salt inclusions in polar ice core location and chemical form of water soluble impurities abstract ice cores retrieved from ice sheets provide the most detailed records of climate over the past several hundred thousand years for example water soluble impurities have been used as proxies for atmospheric chemistry however numerical models warned that the distributions of the trace constituents are significantly altered by rapid diffusion through liquid veins along triple junctions during ice sheet flow although these calculations assumed that the trace constituents are preferentially confined to grain boundaries and form a vein network this assumption has not been confirmed experimentally using micro raman spectroscopy here we show that most of the soluble impurities are confined as salt inclusions within grains these inclusions are mainly composed of the sulfate salts na 2 so 4 10h 2 o mgso 4 12h 2 o and caso 4 2h 2 o we also found that methane sulfonate salts and other complex salts exist only in the glacial period ice our findings imply that these salts form within 185 m of the ice surface and then preserve their composition as the ice is pushed to greater depths this means that depth profiles of the trace constituents should be preserved in deep ice cores as reliable proxies for past climate

distribution of soluble impurities in cold glacial ice understanding the microstructure of ice underpins the interpretation of ice core measurements and many ice sheet properties a detailed study of polar snow and ice using scanning electron microscope sem and x ray analysis revealed the microstructural distribution of soluble impurities sublimation under vacuum etching concentrated impurity from both the bulk and grain boundaries on to the specimen surfaces in detectable quantities sublimation in the cold room before examination preetching collected previously unobservable quantities of impurity at triple junctions a heterogeneous distribution of impurities was observed chloride was frequently found to originate from the lattice but not usually at triple junctions other impurities particularly sodium chloride were detected at grain boundaries and bubble surfaces sulphate was often found at triple junctions in specimens containing a high bulk concentration of the acid frequently in conjunction with cations this suggests the possibility that veins were only filled with significant amounts of impurity when the surrounding grain boundaries were saturated the model of impurity arrangement inferred from the results reconciles differences between previous sem studies additionally it is consistent with and explains recent electrical conduction observations the disconnected arrangement of impurity filled grain boundaries and veins limits opportunities for significant post depositional solute movement

sem eds observations of impurities in polar ice artifacts or not abstract a series of experiments was undertaken to determine the origin of fila ments found in grainboundaries and impurity spots found in grain interiors of polar iceduring observation in the scanning electron microscope it is shown that although thefilamentsareartifacts theydemonstratethepresenceofimpuritiessegregatedtothegrainboundaryplanes itisalsodemonstratedthattheimpuritiesobservedinthegraininteriorreside there and were not transported fromthe grainboundaries during specimen prep arationorobservation introduction inanumberofrecentpapers cullenandbaker 2000 2001 2002 baker and cullen 2002 iliescu and others 2002 bakerand others in press obbard and others inpress wehaveusedsecondaryelectron se imagingandenergy dis persive x ray spectroscopy eds in a low vacuum scan ning electron microscope lvsem to examine the typesandmicrostructurallocationsofimpuritiesinpolarice corespecimens held at 158k specimen preparation involvedshaving the surface flat in a cold room at 253k and thenallowingtheicetosublimateinthelvsemattemperaturesof 158 213k the sublimation caused the impurities to beconcentrated after which the elements present could be

basin modes in a tropical extratropical basin abstract the full spectrum of basin modes in a tropical extratropical basin is studied comprehensively in a linear shallow water system two sets of least damped basin modes are identified at the low frequency end is the planetary wave basin mode whose period is determined by the cross basin time of the planetary wave on the poleward boundary of the basin consistent with recent theories at the higher frequency end is the kelvin wave basin mode whose period is determined by the around basin traveling time of the kelvin wave sensitivity experiments are also performed on the eigenvalue problem to study the dynamics of these basin modes it is found that the period of the planetary wave basin mode is determined by an effective basin boundary that is always at a latitude no higher than the geometric basin boundary the effective poleward boundary is located at the most poleward latitude where the planetary wave can cross the entire basin it is also found that the kelvin wave basin modes are vulnerable t

continuous methane measurements from a late holocene greenland ice core atmospheric and in situ signals abstract ancient air trapped inside bubbles in ice cores can now be analysed for methane concentration utilising a laser spectrometer coupled to a continuous melter system we present a new ultra high resolution record of atmospheric methane variability over the last 1800 yr obtained from continuous analysis of a shallow ice core from the north greenland eemian project neem 2011 s1 during a 4 week laboratory based measurement campaign our record faithfully replicates the form and amplitudes of multi decadal oscillations previously observed in other ice cores and demonstrates the detailed depth resolution 5 3 cm rapid acquisition time 30 m day 1 and good long term reproducibility 2 6 2 of the continuous measurement technique in addition we report the detection of high frequency ice core methane signals of non atmospheric origin firstly measurements of air from the firn ice transition region and an interval of ice core dating from 1546 1560 ad gas age resolve apparently quasi annual scale methane oscillations traditional gas chromatography measurements on discrete ice samples confirm these signals and indicate peak to peak amplitudes of ca 22 parts per billion ppb we hypothesise that these oscillations result from staggered bubble close off between seasonal layers of contrasting density during time periods of sustained multi year atmospheric methane change secondly we report the detection of abrupt 20 100 cm depth interval high amplitude 35 80 ppb excess methane spikes in the neem ice that are reproduced by discrete measurements we show for the first time that methane spikes present in thin and infrequent layers in polar glacial ice are accompanied by elevated concentrations of carbon and nitrogen based chemical impurities and suggest that biological in situ production may be responsible

precise measurement of changes in ice shelf thickness by phase sensitive radar to determine basal melt rates 1 we describe a novel technique for measuring the basal melt rate at a point on an ice shelf the method uses a phase sensitive radar to observe the change in thickness of the ice column between an upper reference horizon and the ice shelf base the observed thickness change is a combination of basal melting horizontal ice divergence and firn compaction the latter two components are determined independently by the repeat survey of surface markers and from estimates of surface accumulation rate and density at the depth of the reference horizon the technique has been applied at a site on george vi ice shelf antarctica where a melt rate of 2 78 0 08 m yr 1 was observed over a twelve day period our technique is applicable to almost any ice shelf or floating glacier tongue and its high precision over short time intervals will permit the measurement of seasonal variations in melt rate

on the role of coastal troughs in the circulation of warm circumpolar deep water on antarctic shelves abstractoceanic exchanges across the continental shelves of antarctica play an important role in biological systems and the mass balance of ice sheets the focus of this study is on the mechanisms responsible for the circulation of warm circumpolar deep water cdw within troughs running perpendicular to the continental shelf this is examined using process oriented numerical experiments with an eddy resolving 1 km 3d ocean model that includes a static and thermodynamically active ice shelf three mechanisms that create a significant onshore flow within the trough are identified 1 a deep onshore flow driven by the melt of the ice shelf 2 interaction between the longshore mean flow and the trough and 3 interaction between a rossby wave along the shelf break and the trough in each case the onshore flow is sufficient to maintain the warm temperatures underneath the ice shelf and basal melt rates of o 1 m yr 1 the third mechanism in particular reproduces several features revealed by moorings from m

dynamics and thermodynamics of a warming event in a coupled tropical atmosphere ocean model abstract a simple coupled ocean atmosphere model similar to that of zebiak and cane is used to examine the dynamic and thermodynamic processes associated with el nino southern oscillation enso the model is run for 300 years the interannual variability which results is regular with a period of either 3 or 4 years quantized by the annual cycle the amplitude 1 5 m s 1 wind and 2 c sst anomalies period and structure of the interannual variability compare well with observations the model warm event is initiated in the spring prior to the event peak and is well described as an instability of the coupled system during instability growth the sea surface temperature sst anomaly is primarily generated by vertical upwelling processes the sst anomaly can be approximately described by the expression t t kth t where t is the sst anomaly t time h the upper layer thickness pycnocline perturbation and an effective damping time which includes heat loss to the atmosphere kt parameterizes

how long is the memory of tropical ocean dynamics combining classic equatorial wave dynamics and midlatitude wave dynamics a unified view is proposed to account for the memory of tropical ocean dynamics in terms of oceanic basin modes it is shown that the dynamic memory of the ocean is bounded by the cross basin time of planetary waves along the poleward basin boundary for realistic ocean basins this memory originates from the mid and high latitude processes and is usually at interdecadal timescales

regulation of algal blooms in antarctic shelf waters by the release of iron from melting sea ice during summer 1995 96 we measured iron in the water column and conducted iron enrichment bottle incubation experiments at a station in the central ross sea 76 30 s 170 40 w first in the presence of melting sea ice and 17 days later in ice free conditions we observed a striking temporal change in mixed layer dissolved iron concentrations at this station from 0 72 2 3 nm with sea ice present to 0 16 0 17 nm in ice free conditions these changes were accompanied by a significant drawdown in macronutrients and an approximate doubling of algal diatom biomass our incubation experiments suggest that conditions were iron replete in the presence of sea ice and iron deficient in the absence of sea ice we surmise that bioavailable iron was released into seawater from the melting sea ice stimulating phytoplankton production and the biological removal of dissolved iron from the mixed layer until iron limited conditions developed these observations suggest that the episodic release of bioavailable iron from melting sea ice is an important factor regulating phytoplankton production particularly ice edge blooms in seasonally ice covered antarctic waters

evidence of microbial consortia metabolizing within a low latitude mountain glacier carbon dioxide co 2 nitrous oxide n 2 o and methane ch 4 concentrations of ice samples from a south american mountain glacier are larger than those in coeval polar ice cores of the six possible mechanisms that may cause the composition of air measured in ice cores to depart from that of the overlying troposphere gravitational fractionation thermal fractionation gases trapped in refrozen meltwater atmospheric heterogeneity abiotic chemical reactions and biologically mediated chemical reactions only metabolism of a consortium of microorganisms within the ice can explain our data

the microstructure of meteoric ice from vostok antarctica the 3623 m long 5g core collected at vostok station antarctica contains alternating layers of meteoric ice with two distinctly different microstructures in this paper we present the microstructure and impurity content of a number of specimens ranging in depth from 97 to 3416 m describe in detail the characteristics of the different layers and propose a mechanism for their microstructural development digital image analysis ion chromatography scanning electron micro scopy and energy dispersive x ray spectroscopy were used to measure texture and the location and type of impurities electron backscatter diffraction was used to determine crystal orientation the ice associated with interglacial periods is characterized by relatively coarse grains and a strong preferred orientation of the c axes in a plane encompassing the coring direction producing a vertical girdle fabric in contrast ice from glacial periods is characterized by a much smaller grain size and a strong single maximum fabric where the c axes are clustered around the vertical calcium is uniquely present in the grain boundaries of the fine grained glacial layers and its effect on grain boundary mobility and the misorientation dependence of mobility can explain the development of the discontinuous micro structure seen in glacial ice at vostok station

application of micro x ray fluorescence to chemical mapping of polar ice synchrotron based micro x ray fluorescence xrf equipment has been used to analyze impurities in polar ice a customized sample holder has been developed and the xrf equipment has been adapted with a thermal control system to keep samples unaltered during analyses artificial ice samples prepared from ultra pure water were analyzed to investigate possible contamination and or experimental artefacts analyses of polar ice from antarctica dome c and vostok confirm this xrf technique is non destructive and sensitive experiments can be reproduced to confirm or refine results by focusing on interesting spots such as crystal grain boundaries or specific inclusions integration times and resolution can be adjusted to optimize sensitivity investigation of unstable particles is possible due to the short analysis time in addition to identification of elements in impurities xrf is able to determine their speciations the accuracy and reliability of the results confirm the potential of this technique for research in glaciology

chemical analysis of ice vein microenvironments ii analysis of glacial samples from greenland and antarctica chemical constituents trapped within glacial ice provide a unique record of climate as well as repositories for biological material such as pollen grains fungal spores viruses bacteria and dissolved organic carbon past research suggests that the veins of polycrystalline ice may provide a liquid microenvironment for active microbial metabolism fueled by concentrated impurities in the veins despite these claims no direct measurements of impurity concentration in ice veins have been made using micro raman spectroscopy we show that sulfate and nitrate concentrations in the veins of glacial ice from greenland greenland ice sheet project 2 and antarctic newall glacier and a dominion range glacier core samples were 10 4 and 10 5 times greater than the concentrations measured in melted bulk core water methanesulfonate was not found in the veins consistent with its presence as particulate matter within the ice the measured vein concentration of molecular anions implies a highly acidic ph 3 vein environment with high ionic strength mm m we estimate that the vein volume provides 16 7 and 576 km 3 of habitable space within the greenland and antarctic ice sheets respectively which could support the metabolism of organisms that are capable of growing in cold high ionic strength solutions with low ph

subsurface ice as a microbial habitat we determine the physicochemical habitat for microorganisms in subsurface terrestrial ice by quantitatively constraining the partitioning of bacteria and fluorescent beads 1 10 m between the solid ice crystals and the water filled veins and boundaries around individual ice crystals we demonstrate experimentally that the partitioning of spherical particles within subsurface ice depends strongly on size but is largely independent of source particle concentration although bacteria are shown consistently to partition to the veins larger particles which would include eukaryotic cells become trapped in the crystals with little potential for continued metabolism we also calculate the expected concentrations of soluble impurities in the veins for typical bulk concentrations found in natural ice these calculations and scanning electron microscope observations demonstrate a concentrated chemical environment 3 5 m total ions at 10 c in the veins where bacteria were found to reside with a mixture of impurities that could sustain metabolism our calculations show that typical bacterial cells in glacial ice would fit within the narrow veins which are a few micrometers across these calculations are confirmed by microscopic images of spherical 1 9 m diameter fluorescent beads and stained bacteria in subsurface veins typical bacterial concentrations in clean ice 102 103 cells ml would result in concentrations of 106 108 cells ml of vein fluid but occupy only a small fraction of the total available vein volume 0 2 hence bacterial populations are not limited by vein volume with the bulk of the vein being unoccupied and available to supply energy sources and nutrients

application of cryo sims to the analysis of polar ice the suitability of secondary ion mass spectrometry sims for the analysis of polar ice is assessed a magnetic sector sims instrument modified to permit analysis of cryogenically prepared specimens was used to analyze a sample of naled ice from in front of midre lovenbreen svalbard the ion induced secondary electron imaging capability of the instrument permitted identification of features such as grain boundaries triple junctions filaments pore spaces and cracks secondary ion maps were acquired with sub micron resolution permitting the characterization of chemical impurities at grain boundaries two regions of interest were analyzed and are described in detail in the first discrete particles of impurity possibly precipitates containing na mg k and cl were identified along a grain boundary additionally mg was found to be present along the full length of the boundary in the second analysis impurity containing na mg k and cl was found at a triple junction and some evidence for segregation of impurity to grain boundaries was gained in both regions of analysis na k and cl were more apparent in grain interiors than mg despite the presence of the latter element at the boundaries results corroborate previous scanning electron microscopy with energy dispersive x ray spectrometry sem eds observations

a scanning electron microscope technique for identifying the mineralogy of dust in ice cores dust particles in an ice core from east rongbuk glacier on the northern slope of qomolangma mount everest 28 01 n 86 58 e 6518 m a s l central himalaya have been identified as mica using a combination of scanning electron microscope based techniques and energy dispersive x ray spectroscopy to identify the elements present and electron backscatter diffraction to identify the crystal type this technique for identifying individual crystalline dust particles in samples of glacial ice could be especially useful in the future for identifying water soluble crystals in ice for studying the strain history glaciotectonics of basal ice or in studies of ice mica composites used as analogs of quartz mica rocks

ice seawater turbulent boundary layer interaction with melting or freezing abstract a second moment turbulence closure model is applied to the problem of the dynamic and thermodynamic interaction of sea ice and the ocean surface mixed layer in the case of ice moving over a warm ocean surface layer melting is intrinsically a transient process that is melting is rapid when warm surface water initially contacts the ice then the process slows when surface water is insulated from deeper water due to the stabilizing effect of the melt water and the thermal energy stored in the surface layer is depleted effectively the same process prevails when ocean surface water flows under stationary ice in which case after an initial rapid increase the melting process decreases with downstream distance accompanying the stabilizing effect of the melt water is a reduction in the ice seawater interfacial shear stress this process and model simulators are used to explain field observations wherein ice near the marginal ice zone diverges from the main pack when the surface ice layer is m

an optimized estimate of glacial melt from the ross ice shelf using noble gases stable isotopes and cfc transient tracers 1 isotopes of helium and neon and the h218o h216o ratio of water are proven proxies for melt from glacial ice beneath floating ice shelves and at ice shelf fronts their high concentrations in glacial meltwater compared to other environmental sources make them ideal tracers for studies of the pathways of glacial meltwater from its origins into the ocean interior we combine noble gas and stable isotopes with temperature salinity and dissolved oxygen measurements from three cruises along the ross ice shelf during the austral summers of 1993 1994 and 1999 2000 and to the ross sea in 2000 2001 and use optimal multiparameter analysis to compute the water mass concentration including glacial meltwater the distribution of meltwater at the front of the ross ice shelf extended east from 180 w with the highest concentrations found near 165 w in both 1994 and 2000 the mean meltwater concentration at the ice shelf front was 2 0 0 33 in 1994 2 2 0 36 in 2000 and 0 25 0 1 in the western ross sea in 2001 water mass concentrations are used to correct for bias in the cfc age introduced by mixing with cfc free waters an effect revealed by comparing cfc age with transit time distribution curves the water residence time within the ice shelf cavity using cfcs and the mean meltwater concentration implies a basal melt rate of 33 50 km3 a 1

on the characteristics of circumpolar deep water intrusions to the west antarctic peninsula continental shelf 1 hydrographic and current velocity observations collected from march 2001 to february 2003 on the west antarctic peninsula shelf as part of the southern ocean global ecosystems dynamics program are used to characterize intrusions of upper circumpolar deep water ucdw and lower circumpolar deep water lcdw onto the shelf and marguerite bay ucdw is found on the middle and outer shelf along marguerite trough which connects the shelf break to marguerite bay and at another location farther south ucdw intrudes in the form of frequent four per month and small horizontal scales 4 km warm eddy like structures with maximum vertical scales of a few hundred meters however no evidence of ucdw intrusions was found in marguerite bay lcdw was found in several deep depressions connected to the shelf break including marguerite trough forming a tongue of relatively dense water 95 m thick on average that reaches into marguerite bay through marguerite trough a steady advective diffusive balance for the lcdw intrusion is used to make an estimation of the average upwelling rate and diffusivity in the deep layer within marguerite trough which suggest the lcdw layer is renewed approximately every six weeks

oceanic heat transport onto the amundsen sea shelf through a submarine glacial trough glaciers which drain the west antarctic ice sheet wais into the amundsen sea are accelerating and thinning rapidly these observations have been attributed to the regional oceanography whereby heat contained within circumpolar deep water cdw drives the basal melting of floating glaciers on the basis of new data we calculate that 2 8 terra watts 1012 of oceanic heat flow onto the continental shelf and toward the glaciers via a submarine glacial trough this is enough to account for most of the basal melting in the entire region suggesting the ocean is supplying an excess of heat toward the antarctic continent

geographical variability of the first baroclinic rossby radius of deformation global 1 83 18 climatologies of the first baroclinic gravity wave phase speed c1 and the rossby radius of deformation l1 are computed from climatological average temperature and salinity profiles these new atlases are compared with previously published 5 83 58 coarse resolution maps of l1 for the northern hemisphere and the south atlantic and with a 1 83 18 fine resolution map of c1 for the tropical pacific it is concluded that the methods used in these earlier estimates yield values that are biased systematically low by 5 15 owing to seemingly minor computational errors geographical variations in the new high resolution maps of c1 and l1 are discussed in terms of a wkb approximation that elucidates the effects of earth rotation stratification and water depth on these quantities it is shown that the effects of temporal variations of the stratification can be neglected in the estimation of c1 and l1 at any particular location in the world ocean this is rationalized from consideration of the wkb approximation

meridianiite detected in ice inclusions affect the behavior of ice and their characteristics help us understand the formation history of the ice recently a low temperature magnesium sulfate salt was discovered this paper describes this naturally occurring mgso4 11h2o mineral meridianiite derived from salt inclusions in sea ice of lake saroma japan and in antarctic continental core ice its occurrence is confirmed by using micro raman spectroscopy to compare raman spectra of synthetic mgso4 11h2o with those of the inclusions

water mass properties and circulation on the west antarctic peninsula continental shelf in austral fall and winter 2001 abstract hydrographic measurements made during the us southern ocean global ocean ecosystem dynamics cruises which took place from april to june and july to september 2001 provide a description of changes in water mass distributions and circulation patterns in the marguerite bay region of the west antarctic peninsula continental shelf that result from seasonal variability and offshore forcing by the southern boundary of the antarctic circumpolar current acc the primary seasonal change in water mass properties is the reduction in antarctic surface water and replacement by a thick winter water layer the primary effect of the acc is to pump warm 1 5 c salty 34 65 34 7 and nutrient rich circumpolar deep water cdw onto the continental shelf below 200 m at specific sites that correspond to bathymetric features such as marguerite trough the cdw intruded onto the continental shelf moved across shelf and entered marguerite bay this flow pattern was observed during both cruises suggesting that onshelf intrusions of cdw are a regular occurrence on this shelf the number of cdw intrusions observed suggests that 4 6 events can occur in a year regions where cdw intrusions occur are characterized by surface waters that are above freezing in winter diffusive heat fluxes based on estimated diffusivities are insufficient for the observed rate of temperature decay of cdw intrusions localized bathymetrically controlled vertical mixing is suggested as the primary heat transfer mechanism the hydrographic and acoustic doppler current profiler measurements show a southwesterly flowing coastal current along adelaide island that enters the north side of marguerite bay and exits around alexander island this current which may result from seasonal coastal buoyancy forcing was present in fall and winter but was better developed in fall this current may be part of a larger cyclonic gyre that overlies the northern part of the area surveyed during the two cruises

the interaction of a two layer isolated mesoscale eddy with bottom topography abstract the propagation of an isolated mesoscale eddy onto a western bounding topographic slope is examined through the use of a two layer primitive equation numerical model variable parameters in the study are sense of rotation cyclonic anticyclonic vertical structure baroclinic barotropic and layer thickness ratio h1 h2 eddy size and strength rotational velocity and frictional parameterization are fixed dispersion in the isolated eddy is induced by planetary and topographic beta effects giving the eddy an asymmetric distribution this asymmetric distribution allows for nonlinear self advective propagation tendencies these nonlinear tendencies play a key role in the direction of propagation of the eddy specifically in a quiescient background an anticyclone can have eastward propagation tendencies which can overcome planetary and topographic beta effects conversely cyclones can have westward propagation velocities which are augmented greater than maximum rossby wave phase speed b

possible displacement of the climate signal in ancient ice by premelting and anomalous diffusion the best high resolution records of climate over the past few hundred millennia are derived from ice cores retrieved from greenland and antarctica the interpretation of these records relies on the assumption that the trace constituents used as proxies for past climate have undergone only modest post depositional migration many of the constituents are soluble impurities found principally in unfrozen liquid that separates the grain boundaries in ice sheets this phase behaviour termed premelting is characteristic of polycrystalline material here we show that premelting influences compositional diffusion in a manner that causes the advection of impurity anomalies towards warmer regions while maintaining their spatial integrity notwithstanding chemical reactions that might fix certain species against this prevailing transport we find that under conditions that resemble those encountered in the eemian interglacial ice of central greenland from about 125 000 to 115 000 years ago impurity fluctuations may be separated from ice of the same age by as much as 50 cm this distance is comparable to the ice thickness of the contested sudden cooling events in eemian ice from the grip core

location of cation impurities in ngrip deep ice revealed by cryo cell uv laser ablation icpms in polar ice sheets the average grain size varies with depth ice grain size increases due to several factors including ice temperature and impurity content which in turn varies with climate the effect of impurities on grain growth is thought to be crucial but has never been observed experimentally using a methodology recently developed at royal holloway university of london in situ chemical analysis of frozen ice at sub ppm concentrations with unprecedented spatial resolution 150 m is achievable using ultraviolet laser ablation inductively coupled plasma mass spectrometry uv la icpms featuring a two volume cryo la cell following surface cleaning with a custom built vice equipped with a ceramic blade ngrip ice slabs 86 ka before ad 2000 have been analysed using a series of one dimensional profiles and two dimensional maps of laser spots at a resolution of 200 300 m results demonstrate that cation impurities are not uniformly distributed in ice layers and show significant variations in concentration on a sub millimetre scale furthermore a different pattern of elemental distribution between clear ice and layers enriched in impurities cloudy bands has been identified while concentration differences for cloudy bands are not resolvable between boundaries and inner grain domains within clear ice grain boundaries and junctions are significantly up to 100 times impurity enriched relative to corresponding grain interiors

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

anomalous diffusion of multiple impurity species predicted implications for the ice core climate records 1 we investigate the transport of impurities that are interpreted as climate proxies and are soluble in the premelted liquid that separates ice grains in the polar ice sheets even at subfreezing temperatures spatial variations in the relative abundances of multiple impurity species lead to gradients in their intergranular concentrations defined as the ratio of the mass of dissolved impurity to the mass of premelted liquid we show how diffusion down these intergranular concentration gradients affects anomalies in the bulk concentrations defined as the ratio of the impurity mass to the mass of a polycrystalline sample which are measured in polar ice cores to illustrate these processes we show that two initially asynchronous periodic signals evolve to become in phase after a short time similar behavior is evident in coastal antarctica where there is a migration of methane sulfonate msa from summer to winter peaks and it becomes in phase with the primary deposition of sea salt moreover the approach allows us to examine how an initially constant bulk concentration profile is influenced by an abrupt change to the bulk concentration of a second component the resulting profiles share features with those observed in the eemian compositional record from the greenland ice core project grip ice core

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

characteristics of salt inclusions in polar ice from dome fuji east antarctica 1 we studied the depth profile of the chemical properties number concentration and average diameter of micro inclusions in antarctic ice from dome fuji analysis of the data indicated that the distribution of inclusions was not significantly modified during ice sheet flow although a main constituent na2so4 10h2o changed into another solid phase in the deep ice in the chemical form sodium sulfate and magnesium sulfate were dominant in the interglacial and early glacial ice but were not detected in the glacial maximum ice instead the sulfate in the glacial maximum ice was mainly in the form of calcium sulfate this is strong support for the hypothesis that the neutralization regime of acid aerosols in the atmosphere and snowpack dramatically changed from chemical reaction with sea salt to that with dust during glacial maxima

microstructural evolution of fine grained layers through the firn column at summit greenland we present a microstructural characterization of fine grained layers from the top 90 m of firn from summit greenland performed using a combination of scanning electron microscopy techniques including secondary electron imaging energy dispersive spectroscopy and electron backscattered patterns and x ray microcomputed tomography the impurities in the firn both soluble impurities and dust particles were found largely in the grain interiors both c and a axis pole figures do not show strong evidence of a preferred orientation of the grains even at the bottom of the firn column the firn structure became increasingly anisotropic with vertical alignment in the top 3 m probably due to vapor transport associated with dry snow metamorphism the anisotropy decreases below this level until at 50 m the average firn structure is close to isotropic in the near surface the level of anisotropy is weaker than at hercules dome antarctica confirming that differences in accumulation rates and temperatures leave enduring evidence in the structure of the firn the fraction of closed off pores is relatively low until 65 m below that it rises through the end of our sampling at 90 m our microstructure measurements on the microscale are consistent with in situ firn air sampling measurements on a decimeter scale both indicating the existence of the lock in zone starting near 69 m depth and pore close off at 81 m at this site

an active subglacial water system in west antarctica mapped from space satellite laser altimeter elevation profiles from 2003 to 2006 collected over the lower parts of whillans and mercer ice streams west antarctica reveal 14 regions of temporally varying elevation which we interpret as the surface expression of subglacial water movement vertical motion and spatial extent of two of the largest regions are confirmed by satellite image differencing a major previously unknown subglacial lake near the grounding line of whillans ice stream is observed to drain 2 0 cubic kilometers of water into the ocean over 3 years while elsewhere a similar volume of water is being stored subglacially these observations reveal a wide spread dynamic subglacial water system that may exert an important control on ice flow and mass balance

a flow band model of the ross ice shelf antarctica response to co2 induced climatic warming a time dependent model is applied to the ross ice shelf flow band discharging ice stream b west antarctica the model includes the effects of temperature depth dependent density and backpressure from the coasts of the ross embayment and crary ice rise data from the ross ice shelf geophysical and glaciological survey and the siple coast project are used as input data accuracy and stability are verified by reproducing the flow band for 10 000 model years with equilibrium distributions of accumulation surface temperature and basal balance sensitivity is tested by forcing the model with increasing accumulation rates surface temperatures and basal melt rates respectively while other factors are held constant the response of the ice shelf to three climatic scenarios that may result from increasing carbon dioxide and trace greenhouse gases is simulated the results range from slight thickening with moderately increased backpressure in the grounding zone to rapid thinning accompanied by rapidly decreasing backpressure during 175 to 600 year simulations depending primarily upon whether increasing surface temperatures and accumulaton rates are accompanied by increased rates of basal melting the central ice shelf about 400 km upglacier from the calving front thins by 22 in 600 years when basal melting is increased linearlymore to a maximum of 0 5 m yr after 150 years then held steady the ice shelf thins by 40 in 175 years at the same location when basal melting is increasedlinearly to 2 0 m yr after 150 years then held steady the present calculated equilibrium rate of basal melting averaged over the bottom surface of the flow band is 0 17 m yr less

grain growth in polar ice i theory many observations regarding grain growth in ice sheets are glaciologically interesting but imperfectly understood here we develop the theory of grain growth in ice that is not deforming rapidly and in the succeeding paper we use this theory to explain observations from glacial ice in the absence of significant strain energy the driving force for grain growth arises from grain boundary curvature grain growth is slowed by the interaction of grain boundaries with extrinsic materials microparticles bubbles and dissolved impurities if the driving force for growth is not large enough to cause boundaries to separate from an extrinsic material then the grain boundary velocity is determined by the velocity characteristic of the extrinsic material low velocity regime if the driving force is large enough to cause separation then boundaries migrate more rapidly than the extrinsic material high velocity regime but the net driving force is reduced through transient pinning by the extrinsic material polar ice is typically in the low velocity regime relative to dissolved impurities and the high velocity regime relative to microparticles and bubbles cross sectional area of grains is predicted to increase linearly with time under most but not all circumstances

decadal north pacific bred vectors in a coupled gcm a number of recent studies done with simple numerical models suggest that the decadal variability in the extratropical north pacific ocean is a result of the excitation of low frequency ocean basin modes to test this assumption low frequency north pacific variability was examined using a state of the art coupled general circulation model cgcm earlier studies had shown that slowly varying dynamical modes in a cgcm can be effectively isolated using the breeding technique in this study the breeding method was applied to the center for ocean land atmosphere studies cola anomaly coupled gcm acgcm and it was found that several types of slow modes can be isolated depending on the parameters of the breeding cycle tropical bred vector sst and upper ocean heat content are dominated by the enso which is consistent with the results obtained earlier using other cgcms extratropical bred vector upper ocean heat content is dominated by oceanic instability localized east of japan varying on seasonal to interannual time scales and decadal modes with the large scale pattern over the central and eastern extratropical north pacific similar to ocean basin modes the decadal modes have a signature of westward propagating long baroclinic rossby waves but do not exhibit the global imprint typical for global basin modes the relationship between the decadal bred vectors and the background anomalies is consistent with linear damped dynamics presumably the growth of the decadal bred vectors is due to the atmospheric stochastic forcing but the existence of extratropical instability on decadal time scales still needs to be verified

linear and non linear relations between the high frequency limit conductivity ac ecm signals and ecm signals of dome f antarctic ice core from a laboratory experiment

low frequency modes of tropical ocean dynamics abstract basinwide very low frequency vlf modes with zonal uniformly deepening and shoaling of the equatorial thermocline are found as solutions of linear shallow water equations with the meridional basin boundaries under an equatorial plane they can be understood as the free heat content recharge oscillations the interannual vlf modes had been recognized as the essential part of the coupled recharge oscillator theory for the el nino southern oscillation it is suggested that the decadal vlf modes may also be transformed into coupled modes relevant to the pacific decadal climate variability through the ocean atmosphere interaction in the tropics

tropical ocean decadal variability and resonance of planetary wave basin modes part ii numerical study abstract oceanic response to stochastic wind forcing is studied in a tropical extratropical basin using two shallow water models a periodically forced model and a time forward model consistent with theory extratropical stochastic wind forces a decadal spectral peak in the tropical and eastern boundary ocean as a resonant response of the planetary wave basin mode this resonant response is characterized by a rather uniform amplitude and phase in the equatorial and eastern boundary region in comparison away from the eastern boundary the extratropical ocean is affected significantly by the local ekman pumping forcing with spectral peaks varying with location a complex eof ceof analysis of the time forward model simulation further suggests that these resonant responses are robust and can be extracted as the leading ceof modes thus the resonance of the planetary wave basin mode gives a physically based guideline for the interpretation of decadal oceanic variability in the tropical extratropical ocean

shelf circulation and cross shelf transport out of a bay driven by eddies from an open ocean current part i interaction between a barotropic vortex and a steplike topography abstractthis paper examines interaction between a barotropic point vortex and a steplike topography with a bay shaped shelf the interaction is governed by two mechanisms propagation of topographic rossby waves and advection by the forcing vortex topographic waves are supported by the potential vorticity pv jump across the topography and propagate along the step only in one direction having higher pv on the right near one side boundary of the bay which is in the wave propagation direction and has a narrow shelf waves are blocked by the boundary inducing strong out of bay transport in the form of detached crests the wave boundary interaction as well as out of bay transport is strengthened as the minimum shelf width is decreased the two control mechanisms are related differently in anticyclone and cyclone induced interactions in anticyclone induced interactions the pv front deformations are moved in opposite directions by the point vortex and topographic waves a topographic cyclone forms out

brine micro droplets and solid inclusions in accreted ice from lake vostok east antarctica 1 lake vostok the largest antarctic sub glacial lake 14 000 km2 lies beneath nearly 4 km of ice sub glacial geophysical observations and studies of ice accreting at the lake glacier interface are the only means available to obtain information on the environment and dynamics of this huge water body formed several million years ago accretion ice has been studied using high resolution synchrotron x ray micro fluorescence for the first time liquid brine micro droplets 3 10 m are observed coexisting with large irregular sulfur rich aggregates 10 800 m containing gases and a mixture of very fine particles most of these objects are sequestered inside large crystals that grew slowly after ice formation their structure and composition support the existence of hydrothermal activity at the lake bottom and the occurrence of haline water pulses carrying fine solid debris and eventually biota from a deeper evaporitic reservoir into the lake

polar ice structure and the integrity of ice core paleoclimate records abstract polar ice is a unique archive of the climatic conditions in the past however ice sheets flow and this flow may affect the integrity of paleoclimate records a useful method to analyze the effect of ice flow upon climate records is the combination of microstructure mapping with ice core line scanning microstructure and stratigraphy have been mapped along the entire epica dml ice core with this combined method on the macroscale the stratigraphy seems perfectly preserved down to ca 1700 m depth mis4 below which minor undulations start to develop layers inclined up to 15 and millimeter scale z folds are observed below 2050 m depth notwithstanding the epica dml climate record appears not seriously disturbed down to ca 2400 m depth which marks the climatic transition from the last interglacial mis5e to the mis6 glacial period below this depth the synchronization with the epica dome c record is lost and stratigraphic disturbances appear up to the meter scale on the microscopic scale we observe dynamic recrystallization already in deep firn leading to substantial microstructural changes prior to bubble close off the concentration of visible micro inclusions in the holocene part of the core seems to increase with depth which could possibly indicate post depositional formation of salts in glacial period ice the concentration of visible micro inclusions in certain layers is so high that these strata appear as light scattering bands often called cloudy bands another interesting stratigraphic feature is what we call bubble free bands viz millimeter thick strata deprived of bubbles and rich in clathrate hydrates which are found within the bubble hydrate transition zone 800 1200 m depth and are probably caused by anomalously fast clathration while there is hardly any interaction between visible micro inclusions and grain boundaries down to 2500 m depth in the deeper ice warmer than 10 c many grain boundaries seem to harvest micro inclusions here we discuss these observations and their relevance for the interpretation of climate records

modelling the liquid water vein system within polar ice sheets as a potential microbial habitat based on the fundamental and distinctive physical properties of polycrystalline ice ih the chemical and temperature profiles within the polar ice sheets and the observed selective partitioning of bacteria into liquid water filled veins in the ice we consider the possibility that microbial life could survive and be sustained within glacial systems here we present a set of modelled vertical profiles of vein diameter vein chemical concentration and vein water volume variability across a range of polar ice sheets using their ice core chemical profiles a sensitivity analysis of veinsinice1 0 the numerical model used in this study shows that the ice grain size and the local borehole temperature are the most significant factors that influence the intergranular liquid vein size and the amount of freeze concentrated impurities partitioned into the veins respectively model results estimate the concentration and characteristics of the chemical broth in the veins to be a potential extremophilic microbial medium the vein sizes are estimated to vary between 0 3 m to 8 m across the vertical length of many polar ice sheets and they may contain up to 2 l of liquid water per litre of solid ice the results suggest that these veins in polar ice sheets could accommodate populations of psychrophilic and hyperacidophilic ultra small bacteria and in some regions even support the habitation of unicellular eukaryotes this highlights the importance of understanding the potential impact of englacial microbial metabolism on polar ice core chemical profiles and provides a model for similar extreme habitats elsewhere in the universe

tropical ocean decadal variability and resonance of planetary wave basin modes part i theory abstract oceanic response to decadal wind forcing is studied in a tropical extratropical basin using two classical theoretical shallow water wave models the equatorial wave model and the planetary wave model extratropical winds are found to generate significant thermocline variability in the tropical ocean with a spectral peak at decadal timescale the preferred decadal time of the response is due to the resonance of the gravest planetary wave basin modes the resonant response however is unimportant in the interior extratropical ocean where it is distorted by the forced response to local ekman pumping it is proposed that the resonance of planetary wave basin modes may provide a mechanism for the generation of decadal variability in the tropical ocean and potentially in the coupled ocean atmosphere system

on the width of the equatorial deep jets the equatorial deep jets edj are a striking feature of the equatorial ocean circulation in the atlantic ocean the edj are associated with a vertical scale of between 300 and 700 m a time scale of roughly 4 5 years and upward energy propagation to the surface it has been found that the meridional width of the edj is roughly 1 5 times larger than expected based on their vertical scale here we use a shallow water model for a high order baroclinic vertical normal mode to argue that mixing of momentum along isopycnals can explain the enhanced width a lateral eddy viscosity of 300 m2 s 1 10 is found to be sufficient to account for the width implied by observations

physical and structural properties of the greenland ice sheet project 2 ice core a review substantial data sets have been collected on the relaxation characteristics density grain size c axis fabrics and ultrasonic velocities of the greenland ice sheet project 2 gisp2 core to its contact with bedrock at 3053 4 m changes in all these properties paralleled closely those found in cores from byrd station antarctica and dye 3 greenland density increased progressively with depth to a maximum of 0 921 mg m3 at about 1400 m at which depth the ice became bubble free below about 2000 m in situ densities began to decrease in response to increasing ice sheet temperatures since drilling much of the ice core has undergone significant volume expansion relaxation due to microcracking and the exsolving of enclathratized gases especially in the brittle ice zone between 650 and 1400 m grain size increased linearly to about 1000 m thereafter remaining fairly constant until the younger dryas event at 1678 m where a twofold to threefold decrease in grain size occurred these grain size changes were accompanied by a progressive clustering of crystal c axes toward the vertical including a small increase in c axis concentration across the younger dryas holocene boundary increased dust levels in the wisconsin ice have contributed to the maintenance of a fine grained texture which with its strong vertical c axis fabric persisted to nearly 3000 m however beginning at about 2800 m layers of coarse grained ice intermixed with the much finer grained matrix ice are observed below 3000 m the ice became very coarse grained this change attributed to annealing recrystallization at elevated temperatures in the ice sheet was accompanied by a dispersed or ring like redistribution of the c axes about the vertical ultrasonic measurements of vertical and horizontal p wave velocities made at 10 m intervals along the entire length of the gisp2 core fully confirmed the results of the crystallo optical observations a return to fine grained ice coincided with the first appearance of brown silty ice 13 m above bedrock bedrock material consisted of 48 cm of till including boulders and cobbles overlying gray biotite granite comprising the true bedrock there is evidence that disturbed structure in the gisp2 cores begins little more than 70 of the way through the ice sheet this disturbance increases with depth until it becomes large enough to cast suspicion on features lasting centuries or more in the bottom 10 of the ice sheet

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

effects of impurities and their redistribution during recrystallization of ice crystals in order to examine the effects of solutes on recrystallization and subsequent grain growth in ice both doped and undoped ice single crystals were extruded through a 120 equal channel angular extrusion jig in order to impart a large shear strain 1 15 upon subsequent annealing at 3 c the original single crystals recrystallized in most cases to a new single crystal with a different orientation increasing the solute concentration for h 2 so 4 to 200 300 ppb and for naci kci and mgso 4 to 5 ppm was found to significantly retard the growth and possibly for h 2 so 4 doped ice the nucleation of new grains in the strained ice single crystals this is indicative of how soluble impurities can retard grain growth in ice cores it was also found that the migrating grain boundaries surrounding the newly formed grains contained large concentrations of impurities often observed as filaments these could have formed by the grain boundaries sweeping up impurities from the lattice into the boundary or by their diffusion to the boundary mechanisms whereby impurities could be concentrated into the grain boundaries in ice cores although the latter mechanism seems unlikely since it would require very high diffusion rates

the structure and chemistry of 94 m greenland ice sheet project 2 ice optical microscopy x ray topography scanning electron microscopy and x ray spectroscopy have been used for microstructural analysis of ice from 94 m depth from greenland ice sheet project 2 the ice had a high density of air bubbles a 2 mm grain size and contained a high dislocation density in most grains 1 10 10 m 2 although a few lower dislocation density grains were present the main impurities na and cl were found in several grain boundaries and triple points often as filaments na and cl were also found in the lattice but to a lesser extent along with s mg k and ca these observations are compared to previous studies of dislocations and impurity locations in natural ice

bedmap a new ice thickness and subglacial topographic model of antarctica measurements of ice thickness on the antarctic ice sheet collected during surveys undertaken over the past 50 years have been brought together into a single database from these data a seamless suite of digital topographic models have been compiled for antarctica and its surrounding ocean this includes grids of ice sheet thickness over the grounded ice sheet and ice shelves water column thickness beneath the floating ice shelves bed elevation beneath the grounded ice sheet and bathymetry to 60 s including the sub ice shelf cavities these grids are consistent with a recent high resolution surface elevation model of antarctica while the digital models have a nominal spatial resolution of 5 km such high resolution is justified by the original data density only over a few parts of the ice sheet the suite does however provide an unparalleled vision of the geosphere beneath the ice sheet and a more reliable basis for ice sheet modeling than earlier maps the total volume of the antarctic ice sheet calculated from the bedmap grid is 25 4 million km3 and the total sea level equivalent derived from the amount of ice contained within the grounded ice sheet is 57 m comprising 52 m from the east antarctic ice sheet and 5 m from the west antarctic ice sheet slightly less than earlier estimates the gridded data sets can be obtained from the authors

pacific decadal variability in the view of linear equatorial wave theory it has recently been proposed within the framework of the linear shallow water equations that tropical pacific decadal variability pdv can be accounted for by basin modes with eigenperiods of 10 to 20 yr amplifying a midlatitude wind forcing with an essentially white spectrum here the authors use a different formalism of linear equatorial wave theory the green s function is computed for the wind forced response of a linear equatorial shallow water ocean and uses the earlier results of cane and moore to obtain a compact closed form expression for the motion of the equatorial thermocline which applies to all frequencies lower than seasonal this expression is new and allows a systematic comparison of the effect of low and high latitude winds on the equatorial thermocline at very low frequencies decadal time scales the planetary geostrophic solution used by cessi and louazel is recovered as well as the equatorial wave solution of liu and a formal explanation for this convergence is given nonetheless this more general solution leads one to a different interpretation of the results in contrast to the aforementioned studies the authors find that the equatorial thermocline is inherently more sensitive to local than to remote wind forcing and that planetary rossby modes only weakly alter the spectral characteristics of the response tropical winds are able to generate a strong equatorial response with periods of 10 to 20 yr while midlatitude winds can only do so for periods longer than about 50 yr the results suggest that ocean basin modes are an unlikely explanation of decadal fluctuations in tropical pacific sea surface temperature

rossby wave coastal kelvin wave interaction in the extratropics part i low frequency adjustment in a closed basin abstract the interaction of open and coastal oceans in a midlatitude ocean basin is investigated in light of rossby and coastal kelvin waves the basinwide pressure adjustment to an initial rossby wave packet is studied both analytically and numerically with the focus on the low frequency modulation of the resulting coastal kelvin wave it is shown that the incoming mass is redistributed by coastal kelvin waves as well as eastern boundary planetary waves while the incoming energy is lost mostly to short rossby waves at the western boundary the amplitude of the kelvin wave is determined by two mass redistribution processes a fast process due to the coastal kelvin wave along the ocean boundary and a slow process due to the eastern boundary planetary wave in the interior ocean the amplitude of the kelvin wave is smaller than that of the incident planetary wave because the initial mass of the rossby wave is spread to the entire basin in a midlatitude ocean basin the slow eastern boundary planetary wave

advanced microstructural characterization of four east antarctic firn ice cores the microstructures and microchemistry of four us international trans antarctic scientific expedition ice cores were examined at three depths 30 60 90m each using scanning electron microscopy including electron backscattered patterns and energy dispersive spectroscopy eds in order to assess the relationship between chemical and physical properties the physical characteristics grain size porosity density internal surface volume and crystallographic orientation at the four sites were inhomogeneous as expected on the basis of differences in the moisture content of deposited snow and the accumulation rate at their respective locations evidence of shallow subgrain boundary formation and trends in internal surface volume having implications for the study of firn densification and ice sheet modeling were also found chemical characterization revealed that site specific variations in particulate concentration and source could accurately be determined using eds analysis it was also found that the combination of elements predominant within the sample controls the morphology and microstructural location of the impurities

observations of polar ice from the holocene and the glacial period using the scanning electron microscope samples taken from the dome c ice core antarctica and the grip ice core greenland are examined using the scanning electron microscope to determine their microstructure in both cores samples are taken from two differing climatic periods the holocene and the last glacial period many of the usual features observed in similar samples under the light microscope are observed including bubbles grain boundaries and clathrate hydrates features not resolvable using the light microscope are also found dust particles are found in situ eighty five per cent of those observed contained silicon which was generally associated with aluminium and magnesium an estimation is made of the relative proportions of dust particles located at grain boundaries and in the bulk of the ice grain at dome c a higher proportion than expected from a random distribution of particles was found located at grain boundaries although in greenland this was not found to be the case for most samples direct evidence is also presented indicating the role of dust particles and microscopical inclusions in impeding or pinning grain boundary migration soluble impurities are also detected at some triple junctions and grain boundaries

the evolution of boundary pressure in ocean basins abstract the boundary pressure adjustment process on an ocean basin scale is elucidated in two sets of numerical experiments first an initial value problem is posed in a primitive equation shallow water model that leads to significant changes in the pressure averaged along the boundary in a closed rectangular ocean basin these results are compared with the analogous problem in a shallow water quasigeostrophic model where the boundary pressure adjustment is parameterized by a consistency constraint that closes the mass circulation and energy balances in quasigeostrophy there is very good agreement in the evolution of the boundary average pressure and qualitative agreement in the evolution of the balanced motions in the interior second idealized kelvin wave experiments are posed in the primitive equation system on an f plane a plane and a plane in a domain of doubled dimensions for 0 a scattering process is evident as the initial kelvin wave transits the first meridional boundary it encoun

high resolution biogeochemical investigation of the ross sea antarctica during the aesops u s jgofs program 1 the results of high resolution biogeochemical measurements in the upper 200 m of the ross sea antarctica obtained during the aesops u s jgofs program using the lamont pumping seasoar lps are presented they consist of three west east transects from 170 e to 180 longitude along the aesops study line at 76 5 s and three short north south transects in the ross sea polynya during the initial and maturing stages of phytoplankton blooms in the austral spring and early summer of 1997 the lps carried an in situ instrument array for measurement of temperature salinity fluorescence photosynthetically active radiation par and dissolved oxygen in addition a highpressure pump mounted aboard the lps fish delivered a continuous seawater sample stream to the shipboard laboratory for high speed analysis of its nutrient nitrate plus nitrate phosphate and silicate and total co2 concentrations and co2 partial pressure pco2 vertical resolution of this sampling equaled or exceeded that of hydrostation style conductivity temperature depth ctd casts horizontal resolution nominally equal to a vertical cast every 3 5 km exceeded station resolution by a factor of 10 while not perfectly synoptic the 20 hour duration of these transects is far shorter than the time typically taken to complete the line with conventional sampling methods these surveys clearly identified three distinct deep water masses below about 100 m high salinity shelf water hssw in the western end of the transects modified circumpolar deep water mcdw in the middle of the transects and low salinity shelf water lssw to the east the regions to the west were characterized by high biological productivity with high n p and c p uptake ratios but little si uptake indicating that the production was dominated by phaeocystis to the east biological productivity was lower than in the west and low n p and c p uptake ratios and high si uptake indicated the dominance of diatoms the difference in uptake ratios appears to be entirely due to anomalously high p uptake by diatoms n c uptake ratios are similar in the two regions and very near canonical redfield stoichiometry the area in the center of the transects was characterized by high stratification and low diatom dominated productivity the reason for this low productivity is unclear but is speculated to be due to the short time which this water has been exposed to an ice free surface the presence of strong variability at horizontal length scales of order 10 km is evident in nearly all fields especially in upper 100 m although many of the features are resolved only by two or three lps tracks each separated by only a few kilometers physical bio optical and chemical variability is observed to extend vertically from sea surface to depths as deep as 140 m far below the 1 light level and the mixed layer depth this may be attributed to downwelling of waters associated with eddies and or meandering a simple statistical measure presented to quantify the errors associated with the undersampling of such a highly variable field shows that biogeochemically important parameters like pco2 and oxygen and chlorophyll concentrations are poorly resolved by a commonly used 50 km hydro station spacing longitudinal averages of these parameters however are predicted fairly well at coarser resolutions index terms 4207 oceanography general arctic and antarctic oceanography 4805

antarctic bottom water production and export by tides in the ross sea 1 current measurements in the western ross sea show that antarctic bottom water is produced at the outer edge of the continental shelf by tidal stirring of antarctic surface water circumpolar deep water and shelf water current amplitudes during spring tides are greater than 1 m s sufficient to carry circumpolar deep water onto the shelf from offshore and stir at least the lower portion of the water column to a nearly homogeneous mixture the antarctic bottom water produced every day during spring tides does not appear to have a seasonal signal its export rate is estimated to be 1 95 1 85 10 6 m 3 s

grain growth in polar ice ii application grain growth observed in polar ice that is not deforming rapidly can be accounted for if concentrations and distributions of extrinsic materials microparticles bubbles and dissolved impurities are characterized fully dissolved impurities segregate to grain boundaries and slow grain growth in all cold glacial ice the high concentration of soluble impurities in wisconsinan ice from the dome c antarctica ice core and perhaps other ice cores probably causes the small grain sizes observed in that ice microparticles have little effect on grain growth in ordinary ice in ice layers that appear dirty owing to concentrations of volcanic tephra such as in the byrd station antarctica ice core or of morainal material micro particles reduce grain growth rates significantly the relatively high vapor pressure of ice allows rapid growth and high mobility of intergranular necks so grain growth in firn is limited by boundary migration rather than by neck growth bubbles formed by pore close off at the firn ice transition are less mobile than grain boundaries causing bubble boundary separation whenever geometric constraints are satisfied however such separation reduces grain growth rates by only about 10 the observed linear increase of grain area with time is thus predicted by theory but the growth rate depends on soluble impurity concentrations as well as on temperature

subtidal currents over the central california slope evidence for offshore veering of the undercurrent and for direct wind driven slope currents abstract in february 1991 an array of six current meter moorings was deployed for one year across the central california outer shelf and slope the main line of the array extended 30 km offshore of the shelf break out to water depths of 1400 m a more sparsely instrumented line displaced 30 km to the northwest extended 14 km offshore though shorter the northern line spanned similar water depths because the gradient of the topography steepened in the northern region a poleward flow pattern typical of the california undercurrent was seen across both lines in the array over most of the year the poleward flow was surface intensified in general the portion of the undercurrent that crossed the southern line had larger amplitudes and penetrated more deeply into the water column than the portion that crossed the northern line transport over the year ranged from 0 to 2 5 sverdrups sv poleward across the southern line 0 to 1 sv poleward across the northern line we suggest the difference in transport was caused by topographic constraints which tended to force the poleward flow offshore of the northern measurement sites the slope of the topography steepened too abruptly to allow the poleward flow to follow isobaths when currents were strong when current velocities lessened a more coherent flow pattern was seen across both lines in the array in general the poleward flow patterns in the undercurrent were not affected by local winds or by the local alongshore pressure gradient nor was a strong seasonal pattern evident rather unexpectedly a small but statistically significant fraction of the current variance over the mid and outer slope was driven by the surface wind stress an alongshelf wind stress caused currents to flow along the slope parallel to the wind field down to depths of 400 m below the surface and out to distances of 2 rossby radii past the shelf break the transfer functions were weak 3 4 cm s per dyn cm 2 but comparable to wind driven current amplitudes of 4 6 cm s per unit wind stress over the middle shelf equatorward alongshelf winds also caused water from 200 300 m over the slope to upwell onto the shelf as the surface water moved offshore

energetic plumes over the western ross sea continental slope rapid descent of dense drygalski trough western ross sea antarctica shelf water over the continental slope within 100 to 250 m thick benthic plumes is described speeds of up to 1 0 m s are recorded flowing at an average angle of 35 to the isobaths entraining ambient lower circumpolar deep water en route this process is predominant in determining the concentration and placement of the shelf water injected into the deep sea as a precursor antarctic bottom water nonetheless a 4 hour duration pulse of undiluted shelf water was observed at depth 1407 m directly north of the drygalski trough moving at around 90 degrees to isobaths and at a speed of 1 4 m s thus the export of ross sea shelf water to the deep sea is accomplished within plumes descending at moderate angle to isobaths punctuated by rapid downhill cascades

holocene electrical and chemical measurements from the epica dome c ice core the comparison between electric electric conductivity measurement ecm and dielectric profiling dep and chemical sulphate and chloride depth profiles along the first 400 m of the epica dome c ice core revealed a very good fit especially for peaks related to volcanic emissions from the comparison between these profiles a dominant contribution of sulphuric acid to the ionic balance of antarctic ice for the holocene was confirmed a progressive increase with depth was observed for chloride concentrations showing a change of relative contribution between sulphate and chloride a higher increase of chloride was evident between 270 and 360 m depth probably due to a change in source or transport processes or to an increase of the annual snow accumulation rate the dep ecm and sulphate ice signatures of tambora ad 1816 and el chichon ad 1259 eruptions are described in detail a characteristic peak series due to hcl deposition was identified at 103 109 m depth from the ecm dep and chloride profiles

on the effect of topography and wind on warm water inflow an idealized study of the southern weddell sea continental shelf system an idealized eddy resolving numerical model with topographic features common to the southern weddell sea is constructed to study mechanisms through which warm deep water enters a wide continental shelf with a trough the open ocean represented by a 1700 m deep channel is connected to a 400 m deep shelf with a continental slope the shelf is narrow 50 km in the east but widens to 300 km at the center of the model domain over the narrow shelf the slope front is balanced by wind driven ekman downwelling and counteracting eddy overturning favoring on shelf transport of warm water in summer scenarios when fresher surface water is present over the wide shelf the ekman downwelling ceases and the mesoscale eddies relax the front inflow of warm water is sensitive to along shelf salinity gradients and is most efficient when denser water over the wide shelf favors up slope eddy transport along isopycnals of the v shaped slope front inflow along the eastern side of the trough cannot penetrate the sill region due to potential vorticity constraints while along the western trough flank eddy induced inflow crosses the sill and reaches the ice front the warm inflow into the trough is sensitive to the density of the outflowing dense shelf water for weaker winds absence of the dense water outflow leads to a reversal of the trough circulation and a strong inflow of warm water while for stronger winds baroclinic effects become less important and the inflow is similar to experiments including dense water outflow this article is protected by copyright all rights reserved

characterizing the internal structure of laboratory ice samples with nuclear magnetic resonance due to solute impurities and freezing point depression in polycrystalline ice a complicated and dynamic network of liquid water forms within the solid ice matrix at the boundaries between ice crystal grains impurity concentrations temperature and pressure influence this network structure and impact physical transport and rheological properties of ice however the nature of this internal network structure is not fully understood here we utilize nuclear magnetic resonance nmr measurements of diffusion and magnetic relaxation to study the geometry and interconnectivity of the liquid filled network in laboratory ice formed from a 7gl 1 nacl solution and its evolution due to recrystallization processes additionally we apply these nmr measurements to observe the impact on ice microstructure of an ice binding protein ibp excreted by the v3519 10 organism flavo bacteriaceae family isolated from the vostok ice core in antarctica recrystallization inhibition was observed as a function of ibp concentration this work demonstrates the utility of advanced nmr techniques for applications to ice microstructure and has broader implications for understanding geophysical properties of cryospheric systems

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

long rossby wave basin crossing time and the resonance of low frequency basin modes the ability of long wave low frequency basin modes to be resonantly excited depends on the efficiency with which energy fluxed onto the western boundary can be transmitted back to the eastern boundary this efficiency is greatly reduced for basins in which the long rossby wave basin crossing time is latitude dependent in the singular case where the basin crossing time is independent of latitude the amplitude of resonantly excited long wave basin modes grows without bound except for the effects of friction the speed of long rossby waves is independent of latitude for quasigeostrophic dynamics and the rectangular basin geometry often used for theoretical studies of the wind driven ocean circulation is such a singular case for quasigeostrophic dynamics for more realistic basin geometries where only a fraction of the energy incident on the western boundary can be transmitted back to the eastern boundary the modes have a finite decay rate that in the limit of weak friction is independent of the choice of frictional parameters explicit eigenmode computations for a basin geometry similar to the north pacific but closed along the equator yield basin modes sufficiently weakly damped that they could be resonantly excited

loop current eddy interaction with the western boundary in the gulf of mexico abstract a two layer intermediate equations model that uniquely allows for the intersection of the bathymetry with the layer interface is used to study the interaction of isolated loop current eddy lce type anticyclones with western boundary topography two idealized topography configurations representative of the gulf of mexico gom coastal topography at 25 and 23 n are studied the 25 n topography configuration is characterized by a relatively wide shelf and a narrow continental slope and the 23 n configuration is characterized by a relatively narrow shelf and a wide continental slope the physical mechanism that has the most significant effect on the evolution of the lce in both topographic configurations is the interaction of the lce with cyclones formed directly to its north through the process of off shelf advection of potential vorticity in the upper layer the lce interaction with those cyclones that are generated through this mechanism results in the lce becoming elliptic and rotating clo

reconstructing past atmospheric co2 concentration based on ice core analyses open questions due to in situ production of co2 in the ice analysis of air extracted from bubbles of polar ice showed the anthropogenic increase of atmospheric co2 concentration during the past few hundred years preindustrial concentration 280 ppmv and unexpectedly that the concentration also increased due to natural causes from 200 to 280 ppmv during the transition from the last glacial epoch to the holocene however more detailed reconstructions based on ice core analyses suggested that some of the additional observed variations were actually due to the modification of co2 concentration in the bubbles by chemical reactions between impurities in the ice detailed analyses of acidity the carbonate concentration the concentration of oxidation agents like hydrogen peroxide h2o2 and organic compounds e g formaldehyde hcho along short intervals of ice cores representing only a few annual layers allowed us to investigate these chemical reactions the records are not conclusive but they indicate that the oxidation of organic compounds is at least as important as acid carbonate reactions ice containing a low mean carbonate and a low h2o2 concentration as well as a small scattering of co2 results obtained on several adjacent samples representing a few annual layers at most is at present the best guarantee for reliable results of the atmospheric co2 concentration

the role of acids in electrical conduction through ice 1 electrical conduction through meteoric polar ice is controlled by soluble impurities that originate mostly from sea salt biomass burning and volcanic eruptions the strongest conductivity response is to acids yet the mechanism causing this response has been unclear here we elucidate conduction mechanisms in ice using broadband dielectric spectroscopy of meteoric polar ice cores we find that conduction through polycrystalline polar ice is consistent with jaccard theory for migration of charged protonic point defects through single ice crystals except that bulk dc conduction is impeded by grain boundaries neither our observations nor modeling using archie s law support the hypothesis that grain boundary networks of unfrozen acids cause significant electrolytic conduction common electrical logs of ice cores by electrical conductivity measurement ecm or dielectric profiling dep and the attenuation of radio waves in ice sheets thus respond to protonic point defects only this response implies that joint interpretation of electrical and chemical logs can determine impurity partitioning between the lattice and grain boundaries or inclusions for example in the greenland ice core project grip ice core from central greenland on average more than half of the available lattice soluble impurities h cl nh4 create defects understanding this partitioning could help further resolve the nature of past changes in atmospheric chemistry

cross shelf and out of bay transport driven by an open ocean current abstractthis paper studies the interaction of an antarctic circumpolar current acc like wind driven channel flow with a continental slope and a flat bottomed bay shaped shelf near the channel s southern boundary interaction between the model acc and the topography in the second layer induces local changes of the potential vorticity pv flux which further causes the formation of a first layer pv front near the base of the topography located between the acc and the first layer slope the newly formed pv front is constantly perturbed by the acc and in turn forces the first layer slope with its own variability in an intermittent but persistent way the volume transport of the slope water across the first layer slope edge is mostly directly driven by eddies and meanders of the new front and its magnitude is similar to the maximum ekman transport in the channel near the bay s opening the effect of the topographic waves excited by offshore variability dominates the cross isobath exchange and induces a

multiple equilibria and low frequency variability of the wind driven ocean circulation abstract the link between low frequency time dependent variability and the existence of multiple unstable steady state solutions in a reduced gravity quasigeostrophic ocean model for the midlatitude wind driven circulation is investigated it is shown that a sequence of successive symmetry breaking pitchfork bifurcations lead to multiple equilibria that differ from each other primarily in the elongation of the recirculation cell in the amount of meandering present in the intergyre jet and in a north south shift in the eastward jet the elongation of the recirculation cells and the meandering of the jet play compensating roles in the establishment of the global energy and vorticity balance the solutions also have distinct energy levels but general agreement between them and the bumps in a histogram of the total energy obtained from a 1200 yr time dependent simulation is not found nevertheless a substantial fraction of the variance 30 can be accounted for by four coherent structures that capture th

hydrochemistry of ice stream beds evaporitic or microbial effects recently new data have been acquired on the chemical composition of waters within the glacial till beneath the kamb ice stream kis formerly ice stream c and the bindschadler ice stream bis formerly ice stream d two of the arteries of ice loss from the antarctic ice sheet ais we compare this water chemistry with basally stored subglacial waters from arctic and alpine glaciers and the only other measurements of sub ice sheet chemistry to date that emerging from beneath law dome near casey station sw antarctica during a jokulhlaup we find that the chemistries pose significant questions about the hydrology and biogeochemistry of ice sheet beds copyright 2010 john wiley sons ltd