polynya flux model solutions incorporating a parameterization for the collection thickness of consolidated new ice previous polynya flux models have specified a constant value for the collection thickness of frazil ice h at the polynya edge in certain circumstances this approach can cause the frazil ice depth h within the polynya to exceed h a result which violates assumptions made in the formulation of the ice flux balance equations at the polynya edge to overcome this problem a parameterization for h is derived in terms of the depth of frazil ice arriving at the polynya edge and the component normal to the polynya edge of the frazil ice velocity relative to the velocity of the consolidated ice pack thus h is coupled to the unknown polynya edge using the new parameterization for h an analysis of the unsteady one dimensional opening of a coastal polynya is presented analytical solutions are also derived using the new parameterization for h for steady state two dimensional polynyas adjacent to a semi infinite and finite length coastal barrier the latter case representing a prototype island in all cases the solutions show close qualitative and quantitative agreement with those derived using a constant value for h however the steady state two dimensional polynya edge can in certain circumstances exhibit a corner at the point where the offshore equilibrium width is reached precise conditions for the existence of a corner are derived in terms of the orientation of the frazil ice velocity u and the consolidated ice velocity u upper and lower bounds are also obtained for the area of the steady state island polynya and it is shown that over a large range of orientations of u and u the area exceeds that associated with the island polynya with constant h finally two simulations of the st lawrence island polynya are presented using the new parameterization for h and the results are compared with the h constant theory

an ice ocean coupled model an ice model an ocean model and a method of coupling the models are described the ice model is a synthesis with variations and extensions of previous modeling ideas ice thickness concentration velocity and internal energy are prognostic variables the ice thermodynamics are represented by temperatures at the snow surface ice surface the interior and the bottom surface melting and freezing rates are calculated at the ice atmosphere ice ocean and atmosphere ocean interfaces a prescribed portion of summer meltwater can be stored on the surface and refrozen in the fall the ocean model includes a second moment turbulence closure submodel and enables one to solve for oceanic heat flux the interfacial stress and subsurface properties in this paper the model is applied to one dimensional simulations but the equations are cited in a form for implementation by two and three dimensional models in a companion paper kantha and mellor this issue the model is used for two dimensional vertical plane simulations in the bering sea several one dimensional sensitivity studies are performed in the case where the ice model is decoupled from the ocean here the oceanic heat flux and sea surface temperature are prescribed constants the studies reveal the role and sensitivity of surface trapped meltwater ice concentration and ice divergence with the coupled ice ocean model the seasonally varying oceanic heat flux and mixed layer properties are determined by the model some comparisons with observations in the central arctic ocean are possible the role of the molecular sublayer immediately adjacent to the ice is examined frazi ice production is related to the large disparity in the molecular diffusivities for temperature and salinity the mixed layer model contains empirical constants which are known from turbulence data the molecular sublayer parameterization requires one empirical parameter b which is uncertain but from this study is assuredly greater than zero the value implicit in previous models the ice model requires the empirical parameters ci f and ci u to quantitatively account for freezing or melting processes in open leads their values are also uncertain but we present reasoning and sensitivity studies to suggest specific values finally an empirical parameter g is introduced it is the ratio of the value of the ice thickness used to represent average ice volume in the dynamic and thermodynamic equations to the value of the thickness needed in the heat conduction equation estimates of g are made from observed thickness distribution functions sensitivity studies show it to be an important parameter

frazil ice entrainment of sediment large tank laboratory experiments laboratory experiments that simulate natural ice formation processes and sediment entrainment in shallow water are presented a 10 30 cm s 1 current was forced with impellers in a 20 m long 1 m deep indoor tank turbulence in the flow maintained a suspension of sediments at concentrations of 10 20 mg l 1 at 0 5 m depth low air temperatures 15 c and 5 m s 1 winds resulted in total upward heat fluxes in the range 140 260 w m 2 the cooling produced frazil ice crystals up to 2 cm in diameter with concentrations up to 4 5 g l 1 at 0 5 m depth considerable temporal variability with time scales of 1 min was documented a close to constant portion of the smaller frazil crystals remained in suspension after some hours the larger crystals which made up most of the ice volume accumulated as slush at the surface current measurements were used to calculate the turbulent dissipation rate and estimates of vertical diffusion were derived after 5 8 hours sediment concentrations in the surface slush were normally close to those of the water after 24 hours however they were 2 4 times higher data indicate that sediment entrainment depends on high heat fluxes and correspondingly high frazil ice production rates as well as sufficiently strong turbulence waves do not seem to increase sediment entrainment significantly

polynya dynamics a review of observations and modeling 1 polynyas are nonlinear shaped openings within the ice cover ranging in size from 10 to 105 km2 polynyas play an important climatic role first winter polynyas tend to warm the atmosphere thus affecting atmospheric mesoscale motions second ocean surface cooling and brine rejection during sea ice growth in polynyas lead to vertical mixing and convection contributing to the transformation of intermediate and deep waters in the global ocean and the maintenance of the oceanic overturning circulation since 1990 there has been an upsurge in polynya observations and theoretical models for polynya formation and their impact on the biogeochemistry of the polar seas this article reviews polynya research carried out in the last 2 decades focusing on presenting a state of the art picture of the physical interactions between polynyas and the atmosphere sea ice ocean system observational and modeling studies the surface heat budget and water mass transformation within these features are addressed

ice ocean interactions during shallow convection under conditions of steady winds three dimensional numerical studies abstract a three dimensional hydrodynamic ocean model coupled to a thermohydrodynamic model for young sea ice is applied to study shallow haline convection in the central greenland sea with an emphasis on sub mesoscale ice ocean interactions two types of young sea ice are distinguished i e frazil and pancake ice both acting different on surface heat salt and momentum fluxes two scenarios are considered a continued frazil ice production during steady winds and b the same scenario but with the intermittent formation of pancake ice during a short intervening period of low winds brine release due to new ice production creates shallow convection in both cases under conditions of continued frazil ice production ice streaks develop at the sea surface finally becoming oriented roughly parallel to the wind these streaks are the result of convective plumes that induce organized patterns of convergent and divergent surface currents frazil ice is herded into convergence zones where it becomes as thick as 6 m within 24 h the studies suggest a strong relationship between streak spacing and the penetration depth of convection given by an aspect ratio in the range of 2 3 after pancake ice has been formed however the organized ice streaks vanish developing into complex patterns of pancake ice this finding is in agreement with recent field observations in the greenland sea is odden ice tongue with the existence of pancake ice moreover the surface averaged buoyancy flux decreases and is determined from the integral of local sub mesoscale ice ocean interactions

supercooled water in an arctic polynya observations and modeling in situ field measurements of an active polynya in storfjorden svalbard during april 2006 are presented a surface heat flux estimated to be 400 w m 2 produced frazil ice that was advected away from the fast ice edge during the end of a polynya event driven by cold winds from the northeast conductivity temperature and depth casts from the fast ice edge of the polynya were calibrated by accompanying water samples and reveal a supercooling event that lasted for 3 days in a 5 m deep water column surface salinity reached 35 9 psu from brine release during ice growth the maximum supercooling measured was 0 037 0 005 c below the in situ freezing point near the surface and 0 016 0 005 c at the bottom the mean supercooling gradient was 0 020 0 005 c between the surface and the bottom these measurements are consistent with results from a one dimensional frazil ice model confirming that such supercooling levels can be expected frazil ice concentrations in the water were modeled to be lower than 0 02 g l 1 due to advection in the surface layer seven frazil grease ice samples taken from a place where advection was blocked along the fast ice edge showed a mean salinity of 26 2 psu indicating 25 frazil ice and 75 sea water in the grease ice the water column salinity decreased during the measurement period due to less saline water replacing newly formed brine enriched shelf water flowing down to deeper parts of storfjorden the supercooling ceased when the wind direction turned to the east with higher air temperatures and warmer and less saline water being pushed into storfjorden by the northward ekman transport these are the first in situ observations from an active arctic polynya with concurrent sampling of hydrography and frazil ice and the supercooling is the maximum observed in recent years with modern and accurate instrumentation

observations of ice thickness and frazil ice in the st lawrence island polynya from satellite imagery upward looking sonar and salinity temperature moorings 1 for the 1999 winter this paper examines the behavior of the bering sea st lawrence island polynya using a combination of advanced very high resolution radiometer avhrr radarsat synthetic aperture radar sar meteorological data over winter moored upward looking sonars uls and seabird salinity temperature sensors we define a thermal ice thickness from the avhrr retrieval of ice surface temperature combined with meteorological observations and a heat flux model south of the island we compare the uls and thermal thicknesses for congelation and frazil ice when the satellites observe congelation ice over the ulss the uls and thermal ice thicknesses generally agree when sar observes langmuir plumes over the ulss which indicate frazil ice formation the ulss show scatterers at 5 20 m depths in the water column and the seawater temperatures are either within 0 01 c of freezing or are slightly supercooled this suggests that during frazil events crystals either nucleate at depth or are transported to depth by the langmuir circulation the combination of the sar imagery and uls observations also allow measurement of the pack ice advection velocity the polynya width and the downwind frazil accumulation thickness giving widths of 10 to 30 km and thicknesses of 0 1 0 2 m substitution of these observed values with the heat flux into the pease polynya model yields polynya widths that approximately agree with the observed

development and properties of sea ice in the coastal regime of the southeastern weddell sea from october to december 1986 a program consisting of sea ice core analysis in combination with sea ice observations was carried out from the icebreaker r v polarstern as part of the winter weddell sea project the ship operated in the central and southeastern weddell sea with interests focusing on the ice shelf front between 70 s and 77 s where a system of coastal polynyas extended for several tens to hundreds of kilometers opened and maintained despite temperatures well below freezing by offshore wind forcing three wind controlled ice formation regimes may be distinguished 1 for wind speeds 10 m s the ice cover is heavily ridged and rafted 50 and formation of granular ice predominates of the total length of cores sampled in the coastal regime 32 consisted of columnar and 35 of granular ice in addition we observed two unique ice classes along the coast platelet ice formed through consolidation of underwater ice platelets underneath the solid ice cover contributed 11 to our core samples another 22 consisted of intermediate columnar granular ice which originates under the dynamic hydrographic conditions of the near ice shelf region

thermodynamic investigation of an evolving grease to pancake ice field we present results from a laboratory tank study of ice growing from saline water in a wave field focusing on the transition from a predominantly frazil grease ice cover to a pancake ice cover combining surface temperature observations with direct and indirect determinations of ice salinity and solid fraction we describe the evolution of frazil and pancake ice area fraction salinity and solid ice volume fraction over the course of 1 day in the investigated stage of transition frazil ice surrounding the pancakes was found to have rather constant properties a surface temperature 0 4 0 6 k below the freezing point of the underlying sea water a salinity of 24 26 g kg 1 and a solid volume fraction of 0 25 0 29 the average salinity of young pancake ice estimated from heat and salt budgets decreased from 18 to 15 g kg 1 while average solid volume fractions increased from 0 6 to 0 7 the transition from frazil to pancake is estimated to take place when solid fractions reach 0 37 0 40 and surface temperatures are 0 7 0 9 k below the freezing point we find that for proper modelling of the grease pancake system it is important to distinguish between a surface and volumetric fraction of pancakes and grease ice

the relation between ice deformation oceanic heat flux and the ice thickness distribution in the arctic ocean a one dimensional ocean model coupled with an ice model where the ice cover is partitioned into a number of thickness categories is used to investigate how the ice thickness distribution in the arctic ocean depends on the two deformation processes export net divergence and ridging the model standard case generates vertical profiles of temperature salinity and an ice thickness distribution similar to the observations the standard case oceanic heat flux agrees well with recently deduced heat fluxes from arctic ice dynamics joint experiment aidjex data the oceanic heat flux is about 18 w m 2 during summer and about 1 w m 2 during winter it is found that the mean ice thickness decreases with increasing ice export in close agreement with other investigations however the dependence of the mean ice thickness on ridging activity is found to be very weak the change of the mean ice thickness is only 12 cm when increasing the ridging activity in the model from 0 to 0 4 yr 1 where the larger value represents an estimate of the actual ridging activity in the arctic ocean in a sensitivity study different types of ridging and albedo parameterizations are tested and this weak dependence is found to be very robust other properties of the model ice cover are sensitive to ridging though the equilibrium thickness of undeformed ice decreases with both export and ridging activity the annual maximum open water fraction and the amplitude of the seasonal thickness variation increases with export and ridging

simulation of the crystal growth of platelet sea ice with diffusive heat and mass transfer antarctic coastal sea ice often grows in water that has been supercooled by interaction with an ice shelf in these situations ice crystals can form at depth rise and deposit under the sea ice cover to form a porous layer that eventually consolidates near the base of the existing sea ice the least consolidated portion is called the sub ice platelet layer congelation growth eventually causes the sub ice platelet layer to become frozen into the sea ice cover as incorporated platelet ice in this study we simulate these processes in three dimensions using voronoi dynamics to govern crystal growth kinetics platelet deposition in situ growth and incorporation into the sea ice cover are integrated into the model heat and mass transfer are controlled by diffusion we extract and compare spatial temporal distributions of porosity salinity temperature and crystallographic c axes with observations from mcmurdo sound antarctica the model captures the crystallographic structure of incorporated platelet ice as well as the topology of the sub ice platelet layer the solid fraction which has previously been poorly constrained is simulated to be 0 22 in good agreement with an earlier estimate of 0 25 0 06 this property of the sub ice platelet layer is important for biological processes and for the freeboard thickness relationship around antarctica

dependence of the arctic ocean ice thickness distribution on the poleward energy flux in the atmosphere 1 the sensitivity of the arctic ocean ice cover on the atmospheric poleward energy flux d is studied using a coupled column model of the ocean ice and atmosphere in the model the ice cover is described by a thickness distribution and the atmosphere is a simple two stream gray body in radiative equilibrium it is shown that the thickness distribution in combination with the albedo function gives a strong nonlinear response to positive perturbations of d the response on d is sensitive to the albedo parameterization and the shape of the thickness distribution controlled by ridging and divergence an increase of about 9 w m 2 from a standard value of d 103 w m 2 has a dramatic effect reducing the ice thickness by more than 2 m and generates a large open water fraction during summer the reduction of ice thickness is characterized by a clear transition between two regimes going from a regime where first year ice survives the next summer melt period to a seasonal ice regime where the first year ice melts completely it is shown that the existence of seasonal ice regime is dependent on the surface mixed layer thickness the model enters a completely ice free state if the thickness of the mixed layer is increased above a threshold value the adjustment timescale for the ice cover is 6 years for small positive and negative perturbations in d for larger positive perturbations of about 10 w m 2 the adjustment timescale is up to 20 years

pancake ice formation in the weddell sea 1 the ice formation resulting from two low temperature events at the weddell sea ice edge during april 2000 is presented pancake and frazil ice were sampled at seven stations at varying distances from the ice edge the ice cover was further characterized from above using helicopter aerial photography and from below using a remotely operated vehicle previously undescribed two layer pancake types were observed and classified a novel pancake growth mechanism is introduced to account for these involving the washing of frazil ice over the pancake top surface and its subsequent freezing the process was directly observed in ice tank experiments layer thicknesses seen in the field were compared to the ice growth that would occur both under calm conditions and from free surface frazil ice growth classical bottom accretion pancake growth was found to proceed at a rate similar to that of thin congelation ice top layer growth was more rapid at approximately double the congelation rate overall ice volume production was similar to congelation ice for the thin pancakes considered 20 cm though subsequent thickening was expected to be faster as the rapid top layer process continued and the equivalent congelation growth slowed it is suggested that parameterization of this new process is important for models that aim to simulate the rapid advance and thickening of wave influenced ice covers

scattering of long period rayleigh waves in western north america and the interpretation of coda q measurements abstract the codas of long period rayleigh waves recorded at wwssn and canadian network stations in western north america from eight underground explosions at nts are examined in an effort to separate scattering and anelastic attenuation effects coda behavior of 0 1 and 0 2 hz rayleigh waves follows coda characteristics seen in studies of short period s waves coda decay rate is seen to be a stable observation over most stations in western north america and is consistent with the hypothesis that backscattered surface waves from heterogeneities contained within the western half of the continent form the rayleigh wave coda the basic data observables of coda level and decay are interpreted using several plausible models the single scattering model yields a coda q consistent with previously determined rayleigh anelastic attenuation coefficients separation of anelastic and scattering q is possible using an energy flux model and shows that scattering q is one to two orders of magnitude higher than anelastic q however an energy flux model that incorporates a layer of scatterers over a homogeneous half space shows that all rayleigh wave attenuation can be explained purely by scattering effects which include rayleigh to body wave conversion coda can be fit equally well by these mutually incompatible models it is not likely that the mechanisms of scattering or anelastic attenuation can be addressed by coda observations of a single homogeneous data set

a model for entrainment of sediment into sea ice by aggregation between frazil ice crystals and sediment grains avertical numerical model has been developed that simulates tank experiments of sediment entrainment into sea ice physical processes considered were turbulent vertical diffusion of heat salt sediment frazil ice and their aggregates differential growth of frazil ice crystals secondary nucleation of crystals and aggregation between sediment and ice the model approximated the real size distribution of frazil ice and sediment using five classes of each frazil crystals 25 m to 1 5 cm were modelled as discs with a constant thickness of their diameter each class had a constant rise velocity based on the density of ice and drag forces sediment grains 1 600 m were modelled as constant density spheres with corresponding sinking velocities the vertical diffusion was set constant for experiments based on calculated turbulent rms velocities and dissipation rates from current data the balance between the rise sinking velocities and the constant vertical diffusion is an important feature of the model the efficiency of the modeled entrainment process was estimated through a an aggregation factor values for a are in the range but average values are often close to 0 01 entrainment increases with increasing sediment concentration and turbulence of the water and heat flux to the air

the physical properties of sea ice in the odden ice tongue abstract the odden ice tongue developed prominently during the winter of 1992 1993 but did not appear at all during the two subsequent winters of the esop period during 1992 1993 the in situ sea ice characteristics within odden were studied on four occasions in addition to direct observation and aerial photography the measurement programme included retrieval and on board analysis of frazil and pancake ice samples wave measurements within odden and near surface ctd measurements to examine the effect of melt on the upper ocean reported in brandon and wadhams 1999 the near surface hydrography beneath the odden ice tongue deep sea research in press this paper reports on the characteristics of the frazil and pancake ice observed and sampled during this season expanding on early results reported in wadhams et al 1996 journal of geographical research 101 c8 18 213 18 235 by combining the results of in situ sampling with the analysis of passive microwave and sar data of the sea ice extent through the winter it was possible to estimate the salt flux into the ocean originating from brine release from sea ice during the growth phases of odden

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

simulating pancake and frazil ice growth in the weddell sea a process model from freezing to consolidation 1 processes controlling the formation and transformation of frazil to pancake ice are examined using data from an array of drifting buoys deployed at the advancing ice edge in the weddell sea a simple thermodynamic model is coupled to the buoy dynamics and to an ice redistribution model to determine the influence of deformation thermodynamics and mechanical scavenging incorporating frazil crystals from the surrounding slick into the pancakes on the partitioning of ice volume between frazil and pancakes ice production was examined from the time the buoys were deployed until the frazil pancake cover consolidated into the more familiar pack ice the model reproduced the expected ice cover thickness at consolidation 60 cm rafting was the dominant contribution to thickening in the region owing to large scale compression of the initial area by northerly winds from passing low pressure weather systems which are rather typical in the region high resolution positional forcing from the buoys 20 min intervals doubled the contribution of mechanical scavenging to final pancake thickness compared to the coarser 2 h result owing to the larger path length that the pancakes traverse through the frazil slick and produced a significantly larger volume of ice in the pancake phase the ice cover generated at consolidation was approximately twice as thick as would have formed by the more familiar congelation ice growth under the same forcing reinforcing the importance of correctly parameterizing the early stages of ice formation in the antarctic the study highlighted uncertainties in the effect of the frazil pancake cover on ocean atmosphere heat exchange both in terms of the area contributing to ice production and the effect on turbulent exchange coefficients further work placing the empirical parameters into a more constrained physical framework and introducing wave properties is suggested

a field and laboratory study of wave damping by grease ice in a field and laboratory study we discuss the formation growth and wave absorption properties of grease ice our field observations show that grease ice formation occurs under cold windy conditions in both leads and polynyas in leads grease ice forms in the open water then is herded to the down wind edge of the lead in polynyas a langmuir circulation herds the grease ice into long plumes parallel to the wind in the laboratory we grow grease ice in a wave tank and measure its wave absorption properties for single frequency two dimensional waves on a large scale we find that the thickness of the grease ice which increases away from the paddle is determined by a balance between the wave momentum flux and the free surface tilt on a small scale our photographs show that the crystals which make up the grease ice consist of discs measuring about 1 mm in diameter and 1 10 m thick which at low rates of shear sinter together into larger clumps yielding a viscosity increase to measure this non linear viscosity we study the decay of wave amplitude between two critical distances measured inwards from the leading edge the first occurs when the depth of grease ice exceeds k 1 where k is the wave number the second further distance is a line of transition from liquid to solid behavior which we call the dead zone between these two distances the wave amplitude decays with a linear slope which increases as a 0 k 2 where a0 is the wave amplitude in open water concurrent measurements of ice concentration show that it increases from values of 18 22 at the leading edge to a local maximum of 32 44 at the dead zone while the values at the dead zone increase non linearly with a0k finally comparison of the observed to that calculated from a yield stress viscosity model shows if the yield stress coefficient is proportional to the incident wave momentum flux the model predicts the observed

coefficients for sea surface wind stress heat flux and wind profiles as a function of wind speed and temperature surface layer coefficients for wind profiles wind stress and heat flux in typical open sea conditions are briefly reviewed businger dyer flux gradient relationships and a charnock wind stress formula fit the empirical data and are dimensionally consistent these have been solved by an iterative method and the results are presented in a tabular form suitable for climatological calculations from marine wind and temperature data

grease ice in basin scale sea ice ocean models the first stage of sea ice formation is often grease ice a mixture of sea water and frazil ice crystals over time grease ice typically congeals first to pancake ice floes and then to a solid sea ice cover grease ice is commonly not explicitly simulated in basin scale sea ice ocean models though it affects oceanic heat loss and ice growth and is expected to play a greater role in a more seasonally ice covered arctic ocean we present an approach to simulate the grease ice layer with as basic properties the surface being at the freezing point a frazil ice volume fraction of 25 and a negligible change in the surface heat flux compared to open water the latter governs grease ice production and a gradual transition to solid sea ice follows with 50 of the grease ice solidifying within 24 hours the new parameterization delays lead closing by solid ice formation enhances oceanic heat loss in fall and winter and produces a grease ice layer that is variable in space and time results indicate a 10 30 increase in mean winter arctic ocean heat loss compared to a standard simulation with instant lead closing leading to significantly enhanced ice growth

fram strait sea ice outflow 1 we summarize 24 years 1978 2002 of ice export estimates and examine over a 9 year record the associated variability in the time varying upward looking sonar uls thickness distributions of the fram strait a more thorough assessment of the pmw passive microwave ice motion with 5 years of synthetic aperture radar sar observations shows the uncertainties to be consistent with that found by kwok and rothrock 1999 giving greater confidence to the record of ice flux calculations interesting details of the cross strait motion profiles and ice cover characteristics revealed by high resolution sar imagery are discussed the average annual ice area flux over the period is 866 000 km2 yr between the 1980s and 1990s the decadal difference in the net exported ice area is 400 000 km2 approximately half the annual average except for the years with extreme negative nao correlation of winter ice area export with the nao index remains high r2 0 62 with thickness estimates from uls moorings we estimate the average annual ice volume flux 8 years to be 2218 km3 yr 0 07 sv over the 9 year uls ice thickness data set there is an overall decrease of 0 45 m in the mean ice thickness over the entire time series and a decrease of 0 23 m over the winter months december through march correspondingly the mode of the my ice thickness exhibits an overall decrease of 0 55 m and a winter decrease of 0 42 m these are significant trends whether these trends are indicative of the thickness trends of the arctic ocean is examined as the time varying behavior of the monthly uls thickness distributions can be related not only to the seasonal cycle in the basal growth and melt but also to the magnitude and pattern of ice motion in the arctic ocean and the proximity of the uls moorings to the ice edge

assessing the impact of vertical land motion on twentieth century global mean sea level estimates near global and continuous measurements from satellite altimetry have provided accurate estimates of global mean sea level in the past two decades extending these estimates further into the past is a challenge using the historical tide gauge records not only is sampling nonuniform in both space and time but tide gauges are also affected by vertical land motion vlm that creates a relative sea level change not representative of ocean variability to allow for comparisons to the satellite altimetry estimated global mean sea level gmsl typically the tide gauges are corrected using glacial isostatic adjustment gia models this approach however does not correct other sources of vlm that remain in the tide gauge record here we compare global positioning system gps vlm estimates at the tide gauge locations to vlm estimates from gia models and assess the influence of non gia related vlm on gmsl estimates we find that the tide gauges on average are experiencing positive vlm i e uplift after removing the known effect of gia resulting in an increase of 0 24 0 08 mm yr 1 in gmsl trend estimates from 1900 to present when using gps based corrections while this result is likely dependent on the subset of tide gauges used and the actual corrections used it does suggest that non gia vlm plays a significant role in twentieth century estimates of gmsl given the relatively short gps records used to obtain these vlm estimates we also estimate the uncertainty in the gmsl trend that results from limited knowledge of non gia related vlm