physical and stable isotopic properties and growth processes of sea ice collected in the southern sea of okhotsk this study presents physical and stable isotopic properties of sea ice in the southernmost section of the sea of okhotsk on the basis of observations and measurements made in 1995 and 1996 midwinter cruises structural analysis revealed that ice was predominantly of the granular type saucer shaped cores and wedges were seen in the cross sections of the pancakes which indicate a rafting event in the early stage of the pancake formation the fraction of snow with respect to the total ice mass was estimated at 8 from independent 18o and density measurements from these findings we conclude that the initial growth mechanisms of the sea ice over this region are by the frazil pancake cycle with rafting and by the snow ice formation analysis also shows that the formation of the snow ice induces 10 more salt flux through the additional freezing of the seawater in a short synoptic timescale this implies that snow becomes a negative salting rather than a positive freshening source for the buoyancy flux these results suggest critical influence of the rapid formation of the frazil pancakes and snow ice under stormy conditions on the salt and buoyancy fluxes over the region

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

effects of lateral friction on the structural evolution of fold and thrust belts insights from sandbox experiments with implications for the origin of landward vergent thrust wedges in cascadia various factors are inferred to influence the structural evolution of fold and thrust belts or thrust wedges but the effects of lateral friction such as that exerted by the opposite block of a strike slip fault in nature or by sidewalls in analogue models have rarely been given sufficient attention and hence are still far from being fully understood up to now seaward vergent and dually vergent thrust wedges have been satisfactorily explained by the classic coulomb wedge theory and can be well reproduced in analogue and numerical models in contrast landward vergent thrust wedges which are uncommon in nature e g those occurring in the cascadia subduction zone have not yet been adequately explained by the classic coulomb wedge theory and can only be reproduced in a few analogue models under particular conditions in order to look closer at the effects of lateral friction on the structural evolution of fold and thrust belts and to explore the origin of landward vergent thrust wedges we conducted a series of sandbox models under different conditions of lateral friction and various ratios of initial average lateral frictional stress to basal shear stress s d results of our models revealed that in the presence of a weak or ductile basal decollement the direction of lateral friction can dictate not only the deformation propagation direction and the surface slope direction but also the structural vergence of fold and thrust belts fold and thrust belts normally show a structural vergence in the same direction as the direction of lateral friction but a deformation propagation direction and surface slope direction opposite to the direction of lateral friction according to the results of models and the relationships between structural vergence and lateral friction direction occurring both in cascadia and the analogue models we propose that an extremely high s d ratio due to an extremely weak basal decollement and landward directed lateral friction exerted by the opposite blocks of basement involved strike slip faults are probably the two key factors responsible for the origin of landward vergent thrust wedges in cascadia this work illustrates that effects of lateral friction should be properly taken into account both in the kinematic analysis and designs of models to simulate fold and thrust belts in the presence of weak or ductile basal decollements

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

mapping of different sea ice regimes using images from sentinel 1 and alos synthetic aperture radar airborne c and l band synthetic aperture radar sar images were acquired for three test sites over different sea ice regimes around svalbard in march 2007 complemented by optical imagery environmental data and ice observations one objective was to use the high resolution low noise radar data for investigations on the technical performance of european space agency s sentinel 1 mission for sea ice mapping the other to assess the potential gain of additional use of l band sar data currently available from advanced land observing satellite alos the airborne sar images were employed to simulate data products resembling the interferometric wide swath mode iwsm of sentinel 1 and alos palsar fine resolution mode frm in order to quantify the information loss due to the higher noise level and coarser spatial resolution at the iwsm noise level zones of deformation level ice and new ice can be well separated at like polarization at cross polarization the noise level is too high for a robust automated classification including thin ice but deformed and level ice can be discriminated palsar frm is on average better suited to distinguish deformed and level ice over all ice regimes it was worse for separating new from thicker level ice at two test sites for the third test site with very few patches of new ice the palsar frm showed larger intensity contrasts between new and level ice than sentinel 1 iwsm the spatial resolution provided by the iwsm and frm is sufficient to identify most ice features and types without ambiguities typical characteristics of the imaged ice regimes are described

range dependent seabed characterization by inversion of acoustic data from a towed receiver array the mapex2000 experiments were conducted in the mediterranean sea in march 2000 to determine seabed properties using a towed acoustic source and receiver array towed systems are advantageous because they are easy to deploy from a ship and the moving platform offers the possibility for estimating spatially variable range dependent seabed properties in this paper seabed parameters are determined using a matched field geoacoustic inversion approach with measured towed array data previous research has successfully applied matched field geoacoustic inversion techniques to measured acoustic data however in nearly all cases the inverted data were collected on moored vertical receiver arrays results here show that seabed parameters can also be extracted by inverting acoustic measurements from a towed array of receivers and these agree with those inverted using data received simultaneously on a vertical array these findings imply that a practical technique could be developed to map range dependent seabed parameters over large areas using a towed acoustic system an example of such a range dependent inversion is given using measurements from the mapex2000 experiments

statistical estimation of transmission loss from geoacoustic inversion using a towed array geoacoustic inversion estimates environmental parameters from measured acoustic fields e g received on a towed array the inversion results have some uncertainty due to noise in the data and modeling errors based on the posterior probability density of environmental parameters obtained from inversion a statistical estimation of transmission loss tl can be performed and a credibility level envelope or uncertainty band for the tl generated this uncertainty band accounts for the inherent variability of the environment not usually contained in sonar performance prediction model inputs the approach follows gerstoft et al ieee j ocean eng 31 299 307 2006 and is demonstrated with data obtained from the mapex2000 experiment conducted by the nato undersea research center using a towed array and a moored source in the mediterranean sea in november 2000 based on the geoacoustic inversion results the tl and its variability are estimated and compared with the measured tl

control of clay mineral stratigraphy by selective transport in late pleistocene holocene sediments of northern cascadia basin juan de fuca abyssal plain implications for studies of clay mineral provenance abstract previous investigations duncan and others 1970 stokke and carson 1974 of cascadia basin clay mineralogy indicate a general trend in which montmorillonoids smectites 17 a are enriched relative to illite 10 a and chlorite 7 a in holocene lutites whereas illite and chlorite dominate in late pleistocene deposits the apparent crystallinity of all clay mineral groups declines from pleistocene to holocene russell 1967 there exist however numerous local exceptions to these general patterns which are not readily explained by the previous works fifteen samples from 5 cores in northern cascadia basin and juan de fuca abyssal plain were fractionated into 6 size classes semi quantitative determinations of clay mineralogy and crystallinity were made on each of the 90 subsamples the results indicate a definite size dependency in clay mineralogy and crystallinity which is consistent both areally and temporally discriminant function analysis indicates that clay mineralogy and crystallinity of some individual size fractions are statistically distinct but that the stratigraphic units late holocene early holocene and late pleistocene are not statistically discernible textural variations within and between holocene and pleistocene parallel sediment clay mineral changes and mineralogy can be predicted on the basis of clay min ral size dependency and grain size distribution it is inferred that the stratigraphic textural mineralogic variations result from selective transport and deposition and not from contrasting source areas or weathering conditions as had previously been suggested duncan and others 1970 stokke and carson 1974 future investigations of clay mineral provenance dispersal or correlation in any area should be based upon data which has been corrected for the effects of clay mineral size dependency

equations for determining the gas and brine volumes in sea ice samples on a etabli des equations utilisables pour determiner le taux de gaz inclus dans la glace de mer a partir de mesures de densite de salinite et de temperature dans des gammes de temperatures entre 2 c et 30 c inversement ces relations peuvent etre utilisees pour calculer la densite de la glace de mer en fonction de la temperature et de la salinite en prenant en compte a la fois la presence de gaz et de cristaux de sel dans la glace on donne aussi des equations qui permettent le calcul du volume de gaz et d eau salee dans la glace a des temperatures autres que celle pour laquelle la densite a ete determinee

frictional properties of shale reservoir rocks 1 we performed laboratory friction experiments on shale samples from three hydrocarbon reservoirs to assess compositional controls on fault slip behavior accompanying hydraulic stimulation the samples span a range of clay and total organic content from 10 to 60 by weight and demonstrate fine scale heterogeneity within each reservoir friction measurements demonstrate strong dependence of strength and rate state constitutive properties on shale composition shale samples with clay and organic content above 30 by weight show coefficient of friction 0 4 and consistently velocity strengthening behavior while those below this threshold show increased strength and velocity weakening behavior this transition in frictional strength and stability suggests a change in the shale grain packing framework from rigid clast supported to clay mineral and organic matter supported measurements of gouge dilatancy further support these relationships showing a negative correlation with clay and organic content critical slip evolution distance exhibits similar dependence on composition implying common micromechanical mechanisms for the observed transition in frictional behavior we performed microstructural characterization of the experimental samples and observe changes in the gouge load bearing framework and shear localization features consistent with these mechanical data while these results can be applied generally to infer slip stability on faults in clay bearing sedimentary rock we employ the experimental data to place constraints on microearthquake magnitudes and the occurrence of slow shear slip on preexisting faults during hydraulic stimulation in shale reservoirs

provenance stratigraphic architecture and hydrogeologic influence of turbidites on the mid ocean ridge flank of northwestern cascadia basin pacific ocean abstract the northwestern edge of cascadia basin north pacific ocean is unusual because late pliocene to holocene turbidites lap onto juvenile oceanic crust of the juan de fuca ridge subsidence of the ridge flank combines with irregular westward progradation of the turbidite facies to create a stratigraphic section that coarsens and thickens upward the sand provenance is mixed individual turbidity currents have funneled into the area through several shelf slope and abyssal floor conduits including vancouver valley juan de fuca channel barkley canyon and nitinat canyon local bathymetric blockage deflection and reflection of flow paths by basement relief remobilization by intrabasinal submarine slides and debris flows episodic channel switching and sporadic overbank flooding have combined to produce erratic recurrence intervals for the turbidity currents only the tallest basement highs have remained isolated from turbidite deposition during the last 500 000 years spatial and temporal differences in sediment accumulation are important because they modulate the three dimensional responses of compaction and consolidation those changes in physical properties govern where and when hydraulic communication with the underlying basement shuts down the basal hemipelagic layer of cascadia basin transforms to an effective hydrologic seal seepage rates 1 mm yr once the sediment basalt interface is buried by 100 150 m of strata rapid accumulation of turbidites therefore accelerates the hydrogeologic conversion of igneous basement from open to sealed

mirages in shallow water matched field processing broadband matched field processing mfp derived estimates of 3d source location using data from hydrophone line arrays deployed in various geometries i e vertical horizontal and tilted 45 from vertical are presented in this paper these data were collected in two shallow water 100 200 m experiments off the coast of san diego results show that estimates of source range and depth remain surprisingly coherent in the presence of large mismatch in bathymetry but are offset from the true position by as much as 100 the offsets are independent of array geometry in contrast for estimates of source azimuth bathymetry mismatch typically causes a degradation in mfp correlation rather than an appreciable offset however errors in the assumed tilt from vertical of an array can lead to large offsets in the estimated source azimuth particularly as the nominal angle of the array from vertical becomes smaller predictions from a simple analytical model based on adiabatic normal modes in ideal waveguides provide good fits to the broadband mfp results

surface based passive microwave studies of multiyear sea ice multifrequency passive microwave observations are reported from surface based field experiments carried out over multiyear sea ice in the eastern arctic basin the beaufort sea the canadian archipelago and the northern greenland sea dual polarized brightness temperatures at 6 7 10 18 7 37 and 90 ghz were obtained at selected multiyear ice sites covering a wide range of surface properties considerable variation was found in the observed spectra over short distances on individual floes under winter conditions where values of ev 37 ghz ev 18 ghz ev 37 ghz ev 18 ghz ranged from nearly zero to approximately 0 08 concurrent surface characterization observations consisting of temperature density salinity and grain size profiles in the snow and the upper meter of the ice were carried out frequently in conjunction with cold regions research and engineering laboratory personnel the present analysis shows that the magnitude of the spectral gradient of emissivity is directly related to the existence and thickness of a decomposed surface ice layer with very high porosity spectra for melt ponds with a frozen surface layer closely resembled those of lake ice and show a positive spectral gradient as soon as the ponds were completely frozen their spectra became nearly the same as those for first year ice fine grained winter snow produced a mild decrease in the emissivities at 90 ghz with increasing snow thickness from 0 to 0 2 m at which point the snow appears to be optically thick during the melt season the ice emissivities e depend most strongly on whether the surface layers are experiencing temporary freezing or not under melting conditions e depends on the liquid water content only over a very small range e g 0 5 by mass at 90 ghz if the liquid water in the surface layers is freezing which can occur at intervals throughout the melt season the spectral gradient is negative with a slope which depends on the thickness of the refrozen layer the variance among emissivity spectra for multiyear ice appears to be influenced primarily by the distribution of melt ponds and by the presence of significant amounts of scattering inhomogeneities greater than 1 mm in diameter in the snow and in the upper 20 30 cm of the ice we expect the signatures of multiyear ice to be regionally dependent perhaps yielding environmental information about the arctic ice pack

high resolution geoacoustic inversion in shallow water a joint time and frequency domain technique high resolution geoacoustic data are required for accurate predictions of acoustic propagation and scattering in shallow water since direct measurement of geoacoustic data is difficult time consuming and expensive inversion of acoustic data is a promising alternative however the main problem encountered in geoacoustic inversion is the problem of uniqueness i e many diverse geoacoustic models can be made to fit the same data set a key and perhaps unique aspect of this approach is the combination of data analysis in both the space time and the space frequency domains this combination attempts to ameliorate the uniqueness problem by exploiting as much independent data as possible in order to meet the stringent requirements of high spatial resolution and uniqueness an entire method has been developed including a new measurement technique processing analysis technique and inversion strategy these techniques are described and then illustrated with a shallow water data set sound speed gradients in the upper few meters of the sub bottom appear to be much higher one order of magnitude than generally assumed and although often ignored a large density gradient was observed in the top layer that played an acoustically significant role

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

landward vergence and oblique structural trends in the oregon margin accretionary prism implications and effect on fluid flow abstract the central oregon margin spans a regional transition in accretionary structures from seaward verging in the south to landward verging in the north new multichannel seismic mcs data image both landward and seaward vergent provinces along the central and northern oregon margin landward vergence is characterized by a deep decollement with deformation distributed across a broad lower continental slope in a coherent structural style in the landward vergent area virtually all 4 km of incoming trench sediments overthrust the preceding thrust sheet forming fault bend folds and a distinctive ridge trough morphology this style of landward vergence is not explained by existing models in contrast seaward vergence correlates with a shallower decollement approximately 1 4 km above the oceanic crust and a more intense style of deformation within a narrower slope initial thickening of the trench sediments occurs across a well developed protothrust zone the frontal thrust forms a ramp anticline that is cut by a prominent backthrust previously observed seafloor vent sites in both regions correlate with thrusts that exhibit high amplitude reversed polarity reflections suggestive of enhanced porosity along the faults potential fluid sources and migration paths are strongly influenced by changes in the level of the decollement and vergence along the margin abrupt changes in structural style occur both along strike and updip and are bounded by two sets of oblique slip faults three nw striking left lateral faults are imaged in both mcs and seabeam data plunging anticlines developed along the nw striking faults are venting fluids and were previously interpreted as mud volcanoes the deformation front is locally disrupted where these faults intersect the prism but they appear to have limited influence on the structural evolution of the prism in contrast the ne striking right lateral faults are confined to the deforming sediments of the upper plate these faults interact with the thrusts within the prism forming a rhomboidal pattern of three dimensional deformation

microwave and physical properties of sea ice in the winter marginal ice zone surface based active and passive microwave measurements were made in conjunction with ice property measurements for several distinct ice types in the fram strait during march and april 1987 synthetic aperture radar imagery downlinked from an aircraft was used to select study sites the surface based radar scattering cross section and emissivity spectra generally support previously inferred qualitative relationships between ice types exhibiting expected separation between young first year and multiyear ice gradient ratios calculated for both active and passive data appear to allow clear separation of ice types when used jointly surface flooding of multiyear floes resulting from excessive loading and perhaps wave action causes both active and passive signatures to resemble those of first year ice this effect could possibly cause estimates of ice type percentages in the marginal ice zone to be in error when derived from aircraft or satellite borne sensors

shortening of analogue models with contractive substrata insights into the origin of purely landward vergent thrusting wedge along the cascadia subduction zone and the deformation evolution of himalayan tibetan orogen abstract origin of certain uncommon fold and thrust belts such as the purely landward vergent rearward vergent thrusting wedge along the cascadia subduction zone and the wide flat toped himalayan tibetan orogen were proposed to be closely related to their ductile substrata results of a series of sandbox models with contractive substrata of various contracting velocities and different contracting directions designed to study the influences of horizontal contraction of ductile substrata on deformation evolution and structural style of fold and thrust belts show that purely rearward vergent thrusting wedges can be reproduced under the condition of syn directionally horizontal contraction of the ductile substrata without other requirements of forward dipping backstops landward dipping detachments and strong wedges relative to weak bases therefore syn directionally horizontal contraction of the ductile substrata can be considered an important cause for the formation of purely landward vergent thrusting wedge along the cascadia subduction zone our modeling results together with the results of some other previous physical and numerical models reinforce the opinion that the deformation evolution of the himalayan tibetan orogen were likely governed by its weak lower crust and suggest that the north and south edges of the himalayan tibetan orogen may have undergone almost synchronous cenozoic deformation evolution owing to the existence of weak lower crust it is also proposed that 1 development of thrusts in the himalayan tibetan orogen may not necessarily occur in a frontward sequence 2 much later uplift deduced from cenozoic sedimentary records in the basins along the northeastern margin of the himalayan tibetan orogen does not necessarily imply much later initiation of uplift and deformation at the northeastern margin of the orogen

experimental study of geo acoustic inversion uncertainty due to ocean sound speed fluctuations acoustic data measured in the ocean fluctuate due to the complex time varying properties of the channel when measured data are used for model based geo acoustic inversion how do acoustic fluctuations impact estimates for the seabed properties in may 1999 saclant undersea research center and tno physics and electronics laboratory fel conducted a shallow water experiment on the adventure bank off the southwest coast of sicily italy to assess the effects of a time varying ocean on acoustic propagation and geo acoustic inversion a favorable area for acoustic propagation was identified which had slight internal wave activity and a weakly range dependent bathymetry with sand like bottom properties oceanographic and acoustic measurements were performed continuously over a 3 day period broadband 0 2 3 8 khz acoustic signals from a bottom moored source were transmitted over fixed paths and received on a moored vertical hydrophone array during the transmissions extensive environmental measurements e g sound speed current sea surface waveheight etc were made to correlate the time varying environmental and acoustic data modeled acoustic data show time variability which agrees with the measurements results illustrate severe problems when modeling shallow water acoustic propagation at ranges beyond a few kilometers in the frequency band considered further the acoustic fluctuations in time caused erroneous time variability in inverted seabed properties

greenland sea odden sea ice feature intra annual and interannual variability the odden is a large sea ice feature that forms in the east greenland sea that may protrude eastward to 5 e from the main sea ice pack at about 8 w between 73 and 77 n it generally forms at the beginning of the winter season and can cover 300 000 km2 throughout the winter the outer edge of the odden may advance and retreat by several hundred kilometers on timescales of a few days to weeks satellite passive microwave observations from 1978 through 1995 provide a continuous record of the spatial and temporal variations of this extremely dynamic phenomenon aircraft synthetic aperture radar satellite passive microwave and ship observations in the odden show that the odden consists of new ice types rather than older ice types advected eastward from the main pack the 17 year record shows both strong interannual and intra annual variations in odden extent and temporal behavior for example in 1983 the odden was weak in 1984 the odden did not occur and in 1985 the odden returned late in the season an analysis of the ice area and extent time series derived from the satellite passive microwave observations along with meteorological data from the international arctic buoy program iabp determined the meteorological forcing associated with odden growth maintenance and decay the key meteorological parameters that are related to the rapid ice formation and decay associated with the odden are in order of importance air temperature wind speed and wind direction oceanographic parameters must play an important role in controlling odden formation but it is not yet possible to quantify this role because of a lack of long term oceanographic observations

release of mineral bound water prior to subduction tied to shallow seismogenic slip off sumatra plate boundary fault rupture during the 2004 sumatra andaman subduction earthquake extended closer to the trench than expected increasing earthquake and tsunami size international ocean discovery program expedition 362 sampled incoming sediments offshore northern sumatra revealing recent release of fresh water within the deep sediments thermal modeling links this freshening to amorphous silica dehydration driven by rapid burial induced temperature increases in the past 9 million years complete dehydration of silicates is expected before plate subduction contrasting with prevailing models for subduction seismogenesis calling for fluid production during subduction shallow slip offshore sumatra appears driven by diagenetic strengthening of deeply buried fault forming sediments contrasting with weakening proposed for the shallow tohoku oki 2011 rupture but our results are applicable to other thickly sedimented subduction zones including those with limited earthquake records

effect of clay content and mineralogy on frictional sliding behavior of simulated gouges binary and ternary mixtures of quartz illite and montmorillonite 1 we investigated the frictional sliding behavior of simulated quartz clay gouges under stress conditions relevant to seismogenic depths conventional triaxial compression tests were conducted at 40 mpa effective normal stress on saturated saw cut samples containing binary and ternary mixtures of quartz montmorillonite and illite in all cases frictional strengths of mixtures fall between the end members of pure quartz strongest and clay weakest the overall trend was a decrease in strength with increasing clay content in the illite quartz mixture the trend was nearly linear while in the montmorillonite mixtures a sigmoidal trend with three strength regimes was noted microstructural observations were performed on the deformed samples to characterize the geometric attributes of shear localization within the gouge layers two micromechanical models were used to analyze the critical clay fractions for the two regime transitions on the basis of clay porosity and packing of the quartz grains the transition from regime 1 high strength to 2 intermediate strength is associated with the shift from a stress supporting framework of quartz grains to a clay matrix embedded with disperse quartz grains manifested by the development of p foliation and reduction in riedel shear angle the transition from regime 2 intermediate strength to 3 low strength is attributed to the development of shear localization in the clay matrix occurring only when the neighboring layers of quartz grains are separated by a critical clay thickness our mixture data relating strength degradation to clay content agree well with strengths of natural shear zone materials obtained from scientific deep drilling projects

snow contribution to first year and second year arctic sea ice mass balance north of svalbard the salinity and water oxygen isotope composition 18o of twenty nine first year fyi and second year syi arctic sea ice cores total length 32 0 m from the drifting ice pack north of svalbard were examined to quantify the contribution of snow to sea ice mass five cores total length 6 4 m were analyzed for their structural composition showing variable contribution of 10 30 by granular ice in these cores snow had been entrained in 6 to 28 of the total ice thickness we found evidence of snow contribution in about three quarter of the sea ice cores when surface granular layers had very low 18o values snow contributed 7 5 9 7 to sea ice mass balance on average including also cores with no snow using 18o mass balance calculations in syi cores snow fraction by mass 12 7 16 3 was much higher than in fyi cores 3 3 4 4 while the bulk salinity of fyi 4 9 was distinctively higher than for syi 2 7 we surmise that oxygen isotopes and salinity profiles can give information on the age of the ice and allows to distinguish between fyi and syi or older ice in the area north of svalbard this article is protected by copyright all rights reserved

development and properties of sea ice in the coastal regime of the southeastern weddell sea from october to december 1986 a program consisting of sea ice core analysis in combination with sea ice observations was carried out from the icebreaker r v polarstern as part of the winter weddell sea project the ship operated in the central and southeastern weddell sea with interests focusing on the ice shelf front between 70 s and 77 s where a system of coastal polynyas extended for several tens to hundreds of kilometers opened and maintained despite temperatures well below freezing by offshore wind forcing three wind controlled ice formation regimes may be distinguished 1 for wind speeds 10 m s the ice cover is heavily ridged and rafted 50 and formation of granular ice predominates of the total length of cores sampled in the coastal regime 32 consisted of columnar and 35 of granular ice in addition we observed two unique ice classes along the coast platelet ice formed through consolidation of underwater ice platelets underneath the solid ice cover contributed 11 to our core samples another 22 consisted of intermediate columnar granular ice which originates under the dynamic hydrographic conditions of the near ice shelf region

nonlinear inversion for ocean bottom properties high resolution methods based on simulated annealing and full wave sound propagation models are developed for nonlinear inversion for ocean bottom properties simulated annealing is used to search the high dimensional parameter space of ocean bottoms for the parameter set corresponding to the best replica field the parabolic equation method is used to solve range dependent inversion problems for data taken by lynch et al from a range dependent region of the gulf of mexico j acoust soc am 89 648 665 1991 this approach achieves excellent agreement between the theoretical and measured acoustic pressures the recovered sediment parameters suggest that a sound speed boundary layer exists in the upper part of the sediment and that the depth of an interface in the sediment is range dependent for locally range independent problems inversion is performed in wave number space large efficiency gains are possible with this approach because the number of wave number samples required for inversion is mu

sources and dispersal patterns of clay minerals in surface sediments from the continental shelf areas off alaska the three mineral suites were recognized in the gulf of alaska the glaciomarine sediments of fjords and the eastern shelf consist typically of the primary phyllosilicates micas and chlorites derived locally from argillite graywacke and metavolcanics under conditions of mild chemical weathering more glycol expandable clay minerals gecm in the north gulf substantiate clay supply to that region primarily from the yakataga and poul creek formations and to a lesser extent from the copper river the northern gulf clay mineral suite is transported to central prince william sound and northeast kodiak shelf by the alaska coastal current in the western gulf clay minerals adjacent to the alaska peninsula are derived principally from the susitna river via cook inlet whereas those of the outer shelf presumably have their provenance in kodiak island and the katmai ash submarine deposit in the southeast bering sea a progressive northwestward decrease in gecm from 65 to 11 is caused by a gradually decreased sediment export from the alaska peninsula and the aleutians with a possible minor increase in illite from the kuskokwin river the yukon river is the predominant clay source for the north bering sea as signified by an abrupt increase in that area of gecm 20 to 35 and of kaolinite chlorite ratios clay mineralogy indicates that the central chukchi sea is the major repository of the yukon clays suggesting that clay mineral stratigraphic studies have implications for interpretation of the quaternary paleogeography of beringia in the beaufort sea nearshore influence of different fluvial inputs and their dispersals by currents are sharply defined the lack of a definite pattern to the distribution of clay minerals in the outer continental shelf may be due to haphazard transport of clays by ice rafting and or reworking and redistribution of sediments resulting from ice gouging of the sea substrate movement of sediment to the west in the alaskan portion of the inner shelf of beaufort sea is evident an apparent seaward increase in illite gecm ratio in the colville delta is tentatively ascribed to regeneration of degraded illite micas by k fixation in saline waters an isolated area of sediment rich in expandable clay minerals in the central beaufort shelf presumably is relict

an evaluation of the accuracy of shallow water matched field inversion results in this article the accuracy of geo acoustic and geometric parameter estimates obtained through matched field inversion mfi was assessed multi frequency mfi was applied to multi tone data 200 600 hz received at a 2 km source receiver range the acoustic source was fixed and the signals were received at a vertical array simultaneously with the acoustic transmissions a ctd conductivity temperature and depth chain was towed along the acoustic track a genetic algorithm was used for the global optimization whereas a normal mode model was applied for the forward acoustic calculations acoustic data received at consecutive times were inverted and the stability of the inverted parameters was determined also the parameter estimates were compared with independent measurements such as multi channel seismic surveys for geo acoustic parameters the obtained uncertainty in the inversion results was assumed to have two distinct origins the first origin is the inversion method itself since each optimization will come up with some solution close to the exact optimum parameter coupling and the fact that some parameters hardly influence the acoustic propagation further contribute to this uncertainty the second is due to oceanographic variability both contributions were evaluated through simulation the contribution of oceanographic variability was evaluated through synthetic inversions that account for the actual sound speed variations as measured by the towed ctd chain

towards identification of optimum radar parameters for sea ice monitoring modele theorique permettant de prevoir la diffusion par la glace multi annuelle et par la glace de premiere annee en conditions froides les resultats experimentaux montrent que les bandes de frequence ku et x ainsi que les angles d incidence superieure a 30 sont les meilleurs pour distinguer les types de glace de mer

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

accretion and recent deformation of sediments along the northern cascadia subduction zone new multichannel seismic reflection profiles acoustic imagery and swath bathymetric data from the vancouver island continental margin reveal the surface morphology cross sectional geometry and deformation style of this part of the cascadia accretionary prism the incoming 3 to 5 km thick sediment section fails most commonly along landward dipping thrusts that penetrate to or very close to the top of the underlying oceanic crust the faults are listric with approximately circular cross sections and hanging wall sediments are back tilted in a planar manner high near lithostatic pore pressures in the deeper part of the section are inferred from the flattening of the faults near the decollement and from the long distances over which the decollement has propagated seaward the faults dip more steeply at 40 45 near the surface where pleistocene turbidites are displaced similar folds have developed where the turbidites are particularly thick 4 km and near hydrostatic pore pressures are inferred to occur in the turbidite part of the section an increase in pore pressure with depth is expected as a consequence of sedimentation and tectonic loading particularly because the deeper hemipelagic sediments are probably far less permeable than are the overlying turbidites the top of the downgoing juan de fuca plate which defines the base of the accreted sedimentary wedge beneath the margin is well imaged in the new seismic reflection profiles and is further defined by land reflection data seismic refraction and earthquake hypocenters the landward dipping continental backstop to the prism is also well located if these constraints are used for the geometry of the accretionary prism a general balance is found between the present prism volume and the estimated total sediment supply over the approximately 42 m y accretion history this result along with the observation that deformation front faults penetrate most or all of the sediment section suggests that little or no sediment has been subducted since initiation of the present phase of subduction in the eocene application of the critically tapered wedge model of davis and others to the observed prism geometry suggests that high average pore pressures occur in the prism particularly the seawardmost part beneath the lower slope beneath the continental shelf the dip of the subducting slab increases to greater than 11 a dip that according to the critically tapered wedge model is too steep to allow upward growth of an accretionary prism this provides a simple explanation for ongoing subsidence of the tofino sedimentary basin over the older part of the accretionary complex to the southeast the juan de fuca plate dips much more gently beneath the olympic peninsula of northern washington allowing the accretionary prism to grow upward well above sea level to form the olympic mountains

investigations of newly formed sea ice in the cape bathurst polynya 2 microwave emission 1 this study examines the role of newly formed sea ice geophysical state on microwave emission coincident with sea ice geophysical sampling ship based passive microwave emission data dual polarized at 19 37 and 85 ghz were collected in the cape bathurst polynya during 18 october and 13 november 2003 using polarization ratios prs we found that bare thin ice was separable from snow covered ice thin snow equal to 0 02 0 13 m thickness is significantly correlated with the spectral gradient ratios grv 85 19 r2 0 55 p value 0 2 the relationship between atmospherically corrected r37 and bare ice thickness showed an exponential relationship very comparable to that reported by martin et al 2004 which is ascribed to the reduction of bare ice surface salinity based on both observational and modeling studies however the relationship quickly becomes invalid for even thin snow covered ice due to significant impact of thin wet liquid water fraction 0 02 0 04 snow on microwave emission our results suggest that the sea ice algorithms nasa team and nasa team 2 could underestimate total ice concentration over thin bare ice by 35 on average while both algorithms underestimate the total ice concentration by 20 over snow covered ice using pr 85 sea ice could be delineated from open water using a properly adjusted threshold value accounting for cloud or fog effects possibly with the exception of dark nilas and or bare consolidated pancakes

fluid history related to the early eocene middle miocene convergent system of the northern apennines italy constraints from structural and isotopic studies 1 the late eocene middle miocene erosive plate boundary between the european and the adriatic plates is exhumed in the northern apennines of italy the fossil fault zone is 500 m thick and the outcropping portion exposes the first 5 km of its depth at this plate boundary basal and frontal tectonic erosion incorporated unlithified fluid rich sediments into the fault zone the deformation and nature of the material along the plate boundary define a fossil subduction channel here we couple a detailed structural analysis of the apennine subduction channel focusing in particular on calcite veins with a stable isotope analysis to characterize the fluid regime along an active subduction channel the 13c and 18o composition of calcite vein and host rock samples within the fault zone indicates that there is a deep metamorphic source of fluids migrating upward along the subduction channel in addition to locally derived fluid components dewatering of subducting turbidites contributes significantly only in the shallowest part of the channel structural observations indicate fluid flow along and across the subduction channel at deep levels fluid flow is associated with discrete deformation events on shear faults offset by dilational jogs filled with implosion breccias at intermediate levels deformation is still cyclic and associated with repeated crack and seal events at the shallowest levels deformation occurred while portions of the subducting material were still unlithified here the deformation was quasicontinuous without associated vein development both isotope and structural analyses indicate that this erosive subduction channel behaved as a weak fault with a vertical maximum principal stress

interseismic uplift rates for western oregon and along strike variation in locking on the cascadia subduction zone 1 we quantify the spatial pattern of uplift rate in western oregon and northernmost california using tidal and leveling records to better understand the pattern of interseismic locking on the cascadia subduction zone we extend relative sea level time series of the six primary noaa tide gauges to include all observations from 1925 to 2006 previously unidentified bench mark instability biases portions of tidal records by 1 6 mm a 1 before correction we determine precise relative uplift rates at the six tidal sites with an adjustment that includes rates of differenced time series as additional constraints our analysis of national geodetic survey leveling data between tide gauges corrects errors in 1941 leveling and 184 secondary ties double the number of highest quality uplift rate estimates relative uplift rates from leveling are adjusted to the tidal rates accounting for uncertainties in both data types tidal and leveling uplift rates agree within error for all but one of the coastal segments where we infer systematic leveling error affects the 1988 line uplift rates are made absolute using an interval and location specific geocentric sea level rise rate of 2 3 0 2 mm a 1 total propagated one sigma errors for the absolute uplift rates of bench marks are 0 4 mm a 1 along strike changes in uplift rate near 45 n and 42 8 n require two distinct changes in locking depth as inferred from elastic dislocation modeling the along strike changes in locking on this portion of the cascadia subduction zone interface correlate to the western and southern extent of the mafic siletzia block in the fore arc

bayesian inversion of reverberation and propagation data for geoacoustic and scattering parameters this paper applies nonlinear bayesian inference theory to quantify the information content of reverberation and short range propagation data both individually and in joint inversion to resolve seabed geoacoustic and scattering properties the inversion of reverberation data alone is shown to poorly resolve seabed properties because of strong multi dimensional correlations between parameters inversion of propagation data alone is limited by different correlations but better constrains the geoacoustic parameters however propagation data are insensitive to scattering parameters such as lambert s scattering coefficient in each case the parameter correlations are inherent in the physics of the forward problem reverberation and propagation and cannot be overcome by processing or inversion techniques rather the inversion of more informative data is required this is accomplished here by joint inversion of reverberation and propagation data weighted according to their respective maximum likelihood error estimates joint inversion of reverberation and propagation data collected on the malta plateau strait of sicily resolves both geoacoustic and scattering properties and achieves smaller uncertainties for all parameters than obtained by the inversion of either data set alone

inversion for geometric and geoacoustic parameters in shallow water experimental results experimental results on the estimation of both geometric and geoacoustic parameters in shallow water are presented genetic algorithms are used for estimation of the forward model parameters the estimated parameters are then used by a standard bartlett processor for source localization a stationary source at a range of 5 6 km and a moving source at ranges from 5 8 7 7 km were successfully localized in range and depth using a single frequency bartlett processor the results indicate that global estimation of the forward model parameters significantly improves source localization performance

an arctic sea ice multi step classification based on gnss r data from the tds 1 mission abstract this study examines the potential of using bistatic radar reflections from the global navigation satellite system gnss to classify sea ice types in the arctic ocean during the sea ice formation period for this study we used data obtained from the united kingdom uk techdemosat 1 tds 1 satellite mission the main objective of the tds 1 mission is to provide l band radar reflections of the ocean surface in order to infer wind speed through an estimation of the ocean surface roughness given the orbit inclination of tds 1 polar coverage is obtained providing datasets over the arctic sea ice cover recent studies demonstrated the use of tds 1 data for accurately deriving ocean ice detection using the shape of the bistatic radar waveforms derived from delay doppler maps we aim to advance this previous research by demonstrating the sensitivity of gnss bistatic radar signals to sea ice types the originality of the study presented in this manuscript is the classification of sea ice types never implemented before with any gnss r mission for this study we examined the fall period of october 2015 in the beaufort and chukchi seas region when considerable expanses of young ice first year ice fyi and multi year ice myi were present we developed a sea ice multi step classification approach based on bistatic radar reflections to generate not only an ocean ice classification but to classify between the three dominant ice types present the classification was done in multiple steps based on gnss bistatic radar observations only and includes checks for spatio temporal consistency with each dominant class validation results are based on the comparison of the gnss classification against sar derived sea ice type maps produced at the us national ice center first we derived classifications of sea ice open water samples with a success rate of 97 comparable to previous studies next the sea ice type classification results identified fyi myi and young ice with success rates of 70 82 and 81 respectively indicating a strong sensitivity of the l band gnss bistatic radar signals to the different surface scattering properties of these primary ice types with this manuscript we demonstrate the potential of the gnss bistatic radar signals to classify ice types during the sea ice formation period gnss bistatic radar signals provide unique forward scattered measurements at l band potentially on a daily temporal revisit that can be used to produce enhanced information on sea ice characteristics such as those currently generated by other sensors in order to determine the use of gnss r measurements on an operational basis further studies are needed over a year long period of sea ice growth and melt to determine the full benefit of gnss for improving and providing complementary information to that generated by both microwave and optical sensors

negative polarity seismic reflections along faults of the oregon accretionary prism indicators of overpressuring either thrusting of higher over lower impedance sediment or reduction of impedance locally in the fault zone can produce negative polarity reflections along the protothrusts and the frontal thrust of the oregon accretionary prism the vertical displacement of protothrusts averages only 27 m is uncorrelated to the occurrence of polarity reversals and is insufficient to generate the impedance contrasts associated with the negative polarity reflections the negative polarity reflections from the protothrusts are probably due to localized impedance reduction in the fault zone waveform modeling of these negative polarity reflections indicates they develop due to a single interface with negative impedance contrast this seismic signal could be produced by a fault zone with a sharp upper boundary with low impedance fault material and a transition down section to sediment of higher impedance an impedance inversion due to the 1 km throw on the frontal thrust could create the observed negative polarity reflections interval velocities do not decrease across the frontal thrust but core scale velocity measurements indicate a velocity decrease in the frontal thrust therefore the negative polarity reflections are apparently produced by a localized decrease in impedance waveform modeling of frontal thrust reflections suggests the low impedance interval is about 20 m thick with discrete upper and lower boundaries moderately dipping faults are an efficient path for fluid expulsion across the turbidites with low equivalent vertical permeability fluid migration from the over pressured section up the faults can locally reduce the velocity sufficiently to cause the negative polarity reflections

estimation of seabed reflection loss properties from direct blast pulse shape l the decay rate of a smeared multipath arrival received many water depths from a broadband source has been shown to be closely related to bottom reflection loss properties smith j acoust soc am 50 332 336 1971 harrison j acoust soc am 114 2744 2756 2003 this suggests a simple way of measuring bottom properties with active sonars the method is demonstrated with experimental data measured in a shallow water region of the mediterranean sea seabed properties are deduced directly by the method in the form of the rate of change of reflection loss with respect to angle close to grazing agreement is shown between the results of the method and the results of matched field inversions carried out in the same area good agreement is also shown between measurements and predictions of propagation loss made using seabed properties deduced via the method

geoacoustic inversion in time domain using ship of opportunity noise recorded on a horizontal towed array a time domain geoacoustic inversion method using ship noise received on a towed horizontal array is presented the received signal containing ship noise as a source of opportunity is time reversed and then back propagated to the vicinity of the ship the back propagated signal is correlated with the modeled signal which is expected to peak at the ship s location in case of a good match for the environment this match is utilized for the geoacoustic parameter inversion the objective function for this optimization problem is thus defined as the normalized power focused in an area around the source position using a matched impulse response filter a hybrid use of global and local search algorithms i e ga and powell s method is applied to the optimization problem applications of the proposed inversion method to mapex 2000 noise experiment conducted north of the island of elba show promising results and it is shown that the time domain inversion takes advantage of dominant frequencies of the source si

observations of flooding and snow ice formation in a thinner arctic sea ice regime during the n ice2015 campaign influence of basal ice melt and storms seven ice mass balance instruments deployed near 83 n on different first year and second year ice floes representing variable snow and ice conditions documented the evolution of snow and ice conditions in the arctic ocean north of svalbard in january march 2015 frequent profiles of temperature and thermal diffusivity proxy were recorded to distinguish changes in snow depth and ice thickness with 2 cm vertical resolution four instruments documented flooding and snow ice formation flooding was clearly detectable in the simultaneous changes in thermal diffusivity proxy increased temperature and heat propagation through the underlying ice slush then progressively transformed into snow ice flooding resulted from two different processes i after storm induced breakup of snow loaded floes and ii after loss of buoyancy due to basal ice melt in the case of breakup when the ice was cold and not permeable rapid flooding probably due to lateral intrusion of seawater led to slush and snow ice layers at the ocean freezing temperature 1 88 c after the storm the instruments documented basal sea ice melt over warm atlantic waters and ocean to ice heat flux peaked at up to 400 w m 2 the warm ice was then permeable and flooding was more gradual probably involving vertical intrusion of brines and led to colder slush and snow ice 3 c the n ice2015 campaign provided the first documentation of significant flooding and snow ice formation in the arctic ice pack as the slush partially refroze snow ice formation may become a more frequently observed process in a thinner ice arctic

extraction of marginal ice zone thickness using gravity wave imagery synthetic aperture radar sar imagery of gravity waves in the marginal ice zone miz was acquired during 1987 and 1989 using aircraft flying over the greenland sea the dominant gravity wavelengths acquired during 1987 exhibit a systematic lengthening with penetration distance into the miz for three different regions examined the extracted dominant wavelengths were analyzed using a linear least squares fit with penetration distance and a flexure gravity wave model to estimate mean ice thickness the extracted mean thickness varies from about 1 0 4 m near the ice edge to approximately 2 0 4m near the deepest detectable penetration of the waves about 20 km these thicknesses are in agreement with 31 in situ measurements taken in the fram strait miz within 2 weeks of the sar measurements we also acquired wave imagery across a 150 km section of newly forming ice called the odden a tongue shaped region during 1989 these sar images at l c and x bands display small wave modulation signatures at the northern edge of the odden which we interpret as arising from rapidly growing new ice

clay mineralogy of a glacially dominated subarctic continental shelf northeastern gulf of alaska abstract glaciation is the single most important process responsible for contributing sediment to the northeastern gulf of alaska continental shelf over 75 percent of the northeastern gulf s drainage basin is presently ice covered or only recently has emerged from beneath holocene glacial ice many glaciers terminate in rivers that drain into the gulf or terminate in tidewater bays this study examines the mineralogy of the northeastern gulf of alaska continental shelf clay minerals in light of the glacially dominant nature of the area analyses of 110 bottom samples from the gulf of alaska continental shelf between icy point and prince william sound show an average clay mineral assemblage of 61 percent kaolinite chlorite 37 percent illite and 2 percent smectite over most of the shelf deviations from the average composition are generally 10 percent one significant exception is an area south of the copper river where illite content is as high as 65 percent and kaolinite chlorite ranges from 35 to 48 percent suspended sediment and bottom samples collected in successive years from the copper river the largest sediment source to the gulf have variations in clay mineralogy suggesting that different tributaries and hence different source areas control the composition of the river s mineralogy during different years upper river sources are rich in kaolinite chlorite whereas illite rich sediment is introduced in the lower 100 km transportation of sediment south of the copper river across the shelf and into prince william sound is documented by a decrease in illite from a continental shelf point source south of the river s mouth in addition to modern fluvial input a second source of the modern shelf sediment appears to be the glacially derived miocene to quaternary yakataga formation older formations such as the poul creek and katalla formations show fewer compositional similarities to nearby shelf sediment

seismically inferred dilatancy distribution northern barbados ridge decollement implications for fluid migration and fault strength a 5 x 25 km three dimensional seismic survey of the lower part of the northern barbados ridge accretionary prism creates a three dimensional image of a major active decollement fault the fault is usually a compound negative polarity reflection modeled as a low velocity high porosity zone less than 14 m thick this thickness is significantly less than that defined by drilling of a 40 m zone of deformation at ocean drilling program odp site 671b located within the surveyed area we infer that the seismically defined fault is a thin high porosity zone and is thus an undercompacted high fluid pressure dilatant section if these inferences are correct then map view variations in seismic reflection waveform and amplitude illustrate complex patterns of fault zone fluid content and fluid migration paths the amplitude map suggests kilometre wide channels of locally high porosity and thus focused fluid flow these paths are only subparallel to the expected minimum head as inferred from the shape of the overlying sediment wedge other factors must modify fluid concentrations and ultimately migration several areas of positive polarity fault reflections define square kilometre sized regions inferred to be lower porosity sections producing strong asperities in an otherwise weak fault one coincident with site 671b may explain the success of drilling through the fault here all other holes drilled in the area were within the negative polarity regions and were unsuccessful in penetrating through the entire fault zone possibly because of instability associated with high fluid pressures and a weak fault odp leg 156 planned for 1994 will test inferences related to fault permeability and fluid pressures

strike parallel variations in clay minerals and fault vergence in the cascadia subduction zone clay minerals probably affect the zonation of mechanical properties within a thick unit of abyssal plain deposits as they enter the cascadia subduction zone landward vergent thrust faults develop above a deeper decollement because smectite rich mudrocks within that corridor release more water during clay dehydration which in turn elevates pore pressure and reduces basal shear stress relative to wedge strength conversely di lution of smectite by illite and chlorite increases the frictional coefficient and fluid over pressure should drop where smectite dehydration is volumetrically reduced thus thrust faults within chlorite rich segments of the margin are seaward vergent

surface based passive microwave observations of sea ice in the bering and greenland seas measurements of brightness temperatures of sea ice were carried out during both the mizex field experiments in 1983 the first in februrary in the bering sea and the second in june july in the northern greenland sea in the bering sea thin growing sea ice types from black ice to 400 mm thick snow covered floes were investigated brightness temperatures increased with ice thickness up to 100 mm from values of 100 k for open water to as high as 250 k e 0 97 for thick ice and a moderate dependence on snow thickness was found in the greenland sea thick first year and multiyear ice types were studied brightness temperatures were quite variable depending on the daily melt freeze cycle superimposed on the seasonal warming ranging from near blackbody values for melting conditions to multiyear like spectra when the surface layers refroze the melt season was sufficiently advanced however that first year and multiyear ice could not be differentiated radiometrically

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

shallow water waveguide characterization using the hankel transform a coherent processing technique is proposed for the characterization of shallow water channels for a horizontally stratified ocean and bottom the method consists of measuring the magnitude and phase versus range of the pressure due to a cw point source and hankel transforming this data to obtain the depth dependent green s function versus horizontal wave number the green s function contains all the information about the channel necessary to solve the forward problem including the nature of the discrete and continuous spectra and the plane wave reflection coefficient of the bottom characteristics of the green s function can also be used to infer acoustic properties of the bottom results for simple examples are presented using synthetic data and implications for the nonstratified case are discussed

aircraft and satellite passive microwave observations of the bering sea ice cover during mizex west passive microwave measurements of the bering sea ice cover were made with the nasa cv 990 airborne laboratory and with the nimbus 7 scanning multichannel microwave radiometer smmr during february 1983 as part of the bering sea marginal zone experiment mizex west microwave data obtained with the cv 990 include radiances from both imaging and dual polarized fixed beam radiometers spanning a range of frequencies from 10 to 183 ghz the imagery at 19 and 92 ghz provide a description of the marginal ice zone delineating regions of open water ice compactness and ice edge structure comparison of these images with ice concentration maps derived from the smmr data shows that the maps provide an accurate description of the ice edge and interior pack polynyas analysis of the fixed beam data shows that spectral differences increase with a decrease in ice thickness and the polarization at both 18 and 37 ghz distinguishes among new young and first year sea ice types finally these results are shown to agree with surface based radiometric measurements

analyzing lateral seabed variability with bayesian inference of seabed reflection data this paper considers bayesian inversion of seabed reflection coefficient data for multi layer geoacoustic models at several sites with the goal of studying lateral variability of the seabed rigorous uncertainty estimation is carried out to resolve lateral variability of the sediments from inherent inversion uncertainties the uncertainty analysis includes bayesian model selection comprehensive quantification of data error statistics and a markov chain monte carlo approach to transforming data uncertainties to model uncertainties model selection is addressed using the bayesian information criterion to ensure parsimony of the parametrizations data error statistics are quantified by estimating full covariance matrices from data residuals with posterior statistical validation a metropolis hastings sampling algorithm is used to compute posterior probability densities four experiment sites are considered along a track located on the malta plateau mediterranean sea and the inversion results are compared to cores taken at each site differences between profile marginal probability distributions at adjacent sites are quantified using the bhattacharyya coefficient differences that exceed the estimated geoacoustic uncertainties are interpreted as spatial variability of the seabed the results are compared to an interpretation of geologic features evident in a chirp sub bottom profiler section

bayesian geoacoustic inversion of ship noise on a horizontal array this paper applies geoacoustic inversion to low frequency narrow band acoustic data from a quiet surface ship recorded on a bottom moored horizontal line array in shallow water a bayesian matched field inversion method is employed which quantifies geoacoustic uncertainties and allows for meaningful comparison of inversion results from different data sets geoacoustic inversion results for ship noise data are compared with inversion results for multitone data from a towed controlled source collected in the same experiment and with independent geophysical measurements to increase the information content of low level ship noise data the effect of including multiple independent data segments in the inversion is investigated and shown to significantly reduce geoacoustic parameter uncertainties geoacoustic uncertainties are also shown to depend on ship range and orientation with increased uncertainties for long ranges and for the ship stern oriented away from the array

physical properties of summer sea ice in the fram strait the physical properties of sea ice in the fram strait region of the greenland sea were examined during june and july 1984 in conjunction with the marginal ice zone experiment field program most of the ice sampled within fram strait during this period was multiyear thicknesses and other properties indicated that none of the multiyear ice was older than 4 to 5 years snow cover on the multiyear ice averaged 29 cm while that on first year ice averaged only 8 cm deep this difference may be related to enhanced sublimation of the snow on the thinner first year ice the salinity profiles of first year ice clearly show the effects of ongoing brine drainage in that profiles from cores drilled later in the experiment are substantially less saline than earlier cores thin section examinations of crystal structure indicate that about 75 of the ice consisted of congelation ice with typically columnar type crystal structure the remaining 25 consisted of granular ice with only a few occurrences of snow ice the granular ice consisted primarily of frazil found in small amounts at the top of floes but mainly observed in multiyear ridges the horizontally oriented crystal c axes showed various degrees of alignment ranging from no alignment to strong alignments in which the alignment direction changed with depth implying a change in floe orientation with respect to the ocean current at the ice water interface during ice growth evidence of crystal retexturing was observed in the upper meter of nearly every multiyear core this retexturing consisting of grain boundary smoothing and nearly complete obliteration of the ice platelet brine layer substructure is attributed to summer warming

a statistical description of the microstructure of young sea ice in order to fully exploit microwave models of sea ice the standard ice characterization must be supplemented by a statistical description of the ice microstructure for the strong fluctuation theory this statistical description takes the form of the mean and variance of the permittivity plus correlation lengths we have computed these statistics for over 50 samples of young ice including both columnar congelation ice and desalinated bubbly ice samples were taken from different vertical depths and horizontal positions within the ice sheet and encompassed a comprehensive range of ice temperatures and brine volumes for each of these samples horizontal thin sections were photographed then digitized and analyzed on a personal computer based image processing system results indicate that correlation lengths correspond to the physical dimensions of the inclusions the brine pocket size typically tenths of a millimeter for saline ice and the air bubble size typically millimeters for desalinated ice for saline ice the shape of the correlation function was elliptical similar to the shape of the brine pockets in one case as the ice warmed from 20 to 1 c and the brine volume increased from 2 to 37 the correlation length increased from 0 14 to 0 22 mm

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

deepwater fold and thrust belt classification tectonics structure and hydrocarbon prospectivity a review abstract deepwater fold and thrust belts dwftbs are classified into near field stress driven type 1 systems confined to the sedimentary section and type 2 systems deformed by either far field stresses alone or mixed near and far field stresses dwftbs can occur at all stages of the wilson cycle up to early stage continent continent collision type 1 systems have either weak shale or salt detachments they occur predominantly on passive margins but can also be found in convergent related areas such as the mediterranean and n borneo examples include the niger and nile deltas the west coast of africa and the gulf of mexico type 2 systems are subdivided on a tectonic setting basis into continent convergence zones and active margin dwftbs continent convergence zones cover dwftbs developed during continent arc or continent continent collision and those in a deepwater intracontinental setting e g w sulawesi makassar straits active margins include accretionary prisms and transform margins the greatest variability in dwftb structural style occurs between salt and shale detachments and not between tectonic settings changes in fold amplitude and wavelength appear to be more related to thickness of the sedimentary section than to dwftb type in comparison with shale salt detachment dwftbs display a lower critical wedge taper more detachment folds long and episodic duration of deformation and more variation in vergence structures unique to salt include canopies and nappes accretionary prisms also standout from other dwftbs due to their relatively long continuous duration rapid offshore propagation of the thrust front and large amount of shortening in terms of petroleum systems many similar issues affect all dwftbs these include the oceanward decrease in heat flow offshore increase in age of mature source rock and causes of trap failure e g leaky oblique and frontal thrust faults breach of top seal by fluid pipes one major difference between type 1 and type 2 systems is reservoir rock high quality continent derived quartz rich sandstones are generally prevalent in type 1 systems more diagenetically reactive minerals derived from igneous and ophiolitic sources are commonly present in type 2 systems or many are simply poor in well developed turbidite sandstone units however some type 2 systems particularly those adjacent to active orogenic belts are partially sourced by high quality continent derived sandstones e g nw borneo s caspian sea columbus basin in some cases very high rates of deposition in accretionary prisms adjacent to orogenic belts coupled with uplift due to collision results in accretionary prism related fold belts that pass laterally from sub aerial to deepwater conditions e g s caspian sea indo burma ranges the six major hydrocarbon producing regions of dwftbs worldwide gulf of mexico niger delta nw borneo brazil west africa s caspian sea stand out as differing from most other dwftbs in certain fundamental ways particularly the very large volume of sediment deposited in the basins and or the great thickness and extent of salt or overpressured shale sdetachments

passive microwave signatures of fractures and ridges in sea ice at 33 6 ghz vertical polarization as observed in aircraft images an aircraft data set of coincident ka band 33 6 ghz vertical polarization passive microwave images and aerial photographs acquired in the chukchi beaufort sea region in march 1983 was analyzed to evaluate radiometric signatures of deformational features that occur in sea ice a total of 115 fractures and 197 pressure ridges were examined with respect to physical appearance relative age snow cover ice type width orientation as observed in photographs and radiometric character brightness temperature radiometric contrast with respect to adjacent ice radiometric profile across the feature as measured from digital passive microwave images of the deformational features that were observed in aerial photographs 82 had radiometric signatures of sufficient contrast to be observed in passive microwave images fractures and ridges have equal chance of detection but fractures cannot be distinguished from pressure ridges on the basis of brightness temperature radiometric contrast or characteristics of radiometric profiles measured across these features however visual analysis of passive microwave images which takes into account contextual information does allow fractures to be distinguished from pressure ridges in many instances radiometric signatures of both fractures and ridges are more likely to be radiometrically warmer as opposed to cooler than adjacent ice which suggests that saline ice is a significant constituent of most deformational features new ridges are more likely to be radiometrically warm than old ridges probably because brine drains from the ridge as it ages which reduces emissivity and snow accumulates in drifts along the ridge trend which enhances scattering however brightness temperatures of snow covered ridges extend across a range that is approximately 15 k cooler and 10 k warmer than the range observed for snow free ridges old features show higher radiometric contrast with respect to adjacent ice than new features which increases their probability of detection

a quantitative description of sea ice inclusions structurally sea ice consists of an ice matrix with inclusions of brine and air a quantitative description of the size of these inclusions is critical for both interpreting and modeling the electromagnetic properties of sea ice photomicrographs of ice thin sections were analyzed using a personal computer based image processing system to determine the number of inclusions the inclusion size distributions and statistics for brine pockets in young ice and first year ice and for air bubbles in a multiyear hummock inclusions ranging in size from thousandths of square millimeters to a few square millimeters were measured in all cases a two parameter lognormal distribution fits the cumulative inclusion size distributions well correlation coefficient greater than 0 99 this includes brine pockets in both granular and columnar ice and a range of brine volumes from 2 to 40 as ice warms and its brine volume increases the size distribution shifts toward larger brine pockets this increase in brine pocket size is particularly pronounced for brine volumes greater than 10 as individual brine pockets coalesce air bubbles are much larger than brine pockets with mean major axis lengths of the order of millimeters for air bubbles and tenths of a millimeter for brine pockets observations of inclusion shape factors indicate that in general brine pockets are more elongated than air bubbles

eigenray finding and time series simulation in a layered bottom ocean a ray theory approach for simulating the propagation of broadband signals interacting with a layered ocean bottom is presented the range invariant environment consists of the ocean and an arbitrary number of bottom layers each bottom layer has profiles of compressional and shear wave velocity attenuation and density eigenrays including those with multiple interactions and refractions in the ocean and bottom layering are found using a thorough and efficient algorithm based on an analysis of the sound velocity profile and the dependence of ray path geometry on the snell invariant the time series at a receiver due to an arbitrary source waveform is obtained by constructing a frequency domain transfer function from the eigenray characteristics several example applications demonstrate the potential use of this approach and show that reflection from relatively simple layering can severely distort a received time series

non coulomb wedges wrong way thrusting and natural hazards in cascadia landward vergence in accretionary wedges is an uncommon phenomenon not readily explained by classical mohr coulomb critical wedge theory predominantly landward vergent thrust faults are observed along the cascadia convergent margin from 45 n to 48 n we present depth migrated multichannel seismic images of the internal structure of the accretionary wedge offshore washington collected during the orwell project in 1996 these reveal a high p wave velocity 4 km s basal layer that thickens landward and serves as a decollement for a series of overlying landward vergent thrust faults analog modeling using a ductile basal layer consisting of silicone putty produces an array of trenchward propagating landward vergent thrusts and offers a plausible mechanical model for the evolution of these structures the rheological properties of a basal calcareous mudstone layer offshore cascadia are discussed in relation to the mechanics of landward vergence and to rapid loading due to the prograding nitinat and astoria deep sea fans a viscoelastic layer beneath the accretionary wedge is considered to be capable of rupturing during great interplate earthquakes and thus represents an increased risk for both the maximum size of such an event and for the generation of tsunamis

links between sediment consolidation and cascadia megathrust slip behaviour at sediment rich subduction zones megathrust slip behaviour and forearc deformation are tightly linked to the physical properties and in situ stresses within underthrust and accreted sediments yet the role of sediment consolidation at the onset of subduction in controlling the downdip evolution and along strike variation in megathrust fault properties and accretionary wedge structure is poorly known here we use controlled source seismic data combined with ocean drilling data to constrain the sediment consolidation and in situ stress state near the deformation front of the cascadia subduction zone offshore washington where the megathrust is inferred to be strongly locked we find over consolidated sediments near the deformation front that are incorporated into a strong outer wedge with little sediment subducted these conditions are favourable for strain accumulation on the megathrust and potential earthquake rupture close to the trench in contrast offshore central oregon a thick under consolidated sediment sequence is subducting and is probably associated with elevated pore fluid pressures on the megathrust in a region where reduced locking is inferred our results suggest that the consolidation state of the sediments near the deformation front is a key factor contributing to megathrust slip behaviour and its along strike variation and it may also have a significant role in the deformation style of the accretionary wedge consolidated sediments in the cascadia subduction zone may create conditions favourable for megathrust earthquake ruptures over long distances and close to the trench according to analyses of seismic velocity of sediments from the region less consolidated sediments instead may promote aseismic slip of the plate boundary