iceberg trajectory modeling and meltwater injection in the southern ocean this is the first large scale modeling study of iceberg trajectories and melt rates in the southern ocean an iceberg model was seeded with climatological iceberg calving rates based on a calculation of the net surface accumulation from each snow catchment area on the antarctic continent in most areas modeled trajectories show good agreement with observed patterns of iceberg motion though discrepencies in the weddell sea have highlighted problems in the ocean general circulation model output used to force the iceberg model the coriolis force is found to be important in keeping bergs entrained in the coastal current around antarctica and topographic features are important in causing bergs to depart from the coastal regions the modeled geographic distribution of iceberg meltwater joining the ocean has been calculated and is found in many near coastal regions to be comparable in magnitude to the excess of precipitation over evaporation p e

climate response to increasing antarctic iceberg and ice shelf melt mass loss from the antarctic continent is increasing however climate models either assume a constant mass loss rate or return snowfall over land to the ocean to maintain equilibrium numerous studies have investigated sea ice and ocean sensitivity to this assumption and reached different conclusions possibly due to different representations of melt fluxes the coupled atmosphere land ocean sea ice model hadgem3 gc3 1 includes a realistic spatial distribution of coastal melt fluxes a new ice shelf cavity parameterization and explicit representation of icebergs this configuration makes it appropriate to revisit how increasing melt fluxes influence ocean and sea ice and to assess whether responses to melt from ice shelves and icebergs are distinguishable we present results from simulated scenarios of increasing meltwater fluxes and show that these drive sea ice increases and for increasing ice shelf melt a decline in antarctic bottom water formation in our experiments the mixed layer around the antarctic coast deepens in response to rising ice shelf meltwater and shallows in response to stratification driven by iceberg melt we find similar surface temperature and salinity responses to increasing meltwater fluxes from ice shelves and icebergs but midlayer waters warm to greater depths and farther north when ice shelf melt is present we show that as meltwater fluxes increase snowfall becomes more likely at lower latitudes and antarctic circumpolar current transport declines these insights are helpful for interpretation of climate simulations that assume constant mass loss rates and demonstrate the importance of representing increasing melt rates for both ice shelves and icebergs

large icebergs characteristics from altimeter waveforms analysis large uncertainties exist on the volume of ice transported by the southern ocean large icebergs a key parameter for climate studies because of the paucity of information especially on iceberg thickness using icebergs tracks from the national ice center nic and brigham young university byu databases to select altimeter data over icebergs and a method of analysis of altimeter waveforms a database of 5366 icebergs freeboard elevation length and backscatter covering the 2002 2012 period has been created the database is analyzed in terms of distributions of freeboard length and backscatter showing differences as a function of the iceberg s quadrant of origin the database allows to analyze the temporal evolution of icebergs and to estimate a melt rate of 35 39 m yr 1 neglecting the firn compaction the total daily volume of ice estimated by combining the nic and altimeter sizes and the altimeter freeboards regularly decreases from 2 2 104km3 in 2002 to 0 9 104km3 in 2012 during this decade the total loss of ice 1800 km3 yr 1 is twice as large as than the input 960 km3 yr 1 showing that the system is out of equilibrium after a very large input of ice between 1997 and 2002 breaking into small icebergs represents 80 1500 km3 yr 1 of the total ice loss while basal melting is only 18 320 km3 yr 1 small icebergs are thus the major vector of freshwater input in the southern ocean

tracking large tabular icebergs using the seawinds ku band microwave scatterometer abstract knowledge of iceberg locations is important for safety reasons as well as for understanding many geophysical and biological processes originally designed to measure wind speed and direction over the ocean seawinds is a microwave scatterometer that operates at 13 4 ghz ku band on the quikscat satellite radar measurements from seawinds are collected and processed on a daily basis using resolution enhancement techniques to produce daily radar images because icebergs scatter microwave energy more than sea ice and sea water icebergs are detected as high backscatter targets surrounded by lower backscatter regions in daily seawinds images as a result iceberg positions are determined in real time and a time series of iceberg positions is maintained in an antarctic iceberg database by brigham young university s microwave earth remote sensing mers laboratory since seawinds operates independent of both solar illumination and cloud cover and has a large daily spatial coverage this paper demonstrates that seawinds is an excellent platform to detect and track large tabular icebergs these icebergs are generally larger than 5 km and are typically characterized as a rough ice plateau above the surrounding sea water or sea ice the number of icebergs tracked in the mers antarctic iceberg database is found to be generally greater than the number of icebergs tracked by the national ice center the movement patterns of all icebergs detected by seawinds are also analyzed and 90 of icebergs are found to travel a counter clockwise path around antarctica and accumulate in the weddell and scotia seas iceberg detection and tracking is demonstrated via multiple case studies that highlight icebergs c 19a and a 22a using the mers database and through real time operational support of the 2005 2008 and 2009 nsf antarctic cruises iceberg positions are validated by using collocated high resolution satellite imagery and by navigating the nsf ships to physically intercept several large tabular icebergs in the weddell and scotia seas

calving processes and the dynamics of calving glaciers abstract calving of icebergs is an important component of mass loss from the polar ice sheets and glaciers in many parts of the world calving rates can increase dramatically in response to increases in velocity and or retreat of the glacier margin with important implications for sea level change despite their importance calving and related dynamic processes are poorly represented in the current generation of ice sheet models this is largely because understanding the calving problem involves several other long standing problems in glaciology combined with the difficulties and dangers of field data collection in this paper we systematically review different aspects of the calving problem and outline a new framework for representing calving processes in ice sheet models we define a hierarchy of calving processes to distinguish those that exert a fundamental control on the position of the ice margin from more localised processes responsible for individual calving events the first order control on calving is the strain rate arising from spatial variations in velocity particularly sliding speed which determines the location and depth of surface crevasses superimposed on this first order process are second order processes that can further erode the ice margin these include fracture propagation in response to local stress imbalances in the immediate vicinity of the glacier front undercutting of the glacier terminus by melting at or below the waterline and bending at the junction between grounded and buoyant parts of an ice tongue calving of projecting submerged ice feet can be regarded as a third order process because it is paced by first or second order calving above the waterline first order calving can be represented in glacier models using a calving criterion based on crevasse depth which is a function of longitudinal strain rate modelling changes in terminus position and calving rates thus reduces to the problem of determining the ice geometry and velocity distribution realistic solutions to the problem of modelling ice flow therefore depend critically on an appropriate choice of sliding law models that assume that basal velocities are controlled by basal drag can replicate much of the observed behaviour of calving glaciers with grounded termini but an important limitation is that they cannot be used to model floating glacier termini or ice shelves alternative sliding laws that parameterise drag from the glacier margins provide more flexible and robust ways of representing calving in ice sheet models such models can explain a remarkable range of observed phenomena within a simple unifying framework including downglacier increases in velocity and strain rates where basal and or lateral drag diminishes flow acceleration in response to thinning through time the tendency for glaciers to stabilise at pinning points in relatively shallow water or fjord narrowings the constraints on ice shelf stability and the contrasts in calving rates between tidewater and freshwater calving glaciers many unresolved issues remain however including the role played by the removal of backstress in the acceleration of retreating calving glaciers and the controls on melting at and below the waterline

calving and ice shelf break up processes investigated by proxy antarctic tabular iceberg evolution during northward drift using a combination of satellite sensors field measurements and satellite uplinked in situ observing stations we examine the evolution of several large icebergs drifting east of the antarctic peninsula towards south georgia island three styles of calving are observed during drift rift calvings edge wasting and rapid disintegration rift calvings exploit large pre existing fractures generated in the shelf environment and can occur at any stage of drift edge wasting is calving of the iceberg perimeter by numerous small edge parallel sliver shaped icebergs preserving the general shape of the main iceberg as it shrinks this process is observed only in areas north of the sea ice edge rapid disintegration where numerous small calvings occur in rapid succession is consistently associated with indications of surface melt saturation surface lakes firn pit ponding freeboard measurements by icesat indicate substantial increases in ice thinning rates north of the sea ice edge from 30 m a 1 but surface densification is shown to be an important correction 2 m freeboard loss before the firn saturates edge wasting of icebergs in warm surface water sea ice free 1 8 c implies a mechanism based on waterline erosion rapid disintegration larsen b style break up is likely due to the effects of surface or saturated firn water acting on pre existing crevasses or on wave or tidally induced fractures changes in microwave backscatter of iceberg firn as icebergs drift into warmer climate and experience increased surface melt suggest a means of predicting when floating ice plates are evolving towards disintegration

relationship between magnetic susceptibility and sediment grain size since the last glacial period in the southern ocean off the northern antarctic peninsula linkages between the cryosphere and atmospheric circulation abstract magnetic susceptibility ms values in scotia sea sediments showed strong correlations to ice core non sea salt ca2 concentration dust input which emphasizes the role of atmospheric circulation in the southern ocean as a result the correlation between these values was suggested as a powerful tool for age reconstruction of marine sediments in the southern ocean however controls on ms variation in scotia sea sediments are not clear in this study we documented records of grain size ms values 10 6 cgs g of bulk sediments and ms values of sand sized 63 m coarse silt sized 16 63 m and fine sediment fractions

antarctic icebergs distributions 1992 2014 basal melting of floating ice shelves and iceberg calving constitute the two almost equal paths of freshwater flux between the antarctic ice cap and the southern ocean the largest icebergs 100 km2 transport most of the ice volume but their basal melting is small compared to their breaking into smaller icebergs that constitute thus the major vector of freshwater the archives of nine altimeters have been processed to create a database of small icebergs 8 km2 within open water containing the positions sizes and volumes spanning the 1992 2014 period the intercalibrated monthly ice volumes from the different altimeters have been merged in a homogeneous 23 year climatology the iceberg size distribution covering the 0 1 10 000 km2 range estimated by combining small and large icebergs size measurements follows well a power law of slope 1 52 0 32 close to the 3 2 laws observed and modeled for brittle fragmentation the global volume of ice and its distribution between the ocean basins present a very strong interannual variability only partially explained by the number of large icebergs indeed vast zones of the southern ocean free of large icebergs are largely populated by small iceberg drifting over thousands of kilometers the correlation between the global small and large icebergs volumes shows that small icebergs are mainly generated by large ones breaking drifting and trapping by sea ice can transport small icebergs for long period and distances small icebergs act as an ice diffuse process along large icebergs trajectories while sea ice trapping acts as a buffer delaying melting

stable chromium isotopic composition of meteorites and metal silicate experiments implications for fractionation during core formation we present new mass independent and mass dependent cr isotope compositions for meteorites measured by double spike thermal ionisation mass spectrometry small differences in both mass independent 53cr and 54cr relative to the bulk silicate earth are reported and are very similar to previously published values carbonaceous chondrites are characterised by an excess in 54cr compared to ordinary and enstatite chondrites which make mass independent cr isotopes a useful tool for distinguishing between meteoritic groups mass dependent stable cr isotope compositions for the same samples are also reported carbonaceous and ordinary chondrites are identical within uncertainty with average 53cr values of 0 118 0 040 and 0 143 0 074 respectively the heaviest isotope compositions are recorded by an enstatite chondrite and a co carbonaceous chondrite both of which have relatively reduced chemical compositions implying some stable cr isotope fractionation related to redox processes in the circumstellar disk the average 53cr values for chondrites are within error of the estimate for the bulk silicate earth bse also determined by double spiking the lack of isotopic difference between chondritic material and the bse provides evidence that cr isotopes were not fractionated during core formation on earth a series of high pressure experiments was also carried out to investigate stable cr isotope fractionation between metal and silicate and no demonstrable fractionation was observed consistent with our meteorites data mass dependent cr isotope data for achondrites suggest that cr isotopes are fractionated during magmatic differentiation and therefore further work is required to constrain the cr isotopic compositions of the mantles of vesta and mars

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

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

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

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

in situ measurements of antarctic snow compaction compared with predictions of models 1 we describe in situ measurements of the compaction of antarctic snow at three different sites in antarctica the rate of compaction was measured hourly over various depth intervals for up to two years these measurements show that compaction at each of the sites occurs through slow viscous deformation of the snowpack with no significant contribution from sudden collapse of weak layers the measured rates of compaction at the coldest site exhibit a strong seasonality consistent with a temperature dependent sintering mechanism having activation energy of 70 kj mol 1 at the two warmer sites activation energies of 80 and 120 kj mol 1 provide slightly better agreement with the observations published models of snow compaction underestimate the temperature sensitivity a good match to our observations is provided by a semi empirical model based on rate equations for lattice diffusion nabarro herring creep of material around pores combined with normal grain growth this model also provides a theoretical basis for a widely used empirical model of snow compaction the rate coefficient for lattice diffusion inferred from our measurements is considerably higher than published values however and other creep mechanisms cannot be ruled out

modeling of firn compaction for estimating ice sheet mass change from observed ice sheet elevation change changes in ice sheet surface elevation are caused by a combination of ice dynamic imbalance ablation temporal variations in accumulation rate firn compaction and underlying bedrock motion thus deriving the rate of ice sheet mass change from measured surface elevation change requires information on the rate of firn compaction and bedrock motion which do not involve changes in mass and requires an appropriate firn density to associate with elevation changes induced by recent accumulation rate variability we use a 25year record of surface temperature and a parameterization for accumulation change as a function of temperature to drive a firn compaction model we apply this formulation to icesat measurements of surface elevation change at three locations on the greenland ice sheet in order to separate the accumulation driven changes from the ice dynamic ablation driven changes and thus to derive the corresponding mass change our calculated densities for the accumulation driven changes range from 410 to 610kgm 3 which along with 900kgm 3 for the dynamic ablation driven changes gives average densities ranging from 680 to 790kgm 3 we show that using an average or effective density to convert elevation change to mass change is not valid where the accumulation and the dynamic elevation changes are of opposite sign

cooling dilution and mixing of ocean water by free drifting icebergs in the weddell sea abstract iceberg c 18a 35 7 0 184 km was studied repeatedly by five circumnavigational surveys in march april 2009 during the period of the surveys c 18a travelled 109 nautical miles in 23 days covering an area of 8 1 10 3 km 2 this iceberg was formed from iceberg c 18 76 7 km that originated from the ross ice shelf in may 2002 ship based measurements show that this iceberg produced fresh meltwater above the seasonal pycnocline that diluted and chilled the water it passed through from the surface to a depth of approximately 50 m summer mixed layer the surface meltwater effects were detectable as far away as 19 km and persisted for at least 10 days we also found evidence that this iceberg was disrupting the weddell deep water to depths up to 1500 m if we include these deep effects through the water column the estimate of ocean water altered by this single iceberg reaches 3 10 12 m 3 over 23 days chemical and biological effects were detected at the same space and time scales as the physical properties with decreasing partial pressure of carbon dioxide pco 2 close to the iceberg and lower particle and chlorophyll concentration ten days after the passage of c 18a chlorophyll a had increased by 15 these results are consistent with alternative hypotheses regarding the role of icebergs as mediators of a localized geophysical disturbance h 1 as well as promoters of chlorophyll a production h 2

experimental evidence for mo isotope fractionation between metal and silicate liquids stable isotope fractionation of siderophile elements may inform on the conditions and chemical consequences of core mantle differentiation in planetary objects the extent to which mo isotopes fractionate during such metal silicate segregation however is so far unexplored we have therefore investigated equilibrium fractionation of mo isotopes between liquid metal and liquid silicate to evaluate the potential of mo isotopes as a new tool to study core formation we have performed experiments at 1400 and 1600 c in a centrifuging piston cylinder tin was used to lower the melting temperature of the fe based metal alloys to 1400 c while variable fe oxide contents were used to vary oxygen fugacity in graphite and mgo capsules isotopic analyses were performed using a double spike technique in experiments performed at 1400 c the 98mo 95mo ratio of silicate is 0 19 0 03 0 19 0 03 95 confidence interval heavier than that of metal this fractionation is not significantly affected by the presence or absence of carbon molybdenum isotope fractionation is furthermore independent of oxygen fugacity in the range iw 1 79 to iw 0 47 which are plausible values for core formation experiments at 1600 c show that at equilibrium the 98mo 95mo ratio of silicate is 0 12 0 02 0 12 0 02 heavier than that of metal and that the presence or absence of sn does not affect this fractionation equilibrium mo isotope fractionation between liquid metal and liquid silicate as a function of temperature can therefore be described as mometal silicate98 95 4 70 0 59 105 t2 our experiments show that mo isotope fractionation may be resolvable up to metal silicate equilibration temperatures of about 2500 c rendering mo isotopes a novel tool to investigate the conditions of core formation in objects ranging from planetesimals to earth sized bodies

icesat profiles of tabular iceberg margins and iceberg breakup at low latitudes 1 icesat elevation profiles of tabular iceberg margins and the ronne ice shelf edge reveal shapes indicative of two types of bending forces icebergs and shelf fronts in sea ice covered areas have broad 1000 m wide rounded 0 6 m high berms and outer edges that slope down several meters toward the water bergs in warmer water have 2 to 5m ramparts with 1500 m wide edge parallel moats inboard of the edge this latter pattern was first revealed in images from international space station iss showing edge parallel melt ponds on one iceberg just prior to its disintegration model results indicate the patterns are caused by hydrostatic and lithostatic forces acting on the ice face berm profiles arise from differences between ice and water pressure along the face rampart moat profiles result from waterline erosion creating a submerged bench of ice that lifts the ice edge we use the results to discuss iceberg breakup at low latitudes

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

contribution of giant icebergs to the southern ocean freshwater flux 1 in the period 1979 2003 the mass of giant icebergs icebergs larger than 18 5 km in length calving from antarctica averaged 1089 300 gt yr 1 of ice under half the snow accumulation over the continent given by the intergovernmental panel on climate change 2246 86 gt yr 1 here we combine a database of iceberg tracks from the national ice center and a model of iceberg thermodynamics in order to estimate the amount and distribution of meltwater attributable to giant icebergs by comparing with published modeled meltwater distribution for smaller bergs we show that giant icebergs have a different melting pattern an estimated 35 of giant icebergs mass is exported north of 63 s versus 3 for smaller bergs although giant bergs spend more of the earlier part of their history nearer to the coast we combine both estimates to produce the first iceberg meltwater map that takes into account giant icebergs the average meltwater input is shown to exceed precipitation minus evaporation p e in certain areas and is a nonnegligible term in the balance of freshwater fluxes in the southern ocean the calving of giant icebergs is however episodic this might have implications for their impact on the freshwater budget of the ocean it is estimated that over the period 1987 2003 the meltwater flux in the weddell and ross seas has varied by at least 15 000 m3 s 1 over a month because of the potential sensitivity of the production of deep waters to abrupt changes in the freshwater budget variations in iceberg melt rates of this magnitude might be climatologically significant

silicon isotopes in meteorites and planetary core formation the silicon si isotope compositions of 42 meteorite and terrestrial samples have been determined using mc icpms with the aim of resolving the current debate over their compositions and the implications for core formation no systematic 30si differences are resolved between chondrites 30si 0 49 0 15 2 sd and achondrites 30si 0 47 0 11 2 sd although enstatite chondrites are consistently lighter 30si 0 63 0 07 2 sd in comparison to other meteorite groups the data reported here for meteorites and terrestrial samples display an average difference 30sibse meteorite 0 15 0 10 which is consistent within uncertainty with previous studies no effect from sample heterogeneity preparation chemistry or mass spectrometry can be identified as responsible for the reported differences between current datasets the heavier composition of the bulk silicate earth is consistent with previous conclusions that si partitioned into the metal phase during metal silicate equilibration at the time of core formation fixing the temperature of core formation to the peridotite liquidus and using an appropriate metal silicate fractionation factor e 0 89 the 30sibse meteorite value from this study indicates that the earth core contains at least 2 5 and possibly up to 16 8 wt si

geographical distribution and volume of antarctic icebergs derived from ship observation data information on the occurrence spatial distribution and morphometric characteristics of antarctic icebergs is needed in a large number of applications including navigation heat and freshwater balance calculations biochemistry of the ocean and climatology using over 60 000 ship observations of icebergs in the southern ocean collected since the end of the 1940s we have produced a detailed map of the distribution of antarctic icebergs as well as maps of related statistics including the standard deviation minimum and maximum values of the iceberg concentration and the probability of iceberg free observations the study incorporated small and medium sized icebergs with a length of 2 and 16 893 km 3 with uncertainties of 32 33

weddell sea iceberg drift five years of observations since 1999 52 icebergs have been tagged with gps buoys in the weddell seato enable monitoring of their position the chosen icebergs were of small tomedium size with a few icebergs larger than 10 km associatedwith the calving of icebergs a38 and a43 from the ronne ice shelf the majority of icebergs were tagged off neumayer station 8e 70s it was found that smaller bergs with edges shorter than 200 m had the shortestlife cycle 0 5 yr iceberg and thus freshwater export out of theweddell sea was found to be highly variable in one year the majority of buoysdeployed remained in the weddell sea constituting about 40 of the ncep p efreshwater input whereas in other years all of the tagged icebergs were exported the observed drifts of icebergs and sea ice showed a remarkably coherent motion the analysis of an iceberg sea ice buoy array in the western weddell seaand an iceberg array in the eastern weddell sea showed a coherent sea iceiceberg drift in sea ice concentrations above 86 dynamic kinematic parameter dkp during the course of coherent movement were low and deviations from the meancourse associated with the passage of low pressure system the length scale ofcoherent movement was estimated to be less than 250km about half the value found forthe arctic ocean

unlocking the zinc isotope systematics of iron meteorites zinc isotope compositions 66zn and concentrations were determined for metal samples of 15 iron meteorites across groups iab iiab and iiiab also analyzed were troilite and other inclusions from the iab iron toluca furthermore the first zn isotope data are presented for metal silicate partitioning experiments that were conducted at 1 5 gpa and 1650 k three partitioning experiments with run durations of between 10 and 60 min provide consistent zn metal silicate partition coefficients of 0 7 and indicate that zn isotope fractionation between molten metal and silicate is either small at less than about 0 2 0 2 or absent metals from the different iron meteorite groups display distinct ranges in zn contents with concentrations of 0 08 0 24 g g for iiabs 0 8 2 5 g g for iiiabs and 12 40 g g for iabs in contrast all three groups show a similar range of 66zn values reported relative to jmc lyon zn from 0 5 0 5 to 3 0 3 0 with no clear systematic differences between groups however distinct linear trends are defined by samples from each group in plots of 66zn vs 1 zn and these correlations are supported by literature data based on the high zn concentration and 66zn 0 determined for a chromite rich inclusion of toluca modeling is employed to demonstrate that the zn trends are best explained by segregation of chromite from the metal phase this process can account for the observed zn 66zn cr systematics of iron meteorite metals if zn is highly compatible in chromite and zn partitioning is accompanied by isotope fractionation with 66znchr met 1 5 1 5 based on these findings it is likely that the parent bodies of the iab complex iiab and iiiab iron meteorites featured 66zn values of about 1 0 to 0 5 0 5 similar to the zn isotope composition inferred for the bulk silicate earth and results obtained for chondritic meteorites together this implies that most solar system bodies formed with similar bulk zn isotope compositions despite large differences in zn contents

the radiation characteristics of an arbitrary antenna positioned on a polar ice sheet the radiation pattern of an arbitrarily shaped antenna system placed directly on the surface of a polar ice sheet a configuration often used for ice probing radars may be determined at any depth within the ice sheet using a two step process the distribution of the radiated field just beneath the surface may be determined first using the method of moments and geometric optics can then be used to calculate the effects of the exponential density gradient of the ice closed form solutions of the ray tracing equation valid at any depth within the ice sheet allow rapid calculation of the effective look angles and gain increases of any antenna mounted on the surface these solutions asymptotically approach previously determined relations which are valid only at great depths a numerical example demonstrates the use of this procedure in the design of a practical ice probing radar antenna system

the stable cr isotope inventory of solid earth reservoirs determined by double spike mc icp ms abstract we present the first comprehensive set of stable cr isotope data for the major igneous silicate earth reservoirs cr iii rich ores and minerals and hydrothermal chromates these were determined by mc icp ms using a double spike technique mantle xenoliths ultramafic rocks cumulates as well as oceanic and continental basalts share a common cr isotope composition with an average 53 52 cr value of 0 124 0 101 2 sd relative to the isotopically certified chromium standard nist srm 979 an isotopic difference between mantle xenoliths and basalts as was reported for iron was not observed for chromium thus the change in oxidation state that is observed when solid mantle rocks containing only trivalent chromium partially melt to form basaltic melts which predominantly contain bivalent chromium does not cause any measurable cr isotope fractionation chromite separates from major chromitite seams of the bushveld and great dyke layered igneous complexes are invariable in their cr isotope compositions and reproduce within uncertainties the average 53 52 cr srm 979 value of igneous silicate earth reservoirs this is important for environmental stable cr isotope studies because it labels the approximate isotope composition of industrial cr vi pollutants the cr isotope compositions of hydrothermal lead chromates crocoites pbcr vi o 4 from various localities yield 53 52 cr srm 979 values between 0 640 and 1 037 these cr isotope compositions are substantially heavier than those of igneous silicate rocks from which the chromium was leached precipitation experiments revealed an isotope fractionation of 53 52 cr crocoite cr vi aq of only ca 0 10 0 05 at a temperature of 20 c thus the heavy cr isotope signature of crocoites is most likely the result of repeated redox cycling of chromium in hydrothermal processes

calving fluxes and basal melt rates of antarctic ice shelves iceberg calving has been assumed to be the dominant cause of mass loss for the antarctic ice sheet with previous estimates of the calving flux exceeding 2 000 gigatonnes per year1 2 more recently the importance of melting by the ocean has been demonstrated close to the grounding line and near the calving front3 4 5 so far however no study has reliably quantified the calving flux and the basal mass balance the balance between accretion and ablation at the ice shelf base for the whole of antarctica the distribution of fresh water in the southern ocean and its partitioning between the liquid and solid phases is therefore poorly constrained here we estimate the mass balance components for all ice shelves in antarctica using satellite measurements of calving flux and grounding line flux modelled ice shelf snow accumulation rates6 and a regional scaling that accounts for unsurveyed areas we obtain a total calving flux of 1 321 144 gigatonnes per year and a total basal mass balance of 1 454 174 gigatonnes per year this means that about half of the ice sheet surface mass gain is lost through oceanic erosion before reaching the ice front and the calving flux is about 34 per cent less than previous estimates derived from iceberg tracking1 2 7 in addition the fraction of mass loss due to basal processes varies from about 10 to 90 per cent between ice shelves we find a significant positive correlation between basal mass loss and surface elevation change for ice shelves experiencing surface lowering8 and enhanced discharge9 we suggest that basal mass loss is a valuable metric for predicting future ice shelf vulnerability to oceanic forcing

paleoceanographic changes in the southern ocean off elephant island since the last glacial period links between surface water productivity nutrient utilization bottom water currents and ice rafted debris abstract to understand past changes in ocean cryosphere interactions in the southern ocean off the antarctic peninsula multi proxy analyses of three sediment cores located off elephant island were used to reconstruct changes in paleoproductivity nutrient utilization bottom current intensity and iceberg calving since the last glacial period the glacial period was characterized by low surface water productivity with high nutrient utilization indicating surface water stratification during the deglaciation surface water productivity increased with decreasing nutrient utilization implying that the increase is associated with increased nutrient supply from the subsurface water by enhancing antarctic circumpolar current acc influence as fronts migrate southward with warming abundant occurrence of grains 1 mm during the deglacial period indicates rapid ice sheet retreat with large scale melting and calving during the glacial period however coarse silt fine sand sized fraction represented ice rafted debris ird the different ird grain size characteristics are thought to be related to the ird source material characteristics regardless of ird input the running downcore correlation 5 to 9 point between sortable silt mean grain size and percentage showed that sediments are well sorted by bottom current however the cross plot of them showed different temporal relationships sediments were sorted by the acc and southwestward flowing bottom current along with southward migration of fronts and the acc southwestward flowing bottom current influence diminished whereas the acc influence increased particularly from 7 ka our results indicate that the sedimentary processes in the scotia sea largely depend on the regional interactions between the ocean and the cryosphere

delineation of faulting and basin geometry along a seismic reflection transect in urbanized san bernardino valley california fourteen kilometers of continuous shallow seismic reflection data acquired through the urbanized san bernardino valley california have revealed numerous faults between the san jacinto and san andreas faults as well as a complex pattern of downdropped and uplifted blocks these data also indicate that the loma linda fault continues northeastward at least 4 5 km beyond its last mapped location on the southern edge of the valley and to within at least 2 km of downtown san bernardino previously undetected faults within the valley northeast of the san jacinto fault are also imaged including the inferred western extension of the banning fault and several unnamed faults the rialto colton fault is interpreted southwest of the san jacinto fault the seismic data image the top of the crystalline basement complex across 70 of the profile length and show that the basement has an overall dip of roughly 10 southwest between perris hill and the san jacinto fault gravity and aeromagnetic data corroborate the interpreted location of the san jacinto fault and better constrain the basin depth along the seismic profile to be as deep as 1 7 km these data also corroborate other fault locations and the general dip of the basement surface at least 1 2 km of apparent vertical displacement on the basement is observed across the san jacinto fault at the profile location the basin geometry delineated by these data was used to generate modeled ground motions that show peak horizontal amplifications of 2 3 5 above bedrock response in the 0 05 to 1 0 hz frequency band which is consistent with recorded earthquake data in the valley