sea surface height determination in the arctic ocean from ers altimetry 1 accurate sea surface height measurements have been extracted from ers altimeter data in sea ice covered regions for the first time the data have been used to construct a mean sea surface of the arctic ocean between the latitudes of 60 degreesn and 81 5 degreesn based on 4 years of ers 2 data an rms value for the crossover differences of mean sea surface profiles of 4 2 cm was observed in the ice covered canada basin compared with 3 8 cm in the ice free greenland iceland norwegian seas comparisons are made with an existing global mean sea surface osumss95 highlighting significant differences between the two surfaces in permanently ice covered seas in addition we present the first altimeter derived sea surface height variability map of the arctic ocean comparisons with a high resolution coupled ocean sea ice general circulation model reveal a good qualitative agreement in the spatial distribution of variability quantitatively we found that the observed variability was on average a factor of 3 4 greater than model predictions

sea ice thickness estimations from icesat altimetry over the bellingshausen and amundsen seas 2003 2009 1 sea ice thicknesses derived from nasa s ice cloud and land elevation satellite icesat altimetry data are examined using two different approaches buoyancy and empirical equations and at two spatial scales icesat footprint size 70 m diameter spot and advanced microwave scanning radiometer amsr e pixel size 12 5 km by 12 5 km for the bellingshausen and amundsen seas of west antarctica ice thickness from the empirical equation shows reasonable spatial and temporal distribution of ice thickness from 2003 to 2009 ice thickness from the buoyancy equation however additionally needing snow depth information derived from the amsr e shows an overestimation in terms of maximum mean 63 to 75 and standard deviation while underestimation in modal thickness 20 as compared with those from the empirical equation approach when icesat snow freeboard is used as the snow depth in the buoyancy equation i e the zero ice freeboard assumption the derived ice thicknesses match well with those from the empirical equation approach within 5 overall the amsr e therefore may underestimate snow depth and accounts for 95 of the ice thickness overestimation as compared with the buoyancy approach the empirical equation derived ice thickness shows a consistent asymmetrical distribution with a long tail to high values and seasonal median values ranging from 0 8 to 1 4 m over the 2003 2009 period that are always larger than the corresponding modal values 0 6 1 1 m and lower than the mean values 1 0 1 6 m with standard deviation of 0 6 1 0 m an overall increasing trend of 0 03 m year of mean ice thickness is found from 2003 to 2009 although statistically insignificant p 0 11 at the 95 confidence level starting from autumn a general picture of seasonal mean modal and median ice thickness increases progressively from autumn to spring and decreases from spring to the following autumn when new thin ice dominates the ice thickness distribution the asymmetric shape of the thickness distribution reflects the key role of ice deformation processes in the evolution of the thickness distribution the statistical properties of the thickness distribution interannually high range of mean thickness and standard deviation indicate the variability of deformation processes however spring ice volume the product of ice mean thickness and areal extent computed for the spring maximum shows variability year to year but is primarily dominated by ice extent variability with no increasing or decreasing trend over this record length the dependence of the volume on the ice extent primarily suggests that ice thickness changes have also not covaried with the ice extent losses seen over the satellite record in this region unlike the arctic these properties reflect the interactive processes of ice advection thermodynamic growth and ice deformation that all substantially influence ice mass balance in the bellingshausen amundsen seas region

antarctic sea ice altimetry scale and resolution effects on derived ice thickness distribution three ice type regimes at ice station belgica isb during the 2007 international polar year simba sea ice mass balance in antarctica expedition were characterized and assessed for elevation snow depth ice freeboard and thickness analyses of the probability distribution functions showed great potential for satellite based altimetry for estimating ice thickness in question is the required altimeter sampling density for reasonably accurate estimation of snow surface elevation given inherent spatial averaging this study assesses an effort to determine the number of laser altimeter hits of the isb floe as a representative antarctic floe of mixed first and multi year ice types for the purpose of statistically recreating the in situ determined ice thickness and snow depth distribution based on the fractional coverage of each ice type estimates of the fractional coverage and spatial distribution of the ice types referred to as ice towns for the 5 km 2 floe were assessed by in situ mapping and photo visual documentation simulated icesat altimeter tracks with spot size 70 m and spacing 170 m sampled the floe s towns generating a buoyancy derived ice thickness distribution 115 altimeter hits were required to statistically recreate the regional thickness mean and distribution for a three town assemblage of mixed first and multi year ice and 85 hits for a two town assemblage of first year ice only equivalent to 19 5 and 14 5 km respectively of continuous altimeter track over a floe region of similar structure results have significant implications toward model development of sea ice sampling performance of the icesat laser altimeter record as well as maximizing sampling characteristics of satellite airborne laser and radar altimetry missions for sea ice thickness

estimation of sea ice thickness distributions through the combination of snow depth and satellite laser altimetry data 1 combinations of sea ice freeboard and snow depth measurements from satellite data have the potential to provide a means to derive global sea ice thickness values however large differences in spatial coverage and resolution between the measurements lead to uncertainties when combining the data high resolution airborne laser altimeter retrievals of snow ice freeboard and passive microwave retrievals of snow depth taken in march 2006 provide insight into the spatial variability of these quantities as well as optimal methods for combining high resolution satellite altimeter measurements with low resolution snow depth data the aircraft measurements show a relationship between freeboard and snow depth for thin ice allowing the development of a method for estimating sea ice thickness from satellite laser altimetry data at their full spatial resolution this method is used to estimate snow and ice thicknesses for the arctic basin through the combination of freeboard data from icesat snow depth data over first year ice from amsr e and snow depth over multiyear ice from climatological data due to the nonlinear dependence of heat flux on ice thickness the impact on heat flux calculations when maintaining the full resolution of the icesat data for ice thickness estimates is explored for typical winter conditions calculations of the basin wide mean heat flux and ice growth rate using snow and ice thickness values at the 70 m spatial resolution of icesat are found to be approximately one third higher than those calculated from 25 km mean ice thickness values

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

uncertainties in antarctic sea ice thickness retrieval from icesat a sensitivity study was carried out for the lowest level elevation method to retrieve total sea ice snow freeboard from ice cloud and land elevation satellite icesat elevation measurements in the weddell sea antarctica varying the percentage p of elevations used to approximate the instantaneous sea surface height can cause widespread changes of a few to 10 cm in the total freeboard obtained other input parameters have a smaller influence on the overall mean total freeboard but can cause large regional differences these results together with published icesat elevation precision and accuracy suggest that three times the mean per gridcell single laser shot error budget can be used as an estimate for freeboard uncertainty theoretical relative ice thickness uncertainty ranges between 20 and 80 for typical freeboard and snow properties ice thickness is computed from total freeboard using advanced microwave scanning radiometer for earth observing system amsr e snow depth data average ice thickness for the weddell sea is 1 73 0 38 m for icesat measurements from 2004 to 2006 in agreement with previous work the mean uncertainty is 0 72 0 09 m our comparison with data of an alternative approach which assumes that sea ice freeboard is zero and that total freeboard equals snow depth reveals an average sea ice thickness difference of 0 77 m

estimation of sea ice thickness and volume in the sea of okhotsk based on icesat data sea ice thickness in the sea of okhotsk is estimated for 2004 2008 from icesat derived freeboard under the assumption of hydrostatic balance total ice thickness including snow depth h t o t averaged over 2004 2008 is 95 cm the interannual variability of h t o t is large from 77 5 cm 2008 to 110 4 cm 2005 the mode of h t o t varies from 50 60 cm 2007 and 2008 to 70 80 cm 2005 ice thickness derived from icesat data is validated from a comparison with that observed by electromagnetic induction instrument em aboard the icebreaker soya near hokkaido japan annual maps of h t o t reveal that the spatial distribution of h t o t is similar every year ice volume of 6 3 10 11 m 3 is estimated from the icesat derived h t o t and amsr e derived ice concentration a comparison with ice area demonstrates that the ice volume cannot always be represented by the area solely despite the fact that the area has been used as a proxy of the volume in the sea of okhotsk the ice volume roughly corresponds to that of annual ice production in the major coastal polynyas estimated based on heat budget calculations this also supports the validity of the estimation of sea ice thickness and volume using icesat data

ostracods as proxies for past seagrass a review abstract recently attention has been drawn to the recognition of past seagrass for which a number of proxies have been proposed several studies have quoted ostracods as having some value as proxies particularly loxoconcha xestoleberis and aurila although these may be found in a variety of marine environments they are often found with faunas containing seagrass or which can be interpreted as in proximity to seagrass in such situations they may be found with other possible seagrass proxies such as sirenians lucinid bivalves soritid and other benthic foraminiferans the presence of loxoconcha xestoleberis and aurila and other ostracods may be suggestive of past seagrass environments the interpretation of which is strengthened by the presence of other proxies in some collections

snow depth and ice thickness measurements from the beaufort and chukchi seas collected during the amsr ice03 campaign in march 2003 a field validation campaign was conducted on the sea ice near barrow ak the goal of this campaign was to produce an extensive dataset of sea ice thickness and snow properties depth and stratigraphy against which remote sensing products collected by aircraft and satellite could be compared chief among these were products from the polarimetric scanning radiometer psr flown aboard a nasa p 3b aircraft and the aqua advanced microwave scanning radiometer for the earth observing system amsr e the data were collected in four field areas three on the coastal sea ice near barrow ak and the fourth out on the open ice pack 175 km northeast of barrow the snow depth ranged from 9 4 20 8 cm in coastal areas n 9881 for three areas with the thinnest snow on ice that had formed late in the winter out in the main pack ice the snow was 20 6 cm deep n 1906 the ice in all four areas ranged from 138 219 cm thick n 1952 with the lower value again where the ice had formed late in the winter snow layer and grain characteristics observed in 118 snow pits indicated that 44 of observed snow layers were depth hoar 46 were wind slab snow and ice measurements were keyed to photomosaics produced from low altitude vertical aerial photographs using these and a distinctive three way relationship between ice roughness snow surface characteristics and snow depth strip maps of snow depth each about 2 km wide were produced bracketing the traverse lines these maps contain an unprecedented level of snow depth detail against which to compare remote sensing products the maps are used in other papers in this special issue to examine the retrieval of snow properties from the psr and amsr e sensors

sea ice freeboard and thickness in the ross sea from airborne icebridge 2013 and satellite icesat 2003 2008 observations

sea ice thickness in the coastal northeastern chukchi sea from moored ice profiling sonar time series ice draft data were obtained from moored ice profiling sonar ips in the coastal northeastern chukchi sea during 2009 10 time series data show seasonal growth of sea ice draft occasionally interrupted by coastal polynya the sea ice draft distribution indicates a slightly lower abundance of thick deformed ice compared with the eastern beaufort sea in january a rapid increase in the abundance of thick ice coincided with a period of minimal drift indicating compaction again the coast and dynamical thickening the overall mean draft and corresponding derived thickness are 1 27 and 1 38 m respectively the evolution of modal ice thickness observed can be explained mostly by thermodynamic growth the derived ice thicknesses are used to estimate heat losses based on era interim data heat losses from the raw 1 s ips data are 50 and 100 greater than those calculated using ips data averaged over spatial scales of 20 and 100 km respectively this finding demonstrates the importance of subgrid scale ice thickness distribution for heat loss calculation the heat loss estimate based on thin ice data derived from amsr e data corresponds well with that from the 1 s observed ice thickness data validating heat loss estimates from the amsr e thin ice thickness algorithm

satellite remote sensing of sea ice thickness and kinematics a review observations of sea ice thickness and kinematics are essential for understanding changes in sea ice mass balance interactions between the ice cover and the ocean and atmosphere and for improving projections of sea ice response in a warming climate these parameters are not directly observable with current sensor technology but are derived from satellite altimetry and imagery while there is progress in the retrievals of arctic sea ice thickness from satellite altimetry approaches to address southern ocean ice thickness require additional attention on the other hand procedures to derive sea ice motion from satellite imagery are more mature and better understood and have been employed to produce useful results for more than a decade adequate sampling of sub daily ice motion however remains a challenge generally satellite instruments provide large scale coverage but the frequency of temporal sampling is limited by orbit characteristics in this review i focus on the approaches uncertainties sampling limitations and validation issues associated with the estimation of sea ice thickness and motion i provide a summary of current and anticipated capabilities for monitoring sea ice thickness and kinematics from space the prospects for continuing these measurements into the next decade from a satellite remote sensing perspective are discussed

magnetotelluric studies across the kurduwadi gravity feature abstract the deccan traps have a predominantly negative bougner anomaly with two prominent regions of gravity low along the nasik koyna and nasik kurduwadi lines on the basis of these a rift zone was suggested along the nasik kurduwadi region this rift theory was not supported by later deep seismic sounding dss studies subsequent gravity modelling studies indicated that the observed anomalies could be explained in terms of undulations in the crust mantle boundary and the conrad discontinuity it was thus felt that the region should be reinvestigated to check for the rift valley using magnetotelluric mt techniques a linear profile about 100 km long was identified for these studies magnetotelluric data were collected at 11 stations with an average station spacing of 8 15 km the data at ten of these stations were found to be good for the purpose of analysis the rotation of the impedance tensor showed a regional rotation angle of 60 east of north with this rotation the direction of the major resistivity is approximately perpendicular to the direction of gravity low as well as the west coast of the indian peninsula one dimensional 1d analysis at all stations showed a five layered structure a regional geoelectric cross section is proposed using the 1d data the influence of the west coast was studied using two dimensional 2d modelling techniques the deccan basalts were observed to be about 500 m thick overlying the granitic upper crust a mid crustal conductor with a conductance of about 200 s was delineated at a depth of 12 18 km this shows good agreement with the conrad discontinuity reported from the dss and gravity studies the moho discontinuity was not seen in the data presumably because it is not accompanied by any detectable change of electrical resistivity the lithosphere asthenosphere boundary is shallow at a depth of about 80 100 km the asthenosphere is not well formed as is evident from the large resistivities 50 100 m signature of sediments below the traps could not be found in the survey area

influence of the sea ice thickness distribution on polar climate in ccsm3 abstract the sea ice simulation of the community climate system model version 3 ccsm3 t42 gx1 and t85 gx1 control simulations is presented and the influence of the parameterized sea ice thickness distribution itd on polar climate conditions is examined this includes an analysis of the change in mean climate conditions and simulated sea ice feedbacks when an itd is included it is found that including a representation of the subgrid scale itd results in larger ice growth rates and thicker sea ice these larger growth rates represent a higher heat loss from the ocean ice column to the atmosphere resulting in warmer surface conditions ocean circulation most notably in the southern hemisphere is also modified by the itd because of the influence of enhanced high latitude ice formation on the ocean buoyancy flux and resulting deep water formation changes in atmospheric circulation also result again most notably in the southern hemisphere there are indications that the itd also modifies simulated sea

thickness and density of snow covered sea ice and hydrostatic equilibrium assumption from in situ measurements in fram strait the barents sea and the svalbard coast modern satellite measurements of sea ice thickness are based on altimeter measurements of the difference in elevation between the snow or ice surface and the local sea surface for retrieval of sea ice thickness it is assumed that the ice is in hydrostatic equilibrium and that the snow load on the ice and the density of the sea ice and sea water are known this study presents data from in situ sea ice thickness drillings and snow and ice density measurements from fram strait the barents sea and the svalbard coast in the european arctic the error in the altimetry ice thickness products is assessed based on the spatial variability of snow and ice density and snow thickness data ice thickness uncertainty related to snow depth was found to be 40 cm radar altimeter and 90 cm laser altimeter while uncertainty related to ice density is 25 cm for both techniques the assumption of hydrostatic equilibrium at the scales of the measurements 10 100 m was found to hold better in the case of level landfast ice near svalbard than for fram strait drift ice which consists of mixed ice types where the deviation between the calculated and measured ice thicknesses was on average 0 5 m

spring snow conditions on arctic sea ice north of svalbard during the norwegian young sea ice n ice2015 expedition snow is crucial over sea ice due to its conflicting role in reflecting the incoming solar energy and reducing the heat transfer so that its temporal and spatial variability are important to estimate during the norwegian young sea ice n ice2015 campaign snow physical properties and variability were examined and results from april until mid june 2015 are presented here overall the snow thickness was about 20 cm higher than the climatology for second year ice with an average of 55 27 cm and 32 20 cm on first year ice the average density was 350 400 kg m 3 in spring with higher values in june due to melting due to flooding in march larger variability in snow water equivalent was observed however the snow structure was quite homogeneous in spring due to warmer weather and lower amount of storms passing over the field camp the snow was mostly consisted of wind slab faceted and depth hoar type crystals with occasional fresh snow these observations highlight the more dynamic character of evolution of snow properties over sea ice compared to previous observations due to more variable sea ice and weather conditions in this area the snowpack was isothermal as early as 10 june with the first onset of melt clearly identified in early june based on our observations we estimate than snow could be accurately represented by a three to four layers modeling approach in order to better consider the high variability of snow thickness and density together with the rapid metamorphose of the snow in springtime

ice thickness in the arctic ocean the statistical reliability of experimental data the statistical reliability of ice thickness distributions derived from submarine sonar data sets of finite length is examined focusing on the standard error eh l in the mean ice draft h derived from a record of length l km this is important in assessing the significance or otherwise of quoted temporal or spatial differences in mean ice draft estimates for eh 50 are derived from four different submarine surveys each of which involved repeated sampling of apparently homogeneous ice fields values ranged from 7 18 to 15 29 of the mean for climate related comparisons of data sets from different years in the same location a value of 12 75 is recommended derived from data gathered at the north pole this value is used to reassess the significance of published data on ice draft variability quoted variability at the north pole over the 1977 1990 period is found to be not statistically significant but a difference in area averaged ice draft over the eurasian basin between 1976 and 1987 remains highly significant using hitherto unreported 1987 data from the north pole area the statistical variability of other parameters of the ice cover is examined the frequency of lead occurrence the width of leads the fractional cover of smooth ice and the frequency of keel occurrence all show standard errors of 22 24 in their mean values while mean keel draft has a 4 error all over a 50 km track length finally unreported 1987 data for an area extending from the pole to 72 n along the prime meridian and the east greenland shelf break are examined in 1 bins using eh l to assess the significance of variations in the mean a statistically significant decline in mean ice draft is observed starting at 86 n and continuing to 72 n a linear regression gives a thinning rate of 0 22 m deg the decline within the arctic basin itself is tentatively ascribed to a mixture of under ice melt and mixing of ice types since data on young ice occurrence show that divergence did not occur north of fram strait

validating icesat over thick sea ice in the northern canada basin only in the past eight years has the feasibility of using satellite borne altimeters to estimate sea ice freeboard and thickness been demonstrated and these estimates still have uncertainties primarily associated with limited knowledge of snow loading on sea ice because accurate estimates of arctic wide sea ice thickness and volume are fundamental inputs to global climate models validation of satellite derived thickness estimates using independent data is required a detailed assessment of freeboard retrieved by the geoscience laser altimeter system glas aboard the ice cloud and land elevation satellite has been carried out using high resolution laser altimetry from the national aeronautics and space administration s airborne topographic mapper atm the delay doppler radar altimeter and digital photography collected along a 300 km segment of sea ice in the canada basin exploiting the repeat coverage of the aircraft flight line a correction was applied to glas footprint geolocations to adjust for sea ice drift that occurred during the time between satellite and aircraft acquisitions comparisons of glas and atm measurements over sea ice show excellent agreement about a 0 00 m mean with no apparent bias between data sets freeboard estimates were examined using data from glas and atm independently employing measurements over refrozen leads to estimate local sea surface heights sshs the results demonstrate the sensitivity of freeboard and thickness calculations to an accurate estimation of local ssh snow depth derived by differencing laser and radar data was combined with the freeboard estimates to yield a mean sea ice thickness of 5 5 m over a 250 km subsection of the flight track

sea ice albedo climate feedback mechanism abstract the sea ice albedo feedback mechanism over the arctic ocean multiyear sea ice is investigated by conducting a series of experiments using several one dimensional models of the coupled sea ice atmosphere system in its simplest form ice albedo feedback is thought to be associated with a decrease in the areal cover of snow and ice and a corresponding increase in the surface temperature further decreasing the areal cover of snow and ice it is shown that the sea ice albedo feedback can operate even in multiyear pack ice without the disappearance of this ice associated with internal processes occurring within the multiyear ice pack e g duration of the snow cover ice thickness ice distribution lead fraction and melt pond characteristics the strength of the ice albedo feedback mechanism is compared for several different thermodynamic sea ice models a new model that includes ice thickness distribution the ebert and curry model the maykut and untersteiner model and the semtner level 3 an

sea ice topography of the arctic ocean in the region 70 degrees w to 25 degrees e in october 1976 a cooperative experiment was made to survey the sea ice topography in the european sector of the arctic ocean h m submarine sovereign acquired 4000 km of ice draft data by using an upward looking sonar while a canadian forces aircraft flew along the submarine s track and acquired 2200 km of ice elevation data by using a laser profilometer the two types of profile were processed in corresponding 100 km section lengths and the following statistical analyses and comparisons were made i probability density functions o f ice draft and elevation each distribution shows a peak for young ice and for undeformed multi year ice at large ice thicknesses the distributions take the analytical form of a negative exponential the mean drafts enable two distinct geographical ice regimes to be identified there is an offshore zone of very heavy pressure ridging extending up to 400 km from the coasts of ellesmere island and of north greenland with mean ice draft in the range 5 0 to 7 5 m while out in the central arctic ocean the mean ice draft is lower 3 9 5 1 m and the characteristics of the ice cover remain homogeneous over a length scale of 1000 km the transition between the two regimes is abrupt taking place in less than 25 km data from the same part of the central arctic taken in march 1971 showed a mean ice draft 0 3 m lower while data from the central beaufort sea showed a mean draft more than 0 8 m lower ii level ice distributions ice with a local gradient of less than 1 in 40 was defined as level ice and used as an indicator of the quantity and thickness distribution of undeformed i e thermodynamically grown ice in the arctic ocean the distribution has a mode at 3 0 3 1 m draft and level ice percentages are in the range 30 40 bottom side and 70 80 top side in the offshore zone and 45 55 bottom and 85 95 top in the central arctic thus about half of the arctic ice cover consists of deformed ice iii pressure ridge spacings the spacings of ridge keels fit a negative exponential distribution characteristic of randomness except at close spacings where there is a deficit of keels explained as a geometrical effect and at very large spacings where there is an excess due to the contribution of polynyas the distribution of sail spacings exhibits these two effects but also differs from a random distribution at moderate sail separations iv ridge elevations and drafts keel drafts fit a law of form p h d oc exp ah 2 d h except for an excess of keels at drafts beyond 20 m there is a positive correlation between mean keel draft and keel frequency there are 3 5 4 5 keels per kilometre with draft exceeding 9 m in the offshore zone and 2 3 in the central arctic sail elevations fit a law of form p h d h x exp a h d h with a positive correlation between mean sail elevation and sail frequency the sail elevation and ice elevation distributions can be related by assuming that all thick ice is contained in pressure ridges of triangular cross section v keel sail comparison for the 21 corresponding 100 km sections there are positive correlations between mean sail height and mean keel draft and between keel frequency and sail frequency from these it is possible to convert a sail distribution computed from a laser profile into a keel distribution enabling sea ice bulk characteristics to be derived from airborne surveys alone vi leads and polynyas a lead was defined as a continuous sequence of depth points greater than 5 m long and not exceeding 1 m draft the number density n d of leads per kilometre of width d m fits the power law n d 15 d 2 exceptionally wide leads were concentrated in the offshore zone and in the marginal ice zone close to the open water of the greenland sea

comparison of coincident snow freeboard and sea ice thickness profiles derived from helicopter borne laser altimetry and electromagnetic induction sounding 1 sea ice thickness plays a critical role in global climate change but it cannot be measured directly from space alternatively sea ice freeboard is measured and converted to sea ice thickness with assumptions made for snow depth and snow ice densities this paper investigates the relationship between snow freeboard ice freeboard plus snow and total thickness ice thickness plus snow and addresses the uncertainties that arise from the unknown snow depth and snow ice densities a unique data set of coincident measurements of snow freeboard and total thickness was collected in the arctic and antarctic snow freeboard was determined by laser altimetry and total thickness was determined by electromagnetic induction with a helicopter borne instrument obtained total thickness snow freeboard ratios range from 2 to 12 in the arctic and from 2 to 8 in the antarctic the principal finding is that the ratios vary greatly within each region and a fixed ratio per profile should not be used as this can induce incorrect ice thicknesses the ratio uncertainties can induce a relative thickness error of 5 4 and 4 9 in the first year and multiyear ice mode additionally the coincident measurements allow the calculation of snow depth that can be used to densify existing in situ measurements to assess accuracy calculated snow depths were compared to in situ measurements and agree within 5 cm this increases if measurements and calculations differ spatially the method of deriving snow freeboard from laser altimetry is briefly described and the variability of the total thickness snow freeboard ratio is shown for one profile in the lincoln sea and one in the weddell sea

thinning of the arctic sea ice cover comparison of sea ice draft data acquired on submarine cruises between 1993 and 1997 with similar data acquired between 1958 and 1976 indicates that the mean ice draft at the end of the melt season has decreased by about 1 3 m in most of the deep water portion of the arctic ocean from 3 1 m in 1958 1976 to 1 8 m in the 1990s the decrease is greater in the central and eastern arctic than in the beaufort and chukchi seas preliminary evidence is that the ice cover has continued to become thinner in some regions during the 1990s

critical role of snow on sea ice growth in the atlantic sector of the arctic ocean during the norwegian young sea ice n ice2015 campaign in early 2015 a deep snow pack was observed almost double the climatology for the region north of svalbard there were significant amounts of snow ice in second year ice syi while much less in first year ice fyi here we use a 1 d snow ice thermodynamic model forced with reanalyses to show that snow ice contributes to thickness growth of syi in absence of any bottom growth due to the thick snow growth of fyi is tightly controlled by the timing of growth onset relative to precipitation events a later growth onset can be favorable for fyi growth due to less snow accumulation which limits snow ice formation we surmise these findings are related to a phenomenon in the atlantic sector of the arctic where frequent storm events bring heavy precipitation during autumn and winter in a region with a thinning ice cover

large scale surveys of snow depth on arctic sea ice from operation icebridge 1 we show the first results of a large scale survey of snow depth on arctic sea ice from nasa s operation icebridge snow radar system for the 2009 season and compare the data to climatological snow depth values established over the 1954 1991 time period for multiyear ice the mean radar derived snow depth is 33 1 cm and the corresponding mean climatological snow depth is 33 4 cm the small mean difference suggests consistency between contemporary estimates of snow depth with the historical climatology for the multiyear ice region of the arctic a 16 5 cm mean difference climatology minus radar is observed for first year ice areas suggesting that the increasingly seasonal sea ice cover of the arctic ocean has led to an overall loss of snow as the region has transitioned away from a dominantly multiyear ice cover

a method to automatically determine sea level for referencing snow freeboards and computing sea ice thicknesses from nasa icebridge airborne lidar abstract the nasa icebridge flights have obtained critical observations for earth s polar ice since icesat stopped collecting data in 2009 this study develops an automatic method in processing icebridge airborne topographic mapper atm altimeter l1b data one elevation per 3 4 m horizontally to derive a local sea level height for referencing snow freeboards and then computing sea ice thicknesses four 30 km l1b profiles a b c and d flown on october 21 2009 over the bellingshausen sea in antarctica are selected the local sea level reference is first obtained by visual examination of atm l1b heights over leads or thin ice identified on images simultaneously acquired from the digital mapping system camera called manual selection this sea level reference is then used as ground truth to validate sea level heights derived by automatic calculations using five thresholds of 2 1 0 5 0 2 and 0 1 of the lowest l1b data the l1b 0 2 method gives a similar sea level height as from the l1b manual selection by mean absolute difference of 0 01 0 06 m the sea level heights demonstrate a near linear gradient of 0 01 m km to 0 03 m km within each 30 km l1b profile along the flight track from section a to d the resulting mean snow freeboards are 0 59 m 0 67 m 0 53 m and 0 60 m on sections a b c and d respectively three empirical equations and the buoyancy equation with zero ice freeboard assumption all give similar statistics in ice thickness estimation with mean ice thicknesses of 1 91 m for section a 2 16 m for b 1 76 m for c and 1 94 m for d the sea level over leads cannot be accurately resolved from the atm l2 data 60 m x 80 m horizontal averaging however by using a sea level reference obtained from the l1b data the atm l2 data can achieve reasonable ice thickness estimates with mean absolute difference of only 0 10 m compared to thickness derived from the l1b data

arctic ocean gravity geoid and sea ice freeboard heights from icesat and grace 1 icesat laser measurements provide a high resolution mapping of the sea ice surface of the arctic ocean which can be inverted to determine gravity anomalies and sea ice freeboard heights by a lowest level filtering scheme in this paper we use updated terrestrial gravity data from the arctic gravity project in combination with grace gravity field models to derive an improved arctic geoid model this model is then used to convert icesat measurements to sea ice freeboard heights with a coarse lowest level surface method the derived freeboard heights show a good qualitative agreement to the coverage of multi year sea ice however comparison to an airborne lidar underflight north of greenland shows that the lowest level filtering scheme may introduce a bias we finally use the icesat and grace results to derive new gravity anomalies by fourier inversion the satellite only gravity field shows all major tectonic features of the arctic ocean and has an accuracy of 6 mgal compared to recent airborne gravity data illustrating the usefulness of icesat data for gravity field determination

vapor transport grain growth and depth hoar development in the subarctic snow measurements from the subarctic snowpack are used to explore the relationship between grain growth and vapor flow the fundamental processes of dry snow metamorphism due to extreme temperature gradients the subarctic pack undergoes extensive depth hoar metamorphism by the end of the winter a five layered structure with a pronounced weak layer near the base of the snow evolves grain size increases by a factor of 2 3 while the number of grains per unit mass decreases by a factor of 10 observed growth rates require significant net inter particle vapor fluxes stable isotope ratios show that there are also significant net layer to layer vapor fluxes soil moisture enters the base of the pack and mixes with the bottom 10 cm of snow while isotopically light water vapor fractionates from the basal layer and is deposited up to 50 cm higher in the pack end of winter density profiles for snow on the ground compared with snow on tables indicate the net layer to layer vapor flux averages 6 x 10 7 kg m 2 s 1 though detailed measurements show the net flux is episodic and varies with time and height in the pack with peak net fluxes ten times higher than average a model driven by observed temperature profiles reproduces the layer to layer flux pattern and predicts the observed weak layer at the base of the snow calculated layer to layer vapor fluxes are ten times higher than inter particle fluxes which implies that depth hoar grain growth is limited by factors other than the vapor supply this finding suggests that gain and loss of water molecules due to sublimation from grains takes place at a rate many times higher than the rate at which grains grow and it explains why grains can metamorphose into different forms so readily

satellite based estimates of sea ice volume flux through fram strait sea ice volume fluxes through fram strait arctic ocean are estimated for the two icesat measurement periods in february march and october november 2003 by combining sea ice area fluxes determined from space borne microwave observations with estimates of the sea ice thickness distribution inferred from measurements of icesat s geoscience laser altimeter system glas instrument the thickness is derived from icesat data by converting its surface elevation measurements into an ice freeboard estimate combined with prior information about ice density and snow depth and density the freeboard is converted into ice thickness uncertainties in freeboard estimates due to geoid model errors are reduced through the use of the recent geoid from the arctic gravity project missing information about the ocean circulation and ocean tides is approximated locally by interpolating the sea surface height linearly between open leads meridional ice volume fluxes estimated for 798 n using ice drift observed by amsr e quikscat amount to 168 km 3 236 km 3 and 62 km 3 77 km 3 for 30 day periods in february march and october november 2003 respectively these values lie in the range of previous results from similar studies but are considerably smaller than the average ice flux during the 1990s most likely because of a smaller ice drift speed during 2003

icesat measurements of sea ice freeboard and estimates of sea ice thickness in the weddell sea 1 sea ice freeboard heights in the weddell sea of antarctica are derived from the ice cloud and land elevation satellite icesat laser altimeter measurements which have a unique range precision to flat surfaces of 2 cm within 70 m footprints spaced at 172 m along track although elevations of flat surfaces can be obtained to an accuracy of 10 cm 1s per footprint direct determination of freeboard heights is precluded by errors in knowledge of the geoid and temporal variability of the ocean surface therefore freeboards are determined relative to an ocean reference level detected over areas of open water and very thin ice within the sea ice pack using an along track filtering method the open water thin ice selections show good agreement in the combined analysis of icesat segments and envisat synthetic aperture radar sar imagery the average residual between the icesat measured ocean level and the egm96 geoid is 1 4 m estimates of snow depth on the sea ice from amsr e passive microwave data along with nominal densities of snow water and sea ice are used to estimate sea ice thickness four periods of icesat data in may june fall and october november late winter of 2004 and 2005 between longitudes 298e and 360e are analyzed in the fall the mean freeboards are 0 28 m in 2004 and 0 29 m in 2005 and the mean thicknesses are 1 33 m in 2004 and 1 52 m in 2005 in late winter the freeboards grew to 0 37 m in 2004 and 0 35 in 2005 and the thicknesses grew to 2 23 m in 2004 and 2 31 m in 2005 the interannual differences in freeboard are small and the larger interannual change in estimated thickness mainly represents differences in the snow depth estimates seasonal changes in the spatial patterns of freeboard and thickness over the 4 months correlate with the expected circulation of sea ice in the weddell sea as indicated by sea ice velocity fields

an assessment of state of the art mean sea surface and geoid models of the arctic ocean implications for sea ice freeboard retrieval state of the art arctic ocean mean sea surface mss models and global geoid models ggms are used to support sea ice freeboard estimation from satellite altimeters as well as in oceanographic studies such as mapping sea level anomalies and mean dynamic ocean topography however errors in a given model in the high frequency domain primarily due to unresolved gravity features can result in errors in the estimated along track freeboard these errors are exacerbated in areas with a sparse lead distribution in consolidated ice pack conditions additionally model errors can impact ocean geostrophic currents derived from satellite altimeter data while remaining biases in these models may impact longer term multi sensor oceanographic time series of sea level change in the arctic this study focuses on an assessment of five state of the art arctic mss models ucl13 04 dtu15 13 10 and a commonly used ggm egm2008 we describe errors due to unresolved gravity features inter satellite biases and remaining satellite orbit errors and their impact on the derivation of sea ice freeboard the latest mss models incorporating cryosat 2 sea surface height measurements show improved definition of gravity features such as the gakkel ridge the standard deviation between models ranges 0 03 0 25 m the impact of remaining mss ggm errors on freeboard retrieval can reach several decimeters in parts of the arctic while the maximum observed freeboard difference found in the central arctic was 0 59 m ucl13 mss minus egm2008 ggm the standard deviation in freeboard differences is 0 03 0 06 m

taking a look at both sides of the ice comparison of ice thickness and drift speed as observed from moored airborne and shore based instruments near barrow alaska data from the seasonal ice zone observing network sizonet acquired near barrow alaska during the 2009 10 ice season allow novel comparisons between measurements of ice thickness and velocity an airborne electromagnetic survey that passed over a moored ice profiling sonar ips provided coincident independent measurements of total ice and snow thickness and ice draft at a scale of 10 km once differences in sampling footprint size are accounted for we reconcile the respective probability distributions and estimate the thickness of level sea ice at 1 48 0 1 m with a snow depth of 0 12 0 07 m we also complete what we believe is the first independent validation of radar derived ice velocities by comparing measurements from a coastal radar with those from an under ice acoustic doppler current profiler adcp after applying a median filter to reduce high frequency scatter in the radar derived data we find good agreement with the adcp bottom tracked ice velocities with increasing regulatory and operational needs for sea ice data including the number and thickness of pressure ridges coordinated observing networks such as sizonet can provide the means of reducing uncertainties inherent in individual datasets