freeboard and mass extraction of the disintegrated mertz ice tongue with remote sensing and altimetry data abstract in february 2010 the mertz ice tongue mit collapsed and generated a giant iceberg however parameters about this iceberg have not been calculated and published in detail in this study the freeboard map of this iceberg was generated for the first time using a time series icesat glas data methods for producing the freeboard map of this iceberg are suggested field data for ice velocity were used to relocate the footprints collected by different campaigns cross validation was conducted with freeboards extracted from crossovers observed within 30 days of each other the precision of the freeboard extraction is approximately 0 50 m when taking one standard deviation as the precision the freeboard varied from 23 m to 59 m with the mean of 41 m with assumption of hydrostatic equilibrium assuming a snow layer depth of 1 m a snow density of 360 kg m 3 an ice density of 915 kg m 3 and a sea water density of 1024 kg m 3 the minimum maximum and average ice thickness were calculated as 210 m 550 m and 383 m respectively the total ice loss is approximately 8 96 10 11 tons over an area 34 km in width and 75 km in length or approximately 2560 5 km 2 these parameters extracted from remote sensing and altimetry data will provide additional information for studies of the evolution of iceberg especially in iceberg tracking system

larsen ice shelf has progressively thinned the retreat and collapse of antarctic peninsula ice shelves in tandem with a regional atmospheric warming has fueled speculation as to how these events may be related satellite radar altimeter measurements show that between 1992 and 2001 the larsen ice shelf lowered by up to 0 27 0 11 meters per year the lowering is explained by increased summer meltwater and the loss of basal ice through melting enhanced ocean driven melting may provide a simple link between regional climate warming and the successive disintegration of sections of the larsen ice shelf

the footloose mechanism iceberg decay from hydrostatic stresses we study a mechanism of iceberg breakup that may act together with the recognized melt and wave induced decay processes our proposal is based on observations from a recent field experiment on a large ice island in baffin bay east canada we observed that successive collapses of the overburden from above an unsupported wavecut at the iceberg waterline created a submerged foot fringing the berg the buoyancy stresses induced by such a foot may be sufficient to cause moderate sized bergs to break off from the main berg a mathematical model is developed to test the feasibility of this mechanism the results suggest that once the foot reaches a critical length the induced stresses are sufficient to cause calving the theoretically predicted maximum stable foot length compares well to the data collected in situ further the model provides analytical expressions for the previously observed rampart moat iceberg surface profiles

a global view of martian surface compositions from mgs tes thermal emission spectrometer tes data from the mars global surveyor mgs are used to determine compositions and distributions of martian low albedo regions two surface spectral signatures are identified from low albedo regions comparisons with spectra of terrestrial rock samples and deconvolution results indicate that the two compositions are a basaltic composition dominated by plagioclase feldspar and clinopyroxene and an andesitic composition dominated by plagioclase feldspar and volcanic glass the distribution of the two compositions is split roughly along the planetary dichotomy the basaltic composition is confined to older surfaces and the more silicic composition is concentrated in the younger northern plains

icesat s new perspective on ice shelf rifts the vertical dimension 1 the small footprint 70 m and 172 m along track spacing of the geoscience laser altimeter system glas on the ice cloud and land elevation satellite icesat provides unprecedented horizontal resolution for a satellite altimeter this enables icesat to map many previously unresolved features on ice shelves such as crevasses rifts grounding zones and ice fronts we present examples of icesat derived elevation data showing topography over rifts on the amery and ross ice shelves widths of rifts and as estimates of the thickness of melange a collection of ice and snow trapped inside the rifts we show that melange thickness remains constant over the icesat data period and tends to be thicker in older rifts we validate the icesat derived melange depth estimate with an in situ measurement on the ross ice shelf

distribution and modes of occurrence of lunar anorthosite 1 we have utilized telescopic near infrared spectra and multispectral images of the moon provided by the galileo and clementine missions to determine the distribution and modes of occurrence of pure anorthosite anorthosites have now been identified in all portions of the nearside including the site of the putative procellarum basin anorthosite is associated with the rings of orientale grimaldi humorum nectaris nubium mutus vlaq and balmer basins major portions of the inner rings of grimaldi humorum crisium orientale and nectaris are composed of pure anorthosite the large spatial extent of these anorthosites appears to rule out an origin in the upper portions of discrete differentiated mg suite plutons in every instance the anorthosites were exposed from beneath a shallower near surface layer of more pyroxene rich material more mafic material also occurs beneath the pure anorthosite unit large expanses of the northern farside exhibit very low feo values this region contains abundant anorthosite and stands in stark contrast to the mafic composition exhibited by the interior of the south pole aitken basin spa the distribution of compositional units on large portions of the lunar farside as well as the southern portion of the lunar nearside appears to be largely attributable to the spa impact event the distribution and modes of occurrence of anorthosites clearly indicate that a thick global layer of anorthosite is present at various depths beneath most portions of the lunar surface this anorthosite layer dominated the upper portion of the primordial crust and was produced by plagioclase flotation in the global magma ocean

on the role of buoyant flexure in glacier calving interactions between glaciers and the ocean are key for understanding the dynamics of the cryosphere in the climate system here we investigate the role of hydrostatic forces in glacier calving we develop a mathematical model to account for the elastic deformation of glaciers in response to three effects i marine and lake terminating glaciers tend to enter water with a nonzero slope resulting in upward flexure around the grounding line ii horizontal pressure imbalances at the terminus are known to cause hydrostatic in plane stresses and downward acting torque iii submerged ice protrusions at the glacier front may induce additional buoyancy forces that can cause calving our model provides theoretical estimates of the importance of each effect and suggests geometric and material conditions under which a given glacier will calve from hydrostatic flexure we find good agreement with observations this work sheds light on the intricate processes involved in glacier calving and can be hoped to improve our ability to model and predict future changes in the ice climate system

quantitative compositional analysis of martian mafic regions using the mex omega reflectance data 2 petrological implications abstract the primary objectives of this paper are to determine the modal mineralogy of selected low albedo terrains of different ages ranging from noachian to amazonian exposed on the surface of mars this analysis is conducted using the spectral modeling of the observatoire pour la mineralogie l eau les glaces et l activite omega reflectance data results from this work are consistent with the major results of previous spectroscopic studies plagioclase 40 60 in volume and high calcium pyroxene 20 40 hcp are the dominant minerals of the most regions low calcium pyroxene 10 15 lcp and minor amounts of olivine are also present the oldest terrains are characterized by the largest amount of lcp and the lowest concentration of plagioclase these overall compositions are consistent with two pyroxene basalts the particle sizes are in the range of a few hundreds of micrometers which is in good agreement with the thermal inertia of the martian low albedo regions in the region around the nili fossae localized concentrations of olivine up to 40 with millimeter particle size similar to picritic basalts observed in situ by the spirit rover in the gusev crater are inferred chemical compositions are calculated for the first time from omega spectra they are quite consistent with gusev rocks and shergottite compositions but they appear to be significantly sio2 poorer than thermal emission spectrometer data a decreasing low calcium pyroxene abundance with the decreasing age of the low albedo regions is reported this may be indicative of decreasing degree of partial melting as thermal flux decreases with time we propose that the ancient noachian aged lcp rich terrains could have been formed from h2o bearing melts then dry basaltic volcanism occurred leading to decreasing lcp abundance with time due to decreasing degree of partial melting the olivine bearing material modeled in nili fossae resembles the composition of alh77005 and chassigny meteorites consistent with prior studies implications on the formation of the basaltic shergottites are discussed

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

a petrogenetic model for the origin and compositional variation of the martian basaltic meteorites the major element trace element and isotopic compositional ranges of the martian basaltic meteorite source regions have been modeled assuming that planetary differentiation resulted from crystallization of a magma ocean the models are based on low to high pressure phase relationships estimated from experimental runs and estimates of the composition of silicate mars from the literature these models attempt to constrain the mechanisms by which the martian meteorites obtained their superchondritic cao al2o3 ratios and their source regions obtained their parent daughter 87 rb 86 sr 147 sm 144 nd and 176 lu 177 hf ratios calculated from the initial sr nd and hf isotopic compositions of the meteorites high pressure experiments suggest that majoritic garnet is the liquidus phase for mars relevant compositions at or above 12 gpa early crystallization of this phase from a martian magma ocean yields a liquid characterized by an elevated cao al2o3 ratio and a high mg olivine pyroxene garnet dominated cumulates that crystallize subsequently will also be characterized by superchondritic cao al2o3 ratios melting of these cumulates yields liquids with major element compositions that are similar to calculated parental melts of the martian meteorites furthermore crystallization models demonstrate that some of these cumulates have parent daughter ratios that are similar to those calculated for the most incompatible element depleted source region i e that of the meteorite queen alexandra que 94201 the incompatible element abundances of the most depleted que 94201 like source region have also been calculated and provide an estimate of the composition of depleted martian mantle the incompatible element pattern of depleted martian mantle calculated here is very similar to the pattern estimated for depleted earth s mantle melting the depleted martian mantle composition reproduces the abundances of many incompatible elements in the parental melt of que 94201 e g ba th k p hf zr and heavy rare earth elements fairly well but does not reproduce the abundances of rb u ta and light rare earth elements the source regions for meteorites such as shergotty are successfully modeled as mixtures of depleted martian mantle and a late stage liquid trapped in the magma ocean cumulate pile melting of this hybrid source yields liquids with major element abundances and incompatible element patterns that are very similar to the shergotty bulk rock

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

petrological constraints on the density of the martian crust new insights into the chemistry of the martian crust have been made available since the derivation of crustal thickness maps from mars global surveyor gravity and topography data that used a conservative range of density values 2700 3100 kg m3 a new range of crustal density values is calculated from the major element chemistry of martian meteorites 3100 3700 kg m3 igneous rocks at gusev crater 3100 3600 kg m3 and from the surface concentration of fe al ca si and k measured by the gamma ray spectrometer on board mars odyssey 3250 3450 kg m3 in addition the density of mineral assemblages resulting from low pressure crystallization of primary melts of the primitive mantle are estimated for plausible conditions of partial melting corresponding to the noachian to amazonian periods 3100 3300 kg m3 despite the differences between these approaches the results are all consistent with an average density above 3100 kg m3 for those materials that are close to the surface the density may be compatible with the measured mass of mars and the moment of inertia factor but only if the average crustal thickness is thicker than previously thought approaching 100 km a thicker crust implies that crustal delamination and recycling could be possible and may even control its thickness globally or locally alternatively and considering that geoid to topography ratios argue against such a thick crust for the highlands our results suggest the existence of a buried felsic or anorthositic component in the southern hemisphere of mars

magmatic evolution of the moon although incomplete because of the imperfect and somewhat random sampling of rock types by the apollo and luna missions 1969 1976 the history of lunar magmatism has been reconstructed by numerous researchers over the past three decades these reconstructions have illustrated the continuous nature of lunar magmatism from 4 6 to approximately 2 0 ga and the large influence of early differentiation and catastrophic bombardment on lunar mantle dynamics magmatism and eruptive style in this review we group magmatism into multiple stages of activity based on sampled rock types and evaluate the models for each stage stage 1 is early lunar differentiation and associated magmatism partial melting of the moon soon after accretion was responsible for producing an anorthositic crust and a differentiated lunar interior the extent of lunar melting and mantle processing depends strongly on the mechanisms that induced melting estimates for the time over which melting and crystallization occurred range from tens to hundreds of millions of years stage 2 is the disruption of lunar magma ocean cumulates soon after the crystallization of most of the lunar magma ocean the cumulate pile experienced gravitational overturn this resulted in transport of late forming cumulates into the deep lunar mantle and mixing of magma ocean cumulates on a variety of scales stage 3 is the post magma ocean highland magmatism whereas the ferroan anorthositic crust was probably produced during the crystallization of a magma ocean the slightly younger mg suite and alkali suite plutonic rocks may have been generated by decompressional melting of early magma ocean cumulates during cumulate pile overturn a kreep and crustal signature was incorporated into these primitive basaltic magmas through assimilation near the base of the lunar crust or through melting of a hybridized mantle the alkali suite could represent either the differentiation products of mg suite parental magmas or a separate but contemporaneous episode of basaltic magmatism stage 4 is pre basin volcanism sample analysis and remote sensing data indicate that early lunar volcanism kreep basalts and high alumina basalts was contemporaneous with periods of highlands plutonism and catastrophic bombardment of the lunar surface the relationship between early stages of lunar volcanism and the contemporaneous plutonism is not clear the kreep basalts may be volcanic equivalents to both the mg suite and alkali suite stage 5 is the late remelting of magma ocean cumulates and eruption of mare basalts basin associated eruption of mare basalts occurred during and following the late stages of catastrophic bombardment this volcanic activity was possibly an extension of the thermal event that initiated pre basin volcanism mare basalts exhibit a wide range of composition resulting from near surface fractionation of chemically distinct primary basaltic magmas most likely mare basalts were produced by small to moderate degrees of partial melting of hybrid cumulate sources in the deep lunar mantle alternatively the mixed chemical signatures observed in many mare basalts may be interpreted as indicating assimilation of late stage evolved cumulates by melts produced deep in the cumulate pile the wide range of compositions exhibited by the mare basalts compared with earlier episodes of basaltic magmatism may reflect the thermal regime in the lunar mantle that limited the extent of partial melting and melt source homogenization

wave inhibition by sea ice enables trans atlantic ice rafting of debris during heinrich events abstract the last glacial period was punctuated by episodes of massive iceberg calving from the laurentide ice sheet called heinrich events which are identified by layers of ice rafted debris ird in ocean sediment cores from the north atlantic the thickness of these ird layers declines more gradually with distance from the iceberg sources than would be expected based on present day iceberg drift and decay here we model icebergs as passive lagrangian particles driven by ocean currents winds and sea surface temperatures the icebergs are released in a comprehensive climate model simulation of the last glacial maximum lgm as well as a simulation of the modern climate the two simulated climates result in qualitatively similar distributions of iceberg meltwater and hence debris with the colder temperatures of the lgm having only a relatively small effect on meltwater spread in both scenarios meltwater flux falls off rapidly with zonal distance from the source in contrast with the more uniform spread of ird in sediment cores to address this discrepancy we propose a physical mechanism that could have prolonged the lifetime of icebergs during heinrich events the mechanism involves a surface layer of cold and fresh meltwater formed from and retained around large densely packed armadas of icebergs this leads to wintertime sea ice formation even in relatively low latitudes the sea ice in turn shields the icebergs from wave erosion which is the main source of iceberg ablation we find that sea ice could plausibly have formed around the icebergs during four months each winter allowing for four months of sea ice in the model results in a simulated ird distribution which approximately agrees with the distribution of ird in sediment cores

olivine and pyroxene diversity in the crust of mars datafromthe observatoire pour la mineralogie l9eau les glaces et l9activite omega on the mars express spacecraft identify the distinct mafic rock forming minerals olivine low calcium pyroxene lcp and high calcium pyroxene hcp on the surface of mars olivine and hcp rich regions are found in deposits that span the age range of geologic units however lcp rich regions are found only in the ancient noachian aged units which suggests that melts for these deposits were derived from a mantle depleted in aluminum and calcium extended dark regions in the northern plains exhibit no evidence of strong mafic absorptions or absorptions due to hydrated materials

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

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

the flexural dynamics of melting ice shelves a conspicuous precursor of catastrophic ice shelf break up along the antarctic peninsula reported widely in the literature is the gradual increase in surface melting and consequent proliferation of supraglacial lakes and dolines here we present analytical and numerical solutions for the flexure stresses within an ice shelf covered by lakes and dolines both isolated and arrayed we conclude that surface water promotes ice shelf instability in two ways 1 by water assisted crevasse penetration as previously noted and 2 by the inducement of strong tensile flexure stresses exceeding background spreading stress by 10 100 times in response to surface water mass loads and hydrostatic rebound occurring when meltwater lakes drain

the magma ocean concept and lunar evolution the model of lunar evolution in which the anorthositic plagioclase rich oldest crust of the moon is formed over a period of 300 myr or less by crystallization as it floats on a global ocean of magma tens or hundreds of km thick is examined in a review of petrological and theoretical studies consideration is given to the classification of lunar rocks the evidence for primordial deep global differentiation constraints on the depth of the molten zone the effects of pressure on mineral stability relationships mainly liquid vs mainly magmifer ocean models and the evidence for multiple ancient differentiation episodes a synthesis of the model of primordial differentiation and its aftereffects is presented and the generalization of the model to the earth and to mars mercury venus and the asteroids is discussed

the distribution and purity of anorthosite across the orientale basin new perspectives from moon mineralogy mapper data 1 the orientale basin is a multiring impact structure on the western limb of the moon that provides a clear view of the primary lunar crust exposed during basin formation previously near infrared reflectance spectra suggested that orientale s inner rook ring irr is very poor in mafic minerals and may represent anorthosite excavated from the moon s upper crust however detailed assessment of the mineralogy of these anorthosites was prohibited because the available spectroscopic data sets did not identify the diagnostic plagioclase absorption feature near 1250 nm recently however this absorption has been identified in several spectroscopic data sets including the moon mineralogy mapper m3 enabling the unique identification of a plagioclase dominated lithology at orientale for the first time here we present the first in depth characterization of the orientale anorthosites based on direct measurement of their plagioclase component in addition detailed geologic context of the exposures is discussed based on analysis of lunar reconnaissance orbiter narrow angle camera images for selected anorthosite identifications the results confirm that anorthosite is overwhelmingly concentrated in the irr comparison with nonlinear spectral mixing models suggests that the anorthosite is exceedingly pure containing 95 vol plagioclase in most areas and commonly 99 100 vol these new data place important constraints on magma ocean crystallization scenarios which must produce a zone of highly pure anorthosite spanning the entire lateral extent of the 430 km diameter irr

the geological history of nili patera mars nili patera is a 50 km diameter caldera at the center of the syrtis major planum volcanic province the caldera is unique among martian volcanic terrains in hosting i evidence of both effusive and explosive volcanism ii hydrothermal silica and iii compositional diversity from olivine rich basalts to silica enriched units we have produced a new geological map using three mosaicked 18 m pixel context camera digital elevation models supplemented by compact remote imaging spectrometer for mars hyperspectral data the map contextualizes these discoveries formulating a stratigraphy in which nili patera formed by trapdoor collapse into a volcanotectonic depression the distinctive bright floor of nili patera formed either as part of a felsic pluton exposed during caldera formation or as remnants of welded ignimbrite s associated with caldera formation both scenarios deriving from melting in the noachian highland basement after caldera collapse there were five magmatic episodes 1 a basaltic unit in the caldera s north 2 a silica enriched unit and the associated nili tholus cone 3 an intrusive event forming a 300 m high elliptical dome 4 an extrusive basaltic unit emplaced from small cones in the east and 5 an extreme olivine bearing unit formed on the western caldera ring fault the mapping together with evidence for hydrated materials implies magmatic interaction with subsurface volatiles this in an area of elevated geothermal gradient presents a possible habitable environment sampled by the hydrothermal deposits additionally similarities to other highland volcanoes imply similar mechanisms and thus astrobiological potential within those edifices

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

characteristics of the meltwater field from a large antarctic iceberg using δ18o large tabular icebergs represent a disruptive influence on a stable water column when drifting in the open ocean this is a study of one iceberg c18a encountered in the powell basin in the weddell sea in march 2009 formed from iceberg c18 76 7 km originating from the ross ice shelf in may 2002 c18a was lunate in shape with longest dimensions of 31 km 7 km 184 m the meltwater field from c18a was characterized using 18o from water samples collected near c18a near field 0 4 2 km and contrasted with a far field comprised of samples from an away site 19 km from c18a a control site 70 km away and a region populated with small icebergs iceberg alley 175 km away the in sample fractions of meteoric water were calculated relative 18o in iceberg ice and weddell deep water and converted to meteoric water height m and a percentage within 100 m depth bins the near field and far field difference from surface to 200 m was 0 51 0 28 the concentration of meteoric water dropped to approximately half that value below 200 m approximate keel depth of the iceberg although detectable to 600 m from surface to 600 m the overall difference was statistically significant p 0 0001 from this we estimate the near field volume astern of the iceberg 0 16 km3d 1 as a continuous source of meteoric water

alkaline volcanic rocks from the columbia hills gusev crater mars 1 irvine backstay and wishstone are the type specimens for three classes of fine grained or fragmental relatively unaltered rocks with distinctive thermal emission spectra found as float on the flanks of the columbia hills chemical analyses indicate that these rocks are mildly alkaline basalt trachybasalt and tephrite respectively their mineralogy consists of na and k rich feldspar s low and high ca pyroxenes ferroan olivine fe ti and possibly cr oxides phosphate and possibly glass the texture of wishstone is consistent with a pyroclastic origin whereas irvine and backstay are lavas or possibly dike rocks chemical compositions of these rocks plot on or near liquid lines of descent for most elements calculated for adirondack class rocks olivine rich basalts from the gusev plains at various pressures from 0 1 to 1 0 gpa we infer that wishstone backstay and irvine class magmas may have formed by fractionation of primitive oxidized basaltic magma similar to adirondack class rocks the compositions of all these rocks reveal that the gusev magmatic province is alkaline distinct from the subalkaline volcanic rocks thought to dominate most of the planet s surface the fact that differentiated volcanic rocks were not encountered on the plains prior to ascending husband hill may suggest a local magma source for volcanism beneath gusev crater

revised crism spectral parameters and summary products based on the currently detected mineral diversity on mars the investigation of hyperspectral data from the mars reconnaissance orbiter compact reconnaissance imaging spectrometer for mars crism and the observatoire pour la mineralogie l eau les glaces et l activitie omega on mars express has revealed an increasingly diverse suite of minerals present on the martian surface a revised set of 60 spectral parameters derived from corrected spectral reflectance at key wavelengths in crism targeted observations and designed to capture the known diversity of surface mineralogy on mars is presented here as summary products some of the summary products have strong heritage to omega spectral parameter calculations this paper also presents newly derived parameters that highlight locations with more recently discovered spectral signatures type locations for the diversity of currently identified mineral spectral signatures have been compiled into a library presented in this work our analysis indicates that the revised set of summary products captures the known spectral diversity of the surface and successfully highlights and differentiates between locations with differing spectral signatures the revised spectral parameter calculations and related products provide a useful tool for scientific interpretation and for future mission landing site selection and operations

discussion of placed rock as protection against erosion by flow down steep slopes by w l peirson j figlus s e pells and r j cox

round shaped riprap stabilization in overtopping flow a series of 26 tests was performed on a riprap layer in which median round shaped stones ranging from 32 3 to 99 1 mm from 1 27 to 3 90 in were subjected to overtopping flow conditions embankment slopes range from 10 to 45 with median stone sizes ranging from 23 9 to 104 2 mm from 0 94 to 4 1 in the database was analyzed yielding a unique expression in which the median size of a round shaped stone can be predicted as a function of the unit discharge embankment slope and coefficient of uniformity it was determined that the requisite round shaped stones range from 5 to 42 larger than angular stones to stabilize the riprap layer for similar flow conditions with unit flows of 0 2 cm s and slopes of 40 the maximum deviation between rounded and angular shaped stone may approach 70 as flow and bed conditions are extrapolated

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

evolution of ice shelf rifts implications for formation mechanics and morphological controls abstract ice shelf rifts are predecessors to iceberg calving events observations of their morphology over time and interaction with their surroundings are presented newly available landsat derived annual velocity data and laser altimetry from nasa s icesat icesat 2 and operation icebridge missions were used to characterize several ice shelf rift systems actively propagating ice shelf rifts exhibit uplift on both sides with an offset in height between the two rift walls suggesting an asymmetric buoyancy force resulting from the rifting process itself it is observed that the direction of the asymmetry is the same for rifts within a single ice shelf but not between ice shelves this finding suggests a rheological or basal properties influence on rift formation and buoyancy asymmetry it is shown that this asymmetry can be accounted for by modeling ice shelf rifts as subvertical faults with time and inactivity rift walls eventually relax and become rounded off measurements of widening suggest that rift infilling is active on many active rifts active rifts experience higher spreading rates than do dormant rifts lastly two candidate processes are identified for rift nucleation subvertical basal crevassing and localized melt it is found that more than any other ice shelf in this study rifting in pine island glacier is driven by ocean heat variations and is showing signs of increasing destabilization

planetary science evolved magma on mars the surface of mars is dominated by basalt that has undergone little magmatic evolution however minerals now identified in some ancient terrains suggest that extensive magma processing and intrusive volcanism were not uncommon on the red planet

verification of model simulated mass balance flow fields and tabular calving events of the antarctic ice sheet against remotely sensed observations the antarctic ice sheet ais has the greatest potential for global sea level rise this study simulates ais ice creeping sliding tabular calving and estimates the total mass balances using a recently developed advanced ice dynamics model known as segment ice segment ice is written in a spherical earth coordinate system because the ais contains the south pole a projection transfer is performed to displace the pole outside of the simulation domain the ais also has complex ice water granular material bedrock configurations requiring sophisticated lateral and basal boundary conditions because of the prevalence of ice shelves a girder yield type calving scheme is activated the simulations of present surface ice flow velocities compare favorably with insar measurements for various ice water bedrock configurations the estimated ice mass loss rate during 2003 2009 agrees with grace measurements and provides more spatial details not represented by the latter the model estimated calving frequencies of the peripheral ice shelves from 1996 roughly when the 5 km digital elevation and thickness data for the shelves were collected to 2009 compare well with archived scatterometer images segment ice s unique non local systematic calving scheme is found to be relevant for tabular calving however the exact timing of calving and of iceberg sizes cannot be simulated accurately at present a projection of the future mass change of the ais is made with segment ice forced by atmospheric conditions from three different coupled general circulation models the entire ais is estimated to be losing mass steadily at a rate of 120 km3 a at present and this rate possibly may double by year 2100

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

riprap design for overtopping flow near prototype flume studies were conducted in which riprap protected embankments were subjected to overtopping flows embankment slopes of 1 2 8 10 and 20 were covered with riprap layers with median stone sizes of 1 2 4 5 and or 6 in each riprap layer was tested by slowly increasing the discharge to failure riprap design criteria for overtopping flows were developed for estimating incipient stone movement and riprap layer failure as a function of the unit discharge stone shape median stone size and embankment slope incipient stone movement occurred at approximately 74 of the riprap layer failure unit discharge it was determined that rounded shape stone should be oversized approximately 40 to provide comparable protection of an angular shape stone flow channelization was observed to occur at approximately 88 of the unit discharge at failure a flow concentration factor of approximately 1 to 3 was introduced for sizing stone

distribution and variation of plagioclase compositions on mars 1 this study presents the first global compositional maps of plagioclase the most abundant mineral in the martian crust linear deconvolutions of spectra from the thermal emission spectrometer tes allowed calculation of average plagioclase compositions for dust free areas on mars 60 of the equator approximately 40 of the surface for this range of latitudes as a whole surface type 1 and 2 terrains are virtually identical with respect to their average plagioclase compositions an60 the majority of tes observations were modeled as labradorite and bytownite between an50 and an90 while fewer observations were modeled with other plagioclase compositions that did not correlate with specific geologic terrains the lack of diversity in average plagioclase compositions across multiple geologic units may represent an upper martian crust with minimal variation in plagioclase compositions alternatively aeolian fluvial and or impact activity may have redistributed heterogeneous crustal material forming a relatively homogeneous global surface layer

apparent thermal inertia and the surface heterogeneity of mars abstract thermal inertia derivation techniques generally assume that surface properties are uniform at horizontal scales below the footprint of the observing instrument and to depths of several decimeters consequently surfaces with horizontal or vertical heterogeneity may yield apparent thermal inertia which varies with time of day and season to investigate these temporal variations we processed three mars years of mars global surveyor thermal emission spectrometer observations and produced global nightside and dayside seasonal maps of apparent thermal inertia these maps show broad regions with diurnal and seasonal differences up to 200 j m 2 k 1 s 1 2 at mid latitudes 60 s to 60 n and 600 j m 2 k 1 s 1 2 or greater in the polar regions we compared the seasonal mapping results with modeled apparent thermal inertia and created new maps of surface heterogeneity at 5 resolution delineating regions that have thermal characteristics consistent with horizontal mixtures or layers of two materials the thermal behavior of most regions on mars appears to be dominated by layering with upper layers of higher thermal inertia e g duricrusts or desert pavements over fines prevailing in mid latitudes and upper layers of lower thermal inertia e g dust covered rock soils with an ice table at shallow depths prevailing in polar regions less common are regions dominated by horizontal mixtures such as those containing differing proportions of rocks sand dust and duricrust or surfaces with divergent local slopes other regions show thermal behavior that is more complex and not well represented by two component surface models these results have important implications for mars surface geology climate modeling landing site selection and other endeavors that employ thermal inertia as a tool for characterizing surface properties

visible near infrared spectra of experimentally shocked plagioclase feldspars 1 high shock pressures cause structural changes in plagioclase feldspars such as mechanical fracturing and disaggregation of the crystal lattice at submicron scales the formation of diaplectic glass maskelynite and genuine melting past studies of visible near infrared spectra of shocked feldspars demonstrated few spectral variations with pressure except for a decrease in the depth of the absorption feature near 1250 1300 nm and an overall decrease in reflectance new visible near infrared spectra 400 2500 nm of experimentally shocked 17 56 gpa albite and anorthite rich rock powders demonstrate similar trends including the loss of minor hydrated mineral bands near 1410 1930 2250 and 2350 nm however the most interesting new observations are increases in reflectance at intermediate pressures followed by subsequent decreases in reflectance at higher pressures the amount of internal scattering and overall sample reflectance is controlled by the relative proportions of micro fractures submicron grains diaplectic glass and melts formed during shock metamorphism we interpret the observed reflectance increases at intermediate pressures to result from progressively larger proportions of submicron feldspar grains and diaplectic glass the ensuing decreases in reflectance occur after diaplectic glass formation is complete and the proportion of genuine melt inclusions increases the pressure regimes over which these reflectance variations occur differ between albite and anorthite consistent with thermal infrared spectra of these samples and previous studies of shocked feldspars these types of spectral variations associated with different peak shock pressures should be considered during interpretation and modeling of visible near infrared remotely sensed spectra of planetary and asteroidal surfaces

roughness of loose rock riprap on steep slopes a study was conducted to determine the roughness of rock riprap laid on steep slopes tests were conducted in a 1 07 m wide flume and two 2 74 m wide field scale structures using angular riprap with median diameters d50 ranging from 52 to 278 mm and bed slopes s0 ranging from 0 028 to 0 333 m m empirical relationships were developed to predict the manning roughness coefficient as a function of d50 and s0 the darcy weisbach friction factor was predicted as a function of d d84 the relative submergence newly developed equations are applicable for riprap placed on slopes from 2 8 33 roughness coefficients calculated using the developed equations were compared with roughness coefficients calculated using equations developed from observations on natural mountain streams

discussion of round shaped riprap stabilization in overtopping flow by steven r abt christopher i thornton humberto a gallegos and craig m ullmann

surface elevation changes at the front of the ross ice shelf implications for basal melting 1 rapid melting beneath the ross ice shelf ris occurs near the ice front likely in response to a secondary buoyant plume with tidal mixing and is sensitive to seasonal water temperatures in front of the ice shelf the front of the ris is examined using glas icesat laser altimetry data spatial and temporal changes in surface elevations are attributed to enhanced basal melting of the ice shelf near the ice front melt rates b increase exponentially as the front is approached from approximately zero at 40 km from the front to an average of 2 8 1 0 m a 1 within the front kilometer melt estimates within the front 60 km are best fit by the relationship b 2 0 exp x 11900 m a 1 where x denotes distance from the front frontal melt totals approximately 16 km3 a 1 in the front 40 km which accounts for between 10 and 40 of current published estimates of total melt beneath the ris spatial averaging along the front reveals a different pattern of melt in regions that have recently calved as compared to regions that have not calved frontal melt is modeled as a one dimensional buoyant plume with tidal currents included these model results imply that modest increases in sea surface temperatures will lead to considerable increases in melting beneath the ice shelf front

persistent iceberg groundings in the western weddell sea antarctica abstract we use the time average of a series of satellite synthetic aperture radar sar images from 2005 to 2007 to identify grounded icebergs in the western weddell sea satellite laser altimetry along repeated ground tracks confirms that regions of high mean backscatter are associated with stationary tabular icebergs the altimeter data also provide iceberg freeboard from which we infer maximum ice draft assuming the lightly grounded limit and a two layer density model consistent with a source at filchner ronne ice shelf the maximum iceberg draft agrees very well with the ocean depth at a point where the bathymetry is well constrained by ship soundings however for an extensive region near 71 s south of larsen c ice shelf the maximum grounding depth for several icebergs reveals the ocean to be locally more than 200 m shallower than in bathymetry products this previously uncharted bank is expected to have a profound effect on the northward flow of the western weddell gyre and the cross slope transport of offshore warm deep water towards the eastern antarctic peninsula ice shelves passive microwave data also show that sea ice concentration is reduced in the vicinity of this group of grounded icebergs indicating an iceberg influence on ocean atmosphere heat and freshwater exchanges

wind driven upwelling around grounded tabular icebergs temperature and salinity data collected around grounded tabular icebergs in baffin bay in 2011 2012 and 2013 indicate wind induced upwelling at certain locations around the icebergs these data suggest that along one side of the iceberg wind forcing leads to ekman transport away from the iceberg which causes upwelling of the cool saline water from below the upwelling water mixes with the water above the thermocline causing the mixed layer to become cooler and more saline along the opposite side of the iceberg the surface ekman transport moves towards the iceberg which causes a sharpening of the thermocline as warm fresh water is trapped near the surface this results in higher mixed layer temperatures and lower mixed layer salinities on this side of the iceberg based on these in situ measurements we hypothesize that the asymmetries in water properties around the iceberg caused by the opposing effects of upwelling and sharpening of the thermocline lead to differential deterioration around the iceberg analysis of satellite imagery around iceberg pii b 1 reveals differential decay around the iceberg in agreement with this mechanism

hydrous minerals on mars as seen by the crism and omega imaging spectrometers updated global view 1 the surface of mars has preserved the record of early environments in which its basaltic crust was altered by liquid water these aqueous environments have survived in the form of hydrological morphologies and alteration minerals including clays and hydrated salts because these minerals probe on earth aqueous environments compatible with biotic activity understanding their formation processes on mars is of great exobiological relevance and also offers insight into earth s now erased ancient water environments using remote sensing we conducted a large scale investigation of the distribution composition age and geomorphic settings of hydrous minerals on mars providing a sharpened global view of the early aqueous environments and their evolution with time aqueous alteration seems to have produced clays on a planetary scale but these are found to be restricted to the oldest observable terrains on mars 4 gyr however very diverse aqueous environments have also been found which suggest widespread complex aqueous settings from the surface to kilometric depths and spanning over 1 gyr by building a robust statistical sample of detections the global trends inferred here attempt to provide a broad view of our current understanding of hydrous minerals on mars and provide context for more localized in depth analyses collectively these trends suggest that at least transient conditions have existed on mars which may have been favorable for pre biotic to biotic activity

the role of cooperative iceberg capsize in ice shelf disintegration disintegration of several ice shelves along the antarctic peninsula demonstrates a mechanism that involves the conversion of a contiguous ice shelf into an expanding plume of ice shelf fragments that spreads rapidly across the ocean surface the growth of surface area and energetic expansion are hypothesized to be driven by gravitational potential energy release associated with iceberg capsize and break up here we investigate this process using a water tank filled with plastic icebergs scaled to represent a laboratory analogue of an expanding plume of ice shelf fragments icebergs our experiments suggest that hydrodynamic pressure within the water separating neighbouring icebergs is sufficient to couple the motion when their separation is comparable to the iceberg size this allows one iceberg s capsize to initiate a domino like effect where the entire array will subsequently capsize in the same direction and expand across the water surface our experimental results motivate the suggestion that cooperative iceberg hydrodynamics is a process that enhances the expansion of ice shelf fragment plumes during ice shelf disintegration

seismic and hydroacoustic tremor generated by colliding icebergs 1 iceberg harmonic tremor iht emanating from tabular icebergs in the southern ocean and along calving margins of the antarctic ice sheet is a complex evolving signal at frequencies above approximately 0 5 hz iht has been observed as t phases on islands in the equatorial pacific as hydroacoustic signals in the indian ocean and by local and regional antarctic seismic networks to identify the iht source mechanism and to understand its relevance to iceberg calving evolution and breakup we deployed seismometers on a giant 25 by 50 km tabular iceberg called c16 in the ross sea antarctica during a uniquely accessible period austral summer 2003 2004 when it was aground against the northern shore of ross island during the deployment period c16 was in sporadic contact with another giant tabular iceberg b15a that was moving under the influence of local ocean currents this study reveals that the c16 associated iht was a manifestation of extended episodes of discrete repeating stick slip icequakes typically thousands of individual subevents per hour produced when the cliff like edges of the tabular icebergs underwent glancing strike slip collisions the iht signal that we observed is thus not a phenomenon associated with iceberg elastic or fluid resonance modes but is instead the consequence of long sequences of very regularly spaced and similar pulses of seismic radiation from these constituent stick slip subevents iht represents a newly identified glaciogenic source of seismicity that can be used to improve our understanding of iceberg dynamics and possibly of ice shelf disintegration processes

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

ice loss processes in the seal nunataks ice shelf region from satellite altimetry and imagery the seal nunataks ice shelf snis 743 km 2 in 2013 is an unofficial name for a remnant area between the former larsen a and larsen b ice shelves off the northeastern antarctic peninsula analyses using landsat 7 etm and terra aster images from 2001 to 13 and icesat altimetry from 2003 to 09 show it has retreated and thinned following the larsen a 1995 and larsen b 2002 disintegrations despite some regional cooling and more fast ice since 2008 snis continues to lose ice along its margins and may be losing contact with some nunataks detailed analysis of data from four icesat tracks indicates that ice shelf thinning rates range between 1 9 and 2 7 m a 1 and generally increase from west to east an icesat repeat track crossing the adjacent robertson island shows a mean elevation loss of 1 8 m a 1 two tracks crossing the snis s remaining tributary rogosh glacier show sub meter elevation losses comparing shelf remnant and grounded ice thinning rates implies that basal ocean melting augments snis thinning by 1 m a 1 a rate that is consistent with other estimates of ocean driven shelf thinning in the region

evaluation of the relative contribution of meteorological and oceanic forces to the drift of ice islands offshore newfoundland on 29 april 2015 four beacons were deployed onto an ice island in the strait of belle isle to record positional data the ice island later broke up into many fragments four of which were tracked by the beacons the relative influences of wind drag current drag coriolis force sea surface height gradient and sea ice force on the drift of the tracked ice island fragments were analyzed using atmospheric and oceanic model outputs the sea ice force was calculated as the residual of the fragments net forces and the sum of all other forces this was compared against the force obtained through ice concentration dependent relationships when sea ice was present the sea ice forces calculated from the residual approach and concentration dependent relationships were significant only when sea ice was present at medium high concentrations in the vicinity of the ice island fragments the forces from ocean currents and sea surface tilt contributed the most to the drift of the ice island fragments wind however played a minimal role in the total force governing the drift of the four ice island fragments and coriolis force was significant when the fragments were drifting at higher speeds

ancient plutonic processes on mars inferred from the detection of possible anorthositic terrains the formation of the silicate mineral anorthosite is thought to require magmatic processes that are not expected on mars because of its predominately mafic terrains localized spectral detections by the mars reconnaissance orbiter are consistent with anorthosite suggestive of ancient intrusive igneous processes similar to those active on earth