ice pumps and their rates an ice pump is a heat engine driven by the change of freezing point with pressure which will melt ice at depth in the ocean and deposit it at a shallower location it is self starting calculations of the maximum magnitude of this effect are made which show good agreement with field data available for sea and lake ice the discussion is applied to the general case of a moving pack ice sheet with a well mixed surface layer and to floating ice shelves the rate of melt from an 11 m deep pressure ridge keel due to ice pumping is estimated as 26 cm year and that from the front of the ross ice shelf at mcmurdo sound antarctica is estimated as 5 m year for the level of water movement noted in the authors field observations far from the ice front pumping between shelf areas of different thickness will still occur with tidal motion providing the necessary water exchange but its magnitude is now limited by the ability to remove the potentially stable layer of melt water out of the system it is important to realize that the pumping does not depend on the availability of sensible heat in the water column and its effects are additional to any melting caused by the advection of warmer water to the ice water interface

borehole imagery of meteoric and marine ice layers in the amery ice shelf east antarctica a real time video camera probe was deployed in a hot water drilled borehole through the amery ice shelf east antarctica where a total ice thickness of 480 m included at least 200 m of basal marine ice down looking and side looking digital video footage showed a striking transition from white bubbly meteoric ice above to dark marine ice below but the transition was neither microscopically sharp nor flat indicating the uneven nature at centimetre scale of the ice shelf base upstream where the marine ice first started to accrete marine ice features were imaged including platelet structures cell inclusions entrained particles and the interface with sea water at the base the cells are assumed to be entrained sea water and were present throughout the lower 100 150m of the marine ice column becoming larger and more prevalent as the lower surface was approached until near the base they became channels large enough that the camera field of view could not contain them platelets in the marine ice at depth appeared to be as large as 1 2 cm in diameter particles were visible in the borehole meltwater probably marine and mineral particles liberated by the drill but their distribution varied with depth

influence of tides on melting and freezing beneath filchner ronne ice shelf antarctica an isopycnic coordinate ocean circulation model is applied to the ocean cavity beneath filchner ronne ice shelf investigating the role of tides on sub ice shelf circulation and ice shelf basal mass balance including tidal forcing causes a significant intensification in the sub ice shelf circulation with an increase in melting 3 fold and refreezing 6 fold the net melt rate and seawater flux through the cavity approximately doubles with tidal forcing the spatial pattern and magnitude of basal melting and freezing generally match observations the 0 22 m a 1 net melt rate is close to satellite derived estimates and at the lower end of oceanographic values the ice shelf water outflow mixes with shelf waters forming a cold 1 9 degrees c dense overflow 0 83 sv that spills down the continental slope these results demonstrate that tidal forcing is fundamental to both ice shelf ocean interactions and deep water formation in the southern weddell sea citation makinson k p r holland a jenkins k w nicholls and d m holland 2011 influence of tides on melting and freezing beneath filchner ronne ice shelf antarctica geophys res lett 38 l06601 doi 10 1029 2010gl046462

a glimpse beneath antarctic sea ice platelet layer volume from multifrequency electromagnetic induction sounding in antarctica ice crystals emerge from ice shelf cavities and accumulate in unconsolidated layers beneath nearby sea ice such sub ice platelet layers form a unique habitat and serve as an indicator for the state of an ice shelf however the lack of a suitable methodology impedes an efficient quantification of this phenomenon on scales beyond point measurements in this study we inverted multifrequency electromagnetic em induction soundings obtained on fast ice with an underlying platelet layer along profiles of 100 km length in the eastern weddell sea em derived platelet layer thickness and conductivity are consistent with other field observations our results suggest that platelet layer volume is higher than previously thought in this region and that platelet layer ice volume fraction is proportional to its thickness we conclude that multifrequency em is a suitable tool to determine platelet layer volume with the potential to obtain crucial knowledge of associated processes in otherwise inaccessible ice shelf cavities

transient sea ice polynya forced by oceanic flow variability abstract in the weddell sea during the winters of 1974 1976 a significant opening in the sea ice cover occurred in the vicinity of a large bathymetric feature the maud rise seamount the event is commonly referred to as the weddell polynya aside from such a large scale relatively persistent polynya in the weddell sea transient small scale polynya can also appear in the sea ice cover at various times throughout the winter and at various locations with respect to the maud rise the underlying causes for the occurrence of such transient polynya have not been unambiguously identified we hypothesize that variations in the mean ocean currents are one major contributor to such variability in the sea ice cover analysis of the sea ice equations with certain idealized patterns of ocean currents serving as forcing is shown to lead to ekman transports of sea ice favorable to the initiation of transient polynya aside from the actual spatial pattern of the idealized ocean currents many other factors need also be taken into account when looking at such transient polynya two other such factors discussed are variations in the sea ice thickness field and the treatment of the sea ice rheology simulations of a sea ice model coupled to a dynamical ocean model show that the interaction of dynamical oceanic currents with large scale topographic features such as the maud rise does lead to the formation of transient polynya again through ekman transport effects this occurs because the seamount has a dynamic impact on the three dimensional oceanic flow field all the way up through the water column and hence on the near surface ocean currents that are in physical contact with the sea ice further simulations of a sea ice model coupled to a dynamic ocean model and forced with atmospheric buoyancy fluxes show that transient polynya can be enhanced when atmospheric cooling provides a positive feedback mechanism allowing preferential open ocean convection to occur the convection which takes hold at sites where transient polynya have been initiated by sea ice ocean stress interaction has an enhancing effect arising from the convective access to warmer deeper waters to investigate all of these effects in a hierarchical manner we use a primitive equation coupled sea ice ocean numerical model configured in a periodic channel domain with specified atmospheric conditions we show that oceanic flow variability can account for temporal variability in small scale transient polynya and thus point to a plausible mechanism for the initiation of large scale sustained polynya such as the weddell polynya event of the mid 1970s

evidence for platelet ice accretion in arctic sea ice development moderate quantities of platelet ice are reported in ice cores obtained from floes in the central and western beaufort sea arctic ocean the crystal structure characteristics include a fabric of long thin ragged edged crystals with randomly oriented c axes the cellular substructure that is characteristic of congelation ice is not evident in individual platelet ice crystals but they do occur together with congelation ice in layers ranging from 0 05 to 0 6 m thick platelet ice crystals are observed primarily in second year and multiyear floes the structural characteristics of arctic platelet ice are similar to those of antarctic platelet ice the platelet ice layers have a minimum 18o value of 5 3 and in some cases the platelet ice layers have more negative 18o values than the ice layers above and below them the salinity of platelet ice layers is not significantly different from other ice layers a number of platelet ice growth mechanisms and sources are discussed processes associated with the ellesmere ice shelves nearshore processes such as anchor ice growth in shallow waters off the north coast of alaska and ice growth in freshwater impounded behind grounded ice dams might be locally important but are unlikely to contribute significant quantities of platelet ice to pack ice floes two processes probably account for the presence of platelet ice the first is growth in underice melt ponds which form in inverted depressions at the base of floes when meltwater floes off the ice surface the second is the operation of ice pumps in which ice that is melted off the deeper parts of floes and ridges is deposited as platelet ice at a higher level in either case initially loose accumulations of platelet crystals are entrained in the floes by the growth of congelation ice the widespread occurrence of platelet ice in the central and western beaufort sea suggests that ice growth in both underice melt ponds and associated with the operation of ice pumps might be more common than was previously realized

melting characteristics of horizontal ice surfaces in cold saline water the results of an experimental investigation of the buoyancy driven flow adjacent to and below a horizontal ice surface melting in cold water at near oceanic salinity are presented this melting configuration is characteristic of circumstances encountered by sea ice for example by new ice and also on the bottom of tabular ice floes several ambient water temperatures t are investigated from t 1 75 c to t 3 c time exposure photographs of the flow field reveal that distinctively different flow regimes occur across even that narrow range of ambient temperature at all temperature levels the flow immediately below the ice surface is found to be horizontally radially inward toward the center of the ice also another outward moving horizontal layer appeared parallel to and below the inward moving layer the downward extent of penetration of this layer motion was seen to vary with t the lower layer sinks lower into the ambient medium with increasing t measured water ice interface temperatures and ice melt rates are also presented these results are compared with earlier similar measurements for vertical surfaces melting in cold saline water and found to vary in a similar way with ambient temperature t

dielectric properties of jovian satellite ice analogs for subsurface radar exploration a review the first european mission dedicated to the exploration of jupiter and its icy moons jupiter icy moons explorer juice will be launched in 2022 and will reach its final destination in 2030 the main goals of this mission are to understand the internal structure of the icy crusts of three galilean satellites europa ganymede and callisto and ultimately to detect europa s subsurface ocean which is believed to be the closest to the surface among those hypothesized to exist on these moons juice will be equipped with the 9 mhz subsurface penetrating radar rime radar for icy moon exploration which is designed to image the ice down to a depth of 9 km moreover a parallel mission to europa which will host onboard reason radar for europa assessment and sounding ocean to near surface equipped with 9mhz and 60mhz antennas has been recently approved by nasa the success of these experiments strongly relies on the accurate prediction of the radar performance and on the optimal processing and interpretation of radar echoes that in turn depend on the dielectric properties of the materials composing the icy satellite crusts in the present review we report a complete range of potential ice types that may occur on these icy satellites to understand how they may affect the results of the proposed missions first we discuss the experimental results on pure and doped water ice in the framework of the jaccard theory highlighting the critical aspects in terms of a lack of standard laboratory procedures and inconsistency in data interpretation we then describe the dielectric behavior of extraterrestrial ice analogs like hydrates and icy mixtures carbon dioxide ice and ammonia ice building on this review we have selected the most suitable data to compute dielectric attenuation velocity vertical resolution and reflection coefficients for such icy moon environments with the final goal being to estimate the potential capabilities of the radar missions as a function of the frequency and temperature ranges of interest for the subsurface sounders we present the different subsurface scenarios and associated radar signal attenuation models that have been proposed so far to simulate the structure of the crust of europa and discuss the physical and geological nature of various dielectric targets potentially detectable with rime finally we briefly highlight several unresolved issues that should be addressed in near future to improve our capability to produce realistic electromagnetic models of icy moon crusts the present review is of interest for the geophysical exploration of all solar system bodies including the earth where ice can be present at the surface or at relatively shallow depths

the subglacial cavity and implied dynamics under nioghalvfjerdsfjorden glacier ne greenland seismic depth soundings on nioghalvfjerdsfjor den glacier nfg ne greenland reveal an overdeepened trough under thefloating glacier the maximum depth of the trough reaches more than 900m below sea level mass balance calculations indicate considerable ice loss due to strong subglacial melting with a mean melt rate of 8ma 1 the geometry of the cavity and water mass characteristics from ctd measurements suggest the existence of a well de ned regional circulation system warm saline and rather densewaterfollows theinwardinclining basalslope through the deep valley of dijmphna sund towards the grounding line shallow ridges at the eastern glacier front prevent this watermassenteringfromthatdirection thecomparatively cold fresh and less dense melt water follows the subglacial ice topography leaving the cavity through the gaps towards the east the abundance of subglacial melt water east of nfg is most probably one of the main reasons for the semi permanent sea ice cover in this region cold water masses upwelling in the northeast water polynia and detected by satellite remote sensing are very likely influenced and mod ied by the subglacial melt water production

redefinition of the amery ice shelf east antarctica grounding zone 1 new evidence is presented which shows that the amery ice shelf east antarctica extends 240 km upstream of the previously reported position we combine a digital elevation model of the amery ice shelf created from ers 1 satellite radar altimetry with measured ice thicknesses and a simple density model in a hydrostatic buoyancy calculation to map the extent of the floating ice this reveals that the ice is floating as far south as 73 2 s the result is confirmed by static gps measurements collected during three consecutive field campaigns on the amery ice shelf where the vertical component of the gps shows a clear tidal signal at 72 98 s other evidence for the grounding zone position comes from an analysis of satellite imagery mass flux calculations and ice radar data the southward extension of the grounding line substantially alters the shape and dimensions of the ocean cavity beneath the ice shelf which has implications for modeling studies of sub ice shelf processes such as basal melting and freezing ocean circulation and tides the new grounding line position will also improve geophysical studies where the computation of ocean tidal loading corrections is important for postglacial rebound estimates and correction of satellite altimetry measurements within the region

ocean circulation beneath filchner ronne ice shelf from three dimensional model results a high resolution three dimensional ocean circulation model is applied to the cavity beneath filchner ronne ice shelf fris the model predicts predominantly barotropic currents which form a series of cyclonic gyres in the deep basins and anticyclonic circulations around the islands the surface circulation can be such that the water moves in the direction of decreasing or increasing ice thicknesses in the former case leading to freezing while melting at the ice shelf base results in the latter case the pattern of melting and freezing is consistent with known distributions of marine ice and melting areas beneath fris an anticyclonic circulation around the korff and henry ice rises with melting west of korff ice rise and freezing on the eastern side and north of henry ice rise is the main source for an ice pumping mechanism that produces the observed large marine ice body in the central filchner ronne ice shelf the estimates for net melting for realistic conditions at the open ocean boundary are 40 50 km 3 yr 1 indicating that ice shelf ocean interaction is an important contribution to the mass balance of the ice shelf

material transport across europa s ice shell jupiter s moon europa exhibits a deformed icy surface with salt deposits concentrated along the varied geological features the topographic alignment of salt deposits has been speculated to indicate an endogenic sourcing of the material two way transport of salts from a liquid water ocean beneath the ice shell to the surface and vice versa has been speculated we present dynamical models that demonstrate the incorporation of newly frozen ice into convective plumes within the ice shell caused by convection within the ice shell that drives dynamic topography along the ice ocean boundary the new ice that forms at the freezing front can be transported by the rising ice plumes toward the surface until it is blocked by a high viscosity lid at the surface weakening of the lid by tidal or tectonic forces could then lead to the surface detection of ocean trace chemistry captured in the newly formed ice

properties of a marine ice layer under the amery ice shelf east antarctica the amery ice shelf east antarctica undergoes high basal melt rates near the southern limit of its grounding line where 80 of the ice melts within 240 km of becoming afloat a considerable portion of this later refreezes downstream as marine ice this produces a marine ice layer up to 200 m thick in the northwest sector of the ice shelf concentrated in a pair of longitudinal bands that extend some 200 km all the way to the calving front we drilled through the eastern marine ice band at two locations 70 km apart on the same flowline we determine an average accretion rate of marine ice of 1 1 0 2 m a 1 at a reference density of 920 kg m 3 between borehole sites and infer a similar average rate of 1 3 0 2 m a 1 upstream the deeper marine ice was permeable enough that a hydraulic connection was made whilst the drill was still 70 100 m above the ice shelf base below this marine close off depth borehole video imagery showed permeable ice with water filled cavities and individual ice platelets fused together while the upper marine ice was impermeable with small brine cell inclusions we infer that the uppermost portion of the permeable ice becomes impermeable with the passage of time and as more marine ice is accreted on the base of the shelf we estimate an average closure rate of 0 3 m a 1 between the borehole sites upstream the average closure rate is faster at 0 9 m a 1 we estimate an average porosity of the total marine ice layer of 14 20 such that the deeper ice must have even higher values high permeability implies that sea water can move relatively freely through the material and we propose that where such marine ice exists this renders deep parts of the ice shelf particularly vulnerable to changes in ocean properties

ocean driven heating of europa s icy shell at low latitudes on jupiter s icy moon europa enigmatic chaos terrain where the icy crust is cut by a jumble of ridges and cracks occurs most commonly at lower latitudes simulations of convection in the ocean underlying europa s icy crust suggest that ocean dynamics can control an enhanced flow of heat to europa s equatorial surface and hence geological activity

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

modeling interannual dense shelf water export in the region of the mertz glacier tongue 1992 2007 ocean observations around the australian antarctic basin show the importance of coastal latent heat polynyas near the mertz glacier tongue mgt to the formation of dense shelf water dsw and associated antarctic bottom water aabw here we use a regional ocean ice shelf model to investigate the interannual variability of the export of dsw from the adelie west of the mgt and the mertz east of the mgt depressions from 1992 to 2007 the variability in the model is driven by changes in observed surface heat and salt fluxes the model simulates an annual mean export of dsw through the adelie sill of about 0 070 06 sv from 1992 to 1998 the export of dsw through the adelie mertz sills peaked at 0 14 sv 0 29 sv during july to november during periods of mean to strong polynya activity defined by the surface ocean heat loss dsw formed in the adelie depression can spread into the mertz depression via the cavity under the mgt an additional simulation where ocean ice shelf thermodynamics have been disabled highlights the fact that models without ocean ice shelf interaction processes will significantly overestimate rates of dsw export the melt rates of the mgt are 1 20 4 m yr 1 during periods of average to strong polynya activity and can increase to 3 81 5 m yr during periods of sustained weak polynya activity due to the increased presence of relatively warmer water interacting with the base of the ice shelf the increased melting of the mgt during a weak polynya state can cause further freshening of the dsw and ultimately limits the production of aabw

ocean circulation beneath the ronne ice shelf the intimate thermal contact between the base of antarctic ice shelves and the underlying ocean enables changes in climate to have a rapid impact on the outflow of ice from the interior of antarctica1 2 furthermore water modified by passage under ice shelves particularly in the weddell sea is believed to be an important constituent of antarctic bottom water3 a water mass that can be observed as far north as 50 n in the deep oceans4 antarctic bottom water is both cold and oxygen rich and plays an important part in the cooling and ventilation of the world s oceans because of the difficulty in gaining access the oceano graphic regime beneath ice shelves is very poorly sampled5 by successfully drilling through the ice however we were able to obtain oceanographic data from beneath the largest antarctic ice shelf the ronne filchner ice shelf in the southern weddell sea we find that our data agree well with the predictions of a relatively simple oceanographic plume model of sub ice shelf circulation6 this model can therefore be used with some confidence to investigate the links between climate changes ice shelf melting and bottom water production

marine ice formation in a suture zone on the larsen c ice shelf and its influence on ice shelf dynamics 1 antarctic ice shelves are fed primarily by the glaciers flowing into them downstream of promontories separating these glaciers supercooled water can rise and freeze into suture zones leading to the accretion of marine ice marine ice bodies have been found in several antarctic ice shelves but little is known about their detailed geometry rate of accretion or influence on ice dynamics in this study we investigate marine ice in a suture zone downstream of the joerg peninsula in the southern part of the larsen c ice shelf antarctic peninsula we present ground penetrating radar data from which we infer the base of the meteoric ice and in combination with gps data and assuming hydrostatic equilibrium estimate marine ice thickness within a suture zone we show that the joerg peninsula suture zone contains marine ice layer which is increasing in thickness along flow from 140 m to 180 m over 20 km implying an average basal accretion rate of 0 5 m a 1 in our study area we examined the impact of this inferred marine ice on ice shelf dynamics by modeling the suture zone within an ice flow model the results which replicate observed surface velocities and strain rates show that the warmer and thus softer ice of the suture zone serves to channel shear deformation this enables decoupling of neighboring flow units with different flow velocities while maintaining the structural integrity of the ice shelf

thermohaline circulation below the ross ice shelf a consequence of tidally induced vertical mixing and basal melting the warmest water below parts of the ross ice shelf resides in the lowest portion of the water column because of its high salinity vertical mixing caused by tidal stirring can thus induce ablation by lifting the warm but dense water into contact with the ice shelf a numerical tidal simulation indicates that vertically well mixed conditions predominate in the southeastern part of the sub ice shelf cavity where the water column thickness is small basal melting in this region is expected to be between 0 05 and 0 5 m yr and will drive a thermohaline circulation having the following characteristics high salinity shelf water at 1 8oc formed by winter sea ice production in the open ross sea flows along the seabed toward the tidal mixing fronts below the ice shelf and meltwater at 2 2oc produced in the wellmixed region flows out of the sub ice shelf cavity along the ice shelf bottom sensitivity of this ablation process to climatic change is expected to be small because high salinity shelf water is constrained to have the sea surface freezing temperature

future sea level rise due to projected ocean warming beneath the filchner ronne ice shelf a coupled model study a general ocean circulation model is coupled with a 3d thermodynamical ice sheet shelf model to simulate the response of the filchner ronne ice shelf fris antarctica and coastal parts of its catchment basin to a postulated inflow of warm deep water into the ice shelf cavity on a 1000 yr timescale prescribed ocean warming based on climate projections enters the ice shelf cavity in the up to 1500 m deep filchner trough and penetrates deep into the sub ice cavity increasing basal melt rates induce geometry changes of the cavity which in turn have an impact on the ocean circulation and therefore the modelled melt rates highest melt rates of about 20 m yr 1 follow the up to 180 km retreating grounding line basal mass loss reaches about 250 km3 yr 1 doubling the present day value the most vulnerable areas below the fris are the bailey ice stream and the area between the institute and moeller ice streams where the increased melting accounts for about 80 km of the modelled grounding line retreat on the backward sloping bedrock the potential additional contribution to the eustatic sea level rise due to the grounded ice loss simulated in an ensemble approach against a transient control experiment is about 0 05 mm yr 1 during the first 500 yr and about 0 17 mm yr 1 thereafter

investigations of the mass balance of the southeastern ronne ice shelf antarctica data from the filchner v campaign were used to investigate the mass balance conditions in the southeastern ronne ice shelf ris antarctica radio echo sounding and seismic measurements over this area show a maximum ice thickness of 2000 m close to the grounding line of foundation ice stream the measurements also revealed that the position of this grounding line is 40 km further south than previously thought new mass flux calculations result in an estimate or 51 km 3 a 1 for the ice stream transport from the ice sheet into the eastern ice shelf the mollereisstrom mes west of foundation ice stream shows a maximum ice thickness of 1100 1200 m in the grounding line area and a mass flux of 23 km 3 a 1 assuming steady state conditions mass balance calculations based on the new data result in a mean melt rate of about 1 m a 1 at the ice shelf base for the entire southeastern part of the ris the melt rate in the grounding line area of foundation ice stream exceeds 9 m a 1 in contrast other ice streams draining into the filchner ronne ice shelf show maximum melt rates from 1 2 m a 1 mes to 4 m a 1 rutford ice stream our calculations indicate that nearly all of the ice deposited in the drainage area of the eastern ris on the ice sheet does not reach the ice shelf front as original meteoric ice but is melted at the ice shelf base

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

impact of tide topography interactions on basal melting of larsen c ice shelf antarctica 1 basal melting of ice shelves around antarctica contributes to formation of antarctic bottom water and can affect global sea level by altering the offshore flow of grounded ice streams and glaciers tides influence ice shelf basal melt rate wb by contributing to ocean mixing and mean circulation as well as thermohaline exchanges with the ice shelf we use a three dimensional ocean model thermodynamically coupled to a nonevolving ice shelf to investigate the relationship between topography tides andwb for larsen c ice shelf lcis in the northwestern weddell sea antarctica using our best estimates of ice shelf thickness and seabed topography we find that the largest modeled lcis melt rates occur in the northeast where our model predicts strong diurnal tidal currents 0 4 m s 1 this distribution is significantly different from models with no tidal forcing which predict largest melt rates along the deep grounding lines we compare several model runs to explore melt rate sensitivity to geometry initial ocean potential temperature 0 thermodynamic parameterizations of heat and freshwater ice ocean exchange and tidal forcing the resulting range of lcis averagedwb is 0 11 0 44 m a 1 the spatial distribution of wb is very sensitive to model geometry and thermodynamic parameterization while the overall magnitude of wb is influenced by 0 these sensitivities in wbpredictions reinforce a need for high resolution maps of ice draft and sub ice shelf seabed topography together with ocean temperature measurements at the ice shelf front to improve representation of ice shelves in coupled climate system models

melting of ice shelves and the mass balance of antarctica we calculate the present ice budget for antarctica from measurements of accumulation minus iceberg calving run off and in situ melting beneath the floating ice shelves the resulting negative mass balance of 469 gt year 1 differs substantially from other recent estimates but some components are subject to high temporal variability and budget uncertainties of 20 50 annual accumulation from an earlier review is adjusted to include the antarctic peninsula for a total of 2144 gt year 1 an iceberg production rate of 2016 gt year 1 is obtained from the volume of large icebergs calculated from satellite images since 1978 and from the results of an international iceberg census project ice shelf melting of 544 gt year 1 is derived from physical and geochemical observations of meltwater outflow glaciological field studies and modeling of the sub ice ocean circulation the highest melt rates occur near ice fronts and deep within sub ice cavities run off from the ice sheet surface and from beneath the grounded ice is taken to be 53 gt year 1 less than half of the negative mass balance need come from the grounded ice to account for the unattributed 0 45 mm year 1 in the ipcc best estimate of the recent global sea level rise

the seasonal appearance of ice shelf water in coastal antarctica and its effect on sea ice growth 1 in this paper we report measurements from the first year round mooring underneath sea ice in mcmurdo sound antarctica which we combine with full depth ocean profiles to identify the incremental appearance of potentially supercooled ice shelf water isw we investigate the effects of isw on sea ice using observations of sea ice growth and crystal structure together with under ice photography we show that the appearance of isw at the surface leads to a disruption in the columnar texture of the sea ice but that persistent growth enhancement occurs only once the entire water column has cooled to the surface freezing point in doing so we demonstrate the possibility of inferring the presence of isw beneath sea ice through crystallographic analysis of cores these findings will be useful for both modeling and observing the extent of isw enhanced ice growth in addition we found that the local growth of first year landfast sea ice only accounted for half of the observed increase in salinity over the water column which indicates that polynyas are responsible for approximately half of the salt flux into mcmurdo sound

regime of the filchner ronne ice shelves antarctica seismic radio echo twerle balloon and oceanographic data of the filchner ronne ice shelves are analysed a large thin area in the central ronne ice shelf is found to differ from the morphology of the ross and filchner ice shelves this area is partly filled by basal saline ice which can be attributed to regional regelation caused by oceanic circulation

tidal motion ice velocity and melt rate of petermann gletscher greenland measured from radar interferometry over a floating glacier ice tongue or an ice shelf the glacier motion measured by a single repeat pass radar interferogram is difficult to analyze because the long term steady motion of the ice is intermixed with its cyclic downward motion induced by tidal forcing multiple interferograms and a quadruple difference technique are necessary to separate the tidal signal from the long term steady motion of the ice an example of application of this technique is given here using ers 1 radar images of petermann gletscher a major outlet glacier of northern greenland tidal displacements are measured with 5 mm statistical noise the long term ice velocity is measured with a precision of 1 m a 1 the inferred tidal displacements agree well with model predictions from a fixed elastic beam with an elastic damping factor of 0 47 0 01 km 1 the hinge line is mapped with a precision of 20 80 m combining the interferometric ice velocities with ice thickness data the glacier ice discharge is calculated at and below the hinge line at the hinge line the ice flux is 12 1 1 km3 a 1 at the ice front calf ice production is only 0 59 km3 a 1 meaning that 95 of the ice that crosses the grounding line melts before it reaches the calving front assuming steady state conditions the melt rate of the glacier tongue averages 12 1 m a 1 with peak values exceeding 20 m a 1 near the hinge line this high melt rate cannot be accommodated by surface ablation alone only about 2 3 m a 1 and is attributed to pronounced basal melting of the ice tongue basal melting often assumed to be negligible in greenland is the dominant process of mass release from the floating section of petermann gletscher

the temperature and salinity fine structure of the ocean under the ross ice shelf a series of temperature and salinity profiles was made in the ocean under the ross ice shelf at 82 22 5 s 168 37 5 w where the ice was 420 and the underlying seawater 240 m thick the water structure consisted of a fairly well mixed low salinity layer at the in situ freezing point of the ice water interface about 30 m thick a transition layer characterized by intrusions about 85 m thick a strongly stratified layer with increasing temperature and salinity about 50 m thick another transition layer characterized by intrusions about 45 m thick and an isohaline bottom layer with a nearly abiabatic temperature gradient about 30 m thick the temperature fluctuations in the two transition layers can be attributed mainly to intrusive activity even though internal wave activity was highest in these regions in the central stable layer internal waves probably contribute to the temperature fluctuations equally with intrusions the internal wave dropped displacement spectrum seems to be very similar to those found in the open ocean some profiles showed intrusions in the top transition layer colder than the top boundary layer and some showed intrusions in the bottom transition layer warmer than the bottom boundary layer indicating that horizontal shear must be present internal waves of near inertial frequency excited by the semidiurnal tides combined with shear induced instabilities seem to be the likely causes of the observed fine structure

large scale oceanographic constraints on the distribution of melting and freezing under ice shelves previous studies suggest that ice shelves experience asymmetric melting and freezing topography may constrain oceanic circulation and thus basal melt freeze patterns through its influence on the potential vorticity pv field however melting and freezing induce a local circulation that may modify locations of heat transport to the ice shelf this paper investigates the influence of buoyancy fluxes on locations of melting and freezing under different bathymetric conditions an idealized set of numerical simulations the decoupled simulations employs spatially and temporally fixed diapycnal fluxes these experiments in combination with scaling considerations indicate that while flow in the interior is governed by large scale topographic gradients recirculation plumes dominate near buoyancy fluxes thermodynamically decoupled models are then compared to those in which ice ocean heat and freshwater fluxes are driven by the interior flow the coupled simulations near the southern boundary strong cyclonic flow forced by melt induced upwelling drives inflow and melting to the east recirculation is less evident in the upper water column as shoaling of meltwater freshened layers dissipates the dynamic influence of buoyancy forcing yet freezing remains intensified in the west in coupled simulations the flow throughout the cavity is relatively insensitive to bathymetry stratification the slope of the ice shelf and strong meridionally distributed buoyancy fluxes weaken its influence

ocean interactions with the base of amery ice shelf antarctica using a two dimensional ocean thermohaline circulation model we varied the cavity shape beneath amery ice shelf in an attempt to reproduce the 150 m thick marine ice layer observed at the gi ice core site most simulations caused melting rates which decrease the ice thickness by as much as 400 m between grounding line and g1 but produce only minor accumulation at the ice core site and closer to the ice front changes in the seafloor and ice topographies revealed a high sensitivity of the basal mass balance to water column thickness near the grounding line to submarine sills and to discontinuities in ice thickness model results showed temperature salinity gradients similar to observations from beneath other ice shelves where ice is melting into seawater modeled outflow characteristics at the ice front are in general agreement with oceanographic data from prydz bay a freshwater flux across the grounding line derived from melting beneath the grounded ice sheet would have to be anomalously large to produce the basal marine ice layer and account for the ice shelf water outflow we concur with morgan s inference that the g 1 core may have been taken in a basal crevasse filled with marine ice this ice is formed from water cooled by ocean ice shelf interactions along the interior ice shelf base

analysis of velocity field mass balance and basal melt of the lambert glacier amery ice shelf system by incorporating radarsat sar interferometry and icesat laser altimetry measurements 1 by incorporating recently available remote sensing data we investigated the mass balance for all individual tributary glacial basins of the lambert glacier amery ice shelf system east antarctica on the basis of the ice flow information derived from sar interferometry and icesat laser altimetry we have determined the spatial configuration of eight tributary drainage basins of the lambert amery glacial system by combining the coherence information from sar interferometry and the texture information from sar and modis images we have interpreted and refined the grounding line position we calculated ice volume flux of each tributary glacial basin based on the ice velocity field derived from radarsat three pass interferometry together with ice thickness data interpolated from australian and russian airborne radio echo sounding res surveys and inferred from icesat laser altimetry data our analysis reveals that three tributary basins have a significant net positive imbalance while five other subbasins are slightly positive or close to zero balance overall in contrast to previous studies we find that the grounded ice in lambert glacier amery ice shelf system has a positive mass imbalance of 22 9 4 4 gt a 1 the net basal melting for the entire amery ice shelf is estimated to be 27 0 7 0 gt a 1 the melting rate decreases rapidly from the grounding zone to the ice shelf front significant basal refreezing is detected in the downstream section of the ice shelf the mass balance estimates for both the grounded ice sheet and the ice shelf mass differ substantially from other recent estimates

measurements of ice shelf water beneath the front of the ross ice shelf using gliders measurements made by an underwater glider deployed near the ross ice shelf were used to identify the presence of ice shelf water isw which is defined as seawater with its potential temperature lower than its surface freezing point temperature properties logged by the glider included in situ temperature electrical conductivity pressure gps location at surfacings and time for most of the first 30 recorded dives of its deployment evidence suggests the glider was prevented from surfacing due to being under the ice shelf for dives under the ice shelf farthest from the ice shelf front isw layers of varying thicknesses and depth locations were observed between 2 m thick centred at 231 m depth to 93 m thick centred at 360 m for dives under the ice shelf close to the ice shelf front either no isw was observed or isw layers were centred at shallower depths 116 127 m thicker isw layers e g up to 250 m thickness centred at 421 m were observed for some glider dives in open water in front of the ross ice shelf no in situ supercooling water colder than the pressure dependent freezing point temperature was observed

interannual variations in meltwater input to the southern ocean from antarctic ice shelves ocean driven basal melting of antarctica s floating ice shelves accounts for about half of their mass loss in steady state where gains in ice shelf mass are balanced by losses ice shelf thickness changes driven by varying basal melt rates modulate mass loss from the grounded ice sheet and its contribution to sea level and the changing meltwater fluxes influence climate processes in the southern ocean existing continent wide melt rate datasets have no temporal variability introducing uncertainties in sea level and climate projections here we combine surface height data from satellite radar altimeters with satellite derived ice velocities and a new model of firn layer evolution to generate a high resolution map of time averaged 2010 2018 basal melt rates and time series 1994 2018 of meltwater fluxes for most ice shelves total basal meltwater flux in 1994 1090 150 gt yr was not significantly different from the steady state value 1100 60 gt yr but increased to 1570 140 gt yr in 2009 followed by a decline to 1160 150 gt yr in 2018 for the four largest cold water ice shelves we partition meltwater fluxes into deep and shallow sources to reveal distinct signatures of temporal variability providing insights into climate forcing of basal melting and the impact of this melting on the southern ocean

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

a diverse benthic assemblage 100 km from open water under the amery ice shelf antarctica 1 a hot water drill was used to penetrate 480 m of ice to reveal a diverse benthic assemblage dominated by suspension feeding invertebrates under the amery ice shelf east antarctica at a location 100 km from open water and at a depth of 775 m below sea level 840 m below the ice shelf surface this is the first record of a benthic assemblage of this type found at this distance under an ice shelf the few previous reports of life under ice shelves describe assemblages with very different trophic strategies e g sparse assemblages of mobile scavengers or chemotrophs or are in circumstances in which in situ photosynthesis at tide cracks or through the ice cannot be ruled out as a potential source of primary production the physical characteristics of the amery ice shelf and the feeding strategies represented together indicate that the only likely source of primary production to sustain the benthic assemblage is material advected from open water this suggestion is supported by observed current speeds in the vicinity and reported rates of particle settling the observation under an ice shelf of a benthic assemblage that is very similar to those found elsewhere in antarctica in locations dominated by annual sea ice or at depths below the photic zone has implications for the interpretation of sediment paleorecords to represent the history of ice shelf advance and retreat without observations of this living assemblage in situ the remnants of its component species in the sediment record such as sponge spicules echinoderm ossicles and bryozoan fragments could be interpreted reasonably but erroneously to represent open water conditions

development of sea ice in the weddell sea we report on the development and physical properties of sea ice in the central and eastern weddell sea the investigations were part of the winter weddell sea project 1986 which extended over the months of july through december major elements of the glaciological part of this study included continuous shipborne observations of sea ice conditions and occasional helicopter reconnaissance flights extensive measurements of snow and ice thicknesses at daily ice stations and detailed analyses of sampled ice cores from each ice station textural investigations of the sampled ice revealed the dominance of frazil ice in the central weddell sea and the occurrence of an additional ice class called platelet ice together with the commonly known frazil and congelation ice in the coastal region of the eastern weddell sea these results in combination with the visual ice observations reveal two major mechanisms for sea ice generation in the antarctic which were not sufficiently well accounted for in previous investigations in the central weddell sea a cycle of pancake ice formation and its growth into consolidated floes seems to be the dominant process of the advancing sea ice edge in the coastal waters the growing sea ice cover consists to a considerable degree of ice platelets which are formed in the underlying water column in front of the ice shelf edges thus congelation ice growth which is mainly controlled by atmospheric thermodynamic forcing seems to be of less importance in the central and south eastern weddell sea than for example in the arctic basin

thermohaline circulation and interaction between ice shelf cavities and the adjacent open ocean the circulation system in an ice shelf cavity is driven by buoyancy fluxes due to melting and freezing of ice and horizontal pressure gradients at the interface between the cavity and the open ocean hence the inflow and outflow pattern and the hydrography in the open ocean influence the general hydrographic condition in the cavity which at least provides the potential for melting and freezing processes applying a three dimensional ocean general circulation model to an idealized ice shelf cavity geometry coupled with an open ocean at a topographic ice shelf barrier we found an important parameter controlling the interaction between these two systems idealized studies for different ice shelf and sea bottom topographies and forcing mechanisms for the open ocean show that the ice shelf edge represents a natural barrier for barotropic interaction because of the sudden decrease in water column thickness since the water column thickness and the coriolis force determine the characteristics for geostrophic flow separated circulation systems arise for the open ocean and the ice shelf cavity only in areas where constant water column thickness and from the oceanographic point of view constant f h contours can be observed across the barrier an increased barotropic current can surmount the ice edge and ventilate the water mass beneath the ice shelf this is only the case at lateral sloping sidewalls or at deep depressions which can be found for example in the southern weddell sea in all other cases the circulation in the ice shelf cavity is closed and almost unaffected by the hydrography outside the barrier

seasonal evolution of an ice shelf influenced fast ice regime derived from an autonomous thermistor chain ice shelves strongly interact with coastal antarctic sea ice and the associated ecosystem by creating conditions favorable to the formation of a sub ice platelet layer the close investigation of this phenomenon and its seasonal evolution remains a challenge due to logistical constraints and a lack of suitable methodology in this study we characterize the seasonal cycle of antarctic fast ice adjacent to the ekstrom ice shelf in the eastern weddell sea we used a thermistor chain with the additional ability to record the temperature response induced by cyclic heating of resistors embedded in the chain vertical sea ice temperature and heating profiles obtained daily between november 2012 and february 2014 were analyzed to determine sea ice and snow evolution and to calculate the basal energy budget the residual heat flux translated into an ice volume fraction in the platelet layer of 0 18 0 09 which we reproduced by a independent model simulation and agrees with earlier results manual drillings revealed an average annual platelet layer thickness increase of at least 4 m and an annual maximum thickness of 10 m beneath second year sea ice the oceanic contribution dominated the total sea ice production during the study effectively accounting for up to 70 of second year sea ice growth in summer an oceanic heat flux of 21 w m 2 led to a partial thinning of the platelet layer our results further show that the active heating method in contrast to the acoustic sounding approach is well suited to derive the fast ice mass balance in regions influenced by ocean ice shelf interaction as it allows subdiurnal monitoring of the platelet layer thickness

marine ice recycling at the southern mcmurdo ice shelf antarctica marine ice accretes at the base of ice shelves often infilling open structural weaknesses and increasing ice shelf stability however the timing and location of marine ice formation remain poorly understood this study determines marine ice source water composition and origin by examining marine ice crystal morphology water isotope and solute chemistry in ice samples collected from the southern mcmurdo ice shelf smis antarctica the measured co isotopic record together with the output of a freezing model for frazil crystals indicate a spatio temporally varying water source of sea water and relatively fresher water such as melted meteoric or marine ice this is in agreement with the occurrence of primarily banded and granular ice crystal facies typical for frazil ice crystals that nucleate in a supercooled mixture of water masses we propose that marine ice exposed at the surface of smis which experiences summer melt is routed to the ice shelf base via the tide crack here frazil crystals nucleate in a double diffusion mechanism of heat and salt between two water masses at their salinity dependent freezing point recycling of previously formed marine ice facilitates ice shelf selfsustenance in a warming climate

ice formation in subglacial lake vostok central antarctica abstract the investigation of chemical and isotopic properties in the lake ice from the vostok ice core gives clues to the mechanisms involved in ice formation within the lake a small lake water salinity can be reasonably deduced from the chemical data possible implications for the water circulation of lake vostok are developed the characteristics of the isotopic composition of the lake ice indicate that ice formation in lake vostok occurred by frazil ice crystal generation due to supercooling as a consequence of rising waters and a possible contrast in water salinity subsequent consolidation of the developed loose ice crystals results in the accretion of ice to the ceiling of the lake

examining the interaction between multi year landfast sea ice and the mertz glacier tongue east antarctica another factor in ice sheet stability the mertz glacier tongue mgt east antarctica has a large area of multi year fast sea ice myfi attached to its eastern edge we use various satellite data sets to study the extent age and thickness of the myfi and how it interacts with the mgt we estimate its age to be at least 25 years and its thickness to be 10 55 m this is an order of magnitude thicker than the average regional sea ice thickness and too thick to be formed through sea ice growth alone we speculate that the most plausible process for its growth after initial formation is marine frazil ice accretion the satellite data provide two types of evidence for strong mechanical coupling between the two types of ice the myfi moves with the mgt and persistent rifts that originate in the mgt continue to propagate for large distances into the myfi the area of myfi decreased by 50 following the departure of two large tabular icebergs that acted as pinning points and protective barriers future myfi extent will be affected by subsequent icebergs from the ninnis glacier and the imminent calving of the mgt fast ice is vulnerable to changing atmospheric and oceanic conditions and its disappearance may have an influence on ice tongue ice shelf stability understanding the influence of thick myfi on floating ice tongues ice shelves may be significant to understanding the processes that control their evolution and how these respond to climate change and thus to predicting the future of the antarctic ice sheet

supercooling and energy exchange near the arctic ocean surface conductivity temperature and depth ctd measurements made north of svalbard centered around 83 n 10 e show regions in which the surface waters are supercooled to a depth of about 8 m at other locations warm atlantic waters advected into the area by the west spitzbergen current are melting the sea ice the resulting large horizontal salinity gradients cause intrusive layering with layers at depth sometimes being below their surface freezing point supercooling is explained in terms of the pressure dependence of freezing temperature and the existence of ice keels well below the surface it is noted that the potential heat sink for surface freezing provided by supercooling can be of the same order as that available from heat loss to the atmosphere at the same time an equivalent amount of ice is being melted off the keels thus constituting an ice pump

ice ocean interaction on ronne ice shelf antarctica detailed glaciological studies have been completed at 28 sites lying on an approximate flow line extending 760 km across ronne ice shelf parameters measured at each location include ice velocity thickness principal strain rates surface elevation temperature and accumulation rate the data have been used in a steady state model to derive the basal mass flux and the temperature profile with depth at each site from the principles of mass and energy conservation these calculations indicate basal melting in excess of 1 m yr 1 over the first 100 km of the flow line downstream of the grounding line where the ice shelf is between 1200 m and 1600 m thick the maximum melt rates in this region occur near the inland margin and exceed 4 m yr 1 melting continues at a lesser rate over the next 200 km before freezing commences freezing then dominates up to the final 100 km before the ice front resulting in the accumulation of a layer of basal sea ice up to 50 m thick this is rapidly removed as melt rates increase to over 6 m yr 1 at the ice front the cumulative effect of this pattern of basal accumulation and ablation is the wastage by melting of 85 of the mass discharged across the grounding line before it reaches the ice front supporting evidence for a layer of saline ice underlying the ice shelf is provided by the strength of basal radar reflections observed during radio echo sounding of ice thickness in the region where mass balance calculations suggest an accretion of basal sea ice reflection coefficients are consistently low ranging from 6 db to 38 db most of these weak reflections are believed to originate from the true base of the ice shelf the additional energy loss being the result of increased attenuation of the radar signal within the saline layer the derived pattern of basal melting and freezing is consistent with a simple model of sub ice shelf oceanic circulation involving a deep thermohaline convection cell dense saline water which is formed over the continental shelf during winter when the sea surface freezes drains into the deepest parts of the sub ice shelf cavity at the inland margin where this water mass comes into contact with the ice shelf its temperature is 1 c above the local pressure freezing point melting of ice results producing a buoyant outflow of cold relatively fresh water along the ice shelf base basal freezing occurs towards the ice front where the ascending water becomes supercooled this circulation has important implications for the production of antarctic bottom water and for the response of the ice shelf to driving stresses through the temperature dependent viscosity of ice

observations of platelet ice growth and oceanographic conditions during the winter of 2003 in mcmurdo sound antarctica 1 platelet ice is the name given to ice crystals that nucleate in the ocean and grow either at depth or loosely attached to the ice water interface related to the proximity of ice shelves it is known to form in supercooled seawater this study details the conditions for its growth during the austral winter of 2003 in mcmurdo sound antarctica a key finding is that the presence of platelet ice in the sea ice cover is conclusively linked to the time history of the appearance of ice crystals in the water column monitored using the strength of the backscattered signal from an acoustic doppler current profiler as a proxy generally these crystals appeared from mid may as water near the interface became supercooled this near surface supercooling appears to be related to a simultaneous abrupt change in the structure of the upper 250 m of the water column from one that behaved dynamically and contained both the warmest and coolest measured temperatures to one in which the water was essentially isothermal near its surface freezing temperature near surface ocean temperature was also affected by tidal mixing and by an increase in the thickness and density over the course of winter of the surface mixed layer created by salt rejection during ice growth these processes allowed cold water trapped by buoyancy in a band at the base of the mixed layer in early winter to gain access to the ice water interface by midwinter this band of cold water probably had its origin beneath the mcmurdo ice shelf

ocean variability contributing to basal melt rate near the ice front of ross ice shelf antarctica basal melting of ice shelves is an important but poorly understood cause of antarctic ice sheet mass loss and freshwater production we use data from two moorings deployed through ross ice shelf 6 and 16 km south of the ice front east of ross island and numerical models to show how the basal melting rate near the ice front depends on sub ice shelf ocean variability the moorings measured water velocity conductivity and temperature for 2 months starting in late november 2010 about half of the current velocity variance was due to tides predominantly diurnal components with the remainder due to subtidal oscillations with periods of a few days subtidal variability was dominated by barotropic currents that were large until mid december and significantly reduced afterward subtidal currents were correlated between moorings but uncorrelated with local winds suggesting the presence of waves or eddies that may be associated with the abrupt change in water column thickness and strong hydrographic gradients at the ice front estimated melt rate was 1 2 0 5 m a 1 at each site during the deployment period consistent with measured trends in ice surface elevation from gps time series the models predicted similar annual averaged melt rates with a strong annual cycle related to seasonal provision of warm water to the ice base these results show that accurately modeling the high spatial and temporal ocean variability close to the ice shelf front is critical to predicting time dependent and mean values of meltwater production and ice shelf thinning

the southern ocean and its interaction with the antarctic ice sheet the southern ocean exerts a major influence on the mass balance of the antarctic ice sheet either indirectly by its influence on air temperatures and winds or directly mostly through its effects on ice shelves how much melting the ocean causes depends on the temperature of the water which in turn is controlled by the combination of the thermal structure of the surrounding ocean and local ocean circulation which in turn is determined largely by winds and bathymetry as climate warms and atmospheric circulation changes there will be follow on changes in the ocean circulation and temperature these consequences will affect the pace of mass loss of the antarctic ice sheet

the role of tides in ocean ice shelf interactions in the southwestern weddell sea near observed weddell sea gyre continental shelf cavity water masses in interactive ocean sea ice tide ice shelf melt simulations tides amplify basal melt refreeze pattern raising net melt by 50 associated with enhanced time varying kinetic energy at the ice base impacts of additional meltwater production on weddell continental shelf sea ice and newly formed bottom water properties are suggested corresponding author u hausmann uhausc at gmail dot com this article has been accepted for publication and undergone full peer review but has not been through the copyediting typesetting pagination and proofreading process which may lead to differences between this version and the version of record please cite this article as

variability in the distribution of fast ice and the sub ice platelet layer near mcmurdo ice shelf variability in the volume of supercooled ice shelf water outflow in mcmurdo sound is reflected in the thickness and distribution of fast ice and the sub ice platelet layer beneath ground based electromagnetic induction and drill hole surveys of the distribution and thickness of ice shelf influenced fast ice and the sub ice platelet layer in mcmurdo sound were carried out in late spring of 2011 2013 2016 and 2017 in 2011 and 2017 thicker sub ice platelet layers of up to 7 5 and 6 m were observed respectively fast ice formation throughout the winters of 2011 and 2017 was influenced by a higher occurrence of strong southerly wind events and resultant activity of the ross sea polynya in contrast lower wind conditions in 2016 led to largely undisturbed sea ice growth and anomalously extensive fast ice coverage a thinner sub ice platelet layer of up to 4 m was observed in 2016 in 2011 and 2017 substantial and variable sub ice platelet layers were detected in a region of exchange of water masses between the ross sea and the mcmurdo ross ice shelf cavity which were not observed in 2013 and 2016 we hypothesize that a higher frequency of strong southerly wind events resultant polynya activity and high salinity shelf water production over winter accelerates circulation and increases melting in the proximal shallow mcmurdo ice shelf and the deeper ross ice shelf regions of the conjoined cavity the outflow of supercooled ice shelf water and sub ice platelet layer formation in mcmurdo sound are consequently promoted

modeling ice shelf cavities in a z coordinate ocean general circulation model 1 processes at the ice shelf ocean interface and in particular in ice shelf cavities around antarctica have an observable effect on the solutions of basin scale to global coupled ice ocean models despite this these processes are not routinely represented in global ocean and climate models it is shown that a new ice shelf cavity model for z coordinate models can reproduce results from an intercomparison project of earlier approaches with vertical or isopycnic coordinates as a proof of concept ice shelves are incorporated in a 100 year global integration of a z coordinate model in this simulation glacial meltwater can be traced as far as north as 15 s the observed effects of processes in the ice shelf cavities agree with previous results from a coordinate model notably the increase in sea ice thickness however melt rates are overestimated probably because the parameterization of basal melting does not suit the low resolution of this configuration

computing marine ice thickness at an ice shelf base the freezing of sea water to the base of an ice shelf can give rise to large patches of accumulated ice a phenomenon known as marine ice in this study a numerical method is presented for calculating the thickness of the marine ice layer using an ice shelf ocean model the present day modeling paradigm of ice shelf ocean interaction usually involves the fixed specification of the ice shelf geometry while the ocean circulation in the cavity beneath the ice shelf evolves freely this approach relies on several assumptions such as steady state ice shelf thickness and ice shelf flow fields in order to make reasonable quantitative estimates of the thermodynamic exchange processes occurring at the ice shelf base this paper discusses the impact of these and other assumptions on the estimation of the thickness of the marine ice layer model simulation results are presented for an idealized ice shelf ocean configuration as a demonstration of the feasibility of the numerical method a sensitivity analysis is given so as to quantify the relative uncertainty in the marine ice thickness that arises from uncertainties in the model input parameters these being principally the ice shelf flow field the basal accumulation rate and the ice shelf thickness field

meteoric and marine ice crystal orientation fabrics from the amery ice shelf east antarctica the northwestern sector of the amery ice shelf east antarctica has a layered structure due to the presence of both meteoric ice and a marine ice layer resulting from sub shelf freezing processes crystal orientation fabric and grain size data are presented for ice cores obtained from two boreholes 70 km apart on approximately the same flowline multiple maxima crystal orientation fabrics and large mean grain sizes in the meteoric ice are indicative of stress relaxation and subsequent grain growth in ice that has flowed into the amery ice shelf strongly anisotropic single maximum crystal orientation fabrics and rectangular textures near the base of the 200 m thick marine ice layer suggest accretion occurs by the accumulation of frazil ice platelets crystal orientation fabrics in older marine ice exhibit vertical large circle girdle patterns influenced by the complex stress configurations that exist towards the margins of the ice shelf post accumulation grain growth and fabric development in the marine ice layer are restricted by a high concentration of brine and insoluble particulate inclusions differences in the meteoric and marine ice crystallography are indicative of the contrasting rheological properties of these layers which must be considered in relation to large scale ice shelf dynamics

the cavity under the amery ice shelf east antarctica ocean circulation under ice shelves and associated rates of melting and freezing are strongly influenced by the shape of the sub ice shelf cavity we have refined an existing method and used additional in situ measurements to estimate the cavity shape under the amery ice shelf east antarctica a finite element hydrodynamic ocean tide model was used to simulate the major tidal constituents for a range of different sub amery ice shelf cavity water column thicknesses the data are adjusted in the largely unsurveyed southern region of the ice shelf cavity by comparing the complex error between simulated tides and in situ tides derived from gps observations we show a significant improvement in the simulated tides with a combined complex error of 1 8 cm in comparison with past studies which show a complex error of 5 3 cm our bathymetry incorporates ice draft data at the grounding line and seismic surveys which have provided a considerable amount of new data this technique has particular application when the water column beneath ice shelves is inaccessible and in situ gps data are available

snowball earth ice thickness on the tropical ocean 1 on the tropical oceans of a neo proterozoic snowball earth snow free ice would have existed in regions of net sublimation photosynthesis could have continued beneath this bare ice if it was sufficiently thin and sufficiently clear the steady state ice thickness is determined by the necessity to balance the upward conduction of heat with three subsurface heating rates the heat flux from the ocean to the ice base the latent heat of freezing to the ice base and the solar energy absorbed within the ice a preliminary study using a broadband model for solar radiation and assuming a large freezing rate had indicated that tropical ice might be only a few meters thick here we show that the vertical throughput of ice by surface sublimation and basal freezing would be too slow to keep the ice thin and that the broadband model had exaggerated the absorption depth of sunlight we use a spectral model for solar absorption computing radiative transfer at 60 wavelengths considering absorption by the ice and scattering by bubbles with the spectral model the computed ice thickness is much greater for a solar flux of 320 w m 2 at the equatorial surface and expected albedo of 0 5 for bare sea ice we find that surface temperatures below 12 c generate ice layers too thick for photosynthesis 100 m if the albedo were as low as 0 4 thick ice would occur only for surface temperatures below 25 c but such low temperatures would be difficult to maintain with such low albedo for surface temperatures warmer than these limits the ice becomes thin 1 m and is unlikely to represent a coherent ice layer however glacial deformation of thick floating ice from nearby oceanic regions may preclude the existence of thin or ice free patches

the influence of meridional ice transport on europa s ocean stratification and heat content jupiter s moon europa likely hosts a saltwater ocean beneath its icy surface geothermal heating and rotating convection in the ocean may drive a global overturning circulation that redistributes heat vertically and meridionally preferentially warming the ice shell at the equator here we assess the previously unconstrained influence of ocean ice coupling on europa s ocean stratification and heat transport we demonstrate that a relatively fresh layer can form at the ice ocean interface due to a meridional ice transport forced by the differential ice shell heating between the equator and the poles we provide analytical and numerical solutions for the layer s characteristics highlighting their sensitivity to critical ocean parameters for a weakly turbulent and highly saline ocean a strong buoyancy gradient at the base of the freshwater layer can suppress vertical tracer exchange with the deeper ocean as a result the freshwater layer permits relatively warm deep ocean temperatures

the inferred formation of a subice platelet layer below the multiyear landfast sea ice in the wandel sea ne greenland induced by meltwater drainage

observations of the size distribution of frazil ice in an ice shelf water plume the size distribution of frazil ice is currently unconstrained in ice shelf cavity modeling here we observe the time dependent behavior of the number and size of frazil ice particles in an ice she

water drag coefficient of first year sea ice in may 1977 eddy flux measurements of momentum were made with a three component ultrasonic current meter in the oceanic boundary layer under a first year floe of fast sea ice in barrow strait n w t by using eddy correlation methods values of horizontal reynolds stress were computed from each of 20 data runs of about 1 hour duration during which the mean current was reasonably steady a least squares analysis in which water stress was assumed proportional to the square of the mean current yielded a value for the 1 m water drag coefficient of 1 32 10 3 with a standard deviation of 0 06 10 3 the diameter of the floe was greater than 1 km and its mean thickness was 128 cm with a standard deviation of 4 cm and a maximum deviation of 7 cm

acoustic detection of ice crystals in antarctic waters during the voyage of the rsv aurora australis to the region of prydz bay antarctica in january march 1991 ice crystals were encountered at depths from the surface to 125 m in the western area of the bay on two occasions crystals were retrieved by netting and echo sounder records have been used to infer additional regions of occurrence acoustic target strength estimates made on the ice crystal assemblies encountered show significant spatial variation which may relate to crystal size and or aggregation data from a suite of conductivity temperature depth casts have been used to map regions of the study area where in situ water temperatures fell below the computed freezing point such regions correlate well with those selected on the basis of echogram type and imply that ice crystals occurred at depth over large areas of the bay during the cruise period the ice crystal distribution described is consistent with that expected from a plume of supercooled water emerging from under the amery ice shelf and forming part of the general circulation of the bay the magnitude of the supercooled water plume is greater than those reported previously in the prydz bay region if misinterpreted as biota on echo sounder records ice crystals could significantly bias biomass estimates based on echo integration in this and potentially other areas

supercooled southern ocean waters in cold polar waters temperatures sometimes drop below the freezing point a process referred to as supercooling however observational challenges in polar regions limit our understanding of the spatial and temporal extent of this phenomenon we here provide observational evidence that supercooled waters are much more widespread in the seasonally ice covered southern ocean than previously reported in 5 8 of all analyzed hydrographic profiles south of 55 s we find temperatures below the surface freezing point potential supercooling and half of these have temperatures below the local freezing point in situ supercooling their occurrence doubles when neglecting measurement uncertainties we attribute deep coastal ocean supercooling to melting of antarctic ice shelves and surface induced supercooling in the seasonal sea ice region to winter time sea ice formation the latter supercooling type can extend down to the permanent pycnocline due to convective sinking plumes an important mechanism for vertical tracer transport and water mass structure in the polar ocean

the supply of subglacial meltwater to the grounding line of the siple coast west antarctica recent satellite studies have shown that active subglacial lakes exist under the antarctic ice streams and persist almost to their grounding lines when the lowest lying lakes flood the water crosses the grounding line and enters the sub ice shelf cavity modeling results suggest that this additional freshwater influx may significantly enhance melting at the ice shelf base we examine the spatial and temporal variability in subglacial water supply to the grounding lines of the siple coast ice streams by combining estimates for lake volume change derived from ice cloud and land elevation satellite icesat data with a model for subglacial water transport our results suggest that subglacial outflow tends to concentrate towards six embayments in the siple coast grounding line although mean grounding line outflow is 60m3 s 1 for the entire siple coast maximum local grounding line outflow may temporarily exceed 300 m3 s 1 during the synchronized flooding of multiple lakes in a hydrologic basin variability in subglacial outflow due to subglacial lake drainage may account for a substantial portion of the observed variability in freshwater flux out of the ross ice shelf cavity the temporal variability in grounding line outflow results in a net reduction in long term average melt rate but temporary peak melting rates may exceed the long term average by a factor of three

large flux of iron from the amery ice shelf marine ice to prydz bay east antarctica the antarctic continental shelf supports a high level of marine primary productivity and is a globally important carbon dioxide co2 sink through the photosynthetic fixation of co2 via the biological pump sustaining such high productivity requires a large supply of the essential micronutrient iron fe however the pathways for fe delivery to these zones vary spatially and temporally our study is the first to report a previously unquantified source of concentrated bioavailable fe to antarctic surface waters we hypothesize that fe derived from subglacial processes is delivered to euphotic waters through the accretion fe storage and subsequent melting fe release of a marine accreted layer of ice at the base of the amery ice shelf ais using satellite derived chlorophyll a data we show that the soluble fe supplied by the melting of the marine ice layer is an order of magnitude larger than the required fe necessary to sustain the large annual phytoplankton bloom in prydz bay our finding of high concentrations of fe in ais marine ice and recent data on increasing rates of ice shelf basal melt in many of antarctica s ice shelves should encourage further research into glacial and marine sediment transport beneath ice shelves and their sensitivity to current changes in basal melt currently the distribution volume and fe concentration of antarctic marine ice is poorly constrained this uncertainty combined with variable forecasts of increased rates of ice shelf basal melt limits our ability to predict future fe supply to antarctic coastal waters

ice platelets below weddell sea landfast sea ice basal melt of ice shelves may lead to an accumulation of disc shaped ice platelets underneath nearby sea ice to form a sub ice platelet layer here we present the seasonal cycle of sea ice attached to the ekstrom ice shelf antarctica and the underlying platelet layer in 2012 ice platelets emerged from the cavity and interacted with the fast ice cover of atka bay as early as june episodic accumulations throughout winter and spring led to an average platelet layer thickness of 4m by december 2012 with local maxima of up to 10 m the additional buoyancy partly prevented surface flooding and snow ice formation despite a thick snow cover subsequent thinning of the platelet layer from december onwards was associated with an inflow of warm surface water the combination of model studies with observed fast ice thickness revealed an average ice volume fraction in the platelet layer of 0 25 0 1 we found that nearly half of the combined solid sea ice and ice platelet volume in this area is generated by heat transfer to the ocean rather than to the atmosphere the total ice platelet volume underlying atka bay fast ice was equivalent to more than one fifth of the annual basal melt volume under the ekstrom ice shelf

microstructure and electrical properties of marine ice and its relationship to meteoric ice and sea ice a 215 m ice core has penetrated the central part of the ronne ice shelf 76 59 s 52 16 w the core consisted of meteoric ice above 152 8 m depth below this the ice was bubble free and of seawater origin the salinity of the layer below 152 8 m depth is less than 0 05 ppt very much lower than typical sea ice the ice represents an unusual source of ice intermediate in salinity and some physical properties between meteoric ice and sea ice the structure of the ice from four different depths where salinities vary by a factor of 4 has been investigated using a scanning electron microscope sem the fabric and grain structures are unusual and seem to depend on the impurity concentration in the ice chemical impurity localization has also been investigated the dielectric properties of the ice show that the ice has a transitional behavior from the linear dependence of conductivity on chloride concentration found in meteoric ice to the less predictable sea ice behavior the behavior may be interpreted in terms of the structure of the ice the higher salinity samples show convoluted grain boundaries small grain size and brine inclusions there are indications that the brine inclusions were liquid at temperatures between 10 c and 30 c by contrast the lower salinity samples possess larger grain sizes and show no evidence of brine inclusions all samples show brine concentrated at triple grain junctions and also along two grain boundaries in higher salinity samples the dielectric properties of the lower salinity samples are well described by a jaccard mechanism with l defects created in proportion to salinity that also describes the behavior of meteoric ice higher salinity samples exhibit lower conductivity than would be seen if l defects continued to be created in proportion to salinity the dielectric and structural data are consistent with a solubility limit of about 300 m for cl in the ice lattice

a review of water contents and ductile deformation mechanisms of olivine implications for the lithosphere asthenosphere boundary of continents abstract water plays an important role in the ductile deformation and evolution of the upper mantle water contents of natural olivine from 240 samples reveal a wide variation of 0 170 ppm h2o suggesting heterogeneous water distribution in the continental upper mantle the average water contents 17 13 ppm h2o in kimberlite nodules provide the best estimation of water concentrations in olivine in the lithosphere beneath cratons the very low water contents 7 9 ppm h2o of olivine from basalt xenoliths are caused by significant hydrogen loss during transport while the high values 44 34 ppm h2o in olivine megacrysts from kimberlites reflect restricted fluid rich conditions in the upper mantle to compare deformation in different tectonic environments the western superior province canada the dabie mountains and the north jiangsu basin china are selected to represent an archean craton an orogenic belt and a rift basin respectively using recent flow laws of olivine deformation maps of dry and wet olivine are constructed under p t conditions of the three tectonic units and in a continental subduction zone characterized by p 6 28 gpa and t 900 c for dry olivine diffusion creep is the dominant mechanism in all the cases which is contrary to the widely observed crystal preferred orientation of olivine in peridotites and seismic anisotropy observations for wet olivine only a small amount of water 50 h 106 si can remarkably decrease the stress of dislocation creep and increase contribution of dislocation creep to the deformation of olivine the strain rate profiles of olivine indicate a transition from dislocation creep to diffusion creep at a depth of 220 km which can be related with the lehmann discontinuity characterized by a rapid decrease in seismic anisotropy however the pressure induced fabric transition from 100 slip to 001 slip may be responsible for the lehmann discontinuity in subduction zones therefore rheology of the continental upper mantle is controlled by power law creep of wet olivine and diffusion creep is the dominant deformation mechanism in the deep upper mantle especially for fine grained peridotites the mechanical lithosphere asthenosphere boundary lab can be defined by the characteristic pressure derivative of effective viscosity the sharp lab beneath the dabie mountains and the sulu terrane favors the lithosphere asthenosphere decoupling while the diffuse lab beneath the western superior province will protect the continental root from convective erosion and mantle metasomatism the long term preservation of the continental roots can be attributed to a large viscosity contrast temperature contrast at a depth of 150 km

turbulent plumes from a glacier terminus melting in a stratified ocean the melting of submerged faces of marine terminating glaciers is a key contributor to the glacial mass budget via direct thermodynamic ablation and the impact of ablation on calving this study considers the behavior of turbulent plumes of buoyant meltwater in a stratified ocean generated by melting of either near vertical calving faces or sloping ice shelves we build insight by applying a turbulent plume model to describe melting of a locally planar region of ice face in a linearly stratified ocean in a regime where subglacial discharge is insignificant the plumes rise until becoming neutrally buoyant before intruding into the ocean background for strong stratifications we obtain leading order scaling laws for the flow including the height reached by the plume before intrusion and the melt rate expressed in terms of the background ocean temperature and salinity stratifications these scaling laws provide a new perspective for parameterizing glacial melting in response to a piecewise linear discretization of the ocean stratification

ice shelf ocean interactions under the amery ice shelf seasonal variability and its effect on marine ice formation 1 marine ice is an important factor in ice shelf stability an extensive marine ice layer is present under the amery ice shelf ais east antarctica this paper documents observations on the seasonal variability of the ais ocean interaction beneath the marine ice layer we focus on data collected during 2002 through a borehole at am01 100 km from the ice shelf calving front and use additional data from two other boreholes to complement the study at am01 the top 20 m of the water column is super cooled almost year round protecting the marine ice layer and promoting frazil ice formation the mixed layer thickness varies from 50 m in february to at least 160 m by june as the water column cools and freshens high salinity shelf water hssw abruptly arrives at am01 in june august as an eddy like flow we suggest that the flow characteristics are a result of baroclinic instabilities in addition the inflow of hssw results in a steepening of the isopycnals that enhances the upwelling of ice shelf water this study documents for the first time a seasonal signal in the formation of marine ice under the ais our results highlight the vulnerability of the marine ice layer to ocean variability with potential consequences for the overall ice shelf mass balance

a one dimensional model of ice shelf ocean interaction large scale oceanic circulation beneath antarctic ice shelves is driven by the thenmohaline differences which result from mass and energy exchange at the ice ocean interface dense saline waters are drawn underneath the ice shelves and emerge cooled and diluted as plumes of ice shelf water a simple one dimensional model of this process has been developed in which the ice shelf water plume is treated as a turbulent gravity current initiated at the inland margin by a flow of fresh meltwater emerging from beneath the grounded ice subsequent evolution of the plume as it ascends along an ice shelf base of specified geometry can be simulated the model has been applied to a flow line on ronne ice shelf antarctica to explain the observed distribution and rate of basal melting and freezing calculations indicate that the present mean melt rate of 0 6 m yr 1 would increase to 2 6 m yr 1 if the underlying water were to warm by 0 6 c this would not only lead to significant thinning of the ice shelf but could also cause a profound change in ocean circulation on the open continental shelf

platelet ice the southern ocean s hidden ice a review basal melt of ice shelves is not only an important part of antarctica s ice sheet mass budget but it is also the origin of one of the most peculiar types of sea ice found in the polar oceans platelet ice in many regions around coastal antarctica tiny ice crystals form and grow in supercooled plumes of ice shelf water releasing heat into the surrounding ocean they usually rise towards the surface eventually becoming trapped under an ice shelf as marine ice frequently masses of those crystals are advected out of the ice shelf cavity and accumulate below a solid sea ice cover to form a semiconsolidated layer when the overlying sea ice grows into this so called sub ice platelet layer the loose crystals are consolidated adding additional thickness to the sea ice these phenomena are generally referred to as platelet ice although confusion about the terminology is widespread in the literature the presence of platelet ice has a profound impact on sea ice properties and processes in several regions of antarctica with numerous implications for the local polar marine biosphere most notably sub ice platelet layers provide a stable sheltered nutrient and food rich habitat which usually results in a highly productive and uniquely adapted ecosystem it has also been hypothesised that platelet ice may be an indicator of the state of an ice shelf although comprehensive time series are limited to the ross sea this paper clears up the terminology by providing exact definitions of the relevant terms we review platelet ice formation observational methods as well as geographical and seasonal occurrence the physical properties and ecological implications are merged in a way understandable for physicists and biologists alike to lay the foundation for the interdisciplinary research that is necessary to tackle the current knowledge gaps

turbulent heat and momentum transfer in the oceanic boundary layer under melting pack ice a theory for momentum flux in the planetary boundary layer pbl stabilized by continuous surface buoyancy is extended to include turbulent flux of an arbitrary scalar contaminant and then used to estimate how wind driven sea ice melts as it encounters temperatures in the oceanic boundary layer that are above the melting point given wind stress and temperature difference across the oceanic pbl the theory predicts melt rate and ice drift velocity results indicate that the effect of buoyancy on pbl turbulence is significant even with small values of 0 5 k curves of melt rate and ice speed as functions of u the interfacial friction velocity show that melting is strongly dependent on stress at the interface and that the effective drag on the ice undersurface is significantly reduced at oceanic temperatures commonly observed in the marginal ice zone the latter suggests that divergence will occur at the ice margin when off ice winds advect the pack over water above the melting temperature the structure of mean currents beneath the ice is also investigated results indicate that advection will play an important if not dominant role in determining water column properties near an ice edge front