sea ice motion in response to geostrophic winds it is an old rule of thumb that sea ice moves with a speed of about 2 of the surface wind and about 45 to the right of the wind a similar relationship between the ice velocity and the geostrophic wind is examined here it is found that only about half of the long term several month average ice motion is directly related to the geostrophic wind the other half being due to the mean ocean circulation on shorter time scales and in all seasons more than 70 of the variance of the ice velocity in the central arctic ocean is explained by the geostrophic wind within about 400 km of the coasts the geostrophic wind is less successful in explaining the ice motion the spatial variations in ice velocity are also partly explained by the geostrophic wind about half of the variance in the large scale ice vorticity and shear are accounted for on the other hand none of the large scale ice divergence can be explained by the wind the long term average ocean current is estimated by subtracting the share of the ice motion caused by the wind from the total ice motion

gas hydrate reservoir and active methane venting province in sediments on 20 ma young oceanic crust in the fram strait offshore nw svalbard seafloor pockmarks are common indicators for vertical fluid flow and frequently associated with methane discharge through the gas hydrate stability zone ghsz the present day flux through these degassing systems is presumably at a low level on most rifted continental margins a pockmark field on the nw svalbard passive margin is located on young ocean crust 20 ma and shows evidence of ongoing episodic degassing new geophysical data from the vestnesa ridge 79 n a mounded and elongated sediment drift in the eastern fram strait reveal a gas hydrate free gas and venting system that is exceptionally more dynamic than documented elsewhere along the northeastern north atlantic margin the prominent bottom simulating reflection bsr about 200 mbsf separates anomalously high p wave velocities in the ghsz from a remarkable underlying low velocity zone indicating the presence of gas hydrate and gas in the pore space inversion of p wave velocity data using the differential effective medium theory yields a two dimensional concentration model of methane hydrate and free gas the model predicts saturations of up to 11 in the hydrate reservoir which due to the seafloor topography forms a large anticlinal permeability barrier below in the low velocity zone i e 1350 1500 m s up to 3 of free gas is predicted across the apex of the vestnesa ridge and in the immediate vicinity of extensional faults a conservative estimate indicates that 225 kg m2 of pure methane is stored in hydrate and gas in the upper 230 m of the sedimentary column an elongated pockmark field consisting of 100 individual pockmarks up to 600 m wide systematically aligns the apex of the vestnesa ridge active vigorous degassing from the topography controlled pressure valve system was evident from a 750 m high and 150 m wide gas flare observed in the water column during a cruise with r v jan mayen in october 2008 the gas flare documents dynamic degassing through the corresponding chimney which penetrates the entire ghsz and into the underlying free gas zone cruises in 2006 and 2007 did not detect active gas venting above the pockmark field accordingly vigorous degassing may operate in an episodic mode where hydrothermal circulation systems through young ocean crust may play a significant role

dissociation of oceanic methane hydrate as a cause of the carbon isotope excursion at the end of the paleocene isotopic records across the latest paleocene thermal maximum lptm indicate that bottom water temperature increased by more than 4 c during a brief time interval 104 years of the latest paleocene 55 6 ma there also was a coeval 2 to 3 excursion in the 13c of the ocean atmosphere inorganic carbon reservoir given the large mass of this reservoir a rapid 13c shift of this magnitude is difficult to explain within the context of conventional hypotheses for changing the mean carbon isotope composition of the ocean and atmosphere however a direct consequence of warming bottom water temperature from 11 to 15 c over 104 years would be a significant change in sediment thermal gradients and dissociation of oceanic ch4 hydrate at locations with intermediate water depths in terms of the present day oceanic ch4 hydrate reservoir thermal dissociation of oceanic ch4 hydrate during the lptm could have released greater than 1 1 to 2 1 1018 g of carbon with a 13c of approximately 60 the release and subsequent oxidation of this amount of carbon is sufficient to explain a 2 to 3 excursion in 13c across the lptm fate of ch4 in oceanic hydrates must be considered in developing models of the climatic and paleoceanographic regimes that operated during the lptm

a parameterization of the ice ocean drag coefficient 1 a parameterization of the ice ocean drag coefficient cw was developed through partitioning the oceanic drag force into three components 1 form drag on the floe edge 2 form drag on the ridge keel and 3 skin friction on the ice bottom through these quantities cw was expressed as a function of observable sea ice geometric parameters sensitivity studies were carried out to investigate the influence of varying sea ice conditions on cw the results revealed that cw increases first and then decreases with increasing ice concentration a similar to the observations of the air ice drag coefficient and which is mainly attributed to the nonmonotonic variation of the form drag on the floe edge with ice concentration moreover the form drag on the floe edge is always the dominant component having a proportion of more than 60 in sea ice with a large aspect ratio draft length 1 100 indicating the necessity of including this term in sea ice dynamic models particularly for the marginal ice zone miz the form drag on the ridge keel becomes dominant only when the ridging intensity is extremely high depth spacing 1 20 additionally a large value of cw cannot be caused only by the inclusion of form drag terms but also by large skin friction over rough ice bottoms finally for typical situations in the miz with moderate ridging intensity the parameterization will underestimate cw by approximately 30 for a rough ice bottom and by over 80 for a smooth ice bottom if no form drags are considered

fluid methane and energy flux in an active margin gas hydrate province offshore costa rica joint analysis of seafloor temperature data borehole temperature measurements and observations that constrain the position of the top and base of the gas hydrate zone ghz at sites on the non accretionary costa rican margin provide quantitative constraints on the flux of energy fluid and methane through the sediments on the overriding plate a comparison of borehole temperature data obtained in the trench at the toe of the deformed sedimentary wedge and at a midslope location indicates that the thermal regimes are perturbed by appreciable advective flux at 1 km oceanward 19 mm yr 1 and 1 4 km landward 5 7 mm yr 1 of the deformation front this observation is loosely consistent with models that predict the most rapid dewatering and highest rates of fluid expulsion within a few kilometers of the deformation front using data that constrain the thickness of the ghz at three sites on the forearc we estimate methane and fluid flux rates through application of a one dimensional analytical model that constrains the nature of the plumbing system for the gas hydrate reservoir our results indicate a two fold decrease in methane flux between a site located 400 m from the toe of the wedge and a site 12 km from the toe an intermediate site located 1 4 km from the toe of the wedge has a thick ghz extends to at least 340 365 m below seafloor that requires a very high methane supply rate 345 mol m 2 kyr 1 for a mass flux of 5 mm yr 1 we conclude that this site has the most two dimensional fluid flux regime with fluids being fed into the zone laterally by conduits and fractures and vertically by expulsion during compaction of underthrusting sediments

large scale sediment waves and scours on the modern seafloor and their implications for the prevalence of supercritical flows large scale 20 m to 7 km wavelength bedforms are common on the seafloor yet there is a lack of consensus on how they form and thus what to call them we conducted statistical analysis on a dataset of 82 seafloor bedforms that span a range of water depths and environments the data form three distinct groups 1 small scale 20 300 m wavelength sediment waves with mixed relief made of medium sand to cobble sized sediment that form in confined settings which we call small sediment waves 2 large scale 300 7000 m wavelength sediment waves with mixed relief made of fine grained sediment that form in relatively unconfined settings which we call large sediment waves and 3 large scale fully enclosed depressions in the seafloor which we call scours there is a statistically significant data gap in the size of bedforms between small sediment waves and large sediment waves that does not appear to be a sampling artefact this data gap probably results from the environments in which sediment waves form being either confined e g channel or canyon or unconfined e g open slope bedform migration direction is available for 36 of the data and includes small and large scale sediment waves of these examples all are shown to migrate up current up current migration is indicative of supercritical flow thus this data suggests that supercritical flows operate in a wide range of environments and can generate both small and large sediment waves therefore we suggest that small and large sediment waves form by similar processes despite the gap in bedform wavelength and sediment size the migration direction for scours remains unknown scours may form from similar processes to small and large sediment waves or alternatively they may be a completely separate bedform type that form when erosive flows exploit pre existing defects in the seafloor this novel statistical analysis of a global database shows that up current migrating bedforms associated with supercritical flow are unusually widespread and are recognised at two distinct scales

permeability evolution during the formation of gas hydrates in marine sediments 1 fluxes of gas energy and fluid water with dissolved gas are known to control the distribution of gas hydrate and free gas in gas hydrate reservoirs but theoretical studies have so far not focused on the effect of sediment properties e g permeability on these fluxes during the formation of gas hydrate deposits using a transient one dimensional two phase gas hydrate and fluid numerical model based on a coupled conservation approach we examine permeability clogging during gas hydrate formation in end member porous media and fractures initially lacking hydrate and determine the resulting changes in fluid and advective energy flux gas hydrate accumulates most rapidly at depth in both systems a result consistent with borehole logging and seismic studies on the blake ridge consideration of the ratio of surface area to fluid volume explains model results that imply more rapid permeability reduction in the porous media system and more uniform hydrate formation as a function of depth in the fracture system depending on fluid flux fracture aperture or pore sizes and other factors the timescale for permeability clogging due to the accumulation of gas hydrate ranges from thousands to millions of years regenerating gas hydrate to a concentration of 10 15 of pore space in marine settings with fluid fluxes characteristic of hydrate ridge or blake ridge requires 103 105 years meaning that hydrate deposits in these settings cannot be viewed as a naturally renewable resource these results also imply that significant time is required to reestablish gas hydrate deposits after large scale dissociation events associated with global scale climate change

relating arctic pack ice stress and deformation under winter conditions 1 together thermodynamic and dynamic processes determine the thickness distribution of the ice cover on polar oceans which governs the exchange of energy between the atmosphere and the ocean key to the dynamic processes is the mechanical behavior of the ice cover during the surface heat budget of the arctic ocean sheba field experiment we deployed sensors to measure the internal ice stress at several locations within a 15 15 km area these measurements are combined with satellite derived ice motion and imagery products the objective is to make a first step toward using these data sources for evaluating sea ice dynamics models by assessing whether the stress signal can be qualitatively linked to the regional scale 10 100 km deformation activity four case studies are presented each with distinguishing characteristics consolidation of the seasonal ice zone against the alaskan coast 5 7 december 1997 advancement of the consolidation zone into the perennial ice pack 11 13 december extreme divergence 14 17 january and consolidation of the pack against wrangel island and the siberian coast 20 23 february the results of this analysis 1 demonstrate that stress measurements are related to the regional deformation behavior of the ice cover 2 confirm that regional scale ice dynamics is primarily a function of coastal geometry and sustained large scale wind direction and magnitude 3 provide continued evidence that the ice pack behaves as a granular hardening plastic and 4 encourage pursuit of efforts to use direct measurements of ice stress and deformation in the formulation and development of sea ice dynamics models

large scale comparison between buoy and ssm i drift and deformation in the eurasian basin during winter 1992 1993 a method for comparing sea ice velocity divergence and shear at the large scale between buoys and special sensor microwave imager ssm i is presented for initial testing the method is applied in the eurasian basin because of its relatively simple circulation dominated by the wind using eight argos buoys 11 strain rate arrays 100 600 km in size are constructed daily 100 km resolution sea ice motion derived from ssm i 85 ghz brightness temperatures is sampled 100 1000 km from the center of the buoy arrays over this range of possible scales a minimum rms difference rmsd for deformation is used to identify an optimal inclusion radius of 600 km corresponding to a length scale of 1000 km this length scale is typical of local storms confirming a strong connection between wind and observed sea ice motion on the basis of all 11 arrays an average rmsd of 2 48 0 05 cm s 1 for velocity vector and 8 8 0 9 10 8 s 1 using all four deformation components ui j is found at the optimal inclusion radius corresponding to average correlation coefficients of 0 896 0 002 and 0 729 0 030 respectively rmsd are found to scale with the temporal and spatial uncertainties of the ssm i suggesting that even better results can be achieved with higher resolution instruments

acoustic evidence for a gas migration and release system in arctic glaciated continental margins offshore nw svalbard abstract high resolution 3d and 2d seismic data offshore nw svalbard west of prins karls forland provide geophysical evidence for geologically controlled fluid migration pathways gas hydrate occurrence and an active seabed gas expulsion system the investigated seabed area covers 1600 km2 and lies between kongsfjorden cross shelf trough in the north and isfjorden cross shelf trough in the south ranging in water depths from 200 m on the shelf to 800 m on the upper continental slope acoustic evidence for present day methane release from the seabed to the water column comes from more than 220 gas flares at the outer shelf while past methane release activity at the mid shelf area is evident from pockmarks without flares the fluid migration pathways towards the seabed can be drawn from sub seabed acoustic anomalies fluid migration towards the upper slope occurs mostly along strata in upslope direction and largely prevails over vertical focused migration fluids accumulate in the uppermost part of the slope just westward of the shelf break where they are trapped beneath the prograding glacigenic sequence which is not permeable enough for fluids to migrate through fluids are expelled on the shelf where the base of the glacigenic sequence outcrops some gas charged fluids may originate from deep seated hydrocarbon reservoirs and can be temporally stored in gas hydrates in the shallow subsurface though evidence for hydrates on the uppermost slope is missing the seismic data from the lower slope clearly suggest the occurrence of gas hydrate

structure and kinematics along a segment of the mojave sonora megashear a strike slip fault that truncates the jurassic continental magmatic arc of southwestern north america 1 similarities between crystalline crust and overlying pre jurassic cover in northwestern sonora mexico and in the inyo mountains death valley region california are attributed to left lateral displacement along the mojave sonora megashear a late jurassic transform fault related to the opening of the gulf of mexico three exposures of mylonitic rocks extending 25 km along the postulated fault occur within sierra de los tanques sonora mexico the exposures 13 km southwest of sonoita reveal a tripartite assemblage of 1 jurassic volcanic and volcaniclastic strata to the northeast 2 an axial zone of mylonitic rocks and 3 masses of granitic rocks and compositionally banded quartzo feldspathic gneiss of proterozoic and late triassic age to the southwest mylonitic foliation in rocks within the axial zone strikes northwesterly and lineations plunge shallowly microstructues record left lateral shear shallow thrusts folded mylonite and steeply dipping mylonitic foliation with downdip mineral lineation record transpression triassic and precambrian crystalline rocks are emplaced above shallow thrusts onto ductilly deformed jurassic rocks northeast of the principal fault in the central and northwestern exposures pervasively foliated and lineated rocks are cut by weakly foliated cretaceous granite that also may contain inclusions of mylonite the northwesterly strike of steep foliation left lateral kinematics and relationships with cretaceous intrusive rocks preclude correlation with episodes of cretaceous contraction and tertiary extension that are recognized in the southwestern united states the fault is interpreted to have formed in the late jurassic and records a change in tectonic setting from arc magmatism to rifting and basin development

a blast of gas in the latest paleocene simulating first order effects of massive dissociation of oceanic methane hydrate carbonate and organic matter deposited during the latest paleocene thermal maximum is characterized by a remarkable 2 5 excursion in delta 13c that occurred over approximately 10 4 yr and returned to near initial values in an exponential pattern over approximately 2 x 10 5 yr it has been hypothesized that this excursion signifies transfer of 1 4 to 2 8 x 10 18 g of ch4 from oceanic hydrates to the combined ocean atmosphere inorganic carbon reservoir a scenario with 1 12 x 10 18 g of ch4 is numerically simulated here within the framework of the present day global carbon cycle to test the plausibility of the hypothesis we find that 1 the delta 13c of the deep ocean shallow ocean and atmosphere decreases by 2 3 over 10 4 yr and returns to initial values in an exponential pattern over approximately 2 x 10 5 yr 2 the depth of the lysocline shoals by up to 400 m over 10 4 yr and this rise is most pronounced in one ocean region and 3 global surface temperature increases by approximately 2 degrees c over 10 4 yr and returns to initial values over approximately 2 x 10 6 yr the first effect is quantitatively consistent with the geologic record the latter two effects are qualitatively consistent with observations thus significant ch4 release from oceanic hydrates is a plausible explanation for observed carbon cycle perturbations during the thermal maximum this conclusion is of broad interest because the flux of ch4 invoked during the maximum is of similar magnitude to that released to the atmosphere from present day anthropogenic ch4 sources

temporal and spatial evolution of a gas hydrate bearing accretionary ridge on the oregon continental margin a seismic reflection survey on the oregon continental margin conducted in 1989 indicates the widespread presence of gas hydrate beneath the middle and lower slope of this accretionary margin the seismic signature of gas hydrate a bottom simulating reflector bsr with negative polarity that locally cuts across stratigraphic horizons is especially well developed beneath hydrate ridge this anomalously shallow accretionary ridge was drilled during ocean drilling program leg 146 to study fluid venting in this paper we focus on the seismic data from the southern part of hydrate ridge where little evidence of active venting has previously been reported but where the seismic data indicate a complicated subsurface plumbing system apparent disruptions of the bsr beneath the western ridge flank suggest dissociation of gas hydrate in response to slumping a double bsr beneath the southern crest suggests hydrate destabilization in response to tectonic uplift and folding on the basis of these and other observations we propose a qualitative model for the evolution of a hydrate bearing ridge in an active accretionary complex in which gas hydrate initially stabilizes the sea floor permitting construction of large ridges that are then eaten away by slumps along their margins the north to south variation in sea floor venting and subsurface seismic structure along hydrate ridge may reflect different stages in the temporal evolution of one of these ridges

depositional and diagenetic controls on reservoir attributes within a fluvial outcrop analog upper triassic sonsela member of the chinle formation petrified forest national park arizona the upper triassic sonsela member of the chinle formation in the petrified forest national park was evaluated using sedimentologic stratigraphic paleopedologic and petrographic criteria along a continuous 0 5 km 0 3 mi outcrop the study interval consists of interbedded sandstones and mudstones and is composed of a two tiered hierarchy of cyclic alluvial deposits with bounding paleosols the succession is composed of 15 fluvial aggradational cycles facs that comprise two fac sets fac sets the fac sets are composed of architectural elements suggestive of a mixed load fluvial system that is alternately dominated by bed load deposits and suspended load deposits a thinning and fining stacking pattern within fac sets is accompanied by an upward increase in pedogenic modification suggesting that cycles systematically stack in response to a longer period decrease in the rate of accommodation gain sandstones are classified as litharenites feldspathic litharenites and lithic subarkoses and occur within recycled orogen dissected arc and transitional arc provenance fields sandstone compositional maturity increases upward through the fac sets point counts of intergranular volume as a proxy for primary porosity within channel facies and subsequent transform to syndepositional permeability provide a two dimensional depiction of the lateral variability in reservoir quality paleosols are weakly to moderately developed and have little stratigraphic variation these characteristics suggest that climatic fluctuations are not responsible for evolving fluvial depositional style or associated reservoir quality trends in sandstone compositional maturity suggest that fluvial stacking patterns and depositional style are related to pulses of tectonism sandstones are volcanogenic rich and have undergone an almost complete diagenetic loss of porosity caused by the precipitation of authigenic clays paragenetic reconstruction suggests that porosity loss occurred contemporaneous with the silicification of fossil logs in channel deposits log compaction at the time of silicification averaged 9 1 suggesting that log silicification and porosity loss occurred soon after deposition

entrainment induced by near inertial drift of sea ice and its impact on under ice biogeochemical processes in marginal ice zones abstract mooring observation of hydrography hydrodynamics and suspended particles distribution under a drifting sea ice revealed the mixing and entrainment pattern in the upper mixed layer ml of the marginal ice zone the ice floe where the mooring system was installed drifted as near inertial motion with approximately 12 h cycle the mixing pattern induced by this near inertial drift can be divided into two distinct regimes first simple entrainment upward fluxes from the seasonal pycnocline to sea ice water boundary are induced by shear across ml and seasonal pycnocline during the period when ice floes drift toward pack ice the entrainment speed was in the range of 0 25 2 m h 1 which matches well with thickening and thinning of the ml during a near inertial period turbulent wakes on the boundary between sea ice and open water occurred behind the advancing edge of ice in the second regime when ice floes drift toward open ocean the turbulent wakes at the advancing edge of ice are combined with the entrainment caused by near inertial motion which results in a complex mixing pattern of both upward and downward fluxes in the ml the echo intensity observed by the acoustic doppler current profiler and beam attenuation from transmissometer revealed the elevated concentration of suspended particulate materials in the ml which can be direct evidence visualizing the mixing pattern results suggest that the mixing and entrainment found in our study sustain particulate matters in suspension within upper ml for a few months this may provide a potential mechanism to sustain abundant organic particulates in the ml and upper pycnocline for months after under ice bloom under strong wind events like storms the entrainment induced by near inertial motion may also get enhanced which causes elevated supply of nutrients from the deeper permanent pycnocline to the ml

seasonal ice mass balance buoys adapting tools to the changing arctic monitoring the local mass balance of arctic sea ice provides opportunities to attribute the observed changes in a particular floe s mass balance to specific forcing phenomena a shift from multi year to seasonal ice in large portions of the arctic presents a challenge for the existing lagrangian array of autonomous ice mass balance buoys which were designed with a perennial ice cover in mind this work identifies the anticipated challenges of operation in seasonal ice and presents a new autonomous buoy designed to monitor ice mass balance in the seasonal ice zone the new design presented incorporates features which allow the buoy to operate in thin ice and open water and reduce its vulnerability to ice dynamics and wildlife damage while enhancing ease of deployment a test deployment undertaken from april to june 2009 is discussed and results are presented with analysis to illustrate both the features and limitations of the buoy s abilities

geological features controlling factors and potential prospects of the gas hydrate occurrence in the east part of the pearl river mouth basin south china sea abstract logging while drilling lwd and wireline log cwl data were acquired during china s second gas hydrate drilling expedition gmgs 2 in the east of pearl river mouth basin south china sea disseminated and massive gas hydrates deposits were found at different sites gas hydrate bearing lithologies identified from the sample coring included the fine grained sediments and coarse grained sediments lwd logs from site gmgs2 08 indicate significant gas hydrate in clay bearing sediments including two layers with massive gas hydrate with a bulk density near to 1 08 g cm3 high electrical resistivities with a range of 2 5 2000 0 m and high p wave velocities are simultaneously observed in the hydrate bearing sediments the average gas hydrate saturation estimated from the pore water freshing analysis ranges from 45 to 55 of the pore space buried carbonate layers above the massive gas hydrate deposit discovered at sites gmgs2 08 indicate that the formations are likely to have formed initially at the surface and then were buried significant high amplitude seismic anomalies discontinuous bottom simulating reflection bsr and blanking zone are detected in the drilling zone the hydrate bearing sediments predominantly consist of silty clay and limestone grains in which the gas hydrates are deposited primarily in the form of laminated massive veins or nodule the gas hydrates occurrences are subjected to the sediment lithology new tectonic activities migration of fluid and gas and also the factors such as heat flow salinity and time which affect the nucleation of gas hydrates its natural morphologies present massive laminated nodular nugget and disseminated of which the former four often formed in shallow fault inter layer s weak cementation zone and on the seabed the buried gas hydrates with high saturation are good zones for gas hydrate exploitation

late cretaceous fluvial megafan and axial river systems in the southern cordilleran foreland basin drip tank member of straight cliffs formation and adjacent strata southern utah u s a abstract the upper cretaceous lower campanian drip tank member of the straight cliffs formation in the grand staircase region of southern utah is an upward coarsening sandstone rich low sinuosity fluvial deposit in the cordilleran foreland basin the drip tank member thins from 75 m to 30 m eastward across the basin foredeep approximately parallel to its dominant eastward sediment dispersal direction and thins southward along the foredeep to as little as 17 m near its southern outcrop extent along modern cliff lines it overlies and underlies mudstone rich fluvial strata of the john henry member of the straight cliffs formation and lower member of the wahweap formation respectively both of which were deposited by northeast flowing rivers the john henry drip tank contact lies in an interfingering progradational stratigraphic transition from medium grained lenticular sandstone bodies to tabular coarse grained amalgamated sandstone bodies the contact with the overlying wahweap formation is locally a prominent surface of erosion or sediment reworking sandstone petrography and detrital zircon age populations of the strata indicate detrital sources in basement south of the foreland basin thrust sheets to the west and magmatic arc rocks to the southwest the uppermost part of the john henry member contains as much as 10 feldspar and abundant 1 84 1 60 ga detrital zircons derived from yavapai mazatzal basement rocks in the mogollon highlands the drip tank member ranges from quartzarenite to chert bearing sublitharenite with grenville 1 2 1 1 ga neoproterozoic and early paleozoic detrital zircons derived from proterozoic through jurassic strata exposed in the sevier orogenic belt lower member wahweap litharenites contain abundant thrust belt derived detrital carbonate grains absent from compositionally mature drip tank sandstones as well as a broad range of zircon ages the drip tank member constitutes deposits of a sand rich fluvial megafan or distributive fluvial system that displaced a subjacent but partly time equivalent axial fluvial system eastward as the megafan driven in part by seasonally high discharge fed by monsoonal precipitation prograded across the basin foredeep a thick amalgamated fan axis succession present in northern exposures contrasts with a thinner fan flank succession in southern localities tabular sixth order lithosomes each containing channels on the order of 7 m deep define three individual fluvial fans or fan lobes in the megafan system younger wahweap fluvial channels eroded uppermost drip tank deposits of the fan axis and fan flank transverse fan progradation across the foredeep recorded falling accommodation sediment supply in an aggradational to progradational systems tract erosion and reworking of the upper fan surface record decreased accommodation sediment bypass and erosion prior to reoccupation of the foredeep by the wahweap axial fluvial system the upper contact of the drip tank member is thus the primary sequence boundary in this multi component fluvial system and the lower wahweap represents transitional systems tract deposits accumulated as accommodation sediment supply increased

deep water sediment waves as a special gas hydrate reservoirs in the northeastern south china sea abstract the gas hydrate is attracting increasing attention in the sedimentary geology as an alternative energy source in the future recent exploration efforts have indicated that gas hydrate is commonly associated with sediment waves in slope area of quasi passive continental margin based on the deep water seismic data and core data of the northeastern part of the south china sea scs this research describes the seismic and geological characteristics of the sediment waves and gas hydrate reservoirs and discusses the accumulation model of gas hydrate in sediment waves reservoir the results demonstrate that 1 the sediment waves widely appear in study area and those have a wave like bedform and are formed by deep water contour or turbid current sedimentation meanwhile the sediment waves are affected by gas leakage diapirism and neotectonics 2 the stable zone of gas hydrate which simulated calculation by theory is consistent with core data the complete and typical gas hydrate seismic model including a bottom simulating reflection bsr blank zone bz enhanced reflector body ehb structure can be observed in the sediment waves seismic profile of the study area 3 the gas hydrates are stored in sediment waves which are influenced by the original structure of the sediments and have different gas hydrate accumulation dynamics that are driven by diffusion and or leakage thus the sediment waves as a favorable reservoir of gas hydrate have research significance

near inertial internal waves and sea ice in the beaufort sea the evolution of the near inertial internal wavefield from ice free summertime conditions to ice covered wintertime conditions is examined using data from a yearlong deployment of six moorings on the beaufort continental slope from august 2008 to august 2009 when ice is absent from july to october energy is efficiently transferred from the atmosphere to the ocean generating near inertial internal waves when ice is present from november to june storms also cause near inertial oscillations in the ice and mixed layer but kinetic energy is weaker and oscillations are quickly damped damping is dependent on ice pack strength and morphology decay scales are longer in early winter november january when the new ice pack is weaker and more mobile decreasing in late winter february june when the ice pack is stronger and more rigid efficiency is also reduced as comparisons of atmospheric energy available for internal wave generation to mixed layer kinetic energies indicate that a smaller percentage of atmospheric energy is transferred to nearinertial motions when ice concentrations are 90 however large kinetic energies and shears are observed during an event on 16 december and spectral energy is elevated above garrett munk levels coinciding with the largest energy flux predicted during the deployment a significant amount of near inertial energy is episodically transferred to the internal wave band from the atmosphere even when the ocean is ice covered however damping by ice and less efficient energy transfer still leads to low arctic internal wave energy in the near inertial band increased kinetic energy below 300m when ice is forming suggests some events may generate internal waves that radiate into the arctic ocean interior

lower cretaceous strata of the sonora bisbee basin a record of the tectonomagmatic evolution of northwestern mexico lower cretaceous strata of the sonora bisbee basin record four discrete paleozoic and mesozoic magmatic episodes and indicate a previously unrecognized early cretaceous regional tectonic event along the southwestern margin of north america strata of the bisbee group in the sonora bisbee basin overlie upper jurassic strata on an angular unconformity cretaceous strata are predominantly continental fluvial deposits bisbee group sandstones are sublitharenites and litharenites rich in paleovolcanic lithic fragments detrital zircon age populations form five main groups proterozoic early permian early triassic late triassic jurassic earliest cretaceous and late early cretaceous aptian u pb zircon ages from three types of conglomerate clasts in the morita formation match these age groups 1 quartzite clasts are dominated by proterozoic ages 2 rhyolite clasts are middle jurassic ca 172 ma 3 andesite clasts are earliest cretaceous ca 140 ma proterozoic zircons and quartzite clasts were recycled from strata of the caborca block whereas permian and mesozoic grains and andesite and rhyolite clasts were derived from volcanic arc rocks to the west and northwest we identify two separate episodes of early cretaceous volcanism recorded in the basin the first between 145 and 133 ma and the second beginning ca 125 ma and continuing into the albian the presence in the sonora bisbee basin of near source fluvial detritus from the first of these episodes requires either the presence of a continental arc along the north american margin during the earliest cretaceous or the accretion of similar aged material to the margin prior to ca 130 ma neovolcanic zircon grains in the upper part of the morita formation record the initiation of volcanism in the alisitos arc an early cretaceous volcanic arc presently exposed in the peninsular ranges of baja and southern california structural stratigraphic and detrital zircon data suggest that a heretofore unrecognized episode of regional shortening uplift and incision occurred to the southwest of the study area in the interval 148 130 ma

sediment waves on the south china sea slope off southwestern taiwan implications for the intrusion of the northern pacific deep water into the south china sea abstract using an integrated multi beam bathymetry high resolution seismic profile piston core and ams 14 c dating data set the current study identified two sediment wave fields fields 1 and 2 on the south china sea slope off southwestern taiwan field 1 is located in the lower slope and sediment waves within it are overall oriented perpendicular to the direction of down slope gravity flows and canyon axis geometries morphology and internal seismic reflection configurations suggest that the sediment waves in field 1 underwent significant up slope migration field 2 in contrast is located more basinward on the continental rise instead of having asymmetrical morphology and discontinuous reflections as observed in field 1 the sediment waves in field 2 show more symmetrical morphology and continuous reflections that can be traced from one wave to another suggesting that vertical aggradation is more active and predominant than up slope migration three sediment wave evolution stages stage 1 through stage 3 are identified in both field 1 and field 2 during stage 1 the sediment waves are built upon a regional unconformity that separates the underlying mass transport complexes from the overlying sediment waves in both of these two fields there is progressive development of the sediment waves and increase in wave dimensions from the oldest stage 1 to the youngest stage 3 even though up slope migration is dominant in field 1 whereas vertical aggradation is predominant in field 2 throughout these three stages the integrated data and the depositional model show that the upper slope of the study area is strongly dissected and eroded by down slope gravity flows the net result of strong erosion is that significant amounts of sediment are transported further basinward into the lower slope by gravity flows and or turbidity currents the interactions of these currents with bottom contour currents induced by the intrusion of the northern pacific deep water into the south china sea and preexisting wavy topography in the lower slope result in the up slope migrating sediment waves in field 1 and the contourites as observed from cores ts01 and ts02 further basinward on the continental rise turbidity currents are waned and diluted whereas along slope bottom contour currents are vigorous and most likely dominate over the diluted turbidity currents resulting in the vertically aggraded sediment waves in field 2 the results from this study also provide the further evidence for the intrusion of the northern pacific deep water into the south china sea and suggest that this intrusion has probably existed and been capable of affecting sedimentation in south china sea at least since quaternary

increased continental margin slumping frequency during sea level lowstands above gas hydrate bearing sediments we present sup 14 c data on sediment samples from cores of the upper 7 m of the sediment column overlying a major continental rise gas hydrate field on the southern carolina rise and inner blake ridge offshore the southeastern united states the data show that glacial age sediments are underrepresented in the cores the observation is consistent with a previously predicted association between sea level lowstands and increased frequency of sea floor slumping on continental margins containing gas hydrates 26 refs 3 figs

decline in arctic sea ice thickness from submarine and icesat records 1958 2008 1 the decline of sea ice thickness in the arctic ocean from icesat 2003 2008 is placed in the context of estimates from 42 years of submarine records 1958 2000 described by rothrock et al 1999 2008 while the earlier 1999 work provides a longer historical record of the regional changes the latter offers a more refined analysis over a sizable portion of the arctic ocean supported by a much stronger and richer data set within the data release area dra of declassified submarine sonar measurements covering 38 of the arctic ocean the overall mean winter thickness of 3 64 m in 1980 can be compared to a 1 89 m mean during the last winter of the icesat record an astonishing decrease of 1 75 m in thickness between 1975 and 2000 the steepest rate of decrease is 0 08 m yr in 1990 compared to a slightly higher winter summer rate of 0 10 0 20 m yr in the five year icesat record 2003 2008 prior to 1997 ice extent in the dra was 90 during the summer minimum this can be contrasted to the gradual decrease in the early 2000s followed by an abrupt drop to 55 during the record setting minimum in 2007 this combined analysis shows a long term trend of sea ice thinning over submarine and icesat records that span five decades

oceanography gas hydrates on the brink huge amounts of methane are locked up in deposits that lie deep beneath the sea floor new seismic images reveal that these deposits possess unexpected features that might affect their stability

subsynoptic scale spatial variability of sea ice deformation in the western weddell sea during early summer 1 ice station polarstern ispol deployed in the western weddell sea from november 2004 to january 2005 included a study of subsynoptic scale variability in sea ice velocity and deformation using an array of 24 buoys upon deployment the ispol buoy array measured 70 km in both zonal and meridional extent and consisted of subarrays that resolved sea ice deformation on scales from 10 to 70 km across the ispol array divergence varied and did not show a distinct coherent length scale spectral analysis of divergence and shear of subarrays revealed that deformation did not vary smoothly across the array this indicates variability of internal ice stress on the scale of 10 km ice conditions within the ispol array encompassed two distinct regimes separated by shear along the continental shelf break differences in spectral power of the tidal and inertial bands across the two regions do not mirror expected differences due to spatial variability of tide induced deformation on the shelf break instead they indicate that the pack ice s internal stress behaved anisotropically on the scale of the shear zone across the buoy array 70 km

characteristics of pack ice stress in the alaskan beaufort sea ice stresses in a multiyear floe were continuously monitored over 6 months in the fall winter spring of 1993 1994 stresses sensors were installed at sites near the edge and at the center of the floe which was located in the pack ice of the alaskan beaufort sea compressive stresses in the major principal stress component varied significantly among the measurement sites being of greater magnitude and exhibiting more high frequency variations at the edge than at the center of the floe maximum compressive stresses measured at a site 400 m from the edge of the floe ranged from 100 to 300 kpa tensile stresses maximum of 50 kpa and the minor principal stress component 50 kpa were relatively constant at all measurement sites a cross correlation analysis indicates that the minor principal stress is strongly correlated to changes in the ice temperature this result suggests that the minor principal stress component provides a good first order approximation of thermally induced stresses correlation between the major principal stress component and the ice temperature at the center site was also high but weakened near the edges of the floe where the ice motion induced stresses became more significant attempts to filter the major principal stress signal to separate the thermal and ice motion induced stresses were unsuccessful this result implies that the ice motion induced stresses distinguished by variations in magnitude of the order of hours also have a significant low frequency content similar to the thermal stresses these low frequency changes occur over a period of days seasonal variations in the characteristics of the stress were also evident and are likely to reflect the developing continuity of the pack as the winter season progresses

u pb geochronology of the type nazas formation and superjacent strata northeastern durango mexico implications of a jurassic age for continental arc magmatism in north central mexico u pb ages of ignimbrites and detrital zircon analyses from middle jurassic through lowermost cretaceous strata in northeastern durango mexico indicate the age of local volcanism and the age range respectively of the jurassic continental margin arc in north central mexico where it is termed the nazas arc the type nazas formation along the rio nazas consists of red continental sandstone and siltstone ignimbrites and intermediate flows that provide an important record of the extensional jurassic nazas magmatic arc overlying shallow marine sandstone and shale of late jurassic to earliest cretaceous age represent deposits of younger extensional basins that are part of the border rift system which extended from southern arizona to the gulf of mexico the younger strata constitute volcanic litharenite and lithic arkose derived from the jurassic volcanic rocks and from basement rocks of the coahuila block to the north two ignimbrites in the upper part of the nazas formation have statistically indistinguishable ages of 170 2 and 169 2 ma the ages are consistent with their stratigraphic order and position above volcanic lithic sandstone with a maximum depositional age of ca 180 178 ma calculated from detrital zircons six detrital zircon age populations were defined from four sandstone samples n 377 zircon grains of the nazas formation and overlying la casita and carbonera formations the most prominent age clusters 10 of the entire grain population have ranges ca 1277 890 ma grenville 22 of total ca 486 310 ma early paleozoic 11 and ca 202 159 ma jurassic two populations constituting 54 of total grains the jurassic age cluster indicates that nazas arc magmatism in the region took place during the early and middle jurassic and ended by early late jurassic time the nazas formation correlates with arc related middle jurassic strata in sonora southern arizona and southeastern california that contain interbedded eolian sandstone derived from the jurassic ergs of the colorado plateau absence of interbedded eolianite in the nazas formation thus indicates that the outcrops of north central mexico were likely not translated to their present locations along a regional late jurassic transcurrent fault system as postulated by some workers detrital zircon data from the upper jurassic and lowermost cretaceous strata indicate that jurassic volcanic rocks covered the coahuila block directly north of the study area at the end of middle jurassic time sandstone composition and detrital zircon ages record erosional unroofing of the coahuila block whereby removal of lower and middle jurassic volcanic and volcaniclastic strata exposed grenville pan african and peri gondwanan basement of the block during late jurassic time

origin and evolution of fracture hosted methane hydrate deposits 1 fracture hosted methane hydrate deposits exist at many sites worldwide these sites often have hydrate present as vein and fracture fill as well as disseminated through the pore space we estimate that thousands to millions of years are required to form fracture systems by hydraulic fracturing driven by occlusion of the pore system by hydrate this time scale is a function of rates of fluid flow and permeability loss low permeability layers in a sedimentary column can reduce this time if the permeability contrast with respect to the surrounding sediments is of order 10 or greater additionally we find that tensile fracturing produced by hydrate heave around hydrate lenses is a viable fracture mechanism over all but the lowermost part of the hydrate stability zone with our coupled fluid flow hydrate formation model we assess fracture formation at four well studied hydrate provinces blake ridge offshore south carolina hydrate ridge offshore oregon keathley canyon block 151 offshore louisiana and the krishna godavari basin offshore india we conclude that hydraulic fracturing due to pore pressure buildup is reasonable only at hydrate ridge and the krishna godavari basin owing to sediment age constraints and that hydrate filled fractures observed at blake ridge and keathley canyon block 151 are formed either by hydrate heave or in preexisting fractures our findings offer new insight into the processes and time scales associated with fracture hosted hydrate deposits which help further our understanding of hydrate systems

correlation of jurassic eolian strata between the magmatic arc and the colorado plateau new u pb geochronologic data from southern arizona mature quartz rich sandstone interbedded with mesozoic magmatic arc strata in southern arizona has been previously considered correlative with the eolian pleinsbachian to toarcian navajo sandstone on the colorado plateau new u pb zircon data from the mount wrightson formation in the santa rita mountains and from the strata of cobre ridge in the pajarito mountains and in the arivaca area in southern arizona support the hypothesis that sand derived from the navajo sandstone probably did gain access to the magmatic arc and further indicate that sands extending from younger eolian units on the colorado plateau are probably present as well the mount wrightson formation accumulated from 190 ma to 170 ma corresponding to late pleinsbachian to aalenian time time scale of harland 1990 isotopic ratios from zircon fractions from the lower member of the mount wrightson formation define a discordia line with lower intercept of 184 8 ma the lower member is approximately coeval with the 188 2 ma piper gulch monzonite dated by asmerom and others 1990 which intrudes it the middle and upper members of the formation yield somewhat less precise dates that indicate deposition between 183 2 ma and 170 ma quartz rich sandstone occurs in all three members though most abundantly in the middle and upper members and in many places contains sedimentary structures diagnostic of eolian sedimentation our results suggest that sands related to lower jurassic navajo ergs and middle jurassic temple capergs gained access to the arc the age of the strata of cobre ridge is 170 5 ma eighteen fractions taken from three samples of the tuff lie in a cluster near concordia a best fit age of 169 ma is based on near concordance of one fraction and on model discordia trajectories using assumed upper intercepts sandstone horizons interbedded within the strata of cobre ridge in many cases contain sedimentary structures diagnostic of eolian sedimentation and although quartz rich in general have more volcanic detritus than sandstones in the mount wrightson formation the interval between 165 175 ma corresponds to the aalenian and bajocian stages and is within the time span represented by the temple cap and page sandstones of southern utah and northern arizona sandstone interstratified with the strata of cobre ridge may be correlative with either of those units the possibility cannot be discounted however that unconsolidated or weathered navajo equivalent sands from the upper member of the mount wrightson formation were recycled into the strata of cobre ridge these results support the models busby spera 1988 riggs and busby spera 1990 1991 suggesting that during early to middle jurassic time the magmatic arc in southern arizona was low standing and did not constitute an impediment to the south and southwestward movement of continental sediments we suggest that much of the region between the colorado plateau and the arc was topographically low and that tectonic and volcanic basins within the arc provided traps for windblown mature sands for as long as 35 m y we speculate that early to middle jurassic tectonic subsidence within the magmatic arc may have been more continuous than subsidence on the colorado plateau thus providing a depocenter in which major tectonically induced unconformities that characterize the mesozoic record in the back arc are masked by ongoing volcanic activity

sources of atmospheric ch4 in early postglacial time at the terminations that marked the ends of the oldest and younger dryas at the close of the last major glaciation atmospheric methane levels rose sharply biological sources may have played a part in this increase but it is unlikely that they could have accounted for the suddenness of the rise in methane production some fossil methane stores such as marine and continental hydrates may have become unstable at the time of the terminations and there is much geological evidence that many catastrophic releases of methane occurred it is possible that part of the increase in global atmospheric methane may have been the result of these releases which may also have played a partial role in recharging the inventory of carbon in the atmosphere biosphere system the younger dryas cooling may represent a transient response to a later reduction in greenhouse forcing when the ch4 mixing ratio in the atmosphere dropped this transient response would have been more marked in the northern hemisphere than in the southern the termination of the younger dryas may have occurred after a further catastrophic release of fossil methane

spatial and temporal characterization of sea ice deformation in late march 2007 an array of gps ice drifters was deployed in the beaufort sea as part of the sea ice experiment dynamic nature of the arctic sedna the drifters were deployed in an array designed to resolve four nested spatial scales of sea ice deformation from 10 to 140 km with the arrays maintaining appropriate shape for strain rate calculation until mid june in this paper we test whether sea ice deformation displays fractal properties in the vicinity of sedna we identify that deformation time series have different spectral properties depending on the spatial scale at the scales around 100 km deformation is a red noise process indicating the importance of the ice pack surface forcing in determining the deformation rate of sea ice at this scale at smaller scales the deformation becomes an increasingly whiter process it has pink noise properties which suggests an increasing role of dissipative processes at smaller scales at spatial scales of 10 100 km and sub daily scales there is no deformation coherence across scales coherence only becomes apparent at longer scales greater than 100 km the lack of coherence at small scales aids in understanding previous observations where correlation between 10km regions adjacent to each other varied widely with correlation coefficients between 0 3 and 1 this suggests it is not appropriate to think of sea ice as having a decorrelation length scale for deformation we find that lead scale observations of deformation are required when estimating ice growth in leads and ridging time series for the two sedna arrays we find coherence between 140 and 20 km scale deformation up to periods of 16 days this suggests sea ice deformation displays coherent deformation between 100 km scale and the scale of the beaufort sea of order 1000 km over synoptic time periods daily to weekly timescales organization of leads at synoptic and larger scales is an emergent feature of the deformation field that is caused by the smooth variation of surface forcing wind on the ice pack

massive dissociation of gas hydrate during a jurassic oceanic anoxic event in the jurassic period the early toarcian oceanic anoxic event about 183 million years ago is associated with exceptionally high rates of organic carbon burial high palaeotemperatures and significant mass extinction heavy carbon isotope compositions in rocks and fossils of this age have been linked to the global burial of organic carbon which is isotopically light in contrast examples of light carbon isotope values from marine organic matter of early toarcian age have been explained principally in terms of localized upwelling of bottom water enriched in 12c versus 13c refs 1 2 5 6 here however we report carbon isotope analyses of fossil wood which demonstrate that isotopically light carbon dominated all the upper oceanic biospheric and atmospheric carbon reservoirs and that this occurred despite the enhanced burial of organic carbon we propose that as has been suggested for the late palaeocene thermal maximum some 55 million years ago the observed patterns were produced by voluminous and extremely rapid release of methane from gas hydrate contained in marine continental margin sediments

a margin wide bsr gas hydrate assessment canada s atlantic margin abstract it is the intent of this paper to explore a significant extent of an entire passive continental margin for hydrate occurrence to understand hydrate modes of occurrence preferred geologic settings and estimate potential volumes of methane the presence of gas hydrates offshore of eastern canada has long been inferred from estimated stability zone calculations but little physical evidence has been offered an extensive set of 2 d and 3 d single and multi channel seismic reflection data comprising in excess of 140 000 line km was analyzed bottom simulating reflections bsr were unequivocally identified at seven sites ranging between 250 and 445 m below the seafloor and in water depths of 620 2850 m the combined area of the bsrs is 9311 km 2 which comprises a small proportion of the entire theoretical stability zone along the canadian atlantic margin 715 165 km 2 the bsr within at least six of these sites lies in a sedimentary drift deposit or sediment wave field indicating the likelihood of grain sorting and potential porosity and permeability reservoir development although there are a variety of conditions required to generate and recognize a bsr one might assume that these sites offer the most potential for highest hydrate concentration and exploitation total hydrate in formation at the sites of recognized bsr s is estimated at 17 to 190 10 9 m 3 or 0 28 to 3 12 10 13 m 3 of methane gas at stp although it has been shown that hydrate can exist without a bsr the results from this regional study argue that conservative estimates of the global reserve of hydrate along continental margins are necessary

response of sea ice drift to wind forcing on the northeastern newfoundland shelf observations of sea ice drift obtained with satellite tracked ice beacons in march april of 1988 and 1989 have been used to examine the response of sea ice drift to wind forcing over the northern newfoundland continental shelf the short term 5 20 days response of sea ice drift ranges from 2 6 to 5 4 of the local wind over much of the inner continental shelf which is comparable to that in the bering sea and the antarctic but larger than that in arctic sea ice drifts to the right of the local wind at angles ranging from 10 to 63 the response to wind forcing is largest near the ice edge both over the middle portions of the shelf and along the southern margins of the seasonal ice zone and during strong and steady wind of several days duration the large wind driven response of ice drift observed in this study in comparison with the arctic may result from 1 reduced levels of internal ice stress associated with the generally thin ice cover and lower areal concentration of sea ice 2 large atmospheric drag coefficients associated with the small ice floes in areas of comparatively higher ice concentration and 3 smooth ice bottom caused by melting in nearshore areas the ice to wind coupling is reduced owing to larger internal ice stresses experienced locally due to ice pileup

annual cycles of sea ice motion and deformation derived from buoy measurements in the western arctic ocean over two ice seasons data collected by two buoy arrays that operated during the ice seasons of 2014 2015 and 2016 2017 were used to characterize annual cycles of ice motion and deformation in the western arctic ocean an anomalously strong and weak beaufort gyre in 2014 2015 and 2016 2017 induced generally anticyclonic and cyclonic sea ice drift during 2014 2015 and 2016 2017 respectively cyclonic ice motion resulted in higher contributions of ice divergence to total ice deformation in 2016 2017 than in 2014 2015 in 2014 the autumn ice concentration and multiyear ice coverage were higher than in 2016 consequently the response of ice motion to wind forcing was weak and less ice deformation was observed in autumn 2014 during the autumn winter transition the ice wind speed ratio ice deformation rate and its spatial and temporal scaling exponents and localization of ice deformation decreased markedly in both 2014 2015 and 2016 2017 as a result of freeze up and consolidation of ice floes such dynamic behavior was maintained through to spring with the further thickening of ice cover ice deformation increased due to weakened ice strength as summer approached the amplitude of the annual cycle of ice deformation rate in the western arctic ocean in 2014 2015 and especially in 2016 2017 was larger than that observed during the surface heat budget of the arctic ocean sheba program in 1997 1998 we attribute this phenomenon to ice loss during the recent summers especially of thick multiyear ice

hydrocarbon plumbing systems above the snohvit gas field structural control and implications for thermogenic methane leakage in the hammerfest basin sw barents sea abstract based on the analysis of the high resolution 3d seismic data from the sw barents sea we study the hydrocarbon plumbing system above the snohvit and albatross gas field to investigate the geo morphological manifestation and the dynamics of leakage from the reservoir fluid and gas escape to the seafloor is manifested in this area as mega pockmarks 1 2 km wide large pockmarks

positive trend in the mean speed and deformation rate of arctic sea ice 1979 2007 using buoy data from the international arctic buoy program we found that the sea ice mean speed has substantially increased over the last 29 years 17 per decade for winter and 8 5 for summer a strong seasonal dependence of the mean speed is also revealed with a maximum in october and a minimum in april the sea ice mean strain rate also increased significantly over the period 51 per decade for winter and 52 for summer we check that these increases in both sea ice mean speed and deformation rate are unlikely to be consequences of a stronger atmospheric forcing instead they suggest that sea ice kinematics play a fundamental role in the albedo feedback loop and sea ice decline increasing deformation means stronger fracturing hence more lead opening and therefore a decreasing albedo this accelerates sea ice thinning in summer and delays refreezing in early winter therefore decreasing the mechanical strength of the cover and allowing even more fracturing larger drifting speed and deformation and possibly a faster export of sea ice through the fram strait the september minimum sea ice extent of 2007 might be a good illustration of this interplay between sea ice deformation and sea ice shrinking as we found that for both winter 2007 and summer 2007 exceptionally large deformation rates affected the arctic sea ice cover

the force balance of sea ice in a numerical model of the arctic ocean the balance of forces in the sea ice model of hibler 1979 is examined the model predicts that internal stress gradients are an important force in much of the arctic ocean except in summer when they are significant only off the northern coasts of greenland and the canadian archipelago a partition of the internal stress gradient between the pressure gradient and the viscous terms reveals that both are significant although they operate on very different timescales the acceleration term is generally negligible while the sum of coriolis plus sea surface tilt is small thus the seasonal average force balance in fall winter and spring is mostly between three terms of roughly equal magnitudes air drag water drag and internal stress gradients this is also true for the monthly average force balance however we find that there is a transition around the weekly timescale and that on a daily basis the force balance at a particular location and time is often between only two terms either between air drag and water drag or between air drag and internal stress gradients the model is in agreement with the observations of thorndike and colony 1982 in that the correlation between geostrophic wind forcing and the model s ice velocity field is high this result is discussed in the context of the force balance we show that the presence of significant internal stress gradients does not preclude high wind ice correlation a breakdown of the internal stress gradient into component parts reveals that the shear viscous force is far from negligible which casts strong doubt on the theoretical validity of the cavitating fluid approximation in which this component is neglected finally the role of ice pressure is examined by varying the parameter p we find a strong sensitivity in terms of the force balance as well as ice thickness and velocity

compressive shear faults within arctic sea ice fracture on scales large and small 1 we examined fracture features within arctic sea ice as revealed by landsat 7 and radarsat imagery by an aerial survey and through observations in the laboratory of specimens loaded to brittle failure under biaxial compression regardless of scale which spans the range from kilometers to millimeters the features look alike they consist mainly of narrow lineaments that traverse the field of view plus wing like and comb like secondary cracks the lineaments occasionally intersect and generally exhibit either right lateral or left lateral relative movement like strike slip faults within earth s crust we term them brittle compressive shear faults they form through the linking of en echelon arrays of deformation induced secondary cracks from an application of wing crack and comb crack mechanics we estimated the maximum compressive stress near the onset of faulting and found that our estimates compare favorably with in situ measurements by earlier investigators of ice sheet failure stresses to account for the brittle behavior of the sea ice cover we applied a recent model of the ductile to brittle transition in which the key idea is the competition between stress buildup and stress relaxation at stress concentrators in identifying the nature of sea ice fracture features we advance the view that failure occurs on many scales through highly localized as opposed to uniformly distributed deformation via the operation of scale independent mechanisms

on the scaling laws derived from ice beacon trajectories in the southern beaufort sea during the international polar year circumpolar flaw lead study 2007 2008 1 sea ice motion is an important element in mass balance calculations ice thermodynamic modeling ice management plans for industry and ecosystems studies in the historical literature sea ice motion in the beaufort sea was characterized by a predominantly anticyclonic motion during winter months with episodic reversals to cyclonic activity during summer however recent studies have shown an increase in cyclonic activity throughout the annual cycle in this paper we examine circulation in the beaufort sea based on the trajectories of 22 ice beacons launched in the franklin bay area during the international polar year circumpolar flaw lead ipy cfl study during an over wintering experiment in 2007 2008 dispersion characteristics of ice motion show that absolute zonal dispersion follows a t2 scaling law characteristic of advection associated with beaufort gyre circulation whereas absolute meridional dispersion follows a scaling law of t5 4 characteristic of floaters and dispersion in 2 d turbulence temporal autocorrelations of ice velocity fluctuations highlight definitive timescales with values of 1 2 0 7 days in the zonal meridional direction near gaussian behavior is reflected in higher order moments for ice velocity fluctuation probability density functions pdfs non gaussian behavior for absolute displacement pdfs indicates spatial heterogeneity in the ice motion fields atmospheric forcing of sea ice is explored through analysis of daily north american regional reanalysis and in situ wind data where it is shown that ice in the cfl study region travels with an average speed of approximately 0 2 and an average angle of 51 5 to the right of the surface winds during the 2007 2008 winter the results from this analysis further demonstrate seasonality in ice drift to wind ratios and angles that corresponds to stress buoy data indicative of increases in internal ice stress and connectivity due to consolidation of the seasonal ice zone to the coast and perennial ice pack during winter in the beaufort sea region

the impact of an intense summer cyclone on 2012 arctic sea ice retreat 1 this model study examines the impact of an intense early august cyclone on the 2012 record low arctic sea ice extent the cyclone passed when arctic sea ice was thin and the simulated arctic ice volume had already declined 40 from the 2007 2011 mean the thin sea ice pack and the presence of ocean heat in the near surface temperature maximum layer created conditions that made the ice particularly vulnerable to storms during the storm ice volume decreased about twice as fast as usual owing largely to a quadrupling in bottom melt caused by increased upward ocean heat transport this increased ocean heat flux was due to enhanced mixing in the oceanic boundary layer driven by strong winds and rapid ice movement a comparison with a sensitivity simulation driven by reduced wind speeds during the cyclone indicates that cyclone enhanced bottom melt strongly reduces ice extent for about 2 weeks with a declining effect afterward the simulated arctic sea ice extent minimum in 2012 is reduced by the cyclone but only by 0 15 106 km2 4 4 thus without the storm 2012 would still have produced a record minimum

migration of methane gas through the hydrate stability zone in a low flux hydrate province new high resolution seismic data show clear evidence for upward injection of methane gas well into the hydrate stability zone at the stable low methane flux blake ridge crest this movement of gaseous methane through a thermo dynamic regime where it should be trapped as hydrate suggests that dynamic migrations of gas play an important role in the interaction of subseafloor methane with the ocean in the study area none of the seismic amplitude anomalies that provide evidence for gas migration reaches the seafloor instead they terminate at the base of a highly reflective unfaulted capping layer seismic inversions of anomalous regions show 1 increased velocities beneath the hydrate stability zone suggesting less gas and 2 increased velocities within the hydrate stability zone associated with observed low amplitude chimneys and bright spots indicating increased hydrate concentrations these observations and analyses indicate that methane migrates upward as free gas hundreds of meters into the hydrate stability zone before forming hydrate the observations strongly imply that given appropriate permeable pathways free gas can escape into the ocean even in a low flux environment the hydrate stability zone is not an impermeable barrier to free gas migration

scaling properties of sea ice deformation from buoy dispersion analysis 1 a temporal and spatial scaling analysis of arctic sea ice deformation is performed over timescales from 3 h to 3 months and over spatial scales from 300 m to 300 km the deformation is derived from the dispersion of pairs of drifting buoys using the iabp international arctic buoy program buoy data sets this study characterizes the deformation of a very large solid plate the arctic sea ice cover stressed by heterogeneous forcing terms like winds and ocean currents it shows that the sea ice deformation rate depends on the scales of observation following specific space and time scaling laws these scaling properties share similarities with those observed for turbulent fluids especially for the ocean and the atmosphere however in our case the time scaling exponent depends on the spatial scale and the spatial exponent on the temporal scale which implies a time space coupling an analysis of the exponent values shows that arctic sea ice deformation is very heterogeneous and intermittent whatever the scales i e it cannot be considered as viscous like even at very large time and or spatial scales instead it suggests a deformation accommodated by a multiscale fracturing faulting processes

small scale deformation of an arctic sea ice floe detected by gps and satellite imagery abstract small scale 100 200 m deformations of an arctic sea ice floe were detected from multiple gps equipped buoys that were deployed on the same ice floe over a nine month period three deformation events were recorded at each case the event was of limited duration each lasting less than a day the events were highly compressive in nature with the area occupied by the buoy array decreasing by over half of the original area the strain rate during the deformation of the order of 10 5 s 1 is about three orders of magnitude larger than previous estimates for brittle fracturing for cracks of about 100 m in length on the 2 day time scale the strain rate became too small and none of the deformation events could be detected this suggests that satellite data with longer time scales may significantly underestimate the amount of intermittent small scale brittle failure of total deformation taken as a whole our results show the influence that large scale wind stress can have on small scale deformation however it is important to note that the impact of large scale wind stress is also dependent on the properties of sea ice as well as on the spatial and temporal evolution of the underlying forces that influence the fracturing process

triassic plutonism in southern california southward younging of arc initiation along a truncated continental margin earliest cordilleran magnatism in the southwestern united states is recorded by a belt of triassic plutons that inme protemzoic basemint of the mojave crustal province and its cratona miogeoclinal cover the belt extends from the western mojave desert through the trausverse ranges to the colorado river trough triassic plutons are predominantly alkali calcic fe and sr mriched quartz mzrdior tes and monzonites the northern part of the belt is comlx sed of two older plutonic mites 241 231 ma which are high k to shoshonitic the southern part of the belt is a younger 218 213 ma sodic alkalic suite the plutonic record in southern california suggests a short lived southward younging continental margin arc sang for eraplacement of triassic plutons sulim on a continental margin modified by s mistral tranqform faulting triassic plutonism in this region was followed by a magmatic lull prior to the onset of voluminous middle to late jurassic cordilleran arc magmatism

c band polarimetric backscattering signatures of newly formed sea ice during fall freeze up a study of the polarimetric backscattering response of newly formed sea ice types under a large assortment of surface coverage was conducted using a ship based c band polarimetric radar system polarimetric backscattering results and physical data for 40 stations during the fall freeze up of 2003 2006 and 2007 are presented analysis of the copolarized correlation coefficient showed its sensitivity to both sea ice thickness and surface coverage and resulted in a statistically significant separation of ice thickness into two regimes ice less than 6 cm thick and ice greater than 8 cm thick a case study quantified the backscatter of a layer of snow infiltrated frost flowers on new sea ice showing that the presence of the old frost flowers can enhance the backscatter by more than 6 db finally a statistical analysis of a series of temporal spatial measurements over a visually homogeneous frost flower covered ice floe identified temperature as a significant but not exclusive factor in the backscattering measurements

methane hydrate and free gas on the blake ridge from vertical seismic profiling seismic velocities measured in three drill holes through a gas hydrate deposit on the blake ridge offshore south carolina indicate that substantial free gas exists to at least 250 meters beneath the bottom simulating reflection bsr both methane hydrate and free gas exist even where a clear bsr is absent the low reflectance or blanking above the bsr is caused by lithologic homogeneity of the sediments rather than by hydrate cementation the average methane hydrate saturation above the bsr is relatively low 5 to 7 percent of porosity which suggests that earlier global estimates of methane in hydrates may be too high by as much as a factor of 3

stratigraphic evolution of blake outer ridge multichannel seismic data from a reconnaissance survey of the blake outer ridge reveal the seismic stratigraphy down to oceanic basement as well as intracrustal and mantle reflections the depositional history of the outer ridge can now be subdivided into four principal phases based on seismic stratigraphic style 1 jurassic early cretaceous sedimentation which filled in basement irregularities and leveled the sea floor by horizon s barremian time 2 early cretaceous late cretaceous deposition of a seaward thinning wedge typical of atlantic type margins its deeply eroded surface is probably equivalent to the late cretaceous miocene hiatus reflected by horizon au 3 earliest miocene current controlled deposits preferentially deposited along the xis of the incipient blake outer ridge these prograding strata which thin and dip downridge and laterally away from the ridge axis are attributed to the interaction of the florida current and western boundary undercurrent and 4 continuing early miocene preferential deposition on the ridge axis and sculpting by the western boundary undercurrent this phase is characterized by strata thinning and dipping upridge and toward the ridge axis the reversal of dip is explained to a first approximation by a steady state contour current model in which the current position is progressively shifted by the deposition five angular unconformities and associated bathymetric terraces west of the ridge crest are mapped using all lamont doherty seismic data and interpreted as having formed peneconte poraneously during phase four the areal extent of the gas hydrate clathrate horizon is also delineated it is continuous across the northern blake outer ridge and the multichannel seismic data presented here show it to extend onto the shallow blake plateau as well

the record of middle jurassic volcanism in the carmel and temple cap formations of southwestern utah altered volcanic ash beds in the middle jurassic temple cap and carmel formations in southwestern utah record a pulse of active arc related volcanism between 166 and 171 ma a second pulse between 148 and 155 ma has previously been documented in the upper jurassic morrison formation volcanic and volcaniclastic rocks of these same ages have also been identified closer to or within the arc in california in the inyo mountains the cowhole mountains the palen mountains and the central mojave desert the upper part of the volcaniclastic mount wrightson formation and the strata of cobre ridge in southern arizona are ca 170 ma in age and appear to be time correlative with the middle jurassic formations in southwestern utah the altered ash beds found in the temple cap and carmel formations typically contain phenocrysts of sanidine quartz biotite apatite zircon and titanite plagioclase was likely present originally in all of the ashes but was removed by alteration and is now found only in the temple cap red beds quartz and sanidine are absent in two crystal poor ash beds that contain two pyroxenes hornblende and biotite although major and trace element concentrations in the ash beds have been substantially modified compositions of relict phenocrysts reveal that the magmas were calc alkaline rhyolites to andesites two pyroxene two feldspar biotite and biotite apatite thermometers suggest that crystallization occurred at temperatures ranging from 740 to 910 8c hornblende geobarometry yields pressures of 1 2 kilobars for the two ash beds that contain the appropriate buffer assemblage the mafic silicates all have moderately high mg fe ratios this fact combined with the presence of hornblende biotite and titanite suggests that the phenocrysts crystallized at high oxygen fugacities similar to those of the granites of the batholiths of california the ash probably erupted from a low lying arc cut by strikeslip faults in what is now southern california and western nevada major jurassic unconformities occur near or within the ash bearing formations in southwestern utah laser fusion singlecrystal 40 ar 39 ar measurements have defined the ages of the unconformities and the associated volcanism the age of the j 1 unconformity found at the base of the temple cap formation in southwestern utah is older than ca 170 5 ma the j 2 unconformity which lies between the temple cap and carmel formations formed between ca 169 and 168 ma the origin of these unconformities is still unclear but may be related to the middle jurassic pulse of magmatism and the oblique plate convergence along the western margin of north america the age range of ash beds in the carmel formation between 166 3 and 168 0 6 0 5 ma is consistent with a bajocian bathonian boundary of ca 166 ma

escape of methane gas through sediment waves in a large methane hydrate province despite paleoceanographic evidence that large quantities of methane have escaped from marine gas hydrates into the oceans the sites and mechanisms of methane release remain largely speculative new seismic data from the blake ridge a hydrate bearing drift deposit in the western atlantic show clear evidence for methane release and suggest a new mechanism by which methane gas can escape without thermal or mechanical disruption of the hydrate bearing layer rapid post 2 5 ma formation of large sediment waves and associated seafloor erosion created permeable pathways connecting free gas to the seafloor allowing methane gas expulsion the amount of missing methane 0 6 gt is equivalent to 12 of total present day atmospheric methane our results imply that significant amounts of methane gas can bypass the hydrate stability zone and escape into the ocean mechanisms of tapping methane directly from the free gas zone such as widespread seafloor erosion should be considered when seeking the causes of large negative carbon isotope excursions in the geological record

the source and fate of massive carbon input during the latest paleocene thermal maximum lithologic faunal seismic and isotopic evidence from the blake nose subtropical western north atlantic links a massive release of biogenic methane 55 5 million years ago to a warming of deep ocean and high latitude surface waters a large perturbation in the combined ocean atmosphere carbon cycle the largest of the past 90 million years a mass extinction event in benthic faunas and a radiation of mammalian orders the deposition of a mud clast interval and seismic evidence for slope disturbance are associated with intermediate water warming massive carbon input to the global exogenic carbon cycle pelagic carbonate dissolution a decrease in dissolved oxygen and a benthic foraminiferal extinction event these events provide evidence to confirm the gas hydrate dissociation hypothesis and identify the blake nose as a site of methane release

isotopic age of the black forest bed petrified forest member chinle formation arizona an example of dating a continental sandstone zircons from the black forest bed petrified forest member chinle formation in petrified forest national park yield ages that range from late triassic to late archean grains were analyzed by multigrain tims thermal ionization mass spectrometry single crystal tims and shrimp sensitive high resolution ion microprobe multiple grain analysis yielded a discordia trajectory with a lower intercept of 207 6 2 ma which because of the nature of multiple grain sampling of a detrital bed is not considered conclusive analysis of 29 detrital zircon grains by tims yielded upb ages of 2706 6 6m a to 2066 6 ma eleven of these ages lie between 211 and 216 6 6 8 ma our statistical analysis of these grains indicates that the mean of the ages 213 6 1 7 ma reflects more analytical error than geologic variability in sources of the grains grains with ages of ca 1400 ma were derived from the widespread plutons of that age exposed throughout the southwestern cordillera and central united states twelve grains analyzed by shrimp provide 206 pb 238 u ages from 214 6 2m a to 200 6 4 ma we use these data to infer that cores of inherited material were present in many zircons and that single crystal analysis provides an accurate estimation of the age of the bed we further propose that even if some degree of reworking has occurred the very strong concentration of ages at ca 213 ma provides a maximum age for the black forest bed of 213 6 1 7 ma the actual age of the bed may be closer to 209 ma dating continental successions is very difficult when distinct ash beds are not clearly identified as is the case in the chinle formation detrital zircons in the black forest bed however are dominated by an acicular morphology with preserved delicate terminations the shape of these crystals and their inferred environment of deposition in slow water settings suggest that the crystals were not far removed from their site of deposition in space and likely not far in time plinian ash clouds derived from explosive eruptions along the early mesozoic cordilleran margin provided the crystals to the chinle basin where local conditions insured their preservation in the case of the black forest bed the products of one major eruption may dominate the volcanic contribution to the unit volcanic detritus in the chinle formation was derived from multiple distinct sources coarse pebble to cobble size material may have originated in eastern california and or western arizona where triassic plutons are exposed fine grained detritus in contrast was carried in ash clouds that derived from caldera eruptions in east central california or western nevada

accuracy of high rate gps for seismology 1 we built a device for translating a gps antenna on a positioning table to simulate the ground motions caused by an earthquake the earthquake simulator is accurate to better than 0 1 mm in position and provides the ground truth displacements for assessing the technique of high rate gps we found that the root mean square error of the 1 hz gps position estimates over the 15 min duration of the simulated seismic event was 2 5 mm with approximately 96 of the observations in error by less than 5 mm and is independent of gps antenna motion the error spectrum of the gps estimates is approximately flicker noise with a 50 decorrelation time for the position error of 1 6 s we find that for the particular event simulated the spectrum of surface deformations exceeds the gps error spectrum within a finite band more studies are required to determine whether a generally optimal bandwidth exists for a target group of seismic events

a review of methane and gas hydrates in the dynamic stratified system of the blake ridge region offshore southeastern north america abstract the blake ridge region lies on the passive margin of southeastern north america and contains a large amount of methane gas hydrate the methane and methane gas hydrate are predominantly biogenic apparently produced by co2 reduction reflection seismics indicate that bottom simulating reflectors bsrs enclose 55 000 km2 with high amplitude bsrs covering 26 000 km2 ocean drilling program odp leg 164 drilled three deep holes on a 10 km long transect sites 994 995 and 997 water depth 2770 2798 m based on sampling and geochemical thermal seismic and borehole geophysical measurements gas hydrates are most likely present between 190 and 450 m in sediment column gas hydrate is most often disseminated throughout the sediment column although concentrations occur within specific sedimentary horizons within supposed fault zones and at the base of gas hydrate stability bghs where methane recycling produces more pervasive concentrations of gas hydrate estimates of gas hydrate inventory are based on a variety of methods including geochemical proxies vertical seismic profiling electric logging and measurements of in situ methane over the entire sediment column at least 2 4 of pore space volume 1 2 sediment volume is occupied by methane gas hydrates but average and maximum estimates are 5 4 and 12 respectively extrapolation of vertical gas hydrate and methane inventory over the area containing high amplitude bsrs yields estimates of 67 406 gt gigatons 1015 g of methane gas hydrate or 9 52 gt of methane and 2 6 27 gt of methane occurring as gas bubbles below the bghs average values are 185 gt of gas hydrate and 24 gt of methane as gas hydrate any gas hydrate occurring outside the area underlain by bsrs as suggested by geochemical evidence or that associated with low amplitude bsrs may increase these estimates by an unknown factor various data give conflicting pictures of mass transport with blake ridge sediments the data can be reconciled by viewing the upper sedimentary section accumulation of gas hydrate in the blake ridge sediments depends on the amount of methane leaving the system versus the amount of methane entering the gas hydrate stability zone ghsz over geologic time although there are some point sources of methane loss from the sediments e g seafloor seeps odp site 996 of unknown magnitude most of the documented methane loss occurs through diffusion and consumption at the sulfate methane interface smi by anaerobic methane oxidation amo 2 108 mol year 1 methane entering the ghsz at a rate of 1 3 109 mol year 1 indicates a methane trapping efficiency of 85 129i measurements suggest that the blake ridge system has accumulated gas hydrate over as much as 55 million years

recent changes in the dynamic properties of declining arctic sea ice a model study 1 results from a numerical model simulation show significant changes in the dynamic properties of arctic sea ice during 2007 2011 compared to the 1979 2006 mean these changes are linked to a 33 reduction in sea ice volume with decreasing ice concentration mostly in the marginal seas and decreasing ice thickness over the entire arctic particularly in the western arctic the decline in ice volume results in a 37 decrease in ice mechanical strength and 31 in internal ice interaction force which in turn leads to an increase in ice speed 13 and deformation rates 17 the increasing ice speed has the tendency to drive more ice out of the arctic however ice volume export is reduced because the rate of decrease in ice thickness is greater than the rate of increase in ice speed thus retarding the decline of arctic sea ice volume ice deformation increases the most in fall and least in summer thus the effect of changes in ice deformation on the ice cover is likely strong in fall and weak in summer the increase in ice deformation boosts ridged ice production in parts of the central arctic near the canadian archipelago and greenland in winter and early spring but the average ridged ice production is reduced because less ice is available for ridging in most of the marginal seas in fall the overall decrease in ridged ice production contributes to the demise of thicker older ice as the ice cover becomes thinner and weaker ice motion approaches a state of free drift in summer and beyond and is therefore more susceptible to changes in wind forcing this is likely to make seasonal or shorter term forecasts of sea ice edge locations more challenging

estimating the sea ice compressive strength from satellite derived sea ice drift and ncep reanalysis data abstract satellite derived sea ice drift maps and sea level pressure from reanalysis data are used to infer upper and lower bounds on the large scale compressive strength of arctic sea ice to this end the two datasets are searched for special situations in which the wind forcing and its orientation with respect to the coastline allowed the authors to deduce a mean sea ice compressive strength from simple theory many estimates of ice compressive strength were possible for the winter of 1992 93 when the arctic high was confined to the western arctic and deep penetration of the icelandic low produced wind patterns that pushed the ice perpendicular to the coastline in the beaufort and east siberian seas the winter of 1996 97 on the other hand was characterized by a well established arctic high producing wind patterns that generally pushed ice along coastlines rather than against them results show lower and upper bounds on the sea ice compressive strength parameter of 30 and 40 kn m 2 and 35 and 45 kn

active hydrate destabilization in lake baikal siberia abstract in this paper we present new seismic and heat flow data that show the base of the hydrate stability zone bhsz in lake baikal to be locally characterized by abnormal variations in depth with distinct regions of deeper than normal and regions of shallower than normal bhsz these variations are related to strong lateral variations in heat flow and occur in close association with important rift basin faults areas of shallow bhsz are also characterized by the presence of several methane seeps and mud volcanoes at the lake floor we infer that the seeps are the surface expression of escape pathways for overpressured fluids generated by the dissociation of pre existing hydrates in response to a thermal pulse caused by an upward flow of hydrothermal fluids towards the bhsz it thus seems that present day hydrate dissociation in lake baikal is modulated by the tectonic activity in the rift rather than by climatically controlled changes in lake level or water temperature