ca mg carbonates in the holocene lacustrine deltaic deposits of southern mesopotamia authigenic dolomite mg calcite and calcite occur in the holocene near surface marshland ahwar sediments and some subsurface strata of southern mesopotamia dolomite has been detected in evaporitic and brackish marine sedimentary units of both the siliciclastic and carbonate sequences whereas high mg calcite and low mg calcite are mainly restricted to brackish marine and lacustrine carbonate units respectively the dolomite which is polygenetic is highly calcian and has the composition ca 1 12 1 22 mg 0 88 0 78 co 3 2 the calcite is of two distinct phases low mg and high mg consisting of 5 mole or less and 10 mole or more mgco 3 respectively the dolomite samples show a spread of 18 o values from 8 pdb for detrital dolomite 3 to 6 5 for inferred dilute brackish samples 1 to l for mixing zone samples and 3 to 5 for evaporitic types the influence of sea level fluctuations during the holocene evolution of the tigris euphrates delta has resulted in the formation of different sedimentary environments of mixing marine and fresh waters favourable for ca mg carbonates formation evaporitic environments were the main source for dolomite formed in the early holocene

q model building using one way wave equation migration q analysis part 2 3d field data test in part one of this paper we presented an inversion based method wave equation migration q analysis to estimate the quality factor q model for seismic attenuation to demonstrate the feasibility of this method we applied this method to a 3d seismic dataset acquired in the north sea attenuation problems caused by a shallow gas and a shallow channel are observed in this field this study aims at characterizing these attenuation anomalies these attenuation anomalies are correlated with low interval velocities the provided velocity model does not accurately reflect the low velocity anomalies therefore we first applied wave equation migration velocity analysis to update the provided velocity model the updated velocity shows low velocity regions around the gas and channel features the subsurface angle gathers migrated using the updated velocity model are flatter and the events in the migrated images after velocity updating are more coherent then we applied wave equation migration q analysis to inv

seismic attenuation tomography using the frequency shift method we present a method for estimating seismic attenuation based on frequency shift data in most natural materials seismic attenuation increases with frequency the high frequency components of the seismic signal are attenuated more rapidly than the low frequency components as waves propagate as a result the centroid of the signal s spectrum experiences a downshift during propagation under the assumption of a frequency independent q model this downshift is proportional to a path integral through the attenuation distribution and can be used as observed data to reconstruct the attenuation distribution tomographically the frequency shift method is applicable in any seismic survey geometry where the signal bandwidth is broad enough and the attenuation is high enough to cause noticeable losses of high frequencies during propagation in comparison to some other methods of estimating attenuation our frequency shift method is relatively insensitive to geometric spreading reflection and transmission effects source and receiver coupling and radiation patterns and instrument responses tests of crosswell attenuation tomography on 1 d and 2 d geological structures are presented

anisotropic 3d full waveform inversion abstractwe have developed and implemented a robust and practical scheme for anisotropic 3d acoustic full waveform inversion fwi we demonstrate this scheme on a field data set applying it to a 4c ocean bottom survey over the tommeliten alpha field in the north sea this shallow water data set provides good azimuthal coverage to offsets of 7 km with reduced coverage to a maximum offset of about 11 km the reservoir lies at the crest of a high velocity antiformal chalk section overlain by about 3000 m of clastics within which a low velocity gas cloud produces a seismic obscured area we inverted only the hydrophone data and we retained free surface multiples and ghosts within the field data we invert in six narrow frequency bands in the range 3 to 6 5 hz at each iteration we selected only a subset of sources using a different subset at each iteration this strategy is more efficient than inverting all the data every iteration our starting velocity model was obtained using standard psdm model bui

a study of different methods of wavefield separation for application to vsp data1 during the last couple of years there has been much research in the area of wavefield separation of borehole seismic data and several articles have been published on various separation techniques methods involving the application of two dimensional fourier transformation the radon transformation multi level median filters or optimal filters are all suggested as possible approaches to the wavefield separation problem this paper compares some of these methods commonly used in the industry the theories of the chosen methods are described to see how they are related using the different methods on synthetic and real data we show how this theoretical relation is reflected in the relatively similar results obtained we also show how the different filters treat coherent and random noise

suspended sediment transport in the swash zone of a dissipative beach abstract simultaneous high frequency field measurements of water depth flow velocity and suspended sediment concentration were made at three fixed locations across the high tide swash and inner surf zones of a dissipative beach the dominant period of the swash motion was 30 50 s and the results are representative of infragravity swash motion suspended sediment concentrations loads and transport rates in the swash zone were almost one order of magnitude greater than in the inner surf zone the vertical velocity gradient near the bed and the resulting bed shear stress at the start of the uprush was significantly larger than that at the end of the backwash despite similar flow velocities this suggests that the bed friction during the uprush was approximately twice that during the backwash the suspended sediment profile in the swash zone can be described reasonably well by an exponential shape with a mixing length scale of 0 02 0 03 m the suspended sediment transport flux measured in the swash zone was related to the bed shear stress through the shields parameter if the bed shear stress is derived from the vertical velocity gradient the proportionality coefficient between shear stress and sediment transport rate is similar for the uprush and the backwash if the bed shear stress is estimated using the free stream flow velocity and a constant friction factor the proportionality factor for the uprush is approximately twice that of the backwash it is suggested that the uprush is a more efficient transporter of sediment than the backwash because the larger friction factor during the uprush causes larger bed shear stresses for a given free stream velocity this increased transport competency of the uprush is necessary for maintaining the beach otherwise the comparable strength and greater duration of the backwash would progressively remove sediment from the beach

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

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

diagenesis of early permian high latitude limestones lower parmeener supergroup tasmania the darlington sakmarian and berriedale artinskian limestones are neritic deposits that accumulated in high latitude environments along the south eastern margin of pangea in what is now tasmania these rocks underwent a series of diagenetic processes that began in the marine palaeoenvironment continued during rapid burial and were profoundly modified by alteration associated with the intrusion of mesozoic igneous rocks marine diagenesis was important but contradictory although dissolution took place there was also coeval precipitation of fibrous calcite cement phosphate and glauconite as well as calcitization of aragonite shells these processes are interpreted as having been promoted by mixing of shelf and upwelling deep ocean waters and enabled by microbial degradation of organic matter in contrast to warm water carbonates where meteoric diagenesis is important the darlington and berriedale limestones were largely unaffected by meteoric diagenesis only minor dissolution and local cementation took place in this diagenetic environment although mechanical compaction was ubiquitous correlation with burial history curves indicates that chemical compaction became important as burial depths exceeded 150 m promoting precipitation of extensive ferroan calcite this effect resulted from burial by rapidly deposited overlying thick late permian and triassic terrestrial sediments this diagenetic pathway was however complicated by the subsequent intrusion of massive mesozoic diabases and associated silicifying diagenetic fluids finally fractures most probably connected with cretaceous uplift were filled with late stage non ferroan calcite cement this study suggests that both carbonate dissolution and precipitation occur in high latitude marine palaeoenvironments and therefore the cold water diagenetic realm is not always destructive in terms of diagenesis furthermore it appears that for the early permian of southern pangea at least there was no real difference in the diagenetic pathways taken by cool water and cold water carbonates

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

electromagnetic and physical properties of sea ice formed in the presence of wave action estimating the magnitude of brine flux to the upper ocean requires an ability to assess the dynamics of the formation of sea ice in a region brine storage and rate of expulsion is determined by the environmental conditions under which the sea ice forms in this paper the physical and electromagnetic properties of sea ice formed under wave agitated conditions are studied and compared with results obtained from ice formed under quiescent conditions wave agitation is known to have a profound effect on the air ice interface and internal ice structure a variety of sensors both active and passive optical and microwave were used to perform this characterization measured electromagnetic parameters included radar backscatter microwave emission and spectral albedo in the visible and infrared measured physical properties included ice structure brine and temperature distribution profiles of the vertical height of the air ice interface and ice formation processes results showed that emission backscatter and albedo all take different signature paths during the transformation from saline water to young sea ice and that the paths depend on sea surface state during ice formation

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

the determination of the seismic quality factor q from vsp data a comparison of different computational methods1 ten methods for the computation of attenuation have been investigated namely amplitude decay analytical signal wavelet modelling phase modelling frequency modelling rise time pulse amplitude matching technique spectral modelling and spectral ratio in particular we have studied the reliability of each of these methods in estimating correct values of q using three synthetic vsp seismograms for plane p waves with different noise contents the investigations proved that no single method is generally superior rather some methods are more suitable than others in specific situations depending on recording noise or geology the analytical signal method has been demonstrated to be superior if true amplitude recordings are available otherwise spectral modelling or in the noise free case the spectral ratio method is optimal finally two field vsps in sediments are investigated only in the case of the highest quality vsp can significant information be deduced from the computed attenuation

the response of the sea ice edge to atmospheric and oceanic jet formation abstractthe sea ice edge presents a region of many feedback processes between the atmosphere ocean and sea ice maslowski et al here the authors focus on the impact of on ice atmospheric and oceanic flows at the sea ice edge mesoscale jet formation due to the coriolis effect is well understood over sharp changes in surface roughness such as coastlines hunt et al this sharp change in surface roughness is experienced by the atmosphere and ocean encountering a compacted sea ice edge this paper presents a study of a dynamic sea ice edge responding to prescribed atmospheric and oceanic jet formation an idealized analytical model of sea ice drift is developed and compared to a sea ice climate model the los alamos sea ice model cice run on an idealized domain the response of the cice model to jet formation is tested at various resolutions it is found that the formation of atmospheric jets at the sea ice edge increases the wind speed parallel to the sea ice edge and results in the formation of a