c band radar polarimetry useful for detection of icebergs in sea ice this paper is focused on investigations of polarimetric c band radar signatures of icebergs in sea ice covered ocean regions the main objective is to assess the potential improvement of iceberg detection when using radar polarimetry the dominant backscattering mechanisms of icebergs are deduced by evaluating different polarimetric parameters magnitudes of the cross polarization ratios the correlation coefficients between hh and vv polarized signals and the entropy alpha parameters indicate a strong contribution of volume scattering in many cases over most icebergs the phase differences between hh and vv polarization are larger than zero spatial patterns of the polarimetric parameters differ from iceberg to iceberg and between different parameters on some bergs they only exhibit slight variations whereas on others they show noiselike textures but also more systematic changes are observed occasionally radar intensities of icebergs are of similar magnitude as those of sea ice only for a number of these cases the combined use of the investigated polarimetric parameters together with intensity improves the discrimination performance between icebergs and sea ice

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

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

pyrite textures and trace element compositions from the granodiorite hosted gold deposit at jonnagiri eastern dharwar craton india implications for gold mineralization processes

a simulation of small to giant antarctic iceberg evolution differential impact on climatology estimates we present a simulation of antarctic iceberg drift and melting that includes small medium sized and giant tabular icebergs with a realistic size distribution for the first time an iceberg model is initialized with a set of nearly 7000 observed iceberg positions and sizes around antarctica the study highlights the necessity to account for larger and giant icebergs in order to obtain accurate melt climatologies we simulate drift and lateral melt using iceberg draft averaged ocean currents temperature and salinity a new basal melting scheme originally applied in ice shelf melting studies uses in situ temperature salinity and relative velocities at an iceberg s bottom climatology estimates of antarctic iceberg melting based on simulations of small 2 2 km small to medium sized 10 km and small to giant icebergs including icebergs 10 km exhibit differential characteristics successive inclusion of larger icebergs leads to a reduced seasonality of the iceberg meltwater flux and a shift of the mass input to the area north of 58 s while less meltwater is released into the coastal areas this suggests that estimates of meltwater input solely based on the simulation of small icebergs introduce a systematic meridional bias they underestimate the northward mass transport and are thus closer to the rather crude treatment of iceberg melting as coastal runoff in models without an interactive iceberg model future ocean simulations will benefit from the improved meridional distribution of iceberg melt especially in climate change scenarios where the impact of iceberg melt is likely to increase due to increased calving from the antarctic ice sheet

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

ice shelf disintegration by plate bending and hydro fracture satellite observations and model results of the 2008 wilkins ice shelf break ups abstract satellite remote sensing observations of three break up events in 2008 for the wilkins ice shelf 28 february to 6 march 27 may to 31 may and 28 june to mid july provide unprecedented detail of ice shelf calving during rapid break up the observations reveal that the wilkins break ups occur through a distinctive type of shelf calving which we term disintegration as well as more typical rifting and calving here we focus on the disintegration process which is characterized by repeated rapid fracturing that creates narrow ice edge parallel blocks with subsequent block toppling and fragmentation forming an expanding iceberg and ice rubble mass we use these data to develop and test a model of floating ice plate disintegration in which ice plate bending stresses at the ice front arising from buoyancy forces can lead to runaway calving when free mobile water is available high resolution satellite images and laser altimetry of the first break up event provide details of fracture spacings ice thicknesses and plate bending profiles that agree well with our model predictions we suggest that surface or near surface meltwater is the main pre condition for disintegration and that hydro fracture is the main mechanism brine layers from near waterline brine infiltration can support a similar process but this is less effective unless regional ice stress patterns contribute to the net stress available at the crack tip for fracturing a combination of brine enhanced fracturing and changing internal net extensional stresses was the likely mechanism behind the latter two wilkins events

three years of near coastal antarctic iceberg distribution from a machine learning approach applied to sar imagery mass loss around the antarctic ice sheet is driven by basal melting and iceberg calving which constitute the two dominant paths of freshwater flux into the southern ocean although of similarmagnitude icebergs play an important and still not fully understood role in the balance of heat andfreshwater around antarctica this lack of understanding is partly due to operational difficulties inlarge scale monitoring in polar regions despite observational and remote sensing efforts in this study anovel machine learning approach augmented by visual inspection was applied to three syntheticaperture radar sar mosaics of the whole antarctic continent and its adjacent coastal zone althoughoriginally intended for a mapping of the antarctic continent the sar mosaics allow us to document theevolution and distribution of the size and mass of icebergs in the pan antarctic near coastal zone for theyears 1997 2000 and 2008 our novel algorithm identified 7 649 icebergs in 1997 13 712 icebergs in 2000 and 7 246 icebergs in 2008 with surface areas between 0 1 and 4 567 82 km2and total masses of 4 641 53 6 862 81 and 5 263 69 gt respectively large regional variability was observed although a zonal patterndistribution is present this has implications for future climate modeling studies that try to estimate thefreshwater flux from melting icebergs which demands a realistic representation of the interannuallyvarying near coastal iceberg pattern to initialize the simulations

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

strain variations across the proterozoic penokean orogen usa and canada abstract strata in the huron 2 5 2 0 ga and animikie 2 2 1 85 ga basins were deposited on the southern margin of the archean superior province these rocks were deformed during the penokean orogeny 1850 ma followed by subsequent accretionary orogens to the south at 1750 ma yavapai and 1630 ma mazatzal strain patterns are unique to each orogenic belt with no far field effect archean wawa terrane rocks in the penokean foreland preserve deformation associated with archean accretion with no younger penokean yavapai or mazatzal strain overprint the penokean orogeny deformed huron animikie basin sediments into a north vergent fold and thrust belt with no yavapai or mazatzal strain overprint yavapai orogen strains sw ne margin parallel shortening are unique when compared to the younger mazatzal shortening n20 w shortening with no strain overprint penokean deformation is characterized by shortening from the south including uplifted archean gneisses and a northerly thin skinned fold and thrust belt with north vergent nappes and a gently dipping foreland our study of finite and calcite twinning strains n 60 along 1500 km and across 200 km the penokean belt indicate that this orogeny was collisional as layer parallel shortening axes are parallel across the belt or parallel to the tectonic transport direction n s penokean nappe burial near the margin resulted in vertical shortening strain overprints some of which are layer normal the sudbury impact layer 1850 ma is found across the animikie basin and provides a widespread deformation marker with many local unique strain observations we also report new geochronology u pb zircon and apatite for the gneiss mafic dike rocks at wissota chippewa falls wi and arbutus black river falls wi dams respectively which bears on penokean yavapai deformation in the archean marshfield terrane which was accreted during the penokean orogen pseudotachylite formation was common in the superior province archean basement rocks especially along terrane boundaries reactivated by contemporaneous penokean trans hudson cape smith and new quebec deformation in the hinterland south the younger yavapai orogen 1750 ma n 8 deformation is preserved as margin parallel horizontal shortening sw ne in yavapai crust and up to 200 km to the north in the penokean thrust belt as a strain and barrovian metamorphic overprint mazatzal deformation 1630 ma n 16 is preserved in quartzites on yavapai and penokean crust with layer parallel and layer normal shortening strains oriented n20 w

iceberg signatures and detection in sar images in two test regions of the weddell sea antarctica a pixel based methodology has been established for automatic identification of icebergs in satellite synthetic aperture radar sar images acquired during different seasons and for different seaice conditions this includes in particular smaller icebergs longitudinal axis 100m to 18 5 km investigations were carried out for two test regions located in theweddell sea antarctica using images of the envisat advanced sar asar at hh polarization and of the european remote sensing satellite 2 ers 2 sar vv polarized from the former a sequence of image mode and wide swath mode data are available for the whole of 2006 the ers data were acquired around the tip of the antarctic peninsula in spring and summer months of the years 2000 03 the minimum size of icebergs that could be identified in the im images was 0 02km2 radar backscattering coefficients of icebergs sea ice and open water were determined separately we demonstrate that the error in separating icebergs from their surroundings sea ice or open water depends on meteorological oceanographic and sea ice conditions also the pre processing of the sar images e g speckle reduction influences iceberg recognition differences in detection accuracy as a function of season could not be substantiated for our test sites but have in general to be taken into account as results of other investigations indicate

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

near coastal circum antarctic iceberg size distributions determined from synthetic aperture radar images abstract the radarsat 1 antarctic mapping project ramp compiled a mosaic of antarctica and the adjacent ocean zone from more than 3000 high resolution synthetic aperture radar sar images acquired in september and october 1997 the mosaic with a pixel size of 100 m was used to determine iceberg size distributions around antarctica combining an automated detection with a visual control of all icebergs larger than 5 km2 and correction of recognized false detections for icebergs below 5 km2 in size the numbers of false detections and accuracies of size retrievals were analyzed for three test sites nearly 7000 icebergs with horizontal areas between 0 3 and 4717 7 km2 were identified in a near coastal zone of varying width between 20 and 300 km the spatial distributions of icebergs around antarctica were calculated for zonal segments of 20 angular width and related to the types of the calving fronts in the respective section results reveal that regional variations of the size distributions cannot be neglected the highest ice mass accumulations were found at positions of giant icebergs 18 5 km but also in front of ice shelves from which larger numbers of smaller icebergs calve almost continuously although the coastal oceanic zone covered by ramp is too narrow compared to the spatial coverage needed for oceanographic research this study nevertheless demonstrates the usefulness of sar images for iceberg research and the need for repeated data acquisitions extending ocean wards over distances of 500 km and more from the coast to monitor iceberg melt and disintegration and the related freshwater input into the ocean

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

object based landfast sea ice detection over west antarctica using time series alos palsar data abstract landfast sea ice fast ice is an important feature prevalent around the antarctic coast which is affected by climate change and energy exchanges with the atmosphere and ocean this study proposed a method for detection of the west antarctic fast ice using the advanced land observing satellite phased array l band sar alos palsar images the algorithm has combined image segmentation image correlation analysis and machine learning techniques i e random forest rf extremely randomized trees ert and logistic regression lr we used sar images with a baseline of 5 days that are not in the same orbit but overlap each other as overlaps between swaths in adjacent orbits are often available in the polar regions the underlying assumption for the proposed fast ice detection algorithm is that fast ice regions in sar images with a time interval of 5 days are highly correlated the object based approach proposed in this study was well suited to high resolution sar images in deriving spatially homogeneous fast ice regions the image segmentation results using the optimized parameters showed a distinct difference in the backscatter temporal evolution between fast ice and pack ice regions correlation and std of backscattering coefficients were found to be the most significant variables for the object based fast ice detection from two temporally separated images in overall the quantitative and qualitative evaluation demonstrated that the algorithm was an effective approach to detect fast ice with high accuracies the models well detected various fast ice regions in the west antarctica but misclassified some objects the misclassifications occurred toward the edge of fast ice regions with relatively rapid changes in backscattering between both data acquisitions on the other hand few fast ice objects were misclassified as uniform backscattering over time occurred by chance on very small objects far from the coast very old multi year fast ice regions with high backscattered signals were also a source for some misclassifications this may be due to the sensitivity of l band to snow structure to some extent and a thinner ice over the region with either ice growth no deformation or closing slight deformation between both images heavy snow load on the ice could be another error source for some misclassification as well the approach allowed for the reliable detection of fast ice regions by using l band sar images with a small local incidence angle difference

modeling giant iceberg drift under the influence of sea ice in the weddell sea antarctica the drift trajectory of giant iceberg c 7 traversing the weddell sea antarctica for 2 years was successfully simulated application of the classical driving forces like wind and ocean currents resulted in a significant discrepancy between modeled and observed iceberg velocities in the western weddell sea the most realistic drift pattern in space and time was achieved by adding a sea ice force which represents the ability of a dense sea ice cover 90 to lock in icebergs and collect the momentum of the wind over an area much larger than the area of the iceberg proper this process was parameterized using a sea ice strength p which depends on sea ice concentration and thickness both having highest values in winter and in the western weddell sea which is covered with multi year sea ice as a consequence of the sensitivity to sea ice the timing of the iceberg drift becomes important revealing the region off brunt ice shelf eastern weddell sea as a location where bergs either continue westward with the coastal current or follow a southern branch onto the shallow continental shelf

the chronology of early mesozoic arc magmatism in the yerington district of western nevada and its regional implications the yerington district west central nevada is underlain by arc volcanic sedimentary and plutonic rocks ranging in age from middle triassic to middle jurassic twenty three u pb radiometric dates from eight igneous units have been determined for zircon from both plutonic and volcanic rocks in the district which establish two distinct periods of voluminous intermediate to silicic high k calc alkaline magmatism the earlier period is constrained by zircon dates of 232 and 233 ma on a quartz porphyry and a metadiorite respectively which intrude and are possibly comagmatic with andesitic to rhyolitic volcanic rocks the second period of arc magmatism is constrained by 5 concordant zircon dates that define an approximately 4 m y period 169 165 ma in the middle jurassic during which as much as 4 km of volcanic and volcaniclastic strata accumulated and two major batholiths were emplaced middle jurassic magmatism began with eruption of the volcanics of artesia lake they were intruded by the probably comagmatic 250 km 2 yerington batholith which was differentiated emplaced and crystallized within approximately 1 m y 169 4 168 5 ma granite porphyry dikes 168 5 ma are the latest phase of the yerington batholith and are synchronous with porphyry and skarn copper mineralization disconformably overlying the artesia volcanics is a second volcanic suite consisting of as much as 2 km of latitic volcanics of fulstone spring 166 5 ma the volcanics of fulstone spring were subsequently intruded by quartz monzodiorite porphyry dikes 165 ma and the shamrock batholith 165 8 ma the triassic through lower jurassic stratigraphic column was contact metamorphosed and folded adjacent to and at least in part contemporaneously with emplacement of the yerington and shamrock batholiths 169 4 165 8 ma we interpret the early 232 233 ma period of magmatism to represent a minimum age for the establishment of a west facing triassic volcanic arc within west facing triassic volcanic arc within west central nevada following the permian triassic sonoma orogeny the timing of middle jurassic arc magmatism and deformation in the yerington district and surrounding regions is strikingly similar to the timing of magmatic and tectonic events documented in the klamath mountains region of northwestern california we suggest that the similar record of arc magmatism and deformation in these two regions is not fortuitous but reflects a common tectonic evolution within a single west facing arc constructed along the western edge of north america

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

antarctic iceberg distribution and dissolution from ship based observations the australian antarctic program s iceberg dataset from ship based observations including information from the austral summer seasons 1984 85 to 1999 2000 is examined and used to extend earlier studies using snapshots of the iceberg population to provide an idea of the iceberg life cycle the distribution of icebergs between 60 and 1508 e is discussed in terms of calving regions and ocean currents temporal changes are also examined the discussion leads us to the point where we can define an area bounded to the north by the maximum sea ice limit and to the south by the antarctic divergence in which icebergs are confined as they drift eastward this allows estimation of total dissolution in terms of iceberg numbers and volume within 108 longitudinal sectors and with knowledge of drift speeds iceberg movement rates and freshwater input across the sector iceberg dissolution rates are found to be 0 03 0 05 m d 1 and the total mass contribution of fresh water to the ocean as the icebergs traverse our 308 of longitude study sector is 32 gt this amounts to a contribution equivalent to precipitation of 15 5 cm a 1 accounting for 2 of the total iceberg discharge from the antarctic ice sheet

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

an object based sar image iceberg detection algorithm applied to the amundsen sea abstract an object based method for automatic iceberg detection from advanced synthetic aperture radar asar images has been developed and applied in the amundsen sea antarctica the automatic identification is based on brightness and spatial parameters of the asar images at five scale levels and was verified with manual classification in four areas chosen to represent varying environmental conditions the presented algorithm works comparatively well with images of the ocean in freezing temperatures and strong wind conditions common in the amundsen sea the detection rate was 96 2 which corresponds to 93 2 of the icebergs area for all seasons the algorithm generated 3 8 errors in the form of misses and 7 0 of false alarms mainly caused by the presence of ice floes the method was applied on 432 radar images acquired in 2011 under different meteorological oceanographic and sea ice conditions as an output a map showing the probability of finding icebergs has been created it shows that high probability coincides with depth contours and indicates a westward drift of the bergs throughout the whole region