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 ice formation in an ice shelf water plume 1 we present a model for the growth of frazil ice crystals and their accumulation as marine ice at the base of antarctic ice shelves the model describes the flow of buoyant water upward along the ice shelf base and includes the differential growth of a range of crystal sizes frazil ice formation starts when the rising plume becomes supercooled initially the majority of crystals have a radius of similar to0 3 mm and concentrations are below 0 1 g l depending on the ice shelf slope which controls the plume speed frazil crystals increase in size and number typically crystals up to 1 0 mm in radius are kept in suspension and concentrations reach a maximum of 0 4 g l the frazil ice in suspension decreases the plume density and thus increases the plume speed larger crystals precipitate upward onto the ice shelf base first with smaller crystals following as the plume slows down in this way marine ice is formed at rates of up to 4 m yr in some places consistent with areas of observed basal accumulation on filchner ronne ice shelf the plume continues below the ice shelf as long as it is buoyant if the plume reaches the ice front its rapid rise produces high supercooling and the ice crystals attain a radius of several millimeters before reaching the surface similar ice crystals have been trawled at depth north of antarctic ice shelves but otherwise no observations exist to verify these first predictions of ice crystal sizes and volumes

active water exchange and life near the grounding line of an antarctic outlet glacier abstract the grounding line gl of the antarctic ice sheet forms the boundary between grounded and floating ice along the coast near this line warm oceanic water contacts the ice shelf producing the ice sheet s highest basal melt rate despite the importance of this region water properties and circulations near the gl are largely unexplored because in situ observations are difficult here we present direct evidence of warm ocean water transport to the innermost part of the subshelf cavity several hundred meters seaward from the gl of langhovde glacier an outlet glacier in east antarctica our measurements come from boreholes drilled through the glacier s 400 m thick grounding zone beneath the grounding zone we find a 10 24 m deep water layer of uniform temperature and salinity 1 45 c 34 25 psu values that roughly equal those measured in the ocean in front of the glacier moreover living organisms are found in the thin subglacial water layer these findings indicate active transport of water and nutrients from the adjacent ocean meaning that the subshelf environment interacts directly and rapidly with the ocean

modeling the basal melting and marine ice accretion of the amery ice shelf the basal mass balance of the amery ice shelf ais in east antarctica is investigated using a numerical ocean model the main improvements of this model over previous studies are the inclusion of frazil formation and dynamics tides and the use of the latest estimate of the sub ice shelf cavity geometry the model produces a net basal melt rate of 45 6 gt year 1 0 74 m ice year 1 which is in good agreement with reviewed observations the melting at the base of the ice shelf is primarily due to interaction with high salinity shelf water created from the surface sea ice formation in winter the temperature difference between the coldest waters created in the open ocean and the in situ freezing point of ocean water in contact with the deepest part of the ais drives a melt rate that can exceed 30 m of ice year 1 the inclusion of frazil dynamics is shown to be important for both melting and marine ice accretion refreezing frazil initially forms in the supercooled water layer adjacent to the base of the ice shelf the net accretion of marine ice is 5 3 gt year 1 comprised of 3 7 gt year 1 of frazil accretion and 1 6 gt year 1 of direct basal refreezing

the effect of meltwater plumes on the melting of a vertical glacier face abstractfreshwater produced by the surface melting of ice sheets is commonly discharged into ocean fjords from the bottom of deep fjord terminating glaciers the discharge of the freshwater forms upwelling plumes in front of the glacier calving face this study simulates the meltwater plumes emanated into an unstratified environment using a nonhydrostatic ocean model with an unstructured mesh and subgrid scale mixing calibrated by comparison to established plume theory the presence of an ice face reduces the entrainment of seawater into the meltwater plumes so the plumes remain attached to the ice front in contrast to previous simple models ice melting increases with height above the discharge also in contrast to some simple models and the authors speculate that this overcutting may contribute to the tendency of icebergs to topple inwards toward the ice face upon calving the overall melt rate is found to increase with discharge flux only up to a critical value which depends on the channel size

role of the molecular sublayer in the melting or freezing of sea ice abstract in an earlier paper a second moment turbulence closure model was applied to the problem of the dynamic and thermodynamic interaction of sea ice and the ocean surface mixed layer an overly simplistic parameterization of the molecular sublayers of temperature and salinity within the mixed layer was used this paper investigates the use of a more recent parameterization by yaglom and kader which is supported by laboratory data a relatively low melt rate results in the case where ice overlays warm water this agrees with some recent observations in the interior of the marginal ice zone a surface heat sink drives the freezing case which due to the large difference in heat and salt molecular diffusivities produces a strong supercooling effect this is converted into an estimate of frazil ice production through a simple scheme the model results provide an explanation for high frazil ice concentrations observed in the arctic and antarctic

on meltwater under ice shelves the basic features of the flow of meltwater under ice shelves can be described by a set of simple relations and length scales the flow may be divided into two regions with different basic processes dominating in each in the first region melting of the underside of the ice shelf is important and the temperature and salinity of the current tend toward equilibrium values such that the changes due to melting of the ice shelf are balanced by changes due to entrainment of ambient seawater the equilibrium values change with depth owing to the effect of the change in pressure on the freezing point as the current increases in thickness it is no longer able to adjust sufficiently rapidly to the changing equilibrium values arid the flow moves into the second region the extent of the first region is governed by the location of the ambient freezing point in the second region melting is less important and the current behaves as an entraining drag limited gravity current in a stratified ambient fluid leaving the shelf once the current has the same density as the ambient seawater the heights of the two regions depend mainly on the ambient conditions and only indirectly on parameters such as slope angle entrainment constant drag coefficient and turbulent transfer coefficients

a model of ice shelf ocean interaction with application to the filcher ronne and ross ice shelves a simple analytical model has been developed to study the formation of ice shelf water isw isw is assumed to flow as a buoyancy driven layer underneath the ice shelf a relation between potential temperature and salinity in the isw layer is calculated from the mass and energy balance this temperature salinity relation is shown to depend only on the temperature and the salinity of the source water mass and to be practically independent of entrainment and melt rates the model results are obtained without making any assumptions about entrainment and melt rates the model is in good agreement with observations under the ronne ice shelf and it indicates that isw in the filchner depression is formed from western shelf water wsw with salinity higher than 34 75 practical salinity units such high salinity water is only observed in the ronne depression in the western part of the continental shelf this implies a circulation of wsw under the filchner ronne ice shelf from the ronne depression into the filchner depression similarly the model shows that the isw observed under j9 at the ross ice shelf has been formed from low salinity shelf water lssw from the eastern parts of the ross sea continental shelf lssw must therefore circulate under the eastern parts of the ross ice shelf

an analytical derivation of ice shelf basal melt based on the dynamics of meltwater plumes the interaction between ice shelves and the ocean is an important process for the development of marine ice sheets however it is difficult to model in full detail due to the high computational cost of coupled ice ocean simulations so that simplified basal melt parameterizations are required in this work a new analytical expression for basal melt is derived from the theory of buoyant meltwater plumes moving upward under the ice shelf and driving the overturning circulation within the ice shelf cavity the governing equations are nondimensionalized in the case of an ice shelf with constant basal slope and uniform ambient ocean conditions an asymptotic analysis of these equations in terms of small slopes and small thermal driving assumed typical for antarctic ice shelves leads to an equation that can be solved analytically for the dimensionless melt rate this analytical expression describes a universal melt rate curve onto which the scaled results of the original plume model collapse its key features are a positive melt peak close to the grounding line and a transition to refreezing further away comparing the analytical expression with numerical solutions of the plume model generally shows a close agreement between the two even for more general cases than the idealized geometry considered in the derivation the results show how the melt rates adapt naturally to changes in the geometry and ambient ocean temperature the new expression can readily be used for improving ice sheet models that currently still lack a sufficiently realistic description of basal melt

dynamic in stability of thwaites glacier west antarctica 1 thwaites glacier west antarctica has the potential to directly contribute 1 m to sea level and currently is losing mass and thinning rapidly here we report on regional results for the sea level response to ice sheet evolution searise experiments and investigate the impact of i spatial resolution within existing data sets ii grounding zone processes and iii till rheology on the dynamics of this outlet glacier in addition to the searise data sets we use detailed aerogeophysical and satellite data from thwaites glacier as input to a coupled ice stream ice shelf ocean plume model that includes oceanic influences across a several kilometers wide grounding zone suggested by new high resolution data our results indicate that the ice tongue provides limited stability and that while future atmospheric warming will likely add mass to the surface of the glacier strong ice stream stabilization on bedrock highs narrower than the length of the grounding zone may be ephemeral if circulating waters substantially reduce basal resistance and enhance melting beneath grounded ice within this zone however we find that stability is significantly enhanced by effectively plastic till beds accurate projections of future sea level change relies on correct understanding of the till rheology as well as local basal processes near the grounding line

channelized bottom melting and stability of floating ice shelves 1 the floating ice shelf in front of petermann glacier in northwest greenland experiences massive bottom melting that removes 80 of its ice before calving into the arctic ocean detailed surveys of the ice shelf reveal the presence of 1 2 km wide 200 400 m deep sub ice shelf channels aligned with the flow direction and spaced by 5 km we attribute their formation to the bottom melting of ice from warm ocean waters underneath drilling at the center of one of channel only 8 m above sea level confirms the presence of ice shelf melt water in the channel these deep incisions in ice shelf thickness imply a vulnerability to mechanical break up and climate warming of ice shelves that has not been considered previously

simulations of ice ocean dynamics in the weddell sea 2 interannual variability 1985 1993 investigations of sea ice ocean interaction on the continental shelf in the southwestern weddell sea reveal a strong correlation between fluctuations of atmospheric forcing and the variability of sea ice formation anomalies of meridional wind stress in the inner weddell sea are consistent with the phase of the antarctic circumpolar wave acw positive anomalies of northward wind stress cause an increase of sea ice export in the same and of sea ice formation in the following year leading to an increased production of high salinity shelf water driven by a varying zonal density distribution over the continental shelf the circulation in the filchner ronne ice shelf cavity fluctuates between two modes each of which features a characteristic distribution of basal freezing and melting regions thus signals of interannual atmospheric variability propagate into the deep ocean and the sub ice shelf cavities

simulation of subice shelf melt rates in a general circulation model velocity dependent transfer and the role of friction two parameterizations of turbulent boundary layer processes at the interface between an ice shelf and the ocean beneath are investigated in terms of their impact on simulated melt rates and feedbacks the parameterizations differ in the transfer coefficients for heat and freshwater fluxes in their simplest form they are assumed constant and hence are independent of the velocity of ocean currents at the ice shelf base an augmented melt rate parameterization accounts for frictional turbulence via transfer coefficients that do depend on boundary layer current velocities via a drag law in simulations with both parameterizations for idealized as well as realistic cavity geometries under pine island ice shelf west antarctica significant differences in melt rate patterns between the velocity independent and velocity dependent formulations are found while patterns are strongly correlated to those of thermal forcing for velocity independent transfer coefficients melting in the case of velocity dependent coefficients is collocated with regions of high boundary layer currents in particular where rapid plume outflow occurs both positive and negative feedbacks between melt rates boundary layer temperature velocities and buoyancy fluxes are identified melt rates are found to increase with increasing drag coefficient inline image in agreement with plume model simulations but optimal values of cd inferred from plume models are not easily transferable uncertainties therefore remain both regarding simulated melt rate spatial distributions and magnitudes

tidal modulation of buoyant flow and basal melt beneath petermann gletscher ice shelf greenland a set of collocated in situ oceanographic and glaciological measurements from petermann gletscher ice shelf greenland provides insights into the dynamics of under ice flow driving basal melting at a site 16 km seaward of the grounding line within a longitudinal basal channel two conductivity temperature ct sensors beneath the ice base and a phase sensitive radar on the ice surface were used to monitor the coupled ice shelf ocean system a 6 month time series spanning 23 august 2015 to 12 february 2016 exhibited two distinct periods of ice ocean interactions between august and december radar derived basal melt rates featured fortnightly peaks of 15 m yr 1 which preceded the arrival of cold and fresh pulses in the ocean that had high concentrations of subglacial runoff and glacial meltwater estimated current speeds reached 0 20 0 40 m s 1 during these pulses consistent with a strengthened meltwater plume from freshwater enrichment such signals did not occur between december and february when ice ocean interactions instead varied at principal diurnal and semidiurnal tidal frequencies and lower melt rates and current speeds prevailed a combination of estimated current speeds and meltwater concentrations from the two ct sensors yields estimates of subglacial runoff and glacial meltwater volume fluxes that vary between 10 and 80 m3 s 1 during the ocean pulses area average upstream ice shelf melt rates from these fluxes are up to 170 m yr 1 revealing that these strengthened plumes had already driven their most intense melting before arriving at the study site

is the antarctic ice sheet growing a common public perception is that global warming will accelerate the melting of polar ice sheets causing sea level to rise a common scientific position is that the volume of grounded antarctic ice is slowly growing and will damp future sea level rise at present studies supporting recent shrinkage or growth depend on limited measurements that are subject to high temporal and regional variability and it is too early to say how the antarctic ice sheet will behave in a warmer world

iceberg drift and ocean circulation in the northwestern weddell sea antarctica abstract icebergs are distinctive features in the southern ocean and can influence the physicochemical properties of the ocean environment around them their trajectories are influenced by ocean currents sea ice bathymetry and wind action here twenty five icebergs were identified and tracked by applying image classification methods to a series of 142 advanced synthetic aperture radar asar images obtained during 2008 and 2009 tracking these icebergs made it possible to associate the patterns of iceberg drift with the main ocean currents and front systems in this region including the antarctic coastal current the antarctic slope front and the weddell front a case study investigated here revealed the recirculation of a weddell sea iceberg within the bransfield strait in the northern antarctic peninsula as well as its corresponding mass loss starting in the weddell sea and extending throughout the monitoring period the icebergs studied experienced an average disintegration percentage of 21 15 and an average drift speed of 0 22 0 11 km h 1 the icebergs that drifted at least 500 km had an average meltwater injection rate of 62 76 38 27 m3 s 1 in the ocean around the northern antarctic peninsula

measurements of ice thickness and seabed topography under the fimbul ice shelf dronning maud land antarctica 1 this paper presents results from seismic measurements of the ice and water column thickness of the fimbul ice shelf in the northeastern weddell sea seismic reflection measurements were conducted at 183 stations covering most of the ice shelf seismic velocities in the ice were derived from refraction measurements at 12 stations distributed evenly across the area as well as from temperature and density data from the fimbul ice shelf velocities in the water were derived from temperature and salinity data from beneath the fimbul ice shelf ice thicknesses were found to vary between 160 m and 550 m with uncertainties up to 10 m water column thicknesses up to 900 m were found within the central ice shelf cavity and values exceed 2000 m where the ice shelf overhangs the continental slope uncertainties in water column thickness are estimated to be 60 m and are dominated by the uncertainties in the shape of the seabed ice draft and seabed elevation was derived from ice and water column thickness assuming hydrostatic pressure the resulting map of seabed elevation and water column thickness suggests that the strong westward flowing coastal current will be steered under the ice shelf and thus drive a sub ice shelf flow warm deep water does not have direct access to the ice shelf cavity while relatively cold coastal waters shallower than 500 m will interact closely with the fimbul ice shelf

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

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

keel depths of modern antarctic icebergs and implications for sea floor scouring in the geological record abstract icebergs affect the geological record through the scouring or ploughing action of their keels reworking sediments where they contact the sea floor satellite radar altimeter measurements of the surface elevation of the marine margins of the antarctic ice sheet are inverted to produce ice thickness values these data are assumed to represent the keel depths of newly calved icebergs there are three peaks in the frequency distribution of antarctic iceberg keel depths a about 140 200 m in thickness associated with smaller ice shelves fringing antarctica e g wilkins george vi and brunt ice shelves b about 250 300 m from large ice shelves e g ross ronne amery and c approximately 500 600 m from fast flowing ice sheet outlet glaciers e g pine island and dibble glaciers together with the filchner ice shelf controls on iceberg keel depth are ice thickness at the grounding line creep thinning and the rate of melting freezing at the floating ice shelf base with distance to the calving margin the distribution of sea floor scours produced by iceberg grounding is dependent on the changing form and flow of the glaciers and ice sheets from which icebergs are derived and on berg drift tracks and melt rates sea floor evidence for icebergs with particularly deep keels has sometimes been interpreted to indicate the presence of extensive former ice shelves however the largest modern antarctic ice shelves do not produce large numbers of icebergs thicker than about 350 m implying that sea floor scours found in deeper water are unlikely to be an indicator of extensive past ice shelf development iceberg scours found at water depths in excess of about 500 m in the geological record are instead probably indicative of either a the former presence of fast flowing ice sheet outlet glaciers b ice shelves fed from major interior basins where lateral spreading is constrained topographically or c a pulse of large icebergs released during major deglaciation or ice sheet collapse

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

numerical modeling of ocean ice interactions under pine island bay s ice shelf 1 a two dimensional numerical model is used to simulate the dynamics of buoyant meltwater rich plumes flowing beneath the ice shelf occupying much of pine island bay west antarctica recent studies have shown that this ice shelf along with all others fringing the amundsen sea is thinning rapidly in the model both the coriolis effect and subshelf topography are important in controlling plume dynamics and the spatial distribution of ice melt melt is concentrated in a narrow zone within 20 km of the grounding line where steep subshelf slopes and access to warm ambient water allow melt rates to exceed 100 m yr 1 the plume generated by entrainment of ambient water into the meltwater in these areas is guided by the topography of the ice shelf underside and exits the ice shelf at three distinct outflow locations melt rates generated along the course of the plume are higher approximately 2 5 than rates elsewhere the model suggests that the observed ice shelf thinning rates could have resulted from a hypothetical instantaneous 0 25 c warming of the ambient water entrained by the plume a context for this value is provided by the 40 year warming trend documented by jacobs et al 2002 for circumpolar deep water in the nearby ross sea

controls on last glacial maximum ice extent in the weddell sea embayment antarctica the weddell sea sector of the antarctic ice sheet is hypothesized to have made a significant contribution to sea level rise since the last glacial maximum using a numerical flowline model we investigate the controls on grounding line motion across the eastern weddell sea and compare our results with field data relating to past ice extent specifically we investigate the influence of changes in ice temperature accumulation sea level ice shelf basal melt and ice shelf buttressing on the dynamics of the foundation ice stream we find that ice shelf basal melt plays an important role in controlling grounding line advance while a reduction in ice shelf buttressing is found to be necessary for grounding line retreat there are two stable positions for the grounding line under glacial conditions at the northern margin of berkner island and at the continental shelf break global mean sea level contributions associated with these two scenarios are 50 mm and 130 mm respectively comparing model results with field evidence from the pensacola mountains and the shackleton range we find it unlikely that ice was grounded at the continental shelf break for a prolonged period during the last glacial cycle however we cannot rule out a brief advance to this position or a scenario in which the grounding line retreated behind present during deglaciation and has since re advanced better constraints on past ice sheet and ice shelf geometry ocean temperature and ocean circulation are needed to reconstruct more robustly past behavior of the foundation ice stream

basal melting of a 38b a physical model constrained by satellite observations abstract we observed the large tabular iceberg a 38b in the time period from the calving event at the ronne ice shelf in 1998 until its grounding near south georgia in 2004 by means of various space borne sensors the initial ice thickness was determined by radar altimetry the iceberg shape from radar imaging and optical instruments the freeboard change at different stages of the drift was derived from icesat laser altimeter profiles the analysis of the satellite data confirms that the decay of a 38b is governed mainly by basal erosion we then used a numerical model for simulating iceberg melting and fitted the melt rate by varying the turbulent exchange parameters for temperature t and salt s to match the results obtained by icesat data our results show that the iceberg passed through three melting regimes characterized by iceberg drift velocity 1 in the weddell sea melting conditions are similar to the situation under an ice shelf with strong tidal currents which corresponds to a t of 1 0 10 4 m s 1 2 in the scotia sea where the iceberg drifts unhindered with the ocean current and is surrounded by its own melt water t is 0 4 10 4 m s 1 3 at the grounding position friction velocity is again high due to tidal currents and t is 1 8 10 4 m s 1 s is set to 0 00505 t in all cases the analysis shows that icesat glas data together with satellite imagery can provide better estimates of turbulent exchange parameters which is a step forward in improving the knowledge of fresh water input from melting icebergs into the southern ocean

investigation of land ice ocean interaction with a fully coupled ice ocean model 1 model description and behavior 1 antarctic ice shelves interact closely with the ocean cavities beneath them with ice shelf geometry influencing ocean cavity circulation and heat from the ocean driving changes in the ice shelves as well as the grounded ice streams that feed them we present a new coupled model of an ice stream ice shelf ocean system that is used to study this interaction the model is capable of representing a moving grounding line and dynamically responding ocean circulation within the ice shelf cavity idealized experiments designed to investigate the response of the coupled system to instantaneous increases in ocean temperature show ice ocean system responses on multiple timescales melt rates and ice shelf basal slopes near the grounding line adjust in 1 2 years and downstream advection of the resulting ice shelf thinning takes place on decadal timescales retreat of the grounding line and adjustment of grounded ice takes place on a much longer timescale and the system takes several centuries to reach a new steady state during this slow retreat and in the absence of either an upward or downward sloping bed or long term trends in ocean heat content the ice shelf and melt rates maintain a characteristic pattern relative to the grounding line

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

subglacial hydrology at rink isbrae west greenland inferred from sediment plume appearance marine terminating outlet glaciers discharge most of the greenland ice sheet s mass through frontal ablation and meltwater runoff while calving can be estimated by in situ and remote sensing observations submarine melting and subglacial meltwater transport are more challenging to quantify here we investigate the subglacial hydrology of rink isbrae a fast flowing west greenland tidewater glacier using time lapse photography modeled runoff estimates and daily satellite imagery from 2007 to 2011 we find that sediment plumes appear episodically at four distinct locations across the terminus and last between 2 h and 17 d this suggests short term variability in discharge and the existence of persistent pathways the seasonal onset of sediment plumes occurs before supraglacial lake drainages shortly after the onset of runoff and only after the wintertime ice melange has begun disintegrating plumes were also visible after the cessation of runoff 23 5 d which is indicative of subglacial storage the lack of either a seasonal velocity change or a correspondence between meltwater availability and plume occurrence suggests that the subglacial system persists in a state of inefficient drainage subglacial hydrology at tidewater glaciers is of critical importance in understanding dynamics at the ice front

spatial and temporal variability of meiobenthic density in the blanes submarine canyon nw mediterranean abstract meiofaunal density distribution was studied from 400 m to 1500 m depth inside blanes submarine canyon nw mediterranean and on the eastern open slope in autumn 2003 and spring 2004 our multidisciplinary approach allowed to study the hydrodynamics and sedimentary processes in the blanes canyon that characterize it as highly heterogeneous environment inside the canyon area particle fluxes were higher than on the slope area increased from autumn to spring and mostly consisted of lithogenic material moreover the canyon s locations experienced more intense bottoms currents and sediment disturbance being reflected in a greater variability of meiobenthic densities both between stations and sampling times than on the open slope no clear trends e g declining densities associated with increasing depths were observed contrary in the open slope current velocities were relatively lower compared with the canyon area and showed lower temporal variability at the same time the nutritional quality of the particle fluxes at deeper grounds were higher probably allowing the meiofaunal densities not to change over time in conclusion the meiobenthos in our system apparently showed a higher temporal variability inside the canyon area strongly affected by particle fluxes or erosive and sediment mixing processes linked to current modifications induced by the canyon topography

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

ice shelf basal melting at the grounding line measured from seismic observations analysis of seismic data provides a new technique to measure basal melting of an ice shelf close to the grounding line internal reflections have been observed within the ice on a seismic reflection profile at the grounding line of ronne ice shelf the changes in ice thickness above and below these reflections have been used in a steady state model to calculate the basal mass flux of the ice shelf soon after the ice begins to float strain rates within the ice calculated during the modeling agree with values from nearby survey data the calculated melt rates range between 0 and 7 m yr 1 with an estimated standard error of 2 4 m yr 1 in reasonable agreement with earlier estimates based on surface glaciological observations limitations in the method include the difficulties in determining reflector geometry from a single seismic section and also the limitations imposed by the assumption of steady state additional seismic data would greatly reduce these limitations

the effects of antarctic iceberg calving size distribution in a global climate model icebergs calved from the antarctic continent act as moving sources of freshwater while drifting in the southern ocean the lifespan of these icebergs strongly depends on their original size during calving in order to investigate the effects if any of the calving size of icebergs on the southern ocean we use a coupled general circulation model with an iceberg component iceberg calving length is varied from 62 m up to 2 3 km which is the typical range used in climate models results show that increasing the size of calving icebergs leads to an increase in the westward iceberg freshwater transport around antarctica in simulations using larger icebergs the reduced availability of meltwater in the amundsen and bellingshausen seas suppresses the sea ice growth in the region in contrast the increased iceberg freshwater transport leads to increased sea ice growth around much of the east antarctic coastline these results suggest that the absence of large tabular icebergs with horizontal extent of tens of kilometers in climate models may introduces systematic biases in sea ice formation ocean temperatures and salinities around antarctica

modeling thermodynamic ice ocean interactions at the base of an ice shelf abstract models of ocean circulation beneath ice shelves are driven primarily by the heat and freshwater fluxes that are associated with phase changes at the ice ocean boundary their behavior is therefore closely linked to the mathematical description of the interaction between ice and ocean that is included in the code an hierarchy of formulations that could be used to describe this interaction is presented the main difference between them is the treatment of turbulent transfer within the oceanic boundary layer the computed response to various levels of thermal driving and turbulent agitation in the mixed layer is discussed as is the effect of various treatments of the conductive heat flux into the ice shelf the performance of the different formulations that have been used in models of sub ice shelf circulation is assessed in comparison with observations of the turbulent heat flux beneath sea ice formulations that include an explicit parameterization of the oceanic boundary layer give results that

observations of thermohaline convection adjacent to brunt ice shelf observations were made of ocean microstructure and horizontal currents adjacent to brunt ice shelf in the southeastern weddell sea periods of in situ supercooled water extending as deep as 65 m were associated with ice nucleation and frazil formation at depth ascending ice crystals due to convection lead to increased dissipation rates the main outflow of potentially supercooled water from deep beneath ice shelf is suggested to be in the deep channel northeast of the measurement site because this water is advected southward along the front it becomes in situ supercooled leading to suspended ice formation thermohaline convection and enhanced dissipation

sensitivity of the amery ice shelf antarctica to changes in the climate of the southern ocean abstract coupled ocean atmospheric general circulation models indicate that warming of up to 3 c may occur over the next century in waters immediately to the north of the amery ice shelf the impact of this warming on the ocean cavity under the amery ice shelf and the mass exchange at the interface between the ocean cavity and the ice shelf is investigated using a three dimensional ocean model warming of between 0 25 and 3 0 c is applied along the ice front in a series of model runs rather than in a single transient run changes in salinity are also considered for larger amounts of warming the model results show that the circulation in the ocean cavity changes as warming increases particularly in the gyres that dominate the horizontal circulation the changes in the heat flux from the warming increase the melt rates from the base of the amery ice shelf from the present day mean melt rate and net mass loss estimates of 0 28 m yr 1 and 14 2 gt yr 1 respectively by approximately 0 55 m yr 1 c 1 and 2

monitoring the tabular icebergs c28a and c28b calved from the mertz ice tongue using radar remote sensing data abstract we analyzed the evolution processes of two tabular icebergs c28a and c28b originating from iceberg c28 using continuous multisource radar remote sensing data the monitoring began during the calving of iceberg c28 from the mertz ice tongue in february 2010 and ended in april 2012 the evolution of the iceberg area was determined from envisat asar images and the freeboard change was derived from cryosat 2 profiles two patterns of iceberg area decreases are observed during iceberg drifting in austral summer from october to next march iceberg area shows a gradual decrease and it is interpreted to represent edge wasting sidewall melting and wave erosion the gradual decrease of the area of c28a occurred at rates between 8 1 km2 month and 16 5 km2 month in austral winter from april to september iceberg area has several discrete decreases sudden drop while it remained constant for most of the time and it is interpreted to be large rift calving primarily caused by ocean swell and basal melting calving area of the two studied icebergs is observed to be greater in the winter the freeboard decreased at different rates at different locations on the same iceberg between 0 02 0 22 and 0 82 0 28 m month for c28a and c28b suggesting a laterally inhomogeneous melting of icebergs the average rate of change of the c28b freeboard during its 22 month grounding period was 0 03 0 01 m month which is considerably smaller than the 0 76 0 23 m month observed when it was freely drifting in the ocean the cold water regime surrounding the iceberg can help the iceberg maintain a stable state this study reveals the potential use of radar remote sensing when monitoring antarctic icebergs

variability in basal melting beneath pine island ice shelf on weekly to monthly timescales ocean driven basal melting of amundsen sea ice shelves has triggered acceleration thinning and grounding line retreat on many west antarctic outlet glaciers here we present the first year long 2014 record of basal melt rate at sub weekly resolution from a location on the outer pine island ice shelf adjustment of the upper thermocline to local wind forced variability in the vertical ekman velocity is the dominant control on basal melting at weekly to monthly timescales atmosphere ice ocean surface heat fluxes or changes in advection of modified circumpolar deep water play no discernible role at these timescales we propose that during other years a deepening of the thermocline in pine island bay driven by longer timescale processes may have suppressed the impact of local wind forcing on high frequency upper thermocline height variability and basal melting this highlights the complex interplay between the different processes and their timescales that set the basal melt rate beneath pine island ice shelf

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

ocean circulation and ice ocean interaction beneath the amery ice shelf antarctica simulations of the ocean dynamics in the cavity under the amery ice shelf antarctica were carried out using a three dimensional numerical ocean model two different boundary conditions were used to describe the open ocean barotropic exchange at the ice front the simulations show that the circulation in the ocean cavity is predominantly barotropic and is generally steered by the cavity topography the circulation is driven by the density gradient in the cavity which is strongly influenced by the heat and salt fluxes from melting and freezing processes at the ice ocean interface and by the horizontal exchange of heat and salt across the open ocean boundary at the ice front the interaction at the ice ocean interface allows the basal component of the mass loss of the amery ice shelf to be estimated in the two simulations the computed losses were 5 8 gt yr 1 and 18 0 gt yr 1 values consistent with observations the bulk of the melting occurred near the southern grounding line of the ice shelf although substantial melting also occurred in areas where heat transport by horizontal circulation was large accretion was restricted to areas where water from upstream melting became supercooled as it ascended the ice shelf base

where glaciers meet water subaqueous melt and its relevance to glaciers in various settings glacier change is ubiquitous but the fastest and largest magnitude changes occur in glaciers that terminate in water this includes the most rapidly retreating glaciers and also several advancing ones often in similar regional climate settings furthermore water terminating glaciers show a large range in morphology particularly when ice flow into ocean water is compared to that into freshwater lakes all water terminating glaciers share the ability to lose significant volume of ice at the front either through mechanical calving or direct melt from the water in contact here we present a review of the subaqueous melt process we discuss the relevant physics and show how different physical settings can lead to different glacial responses we find that subaqueous melt can be an important trigger for glacier change it can explain many of the morphological differences such as the existence or absence of floating tongues subaqueous melting is influenced by glacial runoff which is largely a function of atmospheric conditions this shows a tight connection between atmosphere oceans and lakes and glaciers subaqueous melt rates even if shown to be large should always be discussed in the context of ice supply to the glacier front to assess its overall relevance we find that melt is often relevant to explain seasonal evolution can be instrumental in shifting a glacier into a different dynamical regime and often forms a large part of a glacier s mass loss on the other hand in some cases melt is a small component of mass loss and does not significantly affect glacier response

current measurements near ronne ice shelf implications for circulation and melting we present the first year long current meter records ever obtained near the floating filchner ronne ice shelf in the weddell sea the currents are steered along the ice front but in the lower layer where the bottom topography is descending toward the west the current has a component toward the ice front of about 3 cm s 1 during winter the temperature stayed near the surface freezing point while the salinity increased indicating that ice was formed and brine released the seasonal variation in salinity was 0 15 0 05 psu corresponding to the formation of 1 2 m of ice on a shelf depth of 400 m the transport of high salinity shelf water hssw into the ice shelf cavity was found to be of the order 0 5 106 m3 s 1 the production of this water due to oscillating tides and off shelf winds was found to be of the same order of magnitude in contact with glacial ice at great depths and because of the depression of the freezing point the hssw is transformed to ice shelf water isw by cooling and melting processes the melting rate was estimated to 1 1011 ton yr 1 this corresponds to the melting of 0 2 m ice per year if the melting is evenly distributed over the filchner ronne ice shelf if the melting is concentrated along a path from the berkner shelf around the berkner island to the filchner depression then melting rates up to 7 m yr 1 must be expected a comparison of hssw characteristics in the ronne depression our winter observations on the berkner shelf and the isw flowing out of the filchner depression indicates that very little water passes through the cavity from the ronne to the filchner depression it appears that most of the isw originating from processes on the berkner shelf escapes the cavity in the filchner depression this leaves the berkner shelf as the important source of isw and subsequently of the weddell sea bottom water formed from isw

the effects of rotation and ice shelf topography on frazil laden ice shelf water plumes a model of the dynamics and thermodynamics of a plume of meltwater at the base of an ice shelf is presented such ice shelf water plumes may become supercooled and deposit marine ice if they rise because of the pressure decrease in the in situ freezing temperature so the model incorporates both melting and freezing at the ice shelf base and a multiple size class model of frazil ice dynamics and deposition the plume is considered in two horizontal dimensions so the influence of coriolis forces is incorporated for the first time it is found that rotation is extremely influential with simulated plumes flowing in near geostrophy because of the low friction at a smooth ice shelf base as a result an ice shelf water plume will only rise and become supercooled and thus deposit marine ice if it is constrained to flow upslope by topography this result agrees with the observed distribution of marine ice under filchner ronne ice shelf antarctica in addition it is found that the model only produces reasonable marine ice formation rates when an accurate ice shelf draft is used implying that the characteristics of real ice shelf water plumes can only be captured using models with both rotation and a realistic topography

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

new oceanographic data from beneath ronne ice shelf antarctica oceanographic data have been obtained via an access hole made through ronne ice shelf the site which is the third in a series of similar studies lies 17 km west of korff ice rise where 825 m of ice overlies a 485 m deep water column measurements included conductivity and temperature profiles and an instrument mooring was deployed for long term measurements of currents temperature and conductivity at the sea floor there was a 150 m layer of well mixed water with a potential temperature and salinity of 1 97 c and 34 72 the water cooled and freshened towards the ice shelf base ultimately reaching 2 41 c and 34 51 the hydrographic and water current data imply a flow into the deepest part of the sub ice shelf cavity of about 200 000 m s 1 of the deeper relatively warm water which would be able to power an average basal melt rate of 0 2 m a 1 for the western portion of ronne ice shelf

seasonal ventilation of the cavity beneath filchner ronne ice shelf simulated with an isopycnic coordinate ocean model 1 the ocean cavity beneath filchner ronne ice shelf is observed to respond to the seasonal cycle of water mass production on the continental shelf of the southern weddell sea here we use a numerical model to investigate the propagation of newly formed shelf waters into the cavity we find that the model reproduces the most distinctive features of the observed seasonality and offers a plausible explanation for those features the most saline shelf waters are produced in the far west where the inflow to the cavity peaks twice each year the major peak occurs during the short period around midwinter when convection reaches full depth and the densest waters are generated once the surface density starts to decline dynamic adjustment of the restratified water column leads to a gradual fall in the salinity at depth and a secondary peak in the inflow that occurs in summer at the western coast beneath the ice shelf the arrival of the wintertime inflow at the instrumented sites is accompanied by a rapid warming while the slower decline in the inflow leads to a more gradual cooling water brought in by the secondary summer peak flows mainly to the eastern parts of the cavity here the seasonality is suppressed because the new inflows mix with older waters that recirculate within a topographic depression this pooling of waters in the east where the primary outflow of ice shelf water is generated dampens the impact of seasonality on the local production of weddell sea bottom water

turbulent heat exchange between water and ice at an evolving ice water interface we conduct laboratory experiments on the time evolution of an ice layer cooled from below and subjected to a turbulent shear flow of warm water from above our study is motivated by observations of warm water intrusion into the ocean cavity under antarctic ice shelves accelerating the melting of their basal surfaces the strength of the applied turbulent shear flow in our experiments is represented in terms of its reynolds number re which is varied over the range 2 0 times 10 3 leqslant re leqslant 1 0 times 10 4 depending on the water temperature partial transient melting of the ice occurs at the lower end of this range of re and complete transient melting of the ice occurs at the higher end following these episodes of transient melting the ice reforms at a rate that is independent of re we fit our experimental measurements of ice thickness and temperature to a one dimensional model for the evolution of the ice thickness in which the turbulent heat transfer is parameterized in terms of the friction velocity of the shear flow applying our model to field measurements at a site under the antarctic pine island glacier ice shelf yields a predicted melt rate that exceeds present day observations

ice shelf basal melting in a global finite element sea ice ice shelf ocean model the finite element sea ice ocean model fesom has been augmented by an ice shelf component with a three equation system for diagnostic computation of boundary layer temperature and salinity ice shelf geometry and global ocean bathymetry have been derived from the rtopo 1 dataset a global domain with a triangular mesh and a hybrid vertical coordinate is used to evaluate sub ice shelf circulation and melt rates for present day climate the model is forced with ncep reanalysis data basal mass fluxes are mostly realistic with maximum melt rates in the deepest parts near the grounding lines and marine ice formation in the northern sectors of ross ice shelf and filchner ronne ice shelf total basal mass loss for the ten largest ice shelves reflects the importance of the amundsen sea ice shelves getz ice shelf is shown to be a major melt water contributor to the southern ocean despite their modest melt rates the cold water ice shelves in the weddell sea are still substantial sinks of continental ice in antarctica discrepancies between the model and observations can partly be attributed to deficiencies in the forcing data or to sometimes unavoidable smoothing of ice shelf and bottom topographies

surface elevation changes at the front of the ross ice shelf implications for basal melting 1 rapid melting beneath the ross ice shelf ris occurs near the ice front likely in response to a secondary buoyant plume with tidal mixing and is sensitive to seasonal water temperatures in front of the ice shelf the front of the ris is examined using glas icesat laser altimetry data spatial and temporal changes in surface elevations are attributed to enhanced basal melting of the ice shelf near the ice front melt rates b increase exponentially as the front is approached from approximately zero at 40 km from the front to an average of 2 8 1 0 m a 1 within the front kilometer melt estimates within the front 60 km are best fit by the relationship b 2 0 exp x 11900 m a 1 where x denotes distance from the front frontal melt totals approximately 16 km3 a 1 in the front 40 km which accounts for between 10 and 40 of current published estimates of total melt beneath the ris spatial averaging along the front reveals a different pattern of melt in regions that have recently calved as compared to regions that have not calved frontal melt is modeled as a one dimensional buoyant plume with tidal currents included these model results imply that modest increases in sea surface temperatures will lead to considerable increases in melting beneath the ice shelf front

application of a three dimensional numerical model to lake vostok an antarctic subglacial lake the circulation in two water column thickness scenarios for lake vostok a subglacial lake in central east antarctica is investigated using a three dimensional numerical model in a scenario with a constant water column thickness the distance between the sloping ice sheet which caps the lake and the lake bed the circulation is barotropic but with a more realistic water column thickness the flow is baroclinic the different circulations result from the geothermal heat flux warming shallow regions of the realistic lake more efficiently thus forming a different horizontal density structure the differences and uncertainties between the two scenarios highlight the importance that the largely unknown water column thickness and geothermal heat flux have in determining the circulation in the lake

dynamics and thermodynamics of the ice upper ocean system in the marginal ice zone of the greenland sea measurements were made of the ice upper ocean system in the marginal ice zone of the greenland sea during a 4 day storm in which wind blew the ice south across a frontal region coinciding with the ice edge that had existed when the storm began in response to wind stress of about 0 2 pa a turbulent boundary layer developed under the ice that exhibited marked ekman rotation in both mean velocity average surface speed about 0 17 m s 1 deflection angle about 33 and turbulent stress profiles typical reynolds stress about 0 1 pa ablation of the ice undersurface increased rapidly after crossing the surface temperature front and the observed melt rate corresponded with direct heat flux measurements in the oceanic boundary layer with maximum upward heat flux of about 200 w m 2 we discuss overall momentum and energy balances interpret observed boundary layer measurements with a numerical model and show that molecular effects are important for heat and mass transport at the hydraulically rough ice ocean interface we also develop a simple model for predicting ice melt from interfacial stress and temperature and salinity of the mixed layer

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

channelization of plumes beneath ice shelves we study a simplified model of ice ocean interaction beneath a floating ice shelf and investigate the possibility for channels to form in the ice shelf base due to spatial variations in conditions at the grounding line the model combines an extensional thin film description of viscous ice flow in the shelf with melting at its base driven by a turbulent ocean plume small transverse perturbations to the one dimensional steady state are considered driven either by ice thickness or subglacial discharge variations across the grounding line either forcing leads to the growth of channels downstream with melting driven by locally enhanced ocean velocities and thus heat transfer narrow channels are smoothed out due to turbulent mixing in the ocean plume leading to a preferred wavelength for channel growth in the absence of perturbations at the grounding line linear stability analysis suggests that the one dimensional state is stable to initial perturbations chiefly due to the background ice advection

scalings for submarine melting at tidewater glaciers from buoyant plume theory abstractrapid dynamic changes at the margins of the greenland ice sheet synchronous with ocean warming have raised concern that tidewater glaciers can respond sensitively to ocean forcing understanding of the processes encompassing ocean forcing nevertheless remains embryonic the authors use buoyant plume theory to study the dynamics of proglacial discharge plumes arising from the emergence of subglacial discharge into a fjord at the grounding line of a tidewater glacier deriving scalings for the induced submarine melting focusing on the parameter space relevant for high discharge tidewater glaciers the authors suggest that in an unstratified fjord the often quoted relationship between total submarine melt volume and subglacial discharge raised to the power is appropriate regardless of plume geometry provided discharge lies below a critical value in these cases it is then possible to formulate a simple equation estimating total submarine melt volume as a function of discharge fjord temperature

alternative ice shelf equilibria determined by ocean environment 1 dynamic and thermodynamic regimes of ice shelves experiencing weak 1 m year 1 to strong 10 m year 1 basal melting in cold bottom temperature close to the in situ freezing point and warm oceans bottom temperature more than half of a degree warmer than the in situ freezing point are investigated using a 1 d coupled ice ocean model complemented with a newly derived analytic expression for the steady state temperature distribution in ice shelves this expression suggests the existence of a basal thermal boundary layer with thickness inversely proportional to the basal melt rate model simulations show that ice shelves afloat in warm ocean waters have significantly colder internal ice temperatures than those that float in cold waters our results indicate that in steady states the mass balance of ice shelves experiencing strong and weak melting is controlled by different processes in ice shelves with strong melting it is a balance between ice advection and basal melting and in ice shelves with weak melting it is a balance between ice advection and deformation sensitivity simulations show that ice shelves in cold and warm oceans respond differently to increase of the ocean heat content ice shelves in cold waters are more sensitive to warming of the ocean bottom waters while ice shelves in warm waters are more sensitive to shallowing of the depth of the thermocline

notes on southern ocean hydrography sea ice and bottom water formation abstract the southern ocean circulation and sea ice distribution is briefly described the formation of extremely cold bottom water in the weddell sea and its relation to the floating ronne filchner ice shelves is discussed it is shown that a concentrated swift eroding bottom current with anomalous low 18 o ratio transports the cold and dense ice shelf water from the shelf towards large depths comments are made on possible implications of this process for the large scale deep water circulation and for the interpretation of sediment cores

oxygen 18 and helium as tracers of ice shelf water and water ice interaction in the weddell sea oxygen 18 and helium isotope data from stations located in the filchner depression on the continental slope of the southern weddell sea and in the central weddell sea are presented and discussed the 18o and 4he signals imprinted on the water circulating under the filchner ronne ice shelf ice shelf water or isw due to melting of glacial ice at the base of the ice shelf are traced across the sill separating the filchner depression from the weddell sea low 18o values are correlated with high 4he concentrations in the isw found in the filchner depression minimum 18o values 0 8 maximum 4he concentrations about 4 7 10 8 cm3 stp g 1 the fraction of glacial meltwater contained in the isw found in the filchner depression is estimated to about 6 to 7 the 18o and helium isotope data from the overflowing shelf water component observed on the continental slope confirm the hypothesis that isw contributes significantly to the weddell sea bottom water wsbw on the basis of a inultiparameter water mass analysis it is discussed which fraction of the wsbw originates from isw and which other shelf waters potentially could contribute to wsbw

subglacial floods beneath ice sheets subglacial floods jokulhlaups are well documented as occurring beneath present day glaciers and ice caps in addition it is known that massive floods have occurred from ice dammed lakes proximal to the laurentide ice sheet during the last ice age and it has been suggested that at least one such flood below the waning ice sheet was responsible for a dramatic cooling event some 8000 years ago we propose that drainage of lakes from beneath ice sheets will generally occur in a time periodic fashion and that such floods can be of severe magnitude such hydraulic eruptions are likely to have caused severe climatic disturbances in the past and may well do so in the future

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

impact of periodic intermediary flows on submarine melting of a greenland glacier the submarine melting of a vertical glacier front induced by an intermediary circulation forced by periodic density variations at the mouth of a fjord is investigated using a nonhydrostatic ocean general circulation model and idealized laboratory experiments the idealized configurations broadly match that of sermilik fjord southeast greenland a largely two layers system characterized by strong seasonal variability of subglacial discharge consistent with observations the numerical results suggest that the intermediary circulation is an effective mechanism for the advection of shelf anomalies inside the fjord in the numerical simulations the advection mechanism is a density intrusion with a velocity which is an order of magnitude larger than the velocities associated with a glacier driven circulation in summer submarine melting is mostly influenced by the discharge of surface runoff at the base of the glacier and the intermediary circulation induces small changes in submarine melting in winter on the other hand submarine melting depends only on the water properties and velocity distribution at the glacier front hence the properties of the waters advected by the intermediary circulation to the glacier front are found to be the primary control of the submarine melting when the density of the intrusion is intermediate between those found in the fjord s two layers there is a significant reduction in submarine melting on the other hand when the density is close to that of the bottom layer only a slight reduction in submarine melting is observed the numerical results compare favorably to idealized laboratory experiments with a similar setup

rock mass response model for circular openings the main parameters affecting the failure and deformation state of the rock mass around a circular opening are the level of vertical and horizontal in situ stresses the characteristics of the rock mass the diameter of the opening and the support pressure the influence of all these parameters on the stress induced final deformations around circular openings was investigated by a finite difference based two dimensional numerical simulation for both hydrostatic and nonhydrostatic stress field conditions from the results of the parametric studies the variation of tunnel strain versus the ratio of uniaxial compressive strength of the rock mass to in situ vertical stress and the ratio of radial support pressure to in situ vertical stress for fair quality and poor quality rock masses was statistically analysed as a result of the three dimensional nonlinear regression analysis and surface curve fitting process by means of a large number of models a best fit model with the best correlation with these dimen