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

ice pumps and their rates an ice pump is a heat engine driven by the change of freezing point with pressure which will melt ice at depth in the ocean and deposit it at a shallower location it is self starting calculations of the maximum magnitude of this effect are made which show good agreement with field data available for sea and lake ice the discussion is applied to the general case of a moving pack ice sheet with a well mixed surface layer and to floating ice shelves the rate of melt from an 11 m deep pressure ridge keel due to ice pumping is estimated as 26 cm year and that from the front of the ross ice shelf at mcmurdo sound antarctica is estimated as 5 m year for the level of water movement noted in the authors field observations far from the ice front pumping between shelf areas of different thickness will still occur with tidal motion providing the necessary water exchange but its magnitude is now limited by the ability to remove the potentially stable layer of melt water out of the system it is important to realize that the pumping does not depend on the availability of sensible heat in the water column and its effects are additional to any melting caused by the advection of warmer water to the ice water interface

study of the impact of ice formation in leads upon the sea ice pack mass balance using a new frazil and grease ice parameterization abstractleads are cracks in sea ice that often form because of deformation during winter months leads expose the ocean to the cold atmosphere resulting in supercooling and the formation of frazil ice crystals within the mixed layer here the authors investigate the role of frazil ice formation in leads on the mass balance of the sea ice pack through the incorporation of a new module into the los alamos sea ice model cice the frazil ice module considers an initial cooling of leads followed by a steady state formation of uniformly distributed single size frazil ice crystals that precipitate to the ocean surface as grease ice the grease ice is pushed against one of the lead edges by wind and water drag that the authors represent through a variable collection thickness for new sea ice simulations of the sea ice cover in the arctic and antarctic are performed and compared to a model that treats leads the same as the open ocean the processes of ice formation in the new module slow down the refreezing o

estimation of sea ice thickness in ross and weddell seas from ssm i brightness temperatures in polar regions ocean atmosphere interactions are strongly influenced by sea ice and its thickness since satellite passive microwave observations became available in the 1970s significant progress has been made in the study of snow depth and sea ice concentration and extent in these regions estimating sea ice thickness sit instead turned out to be considerably more difficult we present a new empirical algorithm to estimate sit in the ross and weddell seas from special sensor microwave imager brightness temperatures this algorithm combines brightness temperature polarization difference and ratio values to obtain sit for seasonal ice up to a thickness of about 90 cm during freezing conditions a series of filters accounts for open water new ice and snow on sea ice our sit estimates are consistent with colocated visual ship based sit observations made according to the antarctic sea ice processes and climate project showing linear correlation values between 0 73 and 0 96 and root mean square error values between 14 and 24 cm the seasonal development of the region average sit derived with our approach agrees with the corresponding values derived from u s national ice center ice charts comparison with colocated polynya distribution maps suggests that the algorithm could be optimized for its performance with regard to sit values around 50 cm and that a closer investigation of the snow impact on the sit retrieval is required

physical structural and isotopic characteristics and growth processes of fast sea ice in lutzow holm bay antarctica a sea ice ocean study was conducted off queen maud land and enderby land antarctica from 1990 to 1991 by the japanese antarctic research expedition observations of multiyear land fast sea ice were made in lutzow holm bay over a period of 2 years to determine the snow and ice characteristics and ice growth processes the snow depth in the bay reached large values of 1 0 to 1 5 m during the winter season at offshore locations from the analysis of ice thickness measurements it is confirmed that the fast ice with deep snow cover grew little in winter but substantially thickened during the summer months on the basis of ice core structure salinity and stable isotopic composition we conclude that the summer growth was caused by upward growth at the top of the ice to which snow ice and superimposed ice formation contribute these processes were the primary contributors to sea ice growth and characteristics only where the snow accumulation was large in areas of low snow accumulation there was no surface growth superimposed ice formation on sea ice in antarctica has not been reported previously evidence for snow cover melting which is a prerequisite for superimposed ice formation was also found

structural characteristics of congelation and platelet ice and their role in the development of antarctic land fast sea ice ice cores were obtained in january 1990 from the land fast ice in mcmurdo sound for a study of variations in texture fabric sub structure composition and development two primary ice types were observed congelation and platelet with a minor amount of frazil ice congelation ice growth precedes platelet ice accretion congelation ice fabrics show frequent moderate to strong alignments a phenomenon believed to be due to water current control of selective ice crystal growth platelet ice originates at the base of the congelation ice initially as a porous latticework of tabular ice crystals which subsequently consolidate by congelation of the interstitial water interstitial congelation ice fabrics generally have little or no alignment indicating the reduced effect of currents within the platelet latticework prior to solidification platelet crystal textures range from small wavy edged forms to large blade like forms platelet crystal fabrics indicate that in addition to being randomly oriented the platelet latticeworks commonly include many crystals with their flat 0001 faces oriented both parallel and normal to the base of the overlying ice plate width data suggest that the interstitial congelation ice growth rates remain similar to those of the overlying congelation ice this effective increase in growth rates probably happens because the latticework of accumulating platelets ahead of the freezing interface ensures that the water within the platelet layer is at the freezing point and less heat has to be removed from platelet rich water than from platelet free water for a given thickness of congelation ice to grow the negative oceanic heat flux associated with platelet ice formation in mcmurdo sound explains why mcmurdo sound fast ice is thicker than ross sea pack ice and also why it reaches a greater thickness than arctic fast ice grown in a similar polar marine climate plate widths in the mcmurdo sound congelation ice suggest however that it grows no faster than arctic congelation ice

winter snow cover on sea ice in the weddell sea measurements of snow thickness temperature salinity density and stratigraphy acquired during the 1992 winter weddell gyre study are presented results indicate that the winter snow cover on sea ice in the weddell sea is extremely variable extreme fluctuations in antarctic synoptic conditions air temperature precipitation humidity and wind speed occur during the austral winter they result in unique modifications and additions to the snow layer during the aging process and act to stabilize an otherwise easily wind redistributed shallow snow cover and develop well packed drift features the latter occur even over relatively undeformed areas of sea ice and have a significant localized effect on the snow thickness distribution significant variability in snow grain size mean 2 73 3 12 mm and density 0 32 0 09 g cm 3 is observed as a result of cyclical switches between high and low temperature gradient metamorphism multiple icy layers indicate multiple thaw freeze events one such event occurred during a 3 day station during which the air temperature rose by 22 c in 12 hours to approximately 0 c this paper also examines mechanisms for flooding of the snow ice interface including snow loading even where the latter is not a factor the layer of snow immediately above the snow ice interface is commonly damp and saline 10 limitations in the data set are discussed and comparisons are drawn with other experiments

the sea ice thickness distribution in the northwestern weddell sea we present new data on distribution of snow and sea ice thicknesses in the northwestern weddell sea the data were obtained through direct measurements along 19 profiles each approximately 100 m long on 17 different floes located between 54 46 w and 59 64 s the overall probability density functions pdfs for ice thicknesses reflect the complex mixture of first second and multi year ice to be expected in the outflowing branch of the weddell gyre further differentiation of the data reveals four distinct thickness classes which reflect differences in the formation and subsequent histories of the ice encountered these classes i iv represent strongly deformed first year ice less deformed first and second year ice and deformed second or multi year ice respectively each of the classes is characterized by a specific set of quantities related to ice texture and surface snow characteristics and by distinct pdfs for snow and ice thicknesses in addition geometric surface and bottom roughness characteristics differ significantly for each of the floe classes

wind and wave influences on sea ice floe size and leads in the beaufort and chukchi seas during the summer fall transition 2014 sea ice floe size distribution and lead properties in the beaufort and chukchi seas are studied in the summer fall transition 2014 to examine the impact on the sea ice cover from storms and surface waves floe size distributions are analyzed from medea landsat8 and radarsat 2 imagery with a resolution span of 1 100 m landsat8 imagery is also used to identify the orientation and spacing of leads the study period centers around three large wave events during august september 2014 identified by swift buoys and wavewatch iii model data the range of floe sizes from different resolutions provides the overall distribution across a wide range of ice properties and estimated thickness all cumulative floe size distribution curves show a gradual bending toward shallower slopes for smaller floe sizes the overall slopes in the cumulative floe size distribution curves from landsat8 images are lower than while those from radarsat 2 are similar to previously reported results in the same region and seasonal period the medea floe size distributions appeared to be sensitive to the passage of storms lead orientations regardless of length correlate slightly better with the peak wave direction than with the mean wave direction their correlation with the geostrophic wind is stronger than with the surface wind the spacing between shorter leads correlates well with the local incoming surface wavelengths obtained from the model peak wave frequency the information derived shows promise for a coordinated multisensor study of storm effects in the arctic marginal ice zone

modeling the winter spring transition of first year ice in the western weddell sea a new halodynamic scheme is coupled with the los alamos sea ice model to simulate western weddell sea ice during the winter spring transition one dimensional temperature and salinity profiles are consistent with the warming and melt stages exhibited in first year ice cores from the 2004 ice station polarstern ispol expedition results are highly sensitive to snowfall simulations which use reanalysis precipitation data do not retain a snow cover beyond mid december and the warming transition occurs too rapidly model performance is greatly improved by prescribing a snowfall rate based on reported snow thicknesses during ice growth prior to ispol simulations indicate a period of thick snow and upper ice salinity enrichment gravity drainage model parameters impact the simulation immediately while effects from the flushing parameter snow porosity at the ice top appear as the freeboard becomes negative simulations using a snow porosity of 0 3 consistent with that of wet snow agree with salinity observations the model does not include lateral sources of sea water flooding but vertical transport processes account for the high upper ice salinities observed in ice cores at the start of the expedition as the ice warms a fresh upper ice layer forms and the high salinity layer migrates downward this pattern is consistent with the early spring development stages of high porosity layers observed in antarctic sea ice that are associated with rich biological production future extensions of the model may be valuable in antarctic ice biogeochemical applications

n2o record spanning the penultimate deglaciation from the vostok ice core nitrous oxide n2o is an important atmospheric trace gas whose concentration is determined by numerous sources and sinks over the past 200 years n2o has increased by 17 3 due primarily to increased anthropogenic emissions over the last glacial interglacial transition data from ice cores show that n2o increased by 35 this increase may be related to increased terrestrial n2o emissions resulting from a global climate amelioration here i describe a new dry extraction technique for measuring the elemental and isotopic composition of n2o in ice core samples results from a shallow gisp ii ice core spanning the last 200 years provide an estimate for the preanthropogenic n2o concentration of 266 4 ppb in addition 11 ice samples from the last interglacial period show fairly uniform n2o values 269 9 ppb during the penultimate glacial period 131 160 ka n2o concentrations of air trapped in the glacier fluctuated between 190 ppb and 320 ppb while co2 and ch4 concentrations were relatively low and stable two local n2o maxima were observed during the penultimate glacial period that actually exceeded normal interglacial n2o values 265 ppb the maxima were located in portions of the core which exhibit both elevated dust concentrations and elevated bacterial counts the 15n and 18o of n2o in this portion of the vostok core were 15 higher and 12 lower than during the warm eemian period respectively the isotopic data and coincidence between the elevated n2o concentrations and the high bacterial counts may be related to in situ n2o production by bacteria the lower 18o values are consistent with the isotopic composition of n2o produced by in situ nitrification

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

simulation of pancake ice dynamics in a wave field from many field observations it has become well known that pancake ice is ubiquitous in a wave dominated sea these strikingly uniform circular floes are consistently found in the antarctic seas during the ice formation season their presence has also been reported in the bering sea the greenland sea and in polynyas and leads within pack ice in one estimate made by p wadhams personal communication 1991 the areal coverage of pancake ice in the southern ocean marginal ice zone is around 6 106 km2 pancake ice forms through a combination of thermodynamic growth and mechanical thickening caused by rafting of floes that is driven by wave motion this complex growth process is much faster than pure thermodynamic growth and hence may be the main factor responsible for ice edge advance in marginal ice zones in this paper we simulate wave ice floe dynamics by combining a new three dimensional discrete element model with wave hydrodynamics in one set of simulations we calculate ice drift speed as a function of wave amplitude and ice collisional dynamics in a second set of simulations we place a non reflecting vertical barrier meant to simulate the fast ice edge the simulation results show the rate of increase of the ice impact force on the barrier and the accompanying thickening of the rafted region in front of the barrier as a function of wave amplitude results from this study will help quantify the formation process for pancake ice covers in a wave field

platelet ice the southern ocean s hidden ice a review basal melt of ice shelves is not only an important part of antarctica s ice sheet mass budget but it is also the origin of one of the most peculiar types of sea ice found in the polar oceans platelet ice in many regions around coastal antarctica tiny ice crystals form and grow in supercooled plumes of ice shelf water releasing heat into the surrounding ocean they usually rise towards the surface eventually becoming trapped under an ice shelf as marine ice frequently masses of those crystals are advected out of the ice shelf cavity and accumulate below a solid sea ice cover to form a semiconsolidated layer when the overlying sea ice grows into this so called sub ice platelet layer the loose crystals are consolidated adding additional thickness to the sea ice these phenomena are generally referred to as platelet ice although confusion about the terminology is widespread in the literature the presence of platelet ice has a profound impact on sea ice properties and processes in several regions of antarctica with numerous implications for the local polar marine biosphere most notably sub ice platelet layers provide a stable sheltered nutrient and food rich habitat which usually results in a highly productive and uniquely adapted ecosystem it has also been hypothesised that platelet ice may be an indicator of the state of an ice shelf although comprehensive time series are limited to the ross sea this paper clears up the terminology by providing exact definitions of the relevant terms we review platelet ice formation observational methods as well as geographical and seasonal occurrence the physical properties and ecological implications are merged in a way understandable for physicists and biologists alike to lay the foundation for the interdisciplinary research that is necessary to tackle the current knowledge gaps

azimuthal modulation of c band scatterometer spl sigma sup 0 over southern ocean sea ice in a continuing evaluation of the ers 1 c band scatterometer as a tool for studying polar sea ice the authors evaluate the azimuthal modulation characteristics of antarctic sea ice ers 1 ami scatterometer mode data sets from several study regions dispersed in the antarctic seasonal sea ice pack are evaluated for azimuthal modulation when appropriate the incidence angle dependence is estimated and removed in a study region before determining whether azimuthal modulation is present in the data other comparisons are made using the fore and aft beam measurement difference the results show that over the ice pack azimuthal modulation is less than 1 db at the scale of observation of the ers 1 c band scatterometer

a one dimensional percolation model of flooding and snow ice formation on antarctic sea ice a one dimensional thermodynamic sea ice growth model is developed with emphasis on seawater flooding and snow ice formation on antarctic sea ice to examine the possibility that flooding is the result of brine percolation through a porous ice matrix and the consequences of this percolation on the salinity structure and mass balance of the ice flooding is modeled in a semiheuristic fashion by examining two possible regimes for seawater and brine infiltration through the porous ice into the snowpack a standard model assumes that the upward flow of brine is horizontally homogeneous and brine flow is modeled using a darcian scheme a simple model assumes that the infiltrating brine does not interact with the internal ice brine network but instead percolates upward through cracks or is restricted in spatial extent results of simulations are shown for the climatology in the ross sea and compared to field data from one autumn and one winter cruise aboard the r v nathaniel b palmer in 1995 sensitivity studies are performed to show the effects of variations in climate forcing the dependence of brine percolation and snow ice formation on key thermophysical parameters is investigated results indicate that the mass balance depends very strongly on the brine flow regime in the standard model ice salinities and brine volumes are greatly affected by brine percolation creating a strong feedback between flooding and future snow ice production snow ice formation for the simple model was much more predictable and depended primarily on snow load comparison of results with field data indicate that if brine percolation is the major mechanism for flooding and snow ice formation then there must be either substantial convective redistribution of salt to maintain ice porosity or the flow must be spatially inhomogeneous

mudball surface dust and snowball earth deglaciation 1 recent modeling results have raised doubts about the ability to deglaciate from a global glaciation at atmospheric carbon dioxide levels that are realistic for a neoproterozoic snowball earth here we argue that over the lifetime of a snowball event ice dynamics should lead to the development of a layer of continental and volcanic dust at the ice surface in the tropics that would significantly lower the tropical surface albedo and encourage deglaciation this idea leads to the prediction that clay drapes found on top of neoproterozoic glaciations should be thicker in tropical than extratropical regions we test this idea by running the foam general circulation model gcm with an added tropical dust layer of different sizes and albedos and find that the tropical dust layer causes snowball deglaciation at pco2 0 01 0 1 bar in a reasonable regime of these parameters we find similar though more nuanced results from a limited number of test cases using national center for atmospheric research s cam gcm

sea ice ridging in the eastern weddell sea in august 1986 sea ice ridge heights and spatial frequency in the eastern weddell sea were measured using a ship based acoustical sounder using a minimum ridge sail height of 0 75 m a total of 933 ridges were measured along a track length of 415 km the ridge frequency varied from 0 4 to 10 5 ridges km 1 the mean height of the ridges was found to be about 1 1 m regardless of the ridge frequency these results are compared to other ridging statistics from the ross sea and found to be similar comparison with arctic data however indicates that the height and frequency of the ridges are considerably less in the weddell sea than in the arctic whereas in the arctic the mean ridge height tends to increase with the ridge frequency we found that this was not the case in the weddell sea where the mean ridge height remained constant irrespective of the ridge frequency estimates of the contribution of deformed ice to the total ice thickness are generally low except for a single 53 km section where the ridge frequency increased by an order of magnitude this resulted in an increase in the equivalent mean ice thickness due to ridging from 0 04 m in the less deformed areas to 0 45 m in the highly deformed section these values were found to be consistent with values obtained from drilled profile lines during the same cruise

the development of the odden ice tongue in the greenland sea during winter 1993 from remote sensing and field observations the odden ice tongue in the central greenland sea believed to be associated with midgyre convection developed prominently during the winter of 1993 january april during this period it was studied by a succession of cruises which formed part of the european subpolar ocean programme and which included direct sampling and measurement of the frazil and pancake ice which constituted the material of the ice tongue as well as studies of the ocean structure passive microwave imagery was used to determine the evolution of odden through the winter and when combined with ers 1 synthetic aperture radar studies and the field data yielded estimates of ice extent and thickness through the winter from these studies it was possible to estimate the salt flux into the ocean originating from brine release from sea ice during the growth phases of odden

studies of antarctic sea ice concentrations from satellite data and their applications large regional and temporal changes in the global sea ice cover have been observed recently because of the relevance of such changes to climate change studies it is important that key ice concentration data sets currently used for evaluating such a phenomenon are assessed for accuracy and interpreted properly sea ice concentrations derived from passive microwave data using the bootstrap and nasa team algorithms are shown to be generally consistent but are also observed to differ by 10 35 in large areas within the ice pack especially in the weddell sea amundsen sea and ross sea regions comparative analyses of such passive microwave data with coregistered visible and infrared i e landsat avhrr and ols data show a predominance of thick consolidated ice in these areas and good agreement with the bootstrap algorithm results the relatively low values from the nasa team algorithm results are likely due to layering within the ice and snow and or surface flooding which are known to affect the polarization ratio large seasonality in the physical characteristics and emissivity of the ice cover is also observed and in predominantly new ice regions the ice concentrations from passive microwave data are usually lower than retrievals from landsat and ols data in which the thresholding technique is used the passive microwave results are biased because of relatively low emissivity of new ice but they may be more useful since the bias allows for the identification of areas of significant divergence and polynya activities such areas need to be identified since heat and salinity fluxes are proportionately increased in these areas compared to those from the thicker ice areas time series data from 1978 through 2000 also show a slight but insignificant positive trend of 0 17 0 33 decade in ice extent which is consistent with slight continental cooling during the period this is a big contrast to the observed negative trend of about 3 decade in the arctic sea ice cover it should be noted however that because the overlap period for key instruments is just 1 month the error due to changes in sensor characteristics calibration and threshold for the 15 ice edge may not be negligible

seasonal variations in the properties and structural composition of sea ice and snow cover in the bellingshausen and amundsen seas antarctica sixty three ice cores were collected in the bellingshausen and amundsen seas in august and september 1993 during a cruise of the r v nathaniel b palmer the structure and stable isotopic composition 18 o 16 o of the cores were investigated in order to understand the growth conditions and to identify the key growth processes particularly the contribution of snow to sea ice formation the structure and isotopic composition of a set of 12 cores that was collected for the same purpose in the bellingshausen sea in march 1992 are reassessed frazil ice and congelation ice contribute 44 and 26 respectively to the composition of both the winter and summer ice core sets evidence that the relatively calm conditions that favour congelation ice formation are neither as common nor as prolonged as the more turbulent conditions that favour frazil ice growth and pancake ice formation both frazil and congelation ice layers have an av erage thickness of 0 12 m in winter evidence that congelation ice and pancake ice thicken primarily by dynamic processes the thermodynamic development of the ice cover relies heavily on the formation of snow ice at the surface of floes after sea water has flooded the snow cover snow ice layers have a mean thickness of 0 20 and 0 28 m in the winter and summer cores respectively and the contribution of snow ice to the winter 24 and summer 16 core sets exceeds most quantities that have been reported previously in other antarctic pack ice zones the thickness and quantity of snow ice may be due to a combination of high snow accumulation rates and snow loads environmental conditions that favour a warm ice cover in which brine convection between the bottom and top of the ice introduces sea water to the snow ice interface and bottom melting losses being compensated by snow ice formation layers of superimposed ice at the top of each of the summer cores make up 4 6 of the ice that was examined and they increase by a factor of 3 the quantity of snow entrained in the ice the accumulation of superimposed ice is evidence that melting in the snow cover on antarctic sea ice floes ran reach an advanced stage and contribute a significant amount of snow to the total ice mass

late weichselian ice sheets in arctic and pacific siberia abstract interpretation of space images coupled with field data on glacial geomorphology and glacial geology of northern eurasia have provided compelling evidence for a continuous late weichselian ice sheet covering the entire arctic margin of the continent in addition to the scandinavian ice sheet three ice sheets of the same order the karan east siberian and beringian are identified within the major eurasian ice sheet also there is evidence and other considerations suggesting a former ice sheet in the sea of okhotsk ice spreading centers of the ice sheets were situated on the continental shelves off the siberian coasts thus we can term the ice sheets siberian so far the conventional stratigraphic approach to the problem of siberian glaciation has proven fruitless and yielded nothing but uncertainty while geomorphological studies have discovered a wealth of glacial landforms in arctic siberia it was these landforms and their spacing that made the existence of former siberian ice sheets evident the east siberian ice sheet rested on the shelves of the eastern laptev and east siberian seas and its flow was directed radially including up the yana and indigirka rivers the beringian ice sheet was grounded on the chukchi bering and beaufort sea shelves overriding the chukchi and seward peninsulas from the north and flowing through the bering strait it was continued by a thick floating ice shelf buttressed by the submarine aleutian commander ridge the okhotsk ice sheet was grounded on the okhotsk shelf specific gemorphic signatures of marine ice sheets the glacially cut corners have been identified on all promontories jutting out into the bering and okhotsk seas the beringian and okhotsk ice sheets are consistent with the results of deep sea drilling in the adjacent north pacific during leg 145 of d v joides resolution

18o concentrations in sea ice of the weddell sea antarctica we present data on ice texture salinity and delta o 18 obtained from identical sections of ice cores during the winter weddell sea project 1986 on rv polarstern from july through august 1986 in the longitude range between 5 degrees w and 7 degrees e we find no uniquely definable relationship between delta o 18 values and ice texture in a particular section however most of the snow ice as well as some sections of frazil ice ar found to have negative delta o 18 concentrations this is due to varying degrees of admixtures of meteoric ice snow and sea water during formation of snow ice in contrast to common assumptions our results seem to indicate that a snow cover contributes positively to sea ice growth rather than slowing down the overall growth rate based on a simple model we have estimated the contributions of meteoric ice mean of 3 3 and the combined meteoric ice sea water fraction a minimum of 7 6 to the total ice thickness for the majority of the sampled floes although this is only a moderate contribution to the overall mass balance in the absence of congelation growth it nevertheless enhances ice growth in general this hypothesis is dependently supported by our snow and ice thickness data wadhams and others 1987 which demonstrate that the depression of the snow ice interface below the water line i e a negative freeboard and the formation of snow ice is a common occurrence in the weddell sea therefore we hypothesize that the major part of the observed apparent increase in ice thickness between our inbound and outbound tracks of wwsp 86 may not be derived from regular thermodynamically driven congelation growth but rather from the snow ice component in floes of the weddell sea

roughness variability of sea ice and snow cover thickness profiles in the ross amundsen and bellingshausen seas investigation of top and bottom surface roughness was carried out on snow and ice thickness profiles sampled on 57 floes in the ross amundsen and bellingshausen seas between may and september 1995 an objective classification scheme was used to group the studied sea ice floes according to the degree of deformation they had undergone different roughness criteria and methods were applied to the classified floes roughness variances and other properties such as fractal dimensions derived from fourier spectra depend critically on the deformational history of the floes under consideration the wavelet transform is presented as a new two dimensional method to find dominant structure lengths and at the same time localize them in the studied profiles finally air water and ice surface drag coefficients are calculated from the surface roughness characteristics air drag coefficients ranged between 1 1 and 1 7 103 and increased with increasingly deformed ice

waves in frazil and pancake ice and their detection in seasat synthetic aperture radar imagery a theoretical model of waves propagating into an ice cover composed of frazil and pancake ice is developed and compared with measurements of wavelength and direction derived from synthetic aperture radar sar imagery obtained from seasat in october 1978 the theoretical model is based on the concept that ice of these types which consists of small crystals or cakes has only a mass loading effect on the water surface we derive the dispersion relation for phase and group velocities finding that there is an upper frequency limit for propagation into the ice from the reflection coefficient at the ice edge we derive the wave radiation pressure exerted on the ice showing that it will cause a slick of frazil ice backed by thicker floes to become more dense or thick with increasing penetration the implications for radar scattering enabling detection on sar are that the bragg resonant wavelength corresponds to waves above the frequency limit for propagation so that a frazil slick appears dark on an sar image when the frazil ice becomes transformed into pancake ice through slick compression or other means the raised edges of the pancakes cause the ice to appear bright despite the fact that there are no waves present at the bragg wavelength these results are applied to a seasat sar image obtained from the chukchi sea the appearance of the ice in the image corresponds to what we expect for frazil ice gradually transforming itself into pancake ice backed by thicker floes we derive directional wave number spectra outside and inside the ice cover by digital fourier analysis of image subscenes and we find that the change of wavelength and angle of refraction of the dominant wave entering the ice field are both characteristic of the dispersion relation derived theoretically mean ice thicknesses extracted from the theory correspond to thicknesses expected for such slicks the technique offers a possible means of extracting the thickness of fields of frazil and pancake ice from sar imagery this may be of considerable utility when ers 1 sar is used to study the advancing winter ice edge in the antarctic which consists of vast areas of these ice types

east antarctic sea ice albedo thickness distribution and snow cover characteristics of springtime sea ice off east antarctica were investigated during a cruise of the australian national antarctic research expedition in october through december 1988 the fractional coverage of the ocean surface the ice thickness and the snow cover thickness for each of several ice types were estimated hourly for the region near the ship these observations were carried out continuously during the 4 weeks the ship was in the ice thin and young ice types were prevalent throughout the region and the observations show a systematic increase in the total area weighted pack ice thickness including open water area from only 0 2 m within 50 km of the ice edge to 0 45 m close to the coast ice thickness averaged over the ice covered region only is also relatively thin ranging from 0 35 m near the ice edge to 0 65 m in the interior these values are probably typical of average winter thickness for the area the average snow cover thickness on the ice increased from 0 05 m near the ice edge to 0 15 m in the interior average ice concentration increased from less than 6 10 near the ice edge to 8 10 in the interior the ship observed concentrations were in good agreement with concentrations derived from passive microwave satellite imagery except in some regions of high concentration in these regions the satellite derived concentrations were consistently lower than those estimated from the ship possibly because of the inability of the satellite sensors to discriminate the appreciable percentage of very thin ice observed within the total area spectral albedo was measured for nilas young grey ice grey white ice snow covered ice and open water at wavelengths from 420 to 1000 nm allwave albedo was computed by using the spectral measurements together with estimates of near infrared albedo and modeled spectral solar flux area averaged albedos for the east antarctic sea ice zone in spring were derived from representative allwave albedos together with the hourly observations of ice types these area averaged surface albedos increased from about 0 35 at the ice edge to about 0 5 at 350 km from the edge remaining at 0 5 to the coast of antarctica the low average albedo is in part due to the large fraction of open water within the pack but extensive fractions of almost snow free thin ice also play an important role

development and properties of sea ice in the coastal regime of the southeastern weddell sea from october to december 1986 a program consisting of sea ice core analysis in combination with sea ice observations was carried out from the icebreaker r v polarstern as part of the winter weddell sea project the ship operated in the central and southeastern weddell sea with interests focusing on the ice shelf front between 70 s and 77 s where a system of coastal polynyas extended for several tens to hundreds of kilometers opened and maintained despite temperatures well below freezing by offshore wind forcing three wind controlled ice formation regimes may be distinguished 1 for wind speeds 10 m s the ice cover is heavily ridged and rafted 50 and formation of granular ice predominates of the total length of cores sampled in the coastal regime 32 consisted of columnar and 35 of granular ice in addition we observed two unique ice classes along the coast platelet ice formed through consolidation of underwater ice platelets underneath the solid ice cover contributed 11 to our core samples another 22 consisted of intermediate columnar granular ice which originates under the dynamic hydrographic conditions of the near ice shelf region

thermodynamic sea ice growth in the central weddell sea observed in upward looking sonar data upward looking sonar uls data were used to analyze thermodynamic sea ice growth the study was carried out for an ocean region in the central weddell sea for which data of sea ice thickness variability and of the oceanic heat flux through the ice are rare in the study area the contribution of sea ice deformation to vertical ice growth is relatively small in some years this provides the opportunity to simulate thermodynamic sea ice growth considering the influence of a snow cover and of the oceanic heat flux to this end a modified version of stefan s law was used the resulting ice thickness variations were then compared with the uls measurements for the investigated cases the best consistency between data and model results was obtained assuming a snow layer of less than 5 cm thickness and average oceanic heat fluxes between 6 and 14 w m 2 it is demonstrated that in conjunction with ice drift data and analytical models for thermal sea ice growth uls ice thickness measurements are useful for studying the seasonal cycle of growth and decay and for inferring the magnitude of the average oceanic heat flux under sea ice

ice composition evidence of marine ice transfer along the bottom of a small antarctic ice shelf the existence of marine ice transfer along the underside of the hell s gate ice shelf victoria land is indicated by an isotopic and chemical study of ice cores because of top surface ablation the marine ice formed at the ice shelf ocean interface ultimately appears at shelf surface a succession of congelation platelet and frazil ice is shown to occur the combined study of stable isotope composition and of the sodium content of these different ice types proves to be a valuable tool for specifying the ice shelf ocean interactions in this area two different freezing zones separated by a melting rone exist the parent water for the frazil ice is meltwater from congelation ice which appears in the upstream zone

sea ice growth in ongul strait antarctica a two year study was conducted on the growth processes of sea ice in ongul strait antarctica routine measurements of snow depth and ice thickness were made and sea ice cores were collected to assess their structure temperature and salinity the snow depth varied from 0 to about 1 m in the winter months the growth rate is higher in bare ice regions than in snow covered regions however over the year the ice thickness itself is lower in the bare ice regions than in the snow covered regions sea ice in the snow covered regions increased in thickness in spring rather than in winter due to the formation of snow ice and by ice formation related to the melting of snow cover

a direct link between the china loess and marine δ 18 o records aeolian flux to the north pacific most studies of quaternary climates conducted during the past 150 years have focused on glacial sequences and for the past 25 years marine sediments have provided significant further understanding of glacial and interglacial palaeoclimates an important goal of palaeoclimatology however to link the well known detailed continental records to marine records of similar resolution has yet to be realized the classic loess sequences of china provide an apparently continuous record of continental climate over the past 2 4 million years1 2 the oxygen isotope 18o timescale developed from the marine record3 gives us a global chrono stratigraphy of late pleistocene climates previously it has been suggested in studies of the aeolian component in pelagic sediments that it may be possible to link these two records directly by finding a suitable core from the north west pacific downwind from china4 5 here we report the results of such an effort for core v21 146 fig 1 and tie the last 500 000 years of the chinese loess soil sequence directly to the 18o timescale and in so doing refine the dating of regional loess and soil horizons

passive microwave in situ observations of winter weddell sea ice the microwave radiative characteristics of antarctic sea ice during a winter period were investigated continuously from r v polarstern during the 1986 winter weddell sea project while the ship went through about 3000 km of ice from the marginal ice zone to the coastal region and back radiometer measurements at 6 10 18 37 and 90 ghz in vertical and horizontal polarizations were complemented by visual and video observations and measurements at 60 stations of ice thickness salinity temperature snow cover density and other physical characteristics two distinct types of ice cover were observed in the marginal ice zone small pancakes evenly distributed during the southbound leg and ice bands with wet pancakes during the northbound leg other ice types observed were first year ice covered by varying thicknesses and states of snow cover and new and young ice found mainly in leads and polynyas analysis of the data shows a large variability in the multispectral microwave emissivities of these ice types especially at 90 ghz over newly refrozen lead or polynya regions several forms of new ice appear radiometrically distinct while over thick consolidated ice with snow cover the brightness temperatures observed at 90 ghz varied by as much as 100 k overall however at 18 ghz and lower frequencies the emissivities of thick and cold first year ice are relatively stable with standard deviations of about 0 02 at the marginal ice zone the emissivity of the ice cover is a lot less predictable and could cause large uncertainties in ice concentration estimates the use of the 90 ghz channel in combination with a lower frequency channel shows strong potential for more detailed characterization of the ice cover including the identification of various forms of new ice and the quantification of varying snow cover and roughness

an isotopic method of estimating conductive heat flux through antarctic first year sea ice the deuterium concentration profile in a first year antarctic sea ice cover is used to deduce a growth rate curve applying a previously published model time variations of the conductive heat flux throughout the growth period are then estimated from this growth rate curve results indicate that the isotopic determination of sea ice growth rate can be considered as an alternate method for determining the conductive heat flux through a young sea ice cover however there is need for a further test of the method by measuring in situ temperatures and growth rates during the formation of first year sea ice and by analyzing the isotopic composition of ice samples taken simultaneously along selected profiles during the growth period

latitudinal temperature trends in the northern hemisphere during the early cretaceous valanginian hauterivian abstract we present the first detailed stable isotope record 13c 18o for the valanginian lower cretaceous of the southern boreal realm the observations are based on the geochemical analysis of 286 belemnite rostra from stratigraphically well dated sections in northwest germany a major positive carbon isotope excursion cie of 2 in the early late valanginian documents a perturbation of the carbon cycle this positive cie which is well known as the weissert event in the tethys is also displayed in composite carbon isotope records based on published and own data from three different palaeolatitudes 35 39 65 north these findings suggest that the environmental changes indicated by the cie in the early late valanginian are synchronous thereby pointing to a global control the combined oxygen isotope data sets show long term fluctuations of up to 7 c with a cooling in the late valanginian for both the southern and the arctic part of the boreal realm whilst tethyan data document only a ca 1 c cooling based on a reliable bio and chemostratigraphic correlation between the different realms this study highlights the amplitude of the environmental perturbations in the valanginian and supports the idea that a combination of regional and global factors caused such shifts

observation and modeling of platelet ice fabric in mcmurdo sound antarctica 1 during the annual growth of landfast ice in mcmurdo sound antarctica an episodic flux of platelet ice crystals from the ocean contributes to the build up of a porous subice platelet layer which is steadily incorporated into the sea ice cover as it thickens over winter in november 2007 we examined the spatial variability of these processes by collecting sea ice cores with simultaneous oceanographic observations along an east west transect in the sound previously identified draped and bladed platelet ice types were observed in addition we identify resumed columnar growth which appears to be a result of geometric selection from the subice platelet layer after the arrival of new platelet crystals from the ocean has ceased a numerical model of mechanical platelet ice processes is developed that predicts crystal texture and c axis distributions producing virtual incorporated platelet ice with known growth history this model demonstrates how a disordered subice platelet layer arises from an initially flat interface and suggests that such a layer is more likely to form later in the growth season the model also suggests how the grain boundary density in incorporated platelet ice responds to changes in the flux of loose platelet crystals from the ocean application of this result to our 2007 platelet ice observations indicates that sea ice in western mcmurdo sound is subject to larger and more persistent platelet fluxes than the ice in the east this is consistent with the pattern of in situ supercooling just beneath the ocean surface

the ice thickness distribution across the atlantic sector of the antarctic ocean in midwinter during the first leg of the winter weddell sea project antarktis v 2 cruise of f s polarstern the entire width of the antarctic sea ice zone was traversed in the vicinity of 0 longitude in the period july 18 to september 10 1986 ice thicknesses were measured by direct drilling and by helicopter profiling using an exstar 100 mhz impulse radar system in addition aerial photography of the ice cover was done from 100 to 2000 m altitude using a 70 mm aerial camera mounted in the helicopter the results of the point measurements drilling are reported in this paper together with an indication of how the radar and photography data will be used to extend them so as to yield area averaged ice thickness distributions it was found that the main ice type across the entire width of the ice cover was consolidated pancake ice occurring in vast floes this formed out of a 250 km wide band at the advancing ice edge which comprised a concentrated field of individual pancakes in a matrix of frazil ice preferred thicknesses of undeformed floes were 40 60 cm of ice covered with 5 15 cm of snow the individual pancakes attained almost all of this thickness before consolidation subsequent congelation growth was slow estimated at 0 4 cm d 1 the floes contained much small scale roughness on the upper and lower surfaces due to rafting of pancakes at the time of consolidation but pressure ridging was modest except in the far south a few very thick 8 11 m multiyear floes were observed embedded in the pack at latitudes beyond 66 s

crystal structure stable isotopes δ18o and development of sea ice in the ross amundsen and bellingshausen seas antarctica the crystal structure and oxygen isotopic composition of ice cores obtained from floes at the end of summer in the eastern ross sea the amundsen sea and the western bellingshausen sea were investigated to determine the ice growth processes and conditions that contribute to sea ice development in the eastern pacific sector of the southern ocean the isotope data indicate that a moderate amount of snow contributes to the development of the sea ice however even the combined use of isotopes and crystal structure analysis does not unambiguously explain the means by which all of the snow is entrained in the ice nevertheless it seems clear that much of the snow is contained in granular snow ice that results from seawater flooding of floes and the base of the snow cover the snow cover in the ross amundsen region was as much as 2 m deep and supported by 7 to 8 m thick floes primarily composed of frazil ice in the bellingshausen region the snow cover and the floes were thinner than in the ross amundsen region the bellingshausen cores were composed primarily of multiple layers of frazil and congelation ice in addition in both regions there were numerous tipped or inclined blocks of congelation ice and layers of rafted nilas in the cores the data indicate that the sea ice develops by multiple mechanisms in a turbulent environment

the use of sar to measure ocean wave dispersion in frazil pancake icefields abstract icefields composed of frazil and pancake ice play important roles in both polar regions in winter during the early to midwinter period pancake ice is a major component of the antarctic sea ice cover while in the arctic the odden ice tongue in the greenland sea associated with deep convection is composed mainly of pancake ice the retrieval of sea ice thickness by remote sensing is in general a very difficult task in this paper the change in dispersion of ocean waves as they penetrate into pancake ice is considered so as to gain insight into its possible relationship with thickness spectral analysis of subscenes from ers 2 second european remote sensing satellite synthetic aperture radar sar images yields the wavelength and direction of the principal spectral component both outside and inside the ice cover there is a decrease of wavelength at the ice edge as well as refraction toward the normal and a loss of amplitude the analysis is complex because the true wave spectrum must be re

development of sea ice in the weddell sea we report on the development and physical properties of sea ice in the central and eastern weddell sea the investigations were part of the winter weddell sea project 1986 which extended over the months of july through december major elements of the glaciological part of this study included continuous shipborne observations of sea ice conditions and occasional helicopter reconnaissance flights extensive measurements of snow and ice thicknesses at daily ice stations and detailed analyses of sampled ice cores from each ice station textural investigations of the sampled ice revealed the dominance of frazil ice in the central weddell sea and the occurrence of an additional ice class called platelet ice together with the commonly known frazil and congelation ice in the coastal region of the eastern weddell sea these results in combination with the visual ice observations reveal two major mechanisms for sea ice generation in the antarctic which were not sufficiently well accounted for in previous investigations in the central weddell sea a cycle of pancake ice formation and its growth into consolidated floes seems to be the dominant process of the advancing sea ice edge in the coastal waters the growing sea ice cover consists to a considerable degree of ice platelets which are formed in the underlying water column in front of the ice shelf edges thus congelation ice growth which is mainly controlled by atmospheric thermodynamic forcing seems to be of less importance in the central and south eastern weddell sea than for example in the arctic basin

pancake ice formation in the weddell sea 1 the ice formation resulting from two low temperature events at the weddell sea ice edge during april 2000 is presented pancake and frazil ice were sampled at seven stations at varying distances from the ice edge the ice cover was further characterized from above using helicopter aerial photography and from below using a remotely operated vehicle previously undescribed two layer pancake types were observed and classified a novel pancake growth mechanism is introduced to account for these involving the washing of frazil ice over the pancake top surface and its subsequent freezing the process was directly observed in ice tank experiments layer thicknesses seen in the field were compared to the ice growth that would occur both under calm conditions and from free surface frazil ice growth classical bottom accretion pancake growth was found to proceed at a rate similar to that of thin congelation ice top layer growth was more rapid at approximately double the congelation rate overall ice volume production was similar to congelation ice for the thin pancakes considered 20 cm though subsequent thickening was expected to be faster as the rapid top layer process continued and the equivalent congelation growth slowed it is suggested that parameterization of this new process is important for models that aim to simulate the rapid advance and thickening of wave influenced ice covers

the thickness distribution of sea ice and snow cover during late winter in the bellingshausen and amundsen seas antarctica data collected from a voyage of rv nathaniel b palmer to the bellingshausen and amundsen seas during august september 1993 are used to investigate the thickness distribution of sea ice and snow cover and the processes that influence the development of the first year pack ice the data are a combination of in situ and ship based measurements and show that the process of floe thickening is highly dependent on ice deformation in particular rafting and ridging play important roles at different stages of floe development rafting is the major mechanism in the early stages of development and core structure data show the mean thickness of individual layers of crystals to be only 0 12 m most ice 0 6 m having some surface deformation blocks within ridge sails are typically in the range 0 3 0 6 m thick and ship based observations estimate approximately 25 of the pack exhibits surface ridging when corrected for biases in the observational methods the data show that the dominant ice and snow thickness categories are 0 7 m and 0 2 0 5 m respectively and account for 40 and 36 of the surface area of the pack ice approximately 8 of the pack is open water an estimate of the effects of ridging on the distribution of ice mass within the pack suggests that between 50 and 75 of the total mass is contained within the 25 of the pack that exhibits surface ridging

stratigraphy stable isotopes and salinity in multi year sea ice from the rift area south george vi ice shelf antarctic peninsula results from a detailed profile in a 5 54m multi year sea ice core from the rift area in the southern part of george vi ice shelf are presented stratigraphy stable isotopes and na content are used to investigate the growth processes of the ice cover and to relate them to melting processes at the bottom of the ice shelf the thickest multi year sea ice in the sampling area appears to be second year sea ice that has survived one melt season combined salinity stable isotope analyses show large scale sympathetic fluctuations that can be related to the origin of the parent water brackish ice occurs between 450 and 530cm in the core it is demonstrated that this results from the feezing of brackish water formed by mixing of normal sea water with melted basal shelf ice with dilution percentages of maximum 80 fresh water from authors

winter sea ice properties in marguerite bay antarctica abstract during the winter 2001 and 2002 cruises of the so globec experiment we investigated the morphological properties growth processes and internal permeability of sea ice in the marguerite bay area of the western antarctic peninsula there was considerable interannual variability in ice thickness with average values of 62 cm in 2001 and 102 cm in 2002 with medians of 43 and 68 cm respectively snow depth averaged 16 cm in 2001 and 21 cm in 2002 at 40 of the thickness holes in 2001 and 17 in 2002 a combination of deep snow and thin ice resulted in negative freeboard and the potential for surface flooding ice production was strongly influenced by the snow cover deep snow resulted in negative freeboard surface flooding and the formation of snow ice but also limited columnar ice growth on the bottom of the ice a stratigraphic analysis of ice thin sections showed that more than half of the ice sampled was granular and that virtually all of the upper 20 cm of the ice cover was granular stable isotope 18 o analysis of samples from 2001 indicated that snow ice formation at the surface contributed significantly to ice formation two thirds of the cores had some snow ice and 15 of the ice sampled in 2001 was snow ice for 95 of the ice sampled the combination of warm ice temperatures and large salinities resulted in brine volumes that were greater than the percolation threshold of 5 autonomous mass balance buoys indicated that the ice was above the percolation threshold throughout late winter and spring the exceeding of the percolation threshold allows continuous flooding to occur throughout the late winter spring period the wap sea ice therefore represents a warm end member of the sea ice covers of antarctica an expected consequence of the lengthy flooding condition at the snow ice interface is an earlier onset of an algal bloom in the flooded snow than elsewhere in antarctic sea ice

arctic ocean deep sea record of northern eurasian ice sheet history the sediment composition of deep sea cores from the central arctic ocean the fram strait and the yermak plateau was analyzed for several parameters to reconstruct the history of marine paleoenvironment and terrestrial glaciation in the last 200 000 years layers with high amounts of coarse terrigenous ice rafted debris ird and often high contents of smectite were deposited during extensive glaciations in northern eurasia when ice sheets reached the northern continental margins of the barents and kara seas and discharged icebergs into the arctic ocean intercalated layers with relatively low ird and smectite contents but abundant planktic foraminifers in the coarse fraction were deposited during periods of atlantic water inflow to the arctic ocean and seasonally open waters leads in a sea ice cover with only few icebergs in the arctic ocean high ird contents in the sediments reflect the presence of ice sheets on the kara and barents seas shelves and the hinterland during the entire oxygen isotope stage 6 ca 190 130 ka in substage 5b ca 90 80 ka at the stage boundary 5 4 around 75 ka and in late stage 4 early stage 3 ca 65 50 ka these results are in excellent correlation with those from recent field work in northern scandinavia european russia siberia and on the shelves relatively low amounts of ird in central arctic ocean sediments from the late weichselian glacial maximum ca 24 18 ka correlate well with the recent reconstruction of a very limited eastern ice sheet extension during this time oxygen and carbon isotope records of planktic foraminifers from the analyzed sediment cores show a number of prominent excursions which can be interpreted as evidence for freshwater events in the arctic ocean the synchroneity of freshwater events and ird input suggests a common source strongest events were associated with deglaciations of the barents and kara seas after the ice sheets had blocked the outflow of large rivers for several millennia the outflow of freshwater from large ice dammed lakes occurred at ca 130 80 75 and 52 ka freshwater events in the central arctic ocean during the last deglaciation ca 18 ka were relatively small compared to the previous events this indicates that during most of the late weichselian glacial maximum a river outflow from northern siberia to the arctic ocean was possible atlantic water inflow to the arctic ocean and seasonally open waters in the ice leads occurred during the interglacials ofoxygen isotope stage 1 and substage 5e during several interstadials stage 3 substages 5a and 5c and to a lesser degree within stadials and glacials stages 2 4 and 6 with the exception ofthe interglacials these periods were times ofstrong ice growth on the continents as revealed by terrestrial data the coincidence suggests that open waters in the arctic ocean and the nordic seas were an important moisture source in addition to more southerly sources which fostered the growth of ice sheets on northern eurasia

sea ice structure and biological activity in the antarctic marginal ice zone ice cores obtained during october november 1981 from weddell sea pack ice were analyzed for physical chemical and biological parameters frazil ice which is associated with dynamic turbulent conditions in the water column predominated 70 both floe thickness and salinity indicate ice which is less than 1 year old chemical analyses particularly with regard to the nutrients revealed a complex picture phosphate values are scattered relative to the dilution curve nitrate and silicate values are lower than expected from simple scaling with salinity and suggest diatom growth within the ice nitrite values are higher in the ice than in adjacent waters frazil ice formation which probably concentrates algal cells from the water column into ice floes results in higher initial chlorophyll a concentrations in the ice than in adjacent waters this mechanical concentration is further enhanced by subsequent reproduction within the ice ice core chlorophyll ranged from 0 09 to 3 8 mg m3 comparable to values previously reported for this area but significantly lower than values for antarctic coastal fast ice the dominance of frazil ice in the weddell is one of the major differences between this area and others consequently we believe that ice structural conditions significantly influence the biological communities in the ice

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

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 physical properties of sea ice in the odden ice tongue abstract the odden ice tongue developed prominently during the winter of 1992 1993 but did not appear at all during the two subsequent winters of the esop period during 1992 1993 the in situ sea ice characteristics within odden were studied on four occasions in addition to direct observation and aerial photography the measurement programme included retrieval and on board analysis of frazil and pancake ice samples wave measurements within odden and near surface ctd measurements to examine the effect of melt on the upper ocean reported in brandon and wadhams 1999 the near surface hydrography beneath the odden ice tongue deep sea research in press this paper reports on the characteristics of the frazil and pancake ice observed and sampled during this season expanding on early results reported in wadhams et al 1996 journal of geographical research 101 c8 18 213 18 235 by combining the results of in situ sampling with the analysis of passive microwave and sar data of the sea ice extent through the winter it was possible to estimate the salt flux into the ocean originating from brine release from sea ice during the growth phases of odden

representing glaciers in a regional climate model a glacier parameterization scheme has been developed and implemented into the regional climate model remo the new scheme interactively simulates the mass balance as well as changes of the areal extent of glaciers on a subgrid scale the temporal evolution and the general magnitude of the simulated glacier mass balance in the european alps are in good accordance with observations for the period 1958 1980 but the strong mass loss towards the end of the twentieth century is systematically underestimated the simulated decrease of glacier area in the alps between 1958 and 2003 ranges from 17 1 to 23 6 the results indicate that observed glacier mass balances can be approximately reproduced within a regional climate model based on simplified concepts of glacier climate interaction however realistic results can only be achieved by explicitly accounting for the subgrid variability of atmospheric parameters within a climate model grid box

biogeochemical impact of snow cover and cyclonic intrusions on the winter weddell sea ice pack sea ice is a dynamic biogeochemical reactor and a double interface actively interacting with both the atmosphere and the ocean however proper understanding of its annual impact on exchanges and therefore potentially on the climate notably suffer from the paucity of autumnal and winter data sets here we present the results of physical and biogeochemical investigations on winter antarctic pack ice in the weddell sea r v polarstern awecs cruise july august 2013 which are compared with those from two similar studies conducted in the area in 1986 and 1992 the winter 2013 was characterized by a warm sea ice cover due to the combined effects of deep snow and frequent warm cyclones events penetrating southwards from the open southern ocean these conditions were favorable to high ice permeability and cyclic events of brine movements within the sea ice cover brine tubes favoring relatively high chlorophyll a chl a concentrations we discuss the timing of this algal activity showing that arguments can be presented in favor of continued activity during the winter due to the specific physical conditions large scale sea ice model simulations also suggest a context of increasingly deep snow warm ice and large brine fractions across the three observational years despite the fact that the model is forced with a snowfall climatology this lends support to the claim that more severe antarctic sea ice conditions characterized by a longer ice season thicker and more concentrated ice are sufficient to increase the snow depth and somehow counter intuitively to warm the ice

simulating pancake and frazil ice growth in the weddell sea a process model from freezing to consolidation 1 processes controlling the formation and transformation of frazil to pancake ice are examined using data from an array of drifting buoys deployed at the advancing ice edge in the weddell sea a simple thermodynamic model is coupled to the buoy dynamics and to an ice redistribution model to determine the influence of deformation thermodynamics and mechanical scavenging incorporating frazil crystals from the surrounding slick into the pancakes on the partitioning of ice volume between frazil and pancakes ice production was examined from the time the buoys were deployed until the frazil pancake cover consolidated into the more familiar pack ice the model reproduced the expected ice cover thickness at consolidation 60 cm rafting was the dominant contribution to thickening in the region owing to large scale compression of the initial area by northerly winds from passing low pressure weather systems which are rather typical in the region high resolution positional forcing from the buoys 20 min intervals doubled the contribution of mechanical scavenging to final pancake thickness compared to the coarser 2 h result owing to the larger path length that the pancakes traverse through the frazil slick and produced a significantly larger volume of ice in the pancake phase the ice cover generated at consolidation was approximately twice as thick as would have formed by the more familiar congelation ice growth under the same forcing reinforcing the importance of correctly parameterizing the early stages of ice formation in the antarctic the study highlighted uncertainties in the effect of the frazil pancake cover on ocean atmosphere heat exchange both in terms of the area contributing to ice production and the effect on turbulent exchange coefficients further work placing the empirical parameters into a more constrained physical framework and introducing wave properties is suggested

numerical simulation of the weddell sea pack ice to investigate the role of ice dynamics on the seasonal cycle of antarctic sea ice a series of 2 year simulations of the weddell sea pack ice are carried out the simulations employ the dynamic thermodynamic model developed by hibler 1979 and use a 1 day time step on an 18 15 grid with a resolution of 222 km daily atmospheric data from 1979 are used to drive the simulations with atmospheric temperature fields modified to reflect buoy observations the simulations yield a seasonal cycle of ice with maximum and minimum extents close to that observed except for portions of the western weddell the advance of the ice is found to be primarily thermodynamic in nature while the rapid decay depends critically on the presence of both leads and lateral ice advection the average fraction of open water is substantial even in winter and varies from a minimum of 10 in september to a maximum of 35 in march these values are in general agreement with estimates from satellite microwave data in early summer the ice motion causes a residual tongue of ice to extend eastward from the antarctic peninsula in agreement with observations mean ice thicknesses are consistent with observations and vary from about 3 m in the perennial ice in the western weddell to 1 m in first year ice in the eastern weddell possible feedback between the ice extent and atmosphere are investigated by simulations with the surface air temperatures constrained to below freezing values in the presence of ice these coupled simulations yield a more realistic rapid decay in summer with dynamics included but an unrealistically small decay without dynamics simulated ice drift results yield mean drift rates of about 5 km day in good agreement with buoy drift observations but with slightly inadequate northward transport in the western weddell near the ice edge the drift rates are relatively insensitive to the ice strength near the coast however lower strengths are found to yield a decrease in northward drift rates

the near surface hydrography beneath the odden ice tongue as part of the european subpolar ocean programme esop the german research icebreaker polarstern worked in the greenland sea in the late winter of 1993 whilst on passage the ship encountered a severe winter storm with winds consistently above 20 m s 1 coupled to air temperatures of below 10 degrees c the underway sensors revealed heat fluxes of greater than 700 w m 2 across most of the nordic basin peaking at greater than 1200 w m 2 when the ship crossed the cold fresh water of the jan mayen current this large heat flux coupled to the unique hydrographic conditions present in the jan mayen current allowed sea ice generation in the form of frazil ice at a rate of 28 cm d 1 this frazil ice then developed into pancake ice measurements also were made in the late winter beneath this pancake ice in two remnants of the odden in the jan mayen current hydrographic conditions are such that the ice can exist for a long period of time before eventually decaying due to short wave radiation at the surface towards the centre of the greenland sea hydrographic measurements reveal that the ice is more transient and decays four times more rapidly than ice in the jan mayen current we discuss the development of the odden ice tongue in light of these results and add evidence to the argument that the eventual fate of the water stored in the ice is important and could be a relevant factor in the formation of greenland sea deep water c 1999 elsevier science ltd all rights reserved

role of orbitally induced changes in tundra area in the onset of glaciation the link between glacial interglacial cycles and changes in insolation due to variations in the earth s orbital parameters is well established1 4 but of the attempts to simulate incipient glaciation using three dimensional general circulation models gcms driven by orbital forcing alone5 10 only one10 has been successful gcm experiments7 11 show that reduced summer insolation 115 000 years ago during an interglacial to glacial climate shift produces sufficient high latitude cooling to cause expansion of tundra at the expense of boreal forest11 which in turn can induce more cooling11 14 here we show using a global climate model that the increase in surface albedo under snow covered conditions that results from a biome model estimate11 of tundra expansion 115 000 years ago is sufficient to induce glaciation over extreme northeastern canada if the additional cooling from this estimated tundra expansion induces further expansion then widespread glaciation occurs at latitudes above 65 n these results suggest that the climate feedback from high latitude tundra expansion might have contributed to the onset of the most recent glaciation

antarctic sea ice mapping using the avhrr abstract a sea ice mapping scheme based on advanced very high resolution radiometer avhrr data from the national oceanic and atmospheric administration noaa polar orbiting satellites has been developed and applied to daylight images taken between november 1989 to january 1990 and november 1990 to january 1991 over the weddell and the ross seas after masking the continent and ice shelves sea ice is discriminated from clouds and open sea using thresholds applied to the multidimensional space formed by avhrr channel 2 3 and 4 radiances sea ice concentrations in cloud free regions are then computed using the tie point method results based on the analysis of more than 70 images show that the proposed scheme is capable of properly discriminating between sea ice open sea and clouds under most conditions thus allowing high resolution sea ice maps to be produced during the austral summer season

ice platelets below weddell sea landfast sea ice basal melt of ice shelves may lead to an accumulation of disc shaped ice platelets underneath nearby sea ice to form a sub ice platelet layer here we present the seasonal cycle of sea ice attached to the ekstrom ice shelf antarctica and the underlying platelet layer in 2012 ice platelets emerged from the cavity and interacted with the fast ice cover of atka bay as early as june episodic accumulations throughout winter and spring led to an average platelet layer thickness of 4m by december 2012 with local maxima of up to 10 m the additional buoyancy partly prevented surface flooding and snow ice formation despite a thick snow cover subsequent thinning of the platelet layer from december onwards was associated with an inflow of warm surface water the combination of model studies with observed fast ice thickness revealed an average ice volume fraction in the platelet layer of 0 25 0 1 we found that nearly half of the combined solid sea ice and ice platelet volume in this area is generated by heat transfer to the ocean rather than to the atmosphere the total ice platelet volume underlying atka bay fast ice was equivalent to more than one fifth of the annual basal melt volume under the ekstrom ice shelf

a wave based model for the marginal ice zone including a floe breaking parameterization 1 the marginal ice zone miz is the boundary between the open ocean and ice covered seas where sea ice is significantly affected by the onslaught of ocean waves waves are responsible for the breakup of ice floes and determine the extent of the miz and floe size distribution when the ice cover is highly fragmented its behavior is qualitatively different from that of pack ice with large floes therefore it is important to incorporate wave ice interactions into sea ice ocean models in order to achieve this goal two effects are considered the role of sea ice as a dampener of wave energy and the wave induced breakup of ice floes these two processes act in concert to modify the incident wave spectrum and determine the main properties of the miz a simple but novel parameterization for floe breaking is derived by considering alternatively ice as a flexible and rigid material and by using current estimates of ice critical flexural strain and strength this parameterization is combined with a wave scattering model in a one dimensional numerical framework to evaluate the floe size distribution and the extent of the miz the model predicts a sharp transition between fragmented sea ice and the central pack thus providing a natural definition for the miz reasonable values are found for the extent of the miz given realistic initial and boundary conditions the numerical setting is commensurate with typical ice ocean models with the future implementation into two dimensional sea ice models in mind

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

life cycle strategy of the antarctic calanoid copepod stephos longipes abstract studies on the life strategy of the small calanoid copepod stephos longipes were carried out in the eastern weddell sea during four expeditions january february 1985 august 1986 october december 1986 and april may 1992 samples were taken from the water column the ice water interface and the sea ice in winter august 1986 s longipes copepodite stage civ occurred mainly in the upper water layers of the ice covered eastern weddell sea while only nauplii were found in the sea ice in late winter early spring october december 1986 very low numbers of s longipes were found in the water column mainly in the upper 50m but high numbers occurred immediately below and within the sea ice adults dominated in the water column and in the under ice water layer while the sea ice contained nauplii and copepodite stage ci during summer january february 1985 the eastern weddell sea was almost entirely free of ice with the exception of fast ice fields atthe ice shelf during this time s longipes was concentrated in the upper 50m of the water column and in the ice water interface where an ice cover was present young copepodite stages ci ciii comprised the largest fraction of the population in autumn april may 1992 as new ice began to develop s longipes dominated by copepodite stage civ occurred in greatest number within mid water layers the abundance of s longipes in autumn was similar to late winter early spring highest in the sea ice and lowest in the water column during all periods of investigation the population structure differed between the various habitats with the youngest population occurring in the sea ice and the oldest in the water column a younger generation of the s longipes population appears to overwinter in the sea ice and ice water interface and an older one in deeper water layers or near the bottom

global regional and local scale factors determining glaciation extent in eastern siberia over the last 140 000 years the aim of this work is to evaluate the effect of variations of greenhouse gas concentrations orbital parameters sea surface conditions vegetation and dust deposition on the extent of east siberian mountain glaciations during the late quaternary an atmosphere only general circulation model is used in a series of 16 sensitivity tests at high spatial resolution over the region of interest to systematically evaluate the relative importance of these different forcing parameters no attempt was made to reproduce in detail the history of late quaternary mountain glaciations in east siberia because given a the temporal and spatial scarcity of available evidence of mountain glaciations in this region and b the large uncertainties concerning the boundary conditions to be prescribed in this model such an exercise must necessarily remain incomplete and partially inconclusive the results of this study suggest that moisture delivery from the atlantic is an important factor determining mountain glacier mass balance in eastern siberia and is very sensitive to the geometry of the west eurasian ice sheet this means that variable moisture blocking by the west eurasian ice sheet during the weichselian is the most important single factor explaining the opposite history of glacier and ice sheet extent in west and east eurasia during the weichselian this work confirms earlier results showing that the large 140 kyr bp west eurasian ice sheet caused regional scale cooling extending towards eastern eurasia nevertheless the simulated response of the regional summer temperature and thus glacier extent because of the strong dependency of glacier mass balance of summer melt rates is to a very large extent directly determined by insolation for the early weichselian this leads to a clear maximum of local glacier extent at 70 kyr bp which is in line with the variations of top of the atmosphere insolation on orbital time scales but to some degree at odds with geological evidence which suggests larger glacier extent at 115 and 90 kyr bp than at 70 kyr bp through snow feedbacks the effects of changes in the prescribed vegetation distribution and dust deposition rate are also substantial in summary it appears that the broad features of late quaternary glaciation history in eastern eurasia can be understood in terms of known forcings

surface properties and processes of perennial antarctic sea ice in summer ice core and snow data from the amundsen bellingshausen and weddell seas antarctica show that the formation of superimposed ice and the development of seawater filled gap layers with high algal standing stocks is typical of the perennial sea ice in summer the coarse grained and dense snow had salinities mostly below 0 1 per mil a layer of fresh superimposed ice had a mean thickness ranging from 0 04 0 12 m 0 04 to 0 08 m thick gap layers extended downwards from 0 02 to 0 14 m below the water level these gaps were populated by diatom standing stocks up to 439 g l chlorophyll a we propose a comprehensive heuristic model of summer processes where warming and the reversal of temperature gradients cause major transformations in snow and ice properties the warming also causes the re opening of incompletely frozen slush layers caused by flood freeze cycles during winter alternatively superimposed ice forms at the cold interface between snow and slush in the case of flooding with negative freeboard combined these explain the initial formation of gap layers by abiotic means alone the upward growth of superimposed ice above the water level competes with a steady submergence of floes due to bottom and internal melting and accumulation of snow

salinity profiles of antarctic sea ice field data and model results in order to describe and compare sea ice salinity distributions which are of interest in the study of physical and biological ice characteristics as well as ice ocean interaction we have computed composite profiles and fitted third degree polynomials to salinity data of 129 cores from the weddell sea four characteristic profile shapes have been recognized and described through the polynomial coefficients c s i and type profiles the field data have been compared with ideal salinity profiles generated by a simulation scheme based on thermodynamic growth under climatological conditions representative of the weddell sea composite salinity profiles agree well with simulations irrespective of the growth mechanism i e frazil or congelation suggesting that ice properties which depend on salinity or porosity may evolve independent of ice growth conditions analysis of salinity and 18o data in conjunction with the simulations demonstrates that apart from meteorological conditions controlling growth velocity and temperature distribution within the ice flooding and upward brine expulsion are important in raising top salinities as frequently observed low top salinities are typical of ice that has undergone retexturing and differential desalination salinity decreases towards the bottom of a floe are a result of high oceanic heat fluxes and snow cover effects as a consequence of these processes the bulk salinity of weddell sea ice cannot be described by a simple linear age thickness relationship as characteristic of arctic first year ice