calcium carbonate as ikaite crystals in antarctic sea ice 1 we report on the discovery of the mineral ikaite caco3 6h2o in sea ice from the southern ocean the precipitation of caco3 during the freezing of seawater has previously been predicted from thermodynamic modelling indirect measurements and has been documented in artificial sea ice during laboratory experiments but has not been reported for natural sea ice it is assumed that caco3 formation in sea ice may be important for a sea ice driven carbon pump in ice covered oceanic waters without direct evidence of caco3 precipitation in sea ice its role in this and other processes has remained speculative the discovery of caco3 6h2o crystals in natural sea ice provides the necessary evidence for the evaluation of previous assumptions and lays the foundation for further studies to help elucidate the role of ikaite in the carbon cycle of the seasonally sea ice covered regions

temporal evolution of decaying summer first year sea ice in the western weddell sea antarctica abstract the evolution of the main physico chemical properties of the unflooded 90 cm thick first year sea ice cover at the ice station polarstern ispol clean site is described ispol was an international experiment of the german research icebreaker r v polarstern the vessel was anchored to an ice floe for an observation period of 5 weeks during the early summer melt onset in the western weddell sea the clean site was specially designed and accessed so as to prevent any trace metal contamination of the sampling area observations were made at 5 day intervals during december 2004 in the central part of the main floe results show the succession of two contrasting phases in the behavior of the brine network brine channels pockets and tubes initially brine salinity was higher than that of sea water leading to brine migration and a decrease in the mean bulk salinity of the ice cover this process is highly favored by the already high bulk porosity 14 which ensures full connectivity of the brine network gravity drainage rather than convection seems to be the dominant brine transfer process half way through the observation period the brine salinity became lower than that of the sea water throughout the ice column the brine network therefore switched to a stratified regime in which exchange with sea water was limited to molecular diffusion strongly stabilizing the bulk mean sea ice salinity during the transition between the two regimes and in areas closer to ridges slush water resulting from a mixture of snow meltwater and sea water accumulated at the snow ice interface penetrated through the growing honeycomb like structure and replaced the downward draining brines this resulted in a slight local replenishment of nutrients as indicated by dissolved silicic acid however as a whole the described decaying regime in this globally unflooded location with limited snow cover should be unfavorable to the development of healthy and active surface and internal microbial communities the switch from gravity to diffusion controlled transport mechanisms within the ice column also should affect the efficiency of gas exchange across the sea ice cover the observed late build up of a continuous impermeable superimposed ice layer should further significantly hamper gas exchange statistical estimates of the evolution of the ice thickness during the observation period and salinity trends of the under ice water salinity down to 30 m corroborate model predictions of a moderate bottom melting 5 10 cm from ocean heat fluxes

the seasonal cycle of carbonate system processes in ryder bay west antarctic peninsula the carbon cycle in seasonally sea ice covered waters remains poorly understood due to both a lack of observational data and the complexity of the system here we present three consecutive seasonal cycles of upper ocean dissolved inorganic carbon dic and total alkalinity measurements from ryder bay on the west antarctic peninsula we attribute the observed changes in dic to four processes mixing of water masses air sea co2 flux calcium carbonate precipitation dissolution and photosynthesis respiration this approach enables us to resolve the main drivers of the seasonal dic cycle and also investigate the mechanisms behind interannual variability in the carbonate system we observe a strong asymmetric seasonal cycle in the carbonate system driven by physical processes and primary production in summer melting glacial ice and sea ice and a reduction in mixing with deeper water reduce the concentration of dic in surface waters the dominant process affecting the carbonate system is net photosynthesis which reduces dic and the fugacity of co2 making the ocean a net sink of atmospheric co2 in winter mixing with deeper carbon rich water and net heterotrophy increase surface dic concentrations resulting in ph as low as 7 95 and aragonite saturation states close to 1 we observe no clear seasonal cycle of calcium carbonate precipitation dissolution but some short lived features of the carbonate time series strongly suggest that significant precipitation of calcium carbonate does occur in the bay the variability observed in this study demonstrates that changes in mixing and sea ice cover significantly affect carbon cycling in this dynamic environment maintaining this unique time series will allow the carbonate system in seasonally sea ice covered waters to be better understood

carbon dynamics in sea ice a winter flux time series 1 a winter time series of the inorganic carbon system above within and beneath the landfast sea ice of the southern beaufort sea confirmed that sea ice is an active participant in the carbon cycle of polar waters eddy covariance measurements above the ice identified significant vertical co2 fluxes mostly upward away from the ice but with short periods of downward fluxes as well a novel in situ method revealed extremely high pco2 values within the ice that are not inconsistent with theory the total carbon content of the ice increased slightly through the winter season and increasing variability in the vertical profiles as spring began indicated that the inorganic carbon became mobile as the ice began to melt during early winter as the ice formed inorganic carbon concentrations in the surface waters increased dramatically along with salinity partly because of rejection from the ice and partly from advective mixing brine drainage was apparently not sufficient to initiate convection and the excess carbon remained in the surface waters into the summer

evolution of first year and second year snow properties on sea ice in the weddell sea during spring summer transition observations of snow properties superimposed ice and atmospheric heat fluxes have been performed on first year and second year sea ice in the western weddell sea antarctica snow in this region is particular as it does usually survive summer ablation measurements were performed during ice station polarstern ispol a 5 week drift station of the german icebreaker rv polarstern net heat flux to the snowpack was 8 w m 2 causing only 0 1 to 0 2 m of thinning of both snow cover types thinner first year and thicker second year snow snow thinning was dominated by compaction and evaporation whereas melt was of minor importance and occurred only internally at or close to the surface characteristic differences between snow on first year and second year ice were found in snow thickness temperature and stratigraphy snow on second year ice was thicker colder denser and more layered than on first year ice metamorphism and ablation and thus mass balance were similar between both regimes because they depend more on surface heat fluxes and less on underground properties ice freeboard was mostly negative but flooding occurred mainly on first year ice snow and ice interface temperature did not reach the melting point during the observation period nevertheless formation of discontinuous superimposed ice was observed color tracer experiments suggest considerable meltwater percolation within the snow despite below melting temperatures of lower layers strong meridional gradients of snow and sea ice properties were found in this region they suggest similar gradients in atmospheric and oceanographic conditions and implicate their importance for melt processes and the location of the summer ice edge

the percolation phase transition in sea ice sea ice exhibits a marked transition in its fluid transport properties at a critical brine volume fraction p c of about 5 percent or temperature t c of about 5 c for salinity of 5 parts per thousand for temperatures warmer than t c brine carrying heat and nutrients can move through the ice whereas for colder temperatures the ice is impermeable this transition plays a key role in the geophysics biology and remote sensing of sea ice percolation theory can be used to understand this critical behavior of transport in sea ice the similarity of sea ice microstructure to compressed powders is used to theoretically predict p c of about 5 percent

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

simulations of ice ocean dynamics in the weddell sea 2 interannual variability 1985 1993 investigations of sea ice ocean interaction on the continental shelf in the southwestern weddell sea reveal a strong correlation between fluctuations of atmospheric forcing and the variability of sea ice formation anomalies of meridional wind stress in the inner weddell sea are consistent with the phase of the antarctic circumpolar wave acw positive anomalies of northward wind stress cause an increase of sea ice export in the same and of sea ice formation in the following year leading to an increased production of high salinity shelf water driven by a varying zonal density distribution over the continental shelf the circulation in the filchner ronne ice shelf cavity fluctuates between two modes each of which features a characteristic distribution of basal freezing and melting regions thus signals of interannual atmospheric variability propagate into the deep ocean and the sub ice shelf cavities

equations for determining the gas and brine volumes in sea ice samples on a etabli des equations utilisables pour determiner le taux de gaz inclus dans la glace de mer a partir de mesures de densite de salinite et de temperature dans des gammes de temperatures entre 2 c et 30 c inversement ces relations peuvent etre utilisees pour calculer la densite de la glace de mer en fonction de la temperature et de la salinite en prenant en compte a la fois la presence de gaz et de cristaux de sel dans la glace on donne aussi des equations qui permettent le calcul du volume de gaz et d eau salee dans la glace a des temperatures autres que celle pour laquelle la densite a ete determinee

antarctic sea ice and palaeoproductivity variation over the last 156 000 years in the indian sector of southern ocean abstract antarctic sea ice plays a vital role in global climate via its impact on ocean circulation biological productivity and co2 partitioning between the ocean and the atmosphere however very little is known about its past history especially in the southwestern indian sector of the southern ocean so we here provide new quantitative records of winter sea ice concentration wsic and duration wsid sea surface temperatures sst and productivity in sediment core sk 200 33 55 s 45 e from the permanently open ocean zone over the last 156 000 years the new records combined with regional records indicate that the hydrological structures migrated northward by a few degrees of latitude during all glacial periods with the southern antarctic circumpolar current front reaching the core site the antarctic polar front located at 46 s and the winter sea ice wsi probably extending to 49 s in contrast hydrological fronts and wsi edge migrated poleward by a couple of degrees of latitude during the early holocene and last interglacial comparison to sst and wsi records from different sectors of the so suggests higher amplitude variations in wsi in the atlantic sector as compared to the indian and western pacific sectors over the last glacial interglacial cycle which we attribute to the presence of the weddell gyre transporting far to the north the sea ice produced in the weddell sea the new records also suggest a drop in productivity in the pooz during glacial periods probably related to greater wsi extent and reduced growing season

ice layer and surface crust permeability in a seasonal snow pack ice layers in snowpacks are thought to retard or obstruct gas and melt water flow through the pack yet there has been little published information on the permeability of ice layers in seasonal snow in this paper investigations of ice layer permeabilities are reported for prominent ice layers 1 to 3 mm thick in a seasonal snowpack for distinct fairly solid ice layers 1 to 3 mm thick permeabilities ranged from 1 to 19 x 10 10 m 2 these values are significantly lower than values for the surrounding snow within 24 h early in the melt season the permeability of the surface crust increased 160 from approximately 70 to 120 x 10 10 m 2 this increase in permeability was accompanied by a small increase in grain size and a decrease in albedo the snow air interface can exhibit dramatic changes in transport properties over relatively short periods of time even without precipitation events these changes driven by the surface meteorology affect transport properties such as permeability as well as albedo

how well does wind speed predict air sea gas transfer in the sea ice zone a synthesis of radon deficit profiles in the upper water column of the arctic ocean we present 34 profiles of radon deficit from the ice ocean boundary layer of the beaufort sea including these 34 there are presently 58 published radon deficit estimates of k the air sea gas transfer velocity in the arctic ocean 52 of these estimates were derived from water covered by 10 sea ice or more the average value of k collected since 2011 is 4 0 1 2 m d 1 this exceeds the quadratic wind speed prediction of weighted kws 2 85 m d 1 with mean weighted wind speed of 6 4 m s 1 we show how ice cover changes the mixed layer radon budget and yields an effective gas transfer velocity we use these 58 estimates to statistically evaluate the suitability of a wind speed parameterization for k when the ocean surface is ice covered whereas the six profiles taken from the open ocean indicate a statistically good fit to wind speed parameterizations the same parameterizations could not reproduce k from the sea ice zone we conclude that techniques for estimating k in the open ocean cannot be similarly applied to determine k in the presence of sea ice the magnitude of k through gaps in the ice may reach high values as ice cover increases possibly as a result of focused turbulence dissipation at openings in the free surface these 58 profiles are presently the most complete set of estimates of k across seasons and variable ice cover as dissolved tracer budgets they reflect air sea gas exchange with no impact from air ice gas exchange

southern ocean co2 sink the contribution of the sea ice we report first direct measurements of the partial pressure of co2 pco2 within antarctic pack sea ice brines and related co2 fluxes across the air ice interface from late winter to summer brines encased in the ice change from a co2 large oversaturation relative to the atmosphere to a marked undersaturation while the underlying oceanic waters remains slightly oversaturated the decrease from winter to summer of pco2 in the brines is driven by dilution with melting ice dissolution of carbonate crystals and net primary production as the ice warms its permeability increases allowing co2 transfer at the air sea ice interface the sea ice changes from a transient source to a sink for atmospheric co2 we upscale these observations to the whole antarctic sea ice cover using the nemo lim3 large scale sea ice ocean and provide first estimates of spring and summer co2 uptake from the atmosphere by antarctic sea ice over the spring summer period the antarctic sea ice cover is a net sink of atmospheric co2 of 0 029 pg c about 58 of the estimated annual uptake from the southern ocean sea ice then contributes significantly to the sink of co2 of the southern ocean

high resolution imaging an approach by incorporating stationary phase implementation into deabsorption prestack time migration abstractwe have improved the so called deabsorption prestack time migration pstm by introducing a dip angle domain stationary phase implementation deabsorption pstm compensates absorption and dispersion via an actual wave propagation path using effective q parameters that are obtained during migration however noises induced by the compensation degrade the resolution gained and deabsorption pstm requires more computational effort than conventional pstm our stationary phase implementation improves deabsorption pstm through the determination of an optimal migration aperture based on an estimate of the fresnel zone this significantly attenuates the noises and reduces the computational cost of 3d deabsorption pstm we have estimated the 2d fresnel zone in terms of two dip angles through building a pair of 1d migrated dip angle gathers using pstm our stationary phase qpstm deabsorption pstm was implemented as a two stage process first we used conventional pstm to obtain the fresnel zones then we p

experimental evidence for carbonate precipitation and co2 degassing during sea ice formation chemical and stable carbon isotopic modifications during the freezing of artificial seawater were measured in four 4 m3 tank incubations three of the four incubations were inoculated with a non axenic antarctic diatom culture the 18 days of freezing resulted in 25 to 27 cm thick ice sheets overlying the residual seawater the ice phase was characterized by a decrease in temperature from 1 9 to 2 2oc in the under ice seawater down to 6 7oc in the upper 4 cm of the ice sheet with a concurrent increase in the salinity of the under ice seawater and brine inclusions of the ice sheet as a result of physical concentration of major dissolved salts by expulsion from the solid ice matrix measurements of ph total dissolved inorganic carbon ct and its stable isotopic composition d13ct all exhibited changes which suggest minimal effect by biological activity during the experiment a systematic drop in ph and salinity normalized ct by up to 0 37 phsws units and 376 mol c kg 1 respectively at the lowest temperature and highest salinity part of the ice sheet were coupled with an equally systematic 13c enrichment of the ct calculations based on the direct ph and ct measurements indicated a steady increase in the in situ concentration of dissolved carbon dioxide co2 aq with time and increasing salinity within the ice sheet partly due to changes in the dissociation constants of carbonic acid in the low temperature high salinity range within sea ice the combined effects of temperature and salinity on the solubility of co2 over the range of conditions encountered during this study was a slight net decrease in the equilibrium co2 aq concentration as a result of the salting out overriding the increase in solubility with decreasing temperature hence the increase in the in situ co2 aq concentration lead to saturation or supersaturation of the brine inclusions in the ice sheet with respect to atmospheric pco2 3 5x10 4 atm when all physico chemical processes are considered we expect co2 degassing and carbonate mineral precipitation from the brine inclusions of the ice sheet which were saturated or highly supersaturated with respect to both the anhydrous calcite aragonite vaterite and hydrated ikaite carbonate minerals

the gas transfer through polar sea ice experiment insights into the rates and pathways that determine geochemical fluxes sea ice is a defining feature of the polar marine environment it is a critical domain for marine biota and it regulates ocean atmosphere exchange including the exchange of greenhouse gases such as co2 and ch4 in this study we determined the rates and pathways that govern gas transport through a mixed sea ice cover n2o sf6 3he 4he and ne were used as gas tracers of the exchange processes that take place at the ice water and air water interfaces in a laboratory sea ice experiment observation of the changes in gas concentrations during freezing revealed that he is indeed more soluble in ice than in water ne is less soluble in ice and the larger gases n2o and sf6 are mostly excluded during the freezing process model estimates of gas diffusion through ice were calibrated using measurements of bulk gas content in ice cores yielding gas transfer velocity through ice kice of 5 10 4 m d 1 in comparison the effective air sea gas transfer velocities keff ranged up to 0 33 m d 1 providing further evidence that very little mixed layer ventilation takes place via gas diffusion through columnar sea ice however this ventilation is distinct from air ice gas fluxes driven by sea ice biogeochemistry the magnitude of keff showed a clear increasing trend with wind speed and current velocity beneath the ice as well as the combination of the two this result indicates that gas transfer cannot be uniquely predicted by wind speed alone in the presence of sea ice

processes controlling the shrinkage of porphyroclasts in gabbroic shear zones abstract this paper presents microstructural and geochemical data on amphibole and clinopyroxene porphyroclasts collected in amphibolite facies ultramylonites of the ivrea verbano zone italy the well rounded porphyroclasts show a concentration of defects including 100 twins stacking faults free dislocations subgrains and microcracks within their rims that indicate stress concentrations localised deformation within the margins of porphyroclasts increases reaction kinetics and supports amphibole clinopyroxene replacement reactions and heterogeneous plagioclase nucleation in addition to microcracking and or subgrain rotation these metamorphic reactions lead to a marginal grain size reduction and the shrinkage of porphyroclasts in order to correlate the defect concentration at the rim of porphyroclasts with stresses a finite element inclusion matrix model is used it depends on the degree of bonding between inclusion and matrix whether strong stress concentrations within the rim of the inclusion occur for well coupled two phase systems shear stresses within the rim of the inclusion can reach a magnitude many times the magnitude of the matrix stresses marginal stress concentrations do not evolve if inclusion and matrix are decoupled this may indicate that mechanically decoupled porphyroclasts can survive to very large strains

multiresolution modeling and seismic wavefield reconstruction in attenuating media the propagation of the seismic wavefield through a viscoelastic medium is a multiresolution process in which depth of propagation and scale are closely associated with one another we propose the multiresolution wavefield reconstruction mrwr as a means to directly integrate such concepts of scale into the backpropagation component of an imaging method mrwr produces a reconstruction of the wavefield at some fixed depth d in which each scale term reconstitutes the resolution that was lost as the wavefield propagated some step length towards the measurement surface away from d concurrently mrwr provides a stable platform for this removal of the effects of absorption in propagation in a multiresolution model of propagation the viscoelastic propagation kernel is seen mathematically to fill the role of the scale function in multiresolution theory as it operates on a wavefield to propagate it through some distance the suppression of high resolution components of the wavefield via this scaling pro

dynamics of pco2 and related air ice co2 fluxes in the arctic coastal zone amundsen gulf beaufort sea we present an arctic seasonal survey of carbon dioxide partial pressure pco 2 dynamics within sea ice brine and related air ice co 2 fluxes the survey was carried out from early spring to the beginning of summer in the arctic coastal waters of the amundsen gulf high concentrations of pco 2 up to 1834 matm were observed in the sea ice in early april as a consequence of concentration of solutes in brines caco 3 precipitation and microbial respiration caco 3 precipitation was detected through anomalies in total alkalinity ta and dissolved inorganic carbon dic this precipitation seems to have occurred in highly saline brine in the upper part of the ice cover and in bulk ice as summer draws near the ice temperature increases and brine pco 3 shifts from a large supersaturation 1834 matm to a marked undersaturation down to almost 0 matm this decrease was ascribed to brine dilution by ice meltwater dissolution of caco 3 and photosynthesis during the sympagic algal bloom the magnitude of the co 2 fluxes was controlled by ice temperature through its control on brine volume and brine channels connectivity and the concentration gradient between brine and the atmosphere however the state of the ice interface clearly affects air ice co 2 fluxes

physical and biological properties of early winter antarctic sea ice in the ross sea this work presents the results of physical and biological investigations at 27 biogeochemical stations of early winter sea ice in the ross sea during the 2017 pipers cruise only two similar cruises occurred in the past in 1995 and 1998 the year 2017 was a specific year in that ice growth in the central ross sea was considerably delayed compared to previous years these conditions resulted in lower ice thicknesses and chl a burdens as compared to those observed during the previous cruises it also resulted in a different structure of the sympagic algal community unusually dominated by phaeocystis rather than diatoms compared to autumn winter sea ice in the weddell sea awecs cruise the 2017 ross sea pack ice displayed similar thickness distribution but much lower snow cover and therefore nearly no flooding conditions it is shown that contrasted dynamics of autumnal winter sea ice growth between the weddell sea and the ross sea impacted the development of the sympagic community mean median ice chl a concentrations were 3 5 times lower at pipers and the community status there appeared to be more mature decaying based on phaeopigments chl a ratios these contrasts are discussed in the light of temporal and spatial differences between the two cruises

first estimates of the contribution of caco3 precipitation to the release of co2 to the atmosphere during young sea ice growth 1 we report measurements of ph total alkalinity air ice co2 fluxes chamber method and caco3 content of frost flowers ff and thin landfast sea ice as the temperature decreases concentration of solutes in the brine skim increases along this gradual concentration process some salts reach their solubility threshold and start precipitating the precipitation of ikaite caco3 6h2o was confirmed in the ff and throughout the ice by raman spectroscopy and x ray analysis the amount of ikaite precipitated was estimated to be 25 mol kg 1 melted ff in the ff and is shown to decrease from 19 to 15 mol kg 1 melted ice in the upper part and at the bottom of the ice respectively co2 release due to precipitation of caco3 is estimated to be 50 mol kg 1 melted samples the dissolved inorganic carbon dic normalized to a salinity of 10 exhibits significant depletion in the upper layer of the ice and in the ff this dic loss is estimated to be 2069 mol kg 1 melted sample and corresponds to a co2 release from the ice to the atmosphere ranging from 20 to 40 mmol m 2 d 1 this estimate is consistent with flux measurements of air ice co2 exchange our measurements confirm previous laboratory findings that growing young sea ice acts as a source of co2 to the atmosphere caco3 precipitation during early ice growth appears to promote the release of co2 to the atmosphere however its contribution to the overall release by newly formed ice is most likely minor

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

prestack depth migration with compensation for absorption and dispersion in prestack depth migration using explicit extrapolators the attenuation and dispersion of the seismic wave has been neglected so far we present a method for accommodating absorption and dispersion effects in depth migration schemes extrapolation operators that compensate for absorption and dispersion are designed using an optimization algorithm the design criterion is that the wavenumber response of the operator should equal the true extrapolator both phase velocity and absorption macro models are used in the wavefield extrapolation in a model with medium to high absorption the images obtained are superior to those obtained using extrapolators without compensation for absorption

physical and biogeochemical properties in landfast sea ice barrow alaska insights on brine and gas dynamics across seasons 1 the impacts of the seasonal evolution of sea ice physical properties on ice ocean biogeochemical exchanges were investigated in landfast ice at barrow alaska from january through june 2009 three stages of brine dynamics across the annual cycle have been identified based on brine salinity brine volume fraction and porous medium rayleigh number ra these are sea ice bottom layer convection full depth convection and brine stratification we further discuss the impact of brine dynamics on biogeochemical compounds in sea ice stable isotopes of water d 18o nutrients no3 po43 nh4 microalgae chlorophyll a and inert gas argon in general full depth convection events favor exchanges between sea ice and seawater while brine stratification limits these exchanges however argon responds differently to brine dynamics than the other biogeochemical compounds analyzed in this study this contrast is attributed to the impact of bubble nucleation on inert gas transport compared to the other biogeochemical compounds we present a scenario for argon bubble formation and evolution in sea ice and suggest that a brine volume fraction approaching 7 5 10 is required for inert gas bubbles to escape from sea ice to the atmosphere

arise antarctic remote ice sensing experiment in the east 2003 validation of satellite derived sea ice data products preliminary results are presented from the first validation of geophysical data products ice concentration snow thickness on sea ice hs and ice temperature ti from the nasa eos aqua amsr e sensor in east antarctica in september october 2003 the challenge of collecting sufficient measurements with which to validate the coarse resolution amsr e data products adequately was addressed by means of a hierarchical approach using detailed in situ measurements digital aerial photography and other satellite data initial results from a circumnavigation of the experimental site indicate that at least under cold conditions with a dry snow cover there is a reasonably close agree ment between satellite and aerial photo derived ice concentrations i e 97 2 3 6 for nt2 and 96 5 2 5 for bba algorithms vs 94 3 for the aerial photos in general the amsr e concentration represents a slight overestimate of the actual concentration with the largest discrepancies occurring in regions containing a relatively high proportion of thin ice the amsr e concentrations from the nt2 and bba algorithms are similar on average although differences of up to 5 occur in places again related to thin ice distribution the amsr e ice temperature ti product agrees with coincident surface measurements to approximately 0 58c in the limited dataset analyzed regarding snow thickness the amsr hs retrieval is a significant underestimate compared to in situ measurements weighted by the percentage of thin ice and open water present for the case study analyzed the underestimate was 46 for the overall average but 23 compared to smooth ice measurements the spatial distribution of the amsr e hs product follows an expected and consistent spatial pattern suggesting that the observed difference may be an offset at least under freezing conditions areas of discrepancy are identified and the need for future work using the more extensive dataset is highlighted

deep crustal extensional faulting in the ivrea zone of northern italy abstract the ivrea zone in northern italy consists of amphibolite and granulite facies metasedimentary metabasic and ultrabasic rocks and is thought to represent a section through the deep continental crust detailed mapping of the high grade part of this zone has revealed a series of high temperature shear zones which after the effects of later low temperature faulting and folding have been removed appears to accommodate extension of the sequence the shear zones formed at temperatures similar to those at which thermal equilibration occurred in the host rocks and locally show evidence for development under prograde conditions these observations fit well with thermal effects calculated from a simple heat flow model for extensional faulting in this model the effects of shear heating and displacement of cool hanging wall rocks against hotter footwall rocks are calculated these observations indicate that faulting as a mode of failure may be important during extension of the lower continental crust especially when basic rocks are the dominant components of the rock pile a restored section through the extended lower crust as observed in the ivrea zone is presented and the extent to which the features observed are able to explain seismic reflectivity of the lower crust is discussed

desalination processes of sea ice revisited 1 we reexamine five processes that have been suggested to be important for the loss of salt from sea ice these processes are the initial fractionation of salt at the ice ocean interface brine diffusion brine expulsion gravity drainage and flushing with surface meltwater we present results from analytical and numerical studies as well as from laboratory and field experiments that show that among these processes only gravity drainage and flushing contribute to any measurable net loss of salt we show that during ice growth the salinity field is continuous across the ice ocean interface hence there is no immediate segregation of salt at the advancing front

ocean acidification and calcium carbonate saturation states in the coastal zone of the west antarctic peninsula the polar oceans are particularly vulnerable to ocean acidification the lowering of seawater ph and carbonate mineral saturation states due to uptake of atmospheric carbon dioxide co2 high spatial variability in surface water ph and saturation states for two biologically important calcium carbonate minerals calcite and aragonite was observed in ryder bay in the coastal sea ice zone of the west antarctic peninsula glacial meltwater and melting sea ice stratified the water column and facilitated the development of large phytoplankton blooms and subsequent strong uptake of atmospheric co2 of up to 55 mmol m 2 day 1 during austral summer concurrent high ph 8 48 and calcium carbonate mineral supersaturation aragonite 3 1 occurred in the meltwater influenced surface ocean biologically induced increases in calcium carbonate mineral saturation states counteracted any effects of carbonate ion dilution accumulation of co2 through remineralisation of additional organic matter from productive coastal waters lowered the ph 7 84 and caused deep water corrosivity aragonite 0 9 in regions impacted by circumpolar deep water episodic mixing events enabled co2 rich subsurface water to become entrained into the surface and eroded seasonal stratification to lower surface water ph 8 21 and saturation states aragonite 1 8 relative to all surface waters across ryder bay uptake of atmospheric co2 of 28 mmol m 2 day 1 in regions of vertical mixing may enhance the susceptibility of the surface layer to future ocean acidification in dynamic coastal environments spatially resolved studies are essential to elucidate the natural variability in carbonate chemistry in order to better understand and predict carbon cycling and the response of marine organisms to future ocean acidification in the antarctic coastal zone

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

strain and kinematic analysis in general shear zones we present a unifying theory for the development and distribution of strain markers and kinematic indicators in zones of general shear and thus provide a framework in which data previously considered contradictory may be understood rigid and deformable porphyroclast systems including and complex grains are potential indicators of both strain and flow the shapes and distribution of such porphyroclast systems may be used to distinguish among different tectonic regimes general shear is divided into two fields sub simple shear in which the rotational component of the strain is less than that for simple shear and super simple shear in which the rotational component is greater than for simple shear sub simple shear may involve narrowing or broadening of shear zones super simple shear regimes are possible in local regions such as the vicinities of deformable porphyroclasts but must be enclosed by regimes of sub simple shear the polar mohr constructions for finite deformation and flow are useful to analyze general shear in theory the hyperbolic net is employed for practical plotting of real data and derivation of the kinematic vorticity number wn this number represents the relative contributions of pure and simple shear in steady flow in nature deformation is thought to build up and decay by processes that may invalidate the assumption of constant flow regime we therefore introduce the concept of accelerating deformation and analyze the implications of non steady flow for the shearing histories of deformed objects

effects of sea ice and biogeochemical processes and storms on under ice water fco2 during the winter spring transition in the high arctic ocean implications for sea air co2 fluxes we performed measurements of carbon dioxide fugacity fco2 in the surface water under arctic sea ice from january to june 2015 during the norwegian young sea ice n ice2015 expedition over this period the ship drifted with four different ice floes and covered the deep nansen basin the slopes north of svalbard and the yermak plateau this unique winter to spring dataset includes the first winter time under ice water fco2 observations in this region the observed under ice fco2 ranged between 315 atm in winter and 153 atm in spring hence was undersaturated relative to the atmospheric fco2 although the sea ice partly prevented direct co2 exchange between ocean and atmosphere frequently occurring leads and breakup of the ice sheet promoted sea air co2 fluxes the co2 sink varied between 0 3 and 86 mmol c m 2 d 1 depending strongly on the open water fractions ow and storm events the maximum sea air co2 fluxes occurred during storm events in february and june in winter the main drivers of the change in under ice water fco2 were dissolution of caco3 ikaite and vertical mixing in june in addition to these processes primary production and sea air co2 fluxes were important the cumulative loss due to caco3 dissolution of 0 7 mol c m 2 in the upper 10 m played a major role in sustaining the undersaturation of fco2 during the entire study the relative effects of the total fco2 change due to caco3 dissolution was 38 primary production 26 vertical mixing 16 sea air co2 fluxes 16 and temperature and salinity insignificant this article is protected by copyright all rights reserved

experimental modelling of mantled porphyroclasts abstract mantled porphyroclasts are commonly used as sense of shear indicators in mylonites analogue experiments have been carried out to model the development of such objects rigid spheres mantled by a viscous plasticene putty mixture with power law behaviour were suspended in an optically transparent newtonian polymer matrix the samples were deformed between two cylinders one placed within the other and with coinciding axes this induces a non coaxial flow between the cylinders and allows the achievement of high finite strain the viscous mantle around the rigid sphere remained undeformed deformed into an ellipsoid or developed wings the final geometry depends mainly on the induced viscosity contrast between the mantle and the matrix which is a function of the flow induced stress on the surface of the mantle winged mantles only develop if the induced viscosity contrast between the mantle and the matrix polymer is sufficiently small if this critical induced viscosity contrast is exceeded the mantled sphere remains undeformed or obtains a stable ellipsoidal shape even at high finite strain shaped winged mantles only develop in simple shear flow if the mantle around a rigid sphere is thin

the seasonal cycle of ocean atmosphere co2 flux in ryder bay west antarctic peninsula approximately 15 million km2 of the southern ocean is seasonally ice covered yet the processes affecting carbon cycling and gas exchange in this climatically important region remain inadequately understood here 3 years of dissolved inorganic carbon dic measurements and carbon dioxide co2 fluxes from ryder bay on the west antarctic peninsula wap are presented during spring and summer primary production in the surface ocean promotes atmospheric co2 uptake in winter higher dic caused by net heterotrophy and vertical mixing with circumpolar deep water results in outgassing of co2 from the ocean ryder bay is found to be a net sink of atmospheric co2 of 0 59 0 94 mol c m 2 yr 1 average of 3 years seasonal sea ice cover increases the net annual co2 uptake but its effect on gas exchange remains poorly constrained a reduction in sea ice on the wap shelf may reduce the strength of the oceanic co2 sink in this region

sea ice and snow cover characteristics during the winter spring transition in the bellingshausen sea an overview of simba 2007 abstract the sea ice mass balance in the antarctic simba experiment was conducted from the rvib n b palmer in september and october 2007 in the bellingshausen sea in an area recently experiencing considerable changes in both climate and sea ice cover snow and ice properties were observed at 3 short term stations and a 27 day drift station ice station belgica isb during the winter spring transition repeat measurements were performed on sea ice and snow cover at 5 isb sites each having different physical characteristics with mean ice snow thicknesses varying from 0 6 m 0 1 m to 2 3 m 0 7 m ice cores retrieved every five days from 2 sites and measured for physical biological and chemical properties three ice mass balance buoys imbs provided continuous records of snow and ice thickness and temperature meteorological conditions changed from warm fronts with high winds and precipitation followed by cold and calm periods through four cycles during isb the snow cover regulated temperature flux and controlled the physical regime in which sea ice morphology changed level thin ice areas had little snow accumulation and experienced greater thermal fluctuations resulting in brine salinity and volume changes and winter maximum thermodynamic growth of 0 6 m in this region flooding and snow ice formation occurred during cold spells in ice and snow of intermediate thickness in contrast little snow ice formed in flooded areas with thicker ice and snow cover instead nearly isothermal highly permeable ice persisted in spring short lived cold air episodes did not effectively penetrate the sea ice nor overcome the effect of ocean heat flux thus favoring net ice thinning from bottom melt over ice thickening from snow ice growth in all cases these warm ice conditions were consistent with regional remote sensing observations of earlier ice breakup and a shorter sea ice season more recently observed in the bellingshausen sea

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

inorganic carbon transport during sea ice growth and decay a carbon pump in polar seas 1 during sea ice formation in polar areas brine rejection increases the density in the underlying water column and thereby contributes to the formation of deep and intermediate water masses in the world ocean here we present evidence that dissolved inorganic carbon tco2 is rejected together with brine from growing sea ice and that low temperatures may result in a significant change in the ratio of tco2 and alkalinity in arctic sea ice compared with surface waters model calculations show that this sea ice driven carbon pump affects surface water partial pressure of co2 significantly in polar seas and potentially sequesters large amounts of co2 to the deep ocean

measurements of total alkalinity calcium and sulfate in natural sea ice we report precise measurements of salinity chlorinity alkalinity calcium and sulphate in various types of sea ice collected at the canadian expedition to study the alpha ridge cesar ice camp in the arctic ocean and in both first year and multiyear ice collected in fram strait several of the samples showed some relative enrichment of alkalinity and sulphate compared to what would be observed in seawater of the same salinity the relative enrichment was quite varied and did not correspond quantitatively with what has been observed in sea ice produced in the laboratory our results indicate that the temperature and salinity history of sea ice must be crucial in determining the relative composition of salts in natural sea ice and that quantitative geochemical predictions based on the composition of sea ice produced in the laboratory or on a particular specimen of natural sea ice must be made with caution