hydrogeochemical characterization of oilfield waters from southeast maracaibo basin venezuela diagenetic effects on chemical and isotopic composition free water and water in emulsion with oil from hydrocarbon wells onshore offshore lake maracaibo were extracted and analyzed the use of classical and new chemical diagrams evidenced that na hco3 and na cl are the main chemical facies whereas na so4 facies was rare and revealed only in faulted areas in which shallow groundwater was involved in deep circulation cretaceous ca cl waters were not revealed but their imprint on some samples was traced and evidenced by langelier ludwig brine differentiation and caexcess vs nadeficit diagrams these square plots allowing a discrimination between the water contributions from the different source rocks should be more exploited as hydrogeochemical tools in hydrocarbon exploration original data on monocarboxylic anions showed acetate concentration higher than ten times that of formate at sampling conditions but speciation under deep conditions indicated a reversed activity dominance calculation of saturation indexes and kinetic modeling showed an active precipitation of chalcedony kaolinite and clays especially where the temperature was lower t 100 c formation waters and lake water showed quite similar chloride concentration and hydrogen isotope composition however thermodynamic calculations at the oilfield p t conditions revealed chlorite and illite produced during previous diagenetic stages of misoa sandstones recrystallization to smectite and vermiculite in present day stage the diagenetic water produced in these reactions could have enriched the 18o isotopic composition of approximately 2 this isotope diagenetic effect was more evident in na hco3 waters which also showed a decrease in chloride at constant boron concentration as a consequence of clay dewatering in this regard a new boron geothermometer useful for formation waters is also proposed t c 5 1364 ln 1 b mg 1 5 728 0 180 0 164 0 012

sensitivity of simulated arctic sea ice to realistic ice thickness distributions and snow parameterizations 1 sea ice and snow on sea ice to a large extent determine the surface heat budget in the arctic ocean in spite of the advances in modeling sea ice thermodynamics a good number of models still rely on simple parameterizations of the thermodynamics of ice and snow based on simulations with an arctic sea ice model coupled to an ocean general circulation model we analyzed the impact of changing two sea ice parameterizations 1 the prescribed ice thickness distribution itd for surface heat budget calculations and 2 the description of the snow layer for the former we prescribed a realistic itd derived from airborne electromagnetic induction sounding measurements for the latter two different types of parameterizations were tested 1 snow thickness independent of the sea ice thickness below and 2 a distribution proportional to the prescribed itd our results show that changing the itd from seven uniform categories to fifteen nonuniform categories derived from field measurements and distributing the snow layer according to the itd leads to an increase in average arctic wide ice thickness by 0 56 m and an increase by 1 m in the canadian arctic archipelago and canadian basin this increase is found to be a direct consequence of 524 km3 extra thermodynamic growth during the months of ice formation january february and march our results emphasize that these parameterizations are a key factor in sea ice modeling to improve the representation of the sea ice energy balance

the last glaciation and deglaciation of the northeast greenland continental shelf revealed by hydro acoustic data about 16 of the greenland ice sheet drains in the area of the northeast greenland shelf between 76 n and 80 5 n via marine terminating glaciers most of it is via the northeast greenland ice stream the largest ice stream of greenland during ice ages the ice sheet extended onto the continental shelf and modern day cross shelf troughs were filled by ice streams in this study high resolution hydro acoustic data acquired during three decades of research were jointly investigated to reveal the past glacial conditions our data shows that westwind trough and norske trough were filled by fast flowing ice streams that extended to the shelf edge during the last glacial maximum in between the cross shelf troughs ice domes resided on shallow banks that may have contributed about a decimetre to global sea level most probably these ice domes initiated fast ice flow through sinks in the inter trough area in westwind trough ice sheet retreat to the inner shelf after the last glacial maximum was intermittent in contrast in norske trough the ice sheet retreat appears relatively rapid with no evidences for phases of grounding line stabilization probably during the younger dryas the ice sheet readvanced to a mid shelf position in both troughs documented by grounding zone wedges during this time a thick ice shelf was present in norske trough releasing tabular icebergs ice sheet retreat from the mid shelf to the coastline during holocene deglaciation was rapid

the response of antarctic icebergs to ocean waves the heave tilt and strain responses of three antarctic tabular icebergs to ocean waves were measured during a 1980 1981 cruise of hms endurance to the south atlantic the three icebergs located near the south sandwich and south orkney islands were instrumented with accelerometers tiltmeters and wire strainmeters while a waverider buoy was used to record the ocean wave field the thickness of the icebergs was surveyed by a helicopter borne radio echo sounder the heave response occurred mainly at the swell period but with outbreaks of bobbing which lasted for a few cycles at a resonant period about 40 s which agreed well with the predictions of a numerical finite element model the roll response occurred mainly at a long resonant period 40 50 s which again agreed well with the model but there was also a significant response at ocean wave periods 5 20 s which exceeded predictions the strain response had a component at very long periods which is unexplained by theory while the surface strain at ocean wave periods agreed with the simple analytical model of goodman et al 1980 using this model it is possible to predict a wave height and period that will cause breakup of the icebergs and we conclude that swell induced breakup is likely to occur during major storms in the open southern ocean

analyzing lead information from sar images leads are relatively linear features in the sea ice cover which are composed of open water or new thin ice because of their composition leads impact the ocean air heat exchange automated analysis of leads from sea ice imagery may provide a means of gathering important information about the sea ice cover and its climatic influence this paper describes 1 a method for extracting and analyzing leads from ers 1 synthetic aperture radar sar images classified by ice type and 2 the results of using this method on images of the beaufort sea the methodology consists of identifying potential lead features in the image and measuring their characteristics both before and after using a thinning or skeletonization technique on the features the measurements obtained using this method include lead area average width number of leads in an area amount of branching and linearity of the lead these measurements were analyzed with respect to the time of year and the latitude of the images results indicate that the measurements produced by the methodology are consistent with lead measurement distributions that others have found the results of the study suggest that the methodology is appropriate to study lead characteristics on a large scale

sea ice ridging in the ross sea antarctica as compared with sites in the arctic at the end of the 1980 austral winter surface roughness measurements were made by laser profilometer during a series of flights over the ross sea pack ice the total track length was 2696 km and 4365 ridges were counted the frequency distribution of individual ridge heights was found to be well described by a negative exponential distribution no clear cut regional variation was noted in ridge heights the distribution of ridge frequencies per kilometer showed a strong positive skew with a modal value of 1 88 the most frequent ridging occurred off the east coast of victoria land comparisons with similar data sets from the arctic indicate that large ridges are significantly more likely in the arctic ocean than in the ross sea utilizing a reasonable model for the geometry of ridges estimates are made of the average thickness of a hypothetical continuous layer composed only of the deformed ice from ridges the noncoastal ross sea value of 0 09 m is less than half of the lowest comparable value from the arctic 0 20 m central beaufort sea where values in excess of 1 0 m have been observed in the shear zones north of greenland

stress induced smectite dehydration ramifications for patterns of freshening and fluid expulsion in the n barbados accretionary wedge abstract presented is new experimental evidence that smectites can partially dehydrate from 18 5 a to 15 4 a hydrates when they are subjected to effective mineral framework stresses above 1 3 0 3 mpa we show here that this process can substantially freshen saline pore fluids and impact our understanding of the hydrogeologic processes in convergent margins where smectites are abundant the general anomalous freshening of pore fluids in the n barbados accretionary wedge was previously proposed to relate to the widespread lateral expulsion of fluids derived from mineral dehydration reactions at great depth in contrast our analysis suggests that a significant part of the widespread anomalous freshening relates to stress induced smectite dehydration that occurred during the ocean drilling program odp pore water extraction process clear evidence for long distance lateral flow appears to be limited to localized chloride and isotopic anomalies developed in a 20 m thick locally mineralized region at the top of decollement horizon at site 948 our reinterpretation is consistent with the fluid flow in the decollement zone being 1 highly transient on time scales of several hundreds of years and 2 channeled laterally into heterogeneous finger like flow paths that are apparently not intersected and or sampled by drilling in most regions at the toe of the wedge the incipient stress induced dehydration of smectite may also be buffering in situ fluid pressures in the wedge maintaining the effective stresses at 1 3 mpa

the sea ice thickness distribution in the northwestern weddell sea we present new data on distribution of snow and sea ice thicknesses in the northwestern weddell sea the data were obtained through direct measurements along 19 profiles each approximately 100 m long on 17 different floes located between 54 46 w and 59 64 s the overall probability density functions pdfs for ice thicknesses reflect the complex mixture of first second and multi year ice to be expected in the outflowing branch of the weddell gyre further differentiation of the data reveals four distinct thickness classes which reflect differences in the formation and subsequent histories of the ice encountered these classes i iv represent strongly deformed first year ice less deformed first and second year ice and deformed second or multi year ice respectively each of the classes is characterized by a specific set of quantities related to ice texture and surface snow characteristics and by distinct pdfs for snow and ice thicknesses in addition geometric surface and bottom roughness characteristics differ significantly for each of the floe classes

detailed seismic velocity of the incoming subducting sediments in the 2004 great sumatra earthquake rupture zone from full waveform inversion of long offset seismic data

estimation of sea ice thickness distributions through the combination of snow depth and satellite laser altimetry data 1 combinations of sea ice freeboard and snow depth measurements from satellite data have the potential to provide a means to derive global sea ice thickness values however large differences in spatial coverage and resolution between the measurements lead to uncertainties when combining the data high resolution airborne laser altimeter retrievals of snow ice freeboard and passive microwave retrievals of snow depth taken in march 2006 provide insight into the spatial variability of these quantities as well as optimal methods for combining high resolution satellite altimeter measurements with low resolution snow depth data the aircraft measurements show a relationship between freeboard and snow depth for thin ice allowing the development of a method for estimating sea ice thickness from satellite laser altimetry data at their full spatial resolution this method is used to estimate snow and ice thicknesses for the arctic basin through the combination of freeboard data from icesat snow depth data over first year ice from amsr e and snow depth over multiyear ice from climatological data due to the nonlinear dependence of heat flux on ice thickness the impact on heat flux calculations when maintaining the full resolution of the icesat data for ice thickness estimates is explored for typical winter conditions calculations of the basin wide mean heat flux and ice growth rate using snow and ice thickness values at the 70 m spatial resolution of icesat are found to be approximately one third higher than those calculated from 25 km mean ice thickness values

transoceanic wave propagation links iceberg calving margins of antarctica with storms in tropics and northern hemisphere 1 we deployed seismometers on the ross ice shelf and on various icebergs adrift in the ross sea including b15a a large 100 km by 30 km fragment of b15 which calved from the ross ice shelf in march 2000 the data reveal that the dominant energy of these floating ice masses is in the 0 01 to 0 1 hz band and is associated with sea swell generated in the tropical and extra tropical pacific ocean in one example a strong storm in the gulf of alaska on 21 october 2005 approximately 13 500 km from the ross sea generated swell that arrived at b15a immediately prior to and during its break up off cape adare on 27 october 2005 if sea swell influences iceberg calving and break up a teleconnection exists between the antarctic ice sheet mass balance and weather systems worldwide

seismic observations of sea swell on the floating ross ice shelf antarctica 1 a seismometer operating on the floating ross ice shelf near its seaward ice front nascent iceberg for 340 days out of 730 days during the 2004 2005 and 2006 antarctic field seasons recorded the arrival of 93 distantly sourced ocean swell events displaying frequency dispersion characteristic of surface gravity waves propagating on deep water comparison of swell event dispersion with the noaa wave watch iii nww3 ocean wave model analysis reveals that 83 of these events were linked to specific storms located in the pacific southern and indian oceans nearly all major storms in the nww3 analysis of the pacific ocean were linked to signals observed at the nascent site during the period of seismometer operation swell induced motion of the ross ice shelf is found to increase by several orders of magnitude over the time period that sea ice surrounding antarctica decreases from its maximum extent october to its minimum extent february the amplitude of vertical vibration of the ice shelf in the frequency band between 0 025 and 0 14 hz varies between tens of micrometers to millimeters as sea ice decays to its minimum seasonal extent this suggests that climate influence on sea ice extent may indirectly modulate swell energy incident on the calving margins of the antarctic ice sheet the largest swell signals observed on the ross ice shelf come from storms in the tropical pacific and gulf of alaska these remote events emphasize how the iceberg calving margin of antarctica is connected to environmental conditions well beyond antarctica

relationship between sea ice freeboard and draft in the arctic basin and implications for ice thickness monitoring we have confirmed our earlier finding that the probability density function pdf of ice freeboard in the arctic ocean can be converted to a pdf of ice draft by applying a simple coordinate transformation based on the measured mean draft and mean elevation this applies in each of six 50 km sections north of greenland of joint airborne laser and submarine sonar profile obtained along nearly coincident tracks from the arctic basin north of greenland and tested for this study detailed differences in the shape of the pdf can be explained on the basis of snow load and can in principle be compensated by the use of a more sophisticated freeboard dependent transformation the measured density ratio r actually mean draft mean elevation ratio for each section was found to be consistent over all sections tested despite differences in the ice regime indicating that a single value of r might be used for measurements done in this season of the year the mean value r from all six sections is 7 89 on the assumption that all six values are drawn from the same population the standard deviation is 0 55 for a single 50 km section and thus 0 22 for 300 km of track in attempting to infer ice draft from laser measured freeboard we would therefore expect an accuracy of about 28 cm in 50 km of track if mean draft is about 4 m and about 11 cm in 300 km of track these accuracies are compatible with the resolution of predictions from numerical models a simple model for the variability of r with season and with mean ice thickness gives results in reasonable agreement with observations they show that although there is a large seasonal variability due to snow load there is a stable period from november to april when the variability is chiefly dependent on the mean ice thickness alone thus in principle r can be mapped over the arctic ocean as a basis for interpreting survey data better field data are needed on the seasonal and spatial variability of three key quantities area averaged snow load mean density of first year and multiyear ice including the effect of ridging with these two ice regimes and density of near surface water

hydrothermal alteration of hemi pelagic sediments experimental evaluation of geochemical processes in shallow subduction zones abstract laboratory hydrothermal experiments provide unique information regarding the fate of volatile and or incompatibles e g b li and as during oceanic crust subduction examination of chemical redistribution between the subducted slab mantle wedge arc volcanics and overlying ocean water during subduction is critical to gain further insight into arc volcanism and chemical oceanic budgets for instance efficient mobilization of b at shallow depths may be a key aspect of its oceanic budget and can help to explain the systematics of b 11b and b 10be in arc lavas fluid rock interactions at elevated temperatures and pressures in accretionary prisms were studied using a rocking autoclave hydrothermal apparatus to monitor sediment porewater interaction over the range of 25 to 350 c at 800 bars clay rich hemi pelagic sediments from the decollement zone of ocean drilling program site 808 nankai trough were reacted with nacl cacl2 solutions at water rock ratios of 3 5 to 1 5 w w to mimic alteration processes in the shallow subduction zone fluids were extracted at 25 50 c intervals and were analyzed for major and trace chemical constituents the fluid chemistry changed significantly during the course of these experiments but there was generally only minor modification of the solid phase only b li as br and pb are significantly depleted during the heating cycle dissolved na mg and so4 decreased sharply and nh4 sio2 k b and li increased at t 300 c calcium drops gradually at low temperatures but concentrations rise sharply at t 300 c decomposition of organic matter so42 depletion and mg fixation dominate at low temperatures however albitization of calcic plagioclase leads to marked na depletions and ca enrichments at t 300 c dissolved sio2 remained below saturation with respect to quartz and amorphous silica throughout the entire experiment b and li mobilization with large isotopic fractionations occurred at low temperature exchangeable b 11b 15 is completely leached before reaching 150 c substantial o2 exchange between fluids and the solid phase occurred at t 200 c in the spiked experiment where 18o varies more than 100 in the fluids during retrograde cooling dissolved mg so4 ca si k and sr are released as a result of carbonate or anhydrite dissolution and marked b re adsorption occurred at temperatures below 60 c

the origin and migration of mud volcano fluids in taiwan evidence from hydrogen oxygen and strontium isotopic compositions abstract mud volcanoes are important gateways for deep fluids to migrate upward and provide windows for studying fluid sediment interaction at depth fluids emitted from 40 terrestrial mud volcanoes were collected in southern and eastern taiwan to study their chemical compositions including h o and sr isotopes 87sr 86sr and 88 86sr relative to seawater the mud volcano fluids are depleted in cl mg so42 and d and are elevated in b ba li and 18o possibly due to water rock interaction and clay dehydration mainly smectite to illite transformation in the source region the distribution of sr in mud volcano fluids shows patterns associated with their localities and geological settings most fluids have higher 87sr 86s than seawater indicating water rock interaction at depth the low na 87sr 86s and high ca fluids emitted from eastern taiwan imply intense interaction with igneous basement most fluids have higher sr cl and lower 88sr than seawater except mud volcanoes in the northern chu kou fault which emit low sr cl and extremely high 88sr up to 0 82 fluids we performed laboratory carbonate precipitation experiments that indicate that these high sr isotope ratios are caused by co precipitation of carbonates from high alkalinity fluids mud volcano fluids in taiwan originate at depth and their chemical compositions are controlled by the host rock degrees of water rock interaction and clay dehydration but also are masked by retrograde progresses such as carbonate precipitation during migration our results show that an approach combining water isotopes d and 18o and strontium isotopes 87sr 86sr and 88 86sr provides a robust tool for tracing fluid sources and migration pathways in accretionary prisms

smectite diagenesis pore water freshening and fluid flow at the toe of the nankai wedge the presence of low chloride fluids in the lowermost sediments drilled at ocean drilling program site 808 at the nankai accretionary wedge has been considered as prime evidence for long distance lateral fluid flow from depth here we re evaluate the potential role of in situ reaction of smectite s to illite i in the genesis of this low chloride anomaly this reaction is known to be occurring at site 808 with both the s content and s to i ratio in the mixed layer clays decreasing substantially with depth we show that the bulk of the chloride anomaly can generate by in situ clay dehydration particularly if pre reaction smectite abundances ai approach 10 15 of the bulk sediment the ai values however are not well constrained at ai values 10 15 an additional source of low cl fluid centered close to the decollement could be required thus there remains the important possibility that the observed low cl anomaly is a compound effect of both lateral flow and in situ smectite dehydration

the role of mud volcanism and deep seated dewatering processes in the nankai trough accretionary prism and kumano basin japan circulation of water at moderate depths in subduction zones is dominantly driven by clay mineral dehydration over distinct pressure and temperature gradients the signature of these dehydration reactions is found in mud volcano pore waters however it is largely unknown how much of the deep seated fluids are emitted at mud volcanoes to unravel this relation for the region off the kii peninsula japan we calculated the water volume that is subducted in the nankai trough using input data from iodp holes c0011 and c0012 and the correspondent water volume released from the subducted plate under the kumano basin in an area where 13 mud volcanoes are located according to our model water released at depth in the mud volcano area is derived almost entirely from basaltic saponite and sedimentary smectite transformation up to 96 nonetheless the mud volcanoes themselves expel 1 of the total volume to test the contribution of the accreted strata and the kumano basin fill to the water budget we run a second model water loss due to compaction of sediments and smectite illite transition below the basin floor have been calculated the results were compared with salinity measurements on background cores scattered in the study area to extrapolate the volume of water loss at depth the comparison of the two methods yielded similar results and led us to conclude that the bulk part of the deep seated fluid re enters the hydrosphere via the basin floor a mechanism rarely taken into account in fluid budgets in the literature

sea ice thickness distribution in fram strait hm nuclear submarine sovereign has obtained the first synoptic measurements of the ice thickness distribution in fram strait the main outflow from the arctic ocean the ice nearest the ice edge is of quite different character from ice in the interior of the strait with a greater proportion of first year ice and less pressure ridging an estimate of the ice flux through fram strait can be made from the distribution of mean ice drafts

winter observations of iceberg frequencies and sizes in the south atlantic ocean the numbers and apparent sizes of icebergs in the south atlantic ocean in midwinter were measured by radar and visually from f s polarstern during the 1986 winter weddell sea project cruise results show that in a heavy sea sea state 7 8 icebergs have to be at least 115 m in diameter to be detected at all and that detectability falls off severely for all bergs at ranges exceeding 8 n mi 15 km that most bergs had diameters of less than 1 km with a preferred size of 400 500 m and that a high density of icebergs in the latitude band 53 56 s at longitude 19 30 w contrasted with a virtual absence of bergs in the same latitude band at longitude 1 9 e the latter effect is ascribed to melt and wave induced deterioration causing the disappearance of this iceberg population between the two sets of longitudes

integrating multibeam sonar and underwater video data to map benthic habitats in an east antarctic nearshore environment abstract an integrated analysis of biological and geoscientific data collected from the nearshore marine environment of the vestfold hills was used to identify benthic habitats and associated communities and examine relationships between benthic community composition and environmental characteristics a 48 km2 area was surveyed using a multibeam echosounder system mbes to produce high resolution bathymetry and backscatter intensity maps of the seabed epibenthic community data and in situ observations of substrate composition and seafloor bedforms and features were obtained from towed underwater video a comparison of top down and bottom up approaches to defining benthic habitats was used to improve understanding of the applicability of mapping methodologies on a broad scale both approaches produced habitat classes distinguished largely by geomorphic features with substrate and depth identified as the main controls of benthic community composition however the relationship between benthic community composition and environmental characteristics is complex with many variables contributing to differences in community composition the top down approach was based on geomorphic units defined using abiotic characteristics and the assemblages identified within the geomorphic were very broad with only weak distinction between assemblages conversely the bottom up approach generated additional habitat classes identified clear defining taxa for each class greater distinction between the benthic communities and allowed identification of additional environmental factors i e sea ice cover that influence benthic community distribution that are not discernible from geomorphic information alone the habitat types identified and mapped using the bottom up approach include shallow boulder fields and exposed bedrock which are dominated by dense macroalgae communities and steep slopes muddy basins and sandy plains which are dominated by invertebrate communities the results indicate that a bottom up approach is preferable for benthic habitat mapping however where detailed information is not available geomorphic information provides a reasonable indication of the distribution of benthic habitats and communities this study highlights the utility of multibeam sonar for interpretation of seafloor morphology and substrate and the multibeam data provide a physical framework for understanding benthic habitats and the distribution of benthic communities this research provides the scientific context and spatial framework for managing the vestfold hills nearshore marine environment and provides a baseline for assessing environmental change

calving and ice shelf break up processes investigated by proxy antarctic tabular iceberg evolution during northward drift using a combination of satellite sensors field measurements and satellite uplinked in situ observing stations we examine the evolution of several large icebergs drifting east of the antarctic peninsula towards south georgia island three styles of calving are observed during drift rift calvings edge wasting and rapid disintegration rift calvings exploit large pre existing fractures generated in the shelf environment and can occur at any stage of drift edge wasting is calving of the iceberg perimeter by numerous small edge parallel sliver shaped icebergs preserving the general shape of the main iceberg as it shrinks this process is observed only in areas north of the sea ice edge rapid disintegration where numerous small calvings occur in rapid succession is consistently associated with indications of surface melt saturation surface lakes firn pit ponding freeboard measurements by icesat indicate substantial increases in ice thinning rates north of the sea ice edge from 30 m a 1 but surface densification is shown to be an important correction 2 m freeboard loss before the firn saturates edge wasting of icebergs in warm surface water sea ice free 1 8 c implies a mechanism based on waterline erosion rapid disintegration larsen b style break up is likely due to the effects of surface or saturated firn water acting on pre existing crevasses or on wave or tidally induced fractures changes in microwave backscatter of iceberg firn as icebergs drift into warmer climate and experience increased surface melt suggest a means of predicting when floating ice plates are evolving towards disintegration

the response of ice floes to ocean waves a precise linear mathematical theory is reported to model the response of a solitary ice floe in ocean waves allowing the floe to bend with the passing wave both infinite and finite water depths are considered and the model is also extended to include a pair of separated floes of different length the case of n floes then being a natural and straightforward development for a single ice floe perfect transmission is achieved whenever the wavelength beneath the ice couples perfectly to the length of the ice floe then the strains induced in the bending ice floe reach a maximum and because multiple cycle tuning can occur in floes which are long compared to the wavelength strain response amplitude operators raos are complicated by considering the case of infinite stiffness heave and roll raos are also found for typical ocean wave periods and these agree well with two dimensional rigid body models finally ice floes of different diameters but constant 1 m thickness are subjected to spectral forcing and the strain spectral density for each is found spectral density envelopes increase gradually with floe diameter achieving a maximum value for a floe of about 102m thereafter strains never decrease below those for the 80 m curve owing to multiple cycle tuning this may explain the presence of zones within an ice field where floe size never exceeds some prescribed value results obtained from the complete theory for two adjacent floes do not differ significantly from those found by applying the single floe model serially except when the separation is very small

ice thickness in the arctic ocean the statistical reliability of experimental data the statistical reliability of ice thickness distributions derived from submarine sonar data sets of finite length is examined focusing on the standard error eh l in the mean ice draft h derived from a record of length l km this is important in assessing the significance or otherwise of quoted temporal or spatial differences in mean ice draft estimates for eh 50 are derived from four different submarine surveys each of which involved repeated sampling of apparently homogeneous ice fields values ranged from 7 18 to 15 29 of the mean for climate related comparisons of data sets from different years in the same location a value of 12 75 is recommended derived from data gathered at the north pole this value is used to reassess the significance of published data on ice draft variability quoted variability at the north pole over the 1977 1990 period is found to be not statistically significant but a difference in area averaged ice draft over the eurasian basin between 1976 and 1987 remains highly significant using hitherto unreported 1987 data from the north pole area the statistical variability of other parameters of the ice cover is examined the frequency of lead occurrence the width of leads the fractional cover of smooth ice and the frequency of keel occurrence all show standard errors of 22 24 in their mean values while mean keel draft has a 4 error all over a 50 km track length finally unreported 1987 data for an area extending from the pole to 72 n along the prime meridian and the east greenland shelf break are examined in 1 bins using eh l to assess the significance of variations in the mean a statistically significant decline in mean ice draft is observed starting at 86 n and continuing to 72 n a linear regression gives a thinning rate of 0 22 m deg the decline within the arctic basin itself is tentatively ascribed to a mixture of under ice melt and mixing of ice types since data on young ice occurrence show that divergence did not occur north of fram strait

development of seasonal pack ice in the beaufort sea during the winter of 1991 1992 a view from below subsea sonars moored in the beaufort sea acquired a spatial section of draft across 941 km of sea ice during the winter of 1991 1992 these observations document the development of seasonal sea ice from an open sea surface in october to an average accumulation exceeding 2 5 m draft by early april initially level ice occupied 85 of the profile but continued ridging reduced this fraction to 50 in late winter three modes of level ice were tracked that of seasonal ice whose growth was initiated at freeze up and two others created during openings of the ice field in january and in march the growth of these modes can be closely matched by calculations based on a slab model of ice formation forced using surface meteorological data initially ridge keels were small and widely spaced by midwinter an exponential dependence of keel frequency on draft was obvious e folding scale 2 16 m and the frequency and mean draft of keels had stabilized the maximum keel draft was a modest 17 4 m the low incidence of deep keels at all times is a statistically significant departure from the exponential dependence valid at lesser drafts the truncation point of the exponential relation is related to the draft of the thinnest level ice present in late winter the formation of deeper keels from thick first year ice was apparently precluded by the presence of younger thinner ice which limited the force available for ridge building through calculation of the seaward transport of ice over the sonars the total production of ice in the coastal flaw lead during 1991 1992 was determined to be about 60 of earlier indirect estimates in general the observations revealed winter ice conditions significantly less severe than those found on the periphery of the polar pack only a few tens of kilometers to the north but more so than conditions in a marginal first year ice zone at the same latitude in davis strait

quantitative analysis of sea ice draft 2 application of stochastic modeling to intersecting topographic profiles a recent upward looking sonar profile survey of a 10 km by 10 km area beneath the arctic ice serves as a basis for an exploratory analysis of the quantitative characteristics of sea ice draft in a companion paper goff this issue a method was developed for estimating profile statistical parameters and their uncertainties these include mean draft rms variation characteristic length fractal dimension and normalized skewness here this methodology is applied to the intersecting profile data set yielding 160 separate estimates for each parameter although not completely two dimensional the data nevertheless allow an opportunity to investigate some aspects of topographic anisotropy our most significant observations are 1 a strong positive correlation exists between fractal dimension and characteristic length while normalized skewness is weakly negatively correlated with both parameters 2 high and low rms mean ice are morphologically distinct in the rms versus characteristic length and fractal dimension versus characteristic length parameter spaces 3 the overall correlation between rms and characteristic length can be explained entirely by the difference between high and low rms mean type morphology and 4 anisotropy appears to exist on a local scale but is highly variable over the entire survey these observations could be explained by a systematic variation in morphology with age perhaps including a progressive superposition of deformation events and or by regionally variable anisotropy

influence of kinetics on the smectite to illite transition in the barbados accretionary prism low chloride pore fluids observed along faults in clay rich accretionary complexes are commonly attributed to the release of interlayer water during the smectite to illite transformation however to date there has been no thorough analysis of the location and quantity of fluids that may be generated by this mechanism to address this problem a temperature and time dependent rate expression describing the dehydration reaction was coupled to a kinematic model of the northern barbados accretionary complex temperatures in the complex were estimated by modeling heat flow through the prism sediments as they thicken arcward the sediments temperature time histories were computed using a model for the velocities of sediment motion through the complex in this model the prism sediments follow uniformly diverging paths from the toe while the underthrust sediments undergo uniaxial strain the model predictions are validated against clay mineralogy data from barbados island mudstones our results show that the location of the peak dehydration rate is 20 km farther arcward in the underthrust sediments than in the prism complex the fresh water produced by the reaction results in pore waters that are 10 30 fresher at a distance of 50 70 km from the prism toe this constraint indicates a probable fluid migration path of more than 50 km from the reaction zone to the sites where freshened pore fluids have been observed the peak rate of fluid production when expressed as the volume of fluid per volume of sediment per second is 2 l0 15

keel depths of modern antarctic icebergs and implications for sea floor scouring in the geological record abstract icebergs affect the geological record through the scouring or ploughing action of their keels reworking sediments where they contact the sea floor satellite radar altimeter measurements of the surface elevation of the marine margins of the antarctic ice sheet are inverted to produce ice thickness values these data are assumed to represent the keel depths of newly calved icebergs there are three peaks in the frequency distribution of antarctic iceberg keel depths a about 140 200 m in thickness associated with smaller ice shelves fringing antarctica e g wilkins george vi and brunt ice shelves b about 250 300 m from large ice shelves e g ross ronne amery and c approximately 500 600 m from fast flowing ice sheet outlet glaciers e g pine island and dibble glaciers together with the filchner ice shelf controls on iceberg keel depth are ice thickness at the grounding line creep thinning and the rate of melting freezing at the floating ice shelf base with distance to the calving margin the distribution of sea floor scours produced by iceberg grounding is dependent on the changing form and flow of the glaciers and ice sheets from which icebergs are derived and on berg drift tracks and melt rates sea floor evidence for icebergs with particularly deep keels has sometimes been interpreted to indicate the presence of extensive former ice shelves however the largest modern antarctic ice shelves do not produce large numbers of icebergs thicker than about 350 m implying that sea floor scours found in deeper water are unlikely to be an indicator of extensive past ice shelf development iceberg scours found at water depths in excess of about 500 m in the geological record are instead probably indicative of either a the former presence of fast flowing ice sheet outlet glaciers b ice shelves fed from major interior basins where lateral spreading is constrained topographically or c a pulse of large icebergs released during major deglaciation or ice sheet collapse

an experimental study of alteration of oceanic crust and terrigenous sediments at moderate temperatures 51 to 350 c insights as to chemical processes in near shore ridge flank hydrothermal systems studies of hydrothermal circulation within partly buried basement on the eastern flank of the juan de fuca ridge jfr have shown that ridge flank geochemical fluxes are potentially important for the global budgets of some elements there are major uncertainties in these flux calculations however because the composition of these basement fluids is strongly dependent on temperature and because they may be modified by interaction with the overlying terrigenous sediments either by diffusive exchange with basement or during upwelling to the seafloor to better understand the nature and temperature control of basalt fluid and sediment fluid reactions at the jfr flank we have conducted laboratory experiments between 51 and 350 c and at 400 bars pressure k rb and si are leached from basalt between 150 and 351 c and sr and u are taken up the direction of exchange of li and ca with basalt varies with temperature li and sr are removed from fluid at 150 c but isotope studies show that there is simultaneous release of both elements from basalt indicating that uptake is controlled by the formation of secondary minerals moreover our experiments confirm that sr isotope exchange with oceanic crust occurs at moderate temperature and is not confined to high temperature axial hydrothermal systems our data and field data from the jdr flank indicate that uptake of u into basalt at moderate temperature could remove between 9 9 and 15 106 mol u yr 1 from the oceans this is higher than a recent estimate based on measurements of u in altered ocean crust 5 7 3 3 106 mol yr 1 which concords with arguments that the element heat ratios of jdr flank fluids are too large to be representative of average global flank fluids k ca sr ba li si and b are leached from terrigenous sediments between 51 and 350 c and u is taken up cs and rb are removed from the fluid below 100 c and leached from the sediment at higher temperature sr isotope data show that sr is preferentially mobilised from volcanic components within terrigenous sediments which may lead to an overestimation of the ridge flank sr isotope flux at the jdr if there is exchange of sediment pore fluids with basement

boron isotopic composition of mud volcano fluids implications for fluid migration in shallow subduction zones abstract mud volcanoes are important conduits for deep fluids to migrate upward providing an important window to study fluid sediment interactions at depth in accretionary prisms fluids emitting from mud volcanoes in southern and eastern taiwan were analyzed for dissolved chemical composition and b isotopes to delineate the sources and chemical alteration occurring during fluid migration concentrations of dissolved major elements cl na k ca mg and so4 in most of the mud volcano fluids were lower than seawater concentrations except for the high ca samples in eastern taiwan which were probably affected by fluids igneous rock interactions the high concentrations of b ba and li in the mud volcano fluids are consistent with a scenario that involves intense sediment alteration and clay dehydration at depth the reaction temperatures estimated using chemical thermometers fall within the range of 70 170 c with some variation by location in nearby mud volcano sites the concentration of dissolved major elements varied little but the b stable isotope compositions varied by as much as 20 supporting the argument that dissolved b concentrations were over printed with effects of sediment adsorption this explains the occurrence of b enriched and heavy 11b fluids at moderate depths in subduction zones it is probable that the fluids in mud volcanoes in taiwan originated from 2 to 5 km depth and are influenced by processes involving tectonic shortening sediment alteration and clay dehydration and subsequent retrograde adsorption during fluid migration

sea ice topography of the arctic ocean in the region 70 degrees w to 25 degrees e in october 1976 a cooperative experiment was made to survey the sea ice topography in the european sector of the arctic ocean h m submarine sovereign acquired 4000 km of ice draft data by using an upward looking sonar while a canadian forces aircraft flew along the submarine s track and acquired 2200 km of ice elevation data by using a laser profilometer the two types of profile were processed in corresponding 100 km section lengths and the following statistical analyses and comparisons were made i probability density functions o f ice draft and elevation each distribution shows a peak for young ice and for undeformed multi year ice at large ice thicknesses the distributions take the analytical form of a negative exponential the mean drafts enable two distinct geographical ice regimes to be identified there is an offshore zone of very heavy pressure ridging extending up to 400 km from the coasts of ellesmere island and of north greenland with mean ice draft in the range 5 0 to 7 5 m while out in the central arctic ocean the mean ice draft is lower 3 9 5 1 m and the characteristics of the ice cover remain homogeneous over a length scale of 1000 km the transition between the two regimes is abrupt taking place in less than 25 km data from the same part of the central arctic taken in march 1971 showed a mean ice draft 0 3 m lower while data from the central beaufort sea showed a mean draft more than 0 8 m lower ii level ice distributions ice with a local gradient of less than 1 in 40 was defined as level ice and used as an indicator of the quantity and thickness distribution of undeformed i e thermodynamically grown ice in the arctic ocean the distribution has a mode at 3 0 3 1 m draft and level ice percentages are in the range 30 40 bottom side and 70 80 top side in the offshore zone and 45 55 bottom and 85 95 top in the central arctic thus about half of the arctic ice cover consists of deformed ice iii pressure ridge spacings the spacings of ridge keels fit a negative exponential distribution characteristic of randomness except at close spacings where there is a deficit of keels explained as a geometrical effect and at very large spacings where there is an excess due to the contribution of polynyas the distribution of sail spacings exhibits these two effects but also differs from a random distribution at moderate sail separations iv ridge elevations and drafts keel drafts fit a law of form p h d oc exp ah 2 d h except for an excess of keels at drafts beyond 20 m there is a positive correlation between mean keel draft and keel frequency there are 3 5 4 5 keels per kilometre with draft exceeding 9 m in the offshore zone and 2 3 in the central arctic sail elevations fit a law of form p h d h x exp a h d h with a positive correlation between mean sail elevation and sail frequency the sail elevation and ice elevation distributions can be related by assuming that all thick ice is contained in pressure ridges of triangular cross section v keel sail comparison for the 21 corresponding 100 km sections there are positive correlations between mean sail height and mean keel draft and between keel frequency and sail frequency from these it is possible to convert a sail distribution computed from a laser profile into a keel distribution enabling sea ice bulk characteristics to be derived from airborne surveys alone vi leads and polynyas a lead was defined as a continuous sequence of depth points greater than 5 m long and not exceeding 1 m draft the number density n d of leads per kilometre of width d m fits the power law n d 15 d 2 exceptionally wide leads were concentrated in the offshore zone and in the marginal ice zone close to the open water of the greenland sea

top bottom multisensor remote sensing of arctic sea ice the arctic sea ice cover has been studied using near simultaneous observations by passive and active synthetic aperture radar sar microwave sensors upward looking and sidescan sonars a lidar profilometer and an infrared sensor data from two aircraft and a submarine over an approximately 100 km track of central arctic sea ice were registered and analyzed to evaluate the characteristics of the ice cover and the utility of each sensor in ice studies the results of comparative and correlation analyses are as follows the probability density functions of ice draft from sonar and elevation from lidar were found to be almost identical when isostasy is taken into account this result suggests that the basic ice thickness distribution can be derived from the surface topography measurements alone reasonable correlation was found between sar backscatter and ice draft or elevation especially when scales were adjusted such that 15 20 sar pixels were averaged however surface roughness derived directly from standard deviations in the lidar elevation data was found to be poorly correlated to the sar backscatter these results indicate that the sar values are affected more by scattering from the ice than from the snow covered surface the active and passive microwave sensors are shown to generally complement each other as the two sensors are especially sensitive to different physical properties of the sea ice undeformed first year ice showed low backscatter values but high brightness temperatures while some multiyear ice showed high backscatter values and low brightness temperature however surfaces identified as multiyear ice by the passive system have a large spread in the unaveraged sar backscatter indicating limitations when using a one channel sar for ice type identification at the highest resolution also ridged ice identified by sonar and sar data covers a large range of passive microwave emissivity suggesting considerable variability in the age and salinity of this type of ice significant variations about 0 11 in the minimum emissivity of consolidated multiyear ice are observed in different regions of the arctic using the high resolution 30 m passive microwave data this suggests that regional variations in texture and scattering characteristics of multiyear ice in the arctic are present likely influenced by different histories of formation of the ice in different regions

the alkali element and boron geochemistry of the escanaba trough sediment hosted hydrothermal system a suite of conjugate pore fluid and sediment samples were collected during leg 169 of the odp from within the clastic sedimentary sequences which host massive sulphides at central hill escanaba trough odp site 1038 we report the alkali element and boron and li and b isotope data for these samples relative to a reference site site 1037 located outside the zone of high heat flow pore fluids from site 1038 show a wide variation in cl 300 800 mm and have far higher concentrations of li up to 6 2 mm b up to 9 7 mm cs up to 5 0 m and rb up to 97 m we show that the pore fluids are derived from hydrothermal circulation that has extended into the basement oceanic crust with input of the alkali elements and b as the rising hydrothermal fluids interact geochemically with the overlying clastic sediments there is however no marked depletion of these elements in the conjugate sediments suggesting that there has been advective transport of fluids away from the primary hydrothermal reaction site this is supported by modelling of the li and b isotope systematics of the pore fluids which shows that they record extensive formation of secondary minerals during cooling of the fluids from 350 to 20 c precipitation of metal rich sulphides would have occurred prior to the formation of these minerals thus the pore fluid li and b isotope data can place important constraints on the locus of sulphide deposition beneath the seafloor at escanaba

the under ice thickness distribution of the arctic basin as recorded in 1958 and 1970 the uss nautilus ssn 571 was the first vessel to cross the arctic basin via the north pole in early august 1958 during this expedition almost continuous acoustic under ice thickness profiles were recorded in august 1970 uss queenfish ssn 651 retraced nautilus route yielding the only duplicate transect of under ice topography across the arctic basin comparisons of the statistical analysis of the under ice draft measurements obtained through use of wide beam and narrow beam and narrow beam only acoustic profilers by nautilus and queenfish respectively along the coincidental route are presented geographic areas found to have distinct under ice characteristics and ice composition are identified the under ice statistics of both cruises are considered in relation to representative field observations and modeling results of other researchers principal findings are 1 nautilus recorded generally more severe ice conditions within the canada basin than did queenfish 12 years later overall mean drafts were 3 08 and 2 39 m respectively 2 the under ice topography becomes progressively more severe when proceeding from the canadian to the eurasian side of the arctic basin 3 the canada basin may contain the most moderate under ice topography and the greatest number of open water and refrozen polynyas and leads within the central arctic basin 4 the makarov and amundsen basins and the arctic mid ocean ridge may contain some of the most severe under ice topography within the arctic basin and 5 the present study indicates an overall arctic basin mean of 3 4 open water new ice less than 30 cm in summer

contour mapping of arctic basin ice draft and roughness parameters a data base of ice draft and roughness parameters has been constructed for selected portions of the arctic ocean based upon analysis of under ice draft distribution data acquired by inverted echo sounder systems on submarines from the voyages of 12 submarines which traversed the alaskan canadian and central arctic regions of the arctic ocean during the summer and winter seasons a series of mean ice draft and deep draft keel statistics was calculated for 50 km segments along each submarine track contour maps of the mean ice draft its standard deviation the mean keel draft and the spatial frequency of ice keels were constructed they show that the greatest ice drafts the roughest ice and the greatest number of deep draft keels are found off the north coasts of the canadian archipelago and greenland due to ice convergence on these land barriers

on the use of lognormal statistics to simulate one and two dimensional under ice draft profiles the probability density function of one dimensional measurements of ice draft is shown to be fitted accurately by a set of lognormal distributions a technique is also described for generating synthetic ice draft data by interspersing filtered random number sequences drawn from the fitted lognormal distributions the sequences are interspersed by random selection to produce one and two dimensional model ice draft profiles the filter characteristics can be chosen so that one dimensional spectra of the model profiles agree well with measurements for features with horizontal length scales greater than 10 m realizations of ice draft data are in good visual agreement with measured profiles

evidence for thinning of the arctic ice cover north of greenland in may 1987 a british submarine carried out an ice profiling experiment in the arctic ocean in which the route closely approximated that of an earlier voyage in october 1976 over a zone extending more than 400 km to the north of greenland there is evidence of a significant decrease in mean ice thickness in 1987 relative to that found in 1976 this thinning amounts to a loss of volume of at least 15 over an area of 300 000 km2 the nature of the ice thickness distributions suggests that the thinning is primarily associated with the presence of a larger fraction of young and first year ice a consequence of wind driven divergence in the ice cover during the months preceding the 1987 observations such a large fluctuation in a region previously believed to possess consistently high ice thicknesses illustrates the importance of monitoring arctic ice thickness more systematically to determine whether such fluctuations fall within the limits of normal inter annual variability

fluid flow and water rock interaction across the active nankai trough subduction zone forearc revealed by boron isotope geochemistry abstract compositional changes dehydration reactions and fluid flow in subducted sediments influence seismogenesis and arc magmatism in subduction zones to identify fluid flow and water rock interaction processes in the western nankai trough subduction zone sw japan we analyzed boron concentration and boron isotope composition 11 b of pore fluids sampled across the subduction zone forearc from depths of up to 922 m below seafloor during four integrated ocean drilling program iodp expeditions the major structural regimes that were sampled by coring include 1 sedimentary inputs 2 the frontal thrust zone 3 the megasplay fault zone and 4 the forearc basin from mass balance consideration we find that consumption of boron b by ash alteration and desorption of b from the solid phase mediated by organic matter degradation produces a net decrease in b concentrations with depth down to 120 m and variable 11 b values in the range of 20 and 49 interstitial water in sediments on the incoming oceanic plate are influenced by more efficient mobilization of exchangeable b from the solid phase due to higher temperatures and alteration of the oceanic crust that acts as a sink for 10 b at the tip of the megasplay fault zone elevated b concentration and b isotopic composition suggest that underthrust coarse grained slope sediments provide a pathway for fluids out of the upper 11 b signature evolves during updip migration through re adsorption mass balance considerations suggest a shallower fluid source depth compared to pore fluids sampled previously near the decollement zone along the central portion of the nankai margin

hydrogeology and mechanics of subduction zone forearcs fluid flow and pore pressure at subduction zones fluid flow pore pressure and tectonic processes are tightly interconnected excess pore pressure is driven by tectonic loading and fluids released by mineral dehydration and it has profound effects on fault and earthquake mechanics through its control on effective stress the egress of these overpressured fluids which is in part governed by the presence of permeable fault zones is a primary mechanism of volatile and solute transport to the oceans recent field measurements new constraints gained from laboratory studies and numerical modeling efforts have led to a greatly improved understanding of these coupled processes here we summarize the current state of knowledge of fluid flow and pore pressure in subduction forearcs and focus on recent advances that have quantified permeability architecture fluxes the nature and timing of transience and pressure distribution thus providing new insights into the connections between fluid metamorphic mechanical and fault slip proc

sea ice draft observations in nares strait from 2003 to 2012 time series observation of sea ice draft and velocity from nares strait between 2003 and 2012 provides new insights on the statistical properties of sea ice leaving the arctic for the atlantic oceans median ice draft is 0 8 m but it varies annually from 1 5 m in 2007 2008 to 0 5 m in 2008 2009 probability density distributions of sea ice draft depend on location across the channel with thicker ice near canada and thinner ice near greenland nevertheless sea ice motion stops seasonally due to arching land fast ice that spans the 30 40 km wide channel for up to 190 days per year such as during the 2011 2012 winter in contrast the 2006 2010 period exhibits a single ice arch lasting 47 days in april may 2008 hence sea ice statistics are weighted by space not by time using sea ice velocities estimated from colocated velocity observations multiyear sea ice with drafts exceeding 5 m constitute between 9 2003 2004 and 16 2007 2008 of the observed sea ice the probability g d of this thick ridged multiyear ice decays exponentially with draft d at an e folding scale d0 of 3 0 0 2 m the trend of d0 with time is statistically indistinguishable from zero this observation suggests a steady export of multiyear sea ice at decadal time scales we speculate that our observations document the draining of the last reservoir of thick ice from the arctic ocean found to the north of ellesmere island and greenland

informational equivalence between synthetic aperture radar imagery and the thickness of arctic pack ice the negative exponential form of the conditional probability of both differences in synthetic aperture radar sar intensity and differences in thickness between neighbors is used as the basis of a representation of structural information in terms of textural information for sea ice the analysis is based on a unique data set involving airborne sar flights over the track of a submarine that simultaneously profiled ice thickness by means of an upwardly directed sonar it is shown that both sets of data namely imagery and thickness possess an identical conditional probability relationship this probability is composed of both a fractal property for spatial separations and a simple negative exponential distribution for intensity or thickness differences for fixed separations these properties allow for the derivation of two forms of information textural and structural an intercomparison of the structural information in terms of the textural information is offered for the same ice field as imaged by a sar and measured from a submarine for its thickness it is shown that the information curves for both the imagery and thickness have a similar geometrical form it is demonstrated that three subranges within the information curves correspond to three visibly identifiable ice types and three thickness ranges associated previously with these ice types it is suggested that an understanding of the transformation between the two sets of information states might provide estimated statistics of arctic ice thickness from sar imagery

sea ice thickness in the southwestern sea of okhotsk revealed by a moored ice profiling sonar 1 using a moored ice profiling sonar along with a moored acoustic doppler current profiler a total spatial section of draft across 3334 km of sea ice was obtained in the southwestern sea of okhotsk near hokkaido in the winters of 1999 2001 using this draft data set the average draft and keel statistics are discussed in this sea for the first time the mean draft was 0 60 m which corresponds to the thickness of 0 71 m over the three winters with the range of 0 49 0 72 m for each winter the classification of level and deformed ice reveals a small range of the monthly mean level ice draft 0 18 0 27 m and the dominance of the deformed ice in terms of volume 80 the mean draft varied with the areal ratio of the deformed ice fairly well these results suggest that dynamic processes such as ridging and rafting are important for the evolution of draft in the region of observation the observed draft probability density distribution and keel statistics show that the thick ice ratio and keel frequency are lower than the similar data in polar regions and closer to those observed in davis strait west of greenland along with the ice concentration and speed derived from the satellite data the southward ice transport to the southwestern sea of okhotsk is estimated on the basis of the observed sea ice thickness the estimated ice transport ranged from 15 to 70 km3 in each winter the heat and freshwater transport associated with the ice transport ranged from 3 9 1017 to 1 8 1018 j and from 12 to 57 km3 respectively

long range acoustic scattering from a shallow water mud volcano cluster analysis of reverberation measurements in the straits of sicily shows high intensity discrete scattered returns 10 20db above background reverberation these returns are due to scattering from mud volcanoes the reverberation from the mud volcanoes at ranges of 15 22km is reasonably consistent over these spatial scales i e kilometers and temporal scales of several hours measurements separated by 4years are also similar statistical characterization indicates that the reverberation associated with a mud volcano cluster is strongly non rayleigh and that the reverberation can be characterized by a single shape parameter roughly independent of frequency the non rayleigh statistics with a concomitant increase in the probability of false alarm indicate that mud volcanoes are a likely source of clutter mean target strengths were estimated at 1 11db over 160 1400hz and are consistent with target strengths measured during a different year at short direct path ranges accumulated evidence points to

ice thickness distribution in davis strait in february from submarine sonar profiles a submarine sonar profile obtained in davis strait by uss queenfish in february 1967 has yielded the first quantitative data on ice thickness distribution in the region within 50 100 km of the ice edge there is a marginal ice zone miz where the mean draft is 0 25 0 51 m most of the ice 93 100 is undeformed and there are many leads but few ridges all of them less than 6 1 m in draft the remainder of the region is an interior zone composed mainly of first year ice with a mean draft of 0 77 1 66 m increasing slightly from ne to sw level ice is less common than in the miz 67 91 of the cover as are leads ridging is more common with a maximum observed keel draft of 19 56 m the overall mean ice thickness distribution has a peak at a draft of 1 05 m 1 18 m thickness identified as the preferred draft of undeformed first year ice at this time ice draft and keel draft distributions followed a negative exponential distribution at depths beyond 3 4 m and the distribution of lead widths followed a power law with exponent 2 29

spectral analysis of canada basin under ice draft distribution as recorded by the uss queenfish august 1970 spectral analysis has been applied to 940 kilometers of under ice thickness data recorded by the uss queenfish in the canada basin august 1970 periodicities of 50 150 m most commonly occurred throughout the track with longer wavelengths common in areas of thicker more variable ice while some regional variations could be discerned unique regional patterns were not apparent supporting the hypothesis that ice characteristics in this region are relatively homogeneous

boron systematics of authigenic carbonates a new approach to identify fluid processes in accretionary prisms boron contents and boron carbon and oxygen stable isotopes were determined for authigenic carbonates recovered from ocean drilling program leg 146 oregon margin carbonate precipitates are the most widespread authigenic phase in the shallow accretionary wedge and carry chemical information about long term variations in pore fluid origin and flow paths in the cascadia subduction zone drilling the first ridge toe area including the frontal thrust and the second ridge or hydrate ridge of the prism demonstrated different fluid regimes with higher b contents in the authigenic precipitates at the toe the 11b of 18 authigenic precipitates analysed ranges from 13 9 to as high as 39 8 extending the upper range of previously reported carbonate 11b values considerably when related to the 11b ratio of their parent solutions these data are characteristic of fluid related processes in accretionary prisms together with 13c and 18o 11b ratios of the carbonate concretions nodules and crusts allow one to distinguish between precipitation influenced by i seawater ii fluid reservoirs at different depth levels within the accretionary prism and iii cage water from dissociated gas hydrates the latter possibly indicating a fluctuation of the bottom simulating reflector during most recent earth s history from this first systematic boron study on authigenic precipitates from an accretionary prism it is suggested that b contents of such carbonate crusts and concretions exceed those reported for other marine carbonates given the abundance of such precipitates at convergent margins they represent a significant b sink in geochemical cycling isotopic compositions of the parent fluids to the carbonates mirror b chemistry of modern pore waters from convergent margins the precipitates carry information of different subduction related fluid processes over a certain period of time and hence are a crucial tracer in the investigation of palaeo fluid flow

laboratory tests on ridging and rafting of ice sheets 1 the mechanical deformation of a sea ice cover takes place through ridging and rafting these processes have been studied in an ice basin by pushing two identical ice sheets together nonuniform ice sheets consisting of floes of thickness t1 and thin ice of thickness t2 connecting the floes were used the major thickness t1 and the thickness ratio t2 t1 were varied ice sheets of uniform thickness t2 t1 1 never formed ridges they only rafted however when ice sheets of nonuniform thickness were used initial rafting transformed into ridging in general high values of t1 and low values for t2 t1 favored ridging while low values of t1 and high values for t2 t1 favored rafting the forces during the tests were measured during the initial rafting stage the force increased linearly with displacement the experiments also suggest that the ridging force has a maximum value this limit can be related to horizontal growth of the ridge or onset of ridging in another site the relation between force and ice sheet thickness has also been analyzed further from the force and the measured ridge profiles it was possible to estimate the ratio of work to change in potential energy this ratio was about 15 for ridging and about 35 for rafting

small scale mapping of sea bed assemblages in the eastern english channel using sidescan sonar and remote sampling techniques abstract a survey was conducted in the eastern english channel to investigate the use of sidescan sonar used in conjunction with traditional biological sampling methods to map the variety and distribution of benthic biotopes i e sea bed habitats and their associated biological communities an area of sea bed approximately 28 km 12 km in size offshore from shoreham u k was surveyed using a digital sidescan sonar system and a mosaic of the output was produced covering 100 of the survey area this was used to divide the area into acoustically distinct regions around which subsequent benthic ground truth surveys were designed benthic communities and sediment types within each of the these regions were sampled using a hamon grab fitted with a video camera and using a heavy duty 2 m beam trawl further information concerning the sea bed was obtained through the application of additional video and photographic techniques substrates within each acoustic region were generally homogeneous in distribution and sediment types ranged across the survey area from cobbles and coarse gravel through to muddy sands analysis of the faunal data revealed the presence of statistically distinct biological assemblages within most of the acoustic regions although species similarity between samples collected from within each acoustic area was often low using a combination of all the data sets five discrete biotopes could be identified and mapped across the area the application of acoustic techniques used in conjunction with biological sampling techniques to map the distribution of sea bed habitats and associated benthic communities is discussed

sea ice thickness distribution in the greenland sea and eurasian basin may 1987 upward sonar data from a 3400 km track in the greenland sea and the eurasian basin of the arctic ocean obtained by a british submarine in may 1987 have been statistically analyzed mean ice thicknesses in the greenland sea show significant melting with downstream distance at an average rate of 0 38 m per degree of latitude equivalent to about 2140 km3 yr 1 of freshwater input between 80 n and 75 n in the region north of fram strait between 82 n and 80 n there is remarkable consistency between mean ice drafts in 1987 and in three previous cruises 1976 1979 1985 while between greenland and the north pole there was a significant thinning in 1987 relative to 1976 in fram strait the mean ice draft shows evidence of thinning within the region of influence of a semipermanent eddy ice draft distributions show that the probability density function of deformed ice follows a negative exponential distribution and that the change of shape of the distribution with downstream distance in the greenland sea is due to preferential melting of thicker ice pressure ridge draft distributions also fit a negative exponential while their spacings fit a lognormal distribution lead width distribution follows a power law with an exponent of 1 45 for narrow leads and 2 50 for wider leads if leads are defined as having a 1 m maximum draft 1 67 and 2 76 for a 0 5 m maximum draft lead spacings follow a negative exponential distribution for moderate spacings 400 1500 m but with an excess of lead pairs at small and very large spacings

on the uncertainty of sea ice isostasy during late winter 2007 coincident measurements of sea ice were collected using various sensors at an ice camp in the beaufort sea canadian arctic analysis of the archived data provides new insight into sea ice isostasy and its related r factor through case studies at three scales using different combinations of snow and ice thickness components at the smallest scale 1m point scale isostasy is not expected so we calculate a residual and define this as zjey to describe vertical displacement due to deformation from 1 to 10m length scales we explore traditional isostasy and identify a specific sequence of thickness calculations which minimize freeboard and elevation uncertainty an effective solution exists when the r factor is allowed to vary ranging from 2 to 12 with mean of 5 17 mode of 5 88 and skewed distribution at regional scales underwater airborne and spaceborne platforms are always missing thickness variables from either above or below sea level for such situations realistic agreement is found by applying small scale skewed ranges for the r factor these findings encourage a broader isostasy solution as a function of potential energy and length scale overall results add insight to data collection strategies and metadata characteristics of different thickness products

past present and impendent hydroelastic challenges in the polar and subpolar seas current and emergent advances are examined on the topic of hydroelasticity theory applied to natural sea ice responding to the action of ocean surface waves and swell with attention focused on methods that portray sea ice more faithfully as opposed to those that oversimplify interactions with a poor imitation of reality a succession of authors have confronted and solved by various means the demanding applied mathematics associated with ocean waves i entering a vast sea ice plate ii travelling between plates of different thickness iii impinging on a pressure ridge iv affecting a single ice floe with arbitrarily specified physical and material properties and v many such features or mixtures thereof the next step is to embed simplified versions of these developments in an oceanic general circulation model for forecasting purposes while targeted on specific sea ice situations many of the reported results are equally applicable to the interaction of waves with very large floating structures such as pontoons floating airports and mobile offshore bases

iceberg calving during transition from grounded to floating ice columbia glacier alaska 1 the terminus of columbia glacier alaska unexpectedly became ungrounded in 2007 during its prolonged retreat visual observations showed that calving changed from a steady release of low volume bergs to episodic flow perpendicular rifting propagation and release of very large icebergs a style reminiscent of calving from ice shelves here we compare passive seismic and photographic observations through this transition to examine changes in calving mechanical changes accompany the visible changes in calving style post flotation generation of seismic energy during calving is substantially reduced we propose this is partly due to changes in source processes

sediment sea water interaction at 200 and 300 c 500 bars pressure the role of sediment composition in diagenesis and low grade metamorphism of marine clay experimental interaction of clay rich marine sediments with sea water at 200 and 300 c 500 bars and a water rock mass ratio of 5 resulted in the generation of relatively acid oxidizing conditions the development of acidity is attributed to the formation of smectite whereas the oxidation state of the fluids was dependent on the relative proportions of ferromanganese oxide phase ferrous rich silicate phases and organic carbon an experiment conducted with an oxidized sediment at 300 c thus produced higher aqueous concentrations of mn and associated base metals at a relatively high fo2 10 15 but an organic carbon rich sediment yielded fluids characterized by a lower fo2 10 20 lower concentrations of mn higher fe and exhibited substantial thermal alteration and dissolution of organic components silica concentrations in the experimental fluids ranged from cristobalite to amorphous silica saturation levels in response to the dissolution of amorphous silica comparison of fluid data and mineralogical assemblages from the gulf coast and salton sea regions with experimental results suggests that alteration processes in sedimentary basins can in large part be attributed to water rock interaction observed differences are apparently due to the higher degree of reaction in the geologic environment and to the increased stability of the illite chlorite assemblage at the lower silica activity characteristic of geologic fluids

further evidence of ice thinning in the arctic ocean a sea ice thickness profile obtained in september 1996 from the eurasian basin of the arctic ocean between fram strait and the north pole was compared with a profile obtained in the same region in september october 1976 a decline in mean ice draft of 43 was observed over the 20 year interval in agreement with changes observed in other parts of the arctic ocean by rothrock et al 1999

mechanical and hydrological effects of seamount subduction on megathrust stress and slip subduction of rough seafloor and seamounts is thought to impact a broad range of geodynamic processes including megathrust slip behaviour forearc fluid flow and long term structural evolution in the overriding plate although there are many conceptual models describing the effects of seamount subduction our quantitative and mechanistic understanding of the underlying deformation and fluid processes remains incomplete here we investigate the interplay between sediment consolidation faulting and the evolution of stress and pore fluid pressure in response to seamount subduction using a numerical model that couples mechanical and hydrological processes and is constrained by laboratory and field observations our results show that subducting topography drives marked spatial variations in tectonic loading sediment consolidation and megathrust stress state downdip of a subducting seamount on its leading flank enhanced compression and drainage lead to large fault normal stress and overconsolidated wall rocks a stress shadow in the seamount s wake leads to anomalously high sediment porosity these variations help explain observed patterns of megathrust slip with earthquakes and microseismicity favoured at the downdip edge of seamounts and aseismic or slow slip in the updip stress shadow changing stresses and pore fluid pressures during subduction of seamounts as simulated with a numerical model that couples mechanical and hydrological processes help explain observed patterns of megathrust slip

roughness of weddell sea ice and estimates of the air ice drag coefficient the roughness of a sheet of sea ice encodes its deformational history and determines its aerodynamic coupling with the overlying air and underlying water here we report snow surface ice surface and ice underside roughness computed from 47 surface elevation profiles collected during a transect of the weddell sea the roughness for each surface parameterized as the standard deviation of the surface elevation segregates according to whether or not a floe has been deformed deformed ice has greater roughness than undeformed ice regardless of deformational history the underside roughness is almost always greater than the snow surface and ice surface roughnesses which are nearly equal roughness spectra for all three surfaces and for both deformed and undeformed ice roll off roughly as k 1 when the wavenumber k is between 0 1 and 3 rad m 1 the snow surface and underside spectra roll off somewhat faster than k 1 and the ice surface spectra roll off somewhat slower than k 1 both top and underside arctic ice roughness spectra on the other hand have been reported to roll off faster than k 2 we speculate that the excess spectral intensity at high wavenumbers in the antarctic ice surface spectra results from the small scale roughness that the ice sheet had on consolidation this excess high wavenumber spectral intensity persists in the ice surface spectra of second year ice evidently once formed the ice surface remains unchanged on the microscale until the entire ice sheet melts with a remote measurement of roughness we should be able to decide whether an ice floe is deformed or undeformed our spectral analysis hints that remote sensing may also be able to differentiate between first year and second year ice from the snow surface spectra we compute a roughness scale that parameterizes the air ice momentum coupling and lets us estimate the neutral stability drag coefficient referenced to a height of 10 m cdn10 typical cdn10 values are 1 1 1 4 10 3 over undeformed ice and 1 3 1 8 10 3 over deformed ice

geochemical and geothermal evidence for fluid migration in the barbados accretionary prism odp leg 110 measured geochemical and geothermal effects of fluid migration in the northern barbados accretionary prism indicate that 1 fluid flows laterally along low angle active faults 2 the entire length of the leg 110 transect is a fluid discharge zone 3 migration results in heating of sediments across the transect but most strongly at the deformation front and 4 migration results in dilution of pore water cl and sup 18 o enrichment more in the arcward than the seaward side of the prism suggesting that the cl poor sup 18 o rich fluids that intrude the prism are derived from smectite illite reactions occurring arcward these conclusions have strengthened those derived from the initial appraisal of shipboard data modified ideas about where fluids are heated most and where the geochemistry is strongly altered and provided new ideas about the sources of fluids and their relative contributions

the underside topography of sea ice over the continental shelf of the beaufort sea in the winter of 1990 a spatial section of draft across 348 km of sea ice was obtained by moored subsea sonars in the beaufort sea in the winter of 1990 the ice field was a mixture of first year and multiyear types with mean draft of the order of 3 m level ice of 0 to 4 m draft occupied approximately 50 of the section within this fraction draft values of 0 and 1 5 m were most common while at 2 to 3 m draft a noticeable contribution was made by rafted first year ice deformed ice was observed to a maximum draft of nearly 27 m keels within the section were identified using both the rayleigh criterion and a new criterion based on level ice both criteria defined exponentially distributed populations but with different e folding scales the observations revealed an ice cover whose statistical properties are consistent with other data from the periphery of the polar pack in the beaufort sea but which are much more severe than those of ice found in the seasonal ice zone only a few tens of kilometres to the south the cross sectional shape of individual keels was highly variable but on average the distribution of ice within a keel was an exponential function of draft the topography of both first year and old ice subsections of the data was fractal in character with a dimension of about 1 5 for both ice types the average mass of sea ice per unit area was estimated as 2540 2970 kg m 2 with 68 73 of this mass contributed by deformed ice the large uncertainties in these estimates arise because the porosity of keels and the burden of snow or melt water upon the ice are not known

seismic observations of glaciogenic ocean waves micro tsunamis on icebergs and ice shelves seismometers deployed over a 3 year period on icebergs in the ross sea and on the ross ice shelf antarctica reveal that impulsive sources of ocean surface waves are frequent e g 200 events per year in the ross sea in the ice shelf and iceberg covered environment of coastal antarctica the 368 events recorded by our field deployment suggest that these impulsive events are generated by glaciological mechanisms such as 1 small scale calving and edge wasting of icebergs and ice shelf fronts 2 edge on edge closing and opening associated with iceberg collisions and 3 possibly the impulsive opening of void space associated with ice shelf rifting and basal crevasse formation the observations described here provide a background of glaciogenic ocean wave phenomena relevant to the ross sea and suggest that these phenomena may be exploited in the future using more purposefully designed observation schemes to understand iceberg calving and ice shelf disintegration processes

tabular icebergs in ocean waves ocean waves are a principal agent in the deterioration and ultimate breakup of antarctic tabular icebergs in the southern ocean we present here some preliminary results from a recent january 1982 field season on board hms endurance during which two tabular icebergs of very different shape were studied in detail the data augment the results of a similar season of work1 2 which took place in 1981 near the south sandwich and south orkney islands instruments to measure rigid body motions and strain gauges to determine wave induced bending were deployed at the surface centre of the two icebergs visited while a waverider buoy simultaneously monitored the ocean wave energy spectrum the precise underwater shape of each iceberg was determined by flying a 60 mhz radar developed for use over land ice 3 4 in a grid pattern across the surface of the iceberg by this means a complete three dimensional picture of the iceberg could be inferred the results show that icebergs tend to act as low pass filters and inhibit short period waves furthermore they selectively resonate at certain wave periods the strain data in particular indicate unexpectedly large flexure which cannot be explained by simple bending alone finally the geometry of icebergs can be such as to render them unstable and liable to turn over

on the spacing and draft distributions for pressure ridge keels the negative exponential distribution is reconsidered as a description of pressure ridge spacings and drafts it is found to give an excellent fit for drafts but not for spacings the spacing distribution is found to be fitted much better by a three parameter lognormal distribution of which the third parameter the threshold is dependent on the beam width of the instrument used to collect the ice bottom profile

toward the modeling of enhanced basal melting in ridge keels observations from sonar data have suggested enhanced melting of thick ridged ice relative to level ice there are several mechanisms that may account for this intensified melting in this paper we examine the effects of two dimensional 2 d heat conduction and enlarged basal surface area due to the sloping sides of the keel on heat conduction and melt rates the cross section of the 2 d ridge is taken to be an isosceles triangle with a rounded crest this is roughly the shape observed and allows a convenient numerical representation in polar coordinates for comparison ridges of similar shape are also represented as a collection of 1 d columns of varying thickness similar to what is implicit in typical ice thickness distribution models the results show that 2 d ridges inhibit the heat conduction compared to 1 d ridges owing to the dominating effect of weaker temperature gradients the slope of the keel is the dominant factor in determining the temperature gradient a size distribution of 2 d ridges reduces heat transfer to the atmosphere by 3 w m 2 compared to a similar distribution of 1 d ridges over an annual cycle basal ablation along the keel is insignificant for 2 d ridges with small slopes whereas ridges with large slopes show ablation rates determined by the ice ocean heat flux these melt rates imply a transition from a triangular to a more rounded shape the 1 d ridge geometry is not adequate to simulate the net melting at the keel base over an annual cycle melt rates are calculated along the ridge keel and for level ice over a 40 day period for comparison with observations for 1 d ridges all ice thicker than 5 m melts more slowly than the corresponding level ice the inclusion of 2 d heat conduction increases the amount of ablation in the thicker ice relative to the 5 m ice especially for ridges with larger slopes however this increase explains only a small fraction of the enhanced basal melting seen in the observations these results suggest that other mechanisms are important in determining the mass loss from thicker ice

annual measurement of sea ice thickness using an upward looking sonar the difficulties in collecting reliable data in polar regions are nowhere more acute than in sampling sea ice growth and thickness yet ice dynamics and the forms the ice takes are of great importance to operators in polar conditions offshore rigs harbours and icebreaking ships for example depend on reliable estimates of the sizes distributions and mechanical properties of pressure ridges and undeformed floes here i report measurements of sea ice thickness in the canadian beaufort sea using a bottom mounted upward looking sonar device operated for 250 consecutive days although carried out over a decade ago the project is as yet the only successful experiment of its kind

east antarctic ice flow dynamic based on subglacial landforms near dibble glacier abstract paleo ice sheet reconstruction in antarctica provides key constrains for understanding and predicting future ice sheet behaviour along the east antarctic margin there are still large sections with little or no information about previous extent and dynamics of the paleo ice sheet here we present new multibeam and chirp subbottom data from the east antarctic continental margin between the frost and dibble glaciers 128 e and 134 e acquired during expedition nbp1503 with the icebreaker nb palmer the inner continental shelf shows a moderately deep seafloor 200 600 m with steep and deeply incised channels most likely created by subglacial meltwater on the mid shelf we identified a 1000 m deep basin with drumlin shaped and linear glacial features the shelf break is relatively shallow 300 400 m and incised by numerous gullies that extent onto the continental slope the presence of these features suggests that grounded streaming ice has reached the shelf break during the last glaciation both the subglacial channels on the continental shelf and the numerous gullies near the shelf break are indicative of melt water underneath the grounding ice our interpretation suggests that compared to toady the ice flow in this area might have been significantly different during glacial times when the paleo ice sheet cover most or all of the continental shelf

modeling iceberg rafted sedimentation in high latitude fjord environments 1 an iceberg model sedberg has been developed to simulate sedimentation in high latitude glaciated fjords sediments deposited in fjords provide an important record of glaciological response to changing climatic conditions the model simulates the formation drift and melt of a population of icebergs utilizing monte carlo based techniques with a number of underlying parametric probability distributions to describe the stochastic behavior of iceberg formation and dynamics the model captures iceberg dynamics and melt in fjord environments and has been applied to kangerdlugssuaq fjord in east greenland as an example of an iceberg dominated sedimentary environment sedimentation has been simulated over the past 1500 years encompassing the climatic intervals of the medieval warm period mwp and the little ice age lia model results have been compared with the observed sedimentary record the model demonstrates that the glaciological regime e g basal debris thickness mean annual calving rate mean iceberg size plays a more important role than the direct influence of climate ocean and air temperatures on iceberg sedimentation rate although often changes in climate result in changes to the glaciological regime

arctic sea ice leads from advanced very high resolution radiometer images a large number of advanced very high resolution radiometer avhrr images from throughout 1989 are analyzed to determine lead characteristics the units of analysis are square 200 km cells and there are 270 such cells in the data set clouds are masked manually leads are determined from images of the potential open water a scaled version of the surface temperature or albedo that weights thin ice by its thermal or brightness impact the lead fraction is determined as the mean the monthly mean lead fraction ranges from 0 02 in winter to 0 06 in summer in the central arctic and is near 0 08 in the winter in the peripheral seas a method of accounting for lead width sampling errors due to the finite sample areas is introduced in the central arctic the observed mean lead width for a threshold of 0 1 ranges from 2 or 3 km near the resolution of the instrument in the winter to 6 km in the summer in the peripheral seas it is about 5 km in the winter width distributions are often more heavily weighted in the tail than exponential distributions and are well approximated by a power law the along track number density power law n aw b has a mean exponent of b 1 60 standard deviation 0 18 and shows some seasonal variability mean floe widths in the central arctic are 40 to 50 km in the winter dropping to about 10 km in the summer for floes the power law has a mean exponent of 0 93 and exhibits a clearer annual cycle lead orientation is determined with a method based on the direction of maximum extent

sea ice thickness data the many vs the few during may 1988 a 1230 m ice thickness profile was drilled across a floe in fram strait the probability density function of this data set corresponds closely to extensive ice draft measurements from submarines and the thickness distribution of floes sampled randomly in the area the observed similarity is attributed to the topography of the pack ice in fram strait where each floe is composed of a spectrum of smaller components this may imply that mutual independence and representativeness of thickness measurements can be satisfied to some degree even for short profiles

effect of smectite dehydration on pore water geochemistry in the shallow subduction zone an experimental approach 1 the diagenetic smectite to illite transition is widely accepted to cause ubiquitous pore water freshening at convergent margins however experimental consolidation tests show that smectite also dehydrates partially with increasing effective stress to shed light on this process three hydrothermal consolidation tests on a silty smectite rich claystone were conducted with stresses p up to 70 mpa and at constant temperatures t of 20 c 60 c and 100 c fluids expelled during the tests were analyzed for major and trace elements to evaluate dehydration and fluid rock interaction with increasing pt conditions the results document that fluid freshening starts when the effective stress exceeds 1 3 mpa the smectite interlayer water content decreases from 27 wt to 20 wt during the experiments which is equivalent to an interlayer collapse from 18 5 to 15 4 a the released interlayer h20 accounts for up to 17 of the total fluid volume released from the consolidating sediment major and volatile element geochemistry is influenced by temperature and smectite interlayer collapse the interlayer collapse is characterized by k and ca uptake while is b released from smectite application of experimental results to the barbados accretionary margin shows that stress dependent smectite dehydration is an important fluid source mechanism and accounts for substantial fluid freshening modeled smectite dehydration suggests a decrease of smectite interlayer water content from 27 wt at the surface down to 22 wt at 2 km depth this leads to chlorinity values as low as 460 mm

a statistical analysis of arctic pressure ridge morphology individual pressure ridges were identified on both sensors the shape on the upward looking sonar was used to obtain draft and apparent slopes and width of each ridge while the orientation of the ridge as revealed by the side scan sonar was used to convert these figures into absolute slopes and width the data set comprises 729 ridges it was found that in addition to ridge spacing ridge drafts fit a lognormal distribution better than a negative exponential that the mean draft of ridges diminishes with downstream distance in the trans 3polar drift stream at about 0 625 m per degree suggesting a faster melt rate for ridge bottoms than for the ice as a whole and that ridge widths and slopes also fit lognormal distributions an empirical relationship was found relating ridge slope to the ratio of half width to draft the mean ridge slope varied with location but always lay in the range 21 7 to 26 5

the 2004 aceh andaman earthquake early clay dehydration controls shallow seismic rupture the physical state of the shallow plate boundary fault governs the updip extent of seismic rupture during powerful subduction zone earthquakes and thus on a first order impacts on the tsunamigenic hazard of such events during the 2004 mw 9 2 aceh andaman earthquake seismic rupture extended unusually far seaward below the accretionary prism causing the disastrous indian ocean tsunami here we show that the formation of a strong bulk sediment section and a high fluid pressured predecollement that likely enabled the 2004 rupture to reach the shallow plate boundary result from thermally controlled diagenetic processes in the upper oceanic basement and overlying sediments thickening of the sediment section to 2 km 160 km seaward of the subduction zone increases temperatures at the sediment basement interface and triggers mineral transformation and dehydration e g smectite illite prior to subduction the liberated fluids migrate into a layer that likely host high porosity and permeability and that is unique to the 2004 rupture area where they generate a distinct overpressured predecollement clay mineral transformation further supports processes of semilithification induration of sediments and coupled with compaction dewatering all amplified by the thick sediment section together strengthens the bulk sediments farther south where the 2005 sumatra earthquake did not include similar shallow rupture sediment thickness on the oceanic plate is significantly smaller therefore similar diagenetic processes occur later and deeper in the subduction zone hence we propose that shallow seismic rupture during the 2004 earthquake is primarily controlled by the thickness and composition of oceanic plate sediments

do marine substrates look and sound the same supervised classification of multibeam acoustic data using autonomous underwater vehicle images in this study we outline the techniques used to transform multibeam acoustic data into spatial layers that can be used for predictive habitat modelling the results allow us to identify multibeam attributes which may act as potential surrogates for environmental variables that influence biodiversity and define which variables may be reliable for predicting the distribution of species in temperate waters we explore a method for analysing the spatially coincident multibeam bathymetric and backscatter data from shallow coastal waters to generate spatial data products that relate to the classes derived from fine scale visual imagery obtained using an autonomous underwater vehicle auv classifications of the multibeam data are performed for substrate rugosity and sponge cover overall classification accuracies for the classes associated with substratum rugosity and sponge structure were acceptable for biodiversity assessment applications accuracies were highest for rugosity classes at 65 followed by substratum classes at 64 and then sponge structure classes at 57 random forest classifiers at a segmentation scale of 30 performed best in classifying substratum and rugosity while k nearest neighbour classifiers performed best for sponge structure classes with no difference in accuracy between scale 30 and 60 incorporating backscatter variables using segmentation improved the overall accuracy achieved by the best performing model by between 1 rugosity and 9 substratum above using topographic variables only in the grid based analyses results suggest that image based backscatter classification show considerable promise for the interpretation of multibeam sonar data for the production of substrate maps a particular outcome of this research is to provide appropriate and sufficiently fine scale physical covariates from the multibeam acoustic data to adequately inform models predicting the distribution of biodiversity on benthic reef habitats

the action of water films at a scales in the earth implications for the nankai subduction system abstract water properties change with confinement within nanofilms trapped between natural charged clay particles we investigated nanofilm characteristics through high stress laboratory compression tests in combination with analyses of expelled pore fluids we utilized sediments obtained from deep drilling of the nankai subduction zone at site c0002 of the integrated ocean drilling program iodp we show that below 1 2 km there should be widespread ultrafiltration of migrating fluids experiments to 100 mpa normal compression collapse pores below a few ion monofilm thicknesses a reduction towards a single condensing dehydrating ion monofilm occurs as stresses rise 100 200 mpa and clay separations are reduced to