characteristics of pebble and cobble sized clasts along the curiosity rover traverse from bradbury landing to rocknest 1 we have assessed the characteristics of clasts along curiosity s traverse to shed light on the processes important in the genesis modification and transportation of surface materials pebble to cobble sized clasts at bradbury landing and subsequently along curiosity s traverse to yellowknife bay reflect a mixing of two end member transport mechanisms the general clast population likely represents material deposited via impact processes including meteorite fragments ejecta from distant craters and impactites consisting of shocked and shock melted materials from within gale crater which resulted predominantly in larger angular clasts a subset of rounded pebble sized clasts has likely been modified by intermittent alluvial or fluvial processes the morphology of this rounded clast population indicates that water was a more important transporting agent here than at other mars sites that have been studied in situ finally we identified populations of basalt clasts and porphyritic clasts of undetermined composition by their morphologic and textural characteristics basalts are confirmed by geochemical data provided by chemcam

constraints on the geologic history of home plate materials provided by clast morphology and texture 1 we quantified and classified the size shape roundness and texture of 333 loose surface particles clasts along the spirit rover traverse from martian solar days 750 to 1889 these data provided clues to origin transport mechanisms association with geologic units and other alteration processes clasts average 15 mm in size and 0 73 sphericity and display a low degree of roundness textures include vesicular smooth and rough flat faceted and granular platy clasts characteristics are comparable to those for clasts outside the home plate region mapped geologic units around home plate are characterized by distinctive clast morphologic parameters and only minor adjustments were made to unit boundaries and definitions mapped by others no new units are suggested by the data consistent roundness values seen from unit to unit coupled with the correlation between unit boundaries and clast characteristics in and outside home plate indicate that no appreciable transport has occurred subsequent to fragmentation from outcrop and emplacement rather clasts have been emplaced through volcanic activity and or impact and have been subjected to weathering processes since that time we interpret vesicular and flat faceted clasts texture types 1 3 to be derived from mitcheltree ridge basalts and the presence of these clasts to provide a general outline of the original extent of this unit platy granular textured clasts texture type 5 are derived from the upper home plate unit

distribution of primary and secondary features in the pahrump hills outcrop gale crater mars as seen in a mars descent imager mardi sidewalk mosaic abstract the mars science laboratory curiosity rover conducted a reconnaissance traverse across the pahrump hills outcrop within gale crater from sols 780 797 during the traverse the mars descent imager mardi acquired a continuous imaging record of primary and secondary sedimentary features throughout the outcrop the characteristics of the features laminae resistant features fractures gray clasts and their spatial distribution provide insight into the processes that contributed to the formation of pahrump hills thin regular laminae mm scale are ubiquitous in the bedrock implying that depositional processes at that scale did not change appreciably during deposition of the mudstone succession at pahrump hills higher bedrock slopes correlate with undulatory bedrock surfaces bedrock with elevated mg contents and fractures exhibiting wide raised edges these collective features are consistent with increased erosional resistance caused by greater quantities of erosionally resistant mg bearing cement within the bedrock permitted by coarser grain sizes resistant features exhibit a range of morphologies elevated mg contents and do not deflect laminae within the bedrock their characteristics implicate the involvement of mg enriched fluids in a late diagenetic overprint affecting the bedrock the variations of fracture fill and edge morphologies and chemistries further suggest repeated fracturing and fluid interaction events within the strata exposed at pahrump hills gray clasts strongly resemble fragments eroded from sandstone horizons interspersed throughout the pahrump hills outcrop

the hydraulics of a stratified fluid flowing through a contraction the steady hydraulics of a continuously stratified fluid flowing from a stagnant reservoir through a horizontal contraction was studied experimentally and theoretically as the channel narrows the flow accelerates through a succession of virtual controls at each of which the flow passes from subcritical to supercritical with respect to a particular wave mode when the narrowest section acts as a control the flow is asymmetric about the narrowest section supercritical in the divergent section and selfsimilar throughout the channel with increased flow rate a new enclosed self similar solution was found with level isopycnals and velocity uniform with depth

ploughing the deep sea floor bottom trawling is a fishing technique whereby heavy nets and gear scrape along the sea bed and is shown here to disturb sediment fluxes and modify the sea floor morphology over large spatial scales the direct impact of bottom trawling on local fish populations has received much attention but trawling also affects other aspects of the ocean environment this paper shows that bottom trawling a commercial practice in which heavy nets and gear are dragged along the ocean floor induces sediment reworking and erosion causing the gradient of the sea floor to become smoother over time this reduces the morphological complexity of deep sea environments the authors draw parallels between the effects of bottom trawling at sea and intensive agriculture on land with the important difference that on land ploughing takes place once or twice a year whereas at sea bottom trawling can be a frequent occurrence bottom trawling is a non selective commercial fishing technique whereby heavy nets and gear are pulled along the sea floor the direct impact of this technique on fish populations1 2 and benthic communities3 4 has received much attention but trawling can also modify the physical properties of seafloor sediments water sediment chemical exchanges and sediment fluxes5 6 most of the studies addressing the physical disturbances of trawl gear on the seabed have been undertaken in coastal and shelf environments7 8 however where the capacity of trawling to modify the seafloor morphology coexists with high energy natural processes driving sediment erosion transport and deposition9 here we show that on upper continental slopes the reworking of the deep sea floor by trawling gradually modifies the shape of the submarine landscape over large spatial scales we found that trawling induced sediment displacement and removal from fishing grounds causes the morphology of the deep sea floor to become smoother over time reducing its original complexity as shown by high resolution seafloor relief maps our results suggest that in recent decades following the industrialization of fishing fleets bottom trawling has become an important driver of deep seascape evolution given the global dimension of this type of fishery we anticipate that the morphology of the upper continental slope in many parts of the world s oceans could be altered by intensive bottom trawling producing comparable effects on the deep sea floor to those generated by agricultural ploughing on land

stereo observation of lakes and coastal zones using aster imagery abstract one of the unique features of the visible and near infrared vnir subsystem of the advanced spaceborne thermal emission and reflection radiometer aster is the near infrared back looking view which is obtained 55 s later than the corresponding nadir view although the stereoscopic capability derived from a combination of these two views was originally designed for use in land applications serendipitous observation has shown that it also represents a promising source of data over water bodies in fact when coupled with surface temperature measurements derived from the sensor s thermal infrared tir component stereo viewing forms a powerful observational capability that can be exploited in the monitoring of lake and marine environments one important aspect introduced by the stereo system is the capability to measure the short term displacements associated with surface currents and waves by comparing the nadir and back looking views in initial results presented here surface motion was deduced from the displacement of a ship wake appearing in the sun glitter regime of an aster image of the izu shoto islands which lie to the southwest of tokyo bay japan within the natural limitations imposed by spatial and temporal resolutions this measurement was found to be consistent with simultaneous surface current values derived from a nearby shore based high frequency hf radar system the success of this basic comparison introduces the possibility that stereo imaging from space if well tuned to follow the motion of surface slicks and other surface features within the sun glitter regime could provide a future means of observing surface current on a global scale data from the vnir stereo system also highlights the influence of observational geometry in the case of a surface with sun glitter this often manifests as a brightness reversal between the nadir and back looking views in which relatively bright dark features at nadir appear dark bright in the back looking view such a region of brightness reversal robr can be indicative of a locally rough or smooth surface texture as may be found for example in the vicinity of internal waves rough or ship wakes smooth simple analysis based on a back to nadir ratio of relative radiances shows that the signal strengths measured by aster within a robr can yield a crude estimate of the mean square surface slope which is an important parameter in theories of sea surface roughness imaging by devices such as synthetic aperture radar sar several other potential applications of vnir stereo data in coastal zone and lake monitoring are considered here including the study of internal waves in the strait of gibraltar derivation of wind velocity at cloud height swell wave propagation suspended sediment transport marine traffic monitoring and ship wake patterns as the reflectivity of water in the near infrared reverses from low to high in the presence of sun glitter most of the applications discussed here involve glitter and hence some discussion of the influence of sensor view geometry is presented the general conclusion of the paper is that future missions such as the advanced land observing satellite alos which aim to deploy high spatial resolution stereo viewing systems primarily for land applications should also return data of considerable value in oceanography and limnology particularly if their observational geometry can be adjusted to permit the imaging of sun glitter from water surfaces

geochemistry of the bagnold dune field as observed by chemcam and comparison with other aeolian deposits at gale crater the curiosity rover conducted the first field investigation of an active extraterrestrial dune this study of the bagnold dunes focuses on the chemcam chemical results and also presents findings on the grain size distributions based on the chemcam remote micro imager and mars hand lens imager images these active dunes are composed of grains that are mostly 150 m grain size dump piles have shown that coarser grains 150 250 m are enriched in the mafic elements fe and mn suggesting a larger content in olivine compared to smaller grains 150 m of the bagnold dunes moreover the chemistry of soils analyzed in the vicinity of the dunes indicates that they are similar to the dune material all these observations suggest that the olivine content determined by x ray diffraction of the 150 m grain size sample should be considered as a lower limit for the bagnold dunes

understanding fine grained river sediment dispersal on continental margins studies of fine grained sediment dispersal in the marine environment have documented diversity in the behavior of depositional systems on continental margins with different oceanographic conditions and morphologies based on the pattern and nature of sediment accumulation for twenty three case studies we propose there are five basic types of dispersal systems and these are related to river wave tide and margin characteristics data suggest that the type of dispersal system on any margin can be predicted with knowledge of sediment load mean significant wave height tidal range and continental shelf width at a river mouth and from these a hierarchical decision tree is developed analysis of the dispersal system type of more than 100 river mouths reveals that proximal accumulation dominated pad and marine dispersal dominated mdd systems are most abundant but estuarine accumulation dominated ead systems also are anticipated to be numerous globally research quantifying marine sediment dynamics in these system types is needed although less common the size and nature of subaqueous delta clinoform sdc and canyon captured cc systems also warrant future attention to their study strong correlations between physical characteristics i e significant wave height and tidal range and the depth and distance to the nearest maximum shelf depocenter provide evidence that in reality a continuum exists between the system types the process related partitioning of sediment in the five different types of marine dispersal systems has important implications for understanding the stratigraphic record and the cycling of carbon

a near uniform basin wide sea level fluctuation of the mediterranean sea abstract a new basin wide oscillation of the mediterranean sea is identified and analyzed using sea level observations from the ocean topography experiment topex poseidon satellite altimeter and a numerical ocean circulation model more than 50 of the large scale nontidal and non pressure driven variance of sea level can be attributed to this oscillation which is nearly uniform in phase and amplitude across the entire basin the oscillation has periods ranging from 10 days to several years and has a magnitude as large as 10 cm the model suggests that the fluctuations are driven by winds at the strait of gibraltar and its neighboring region including the alboran sea and a part of the atlantic ocean immediately to the west of the strait winds in this region force a net mass flux through the strait of gibraltar to which the mediterranean sea adjusts almost uniformly across its entire basin with depth independent pressure perturbations the wind driven response can be explained in part by wind setup

effect of commercial trawling on the deep sedimentation in a mediterranean submarine canyon abstract in order to study sediment accumulation rates in the palamos submarine canyon northwestern mediterranean during the last century three sediment cores were extracted from the canyon axis at depths of 450 1200 and 1750 m respectively where instrumented moorings were previously located estimated sedimentation rates based on 210 pb and 137 cs profiles suggest that the contemporary trends of sediment transfer and accumulation in the canyon may be different from secular trends during the seventies a two fold increase of the sediment accumulation rate took place at the 1750 m depth site this change has been associated to trawling activities and is attributed to the rapid technical development that the local trawling fleet underwent during the seventies the surroundings and rims of submarine canyons are frequently targeted by commercial trawling fisheries an activity that may enhance the input of resuspended particles into canyons and eventually trigger sediment gravity flows our results suggest that the effects of trawling over the dynamics of the seafloor may extend further and deeper from the fishing grounds eventually extending to bathyal depths hence the anthropogenic influence on the sedimentary budget of some deep submarine environments may be more important than previously thought

calcium sulfate veins characterized by chemcam curiosity at gale crater mars the curiosity rover has analyzed abundant light toned fracture fill material within the yellowknife bay sedimentary deposits the chemcam instrument coupled with mastcam and chemcam remote micro imager images was able to demonstrate that these fracture fills consist of calcium sulfate veins many of which appear to be hydrated at a level expected for gypsum and bassanite anhydrite is locally present and is found in a location characterized by a nodular texture an intricate assemblage of veins crosses the sediments which were likely formed by precipitation from fluids circulating through fractures the presence of veins throughout the entire similar to 5 m thick yellowknife bay sediments suggests that this process occurred well after sedimentation and cementation lithification of those sediments the sulfur rich fluids may have originated in previously precipitated sulfate rich layers either before the deposition of the sheepbed mudstones or from unrelated units such as the sulfates at the base of mount sharp the occurrence of these veins after the episodes of deposition of fluvial sediments at the surface suggests persistent aqueous activity in relatively nonacidic conditions

a model of thermal conductivity for planetary soils 2 theory for cemented soils 1 a numerical model of heat conduction through particulate media made of spherical grains cemented by various bonding agents is presented the pore filling gas conductivity volume fraction and thermal conductivity of the cementing phase are tunable parameters cement fractions 0 001 0 01 in volume have small effects on the soil bulk thermal conductivity a significant conductivity increase factor 3 8 is observed for bond fractions of 0 01 to 1 in volume in the 1 to 15 bond fraction domain the conductivity increases continuously but less intensely 25 100 conductivity increase compared to a 1 bond system beyond 15 of cements the conductivity increases vigorously and the bulk conductivity rapidly approaches that of bedrock the composition of the cements i e conductivity has little influence on the bulk thermal inertia of the soil especially if the volume of bond 10 these results indicate that temperature measurements are sufficient to detect cemented soils and quantify the amount of cementing phase but the mineralogical nature of the bonds and the typical grain size are unlikely to be determined from orbit on mars a widespread surface unit characterized by a medium albedo 0 19 0 26 and medium high thermal inertia 200 600 j s 0 5 m 2 k 1 has long been hypothesized to be associated with a duricrust the fraction of cement required to fit the thermal data is less than 1 5 by volume this small amount of material is consistent with orbital observations confirming that soil cementation is an important factor controlling the thermal inertia of the martian surface

is the faroe bank channel overflow hydraulically controlled abstract the overflow of dense water from the nordic seas through the faroe bank channel fbc has attributes suggesting hydraulic control primarily an asymmetry across the sill reminiscent of flow over a dam however this aspect has never been confirmed by any quantitative measure nor is the position of the control section known this paper presents a comparison of several different techniques for assessing the hydraulic criticality of oceanic overflows applied to data from a set of velocity and hydrographic sections across the fbc these include 1 the cross stream variation in the local froude number including a modified form that accounts for stratification and vertical shear 2 rotating hydraulic solutions using a constant potential vorticity layer in a channel of parabolic cross section and 3 direct computation of shallow water wave speeds from the observed overflow structure though differences exist the three methods give similar answers suggesting that the fbc is indeed controlled with a

trawling induced daily sediment resuspension in the flank of a mediterranean submarine canyon abstract commercial bottom trawling is one of the anthropogenic activities causing the biggest impact on the seafloor due to its recurrence and global distribution in particular trawling has been proposed as a major driver of sediment dynamics at depths below the reach of storm waves but the issue is at present poorly documented with direct observations this paper analyses changes in water turbidity in a tributary valley of the la fonera palamos submarine canyon whose flanks are routinely exploited by a local trawling fleet down to depths of 800 m a string of turbidimeters was deployed at 980 m water depth inside the tributary for two consecutive years 2010 2011 the second year an adcp profiled the currents 80 m above the seafloor the results illustrate that near bottom water turbidity at the study site is heavily dominated both in its magnitude and temporal patterns by trawling induced sediment resuspension at the fishing ground resuspended sediments are channelised along the tributary in the form of sediment gravity flows being recorded only during working days and working hours of the trawling fleet these sediment gravity flows generate turbid plumes that extend to at least 100 m above the bottom reaching suspended sediment concentrations up to 236 mg l 1 close to the seafloor 5 m above bottom a few hours after the end of daily trawling activities water turbidity progressively decreases but resuspended particles remain in suspension for several hours developing bottom and intermediate nepheloid layers that reach background levels 2 mg l 1 before trawling activities resume the presence of these nepheloid layers was recorded in a ctd turbidimeter transect conducted across the fishing ground a few hours after the end of a working day these results highlight that deep bottom trawling can effectively replace natural processes as the main driving force of sediment resuspension on continental slope regions and generate increased near bottom water turbidity that propagates from fishing grounds to wider and deeper areas via sediment gravity flows and nepheloid layer development

increasing sediment accumulation rates in la fonera palamos submarine canyon axis and their relationship with bottom trawling activities previous studies conducted in la fonera palamos submarine canyon nw mediterranean found that trawling activities along the canyon flanks cause resuspension and transport of sediments toward the canyon axis 210pb chronology supported by 137cs dating applied to a sediment core collected at 1750 m in 2002 suggested a doubling of the sediment accumulation rate since the 1970s coincident with the rapid industrialization of the local trawling fleet the same canyon area has been revisited a decade later and new data are consistent with a sedimentary regime shift during the 1970s and also suggest that the accumulation rate during the last decade could be greater than expected approaching 2 4 cm yr 1 compared to 0 25 cm yr 1 pre 1970s these results support the hypothesis that commercial bottom trawling can substantially affect sediment dynamics and budgets on continental margins eventually initiating the formation of anthropogenic depocenters in submarine canyon environments

mahli at the rocknest sand shadow science and science enabling activities 1 during martian solar days 57 100 the mars science laboratory curiosity rover acquired and processed a solid sediment sample and analyzed its mineralogy and geochemistry with the chemistry and mineralogy and sample analysis at mars instruments an aeolian deposit herein referred to as the rocknest sand shadow was inferred to represent a global average soil composition and selected for study to facilitate integration of analytical results with observations from earlier missions during first time activities the mars hand lens imager mahli was used to support both science and engineering activities related to sample assessment collection and delivery here we report on mahli activities that directly supported sample analysis and provide mahli observations regarding the grain scale characteristics of the rocknest sand shadow mahli imaging confirms that the rocknest sand shadow is one of a family of bimodal aeolian accumulations on mars similar to the coarse grained ripples interrogated by the mars exploration rovers spirit and opportunity in which a surface veneer of coarse grained sediment stabilizes predominantly fine grained sediment of the deposit interior the similarity in grain size distribution of these geographically disparate deposits support the widespread occurrence of bimodal aeolian transport on mars we suggest that preservation of bimodal aeolian deposits may be characteristic of regions of active deflation where winnowing of the fine sediment fraction results in a relatively low sediment load and a preferential increase in the coarse grained fraction of the sediment load the compositional similarity of martian aeolian deposits supports the potential for global redistribution of fine grained components combined with potential local contributions

characteristics of pebble and cobble sized clasts along the curiosity rover traverse from sol 100 to 750 terrain types potential sources and transport mechanisms abstract we combine the results of orbitally derived morphologic and thermal inertia data with in situ observations of abundance size morphologic characteristics and distribution of pebble to cobble sized clasts along the curiosity rover traverse our goals are to characterize rock sources and transport history and improve our ability to predict upcoming terrain there are ten clast types with nine types interpreted as sedimentary rocks only type 3 clasts had morphologies indicative of significant wear through transport thus most clast types are indicative of nearby outcrops or prior presence of laterally extensive sedimentary rock layers consistent with the erosional landscape a minor component may reflect impact delivery of more distant material types 1 and 4 are heavily cemented sandstones likely associated with a caprock layer types 5 and 6 and possibly 7 are pebble rich sandstones with varying amounts of cement leading to varying susceptibility to erosion wear type 3 clasts are rounded pebbles likely transported and deposited alluvially then worn out of pebbly sandstone conglomerate types 9 and 10 are poorly sorted sandstones with type 9 representing fragments of square top type layers and type 10 deriving from basal or other mt sharp layers types 2 8 and 9 are considered exotics there are few clear links between clast type and terrain surface roughness particularly in identifying terrain that is challenging for the rover to navigate orbital data may provide a reasonable prediction of certain end member terrains but the complex interplay between variables that contribute to surface characteristics makes discriminating between terrain types from orbital data problematic prediction would likely be improved through higher resolution thermal inertia data

gale crater and impact processes curiosity s first 364 sols on mars abstract impact processes at all scales have been involved in the formation and subsequent evolution of gale crater small impact craters in the vicinity of the curiosity msl landing site and rover traverse during the 364 sols after landing have been studied both from orbit and the surface evidence for the effect of impacts on basement outcrops may include loose blocks of sandstone and conglomerate and disrupted fractured sedimentary layers which are not obviously displaced by erosion impact ejecta blankets are likely to be present but in the absence of distinct glass or impact melt phases are difficult to distinguish from sedimentary volcaniclastic breccia and conglomerate deposits the occurrence of individual blocks with diverse petrological characteristics including igneous textures have been identified across the surface of bradbury rise and some of these blocks may represent distal ejecta from larger craters in the vicinity of gale distal ejecta may also occur in the form of impact spherules identified in the sediments and drift material possible examples of impactites in the form of shatter cones shocked rocks and ropy textured fragments of materials that may have been molten have been observed but cannot be uniquely confirmed modification by aeolian processes of craters smaller than 40 m in diameter observed in this study are indicated by erosion of crater rims and infill of craters with aeolian and airfall dust deposits estimates for resurfacing suggest that craters less than 15 m in diameter may represent steady state between production and destruction the smallest candidate impact crater observed is 0 6 m in diameter the observed crater record and other data are consistent with a resurfacing rate of the order of 10 mm myr considerably greater than the rate from impact cratering alone but remarkably lower than terrestrial erosion rates

high resolution thermal inertia mapping from the mars global surveyor thermal emission spectrometer abstract high resolution thermal inertia mapping results are presented derived from mars global surveyor mgs thermal emission spectrometer tes observations of the surface temperature of mars obtained during the early portion of the mgs mapping mission thermal inertia is the key property controlling the diurnal surface temperature variations and is dependent on the physical character of the top few centimeters of the surface it represents a complex combination of particle size rock abundance exposures of bedrock and degree of induration in this work we describe the derivation of thermal inertia from tes data present global scale analysis and place these results into context with earlier work a global map of nighttime thermal bolometer based thermal inertia is presented at 1 4 per pixel resolution with approximately 63 coverage between 50 s and 70 n latitude global analysis shows a similar pattern of high and low thermal inertia as seen in previous viking low resolution mapping significantly more detail is present in the high resolution tes thermal inertia this detail represents horizontal small scale variability in the nature of the surface correlation with albedo indicates the presence of a previously undiscovered surface unit of moderate to high thermal inertia and intermediate albedo this new unit has a modal peak thermal inertia of 180 250 j m 2 k 1 s 1 2 and a narrow range of albedo near 0 24 the unit covering a significant fraction of the surface typically surrounds the low thermal inertia regions and may comprise a deposit of indurated fine material local 3 km resolution maps are also presented as examples of eolian fluvial and volcanic geology some impact crater rims and intracrater dunes show higher thermal inertias than the surrounding terrain thermal inertia of aeolian deposits such as intracrater dunes may be related to average particle size outflow channels and valleys consistently show higher thermal inertias than the surrounding terrain generally correlations between spatial variations in thermal inertia and geologic features suggest a relationship between the hundred meter scale morphology and the centimeter scale surface layer

hydraulic control of sill flow with bottom friction abstract the hydraulics of strait and sill flow with friction is examined using a reduced gravity model it is shown that friction moves the critical or control point from the sill to a location downstream if the strait has constant width the control point lies where the bottom slope is the negative of the drag coefficient cd if cd exceeds the bottom slope everywhere the flow cannot be controlled in the classical sense that energy and flow force are minimized friction also decreases the minimum obstacle height required to establish hydraulically controlled flow in the classical laboratory towing experiment also friction greatly encourages the establishment of stationary hydraulic jumps in the lee of the sill and under certain conditions gives rise to stationary jumps on the upstream face of the obstacle some consequences of these results for deep ocean overflows are given using the iceland faroe overflow as an example

frictional processes in straits friction and mixing can be dynamically significant in straits as in many oceanographic situations for weak time dependent homogeneous flows geostrophy friction and acceleration can all play roles in limiting the flow through a strait and the ratio of the geostrophic elevation difference across the strait to the frictional difference along the strait may be of importance in more general situations a specific question for quasi steady exchange flows through straits concerns the influences of friction and entrainment on hydraulic control within the context of layered models these effects tend to drive a flow towards hydraulic criticality in the downstream direction and to shift control points downstream however friction and entrainment also induce vertical gradients in velocity and density rendering layered models dubious in such situations the conditions for hydraulic control have been uncertain even for a homogeneous fluid there is an apparent contradiction between control conditions based on a similarity assumption for the velocity profile on the one hand and on the speed of long waves on the other the resolution of this contradiction is discussed it seems that if the frictional forces only involve local flow properties then inviscid long waves are arrested at the control section though this is shifted from its location for inviscid flow but that if flow derivatives along the channel are involved the condition changes for a homogeneous flow with shear internal friction and bottom friction the control section is shifted downstream partway to where it would be for a slab flow with bottom friction while the parameterization of bottom friction actually seems to be reasonably well established the nature and quantification of internal and lateral frictional processes are uncertain in a rotating system secondary cross strait flows are expected to be driven by the vertical gradient of the vertical reynolds stress and can provide estimates of the magnitude of bottom and internal friction

numerical modeling of bottom trawling induced sediment transport and accumulation in la fonera submarine canyon northwestern mediterranean sea bottom trawling leads to recurrent sediment resuspension events over fishing grounds recent studies have shown how bottom trawling can drive seascape reshaping at large spatial scales and enhance sediment transport in submarine canyons which subsequently impacts deep sea ecosystems present knowledge on the transfer and accumulation of sediment flows triggered by bottom trawling is based on localized and infrequent measurements whilst a more complete picture of the process is needed the present work focuses on the modeling of sediment transport and accumulation resulting from trawling activities in la fonera submarine canyon northwestern mediterranean sea thus contributing to an improved assessment of trawling impacts based on mooring data within a canyon gully we use an inverse model to retrieve the unknown time series of resuspension due to trawling over the fishing grounds this resuspension is later used as forcing for the direct problem we simulate trawling induced flows through the canyon and provide a 3d visualization of potential trawling impacts on sediment dynamics including the identification of the propagation patterns of sediments resuspended by trawling flows coming from shallower fishing grounds are funneled through canyon flank gullies towards the canyon axis with part of the resuspended sediment reaching the continental rise out of the canyon across the open continental slope trawling induced sediment flows promote sediment accumulation beyond the canyon mouth given the wide geographical distribution of bottom trawling our results have far reaching implications that go much beyond la fonera submarine canyon our study represents a starting point for the assessment of the sedimentary impact of bottom trawling in deep continental margins

diagenetic origin of nodules in the sheepbed member yellowknife bay formation gale crater mars the sheepbed member of the yellowknife bay formation in gale crater contains millimeter scale nodules that represent an array of morphologies unlike those previously observed in sedimentary deposits on mars three types of nodules have been identified in the sheepbed member in order of decreasing abundance solid nodules hollow nodules and filled nodules a variant of hollow nodules whose voids have been filled with sulfate minerals this study uses mast camera mastcam and mars hand lens imager mahli images from the mars science laboratory curiosity rover to determine the size shape and spatial distribution of the sheepbed nodules the alpha particle x ray spectrometer apxs and chemcam instruments provide geochemical data to help interpret nodule origins based on their physical characteristics spatial distribution and composition the nodules are interpreted as concretions formed during early diagenesis several hypotheses are considered for hollow nodule formation including origins as primary or secondary voids the occurrence of concretions interpreted in the sheepbed mudstone and in several other sedimentary sequences on mars suggests that active groundwater systems play an important role in the diagenesis of martian sedimentary rocks when concretions are formed during early diagenetic cementation as interpreted for the sheepbed nodules they have the potential to create a taphonomic window favorable for the preservation of martian organics

the strait surface outflow a three dimensional primitive equation model is used to simulate the flow through a narrow strait the flow within a strait has a simple two layered structure with the interface located approximately at the middepth however the flow experiences a sharp transition at the strait s exit the flow jumps from a subcritical velocity inside the strait to a supercritical velocity immediately outside the strait correspondingly the density interface also slopes sharply upward to the surface after exiting the strait the surface outflow tends to form an anticyclonic gyre to the right of the strait s exit most of the outflow water is trapped within the gyre although some manages to escape through a narrow coastal current these model results compare well with observations in the tiran strait and in the gibraltar strait and alboran sea the model study indicates that the flow transition at the strait s exit and the formation of an anticyclonic gyre are unique features of the nonlinear self advection of the density current

multilayer hydraulic control with application to the alboran sea circulation abstract the flow of a single layer of fluid along a channel of variable dimensions is hydraulically controlled when long gravity waves can no longer propagate upstream at the cross section of minimum area for a multilayer fluid it is shown that a controlled situation exists when there is a separate geometrical extremum for each of the gravity wave modes the structure of each control section must be different reflecting the different vertical structures of the internal modes a channel with three layers of different density is studied in some detail as an analogue to the principal water masses in the alboran sea and strait of gibraltar with the lowest layer at rest and the surface rigid the control for the slowest second internal mode is primarily a width contraction while that for the first mode must also involve a reduction in bottom depth the problem separates into control problems for each mode that for the first mode is a classic lock exchange problem with just two layers controlled at the s

the origin and evolution of the peace vallis fan system that drains to the curiosity landing area gale crater mars the landing site for the curiosity rover is located at the distal end of the peace vallis fan in gale crater peace vallis fan covers 80 km2 and is fed by a 730 km2 catchment which drains an upland plains area through a 15 km wide gap in the crater rim valley incision into accumulated debris delivered sediment through a relatively low density valley network to a main stem channel to the fan an estimated total fan volume of 0 9 km3 matches the calculated volume of removal due to valley incision 0 8 km3 and indicates a mean thickness of 9 m the fan profile is weakly concave up with a mean slope of 1 5 for the lower portion numerous inverted channels outcrop on the western surface of the fan but on the eastern portion such channels are rare suggesting a change in process from distributary channel domination on the west to sheet flow on the eastern portion of the fan runoff discharge watershed area to produce the fan is estimated to be more than 600 m perhaps as much as 6000 m indicating a hydrologic cycle that likely lasted at least thousands of years atmospheric precipitation possibly snow not seepage produced the runoff based on topographic data peace vallis fan likely onlapped bradbury rise and spilled into a topographic low to the east of the rise this argues that the light toned fractured terrain within this topographic low corresponds to the distal deposits of peace vallis fan and in such a setting lacustrine deposits are expected

a habitable fluvio lacustrine environment at yellowknife bay gale crater mars the curiosity rover discovered fine grained sedimentary rocks which are inferred to represent an ancient lake and preserve evidence of an environment that would have been suited to support a martian biosphere founded on chemolithoautotrophy this aqueous environment was characterized by neutral ph low salinity and variable redox states of both iron and sulfur species carbon hydrogen oxygen sulfur nitrogen and phosphorus were measured directly as key biogenic elements by inference phosphorus is assumed to have been available the environment probably had a minimum duration of hundreds to tens of thousands of years these results highlight the biological viability of fluvial lacustrine environments in the post noachian history of mars

a dynamic explanation for the origin of the western mediterranean organic rich layers the eastern mediterranean sapropels are among the most intensively investigated phenomena in the paleoceanographic record but relatively little has been written regarding the origin of the equivalent of the sapropels in the western mediterranean the organic rich layers orls orls are recognized as sediment layers containing enhanced total organic carbon that extend throughout the deep basins of the western mediterranean and are associated with enhanced total barium concentration and a reduced diversity dysoxic but not anoxic benthic foraminiferal assemblage consequently it has been suggested that orls represent periods of enhanced productivity coupled with reduced deep ventilation presumably related to increased continental runoff in close analogy to the sapropels we demonstrate that despite their superficial similarity the timing of the deposition of the most recent orl in the alboran sea is different than that of the approximately coincident sapropel indicating that there are important differences between their modes of formation we go on to demonstrate through physical arguments that a likely explanation for the origin of the alboran orls lies in the response of the western mediterranean basin to a strong reduction in surface water density and a shoaling of the interface between intermediate and deep water during the deglacial period furthermore we provide evidence that deep convection had already slowed by the time of heinrich event 1 and explore this event as a potential agent for preconditioning deep convection collapse important differences between heinrich like and deglacial like influences are highlighted giving new insights into the response of the western mediterranean system to external forcing

mixing in the romanche fracture zone the romanche fracture zone is a major gap in the mid atlantic ridge at the equator which is deep enough to allow significant eastward flows of antarctic bottom water from the brazil basin to the sierra leone and guinea abyssal plains while flowing through the romanche fracture zone bottom water properties are strongly modified due to intense vertical mixing the diapycnal mixing coefficient in the bottom water of the romanche fracture zone is estimated by using the finestructure of ctd profiles the microstructure of high resolution profiler data and by constructing a heat budget from current meter data the finestructure of density profiles is described using the thorpe scaleslt it is shown from microstructure data taken in the bottom water that the ozmidov scale lo is related to lt by the linear relationship lo 5 0 95lt similar to other studies which allows an estimate of the diapycnal mixing coefficient using the osborn relation the thorpe scale and the diapycnal mixing coefficient estimates show enhanced mixing downstream eastward of the main sill of the romanche fracture zone in this region a mean diapycnal mixing coefficient of about 1000 3 1024 m2 s21 is found for the bottom water estimates of cross isothermal mixing coefficient derived from the heat budgets constructed downstream of the current meter arrays deployed in the romanche fracture zone and the nearby chain fracture zone are in agreement with the finestructure estimates of the diapycnal mixing coefficient within the romanche fracture zone although the two fracture zones occupy only 0 4 of the area covered by the sierra leone and guinea abyssal plains the diffusive heat fluxes across the 1 4 8c isotherm in the romanche and chain fracture zones are half that found over the abyssal plains across the 1 88c isotherm emphasizing the role of these passages for bottom water property modifications

synoptic sections of the denmark strait overflow we report on a rapid high resolution survey of the denmark strait overflow dso as it crosses the sill the first such program to incorporate full water column velocity profiles in addition to conventional hydrographic measurements seven transects with expendable profilers over the course of one week are used to estimate volume transport as a function of density our observations reveal the presence of a strongly barotropic flow associated with the nearly vertical front dividing the arctic and atlantic waters the seven section mean transport of water denser than 27 8 is 2 7 0 6sv while the mean transport of water colder than 2 0 c is 3 8 0 8 sv although this is larger than the 2 9 sv of 2 c water measured by a 1973 current meter array we find that a sampling of our sections equivalent to the extent of that array also measures 2 9sv of cold water both the structure and magnitude of the measured flow are reproduced well by a high resolution numerical model of buoyancy driven exchange with realistic topography

martian aeolian activity at the bagnold dunes gale crater the view from the surface and orbit the first in situ investigation of an active dune field on another planetary surface occurred in 2015 2016 when the msl curiosity rover investigated the bagnold dunes on mars hirise images show clear seasonal variations that are in good agreement with atmospheric model predictions of intra annual sand flux and migration directions that together indicate that the campaign occurred during a period of low wind activity curiosity surface images show that limited changes nevertheless occurred with movement of large grains particularly on freshly exposed surfaces two occurrences of secondary grain flow on the slip face of namib dune and a slump on a freshly exposed surface of a large ripple these changes are seen at sol to sol time scales grains on a rippled sand deposit and unconsolidated dump piles show limited movement of large grains over a few hours during which mean friction speeds are estimated at 0 3 0 4 m s 1 overall the correlation between changes and peak rems winds is moderate with high wind events associated with changes in some cases but not in others suggesting that other factors are also at work the distribution of rems 1 hz wind speeds show a tail up to the 20 m s 1 showing that even higher speed winds occur non aeolian triggering mechanisms are also possible the low activity period at the dunes documented by curiosity provides clues to processes that dominated in the martian past under conditions of lower obliquity

hapke mixture modeling applied to vnir spectra of mafic mineral mixtures and shergottites implications for quantitative analysis of satellite data 2018 the authors meteoritics planetary science published by wiley periodicals inc on behalf of the meteoritical society met this is an open access article under the terms of the creative commons attribution license which permits use distribution and reproduction in any medium provided the original work is properly cited

paleoclimate of mars as captured by the stratigraphic record in gale crater a kilometers thick sedimentary sequence in gale crater exhibits stratigraphic changes in lithology that are consistent with transitions in aqueous and climatic conditions purported to be global in scale the sequence is divided into two formations where the lower formation exhibits a net transition in mineralogy from clay sulfate to sulfate oxide assemblages and is separated from the overlying upper formation by an erosional unconformity superposition and crater counts suggest strata in the lower formation lie along the noachian hesperian time stratigraphic boundary whereas beds in the upper formation which lack signatures indicative of clay minerals or sulfates are thinner more regularly spaced and clearly younger the observed stratigraphic trends are consistent with the rocks at gale crater recording a global transition from a climate favorable to clay mineral formation to one more favorable to forming sulfates and other salts

morphology and texture of particles along the spirit rover traverse from sol 450 to sol 745 1 we quantified and classified the shape roundness size and texture of 935 loose surface particles along the spirit rover traverse from sols 450 745 to assess origin transport and other alteration mechanisms that altered particles during and after formation variation in particle morphologic parameters along traverse is consistent with crossing mapped geologic unit boundaries texture is divided into four types vesicular smooth and flat faceted rough and flat faceted and very rough sphericity and roundness are intermediate and low respectively comparable to particles moved by high energy transport or to crushed particles this indicates intermittent high energy emplacement or modification of a single lithology rather than systematic continuous low energy abrasion or wear over time comparison with particle morphology at other mars landing sites is consistent with the hypothesis that no secondary systematic transport or wide scale chemical alteration was active at a significant enough level to alter macromorphology in particular particle morphology at the mars pathfinder site shows stronger evidence of abrasion than along the spirit traverse suggesting mars pathfinder particles have undergone abrasion processes that particles in this study area have not additionally morphology indices have correlation coefficients near zero indicating that a fluvial transport mechanism is likely not responsible for morphology morphology and texture are instead related to origin and composition rather than subsequent modification morphology and texture support a volcanic origin possibly without modification but most likely altered primarily by ballistic impact implying that the spirit landing site and traverse may be utilized in the future as a standard site for characterization of impact derived morphology

global distribution of bedrock exposures on mars using themis high resolution thermal inertia 1 we investigate high thermal inertia surfaces using the mars odyssey thermal emission imaging system themis nighttime temperature images 100 m pixel spatial sampling for this study we interpret any pixel in a themis image with a thermal inertia over 1200 j m 2 k 1 s 1 2 as bedrock which represents either in situ rock exposures or rock dominated surfaces three distinct morphologies ranked from most to least common are associated with these high thermal inertia surfaces 1 valley and crater walls associated with mass wasting and high surface slope angles 2 floors of craters with diameters 25 km and containing melt or volcanics associated with larger high energy impacts and 3 intercrater surfaces with compositions significantly more mafic than the surrounding regolith in general bedrock instances on mars occur as small exposures less than several square kilometers situated in lower albedo 350 j m 2 k 1 s 1 2 and relatively dust free dust cover index 0 95 regions however there are instances that do not follow these generalizations most instances are concentrated in the southern highlands with very few located at high latitudes poleward of 45 n and 58 s suggesting enhanced mechanical breakdown probably associated with permafrost overall mars has very little exposed bedrock with only 960 instances identified from 75 s to 75 n with likely 3500 km 2 exposed representing 1 ofthe total surface area these data indicate that mars has likely undergone large scale surface processing and reworking both chemically and mechanically either destroying or masking a majority of the bedrock exposures on the planet

volumetric estimates of ancient water on mount sharp based on boxwork deposits gale crater mars while the presence of water on the surface of early mars is now well known the volume distribution duration and timing of the liquid water have proven difficult to determine this study makes use of a distinctive boxwork rich sedimentary layer on mount sharp to map fluid based cementation from orbital imagery and estimate the minimum volume of water present when this sedimentary interval was formed the boxwork structures on mount sharp are decameter scale light toned polygonal ridges that are unique compared to previous observations of martian fractured terrain because they are parallel sided ridges with dark central linear depressions this texture and the sedimentary setting strongly imply that the ridges are early diagenetic features formed in the subsurface phreatic groundwater zone high resolution orbital imagery was used to map the volume of light toned cemented ridges based on the cemented volume a minimum of 5 25 105 m 3 of cement was deposited within the fractures using a brine composition based on observations of other martian cements and modeling the degree of evaporation each volume of cement requires 800 6700 pore volumes of water so the mapped boxwork ridge cements require a minimum of 0 43 km 3 of water this is a significant amount of groundwater that must have been present at the 3620 m level 1050 m above the current floor of gale crater providing both a new constraint on the possible origins of mount sharp and a possible future science target for the curiosity rover where large volumes of water were present and early mineralization could have preserved a once habitable environment

accumulation rates of major constituents of hemipelagic sediments in the deep alboran sea a centennial perspective of sedimentary dynamics the accumulation rates of sediment and major constituents in three different geographic areas of the alboran sea have been assessed by means of 210pb and 137cs concentration profiles mixing is present in the top layer of the sedimentary column with mixing coefficients estimated to range from 0 2 to 15 cm2 yr 1 overall apparent sedimentation rates for the last 100 years range from 0 014 to 0 182 g cm 2 yr 1 and show a tendency to decrease with distance to the coast and water column depth however specific characteristics of the sea floor for each physiographic environment govern the actual patterns of sediment accumulation particularly noticeable are the feeding role of submarine canyons the trapping effect of slope terraces and the isolation caused by ridges sediment accumulation induced by turbiditic flows is also observed north of the almeria oran area excess 210pb inventories and surface concentrations reveal a net effect of sediment focussing and point to the role of bottom nepheloid layers in supplying a significant fraction of sediments to the deep areas this is also evidenced by comparison of bottom sediment with the sediment trap data available from the malaga area we estimate that the particle advective input below 30 m above the bottom accounts for as much as 50 70 of the material that is ultimately deposited onto the sea floor the greater abundance of lithogenic material in the malaga zone 80 reflects its larger input in the western alboran sea conversely carbonate contents increase from less than 20 in this area to about 30 in the almeria oran zone reflecting the lesser importance of the dilution by lithogenic components biogenic silica was only detected in some surface samples and no significant preservation was observed below the eh boundary abundance and accumulation rates of organic matter are in accordance with the spatial patterns of primary production in the alboran sea higher in the western part due to the presence of the western alboran gyre however near bottom redistribution leads to the homogenisation of organic matter concentrations in bottom sediments of any given area finally from comparisons with sediment trap data the degradation of organic matter has been estimated to be approximately 30 40 of what reaches the bottom

mixing and entrainment in hydraulically driven stratified sill flows author posting cambridge university press 2004 this article is posted here by permission of cambridge university press for personal use not for redistribution the definitive version was published in journal of fluid mechanics 515 2004 415 443 doi 10 1017 s0022112004000576

understanding the red sea response to sea level here we outline a new pragmatic methodology to derive relative sea level estimates from central red sea oxygen isotope records based on a previously published model in this paper the methodology is described in detail and it is shown that sea level change is the dominant factor responsible for the recorded variability in red sea 18o pdb for sea level changes greater than 12 m variables such as temperature or net evaporation are shown to have relatively small effects on the oxygen isotope record the modelled 18o pdb to sea level relationship is given in terms of a fifth order polynomial which may be used to describe relative sea level from central red sea oxygen isotope records we show how established sea level records from fossil reef terraces for the last 20 kyr are successfully simulated from central red sea oxygen isotope records we also examine the spatial variability of 18o pdb in the basin over the last 13 kyr

hydraulic interpretation of direct velocity measurements in the bab al mandab abstract acoustic doppler current profiler velocity measurements in the bab al mandab during the period june 1995 march 1996 are used to assess the hydraulic character of the exchange flow the strait is 150 km long and contains two distinct geometrical choke points the hanish sill and perim narrows the authors use a three layer approximation of the monthly mean velocity and density structure at the sill and narrows to calculate the phase speeds of the first and second internal long gravity waves the first second mode is generally characterized by in phase out of phase motions of the two interfaces the calculations take cross strait topographic variations into consideration by using a piecewise linear representation of the actual bottom the resulting phase speeds are used to determine whether the flow is subcritical supercritical or critical with respect to the first and second modes subcritical supercritical means that the two wave pairs corresponding to a given mode propagate in opposite

quantitative morphology of rocks at the mars pathfinder landing site 1 we adapt and test a standard terrestrial technique of assessing morphology quantitatively for use with sites on mars based on two dimensional equations and particle outlines whereby images of particles obtained remotely may yield dimensionless numerical shape and roundness values consistent with previous knowledge of the lithology and sedimentary transport history our test site was the particle rich rock garden at the mars pathfinder landing site a location where the primary geologic processes and lithology have been determined by other means a total of 575 particles were assessed in terms of size sphericity elongation and roundness qualitative roundness was determined for 460 particles particles are mostly pebble to cobble sized and have an average sphericity of 0 75 elongation of 0 63 and relative roundness of 0 083 69 of particles are subangular or subrounded particle sphericity is unimodal with a size sphericity profile matching trends for terrestrial populations of similar lithology and elongations nearly identical to those for particles at vikings 1 and 2 this matches the predictions for a site with the single overall lithology implied from other analyses roundness data indicate one or possibly two particle populations representing the primary processes that likely affected particle roundness most strongly impact and catastrophic flooding finally we tested a hypothesis suggesting that darker smaller more angular particles comprise a population transported through impact cratering while larger less dark more rounded particles are associated with catastrophic flood transport the opposite result is seen larger particles throughout the rock garden are more angular than smaller ones

decreasing overflow from the nordic seas into the atlantic ocean through the faroe bank channel since 1950 the overflow of cold dense water from the nordic seas across the greenland scotland ridge and into the atlantic ocean is the main source for the deep water of the north atlantic ocean this flow also helps drive the inflow of warm saline surface water into the nordic seas the faroe bank channel is the deepest path across the ridge and the deep flow through this channel accounts for about one third of the total overflow previous work has demonstrated that the overflow has become warmer and less saline over time here we show using direct measurements and historical hydrographic data that the volume flux of the faroe bank channel overflow has also decreased estimating the volume flux conservatively we find a decrease by at least 20 per cent relative to 1950 if this reduction in deep flow from the nordic seas is not compensated by increased flow from other sources it implies a weakened global thermohaline circulation and reduced inflow of atlantic water to the nordic seas

spatial distribution of sedimentation rate increases in blanes canyon caused by technification of bottom trawling fleet abstract a detailed study of 15 sediment cores from blanes canyon and its immediate surroundings nw mediterranean sea was conducted to compare historic sedimentation rates and evaluate the possible impact of bottom trawling intensification on the sedimentary regimes over the past 50 years the canyon axis and flanks as well as the adjacent open slope were sampled at water depths ranging from 300 m to 2200 m grain size dry bulk density and 210pb concentration profiles were measured to assess possible changes in sedimentation rates over the last century and their temporal and spatial relationship to bottom trawling effort sedimentation rates in the upper canyon axis 900 1200 m had the highest rates of 0 9 2 1 cm yr 1 quantified since the 1970s farther downcanyon sedimentation rates increased two to five times after the 1970s from 0 1 0 2 cm yr 1 to 0 2 0 8 cm yr 1 which coincides with a rapid growth of the total engine power of the fishing fleet operating in the study area the enhanced sedimentation rates occur downslope of the main fishing grounds and decrease downcanyon as the distance from trawling grounds increases these results highlight the ability of bottom trawling to resuspend bottom sediments leading to net erosion of the canyon rims and flanks in turn large volumes of sediment are advected towards the canyon s interior ultimately increasing sediment deposition along the canyon axis natural sedimentation rates at similar along canyon distance from shore in the untrawled continental slope 900 1500 m and in the lower canyon axis 1500 2200 m are comparable 0 08 0 20 cm yr 1 suggesting distance from coastal sediment sources as the main control on regional sedimentation in deeper parts of the margin while submarine canyons have been regarded as preferential cross margin conduits for sediment dispersal they can also potentially function as modern depocenters for trawling induced sedimentation

the deepwater exchange cycle in indian arm british columbia abstract a silled fjord on the british columbia coast indian arm was used to study the exchange processes controlling deepwater exchange in fjords bottom water renewal took place during the winter of 1984 85 hydraulic control of the exchange is exerted over the long sill which restricts access to the fjord the maximum density at the sill occurs during neap tides no distinct peaks in the velocity at the sill are observed during periods of inflow reduced vertical mixing over the long sill during periods of neap tides sets the timing of the bottom water exchange during each inflow over the 1984 85 winter about 20 of the water in the fjord was replaced these exchanges occurred over periods of 5 10 days between the exchange years diffusion of the water in the basin is important in conditioning the water for the next exchange event the vertical diffusion coefficient k t was determined from an analysis of the salinity data and was found to be related to the buoyancy frequency n by the relationship k v n 1 6

observations and preliminary science results from the first 100 sols of msl rover environmental monitoring station ground temperature sensor measurements at gale crater we describe preliminary results from the first 100 sols of ground temperature measurements along the mars science laboratory s traverse from bradbury landing to rocknest in gale the ground temperature data show long term increases in mean temperature that are consistent with seasonal evolution deviations from expected temperature trends within the diurnal cycle are observed and may be attributed to rover and environmental effects fits to measured diurnal temperature amplitudes using a thermal model suggest that the observed surfaces have thermal inertias in the range of 265 375 j m 2 k 1 s 1 2 which are within the range of values determined from orbital measurements and are consistent with the inertias predicted from the observed particle sizes on the uppermost surface near the rover ground temperatures at gale crater appear to warm earlier and cool later than predicted by the model suggesting that there are multiple unaccounted for physical conditions or processes in our models where the mars science laboratory msl descent engines removed a mobile layer of dust and fine sediments from over rockier material the diurnal temperature profile is closer to that expected for a homogeneous surface suggesting that the mobile materials on the uppermost surface may be partially responsible for the mismatch between observed temperatures and those predicted for materials having a single thermal inertia models of local stratigraphy also implicate thermophysical heterogeneity at the uppermost surface as a potential contributor to the observed diurnal temperature cycle

subaqueous shrinkage cracks in the sheepbed mudstone implications for early fluid diagenesis gale crater mars the sheepbed mudstone yellowknife bay formation gale crater represents an ancient lakebed now exhumed and exposed on the martian surface the mudstone has four diagenetic textures including a suite of early diagenetic nodules hollow nodules and raised ridges and later diagenetic light toned veins that crosscut those features in this study we describe the distribution and characteristics of the raised ridges a network of short spindle shaped cracks that crosscut bedding do not form polygonal networks and contain two to four layers of isopachous erosion resistant cement the cracks have a clustered distribution within the sheepbed member and transition laterally into concentrations of nodules and hollow nodules suggesting that these features formed penecontemporaneously because of the erosion resistant nature of the crack fills their three dimensional structure can be observed cracks that transition from subvertical to subhorizontal orientations suggest that the cracks formed within the sediment rather than at the surface this observation and comparison to terrestrial analogs indicate that these are syneresis cracks cracks that formed subaqueously syneresis cracks form by salinity changes that cause sediment contraction mechanical shaking of sediment or gas production within the sediment examination of diagenetic features within the sheepbed mudstone favors a gas production mechanism which has been shown to create a variety of diagenetic morphologies comparable to the raised ridges and hollow nodules the crack morphology and the isopachous layered cement fill show that the cracks were filled in the phreatic zone and that the sheepbed mudstone remained fluid saturated after deposition and through early burial and lithification

large sediment waves over the gulf of roses upper continental slope nw mediterranean recently acquired swath bathymetry and seismic datasets on the gulf of roses continental slope revealed the presence of large sediment waves that have developed between 200 and 400 m water depth geometric parameters were computed from the multibeam dataset and the obtained results showed mean sediment wave lengths of 2000 m and maximum heights of 60 m the analysis of seismic profiles showed the general architecture of the late quaternary deposits over the gulf of roses outer shelf and slope the outer continental shelf is characterized by morphological erosional features affecting the upper part of the most recent seismic unit over the continental slope five main unconformity bounded seismic units are differentiated with sediment waves developed in all of them the sediment waves observed over the continental slope are presumably generated by bottom currents intensified during major dense shelf water cascading events flowing downslope at an oblique angle with respect to the main bathymetry

maximal two layer exchange over a sill and through the combination of a sill and contraction with barotropic flow the analysis of two layer exchange flow through contractions with a barotropic component treated by armi farmer 1986 is extended to include exchange flows over sills and through a combination of a sill and contraction it is shown that exchange over a sill is fundamentally different from exchange through a contraction control at the sill crest acts primarily through the deeper layer into which the sill projects and only indirectly controls the surface layer this asymmetry in the control results in asymmetrical flows the interface depth above the crest is not one half the total depth as assumed in other studies by analogy with flow through contractions but is somewhat deeper the maximal exchange rate is less than for flow through a contraction of equal depth when both a sill and a contraction are present the contraction influences control at the sill crest only if it lies between the sill and the source of denser water the response to barotropic flow is also asymmetrical the transition to single layer flow occurs at much lower speeds for a barotropic component in one direction than the other results of the analysis are applied to exchange flow through the strait of gibraltar which includes both a sill and a contraction it is shown that maximal exchange conditions apply throughout part of the tidal cycle and observations illustrate several of the analytical predictions for barotropic flows including the formation of fronts single layer flow submaximal exchange and reverse flow

martian fluvial conglomerates at gale crater observations by the mars science laboratory mast camera mastcam in gale crater reveal isolated outcrops of cemented pebbles 2 to 40 millimeters in diameter and sand grains with textures typical of fluvial sedimentary conglomerates rounded pebbles in the conglomerates indicate substantial fluvial abrasion chemcam emission spectra at one outcrop show a predominantly feldspathic composition consistent with minimal aqueous alteration of sediments sediment was mobilized in ancient water flows that likely exceeded the threshold conditions depth 0 03 to 0 9 meter average velocity 0 20 to 0 75 meter per second required to transport the pebbles climate conditions at the time sediment was transported must have differed substantially from the cold hyper arid modern environment to permit aqueous flows across several kilometers

seasonal fluctuations of deep megabenthos finding evidence of standing stock accumulation in a flux rich continental slope abstract throughout the deep oceans diversity in the benthos peaks at intermediate slope depths in the western mediterranean lower slope an accumulation of biomass but not diversity at depths of 1200 1350 m has been observed however the precise causes of this biomass peak are unknown we examined the patterns of megafauna benthic biomass in the catalan sea open slope from 900 to 1750 m depth expanding the results in the context of the whole continental margin sampling was carried out by combining an otter trawl maireta system otms and an agassiz trawl during four different seasons in 2008 2009 at the same time current speed temperature and salinity were obtained year round by means of near bottom deployed sensors current meters and temperature conductivity sensors total biomass followed an inverted u shaped pattern peaking at depths of 1050 1350 m range related ecological forcings between shallower and deeper species may have caused this biomass accumulation at intermediate slope depths we also report on the seasonal variations of biomass in the studied depth range identifying a dynamic zone above 1000 m depth where populations of highly mobile species perform year round migrations throughout the slope and a more static region below 1000 m i e the twilight zone end with substantially less inter annual variations the arrival of new western mediterranean deep water from the deep basin to the lower slope in march may may have driven the accumulation of biomass at 900 and 1050 m depth over the same period in addition an adjacent submarine canyon was sampled with the same procedures to characterize its benthic megafauna community analyses revealed higher diversity but not biomass inside the canyon than in the adjacent open slope and a significantly different assemblage composition between the two habitats these results strengthen the concept of submarine canyons as hotspots of biodiversity and underline the importance of their conservation as diversity repositories

elemental geochemistry of sedimentary rocks at yellowknife bay gale crater mars sedimentary rocks examined by the curiosity rover at yellowknife bay mars were derived from sources that evolved from an approximately average martian crustal composition to one influenced by alkaline basalts no evidence of chemical weathering is preserved indicating arid possibly cold paleoclimates and rapid erosion and deposition the absence of predicted geochemical variations indicates that magnetite and phyllosilicates formed by diagenesis under low temperature circumneutral ph rock dominated aqueous conditions analyses of diagenetic features including concretions raised ridges and fractures at high spatial resolution indicate that they are composed of iron and halogen rich components magnesium iron chlorine rich components and hydrated calcium sulfates respectively composition of a cross cutting dike like feature is consistent with sedimentary intrusion the geochemistry of these sedimentary rocks provides further evidence for diverse depositional and diagenetic sedimentary environments during the early history of mars

distribution ecology and taphonomy of the organism trace scolicia in northeast atlantic deep sea sediments abstract the organism burrow scolicia was studied in deep sea sediment cores from several regions of the northeast atlantic including the iceland faeroe ridge rockall plateau and reykjanes ridge the data comprised sedimentological and physical measurements and x ray radiographs scolicia generally can be observed only in radiographs grain size and sorting of sediments control the distribution of the echinoids that produce scolicia if developed under optimum ecological conditions in well sorted coarse silts to fine sands scolicia dominates the biogenic structures with its very characteristic ichnofabrics its distribution pattern is influenced mainly by bottom currents sedimentation rate and the faunal association indirectly a dependence on water depth also seems to exist the preservation and recognition of scolicia in lithified sediments needs special conditions these include restricted competition by organisms of the deeper burrowing tiers its generation within the optimum sediment grain size or its production at the sand silt mud interface

intense mixing of antarctic bottom water in the equatorial atlantic ocean the spreading of antarctic bottom water the densest global scale water mass is highly constrained by ocean floor topography in the atlantic ocean the mid atlantic ridge confines this water mass mainly to the western basins the bottom waters in the eastern basins being renewed by flows through gaps in the ridge1 one such gap is the romanche fracture zone a large offset of the ridge which straddles the equator it has been observed2 that sills within this fracture zone block the passage of waters colder than 0 9 c warmer less dense waters passing over the sills appear to cascade downslope where they are modified by mixing here we present direct measurements which quantify these processes the flow is vertically sheared and exhibits remarkably intense turbulence comparable to that seen at the ocean surface in the presence of winds of l0ms 1 this turbulence mixes the densest waters passing through the fracture zone with the warmer overlying waters so that the coldest waters exiting this region have been warmed by 0 6 c during transit topographic obstructions and turbulent mixing together thus determine the properties of the flows renewing the deepest waters of the atlantic ocean s eastern basins

mineralogy of a mudstone at yellowknife bay gale crater mars sedimentary rocks at yellowknife bay gale crater on mars include mudstone sampled by the curiosity rover the samples john klein and cumberland contain detrital basaltic minerals calcium sulfates iron oxide or hydroxides iron sulfides amorphous material and trioctahedral smectites the john klein smectite has basal spacing of similar to 10 angstroms indicating little interlayer hydration the cumberland smectite has basal spacing at both similar to 13 2 and similar to 10 angstroms the larger spacing suggests a partially chloritized interlayer or interlayer magnesium or calcium facilitating h2o retention basaltic minerals in the mudstone are similar to those in nearby eolian deposits however the mudstone has far less fe forsterite possibly lost with formation of smectite plus magnetite late noachian early hesperian or younger age indicates that clay mineral formation on mars extended beyond noachian time

aeolian processes in proctor crater on mars sedimentary history as analyzed from multiple data sets 1 proctor crater is a 150 km diameter crater in noachis terra within the southern highlands of mars the analysis leading to the sedimentary history incorporates several data sets including imagery elevation composition and thermal inertia mostly from the mars global surveyor mission the resulting stratigraphy reveals that the sedimentary history of proctor crater has involved a complex interaction of accumulating and eroding sedimentation aeolian features spanning much of the history of the crater interior dominate its surface including large erosional pits stratified beds of aeolian sediment sand dunes erosional and depositional streaks dust devil tracks and small bright bed forms that are probably granule ripples long ago up to 450 m of layered sediment filled the crater basin now exposed in eroded pits on the crater floor these sediments are probably part of an ancient deposit of aeolian volcaniclastic material since then some quantity of this material has been eroded from the top layers of the strata small bright dune forms lie stratigraphically beneath the large dark dune field relative to the large dark dunes the bright bed forms are immobile although in places their orientations are clearly influenced by the presence of the larger dunes their prevalence in the crater and their lack of compositional and thermal distinctiveness relative to the crater floor suggests that these features were produced locally from the eroding basin fill dust devil tracks form during the spring and summer following a west southwesterly wind early in the spring the dust devils are largely restricted to dark patches of sand as the summer approaches dust devil tracks become more plentiful and spread to the rest of the crater floor indicating that the entire region acquires an annual deposit of dust that is revealed by seasonal dust devils the dark dunes contain few dust devil tracks suggesting that accumulated dust is swept away directly by saltation rather than by the passage of dust devils spectral deconvolution indicates that the dark dunes have infrared spectra consistent with basalt like materials the average thermal inertia calculated from thermal emission spectrometer bolometric temperatures is 277 17 j m 2 s 0 5 k 1 leading to an effective grain size of 740 170 mm which is consistent with coarse sand and within the range expected for martian sand the coarse sand that composes the large dune field may have originated from outside the crater saltating in from the southwest most of the transport pathway that delivered this sand to the dune field has since been eroded away or buried the sand was transported to the east center of the crater floor where beneath the present day dunes a 50 m high mound of sand has accumulated dune slip faces indicate a wind regime consisting of three opposing winds some of these wind directions are correlated with the orientations of dust devil tracks and bright bed forms the combination of a tall mound of sand and three opposing winds is consistent with a convergent wind regime which produces the large reversing transverse and star dunes that dominate the dune field the dark dunes have both active slip faces and seemingly inactive slip faces suggesting that the dunes vary spatially in their relative activity nevertheless the aeolian activity that has dominated the history of proctor crater still continues today index terms 5415 planetology solid surface planets erosion and weathering 5470 planetology solid surface planets surface materials and properties 5410 planetology solid surface planets

sediment accumulation rates in the southern barcelona continental margin nw mediterranean sea derived from 210pb and 137cs chronology sediment cores were collected from the southern barcelona continental margin including the foix canyon in order to study sediment accumulation in this area for this purpose 210pb 137cs and to a lesser extent 239 240pu and heavy metals were determined in sediment sections using state of the art techniques 210pb concentration profiles and 137cs 239 240pu and heavy metals profile features were used to establish the sediment chronologies further information was also obtained from granulometric analyses the magnitudes studied and correlated in this work included surface activities mixing rates accumulation rates and inventories sediments on the continental shelf showed a varied degree of mixing except possibly cn 23 sedimentation rates were relatively small and the sedimentary material probably had a common origin cores from the slope showed less mixing and in cores cn 36 and eb 2 located in the foix canyon axis the 137cs signal vs depth was clear and well preserved accumulation rates and total 210pb inventories were maximum in core cn 36 at mid slope of the canyon which was considered to be an active depocenter core cn 38 collected on the open slope showed a much smaller accumulation rate therefore it was concluded that shelf material is being transported alongshore by the prevailing currents and becomes focused in the canyon which is acting as a natural trap within the canyon this material is preferentially deposited at a mid slope depocenter little extra material reaches the lower canyon area in this area core eb 2 appeared to show signs of the presence of resuspended material possibly derived from the canyon walls finally observed changes in sedimentation rates during the 1930s could not be explained on the basis of current knowledge and this is suggested to be an important subject for further research

hydraulically controlled front trapping on a tidal flat 1 we report observations of baroclinic surface fronts in skagit bay the fronts formed repeatedly in very shallow 0 7 m deep water along the edge of a tidal channel shortly after the incoming tide flooded the adjacent tidal flat and eventually departed from channel edge as the flood tide progressed the fronts were surface convergence zones trapping gps drifters and other flotsam across front salinity temperature jumps were a few practical salinity units a few degrees with freshwater on the channel side across front transects of velocity from mobile and fixed acoustic doppler current profilers and density from mobile and fixed conductivity temperature depth profilers are presented composite froude numbers indicate that supercritical flow over the flats initially held fronts near the channel edge as flood tide progressed depth averaged flow speeds decreased while internal wave speeds increased owing to increasing depths and density gradients flow over the flats eventually became subcritical at which point fronts departed from the channel edge the front then formed the leading edge of a shallow around 0 3 m thick freshwater plume which propagated across the flats against the incoming tidal flow water was then exchanged between the channel and flats with a channel edge composite froude number near 0 5 consistent with mixing induced reduction in channel flats exchange the across channel velocity shear was correlated with the across channel wind consistent with a simple eddy viscosity model strong winds prevented plume propagation

diapycnal mixing associated with an overflow in a deep submarine canyon abstract in order to close the global overturning circulation the buoyancy loss to the atmosphere associated with the formation of deep and bottom water at high latitudes must be balanced by buoyancy gain elsewhere in case of water that is not in contact with the atmosphere except in its formation region the required buoyancy gain is accomplished primarily by diapycnal mixing recent observations suggest that a significant portion of the diapycnal buoyancy fluxes in the abyss is associated with overflows in submarine valleys or canyons especially on the flanks of slow spreading mid ocean ridges in the present study hydrographic and velocity data from an overflow across a sill rising 1000 m above the floor of the rift valley of the mid atlantic ridge near 36 n were used to infer the associated diapycnal mixing the cross sill density gradients are characterized by a vertical dipole with an upper layer of streamwise density increase overlying a lower layer where the density decreases along the flow this is qualitatively consistent with the effects of diapycnal mixing transferring buoyancy from the upper into the lower layer hydrographic and velocity profiles provide evidence for strong mixing associated with the overflow across the sill in addition to thick layers that are susceptible to shear instability there are numerous density overturns indicating a spatially averaged diffusivity of order 10 2 m 2 s 1 inversions of the density equation reveal that the cross sill gradients can be accounted for either by adiabatic vertical advection or by vertical eddy diffusion although the adiabatic solutions are considered energetically implausible because they require upwelling in the layer of cross sill density increase eddy diffusive solutions both with and without adiabatic downwelling are characterized by diffusivity profiles attaining local maxima of order 10 2 m 2 s 1 250 m above the sill depth the vertical structure of the inversion derived diffusivities is consistent with the thorpe scale based estimates and with observations from overflows in major ocean passages which also are often characterized by local diffusivity maxima of order 10 2 m 2 s 1 a few 100 m above sill depth combining the diffusivity profiles near the sill with budget derived bulk estimates for 150 km of rift valley implies that 50 of the mixing in the rift valley is associated with overflows while the remainder is caused by other processes including the breaking of tidally forced internal waves