use of groundwater lifetime expectancy for the performance assessment of a deep geologic radioactive waste repository 2 application to a canadian shield environment 1 f j cornaton et al 2008 introduced the concept of lifetime expectancy as a performance measure of the safety of subsurface repositories on the basis of the travel time for contaminants released at a certain point in the subsurface to reach the biosphere or compliance area the methodologies are applied to a hypothetical but realistic canadian shield crystalline rock environment which is considered to be one of the most geologically stable areas on earth in an approximately 10 10 1 5 km3 hypothetical study area up to 1000 major and intermediate fracture zones are generated from surface lineament analyses and subsurface surveys in the study area mean and probability density of lifetime expectancy are analyzed with realistic geologic and hydrologic shield settings in order to demonstrate the applicability of the theory and the numerical model for optimally locating a deep subsurface repository for the safe storage of spent nuclear fuel the results demonstrate that in general groundwater lifetime expectancy increases with depth and it is greatest inside major matrix blocks various sources and aspects of uncertainty are considered specifically geometric and hydraulic parameters of permeable fracture zones sensitivity analyses indicate that the existence and location of permeable fracture zones and the relationship between fracture zone permeability and depth from ground surface are the most significant factors for lifetime expectancy distribution in such a crystalline rock environment as a consequence it is successfully demonstrated that the concept of lifetime expectancy can be applied to siting and performance assessment studies for deep geologic repositories in crystalline fractured rock settings

changes in the salinity and porosity of sea ice samples during shipping and storage a theoreti cal examination of salinity and porosity changes introduced in sea ice samples by brine expulsion and gas entrapment caused by thermal cycling during shipping and storage shows that in extreme cases such effects can be significant resulting in 15 reductions in porosity 1 more representative scenarios give porosity changes of less than 2 which assuming that ice property variations scale with n 1 2 result in property variations of less than 1

polarimetric signatures of sea ice 2 experimental observations experimental observations of polarimetric signatures are presented for sea ice in the beaufort sea under cold winter conditions and interpreted with the composite model developed in part 1 polarimetric data were acquired in march 1988 with the jet propulsion laboratory multifrequency airborne synthetic aperture radar sar during the beaufort sea flight campaign the experimental area was located near 75 n latitude and spanned 140 145 w longitude selected sea ice scenes contain various ice types including multiyear thick first year and thin lead ice additionally the c band sar on the first european remote sensing satellite provides supplementary backscattering data of winter beaufort sea ice for small incident angles 20 26 at vertical polarization sea ice characterization and environmental data used in the model were collected at the applied physics laboratory drifting ice station to the northeast of prudhoe bay additional data from field and laboratory experiments are also utilized in this analysis the model relates sea ice polarimetric backscattering signatures to physical structural and electromagnetic properties of sea ice scattering mechanisms contributing to sea ice signatures are explained and sensitivities of polarimetric signatures to sea ice characterization parameters are studied

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

investigations of newly formed sea ice in the cape bathurst polynya 1 structural physical and optical properties 1 the physical structural and optical properties of newly formed ice types were studied in the cape bathurst polynya 71 n 127 w during fall freezeup in october to early november 2003 variable meteorological conditions with occasional snowfall resulted in the formation of numerous ice types and surface conditions ice samples were collected from horizontally homogeneous surfaces representative of the area crystallographic analysis on 33 ice cores revealed highly variable growth conditions and formation mechanisms in the area the mean fraction of granular ice was 33 while intermediate granular columnar and columnar ice contributed 37 and 30 respectively salinity profiles in the ice were c shaped and as the ice grew thicker bulk salinities decreased according to 4 582 13 358 hi cm these conditions resulted in brine volumes ranging from 4 to 46 bare ice surfaces commonly formed a high salinity brine skim layer due to brine expulsion salinities up to 40 were observed in this layer under suitable conditions frost flowers formed on the ice and their presence was related to characteristic ice microstructure with crystals that appeared disc like in shape fine grained snow ice was formed when snow merged with surface brine to create a complex hypersaline surface at the snow ice interface the spectral reflectance for the thin ice types was most strongly related to surface conditions the presence of frost flowers significantly increased the reflectance independent of snow precipitation any increase in ice thickness was found to have little effect on the reflectance once a 20 30 mm thick snow layer was present

modeling and measurement of c band radar backscatter from snow covered first year sea ice in this paper we present model and measurement results for c band hh and vv normalized radar cross sections nrcs from winter snow covered first year sea ice with average snow thicknesses of 16 4 and 3 cm the brine content in snow pack was low in all three case studies which is typical for cold winter conditions we used the first order approximation of the small perturbation theory accounting for surface scattering from the air snow and snow ice rough interfaces and continuously layered snow and sea ice the experimental data were collected during the circumpolar flaw lead system study in the winter of 2008 in the southern beaufort sea from the research icebreaker amundsen good agreement between the model and experimental data were observed for all three case studies the model results revealed that the scattering at the snow ice rough interface is usually stronger than that at the air snow interface furthermore both model and experimental nrcs values at vv and hh polarizations were considerably higher for thin snow cover compared with the thick snow cover case we associate this effect with the lower attenuation of the propagated wave within the thin snow pack in comparison to the thick snow pack we also demonstrated that different brine volume contents in snow with close thicknesses of 4 and 3 cm did not affect the backscattering coefficients at certain incidence angles and polarization our findings provide the physical basis for winter snow thickness retrieval and suggest that such retrievals may be possible from radar observations under particular scattering conditions

evaluating scattering contributions to c band radar backscatter from snow covered first year sea ice at the winter spring transition through measurement and modeling in this paper we present model and measurement results for time series angular dependencies of c band hh and vv normalized radar cross sections nrcs over first year snow covered sea ice during a winter spring transition period experimental scatterometer and physical data were collected near cambridge bay nunavut canada between may 20 and may 28 2014 covering a severe storm event on may 25 we use the small perturbation scattering theory to model small scale surface scattering the mie scattering theory to estimate the level of volume scattering in snow and the kirchhoff physical optics model to compute the large scale surface scattering component we observed good agreement between the model and experimental hh and vv nrcs before the storm r 2 between model and experimental nrcs was 0 88 and 0 82 for vv and hh respectively after the storm r 2 was 0 81 and 0 78 for vv and hh respectively our model results suggest an overall increase in surface roughness after the storm event supported by lidar measurements of the snow surface topography before the storm the large scale and small scale surface scattering from the air snow interface as well as volume scattering components dominated after the storm the large and small scale scattering contributions increased while the volume scattering component considerably dropped we attribute these effects to the increase in surface roughness and snow moisture content during the poststorm period our results could aid in interpretation of time series synthetic aperture radar images with respect to physical properties of snow and ice during the winter spring transition period

the influence of closed brine pockets and permeable brine channels on the thermo elastic properties of saline ice a model of the thermo elastic behaviour of saline ice is formulated and model solutions describing thermo elastic waves tew propagating into a half space of the ice are investigated the model is based on a proposal that saline ice is a matrix which encompasses both closed brine pockets and permeable channels filled with brine experiments on the thermal expansion of saline ice samples and on tew in saline ice have been performed in the cold laboratories of the university centre in svalbard and in university college london the experimental data are compared with theoretical conclusions the experimental data support our hypothesis that the brine in saline ice is divided between closed pockets and open permeable channels this article is part of the themed issue microdynamics of ice

examining the impact of a crude oil spill on the permittivity profile and normalized radar cross section of young sea ice an oil in sea ice mesocosm experiment was conducted at the university of manitoba sea ice environmental research facility from january to march 2016 in which geophysical and electromagnetic parameters of the ice were measured and general observations about the oil contaminated ice were made from the experimental measurements the presence of crude oil appears to affect the temperature and bulk salinity profiles as well as the normalized radar cross section nrcs of the contaminated young sea ice the measured temperature and bulk salinity profiles of the ice as well as the crude oil distribution within the ice were used to model the permittivity profile of the oil contaminated ice by adapting two mixture models commonly used to describe sea ice to account for the presence of oil permittivity modeling results were used to simulate the nrcs of the oil contaminated sea ice in an effort to determine the accuracy of the models in addition the application of x ray microtomography in modeling the dielectric profile of oil contaminated sea ice was examined the sensitivity of the permittivity models for oil contaminated sea ice to changes in temperature frequency and oil volume fraction was also examined

oxygen isotope fractionation during the freezing of sea water the dependence of oxygen isotope fractionation on ice growth rate during the freezing of sea water is investigated based on laboratory experiments and field observations in mcmurdo sound antarctica the laboratory experiments were performed in a tank filled with sea water with sea ice grown under calm conditions at various room temperatures ranging from 58c to 208c in mcmurdo sound the ice growth rate was monitored using thermistor probes for first year landfast ice that grew to 2 m in thickness combining these datasets allows for the first time examination of fractionation at a wide range of growth rates from 0 8 10 7 to 9 3 10 7 ms 1 in the analysis a stagnant boundary layer model is parameterized using these two independent datasets as a result the optimum values of equilibrium pure ice fractionation factor and boundary layer thickness are estimated it is suggested that a regime shift may occur at a growth rate of 2 0 10 7 ms 1 a case study on sea ice in the sea of okhotsk where the growth rate is modeled by coupling the thermodynamic properties of the sea ice with meteorological data demonstrates the utility of the fitted models

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

effects of snow snowmelting and refreezing processes on air sea ice co2 flux the air sea ice co2 flux was measured in the ice covered saroma ko a lagoon on the northeastern coast of hokkaido japan using a chamber technique the air sea ice co2 flux ranged from 1 8 to 0 5 mg c m 2 h 1 where negative values indicate a sink for atmospheric co2 the partial pressure of co2 pco2 in the brine of sea ice was substantially lower than that of the atmosphere primarily because of the influence of the under ice plume from the saromabetsu river located in the southeastern part of the lagoon this suggests that the brine had the ability to take up atmospheric co2 into the sea ice however the snow deposited over the sea ice and the superimposed ice that formed from snowmelting and refreezing partially blocked co2 diffusion acting as an impermeable medium for co2 transfer our results suggest that the air sea ice co2 flux was dependent not only on the difference in pco2 between the brine and the overlying air but also on the status of the ice surface these results provide the necessary evidence for evaluation of the gas exchange processes in ice covered seas

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

circumpolar mapping of antarctic coastal polynyas and landfast sea ice relationship and variability abstractsinking of dense water from antarctic coastal polynyas produces antarctic bottom water aabw which is the densest water in the global overturning circulation and is a key player in climate change as a significant sink for heat and carbon dioxide very recent studies have suggested that landfast sea ice fast ice plays an important role in the formation and variability of the polynyas and possibly aabw however they have been limited to regional and case investigations only this study provides the first coincident circumpolar mapping of antarctic coastal polynyas and fast ice the map reveals that most of the polynyas are formed on the western side of fast ice indicating an important role of fast ice in the polynya formation winds diverging from a boundary comprising both coastline and fast ice are the primary determinant of polynya formation the blocking effect of fast ice on westward sea ice advection by the coastal current would be another key factor these effects on the variability in

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

a broad spectral interdisciplinary investigation of the electromagnetic properties of sea ice this paper highlights the interrelationship of research completed by a team of investigators and presented in the several individual papers comprising this special section on the office of naval research onr arlington va sponsored sea ice electromagnetics accelerated research initiative ari the objectives of the initiative were the following 1 understand the mechanisms and processes that link the morphological and physical properties of sea ice to its electromagnetic em characteristics 2 develop and verify predictive models for the interaction of visible infrared and microwave radiation with sea ice 3 develop and verify inverse scattering techniques applicable to problems involving the interaction of em radiation with sea ice guiding principles for the program were that all em data be taken with concurrent physical property data salinity density roughness etc and that broad spectral data be acquired in as nearly a simultaneous fashion as possible over 30 investigators participated in laboratory field and modeling studies that spanned the em spectrum from radio to ultraviolet wavelengths an interdisciplinary approach that brought together sea ice physicists remote sensing experts in fill measurements and forward and inverse modelers primarily mathematicians and em theorists was a hallmark of the program along with describing results from experiments and modeling efforts possible paradigms for using broad spectral data in developing algorithms for analyzing remote sensing data in terms of ice concentration age type and possibly thickness are briefly discussed

a semianalytical algorithm for quantitatively estimating sediment and atmospheric deposition flux from modis derived sea ice albedo in the bohai sea china quantitative estimates of particulate matter pm concentration in sea ice using remote sensing data is helpful for studies of sediment transport and atmospheric dust deposition flux in this study the difference between the measured dirty and estimated clean albedo of sea ice was calculated and a relationship between the albedo difference and pm concentration was found using field and laboratory measurements a semianalytical algorithm for estimating pm concentration in sea ice was established the algorithm was then applied to modis data over the bohai sea china comparisons between modis derived and in situ measured pm concentration showed good agreement with a mean absolute percentage difference of 31 2 from 2005 to 2010 the modis derived annual average pm concentration was approximately 0 025 g l at the beginning of january after a month of atmospheric dust deposition it increased to 0 038 g l atmospheric dust deposition flux was estimated to be 2 50 t km 2 month similar to 2 20 t km 2 month reported in a previous study the result was compared with on site measurements at a nearby ground station the ground station was close to industrial and residential areas where larger dust depositions occurred than in the sea but although there were discrepancies between the absolute magnitudes of the two data sets they demonstrated similar trends

consolidation of first year sea ice ridges 1 measurements of spatial and temporal temperature development geometry morphology and physical properties in three first year sea ice ridges at spitsbergen and in the gulf of bothnia have been performed the corresponding thickness and the physical properties of the surrounding level ice were also measured the thickness of the consolidated layer was examined through drilling and temperature measurements the temperatures gave a ratio of the thickness of the consolidated layer to the level ice thickness from 1 39 to 1 61 whereas the drillings indicated a ratio of 1 68 1 85 the measured consolidated layer appeared to be 28 thicker when based on drillings in comparison to temperature thus the result depended on the method of investigation the drillings included a partly consolidated layer however the measured growth of the consolidated layer did not depend on the method of investigation the scatter of the physical properties in the consolidated layer was higher than that of the level ice the consistency of the unconsolidated rubble differed markedly at the two sites it was soft and slushy at spitsbergen and harder in the gulf of bothnia three possible explanations for these differences are discussed surrounding currents different keel shapes and difference in salinity

influence of glacial water and carbonate minerals on wintertime sea ice biogeochemistry and the co2 system in an arctic fjord in svalbard the effect of freshwater sources on wintertime sea ice co2 processes was studied from the glacier front to the outer tempelfjorden svalbard in sea ice glacier ice brine and snow march april 2012 was mild and the fjord was mainly covered with drift ice in contrast to the observed thicker fast ice in the colder april 2013 this resulted in different physical and chemical properties of the sea ice and under ice water data from stable oxygen isotopic ratios and salinity showed that the sea ice at the glacier front in april 2012 contained on average 54 of frozen in glacial meltwater this was five times higher than in april 2013 where the ice was frozen seawater in april 2012 the largest excess of sea ice total alkalinity at carbonate ion co32 and bicarbonate ion concentrations hco3 relative to salinity was mainly related to dissolved dolomite and calcite incorporated during freezing of mineral enriched glacial water in april 2013 the excess of these variables was mainly due to ikaite dissolution as a result of sea ice processes dolomite dissolution increased sea ice at twice as much as ikaite and calcite dissolution implying different buffering capacity and potential for ocean co2 uptake in a changing climate

a shear velocity discontinuity in the lower mantle a lower mantle s wave triplication is detected using short and long period sh seismograms in the distance range 70 sup 0 to 95 sup 0 modeling of the observations with synthetic seismograms indicates that the triplication is produced by a 2 75 0 25 shear velocity increase about 280 km above the core mantle boundary the sh data from intermediate and deep focus events for three distinct source region receiver array combinations show generally consistent travel time and relative amplitude behavior of the triplication there are small systematic travel time shifts between the source regions which suggest regional variations in the depth of the discontinuity of up to 40 km

characterization of arctic sea ice thickness using high resolution spaceborne polarimetric sar data in this paper we have investigated the relationship between the depolarization effects and the wintertime sea ice thickness in the landfast ice region where smooth thick first year ice fyi and deformed old ice coexisted by using c and x band spaceborne polarimetric synthetic aperture radar sar data radarsat 2 and terrasar x we have found a strong correlation between the in situ sea ice thickness and the sar derived depolarization factors copolarized correlation and cross polarized ratio the observed relationships have demonstrated not only a categorical difference between fyi and multiyear ice myi but also a one to one continuity in the scatter plots rather than being clustered it clearly shows that the observed correlations are not merely from the categorical difference in scattering mechanism between fyi and myi and that there might exist a one to one relationship between thickness and depolarization factors at least in our deformed ice case this suggests that depolarization factors could be effective sar parameters in the estimation of wintertime sea ice thickness numerical model simulations explained some portions of the correlation by employing multiple scattering on the sea ice surface and volume scattering within the low density subsurface layer

dmsp and dms cycling within antarctic sea ice during the winter spring transition this study describes within ice concentrations of dimethylsulfoniopropionate dmsp its degradation product dimethylsulphide dms as well as nutrients and chlorophyll a that were sampled during the sea ice physics and ecosystems experiment 2 sipex 2 in 2012 dmsp is a methylated substrate produced in large amounts annually by ice associated microalgae while dms plays a significant role in carbon and sulphur cycling in the southern ocean in the east antarctic study area between 115 125 e and 64 66 s ice and slush cores brine under ice seawater and zooplankton antarctic krill samples were collected at 6 ice stations the pack ice was characterised by high snow loading which initiated flooding events and triggered nutrient supply to the sea ice surface while variation in ice conditions influenced sea ice permeability this ranged from impermeable surface and middle sections of the sea ice to completely permeable ice cores at some stations chlorophyll a maxima shifted from the sea ice surface horizon at the first station to the sea ice bottom layer at the last station highest dmsp concentrations were detected in brine samples at the sea ice surface reflecting a mismatch with respect to the distribution of chlorophyll a our data suggest enhanced dmsp production by sea ice surface algal communities and its release into brine during freezing and melting which in turn is coupled to flooding events early in the season a time cycle of dms production by dmsp degradation and dms efflux is evident at the sea ice snow interface when slush is formed during melt seawater under the ice contained only low concentrations of dmsp and dms even when brine drainage was evident and the sea ice became permeable we postulate that in situ grazing by zooplankton may act as sink for the dmsp produced early in the season

kinetics of ikaite precipitation and dissolution in seawater derived brines at sub zero temperatures to 265 k abstract the kinetics of calcium carbonate hexahydrate ikaite precipitation and dissolution were investigated in seawater and seawater derived brines at sub zero temperatures using the constant addition experimental technique the steady state rate of these two processes was found to be a function of the deviation of the solution from equilibrium with respect to ikaite and conformed to the same empirical rate law as the anhydrous caco 3 polymorphs calcite and aragonite in addition to the saturation state of the brine with respect to ikaite the salinity of the brine and the temperature of the reaction evidently exerted some control on the ikaite precipitation kinetics while the dissolution kinetics of the polymorph were not noticeably influenced by these two parameters the experimental salinity and temperature conditions were equivalent to those at thermal equilibrium between brine and ice in the sea ice cover of polar seas simple modelling of the co 2 system by extrapolation of the oceanic equivalent to sea ice brines showed that the physical concentration of seawater ions and the changes in ikaite solubility as a function of salinity and temperature both inherent in the sea ice system would be insufficient to drive the emergent brines to ikaite supersaturation and precipitation in sea ice down to 8 c the loss of dissolved inorganic carbon to the gas phase of sea ice and to sympagic autotrophs are two independent mechanisms which in nature could prompt the brine co 2 system towards ikaite supersaturation and precipitation under these conditions the steady state precipitation rate of ikaite was found to be fast enough for rapid formation within short time scales days to weeks in sea ice the observed ikaite dissolution kinetics were also found conducive to short turn over time scales of a few hours to a few days in corrosive solutions such as surface seawater

estimating the recharge properties of the deep ocean using noble gases and helium isotopes the distribution of noble gases and helium isotopes in the dense shelf waters of antarctica reflect the boundary conditions near the ocean surface air sea exchange sea ice formation and subsurface ice melt we use a non linear least squares solution to determine the value of the recharge temperature and salinity as well as the excess air injection and glacial meltwater content throughout the water column and in the precursor to antarctic bottom water the noble gas derived recharge temperature and salinity in the weddell gyre are 1 95 c and 34 95 psu near 5500 m these cold salty recharge values are a result of surface cooling as well as brine rejection during sea ice formation in antarctic polynyas in comparison the global value for deep water recharge temperature is 0 44 c at 5500 m which is 1 5 c warmer than the southern hemisphere deep water recharge temperature reflecting the contribution from the north atlantic the contrast between northern and southern hemisphere recharge properties highlight the impact of sea ice formation on setting the gas properties in southern sourced deep water below 1000 m glacial meltwater averages 3 5 by volume and represents greater than 50 of the excess neon and argon found in the water column these results indicate glacial melt has a non negligible impact on the atmospheric gas content of antarctic bottom water

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

towards an estimation of sub sea ice platelet layer volume with multi frequency electromagnetic induction sounding ice platelet clusters modify the heat and mass balance of sea ice near antarctic ice shelves and provide a unique habitat for ice associated organisms the amount and distribution of these ice crystals below the solid sea ice provide insight into melt rates and circulation regimes in the ice shelf cavities which are difficult to observe directly however little is known about the circum antarctic volume of the sub sea ice platelet layer because observations have mostly been limited to point measurements in this study we present a new application of multi frequency electromagnetic em induction sounding to quantify platelet layer properties combining in situ data with the theoretical response yields a bulk platelet layer conductivity of 1154 271msm 1 and ice volume fractions of 0 29 0 43 calibration routines and uncertainties are discussed in detail to facilitate future studies our results suggest that multi frequency em induction sounding is a promising method to efficiently map platelet layer volume on a larger scale than has previously been feasible

bio optical and structural properties inferred from irradiance measurements within the bottommost layers in an arctic landfast sea ice cover 1 irradiance spectra were measured at vertical increments within the bottommost layers of landfast sea ice with the aid of divers in franklin bay canada in an effort to obtain input parameters for bio optical modeling of sea ice the study took place between 22 april and 9 may 2004 during the overwintering stage of cases canadian arctic shelf exchange study the ice was about 1 8 m thick with a snow cover of variable thickness 0 04 to 0 4 m ice surface temperatures increased from about 12 to 6 4 c during the sampling period while ice temperatures within the bottommost portion under study ranged from 3 0 to 1 2 c ice algae were visible within the bottommost centimeters of the sea ice this algae layer had a marked effect on the spectral distribution of transmitted irradiance beneath the ice particulate absorption spectra ap measured from melted ice samples showed evidence of chloroplastic pigment degradation and could not fully explain the shape of the in situ diffuse attenuation coefficient kd for the algal layer interior ice layers however did show absorption curves similar to ap from samples suggesting the presence of degraded algal pigments within these layers the discrete ordinates radiative transfer disort code was iterated in an inverse approach to estimate ap and the scattering coefficient btot from the irradiance profiles for the bottom 0 1 m of the sea ice btot was around 400 m 1 while at the 0 1 to 0 2 m layer from the ice bottom it decreased to 165 m 1 using ap combined with wavelength independent btot as inputs to disort seem to adequately explain the radiative transfer near the bottom of first year sea ice provided that adjustments were made to the brine volume fraction

physico ecobiogeochemistry of east antarctic pack ice during the winter spring transition our study provides information on the relationships between physical chemical and biological properties of east antarctic sea ice sampled as part of the sea ice physics and ecosystem experiment sipex during the winter spring transition in 2007 the sampled sea ice showed a high contribution of granular ice indicating the turbulent conditions during sea ice formation off east antarctica the sea ice was cold with brine volumes often below or very close to the theoretical percolation threshold of sea ice dissolved inorganic nutrient concentrations showed both positive and negative deviations from theoretical dilution lines indicating both nutrient uptake as well as nutrient remineralisation in sea ice brines cold temperatures high brine salinities and low brine volumes limited high ice algal biomass to the warmer and more porous sea ice layers at the ice water interface we hypothesise that east antarctic sea ice shows generally low ice algal biomass accumulation due to a combination of relatively low snow loading relatively cold ice temperatures and short persistence of sea ice into the warm forcing regime all of which prevent the development of significant internal and surface communities

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

modeling the transport of passive tracers in sea ice 1 a model for the vertical transport of passive tracers in sea ice is presented two reynolds flux closure approximations are proposed for the tracer velocity dispersion term in the new ice tracer model icet the schemes enhanced molecular diffusion emd and mixing length diffusion mld are suggested parameterizations of gravity drainage the dominant mechanism of desalination in growing sea ice the performance of icet using each parameterization is tested against two experimental studies simulations i compare profiles of brine salinity with passive tracer concentrations during sea ice growth and melt and simulations ii compare bottom boundary salt and brine volume fluxes with passive tracer fluxes and bottom diffusivities icet behavior is evaluated under three salinity forcing prescriptions both schemes successfully reproduce expected tracer concentrations in simulations i when the salinity forcing evolves logarithmically however in simulations ii the mld scheme outperforms emd in two significant ways 1 growth rate trends in the mld diffusivity parallel measurements of brine volume flux while emd bottom diffusivities remain almost constant and 2 mld bottom tracer concentrations decrease with ice growth rate similar to excluded brine salinity while emd trends are contrary hence enhanced molecular diffusion is highly questionable for implementation in models of reactive passive tracers the icet mixing length diffusivity is a viable choice in sea ice biogeochemical modeling it remains a challenge to assess whether mld can provide quantitative estimates of desalination at each time step for use in forcing icet or for implementation in a model of sea ice salinity

investigations of newly formed sea ice in the cape bathurst polynya 2 microwave emission 1 this study examines the role of newly formed sea ice geophysical state on microwave emission coincident with sea ice geophysical sampling ship based passive microwave emission data dual polarized at 19 37 and 85 ghz were collected in the cape bathurst polynya during 18 october and 13 november 2003 using polarization ratios prs we found that bare thin ice was separable from snow covered ice thin snow equal to 0 02 0 13 m thickness is significantly correlated with the spectral gradient ratios grv 85 19 r2 0 55 p value 0 2 the relationship between atmospherically corrected r37 and bare ice thickness showed an exponential relationship very comparable to that reported by martin et al 2004 which is ascribed to the reduction of bare ice surface salinity based on both observational and modeling studies however the relationship quickly becomes invalid for even thin snow covered ice due to significant impact of thin wet liquid water fraction 0 02 0 04 snow on microwave emission our results suggest that the sea ice algorithms nasa team and nasa team 2 could underestimate total ice concentration over thin bare ice by 35 on average while both algorithms underestimate the total ice concentration by 20 over snow covered ice using pr 85 sea ice could be delineated from open water using a properly adjusted threshold value accounting for cloud or fog effects possibly with the exception of dark nilas and or bare consolidated pancakes

thermokarst lake to lagoon transitions in eastern siberia do submerged taliks refreeze as the arctic coast erodes it drains thermokarst lakes transforming them into lagoons and eventually integrates them into subsea permafrost lagoons represent the first stage of a thermokarst lake transition to a marine setting and possibly more saline and colder upper boundary conditions in this research borehole data electrical resistivity surveying and modelling of heat and salt diffusion were carried out at polar fox lagoon on the bykovsky peninsula siberia polar fox lagoon is a seasonally isolated water body connected to tiksi bay through a channel leading to hypersaline waters under the ice cover the boreholes in the centre of the lagoon revealed floating ice and a saline cryotic bed underlain by a saline cryotic talik a thin ice bearing permafrost layer and unfrozen ground the bathymetry showed that most of the lagoon was ice grounded in spring in bedfast ice areas the electrical resistivity profiles suggest that an unfrozen saline layer was underlain by a thick layer of refrozen talik the modelling suggests thermokarst lake taliks refreeze when submerged in saltwater with mean annual bottom water temperatures below or slightly above 0 c this occurs because the top down chemical degradation of newly formed ice bearing permafrost is slower than the cooling of the talik hence lagoons may pre condition taliks with a layer of ice bearing permafrost before encroachment by the sea and this frozen layer may act as a cap on gas migration out of the underlying talik

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

snow thickness retrieval from l band brightness temperatures a model comparison the soil moisture and ocean salinity smos satellite s l band 1 4 ghz measurements have been used to retrieve snow thickness over thick sea ice in a previous study here we consider brightness temperature simulations for 2 5 4 5 m thick arctic multi year ice and compare the results of the relatively simple emission model m2013 used previously for the retrieval with simulations from a more complex model t2011 that combines a sea ice version of the microwave emission model for layered snowpacks memls with a thermodynamic model we find that l band brightness temperature is mainly determined by ice temperature in the m2013 model ice temperature in turn is mainly determined by surface temperature and snow thickness and this dependence has been used previously to explain the potential for a snow thickness retrieval our comparisons suggest that the m2013 retrieval model may benefit from a more sophisticated thermodynamic calculation of the ice temperature or from using independent temperature data e g from 6 ghz channels in both models horizontally polarized brightness temperatures increase with snow thickness while holding surface temperature ice thickness and snow density near constant the increase in the t2011 model is steeper than in m2013 suggesting a higher sensitivity to snow thickness than found earlier

numerical simulations of the profile properties of undeformed first year sea ice during the growth season a simulation scheme is developed that estimates salinity profiles for first year sea ice during the growth season as a function of the growth history of the ice the model considers the dependence of the initial ice salinity on ice growth velocity and sea water salinity and also the subsequent drainage of brine from the ice the equation for ice growth assumes a linear temperature profile within the ice and is driven by surface heat balance equations that are based on smoothed climatic data for the central arctic basin the estimated salinity profiles are in good agreement with natural profiles although temperature and salinity profiles depend upon the time of the year when ice growth is initiated the brine volume profiles which they specify are essentially a unique function of ice thickness a conclusion that holds even when the insulative effects of snow are considered the temperature and brine volume profiles are then utilized to calculate the ice strength and elastic modulus profiles which in turn specify the composite mechanical properties of the ice sheets through the application of a theory developed by assur 1967 significant differences which are largest for thin ice sheets are observed between ice sheet properties as calculated using composite plate theory and properties calculated from uniform plate theory and average ice properties these results provide a justification for the practice common within the ice modeling community of parameterizing the mechanical behavior of pack ice on the basis of the ice thickness distribution

physical and biological controls on dms p dynamics in ice shelf influenced fast ice during a winter spring and a spring summer transitions we report the seasonal and vertical variations of dimethylsulfide dms and its precursor dimethylsulfoniopropionate dmsp in fast ice at cape evans mcmurdo sound antarctica during the spring summer transition in 2011 and winter spring transition in 2012 we compare the variations of dms p observed to the seasonal evolution of the ice algal biomass and of the physical properties of the ice cover with emphasis on the ice texture and brine dynamics isolated dms and dmsp maxima were found during both seasonal episodes in interior ice and corresponded to the occurrence of platelet crystals in the ice texture we show that platelet crystals formation corresponded in time and depth to the incorporation of dinoflagellates strong dmsp producers in the ice cover we also show that platelet crystals could modify the environmental stresses on algal cells and perturb the vertical redistribution of dms p concentrations we show that during the winter spring transition in 2012 the dms p profiles were strongly influenced by the development and decline of a diatom dominated bloom in the bottom ice with dmsp variations remarkably following chl a variations during the spring summer transition in 2011 the increase in brine volume fraction influencing ice permeability on warming was shown to trigger 1 an important release of dms to the under ice water through brine convection and 2 a vertical redistribution of dmsp across the ice

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

passive microwave observations of the weddell sea during austral winter and early spring the results of multispectral passive microwave observations 6 7 to 90 ghz are presented from the cruises of the fs polarstern in the weddell sea from july to december 1986 this paper includes primarily the analysis of radiometric observations taken at ice station sites averaged emissivity spectra for first year fy ice were relatively constant throughout the experiment and were not statistically different from fy ice signatures in the arctic detailed ice characterization was carried out at each site to compare the microwave signatures of the ice with the physical properties absorption optical depths of fy ice were found to be sufficiently high that only the structure in the upper portions of the ice contributed significantly to interstation emissivity variations the emissivities at 90 ghz e 90 had the greatest variance both e 90 at vertical polarization and gr sub e 90 18 7 defined as e sub v 90 e sub v 18 7 e sub v 90 e sub v 18 7 depended on the scattering optical depth which is a function of the snow grain diameter and layer thickness the variance showed a latitude dependence and is probably due to an increase in the strength of snow metamorphism nearer the northern edge of the ice pack the contribution of variations of near surface brine volume to the emissivity was not significant over the range of values encountered at the station sites emissivity spectra are presented for a range of thin ice types unsupervised principal component analysis produced three significant eigenvectors and showed a separation among four different surface types open water thin ice fy ice and fy ice with a thick snow cover a comparison with smmr satellite data showed that average ice concentrations derived from the ship s ice watch log were consistent with the satellite concentrations the surface based emissivities for fy ice were also compared with emissivities calculated from scanning multichannel microwave radiometer smmr satellite radiances best agreement was found at 6 7 and 10 ghz while at 18 and 37 ghz smmr emissivities were slightly lower than surface based results for the three lower frequencies agreement was found within a confidence limit of 95 and for 37 ghz within about 90

indirect measurements of the mass balance of summer arctic sea ice with an electromagnetic induction technique abstract in the framework of the surface heat budget of the arctic ocean sheba study indirect non invasive icemass balance measurements were carried out at a drifting station in the northern chukchi sea between mayand august of 1998 ice thickness was derived from electromagnetic induction em measurements ofapparent conductivity along 13 profiles 60 to 900 m long as shown through sensitivity studies with a 1 d model the apparent conductivity data from individual points can be inverted to yield estimates of icethickness and ablation with an accuracy of approximately 0 05 m for 2 m thick level ice ablation ratesranged between 8 and 18 mm d 1 with total ablation amounting to roughly 0 9 to 1 2 m measurements ofthickness and melt rates along different profiles in undeformed multi year ice corresponded closely indicating that the sampling statistics are adequate the roughness of undeformed ice has been found toincrease during the summer due to deepening of melt ponds and enhanced bottom melt ice under melt pondswas disproportionately thinner most likely a result of thicker snow cover reducing winter accretion

dissolved organic matter in antarctic sea ice sea ice supports highly dynamic and at times highly productive assemblages of auto and heterotrophic organisms central to the biogeochemical cycling of carbon and nitrogen within sea ice is the production and lability of dissolved organic matter dom dom is produced through excretion mortality cell lysis and amplified by inefficient feeding by grazers it has been hypothesised that there are significant dom pools in sea ice systems although measurements of dom in sea ice have only rarely been made the significance of dom for ice based productivity and carbon turnover therefore remains highly speculative the dissolved organic carbon and nitrogen doc don of sea ice from the amundsen bellingshausen and weddell seas were investigated in 1992 1994 and 1997 measurements were made on melted sea ice sections in 1994 and 1997 and in sea ice brines in 1992 these studies confirm that doc and don can reach up to 30 and 8 times higher concentrations compared to those in surface waters respectively this dom tends to be carbon enriched with a mean doc don ratio of 14 measurements made on a limited data set showed that carbohydrates constitute on average 35 of the doc pool with highly variable contributions

thermal expansion coefficients for sea ice coefficients of thermal linear expansion were determined for sea ice using a michelson interferometer over a temperature range of 4 to 15 c the coefficients varied from 45 10 6 to 54 10 6 c 1 for ice with a salinity of 2 ppt and from 33 10 6 to 53 10 6 c 1 for ice with a salinity of 4 ppt initially warming the sea ice resulted in coefficients that were the same as those for fresh water ice within the limits of experimental error subsequent sea ice cooling resulted in coefficients that were initially lower than those for fresh water ice but that asymptotically approached the coefficient values for fresh water ice at colder temperatures on the second warming and cooling cycle the coefficients of thermal linear expansion exhibited hysteresis and a decrease in magnitudes we have also shown that pettersson s 1883 and malmgren s 1927 measurements of the thermal volume expansion of sea ice were the result of phase transitions that caused brine expulsion when air free sea ice was cooled and internal porosity increases when sea ice was warmed our results indicate that petterson s 1883 and malmgren s 1927 measurements of the thermal volume expansion of sea ice are in error consequently theoretical descriptions based on their results are incorrect anderson 1960 zubov and savelyev given in doronin and kheisin 1977 doronin and kheisin 1977 our results for the initial sea ice warming cycle do agree with cox s 1983 analysis

search for proxy indicators of young sea ice thickness the determination of young sea ice thickness from space remains an elusive goal for those interested in the interaction of the oceans and the atmosphere the thermal and chemical state of the ocean and sea ice dynamics recent experiments and models have shown relationships between active and passive microwave signatures of new growing ice and ice thickness the two processes that dominate in determining the microwave signature are changes in dielectric properties and changes in surface roughness in this paper we investigate the competition between these two processes in determining radar backscatter the usefulness of surface roughness as an indicator of young ice thickness and the optimum sensor parameters for observing changes in scattering linked to ice thickness we present simulations that are based on radar observations made on laboratory grown saline ice these observations confirm that surface scattering dominates over volume scattering for 13 9 ghz radar backscatter from young rough ice at most angles and for young smooth ice below 30 although rms roughness and backscatter at 5 3 and 13 9 ghz 23 incidence and vv polarization increase together after about 10 cm of ice growth under quiet conditions it is unlikely that surface roughness and ice thickness are simply connected in real sea ice where surface roughness can change rapidly due to the action of wind waves and snow simulations show however that formation of frost flowers is detectable by spaceborne radar and can serve to classify ice of roughly 5 20 cm thickness since it is a distinct transient event that occurs under physical conditions that constrain the thickness of the ice our experimental data show that future sensors operating near 12 incidence may offer potential for probing the relationship between near surface dielectric properties and ice thickness since the effects of variability in roughness and snowfall are minimized near this angle

in situ measurements of the direct current conductivity of antarctic sea ice implications for airborne electromagnetic sounding of sea ice thickness airborne ship borne and surface low frequency electromagnetic em methods have become widely applied to measure sea ice thickness em responses measured over sea ice depend mainly on the sea water conductivity and on the height of the sensor above the sea ice sea water interface but may be sensitive to the sea ice conductivity at high excitation frequencies we have conducted in situ measurements of direct current conductivity of sea ice using standard geophysical geoelectrical methods sea ice thickness estimated from the geoelectrical sounding data was found to be consistently underestimated due to the pronounced vertical to horizontal conductivity anisotropy present in level sea ice at five sites it was possible to determine the approximate horizontal and vertical conductivities from the sounding data the average horizontal conductivity was found to be 0 017 s m 1 and that in the vertical direction to be 9 12 times higher em measurements over level sea

hydrogeochemistry groundwater ages and sources of salts in a granitic batholith on the canadian shield southeastern manitoba abstract the hydrogeochemistry of the lac du bonnet granitic batholith has been determined for the region of the whiteshell research area wra in southeastern manitoba canada this work forms part of the geosciences studies performed for the canadian nuclear fuel waste management program over the period 1980 1995 by atomic energy of canada limited aecl knowledge of the variation of groundwater chemistry and its causes is useful in assessing the performance and safety of a nuclear fuel waste vault located at depths of up to 1000 m in a crystalline rock formation of the canadian shield groundwaters and matrix pore fluids have been obtained by standard sampling methods from shallow piezometers in clay rich overburden from packer isolated borehole zones intersecting fractures or fault zones in the bedrock and from boreholes in unfractured rock in aecl s underground research laboratory url eighty six individual fracture groundwaters have been sampled and analysed from permeable zones in 53 boreholes drilled to depths of up to 1000 m in the lac du bonnet batholith in addition 28 groundwaters from piezometers in a large wetland area near the url have been sampled and analysed to determine the influence of clay rich overburden on the bedrock hydrogeochemistry analyses have been made for major and minor ions ph eh trace metals and stable and radioactive isotopes to characterise these groundwaters and relate them to their hydrogeologic regimes shallow groundwaters in the fractured bedrock are generally dilute tds 500 m na ca cl so4 waters of increasing salinity up to 50 g l with depth are found and in some fractures the waters have evolved to a ca na cl composition isotopic data indicate that these waters are warm climate and pre glacial in origin with residence times of over 1 ma pore fluids observed to drain from the unfractured rock matrix in the url facility are almost pure ca cl in composition 90 g l salinity and have a 2h 18o composition displaced well to the left of the global meteoric water line about which all other wra groundwaters lie this information indicates that these pore fluids have undergone prolonged water rock interaction and have residence times of 101 103 ma most of the deeper fracture groundwaters and pore fluids have low br cl ratios and moderate to high 34s values of dissolved so4 which indicates that their salinity could be derived from a marine source such as the basinal sedimentary brines and evaporites to the west of the batholith these fluids may have entered the batholith during early paleozoic times when sedimentary rocks were deposited over the granite and were driven by a hydraulic gradient resulting from higher ground in western canada the hydrogeochemical data and interpretations show that below 500 m in the wra fracture hosted groundwaters are very saline reducing and old and are therefore indicative of stagnant conditions over the period of concern for nuclear waste disposal 1 ma the intact rock matrix at these depths is extremely impermeable as indicated by the presence of pore fluids with unusual geochemical and isotopic characteristics the pore fluids may represent basinal brines that have evolved geochemically and isotopically to their current composition over periods as long as 103 ma

crack velocities in freshwater and saline ice this paper presents experimental results on both mode 1 and 2 crack velocities measured in a wide variety of ice types columnar sea ice columnar lake ice laboratory grown columnar saline ice and freshwater columnar and granular ice in the temperature range from 5 to 35 c measurements of ice electrical conductance electrical capacitance and electromagnetic emissions from cracks as a function of time were used to determine crack velocities in samples with dimensions ranging from 0 05 to 30 m in laboratory grown freshwater ice and in lake ice average crack velocities varied from a few hundred to 1320 m s in contrast in natural sea ice and laboratory grown saline ice crack velocity was very low at about 10 m s this remarkable difference in the velocity of cracks growing in freshwater and saline ice is probably due to the dynamic resistance of unfrozen water in brine pockets and or the large size of a crack tip process zone in saline ice it was also found that cracks propagate discontinuously in saline ice owing to the strong interaction with microstructural elements such as drainage channels

first in situ determination of gas transport coefficients do2 dar and dn2 from bulk gas concentration measurements o2 n2 ar in natural sea ice we report bulk gas concentrations of o2 n2 and ar as well as their transport coefficients in natural landfast subarctic sea ice in southwest greenland the observed bulk ice gas composition was 27 5 o2 71 4 n2 and 1 09 ar most previous studies suggest that convective transport is the main driver of gas displacement in sea ice and have neglected diffusion processes according to our data brines were stratified within the ice so that no convective transport could occur within the brine system therefore diffusive transport was the main driver of gas migration by analyzing the temporal evolution of an internal gas peak within the ice we deduced the bulk gas transport coefficients for oxygen do2 argon dar and nitrogen dn2 the values fit to the few existing estimates from experimental work and are close to the diffusivity values in water 10 5 cm2 s 1 we suggest that gas bubbles escaping from the brine to the atmosphereas the ice gets more permeable during meltcould be responsible for the previously reported high transport coefficients these results underline that when there is no convective transport within the sea ice the transport of gas by diffusion through the brines either in the liquid or gaseous phases is a major factor in controlling the ocean atmosphere exchange

optical properties of melting landfast sea ice and underlying seawater in santala bay gulf of finland 1 in march and early april 2000 spectral irradiance measurements were conducted on 10 occasions above and beneath the landfast sea ice in santala bay near the entrance to the gulf of finland the measurements included the spectral albedo and transmittance of the sea ice and the downwelling and upwelling spectral irradiance at different depths in the water column spectral albedos integrated over 400 700 nm photosynthetically active radiation par were in the range of 0 16 0 58 with most common values between 0 33 and 0 42 maximum transmittances for the ice are found close to 570 nm decreasing toward shorter and longer wavelengths correspondingly diffuse attenuation coefficients for both seawater and sea ice agree well with earlier measurements in the baltic sea and have a par attenuation of 0 4 0 7 and 3 1 4 7 m 1 respectively during the measurement period the ice reached its maximum thickness of 28 cm and thereafter started to decay the sea ice was snow free however the formation of high scattering melt freeze layers above the freeboard largely increased the surface reflectance discharged meltwater was retained beneath the sea ice forming a low salinity layer which only disappeared as the ice ablated in april compared with many parts of the arctic the sea ice and seawater in santala bay contain higher amounts of dissolved and particulate matter which are indicated by high absorption at wavelengths below 700 nm and thus potentially increase the melt rate of the sea ice

surface and melt pond evolution on landfast first year sea ice in the canadian arctic archipelago the evolution of landfast sea ice melt pond coverage surface topography and mass balance was studied in the canadian arctic during may june 2011 and 2012 using a terrestrial laser scanner snow and sea ice sampling and surface meteorological characterization initial melt pond formation was not limited to low lying areas rather ponds formed at almost all premelt elevations the subsequent evolution of melt pond coverage varied considerably between the 2 years owing to four principle temporally variable factors first the range in premelt topographic relief was 0 5 m greater in 2011 rougher surface than in 2012 smoother surface such that a seasonal maximum pond coverage of 60 and maximum hydraulic head of 204 mm were reached in 2011 versus 78 and 138 mm in 2012 a change in the meltwater balance production minus drainage caused the ponds to spread or recede over an area that was almost 90 larger in 2012 than in 2011 second modification of the premelt topography was observed during mid june due to preferential melting under certain drainage channels some of the lowest lying premelt areas were subsequently elevated above these deepening channels and unexpectedly became drained later in the season third ice interior temperatures remained 1 2 c colder later into june in 2012 than in 2011 even though the ice was 0 35 m thinner at melt onset thereby delaying permeability increases in the ice that would allow vertical meltwater drainage to the ocean finally surface melt was estimated to account for approximately 62 of the net radiative flux to the sea ice cover during the melt season

improved 1d inversions for sea ice thickness and conductivity from electromagnetic induction data inclusion of nonlinearities caused by passive bucking the porosity of sea ice is a fundamental physical parameter that governs the mechanical strength of sea ice and the mobility of gases and nutrients for biological processes and biogeochemical cycles in the sea ice layer however little is known about the spatial distribution of the sea ice porosity and its variability between different sea ice types an efficient and nondestructive method to measure this property is currently missing sea ice porosity is linked to the bulk electrical conductivity of sea ice a parameter routinely used to discriminate between sea ice and seawater by electromagnetic em induction sensors here we have evaluated the prospect of porosity retrieval of sea ice by means of bulk conductivity estimates using 1d multifrequency em inversion schemes we have focused on two inversion algorithms a smoothness constrained inversion and a marquardt levenberg inversion which we modified for the nonlinear signal bias caused by a passive bucking coil operated in such a highly conductive environment using synthetic modeling studies 1d inversion algorithms and multiple frequencies we found that we can resolve the sea ice conductivity within 0 01 s m using standard assumptions for the conductivity porosity relation of sea ice we were able to estimate porosity with an uncertainty of 1 2 which enables efficient and nondestructive surveys of the internal state of the sea ice cover

high resolution dimethyl sulfide and dimethylsulfoniopropionate time series profiles in decaying summer first year sea ice at ice station polarstern western weddell sea antarctica high resolution profiles of ice dimethyl sulfide dms and dimethylsulfoniopropionate dmsp concentrations were measured together with a suite of ancillary physical and biological properties during a time series of decaying summer level first year sea ice throughout december 2004 during the ice station polarstern drift experiment western weddell sea antarctica ice dmsp and dms concentrations were always maximum at the bottom of the ice sheet 636 2627 and 292 1430 nm respectively where the highest chlorophyll a levels were also found 15 30 g l 1 throughout the observation period the autotrophic surface community 32 205 g c l 1 was dominated by phaeocystis sp while the bottom community 1622 3830 g c l 1 mainly consisted of pennate diatoms this illustrates that although being known for lower dmsp to chlorophyll a ratios than phaeocystis sp diatoms dominated the overall dmsp production because of their much larger biomass decreasing dmsp concentrations and increasing dms to dmsp ratios in the bottom layers with time suggested active dmsp to dms conversion in a slowly degrading environment drastic temporal brine volume and brine salinity changes associated with the decaying sea ice cover are shown to directly impact 1 the migration of dmsp and dms through the brine network 2 the dmsp to dms conversion processes within the ice interior and 3 the physiological response of the ice algae first order flux estimates show that decaying summer level first year sea ice alone can significantly contribute to the regional sulfur budget of the weddell sea with an estimated average loss rate of 5 7 mol dms p m 2 d 1 toward the atmosphere and the ocean copyright 2010 by the american geophysical union

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

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

linkages between salinity and brine channel distribution in young sea ice a high resolution study of bulk salinity was undertaken on laboratory grown sea ice to determine the extent of spatial variability of salinity and whether this was associated with brine channel structures ice samples at two different stages of development were compared with respect to physical state brine distribution and brine channel structures cold growing sea ice is shown to have steep bulk salinity gradients and a highly variable brine distribution that is closely linked to the location and morphology of brine channels areas of high bulk salinity are found to correspond directly to the positions of the brine channels and these areas are surrounded by ice that shows significant brine depletion it is observed that redistribution of the brine occurs as the ice cover goes through warming and melting phases the redistribution is attributed to an increase in porosity and pore connectivity permitting migration of brine through the ice the distribution of brine in warm ice is shown to be more homogeneous and independent of brine channel structures a number of mechanisms exploiting the enhanced mobility of brine in warm sea ice are used to explain the changes in the salinity profiles and brine distribution

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

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

comparing methods of measuring sea ice density in the east antarctic remotely sensed derivation of sea ice thickness requires sea ice density sea ice density was estimated with three techniques during the second sea ice physics and ecosystem experiment sipex ii september november 2012 east antarctica the sea ice was first year highly deformed mean thickness 1 2 m with layers consistent with rafting and 6 7 10 columnar ice and 3 10 granular ice ice density was found to be lower than values 900 920 kg m 3 used previously to derive ice thickness with columnar ice mean density of 870 kg m 3 at two different ice stations the mean density of the ice was 870 and 800 kg m 3 the lower density reflecting a high percentage of porous granular ice at the second station error estimates for mass volume and liquid solid water methods are presented with 0 1 m long 0 1 m core samples the error on individual density estimates is 28 kg m 3 errors are larger for smaller machined blocks errors increase to 46 kg m 3 if the liquid solid volume method is used the mass volume method has a low bias due to brine drainage of at least 5 bulk densities estimated from ice and snow measurements along 100 m transects were high and likely unrealistic as the assumption of isostatic balance is not suitable over these length scales in deformed ice

overview of geological and hydrogeological conditions of the aspo hard rock laboratory site abstract the site of the underground facility the aspo hard rock laboratory was excavated at a depth of 450 m below the island of aspo and has been extensively investigated by geological hydrogeological and hydrochemical methods as part of the geoscientific research for disposal of nuclear waste in sweden the geological history of the area dates back to 1 85 ga and is dominated by granitoids belonging to the trans scandinavian igneous belt but also includes basic sheets and xenoliths and dikes of fine grained granite seven tectonic episodes giving rise to fracture mineralization are recognised the major discontinuities and fracture zones were characterised from surface investigations before the tunnel construction work started these structural features were also identified in the tunnel and are as predicted the major water conducting features sets of open fractures in the nnw nw and n s directions and the brittle fine grained granite are other important water conductors groundwater flow modelling shows that the location of aspo island has a major impact on the current distribution of groundwater salinity due to varying hydraulic boundary conditions in the late and post glacial period

iron biogeochemistry in antarctic pack ice during sipex 2 our study quantified the spatial and temporal distribution of fe and ancillary biogeochemical parameters at six stations visited during an interdisciplinary australian antarctic marine science voyage sipex 2 within the east antarctic first year pack ice zone during september october 2012 unlike previous studies in the area the sea ice chlorophyll a particulate organic carbon and nitrogen poc and pon maxima did not occur at the ice water interface because of the snow loading and dynamic processes under which the sea ice formed iron in sea ice ranged from 0 9 to 17 4 nm for the dissolved 0 2 m fraction our results highlight that the concentration of particulate fe in sea ice was highest when approaching the continent the high poc concentration and high particulate iron to aluminium ratio in sea ice samples demonstrate that 71 of the particulate fe was biogenic in composition our estimated fe flux from melting pack ice to east antarctic surface waters over a 30 day melting period was 0 2 mol m2 d of dfe 2 7 mol m2 d of biogenic pfe and 1 3 mol m2 d of lithogenic pfe these estimates suggest that the fertilization potential of the particulate fraction of fe may have been previously underestimated due to the assumption that it is primarily lithogenic in composition our new measurements and calculated fluxes indicate that a large fraction of the total fe pool within sea ice may be bioavailable and therefore effective in promoting primary productivity in the marginal ice zone

impact of sea ice processes on the carbonate system and ocean acidification at the ice water interface of the amundsen gulf arctic ocean 1 from sea ice formation in november 2007 to onset of ice melt in may 2008 we studied the carbonate system in first year arctic sea ice focusing on the impact of calciumcarbonate caco3 saturation states of aragonite xar and calcite xca at the ice water interface uiw based on total inorganic carbon ct and total alkalinity at and derived ph co2 carbonate ion co3 22 concentrations and x we investigated the major drivers such as brine rejection caco3 precipitation bacterial respiration primary production and co2 gas flux in sea ice brine frost flowers and uiw we estimated large variability in seaice ct at the top mid and bottom ice changes due to caco3 and co2 gas flux had large impact on ct in the whole ice core from march to may bacterial respiration was important at the bottom ice during all months and primary production in may it was evident that the sea ice processes had large impact on uiw resulting in a five times larger seasonal amplitude of the carbonate system relative to the upper 20 m during ice formation co2 increased by 30 mmol kg 21 co 3 22 decreased by 50 mmol kg 21 and the xar decreased by 0 8 in the uiw due to co2 enriched brine from solid caco3 conversely during ice melt co3 22 increased by 90 mmol kg 21 in the uiw and x increased by 1 4 between march and may likely due to caco3 dissolution and primary production we estimated that increased ice melt would lead to enhanced oceanic uptake of inorganic carbon to the surface layer

on the effect of phase transformations on saline ice compliance to obtain a better understanding of the compliance of saline ice we developed a simple conceptual model of a process that presumably takes place in saline ice using elastic models we assessed the role that phase transformations might play when brine is sealed into small cells during crystal growth cooling of a sealed brine cell leading to the precipitation of ice provides a mechanism for the accumulation of large localized stresses based on our analysis this mechanism has the potential to be a significant source for the nucleation of dislocations and can conceivably make a significant contribution to the greater compliance softness of saline ice relative to non saline ice the results of this model are consistent with the observation that laboratory grown saline crystals sometimes display extensive differences in mechanical behavior that appear to be due to variations in the growth and storage conditions experienced by the crystals

regional scale groundwater flow in a canadian shield setting a three dimensional numerical analysis of a 5734 km2 watershed situated in the canadian shield has been conducted to illustrate aspects of regional scale groundwater flow in a crystalline rock setting an essential requirement of the analysis is the preservation and accurate description of the complex topography surface water drainage network groundwater salinity distribution and permeability distributions the postglacial evolution of the groundwater flow system was investigated using the finite difference model swift iii robustness was assessed by exploring the sensitivity of groundwater flow to topography variable matrix permeability distribution models pore water salinity and the dissipation of elevated initial pore pressures that result from ice that overlaid the watershed in the last glacial period groundwater flow analyses indicate that freshwater heads in all model layers are highly correlated with the complex surface topography such that the transition from zones of groundwater recharge t

antarctic sea ice carbon dioxide system and controls 1 in austral summer from december 2008 to january 2009 we investigated the sea ice carbon dioxide co2 system and co2 controls in the amundsen and ross seas antarctica we sampled seawater brine and sea ice for the measurements of total alkalinity at total inorganic carbon dic ph inorganic nutrients particulate organic carbon poc and nitrogen pon chlorophyll a pigments salinity and temperature large variability in all measured parameters was observed in time and space due to the complex sea ice dynamics we discuss the controls of the sea ice co2 system such as brine rejection biological processes calcium carbonate caco3 precipitation dissolution and co2 exchange most 80 to 90 of the dic loss was due to brine rejection which suggests that the sea ice acted as an efficient dic sink from 0 8 and 2 6 mol m 2 yr 1 9 6 31 g c m 2 yr 1 the remaining change in dic was to a large extent explained by net biological production the at dic ratio in the sea ice was higher than in the under ice water uiw with ratios reaching 1 7 which indicated caco3 precipitation and concomitant dic loss in the sea ice elevated at dic ratios and carbonate concentrations were also observed in the uiw which reflect the solid caco3 rejected from the ice during melt the potential for uptake of atmospheric co2 in the mixed layer increased by approximately 56 atm due to the combined effect of caco3 precipitation during ice formation and ice melt in summer

a salt flux model for salinity change through ice production in the greenland sea and its relationship to winter convection 1 a salt flux model which incorporates ice formation advection and melt as well as time dependent brine drainage from frazil pancake ice has been developed for the central greenland sea in winter information from ice drifting buoys suggests that this region can be thought of as similar to a latent heat polynya with the wind blowing newly formed sea ice constantly in a southerly or southeasterly direction such that it melts in a different area from that of its formation the result is a salt refinement process generating a net positive salt flux over the ice formation region which may play an important role in stimulating deep open ocean convection by combining buoy data ecmwf meteorological data and passive microwave ice concentration data the model is used to estimate the sea ice derived salt flux over the 1996 1997 winter salt fluxes of over 40 kg m 2 were obtained in the center of the region which corresponds closely an area where a maximum depth of convection is seen in winter cruises the model gives realistic results when compared with in situ ice and oceanographic data gathered in the region and suggests that ice formation and drift play an important role in the preconditioning of surface waters for deep water formation events

the role of snow on the thermal dependence of microwave backscatter over sea ice our understanding of snow distribution in the polar regions is severely restricted owing to the heterogeneity both in space and time of this solid precipitate processes such as vapor and mass fluxes across the interface are to a large extent controlled by the presence and geophysical state of the snow cover on sea ice numerous studies have shown the importance of snow cover in ecosystem processes and particularly in photosynthetically active radiation extinction researchers are currently exploiting developments in electromagnetic interaction theory in an attempt to measure snow thickness distributions remotely in this paper we investigate the dependence of radar backscatter on snow thickness over smooth first year ice we use data from the seasonal sea ice monitoring and modeling site located in the canadian archipelago results show that the thermodynamics of the snow cover affect wave propagation attenuation and scattering through the control that brine volume exerts on interfacial characteristics of the snow and ice layers the effect is subtle and specific to certain ranges of salinity surface roughness and thickness of sea ice we describe the phenomenon responsible for this effect using a microwave model consistently for both complex effective permittivities and backscatter coefficients coupled to a one dimensional model we validate the physical principles using in situ field data we then discuss the potential of synthetic aperture radar in estimating snow thickness distributions under these specific conditions using both observed and modeled microwave scattering

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

high turnover rates indicated by changes in the fixed n forms and their stable isotopes in antarctic landfast sea ice we report concentration and nitrogen and oxygen isotopic measurements of nitrate total dissolved nitrogen and particulate nitrogen from antarctic landfast sea ice covering almost the complete seasonal cycle of sea ice growth and decay from april to november when sea ice forms in autumn ice algae growth depletes nitrate and accumulates organic n within the ice subsequent low biological activity in winter imposes minor variations in the partitioning of fixed n in early spring the coupling between nitrate assimilation and brine convection at the sea ice bottom traps a large amount of fixed n within sea ice up to 20 times higher than in the underlying seawater at this time remineralization and nitrification also accelerate yielding nitrate concentrations up to 5 times higher than in seawater nitrate 15n and 18o are both elevated indicating a near balance between nitrification and nitrate assimilation these findings require high microbially mediated turnover rates for the large fixed n pools including nitrate when sea ice warms in the spring ice algae grow through the full thickness of the ice the warming stratifies the brine network which limits the exchange with seawater causing the once elevated nitrate pool to be nearly completely depleted the nitrate isotope data point to light limitation at the base of landfast ice as a central characteristic of the environment affecting its n cycling e g allowing for nitrification and impacting algal physiology e g as reflected in the n and o isotope effects of nitrate assimilation

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