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

frazil dynamics and precipitation in a water column with depth dependent supercooling when seawater becomes supercooled collections of small ice crystals known as frazil ice form and grow a model of frazil ice dynamics is presented that deals explicitly with the buoyant settling of frazil crystals onto an overlying surface this yields further insight into transport associated with the ice pump mechanism whereby ice is melted at depth and transferred to a shallower location as a result of the pressure variation of seawater s freezing temperature the model is applied to a vertical cross section through an ice shelf water plume beneath filchner ronne ice shelf antarctica and helps to elucidate the depth variation in its properties for the first time as well as predicting the precipitation rate of frazil crystals the model predicts that frazil ice should be preferentially located in a narrow layer near the ice shelf base as a result of the maximum supercooling there and an influx of crystals rising under their own buoyancy the deposition of these crystals onto the ice shelf is governed by the balance between crystal rising and turbulent transfer of frazil away from the shelf which is investigated in some detail

structural characteristics of congelation and platelet ice and their role in the development of antarctic land fast sea ice ice cores were obtained in january 1990 from the land fast ice in mcmurdo sound for a study of variations in texture fabric sub structure composition and development two primary ice types were observed congelation and platelet with a minor amount of frazil ice congelation ice growth precedes platelet ice accretion congelation ice fabrics show frequent moderate to strong alignments a phenomenon believed to be due to water current control of selective ice crystal growth platelet ice originates at the base of the congelation ice initially as a porous latticework of tabular ice crystals which subsequently consolidate by congelation of the interstitial water interstitial congelation ice fabrics generally have little or no alignment indicating the reduced effect of currents within the platelet latticework prior to solidification platelet crystal textures range from small wavy edged forms to large blade like forms platelet crystal fabrics indicate that in addition to being randomly oriented the platelet latticeworks commonly include many crystals with their flat 0001 faces oriented both parallel and normal to the base of the overlying ice plate width data suggest that the interstitial congelation ice growth rates remain similar to those of the overlying congelation ice this effective increase in growth rates probably happens because the latticework of accumulating platelets ahead of the freezing interface ensures that the water within the platelet layer is at the freezing point and less heat has to be removed from platelet rich water than from platelet free water for a given thickness of congelation ice to grow the negative oceanic heat flux associated with platelet ice formation in mcmurdo sound explains why mcmurdo sound fast ice is thicker than ross sea pack ice and also why it reaches a greater thickness than arctic fast ice grown in a similar polar marine climate plate widths in the mcmurdo sound congelation ice suggest however that it grows no faster than arctic congelation ice

basal ice accretion and debris entrainment within the coastal ice margin law dome antarctica basal ice stratigraphy in coastal ice cliffs at the law dome margin has revealed the basal accretion of clean and debris bearing ice marine congelation ice and granular marine ice inland of the margin co isotopic analysis of 18 o and d isotopes together with solute chemistry were applied to determine the modes of accretion and debris entrainment

spatial and temporal evolution of pine island glacier thinning 1995 2006 we use ers 2 and envisat satellite radar altimetry to examine spatial and temporal changes in the rate of thinning of the pine island glacier west antarctica during the period 1995 to 2006 we show that the pattern of thinning has both accelerated and spread inland to encompass tributaries flowing into the central trunk of the glacier within the 5 400 km 2 central trunk the average rate of volume loss quadrupled from 2 6 0 3 km 3 yr 1 in 1995 to 10 1 0 3 km 3 yr 1 in 2006 the region of lightly grounded ice at the glacier terminus is extending upstream and the changes inland are consistent with the effects of a prolonged disturbance to the ice flow such as the effects of ocean driven melting if the acceleration continues at its present rate the main trunk of pig will be afloat within some 100 years six times sooner than anticipated citation wingham d j d w wallis and a shepherd 2009 spatial and temporal evolution of pine island glacier thinning 1995 2006 geophys res lett 36 l17501 doi 10 1029 2009gl039126

tidally induced increases in melting of amundsen sea ice shelves 1 tidal effects on the circulation under the ice shelves and ice shelf melting in the amundsen sea were investigated using a numerical model through comparison of simulations with and without tides in the amundsen sea tidal impacts were dependant on the location of the ice shelf front with respect to the m2 effective critical latitude the critical latitude is the latitude where the tidal frequency equals the inertial frequency the effective critical latitude is where the tidal frequency equals the inertial frequency adjusted by relative vorticity such as that associated with a wind driven gyre for ice shelves located equatorward of the m2 effective critical latitude tides increased both mixing in front of and under the ice shelf and flow into the ice shelf cavities by as much as 50 despite weak tides compared with the mean flows tides also increased melting for these ice shelves by 1 3 5 m yr 1 a 50 increase for dotson ice shelf and 25 for pine island ice shelf these enhancements were not a result of tidal residual flows but instead originated from resonant effects increases in the baroclinity of the velocities and higher mixing all of which are associated with critical latitude effects on internal tides for ice shelves located poleward of the effective critical latitude tides very slightly retarded flow into the cavity and slightly reduced melting

marine ice deformation experiments an empirical validation of creep parameters 1 marine ice is increasingly recognized as an important component of ice shelves in antarctica because it mainly accretes in weak locations it plays a crucial role in ice shelf stability little is known however on the rheology of this particular material low salinity no bubbles specific fabrics we present marine ice deformation experiments in unconfined uniaxial compression at 10 c 6 c and 3 c generally marine ice samples confirm the value of n 3 for glen s power law it also appears to behave systematically harder than artificial or meteoric isotropic ice samples used in the past in the studied stress condition bulk salinity does not seem to have a significant impact on the viscosity all deformation curves compare well with a generalized empirical temperature viscosity relationship they represent the first experimental validation of the lower boundary of this rheological relationship recommended for use in modeling ice dynamics

airborne thickness and freeboard measurements over the mcmurdo ice shelf antarctica and implications for ice density 1 we present airborne measurements to investigate the thickness of the western mcmurdo ice shelf in the western ross sea antarctica because of basal accretion of marine ice and brine intrusions conventional radar systems are limited in detecting the ice thickness in this area in november 2009 we used a helicopter borne laser and electromagnetic induction sounder em bird to measure several thickness and freeboard profiles across the ice shelf the maximum electromagnetically detectable ice thickness was about 55 m assuming hydrostatic equilibrium the simultaneous measurement of ice freeboard and thickness was used to derive bulk ice densities ranging from 800 to 975 kg m 3 densities higher than those of pure ice can be largely explained by the abundance of sediments accumulated at the surface and present within the ice shelf and are likely to a smaller extent related to the overestimation of ice thickness by the electromagnetic induction measurement related to the presence of a subice platelet layer the equivalent thickness of debris at a density of 2800 kg m 3 is found to be up to about 2 m thick a subice platelet layer below the ice shelf similar to what is observed in front of the ice shelf below the sea ice is likely to exist in areas of highest thickness the thickness and density distribution reflects a picture of areas of basal freezing and supercooled ice shelf water emerging from below the central ice shelf cavity into mcmurdo sound

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

complete determination of ice crystal orientation using laue x ray diffraction method ice crystal orientation fabric data from ice cores contain important information concerning the internal structure and the flow behaviour of ice sheets when ice cores are recovered from the antarctic and greenland ice sheets crystal orientation measurements are performed immediately to obtain fundamental physical property information in the past we have measured the c axis orientation of ice crystals by a manual optical method using a universal stage this method is very time consuming involving tedious work in a cold laboratory recently automated systems have been developed that enable measurement of c axis orientation grain size and other microstructures however in order to detect the full crystal orientation of an ice crystal we also need information on its a axis orientation a variety of other crystal orientation measurement methods have previously been discussed but some shortcomings for ice core studies cannot be neglected we have developed a crystal orientation analysing device using the laue x ray diffraction method as this device can measure the orientations of all crystal axes with high accuracy it is possible to obtain new microstructure information on natural ice crystals for the first time we are able to quantify very low subgrain misorientation angles in polar ice core samples allowing us to investigate micro deformation features of individual crystals here we discuss the analysis process which is customized to measure standard ice thin sections and show preliminary results

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 distribution and formative processes of latent heat polynyas in east antarctica a study of polynya characteristics in east antarctica was undertaken using ice concentrations derived from special sensor microwave imager data for the period july 1987 august 1994 the areas of polynyas were defined as having an ice concentration 75 the analysis revealed a total of 28 coastal polynyas within the study region the spatial and temporal variability in areal extent was quantified the timing of mean maximum areal extent varied from june to october the bathymetry and wind regime at each polynya site was examined to gauge the relative importance of these parameters in polynya formation and maintenance in 20 locations shallow banks and shoals form grounding zones for icebergs and anchoring sites for fast ice which form barriers to the predominantly westward drift of the pack ice elsewhere north south coastal protrusions or alignments form similar barriers the subsequent removal of newly formed sea ice from the lee of such barriers by katabatic and synoptic winds maintains areas of reduced ice concentration and open water very few coastal polynyas are attributed solely to katabatic outflow the combined influence of bathymetry topography and winds is responsible for the characteristics of the majority of polynyas many were considered to be marginal characterised by occasional periods when the ice concentration falls below 75 an analysis of annual winter totals of areas with ice concentrations 75 shows no trends in total polynya areal extent over the period 1987 94 known locations of emperor penguin aptenodytes forsteri rookeries were also found to be associated with the locations of coastal polynyas

circulation of modified circumpolar deep water and basal melt beneath the amery ice shelf east antarctica antarctic ice sheet mass loss has been linked to an increase in oceanic heat supply which enhances basal melt and thinning of ice shelves here we detail the interaction of modified circumpolar deep water mcdw with the amery ice shelf the largest ice shelf in east antarctica and provide the first estimates of basal melting due to mcdw we use subice shelf ocean observations from a borehole site am02 situated 70 km inshore of the ice shelf front together with open ocean observations in prydz bay we find that mcdw transport into the cavity is about 0 22 0 06 sv 1 sv 106 m3 s 1 the inflow of mcdw drives a net basal melt rate of up to 2 0 5 m yr 1 during 2001 23 9 6 52 gt yr 1 from under about 12 800 km2 of the north eastern flank of the ice shelf the heat content flux by mcdw at am02 shows high intra annual variability up to 40 our results suggest two main modes of subice shelf circulation and basal melt regimes 1 the ice pump high salinity shelf water circulation on the western flank and 2 the mcdw meltwater driven circulation in conjunction with the ice pump on the eastern flank these results highlight the sensitivity of the amery s basal melting to changes in mcdw inflow improved understanding of such ice shelf ocean interaction is crucial to refining projections of mass loss and associated sea level rise

frazil formation in water of different salinities and supercoolings les experiences de formation de frazil ont ete realisees dans des eaux de mer naturelles et artificielles on trouve que la vitesse de production du frazil est tres sensible a la surfusion initiale

sea ice freeboard in mcmurdo sound antarctica derived by surface validated icesat laser altimeter data 1 previous investigations have linked changes in the multiyear sea ice area of mcmurdo sound antarctica from 1213 km2 in 2003 to 4923 km2 in 2005 to the passage of large tabular icebergs preventing the annual sea ice breakout this maximum coverage then gradually diminished by 2009 covering 1453 km2 this investigation employs the use of the ice cloud and land elevation satellite icesat laser altimeter to derive freeboard of sea ice in mcmurdo sound from 2003 to 2009 and hence infer thickness changes over this time period two techniques for freeboard retrieval are compared method 1 m 1 follows those previously presented in the literature using the lowest elevations to construct an estimate of sea surface height however the lack of leads in the study area motivated the development of method 2 m 2 which utilizes tide models each year is divided into two investigation periods from september to december and february to june and these investigations were further segmented by sea ice type first year fy and multiyear my both applied methods reveal a statistically significant linear increase in multiyear sea ice freeboard for m 1 the mean freeboard increased over the study period from 0 53 to 1 00 m and for m 2 from 0 46 to 0 95 m evidence is presented that the multiyear sea ice freeboard increase is strongly linked to the development and incorporation of a subice platelet layer no statistically significant trends were observed for first year sea ice icesat derived freeboards over first year and multiyear sea ice areas compare within one standard deviation of airborne measured freeboard in november 2009

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

evolution of a supercooled ice shelf water plume with an actively growing subice platelet matrix we use new observations in western mcmurdo sound combined with longitudinal hydrographic transects of the sound to identify a northward flowing ice shelf water isw plume exiting the cavity of the mcmurdo ross ice shelf we estimate the plume s net northward transport at 0 4 0 1 sv carving out a corridor approximately 35 km wide aligned with the victoria land coast basal topography of the mcmurdo ice shelf is such that the plume is delivered to the surface without mixing with overlying warmer water and is therefore able to remain below the surface freezing temperature at the point of observation beneath first year ice thus the upper ocean was supercooled by up to 50 mk at the surface due to pressure relief from recent rapid ascent of the steep basal slope the 70 m thick supercooled layer supports the growth and maintenance of a thick semirigid and porous matrix of platelet ice which is trapped by buoyancy at the ice ocean interface continued growth of individual platelets in supercooled water creates significant brine rejection at the top of the water column which resulted in convection over the upper 200 m thick homogeneous layer by examining the diffusive nature of the intermediate water between layers of isw and high salinity shelf water we conclude that the isw plume must have originated beneath the ross ice shelf and demonstrate that it is likely to expand eastward across mcmurdo sound with the progression of winter

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

influence of sea ice cover and icebergs on circulation and water mass formation in a numerical circulation model of the ross sea antarctica 1 satellite imagery shows that there was substantial variability in the sea ice extent in the ross sea during 2001 2003 much of this variability is thought to be due to several large icebergs that moved through the area during that period the effects of these changes in sea ice on circulation and water mass distributions are investigated with a numerical general circulation model it would be difficult to simulate the highly variable sea ice from 2001 to 2003 with a dynamic sea ice model since much of the variability was due to the floating icebergs here sea ice concentration is specified from satellite observations to examine the effects of changes in sea ice due to iceberg c 19 simulations were performed using either climatological ice concentrations or the observed ice for that period the heat balance around the ross sea polynya rsp shows that the dominant term in the surface heat budget is the net exchange with the atmosphere but advection of oceanic warm water is also important the area average annual basal melt rate beneath the ross ice shelf is reduced by 12 in the observed sea ice simulation the observed sea ice simulation also creates more high salinity shelf water another simulation was performed with observed sea ice and a fixed iceberg representing b 15a there is reduced advection of warm surface water during summer from the rsp into mcmurdo sound due to b 15a but a much stronger reduction is due to the late opening of the rsp in early 2003 because of c 19

observations beneath pine island glacier in west antarctica and implications for its retreat thinning ice in west antarctica is currently contributing about 10 of the observed rise in global sea level observations obtained from an autonomous underwater vehicle operating beneath pine island glacier west antarctica reveal that the glacier was recently grounded on a transverse ridge in the sea floor but now warm sea water flows through the widening gap above the ridge thinning ice in west antarctica resulting from acceleration in the flow of outlet glaciers is at present contributing about 10 of the observed rise in global sea level1 pine island glacier in particular has shown nearly continuous acceleration2 3 and thinning4 5 throughout the short observational record the floating ice shelf that forms where the glacier reaches the coast has been thinning rapidly6 driven by changes in ocean heat transport beneath it as a result the line that separates grounded and floating ice has retreated inland7 these events have been postulated as the cause for the inland thinning and acceleration8 9 here we report evidence gathered by an autonomous underwater vehicle operating beneath the ice shelf that pine island glacier was recently grounded on a transverse ridge in the sea floor warm sea water now flows through a widening gap above the submarine ridge rapidly melting the thick ice of the newly formed upstream half of the ice shelf the present evolution of pine island glacier is thus part of a longer term trend that has moved the downstream limit of grounded ice inland by 30 km into water that is 300 m deeper than over the ridge crest the pace and ultimate extent of such potentially unstable retreat10 are central to the debate over the possibility of widespread ice sheet collapse triggered by climate change11 12

two years of oceanic observations below the fimbul ice shelf antarctica 1 the mechanisms by which heat is delivered to antarctic ice shelves are a major source of uncertainty when assessing the response of the antarctic ice sheet to climate change direct observations of the ice shelf ocean interaction are extremely scarce and in many regions melt rates from ice shelf ocean models are not constrained by measurements our two years of data 2010 and 2011 from three oceanic moorings below the fimbul ice shelf in the eastern weddell sea show cold cavity waters with average temperatures of less than 0 1 c above the surface freezing point this suggests low basal melt rates consistent with remote sensing based steady state mass balance estimates for this sector of the antarctic coast oceanic heat for basal melting is found to be supplied by two sources of warm water entering below the ice i eddy like bursts of modified warm deep water that access the cavity at depth for eight months of the record and ii fresh surface water that flushes parts of the ice base with temperatures above freezing during late summer and fall this interplay of processes implies that basal melting at the fimbul ice shelf cannot simply be parameterized by coastal deep ocean temperatures but instead appears directly linked to both solar forcing at the surface as well as to the dynamics of the coastal current system

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

thermal conductivity of landfast antarctic and arctic sea ice 1 we present final results from a program to measure the thermal conductivity of sea ice with in situ thermistor arrays using an amended analysis of new and previously reported ice temperatures results from landfast first year fy ice near barrow alaska and mcmurdo sound antarctica are consistent with predictions from effective medium models but 10 15 higher than values from the parameterization currently used in most sea ice models we observe no previously reported anomalous near surface reduction which is now understood to have been an artifact nor a convective enhancement to the heat flow although our analysis is limited to temperatures below 5c at which brine percolation is restricted results for landfast multiyear my ice in mcmurdo sound are also consistent with effective medium predictions and emphasize the density dependence we compare these and historical measurements with effective medium predictions and the representation commonly used in sea ice models developed originally for my arctic ice we propose an alternative expression derived from effective medium models appropriate for both my and fy ice that is consistent with

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

improved 1d inversions for sea ice thickness and conductivity from electromagnetic induction data inclusion of nonlinearities caused by passive bucking the porosity of sea ice is a fundamental physical parameter that governs the mechanical strength of sea ice and the mobility of gases and nutrients for biological processes and biogeochemical cycles in the sea ice layer however little is known about the spatial distribution of the sea ice porosity and its variability between different sea ice types an efficient and nondestructive method to measure this property is currently missing sea ice porosity is linked to the bulk electrical conductivity of sea ice a parameter routinely used to discriminate between sea ice and seawater by electromagnetic em induction sensors here we have evaluated the prospect of porosity retrieval of sea ice by means of bulk conductivity estimates using 1d multifrequency em inversion schemes we have focused on two inversion algorithms a smoothness constrained inversion and a marquardt levenberg inversion which we modified for the nonlinear signal bias caused by a passive bucking coil operated in such a highly conductive environment using synthetic modeling studies 1d inversion algorithms and multiple frequencies we found that we can resolve the sea ice conductivity within 0 01 s m using standard assumptions for the conductivity porosity relation of sea ice we were able to estimate porosity with an uncertainty of 1 2 which enables efficient and nondestructive surveys of the internal state of the sea ice cover

textural characteristics and impurity content of meteoric and marine ice in the ronne ice shelf antarctica the texture and physical properties of an ice core recovered to 215 m depth from the ronne ice shelf antarctica have been studied with regard to formation and transformation of the ice at a depth of 152 8 m a sharp discontinuity marks the transition between meteoric ice accumulated from above and marine ice accreted from below as testified by electrolytical conductivity and stable isotope measurements as well as geophysical field surveys automated image analysis of thin sections indicates that the decrease in grain boundary density and the increase in grain cross sectional area with depth is commensurate with though not necessarily caused bythermodynamically driven grain growth down to 120m depth corresponding to a vertical strain of roughly 65 as computed with a simple temperature history particle path model the observed increase of grain boundary density i e a decrease of grain size with age in the marine ice is in part explained by the thermal history of this layer sediment inclusions at the top of the marine ice layer affect the observed grain boundary density profile by inhibiting grain growth and dynamic recrystallization this may allow some conclusions on the role of temperature particulate inclusions stress and strain rate in controlling the grain size evolution of deforming ice supplementing earlier laboratory experiments conducted at much shorter time scales salinities 0 026 parts per thousand brine volumes 0 09 0 2 parts per thousand and solid salt concentrations have been computed from electrolytical conductivity measurements mean of 51 0 x 10 6 s cm 1 for the marine ice an assessment of salt incorporation and desalination rates shows that these low salinities can at present only be explained by a unique densification mechanism of under water ice crystals at the base of the ice shelf

evidence for basal marine ice in the filchner ronne ice shelf the filchner ronne ice shelf which drains most of the marine based portions of the west antarctic ice sheet is the largest ice shelf on earth by volume the origin and properties of the ice that constitutes this shelf are poorly understood because a strong reflecting interface within the ice and the diffuse nature of the ice ocean interface make seismic and radio echo sounding data difficult to interpret1 2 ice in the upper part of the shelf is of meteoric origin but it has been proposed2 5 that a basal layer of saline ice accumulates from below here we present the results of an analysis of the physical and chemical characteristics of an ice core drilled almost to the bottom of the ronne ice shelf we observe a change in ice properties at about 150 m depth which we ascribe to a change from meteoric ice to basal marine ice the basal ice is very different from sea ice formed at the ocean surface and we propose a formation mechanism in which ice platelets in the water column accrete to the bottom of the ice shelf

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

spatial temporal relationships of mesozoic volcanic rocks in ne china constraints on tectonic overprinting and transformations between multiple tectonic regimes abstract la icp ms zircon u pb ages and geochemical data are presented for the mesozoic volcanic rocks in northeast china with the aim of determining the tectonic settings of the volcanism and constraining the timing of the overprinting and transformations between the paleo asian ocean mongol okhotsk and circum pacific tectonic regimes the new ages together with other available age data from the literature indicate that mesozoic volcanism in ne china can be subdivided into six episodes late triassic 228 201 ma early middle jurassic 190 173 ma middle late jurassic 166 155 ma early early cretaceous 145 138 ma late early cretaceous 133 106 ma and late cretaceous 97 88 ma the late triassic volcanic rocks occur in the lesser xing an zhangguangcai ranges where the volcanic rocks are bimodal and in the eastern heilongjiang jilin provinces where the volcanics are a type rhyolites implying that they formed in an extensional environment after the final closure of the paleo asian ocean the early middle jurassic 190 173 ma volcanic rocks both in the erguna massif and the eastern heilongjiang jilin provinces belong chemically to the calc alkaline series implying an active continental margin setting the volcanics in the erguna massif are related to the subduction of the mongol okhotsk oceanic plate beneath the massif and those in the eastern jilin heilongjiang provinces are related to the subduction of the paleo pacific plate beneath the eurasian continent the coeval bimodal volcanic rocks in the lesser xing an zhangguangcai ranges were probably formed under an extensional environment similar to a backarc setting of double direction subduction volcanic rocks of middle late jurassic 155 166 ma and early early cretaceous 145 138 ma age only occur in the great xing an range and the northern hebei and western liaoning provinces limited to the west of the songliao basin and they belong chemically to high k calc alkaline series and a type rhyolites respectively combined with the regional unconformity and thrust structures in the northern hebei and western liaoning provinces we conclude that these volcanics formed during a collapse or delamination of a thickened continental crust related to the evolution of the mongol okhotsk suture belt the late early cretaceous volcanic rocks widely distributed in ne china belong chemically to a low to medium k calc alkaline series in the eastern heilongjiang jilin provinces i e the eurasian continental margin and to a bimodal volcanic rock association within both the songliao basin and the great xing an range the volcanics in the eastern heilongjiang jilin provinces formed in an active continental margin setting related to the subduction of the paleo pacific plate beneath the eurasian continent and the bimodal volcanics formed under an extensional environment related either to a backarc setting or to delamination of a thickened crust or both late cretaceous volcanics limited to the eastern heilongjiang jilin provinces and the eastern north china craton ncc consist of calc alkaline rocks in the eastern heilongjiang jilin provinces and alkaline basalts in the eastern ncc suggesting that the former originated during subduction of the paleo pacific plate beneath the eurasian continent whereas the latter formed in an extensional environment similar to a backarc setting taking all this into account we conclude that 1 the transformation from the paleo asian ocean regime to the circum pacific tectonic regime happened during the late triassic to early jurassic 2 the effect of the mongol okhotsk suture belt on ne china was mainly in the early jurassic middle late jurassic and early early cretaceous and 3 the late early cretaceous and late cretaceous volcanics can be attributed to the subduction of the paleo pacific plate beneath the eurasian continent

glaciological and oceanographic evidence of high melt rates beneath pine island glacier west antarctica satellite imagery indicates that the floating terminus of pine island glacier has changed little in extent over the past two decades data on the velocity and thickness of the glacier reveal that calving of 28 4 gt a 1 accounts for only half of the ice input near the grounding line the apparently steady configuration implies that the remainder of the input is lost by basal melting at a mean rate of 12 3 m a 1 ocean circulation in pine island bay transports 1 c waters beneath the glacier and temperatures recorded in melt laden outflows show that heat loss from the ocean is consistent with the requirements of the calculated melt rate the combination of iceberg calving and basal melting lies at the lower end of estimates for the total accumulation over the catchment basin drawing into question previous estimates of a significantly positive mass budget for this part of the ice sheet

melting and freezing beneath filchner ronne ice shelf antarctica 1 we use remote sensing data sets to evaluate the spatial distribution of melt beneath the filchner ronne ice shelf fris the net melt rate of 83 4 24 8 gtons yr is 2 5 5 times lower than previous glaciological estimates but is similar to existing oceanographic estimates the spatial distribution however differs significantly from standard conceptual and numerical models in which most melt occurs along the grounding lines our results suggest most grounding line melt is refrozen while the dominant ice shelf water isw source is melting near the ice shelf front probably associated with tidal action this suggests that changes in ice shelf extent can impact isw production rates in the weddell sea

observed platelet ice distributions in antarctic sea ice an index for ocean ice shelf heat flux antarctic sea ice that has been affected by supercooled ice shelf water isw has a unique crystallographic structure and is called platelet ice in this paper we synthesize platelet ice observations to construct a continent wide map of the winter presence of isw at the ocean surface the observations demonstrate that in some regions of coastal antarctica supercooled isw drives a negative oceanic heat flux of 30 wm 2 that persists for several months during winter significantly affecting sea ice thickness in other regions particularly where the thinning of ice shelves is believed to be greatest platelet ice is not observed our new data set includes the longest ice ocean record for antarctica which dates back to 1902 near the mcmurdo ice shelf these historical data indicate that over the past 100 years any change in the volume of very cold surface outflow from this ice shelf is less than the uncertainties in the measurements

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

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

a model study of circumpolar deep water on the west antarctic peninsula and ross sea continental shelves abstract transport of relatively warm nutrient rich circumpolar deep water cdw onto continental shelves around antarctica has important effects on physical and biological processes however the characteristics of the cdw along the shelf break as well as what happens to it once it has been advected onto the continental shelf differ spatially in the present study high resolution 4 5 km regional models of the ross sea and the west antarctic peninsula coastal ocean are used to compare differences in cdw transport the models compared very well with observations from both regions examining the fluxes not only of heat but also of a simulated dye representing cdw shows that in both cases cdw crosses the shelf break in specific locations primarily determined by the bathymetry but eventually floods much of the shelf the frequency of intrusions in marguerite trough was ca 2 3 per month similar to recent mooring observations a significant correlation between the along shelf break wind stress and the cross shelf break dye flux through marguerite trough was observed suggesting that intrusions are at least partially related to short duration wind events the primary difference between the cdw intrusions on the ross and west antarctic peninsula shelves is that there is more vigorous mixing of the cdw with the surface waters in the ross sea especially in the west where high salinity shelf water is created the models show that the cdw moving across the antarctic peninsula continental shelf towards the base of the ice shelves not only is warmer initially and travels a shorter distance than that advected towards the base of the ross ice shelf but it is also subjected to less vertical mixing with surface waters which conserves the heat available to be advected under the ice shelves this difference in vertical mixing also likely leads to differences in the supply of nutrients from the cdw into the upper water column and thus modulates the impacts on surface biogeochemical processes