a microwave technique for mapping thin sea ice a technique is presented for mapping the distribution of new young and first year sea ice in seasonal sea ice zones that utilizes microwave spectral and polarization information from the defense meteorological satellite program special sensor microwave imager the motivation for this work stems from the need for accurate estimates of open water and thin ice within the arctic ice pack the technique utilizes the microwave polarization and spectral characteristics of these three ice types through two microwave radiance ratios the 19 4 ghz polarization and the spectral gradient ratio which is a measure of the spectral difference between the 19 4 ghz and the 37 0 ghz vertically polarized radiance components the combined use of the spectral gradient ratio and polarization reduces the low ice concentration bias generally associated with the presence of thin ice types the microwave polarization which is sensitive to changes in ice thickness and ice surface characteristics is used to classify new young and first year ice types the polarization varies from about 0 3 for calm ice free water to about 0 15 for new ice and to 0 03 for thick first year ice on the basis of this parameterization improved sea ice concentration maps and maps of new young and first year ice type distributions are derived examples from the bering sea are presented and comparisons are made with analyzed noaa avhrr imagery

halocline structure in the canada basin of the arctic ocean 1 we examine the varieties and spatial distributions of pacific and eastern arctic origin halocline waters in the canada basin using 2002 2003 hydrographic data the halocline structure in the canada basin is different from the eastern arctic halocline because it includes fresher pacific winter waters that form a cold halostad which lies above the eastern arctic origin lower halocline waters the structure of the halostad in the canada basin however is not spatially uniform and depends on the pathway and history of the source water pacific winter water entering through the bering strait becomes salty due to sea ice formation and this in turn is dependent on the occurrence and distribution of polynyas in particular saline water from the eastern chukchi sea forms thick halostad and causes depression of the isohalines in the southern canada basin this depression influences thermohaline structure of the oceanic beaufort gyre

the oldest handaxes in europe fact or artefact abstract hominin presence is well documented in a number of early pleistocene and early middle pleistocene european localities however the evidence currently available indicates that acheulean handaxes spread in the fluvial basins of western europe during mis 11 400 kyr ago associated with homo heidelbergensis although a number of early middle pleistocene acheulean assemblages have been dated from mis 16 onwards for this reason the magnetostratigraphic dating in southeast spain of two archaeological localities the open air site of solana del zamborino sz and the rock shelter site of cueva negra del estrecho del quipar eq that put back the appearance of handaxes to the early middle pleistocene limit scott and gibert 2009 is of particular interest as the new ages suggest that h heidelbergensis was a contemporary of h antecessor that had the ability to produce levallois debitage and to control fire during the early middle pleistocene transition however we have detected a number of errors in the interpretation of the archaeological assemblage from the first site as well as striking discrepancies with the original faunal lists published for both localities with several large mammal species that are omitted or arbitrarily changed to make the assemblages consistent with the new ages deduced from magnetostratigraphy for this reason we suggest that 1 the finding of reverse polarity in the sediments sampled for paleomagnetism in sz may simply record one of the polarity reversals that took place during the brunhes chron although the use by scott and gibert 2009 of a composite stratigraphic column precludes correlating these levels with a specific reversal and 2 the fauna and tools of eq correspond to the late middle pleistocene sedimentary infillings of this karst site while the samples taken for paleomagnetism belong to a previous sedimentary cycle during the matuyama chron such interpretations would be in better agreement with the age estimates provided by biostratigraphy and also with the currently accepted chronology for the appearance of acheulean industries in western europe

modeling global sea ice with a thickness and enthalpy distribution model in generalized curvilinear coordinates abstract a parallel ocean and ice model poim in generalized orthogonal curvilinear coordinates has been developed for global climate studies the poim couples the parallel ocean program pop with a 12 category thickness and enthalpy distribution ted sea ice model although the poim aims at modeling the global ocean and sea ice system the focus of this study is on the presentation implementation and evaluation of the ted sea ice model in a generalized coordinate system the ted sea ice model is a dynamic thermodynamic model that also explicitly simulates sea ice ridging using a viscous plastic rheology the ted model is formulated such that all the metric terms in generalized curvilinear coordinates are retained following the pop s structure for parallel computation the ted model is designed to be run on a variety of computer architectures parallel serial or vector when run on a computer cluster with 10 parallel processors the parallel performance of the poim is close to that of a correspon

flow of winter transformed pacific water into the western arctic abstract the dynamics of the flow of dense water through barrow canyon is investigated using data from a hydrographic survey in summer 2002 the focus is on the winter transformed bering water the highest volumetric mode of winter water in the chukchi sea which drains northward through the canyon in spring and summer the transport of this water mass during the time of the survey was 0 2 0 3 sv as the layer flowed from the head of the canyon to the mouth it sank decelerated and stretched strong cyclonic relative vorticity was generated on the seaward side of the jet which compensated for the stretching this adjustment was incomplete however in that it did not extend across the entire current possibly because of internal mixing due to shear instabilities the resulting vorticity structure of the flow at the canyon mouth was conducive for baroclinic instability and eddy formation multiple eddies of winter transformed bering water were observed along the chukchi beaufort shelfbreak those to the west of barrow canyon were in the process of being spawned by the eastward flowing shelfbreak current emanating from herald canyon while the single eddy observed to the east originated from the barrow canyon outflow it is argued that such an eddy formation is a major source of the ubiquitous cold core anti cyclones observed historically throughout the canada basin implications for the ventilation of the upper halocline of the western arctic are discussed

polynya dynamics a review of observations and modeling 1 polynyas are nonlinear shaped openings within the ice cover ranging in size from 10 to 105 km2 polynyas play an important climatic role first winter polynyas tend to warm the atmosphere thus affecting atmospheric mesoscale motions second ocean surface cooling and brine rejection during sea ice growth in polynyas lead to vertical mixing and convection contributing to the transformation of intermediate and deep waters in the global ocean and the maintenance of the oceanic overturning circulation since 1990 there has been an upsurge in polynya observations and theoretical models for polynya formation and their impact on the biogeochemistry of the polar seas this article reviews polynya research carried out in the last 2 decades focusing on presenting a state of the art picture of the physical interactions between polynyas and the atmosphere sea ice ocean system observational and modeling studies the surface heat budget and water mass transformation within these features are addressed

offshore transport of dense shelf water in the presence of a submarine canyon the formation and offshore transport of dense water over a uniformly sloping shelf crosscut by a submarine canyon is examined using a three dimensional primitive equation numerical model a constant negative buoyancy flux is applied in a limited region adjacent to a straight coast to represent brine rejection from ice production in an idealized coastal polynya a sharp density front forms at the edge of the forcing region with surface and bottom intensified jets along the front the flow around the head of the submarine canyon triggers a frontal instability that initially grows only on one side of the canyon the unstable waves on the other side of the canyon are blocked by a localized barotropic flow that develops near the canyon head unstable waves also grow where the forcing region intersects the coast the frontal waves grow rapidly with o 1 day e folding timescales and form eddies with horizontal scales of o 15 km which extract the densest water from the forcing region and carry it offshore directly across isobaths in this way the eddies limit the maximum water density that appears in the model despite continued negative buoyancy forcing some dense water descends into the canyon forming a bottom trapped plume that transports the dense water offshore ahead of the eddies the plume moves relatively slowly i e small froude number with little turbulent entrainment so the advancement and structure of the plume nose can be described successfully as a simple gravity current with an advective diffusive heat balance eddies may slump into the canyon from the side altering both the density anomaly and speed of the canyon plume suggesting that canyon plumes are likely to be highly variable in both space and time

source and pathway of the western arctic upper halocline in a data constrained coupled ocean and sea ice model abstracta coupled ocean and sea ice model is used to investigate dense water dw formation in the chukchi and bering shelves and the pathways by which this water feeds the upper halocline two 1992 2008 data constrained solutions at 9 and 4 km horizontal grid spacing show that 1 winter sea ice growth results in brine rejection and dw formation 2 the dw flows primarily down barrow and central herald canyons in the form of bottom trapped intermittent currents to depths of 50 150 m from the late winter to late summer seasons and 3 eddies with diameters 30 km carry the cold dw from the shelf break into the canada basin interior at depths of 50 150 m the 4 km data constrained solution does not show eddy transport across the chukchi shelf at shallow depths instead advection of dw downstream of polynya regions is driven by a strong 0 1 m s 1 mean current on the chukchi shelf upper halocline water uhw formation rate was obtained from two methods one is based on satellite data and on a simple p

the production of ice and dense shelf water in the okhotsk sea polynyas this paper examines the ice and dense water production in the okhotsk sea coastal polynyas for the 1990 1995 winters the dominant polynyas occur on the northwest and northern shelves and in shelikhov bay we use an algorithm developed for the special sensor microwave imager ssm i to derive for each polynya the area and composition of thin ice and open water and a heat flux algorithm to derive the ice and brine production historic oceanographic observations show that the northwest shelf is the only north pacific region where the 26 8 potential density surface outcrops to the surface and is also that part of the okhotsk shelf where the densest water is observed to occur in support of these observations we find that the northwest shelf polynya is the dominant ice and brine producer contributing on average about 55 of the total production shelikhov bay is the second largest producer with about 25 of the total this region has been previously neglected by both oceanographic and remote sensing studies using a combination of two dense water production models we find that the 6 year average dense water production lies between 0 2 0 4 sv the ice and brine production for the dominant northwest shelf vary interannually by a factor of 3 while the production from all the northern polynyas varies by factor of 2 the source of the variability for the northwest shelf comes from the fact that the southwest to northeast trend of the coastline and the mean winter geostrophic wind velocities are roughly parallel which means that small variations in the wind direction yield large changes in the ice production

numerical study of winter water formation in the chukchi sea roles and impacts of coastal polynyas winter water formation is examined in the chukchi sea for the winters of 1992 2006 using a primitive equation ocean model forced by ncep wind and surface salinity flux derived from ssm i thin ice thickness estimates the model is also forced by an external inflow of 0 8 sv through the bering strait the model successfully reproduces the oceanic circulation on the chukchi shelf thus providing numerous insights into behaviors of salt enriched water produced on the shelf the experiments show that under northeasterly winds northward throughflow across barrow canyon is reduced this results in salinity buildup under freezing conditions and ultimately in greater enhancement of salinity of the waters carried into the arctic basin the flow and salinity enhancement of the flow through herald canyon is less extreme but more steady than through barrow canyon together with moored salinity in the bering strait the model results estimate the actual salinity to be 32 9 0 8 psu and 32 7 0 3 psu respectively for waters moving through the barrow and herald canyons both estimates are less than 33 1 psu that is typically observed for the cold halostad layer in the canada basin suggesting the importance of diapycnal mixing with saltier atlantic origin water

evidence of arctic sea ice thinning from direct observations the arctic sea ice cover is rapidly shrinking but a direct longer term assessment of the ice thinning remains challenging a new time series constructed from in situ measurements of sea ice thickness at the end of the melt season in fram strait shows a thinning by over 50 during 2003 2012 the modal and mean ice thickness along 79 degrees n decreased at a rate of 0 3 and 0 2 m yr 1 respectively with long term averages of 2 5 and 3 m airborne observations reveal an east west thickness gradient across the strait in spring but not in summer due to advection from more different source regions there is no clear relationship between interannual ice thickness variability and the source regions of the ice the observed thinning is therefore likely a result of arctic wide reduction in ice thickness with a potential shift in exported ice types playing a minor role

steady models of arctic shelf basin exchange steady state exchanges between the arctic shelves and the central basins are estimated using an inverse box model estimates based only on mass heat and salt conservation are highly uncertain and cannot determine how the shelf basin exchange is partitioned between dense overflows and surface layer exchange inclusion of 18o conservation greatly reduces the uncertainty with the 18o constraints dense water fluxes from the shelves of 0 2 0 1 sv in the canadian basin and 1 4 0 3 sv in the eurasian basin with a small o 0 1 sv surface layer transport from shelves to basins best satisfy the requirements of steady state up to 3 8 sv of shelfbreak upwelling is consistent within error bars with steady state but none is required water leaving the shelves is replaced primarily from the bering strait the barents sea inflow and runoff and not from the basin surface layer proper representation of these external sources for the shelves is important for capturing the full range of plausible steady solutions the steady state solutions identify the balances which if upset could lead to arctic change

ross sea polynyas response of ice concentration retrievals to large areas of thin ice 1 for a 3 month period between may and july of 2005 we examine the response of the advanced microwave scanning radiometer amsr e enhanced nasa team 2 nt2 and amsr e bootstrap aba ice concentration algorithms to large areas of thin ice of the ross sea polynyas coincident envisat synthetic aperture radar sar coverage of the region during this period offers a detailed look at the development of the polynyas within several hundred kilometers of the ice front the high resolution imagery and derived ice motion fields show bands of polynya ice covering up to 105 km2 of the ross sea that are associated with wind forced advection in this study ice thickness from amsr e 36 ghz polarization information serves as the basis for examination of the response the quality of the thickness of newly formed sea ice 10 cm from amsr e is first assessed with thickness estimates derived from ice surface temperatures from the moderate resolution imaging spectroradiometer modis instrument the effect of large areas of thin ice in lowering the ice concentration estimates from both nt2 aba approaches is clearly demonstrated results show relatively robust relationships between retrieved ice concentrations and thin ice thickness estimates that differ between the two algorithms these relationships define the approximate spatial coincidence of ice concentration and thickness isopleths using the 83 aba and 91 nt2 isopleths as polynya boundaries we show that the computed coverage compares well with that using the estimated 10 cm thickness contour the thin ice response characterized here suggests that in regions with polynyas the retrieval results could be used to provide useful geophysical information namely thickness and coverage

estimation of thin sea ice thickness from noaa avhrr data in a polynya off the wilkes land coast east antarctica antarctic coastal polynyas are major areas of intense ocean atmosphere heat and moisture flux and associated high sea ice production and dense water formation their accurate detection including an estimate of thin ice thickness is therefore very important in this paper we apply a technique originally developed in the arctic to an estimation of sea ice thickness using us national oceanic and atmospheric administration noaa advanced very high resolution radiometer avhrr data and meteorological data in the vincennes bay polynya off wilkes land east antarctica the method is based upon the heat flux calculation using sea ice surface temperature estimates from the satellite thermal infrared data combined with global objective analysis european centre for medium range weather forecasts ecmwf data the validity of this method is assessed by comparing results with independent ice surface temperature and ice thickness data obtained during an australian led research cruise to the region in 2003 in thin ice polynya regions ice thicknesses estimated by the heat flux calculation using avhrr and ecmwf data show reasonable agreement with those estimated by a applying the heat flux calculation to in situ radiation thermometer and meteorological data and b in situ observations the standard deviation of the difference between the avhrr derived and in situ data is 0 02 m comparison of the avhrr ice thickness retrievals with coincident satellite passive microwave polarization ratio data confirms the potential of the latter as a means of deriving maps of thin sea ice thickness on the wider scale uninterrupted by darkness and cloud cover

pacific ventilation of the arctic ocean s lower halocline by upwelling and diapycnal mixing over the continental margin 1 pacific winter waters a major source of nutrients and buoyancy to the arctic ocean are thought to ventilate the arctic s lower halocline either by injection isopycnal or penetrative of cold saline shelf waters or by cooling and freshening atlantic waters upwelled onto the shelf although ventilation at salinity s 34 psu has previously been attributed to hypersaline polynya waters temperature salinity nutrient and tracer data suggest instead that much of the western arctic s lower halocline is in fact influenced by a diapycnal mixing of pacific winter waters with s 33 1 psu and denser eastern arctic halocline atlantic waters the mixing taking place possibly over the northern chukchi shelf slope estimates from observational data confirm that sufficient quantities of atlantic water may be upwelled to mix with the inflowing pacific waters with volumes implying the halocline over the chukchi borderland region may be renewed on timescales of order a year

estimation of the thin ice thickness and heat flux for the chukchi sea alaskan coast polynya from special sensor microwave imager data 1990 2001 1 one of the largest arctic polynyas occurs along the alaskan coast of the chukchi sea between cape lisburne and point barrow for this polynya a new thin ice thickness algorithm is described that uses the ratio of the vertically and horizontally polarized special sensor microwave imager ssm i 37 ghz channels to retrieve the distribution of thicknesses and heat fluxes at a 25 km resolution comparison with clear sky advanced very high resolution radiometer data shows that the ssm i thicknesses and heat fluxes are valid for ice thicknesses less than 10 20 cm and comparison with several synthetic aperture radar sar images shows that the 10 cm ice ssm i ice thickness contour approximately follows the sar polynya edge for the twelve winters of 1990 2001 the ice thicknesses and heat fluxes within the polynya are estimated from daily ssm i data then compared with field data and with estimates from other investigations the results show the following first our calculated heat losses are consistent with 2 years of over winter salinity and temperature field data second comparison with other numerical and satellite estimates of the ice production shows that although our ice production per unit area is smaller our polynya areas are larger so that our ice production estimates are of the same order because our salinity forcing occurs over a larger area than in the other models the oceanic response associated with our forcing will be modified index terms 4540 oceanography physical ice mechanics and air sea ice exchange processes 3360 meteorology and atmospheric dynamics remote sensing 4504 oceanography physical air sea interactions 0312 4572 oceanography physical upper ocean processes 4207 oceanography general arctic and antarctic oceanography keywords chukchi sea coastal polynya remote sensing

shallow convection and buoyancy equilibration in an idealized coastal polynya abstract the recent theoretical approach of visbeck marshall and jones is used to examine shallow convection and offshore transport of dense water from an idealized coastal polynya a constant negative buoyancy flux is applied in a half elliptical region adjacent to a coastal boundary surrounded by a forcing decay region with uniform width w over which the imposed buoyancy flux decreases smoothly to zero initially the density beneath the forcing increases linearly with time a baroclinically unstable front forms at the edge of the forcing region the width of the front is imposed by the width of the forcing decay region provided this distance is larger than the baroclinic rossby radius baroclinic eddies whose velocities are inversely proportional to w develop along the front and exchange dense water from the forcing region with ambient water eventually reaching an equilibrium in which the lateral buoyancy flux by eddies balances the prescribed surface buoyancy flux the time to reach equilibrium

arctic ice ocean simulation with optimized model parameters approach and assessment 1 we present an optimized 1992 2008 coupled ice ocean simulation of the arctic ocean a green s function approach adjusts a set of parameters for best model data agreement overall model data differences are reduced by 45 the optimized simulation reproduces the negative trends in ice extent in the satellite records volume and thickness distributions are comparable to those from the ice cloud and land elevation satellite 2003 2008 the upper cold halocline is consistent with observations in the western arctic the freshwater budget of the arctic ocean and volume heat transports of pacific and atlantic waters across major passages are comparable with observation based estimates we note that the optimized parameters depend on the selected atmospheric forcing the use of the 25 year japanese reanalysis results in sea ice albedos that are consistent with field observations simulated pacific water enters the bering strait and flows off the chukchi shelf along four distinct channels this water takes 5 10 years to exit the arctic ocean at the canadian arctic archipelago nares or fram straits atlantic water entering the fram strait flows eastward merges with the st ana trough inflow and splits into two branches at the southwest corner of the makarov basin one branch flows along lomonosov ridge back to fram strait the other enters the western arctic circulates cyclonically below the halocline and exits mainly through the nares and fram straits this work utilizes the record of available observations to obtain an arctic ocean simulation that is in agreement with observations both within and beyond the optimization period and that can be used for tracer and process studies

stratified separated flow around a mountain with an inversion layer below the mountain top this paper presents analytical and numerical results for separated stratified inviscid flow over and around an isolated mountain in the limit of small fronde number the vertical density profile consists of a lower strongly stratified layer whose depth is just less than that of the mountain it is separated from a semi infinite upper stably stratified layer by a thin highly stable inversion layer the paper aims to provide for this particular profile a thorough analysis of the three dimensional separated flow over a mountain top with strong stratification the froude numbers f and f of the lower layer and the interface are small with f 1 f 1 but the upper layer froude number is arbitrary the flow at each height in the lower layer is governed by the two dimensional euler equations and moves horizontally around the mountain it is given by a modification of a previous model using kirchhoff free streamline theory for the separated flow region downstream of the mountain the pressure variations associated with the lower layer flow are of the same order as the dynamic head and induce significant displacements of the inversion layer when the inversion is near the top of the mountain these deflections are of the same order as the height of the projecting part of the mountain top and combine with the flow over the mountain top to excite vertically propagating internal waves in the upper layer the resultant pressure field vertical stream surface displacements and surface streamlines in the upper layer are described consistently in the hydrostatic limit many of the features of the upper flow including the perturbations of the critical dividing streamlines are similar to those in flows with uniform stable stratification at low froude number comparisons are made with experiments and approximate models for these summit flows based on the assumption that the dividing streamlines have small vertical displacement

observations of the terra nova bay antarctica polynya by modis ice surface temperature imagery from 2005 to 2010 abstract ice surface temperature ist imagery from the thermal infrared bands of the satellite borne moderate resolution imaging spectroradiometer modis has been used to analyze the activity of the terra nova bay polynya from 2005 to 2010 in clear sky conditions the shape of the open water area of the polynya i e the portion of the ocean free of sea ice is revealed by the skin sea ice temperatures close to the water freezing point provided by the modis derived ist product the swaths of the modis sensors onboard terra and aqua satellites over the terra nova bay consist of about 5500 scenes per year useful to estimate the cloud cover too the open water area was extracted from clear sky scenes and from scenes affected by fog but providing continuity of the shape of the polynya using about 40 of the available swaths the polynya was detected for more than 80 of the sea ice period with a revisit time below 24 h and for more than 50 with a revisit time below 3 h the open water area was extracted using thresholds of ist based on the ist values detected within the open water area and within the band of sea ice surrounding the polynya obtained scene by scene an ice free area larger than 100 km 2 was observed near the nansen ice shelf for more than 70 of time larger than 500 km 2 for 50 of time the mean annual open water area around 900 km 2 was close to the lower limit of the reported range except during 2006 around 600 km 2 due to the limited activity in the second half of the cold season the largest extents between 6000 and 8500 km 2 occurred in different periods of the antarctic winter and exceeded maxima estimated in previous studies by thermal infrared data polynya openings developed from a few hours to several days in the latter case sustained by subsequent katabatic events visible in the ist sequence peaks of growing rate above 300 km 2 h were observed during intense katabatic events with gusts of 50 m s the fluctuations of the open water area resulted well correlated with wind records available from local automatic weather stations within the main katabatic routes and followed katabatic events at intervals between 0 and 6 h the analysis of the ist data set derived from the thermal infrared bands of modis provides new polynya observations of high horizontal resolution 1 km and frequent revisit time during the winter season complementing previously available observations with passive microwave imagery

sea ice thickness variability in the chukchi sea spring and summer 2002 2004 abstract measurements of sea ice thickness were obtained from drill holes an ice based electromagnetic induction instrument iem and a ship borne electromagnetic induction instrument sem during the early melt season in the southern chukchi sea in 2002 and 2004 and in late summer 2003 at the time of minimum ice extent in the northern chukchi sea an ice roughness criterion was applied to distinguish between level and rough or ridged ice ice thickness modes in the probability density functions pdfs derived from drill hole and iem measurements agreed well with modes at 1 5 1 6 and 1 8 1 9 m for all data from level ice the pdfs derived from sem measurements show that the primary modes are at 0 1 and 1 1 m in 2003 and 0 7 m in 2004 in 2002 and 2004 significant fractions between one third and one half of level ice were found to consist of rafted ice segments snow depth varied significantly between years with 2004 data showing more than half the snow cover on level ice to be at or below 0 05 m depth in late spring ice growth simulations and examination of ice drift and deformation history indicate that impacts of atmospheric and oceanic warming on level ice thickness in the region over the past few decades are masked to a large extent by variability in snow depth and the contribution of deformation processes in comparison with submarine sonar ice thickness data from previous decades a reduction in ice thickness by about 0 5 1 m is in part explained by the replacement of multi year with first year ice over the chukchi and beaufort shelves

the contribution of alaskan siberian and canadian coastal polynyas to the cold halocline layer of the arctic ocean numerous arctic ocean circulation and geochemical studies suggest that ice growth in polynyas over the alaskan siberian and canadian continental shelves is a source of cold saline water which contributes to the maintenance of the arctic ocean halocline the purpose of this study is to estimate for the 1978 1987 winters the contributions of arctic coastal polynyas to the cold halocline layer of the arctic ocean the study uses a combination of satellite oceanographic and weather data to calculate the brine fluxes from the polynyas then an oceanic box model is used to calculate their contributions to the cold halocline layer of the arctic ocean this study complements and corrects a previous study of dense water production by coastal polynyas in the barents kara and laptev seas recurrent polynyas form on the canadian and alaskan coasts from banks island to the bering strait and on the siberian coast from the bering strait to the new siberian islands in the bering sea polynyas form in norton sound south and west of st lawrence island and in the gulf of anadyr two regions that account for almost 50 of the total dense water production are the siberian coastal polynyas in the adjacent regions of the gulf of anadyr and anadyr strait and the alaskan coastal polynyas which occur along the coast from cape lisburne to point barrow for all of the western arctic coastal regions examined the mean annual total brine flux is 0 5 0 2 sv combination of this flux with the contribution from the barents kara and laptev seas which is recalculated from data in the earlier study shows that over the entire arctic coastal polynyas generate about 0 7 1 2 sv of dense water this compares well with the theoretical estimates of 1 1 5 sv because an unknown fraction of the barents kara and laptev brine flux must go to the eurasian basin deep water the coastal polynyas alone cannot renew the halocline layer other potential brine generation mechanisms include overall freezing on the shelves and the response of the ice to infrequent violent storms for example during february 1982 an intense storm generated a large region of low ice concentration in the eastern chukchi sea over barrow canyon the refreezing of the region was followed by the flow of a dense plume down barrow canyon although the ocean dynamical response to this refreezing needs to be established the possible response of a barrow canyon flow to this refreezing event suggests that the overall refreezing in response to infrequent violent storms may be a potential source of the additional brine needed to maintain the arctic ocean halocline

variability of fram strait ice flux and north atlantic oscillation we estimate the winter sea ice export through the fram strait using ice motion from satellite passive microwave data sea ice motion october may is obtained by tracking the displacement of common features in sequential 85 and 37 ghz brightness temperature fields the average winter area flux over the 18 year record 1978 1996 is 670 000 km2 7 of the area of the arctic ocean the winter area flux ranges from a minimum of 450 000 km2 in 1984 to a maximum of 906 000 km2 in 1995 the daily monthly and interannual variabilities of the ice area flux are high there is an upward trend in the ice area flux over the 18 year record the average winter volume flux over the winters of october 1990 through may 1995 is 1745 km3 ranging from a low of 1375 km3 in the 1990 flux to a high of 2791 km3 in 1994 the sea level pressure gradient across the fram strait explains more than 80 of the variance in the ice flux over the 18 year record we use the coefficients from the regression of the time series of area flux versus pressure gradient across the fram strait and ice thickness data to estimate the summer area and volume flux the average 12 month area flux and volume flux are 919 000 km2 and 2366 km3 we find a significant correlation r 0 86 between the area flux and positive phases of the north atlantic oscillation nao index over the months of december march correlation between our 5 years of volume flux estimates and the nao index gives r 0 56 during the high nao years a more intense icelandic low increases the gradient in the sea level pressure by almost 1 mbar across the fram strait thus increasing the atmospheric forcing on ice transport correlation is reduced during the negative nao years because of decreased dominance of this large scale atmospheric pattern on the sea level pressure gradient across the fram strait

hydrothermal activity and its paleoecological implications in the latest miocene to middle pleistocene lacustrine environments of the baza basin betic cordillera se spain the continental sedimentary record of the baza basin guadix baza depression betic cordillera se spain shows six sedimentary units of lacustrine origin deposited from the latest miocene to the middle pleistocene depending on the interval considered the lacustrine deposits are mainly composed of marls carbonates or gypsiferous evaporites showing lithological mineralogical and geochemical features i e magnesium strontium and sulfur contents celestine deposits and travertine growths that are evidence of intense tectonically induced hydrothermal activity according to the high concentrations of strontium and sulfur as well as the abundance of travertines and magnesium clays the supply of hot waters was greater during the zanclean the gelasian and the calabrian as a result of tectonic activity hydrothermal activity has continued until the present time and is responsible of the hot springs that are nowadays active in the guadix baza depression the paleoenvironmental consequences of these sublacustrine hot springs were that during some intervals the lakes maintained a relatively permanent water table not subject to periodic desiccations in the dry season and warmer temperatures throughout the year this resulted in a high level of organic productivity especially for the calabrian which allowed the development of a rich and well diversified mammalian community similar to those of modern african savannas with tree patches in this mild environment the permanent water sheet favored the presence of drought intolerant megaherbivores such as the giant extinct hippo hippopotamus antiquus the high standing crop biomass of ungulates resulted in the availability of abundant carcasses for scavengers such as hyenas and hominins which explains the very high densities of skeletal remains preserved in the sediments distributed along the lake surroundings

thickness and production of sea ice in the okhotsk sea coastal polynyas from amsr e 1 from comparisons with thickness of sea ice from advanced very high resolution radiometer avhrr and ice profiling sonar data we have developed an advanced microwave scanning radiometer eos amsr e thin ice thickness algorithm for the sea of okhotsk this algorithm can estimate ice thickness of 0 2 m without snow using the polarization ratio of amsr e brightness temperature at a 36 5 ghz channel from a linear relationship with avhrr ice thickness when a snow cover exists on the thin ice surface as occurred a few times in each winter it is shown that the algorithm cannot detect the thin ice sea ice and dense shelf water dsw production in coastal polynya are estimated on the basis of heat flux calculation with the daily amsr e ice thickness for three winters december march of 2002 2003 to 2004 2005 the ice production is largest in the northwest shelf nws polynya which accounts for 45 of the sum of ice production in major coastal polynyas the ice production in major coastal polynyas would cover the maximum ice area of the okhotsk sea if the average ice thickness is assumed to be 1 m variability of the ice production is mainly modulated by air temperature in the nws polynya which is the main dsw production area the annual dsw formation rate is estimated to be 0 36 sv

estimation of sea ice production in the bering sea from amsr e and amsr2 data with special emphasis on the anadyr polynya

palaeoecological and biostratigraphical implications of the microvertebrates of qesem cave in israel abstract microvertebrates are generally well suited for drawing inferences on past environmental conditions because they are closely bound to the areas in which they lived in this paper we discuss palaeoecological implications of two microvertebrate concentrations in the middle pleistocene site qesem cave in israel the ecological preferences of the nearest living relatives of the microvertebrate taxa recorded in concentration 1 squares l n 13 15 and 2 squares g h 16 17 at qesem cave allow us to infer a mosaic of open palaeoenvironment with sparse vegetation shrubland mediterranean forest rocky areas and riverbanks additionally we infer palaeoclimate from the bioclimatic distribution of extant species using the coexistence approach to our knowledge this is the first time the approach has been applied to microfaunal assemblages these data suggest cooler and slightly drier winters and somewhat lower seasonality than at present around qesem cave the differences are more pronounced for the time covered by concentration 2 than concentration 1 among microvertebrates micromammals are most suitable for biostratigraphic purposes with the exception of rattus cf haasi and the myomimus judaicus setzeri group the small mammal fauna of qesem cave comprises only taxa that live today in the levant r haasi and m judaicus have been found in israel in the early and middle pleistocene and their latest known record was from the acheulian site of oumm qatafa their presence in qesem cave extends the previously known stratigraphic range of these species the absence of r haasi in mousterian sites is thus consistent with the pre mousterian age of qesem cave morphometric data on molars of guenther s vole show that the lineage segment preserved in concentration 2 is more primitive than in concentration 1 indicating that the former concentration is older the evolutionary level of the sample from qesem concentration 1 is similar to tabun d boundary of acheulo yabrudian cultural complex and mousterian and that from qesem concentration 2 similar to tabun eb acheulo yabrudian

deterioration of perennial sea ice in the beaufort gyre from 2003 to 2012 and its impact on the oceanic freshwater cycle time series of ice draft from 2003 to 2012 from moored sonar data are used to investigate variability and describe the reduction of the perennial sea ice cover in the beaufort gyre bg culminating in the extreme minimum in 2012 negative trends in median ice drafts and most ice fractions are observed while open water and thinnest ice fractions 0 3 m have increased attesting to the ablation or removal of the older sea ice from the bg over the 9 year period monthly anomalies indicate a shift occurred toward thinner ice after 2007 in which the thicker ice evident at the northern stations was reduced differences in the ice characteristics between all of the stations also diminished so that the ice cover throughout the region became statistically homogenous the moored data are used in a relationship with satellite radiometer data to estimate ice volume changes throughout the bg summer solid fresh water content decreased drastically in consecutive years from 730 km3 in 2006 to 570 km3 in 2007 and to 240 km3 in 2008 after a short rebound solid fresh water fell below 220 km3 in 2012 meanwhile hydrographic data indicate that liquid fresh water in the bg in summer increased 5410 km3 from 2003 to 2010 and decreased at least 210 km3 by 2012 the reduction of both solid and liquid fresh water components indicates a net export of approximately 320 km3 of fresh water from the region occurred between 2010 and 2012 suggesting that the anticyclonic atmosphere ocean circulation has weakened

rectilinear evolution in arvicoline rodents and numerical dating of iberian early pleistocene sites abstract lozano fernandez et al 2013a have recently published a method intended for numerical dating of early pleistocene sites which is based on the assumption of uniform constant rate increase through time of mean lower molar tooth length of water voles mimomys savini in a number of levels sampled in the stratigraphic sequence of atapuerca td site they suggest that the regression equation obtained in this local section for site chronology on tooth size could be useful for estimating the numerical age of other localities from southwestern europe however in our opinion this biostratigraphic approach has severe conceptual and methodological problems which discourage its use as a chronometric tool these problems include that 1 the logic behind their approach represents a fallacy of hasty generalization because the results obtained for a local section are generalized to all possible stratigraphic sequences 2 the study is based on tooth measurements from a limited set of samples taken in a single locality which are represented by small numbers of specimens cover a short time span and have a high level of age uncertainty 3 the samples analyzed show small statistically non significant differences between their mean tooth length values 4 the approach assumes a linear straight orthoevolutionary model of change at constant monotonic rate for the apparent trend to increasing tooth size in the m savini lineage 5 these changes are better described in the atapuerca td section by a random walk or even by a series of independent events than by a model of rectilinear change and 6 the application of this methodology to other localities such as the orce sites which preserve the oldest evidence of human presence in europe would mean that an equation adjusted within a restricted chronological range 1 01 0 8 ma is used for extrapolating the ages of sites that are clearly older 1 4 ma

revisiting the esr chronology of the early pleistocene hominin occupation at vallparadis barcelona spain abstract esr dating was applied to fossil teeth and optically bleached quartz grain samples from two units of the sequence at vallparadis barcelona spain weighted mean esr age estimates of 858 87 ka and 849 48 ka were obtained for evt 7 which includes the archaeological level 10 and evt 8 respectively these results are in good agreement with the existing magneto biostratigraphic framework that constrain these deposits between 780 and 990 ka and indicate that vallparadis evt 7 has a chronology very close to that of atapuerca gran dolina td 6 spain

retreat of the cold halocline layer in the arctic ocean we present a comparison of arctic ocean hydrographic data sets from the 1990s with a focus on changes in the upper few hundred meters of the eurasian basin the most recent observations discussed here were collected during the spring 1995 scientific ice expedition scicex 95 the second in a series of scientific cruises to the arctic ocean aboard u s navy nuclear submarines although the 1990s have seen an abundance of synoptic cruises to the arctic this was the only one to take place in winter spring conditions other data considered here were collected during the first scicex cruise in summer 1993 scicex 93 and during an icebreaker cruise to the eurasian basin in summer 1991 oden 91 a new russian american winter climatology is also used as a reference these comparisons reveal that the eurasian basin cold halocline layer has retreated during the 1990s to cover significantly less area than in previous years specifically we find a retreat from the amundsen basin back into the makarov basin the latter is the only region with a true cold halocline layer during scicex 95 changes are also seen in other halocline types and in the atlantic water layer heat content and depth since the cold halocline layer insulates the surface layer and thus the overlying sea ice from the heat contained in the atlantic water layer this should have profound effects on the surface energy and mass balance of sea ice in this region using a simple mixing model we calculate maximum ice ocean heat fluxes of 1 3 w m 2 in the eurasian basin where during scicex 95 the surface layer lay in direct contact with the underlying atlantic water layer the overall cause of water mass changes in the 1990s might have been a shift in the atmospheric wind forcing and resulting sea ice motion during the late 1980s which we speculate influenced the location where fresh shelf waters flow into the deeper basins of the arctic ocean finally we discuss two different mechanisms that have been proposed for cold halocline water formation and we propose a compromise that best fits these data

western arctic shelfbreak eddies formation and transport abstract the mean structure and time dependent behavior of the shelfbreak jet along the southern beaufort sea and its ability to transport properties into the basin interior via eddies are explored using high resolution mooring data and an idealized numerical model the analysis focuses on springtime when weakly stratified winter transformed pacific water is being advected out of the chukchi sea when winds are weak the observed jet is bottom trapped with a low potential vorticity core and has maximum mean velocities of o 25 cm s 1 and an eastward transport of 0 42 sv 1 sv 106 m3 s 1 despite the absence of winds the current is highly time dependent with relative vorticity and twisting vorticity often important components of the ertel potential vorticity an idealized primitive equation model forced by dense weakly stratified waters flowing off a shelf produces a mean middepth boundary current similar in structure to that observed at the mooring site the model boundary current is also highly v

on the dynamics of hawaiian cloud bands island forcing abstract this study focuses on basic island scale forcing mechanisms for the formation and evolution of a band cloud typically present upwind of the island of hawaii by means of numerical experiments and verification of our results against observations and laboratory experiments reported in the literature we show that the band cloud is a complex three dimensional phenomenon which is inseparable from the airflow around the island in particular we demonstrate that the event needs to be analyzed in terms of the basic fluid dynamics of strongly stratified flow past a three dimensional obstacle the band cloud is found to arise primarily from the dynamic interaction of the trade winds with the island the upwind surface flow forms a separation line with an associated stagnation point a low level convergence zone forms along this line resulting in an updraft line if the updrafts are strong enough a band cloud forms formation and characteristics of such a system are mostly controlled by the environmenta

a numerical study of dense water formation and transport on a shallow sloping continental shelf the circulation and transport of dense water generated by an idealized coastal polynya is studied using a three dimensional primitive equation model starting with a homogeneous quiescent ocean a constant negative buoyancy flux is imposed at the surface over a half elliptical region adjacent to the coastal boundary on a gently sloping continental shelf the flow response can be divided into the following three phases geostrophic adjustment instability and offshore eddy transport during geostrophic adjustment the fluid within the forcing region becomes denser and the flow at the edge of the forcing region accelerates in response to the strong density gradient there eventually the flow at the leading edge of the forcing region relative to kelvin wave propagation becomes unstable and a train of counterrotating eddies develops these eddies then form a complex three dimensional flow field and rapidly transport dense water offshore across isobaths the density within the forcing region reaches a maximum which remains fairly constant after the eddies begin to transport the dense fluid offshore the results are qualitatively insensitive to weakening of the negative buoyancy forcing and to changing the bottom slope eddy scales and velocities are consistent with observations in the arctic the results suggest that instability processes and eddy fluxes are important in transporting dense water off continental shelves and into marginal seas

assimilating summer sea ice concentration into a coupled ice ocean model using a lseik filter the decrease in summer sea ice extent in the arctic ocean opens shipping routes and creates potential for many marine operations for these activities accurate predictions of sea ice conditions are required to maintain marine safety in an attempt at arctic sea ice prediction the summer of 2010 is selected to implement an arctic sea ice data assimilation da study the da system is based on a regional arctic configuration of the massachusetts institute of technology general circulation model mitgcm and a local singular evolutive interpolated kalman lseik filter to assimilate special sensor microwave imager sounder ssmis sea ice concentration operational products from the us national snow and ice data center nsidc based on comparisons with both the assimilated nsidc ssmis concentration and concentration data from the ocean and sea ice satellite application facility the forecasted sea ice edge and concentration improve upon simulations without data assimilation by the nature of the assimilation algorithm with multivariate covariance between ice concentration and thickness sea ice thickness fields are also updated and the evaluation with in situ observation shows some improvement compared to the forecast without data assimilation

effects of ambient stratification and shelfbreak topography on offshore transport of dense water on continental shelves the transport of dense water offshore from an idealized coastal polynya is examined using a primitive equation numerical model first the prior scaling of the equilibrium density of water produced within the polynya is extended to include the effects of linear bottom slope next ambient linear stratification is added the equilibrium density is modified slightly by the density at the bottom at the initial time next shelfbreak topography is included with both weak and strong ambient stratification for the case of weak stratification dense water carried to the shelfbreak within eddies moves rapidly downslope and is trapped near the bottom the along shelf scale of the dense water cascading down the slope is set by the diameter of the dense water eddies that form along the periphery of the coastal polynya for the case of strong stratification dense water is carried offshore across the shelfbreak at an intermediate depth injecting water originally within the polynya across the shelf and over the continental slope a bottom trapped current flowing near the shelfbreak in the direction of coastal trapped wave propagation also forms these results suggest that water formed within coastal polynyas over arctic shelves may be capable of ventilating the continental slope regions and possibly central basins of the arctic ocean via eddy fluxes

using sea ice deformation fields to constrain the mechanical strength parameters of geophysical sea ice we investigate the ability of viscous plastic vp sea ice models with an elliptical yield curve and normal flow rule to reproduce the shear and divergence distributions derived from the radarsat geophysical processor system rgps in particular we reformulate the vp elliptical rheology to allow independent changes in the ice compressive shear and isotropic tensile strength parameters p s t respectively in order to study the sensitivity of the deformation distributions to changes in the ice mechanical strength parameters our 10 km vp simulation with standard ice mechanical strength parameters p 27 5 knm 2 s 6 9 knm 2 and t 0 knm 2 ellipse aspect ratio of e 2 does not reproduce the large shear and divergence deformations observed in the rgps deformation fields and specifically lacks well defined active linear kinematic features lkfs probability density functions pdfs for the shear and divergence of are nonetheless not gaussian simulations with a reduced compressive or increased shear strength are in good agreement with rgps derived shear and divergence pdfs with relatively more large deformations compared to small deformations the isotropic tensile strength of sea ice on the other hand does not significantly affect the shear and divergence distributions when considering additional metrics such as the ice drift error mean ice thickness fields and spatial scaling of the deformations our results suggest that reducing the ice compressive strength is a better solution than increasing the shear strength when performing arctic wide simulations of the sea ice cover with the vp elliptical rheology

landfast ice affects the stability of the arctic halocline evidence from a numerical model landfast ice covers large surface areas of the winter siberian seas the immobile landfast ice cover inhibits divergent and convergent motion hence dynamical sea ice growth and redistribution decouples winter river plumes in coastal seas from the atmosphere and positions polynyas at the landfast ice edge offshore in spite of the potentially large effects state of the art numerical models usually do not represent landfast ice in its correct extent a simple parametrization of landfast ice based on bathymetry and internal sea ice strength is introduced and its effects on the simulated arctic ocean are demonstrated the simulations suggest that the siberian landfast ice impacts the arctic halocline stability through enhanced brine production in polynyas located closer to the shelf break and by redirecting river water to the canadian basin these processes strengthen the halocline in the canadian basin but erode its stability in the makarov and eurasian basins

aerial observations of hawaii s wake abstract under the influence of the east northeasterly trade winds the island of hawaii generates a wake that extends about 200 km to the west southwest during the harp project in july and august 1990 five wake surveys were carried out by the ncar electra the patterns of wind and aerosol concentration revealed by these flights suggest that hawaii s wake consists of two large quasi steady counterrotating eddies the southern clockwise rotating eddy carries a heavy aerosol load due to input from the k volcano at the eastern end of the wake the eddies are potentially warmer and more humid than the surrounding trade wind air several other features are discussed sharp shear lines near the northern and southern tips of the island dry and warm air bands along the shear lines a small embedded wake behind the kohala peninsula wake centerline clouds hydraulic jumps to the north and south of the island a descending inversion connected with accelerating trade winds and evidence for side to side wake mo

on the limits of using combined u series esr method to date fossil teeth from two early pleistocene archaeological sites of the orce area guadix baza basin spain abstract article history received 6 june 2011available online 9 february 2012keywords combined u series esr dating methodfossil teethfuente nueva 3barranco leonorceearly pleistocene the combined u series electron spin resonance esr dating method was applied to nine teeth from twoearly pleistocene archaeological sites located in the orce area guadix baza basin southern spain fuentenueva 3 fn 3 and barranco leon bl the combination of biostratigraphy and magnetostratigraphy placesboth sites between the olduvai and jaramillo subchrons 1 78 1 07 ma our results highlight the dif culty of dating such old sites and point out the limits of the combined u series esr dating method based on the us model we identi ed several sources of uncertainties that may lead toinaccurate age estimates seven samples could not be dated because the dental tissues had 230 th 234 u ac tivity ratios higher than equilibrium indicating that uranium had probably leached from these tissues it washowever possible to calculate numerical estimates for two of the teeth both from fn 3 one yielded a middlepleistocene age that seems to be strongly underestimated the other provided an age of 1 19 0 21 ma inagreement with data obtained from independent methods the latter result gives encouragement thatthere are samples that can be used for routine dating of old sites 2012 university of washington published by elsevier inc all rights reserved

the influence of an alongshelf current on the formation and offshore transport of dense water from a coastal polynya the influence of an ambient alongshelf current on the formation and offshore transport of dense water from an idealized coastal polynya is examined by using a primitive equation numerical model brine rejection during ice formation within the polynya is modeled by a prescribed surface buoyancy flux over a limited region along a straight coastline a uniform alongshelf current is imposed at one end of the model domain the basic ocean response is unchanged by the ambient current i e an unstable density front forms around the polynya perimeter and breaks up into small scale 15 30 km eddies that carry the dense water away from the polynya the ambient current continuously carries water out of the polynya region thereby both increasing the alongshelf density flux and reducing the typical density anomaly generated the total volume of dense water formed is not appreciably altered the influence of a submarine canyon located downstream of the polynya in the direction of the imposed alongshelf current is examined almost no dense water enters a canyon oriented normally or diagonally to the coast because the ambient flow tends to follow isobaths and carries virtually all of the dense water around and past the canyon an appreciable fraction of densified water may flow down a canyon oriented parallel to the coast the details depending on the canyon geometry and the strength of the ambient current thus both the density anomalies produced by coastal polynyas and the pathways of dense water transport are sensitive to ambient shelf currents potentially providing a source of interannual variability in dense water formation and export from the shelf

dynamics of the terra nova bay polynya the potential of multi sensor satellite observations research on processes leading to formation maintenance and disappearance of polynyas in the polar regions benefits significantly from the use of different types of remote sensing data the sentinels of the european space agency esa together with other satellite missions provide a variety of data from different parts of the electromagnetic spectrum at different spatial scales and with different temporal resolutions in a case study we demonstrate the advantage of merging data from different spaceborne instruments for analysing ice conditions and ice dynamics in and around the frequently occurring terra nova bay polynya tnbp in the ross sea in the antarctic starting with a list of polynya parameters that are typically retrieved from satellite images we assess the usefulness of different sensor types on regional scales several 100 km passive microwave radiometers provide a view on the mutual influence of the three ross sea polynyas on sea ice drift and deformation patterns optical sensors with meter scale resolution on the other hand allow very localized analyses of different polynya zones the combination of different ranges of the electromagnetic spectrum is essential for recognition and classification of ice types and structures radar images together with data from thermal infrared sensors operated at tens to hundreds of meters resolution improve the separation of the outlet zone of the polynya from the adjacent pack ice the direct comparison of radar and passive microwave images reveals the visibility of deformed ice zone in the latter a sequence of radar images was employed to retrieve ice drift around the tnb which allows analysing the temporal changes of the polynya area and the extension and structure of the outlet zone as well as ice movements and deformation that are influenced by the katabatic winds

characteristics of stable flows over southern greenland the main characteristic features of stable atmospheric flows over a large mountain plateau are summarised and then compared with mesoscale and synoptic scale numerical simulation meteorological analysis satellite imagery and surface observations for the cases of flows over southern greenland for four wind directions the detailed features are identified using the concepts and scaling of stably stratified flow over large mountains with variations in surface roughness elevation and heating for westerly and easterly winds detached jets form at the southern tip where coastal jets converge which propagate large distances across the ocean near coasts katabatic winds can combine with barrier jets and wake flows generated by synoptic winds note how the approach flow rises falls over southern greenland for easterly westerly winds leading in both cases to more cloud on the western side some conclusions are drawn about the large scale influences of these flows detached jets in the atmosphere air sea interaction formation of low pressure systems for accurate simulations of these flows mesoscale models are necessary with resolutions of order of 20 km or less

a new subgrid scale orographic drag parametrization its formulation and testing a scheme for the representation of subgrid scale orography sso in numerical weather prediction and climate models is presented the new scheme arose in part from a desire to represent nonlinear low level mountain drag effects not currently parametrized an important feature of the scheme is that it deals explicitly with a low level flow which is blocked when the effective height of the subgrid scale orography is sufficiently high in this new scheme it is assumed that for this blocked flow separation occurs at the mountain flanks resulting in a form drag this drag is parametrized on model levels which are intersected by the sso and provides a dynamically based replacement for envelope orography the upper part of the low level flow goes over the orography and generates gravity waves at the model resolutions considered t106 and t213 it is assumed that the length scales characteristic of the sso are sufficiently small for the coriolis force to be neglected the various parameters of the scheme are adjusted using an off line procedure in which the scheme is used to estimate the mountain drag and the momentum profiles above the pyrenees and these estimates are validated with the pyrex data forecasts using t106 and t213 resolutions with this new scheme and with mean orography show that the forecast mountain drag consistently reproduces the drag measured during pyrex whenever the flow component normal to the ridge is large isentropic flow diagnostics further show that the new scheme has a realistic impact on the flow dynamics reinforcing the low level wake observed in mesoscale analyses of the flow with this new scheme and a mean orography the ecmwf model outperformed in forecast skill a version of the model which had an envelope orography and the old gravity wave drag scheme while no longer suffering any disadvantages of envelope orography the proposed low level drag parametrization should also be relevant at model horizontal resolutions much higher than t213

circulation dense water formation and outflow on the northeast chukchi shelf we investigated circulation and water mass modification processes in the chukchi sea using 1 temperature salinity and velocity data collected between september 1991 and september 1992 from moorings in bering strait and the northeast shelf and 2 meteorological data and ice concentrations derived from special sensor microwave imager ssm i imagery in october 1991 and from february to august 1992 the mean monthly circulation was steady and northward from november to january strong northeast winds diverted the low salinity bering inflow onto the western shelf and weakened and reversed flow over the northeast shelf the winds also opened extensive polynyas wherein cold hypersaline salinity 34 waters formed the fall winter circulation enhanced dense water formation by diverting low salinity waters away from and prolonging the residence time of water within the polynyas alongshore convergence of the coastal flow swept some of the cold hypersaline water offshore across isobaths but the coastal current carried most of it into the arctic ocean through barrow canyon the dense outflow mixed little during its descent through the upper canyon where bottom friction and rotation but not entrainment were important in the plume momentum balance if the outflow is not diluted by mixing in the lower canyon where theory suggests this will occur then the densest shelf waters can ventilate layers deeper than the halocline salt rejection estimates using ssm i data and surface heat budget calculations agree within a factor of 2 with independent estimates from the mooring hence remote sensing techniques can monitor winter salt rejection rates in the chukchi sea

observations of supercooled water and frazil ice formation in an arctic coastal polynya from moorings and satellite imagery formation of supercooled water and frazil ice was studied in the chukchi sea coastal polynya off barrow alaska usa in winter 2009 10 using moored salinity temperature sensors and ice profiling sonar ips data along with satellite data oceanographic data from two moorings revealed episodic events of potential supercooling at 30 40m depth including the possibility of in situ supercooling while the polynya was open we identified frazil ice like signals in the ips data down to 5 15 m depth associated with large heat loss and windy turbulent conditions in an active polynya this likely represents the first ips observation of frazil ice in the marine environment on the day of the maximum signal of frazil ice spaceborne synthetic aperture radar shows streaks of high backscatter within the polynya indicating active frazil ice formation just downwind of the mooring sites in addition the longer term potential supercooling that persisted for 1 3 weeks occurred twice despite the absence of polynya activity at the mooring sites these events occurred during periods dominated by the northeastward current a series of coastal polynyas had formed southwest of the mooring sites prior to these events thus the water masses with potential supercooling were likely advected from these polynyas

early human occupation of iberia the chronological and palaeoclimatic inferences from vallparadis barcelona spain abstract vallparadis is one of the best calibrated and most accurately dated archaeological sites from the european early pleistocene chronological analyses combined with palaeomagnetism esr u series and osl and the biochronology of macro and micromammals are fully consistent and situate the site just above the upper limit of the jaramillo subchron in this article we compare the mandibular first molar m1 of individual adult specimens of mimomys savini recovered from level 10 evt7 at vallparadis with specimens from the stratigraphic sequence at gran dolina atapuerca fuente nueva 3 and barranco leon d orce this comparison allows us to chronostratigraphically relate level 10 at vallparadis with level td5 at gran dolina and to fix the former s chronology to around 0 98 0 95 ma mis 27 and therefore prior to level td6 in which fossil remains of homo antecessor were recovered the chronology of vallparadis and the set of contemporary palaeoclimatic proxies regarding the iberian peninsula strengthen the hypothesis that hominins continuously populated europe at least in iberia throughout the late early pleistocene between the jaramillo subchron and the matuyama brunhes boundary by overcoming the climatic fluctuations and changes to the landscape that occurred during this period

observations of ice thickness and frazil ice in the st lawrence island polynya from satellite imagery upward looking sonar and salinity temperature moorings 1 for the 1999 winter this paper examines the behavior of the bering sea st lawrence island polynya using a combination of advanced very high resolution radiometer avhrr radarsat synthetic aperture radar sar meteorological data over winter moored upward looking sonars uls and seabird salinity temperature sensors we define a thermal ice thickness from the avhrr retrieval of ice surface temperature combined with meteorological observations and a heat flux model south of the island we compare the uls and thermal thicknesses for congelation and frazil ice when the satellites observe congelation ice over the ulss the uls and thermal ice thicknesses generally agree when sar observes langmuir plumes over the ulss which indicate frazil ice formation the ulss show scatterers at 5 20 m depths in the water column and the seawater temperatures are either within 0 01 c of freezing or are slightly supercooled this suggests that during frazil events crystals either nucleate at depth or are transported to depth by the langmuir circulation the combination of the sar imagery and uls observations also allow measurement of the pack ice advection velocity the polynya width and the downwind frazil accumulation thickness giving widths of 10 to 30 km and thicknesses of 0 1 0 2 m substitution of these observed values with the heat flux into the pease polynya model yields polynya widths that approximately agree with the observed