basal conditions and ice dynamics inferred from radar derived internal stratigraphy of the northeast greenland ice stream we analyze the internal stratigraphy in radio echo sounding data of the northeast greenland ice stream to infer past and present ice dynamics in the upper reaches of the ice stream we propose that shear margin steady state folds in internal reflecting horizons irhs form due to the influence of ice flow over spatially varying basal lubrication irhs are generally lower in the ice stream than outside likely because of greater basal melting in the ice stream from enhanced geothermal flux and heat of sliding strain rate modeling of irhs deposited during the holocene indicates no recent major changes in ice stream vigor or extent in this region downstream of our survey irhs are disrupted as the ice flows into a prominent overdeepening when combined with additional data from other studies these data suggest that upstream portions of the ice stream are controlled by variations in basal lubrication whereas downstream portions are confined by basal topography

weak bed control of the eastern shear margin of thwaites glacier west antarctica recent acceleration and thinning of thwaites glacier west antarctica motivates investigation of the controls upon and stability of its present ice flow pattern its eastern shear margin separates thwaites glacier from slower flowing ice and the southern tributaries of pine island glacier troughs in thwaites glacier s bed topography bound nearly all of its tributaries except along this eastern shear margin which has no clear relationship with regional bed topography along most of its length here we use airborne ice penetrating radar data from the airborne geophysical survey of the amundsen sea embayment antarctica agasea to investigate the nature of the bed across this margin radar data reveal slightly higher and rougher bed topography on the slower flowing side of the margin along with lower bed reflectivity however the change in bed reflectivity across the margin is partially explained by a change in bed roughness from these observations we infer that the position of the eastern shear margin is not strongly controlled by local bed topography or other bed properties given the potential for future increases in ice flux farther downstream the eastern shear margin may be vulnerable to migration however there is no evidence that this margin is migrating presently despite ongoing changes farther downstream

predicting radar attenuation within the antarctic ice sheet abstract to better understand the ability of ice penetrating radar to diagnose the subglacial environment from bed returned power we model the englacial radar attenuation of antarctic ice first we use a one dimensional thermo mechanical model to evaluate the sensitivity of the depth averaged attenuation rates to ice temperature as a function of surface accumulation rate geothermal flux and ice thickness we find that attenuation is most sensitive to variations in geothermal flux and accumulation rate when the bed temperature is close to the pressure melting point but even if geothermal flux and accumulation rate remain fixed attenuation can easily vary with ice thickness such high sensitivities show that one should not assume a uniform attenuation rate in the radar data analysis then using ensembles of modeled ice temperatures with different boundary conditions we generate multiple attenuation predictions for the antarctic ice sheet and evaluate the resulting uncertainties the largest contributor to uncertainty in these predictions is the geothermal flux this uncertainty is localized within the deeper half of the ice sheet by combining these temperature ensembles with ice core chemistry data we show that the sea salt adds little to the attenuation but the contribution from acids accounts for 29 inland to 53 coast of the total attenuation we conclude that improving radar diagnosis of the subglacial environment using bed returned power requires both 1 better data interpretation algorithms that account for attenuation variations and 2 better constraints of geothermal flux and bulk chemistry

radar characterization of the basal interface across the grounding zone of an ice rise promontory in east antarctica radar power returned from the basal interface along a 42 km long profile over an ice rise promontory and the adjacent roi baudouin ice shelf dronning maud land east antarctica is analyzed to infer spatial variations in basal reflectivity and hence the basal environment extracting basal reflectivity from basal returned power requires an englacial attenuation model we estimate attenuation in two ways 1 using a temperature dependent model with input from thermomechanical ice flow models and 2 using a radar method that linearly approximates the geometrically corrected returned power with ice thickness the two methods give different results we argue that attenuation calculated using a modeled temperature profile is more robust than the widely used radar method especially in locations where depth averaged attenuation varies spatially or where the patterns of basal reflectivity correlate with the patterns of the ice thickness

three dimensional flow influences on radar layer stratigraphy variations in the depth of radar detectable englacial layers isochrones are commonly used to assess past variability in accumulation rates but little is known about the effect of internal and basal flow variations on isochrone deflections e g bumps troughs in this paper we show how the isochrones are affected by such variation using a three dimensional flow model to investigate changes in the flow mode and in increased basal melting we also investigate how transverse flows with lateral velocity gradients affect the development of isochrones we use the model to visualize how such variations will be seen in radar lines which cross the flow direction we show that in the presence of lateral gradients in the flow field we can produce bumps and troughs when viewed along transects perpendicular to the flow the model results show that the influences of flow convergence melting and changes in flow mode when coupled together affect isochrones over the whole depth of the ice sheet finally changes in the near surface layers cannot be solely attributed to spatial variation in the accumulation rate there can also be a strong signal from changes in the flow mode

dilatant till facilitates ice stream flow in northeast greenland abstract we present radio echo sounding res global positioning system gps and active source seismic data across the central portion of the northeast greenland ice stream negis negis widens downglacier from a small region of high geothermal flux near the ice divide our data reveal high porosity 40 water saturated till lubricating the ice stream ice accelerates and thins as it flows into negis producing marginal troughs in surface topography these troughs create steep gradients in the subglacial hydropotential that generate parallel sticky and slippery bands beneath the shear margins the low porosity sticky sediment bands limit ice entrainment across the margins and thus restrict further widening producing the long narrow and relatively stable ice stream however the observed relations among surface elevation basal water routing broad sedimentary drape and till dilatancy suggest that rapid shifts in ice dynamics are possible including rapid transmission of ocean forcing inland the source and routing of the subglacial till are unclear but our data help constrain hypotheses

the basal stress distribution of ice stream e antarctica inferred by control methods the irregular spatial distribution and velocity independence of basal friction derived from landsat measured surface velocity suggests that ice stream flow is not controlled by the properties of a deformable basal till alone rigid bedrock substrata may contact the base of the ice stream in small 100 km2 areas where the velocity field displays strong vorticity and where the ice stream surface appears rumpled in landsat images

deformation induced melting in the margins of the west antarctic ice streams flow of glacial ice in the west antarctic ice sheet localizes in narrow bands of fast flowing ice streams bordered by ridges of nearly stagnant ice but our understanding of the physical processes that generate this morphology is incomplete here we study the thermal and mechanical properties of ice stream margins where flow transitions from rapid to stagnant over a few kilometers our goal is to explore under which conditions the intense shear deformation in the margin may lead to deformation induced melting we propose a 2 d model that represents a cross section through the ice stream margin perpendicular to the downstream flow direction we limit temperature to the melting point to estimate melt rates based on latent heat using rheology parameters as constrained by laboratory data and observations we conclude that a zone of temperate ice is likely to form in active shear margins

basal shear stress of the ross ice streams from control method inversions 1 we used control method inversions to determine the basal shear stress beneath the ross ice streams where new high resolution velocity data sets have recently become available the inversion algorithm was adapted from an earlier viscous bed algorithm to allow solution for the basal shear stress corresponding to a weak plastic bed we performed several experiments using synthetic data to determine the quality of the inversions these experiments indicate that with high quality surface elevation data e g errors 5 m the inversions are relatively robust with respect to errors in ice flow velocity and bed topography the inversions are consistent with seismic and borehole observations and indicate that the ross ice streams lie atop a bed that is nearly everywhere weak in contrast the tributaries feeding these ice streams overlie alternating patches of strong and weak bed

intraseasonal variability in the equatorial atlantic west africa during march june intraseasonal 30 80 days variability in the equatorial atlantic west african sector during march june is investigated using various recently archived satellite measurements and the ncep doe amip ii reanalysis daily data the global connections of regional intraseasonal signals are first examined for the period of 1979 2006 through lag regression analyses of convection olr and other dynamic components against a regional intraseasonal convective olr index the eastward propagating features of convection can readily be seen accompanied by coherent circulation anomalies similar to those for the global tropical intraseasonal mode i e the madden julian oscillation mjo the regressed trmm rainfall 3b42 anomalies during the trmm period 1998 2006 manifest similar propagating features as for the regressed olr anomalies during 1979 2006 these coherent features hence tend to suggest that the regional intraseasonal convective signals might be mostly a regional response to or closely associated with the mjo and probably contribute to the mjo s global propagation atmospheric and surface intraseasonal variability during march june of 1998 2006 are further examined using the high quality trmm microwave imager tmi sea surface temperature sst columnar water vapor and cloud liquid water and the quikscat oceanic winds 2000 2006 enhanced suppressed convection or positive negative rainfall anomalies approximately cover the entire basin 0 10 n 30 w 10 e during the passage of intraseasonal convective signals accompanied by anomalous surface westerly easterly flow furthermore a unique propagating feature seems to exist within the tropical atlantic basin rainfall anomalies always appear first in the northwestern basin right off the coast of south america and gradually extend eastward to cover the entire basin a dipolar structure of rainfall anomalies with cross equatorial surface wind anomalies can thus be observed during this evolution similar to the anomaly patterns on the interannual time scale discovered in past studies coherent intraseasonal variations and patterns can also be found in other physical components

draping or overriding the effect of horizontal stress gradients on internal layer architecture in ice sheets internal isochronic layers in ice sheets sensed by radar show two characteristic relationships to the basal topography either they override it with layers above the crests of rises lying essentially flat or they drape over it with the layers following rises and falls in basal topography a mechanical theory is presented which shows that overriding is the expected behavior when topographic wavelengths are comparable with or less than the ice thickness while draping occurs at longer wavelengths this is shown with analytical perturbation solutions for newtonian fluids numerical perturbation solutions for nonlinear fluids and finite element solutions for nonlinear fluids and large amplitude variations bed variation from topography and changes in the basal boundary condition are considered for fixed bed and sliding beds as well as three dimensional flows and thermomechanically coupled flows in all cases the dominant effect on draping overriding is the wavelength of the topography or variation in basal boundary conditions results of these full mechanical system calculations are compared with those from the shallow ice approximation and the longitudinal stress approximation some calculations are carried out for zero accumulation where the age of the ice and therefore isochrone geometry is not defined it is shown that there is a close relationship between isochrones and streamlines and that they behave similarly when bed wavelength divided by the ice thickness is small compared with the ratio of ice velocity and accumulation rate which is a useful approximation numerical comparisons of isochrones and streamlines show them to be virtually coincident

subglacial hydrology and ice stream margin locations fast flowing ice streams in west antarctica are separated from the nearly stagnant ice in the adjacent ridge by zones of highly localized deformation known as shear margins it is presently uncertain what mechanisms control the location of shear margins and possibly allow them to migrate in this paper we show how subglacial hydrological processes can select the shear margin location leading to a smooth transition from a slipping to a locked bed at the base of an ice stream our study uses a two dimensional thermomechanical model in a cross section perpendicular to the direction of flow we confirm that the intense straining at the shear margins can generate large temperate regions within the deforming ice assuming that the melt generated in the temperate ice collects in a drainage channel at the base of the margin we show that a channel locally decreases the pore pressure in the subglacial till therefore the basal shear strength just outside the channel assuming a coulomb plastic rheology can be substantially higher than that inferred under the majority of the stream results show that the additional basal resistance produced by the channel lowers the stress concentrated on the locked portion of the bed matching the model to surface velocity data we find that shear margins are stable when the slipping to locked bed transition occurs less than 500 m away from a channel operating at an effective pressure of 200 kpa and for a hydraulic transmissivity equivalent to a basal water film of order 0 2 mm thickness

radar attenuation and temperature within the greenland ice sheet 2015 american geophysical union all rights reserved the flow of ice is temperature dependent but direct measurements of englacial temperature are sparse the dielectric attenuation of radio waves through ice is also temperature dependent and radar sounding of ice sheets is sensitive to this attenuation here we estimate depth averaged radar attenuation rates within the greenland ice sheet from airborne radar sounding data and its associated radiostratigraphy using existing empirical relationships between temperature chemistry and radar attenuation we then infer the depth averaged englacial temperature the dated radiostratigraphy permits a correction for the confounding effect of spatially varying ice chemistry where radar transects intersect boreholes radar inferred temperature is consistently higher than that measured directly we attribute this discrepancy to the poorly recognized frequency dependence of the radar attenuation rate and correct for this effect empirically resulting in a robust relationship between radar inferred and borehole measured depth averaged temperature radar inferred englacial temperature is often lower than modern surface temperature and that of a steady state ice sheet model particularly in southern greenland this pattern suggests that past changes in surface boundary conditions temperature and accumulation rate affect the ice sheet s present temperature structure over a much larger area than previously recognized this radar inferred temperature structure provides a new constraint for thermomechanical models of the greenland ice sheet

antarctic subglacial conditions inferred from a hybrid ice sheet ice stream model abstract subglacial conditions of large polar ice sheets remain poorly understood despite recent advances in satellite observation major uncertainties related to basal conditions such as the temperature field are due to an insufficient knowledge of geothermal heat flow here a hybrid method is presented that combines numerical modeling of the ice sheet thermodynamics with a priori information using a simple assimilation technique additional data are essentially vertical temperature profiles measured in the ice sheet at selected spots as well as the distribution of subglacial lakes in this way geothermal heat flow datasets are improved to yield calculated temperatures in accord with observations in areas where information is available results of the sensitivity experiments show that 55 of the grounded part of the antarctic ice sheet is at pressure melting point calculated basal melt rates are approximately 65 gt year 1 which is 3 of the total surface accumulation although these sensitivity experiments exhibit small variations in basal melt rates the impact on the ice age of basal layers is quite important in areas that are characterized by relatively low melt rates this may lead to standard deviations up to 50 in a model run over a period of 10 6 years subglacial water flow is concentrated underneath the large outlet glaciers of antarctica the larger subglacial lakes are perched at the head of these subglacial water systems an exception however is the lake system of the recovery ice stream catchment that receives a substantial amount of subglacial melt water from the upstream catchment

thermally driven migration of ice stream shear margins ice stream shear margins are the lateral boundaries of narrow fast flowing bands of ice within an ice sheet we develop a theory for the migration of shear margins over time driven by viscous dissipation of heat within the ice focusing on widening of the ice stream the location of the margin is modelled as a transition from a cold to a temperate ice sheet bed and simultaneously as the transition from no slip to free slip at the same location the temperature field in the ice is affected by intense shear heating as well as by the migration velocity of the margin i e by the widening rate of the ice stream if migration is too fast there is little time for the ice to warm up and the margin remains cold causing the bed to freeze this suppresses widening conversely if the migration speed is too slow the ice in the margin warms up causing the bed on the far side of the cold temperate transition to reach the melting point and migration to speed up using a wiener hopf method we show that for a given far field shear stress geothermal heat flux and ice geometry there is a single migration velocity that balances the two effects and permits widening at a steady rate this velocity increases with the far field lateral shear stress imposed by the ice stream which controls shear heating in the margin our results also indicate that i a region of temperate ice must form in the margin and that ii lateral advection of ice may play a significant role in controlling migration speeds

subglacial hydrology as a control on emergence scale and spacing of ice streams observations have long associated ice streams with the presence of meltwater at the bed more recently theoretical models have been able to reproduce ice stream behavior as a consequence of the coupled dynamics of ice and subglacial meltwater in this paper we analyze the properties of ice streams that form in a coupled model of ice flow and subglacial hydrology we see that there is a natural length scale defining ice stream separation and width this arises as a result of the balance between effective pressure gradients driving meltwater away from ice streams and the enhanced water production in the streams due to the fast ice flow we further discuss how the model interacts with topography and we show that small perturbations to a uniform bed have a strong effect on where ice streams emerge in the model however in many cases ice streams then evolve to be closer to the dimensions defined by the natural length scale of the unperturbed system the nondimensional parameter that defines this length scale is therefore of fundamental importance in the model

a full stokes flow thermo mechanical model for firn and ice applied to the gorshkov crater glacier kamchatka the gorshkov crater glacier at ushkovsky volcano kamchatka is characterized by a large aspect ratio and special thermodynamic conditions at the bedrock caused by a locally enhanced and spatially varying geothermal heat flux furthermore large parts of this glacier consist of firn rather than pure ice which alters the rheological properties such as viscosity and compressibility of the glacier we present a newly developed thermo mechanically coupled three dimensional flow model based on the finite element fe modeling software elmer and apply it to the gorshkov crater glacier by assuming steady state conditions the present day velocity field temperature field basal melting rate and age distribution are simulated we find that flow velocities are generally small 10 s of centimeters per year horizontal and vertical velocities are of comparable magnitude which shows that the shallow ice approximation is not applicable owing to the spatially variable volcanic heat flux the thermal regime at the ice base is cold in the deeper parts of the glacier and temperate in the shallower parts the measured temperature profile and age horizons at the k2 borehole are reproduced quite well and remaining discrepancies may be attributed to transient non steady state conditions firn compressibility is identified as a crucial element for the modeling approach

shear heating and weakening of the margins of west antarctic ice streams ice streams are fast flowing bands of ice separated from stagnant ridges by shear margins the mechanisms controlling the location of the margins remain unclear we use published ice deformation data and a simple one dimensional thermal model to show that west antarctic ice stream margins have temperate ice over a substantial fraction of their thickness a condition that may control their width the model predicts a triple valued relation between the thickness averaged lateral shear stress and the lateral shear strain rate observed strain rates at the margins imply that they support slightly less lateral shear stress than adjacent ice within the stream this requires enhanced basal resistance near the margin we suggest in agreement with the limited observations the presence of a channelized drainage system at the margin that reduces the pore fluid pressure at the ice till interface thus increasing the shear stress acting on the yielding coulomb plastic bed

sequential stagnation of kamb ice stream west antarctica 1 ice penetrating radar data confirm the presence of two relict northern margins of kamb ice stream kis west antarctica in an area called the duckfoot between the two relict margins deep layers are preserved and buried crevasses remain at a constant depth until roughly 1 5 km from the innermost youngest margin suggesting that this outer portion of the ice stream stagnated suddenly 10 years stagnation was likely accomplished through changes in basal conditions i e reduced lubrication beneath this outer portion of the ice stream and resulted in a narrowing of the ice stream trunk by 27 and a reduction in flow speed 200 years prior to complete stagnation flowstripe deformation as a result of duckfoot stagnation provides an estimate of kis paleo velocity of 210 m a after duckfoot stagnation

subsidence structures associated with subaerial desiccation crack piping and their role in drainage evolution on a drained proglacial lake bed hagavatn iceland abstract a range of subsidence structures associated with desiccation crack piping are described from the drained proglacial lake bed of hagavatn iceland subsurface drainage along desiccation cracks leads to the formation of small scale subsidence structures these subsidence structures include linear fissures located along the limbs of desiccation cracks and crater like depressions that form at crack intersections the controls on subsurface piping are discussed and the role of these subsidence structures in determining the pattern of surface drainage on the former lake bed is identified preservation potential of these sedimentary structure is considered to be high given renewed lacustrine sedimentation the potential for similar structures to be found in the geological record is considered likely and consequently these structures may be of importance in the interpretation of crack networks in the geological record as being of subaerial as opposed to subaqueous origin

a boundary layer model for ice stream margins the majority of antarctic ice is discharged via long and narrow fast flowing ice streams at ice stream margins the rapid transition from the vertical shearing flow in the ice ridges surrounding the stream to a rapidly sliding plug flow in the stream itself leads to high stress concentrations and a velocity field whose form is non trivial to determine in this paper we develop a boundary layer theory for this narrow region separating a lubrication type ice ridge flow and a membrane type ice stream flow this allows us to derive jump conditions for the outer models describing ridge and stream self consistently much of our focus is however on determining the velocity and shear heating fields in the margin itself ice stream margins have been observed to change position over time with potentially significant implications for ice stream discharge our boundary layer model allows us to extend previous work that has determined rates of margin migration from a balance between shear heating in the margin and the cooling effect of margin migration into the colder ice of the surrounding ice ridge solving for the transverse velocity field in the margin allows us to include the effect of advection due to lateral inflow of ice from the ridge on margin migration and we demonstrate that this reduces the rate of margin migration as previously speculated

tracing the depth of the holocene ice in north greenland from radio echo sounding data radio echo sounding surveys over the greenland ice sheet show clear extensive internal layering and comparisons with age depth scales from deep ice cores allow for dating of the layering along the ice divide we present one of the first attempts to extend the dated layers beyond the ice core drill sites by locating the depth of the bolling allerod transition in 400 flight lines using an automated fitting method results show that the transition is located in the upper one third of the ice column in the central part of north greenland while the transition lowers towards the margin this pattern mirrors the present surface accumulation and also indicates that a substantial amount of pre holocene ice must be present in central north greenland

thermal effects on the location of ice stream margins west antarctic ice streams move rapidly over beds that are thawed by heat generated by the motion intervening zones of slow moving ice are probably freezing at their bases where heat generation is absent heat is also generated in the shear zone between the slow and fast moving ice through modeling of coupled heat and mass flow we show that the position of the boundary between freezing and melting at the bed is unstable for an otherwise morphologically uniform bed above a threshold speed in the ice stream heat generation in the shear zone allows melting beneath the slow ice and possible widening of the stream below this threshold heat generation at the edge of the thawed zone is insufficient to maintain melting leading to freezing and narrowing of the stream the threshold speed appears to be a function of the temperature at the base of slow ice relative to the melting point and is also highly sensitive to the inflow of colder ice from the slow zone for environmental conditions typical of west antarctica the threshold speed is about 100 m yr 1 in the absence of inflow and increases to typical ice stream speeds 500 m yr 1 for inflow speeds of a few meters per year thus the ice streams can be in a delicate thermal balance with the potential of melting outward or freezing inward rapidly moving ice streams could expand unless blocked by bed properties that would prevent fast motion even when there is melting at the bed

bed radar reflectivity across the north margin of whillans ice stream west antarctica and implications for margin processes surface based ice penetrating radar profiles were made across the active north margin the snake of the upper part of whillans ice stream formerly ice stream b branch b2 west antarctica at three locations low frequency about 2 mhz and the ground deployment of the radar allowed penetration through the near surface zone of fracturing to detect internal layering and bed reflection characteristics on continuous profiles spanning from the slow moving ice of engelhardt ridge well into the chaotic zone of the shear margin internal layers were tracked beneath the chaotic zone where they are warped but remain continuous the energy returned from internal layers showed no systematic changes associated with the transition from the undisturbed surface of the slow moving ice into the fractured surface of the shear margin thus indicating little effect from the surface crevasses on the penetration of the radar signal based on this calibration of the near surface effects and corrections for path length spreading and attenuation we examine the spatial variation of bed reflectivity low bed reflectivity found under engelhardt ridge extends under the chaotic zone of the margin into fast moving ice we argue that the fast motion in a band along the margin is mediated by processes other than deformation of thick dilated till that is the source of lubrication allowing fast motion in the interior of the ice stream

influence of subglacial geology on the position of a west antarctic ice stream from seismic observations ice streams drain much of the interior west antarctic ice sheet and buffer the main ice reservoir from oceanic influences1 2 the slow flowing interior feeds the floating ross ice shelf with ice via fast flowing ice streams3 that are believed to modulate sea level change through their control of inland ice storage understanding ice stream behaviour and predicting the response to climate change4 requires a better knowledge of the subglacial geology5 6 it is known that a thawed ice bed and high pressure basal water are necessary but not sufficient conditions to cause ice streaming7 8 moreover it has been hypothesized that a soft sedimentary bed is also required because of its intrinsic low frictional resistance to flow9 and owing to its high erodibility so as to generate till that can deform and lubricate ice motion10 11 or to bury rough features and smooth the bed for sliding here we use seismic observations to provide evidence that one margin of the upglacier part of an ice stream is directly above the boundary of a basin with such sedimentary fill the ice stream is within the basin and the ice outside the basin is slow flowing the basin fill presents an order of magnitude lower frictional resistance to ice flow than the subglacial material outside the basin we conclude that the ice stream position is dependent on subglacial geology

primary aerosol sea salt and soil dust deposited in greenland ice during the last climatic cycle comparison with east antarctic records ion chromatography data of ca mg cl and ca and coulter counter particle measurements are used to study the cycle of marine and continental primary aerosol reaching greenland in relation to climatic changes over the last 150 kyr a detailed comparison between greenland dome summit and antarctic vostok records provides new insight on a potential link between northern and southern patterns ca is a good indicator of continental input and is mainly emitted as caco3 an attempt is made to estimate the contribution of aluminosilicates using the concentration of insoluble particles greater than 0 5 m in diameter the relative abundance of non sea salt mg and ca and of aluminosilicate shows that the calcium content of continental background aerosol over greenland was much higher during the glacial age the neutralization capacity of carbonaceous aerosol is estimated the inverse relationship between 18o and continental input as well as the response of this input to the rapid climatic variations that have occurred during the second part of the glacial age are discussed in terms of source and transport modification in relation to the presence and the extent of the great laurentide ice cap the corresponding vostok profiles strongly suggest that some of the phenomena observed at high northern latitudes are of global concern the marine component of na nam is a good tracer of sea salt aerosol similarly to continental input it shows an inverse but more linear relationship with 18o the sensitivity of greenland and antarctic marine input to climate variations of small and large amplitude is compared and a corresponding estimation is made for the aeolian contribution the respective influence of atmospheric circulation and the water vapor cycle is discussed the chlorine to marine sodium weight ratio increases with temperature from values very close to the bulk seawater ratio during the last glacial maximum 18 20 kyr b p to values significantly higher during the holocene and warm eemian the corresponding excess of chloride hcl is discussed in terms of atmospheric transport taking into account the role of atmospheric acidity on sea salt fractionation processes owing to postdepositional phenomena similar vostok data must be considered cautiously nevertheless aerosol fractionation seems to have been much more important over the vostok site except during glacial extrema