coarse grained sediment flow facies in a large supraglacial lake discussion sur l article de eyles n clark b m and clague j j 1987 sedimentology vol 34 93 216

potential for estimation of snow depth on arctic sea ice from cryosat 2 and saral altika missions abstract the scattering properties of the radar signal at ka and ku band frequencies are investigated using a theoretical model and snow grain observations obtained during previous field campaigns our results show that the combination of radar altimeters operating at these two frequencies should allow for the retrieval of snow depth over arctic sea ice we estimate uncertainties of the ice surface position in relation to crossover observations over sea ice and show that the accuracy of the crossover methodology with short time gap 3 days or less is better than 3 cm comparison of the cryosat 2 altika retrieved snow depth with in situ measurements provided by operation icebridge shows a good agreement with a root mean square error rmse of 5 cm analysis of the cryosat 2 altika retrieved snow depths over three winters 2013 2015 reveals a thinner snow cover on both multi year 32 57 and first year ice 63 75 relative to the 1954 91 warren climatology suggesting the need for more contemporary year round and basin scale snow depth fields

modeling the radio echo reflections inside the ice sheet at summit greenland 1 radio echo surveys to determine the thickness of ice sheets often record reflections from inside the ice to increase our understanding of these internal reflections we have used synthetic seismogram techniques from early seismic modeling to construct two models both models were one dimensional the first considered only primary reflections while the second included both primary and multiple reflections the inputs to both models were a radio pulse and data from the greenland ice core project grip core of length 3028 m the ice core data consisted of a profile of the high frequency conductivity calculated from dielectric profile dep measurements and a smooth profile of the real permittivity the models produced synthetic radargrams which are the energy reflected from conductivity variations as a function of the two way travel time both models gave similar results indicating that multiples do not alter the travel time of the reflections i e no o doherty anstey effect at our time resolution one of the results was then processed to simulate the reflected energy passing through the receiver circuit of a radio echo system and then compared with a recorded trace the processed result contained many of the larger reflections recorded below about 500 m including nearly all the features from depths greater than 1500 m in particular several interstadial events in the wisconsin age ice since high frequency conductivity variations are dominated by chemical changes which are caused by deposition on the surface of the ice sheet it is possible to conclude that the reflections deep inside the greenland ice sheet can be treated as isochrons

thinning and volume loss of the arctic ocean sea ice cover 2003 2008 1 we present our best estimate of the thickness and volume of the arctic ocean ice cover from 10 ice cloud and land elevation satellite icesat campaigns that span a 5 year period between 2003 and 2008 derived ice drafts are consistently within 0 5 m of those from a submarine cruise in mid november of 2005 and 4 years of ice draft profiles from moorings in the chukchi and beaufort seas along with a more than 42 decrease in multiyear my ice coverage since 2005 there was a remarkable thinning of 0 6 m in my ice thickness over 4 years in contrast the average thickness of the seasonal ice in midwinter 2 m which covered more than two thirds of the arctic ocean in 2007 exhibited a negligible trend average winter sea ice volume over the period weighted by a loss of 3000 km3 between 2007 and 2008 was 14 000 km3 the total my ice volume in the winter has experienced a net loss of 6300 km3 40 in the 4 years since 2005 while the first year ice cover gained volume owing to increased overall area coverage the overall decline in volume and thickness are explained almost entirely by changes in the my ice cover combined with a large decline in my ice coverage over this short record there is a reversal in the volumetric and areal contributions of the two ice types to the total volume and area of the arctic ocean ice cover seasonal ice having surpassed that of my ice in winter area coverage and volume became the dominant ice type it seems that the near zero replenishment of the my ice cover after the summers of 2005 and 2007 an imbalance in the cycle of replenishment and ice export has played a significant role in the loss of arctic sea ice volume over the icesat record

improvement of lake ice thickness retrieval from modis satellite data using a thermodynamic model observations of ice thickness are limited in high latitude regions at a time when they are increasingly being requested by operational ice centers this study aims to improve the retrieval of lake ice thickness using data from the moderate resolution imaging spectroradiometer modis on board nasa s aqua p m and terra a m satellites the accuracy of ice thickness retrievals based on modis lake ice surface temperature list is investigated using a commonly used heat balance equation and the retrieved ice thicknesses are compared to in situ measurements from the canadian ice service the accuracy of ice thickness estimates is improved when using snow depth from the 1 d thermodynamic lake ice model canadian lake ice model climo rather than an empirical relationship between snow depth and ice thickness utilized in the recent investigations taking into account all data over the study period 2002 2014 the mean bias error and the root mean square error are reduced from 0 42 to 0 07 m and 0 58 to 0 17 m respectively with the novel approach proposed herein however this approach is limited to ice thickness estimations of less than ca 1 7 m

ku band radar penetration into snow cover on arctic sea ice using airborne data satellite radar altimetry provides data to monitor winter arctic sea ice thickness variability on interannual basin wide scales when using this technique an assumption is made that the peak of the radar return originates from the snow ice interface this has been shown to be true in the laboratory for cold dry snow as is the case on arctic sea ice during winter however this assumption has not been tested in the field we use data from an airborne normal incidence ku band radar altimeter and in situ field measurements collected during the cryosat validation experiment cryovex bay of bothnia 2006 and 2008 field campaigns to determine the dominant scattering surface for arctic snow covered sea ice in 2006 when the snow temperatures were close to freezing the dominant scattering surface in 25 of the radar returns appeared closer to the snow ice interface than the air snow interface however in 2008 when temperatures were lower the dominant scattering surface appeared closer to the snow ice interface than the air snow interface in 80 of the returns

sea ice thickness in the eastern canadian arctic hudson bay complex baffin bay abstract past observations of sea ice thickness in the eastern canadian arctic eca have generally been restricted to drill hole measurements at a few local sites on landfast ice here we use data from the laser altimeter icesat and the radar altimeter cryosat 2 to present a 14 year record 2003 2016 of high resolution and spatially extensive ice thickness observations for the eca and identify 12 sub regions with distinct patterns the mean sea ice growth rate within the seasonally ice covered eca from november to april is 23 cm mo 1 565 km 3 mo 1 with the fastest increase in thickness occurring through strong ice convergence and deformation in eastern hudson bay and foxe basin our results demonstrate characteristically asymmetrical distributions of sea ice thickness in both hudson bay and baffin bay but in opposing directions in hudson bay the spring ice cover is 40 cm thicker in the eastern region compared to the northwestern region whereas in baffin bay the ice is 20 cm thicker in the western half of the bay compared to the eastern half in hudson bay we find that years with strong and positive ice drift vorticity i e cyclonic and convergent conditions correlate with increasingly asymmetrical sea ice covers with the level of west east asymmetry varying from 2 to 11 cm per 100 km however in baffin bay the ice drift vorticity is typically negative i e anticyclonic and divergent with no obvious link to the asymmetry of the spring ice cover finally we estimate that large interannual variations in spring sea ice volume within the eca lead to 15 variations in the volume of freshwater available at the ocean surface during summer

simulation and parameterization of superimposed ice formation in cold arctic snowpacks meltwater retention is a significant factor controlling the timing and magnitude of runoff meltwater percolates vertically through the snowpack until it reaches an impermeable horizon whereupon a saturated zone is established if the underlying media is below the freezing point accretive ice formation takes place this process has previously been crudely parameterized or modelled numerically such ice is called either superimposed ice on glaciers or basal ice on bare land using theory derived from sea ice formation an analytical solution to basal ice growth is proposed results are compared against growth rates derived from numerical modelling in addition model results are compared to field observations of ice temperatures the analytical solution is further extended to account for the temperature gradient inside the underlying media and the variable thermal properties of the underlying media in the analysis observations and references have predominantly relied on knowledge from glaciers however the process of accretive ice growth is equally important in seasonal snow packs with a cold snow ground interface and on arctic sea ice where the ice snow interface is well below freezing point the simplification of this accretive ice growth problem makes the solution attractive for incorporation in large scale cryospheric models copyright 2007 john wiley sons ltd

remote sensing of sea ice thickness and salinity with 0 5 2 ghz microwave radiometry an ultrawideband radiometer was used to measure microwave brightness temperature spectra over arctic sea ice in the lincoln sea near the north coast of greenland spectra over the range of 0 5 2 ghz were compared to thermal infrared images collected during the airborne campaign and also compared to nearly concurrent sentinel 1 c band synthetic aperture radar sar data based on those comparisons spectral signatures were associated with thick multiyear ice and thin ice a radiative transfer rt model consisting of a homogeneous slab of sea ice bounded by sea water and air was then used to invert the spectra for sea ice thickness and salinity inferred thicknesses were consistent with ice thickness climatology for ice floes in the lincoln sea salinities are higher than expected which may be a consequence of neglecting surface and volume scattering contributions in the models

smos sea ice product operational application and validation in the barents sea marginal ice zone brightness temperatures at 1 4 ghz l band measured by the soil moisture and ocean salinity smos mission have been used to derive the thickness of sea ice the retrieval method is applicable only for relatively thin ice and not during the melting period hitherto the availability of ground truth sea ice thickness measurements for validation of smos sea ice products was mainly limited to relatively thick ice the situation has improved with an extensive field campaign in the barents sea during an anomalous ice edge retreat and subsequent freeze up event in march 2014 a sea ice forecast system for ship route optimisation has been developed and was tested during this field campaign with the ice strengthened research vessel rv lance the ship cruise was complemented with coordinated measurements from a helicopter and the research aircraft polar 5 sea ice thickness was measured using an electromagnetic induction em system from the bow of rv lance and another em system towed below the helicopter polar 5 was equipped among others with the l band radiometer emirad 2 the experiment yielded a comprehensive data set allowing the evaluation of the operational forecast and route optimisation system as well as the smos derived sea ice thickness product that has been used for the initialization of the forecasts two different smos sea ice thickness products reproduce the main spatial patterns of the ground truth measurements while the main difference being an underestimation of thick deformed ice ice thicknesses derived from the surface elevation measured by an airborne laser scanner and from simultaneous emirad 2 brightness temperatures correlate well up to 1 5 m which is more than the previously anticipated maximal smos retrieval thickness

comparing l and c band synthetic aperture radar estimates of sea ice motion over different ice regimes abstract estimating sea ice motion from synthetic aperture radar sar imagery at c band is the most reliable approach because of its high spatial resolution and ever increasing temporal resolution given the multiple current and upcoming sar platforms however there is still uncertainty in sar derived sea ice motion depending on the ice type and its thermodynamic state there have been suggestions mostly theoretical that use of l band sar and its inherent longer wavelength 15 30 cm and subsequent increased penetration capability could be beneficial for estimating sea ice motion especially during the melt season here we estimate and analyze sea ice motion for 9 pairs of c and l band sar imagery from radarsat 2 palsar 1 and palsar 2 located in the canadian arctic over a variety of sea ice types at different thermodynamic states results show that the increased signal penetration of l band sar into multi year ice myi during the melt season facilitates the detection of more motion vectors with stronger cross correlation coefficients compared to c band sar over newly formed ice and dry first year ice the reduced sensitivity to surface scattering and richer texture from l band sar imagery facilitates the detection of more motion vectors with stronger cross correlation coefficients compared to c band sar over dry myi l band provided stronger cross correlation coefficients but c band detected more motion vectors with a more representative spatial distribution with arctic sea ice continuing shift from a multi year to first year dominated icescape coupled with an increasing melt season length l band sar s ability to provide improved sea ice motion estimates during both the melt and freeze up time periods could prove even more useful in the coming decades

summer sea ice motion from the 18 ghz channel of amsr e and the exchange of sea ice between the pacific and atlantic sectors 1 we demonstrate that sea ice motion in summer can be derived reliably from the 18ghz channel of the amsr e instrument on the eos aqua platform the improved spatial resolution of this channel with its lower sensitivity to atmospheric moisture seems to have alleviated various issues that have plagued summer motion retrievals from shorter wavelength observations two spatial filters improve retrieval quality one reduces some of the microwave signatures associated with synoptic scale weather systems and the other removes outliers compared with daily buoy drifts uncertainties in motion are 3 4 km day using the daily motion fields we examine five years of summer ice area exchange between the pacific and atlantic sectors of the arctic ocean with the sea level pressure patterns during the summer of 2006 and 2007 favoring the export of sea ice into the atlantic sector the regional outflow is 21 and 15 of the total sea ice retreat in the pacific sector

ice and snow thickness variability and change in the high arctic ocean observed by in situ measurements in april 2017 we collected unique extensive in situ data of sea ice and snow thickness at 10 sampling sites located under a cryosat 2 overpass between ellesmere island and 87 1 n mean and modal total ice thicknesses ranged between 2 to 3 4 m and 1 8 to 2 9 m respectively coincident snow thicknesses ranged between 0 3 to 0 47 m mean and 0 1 to 0 5 m mode the profile spanned the complete multiyear ice zone in the lincoln sea into the first year ice zone farther north complementary snow thickness measurements near the north pole showed a mean thickness of 0 31 m compared with scarce measurements from other years multiyear ice was up to 0 75 m thinner than in 2004 but not significantly different from 2011 and 2014 we found excellent agreement with a commonly used snow climatology and with published long term ice thinning rates there was reasonable agreement with cryosat 2 thickness retrievals

a facet based numerical model for simulating sar altimeter echoes from heterogeneous sea ice surfaces cryosat 2 has provided measurements of pan arctic sea ice thickness since 2010 with unprecedented spatial coverage and frequency however it remains uncertain how the ku band radar interacts with the vast range of scatterers that can be present within the satellite footprint including sea ice with varying physical properties and multiscale roughness snow cover and leads here we present a numerical model designed to simulate delay doppler synthetic aperture radar sar altimeter echoes from snow covered sea ice such as those detected by cryosat 2 backscattered echoes are simulated directly from triangular facet based models of actual sea ice topography generated from operation icebridge airborne topographic mapper data as well as virtual statistical models simulated artificially we use these waveform simulations to investigate the sensitivity of sar altimeter echoes to variations in satellite parameters height pitch and roll and sea ice properties physical properties roughness and presence of water we show that the conventional gaussian assumption for sea ice surface roughness may be introducing significant error into the cryosat 2 waveform retracking process compared to a more representative lognormal surface an echo simulated from a gaussian surface with rms roughness height of 0 2 m underestimates the ice freeboard by 5 cm potentially underestimating sea ice thickness by around 50 cm we present a set of ideal waveform shape parameters simulated for sea ice and leads to inform existing waveform classification techniques this model will ultimately be used to improve retrievals of key sea ice properties including freeboard surface roughness and snow depth from sar altimeter observations

beaufort gyre freshwater reservoir state and variability from observations 1 we investigate basin scale mechanisms regulating anomalies in freshwater content fwc in the beaufort gyre bg of the arctic ocean using historical observations and data collected in 2003 2007 specifically the mean annual cycle and interannual and decadal fwc variability are explored the major cause of the large fwc in the bg is the process of ekman pumping ep due to the arctic high anticyclonic circulation centered in the bg the mean seasonal cycle of liquid fwc is a result of interplay between the mechanical ep and thermal ice transformations factors and has two peaks one peak occurs around june july when the sea ice thickness reaches its minimum maximum ice melt the second maximum is observed in november january when wind curl is strongest maximum ep and the salt input from the growing ice has not yet reached its maximum interannual changes in fwc during 2003 2007 are characterized by a strong positive trend in the region varying by location with a maximum of approximately 170 cm a 1 in the center of ep influenced region decadal fwc variability in the period 1950 2000 is dominated by a significant change in the 1990s forced by an atmospheric circulation regime change the center of maximum fwc shifted to the southeast and appeared to contract in area relative to the pre 1990s climatology in spite of the areal reduction the spatially integrated fwc increased by over 1000 km 3 relative to climatology

sea ice motion from satellite passive microwave imagery assessed with ers sar and buoy motions observing the motion of sea ice from space is analogous to observing wind stress over the wet oceans both provide surface forcing for modeling ocean dynamics ice motion also directly provides the advective component of the equations governing the mass balance of the sea ice cover thus its routine observation from space would be of great value to understanding ice and ocean behavior to demonstrate the feasibility of creating a global multidecadal ice motion record from satellite passive microwave imagery and to quantitatively assess the errors in the estimated ice motions we have tracked ice every 3 days in the arctic ocean and daily in the fram strait and baffin bay during the 8 winter months from october 1992 to may 1993 and daily in the weddell sea during the 8 winter months from march to october 1992 the method which has been well used previously involves finding the spatial offset that maximizes the cross correlation of the brightness temperature fields over 100 km patches in two images separated in time by from 1 to 3 days the resulting ice motions are compared with contemporaneous buoyand sar derived ice motions the uncertainties in the displacement vectors between 5 and 12 km are better than the spatial resolution of the data both 85 ghz data with 12 km spatial resolution and 37 ghz data with 25 km resolution are tracked these trials with the 37 ghz data are new and show quite surprisingly that the error is only about 1 km larger with these data than with the 12 km 85 ghz data errors are typically larger than average in areas of lower ice concentration in the most dynamic regions particularly near the ice edge in the barents and greenland seas and in zones of high shear these passive microwave ice motions show a large increase in spatial detail over motion fields optimally interpolated from buoy and wind observations especially where buoy data are virtually absent such as near coasts and in some passages between the arctic ocean and its peripheral seas the feasibility of obtaining ice motion from the 37 ghz data in addition to the 85 ghz data should allow an important record of ice motion to be established for the duration of the scanning multichannel microwave radiometer smmr special sensor microwave imager ssm i and future microwave sensors that is from 1978 into the next millenium

can we extend local sea ice measurements to satellite scale an example from the n ice2015 expedition knowledge of arctic sea ice conditions is of great interest for arctic residents as well as for commercial usage and to study the effects of climate change information gained from analysis of satellite data contributes to this understanding in the course of using in situ data in combination with remotely sensed data the question of how representative local scale measurements are of a wider region may arise we compare in situ total sea ice thickness measurements from the norwegian young sea ice expedition in the area north of svalbard with airborne derived total sea ice thickness from electromagnetic soundings a segmented and classified synthetic aperture radar sar quad pol alos 2 palsar 2 satellite scene was grouped into three simplified ice classes the area fractions of the three classes are 11 2 thin 74 4 level and 14 4 deformed the area fractions of the simplified classes from ground and helicopter based measurements are comparable with those achieved from the sar data thus this study shows that there is potential for a stepwise upscaling from in situ to airborne to satellite data which allow us to assess whether in situ data collected are representative of a wider region as observed by satellites

sea ice thickness from field measurements in the northwestern barents sea the barents sea is one of the fastest changing regions of the arctic and has experienced the strongest decline in winter time sea ice area in the arctic at 23 4 per decade sea ice thickness in the barents sea is not well studied we present two previously unpublished helicopter borne electromagnetic hem ice thickness measurements from the northwestern barents sea acquired in march 2003 and 2014 the hem data are compared to ice thickness calculated from ice draft measured by uls deployed between 1994 and 1996 these data show that ice thickness varies greatly from year to year influenced by the thermodynamic and dynamic processes that govern local formation vs long range advection in a year with a large inflow of sea ice from the arctic basin the barents sea ice cover is dominated by thick multiyear ice as was the case in 2003 and 1995 in a year with an ice cover that was mainly grown in situ the ice will be thin and mechanically unstable as was the case in 2014 the hem data allow us to explore the spatial and temporal variability in ice thickness in 2003 the dominant ice class was more than 2 years old and modal sea ice thickness varied regionally from 0 6 to 1 4 m with the thinner ice being either first year ice or multiyear ice which had come into contact with warm atlantic water in 2014 the ice cover was predominantly locally grown ice less than 1 month old regional modes of 0 5 0 8 m these two situations represent two extremes of a range of possible ice thickness distributions that can present very different conditions for shipping traffic or have a different impact on heat transport from ocean to atmosphere

consistent ice and open water classification combining historical synthetic aperture radar satellite images from ers 1 2 envisat asar radarsat 2 and sentinel 1a b

greater role for atlantic inflows on sea ice loss in the eurasian basin of the arctic ocean arctic sea ice loss is a leading indicator of climate change and can be attributed in large part to atmospheric forcing here we show that recent ice reductions weakening of the halocline and shoaling of the intermediate depth atlantic water layer in the eastern eurasian basin have increased winter ventilation in the ocean interior making this region structurally similar to that of the western eurasian basin the associated enhanced release of oceanic heat has reduced winter sea ice formation at a rate now comparable to losses from atmospheric thermodynamic forcing thus explaining the recent reduction in sea ice cover in the eastern eurasian basin this encroaching atlantification of the eurasian basin represents an essential step toward a new arctic climate state with a substantially greater role for atlantic inflows

the decline in arctic sea ice thickness separating the spatial annual and interannual variability in a quarter century of submarine data 1 naval submarines have collected operational data of sea ice draft 93 of thickness in the arctic ocean since 1958 data from 34 u s cruises are publicly archived they span the years 1975 to 2000 are equally distributed in spring and autumn and cover roughly half the arctic ocean the data set is strong we use 2203 values of mean draft each value averaged over a nominal length of 50 km these values range from 0 to 6 m with a standard deviation of 0 99 m multiple regression is used to separate the interannual change the annual cycle and the spatial field the solution gives a climatology for ice draft as a function of space and time the residuals of the regression have a standard deviation of 0 46 m slightly more than the observational error standard deviation of 0 38 m the overall mean of the solution is 2 97 m annual mean ice draft declined from a peak of 3 42 m in 1980 to a minimum of 2 29 m in 2000 a decrease of 1 13 m 1 25 m in thickness the steepest rate of decrease is 0 08 meters per year m a in 1990 the rate slows to 0 007 m a at the end of the record the annual cycle has a maximum on 30 april and a peak to trough amplitude of 1 06 m 1 12 m in thickness the spatial contour map of the temporal mean draft varies from a minimum draft of 2 2 m near alaska to a maximum just over 4 m at the edge of the data release area 200 miles north of ellesmere island

calibration of the cryosat 2 interferometer and measurement of across track ocean slope this paper describes the calibration of the cryosat 2 interferometer whose principal purpose is to accurately measure the height of the antarctic and greenland ice sheets a sequence of cryosat 2 data acquisitions over the tropical and midlatitude oceans were obtained between june and september 2010 from the siral a and redundant siral b radars operating in their sarin mode during a sequence of satellite rolls between 0 6 and 0 4 using the arrival angle of the echo relative to the interferometer baseline the attitude of the satellite determined by the star trackers and estimates of the ocean surface across track slope from the egm08 geoid we determined the errors in the interferometer estimate of surface slope as functions of the roll angle and ocean surface waveheight these were found to be in close agreement with the theoretical description the scale factor of the interferometric measurement of angle was determined to be 0 973 0 002 we estimate the accuracy of the across track slope measurement of the interferometer by applying this scale factor to the measured phase in applying this scale factor to the measurements the across track slope of the marine geoid was obtained with an accuracy of 26 rad at 10 km and 10 rad at 1000 km we conclude that the instrument performance considerably exceeds that needed for the accurate determination of height over the sloping surfaces of the continental ice sheets the results also demonstrate that cryosat 2 provides the first observations of the instantaneous vector gradient of the ocean surface and that the normal incidence interferometric configuration has a greater potential for the measurement of the ocean across track slope than has been previously recognized

comparing coincident elevation and freeboard from icebridge and five different cryosat 2 retrackers the airborne operation icebridge and spaceborne cryosat 2 missions observe polar sea ice at different spatial and temporal scales as well as with different sensor suites comparison of data products from icebridge and cryosat 2 is complicated by the fact that they use different geophysical corrections reference ellipsoid geoid model tide model and atmospheric corrections to derive surface elevation and sea ice freeboard in this paper we compare sea ice surface elevation and freeboard using eight coincident cryosat 2 airborne topographic mapper atm and land vegetation and ice sensor lvis observations with direct icebridge underflights of cryosat 2 ground tracks we apply identical geophysical corrections to cryosat 2 and icebridge data to eliminate elevation biases due to these differences and focus on differences due to retracker performance the icebridge atm and lvis elevation and freeboard and snow radar snow depth data sets are averaged to each cryosat 2 footprint for comparison with snow depth measurements we are able to compare elevations and freeboards at the snow ice interface for five different cryosat 2 retrackers esa gsfcv1 awi jpl and gsfcv2 and icebridge the overall mean of freeboard differences between gsfcv2 esa awi jpl retrackers and atm are in agreement within 0 05 m however the five different cryosat 2 retrackers show distinct differences in mean elevation over leads and over floes this suggests that the physical interpretation of the different retrackers needs to be considered depending on usage for example elevations from cryosat 2 retrackers need to be carefully calibrated before comparing with elevation from other satellites for long term surface elevation trends

decline in arctic sea ice thickness from submarine and icesat records 1958 2008 1 the decline of sea ice thickness in the arctic ocean from icesat 2003 2008 is placed in the context of estimates from 42 years of submarine records 1958 2000 described by rothrock et al 1999 2008 while the earlier 1999 work provides a longer historical record of the regional changes the latter offers a more refined analysis over a sizable portion of the arctic ocean supported by a much stronger and richer data set within the data release area dra of declassified submarine sonar measurements covering 38 of the arctic ocean the overall mean winter thickness of 3 64 m in 1980 can be compared to a 1 89 m mean during the last winter of the icesat record an astonishing decrease of 1 75 m in thickness between 1975 and 2000 the steepest rate of decrease is 0 08 m yr in 1990 compared to a slightly higher winter summer rate of 0 10 0 20 m yr in the five year icesat record 2003 2008 prior to 1997 ice extent in the dra was 90 during the summer minimum this can be contrasted to the gradual decrease in the early 2000s followed by an abrupt drop to 55 during the record setting minimum in 2007 this combined analysis shows a long term trend of sea ice thinning over submarine and icesat records that span five decades

precise dielectric profiling of ice cores a new device with improved guarding and its theory dielectric profiling dep a capacitive method for measuring an ice core s electrical conductivity and permittivity has been in use for several years we have built an improved dep instrument with a modified guarded electrode geometry whose capacitance can be determined from potential theory the new instrument can measure an ice core s conductivity and permittivity to within a few per cent error a high enough accuracy to infer its density using well known models

outflow of arctic ocean sea ice into the greenland and barents seas 1979 2007 abstract twenty nine years of arctic sea ice outflow into the greenland and barents seas are summarized outflow is computed at three passages fram strait between svalbard and franz josef land s fjl and between franz josef land and severnaya zemlya fjl sz ice drift at the flux gates has been reprocessed using a consistent and updated time series of passive microwave brightness temperature and ice concentration ic fields over the record the mean annual area outflow at the fram strait is 706 113 103 km2 it was highest in 1994 95 1002 103 km2 when the north atlantic oscillation nao index was near its 29 yr peak the strength of the transpolar drift stream tds was high during the late 1980s through the mid 1990s there is no statistically significant trend in the fram strait area flux even though there is a positive trend in the gradient of cross strait sea level pressure the outflow has not increased because of a negative trend in ic seasonally the area outflow during recent sum

asiras airborne radar resolves internal annual layers in the dry snow zone of greenland 1 we present data from the european space agency s airborne sar interferometric radar altimeter system asiras flown during the cryovex 2004 field calibration validation campaign and new high resolution depth profiles of snow density measured in the field by neutron scattering we combine these data to calculate the depth of internal reflecting horizons in the asiras data the high resolution density data allow us to identify annual layers in the snow density profile and correlate their peaks with the reflecting horizons we use the thickness of the annual layers combined with the density profile to determine the spatial and temporal pattern of snow accumulation along the radar track for a period of 6 years from 1995 2002 our mean annual accumulation rate is 0 47 0 09 ma 1 water equivalent in agreement with the value determined from a core taken in this location in 1992 similarly our inter annual variability shows the same trends as recent model estimates over the entire ice sheet because asiras was designed to mimic as closely as possible the characteristics of the sar interferometric radar altimeter siral the principal payload of cryosat the detection of internal layering with asiras illuminates the possibility of detecting internal layers with a space borne radar and thus the possible application of this technique to the dry snow zones of antarctica greenland and smaller ice bodies

combined observations of arctic sea ice with near coincident colocated x band c band and l band sar satellite remote sensing and helicopter borne measurements in this study we compare colocated near coincident x c and l band fully polarimetry sar satellite images with helicopter borne ice thickness measurements acquired during the norwegian young sea ice 2015 n ice2015 expedition in the region of the arctic ocean north of svalbard in april 2015 the air borne surveys provide near coincident snow plus ice thickness surface roughness data and photographs this unique data set allows us to investigate how the different frequencies can complement one another for sea ice studies but also to raise awareness of limitations x band and l band satellite scenes were shown to be a useful complement to the standard sar frequency for sea ice monitoring c band for lead ice and newly formed sea ice identification this may be in part be due to the frequency but also the high spatial resolution of these sensors we found a relatively low correlation between snow plus ice thickness and surface roughness therefore in our dataset ice thickness cannot directly be observed by sar which has important implications for operational ice charting based on automatic segmentation

deterioration of perennial sea ice in the beaufort gyre from 2003 to 2012 and its impact on the oceanic freshwater cycle time series of ice draft from 2003 to 2012 from moored sonar data are used to investigate variability and describe the reduction of the perennial sea ice cover in the beaufort gyre bg culminating in the extreme minimum in 2012 negative trends in median ice drafts and most ice fractions are observed while open water and thinnest ice fractions 0 3 m have increased attesting to the ablation or removal of the older sea ice from the bg over the 9 year period monthly anomalies indicate a shift occurred toward thinner ice after 2007 in which the thicker ice evident at the northern stations was reduced differences in the ice characteristics between all of the stations also diminished so that the ice cover throughout the region became statistically homogenous the moored data are used in a relationship with satellite radiometer data to estimate ice volume changes throughout the bg summer solid fresh water content decreased drastically in consecutive years from 730 km3 in 2006 to 570 km3 in 2007 and to 240 km3 in 2008 after a short rebound solid fresh water fell below 220 km3 in 2012 meanwhile hydrographic data indicate that liquid fresh water in the bg in summer increased 5410 km3 from 2003 to 2010 and decreased at least 210 km3 by 2012 the reduction of both solid and liquid fresh water components indicates a net export of approximately 320 km3 of fresh water from the region occurred between 2010 and 2012 suggesting that the anticyclonic atmosphere ocean circulation has weakened

variability of arctic sea ice thickness and volume from cryosat 2 we present our estimates of the thickness and volume of the arctic ocean ice cover from cryosat 2 data acquired between october 2010 and may 2014 average ice thickness and draft differences are within 0 16 m of measurements from other sources moorings submarine electromagnetic sensors icebridge the choice of parameters that affect the conversion of ice freeboard to thickness is discussed estimates between 2011 and 2013 suggest moderate decreases in volume followed by a notable increase of more than 2500 km 3 or 0 34 m of thickness over the basin in 2014 which could be attributed to not only a cooler summer in 2013 but also to large scale ice convergence just west of the canadian arctic archipelago due to wind driven onshore drift variability of volume and thickness in the multiyear ice zone underscores the importance of dynamics in maintaining the thickness of the arctic ice cover volume estimates are compared with those from icesat as well as the trends in ice thickness derived from submarine ice draft between 1980 and 2004 the combined icesat and cryosat 2 record yields reduced trends in volume loss compared with the 5 year icesat record which was weighted by the record setting ice extent after the summer of 2007

recent ice sheet growth in the interior of greenland a continuous data set of greenland ice sheet altimeter height from european remote sensing satellites ers 1 and ers 2 1992 to 2003 has been analyzed an increase of 6 4 0 2 centimeters per year cm year is found in the vast interior areas above 1500 meters in contrast to previous reports of high elevation balance below 1500 meters the elevation change rate is 2 0 0 9 cm year in qualitative agreement with reported thinning in the ice sheet margins averaged over the study area the increase is 5 4 0 2 cm year or 60 cm over 11 years or 54 cm when corrected for isostatic uplift winter elevation changes are shown to be linked to the north atlantic oscillation

k u band airborne radar altimeter observations of marginal sea ice during the 1984 marginal ice zone experiment pulse limited airborne radar data taken in june and july 1984 with a 13 8 ghz altimeter over the fram strait marginal ice zone are analyzed with the aid of large format aerial photography airborne synthetic aperture radar data and surface observations variations in the radar return pulse waveforms are quantified and correlated with ice properties recorded during the marginal ice zone experiment results indicate that the wide beam altimeter is a flexible instrument capable of identifying the ice edge with a high degree of accuracy calculating the ice concentration and discriminating a number of different ice classes this suggests that microwave radar altimeters have a sensitivity to sea ice which has not yet been fully exploited when fused with ssm i avhrr and ers 1 synthetic aperture radar imagery future ers 1 altimeter data are expected to provide some missing pieces to the sea ice geophysics puzzle

the biogeography and ecology of common diatom species in the northern north atlantic and their implications for paleoceanographic reconstructions abstract sound knowledge of present day diatom species and their environments is crucial when attempting to reconstruct past climate and environmental changes based on fossil assemblages for the north atlantic region the biogeography and ecology of many diatom taxa that are used as indicator species in paleoceanographic studies are still not well known using information contained in large diatom environment calibration datasets can greatly increase our knowledge on diatom taxa and improve the accuracy of paleoenvironmental reconstructions a diatom calibration dataset including 183 surface sediment samples from the northern north atlantic was used to explore the distribution and ecology of 21 common northern hemisphere diatom taxa we define the ecological responses of these species to april sea ice concentrations and august sea surface temperatures assts using huisman olff fresco hof response curves provide distribution maps temperature optima and ranges and high quality light microscope images based on the results we find species clearly associated with cold warm and temperate waters all species have a statistically significant relationship with asst and 15 species with sea ice of these actinocyclus curvatulus fragilariopsis oceanica and porosira glacialis are most abundant at high sea ice concentrations whereas coscinodiscus radiatus shionodiscus oestrupii thalassionema nitzschioides thalassiosira angulata thalassiosira nordenskioeldii and thalassiosira pacifica are associated with low sea ice concentrations ice free conditions interestingly some species frequently used as sea ice indicators such as fragilariopsis cylindrus show similar abundances at high and low sea ice concentrations with no statistically significant relationship to sea ice

the thermal regime of sub polar glaciers mapped by multi frequency radio echo sounding radio echo soundings provide an effective tool for mapping the thermal regimes of polythermal glaciers on a regional scale radar signals of 320 370 mhz penetrate ice at sub freezing temperatures but are reflected from the top of layers of ice which are at the melting point and contain water radar signals of 5 20 mhz on the other hand see through both the cold and the temperate ice down to the glacier bed radio echo soundings at these frequencies have been used to investigate the thermal regimes of four polythermal glaciers in svalbard kongsvegen uversbreen midre lovenbreen and austre broggerbreen in the ablation area of kongsvegen a cold surface layer 50 160m thick was underlain by a warm basal layer which is advected from the temperate accumulation area the surface ablation of this cold layer may be compensated by freezing at its lower cold temperate interface this requires that the free water content in the ice at the freezing interface is about 1 of the volume the cold surface layer is thicker beneath medial moraines and where cold based hanging glaciers enter the main ice stream on uversbreen the thermal regime was similar to that of kongsvegen a temperate hole was found in the otherwise cold surface layer of the ablation area in a surface depression between kongsvegen and uversbreen where meltwater accumulates during the summer near the subglacial lake setevatnet 250 m a s l lovenbreen was frozen to the bed at the snout and along all the mountain slopes but beneath the central part of the glacier a warm basal layer up to 50m thick was fed by temperate ice from two cirques on austre broggerbreen a temperate basal layer was not detected by radio echo soundings but the basal ice was observed to be at the melting point in two boreholes

contributions of growth and deformation to monthly variability in sea ice thickness north of the coasts of greenland and the canadian arctic archipelago regional variability in monthly cryosat 2 sea ice thickness is partitioned into contributions from dynamics and thermodynamics using ice deformation calculated from large scale ice drift for five winters december to april 2011 2015 over a region of persistent convergence north of the coasts of greenland and the canadian arctic archipelago deformation explains 34 of the overall variance up to 69 in 2014 2015 in monthly thickness changes approximately 42 56 or 0 6 m of the seasonal changes in mean regional ice thickness can be attributed to divergence and shear the estimated area averaged growth of 0 12 0 03 m month compares favorably with measurements from ice mass balance buoys examination of the time variable thickness distributions shows areas covered by ice 3 m increased albeit at fairly coarse resolution this coupled analysis of thickness changes and deformation offered a first look at the character of the regional thickness redistribution process

synoptic airborne thickness surveys reveal state of arctic sea ice cover 1 while summer arctic sea ice extent has decreased over the past three decades it is subject to large interannual and regional variations methodological challenges in measuring ice thickness continue to hamper our understanding of the response of the ice thickness distribution to recent change limiting the ability to forecast sea ice change over the next decade we present results from a 2400 km long pan arctic airborne electromagnetic em ice thickness survey in april 2009 the first ever large scale em thickness dataset obtained by fixed wing aircraft over key regions of old ice in the arctic ocean between svalbard and alaska the data provide detailed insight into ice thickness distributions characteristic for the different regions comparison with previous em surveys shows that modal thicknesses of old ice had changed little since 2007 and remained within the expected range of natural variability

measurements of polar mesospheric clouds in infrared emission by mipas envisat 1 we report on the infrared emission 10 13 m of polar mesospheric clouds pmcs as measured by michelson interferometer for passive atmospheric sounding mipas on board the environmental satellite mipas envisat during 19 21 july 2005 in the summer northern hemisphere the spectral distribution of mipas radiances is well described by that simulated for ice particle emission at low temperatures and hence provides further evidence of the water ice nature of the pmc particles the vertical profiles of integrated radiance clearly show an emission peak at tangent heights of 81 83 km as expected from pmc emission ice particles volume density retrieved from mipas spectra shows a layer of ice particles extending from 80 5 to 87 km and from about 60 n to the north pole well confined within the region where temperature is below approximately 150 k the upper part of the ice particle layer then extends to altitudes higher than that observed by uv visible measurements which confirms the current understanding that pmcs cover the entire polar mesopause region the altitude of the layer peak changes from 82 5 83 km at 70 n 90 n to slightly higher altitudes 83 85 km at lower latitudes 60 n 70 n mipas ice particle altitude latitude distribution suggests that they are formed mainly close to the pole and then are transported upward and to lower latitudes by the ascending branch of the meridional circulation confirming previous modeling

ice sheet elevation changes caused by variations of the firn compaction rate induced by satellite observed temperature variations 1982 2003 changes in the surface elevation of the greenland and antarctic ice sheets and ice shelves caused by variations in the rate of firn compaction are calculated with a time dependent firn densification model driven by two decades 1982 2003 of satellite observed monthly surface temperatures the model includes the effects of melting and refreezing both the direct changes in density and the subsequent effects on the densification rate as previously shown the temperature dependent rate of densification is largest in summer but changes in winter temperatures also have a significant effect over the last decade climate warming has enhanced the rate of compaction and lowered the average surface elevation of greenland by 1 8 cma 1 and most of west antarctica by 1 9 cma 1 in east antarctica a small cooling raised the average surface elevation by 0 14 cma 1

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

comparison of freeboard retrieval and ice thickness calculation from als asiras and cryosat 2 in the norwegian arctic to field measurements made during the n ice2015 expedition we present freeboard measurements from airborne laser scanner als the airborne synthetic aperture and interferometric radar altimeter system asiras and cryosat 2 siral radar altimeter ice thickness measurements from both helicopter borne and ground based electromagnetic sounding and point measurements of ice properties this case study was carried out in april 2015 during the n ice2015 expedition in the area of the arctic ocean north of svalbard the region is represented by deep snow up to 1 12 m and a widespread presence of negative freeboards the main scattering surfaces from both cryosat 2 and asiras are shown to be closer to the snow freeboard obtained by als than to the ice freeboard measured in situ this case study documents the complexity of freeboard retrievals from radar altimetry we show that even under cold below 15 c conditions the radar freeboard can be close to the snow freeboard on a regional scale of tens of kilometers we derived a modal sea ice thickness for the study region from cryosat 2 of 3 9 m compared to measured total thickness 1 7 m resulting in an overestimation of sea ice thickness on the order of a factor 2 our results also highlight the importance of year to year regional scale information about the depth and density of the snowpack as this influences the sea ice freeboard the radar penetration and is a key component of the hydrostatic balance equations used to convert radar freeboard to sea ice thickness

radar response of firn exposed to seasonal percolation validation using cores and fdtd modeling we use ground penetrating radars gprs firn cores and electromagnetic finite difference time domain fdtd numerical modeling to characterize the gpr response to a frozen high arctic firn pack as a result of extensive summertime percolation the firn pack comprises a high fraction of ice layers lenses and vertical glands we show that the gpr response on the firn pack mainly depends on the following 1 the thickness of the ice layers 2 the distance between layers 3 the layer roughness and 4 the presence or absence of elliptical ice lenses using 3 d fdtd modeling we show that the gpr is not sensitive to typical ice glands which implies that the gpr underestimates firn heterogeneity such that firn stratigraphy in percolation and wet snow zones could be incorrectly interpreted as being better preserved than it actually is we find that thin ice layers 0 05 m or multiple thin ice layers give a strong response thicker ice layers typically give a weaker backscatter per unit area mainly due to the lack of interference of the reflections from the upper and lower interfaces but are due to their continuity easily trackable ice layers with a thickness comparable to the gpr wavelength give 180deg phase shifted upper and lower reflections and are in general separated by a band of low gpr response due to the lack of permittivity contrast within the ice layers despite the ice lenses relatively short horizontal correlation length as inferred from cores bands of high amplitude clutter caused by these features can be traced over several kilometers in gpr profiles

simulated effects of a snow layer on retrieval of cryosat 2 sea ice freeboard the impact of a snow layer on the location of the tracking point rp for ranging to the sea ice surface in cryosat 2 synthetic aperture interferometric radar altimeter waveforms is simulated with a range resolution of 47 cm the response of the air snow a s interface broadens the response of the snow ice s i interface and displaces the rp toward the altimeter this effect is largest when the strengths of their returns are comparable and when snow thicknesses are 20 cm on the other hand the rp is displaced away from the altimeter when the reduced propagation speed in the snow layer is not accounted for this analysis examines the dependence of these competing corrections on snow thickness and the relative scattering strengths of the interfaces and the sensitivity of two different tracking approaches leading edge and centroid to these snow parameters expected errors depend on a better understanding of the relative scattering strengths of the interfaces and snow layer

short pulse radar wavelet recovery and resolution of dielectric contrasts within englacial and basal ice of matanuska glacier alaska u s a wavelets transmitted by short pulse radar are recovered from continuous profiles and used to determine interfacial dielectric contrasts within the englacial and basal ice at the terminus area of matanuska glacier alaska u s a the field studies were in the ablation region where radar horizons could at some point be identified with interfaces between clear ice and air water or basal ice and were performed in early spring before drainage fully developed the profiles usedclosely spaced antennas with bandwidths centered near 50 and 400 mhz transmitted wavelets reflected from interfaces of known dielectric contrasts are used to establish a phase reference for other events from interfaces between unknown contrasts migration and fourier transform filtering are then applied to the profiles and shown to recover these wavelets from diffractions and reflections interfacial dielectric contrasts are determined from the relative phase of the wavelets near the terminus lake some basal ice events above 8 m depth are interpreted as voids further up glacier most englacial events are interpreted as voids but deeper localized reflectors and horizons to 90 m depth and within the basal zone are interpreted as voids water or debris phase cannot be determined for the basal substrate transition reflections recommendations are made for improving the wavelet recovery process and the quality of gpr migration

revealing the nature of radar reflections in ice dep based fdtd forward modeling 1 successful simulation of ground penetrating radar gpr traces in polar ice is achieved by numerical finite difference time domain fdtd forward modeling properties of the modeled medium are taken from high resolution dielectric profiling dep of the upper 100 m of an ice core from dronning maud land antarctica the gpr reference trace is calculated from stacking of a normal moveout corrected common midpoint survey carried out near the borehole location the excellent agreement of synthetic and gpr based results demonstrates the capability of fdtd models to reproduce radargrams from ice core properties for interpretation of radio echo sounding data and emphasizes the exploitation of radar data for improved interpretations of glaciological climate proxys in addition to presenting modeling results we perform sensitivity experiments to investigate the nature and origin of radar reflection in ice discuss reasons for the failure of modeling studies in the past and indicate new approaches

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

thin sea ice thick snow and widespread negative freeboard observed during n ice2015 north of svalbard in recent years sea ice conditions in the arctic ocean changed substantially toward a younger and thinner sea ice cover to capture the scope of these changes and identify the differences between individual regions in situ observations from expeditions are a valuable data source we present a continuous time series of in situ measurements from the n ice2015 expedition from january to june 2015 in the arctic basin north of svalbard comprising snow buoy and ice mass balance buoy data and local and regional data gained from electromagnetic induction em surveys and snow probe measurements from four distinct drifts the observed mean snow depth of 0 53 m for april to early june is 73 above the average value of 0 30 m from historical and recent observations in this region covering the years 1955 2017 the modal total ice and snow thicknesses of 1 6 and 1 7 m measured with ground based em and airborne em measurements in april may and june 2015 respectively lie below the values ranging from 1 8 to 2 7 m reported in historical observations from the same region and time of year the thick snow cover slows thermodynamic growth of the underlying sea ice in combination with a thin sea ice cover this leads to an imbalance between snow and ice thickness which causes widespread negative freeboard with subsequent flooding and a potential for snow ice formation with certainty 29 of randomly located drill holes on level ice had negative freeboard

sea ice convergence along the arctic coasts of greenland and the canadian arctic archipelago variability and extremes 1992 2014 after the summer of 2013 a convergence induced tail in the thickness distribution of the ice cover is found along the arctic coasts of greenland and canadian arctic archipelago prompted by this a normalized ice convergence index ici is introduced to examine the variability and extremes in convergence in a 23 year record 1992 2014 of monthly ice drift large scale composites of circulation patterns characteristic of regional convergence and divergence are examined indeed the ici shows the june 2013 convergence event to be an extreme i e ici 2 furthermore there is a cluster of 9 months over a 17 month period with positive icis i e 1 following the record summer minimum ice extent smie in 2012 the imprint of ice dynamics from this cluster of positive icis likely contributed to higher smies in 2013 and 2014 the impact of convergence on smie is discussed and the increase in arctic ice volume in 2013 is underscored