influence of snow depth and surface flooding on light transmission through antarctic pack ice snow on sea ice alters the properties of the underlying ice cover as well as associated physical and biological processes at the interfaces between atmosphere sea ice and ocean the antarctic snow cover persists during most of the year and contributes significantly to the sea ice mass due to the widespread surface flooding and related snow ice formation snow also enhances the sea ice surface reflectivity of incoming shortwave radiation and determines therefore the amount of light being reflected absorbed and transmitted to the upper ocean here we present results of a case study of spectral solar radiation measurements under antarctic pack ice with an instrumented remotely operated vehicle in the weddell sea in 2013 in order to identify the key variables controlling the spatial distribution of the under ice light regime we exploit under ice optical measurements in combination with simultaneous characterization of surface properties such as sea ice thickness and snow depth our results reveal that the distribution of flooded and nonflooded sea ice areas dominates the spatial scales of under ice light variability for areas smaller than 100 m by 100 m however the heterogeneous and highly metamorphous snow on antarctic pack ice obscures a direct correlation between the under ice light field and snow depth compared to the arctic light levels under antarctic pack ice are extremely low during spring 0 1 this is mostly a result of the distinctly different dominant sea ice and snow properties with seasonal snow cover including strong surface melt and summer melt ponds in the arctic and a year round snow cover and widespread surface flooding in the southern ocean

seasonal contrasts in snow cover characteristics on ross sea ice floes snow cover characteristics on ice floes in the ross sea antarctica were examined during cruises in autumn 1998 and summer 1999 the autumn snow cover was shallower colder and had higher and more variable salinity and smaller single and composite grain sizes than the summer snow cover the autumn snow cover was dominated by rounded particles in chains of grains and clusters while the summer snow cover was composed primarily of melt clusters there was extensive flooding of the summer snow cover at the snow ice interface the summer snow cover was nearly isothermal and close to the melting point it exhibited obvious signs of melting and refreezing in the form of ice lenses pipes and superimposed ice although no melt ponds were evident many of the ice lenses were located directly above the saline standing water found on most of the summer ice floes

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

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

meltwater circulation and permeability of arctic summer sea ice derived from hydrological field experiments abstractpermeability and meltwater flow have been studied in sea ice in the siberian and central arctic during the summers of 1995 and 1996 a bail test technique has been adapted to allow for measurements of in situ permeability found to range between 1011 and 108 m2 permeability varied by about a factor of 2 between 1995 above normal melt rates and 1996 below normal melt rates release of fluorescent tracers fluoresceine rhodamine furthermore allowed the derivation of flow velocities and assessment of the relevant driving forces hydraulic gradients in rough ice and wind stress in ponded ice were found to be particularly important driving meltwater over distances of several m day1 the mid to late summer ice was found permeable enough to completely divert meltwater from the surface into the ice interior it could be shown however that lower permeabilities of the upper ice layers as well as refreezing of meltwater are associated with significantly lower permeabilities in particular during the early melt season fostering development of surface melt ponds

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

sea ice atmosphere and upper ocean variability in the weddell sea antarctica a frequency domain singular value decomposition is performed on 20 years 1979 1998 of monthly sea ice concentration sea ice drift and sea level pressure data in the weddell sea antarctica interannual oscillations with periods of around 3 4 years are found to dominate the variability in this region anomalous atmospheric patterns periodically reach the weddell sea from the west and perturb the sea ice circulation and distribution in the weddell gyre through changes in the intensity and direction of the climatological winds sea ice accumulates in the southeastern weddell sea every 3 4 years owing to two atmospherically driven processes 1 weak ice export to the north due to a weak northward branch of the gyre driven by weak southerly winds and 2 large ice import from the east due to a strong east wind drift driven by strong easterly winds along the coast the opposite situation gives rise to a depletion of sea ice in the same region half a cycle later sea ice anomalies are then advected north northeastward before turning eastward in the gyre circulation the eastward propagation of ice anomalies along the ice margin accounts for the passage of the antarctic circumpolar wave through the atlantic sector of the southern ocean a low frequency signal is also detected in the weddell sea variations albeit rather speculatively in this 20 year long record sea ice variability on this timescale appears to be associated with a change in the shape and characteristics of the weddell gyre circulation around 1990 this mode of variability implicates feedbacks between the gyre and weddell deep water temperature variations whose impact is observed near the maud rise topographic feature

snow thickness profiling on antarctic sea ice with gpr rapid and accurate measurements with the potential to upscale needles to a haystack snow thickness on sea ice is a largely under sampled parameter yet of importance for the sea ice mass balance and for satellite based sea ice thickness estimates and thus our general understanding of global ice volume change traditional direct thickness measurements with meter sticks can provide accurate but only spot information referred to as needles due to their pinpoint focus and information while airborne and satellite remote sensing snow products referred to as the haystack have large uncertainties due to their scale we demonstrate the remarkable accuracy and applicability of ground penetrating radar gpr snow thickness measurements by comparing them with in situ meter stick data from two field campaigns to antarctica in late winter early spring the efficiency and millimeter to centimeter accuracy of gpr enables practitioners to acquire extensive semi regional data with the potential to upscale needles to the haystack and to potentially calibrate satellite remote sensing products that we confirm to derive roughly 30 of the in situ thickness we find the radar wave propagation velocity in snow to be rather constant 6 encouraging regional snow thickness surveys snow thinner than 10 cm is under the detection limit with the off the shelf gpr setup utilized in our study

upper mantle structure at walvis ridge from pn tomography abstract passive continental margins offer the unique opportunity to study the processes involved in continental extension and break up within the lispwal lithospheric structure of the namibian continental passive margin at the intersection with the walvis ridge from amphibious seismic investigations project combined on and offshore seismic experiments were designed to characterize the southern african passive margin at the walvis ridge in northern namibia in addition to extensive analysis of the crustal structures we carried out seismic investigations targeting the velocity structure of the upper mantle in the landfall region of the walvis ridge with the namibian coast upper mantle pn travel time tomography from controlled source amphibious seismic data was used to investigate the sub moho upper mantle seismic velocity we succeeded in imaging upper mantle structures potentially associated with continental break up and or the tristan da cunha hotspot track we found mostly coast parallel sub moho velocity anomalies interpreted as structures which were created during gondwana break up

sea ice and snow thickness and physical properties of an ice floe in the western weddell sea and their changes during spring warming helicopter borne and ground based electromagnetic em ice thickness and ruler stick snow thickness measurements as well as ice core analyses of ice temperature salinity and texture were performed over a 5 week observation period between november 27 2004 and january 2 2005 on an ice floe in the western weddell sea at approximately 67 s 55 w the study was part of the ice station polarstern ispol expedition of german research icebreaker r v polarstern investigating changes of physical biological and biogeochemical properties during the spring warming as a function of atmospheric and oceanic boundary conditions the ice floe was composed of fragments of thin and thick first year ice and thick second year ice with modal total thicknesses of 1 2 1 3 2 1 and 2 4 2 9 m respectively this included modal snow thicknesses of 0 2 0 5 m on first year ice and 0 75 m on second year ice during the observation period snow thickness decreased by less than 0 2 m there was hardly any ice thinning warming of snow and ice between 0 1 and 1 9 c resulted in decreased ice salinity and increased brine volume direct current dc geoelectric and electromagnetic em induction depth sounding were performed to study changes of electrical ice conductivity as a result of the observed ice warming bulk ice conductivity increased from to 37 to 97 ms m analysis of conductivity anisotropy showed that the horizontal ice conductivity changed from 9 to 70 ms m these conductivity changes have only negligible effects on the thickness retrieval from em measurements

tidal forcing on sea ice drift and deformation in the western weddell sea in early austral summer 2004 abstract sea ice drift and deformation in the western weddell sea in early austral summer of 2004 are characterised using in situ data from a meso scale array of 24 drifting ice buoys horizontal gps derived position measurements are available from drifting buoys deployed as part of the ice station polarstern ispol experiment for 26 days during late november and december 2004 at various temporal resolutions and spatial accuracies these data form the basis for sea ice velocity and deformation measurements across the meso scale ispol array and at two remote sites analysis of the sea ice velocities reveals coherence for sea ice drift at separations of less than 70 km and a correlation length scale of 60 km within the limits of the ispol array at larger separations zonal ice drift remains correlated while meridional ice drift becomes uncorrelated this together with the east west gradient in ice velocities indicates the influence of bathymetry via tidal forcing on local dynamic processes atmospheric forcing also contributes to the sea ice drift about 40 of variability in the sea ice velocity is explained by changes in wind velocity which is significantly less than other studies have found for the region during winter sea ice deformation has been derived for the overall array and four sub arrays there appeared to be no spatial scale dependency of ice deformation although considerable spatial variability was observed between sub arrays the net divergence of the ispol array was in excess of 30 with the largest contributions to divergence being from the southern section and along the eastern side of the overall ispol array temporal variability for all deformation parameters is dominated by high frequency sub daily processes namely tidal forcing and inertial response low frequency multiple days processes including atmospheric changes played a secondary role in forcing sea ice deformation during ispol

snow depth of the weddell and bellingshausen sea ice covers from icebridge surveys in 2010 and 2011 an examination we examine the snow radar data from the weddell and bellingshausen seas acquired by eight icebridge oib flightlines in october of 2010 and 2011 in snow depth retrieval the sidelobes from the stronger scattering snow ice s i interfaces could be misidentified as returns from the weaker air snow a s interfaces in this paper we first introduce a retrieval procedure that accounts for the structure of the radar system impulse response followed by a survey of the snow depths in the weddell and bellingshausen seas limitations and potential biases in our approach are discussed differences between snow depth estimates from a repeat survey of one weddell sea track separated by 12 days without accounting for variability due to ice motion is 0 7 13 6 cm average snow depth is thicker in coastal northwestern weddell and thins toward cape norvegia a decrease of 30 cm in the bellingshausen the thickest snow is found nearshore in both octobers and is thickest next to the abbot ice shelf snow depth is linearly related to freeboard when freeboards are low but diverge as the freeboard increases especially in the thicker rougher ice of the western weddell we find correlations of 0 71 0 84 between snow depth and surface roughness suggesting preferential accumulation over deformed ice retrievals also seem to be related to radar backscatter through surface roughness snow depths reported here generally higher than those from in situ records suggest dissimilarities in sample populations implications of these differences on antarctic sea ice thickness are discussed

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

mapping spherical seismic into physical structure biases from 3 d phase transition and thermal boundary layer heterogeneity summary earth s mantle is to a very good first approximation spherically symmetric with lateral deviations in seismic velocities and density of only a few per cent this observation has led to the common assumption that average radial seismic models reflect the mantle s average physical structure we test this assumption by using a set of dynamically generated mantle structures and comparing seismic velocities for the average radial physical state with laterally averaged seismic velocities the thermal and thermochemical dynamic circulation models are earth like in terms of convective vigour thermal structure and geographical pattern of heterogeneity we find that in general averaged seismic structure is not distinguishable from the seismic structure of the physical average within the uncertainty bounds of seismic reference models an exception is near phase boundaries where phase boundary topography broadens the averaged seismic jump relative to the discontinuity at physical reference conditions in an inversion for 1 d seismic structure where narrow discontinuities are imposed these biases may map into a lower jump and substantially stronger velocity gradients above and below the interface than are actually present other small biases in averaged structure occur in thermal boundary layers including those that form above chemical piles these biases are caused by large lateral variations in temperature not compositional variability

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

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

the importance of diurnal processes for the seasonal cycle of sea ice microwave brightness temperatures during early summer in the weddell sea antarctica over the perennial sea ice in the western and central weddell sea antarctica the onset of summer is accompanied by a significant decrease of sea ice brightness temperatures tb as observed by passive microwave radiometers such as the special sensor microwave imager ssm i the summer specific tb drop is the dominant feature in the seasonal cycle of tb data and represents a conspicuous difference to most arctic sea ice regions where the onset of summer is mostly marked by a rise in tb data from a 5 week drift station through the western weddell sea in the 2004 05 austral summer ice station polarstern ispol helped with identifying the characteristic processes for antarctic sea ice in situ glaciological and meteorological data in combination with ssm i swath satellite data indicate that the cycle of repeated diurnal thawing and refreezing of snow freeze thaw cycles is the dominant process in the summer season with the absence of complete snow wetting the resulting metamorphous snow with increased grain size as well as the formation of ice layers leads to decreasing emissivity enhanced volume scattering and increased backscatter this causes the summer tb drop

spatial and temporal variability in snowmelt onset over arctic sea ice climate models suggest surface warming in the arctic will be rapid and pronounced implying substantial changes in snowmelt onset are likely this research therefore examines spatial and temporal variability in passive microwave derived snowmelt onset dates over arctic sea ice the objectives are to understand better the regional characteristics of snowmelt and to document whether the snowmelt onset record shows signs of climate change snowmelt onset dates are derived with scanning multichannel microwave radiometer and special sensor microwave imager brightness temperature data and they are subsequently stratified into 13 regions to analyze spatial and temporal variability results illustrate significant spatial variability in snowmelt onset with the median annual snowmelt onset date in one region of the arctic typically being statistically different from most other regions the examination of temporal variability also shows large interannual differences in the median snowmelt onset date in most regions additionally trends towards earlier snowmelt onset are documented in the vvest central arctic lincoln sea beaufort sea and canadian arctic archipelago regions

weddell sea ice drift kinematics and wind forcing ice drift in the weddell sea was studied on the basis of positional and meteorological data from argos buoys drifting in 1990 1992 and surface pressure analyses from the european centre for medium range weather forecasts ecmwf the drift kinematics showed differences between the eastern and western parts of the weddell sea close to the antarctic peninsula the ice drifted as an almost nonrotating uniform field at a low speed having reduced small scale motions with little meandering compared to regions further to the east inertial motion was detected from the ice drift in areas east of 35 w and in the region of the antarctic circumpolar current on timescales of days wind was the primary forcing factor for the drift a linear model between the wind and ice drift explained 40 80 of the drift velocity variance the degree of explanation was higher in the central weddell sea around 40 w and lower closer to the antarctic peninsula the geostrophic wind was found to provide almost as good a basis for the general drift estimation as the surface wind observed by the buoys although strong cyclones were not well detected by the ecmwf analyses the data suggest a dependency upon atmospheric stability such that stable stratification reduces the wind forcing on the drift for 60 80 of the time the direction of the drift deviated less than 45 from the geostrophic wind and for 45 70 of the time less than 45 from the ocean current ice transport through a transect crossing the weddell sea from the antarctic peninsula tip to kapp norwegia was estimated on the basis of the geostrophic winds the drift s observed response to the wind and literature based information on ice concentration and thickness the estimated annual mean net export in 1992 1994 varied from 8000 to 22 000 m3 s most of the net export took place in winter and spring export prevailing west of 35 w and import east of it

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

a new snow thermodynamic scheme for large scale sea ice models this paper assesses the capabilities of a new one dimensional snow scheme developed for the thermodynamic component of the louvain la neuve sea ice model lim the model is validated at point barrow alaska and at ice station polarstern ispol in the western weddell sea southern ocean the new snow thermodynamic scheme leads to better snow internal temperature profiles with a set up dependent increase in the correlation between simulated and observed temperature profiles on average over all runs these correlations are 27 better with the six layer configuration the model s ability to reproduce observed temperatures improves with the number of snow layers but stabilizes after a threshold layer number is reached the lowest and highest values for this threshold are 3 at point barrow and 6 at ispol respectively overall the improvement of the model s ability to simulate sea ice thickness is not as significant as for snow temperature probably because of the rather crude representation of the snow stratigraphy in the model

winter snow cover variability on east antarctic sea ice copyright 1998 by the american geophysical union analysis of the first detailed data set of snow characteristics collected over east antarctic sea ice in winter confirms that on small scales snow on antarctic sea ice is highly variable in both thickness and properties high amplitude cyclical variability in atmospheric forcing related to the passage of storms is responsible for the high degree of textural heterogeneity observed changes in snow properties were examined over a 3 week period during which a largely icy snow cover formed at near freezing temperatures metamorphosed to snow in which facetted crystals and depth hoar dominated as the air temperature plummeted even on flat ice significant localized thickening of snow occurs in the form of barchan dunes although we observed great variability in snow thickness and properties on local scales overall snow thickness distribution and the complex textural assemblage of snow types are similar from region to region similar observations were made by sturm et al 1998 in west antarctica large scale similarities are also apparent in mean snow density grain size and bulk snow salinity although high variability is again found across individual floes rapid depth hoar formation is a ubiquitous process that greatly affects the density texture grain size and effective thermal conductivity of the snow cover the observed heterogeneity results in varying snow effective thermal conductivities the mean bulk effective thermal conductivity computed from the proportion of observed snow types is 0 164 w m 1 k 1 significantly lower than values typically used in large scale sea ice modeling but similar to that derived by sturm et al 1998 in a near simultaneous experiment in the bellingshausen and ross seas it varies from 0 097 to 0 383 w m 1 k 1 in different snow pits the findings support those of sturm et al 1998 that periodic flooding and subsequent snow ice formation which are also ubiquitous processes effectively diminish the degree to which basal snow processes create inhomogeneities in the snow pack

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

relationship between the upper ocean and sea ice during the antarctic melting season during the antarctic ice melting season high resolution sea ice data were collected with the video monitoring system aboard the icebreaker shirase along with the monitoring of temperature and salinity in the upper ocean on the basis of these data relationships among sea ice concentration temperature and salinity are investigated in the ice interior region away from the ice free ocean ice concentration is negatively correlated with temperature and positively correlated with salinity for the spatially averaged data which suggests that the local balances of heat and salt nearly hold in a bulk area at the ice margin ice concentration is negatively correlated with both temperature and salinity suggesting that the local balances are overwhelmed by the effects of ice advection the expendable bathythermograph profiles at the ice margin also show that a considerable amount of sea ice was advected into the ice free ocean and subsequently melted there it is pointed out that a polynya works as an ice melting factory in summer it absorbs solar radiation during the period of opening and then melts the ice advected there prom a heat budget analysis and ocean structure in the melting season we propose a simple ice upper ocean coupled model in which sea ice melts on the bottom and lateral faces with the heat source supplied to the open water area by solar radiation the relations among ice concentration temperature and salinity derived from the model are consistent with the observed relations the analytic solution for the no lateral melting case shows that the concentration temperature relation converges to a certain asymptotic curve with time which explains that the temperature concentration plot shows a similar relation for any region dependence of the relations among ice concentration temperature and salinity on the spatial scale is also discussed

copepods in sea ice of the western weddell sea during austral spring 2004 in the framework of the r v polarstern expedition ice station polarstern ispol spatial and temporal trends in composition abundance and age structure of sea ice inhabiting copepods were investigated in the western weddell sea during the transition from the spring to the summer state for the spatial scale sea ice coring was performed at six locations on a transect from the ice edge to the ice drift station between 14 and 24 november 2004 the temporal changes were investigated in a time series study on a drifting sea ice floe from 29 november to 30 december 2004 a relatively large number of copepod species 15 were found in the ice with a higher number at the time station 13 than at the transect 9 drescheriella spp was by far the most abundant taxon encountered in the sea ice throughout the present study 72 87 on the transect idomene antarctica ranked second in abundance 7 followed by stephos longipes 2 and ectinosoma sp 2 in contrast diarthrode cf lilacinus which was not found on the transect was the second most abundant species 11 at the time station followed by i antarctica 9 ectinosoma sp 6 and s longipes 1 naupliar stages dominated the populations of drescheriella spp and s longipes both on the transect and during the time series the ectinosoma sp population was dominated by nauplii only at the stations of the transect while copepodite stages made up the largest fraction during the time series copepodids always predominated the i antarctica populations and it was the only species in which adults occurred in high densities contributing significantly to the abundance only drescheriella spp and s longipes occurred throughout the sea ice cores while the occurrence of all other species was restricted to the bottom layer of the ice the distribution of all species was very patchy and varied greatly between the sampling sites

timing and regional patterns of snowmelt on antarctic sea ice from passive microwave satellite observations an improved understanding of the temporal variability and the spatial distribution of snowmelt on antarctic sea ice is crucial to better quantify atmosphere ice ocean interactions in particular sea ice mass and energy budgets it is therefore important to understand the mechanisms that drive snowmelt both at different times of the year and in different regions around antarctica in this study we combine diurnal brightness temperature differences dtb 37ghz and ratios tb 19ghz tb 37ghz to detect and classify snowmelt processes we distinguish temporary snowmelt from continuous snowmelt to characterize dominant melt patterns for different antarctic sea ice regions from 1988 89 to 2014 15 our results indicate four characteristic melt types on average 38 9 6 0 of all detected melt events are diurnal freeze thaw cycles in the surface snow layer characteristic of temporary melt type a less than 2 reveal immediate continuous snowmelt throughout the snowpack i e strong melt over a period of several days type b in 11 7 4 0 type a and b take place consecutively type c and for 47 8 6 8 no surface melt is observed at all type d continuous snowmelt is primarily observed in the outflow of the weddell gyre and in the northern ross sea usually 17 days after the onset of temporary melt comparisons with snow buoy data suggest that also the onset of continuous snowmelt does not translate into changes in snow depth for a longer period but might rather affect the internal stratigraphy and density structure of the snowpack considering the entire data set the timing of snowmelt processes does not show significant temporal trends

early summer thermohaline characteristics and mixing in the western weddell sea abstract the ice station polarstern ispol cruise revisited the western weddell sea in late 2004 and obtained a comprehensive set of conductivity temperature depth ctd data this study describes the thermohaline structure and diapycnal mixing environment observed in 2004 and compares them with conditions observed more than a decade earlier hydrographic conditions on the central western weddell sea continental slope off larsen c ice shelf in late winter early spring of 2004 2005 can be described as a well stratified environment with upper layers evidencing relict structures from intense winter near surface vertical fluxes an intermediate depth temperature maximum and a cold near bottom layer marked by patchy property distributions a well developed surface mixed layer isolated from the underlying warm deep water wdw by a pronounced pycnocline and characterized by lack of warming and by minimal sea ice basal melting supports the assumption that upper ocean winter conditions persisted during most of the ispol experiment much of the western weddell sea water column has remained essentially unchanged since 1992 however significant differences were observed in two of the regional water masses the first modified weddell deep water mwdw comprises the permanent pycnocline and was less saline than a decade earlier whereas weddell sea bottom water wsbw was horizontally patchier and colder near bottom temperatures observed in 2004 were the coldest on record for the western weddell sea over the continental slope minimum temperatures were 0 4 and 0 3 c colder than during 1992 1993 respectively the 2004 near bottom temperature salinity characteristics revealed the presence of two different wsbw types whereby a warm fresh layer overlays a colder saltier layer both formed in the western weddell sea the deeper layer may have formed locally as high salinity shelf water hssw that flowed intermittently down the continental slope which is consistent with the observed horizontal patchiness the latter can be associated with the near bottom variability found in powell basin with consequences for the deep water outflow from the weddell sea

superimposed ice formation in summer on ross sea pack ice floes austral summer sea ice processes were investigated in january 1999 during a cruise of the r v nathaniel b palmer in the central and eastern ross sea antarctica the crystal texture 18o 16o ratios density and salinity of ice cores and of ice blocks perched on slush at the ice surface were studied the perched ice blocks had a distinctive polygonal granular pg crystal texture and very negative isotope signature that were also characteristic of layers at the top of first year floes and of layers buried below the surface in multi year floes the pg ice is superimposed ice that results from melting in the snow cover and refreezing at the slush surface and directly on top of ice floes if pg ice is buried after the ice surface floods and the resultant slush freezes then snow ice forms above the pg ice the contribution of superimposed ice to floe surface mass balance and some implications with respect to weather and climate are discussed

on the transient nature of mantle plumes 1 we present new experiments focussing on the transient behaviour of thermal plumes in a fluid heated from below plumes develop once the hot thermal boundary layer tbl reaches a critical thickness howard 1964 they rise through the fluid owing to their thermal buoyancy and comprise tbl material which empties itself into the plumes as the tbl becomes exhausted plumes start disappearing from the bottom up sometimes even before reaching the upper boundary depending on the convection intensity then they finally fade away by thermal diffusion this sequence of events shows that time dependence is a key factor when interpreting present day tomographic images of mantle upwellings in particular it could be erroneous to identify the depth of a present day slow seismic anomaly with the depth of its origin or to interpret the absence of a long tail as the absence of a plume

a model study of differences of snow thinning on arctic and antarctic first year sea ice during spring and summer the one dimensional snow model sntherm is validated using field measurements of snow and superimposed ice thickness and surface energy fluxes these were performed during the spring to summer transition in svalbard and in the weddell sea antarctica both the seasonal snow thickness decrease and the formation of superimposed ice are well reproduced by the model during the three observation periods observed and modeled snow thickness differ only by 13 1 27 1 mm on average in regional studies the model is forced with atmospheric re analysis data european centre for medium range weather forecasts and applied to several meridional transects across the arctic and southern ocean these show fundamental regional differences in the onset duration and magnitude of snow thinning in summer in the central arctic snowmelt onset occurs within a narrow time range of 11 days and without significant regional differences in contrast the snow cover on antarctic sea ice begins to melt about 25 days earlier and the length of the antarctic snow thinning season increases with increasing latitude the importance of melting and evaporation for the modeled snow thickness decrease is very different in the two hemispheres the ratio of evaporated snow mass to melted snow mass per unit area is derived from the model and amounts to approximately 4 2 in the antarctic and only 0 75 in the arctic this agrees with observations and model results of the surface energy balance and illustrates the dominance of surface cooling by upward turbulent fluxes in the antarctic

superimposed ice formation and surface energy fluxes on sea ice during the spring melt freeze period in the baltic sea the development of land fast sea ice and overlying snow was monitored during a 4 week period until the snow cover had completely disappeared at a site in the gulf of bothnia baltic sea 63 57 n 19 85 e the meteorological and radiative boundary conditions were continuously recorded during the observation period a 15 cm thick snow layer on the ice was transformed into a 7 cm thick granular ice layer superimposed ice on the ice surface contributing significantly about 11 to the total ice thickness approximately 1 cm w e of the snow was sublimated neither snow ice formation nor basal ice growth was significant during the same period the salinity and isotopic 18 o composition of the ice indicated that prior to the experiment a 7 cm layer of superimposed ice had already formed hence superimposed ice layers contributed 22 of the total ice thickness by the time all snow had disappeared the advancing spring decrease in surface albedo diurnal cycle in the incoming solar radiation and synoptic scale changes in the cloud cover and the air ice turbulent heat fluxes caused variations in the heat budget of the snowpack superimposed ice formation due to refreezing of meltwater occurred during most nights of the study period and the most important refreezing periods were under such synoptic conditions that the air and snow surface temperatures also remained below zero during daytime in contrast to typical summer conditions in polar oceans low snow surface temperatures acted as the primary heat sink for the refreezing of meltwater

spectral albedos of sea ice and incident solar irradiance in the southern beaufort sea spectral albedos and incident spectral irradiances have been measured over the wavelength range 400 to 2400 nm on the sea ice near the naval arctic research laboratory narl at pt barrow alaska the observation interval extended from mid may when the ice was still relatively cold until mid june when summer melting was fully established the temporal dependence of albedo for the available surface types was obtained over this time interval showing a general decrease from snow and snow covered ice to blue ice and melt ponds data were also obtained for glacier ice on the athabasca glacier for melting lake ice and for certain other nonice surfaces in the vicinity of narl snow and ice albedos are characteristically highest at visible wavelengths decreasing strongly in the infrared because of the increase in absorption by ice and water local maxima in the spectra correspond to minima in the ice and water absorption variations in albedo are due primarily to differences in the vapor bubble density crystal structure and free water content of the upper layers of the ice incident spectral shortwave radiation was measured as a function of cloudiness and the optical thickness of arctic clouds is significantly less than the thickest clouds at lower latitudes the decrease of the infrared component relatiave to the visible portion of the irradiance with increasing cloud cover is determined this can give rise to an increase in wavelength integrated albedos of as much as 15 using the present data a graphical method is outlined by which visible near infrared satellite imagery can be used to distinguish among melt ponds open leads and other spring and summer sea ice surface types

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

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

reduced ice thickness in arctic transpolar drift favors rapid ice retreat 1 helicopter borne electromagnetic sea ice thickness measurements were performed over the transpolar drift in late summers of 2001 2004 and 2007 continuing ground based measurements since 1991 these show an ongoing reduction of modal and mean ice thicknesses in the region of the north pole of up to 53 and 44 respectively since 2001 a buoy derived ice age model showed that the thinning was mainly due to a regime shift from predominantly multi and second year ice in earlier years to first year ice in 2007 which had modal and mean summer thicknesses of 0 9 and 1 27 m measurements of second year ice which still persisted at the north pole in april 2007 indicate a reduction of late summer second year modal and mean ice thicknesses since 2001 of 20 and 25 to 1 65 and 1 81 m respectively the regime shift to younger and thinner ice could soon result in an ice free north pole during summer