glacier subsurface heat flux characterizations for energy balance modelling in the donjek range southwest yukon canada we apply a point scale energy balance model to a small polythermal glacier in the st elias mountains of canada in order to investigate the applicability and limitations of different treatments of the glacier surface temperature and subsurface heat flux these treatments range in complexity from a multilayer subsurface model that simulates snowpack evolution to the assumption of a constant glacier surface temperature equal to 0 c the most sophisticated model includes dry densification of the snowpack penetration of shortwave radiation into the subsurface internal melting refreezing of percolating meltwater and generation of slush layers measurements of subsurface temperature and surface lowering are used for model validation and highlight the importance of including subsurface penetration of shortwave radiation in the model using an iterative scheme to solve for the subsurface heat flux as the residual of the energy balance equation results in an overestimation of total ablation by 18 while the multilayer subsurface model underestimates ablation by 6 by comparison the 0 c surface assumption leads to an overestimation of ablation of 29 in this study where the mean annual air temperature is about 8 c

geology and tectonic setting of paleoproterozoic granitoid suites in the island harbour bay area makkovik province labrador paleoproterozoic granitoid rocks in the island harbour bay area kaipokok domain makkovik province labrador are divided into four separate suites on the basis of field relations petrology and age the redefined island harbour bay plutonic suite consists of ca 1895 1870 ma dioritic to granitic mainly granodioritic and granitic units the rocks are variably foliated as a result of emplacement under amphibolite facies conditions in a dextral transpressive regime during andean type subduction the dominant mafic mineral is biotite and accessory epidote allanite and titanite are abundant the suite is calc alkalic but with rare earth element patterns similar to those of archean tonalitic trondhjemitic granodioritic suites it is interpreted to have formed deep in an andean type magmatic arc at the margin of the nain continent in contrast the younger hares islands and drunken harbour granites emplaced at ca 1805 and 1790 ma respectively were part of widespread late orogenic magmatic activity i

tidal mixing and trapping in mangrove swamps lateral trapping in mangrove swamps is a dominant process controlling longitudinal mixing in mangrove fringed tidal rivers in the dry season the effective value of the longitudinal diffusivity is increased by the trapping effect by typically two orders of magnitude from its value in the absence of swamps in the wet season freshwater is trapped within the swamp and the adjoining boundary in the tidal river for long periods following the passage of a short lived flood this may have important ecological implications a fluid mud layer appears to be created by strong tidal currents over colloidal mangrove mud

episodic early proterozoic granitoid plutonism in the makkovik province labrador u pb geochronological data and geological implications episodic granitoid plutonism in the early proterozoic makkovik province of the easternmost canadian shield is revealed by high precision u pb zircon studies of a range of intrusive rock types the

negative estuarine circulation in the ria of pontevedra nw spain an along estuary negative circulation was measured in the ria of pontevedra nw spain on may 13 1998 this two layered circulation pattern with near bed water moving seaward and near surface water landward was generated by the existence of two different water masses at intermediate depths water in the inner part of the estuary was a mixture of estuarine water and eastern north atlantic central water enacw which had entered the estuary some days before due to an intense upwelling event water in the middle part of the estuary was a mixture of estuarine water and fresh water coming from the river discharge which had been higher during the days previous to may 13 this water mass distribution gave rise to the existence of denser water in the inner part of the estuary than in the middle one generating the observed negative circulation pattern

outwelling from tropical tidal salt flats abstract the norman river flows into the gulf of carpentaria north east australia the estuary is surrounded by 250 km2 of vegetation free saline supratidal mud flats which are only inundated by the tides at spring high tide in summer when the seasonal sea level is 0 5 1 m higher than in winter the first summer tidal inundation of the salt flats in november 1985 resulted in a readily measurable export from the salt flats of salt and nutrients outwelling values of 90 g salt m 2 per tidal cycle 1 0 mmol silicate m 2 and 3 10 2 mmol orthophosphate m 2 were measured about a quarter of the 4000 km2 of salt flats along the southern shore of the gulf of carpentaria outwell into the gulf the rest outwell into the estuaries where salt outwelling increases the strength of the salinity maximum zone of the estuaries further isolating the rivers from the gulf during the dry season

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

dynamics of hypersaline coastal waters in the great barrier reef the coastal waters of the great barrier reef gbr are hypersaline salinity 37 during the dry season as a result of evaporation greatly exceeding rainfall of shallow waters and of the presence of numerous bays along the coast preventing rapid flushing these hypersaline waters are not flushed out by salinity driven baroclinic currents because these waters are vertically well mixed instead these waters are transported by a longshore residual current and thus form a coastal boundary layer of hypersaline waters as a result the hypersalinity distribution is 2 d with both cross shelf and longshore gradients of salinity the cross shelf gradients are largely controlled by turbulent diffusion while the longshore gradients are controlled by the residual currents that transport hypersaline waters longshore south ward in the central and southern regions of the gbr because every bay supplies hypersaline waters the width of the coastal hypersaline layer increases southwards steady state is reached in about 100 days which is the typical duration of the dry season the dynamics of the gbr hypersaline coastal boundary layer thus differ from the classical inverse hypersaline systems e g in saloum river estuary laguna san ignacio mission bay tomales bay san diego bay hervey bay shark bay coorong coast lagoon spencer gulf gulf of california and many others where the salinity gradient is mainly 1 d with a dominant along channel salinity gradient

nd and pb isotope mapping of crustal domains within the makkovik province labrador the makkovik province of eastern labrador represents part of an accretionary orogen active during an early stage in the development of the palaeoproterozoic southern laurentian continental margin new nd isotope data for the eastern makkovik province suggest that accreted juvenile makkovik crust was generated in the cape harrison domain during a single crust forming event at c 2 0 ga pb isotope data support this model and show a strong similarity to radiogenic crustal signatures in the juvenile palaeoproterozoic crust of the ketilidian mobile belt of southern greenland as previously proposed an arc accretion event at c 1 9 ga triggered subduction zone reversal and the development of an ensialic arc on the composite margin after the subduction flip a temporary release of compressive stress at c 1 87 ga led to the development of a retro arc foreland basin on the downloaded archean continental edge forming the aillik group unlike previous models a second arc is not envisaged instead a compressive regime at c 1 82 ga is attributed to continued ensialic arc plutonism on the existing margin the tectonic model for the makkovikian orogeny proposed here is similar to that for the ketilidian orogeny major and trace element analyses suggest that much of the magmatism in the makkovik orogen results from post accretionary ensialic arc activity and that few vestiges remain of the original accreted volcanic arc this pattern of arc accretion and intense post accretion reworking is common to many accretionary orogens such as the south american andes and north american cordillera

transformation of a subtropical river into a hyperhaline estuary the casamance river senegal paleogeographical implications abstract located in the south of senegal in the transitional guineo congolian soudanian zone the casamance system is composed of a small river supplied by a narrow drainage basin and followed by a 250 km long estuary the continuous rainfall decrease experienced by the region since the beginning of the century drastically affected the casamance river this climatic change suddenly accelerated during 1968 1970 which led to a four stage succession before 1968 1970 stage 1 rainfall 1300 mm the casamance estuary showed the customary negative upstream salinity gradient between 1968 1970 and 1978 stage 2 rainfall 1000 mm under decreasing rainfall the casamance estuary shifted to a hyperline inverse estuary it showed well defined physical chemical and biological zonations fresh groundwater resources supplying the upper reaches of the river during the dry season were progressively depleted between 1978 and 1986 1987 stage 3 the salinity peak of the end of the dry season progressively rose and shifted upward the ecological zonation showed the increasing marine influence until 1986 between 1986 1987 and 1990 stage 4 the dry season fresh water input had weakened with the depletion of groundwater resources a slight increase in rainfall was insufficient to repulse the hyperhaline waters and the restricted area extended upstream and downstream the physical chemical and biological zonations strongly widened and flattened in the future the return to stage 1 conditions by an increase in average rainfall would take decades inevitably it will be much longer than the transformation into a hyperhaline estuary thus a slight decrease of the average rainfall in the region provoked a drastic change of the hydrological and biological patterns of the ria the result seems to be a major crisis in the region and might be recorded in the fossil records we discuss these observations in terms of possible misreadings of paleoenvironments and in relation with long term climate trends

soil moisture wind speed and depth hoar formation in the arctic snowpack basal depth hoar that forms in arctic snowpacks often has a low thermal conductivity strongly contributing to the snowpack thermal insulance and impacting the permafrost thermal regime at ward hunt island canadian high arctic 83 05 n 74 07 w almost no depth hoar was observed in spring 2016 despite favorable thermal conditions we hypothesize that depth hoar formation was impeded by the combination of two factors 1 strong winds in fall that formed hard dense wind slabs where water vapor transport was slow and 2 low soil moisture that led to rapid ground cooling with no zero curtain period which reduced soil temperature and the temperature gradient in the snowpack comparisons with detailed data from the subsequent winter at ward hunt and from bylot island 73 09 n 80 00 w and with data from barrow and alert indicate that both high wind speeds after snow onset and low soil moisture are necessary to prevent arctic depth hoar formation the role of con vection to form depth hoar is discussed a simple preliminary strategy to parameterize depth hoar thermal conductivity in snow schemes is proposed based on wind speed and soil moisture finally warming induced vegetation growth and soil moisture increase should reduce depth hoar thermal conductivity potentially affecting permafrost temperature

chemical composition of the snowpack during the oasis spring campaign 2009 at barrow alaska 1 the chemical composition of the seasonal snowpack was determined close to barrow an arctic coastal location in northern alaska one hundred and twelve samples of different snow types including fresh snow surface hoar diamond dust blowing snow rounded snow grains and depth hoar were collected and analyzed for major sea salt components bromide and nitrate sodium chloride sulfate and potassium are mainly introduced into the snowpack by the deposition of sea salt while magnesium and calcium result from a combination of sea salt and dust sulfate was strongly depleted in most samples compared to other sea salt components this is attributed to the precipitation of mirabilite in newly formed sea ice and frost flowers that leads to an efficient fractionation of sulfate uptake of volatile but soluble species from the gas phase also contributed to the observed chloride sulfate and nitrate in the snow however for chloride and sulfate the input from the marine sources was overwhelming and the uptake from the gas phase was only visible in the samples with low concentrations like fresh snow diamond dust and surface hoar nitrate concentrations in the snowpack were less variable and for aged snow nitrate was related to the specific surface area of the snow indicating the adsorption of nitric acid can be an important nitrate source in the aged snow bromide was also introduced into the snowpack from marine sources but due to its high reactivity it was partly transferred back to the atmosphere in the form of reactive species the result of these processes was evident in bromide concentrations which were both enriched and depleted at the snowpack surface while deeper layers were mostly depleted blowing snow also exhibited a depleted bromide composition for all compounds except nitrate many depth hoar samples exhibited the greatest concentrations probably as a result of higher input earlier in the season as well as increases due to the sublimation of water during the metamorphism of the snow

u pb geochronologic constraints on paleoproterozoic orogenesis in the northwestern makkovik province labrador canada a 45 km wide shear zone bounded segment of the northwestern makkovik province labrador is underlain by archean gneisses derived from the adjacent nain craton this lithotectonic block kaipokok domain was reworked at high metamorphic grade overthrust by supracrustal sequences lower aillik and moran lake groups and intruded by granitoid plutons during the paleoproterozoic initial amphibolite facies reworking of the kaipokok domain at 1896 6 ma is indicated by u pb ages of metamorphic zircon from a foliated kikkertavak metadiabase dyke this is one of the oldest paleoproterozoic tectonic events dated thus far in northeast laurentia and may be linked with ca 1890 ma plutonism documented elsewhere in the kaipokok domain intrusion of granitoid plutons at 1877 5 and in the kaipokok bay area postdates early thick and thin skinned thrusting possibly east to northeast directed that involved lower aillik group strata u pb titanite ages of 1866 1847 ma in part record a metamorphic event that fo

the knudsen theorem and the total exchange flow analysis framework applied to the baltic sea abstract the knudsen theorem for estuarine exchange flow based on mass conservation of water and salt and its generalization with resolution in salinity coordinates the total exchange flow tef analysis framework are reviewed here the former had been developed and applied to quantify exchange flow between the north sea and the baltic sea more than a century ago in this paper the underlying short research paper published in 1900 by martin knudsen originally written in german is translated into english reaching far beyond the knudsen relation in particular the extensive scientific achievements of martin knudsen on the salinity of seawater are reviewed using the knudsen theorem and the tef analysis framework validated multi decadal years 1949 2013 model simulations are analyzed in terms of exchange flow through straits of the western baltic sea when comparing the model results to the original findings of martin knudsen it is impressive to see how relevant his analysis of ratios of averaged inflowing and outflowing water masses still is today given that they were based on just a few salinity observations the model based long term knudsen and tef analyses of exchange flow in the western baltic sea reproduces the major baltic inflows mbis that have occurred since the 1950s for the complex inflow years 2002 2003 with two baroclinic summer inflows and one barotropic winter inflow in between the strong underestimation of the exchange flow by eulerian analysis as compared to tef analysis is demonstrated

water circulation and coastal trapping of brackish water in a tropical mangrove dominated bay in kenya water circulation patterns in a tropical mangrove fringed bay with seagrass and coral reef are driven by tides that generate strong reversing tidal currents the wind which has an onshore component generates a net clockwise rotating eddy the dominant tidally driven water circulation pattern coupled with the effects of onshore wind and alongshore current generated by wave breaking promotes the coastal trapping of turbid brackish water and its inherent nutrient content this brackish water inundates the mangrove swamp and seagrass beds but not the coral reef ecosystem weak stratification prevails during the wet season in the upper parts of kidogoweni creek as a result of freshwater influx from rivers in the dry season well mixed homogeneous water is found in most regions of the bay a small zone of hypersaline water salinity reaching 38 psu is found in the upper region of the mangrove dominated creeks during the dry season the connection between the mangrove swamp with its wide salinity variations and seagrass beds is apparently through river plumes and tidal effects the link between seagrass beds and coral reefs is mainly through tidal influences

the importance of late and post orogenic crustal growth in the early proterozoic evidence from smnd isotopic studies of igneous rocks in the makkovik province canada abstract sm nd isotopic studies suggest that large tracts of 1900 1700 ma old crust in laurentia baltica is of juvenile origin this crust has generally been ascribed to arc magmatism sustained over long periods and most conceptual models for crustal growth emphasize this process the late to post orogenic granitoid rocks that areally dominate many ancient orogenic belts are commonly viewed as anatectic derivatives of the earlier arc type crust however in regions of short crustal residence the time resolution of isotopic tracers such as the sm nd system does not permit discrimination between this model and continued growth of the crust during post orogenic magmatism the relative contributions of recycled crust and new mantle derived material in late to post orogenic magmas can only be assessed where they also transect much older crustal blocks the nd isotopic signatures of 1800 1720 ma igneous suites in the makkovik province define such a boundary between an archean craton and a juvenile proterozoic domain in the juvenile domain the nd signatures of most igneous suites are equivocal initial nd 0 to 2 and they could be anatectic derivatives of slightly older orthogneisses however addition of new mantle derived material is documented by a type granites with initial nd up to 4 in the cratonic domain temporally and compositionally equivalent igneous suites mostly have initial nd of 7 to 3 significantly above local archean basement which has nd of 15 at 1800 ma conservative calculations suggest that most of these suites contain more than 50 new mantle derived material these results suggest significant crustal growth via late stage magmatism and direct interaction of mantle derived magmas and lower crustal rocks in contrast 1650 ma igneous suites lack clear systematic variation in nd and are interpreted as representing crustal growth via later distal arc type magmatism with crust mantle mixing mainly facilitated by sediment subduction crustal growth in this area thus involved significant addition of new material through late to post orogenic magmatism this process may partially explain the unusually high growth rates calculated for some segments of proterozoic crust which approach or exceed modern global arc addition rates this stage 3 crustal growth may have been proportionally more important in early earth history due to higher ambient mantle temperatures

dynamics of the turbidity maximum in king sound tropical western australia king sound is a 100 km long embayment located in tropical northwestern australia with a spring tidal range of 11 m this is the second largest tide in the world after the bay of fundy in canada intertidal areas cover about 800 km2 the upper reaches of the sound are turbid with fine suspended sediment concentration reaching 3 kg m 3 field studies of the dynamics of water and fine sediment were carried out in the dry seasons of 1997 and 1998 the tide was a propagating wave shoaling and dissipating by friction as it entered the sound this mode of propagation generated an asymmetric tidal current with a stronger current at flood than at ebb an evaporation driven salinity maximum zone was found in the upper reaches of the sound and this was also where the turbidity maximum occurred tidal pumping by the tidal asymmetry and possibly the biological filter formed by muddy marine snow trapped the fine sediment in the upper regions of king sound wind driven waves contributed significantly to entrainment of bottom fine sediment possibly through wave pumping of the sediment and not wave induced orbital velocities field data suggest that erosion of bottom fine sediment was proportional to the sixth power of the tidal current and the third power of the wave height

field observations of hypersaline runoff through a shallow estuary abstract this study investigates a rare situation at the mond river estuary in the persian gulf in which the classical estuarine density gradient coincides with hypersaline runoff entering from saline soils upstream of the estuary after severe precipitation this builds a unique estuarine setting where two salt water masses one originating from the coastal ocean and the other being discharged from upstream confine a range of almost freshwater in the middle of estuary this freshwater lens estuary fle situation includes two saltwater sources with opposing senses of estuarine circulation therefore the tidal damping by the strong river flood can occur especially during neap tide when high unsteadiness number 0 04 signified ebb oriented condition which was induced by straining residual lateral circulation near the fle mouth transition from well mixed to weak strain induced periodic stratification regimes indicated the importance of the spring neap tidal variations close to the mouth a 13 66 day periodic tidal asymmetry from the triad k1 o1 m2 ebb dominance during spring tide and flood dominance in neap tide was overcome by higher harmonics

alkaline mafic and ultramafic lamprophyres from the aillik bay area labrador the aillik bay lamprophyric dyke swarm comprises abundant sannaites plus rarer olivine sannaites aillikites and carbonatites sannaites are characterized by phenocrysts of ti al titansalite plus rarer olivine and phiogopite in a groundmass dominated by pyroxene biotite titanomagnetite and k feldspar minor mineral phases may include apatite nepheline analcime carbonate rutile and pyrite most sannaites contain well developed leucocratic ocelli which are commonly zoned olivine sannaites are similar but olivine fo77 85 is more abundant and ocelli are rarer both types occur together as banded dykes and calculations support the suggestion of a common parental melt aillikites have zoned phenocrysts of olivine fo71 87 and mica in a groundmass of carbonate apatite mica titanomagnetite and perovskite carbonatite dykes usually exhibit textures with features akin to those of the aillikites the mineraiogical and geochemical characteristics of the aillikites are distinct from those of kimber

development of depth hoar and its effect on stable oxygen isotopic content in snow firn stratigraphy on urumqi glacier no 1 eastern tien shan china we report on the development of depth hoar and its relation to stable oxygen isotopic content in snow firn stratigraphy in the percolation zone of urumqi glacier no 1 eastern tien shan china during the period september 2004 august 2006 the essential condition for the development of depth hoar in the snow firn pack is the temperature gradient when the temperature gradient of the snow firn pack reaches a maximum value of 13 08cm in mid october depth hoar begins to develop by the end of march the depth hoar might account for 25 of the total snow firn pack depth from april to june as the weather becomes warm the transport of water vapor diminishes and melting regelation metamorphism replaces metamorphism caused by the temperature gradient as a result the depth hoar turns into coarse grained firn fractionation of the oxygen isotopic content also occurs during formation of the depth hoar the bottom 15 cm of the depth hoar do values were depleted in the lighter isotopic species as the snow sublimated from the lower to the upper crystals and the d values increased from 9 4 to 7 0 from 8 september 2004 to 25 january 2005 the upper 10 cm of the depth hoar do values were enriched in the lighter isotopic species and the d values decreased from 6 8 to 9 3 during the same period

structural evolution of the makkovik province labrador canada tectonic processes during 200 myr at a paleoproterozoic active margin in the makkovik province the structures and plutonic rocks of the reworked southern edge of the archean nain craton parautochthon and an adjacent juvenile domain form a spatially concentrated record of 200 ma at a paleoproterozoic active margin d1 thin and thick skinned structures formed during terrane collision before ca 1896 ma were nearly erased by d2 transpressive structures present across the entire parautochthon that had been thermally softened by emplacement of arc plutons at ca 1895 1870 ma d3 transpressive inversion of a back arc rift and d4 strike slip shearing formed structures at the oceanward margin of the parautochthon and were responses to events in the active arc that was now widely separated from the parautochthon by accreted terranes the tectonic isolation of the parautochthon ended by the time of d5 ca 1740 1710 ma and d6 with the reappearance there of granite and low grade shear zones structural and plutonic style varied at each stage primarily controlled by the crustal level attained

anatomy and orogenic history of a paleoproterozoic accretionary belt the makkovik province labrador canada the makkovik province is a segment of a paleoproterozoic accretionary belt the makkovik ketilidian orogen that developed on the southern margin of laurentia at 1 9 1 7 ga in contrast to coeval laurentian orogenic belts that mainly resulted from collision of archean plates makkovikian ketilidian orogenesis was dominated by active margin processes including continental margin arc plutonism and juvenile terrane accretion both of which were accompanied by regional transpression in the makkovik province earliest deformation and amphibolite facies metamorphism of paleoproterozoic rift drift assemblages post hill and moran lake groups and the archean foreland nain province occurred at 1 9 ga in response to accretion of a paleoproterozoic island arc following this collision cratonward dipping subduction was established resulting in the formation of the 1895 1870 ma island harbour bay plutonic suite a calc alkaline magmatic arc built on reworked archean crust crust formation continued between ca 1

geochemistry and age of the aillik group and associated plutonic rocks makkovik bay area labrador implications for tectonic development of the makkovik province the aillik domain of the makkovik province is dominated by deformed and metamorphosed sedimentary and bimodal volcanic rocks of the redefined aillik group and abundant unfoliated late to post orog

a prominent colour front in false bay south africa cross frontal structure composition and origin abstract colour fronts are a frequent occurrence in false bay south africa and their occurrence has been the subject of previous study and anecdotal conjecture the opportunity arose to make a cross frontal study of this feature in november 2005 photographs were taken and subsequently satellite imagery was obtained measurements were made of temperature salinity turbidity dissolved oxygen suspended solids plant nutrients and chlorophyll a cross frontal comparisons were also made on particulate material using a scanning electron microscope sem and elemental dispersive x ray edx analysis frontal waters were milky white green in colour in stark contrast to the adjacent clearer green blue waters the milky white green water mw gw was found to be warmer apparently less saline more turbid richer in nitrate and silicate and had a higher chlorophyll a concentration the dissolved oxygen signal was less pronounced both water types being supersaturated paradoxically in spite of the higher turbidity in the mw gw both water types had similar weights of suspended solids although the mw gw material was found to be more abundant and fragmentary when compared with its green blue water g bw counterpart the mw gw was rich in calcium whereas the g bw was silicon enriched the central findings of this study are that the strong southerly onshore wind conditions prior to mw gw formation introduced calcium rich fine particulates into the waters of the surf zone the sources of these particulates are thought to be the sea bed sediments and the sea land interface the particulates are close to neutral buoyancy enabling the mw gw to persist over the time scale of days a mechanism reinforced by the warming of this water in the nearshore zone the water was then advected by wind forcing and subsequently its own inertia around the north west corner of false bay at which stage it was easily observed and sampled it is suggested that the eventual collapse of the front was due to the slowing down of inertial movement in combination with the passive sinking of fine particulates and evaporative cooling resulting in downward convection

air permeability and capillary rise as measures of the pore structure of snow an experimental and theoretical study air permeability and capillary pressure are macroscopic snow properties that are influenced by the pore structure of the snow cover formulas for predicting fluid transport species elution and acoustive wave propagation require parameterization of one or both of these properties we report paired measurements of permeability and capillary rise from snow samples at field sites in hanover new hampshire and sleepers river research watershed danville vermont we augment these data with laboratory tests on sieved snow and glass beads our measurements demonstrate a linear relationship between permeability and the ratio of porosity and the square of capillary rise which we corroborate theoretically using a simple conduit model of the pore space we propose that scatter in the data results in part from the effect of crystal shape on air flow and imbibitior contact angle since the early measurements and classification schemes of bader in 1939 many investigators have expanded the database of permeability observations for a wide range of snow types we summarize these data and report our own recent observations from the new england sites and from an additional site in manitoba canada our measurements are in the high range of reported values however after normalizing our data by the square of grain diameter they follow the empirical function of shimizu fairly closely this agreement supports our measurements and demonstrates the usefulness of shimizu s function for snow types other than the relatively dense fine grained snow used in his analysis our normalized permeability data for low density snow as well as the shimizu function are below theoretical predictions for suspensions of spheres and infinite cylinders by extending the model for spheres to oblate spheroids and discs we estimate permeability that is in closer agreement with our data we suggest that a decrease in surface to volume ratio as snow ages may account for a relative increase in normalized permeability

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

growth forms of large frost crystals in the antarctic a variety of frost crystal forms found growing from the vapor in ice caves and tunnels in the antarctic are described and illust rated complex layered structures found within large skeletal crystals are ascribed to the action of the temp erature gradient some novel e axis growth forms and a rare type of bic rystal growth accelerated growth in a particul ar dir ection

two stage felsic volcanism in the lower proterozoic upper aillik group labrador canada its relationship to syn and post kinematic plutonism

u pb ages of granitoid rocks in the northwestern makkovik province labrador evidence for 175 million years of episodic synorogenic and postorogenic plutonism new u pb zircon titanite and monazite ages reported here along with existing age data demonstrate that granitoid bodies in the northwestern segment of the paleoproterozoic makkovik province labrador are of three distinct ages the redefined island harbour bay plutonic suite consists of varied dioritic to granitic units that were syntectonically emplaced into archean crust of the kaipokok domain between ca 1895 ma and 1870 2 ma this plutonism occurred during the early stages of the makkovikian orogeny in an obliquely convergent andean continental margin setting the hares islands and drunken harbour granites form smaller discrete plutons that were emplaced in or adjacent to the island harbour bay plutonic suite at 1805 5 ma and 1791 2 ma respectively during dextral strike slip deformation that accompanied accretion of an outboard juvenile terrane magmatic activity during this period was preferentially sited along active structural zones but also occurred outside of these zones the undeformed blacklers bight a type granite was emplaced in the kaipokok domain at 1716 1 ma late in the development of the orogen a type granites of this age form a significant component of the southeastern makkovik province and their generation is linked to mafic underplating and heterogeneous regional extension the new age data support the conclusion of earlier workers that crustal growth via synorogenic and postorogenic plutonism was episodic and allow along with field and geochemical data inferences to be made regarding the tectonic setting of individual plutonic events

new reflections on the structure and evolution of the makkovikian ketilidian orogen in labrador and southern greenland marine seismic reflection profiles across the early proterozoic makkovikian ketilidian orogen in the labrador sea region suggest that it is a doubly vergent asymmetric orogenic belt comparable in width to younger collisional orogens a southeast dipping reflector package is correlated with on land shear zones that mark the southeastern limit of exposed reworked archean crust and is also associated with a cryptic isotopic boundary in granites which documents a transition from ancient to juvenile basement this boundary is interpreted as a suture along which juvenile proterozoic crust has been juxtaposed over thrust over the archean craton a major synorogenic to postorogenic plutonic terrane to the southeast has a poorly reflective upper crust but shows strong subhorizontal reflectivity in the lower crust and moho regions the southeastern part of the profile correlates with metasedimentary terranes of the ketilidian belt in greenland and contains low angle northwest dipping reflector packages suggestive of large scale crustal imbrication by thrusting at least two broad zones of reflectivity at mantle depths up to 16 s are also recognized one dips northwest below the archean craton but the most widespread mantle reflectivity is southeast dipping in opposition to the dominant fabric in the overlying crust these contrasting crustal and subcrustal reflectivity patterns define a geometric focus beneath the orogenic belt and may provide information about subduction polarity during its development the doubly vergent reflectivity pattern resembles images from possibly correlative precambrian orogenic belts such as the penokean and svecofennian and also younger small collisional orogens such as the appalachian and pyrenean belts it also broadly resembles some results of geodynamic crustal deformation models based on detachment and underthrusting of mantle lithosphere following collision and the squeezing of weak zones between rigid bounding blocks a speculative multistage model for the belt incorporates initial northward subduction beneath the craton shifting to later southward subduction followed by oblique accretion of a composite arc terrane and juvenile continental block the accreted hotter juvenile proterozoic crust behaved differently than the stable cool archean crust and experienced subhorizontal shearing in lower crustal and moho regions associated with southeast directed imbrication of the middle and upper crust by thrusting however the present reflectivity pattern of the orogen may also include elements related to post collisional extensional collapse

crustal structures of grenville makkovik and southern nain provinces along the lithoprobe ecsoot transect regional seismic refraction and gravity models and their tectonic implications crustal structures of the eastern grenville makkovik and southern nain provinces are determined using seismic reflection refraction and gravity data along the lithoprobe eastern canadian shield onshore offshore transect ecsoot within the grenville province the velocity model contains a 5 km thick upper crust and a variable thickness middle to lower crust the total crustal thickness varies from 25 to 43 km with the thickest crust in the south and thinnest crust in the north a high velocity lower crustal wedge is coincident with a strong band of northward dipping reflectors the two dimensional velocity structure is compatible with modelling of a 60 mgal gravity high over the hawke river terrane in the makkovik province the thickness of upper crustal velocities increases to 17 km the velocity decrease in the upper to middle crust from the grenville province to the makkovik province is similar to that of refraction models across the grenville front in ontario and quebec it is possibly related t

u pb age and hf isotope geochemistry of zircon from felsic volcanic rocks of the paleoproterozoic aillik group makkovik province labrador abstract u pb zircon shrimp geochronology and lu hf zircon la mc icpms isotope geochemistry are used to constrain the ages of paleoproterozoic felsic magmatism and their crustal sources in the aillik group makkovik province of labrador this information is important for understanding the extent of crustal reworking vs juvenile crustal growth in subduction related magmatism during the paleoproterozoic and improves framework knowledge for uranium exploration in the central mineral belt of labrador u pb shrimp zircon geochronology from four felsic tuff samples collected from two different areas of the aillik group yield magmatic 207pb 206pb ages of 1852 7 ma 2 1854 7 ma 2 1861 7 ma 2 and 1862 7 ma 2 the ages fall within the range of previous u pb zircon dates reported for felsic volcanic rocks of the aillik group altogether these dates indicate that felsic volcanism spanned at least 30 m y and was perhaps most intense during the last 10 m y of that interval a foliated syn deformational monzogranite in the aillik group cross lake granite yields a 207pb 206pb zircon date of 1805 6 ma 2 which indicates that development of a pervasive planar fabric associated with northwestward thrusting of the aillik group continued after this time initial e h f s t values for magmatic zircons from the four felsic tuffs 4 8 to 1 9 1 7 to 2 2 11 8 to 3 8 9 0 to 4 6 and monzogranite 4 8 to 1 5 exhibit significant variability which indicates heterogeneous sources most of the zircon grains have negative initial e h f s t values and calculated crust formation hf isotope tdm model ages point to substantial contributions from melts of ancient crust ranging in age from ca 2200 to 2900 m y and clustering at ca 2500 m y inherited zircon grains in the felsic tuffs and monzogranite mainly have u pb ages of ca 1880 1920 ma though others are older up to ca 2743 ma hf isotope tdm model ages for the inherited zircons are similar to those of the magmatic zircons the hf isotope results indicate that subduction related felsic magmatism in the makkovik orogen involved significant crustal reworking 80 during formation of the aillik group

water and suspended sediment division at a stratified tidal junction 1 tidal junctions play a crucial role in the transport of water salt and sediment through a delta distributary network water salt and sediment are exchanged at tidal junctions thereby influencing the transports in the connecting branches and the overall dynamics of the system this paper presents observations of water salt and sediment transports in three channels that connect at a stratified tidal junction flow variation in one channel was found to lag behind flow variation in a connected channel by more than 1 h which is largely attributed to channel length differences from the junction to the sea the water columns in the three channels were periodically stratified during spring tide whereas the salinity structure represented a salt wedge during neap tide salinity differences between the three channels were substantial the channels contain water bodies of different salinity and act largely independently flow velocities in the upper and lower layers differed substantially flow in the lower layer was generally in the direction of acceleration produced by the baroclinic pressure gradient interestingly baroclinic pressure gradients were sometimes directed landward indicating the presence of saltier water at the land side of the estuary in sharp channel bends close to the junction secondary flow was strongest at the highest axial flow velocity during spring tide in one channel bend these circulations steered the suspended sediment toward the inner bend which affected the suspended sediment division

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

an evaporation driven salinity maximum zone in australian tropical estuaries abstract the distribution of temperature and salinity in three tropical australian estuaries was measured in october 1983 in the hot dry season as a result of evaporation a salinity maximum zone exists near the mouth of the river where downwelling occurs and a classical and an inverse internal estuarine circulation prevail respectively upstream and downstream of the salinity maximum zone the zone of salinity maximum can be thought of as a high salinity plug inhibiting so much the mixing of estuarine and ocean waters that in some cases freshwater dose not reach the ocean

density driven secondary circulation in a tropical mangrove estuary abstract observations of suspended sediment concentration ssc salinity and current were made in the normanby river estuary cape york peninsula northern australia the estuarine reaches are approximately 80 km in length and are fringed by mangroves a well developed axial convergence was found to exist almost unbroken for a distance of at least 30 km on flood tides clearly delineated by an accumulation of mangrove leaves and seed pods on the water surface the convergence migrated to the inside of most bends suspended sediment concentration profiles were very well mixed both vertically and laterally salinity profiles showed a cross channel salinity gradient of 0 2 25 m sufficient to form density driven secondary cells the cells produce an effective transverse mixing coefficient of 0 25 m 2 s 1 of the same order of magnitude as the conventional transverse diffusion coefficients for natural meandering channels mangrove seeds were present in the channel centre during flood tides and were moved to the channel banks during ebb tides due to the lateral shear in longitudinal currents mangrove seeds are predicted to move landward up the estuary at a rate of 1 km per day when density driven circulation cells are active influencing mangrove seed dispersal

winter snow cover on the sea ice of the arctic ocean at the surface heat budget of the arctic ocean sheba temporal evolution and spatial variability 1 the evolution and spatial distribution of the snow cover on the sea ice of the arctic ocean was observed during the surface heat budget of the arctic ocean sheba project the snow cover built up in october and november reached near maximum depth by mid december then remained relatively unchanged until snowmelt ten layers were deposited the result of a similar number of weather events two basic types of snow were present depth hoar and wind slab the depth hoar 37 of the pack was produced by the extreme temperature gradients imposed on the snow the wind slabs 42 of the snowpack were the result of two storms in which there was simultaneous snow and high winds 10 m s 1 the slabs impacted virtually all bulk snow properties emphasizing the importance of episodic events in snowpack development the mean snow depth n 21 169 was 33 7 cm with a bulk density of 0 34 g cm 3 n 357 r2 of 0 987 giving an average snow water equivalent of 11 6 cm 25 higher than the amount record by precipitation gauge both depth and stratigraphy varied significantly with ice type the greatest depth and the greatest variability in depth occurring on deformed ice ridges and rubble fields across all ice types a persistent structural length in depth variations of 20 m was found this appears to be the result of drift features at the snow surface interacting with small scale ice surface structures a number of simple ways of representing the complex temporal and spatial variations of the snow cover in ice ocean atmosphere models are suggested

amphibole and mica 40ar 39ar ages from the kaipokok and aillik domains makkovik province labrador towards a characterization of back arc processes in the paleoproterozoic we report amphibole and mica 40ar 39ar ages from the makkovik province amphibole ages from metamorphic rocks decrease towards the interior of the province indicating a first order pattern of monotonic cooling with progressive migration of the province into a more distal back arc location the amphibole data in combination with muscovite ages reveal a second order pattern consisting of four stages corresponding to changing spatial and temporal configurations of plutonism and deformation 1 the western kaipokok domain cooled through muscovite closure by 1810 ma long after the cessation of arc magmatism 2 the kaipokok bay shear zone bounding the kaipokok and aillik domains cooled through amphibole closure during 1805 1780 ma synchronous with emplacement of syn tectonic granitoid plutons 3 between 1740 and 1700 ma greenschist facies shearing occurred along the boundary between the kaipokok domain and nain province synchronous with a type plutonism and localized shearing in the western kaipoko

proterozoic orogens of the northeastern canadian shield new information from the lithoprobe ecsoot crustal reflection seismic survey as part of the eastern canadian shield onshore offshore transect ecsoot lithoprobe acquired 1250 km of deep seismic reflection data along the coast of labrador and across ungava bay to image evidence of proterozoic crustal accretion to the archean nuclei of the nain and superior provinces of the canadian shield the relatively pristine archean crust of the nain province has low reflectivity and generally lacks systematic reflector orientations reworking of archean crust on the margins of the makkovik province has little effect on this weak signature in contrast the archean crust in the eastern churchill rae province appears to have been overprinted by a strongly developed whole crustal easterly dipping reflection fabric interpreted to result from proterozoic collision of the nain and superior provinces in the paired new quebec and torngat orogens juvenile proterozoic crust in the makkovik and grenville provinces also shows strong whole crustal dipping reflection fabrics interpretable as outw

episodic paleoproterozoic crustal growth preserved in the aillik domain makkovik province labrador abstract the convergent margin of southeastern laurentia consists of reworked continental crust as well as accretion of continental ribbons and juvenile arc terranes forming part of the great proterozoic accretionary orogen the makkovik orogen in labrador preserves evidence of the timing duration and complexities of these accretionary events during the interval 1 88 1 78 ma new regional bedrock geological mapping combined with new u pb zircon shrimp ages constrain the paleoproterozoic felsic magmatism in the aillik group of the makkovik orogen nine samples from the aillik group yield magmatic 207pb 206pb ages between 1883 7 ma and 1858 3 ma the ages extend the previously documented ages of felsic volcanism providing evidence for periodic volcanism spanning 35 m y with the most prolific volcanic activity occurring ca 1860 ma combined with previous studies the aillik group is now constrained between 1883 7 and 1848 2 7 ma development of a pervasive planar fabric associated with the northwestward thrusting of the aillik group d3 occurred after 1848 ma lithotectonic evolution in the makkovik province comprised significant crustal reworking magmatism and minor preserved juvenile crustal growth between ca 1883 and 1848 ma the revised model for formation of the aillik group proposed herein suggests that the aillik group formed in a continental back arc setting these new ages further refine the timing of the accretionary events as well as characterizing the age of the crustal root of the arc which could be a juvenile substrate neoarchean paleoproterozoic or reworked archean crust possibly the 2 3 2 6 ma mistinibi raude crust of the southeast churchill province

uranium in iron oxide copper gold iocg systems the olympic dam iron oxide copper gold iocg deposit is currently the world s largest producer of uranium other iocg deposits generally have anomalous though uneconomic uranium grades the fluids that generate iocg deposits are thought to be saline and highly oxidized and would be capable of leaching and transporting significant uranium the reasons for uranium enrichment in certain iocg deposits remain speculative but could include the composition of mineralization related magmas of the wall rocks altered by hydrothermal fluids or of the fluids mixing at the site of mineralization there is sparse data available on uranium abundance in iocg ores there is even less reliable data on the uranium content of unaltered wall rocks for the deposits however the data that is available suggest that the uranium grade of iocg deposits may be primarily related to the uranium content of their unaltered host rocks many iocg deposits appear to have approximately 10 to 40 times enrichment in the ore compared to unaltered host rocks this suggests that exploration for uranium rich iocg deposits should focus on areas with anomalously high uranium contents in host rock sequences

natural convection in the subarctic snow cover the purpose of this study was to determine if air convects in a natural snow cover to detect convection the temperature field in the subarctic snow cover in fairbanks alaska was measured hourly during three winters 1984 1987 using an array of thermistors which were suspended on threads and allowed to be buried by snowfall the results indicate that convection occurred sporadically in 1984 1985 and almost continuously in 1985 1986 and 1986 1987 the evidence was 1 simultaneous warming and cooling at different locations in a horizontal plane in the snow and 2 horizontal temperature gradients of up to 16 c m 1 during the winter warm and cold zones developed in the snow and remained relatively fixed in space we interpret these zones to be the result of a diffuse plumelike convection pattern linked to spatial variations in the temperature of the snow soil interface air flow was inferred to have been primarily horizontal near the base of the snow and vertical elsewhere calculated flow speeds were of the order of 0 2 mm s 1 with a maximum value of 2 mm s 1 the convective circulation was time dependent with perturbations such as high wind or rapid changes in air temperature triggering periods when horizontal temperature gradients were strongest suggesting that these were also periods when the air flow was fastest the coincidence of depth hoar crystals with horizontal c axes and the horizontal flow lines at the base of the snow suggests that convection may have affected crystal growth directions

ice crystals grown from vapor onto an orientated substrate application to snow depth hoar development and gas inclusions in lake ice a laboratory experiment was conducted in which new ice crystals were nucleated from the vapor phase onto large existing ice crystals obtained from antarctic lake ice flat smooth ice crystal surfaces were prepared with c axes oriented either vertically or horizontally when these were subjected to a supersaturated vapor environment multiple individual crystals nucleated onto the substrates adopting the same crystallographic orientation as the parent a dominant grain growth scenario for kinetic growth metamorphism in snow which in some ways is analogous to the oriented morphologies in lake ice is hypothesized in the lake ice growth scenario optimally oriented crystals will grow at the expense of those less preferentially positioned the proposed dominant grain growth theory for snow is in agreement with the observed decrease in the number of grains and the proximal similarity of crystal habit in kinetic growth metamorphism in snow similarly kinetic crystal growth on the interior of gas inclusions in antarctic lake ice will also acquire the crystallographic orientation of the substrate ice these small faceted interior crystals significantly influence light scattering and penetration in the lake ice cover

mapping the spatial distribution and time evolution of snow water equivalent with passive microwave measurements this paper presents an algorithm that estimates the spatial distribution and temporal evolution of snow water equivalent and snow depth based on passive remote sensing measurements it combines the inversion of passive microwave remote sensing measurements via dense media radiative transfer modeling results with snow accumulation and melt model predictions to yield improved estimates of snow depth and snow water equivalent at a pixel resolution of 5 arc min in the inversion snow grain size evolution is constrained based on pattern matching by using the local snow temperature history this algorithm is applied to produce spatial snow maps of upper rio grande river basin in colorado the simulation results are compared with that of the snow accumulation and melt model and a linear regression method the quantitative comparison with the ground truth measurements from four snowpack telemetry snotel sites in the basin shows that this algorithm is able to improve the estimation of snow parameters

spatio temporal influence of tundra snow properties on ku band 17 2 ghz backscatter during the 2010 11 boreal winter a distributed set of backscatter measurements was collected using a ground based ku band 17 2ghz scatterometer system at 26 open tundra sites a standard snow sampling procedure was completed after each scan to evaluate local variability in snow layering depth density and water equivalent swe within the scatterometer field of view the shallow depths and large basal depth hoar encountered presented an opportunity to evaluate backscatter under a set of previously untested conditions strong ku band response was found with increasing snow depth and snow water equivalent swe in particular co polarized vertical backscatter increased by 0 82db for every 1cm increase in swe r 2 0 62 while the result indicated strong potential for ku band retrieval of shallow snow properties it did not characterize the influence of sub scan variability an enhanced snow sampling procedure was introduced to generate detailed characterizations of stratigraphy within the scatterometer field of view using near infrared photography along the length of a 5m trench changes in snow properties along the trench were used to discuss variations in the collocated backscatter response a pair of contrasting observation sites was used to highlight uncertainties in backscatter response related to short length scale spatial variability in the observed tundra environment

siberia snow depth climatology derived from ssm i data using a combined dynamic and static algorithm abstract one of the major challenges in determining snow depth sd from passive microwave measurements is to take into account the spatiotemporal variations of the snow grain size static algorithms based on a constant snow grain size cannot provide accurate estimates of snow pack thickness particularly over large regions where the snow pack is subjected to big spatial temperature variations a recent dynamic algorithm that accounts for the dependence of the microwave scattering on the snow grain size has been developed to estimate snow depth from the special sensor microwave imager ssm i over the northern great plains ngp in the us in this paper we develop a combined dynamic and static algorithm to estimate snow depth from 13 years of ssm i observations over central siberia this region is characterised by extremely cold surface air temperatures and by the presence of permafrost that significantly affects the ground temperature the dynamic algorithm is implemented to take into account these effects and it yields accurate snow depths early in the winter when thin snowpacks combine with cold air temperatures to generate rapid crystal growth however it is not applicable later in the winter when the grain size growth slows combining the dynamic algorithm to a static algorithm with a temporally constant but spatially varying coefficient we obtain reasonable snow depth estimates throughout the entire snow season validation is carried out by comparing the satellite snow depth monthly averages to monthly climatological data we show that the location of the snow depth maxima and minima is improved when applying the combined algorithm since its dynamic portion explicitly incorporate the thermal gradient through the snowpack the results obtained are presented and evaluated for five different vegetation zones of central siberia comparison with in situ measurements is also shown and discussed

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

snow carrots after the chelyabinsk event and model implications for highly porous solar system objects after the catastrophic disruption of the chelyabinsk meteoroid small fragments formed funnels in the snow layer covering the ground we constrain the pre impact characteristics of the fragments by simulating their atmospheric descent with the atmospheric entry model fragments resulting from catastrophic breakup may lose about 90 of their initial mass due to ablation and reach the snow vertically with a free fall velocity in the range of 30 90 m s 1 the fall time of the fragments is much longer than their cooling time and as a consequence fragments have the same temperature as the lower atmosphere i e of about 20 c then we use the shock physics code isale to model the penetration of fragments into fluffy snow the formation of a funnel and a zone of denser snow lining its walls we examine the influence of several material parameters of snow and present our best fit model by comparing funnel depth and funnel wall characteristics with observations in addition we suggest a viscous flow approximation to estimate funnel depth dependence on the meteorite mass we discuss temperature gradient metamorphism as a possible mechanism which allows to fill the funnels with denser snow and to form the observed snow carrots this natural experiment also helps us to calibrate the isale code for simulating impacts into highly porous matter in the solar system including tracks in the aerogel catchers of the stardust mission and possible impact craters on the 67p churyumov gerasimenko comet observed recently by the rosetta mission

post depositional modification of stable water isotopes in winter snowpacks in the canadian rocky mountains to assess the seasonal stability of the do stratigraphy in winter snowpacks in the canadian rocky mountains snow pits were sampled over three accumulation seasons at two field sites these sites opabin and haig glaciers are 160 km apart at similar elevations and represent windward and lee slope environments respectively at both sites snow pits were sampled at one glacier and one forefield location throughout each accumulation season intra seasonal changes in do at each site were examined to determine the extent of post depositional modification of isotope stratigraphies at both glacier sites there was minimal temporal change before the onset of spring melt in all years in addition the similar structure of do profiles from both glacier sites suggests that regional controls govern the isotopic composition of solid phase precipitation across the study area at forefield locations the absence of an insulating layer of ice at the base of the snowpack allowed for vapour transport and post depositional modification of the seasonal do signal this did not result in consistent changes to the mean do deuterium excess and dd do regression line slopes in the lower layers of snow and the observed smoothing of do profiles was less than that simulated by applying a diffusion model to these snowpacks

factors influencing permafrost temperatures across tree line in the uplands east of the mackenzie delta 2004 20101this article is one of a series of papers published in this cjes special issue on the theme of fundamental and applied research on permafrost in canada 2polar continental shelf contribution 03611 air and near surface ground temperatures late winter snow conditions and characteristics of the vegetation cover and soil were measured across the forest tundra transition in the uplands east of the mackenzie delta northwest territories in 2004 2010 mean late winter snow depth decreased northward from 73 cm in the subarctic boreal forest near inuvik to 22 cm in low shrub tundra annual near surface ground temperatures decreased northward by 0 1 0 3 c km near the northern limit of trees in association with an abrupt change in snow depth the rate decreased to 0 01 0 06 c km in the tundra the freezing season is twice as long as the thawing season in the region so measured differences in the regional ground thermal regime were dominated by the contrast in winter surface conditions between forest and tundra

seabed drifter movement in san diego bay and adjacent waters the seabed drifter has been used successfully to provide valuable information in many estuarine and open sea environments it was therefore selected for use in the san diego area five hundred drifters were released in san diego bay and adjacent ocean waters to delineate bottom flow patterns four significant bottom drift regimes are differentiated off coastal main bay channel open and semi enclosed docking basins mean residual bottom drift ranged between 0 17km day 1 off the coast to essentially zero in the docking basins off coast drifter results 31 recovery showed a persistent northmoving bottom current with shallow near coast drift distances between 4 and 25 km this nearshore north moving bottom current appears to cause a net bottom water inflow into the main san diego bay channel 44 recovery in the open bay a reverse trend was observed from the 16 of the drifters recovered at the head of the estuary evaporative densification is believed to occur with the heavier water sinking and moving outward towards the estuary mouth resulting in an area of opposing bottom water currents in this area san diego gas and electric power plant takes in an average 150 million gallons of cooling water daily which discharged as warm surface water is suggested as the surface divergence mode required to reconcile the observed flow with the three san diego bay electric power plants utilizing more than 5 of the maximum tidal prism for cooling purposes this flow may play a major role in the overall bay circulation and requires quantitative investigation

hydro sedimentary processes of a shallow tropical estuary under amazon influence the mahury estuary french guiana along the guianas coast coastal dynamic is characterized by the migration of mud banks originating from the amazon this singular feature affects the dynamic and the morphology of local estuaries and can induce rapid bathymetric evolution in lower estuaries since 2012 the navigation channel of the mahury estuary french guiana is enduring a severe siltation whose origin comes from a mud bank crossing the estuary mouth this study aims to determine how the migration of a mud bank through an estuary mouth could influence the transport and fluxes in the estuary field measurements were performed over a year with the monitoring of the salt intrusion length mooring surveys during spring neap cycles and shipboard profiling surveys during semi diurnal cycles salt intrusion lengths underline a significant seasonal variation characterized by the transition from a steady state length during high river discharge and a wide range of lengths with the tidal range during low to moderate river discharge during the rainy season measurements indicate a fluvial dominated condition with low suspended sediment concentrations most of the semi diurnal cycle residual sediment fluxes are usually seaward excepted when river discharge is below seasonal average during the dry season maximum suspended sediment concentrations are higher in the middle part of the estuary residual sediment fluxes are landward along the estuary and stronger during neap tides in the estuary mouth and few kilometers upstream in this area a persistent density stratification traps sediments in the bottom layer and generates a gravitational circulation during neap tides which enhances landward transports up to 2 56 t m 1 over a semi diurnal cycle in the middle estuary landward fluxes are most significant during the dry season and also during the rainy season when the river discharge is below the seasonal average although this study includes temporal and spatial limitations it underlines significant mud inflows in the middle part of the estuary during low to moderate river discharges comparison with old data suggests higher sediment loads in the estuary during the migration of a mud bank but must be confirmed by further studies during the interbank period

a seasonal snow cover classification system for local to global applications abstract a new classification system for seasonal snow covers is proposed it has six classes tundra taiga alpine maritime prairie and ephemeral each class defined by a unique ensemble of textural and stratigraphic characteristics including the sequence of snow layers their thickness density and the crystal morphology and grain characteristics within each layer the classes can also be derived using a binary system of three climate variables wind precipitation and air temperature using this classification system the northern hemisphere distribution of the snow cover classes is mapped on a 0 5 lat 0 5 long grid these maps are compared to maps prepared from snow cover data collected in the former soviet union and alaska for these areas where both climatologically based and texturally based snow cover maps are available there is 62 and 90 agreement respectively five of the six snow classes are found in alaska from 1989 through 1992 hourly measurements consisting of 40 thermal and

so42 minimum in summer snow layer at dome fuji antarctica and the probable mechanism 1 by chemically analyzing snow samples at dome fuji antarctica we found that the snowdrift deposited just after snowfall and the snow layer down to 3 4 m have summer minima in the non sea salt nss so42 and na concentrations and summer maxima of cl na such a summer nss so42 minimum in either snowdrift or the snow layer has not been reported at any other site in antarctica and arises in spite of the known maximum in the nss so42 concentration in aerosol at dome fuji in summer we then did laboratory experiments to better understand the phenomenon the results supported the following mechanism for the summer nss so42 minimum in the snowdrift and snow layer in summer water vapor sublimates from within the snow in the daytime and condenses on the surface as frost in the nighttime resulting in a dilution of the nss so42 concentration this sublimation condensation process likely occurs at other cold inland regions in addition the results might be useful for obtaining a high resolution dating method for dome fuji deep ice cores by counting the number of layers with low nss so42 concentration