physical and stable isotopic properties and growth processes of sea ice collected in the southern sea of okhotsk this study presents physical and stable isotopic properties of sea ice in the southernmost section of the sea of okhotsk on the basis of observations and measurements made in 1995 and 1996 midwinter cruises structural analysis revealed that ice was predominantly of the granular type saucer shaped cores and wedges were seen in the cross sections of the pancakes which indicate a rafting event in the early stage of the pancake formation the fraction of snow with respect to the total ice mass was estimated at 8 from independent 18o and density measurements from these findings we conclude that the initial growth mechanisms of the sea ice over this region are by the frazil pancake cycle with rafting and by the snow ice formation analysis also shows that the formation of the snow ice induces 10 more salt flux through the additional freezing of the seawater in a short synoptic timescale this implies that snow becomes a negative salting rather than a positive freshening source for the buoyancy flux these results suggest critical influence of the rapid formation of the frazil pancakes and snow ice under stormy conditions on the salt and buoyancy fluxes over the region

paired carbon isotopic analysis of ordovician bulk carbonate δ 13 c carb and organic matter δ 13 c org spanning the great ordovician biodiversification event abstract paired measurements of bulk carbonate 13ccarb organic matter 13corg and their difference 13c can be used to estimate changes in isotopic fractionation through time as a function of o2 co2 in the atmosphere however because local scale processes can also affect 13c it is essential to compare sections from widely separated water masses here we present new 13corg data from ordovician carbonate rocks from the great basin oklahoma and appalachian basin and compare with published 13ccarb records from these sections and paired 13c values from other carbonate successions around north america these new data complement previous studies that focused on upper ordovician 13ccarb excursions and now provide a composite ordovician 13corg record new lower ordovician tremadocian stage 13corg data range from ca 26 to 28 decreasing throughout the lower middle ordovician floian dapingian stages to ca 29 to 31 13corg values remain at their lowest throughout the sandbian and are similar to other published upper ordovician sandbian katian 13corg data from north america 13c values from well preserved intervals generally vary between 26 to 28 throughout the lower to middle ordovician tremadocian to early darriwilian but increase to 31 during the mid late darriwilian and mid sandbian similar to published data from younger late ordovician positive 13c excursions known as the guttenberg gice and hirnantian hice events the overall 13c trend shows a 3 increase throughout the early middle ordovician and coincides with a previously interpreted period of ocean cooling and some of the earliest pulses of global biodiversity of marine invertebrates and planktonic organisms modeling studies predict that pco2 decreased during this time suggesting that the effect of pco2 on 13c may have been overwhelmed by other controls such as an in increase in po2 or a higher o2 co2 ratio during this biodiversification event

abrupt change in slope causes variation in the deposit thickness of concentrated particle driven density currents abstract abrupt changes in slope occur frequently in some marine environments laterally confined laboratory experiments show that when dense surge like particulate flows travel over abrupt slope reductions their deposits may have an asymmetric bell shaped thickening near the break of slope this thickening is herein called a slope break deposit and is related to the change in kinetic energy of the flow slope break deposits are particularly pronounced under relatively high velocity flows in our experiments these are flows with high particle concentrations c 5 10 by volume silicon carbide moving down slopes steeper than 3 the experiments were designed such that currents generated by a lock exchange mechanism flowed down a slope variable slope angle onto a flat surface the bodies of the flows became thicker and slower just downstream of the slope break because the flow body slows very rapidly particles are dumped forming the slope break deposit the peak in sediment thickness of the slope break deposit is downstream of the break in slope because falling particles continue to move forward in the flow during settling the slope break deposits may be several tens of percent thicker than deposits from an equivalent flow in which no change in slope occurred the parameters of the slope break deposit correlate with slope angle change

the road river group of northern yukon canada early paleozoic deep water sedimentation within the great american carbonate bank cambrian devonian sedimentary rocks of the northern canadian cordillera record both the establishment and demise of the great american carbonate bank a widespread carbonate platform system that fr

the middle cambrian mount roosevelt formation new of northeastern british columbia evidence for rifting and development of the kechika graben system the eastern margin of the kechika graben in the vicinity of muncho and moose lakes northeastern british columbia contains middle cambrian rift related strata herein named the mount roosevelt formation the formation conformably overlies a quartzite package equivalent to the uppermost clastic unit of the informal late early cambrian gataga group bonnia olenellus zone and is conformably overlain by a thick unnamed carbonate sequence of middle cambrian age plagiura poliella zone the mount roosevelt formation is subdivided into three members the lowermost member is characterized by ooid bearing siltstone and sandstone interbedded with dolostone limestone and hematitic conglomerate conformably above this the middle member is a thick sequence of polymict cobbly pebble conglomerate the upper member includes karstified dolostone calcareous cemented conglomerate and sandstone and limestone collectively the mount roosevelt formation reflects alluvial fan delta progradation into a transgressive mar

carbonate platforms of passive extensional continental margins types characteristics and evolution abstract carbonate platforms of extensional margins may be grouped into several major categories homoclinal ramps have gentle slopes into deep water may have skeletal or ooid pellet sand shoal complexes that grade without break in slope into deep ramp nodular limestone and then into pelagic hemipelagic basin facies they generally lack significant slump and sediment gravity flow deposits in the deeper water facies distally steepened ramps differ from the above in having a marked increase in slope at the seaward edge of the deep ramp and abundant slumps slope breccias and turbidites however clasts of shallow platform margin facies are generally absent from breccias rimmed shelves have linear trends of shelf edge lime sands and reefs a marked increase in slope into deep water and foreslope and slope sands breccias with clasts of platform margin rocks and turbidites grading seaward into basin hemipelagic pelagic muds they may be divided into accretionary bypass and erosional margins isolated platforms are broad flat topped shallow platforms surrounded by deeper water few hundred meters to 4 km deep many are bypass margins but accretionary and erosional margins also occur finally incipiently to completely drowned or open platforms may develop by rapid submergence of ramps shelves or isolated platforms shallow platform margin facies are shifted landward and the earlier shallow water platform is covered with transgressive lags and deeper water blankets of hemipelagic or pelagic facies or open marine whole fossil wackestone the carbonate prisms commonly develop above a basal clastic phase ramps develop early and evolve into rimmed shelves however with drowning rimmed shelves may evolve up into ramps rimmed shelves may also develop into ramps where miogeoclinal faces prograde into filling marginal basins carbonate miogeocline deposition terminates when the shelf becomes a prograding clastic shelf or where it becomes part of a collisional orogen the various platform types may be recognized from continental margin sequences ranging from proterozoic to holocene in age

an ice ocean coupled model an ice model an ocean model and a method of coupling the models are described the ice model is a synthesis with variations and extensions of previous modeling ideas ice thickness concentration velocity and internal energy are prognostic variables the ice thermodynamics are represented by temperatures at the snow surface ice surface the interior and the bottom surface melting and freezing rates are calculated at the ice atmosphere ice ocean and atmosphere ocean interfaces a prescribed portion of summer meltwater can be stored on the surface and refrozen in the fall the ocean model includes a second moment turbulence closure submodel and enables one to solve for oceanic heat flux the interfacial stress and subsurface properties in this paper the model is applied to one dimensional simulations but the equations are cited in a form for implementation by two and three dimensional models in a companion paper kantha and mellor this issue the model is used for two dimensional vertical plane simulations in the bering sea several one dimensional sensitivity studies are performed in the case where the ice model is decoupled from the ocean here the oceanic heat flux and sea surface temperature are prescribed constants the studies reveal the role and sensitivity of surface trapped meltwater ice concentration and ice divergence with the coupled ice ocean model the seasonally varying oceanic heat flux and mixed layer properties are determined by the model some comparisons with observations in the central arctic ocean are possible the role of the molecular sublayer immediately adjacent to the ice is examined frazi ice production is related to the large disparity in the molecular diffusivities for temperature and salinity the mixed layer model contains empirical constants which are known from turbulence data the molecular sublayer parameterization requires one empirical parameter b which is uncertain but from this study is assuredly greater than zero the value implicit in previous models the ice model requires the empirical parameters ci f and ci u to quantitatively account for freezing or melting processes in open leads their values are also uncertain but we present reasoning and sensitivity studies to suggest specific values finally an empirical parameter g is introduced it is the ratio of the value of the ice thickness used to represent average ice volume in the dynamic and thermodynamic equations to the value of the thickness needed in the heat conduction equation estimates of g are made from observed thickness distribution functions sensitivity studies show it to be an important parameter

the arctic ocean ice balance a kalman smoother estimate the methodology of kalman filtering and smoothing is used to integrate a 7 year time series of buoy derived ice motion fields and satellite passive microwave observations the result is a record of the concentrations of open water first year ice and multiyear ice that we believe is better than the estimates based on the microwave data alone the kalman procedure interprets the evolution of the ice cover in terms of advection melt growth ridging and aging of first year into multiyear ice generally the regions along the coasts of alaska and siberia and the area just north of fram strait are sources of first year ice with the rest of the arctic ocean acting as a sink for first year ice via ridging and aging all the arctic ocean except for the beaufort and chukchi seas is a source of multiyear ice with the chukchi being the only internal multiyear ice sink export through fram strait is a major ice sink but we find only about two thirds the export and greater interannual variation than found in previous studies there is no discernible trend in the area of multiyear ice in the arctic ocean during the 7 years

relationship between sea ice freeboard and draft in the arctic basin and implications for ice thickness monitoring we have confirmed our earlier finding that the probability density function pdf of ice freeboard in the arctic ocean can be converted to a pdf of ice draft by applying a simple coordinate transformation based on the measured mean draft and mean elevation this applies in each of six 50 km sections north of greenland of joint airborne laser and submarine sonar profile obtained along nearly coincident tracks from the arctic basin north of greenland and tested for this study detailed differences in the shape of the pdf can be explained on the basis of snow load and can in principle be compensated by the use of a more sophisticated freeboard dependent transformation the measured density ratio r actually mean draft mean elevation ratio for each section was found to be consistent over all sections tested despite differences in the ice regime indicating that a single value of r might be used for measurements done in this season of the year the mean value r from all six sections is 7 89 on the assumption that all six values are drawn from the same population the standard deviation is 0 55 for a single 50 km section and thus 0 22 for 300 km of track in attempting to infer ice draft from laser measured freeboard we would therefore expect an accuracy of about 28 cm in 50 km of track if mean draft is about 4 m and about 11 cm in 300 km of track these accuracies are compatible with the resolution of predictions from numerical models a simple model for the variability of r with season and with mean ice thickness gives results in reasonable agreement with observations they show that although there is a large seasonal variability due to snow load there is a stable period from november to april when the variability is chiefly dependent on the mean ice thickness alone thus in principle r can be mapped over the arctic ocean as a basis for interpreting survey data better field data are needed on the seasonal and spatial variability of three key quantities area averaged snow load mean density of first year and multiyear ice including the effect of ridging with these two ice regimes and density of near surface water

thickness distribution texture and stratigraphy and a simple probabilistic model for dynamical thickening of sea ice in the southern sea of okhotsk 1 sea ice thickness data and sea ice samples were analyzed to examine the characteristics of the ice thickness distribution and ice texture and to understand ice growth processes in the southern sea of okhotsk ice thickness data and samples were obtained aboard the icebreaker soya in early february the ice growth season ice thickness data which were obtained with a video monitoring system installed on the side deck of the ship each winter from 1991 to 2000 except 1995 show that the average thickness ranges from 19 7 to 55 23 cm and that it matches the characteristics of a poisson distribution ice structure analysis reveals that granular texture occupies about three quarters of the total ice thickness and that the ice exhibits a layered structure with unit thickness averaging 5 to 10 cm stratigraphy and stable isotopic composition of the ice indicate that snow ice accounts for 10 and frazil ice accounts for 64 of the total ice thickness this suggests that dynamic ice thickening processes such as frazil ice growth and piling up are more significant than congelation growth on the basis of these characteristics which resemble more those of antarctic than arctic sea ice we propose a conceptual model for the ice thickening process in this region it is shown that this model can explain the shape of the ice thickness distribution well and is analogous with the concept of the pancake cycle and multiple rafting of antarctic sea ice growth and thickening

anisotropic internal thermal stress in sea ice from the canadian arctic archipelago results from an ice stress buoy deployed near the center of a multi year floe in the viscount melville sound of the canadian arctic archipelago between 10 october 2010 and 17 august 2011 are presented the position record indicates the landlocked season was approximately 5 months from 18 january to 22 june when the sea ice was fast to melville island and victoria island thermal stresses ranging from 84 to 66 kpa dominate the internal stress record with only a few dynamic stress events 50 kpa recorded before the landlocked season intriguingly the thermal stresses are isotropic before the landlocked ice onset and anisotropic during the landlocked season two possible causes to explain anisotropy in thermal stresses are considered preferred c axis alignment of the ice crystal and land confinement associated with the nearby coastline the orientation of the principal stresses indicates that land confinement is responsible for the anisotropy the stress record also clearly shows the presence of residual compressive stresses at the melt onset suggesting a viscous creep relaxation time constant of several days finally results show an interesting reversal in the sign of the correlation from negative to positive between surface air temperature and thermal stress after the onset of surface melt we attribute this to the onset of water infiltration within sea ice after which colder night temperature leads to refreezing and compressive stresses to the best of the authors knowledge this is the first time that anisotropic thermal stresses have been reported in sea ice

tank study of physico chemical controls on gas content and composition during growth of young sea ice during an ice tank experiment samples were taken to study the processes of acquisition and alteration of the gas properties in young first year sea ice during a complete growth warming cooling cycle the goal was to obtain reference levels for total gas content and concentrations of atmospheric gases o2 n2 co2 in the absence of significant biological activity the range of total gas content values obtained 3 5 to 18 ml of gas per kilo of ice was similar to previous measurements or estimates however major differences occurred between the current and quiet basins showing the role of water dynamics at the ice water interface in controlling bubble nucleation processes extremely high co2 concentrations were observed in all the experiments up to 57 in volume parts it is argued that these could have resulted from two unexpected biases in the experimental settings concentrations of bubbles nucleated at the interface are controlled by diffusion both from the ice water interface towards the well mixed reservoir and between the interface water and the bubble itself this double kinetic effect results in a transition of the gas composition in the bubbles from values close to solubility in sea water towards values close to atmospheric as the ice cover builds up

modeling sea ice surface emissivity at microwave frequencies impact of the surface assumptions and potential use for sea ice extent and type classification in this paper the surface emissivity is retrieved over the arctic sea ice open seas using observations from the advanced microwave sounding unit window channels during the year 2009 the emissivity computation is performed using two contrasted surface assumptions specular and lambertian assumptions the obtained sea ice surface emissivities are studied in this paper with a focus on the effect of the surface assumption some factors of variability of the obtained emissivities are analyzed variability in space in time with the zenith angle and with respect to the frequency we show that the near nadir surface emissivity and emissivity difference obtained using two contrasted surface assumptions could be used as an excellent proxy to detect ice no ice regions we also show that near nadir sea ice emissivity at some selected frequencies and the combination of both high and low window frequencies could also be very useful to better characterize sea ice surface physical properties and provide additional information for existing sea ice classifications as they bring relevant information about first year and multiyear sea ice properties and their seasonal evolution

on the nature and significance of rarity in mineralogy more than half of the 5000 approved mineral species are known from five or fewer localities and thus are rare mineralogical rarity arises from different circumstances but all rare mineral species conform to one or more of four criteria 1 p t x range minerals that form only under highly restricted conditions in pressure temperature composition space 2 planetary constraints minerals that incorporate essential elements that are rare or that form at extreme conditions that seldom occur in earth s near surface environment 3 ephemeral phases minerals that rapidly break down under ambient conditions and 4 collection biases phases that are difficult to recognize because they lack crystal faces or are microscopic or minerals that arise in lithological contexts that are difficult to access minerals that conform to criterion 1 2 or 3 are inherently rare whereas those matching criterion 4 may be much more common than represented by reported occurrences rare minerals though playing minimal roles in earth s bulk properties and dynamics are nevertheless of significance for varied reasons uncommon minerals are key to understanding the diversity and disparity of earth s mineralogical environments for example in the prediction of as yet undescribed minerals novel minerals often point to extreme compositional regimes that can arise in earth s shallow crust and they are thus critical to understanding earth as a complex evolving system many rare minerals have unique crystal structures or reveal the crystal chemical plasticity of well known structures as dramatically illustrated by the minerals of boron uncommon minerals may have played essential roles in life s origins conversely many rare minerals arise only as a consequence whether direct or indirect of biological processes the distribution of rare minerals may thus be a robust biosignature while these phases individually and collectively exemplify the co evolution of the geosphere and biosphere finally mineralogical rarities as with novelty in other natural domains are inherently fascinating

boundary layer upper ocean and ice observations in the greenland sea marginal ice zone during the 1984 marginal ice zone experiment a coordinated ocean boundary layer and mixed layer experiment was carried out in concert with a complete heat and mass balance study in the summer marginal ice zone miz of the greenland sea the measurements were made at two drifting ice stations and included observations of ocean boundary layer turbulence profiles of water temperature salinity and velocity ice ablation ice concentration solar radiation and spectral albedos ocean conditions were found to be extremely variable the ice and water velocities were heavily influenced by tidal and inertial motions with amplitudes from 6 to 12 cm s 1 in the course of the drift a 30 km eddy was crossed wherein ice and water velocities exceeded 15 cm s 1 the northern extension of the east greenland polar front was encountered and a northward flow of atlantic water into the arctic basin was observed below the eastern edge of the front but the drift station never moved quite far enough west to be caught in the southward transport of arctic surface water heat from the ocean was a major factor in ice melt and when the ice was over atlantic water it was the dominant factor the events that had the greatest impact on the ice were two outbreaks during which off ice winds blew the ice across warm ice edge ocean fronts once south of these fronts and over surface water as warm as 1 c the ice bottom melted at rates up to 100 kg m 2 d 1 the rapid changes in stratification associated with the outbreaks had a dramatic impact on the drag and heat transfer coefficients the drag coefficient relative to the square of the relative water velocity at 30 m ranged from 0 002 to 0 02 and averaged 0 006 the heat transfer coefficient relative to the friction velocity u and the mixed layer temperature elevation above freezing ranged from 0 0025 to 0 009 and averaged 0 0038 in agreement with the idea that stratification inhibits turbulent exchange the heat transfer coefficient decreased when stratification increased in fact the observed melt rates can be simulated well if molecular heat and salt transfer through a thin near surface laminar boundary layer are accounted for as well as transfer through the turbulent outer boundary layer also in agreement with turbulent boundary layer theory the drag coefficient decreased when stratification increased slightly above neutral however for the large increases in surface stratification the drag coefficient increased this was due to the generation of internal gravity waves by ice bottom roughness because the surface exchange coefficients are so sensitive to surface stratification which is in turn highly variable in the miz accurate simulations of ice motion and ice melt will require realistic estimates of stratification and a good understanding of the relation between the ice ocean interactions and upper ocean conditions

carbon isotope δ13ccarb stratigraphy of the lower middle ordovician tremadocian darriwilian in the great basin western united states implications for global correlation abstract new stable carbon isotope data 13ccarb from lower middle ordovician tremadocian to darriwilian carbonate mudstone and wackestone rocks of the pogonip group are presented from two sections in the great basin region usa shingle pass east central nevada and the ibex area western utah the pogonip group is a succession of mixed carbonate and siliciclastic rocks that accumulated on a carbonate ramp under normal marine conditions during the late cambrian furongian to middle ordovician darriwilian the shingle pass and ibex area sections have been previously studied for their conodont biostratigraphy and contain a north american midcontinent conodont fauna that range from the cordylodus intermedius zone uppermost cambrian to the phragmodus polonicus zone darriwilian the 13c trend has four distinct characteristics recognized in both great basin sections 1 a drop in 13c from 1 at the base of the ordovician tremadocian to 0 7 2 a 1 to 2 positive 13c shift in the uppermost rossodus manitouensis zone during the late tremadocian 3 a gradual 13c increase from 2 to ca 0 during the end of the early ordovician floian and 4 a steady 13c decrease from 0 to 4 to 5 during middle ordovician dapingian darriwilian in the lower ordovician 13c trends reported here from the great basin are not consistent with a causal mechanism involving sea level change and the migration of isotopically distinct water bodies instead these lower ordovician isotope data most likely reflect primary seawater chemistry and changes in 13c on a global scale this interpretation is supported by the excellent correlation of 13c in the lower ordovician to other 13c trends reported from the sections in the argentine precordillera la silla and san juan formations and in western newfoundland st george and table head groups these correlations using 13c are consistent with published biostratigraphic data and provide an integrated and high resolution chemo biostratigraphic framework for the lower ordovician sedimentary record of the laurentian margin the middle ordovician portion of the 13c curves in the great basin represented by the kanosh and lehman formations shows significant isotopic depletion relative to the section in argentina thus although there is some indication that minima and maxima in the middle ordovician curves can be correlated the great basin sections show clear evidence of overprinting by local variables related to both diagenesis dolomitization and platform restriction

modeling the salinity profile of undeformed arctic sea ice the salinity of sea ice affects its physical and ecological properties here a multilayer one dimensional halo thermodynamic sea ice model is used to simulate the vertical salinity profile of undeformed arctic sea ice the model successfully reproduces the desalination pattern observed in first year fy and multi year my ice the model can also be integrated with a prescribed time independent salinity profile substantial differences in the simulated mass balance and ice ocean salt flux arise depending on the salinity after 10 years into the simulation the annual mean ice thickness is 2 85 m with the interactive halodynamic component compared to 2 53 m 2 29 m with a prescribed time independent vertically varying constant salinity profile modelling sea ice salinity is especially important when sea ice is transitioning from a my to fy ice regime thus including a halodynamic component in sea ice models would significantly improve simulations of future climate

microwave and physical properties of sea ice in the winter marginal ice zone surface based active and passive microwave measurements were made in conjunction with ice property measurements for several distinct ice types in the fram strait during march and april 1987 synthetic aperture radar imagery downlinked from an aircraft was used to select study sites the surface based radar scattering cross section and emissivity spectra generally support previously inferred qualitative relationships between ice types exhibiting expected separation between young first year and multiyear ice gradient ratios calculated for both active and passive data appear to allow clear separation of ice types when used jointly surface flooding of multiyear floes resulting from excessive loading and perhaps wave action causes both active and passive signatures to resemble those of first year ice this effect could possibly cause estimates of ice type percentages in the marginal ice zone to be in error when derived from aircraft or satellite borne sensors

depletion of perennial sea ice in the east arctic ocean 1 the extent of perennial sea ice in the east arctic ocean 0 180 e decreased by nearly one half with an abrupt reduction of 0 95 106 km2 while the west arctic ocean 0 180 w had a slight gain of 0 23 106 km2 between 2004 and 2005 as observed by satellite scatterometer data during november december the net decrease in the total perennial ice extent is 0 72 106 km2 about the size of texas perennial ice in the east arctic ocean continued to be depleted with an areal reduction of 70 from october 2005 to april 2006 with the east arctic ocean dominated by seasonal sea ice a strong summer melt may open a vast ice free region with a possible record minimum ice extent largely confined to the west arctic ocean simultaneous scatterometer measurements of sea ice and winds will be crucial for sea ice monitoring and forecasts

high resolution chemostratigraphy of the cambrian ordovician gssp enhanced global correlation tool abstract the green point formation of the cow head group in western newfoundland canada represents the global stratotype section and point gssp for the cambrian ordovician boundary on laurentia the formation consists of the martin point lower and the broom point upper members which constitute a thick 170 m deep subtidal to slope marine carbonate sequence preservation of the micritic carbonates of the green point formation was evaluated by multiple petrographic and geochemical screening tools the 13 c and 18 o values of near primary micrites range from 4 7 to 1 7 vpdb and from 8 7 to 5 5 vpdb respectively with no significant correlation r 2 0 002 similarly the 13 c values show no significant correlation with mn sr ratios or total ree contents which suggest that the investigated carbonates retain their near primary 13 c signatures that can be utilized to construct a high resolution carbon isotope profile for the gssp the 13 c carb profile about the gssp trends generally positive into bed 22 of the green point formation the top of the c intermedius zone marks the onset of a negative 13 c carb shift to about 6 0 culminating in the upper part of the zone subsequently the 13 c carb profile trends positive with a double switch back about the boundary point and then continues on to the highest value in the uppermost part of bed 23 in addition the ce ce values approximately between 0 8 and 1 0 through the gssp suggest generally dysoxic waters before during and immediately after the boundary the high resolution chemostratigraphic results curve and trends covering the gssp should facilitate correlation of the cambrian ordovician boundary sections sequences from other locations

sea ice motion as a drunkard s walk observations of sea ice displacement over short periods of time are used to deduce some statistics of the ice motion over long periods of time the objective is to follow the trajectory of a piece of ice starting at a randomly selected time and location and ending when the ice either melts or leaves the arctic basin trajectories are also followed backward in time to the time and location where the piece of ice was formed statistical properties considered are the age and remaining lifetime of ice in various locations and the probability that ice presently occupying a particular location was originally created or will ultimately melt in certain regions possible applications are to the distribution of pollutants by sea ice and to the design of experiments involving drifting measurement platforms

observations of banding in first year arctic sea ice 1 horizontal banding features alternating dark and bright horizontal bands apparent in ice cores and stratigraphic cross sections have long been observed in first year sea ice and are frequently associated with bands of high and low brine or gas porosity observations on the land fast ice near barrow alaska in recent years have revealed particularly striking banding patterns and prompted a study of their macroscopic and microscopic characteristics the banding patterns are quantified from photographs of full depth sections of the ice and examples are presented from the chukchi sea and elson lagoon statistics on band spacing are presented and the growth records for three seasons are employed to estimate their time of formation these data provide insight into the periodicity of the underlying phenomena micrographs are used to examine the microstructural variations associated with various banding features and to quantify the geometry of the constituent brine inclusions associated with high and low porosity bands the micrography revealed that the area fraction of brine inclusions varied by a factor of nearly 3 through the more pronounced high and low porosity bands vertical micrographs obtained shortly after the materials removal from the ice sheet showed that significantly larger inclusions form abruptly at the start of the high porosity bands and frequently terminate abruptly at the end of the band crystallographic observations indicated that the high porosity bands supported the nucleation and growth of crystals having substantially different orientations from the very well aligned columnar structure that characterized the bulk of the sheet

evolution of microwave sea ice signatures during early summer and midsummer in the marginal ice zone emissivities at frequencies from 5 to 94 ghz and backscatter at frequencies from 1 to 17 ghz were measured from sea ice in fram strait during the marginal ice zone experiment in june and july of 1983 and 1984 the ice observed was primarily multiyear the remainder first year ice was often deformed results from this active and passive microwave study include the description of the evolution of the sea ice during early summer and midsummer the absorption properties of summer snow the interrelationship between ice thickness and the state and thickness of snow and the modulation of the microwave signature especially at the highest frequencies by the freezing of the upper few centimeters of the ice

sequestration of 12c in the deep ocean during the early wenlock silurian positive carbon isotope excursion abstract marine carbonates from three biostratigraphically well dated silurian sections from the mid continent of north america were analyzed for carbon isotopic 13 c carb study the early wenlock positive carbon isotope excursion ireviken excursion is recorded in three sections from tennessee iowa and ohio with values of 4 5 this global shift in the carbon isotopic ratio of marine waters began during a protracted extinction event ireviken event that spanned the llandovery wenlock boundary although several oceanographic models have been developed to account for the coincident changes in lithology biology and carbon isotope stratigraphy during this interval of the silurian their proposed causal connections among glaciation oceanography primary productivity and the global carbon cycle remain a matter of debate this investigation provides carbon isotopic and lithologic evidence that the ireviken excursion occurred during a time of relatively oligotrophic conditions a third order transgressive regressive cycle and increased carbonate production throughout the mid continent of north america the ireviken excursion is recorded in relatively pure carbonate sequences and is immediately preceded by a significant unconformity in each of the measured sections it is proposed that the ireviken excursion was the product of sequestration and burial of 12 c in deep water as a result of altered deep ocean circulation

the formation and morphology of ice stalactites observed under deforming lead ice during the leadex main field experiment held in april 1992 in the alaskan beaufort sea a number of large ice stalactites were observed growing under young lead ice formation of the stalactites was associated with rafting of the thin highly saline ice the rafting caused the brine to drain rapidly from the ice at a temperature well below the freezing point of the surrounding water which in turn caused ice to form in a hollow cylinder around the brine plume within a 15 h period after the rafting event the stalactites which were located approximately 10 m apart in a line along the up wind edge of a 150 m wide lead had grown to a length of 2 m a detailed structural analysis of the upper part of one of these stalactites revealed that the interior channel down which the brine flowed was bounded by a zone of frazil ice that developed into a shell of columnar ice the growth of the columnar ice was directed radially outward and the c axes of these crystals were oriented perpendicular to their growth direction development of the stalactites illustrates the impact ice deformation can have on the process of brine rejection in freezing leads and potentially on the thermohaline structure of the upper ocean in ther immediate vicinity of the lead

ridging and strength in modeling the thickness distribution of arctic sea ice a theory describing evolution of the ice thickness distribution the probability density of ice thickness was proposed by thomdike et al 1975 and has been used in several sea ice models the advantage of this theory over the widely used two level formulation is that it treats ridging explicitly as a redistribution of ice thickness and ice strength as a function of energy losses incurred by ridge formation however the parameterization of these processes remains rather speculative and largely untested and so our purpose here is to explore these parameterizations using a numerical model based on this theory the model uses a 160 km resolution grid of the arctic and 7 years of observed atmospheric forcing data 1979 1985 monthly oceanic heat flux and current fields are obtained from a 40 km resolution coupled ice ocean model run separately with the same forcing by requiring the computed monthly mean ice drift to have the same magnitude as observed buoy drift we estimate the primary strength parameter the ratio of total to potential energy change during ridging this ratio depends on the value of other parameters however the standard case has a ratio of 17 which is within the range estimated by hopkins 1994 in simulations of individual ridging events the effects of ridge redistribution and shear ridging parameters are illustrated by a series of sensitivity studies and comparisons between observed and modeled ice thickness distributions and ridge statistics in addition these comparisons highlight the following shortcomings of the thickness distribution theory as it is presently implemented first the process of first year to multiyear ridge consolidation is ignored and second the observed preferential melt of thick ridged ice is not reproduced

diatom induced silicon isotopic fractionation in antarctic sea ice 1 in this study we measure the silicon isotopic composition 29si relative to nbs28 quartz standard of dissolved silicon and biogenic silica collected by sequential melting from spring antarctic pack ice collected near 117 e 64 5 s this work aims to investigate the use of si isotopes to quantify the activity of sea ice diatoms in the different brine structures and the influence of sea ice diatoms on the spring ice edge blooms from three cores with contrasted physico chemical characteristics we report significant isotopic fractionations linked to diatom activity with distinct silicon biogeochemical dynamics between different brine structures the diatoms in snow ice and in brine pockets of frazil or congelation ice have the heavier silicon isotopic composition 0 53 to 0 86 indicating that they grow in a closed system and use a significant fraction of the small dissolved silicon pool available in the brine channels and skeletal layer diatoms display a relatively lower silicon isotopic composition 0 41 to 0 70 although it is still relatively positive compared to expected equilibrium fractionation this suggests that the diatoms have grown in a semi closed system where the dissolved silicon pool i e brine is partially replenished the silicon isotopic composition 0 63 of the sea ice diatoms is much heavier than the one of biogenic silica in the seasonal ice zone mixed layer 0 09 our results suggest that sea ice diatoms either contribute to an insignificant part of the whole diatom biomass in the upper water layer or that they are directly exported below the mixed layer

an estimate of the mean field of arctic sea ice motion the observational basis for our understanding of sea ice motion comes from the trajectories of particular ice floes these ice floes may have been marked by a manned research station or more recently by an automatic data buoy since 1893 almost 100 station years of drift data have been recorded using the principles of optimal linear estimation these data are used to obtain a quantitative estimate of the field of mean motion

monitoring ice thickness in fram strait time series of ice thickness in fram strait are evaluated together with ice drift for estimation of the ice flux from the arctic ocean ice draft was measured from moored sonars every 4 min suggesting a nominal sampling interval of 30 m on the basis of these data the annual cycle of many statistics can be resolved the modal ice thickness shows a maximum of 3 15 m in may and a minimum in september of 2 43 m indicating an annual variation range of 0 72 m this compares with model results comprehensive drillings and most of the submarine observations during the last 2 3 decades indicating no significant long term ice thickness change this is also concurrent with the lack of significant temperature changes in the arctic ocean during the same period the mean ice thickness in the central core of the ice stream shows an annual amplitude of 1 m with a minimum in september of 2 25 m and a maximum in april may of 3 25 m the mean thickness of ice only open water excluded is 3 27 m and compares with 3 29 m which is the mean thickness of ice only from 17 submarine tracks in the arctic ocean 1960 1982 the mean annual ice export which is equal to the mean annual net production of ice in the arctic ocean is 2850 km 3 yr 1 for the period 1990 1996 this efflux shows significant variations from year to year with a minimum in 1990 1991 of 2050 km 3 yr 1 and a maximum in 1994 1995 of 4700 km 3 yr 1 this significant variation of nearly 130 is mainly caused by an increased atmospheric forcing and to a lesser degree by an increase in the annual mean ice thickness of 20 over the same period

bidirectional anisotropic reflectance of snow and sea ice in avhrr channel 1 and channel 2 spectral regions ii correction applied to imagery of snow on sea ice for pt i see ibid vol 37 no 1 p 543 54 1999 advanced very high resolution radiometer avhrr images acquired over the arctic ocean often show strong bidirectional reflectance of snow on sea ice the observed anisotropic reflectance characteristics of these images are consistent with the theoretical analysis presented in part i of this study the anisotropic reflectance at the top of atmosphere toa is simulated by radiative transfer modeling and the results show a good model observation agreement based on these modeling results a method was developed to correct the effect of anisotropic reflectance on avhrr images in channels 1 and 2 results show the method is effective and efficient comparisons of toa snow reflectance before and after anisotropic correction show that the systematic and large variation of snow reflectance across the scan lines of an image due to satellite viewing illumination geometry can either be eliminated or greatly reduced by applying the correction algorithm

top bottom multisensor remote sensing of arctic sea ice the arctic sea ice cover has been studied using near simultaneous observations by passive and active synthetic aperture radar sar microwave sensors upward looking and sidescan sonars a lidar profilometer and an infrared sensor data from two aircraft and a submarine over an approximately 100 km track of central arctic sea ice were registered and analyzed to evaluate the characteristics of the ice cover and the utility of each sensor in ice studies the results of comparative and correlation analyses are as follows the probability density functions of ice draft from sonar and elevation from lidar were found to be almost identical when isostasy is taken into account this result suggests that the basic ice thickness distribution can be derived from the surface topography measurements alone reasonable correlation was found between sar backscatter and ice draft or elevation especially when scales were adjusted such that 15 20 sar pixels were averaged however surface roughness derived directly from standard deviations in the lidar elevation data was found to be poorly correlated to the sar backscatter these results indicate that the sar values are affected more by scattering from the ice than from the snow covered surface the active and passive microwave sensors are shown to generally complement each other as the two sensors are especially sensitive to different physical properties of the sea ice undeformed first year ice showed low backscatter values but high brightness temperatures while some multiyear ice showed high backscatter values and low brightness temperature however surfaces identified as multiyear ice by the passive system have a large spread in the unaveraged sar backscatter indicating limitations when using a one channel sar for ice type identification at the highest resolution also ridged ice identified by sonar and sar data covers a large range of passive microwave emissivity suggesting considerable variability in the age and salinity of this type of ice significant variations about 0 11 in the minimum emissivity of consolidated multiyear ice are observed in different regions of the arctic using the high resolution 30 m passive microwave data this suggests that regional variations in texture and scattering characteristics of multiyear ice in the arctic are present likely influenced by different histories of formation of the ice in different regions

investigation of the effects of summer melt on the calculation of sea ice concentration using active and passive microwave data active and passive microwave data sets acquired during the 1984 marginal ice zone miz experiment aircraft flights in the fram strait region are used to examine the effects of ice surface melt on microwave signatures and their resulting error in the calculation of sea ice concentration conditions examined with the active passive data set include ice floes with moist and dry snow cover and both heavily ponded and ridged surfaces passive sensors on the nasa cv 990 aircraft included the aircraft electrically scanning microwave radiometer esmr operating at 19 4 ghz and aircraft multichannel microwave radiometer ammr operating at 10 7 18 0 21 0 and 37 0 ghz active microwave sensors flown on the canadian centre for remote sensing cv 580 aircraft included the environmental research institute of michigan synthetic aperture radar sar operating at 1 2 and 9 4 ghz coincident ammr and sar measurements of individual floes identified in aerial photography are used to describe the effects of surface melt on the calculation of sea ice concentration and in particular the response of the passive microwave polarization and spectral gradient characteristics to different stages of surface melt although the onset and progression of summer melt are not uniform throughout the arctic the stages of summer melt observed in the miz are also observed on a large scale in the central arctic this is demonstrated using nimbus 7 smmr data and arctic ocean buoy temperature data over one annual cycle finally the potential of optimally combining both active and passive microwave data in an effort to ameliorate these surface melt effects during the summer months is also explored

investigations on physical and textural properties of arctic first year sea ice in the amundsen gulf canada november 2007 june 2008 ipy cfl system study we report sea ice temperature and bulk salinity measurements as well as textural analysis from 33 first year drift and fast ice stations sampled between november 2007 and june 2008 in the southern beaufort sea amundsen gulf canadian arctic during the international polar year circumpolar flaw lead ipy cfl system study we use this significant dataset to investigate the halo thermodynamic evolution of sea ice from growth to melt a strong desalination phase is observed over a small time window in the spring using calculated proxies of sea ice permeability brine volume fraction and of the intensity of brine convection rayleigh number we demonstrate that this phase corresponds to full depth gravity drainage initiated by a restored connectivity of the brine network with warming in the spring most stations had a textural sequence typical of arctic first year ice with granular ice overlying columnar ice unusual textural features were observed sporadically sandwiched granular ice platelet ice and draped platelet ice we suggest that turbulence in leads and double diffusion in strong brine plumes following the refreeze of cracks are plausible mechanisms for the formation of these textures

paleozoic continental margin sedimentation in east central alaska a thick unusually continuous record of late proterozoic and paleozoic continental margin sedimentation exists in east central alaska depositional and lithofacies relationships show that shelf conditions and source areas persisted to the northeast whereas open marine conditions existed to the south and west lithostratigraphic correlations with units of equivalent age elsewhere in alaska are poor but very good correlations can be made with cordilleran rocks in northwest canada the geology is consistent with what would be expected along a rifted or collapsed continental margin along a south to west facing depositional system insufficient data exist to demonstrate westward continuation of this margin into other parts of alaska this may indicate that a major re entrant in or the western terminus of the paleozoic north american continent was in east central alaska

sea ice concentration derived from gnss reflection measurements in fram strait reflection power derived from the global navigation satellite system gnss observations and its sensitivity to sea ice concentration are investigated in this article a corresponding experiment has been conducted during the fram strait cruise of the norwegian research vessel lance in summer 2016 the dedicated setup with a gnss occultation reflectometry scatterometry gors receiver and dual polarization left and right handed antenna links recorded 1922 h of reflection events during the 20 day cruise of the ship the antenna setup mounted 25 0 m above the waterline serves to acquire sea surface reflections at grazing angles below 30 within a 5 min coherent integration period direct and reflected signal contributions can be separated except for the highest sea states with roll angle changes of 20 peak to peak the separation allows to retrieve the reflection power and quantifies it in cross co and cross to co polar ratios the sea ice concentration is inverted from power ratios using a non linear least squares algorithm additional data on sea ice concentration gathered by a watchman on the ship are used for validation the inversion results have a 20 resolution in concentration and 3 h resolution in time the validation shows that the cross and cross to co polar data are sensitive to the sea ice concentration the respective pearson correlation of 0 75 and 0 67 further suggests studies to foster the application of the gnss data for sea ice reflectometry

mcbirneyite cu3 vo4 2 a new sublimate mineral from the fumaroles of izalco volcano el salvador abstract mcbirneyite cu3 vo4 2 a new copper vanadate mineral has been discovered in the summit crater fumaroles of izalco volcano el salvador the mineral formed as a sublimate from the volcanic gases and is associated with stoiberite fingerite ziesite euchlorine and thenardite mcbirneyite is the naturally occurring analog of synthetic cu3v2o8 mcbirneyite is triclinic p 1 a 5 3418 9 a b 6 5100 8 a c 5 1798 7 a 88 61 1 68 11 1 69 22 1 the five most intense lines in the diffraction pattern are 4 01 80 01 1 3 12 100 120 2 82 100 10 1 2 641 80 211 and 2 428 a 80 021 the crystal structure of the mineral has been determined the independent structure solution demonstrates that mcbirneyite is isostructural with stranskiite cuzn2 aso4 2 and a synthetic cu phosphate cu3 po4 2 the structure is constructed of 1 1 0 layers of cu atoms in square planar and square based pyramidal coordination with oxygen adjacent layers are linked by isolated vo4 tetrahedra mcbirneyite is black with a metallic luster the calculated density z 1 is 4 50 g cm 3 the mineral is opaque to transmitted light in reflected light in air the mineral is medium dark gray and nonpleochroic with reflectance values as follows 470 nm 18 5 546 nm 17 5 589 nm 18 7 650 nm 20 6 the mineral is named in honor of alexander r mcbirney editor in chief journal of volcanology and geothermal research

nd isotope records of late ordovician sea level change implications for glaciation frequency and global stratigraphic correlation abstract detailed records of ice sheet advances and retreats are reconstructed for the hirnantian and katian ages of the late ordovician using nd isotopes e nd as a sea level proxy in three study sections from the western margin of laurentia two shallow water platform sections located south and north of the paleo equator and one deep water section located in a continental slope rise setting when sea level was high and paleo shorelines had migrated eastward the e nd value of seawater in the vicinity of each of the study sections shifted toward the e nd value of the eastern panthalassa ocean 4 0 by contrast when sea level was low and paleo shorelines had migrated westward the e nd value of seawater shifted toward the e nd value of the continental weathering flux from laurentia 8 5 0 2 2 mean these stratigraphic patterns of changing e nd values are interpreted to reflect the eustatic sea level fluctuations that previous studies have documented in response to gondwanan ice sheet advances and retreats thus linking the e nd sea level proxy to late ordovician global scale climate changes the e nd profiles for the two platform sections yielded similar proxy sea level curves with five cycles of oscillation recorded during the latest katian and hirnantian three additional cycles of late katian sea level change are recognized in the e nd profile of the deep water continental slope rise section the combination of e nd 13 c and graptolite biostratigraphic data facilitates a precise interregional correlation of the hirnantian age and the paleoclimate changes that took place during this interval the new correlations support previous findings that the hirnantian ice age comprised two major glacial periods separated by a minor interglacial during the early part of the metabolograptus persculptus biozone the younger glacial confined to mid m persculptus biozone time led to more extensive sea surface cooling than did the earlier one and resulted in extensive eustatic sea level drawdown and c cycle changes it records the strata most often recognized as hice the hirnantian carbon isotope excursion in sedimentary successions worldwide such as anticosti island scotland estonia siberia and south china the results of this study support and strengthen the view that glaciation predated the hirnantian age in the late ordovician and that the records of small positive 13 c excursions in katian successions from baltica and eastern north america are themselves proxy indicators of glaciation frequency and eustatic sea level changes

the ice cover in the greenland and norwegian seas the seasonal sea ice cover of the northern north atlantic is reviewed comprising the ice of the east greenland current the ice cover around svalbard and the ice of the barents sea as far east as franz josef land the review considers various types of ice cover 1 the fast ice along the coasts and in fjords including sikussak or very old fast ice of exceptional thickness 2 the transition zone between the fast ice and the main pack including the positions and causes of recurring winter polynyas and the nature of the shear zone in ne greenland 3 the constitution dynamics and seasonal extent of the drifting pack ice including interannual variations 4 the processes of air ice ocean interaction which occur in the marginal ice zone where the pack ice is influenced by an open ocean boundary

k u band airborne radar altimeter observations of marginal sea ice during the 1984 marginal ice zone experiment pulse limited airborne radar data taken in june and july 1984 with a 13 8 ghz altimeter over the fram strait marginal ice zone are analyzed with the aid of large format aerial photography airborne synthetic aperture radar data and surface observations variations in the radar return pulse waveforms are quantified and correlated with ice properties recorded during the marginal ice zone experiment results indicate that the wide beam altimeter is a flexible instrument capable of identifying the ice edge with a high degree of accuracy calculating the ice concentration and discriminating a number of different ice classes this suggests that microwave radar altimeters have a sensitivity to sea ice which has not yet been fully exploited when fused with ssm i avhrr and ers 1 synthetic aperture radar imagery future ers 1 altimeter data are expected to provide some missing pieces to the sea ice geophysics puzzle

middle and upper ordovician carbon isotope chemostratigraphy in baltoscandia a correlation standard and clues to environmental history abstract the baltoscandian epeiric sea was characterised by relatively slow but continuous carbonate deposition from the middle ordovician up to the silurian relatively good preservation of ordovician and silurian carbonate rocks in baltoscandia makes this region unique for chemostratigraphical and palaeoenvironmental studies previous palaeozoic carbon isotope studies have revealed isotopic events in different lithologies over the baltoscandian palaeobasin and some of them on different palaeocontinents we propose a composite carbon isotope curve for the baltoscandian region a new subdivision of the middle and upper ordovician succession into seventeen chemostratigraphic zones and an improved nomenclature of isotopic excursions based on analyses of 13 c carb data from 25 drillcore and outcrop sections of estonia latvia and sweden the composite carbon isotope curve is compared with biostratigraphical data on conodont and chitinozoan distribution the katian hirnantian interval with highly fluctuating isotopic values shows climatic cyclicity of about two million years in baltoscandia no abrupt changes occur in the dapingian sandbian part of the baltoscandian isotope curve but the mid darriwilian excursion nearly coincides with the onset of cooler temperatures similar to modern like equatorial sea surface temperatures and related global biodiversification increase suggesting a climatic background for this event

fluctuations in epeiric sea carbonate production during silurian positive carbon isotope excursions a review of proposed paleoceanographic models positive excursions in the carbon isotopic ratio of marine carbonates 13ccarb are commonly attributed to an increase in the burial ratio of organic versus carbonate carbon in the global oceans regardless of whether this increased deposition of organic carbon was oceanographically or biologically induced the fact that high carbon isotope values are most often attributed to the sequestration and burial of organic carbon remains the notion that high 13ccarb values should be the result of organic rich deposition in epeiric sea settings is not surprising considering that the overwhelming majority of organic carbon burial in the modern oceans occurs in continental shelf and margin settings what is surprising is that major positive carbon isotope excursions during the silurian are recorded in clean carbonate successions with little to no appreciable black shale deposition in epeiric seas in fact silurian 13ccarb excursions occurred during intervals of prolific reef development and an overall expansion of carbonate platform environments globally this discrepancy has sparked considerable debate among silurian carbon isotope specialists but has offered a valuable opportunity to re examine the intricate connections among nutrients primary productivity carbonate sedimentology and the global carbon cycle in the lower paleozoic here we consider several sedimentological and geochemical features of one of these silurian positive carbon isotope 13ccarb excursions and discuss the broader implications of current silurian 13ccarb models to the interpretation of lower paleozoic carbonate sequences

physical characteristics of summer sea ice across the arctic ocean sea ice characteristics were investigated during july and august on the 1994 transect across the arctic ocean properties examined from ice cores included salinity temperature and ice structure salinities measured near zero at the surface increasing to 3 4 at the ice water interface ice crystal texture was dominated by columnar ice comprising 90 of the ice sampled surface albedos of various ice types measured with radiometers showed integrated shortwave albedos of 0 1 to 0 3 for melt ponds 0 5 for bare discolored ice and 0 6 to 0 8 for a deteriorated surface or snow covered ice aerial photography was utilized to document the distribution of open melt ponds which decreased from 12 coverage of the ice surface in late july at 76 n to almost none in mid august at 88 n most melt ponds were shallow and depth bore no relationship to size sediment was pervasive from the southern chukchi sea to the north pole occurring in bands or patches it was absent in the eurasian arctic where it had been observed on earlier expeditions calculations of reverse trajectories of the sediment bearing floes suggest that the southernmost sediment was entrained during ice formation in the beaufort sea while more northerly samples probably originated in the east siberian sea some as far west as the new siberian islands

observations of the polarization of light reflected from sea ice as part of a large interdisciplinary program investigating the electromagnetic properties of sea ice we made spectral measurements of the albedo reflectance and stokes vector of the reflected radiance field the overall program encompassed observations of sea ice physical properties optical properties and microwave properties plus an extensive modeling effort measurements were made of an evolution sequence including young sea ice pancake ice snow covered ice first year ice and ponded ice the effects of surface roughness were investigated by artificially roughening part of a 31 cm thick smooth young ice sheet spectral and total albedos were sensitive to surface conditions consistent with earlier studies stokes vector observations exhibited the greatest variability in the plane of incidence of the solar beam reflectances at 0 azimuth increased sharply with zenith angle smoother surfaces such as melt ponds pancakes and bare ice exhibited a larger increase than the snow covered cases with their rougher surfaces since the solar zenith angle was close to brewster s angle specularly reflected light was highly polarized in the smooth ice cases there was significant polarization associated with the increase in reflectance implying a substantial contribution from specular reflection this contribution was greater at longer wavelengths where specular reflection was a larger component of the reflected radiance away from the plane of incidence the stokes vector showed little angular variation and the reflected light at these angles was largely unpolarized

the anatomy of a freezing lead winter leads are regions of intense ice growth with resultant large fluxes of heat to the atmosphere and salt to the ocean they constitute a major source of new ice in the arctic basin during the 1988 drift phase of the coordinated eastern arctic experiment we were afforded a unique opportunity to conduct a detailed long term study of a freezing lead measurements were made from september 17 to november 18 during which time the ice grew from open water to a thickness of 0 56 m cores were removed from the lead ice on a routine basis and analyzed for ice temperature salinity density and structure from these measurements the derived quantities of brine volume porosity heat flux to the atmosphere and salt flux to the ocean were computed in addition to this 2 month time series study of ice cores the spatial variation in lead ice properties was investigated on september 30 thin section studies of ice structure indicated that the upper 0 05 0 15 m of the ice sheet was granular and that the lower portion was columnar typically a portion of the granular layer was snow ice once the transition from granular to columnar ice had occurred granular ice did not reappear as the ice grew thicker the c axes of the ice crystals became aligned within the horizontal plane this alignment direction corresponded closely with the inferred direction of the current at the ice water interface vertical temperature profiles in the ice were approximately linear salinity profiles were usually c shaped with bulk salinities ranging from 9 to 6 before stabilizing at 6 for ice thicker than 0 35 m core data were used to compute the flux of heat to the atmosphere and the flux of salt to the ocean for seven time intervals during the experiment heat fluxes ranged from 89 to 29 w m2 with an average of 50 w m 2 roughly 3 times the corresponding value from multiyear ice the flux of salt from the lead ice to the ocean varied from 0 51 to 0 06 kg m 2 d 1 averaging 0 21 kg m 2 d 1

physical and morphological properties of sea ice in the chukchi and beaufort seas during the 2010 and 2011 nasa icescape missions abstract physical and morphological properties of sea ice in the chukchi and western beaufort seas were measured during the 2010 and 2011 june july icescape impacts of climate on the eco systems and chemistry of the arctic pacific environment missions aboard the uscgc healy observations of ice conditions including ice thicknesses types and concentrations of primary secondary and tertiary categories were reported at 2 h intervals while the ship was in transit using the antarctic sea ice processes and climate aspect protocol on ice surveys of ice thickness melt pond depth and ice properties including profiles of internal temperature salinity and isotopic composition were conducted at 21 total ice stations 12 in 2010 and 9 in 2011 comparison to historical ship based observations confirms a multi decadal transition from a multiyear to thinner first year dominated seasonal sea ice pack in the region with much earlier ice retreat than in past decades the ice encountered was predominantly 98 first year with un deformed ice thicknesses ranging from 0 73 to 1 2 m pond coverage was extensive averaging 29 in 2010 and 19 in 2011 resulting in considerable light absorption in the ice and transmission of light to the ocean enhanced melting near the ice edge is consistent with transport of pacific origin heat and or ice albedo feedbacks sediment entrainment was visible in 7 5 and 10 9 of the ice in 2010 and 2011 respectively overall the results indicate a regime shift in the characteristics of the ice cover has occurred in the region over recent decades with substantive implications for thermodynamic forcing light availability in the upper ocean and biological and biogeochemical processes in the ice and water column beneath the results presented have applications for the interpretation of optical and biological measurements in the chukchi sea and serve as record of ice conditions for assessing long term change

ice properties in the greenland and barents seas during summer resultats d analyse de carotte de glace de mer dans l arctique europeen les proprietes de la glace sont mises en rapport avec les conditions generales de la distribution de glace leur epaisseur et leur relief dans la zone exploree interpretation de la salinite sur les glaces de premiere annee et pluri annuelles

roughness of weddell sea ice and estimates of the air ice drag coefficient the roughness of a sheet of sea ice encodes its deformational history and determines its aerodynamic coupling with the overlying air and underlying water here we report snow surface ice surface and ice underside roughness computed from 47 surface elevation profiles collected during a transect of the weddell sea the roughness for each surface parameterized as the standard deviation of the surface elevation segregates according to whether or not a floe has been deformed deformed ice has greater roughness than undeformed ice regardless of deformational history the underside roughness is almost always greater than the snow surface and ice surface roughnesses which are nearly equal roughness spectra for all three surfaces and for both deformed and undeformed ice roll off roughly as k 1 when the wavenumber k is between 0 1 and 3 rad m 1 the snow surface and underside spectra roll off somewhat faster than k 1 and the ice surface spectra roll off somewhat slower than k 1 both top and underside arctic ice roughness spectra on the other hand have been reported to roll off faster than k 2 we speculate that the excess spectral intensity at high wavenumbers in the antarctic ice surface spectra results from the small scale roughness that the ice sheet had on consolidation this excess high wavenumber spectral intensity persists in the ice surface spectra of second year ice evidently once formed the ice surface remains unchanged on the microscale until the entire ice sheet melts with a remote measurement of roughness we should be able to decide whether an ice floe is deformed or undeformed our spectral analysis hints that remote sensing may also be able to differentiate between first year and second year ice from the snow surface spectra we compute a roughness scale that parameterizes the air ice momentum coupling and lets us estimate the neutral stability drag coefficient referenced to a height of 10 m cdn10 typical cdn10 values are 1 1 1 4 10 3 over undeformed ice and 1 3 1 8 10 3 over deformed ice

the sequence and correlation of early ordovician arenig graptolite faunas in the richardson trough and misty creek embayment yukon territory and district of mackenzie canada four graptolite biozones are recorded from the arenig portion of the road river group in the richardson and mackenzie mountains in the yukon and northwest territories in ascending order these zones are tetragraptus approximatus pendeograptus fruticosus didymograptus bifidus and parisograptus caduceus australis new the castlemainian stage may be represented by nongraptolitic massive bedded chert the arenig llanvirn boundary is drawn below the first occurrence of undulograptus austrodentatus fifty four graptolite taxa are present and 16 of these species and subspecies are recorded for the first time in this deep water biotope namely didymograptus cf adamantinus d asperus d dilatans d cf kurcki d validus communis holmograptus aff leptograptoides h sp a isograptus sp nov a i dilemma keblograptus geminus pseudisograptus manubriatus harrisi ps m koi ps m janus ps cf tau xiphograptus lofuensis and zygograptus cf abnormis

thickness structure and properties of level summer multiyear ice in the eurasian sector of the arctic ocean in august and september 1991 thickness structure and properties of level multiyear ice were studied at 66 locations in the eurasian sector of the arctic ocean the mean ice thickness was 2 86 m with 0 31 m of freeboard including 0 08 m deteriorated ice of mean density 370 kg m 3 on the basis of the study of ice cores 61 of the ice cover consisted of undeformed columnar ice the remaining 39 consisted of a mixture of ice types including frazil 18 and deformed ice 9 through microstructural studies six main classes of pores could be identified the mean density of the ice cover increased from 720 kg m 3 at the top to 880 kg m 3 below 0 4 m depth sea ice salinities mean value 2 1 correlate with ice thickness on average salinity profiles exhibit a linear increase from values close to 0 at the top to 2 at 1 m depth with less steep salinity gradients below sampling from different depths within the ice cover indicates that the brine in summer sea ice is strongly stratified the influence of meltwater percolation is evident with salinities around 5 and ph values 15 and 8 at greater depths brine volumes ranging from 80 to 150 are controlled by the thermodynamic equilibrium between the solid and liquid phases gas volumes decrease from 200 at the top to 50 below 1 m depth pore microstructure is highly variable even on small scales salinity and other ice properties do not vary to a large degree between different regions the evolution of level multiyear sea ice is discussed with particular reference to hidden occurrence of deformed ice and the importance of ablation processes

physical properties of summer sea ice in the fram strait the physical properties of sea ice in the fram strait region of the greenland sea were examined during june and july 1984 in conjunction with the marginal ice zone experiment field program most of the ice sampled within fram strait during this period was multiyear thicknesses and other properties indicated that none of the multiyear ice was older than 4 to 5 years snow cover on the multiyear ice averaged 29 cm while that on first year ice averaged only 8 cm deep this difference may be related to enhanced sublimation of the snow on the thinner first year ice the salinity profiles of first year ice clearly show the effects of ongoing brine drainage in that profiles from cores drilled later in the experiment are substantially less saline than earlier cores thin section examinations of crystal structure indicate that about 75 of the ice consisted of congelation ice with typically columnar type crystal structure the remaining 25 consisted of granular ice with only a few occurrences of snow ice the granular ice consisted primarily of frazil found in small amounts at the top of floes but mainly observed in multiyear ridges the horizontally oriented crystal c axes showed various degrees of alignment ranging from no alignment to strong alignments in which the alignment direction changed with depth implying a change in floe orientation with respect to the ocean current at the ice water interface during ice growth evidence of crystal retexturing was observed in the upper meter of nearly every multiyear core this retexturing consisting of grain boundary smoothing and nearly complete obliteration of the ice platelet brine layer substructure is attributed to summer warming

massive ancient sea ice strata and preserved physical structural characteristics in the ward hunt ice shelf two sea ice layers one measured as 9 m thick the other at least 12 m thick and estimated to be 24 5 m thick have been located by ice core drilling in the west ward hunt ice shelf to examine the preservation of physical structu ral characteristics over long time intervals the crystal structure and brine volumes in the sea ice which possibly dates back to about 3000 bp have been studied the structural characteristics are immediately recognizable as those of undeformed congelation sea ice accreted by stefan growth brine volumes in the ancient sea ice are higher than those in modern multi year ice at the same temperature the preservation of brine over a time span of hundreds to thousands of years is attributed to an absence of surface meltwater to effect brine flushing and the very slow even negligible action of gravity drainage brine pocket migration and brine expulsion the congelation structures indicate that sea ice can grow by the stefan accretion mechanism to thicknesses exceeding the equilibrium thickness 2 5 5 m of most undeformed multi year ice the observed physical structu ral characteristics of the ward hunt sea ice strongly suggest that many of the properties attained by sea ice are permanent and not affected by slow acting physical processes

under ice salinity and stable isotope distribution of saroma ko lagoon hokkaido northern japan in winter lakes and lagoons at high altitudes or high latitudes have interesting hydrological cycles that differ from those in other seasons or in other regions because water surfaces are covered with ice hydrological balances of lakes and lagoons are complex dynamic systems and to elucidate them isotopic tracers of water have been used as effective tools along with observations of precipitation evaporation inflows and outflows here to understand hydrological processes during freezing periods in the brackish saroma ko lagoon hokkaido northern japan we examined horizontal and vertical distributions of salinity and isotope compositions of lagoon water and ice in 2005 and 2006 horizontal and vertical gradients of salinity and isotope compositions were observed from the river mouth to the sea channel and factors determining these distributions were considered the mixing of freshwater and seawater and a freezing effect were presumed to be factors in relationships between salinity and isotopes and in relationships between surface waters and ice just above the water a simple box model for water balance was constructed based on these putative factors to reproduce the distributions of salinity and isotope compositions of surface waters and ice an evaluation of the model revealed that this hydrological system is controlled primarily by horizontal advection of the epilimnion freshwater influx and the ice growth rate

a comparison of physical properties and strength of decaying first year ice in the arctic and sub arctic measurements made on first year ice in the arctic and sub arctic are used to show that ice from both regions decays in a similar manner during the spring summer melt season one notable difference is that melt induced changes in sub arctic labrador occur about 2 months earlier than in the arctic in both regions the temperature and strength of the ice change gradually over the season whereas the bulk salinity and thickness of the ice do not change substantially until later in the season when the ice becomes isothermal at a temperature of 1 88c results show that the seasonal decrease in the strength of first year sea ice and the temperature induced increase in brine volume are correlated once the ice is devoid of salt in late summer the air volume continues to increase but has minimal effect on the ice strength

new data on late silurian and early devonian brachiopods from the royal greek area yukon territory late silurian and early devonian brachiopod species are listed from two new sections in the royal creek area yukon the data from these sections fill in knowledge of the biostratigraphy of brachiopods of late silurian ludlovian and pridolian and more importantly of early zlichovian late early devonian ages of the northern cordillera thirteen species of brachiopods are described in this study five none new from the late silurian and eight from the early zlichovian late early devonian of which species of phragmostrophia linguopugnoides vagrania salairina and metaplasia are probably new but have not been given formal species names

rhenium and osmium isotopes in black shales and ni mo pge rich sulfide layers yukon territory canada and hunan and guizhou provinces china rhenium and osmium abundances and osmium isotopic compositions were determined by negative thermal ionization mass spectrometry for samples of devonian black shale and an associated ni enriched sulfide layer from the yukon territory canada the same composition information was also obtained for samples of early cambrian ni mo rich sulfide layers hosted in black shale in guizhou and hunan provinces china this study was undertaken to constrain the origin of the pge enrichment in the sulfide layers samples of the ni sulfide layer from the yukon territory are highly enriched in re os and other pge with distinctly higher re 192os but similar pt re compared to the black shale host re os isotopic data of the black shale and the sulfide layer are approximately isochronous and the data plot close to reference isochrons which bracket the depositional age of the enclosing shales samples of the chinese sulfide layers are also highly enriched in re os and the other pge re 192os are lower than in the yukon sulfide layer re os isotopic data for the sulfide layers lie near a reference isochron with an age of 560 ma similar to the depositional age of the black shale host the osmium isotopic data suggest that re and pge enrichment of the brecciated sulfide layers in both the yukon territory and in southern china may have occurred near the time of sediment deposition or during early diagenesis during the middle to late devonian and early cambrian respectively

observation of sea ice using the 36 ghz surface contour radar in january 1984 a 36 ghz scanning pencil beam radar was used at 175 m altitude over ice in the greenland sea to produce high spatial resolution 3 m by 5 m topographic and backscattered power maps incidence angles from nadir to approximately 300 offnadir were included in the data set when the radar maps were compared with the ice topography indicated by simultaneous photography and an analysis of the shadows of the ridges cast by the low sun angle 3 5 it was found that the backscattered power data sharply delineated many of the features observed in the photography the elevation data were less impressive but still consistent with the general variation of the topography

conodonts from the kechika formation and road river group lower to upper ordovician of the cassiar terrane northern british columbia this study examines the lower paleozoic stratigraphy of the cassiar terrane from three key sections comprising an east west transect across the terrane the cassiar terrane west of the northern rocky mountain trench consists of a neoproterozoic to triassic succession and is a fragment of the cordilleran miogeocline that has been displaced northward the amount of displacement from its original position remains controversial conodonts from the cassiar terrane have been previously reported from only a few reconnaissance studies more than 3000 m of strata have been measured and examined in detail and 85 conodont samples collected a total of 926 identifiable conodont elements are assigned to 31 species representing 21 genera the conodonts are mainly representative of the midcontinent faunal realm but some also represent the atlantic realm conodonts from the upper kechika formation and base of the road river group are early ordovician tremadocian in age and those from the upper road river group rang

a statistical description of the microstructure of young sea ice in order to fully exploit microwave models of sea ice the standard ice characterization must be supplemented by a statistical description of the ice microstructure for the strong fluctuation theory this statistical description takes the form of the mean and variance of the permittivity plus correlation lengths we have computed these statistics for over 50 samples of young ice including both columnar congelation ice and desalinated bubbly ice samples were taken from different vertical depths and horizontal positions within the ice sheet and encompassed a comprehensive range of ice temperatures and brine volumes for each of these samples horizontal thin sections were photographed then digitized and analyzed on a personal computer based image processing system results indicate that correlation lengths correspond to the physical dimensions of the inclusions the brine pocket size typically tenths of a millimeter for saline ice and the air bubble size typically millimeters for desalinated ice for saline ice the shape of the correlation function was elliptical similar to the shape of the brine pockets in one case as the ice warmed from 20 to 1 c and the brine volume increased from 2 to 37 the correlation length increased from 0 14 to 0 22 mm

a quantitative description of sea ice inclusions structurally sea ice consists of an ice matrix with inclusions of brine and air a quantitative description of the size of these inclusions is critical for both interpreting and modeling the electromagnetic properties of sea ice photomicrographs of ice thin sections were analyzed using a personal computer based image processing system to determine the number of inclusions the inclusion size distributions and statistics for brine pockets in young ice and first year ice and for air bubbles in a multiyear hummock inclusions ranging in size from thousandths of square millimeters to a few square millimeters were measured in all cases a two parameter lognormal distribution fits the cumulative inclusion size distributions well correlation coefficient greater than 0 99 this includes brine pockets in both granular and columnar ice and a range of brine volumes from 2 to 40 as ice warms and its brine volume increases the size distribution shifts toward larger brine pockets this increase in brine pocket size is particularly pronounced for brine volumes greater than 10 as individual brine pockets coalesce air bubbles are much larger than brine pockets with mean major axis lengths of the order of millimeters for air bubbles and tenths of a millimeter for brine pockets observations of inclusion shape factors indicate that in general brine pockets are more elongated than air bubbles

growth rate and salinity profile of first year sea ice in the high arctic this paper describes the growth of sea ice and the salinity profiles observed in eclipse sound near pond inlet baffin island canada during the winter of 1977 78 a numerical method of calculation has been developed to incorporate the variations in snow conditions and physical properties of ice and snow during the growth season it is shown that the growth rate can be predicted reasonably well it is also shown that the vertical salinity profile in the ice towards the end of the season provides a record of previous climatological conditions a dependence has been shown between the predicted growth rate and the measured salinity

lower paleozoic stratigraphic and biostratigraphic correlations in the canadian cordillera implications for the tectonic evolution of the laurentian margin the ancient laurentian margin rifted in the latest neoproterozoic to early cambrian but appears not to have developed as a simple passive margin through a long post rift drift phase stratigraphic and conodont biostratigraphic information from four platform to basin transects across the margin has advanced our knowledge of the early paleozoic evolution of the margin in northeastern british columbia two northern transects span the macdonald platform to kechika trough and ospika embayment and a third transect spans the parautochthonous cassiar terrane in the southern rocky mountains new conodont biostratigraphic data for the ordovician succession of the bow platform is correlated to coeval basinal facies of the white river trough in total from 26 stratigraphic sections over 25 km of strata were measured and 1200 conodont samples were collected that yielded over 100 000 conodont elements key zonal species were used for regional correlation of uppermost cambrian to middle devonian strata along the cordillera the biostratigraphy temporally constrains at least two periods of renewed extension along the margin in the latest cambrian and late early ordovician alkalic volcanics associated with abrupt facies changes across the ancient shelf break intervals of slope debris breccia deposits and distal turbidite flows suggest the margin was characterized by intervals of volcanism basin foundering and platform flooding siliciclastics in the succession were sourced by a reactivation of tectonic highs such as the peace river arch prominent hiatuses punctuate the succession including unconformities of early late ordovician sub llandovery possibly early to middle silurian and early devonian ages

the ireviken event in the lower silurian of gotland sweden relation to similar palaeozoic and proterozoic events abstract for a long time the silurian was thought to represent a time of stable environmental conditions in the greenhouse period that followed the late ordovician glaciation during the past decade knowledge about the silurian has increased markedly and today it is known that the conditions in the silurian were much more variable than previously assumed detailed isotopic investigations have revealed several distinct positive excursions in both carbon and oxygen isotope values in low latitudes these periods of high c and o isotope values are in many cases characterised by the growth of reefs and the formation of extended carbonate platforms the sediments deposited during these excursions contain impoverished fossil assemblages especially with respect to conodonts graptolites and trilobites a conspicuous isotope excursion coincident with facies changes and a marked mass extinction is observed near the llandovery wenlock boundary this event is called the ireviken event after its type locality on the island of gotland sweden jeppsson l 1987 in palaeobiology of conodonts ellis horwood ltd chichester pp 129 145 here isotope data from nine sections at the nw coast of gotland are presented that cover the time interval of the ireviken event the 13c mean values rise from 1 4 to 4 5 and the 18o values increase from 5 6 to 5 0 the relative timing of stable isotope development extinctions and facies development is discussed it is shown that first extinctions precede the isotope excursion this indicates that extinction events and stable isotope development are only indirectly connected but might reflect the same causes other events characterised by similar relationships between positive isotope excursions mass extinctions and facies development are found in younger parts of the silurian late wenlock and ludlow in the late ordovician the late cambrian and with some reservations in the proterozoic the similarities between these events indicate analogous controlling mechanisms for the silurian climatic changes between humid and arid conditions in low latitudes were postulated in an earlier study of the authors a palaeoceanographic climatic model was postulated which is consistent with most of the sedimentological palaeontological and geochemical data here we demonstrate that this model may be applicable also for the older events

conodont biostratigraphy of the lower to middle devonian deserters formation new road river group northeastern british columbia a new lower to middle devonian basinal unit of the road river group herein formally named the deserters formation contains argillaceous crinoidal limestone and black shale deposited in a linear sub basin of the ospika embayment southern kechika trough the abrupt lateral facies changes in the region facies thickness and occurrence of volcanics indicate a period of extensional tectonism a total of 53 4 5 kg each samples from the deserters formation yielded 7766 conodont elements assigned to 14 genera representing 33 species the formation ranges from the lochkovian eleanorae zone or lower part of the delta zone of the cordilleran region to eifelian australis zone the temporal constraints established by conodont biostratigraphy allow correlation to the grizzly bear formation a regionally restricted lower to middle devonian unit in the selwyn basin to the north

transpolar observations of the morphological properties of arctic sea ice save for an area between 8830 0 n and 8930 0 n where polynyas and thin ice were observed surveys of snow depth ice thickness and ice properties were conducted at ice stations thickness observations suggest a general latitudinal trend of increasing ice thickness moving northward with considerable variability from floe to floe and within a single floe average floe thicknesses varied from 1 0 to 2 8 m and the standard deviation of thickness on an individual floe was as large as 1 m ice crystallography showed a large amount of granular ice the average optical equivalent soot content was 4n g cg 1 for new snow 8 ng c g 1 for the surface granular layer of multiyear ice and 18 ng c g 1 for the interior of multiyear ice indicating a tendency of the particulates to concentrate at the surface with melting