surface energy balance and melt thresholds over 11 years at taylor glacier antarctica 11 years ablation 18 cm a 1 was dominated by sublimation with very few occurrences of melt 42 days during 11 years results also indicated that above freezing air temperatures did not necessarily result in melt and in turn melt occurred during subfreezing air temperatures under some conditions for air temperatures near freezing low wind speed was critically important for melt initiation according to the model subsurface melt away from rocks and sediment in the ice occurred three times more frequently than surface melt occurs no deeper than 50 cm below the glacier surface and was small never exceeding 8 by mass the magnitude of subsurface melting and the energy balance indicate that taylor glacier ice is intermediate in optical properties between snow and blue ice

debris flows and water tracks in northern victoria land continental east antarctica a new terrestrial analogue site for gullies and recurrent slope lineae on mars although the present environmental conditions on mars prohibit the generation of significant volumes of liquid water observations of several very young landforms such as gullies and recurrent slope lineae have been interpreted as signals for aqueous processes to explore the range of conditions under which such features can be formed on earth a field site in northern victoria land east antarctica was geomorphologically investigated despite the small size of the icefree area the site displays gullies water tracks and other traces of liquid water the gullies show clear evidence of sediment transport by debris flows and are typical of paraglacial processes on steep slopes in a recently deglaciated area water tracks appear in different forms and seem to recur seasonally in the austral summer melting of snow and surface glacier ice is the major water source for both debris flows and water tracks the observations presented here highlight the potential for hyperarid polar deserts to generate morphogenetically significant amounts of meltwater the gullies are morphologically analogous to martian gullies and water tracks on steep slopes appear very similar to recurrent slope lineae the observations suggest that even small icefree sites in continental antarctica may enable observations which can serve as a basis for working hypotheses in mars analogue studies and future field work should consider more areas in antarctica in addition to the mcmurdo dry valleys to search for mars analogue landforms

reconciling astrochronological and 40ar 39ar ages for the matuyama brunhes boundary and late matuyama chron when five matuyama brunhes m b boundary records from the north atlantic are placed on isotope age models produced by correlation of the 18o record directly or indirectly to an ice volume model the m b boundary lies consistently at the young end of marine isotope stage 19 with a mean age for the midpoint of the reversal of 773 1 ka standard deviation 0 4 kyr 7 kyr younger than the presently accepted astrochronological age for this polarity reversal 780 781 ka two recently proposed revisions of the age of the 40ar 39ar fish canyon sanidine fcs standard to 28 201 0 046 ma and 28 305 0 036 ma would adjust 40ar 39ar ages applicable to the m b boundary and other reversals and excursions back to 1 2 ma to ages older than the new astrochronological ages by 8 24 kyr the variables used to construct the ice volume models cannot account for the discrepancy the fcs standard age that best fits the astrochronological ages is 27 93 ma which is within the uncertainty associated with the commonly used value of 28 02 0 16 ma but younger than the recently proposed fcs ages the edc2 and edc3 age models in the dome c antarctic ice core yield ages of 771 7 ka and 766 4 ka respectively for the 10be flux peak that denotes the paleointensity minimum at the reversal boundary implying that the edc2 rather than edc3 age model is consistent with the observations from marine sediments at least close to the m b boundary

evolution of ocean island rifts the northeast rift zone of tenerife canary islands the northeast rift zone of tenerife presents a superb opportunity to study the entire cycle of activity of an oceanic rift zone field geology isotopic dating and magnetic stratigraphy provide a reliable temporal and spatial framework for the evolution of the ne rift zone which includes a period of very fast growth toward instability between ca 1 1 and 0 83 ma followed by three successive large landslides the micheque and guimar collapses which occurred approximately contemporaneously at ca 830 ka and on either side of the rift and the la orotava landslide between 690 10 and 566 13 ka our observations suggest that canarian rift zones show similar patterns of development which often includes overgrowth instability and lateral collapses collapses of the rift flanks disrupt established fissural feeding systems favoring magma ascent and shallow emplacement which in turn leads to magma differentiation and intermediate to felsic nested eruptions rifts and their collapses may therefore act as an important factor in providing architectural and petrological variability to oceanic volcanoes conversely the presence of substantial felsic volcanism in rift settings may indicate the presence of earlier landslide scars even if concealed by postcollapse volcanism comparative analysis of the main rifts in the canary islands outlines this general evolutionary pattern 1 growth of an increasingly high and steep ridge by concentrated basaltic fissure eruptions 2 flank collapse and catastrophic disruption of the established feeder system of the rift 3 postcollapse centralized nested volcanism commonly evolving from initially ultramafic mafic to terminal felsic compositions trachytes phonolites and 4 progressive decline of nested eruptive activity

the surface accumulation and ablation of a coastal blue ice area near cap prudhomme terre adelie antarctica a record of accumulation and ablation from a network of 47 stakes at a coastal blue ice area in terre adelie antarctica is presented and analyzed the record covers early 2004 to early 2006 from 25 field surveys including some in austral winter the two years are very different with a virtually null surface mass balance during the 2004 winter but large accumulation during the 2005 winter a snow ice energy and mass balance model is used to reproduce the accumulation and ablation record a parameterization for snow erosion by wind is included input meteorology is from the european centre for medium range weather forecasts ecmwf analyses and forecasts corrected using 1 year of local meteorological observations from an automatic weather station model results agree reasonably well with the observations wind erosion is the largest contributor to ablation removing much of the precipitation sublimation and to a lesser extent melt runoff together account for 60 cm w e of ablation in 2 years mainly in summer although the record is short it confirms high interannual variability and thus high sensitivity to meteorology and climate monitoring and understanding the mass balance of such coastal blue ice areas may help monitor and detect climate change in the antarctic coastal regions

geographical distribution of transitional vgps evidence for non zonal equatorial symmetry during the matuyama brunhes geomagnetic reversal abstract paleomagnetic records of the matuyama brunhes polarity reversal obtained recently from the northern equatorial and southern latitudes of the atlantic sector display a distinct symmetry with respect to the equator the virtual geomagnetic pole vgp paths from the mid latitude sites in the northern and southern hemispheres dsdp site 609 and core v16 58 are nearly coincident tracking northward through the americas the vgp path from the equatorial site odp site 664 tracks northward through eastern asia nearly antipodal to the other two paths modeling results indicate that superimposing an h 1 3 geometry onto a reversing axial dipole explains the sense of equatorial symmetry exhibited by these three records these results are consistent with the bulk of the data available from other records of this polarity transition suggesting that the transitional vgps during this reversal tend to fall along two distinct longitudinal bands the grouping of transitional vgps suggests that there is a strong geographical control over the reversal process an apparent correlation between the longitudinal bands of transitional vgps and the location of the major flux concentrations in the radial component of the historical geomagnetic field at the core mantle boundary 1 suggests that the processes which cause these flux concentrations may have influenced the geometry of the matuyama brunhes transitional field

cirque infills in the khibiny mountains kola peninsula russia palaeoglaciological interpretations and modern analogues in east antarctica we report here on cirque infills mapped in the khibiny mountains kola peninsula russia cirque infills are morainic deposits located near the headwalls of valleys and cirques their location and shape often with concave margins towards the valley side indicate that they were deposited by ice flowing up valley into the mountains rather than by local glaciers we suggest that they formed during the last deglaciation when khibiny was a nunatak and fennoscandian ice sheet lobes extended into valleys and cirques of the massif the formation of cirque infills is probably more related to ice sheet dynamic factors occurring when the ice margin retreated from the cirques than to climate driven interruption in the ice marginal retreat glacial conditions similar to those prevalent when the khibiny cirque infills were formed occur today in antarctica where the ice sheets engulf nunatak ranges in heimefrontfjella antarctica the formation of supraglacial moraines at the head of cirques are linked to blue ice conditions indicating locally low accumulation rates a dry continental climate and sublimation dominated ablation we suggest that these antarctic moraines are modern analogues of cirque infills on the kola peninsula and possibly that the cirque infills may be used as palaeoenvironmental indicators copyright 2007 john wiley sons ltd

detailed observations of the rippled surface of antarctic blue ice areas this paper presents detailed observations of the regularly rippled surface on an antarctic blue ice area near svea at five sites the wavelength of the ripples was found to be 20 24 cm while the wave height crest trough was 1 2 cm the ripple crests are generally oriented perpendicular to the direction of the strongest winds repeated measurements show that wave heights increase throughout the summer with most ablation occurring in the wave troughs this implies that traditional methods of measuring ablation such as stakes when a rod on the ice surface is used to define a mean surface height tend to underestimate total ablation because they sample only crests one site exhibited significant migration of the surface ripples of about 2 cm month 1 in the downwind direction whereas three other sites showed no significant wave movement the formation and the specific characteristics of the surface ripples are most likely caused by self amplifying interaction mechanisms between the free ice surface and the overlying turbulent atmosphere which necessarily involve spatial variations in sublimation a simple model was used to quantify the interaction between the surface ripples the airflow aloft and the sublimation rate the model is able to predict wavelengths and migration rates that are in reasonable agreement with the observations

mapping blue ice areas in antarctica using etm and modis data blue ice areas bias and their geographical distribution in antarctica were mapped using landsat 7 etm images with 15 m spatial resolution obtained during the 1999 2003 austral summers and covering the area north of 82 58 s and a snow grain size image of the modis based mosaic of antarctica moa dataset with 125 m grid spacing acquired during the 2003 04 austral summer from 82 58 s to the south pole a map of bias was created with algorithms of thresholds based on band ratio and reflectance for etm data and thresholds based on snow grain size for the moa dataset the underlying principle is that blue ice can be separated from snow or rock by their spectral discrepancies and by different grain sizes of snow and ice we estimate the total area of bias in antarctica during the data acquisition period is 234 549 km 2 or 1 67 of the area of the continent blue ice is scattered widely over the continent but is generally located in coastal or mountainous regions the bia dataset presented in this study is the first map covering the entire antarctic continent sourced solely from etm and modis data this dataset can potentially benefit other studies in glaciology meteorology climatology and paleoclimate meteorite collection and airstrip site selection

abrupt cold spells in the northwest mediterranean hitherto unknown abundance peaks of left coiling l c neogloboquadrina pachyderma from a gulf of lions piston core indicate that abrupt cold spells associated with atlantic heinrich events affected the mediterranean n pachyderma l c is typical of sub polar waters in the open ocean the southern edge of its glacial north atlantic bioprovince reached south portugal only trace abundances of n pachyderma l c are known from quaternary mediterranean sediments suggesting that no significant invasions occured via the strait of gibraltar the gulf of lions abundance peaks therefore seem to reflect area specific thriving of a normally rare but indigenous taxon in the western mediterranean through local favorable habitat development the general planktonic foraminiferal record suggests that the basic hydrographic regime in the gulf of lions with wintertime deep convective overturn was relatively stable over the past 60 kyr under these conditions high abundances of n pachyderma l c would essentially imply temperature reductions of the order of 5 8 relative to the present

age of allan hills 82102 a meteorite found inside the ice the recovery of thousands of meteorites in the antarctic since 1969 has not only greatly increased knowledge of the meteorites themselves but has also provided a new tool for glaciology most antarctic meteorites are found on blue ice areas where old ice is continuously ablated a measurement of the age of this ice helps us understand meteorite accumulation mechanisms and the dynamics of ice movement the terrestrial age of a meteorite the time period since the date of meteorite fall can be determined from the reduction in concentration of cosmogenic radionuclides during the time the meteorite has been shielded by the earth s atmosphere here we report the terrestrial age of a meteorite that was recovered from below the surface of the ice and argue that this represents a measurement of the age of the ice itself we measured the cosmogenic radionuclides 10be half life 1 5 myr 14c 5 730 yr 26a1 0 71 myr 36c1 0 30 myr and 53mn 3 7 myr in the meteorite and 10be and 36c1 in the ice we obtained a terrestrial age of 11 000 years for the meteorite which suggests that the snow accumulation area where it fell was only a few tens of kilometres away

a combined paleomagnetic dating investigation of the upper jaramillo transition from a volcanic section at tenerife canary islands abstract a coupled paleomagnetic dating investigation has been conducted on a sequence of 25 successive lava flows emplaced during the upper transition of the jaramillo subchron in tenerife canary islands this sequence is located along the western wall of the guimar collapse scar in the south central part of the island nine flows distributed throughout this sequence were dated using unspiked k ar and 40 ar 39 ar methods they bracket the section between 1009 22 ka and 971 21 ka 2 a first group of 8 flows at the bottom of the sequence is characterized by normal polarity with paleointensity values of the order of present day field intensity in the canary islands the virtual geomagnetic poles vgp of these 8 flows describe a short loop at high latitudes seven overlying flows are transitional in directions and dated between 991 14 ka and 1002 11 ka consistently with published ages of the upper jaramillo reversal this second group of flows is characterized by low paleointensity values around 8 12 t that are less than 30 of the present dipole value in tenerife the vgps of the first two transitional flows lie over northeastern pacific whereas the five following transitional flows have all negative inclinations and their vgps lie initially over east antarctica then describe a northward loop almost reaching new zealand the final group of ten flows yield intensities varying between 20 and 35 t and vgps close to the southern pole with two of them describing a small amplitude second loop to southeastern pacific assuming a constant extrusion rate as a very first approximation the distribution of the obtained ages suggests a duration of 7 6 5 6 ka for the transitional interval the obtained transitional positions of vgps are consistent with the path reported for the same reversal from north atlantic sediments but are different from the only other volcanic record from tahiti the intensity low characterizing the transitional interval remains the best tie point centered at 996 7 ka 2 relative to 28 02 ma fc sanidine

soil and landform interplay in the dry valley of edson hills ellsworth mountains continental antarctica abstract the main relief units from the dry valley of edson hills ellsworth mountains antarctica 79 49 12 4 83 40 16 1 were assessed emphasizing the analysis of soil and landform interplay soil morphological physical and chemical properties salinity surface boulder weathering frequency and feature classification and weathering stages were analyzed three distinct landforms summarize the geomorphology of the dry valley of edson hills ellsworth mountains i periglacial features like slightly creeping debris mantled slopes steep debris mantled slopes patterned grounds and thermokarst ii glacial features like hummocky moraines lateral moraines supraglacial lakes kettle hole proglacial cirques infill subglacial horn and arete erosional glacial and iii nonglacial features like scree slopes and talus deposits all these glacial and periglacial features are related to the west antarctica ice sheet variations soils in the dry valley of edson hills are pedologically poorly developed however the degree of development in soils associated with patterned ground and moraine systems is remarkable all soils present desert pavement owing to the action of severe aeolian erosion in addition soils accumulate salts depending on the local drainage conditions the most expressive soil classes among the studied soils were typic haploturbel and typic anhyorthel especially because of i a general trend of ice cemented permafrost occurrence in lower portions of the landscape particularly in the patterned ground area and in the hummocky moraine and ii the presence of dry permafrost in higher positions of the landscape in relief units such as in debris mantled slopes and talus deposits thus a close relationship among soil characteristics and landforms were observed in the dry valley of edson hills

spatial and temporal variation of sublimation on antarctica results of a high resolution general circulation model in this paper we use output of a high resolution general circulation model echam 3 t106 resolution 1 1 x 1 1 to study the spatial and temporal variation of sublimation on antarctica first we compare model results with available observations of sublimation rates the yearly cycle with small latent heat fluxes during the winter is well reproduced and the agreement with sparsely available spot observations is fair the model results suggest that a significant 10 15 of the annual precipitation over antarctica is lost through sublimation and that sublimation plays an important role in the formation of blue ice areas a preliminary analysis of the atmospheric boundary layer moisture budget shows that the spatial variation of sublimation in the coastal zone of east antarctica can be explained by variations of horizontal advection of dry air dry air advection and thus surface sublimation is enhanced in areas where katabatic winds are strong and have a large downslope component and where the antarctic topography drops suddenly from the plateau to the coastal zone in areas where horizontal advection is small like the plateau and the large ice shelves special conditions must be met to make significant sublimation at the surface possible

widespread movement of meltwater onto and across antarctic ice shelves surface water and its drainage across the surface of antarctic ice is shown to be widespread large scale and to have persisted for decades melt ponds and streams form across antarctica but their full extent and the duration of their existence have remained unclear now jonathan kingslake et al show that surface drainage systems including interconnected ponds and streams have existed for decades as far as 85 s and up to 1 300 metres elevation they show that surface water can be transported more than 100 kilometres creating pond networks almost 80 kilometres long although the implications of the findings for ice sheet dynamics are not explored the study demonstrates that surface water drainage is more extensive than previously thought and is probably a persistent feature of the antarctic ice sheet elsewhere in this issue robin bell et al report on the influence of surface meltwater on antarctic ice shelf stability and find that it might not be a universally destructive force as was previously thought surface meltwater drains across ice sheets forming melt ponds that can trigger ice shelf collapse1 2 acceleration of grounded ice flow and increased sea level rise3 4 5 numerical models of the antarctic ice sheet that incorporate meltwater s impact on ice shelves but ignore the movement of water across the ice surface predict a metre of global sea level rise this century5 in response to atmospheric warming6 to understand the impact of water moving across the ice surface a broad quantification of surface meltwater and its drainage is needed yet despite extensive research in greenland7 8 9 10 and observations of individual drainage systems in antarctica10 11 12 13 14 15 16 17 we have little understanding of antarctic wide surface hydrology or how it will evolve here we show widespread drainage of meltwater across the surface of the ice sheet through surface streams and ponds hereafter surface drainage as far south as 85 s and as high as 1 300 metres above sea level our findings are based on satellite imagery from 1973 onwards and aerial photography from 1947 onwards surface drainage has persisted for decades transporting water up to 120 kilometres from grounded ice onto and across ice shelves feeding vast melt ponds up to 80 kilometres long large scale surface drainage could deliver water to areas of ice shelves vulnerable to collapse as melt rates increase this century while antarctic surface melt ponds are relatively well documented on some ice shelves we have discovered that ponds often form part of widespread large scale surface drainage systems in a warming climate enhanced surface drainage could accelerate future ice mass loss from antarctic potentially via positive feedbacks between the extent of exposed rock melting and thinning of the ice sheet

the last two geomagnetic polarity reversals recorded in high deposition rate sediment drifts high resolution records of geomagnetic polarity transitions are rare owing to the difficulty of preserving in the geological record details of a process with a duration of only a few thousand years lavas can record the instantaneous field on cooling but lava records are themselves discontinuous and therefore polarity transition fields are seldom captured sedimentary records are more continuous but typical deep sea sedimentation rates of a few cm kyr 1are too low to record transition fields adequately here we report transition records from north atlantic drift deposits with high sedimentation rates 12 cm kyr 1 at the ocean drilling program sites 983 and 984 virtual geomagnetic polar vgp paths are similar within and between sites for the last two geomagnetic reversals attesting to a memory effect spanning back to back reversals the complex vgp paths feature two vgp clusters one located in northeastern asia and the other in the south atlantic ocean off south america and provide a link between the longitudinally constrained transitional vgps often recorded in sediments1 2 which represent highly smoothed renditions of transition fields and the scattered transitional vgps3 and vgp clusters4 observed in lava records

inferences from stable water isotopes on the holocene evolution of scharffenbergbotnen blue ice area east antarctica we show that it is possible to extract a high resolution annual paleoclimate record from the surface of a blue ice area bia the variability of the surface stable isotope values suggests that almost all the surface ice in scharffenbergbotnen bia east antarctica is of holocene age the isotopic changes across the bia show that the modern climate there is warmer than the climate in the early holocene optimum 11 kyr bp a volume conserving ice flow model for the bia constrained by isotopic variability and layer thicknesses and a series of 14 c ages indicate both that the bia has been smaller than now and that the surface velocities were considerably smaller during the last glacial maximum changes in ice sheet thickness drive the bia towards present day conditions the relatively young age of the majority of the bia also explains the lack of meteorite finds in this area and may be typical for many bias in low elevation nunatak areas

meteorological conditions over antarctic blue ice areas and their influence on the local surface mass balance this paper addresses the causes of the prevailing meteorological conditions observed over an antarctic blue ice area and their effect on the surface mass balance over blue ice areas net accumulation is zero and ablation occurs mainly through sublimation sublimation rates are much higher than over adjacent snowfields the meteorological conditions favourable for high sublimation rates warm dry and gusty are due to the specific orographic setting of this blue ice area with usually a steep upwind mountainous slope causing strong adiabatic heating diabatic warming due to radiation and entrainment of warm air from aloft into the boundary layer augment the warming the prevailing warm dry conditions explain roughly 50 of the difference in sublimation and the different characteristics of blue ice mainly its lower albedo the other 50 most of the annual sublimation 70 takes place during the short summer mainly in daytime with winter ablation being restricted to occasional warm dry fohn like events the additional moisture is effectively removed by entrainment and horizontal advection which are maximum over the blue ice area low frequency turbulent motions induced by the upwind mountains enhance the vertical turbulent transports strong gusts and high peak wind speeds over blue ice areas cause high potential snowdrift transports which can easily remove the total precipitation thereby maintaining zero accumulation

modeling the microwave emission of bubbly ice applications to blue ice and superimposed ice in the antarctic and arctic passive microwave remote sensing is extensively used in polar regions to study the cryosphere to better understand the measured signal above continental ice covered areas our objective is to estimate the microwave emission of bubbly ice surfaces using a physically based multilayer electromagnetic model i e the dense media radiative transfer multilayer model dmrt ml this model accounts for ice layers with variable amounts of bubbles each layer is fully described by its temperature density thickness and air bubble radius simulations are performed using in situ data from two distinct sites one in antarctica on a coastal blue ice area near the cap prud homme cph station in adelie land and the other on the barnes ice cap bic located on baffin island in the arctic on this ice cap superimposed ice with seasonal snow cover about 1 m thick was observed in both cases several ice parameters were measured or estimated and the others were optimized results of the dmrt ml simulations are compared with in situ surface based radiometer sbr measurements at 11 19 and 37 ghz at both horizontal and vertical polarizations results show that dmrt ml is able to reproduce the microwave emission of different ice types with good accuracy when accounting for ice bubbles final hbox rmse 7 37 hbox k and 8 42 k for cph and bic respectively compared with rmse ranging from 15 k to 40 k without bubbles comparisons between sbr measurements and satellite data for the bic also show good agreement hbox rmse 4 1 hbox k for 19 and 37 ghz both polarizations

surface roughness characterizations of sea ice and ice sheets case studies with misr data this work is an examination of potential uses of multiangular remote sensing imagery for mapping and characterizing sea ice and ice sheet surfaces based on surface roughness properties we use data from the multi angle imaging spectroradiometer misr to demonstrate that ice sheet and sea ice surfaces have characteristic angular signatures and that these angular signatures may be used in much the same way as spectral signatures are used in multispectral classification three case studies are examined sea ice in the beaufort sea off the north coast of alaska the jakobshavn glacier on the western edge of the greenland ice sheet and a region in antarctica south of mcmurdo station containing glaciers and blue ice areas the misr sea ice image appears to delineate different first year ice types and to some extent the transition from first year to multiyear ice the misr image shows good agreement with sea ice types that are evident in concurrent synthetic aperture radar sar imagery and ice analysis charts from the national ice center over the jakobshavn glacier surface roughness data from airborne laser altimeter transects correlate well with misr derived estimates of surface roughness in antarctica ablation related blue ice areas which are difficult to distinguish from bare ice exposed by crevasses are easily detected using multiangular data

ages ablation and accumulation rates from 14c measurements on antarctic ice shallow ice cores from an antarctic blue ice area at scharllenbergbotncn were 14c analyzed using a dry extraction technique and accelerator mass spectrometry the in situ production was determined from the 14co component and used to deduce the natural 14co2 component the ages were measured at 10 000 3000 bp the accumulation and ablation rates determined from the in situ production are 7 20 and 10 cm a 1 respectively showing agreement with field observations the derived ages and air yield data show a nearby origin for the surface ice

on the glaciological meteorological and climatological significance of antarctic blue ice areas this paper presents the current state of our knowledge about antarctic blue ice areas scattered widely over the antarctic continent yet covering only approximately 1 of its surface area blue ice areas have some peculiar characteristics that make them of particular interest for planetary geologists glaciologists meteorologists and climatologists for instance blue ice areas are subject to net ablation mainly by sublimation since any accumulation is easily swept off their smooth surfaces by winds moreover they are significantly warmer than their surroundings and the wind over them is generally more gusty an important feature of blue ice is its relatively low albedo 0 56 compared with that of snow 0 80 blue ice is probably considerably smoother than snow in the aerodynamic sense with roughness lengths as low as 3 10 6 m which indicates that blue ice is probably the only permanent natural surface over which the air flow is mainly in the aerodynamic smooth regime further since it is likely that very old ice is exposed at the surface of some blue ice areas this ice would be of great interest for paleoclimatic studies it has also been suggested that blue ice areas are sensitive to climate change this would make them useful as antarctic climate indicators because they can easily be monitored by satellite finally this paper addresses several gaps in our knowledge about blue ice areas and gives suggestions for future blue ice area research

sublimation and surface energy budget of taylor glacier antarctica taylor glacier an outlet of the east antarctic ice sheet flows through the transantarctic mountains and terminates in the dry valleys understanding how this glacier fluctuates is important for studies of glacial geology paleoclimate ice dynamics and ecology sublimation is the primary mass loss process for most of the glacier four years of specific balance measurements from the ablation zone show sublimation rates up to 40 cma 1 we used data from an array of weather stations as inputs to a model for latent heat flux and hence sublimation rate calculated and measured ablation rates agree to within uncertainties indicating that wind speed and vapour pressure gradient a function of temperature and humidity are the governing variables as expected from theory measurements and model results together allowed us to examine the spatial and temporal variations of sublimation on the glacier on average sublimation is about two times faster in summer than winter rapid sublimation occurs during storms and katabatic wind events but such periods contribute less to the annual total than do slow persistent losses spatially sublimation reaches a maximum midway along the glacier where descending surface air currents are focused by the topography of the aptly named tributary windy gully

confounding influence of magnetic fabric on sedimentary records of a field reversal recent compilations of geomagnetic reversal records have generated a controversy as to whether the geomagnetic field is geographically biased during polarity transitions at present there is general agreement that the virtual geomagnetic poles recorded from cenozoic sediments preferentially lie over the americas or the antipodal longitude yet such a preference is not statistically established however it is intriguing that the claimed preferred paths lie 90 away from the site longitude although this may be partly inherent in the very poor geographical distribution of the sites we prefer not to rely on fortuitous coincidences several authors have argued that sedimentary palaeomagnetic records may be modified by artefacts linked to the acquisition of magnetization here we report that in two sedimentary records of the upper olduvai reversal from confidence hills california the declinations of the remanent magnetization recorded during the reversal are similar to the directions of the maximum horizontal axes of the ellipsoids of magnetic anisotropy this supports the idea that at times of low geomagnetic intensity such as during a reversal factors other than the geomagnetic field influence the orientation of elongated grains

extreme snow metamorphism in the allan hills antarctica as an analogue for glacial conditions with implications for stable isotope composition understanding physical processes in near zero accumulation areas can help us to better understand polar ice core records particularly during periods when accumulation rates were lower than today we report measurements from a 5 m firn core from the allan hills antarctica which include physical properties using computer tomography stable isotope ratios d and 18 o and 210 pb activity the core shows a highly metamorphosed firn with homogeneous and stable structure but with discrete layers near the surface the observed firn structure is caused by a combination of unique depositional and post depositional processes the irregular d and 18 o signal does not follow the stratigraphic sequence and implies post depositional modification caused by microscopic pressure gradients in the firn that can result from either forced ventilation over rough surfaces in the presence of wind or alternating temperature gradients between the firn and the atmosphere our results also indicate impact snow deposition under high winds and with a high initial density and air exchange between the atmosphere and the snowpack 210 pb activity below 0 3 m falls below the detection limit implying that most of the core is more than 100 years old we conclude that the allan hills record provides a unique opportunity to investigate important processes that would have affected ice core records from glacial periods

the interaction of katabatic winds and the formation of blue ice areas in east antarctica blue ice areas bias are an extreme example of a local mass balance gradient and are furthermore reasonably stable in time and space owing to local feed back mechanisms a meteorological experiment performed in and around a blue ice area in dronning maud land east antarctica showed that during driftingsnow conditions surface wind speed over the blue ice behind the mountain barrier is equal to that away from the mountains when corrected for surface roughness and stability this implies that use of diagnostic katabatic wind models to estimate divergence of drifting snow can be extended to the situation where nunataks are involved in preventing the drifting snow from passing which is the case for most bias a diagnostic model is tested for a two dimensional profile in terre adelie after which it is applied to entire east antarctica the present order of magnitude estimate shows that areas sensitive to blue ice formation appear where precipitation is low and mean annual wind speed is high i e in dronning maud land and the drainage basin of lambert glacier the results appeared to be especially sensitive to a change in inversion strength a decrease in inversion strength weakens the katabatic flow and thus the amount of snowdrift transport reducing the area where bias can develop

relative geomagnetic field intensity and reversals for the last 1 8 my from a central equatorial pacific core we have made a new analysis of core kk78o30 from the central equatorial pacific this core has recorded the last 4 reversals mineral magnetic analysis establishes that these sediments meet the current criteria for reliable relative paleointensity determinations normalisation with arm irm and yields very similar results there is no evidence for a saw tooth pattern such as the one obtained by valet and meynadier 1993 and meynadier et al 1994 for the last 4 million years rather the average field intensity record appears to display more or less symmetric peaks and troughs superposed to a broad high between reversals

catch a falling star meteorites and old ice a model for the process of meteorite concentration in blue ice regions of the antarctic ice sheet is proposed based on data from near the allan hills and the assumptions that both meteorite influx and glacial flow have been constant the meteorite influx is calculated to be 60 x 10 6 kilogram per square kilometer per year and the age of the exposed ice to be 0 to 600 000 years varying with distance from the allan hills these results are in line with other estimates of influx rate and with measurements of the terrestrial ages of the meteorites providing support for the assumption of steady flow and meteorite influx this may be the oldest sequence of ice in stratigraphic order yet discovered and the results imply that this part of the east antarctic ice sheet has been approximately steady during this time interval