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

a two phase approach to the simulation of the combined isotope salinity signal of marine ice a modified boundary layer box diffusion model is used to simulate the production of the combined oxygen isotope salinity signal of a body of marine ice the final signal is considered to be the result of fractionation and segregation processes occurring first upon the formation of frazil crystals in suspension and second during their accumulation and consolidation due to the advancement of a freezing front the model results are compared to oxygen isotope and salinity values in a 45 m marine ice core from the nansen ice shelf antarctica parameters more suitable to the modeling of marine ice as opposed to sea ice are introduced and conclusions are drawn on the origin of the impurity characteristics of marine ice including the still unresolved question of its anomalously low salinity

constant holocene southern ocean 14c reservoir ages and ice shelf flow rates article i nfo southern ocean radiocarbon reservoir ages i e non zero radiocarbon ages in seawater are the highest in the world s surface ocean constraining these reservoir ages at present and in the past is important not only because unknown reservoir ages limit the interpretation of antarctic radiocarbon chronologies but also because reservoir ages provide information about ocean circulation as a recorder of past circulation and as an end member for major deep water masses in today s ocean in this study we use paired u th and 14 c ages of an unusual set of solitary coral samples trapped by fringing ice shelves in the ross sea to provide the first detailed study of holocene reservoir ages for the southern ocean our results indicate a relatively constant marine radiocarbon reservoir age of 1144 120 years for the past 6000 years these results are consistent with extrapolation of the relationship between 14 c and alkalinity seen elsewhere supporting the use of this empirical relationship in high latitudes the results also suggest constant deep ocean circulation and air sea exchange during the holocene and provide a good target for tuning ocean models of modern circulation combining the new ages for corals with their distance from the modern day ice shelf grounding line provides some of the first long term records of ice shelf velocities for any region and indicates constant flow of the mcmurdo ice shelf during the holocene at a rate similar to that observed today

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

investigating processes of marine ice formation in a floating ice tongue by a high resolution isotopic study a better knowledge of boundary conditions near a grounding line is critical for understanding the behavior of ice shelves and floating glaciers we show here thatsignificant information can be gained from a high resolution isotopic and textural studyof marine ice accreted at the bottom of a floating glacier near its grounding line two different types of marine ice have been found type 1 is bubble and debris free icewith properties which we believe can be explained by intrusion of brackish water inopen basal fissures closing of the fissures by progression of a freezing front from thesides is precluded and filling by frazil ice is favored type 2 is made of thin clear iceand debris layers which are thought to have formed when a subglacial water filledsediment enters into contact with seawater and is subjected to freezing under a double diffusion process the paper also stresses that in a d 18o diagram the alignment of marine ice samples on a mixing line does not necessarily imply a mixture of continental water and seawater in varying proportions

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

ice discharge of eastern dome c drainage area antarctica determined from airborne radar survey and satellite image analysis eastern dome c southern talos dome and northern taylor dome are drained by the priestley reeves david mawson and mackay outlet glaciers which flow into the scott coast on the west side of the ross sea antarctica airborne radar surveys were conducted on these glaciers to determine ice thickness and bed morphology along transverse and longitudinal profiles of the grounded and floating segments a new analysis of a i andsat thematic mapper satellite image using a tracking technique was used to measure ice velocity at grounding lines and along ice tongues the integration of radar and satellite data helped to locate grounding lines and to calculate the ice discharge changes in ice fluxes of floating glaciers were used to determine basal melting and freezing rates the ice discharge calculated is less than half that required for a zero net surface mass balance according to the inputs given by the accumulation estimates widely adopted at present the basal melting rates of meteoric ice represent 50 of the net ablation rate

katabatic wind influence on meltwater supply to fuel glacier substrate interactions at the grounding line terra nova bay east antarctica the co isotopic composition both in d and in 18o of interbedded debris rich and clear ice layers thought to have been formed at the grounding line of hells gate ice shelf indicates freezing by a double diffusion effect between continental meltwater and sea water within a subglacial sediment a source of meltwater is required to sustain the process since the temperature of the bed is below the freshwater melting point the most likely source is a surficially frozen meltwater lake rock outcrops kept mostly snow free by the action of katabatic winds absorb solar radiation so local production of liquid water becomes possible in an area with year round subfreezing air temperature conditions the meltwater accumulated in a marginal lake can eventually reach the subglacial substratum near a pinning point where the ice is relatively thin and fractured

the origin of green icebergs in antarctica a comparison of samples from a translucent green iceberg with a core from the ronne ice shelf revealed an excellent agreement in isotopic composition crystal structure and incorporated sediment particles marine shelf ice which constitutes the basal portion of some ice shelves is considered to be the source of green icebergs it most likely results from ice pump processes which produce large amounts of ice platelets in the water column beneath ice shelves these subsequently accumulate and become compacted into bubble free desalinated ice iceberg and drift buoy trajectories indicate that green icebergs observed in the weddell sea originate from the amery ice shelf rather than from the ronne ice shelf although the latter ice shelf is also a potential source

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

green icebergs formed by freezing of organic rich seawater to the base of antarctic ice shelves although most icebergs are blue green icebergs are seen occasionally in the antarctic ocean chemical and isotopic analysis of samples from green icebergs indicate that the ice consists of desalinated frozen seawater as does the basal ice from the amery ice shelf spectral reflectance of a green iceberg measured near 67 s 62 e confirms that the color is inherent to the ice not an artifact of the illumination pure ice appears blue owing to its absorption of red photons addition of a constituent that absorbs blue photons can shift the peak reflectance from blue to green such a constituent was identified by spectrophotometric analysis of core samples from this iceberg and from the amery basal ice and of seawater samples from prydz bay off the amery ice shelf analysis of the samples by fluorescence spectroscopy indicates that the blue absorption and hence the inherent green color is due to the presence of marine derived organic matter in the green iceberg basal ice and seawater thick accumulations of green ice in icebergs and at the base of ice shelves indicate that high concentrations of organic matter exist in seawater for centuries at the depth of basal freezing

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

on the isotopic composition in δd and δ18o of water and ice during freezing experiments on progressive unidirectional freezing are coi1 ducted to determine rhe evol ution in 00 and 51 bo of successive water samples and ice layers ta ken during the course of freezing r es ults indicate t hal lhi s evoluti on takes pl ace in a bd bibo diagram a long a strai ght line wi th a characteri sti c slope this slope different from that due to the precip itation effec t gives a finger print of the occurrence of a freezing or of a melt ing refreez ing process in the stud ied reservoir residual water was sampled at the beginning of the experiment after 40 80 85 90 and 95 of the material had frozen when the freezing process was complete the ice core was recovered and sectioned the samples covered the freezing ranges from 0 to 10 10 to 20 20 to 50 50 to 60 60 to 70 70 to 80

segmentation and crustal structure of the western mid atlantic ridge flank 25 25 27 10 n and 0 29 m y we conducted a detailed geological geophysical survey of the west flank of the mid atlantic ridge between 25 25 n and 27 10 n and from the ridge axis out to 29 ma crust acquiring hydrosweep multibeam bathymetry hawaii mr1 sidescan sonar imagery gravity magnetics and single channel seismic reflection profiles the survey covered all or part of nine spreading segments bounded by mostly nontransform right stepping discontinuities which are subparallel to flow lines but which migrated independently of one another some discontinuities alternated between small right and left stepping offsets or exhibited zero offset for up to 3 4 m y despite these changes the spreading segments have been long lived and extend 20 m y or more across isochrons a large shift 9 in relative plate motion about 24 22 ma caused significant changes in segmentation pattern the nature of this plate boundary response together with the persistence of segments through periods of zero offset at their bounding discontinuities suggest that the position and longevity of segments are controlled primarily by the subaxial position of buoyant mantle diapirs or focused zones of rising melt within segments there are distinct differences in seafloor depth morphology residual mantle bouguer gravity anomaly and apparent crustal thickness between inside corner and outside corner crust this demands fundamentally asymmetric crustal accretion and extension across the ridge axis which we attribute to low angle detachment faulting near segment ends cyclic variations in residual gravity over the crossisochron run of segments also suggest crustal thickness changes of at least 1 2 km every 2 3 m y these are interpreted to be caused by episodes of magmatic versus relatively amagmatic extension controlled by retention and quasiperiodic release of melt from the upwelling mantle detachment faulting appears to be especially effective in exhuming lower crust to upper mantle at inside corners during relatively amagmatic episodes creating crustal domes analogous to turtleback metamorphic core complexes that are formed by low angle detachment faulting in subaerial extensional environments

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

melting and refreezing beneath roi baudouin ice shelf east antarctica inferred from radar gps and ice core data indicate that this reflector pattern is best fit by including basal melting of at least 15 cm a 1 this rate of melting is low compared with rates observed on larger ice shelves in both west and east antarctica ice cores extracted from a rift system close to the ice rise promontory show several meters of marine ice accreted beneath the shelf these observations of low rates of basal melting and limited distribution of accreted marine ice suggest that either antarctic surface water may reach the ice shelf base or that circulation beneath the shelf is likely dominated by the production of high salinity shelf water rather than the incursion of circumpolar deep water implying a weak sub shelf circulation system here many of the ice shelves located along the coast of dronning maud land are like roi baudouin ice shelf characterized by frequent ice rises and promontories therefore it is highly likely that these are also of shallow bathymetry and are subject to similarly weak side shelf basal melting and refreezing

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

submersible study of an oceanic megamullion in the central north atlantic recently discovered megamullions on the seafloor have been interpreted to be the exhumed footwalls of long lived detachment faults operating near the ends of spreading segments in slow spreading crust we conducted five submersible dives on one of these features just east of the rift valley in the mid atlantic ridge at 26 35 n and obtained visual rock sample gravity and heat flow data along a transect from the breakaway zone where the fault is interpreted to have first nucleated in 2 0 2 2 ma crust westward to near the termination 0 7 ma our observations are consistent with the detachment fault hypothesis and show the following features in the breakaway zone faulted and steeply backtilted basaltic blocks suggest rotation above a deeper shear zone the youngest normal faults in this sequence are interpreted to have evolved into the long lived detachment fault in younger crust the interpreted detachment surface rises as monotonously flat seafloor in a pair of broad gently sloping domes that formed simultaneously along isochrons and are now thinly covered by sediment the detachment surface is locally littered with basaltic debris that may have been clipped from the hanging wall the domes coincide with a gravity high that continues along isochrons within the spreading segment modeling of on bottom gravity measurements and recovery of serpentinites imply that mantle rises steeply and is exposed within 7 km west of the breakaway but that rocks with intermediate densities prevail farther west within 5 km of the termination small volcanic cones appear on the detachment surface indicating melt input into the footwall we interpret the megamullion to have developed during a phase of limited magmatism in the spreading segment with mantle being exhumed by the detachment fault 0 5 m y after its initiation increasing magmatism may eventually have weakened the lithosphere and facilitated propagation of a rift that terminated slip on the detachment fault progressively between 1 3 m y and 0 7 m y identifiable but low amplitude magnetic anomalies over the megamullion indicate that it incorporates a magmatic component we infer that much of the footwall is composed of variably serpentinized peridotite intruded by plutons and dikes

a framework for estimating anchor ice extent at potential formation sites in mcmurdo sound antarctica a distinctive feature of polar regions is the formation of ice clusters attached to the seabed known as anchor ice anchor ice plays an important role in mobilizing bed sediments and serves ecological roles providing habitats or as an agent of disturbance creating potentially fatal environments to benthic fauna the sublittoral zone associated with the landward margin represents the most likely environment for anchor ice formation where conditions conducive to the advection of supercooled water from sub ice shelf cavities are favourable we develop a framework to estimate the areal extent of anchor ice formation assuming a northerly flow of 75m deep supercooled water plumes from the ross and mcmurdo ice shelf cavities antarctica in mcmurdo sound our results indicate that regions beneath the mcmurdo ice shelf extending along brown peninsula and white and black islands are likely conducive to anchor ice formation anchor ice may also form along the hut point peninsula and around ross island and in pockets along the southern victoria land coast the limitations of our approach include an imposed northerly flow of ice shelf water poorly constrained sub ice shelf bathymetry and temporal variability in supercooled water depth production particularly in the

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

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

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

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

ensemble prediction and intercomparison analysis of grace time variable gravity field models precise measurements of the earth s time varying gravitational field from the nasa deutsches zentrum fur luft und raumfahrt gravity recovery and climate experiment grace mission allow unprecedented tracking of the transport of mass across and underneath the surface of the earth and give insight into secular seasonal and subseasonal variations in the global water supply several groups produce these estimates and while the various gravity fields are similar differences in processing strategies and tuning parameters result in solutions with regionally specific variations and error patterns this study examined the spatial temporal and spectral variations between the different gravity field products and developed an ensemble gravity field solution from the products of four such analysis centers the solutions were found to lie within a certain analysis scatter regardless of the local relative water height variation and the ensemble model is clearly seen to reduce the noise in the gravity field solutions within the available scatter of the solutions

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

ridge axis deformation and coeval melt migration within layer 3 gabbros evidence from the lizard complex u k ridge parallel extensional shear zones within the layer 3 gabbros of the lizard ophiolite have recorded varied and numerous chemical and mineralogical changes under a variety of p t conditions these changes accompany tectonic exhumation of lower crustal levels by a listric fault mechanism during amagmatic extension at a slow spreading centre deformation within the mid crustal level of layer three resulted in the migration and impregnation of an evolved iron titanium rich silica poor melt along the shear zones this syntectonic infiltration occurred along the lowermost portions of listric faults which rooted in a partially molten zone beneath the ridge axis residual melt was tapped from this underlying zone and tectonically redistributed about deforming gabbros situated immediately above the partially molten zone the occurrence of sub solidus synkinematic assemblages within the shear zones which were generated at various temperatures and water rock ratios is explained in terms of their simultaneous development on listric fault planes in the presence of a hydrothermal fluid phase the sequential overprinting of pre existing assemblages arises from repeated block rotation during amagmatic episodes of extension within an oceanic slow spreading environment

the influence of the drygalski ice tongue on the local ocean the drygalski ice tongue presents an 80 km long floating obstacle to alongshore flows in the victoria land coastal ocean region of the western ross sea here we use oceanographic data from near to the tongue to explore the interplay between the floating glacier and the local currents and stratification a vessel based circuit of the glacier recording ocean temperature and salinity profiles reveals the southwest corner to be the coldest and most complex in terms of vertical structure the southwest corner structure beneath the surface warm salty layer sustains a block of very cold water extending to 200 m depth in this same location there was a distinct layer at 370 m not seen anywhere else of water at 1 93 c the new observations broadly but not directly support the presence of a coherent victoria land coastal current the data suggest the northward moving coastal current turns against the coriolis force and works its way anticlockwise around the glacier but with leakage beneath the glacier through the highly rippled underside resulting in a spatially heterogeneous supply to the terra nova bay polynya region an important location for the formation of high salinity shelf water

ice composition evidence of marine ice transfer along the bottom of a small antarctic ice shelf the existence of marine ice transfer along the underside of the hell s gate ice shelf victoria land is indicated by an isotopic and chemical study of ice cores because of top surface ablation the marine ice formed at the ice shelf ocean interface ultimately appears at shelf surface a succession of congelation platelet and frazil ice is shown to occur the combined study of stable isotope composition and of the sodium content of these different ice types proves to be a valuable tool for specifying the ice shelf ocean interactions in this area two different freezing zones separated by a melting rone exist the parent water for the frazil ice is meltwater from congelation ice which appears in the upstream zone

significant marine ice accumulation in the ablation zone beneath an antarctic ice shelf high resolution crystallographic salinity and isotopic analyses of a 45 m ice core reveal the presence of a thick layer of marine ice near the grounding line of the nansen ice shelf antarctica the anomalous formation of marine ice in a zone assumed to be the site of active basal melting leads us to propose the hypothesis of large basal crevasses as a favorable environment for important marine ice accretion this hitherto unexplored possibility is supported by the overall field configuration and by the discrepancy in some ice properties between this core and the marine ice sections of previous drilling projects these findings could have important implications for the general stability of ice shelves and their disintegration processes the specific properties of this core reveal that marine ice is post genetically deformed