sandy contourite drift in the late miocene rifian corridor morocco reconstruction of depositional environments in a foreland basin seaway abstract the rifian corridor was a seaway between the atlantic ocean and the mediterranean sea during the late miocene the seaway progressively closed leading to the messinian salinity crisis in the mediterranean sea despite the key palaeogeographic importance of the rifian corridor patterns of sediment transport within the seaway have not been thoroughly studied in this study we investigated the upper miocene sedimentation and bottom current pathways in the south rifian corridor the planktic and benthic foraminifera of the upper tortonian and lower messinian successions allow us to constrain the age and palaeo environment of deposition encased in silty marls deposited at 150 300 m depth there are i 5 to 50 m thick mainly clastic sandstone bodies with unidirectional cross bedding and ii 50 cm thick mainly clastic tabular sandstone beds with bioturbation mottled silt lack of clear base or top and bi gradational sequences furthermore seismic facies representing elongated mounded drifts and associated moat are present at the western mouth of the seaway we interpret these facies as contourites the products of a westward sedimentary drift in the south rifian corridor the contourites are found only on the northern margin of the seaway thus suggesting a geostrophic current flowing westward along slope and then northward this geostrophic current may have been modulated by tides by comparing these fossil examples with the modern gulf of cadiz we interpret these current dominated deposits as evidence of late miocene mediterranean overflow into the atlantic ocean through the rifian corridor this overflow may have affected late miocene ocean circulation and climate and the overflow deposits may represent one of the first examples of mainly clastic contourites exposed on land

high resolution image treatment in ichnological core analysis initial steps advances and prospects abstract ichnological studies have become popular during the last decades particularly those associated with the development of two major concepts the ichnofacies model and ichnofabric approach they have driven ichnology into diverse fields of earth sciences including paleoecology sedimentology paleoceanography and basin analysis as well as applied fields for the oil and gas industry and aquifer characterization whereas early ichnological analyses focused on outcrops later the number of ichnological studies on well cores increased noticeably still ichnological research on cores is hampered by certain limitations i e mainly narrow exposed surface and the characterization of ichnological properties is complicated when cores are involved to facilitate ichnological analysis in cores from modern deposits several techniques among them x rays magnetic resonance and computed tomography have been used with the development of computer software a new high resolution image treatment has emerged as a powerful tool in different branches of ichnological studies especially for cores from modern marine deposits because applications are numerous and perhaps not familiar to all the scientific community this paper provides an overview of the usefulness of image treatment in ichnological analysis its first steps and subsequent development the novel techniques most recently used in the study of cores from modern marine deposits and some challenges for future research

macaronichnus and contourite depositional settings bottom currents and nutrients as coupling factors abstract the trace fossil macaronichnus segregatis degiberti 7 15 mm in diameter is recorded for the first time in deep marine contourites which were deposited in a late miocene outer shelf to upper slope of the rifian corridor morocco macaronichnus is typical of shallow marine mainly foreshore environments it is produced by deposit feeding opheliid polychaetes in high to intermediate latitudes this record supports the significance of bottom current processes on environmental conditions as a major limiting factor affecting the macrobenthic trace maker community mediterranean overflow water during the late miocene enabled a high nutrient supply to the seafloor favouring colonization by macaronichnus producers thus m s degiberti should be used as an indicator for nutrient availability instead of mainly a palaeodepth indicator this finding provides significant information for oceanographic and environmental reconstructions related to contouritic processes as well as to contourite characterization

calibrating a viscoelastic sea ice model for wave propagation in the arctic fall marginal ice zone this paper presents a wave in ice model calibration study data used were collected in the thin ice of the advancing autumn marginal ice zone of the western arctic ocean in 2015 where pancake ice was found to be prevalent multiple buoys were deployed in seven wave experiments data from four of these experiments are used in the present study wave attenuation coefficients are calculated utilizing wave energy decay between two buoys measuring simultaneously within the ice covered region wavenumbers are measured in one of these experiments forcing parameters are obtained from simultaneous in situ and remote sensing observations as well as forecast hindcast models cases from three wave experiments are used to calibrate a viscoelastic model for wave attenuation dispersion in ice cover the calibration is done by minimizing the difference between modeled and measured complex wavenumber using a multi objective genetic algorithm the calibrated results are validated using two methods one is to directly apply the calibrated viscoelastic parameters to one of the wave experiments not used in the calibration and then compare the attenuation from the model with measured data the other is to use the calibrated viscoelastic model in wavewatch iii over the entire western beaufort sea and then compare the wave spectra at two remote sites not used in the calibration both validations show reasonable agreement between the model and the measured data the completed viscoelastic model is believed to be applicable to the fall marginal ice zone dominated by pancake ice

ichnofacies distribution in the eocene early miocene petra tou romiou outcrop cyprus sea level dynamics and palaeoenvironmental implications in a contourite environment ichnological analysis of the carbonate contourite drift at the petra tou romiou outcrop southern cyprus reveals a relationship between sea level dynamics shoreline position sedimentation rate flow hydrodynamics and trace fossil assemblages the base of the outcrop is composed of chalky deposits showing the zoophycos ichnofacies attributes the transition to the first contouritic interval beds is marked by the gradual disappearance of zoophycos and dominance of horizontal traces this change is caused by a gradual sea level fall determining an increase in proximity and energy conditions in the environment that favoured the development of distal cruziana ichnofacies upper contouritic interval beds contain abundant burrow systems with vertical components increased ichnodiversity particularly among vertical morphologies coincides with the appearance of teichichnus gyrolithes and rare ophiomorpha revealing a transition to the proximal cruziana ichnofacies related with the maintenance of the previous trend toward more proximal and higher energy settings the differentiated ichnofacies in the petra tou roumiou carbonate drifts are controlled by complex interactions between variable environmental factors with sea level dynamics playing a major role

a deep sea benthic community exposed to strong near bottom currents on the scotian rise western atlantic abstract this paper gives an overview of the structure of a benthic community at 4626 m depth on the nova scotian continental rise here abundances of polychaetes bivalves isopods and tanaids are conspicuously high compared to those reported from comparable depths bacterial numbers and atp concentrations are also high we suspect that these anomalous abundances result from enhanced food availability caused by the strong near bottom currents that flow through the area the polychaete and bivalve faunas have few adults and high species dominance suggesting that currents create large scale sediment transporting disturbances the composition of the crustacean fauna supports this inference in that it is dominated by forms that can enter the seabed and thereby escape adverse conditions on the sediment surface

wave attenuation through an arctic marginal ice zone on 12 october 2015 1 measurement of wave spectra and ice features from sentinel 1a a storm with significant wave heights exceeding 4 m occurred in the beaufort sea on 11 13 october 2015 the waves and ice were captured on 12 october by the synthetic aperture radar sar on board sentinel 1a with interferometric wide swath images covering 400 x 1 100 km at 10 m resolution this data set allows the estimation of wave spectra across the marginal ice zone miz every 5 km over 400 km of sea ice since ice attenuates waves with wavelengths shorter than 50 m in a few kilometers the longer waves are clearly imaged by sar in sea ice obtaining wave spectra from the image requires a careful estimation of the blurring effect produced by unresolved wavelengths in the azimuthal direction using in situ wave buoy measurements as reference we establish that this azimuth cutoff can be estimated in mixed ocean ice conditions wave spectra could not be estimated where ice features such as leads contribute to a large fraction of the radar backscatter variance the resulting wave height map exhibits a steep decay in the first 100 km of ice with a transition into a weaker decay further away this unique wave decay pattern transitions where large scale ice features such as leads become visible as in situ ice information is limited it is not known whether the decay is caused by a difference in ice properties or a wave dissipation mechanism the implications of the observed wave patterns are discussed in the context of other observations plain language summary our work entitled wave attenuation through an arctic marginal ice zone on 12 october 2015 1 measurement of wave spectra and ice features from sentinel 1a uses a newly developed method to extract wave spectra from radar imagery over sea ice this is possible since the sea ice rapidly removes the short waves which usually distort the radar imagery we are able to estimate thousands of wave spectra across several hundred kilometers at kilometer scale resolution for the first large scale view of wave attenuation across the marginal ice zone our results show a unique wave attenuation pattern described by a piecewise exponential decay that changes by a factor of 10 the transition between the different wave attenuation regions occurs near a change in sea ice conditions we estimate from the sar backscatter this suggests the wave ice interaction mechanisms are indeed changing over these large scales

measurements of mid winter spatial distribution of meltwater saturation under melt freeze conditions crusts may evolve within a snowpack which may favour avalanche initiation by forming a hard bed surface for weakly bonded faceted grains we used a parallel probe saturation profiler ppsp to record the distribution of water contents within the snowpack diurnal effects of melt freeze action on the growth of crusts were monitored with the help of the ppsp device saturation profiles were collected from a partially wet snow cover snow stratigraphy was conducted manually in the morning after overnight freezing to identify the location and the granular compositions of the crusts that had evolved a one to one correspondence between the saturation spikes collected using the ppsp and the actual positions of the crusts was established the ppsp was also used to monitor three dimensional variations in the maximum percolation depths within a south facing snowpack the operation of the ppsp is faster than existing dielectric measurement techniques so it was applied to study the spatial variability of maximum percolation depths on the slopes of different aspects

explicit iterative computation of diffusive vapour field in the 3 d snow matrix preliminary results for low flux metamorphism the metamorphism of seasonal snow is classically considered as limited by vapour diffusion in the pore phase to account for the lack of knowledge of the ice vapour reaction coefficient near 0 c the assumption of a reaction limited metamorphism was first tested in three dimensional simulations at low and very low temperature gradients however the validity of such results is difficult to verify experimentally by a reasoned use of traditional iterative schemes vapour diffusion is now simulated in three dimensions on tomographic snow data mapping the gradient of vapour pressure near the grains repeating this process may provide a way to simulate the isothermal metamorphism without grain packing at a reasonable expense of computation time preliminary results are compared with existing computations made within the reaction limited hypothesis

the former presence of organic matter caused its later absence burn down of organic matter in oceanic red beds enhanced by bioturbation eocene variegated shale carpathians eocene oceanic red beds that formed in a well oxygenated setting at low sedimentation rates below the calcite compensation depth are effectively barren of organic carbon in the present state recurrent distal low erosive turbidites preserve the bioturbated zone underneath that documents seasonal and long term fluctuating accumulation of considerable amounts of organic matter on the sea floor as evidenced by scolicia the producers of this trace fossil exploited nutritious organic matter conserved in turbidite buried sea floor deposits over the long term slow average sedimentation of hemi pelagic oxic red mud led to long oxygen exposure times and low burial of organic matter consequently trace fossils representing persistent sediment feeding modes are of small size although the food limited setting appears appropriate for producers of graphoglyptids such stationary burrows have not been encountered because seasonal deposition of organic matter fostered at least temporary surface layer feeding organisms for instance producers of nereites irregularis that intensively reworked the sediment and hence hindered graphoglyptid production these findings confirm palaeoceanographic modelling results that suggest upwelling in the study area during the eocene this article is protected by copyright all rights reserved

palaeogeographic evolution of the late miocene rifian corridor morocco reconstructions from surface and subsurface data abstract the rifian corridor was one of the mediterranean atlantic seaways that progressively restricted and caused the messinian salinity crisis msc many key questions concerning the controls on the onset progression and termination of the msc remain unanswered mainly because the evolution of these seaways is poorly constrained uncertainties about the age of restriction and closure of the rifian corridor hamper full understanding of the hydrological exchange through the msc gateways required connections to sustain transport of salt into the mediterranean for the primary lower gypsum and halite stages here we present integrated surface subsurface palaeogeographic reconstructions of the rifian corridor with improved age control information about age and timing of the closure have been derived from high resolution biostratigraphy palaeoenvironmental indicators sediment transport directions and the analysis of published onshore subsurface core and seismic datasets we applied modern taxonomic concepts to revise the biostratigraphy of the rifian corridor and propose astronomically tuned minimum maximum ages for its successions finally we summarise the palaeogeographic evolution in four time slices corresponding to the middle tortonian 10 57 8 37 late tortonian 8 37 7 25 ma early messinian 7 25 6 35 ma and late messinian 6 35 5 33 ma several successions record the closure of the corridor via a continuous marine to continental lacustrine transition the youngest dated marine sediments represent a good approximation of the age of seaway closure the closure of the south rifian corridor is constrained to 7 1 6 9 ma that of the north rifian corridor is more uncertain and ranges from 7 35 to ca 7 ma we conclude that the rifian corridor was already closed in the early messinian and did not contribute to the restriction events that resulted in the msc because the betic corridor is also closed by the early messinian the modern gibraltar straits remain the sole option in the western mediterranean as last messinian seaway that was open during the msc our results imply that the gibraltar straits could have been established as the exclusive mediterranean atlantic portal already in the late miocene and therefore we suggest that future field and drilling campaigns should target the alboran sea and the gibraltar region to investigate water exchange before and during the messinian salinity crisis and its impact on atlantic circulation and global climate

palaeoenvironmental and palaeogeographical implications of modern macaronichnus segregatis like traces in foreshore sediments on the pacific coast of central japan traces produced by modern animals provide useful information for our understanding of comparable trace fossils this paper reports on a polychaete worm euzonus producing traces which fall within the definition of the ichnotaxon macaronichnus segregatis observation on the wave dominated pacific sandy coast of central japan revealed that this animal and its trace occur exclusively in sediments of the mid foreshore portion of the beach owing to such a limited occurrence of the modern trace the ichnofossil m segregatis might be useful as an indicator of mid foreshore environment the longer axes of modern m segregatis like traces on a bedding plane are arranged perpendicular to the shoreline and accordingly its fossil counterpart can be utilized for reconstructions of the ancient shoreline orientation in support of this assumption a similar mode of m segregatis occurrence is reported from pleistocene shallow marine deposits in japan

evolution of the specific surface area of snow during high temperature gradient metamorphism the structural evolution of low density snow under a high temperature gradient over a short period usually takes place in the surface layers on clear cold nights in this paper x ray computed microtomography microct was combined with numerical simulations to investigate the temperature gradient metamorphism tgm on different types of snow precipitation particles pp small rounded particles rgsr and large rounded particles rglr were each observed in high temperature gradients 100 500 k m 1 at a mean temperature of 4 c the specific surface area ssa was used to characterize the tgm which were influenced by both the magnitude of the temperature gradient and the initial snow structures pp samples experienced a logarithmic decrease of ssa with time and the depth hoar structures created under high tgm 500 k m 1 have higher ssa compared to those under lower tgm unlike previous observations for initial rounded and connected structures like rglr samples the ssa increased during tgm simulated normal vapor flux distributions for different snow types were used to help understand the structural evolution under tgm understanding the ssa increase is important in order to predict the enhanced uptake of chemical species by snow or increase in snow albedo

evolution of the late miocene mediterranean atlantic gateways and their impact on regional and global environmental change marine gateways play a critical role in the exchange of water heat salt and nutrients between oceans and seas as a result changes in gateway geometry can significantly alter both the pattern of global ocean circulation and associated heat transport and climate as well as having a profound impact on local environmental conditions mediterranean atlantic marine corridors that pre date the modern gibraltar strait closed during the late miocene and are now exposed on land in northern morocco and southern spain the restriction and closure of these miocene connections resulted in extreme salinity fluctuations in the mediterranean leading to the precipitation of thick evaporites this event is known as the messinian salinity crisis msc the evolution and closure of the mediterranean atlantic gateways are a critical control on the msc but at present the location geometry and age of these gateways are still highly controversial as is the impact of changing mediterranean outflow on northern hemisphere circulation here we present a comprehensive overview of the evolution of the late miocene gateways and the nature of mediterranean atlantic exchange as deduced from published studies focussed both on the sediments preserved within the fossil corridors and inferences that can be derived from data in the adjacent basins we also consider the possible impact of evolving exchange on both the mediterranean and global climate and highlight the main enduring challenges for reconstructing past mediterranean atlantic exchange

snow crystal growth with varying surface temperatures and radiation penetration the temperature field is derived for a sinusoidally varying surface temperature with varying solar radiation penetration the growth rates of snow crystals are calculated to explain the rapidly growing layers of faceted crystals i e depth hoar that form just below the surface at high altitudes and in polar snow the solutions also show that a layer of wet snow can exist just below the surface even on days when the surface temperature remains sub freezing

the fauna of the hebble site patterns in standing stock and sediment dynamic effects abstract at the high energy benthic boundary layer experiment hebble site at 4820 m depth on the nova scotia rise 40 27 n 62 20 w abundances of polychaetes bivalves tanaids and isopods were conspicuously greater than expected for the depth whereas those of nematodes and harpacticoids the two dominant meiofaunal taxa were not further the abundances of polychaetes bivalves tanaids and nematodes were consistent over time and appeared to be unaffected by the periods of strong near bottom flow that characterized the site in contrast isopods and harpacticoid copepods were less abundant in samples taken as a storm abated apparently because they were eroded during benthic storms we explore implications of the difference between macrofaunal and meiofaunal abundance for community structure in addition because a goal of the hebble project was the parameterization of sediment transport in the deep sea we summarize ways that the biota affects sediment transport at this high energy site

model for dry snow metamorphism by interparticle vapor flux kinetic growth metamorphism lowers the mean number of bonds between the ice particles in snow during the beginning state of snow metamorphism at a large mean temperature gradient significant particle growth occurs only at preferred growth sites three dimensional approximations of the sink source geometry are introduced to model particle growth and shrink rates the calculations show that enhanced growth occurs at very small and at large sink source distances the consideration of growth rate enhancement by differences in radii of curvature between sink source particles accounts for metamorphism at very low mean temperature gradients final particle size distributions and the reduction of the particle number density by metamorphism are calculated and may be compared with measured distributions

in situ measurements of an energetic wave event in the arctic marginal ice zone r v lance serendipitously encountered an energetic wave event around 77 n 26 e on 2 may 2010 onboard gps records interpreted as the surface wave signal show the largest waves recorded in the arctic region with ice cover comparing the measurements with a spectral wave model indicated three phases of interaction 1 wave blocking by ice 2 strong attenuation of wave energy and fracturing of ice by wave forcing and 3 uninhibited propagation of the peak waves and an extension of allowed waves to higher frequencies above the peak wave properties during fracturing of ice cover indicated increased groupiness wave ice interaction presented binary behavior there was zero transmission in unbroken ice and total transmission in fractured ice the fractured ice front traveled at some fraction of the wave group speed findings do not motivate new dissipation schemes for wave models though they do indicate the need for two way wave ice coupling

ichnological analysis of contourites past present and future abstract contourite deposits are significant facies in deep water sedimentary environments because they record critical paleoclimatological and paleoceanographic data contourite research also informs slope stability geological hazard assessment and petroleum exploration scientific consensus has not converged on several key aspects of contourite interpretation however some researchers interpret bioturbation as a diagnostic feature that differentiates contourites from associated facies e g turbidites while other researchers consider bioturbation to be of second order importance this work reviews existing literature and relevant field data to better define the role of ichnological analysis in contourite research review of significant contributions by earlier studies including formalization of terminology bioturbation burrow etc can help constrain wider usage of ichnological concepts e g ichnofacies and ichnotaxonomic analysis this paper also revisits ichnological data in paleoenvironmental interpretations reservoir characterization and the rare example of ichnofacies and ichnofabric analyses designation of diagnostic criteria can promote the use of ichnological information in contourite research regardless of consensus concerning bioturbation as a diagnostic criterion in contourite characterization ichnological data can still inform interpretations and integrate with other techniques to advance understanding of contourite sedimentary facies for a broad range of applications

metamorphic signature of snow revealed in ssm i measurements brightness temperatures 19 22 37 85 ghz measured by the special sensor microwave imager ssm i are analyzed using data from the snow monitoring network within the former soviet union during the 1987 1988 winter period it is shown that in the beginning of winter the ssm i measurements display the classical snow scattering signature i e the brightness temperatures decrease with increasing depth and the largest decrease occurs at the highest frequency dramatic deviations from this pattern are observed in the middle of winter where the brightness temperature approaches a minimum and then begins to increase despite the fact that the snow depth remains constant or continues to grow the two stream radiative transfer model is combined with results from dense media theory to help explain the phenomenon model results suggest that the increase in brightness temperature is due to a decrease of the single scattering albedo as the snowpack ages this decrease of the albedo is related to changes in the snow crystalline structure due to metamorphism consequences for the interpretation of satellite measurements and development of algorithms for deriving snow water equivalent are discussed

the layered character of snow covers snow studies have generally ignored the layered nature of snow covers having achieved a good understanding of the properties and processes in homogeneous snow snow scientists should develop more insight into the evolution of the layers and their effects on overall snow response many of the outstanding problems in snow studies can only be solved by dealing with snow as a layered medium the various mechanisms by which layers are generated their effects and some of the outstanding research problems are described here

the connectivity of crystallite agglomerates in low density firn at kohnen station dronning maud land antarctica in this study the three dimensional 3 d microstructure of polar firn is investigated by means of x ray microfocus computer tomography mct basic topological properties including the euler and coordination numbers are derived from the reconstructed 3 d volume images it is shown that sample volumes of about 4 cm 3 are representative for polar firn in terms of their connectivity the connectivity function defined as the change of euler number with structure size is calculated via image processing routines it is used to split the ice phase at small bridges into single crystallite agglomerates the bond size distributions and the mean size of the agglomerates are estimated all mct measurements were carried out on the uppermost 9 m of a shallow firn core b35 drilled during the 2005 06 field campaign at kohnen station dronning maud land dml antarctica the results are compared with estimates from classical two dimensional 2 d surface section observations the 3 d approach confirms the linear relationship between coordination number and density which hitherto has only been derived from 2 d observations layers of buried snow dunes show a stronger connectivity than layers of moderate crystal size and density the formation of agglomerates made of crystallites is a common feature of polar firn in dml it is proposed that the growth of agglomerates leads to reduced critical densities for the transition between the densification regime of grain boundary sliding and plastic deformation

theory of metamorphism of dry snow the growth of ice particles in dry seasonal snow is caused by vapor diffusion among particles due to temperature gradients imposed on the snow cover the diffusion is calculated by using the potential field solutions for electrostatically charged particles the stereography of snow is represented by using a log normal distribution function for a geometrical enhancement factor defined here reasonable crystal growth rates and supersaturations are found the transition between the growth of highly faceted crystals and the growth of highly rounded crystals is determined by the critical supersaturation for the onset of dislocation aided growth thermal convection and the continuous movement of vapor around the particles due to the imposed temperature gradient are accommodated in the theory although both have little effect relative to the interparticle diffusion the growth of a layer of faceted crystals just below semi permeable crusts is explained by showing that crusts can cause the local supersaturation to exceed the critical value faceted crystals are shown to grow most rapidly in the lower warmer portions of the snow cover because of temperature effects on growth rate

growth of melt freeze clusters and formation of impeding layers to water flow in snow irradiated by a sun simulator under controlled laboratory conditions stratigraphic boundaries at fine to coarse transitions in snow can introduce impeding layers to infiltrating water in our present investigation such impeding horizons were observed within sub freezing homogeneous snow as a consequence of subsurface melting caused by the penetration of solar radiation this new texture impeded the further downward flow of meltwater at fine to coarse transitions leading to the formation of low permeability melt freeze crusts following multiple melt freeze cycles in this work a large sub freezing 6 c homogeneous sample consisting of small rounded grains was periodically exposed to intense radiation generated by a sun simulator due to the penetration of shortwave radiation into the snow subsurface melting caused the growth of melt freeze polycrystals from clustered rounded crystals variations in mass growth of melt freeze polycrystals and mass loss of grain clusters were studied within the sub freezing snow with respect to different melt freeze cycles in this work we study the growth of melt freeze polycrystals in the top and bottom sub layers with respect to collective saturation saturation profiles from the snow were recorded with a parallel probe saturation profiler ppsp device sampling at vertical intervals of 7 mm after each melting cycle intrinsic permeabilities across different stratified sub layers were monitored in relation to saturation as a function of different melt freeze cycles our observations revealed that there is a significant decrease in intrinsic permeability for the first few top sub layers also permeability in the second topmost sub layer was less than that in the topmost sub layer directly interacting with the radiation these results support the evolution of a new coarse grain texture within the homogeneous snow that subsequently converts into a layer of low permeability in the various transects of the snow sample two melt freeze crusts and one ice crust were manually identified through stratigraphic mapping a correlation was also established between the saturation spikes recorded with the help of the ppsp and corresponding depth positions of the crusts

the impact of accumulation rate on anisotropy and air permeability of polar firn at a high accumulation site the first three dimensional properties of polar firn obtained by x ray microtomography are used to study the microstructure of snow on a 15 m deep firn core from west antarctica the snow is found to undergo coarsening down to approximately 2 5 m depth before grain growth and densification become the prevalent mechanisms of microstructure change in contrast to previous assumptions distinct anisotropy of the ice and pore geometry is observed throughout the profile with a maximum at 2 5 m depth the air permeability and the degree of anisotropy vary with depth and can be linked to short term changes in accumulation rate via the residence time for which a certain snow layer stays in the uppermost 2 5 m patterns of the degree of anisotropy and air permeability of buried polar firn are relative indicators of past accumulation rates

attenuation of ocean surface waves in pancake and frazil sea ice along the coast of the chukchi sea alaskan arctic coastlines are protected seasonally from ocean waves by presence of coastal and shorefast sea ice this study presents field observations collected during the autumn freeze up of 201

palaeoecology of macaronichnus segregatis degiberti reconstructing the infaunal lives of the travisiid polychaetes abstract macaronichnus segregatis degiberti a relatively large ichnosubspecies of macaronichnus segregatis is an almost straight to gently curved cylindrical fossilized burrow oriented horizontal to oblique to the bedding plane it is interpreted as a pascichnial trace fossil formed through selective sand feeding and excretion of a free living polychaete such as a relatively large travisiid formerly classified as opheliid or scalibregmatid polychaete travisia while the other ichnosubspecies i e m s segregatis m s lineiformins m s meandriformis and m s spiriformis are commonly 2 5 mm in diameter and occur exclusively in foreshore deposits m s degiberti attains a diameter of up to 15 mm and shows wide environmental distribution ranging from tidal channels tidal sand bars tidal sandridges tidal flats upper to lower shorefaces bioturbated sandy shelves shelf storm sheets to shelf sand ridges the core of m s degiberti consisting mainly of light mineral rich sand grains is composed of alternating lamellae of light mineral rich and heavy mineral rich sands arranged oblique to the bedding plane on the other hand the mantle composed mainly of heavy mineral rich sands has a smooth outline or evenly spaced lobes flanked on both sides the morphology of the mantle lobes and core lamellae suggests repeated pulses of sediment probing and excreting behaviour of the tracemaker two or more burrows of this ichnosubspecies tend to occur adjacently sometimes intertwining as travisia develops directly lacking any planktic larval stages aggregations of the burrows can be interpreted to reflect the burrowers interindividual exploratory behaviour with the aim of copulation travisia also known as a stink worm secretes volatile chemical substances that might act as sex pheromones to attract other individuals for reproduction within the substrate therefore a new category of ethological classification of trace fossils sequorichnia sequor follow and ichnia traces for exploration of other individuals is proposed here this is the first record of interindividual exploratory behaviour of infaunae

depth hoar growth rates near a rocky outcrop observ atio ns of slab a ala nche releases in alpine terrai n ha e led to the hypoth esis that rocky outcrops can inf luence thc spati al distribut ion s of tempe rat ure and heat flow in dry alpine snow covers and thus c011lr ol the local dist ributio n of depth hoar vc investigate the effects of ter rain on crystal growth by using a two di mensional finite elem ent model of heat flow coup led with a model of crystal growth from vapor we used the model to exa mine the inf luence of snow prop ert ies terrain geome try and snow depth on this phenomenon the effect is stron ger in the early winter than in the late win ter because the rock has then had ti me to cool in all cas es wc found that depth hoar grow th occurs pref erentially o er th e rock this sugg est s that snow pit im cstigat ions made over soi l can be m isle ading if rocky out crops are prese nt

vapor transport grain growth and depth hoar development in the subarctic snow measurements from the subarctic snowpack are used to explore the relationship between grain growth and vapor flow the fundamental processes of dry snow metamorphism due to extreme temperature gradients the subarctic pack undergoes extensive depth hoar metamorphism by the end of the winter a five layered structure with a pronounced weak layer near the base of the snow evolves grain size increases by a factor of 2 3 while the number of grains per unit mass decreases by a factor of 10 observed growth rates require significant net inter particle vapor fluxes stable isotope ratios show that there are also significant net layer to layer vapor fluxes soil moisture enters the base of the pack and mixes with the bottom 10 cm of snow while isotopically light water vapor fractionates from the basal layer and is deposited up to 50 cm higher in the pack end of winter density profiles for snow on the ground compared with snow on tables indicate the net layer to layer vapor flux averages 6 x 10 7 kg m 2 s 1 though detailed measurements show the net flux is episodic and varies with time and height in the pack with peak net fluxes ten times higher than average a model driven by observed temperature profiles reproduces the layer to layer flux pattern and predicts the observed weak layer at the base of the snow calculated layer to layer vapor fluxes are ten times higher than inter particle fluxes which implies that depth hoar grain growth is limited by factors other than the vapor supply this finding suggests that gain and loss of water molecules due to sublimation from grains takes place at a rate many times higher than the rate at which grains grow and it explains why grains can metamorphose into different forms so readily

formation of refrozen snowpack layers and their role in slab avalanche release 1 in a variety of snow climates numerous slab avalanches release over crusts consisting of refrozen snow slab avalanches sometimes release in weak layers of faceted crystals that developed while underlying wet layers froze into crusts often within a day weak layers of faceted crystals can also develop when less permeable and more conductive crusts alter the temperature and vapor pressure gradients these processes create interfaces where differences in grain radii can contribute to weak bonding in western canada layers of faceted crystals facet layers on crusts are most common in early and late winter when thaws and rain are more frequent also thin facet layers occur in spring when surface melting by solar radiation is common shear strength tests on facet layers show an initial strength loss during faceting followed by a slow strength increase the spatial distribution of poorly bonded crusts can be interpreted from the interaction of terrain and meteorology that caused the antecedent wet layer

deciphering bottom current velocity and paleoclimate signals from contourite deposits in the gulf of cadiz during the last 140 kyr an inorganic geochemical approach contourites in the gulf of cadiz gc preserve a unique archive of mediterranean outflow water mow variability over the past 5 3 ma in our study we investigate the potential of geochemical data obtained by xrf scanning to decipher bottom current processes and paleoclimatic evolution at two different sites drilled during iodp expedition 339 through contourites in the northern gc site u1387 which is bathed by the upper mow core and site u1389 located more proximal to the strait of gibraltar the lack of major downslope transport during the pleistocene makes both locations ideally suited for our study the results indicate that the zr al ratio representing the relative enrichment of heavy minerals zircon over less dense alumnosilicates under fast bottom current flow is the most useful indicator for a semiquantitative assessment of current velocity although most elements are biased by current related processes the bromine br record representing organic content preserves the most pristine climate signal rather independent of grain size changes hence br can be used for chronostratigraphy and site to site correlation in addition to stable isotope stratigraphy based on these findings we reconstructed mow variability for marine isotope stages mis 1 5 using the zr al ratio from site u1387 the results reveal abrupt millennial scale variations of mow strength during greenland stadials gs and interstadials gi with strong mow during gs and glacial terminations and a complex behavior during heinrich stadials millennial scale variability persisting during periods of poorly expressed gs gi cyclicities implies a strong internal oscillation of the mediterranean north atlantic climate system

the principle of minimum entropy production and snow structure an essential problem in snow science is to predict the changing form of ice grains within a snow layer present theories are based on the idea that form changes are driven by mass diffusion induced by temperature gradients within the snow cover this leads to the well established theory of isothermal and temperature gradient metamorphism although diffusion theory treats mass transfer it does not treat the influence of this mass transfer on the form the curvature radius of the grains and bonds directly empirical relations based on observations are additionally required to predict flat or rounded surfaces in the following we postulate that metamorphism the change of ice surface curvature and size is a process of thermodynamic optimization in which entropy production is minimized that is there exists an optimal surface curvature of the ice grains for a given thermodynamic state at which entropy production is stationary this state is defined by differences in ice and air temperature and vapor pressure across the interfacial boundary layer the optimal form corresponds to the state of least wasted work the state of minimum entropy production we show that temperature gradients produce a thermal non equilibrium between the ice and air such that depending on the temperature flat surfaces are required to mimimize entropy production when the temperatures of the ice and air are equal larger curvature radii are found at low temperatures than at high temperatures thus what is known as isothermal metamorphism corresponds to minimum entropy production at equilibrium temperatures and so called temperature gradient metamorphism corresponds to minimum entropy production at non equilibrium temperatures the theory is in good agreement with genera observations of crystal form development in dry seasonal alpine snow

the role of eolian processes in forming surface features of the martian polar layered deposits abstract the major topographic features of the martian polar layered deposits include the conspicuous spiral troughs subtle undulations broad reentrants chasma steep arcuate scarps and dune fields a prominent role for eolian processes in the formation of all of these features is proposed strong katabatic winds occur on the north polar cap producing widespread frost streaks these cold drainage winds are analogous to those on the terrestrial antarctic cap in the chasmae convergent katabatic winds create yardangs and erode arcuate scarps in the layered deposits that are also the source for local dune fields migrating outward from the polar cap the chasmae are postulated to originate by long term erosion by katabatic wind wind plays a role in formation of the troughs and scarps primarily through removal of dust freed from exposed layered deposits by ablation of ice on defrosted equator facing slopes the undulations are created by interaction between surface erosion or deposition of perennial ice and standing waves in the shallow katabatic windflow the south polar layered deposits exhibit topographic features similar to those at the north polar cap but erosion and depositional processes creating these features may be inactive during the current epoch because of the lack of an extensive perennial ice cover and associated katabatic wind

observations of the shape and group dynamics of rogue waves surface elevation records from two locations in the northeast pacific are used to examine rogue waves and the relationship to wave groups three hundred individual rogue waves with heights greater than 2 2 times the significant wave height are found in analyzing 2 106 wave groups in contrast to recent nonlinear modeling results we do not find that rogue waves occur at the front of wave groups there is a tendency for steep waves to occur at the front of a group but these are not the largest waves of the group and do not meet the rogue wave criterion rogue waves are most commonly located in the center of the group but their height ratio to the neighboring crest is greater than in the average wave group assessing group dynamics in terms of spectral width suggests that random superposition of nonlinear waves is sufficient to explain the observations of individual rogue waves

structural evolution of the rides prerifaines morocco structural and seismic interpretation and analogue modelling experiments the rides prerifaines rp of morocco constitute the leading edge of the rif chain they involve a triassic palaeocene succession deposited on a peneplained palaeozoic fold belt and accumulated in basins delimited by ne sw trending normal fault systems a significant hiatus separates an overlying middle miocene upper miocene foredeep sequence the reconstruction of the complex structural evolution of the rp during the later compressive phases that affected the rif chain since middle miocene time has been the aim of this paper we integrated field structural analyses seismic line interpretation and analogue modelling in order to evaluate the control exerted by the late triassic jurassic normal fault systems onto the later compressive tectonics the maximum compression direction associated with the first compressive phase is roughly ne sw to ene wsw oriented during this phase the mesozoic basin fill was scooped out from the graben and the main decollement level were the triassic evaporites since pliocene times the maximum compression direction was oriented roughly n s during this phase the rp assumed their present structural setting the earlier normal faults delimiting the mesozoic graben were reactivated in a strike slip mode also involving the palaeozoic basement the analogue modelling experiments demonstrated that the basement reactivation promoted salt tectonics and favoured fluid circulation

is the trace fossil macaronichnus an indicator of temperate to cold waters exploring the paradox of its occurrence in tropical coasts the trace fossil macaronichnus is reported for the first time from low latitude tropical settings based on its occurrence in nearshore deposits in the upper oligocene lower miocene naricual formation and in the middle to upper miocene urumaco formation in northern venezuela macaronichnus is an intrastratal trace fossil attributed to the deposit feeding of worms in high energy sandy shallow marine environments the majority of its occurrences are from mesozoic to cenozoic high to intermediate latitude shorelines the opheliid polychaetes ophelia limacina and euzonus mucronata make structures identical to those described from the fossil record in modern intertidal and shallow subtidal sediments of northwestern united states western canada and japan macaronichnus shows a geographical and environmental distribution in the fossil record similar to that of its modern producers and has been proposed as an indicator of high to intermediate latitudes accordingly its presence in the neogene of venezuela is highly anomalous and seems to challenge its paleoclimatic value however this occurrence may be related to seasonal coastal upwelling of nutrient rich cold waters such oceanographic conditions were prevalent in the northern coast of south america at least from the late oligocene to the early pliocene prior to the final closure of the strait of panama this study underscores the value of macaronichnus because its presence in the tropics may indicate upwelling conditions providing high resolution information in paleoceanographic reconstructions

danian lower selandian microcodium rich calcarenites of the subbetic zone se spain record of nereites ichnofacies in a deep sea base of slope system abstract the olivares formation a lower paleogene unit of the subbetic zone in southern spain is mostly composed of calcarenites comprising 60 90 of resedimented microcodium remains which are intercalated in hemipelagic marls rich in planktonic foraminifera microcodium is formed on the roots of terrestrial plants adapted to live on carbonate rich substrates its occurrence in the olivares formation entailing a massive resedimentation from a subaerially exposed carbonate source area new field observations demonstrate that the unit was deposited at the base of a faulted slope within a graben flanked by massifs of mostly jurassic carbonates while an ichnological analysis shows an abundant and moderately diverse trace fossil assemblage consisting of 30 ichnospecies belonging to 21 ichnogenera the nongraphoglyptid assemblage 24 ichnospecies 16 ichnogenera is dominated by chondrites ophiomorpha planolites and scolicia zoophycos isp is common while cladichnus gordia helminthopsis multina nereites parahaentzscheliana polykampton spirophycus strobilorhaphe and thalassinoides isp are scarce or rare in the graphoglyptid assemblage 6 ichnospecies 5 ichnogenera helminthorhaphe is common scarce and belorhaphe desmograpton paleodictyon and urohelmintoida are scarce rare this trace fossil assemblage with abundant scolicia and nereites and frequent graphoglyptids can be assigned to the deep sea nereites ichnofacies within the nereites ichnofacies the ophiomorpha rudis and paleodictyon subichnofacies are readily differentiated and the nereites subichnofacies probably also occurs pointing to vertical changes in the turbiditic system most likely related to a coeval sea level rise that eventually resulted in the flooding of the emergent microcodium producing carbonate massifs

late neogene evolution of the taza guercif basin rifian corridor morocco and implications for the messinian salinity crisis abstract magnetostratigraphic and biostratigraphic results are presented from neogene deposits in the taza guercif basin located at the southern margin of the rifian corridor in morocco this corridor was the main marine passageway which connected the mediterranean with the atlantic during messinian times correlation of the biostratigraphy and polarity sequence of the taza guercif composite section to the astronomical time scale allows an accurate dating of three subsequent events in the rifian corridor 1 the oldest marine sediments marking the opening of the rifian corridor were deposited at 8 ma at this age a deep 600 m marine basin developed in the taza guercif area marked by deposition of precession controlled turbidite marl cycles 2 paleodepth reconstructions indicate that a rapid 5 m ka shallowing of the marine corridor took place at the tortonian messinian boundary at an age of 7 2 ma this shallowing phase is primarily related to active tectonics although a small glacio eustatic sea level lowering also took place 3 the taza guercif basin was emergent at an age of 6 0 ma and subsequently continental sedimentation continued well into the early pliocene we suggest that shallowing and restricting the marine passageway through the rifian corridor actually initiated the messinian salinity crisis well before the deposition of the messinian evaporites in the mediterranean

biological activity and associated sedimentary structures in hebble area deposits western north atlantic abstract biological and sedimentologic samples along with x radiographs of sediment slabs were taken from box cores in the hebble area 4700 m on the lower continental rise of nova scotia these data suggest that this bottom region is influenced by periods of strong near bottom currents which erode and physically transport sediments these high periods alternate with periods of weaker flow biogenic reworking of sediments by an active benthic infauna dominates particle transport during low flow conditions

large macaronichnus in modern shoreface sediments identification of the producer the mode of formation and paleoenvironmental implications abstract the trace fossil macaronichnus segregatis is an intrastratal trail occurring in shallow marine deposits previous studies have shown that this trace fossil can be used as a powerful indicator of ancient sea level shoreline orientation beach morphodynamics and paleoceanographic conditions here we describe another type of macaronichnus an incipient large macaronichnus isp which is 5 12 mm in diameter from upper shoreface deposits of a modern sandy beach in western japan the burrow is produced by selective sand grain feeding of the opheliid polychaete travisia japonica although the detailed mechanism remains unclear based on the distribution of t japonica and other travisia species large macaronichnus isp seems to be more widely distributed across tidal flats the upper lower shoreface the continental shelf and possibly even the deep sea floor the distribution of the large burrow is quite different to that of the standard m segregatis it is therefore necessary to distinguish between the sizes of the burrows in order to use the ichnogenus macaronichnus as a paleoenvironmental indicator

an overview of seasonal snow metamorphism the grains in seasonal snow undergo rapid and radical transformations in size shape and cohesion these grain characteristics affect all of the basic properties of snow snow is characterized as either wet or dry depending on the presence of liquid water wet snow is markedly different at low and high liquid contents dry snow is characterized as either an equilibrium form or a kinetic growth form that is it is either well rounded or faceted of course many snow grains display either transitional features between two of these categories or features which arise from other processes snow is classified depending on the dominant processes of its metamorphism