submarine melting at the terminus of a temperate tidewater glacier leconte glacier alaska u s a heat fresh and sea water balances indicate that the late summer rate of submarine melting at the terminus of tidewater leconte glacier alaska u s a in 2000 was about 12md 1 w e averaged over the submerged face this is 57 of the estimated total ice loss at the terminus calving plus melting at this time submarine melting may thusprovidea significantcontributiontotheoverallablationofatidewaterglacier oceano graphic measurements conductivity temperature depth made 200 500m from the ter minus identified an isohaline 27ppt and isothermal 7 2 c layer extending from 130m depthto the fjord floor capping this is a 40mthick overflow plume distinguishedby high outflow rates low salinity 22 25ppt and lower temperatures 5 6 c mixing models indicate that fresh water comprised about11 of this plume it originates mostly as sub glacial discharge whose buoyancy drives convection at the terminus deep warm saline watersareincorporatedintotheplumeasitascends causingsubstantialmeltingoficealong the submarine face the calving terminus undergoes seasonal changes that coincide with changes in subglacial discharge and fjord water temperatures and we suggest that these fluctuations interminuspositionare directly relatedto changes in submarine melting

a new calibration to determine the closure temperatures of fe mg ordering in augite from nakhlites recently it has been shown that the relatively low closure temperature tc of 500 100 c calculated for augite from miller range nakhlite mil 03346 13 using the available geothermometers would correspond to a slow cooling rate inconsistent with the petrologic evidence for an origin from a fast cooled lava flow moreover previous annealing experiments combined with hr sc xrd on an augite crystal from mil 03346 clearly showed that at 600 c the fe2 mg degree of order remained unchanged thus suggesting that the actual tc is close to this temperature in order to clarify this discrepancy we undertook an ex situ annealing experimental study at 700 800 and 900 c until the equilibrium in the intracrystalline fe2 mg exchange is reached using an augite crystal from miller range nakhlite mil 03346 13 with a composition of about en36fs24wo40 these data allowed us to calculate the following new geothermometer calibration for martian nakhlites where the application of this new equation to other martian nakhlites nwa 988 and nakhla suggests that for augite with composition close to that of mil 03346 the tc is up to 170 c higher with respect to the one calculated using the previous available geothermometer equation thus suggesting a significantly faster cooling in agreement with petrologic evidence

rapid submarine melting of the calving faces of west greenland glaciers widespread glacier acceleration has been observed in greenland in the past few years oceanographic observations taken in summer 2008 show that ocean waters melted a substantial fraction of ice along the calving fronts of three west greenland glaciers indicating that submarine melting has a profound influence on grounding line stability widespread glacier acceleration has been observed in greenland in the past few years1 2 3 4 associated with the thinning of the lower reaches of the glaciers as they terminate in the ocean5 6 7 these glaciers thin both at the surface from warm air temperatures and along their submerged faces in contact with warm ocean waters8 little is known about the rates of submarine melting9 10 11 and how they may affect glacier dynamics here we present measurements of ocean currents temperature and salinity near the calving fronts of the eqip sermia kangilerngata sermia sermeq kujatdleq and sermeq avangnardleq glaciers in central west greenland as well as ice front bathymetry and geographical positions we calculate water mass and heat budgets that reveal summer submarine melt rates ranging from 0 7 0 2 to 3 9 0 8 m d 1 these rates of submarine melting are two orders of magnitude larger than surface melt rates but comparable to rates of iceberg discharge we conclude that ocean waters melt a considerable but highly variable fraction of the calving fronts of glaciers before they disintegrate into icebergs and suggest that submarine melting must have a profound influence on grounding line stability and ice flow dynamics

how large are departures from lithostatic pressure constraints from host inclusion elasticity minerals trapped as inclusions within other host minerals will develop non lithostatic pressures during both prograde and retrograde metamorphism because of the differences between the thermoelastic properties of the host and inclusion phases there is only a single possible path in p t space the entrapment isomeke along which no residual pressure would be developed in a host inclusion system non lithostatic pressures are developed in inclusions as a result of the external pressure and temperature deviating from the isomeke that passes through the entrapment conditions with modern equation of state and elasticity data for minerals now available it is possible to perform precise calculations of the isomekes for mineral pairs these show that isomeke lines are not straight lines in p t space at metamorphic conditions we show that silicate inclusions in silicate hosts tend to have flat isomekes with small values of because of the small range of thermal expansion coefficients of silicate minerals as a consequence the general behaviour under decompression is for soft silicate inclusions in stiffer hosts to develop excess pressures whereas a stiff silicate inclusion in a softer matrix will experience lower pressures than lithostatic pressure the opposite effects occur for compression after entrapment on the prograde path the excess pressures in inclusions including allowance for mutual elastic relaxation of the host and inclusion are most easily calculated by using the isomeke as a basis analysis of the simplest possible model of a host inclusion system indicates that deviations from lithostatic pressure in excess of 1 gpa can be readily produced in quartz inclusions within garnet in metamorphic rocks for softer host minerals such as feldspar the pressure deviations are smaller because of greater elastic relaxation of the host the maximum pressure deviation from lithostatic pressure in the host phase around the inclusion is one third of the pressure deviation in the inclusion routines for performing these calculations have been added to the eosfit7c software package

the crystal structure of diopside at pressure to 10 gpa the crystal structure of diopside has been determined at various pressures to 10 16 gpa the results to 5 gpa are consistent with levien and prewitt 1981 the crystal structures have been analyzed using the geometric pyroxene model of thompson and downs 2004 the anion packing algorithm of thompson and downs 2001 and a new algorithm that quantifies the distortion of observed pyroxenes from their geometric model equivalents diopside is shown to compress via three main mechanisms isotropic scaling kinking of the tetrahedral chains and collapse of the m1 chain toward its axis the kinking of the chains accounts for most of the anisotropy of compression observed in the a c plane and the collapse of the m1 chain explains the anisotropy seen in the b c plane model behavior is shown to reproduce many of the observations of previous workers anion anion interactions are shown to be important in the distortion of observed diopside from its geometric model equivalent

convection driven melting near the grounding lines of ice shelves and tidewater glaciers subglacial meltwater draining along the bed of fast flowing marine terminating glaciers emerges at the groundingline wheretheiceeithergoesafloattoformaniceshelforterminates inacalvingface theinputof freshwater to the ocean provides a source of buoyancy and drives convective motion alongside the ice ocean interface this process is modeled using the theory of buoyant plumes that has previously been applied to the study of the larger scale circulation beneath ice shelves the plume grows through entrainment of ocean waters and the heat brought into the plume as a result drives melting at the ice ocean interface the equations are nondimensionalized by using scales appropriate for the region where the subglacial drainage rather than the subsequent addition of meltwater supplies the majority of the buoyancy forcing it is found that the melt rate within this region can be approximated reasonably well by a function that is linear in ocean temperature has a cube root dependence on the flux of subglacial meltwater and has a complex dependency on the slope of the ice ocean interface the model is used to investigate variability in melting induced by changes in both ocean temperature and subglacial discharge for a number of realistic examples of ice shelves and tidewater glaciers the results show how warming ocean waters and increasing subglacial drainage both generate increases in melting near the grounding line

crystal structure refinement of na bearing clinopyroxenes from mantle derived eclogite xenoliths nine omphacitic clinopyroxenes with a jadeitic content between 25 and 57 from the udachnaya and zagadochnaya diamond bearing kimberlites were investigated using single crystal x ray diffraction electron microprobe analysis and mossbauer and infrared spectroscopy crystal structure refinements incorporating constraints from chemical analyses and mossbauer data show a significant concentration of vacancies at the m2 site in three of the samples the cell volumes of the non stoichiometric samples plot below the linear trend defined by stoichiometric diopside jadeite compositions where the deviation from the linear trend is positively correlated with the concentration of vacancies charge balance appears to be achieved primarily through substitution of al3 for mg2 on the m1 site which causes a contraction of the m1 site volume compared to stoichiometric clinopyroxenes with the same composition vacancies are not associated with oh incorporation as the sample with the highest concentration of vacancies contains only 89 ppm wt h2o significant hydrogen loss through iron oxidation during ascent is ruled out based on the low fe3 concentrations h content in omphacite samples from kimberlites could provide a sensitive tool for determining f h2o during diamond formation

does calving matter evidence for significant submarine melt abstract during the summer in the northeast pacific ocean the alaska coastal current sweeps water with temperatures in excess of 12 c past the mouths of glacierized fjords and bays the extent to which these warm waters affect the mass balance of alaskan tidewater glaciers is uncertain here we report hydrographic measurements made within icy bay alaska and calculate rates of submarine melt at yahtse glacier a tidewater glacier terminating in icy bay we find strongly stratified water properties consistent with estuarine circulation and evidence that warm gulf of alaska water reaches the head of 40 km long icy bay largely unaltered a 10 20 m layer of cold fresh glacially modified water overlies warm saline water the saline water is observed to reach up to 10 4 c within 1 5 km of the terminus of yahtse glacier by quantifying the heat and salt deficit within the glacially modified water we place bounds on the rate of submarine melt the submarine melt rate is estimated at 9 m d 1 at least half the rate at which ice flows into the terminus region and can plausibly account for all of the submarine terminus mass loss our measurements suggest that summer and fall subaerial calving is a direct response to thermal undercutting of the terminus further demonstrating the critical role of the ocean in modulating tidewater glacier dynamics

rapid submarine melting driven by subglacial discharge leconte glacier alaska 1 we show that subglacial freshwater discharge is the principal process driving high rates of submarine melting at tidewater glaciers this buoyant discharge draws in warm seawater entraining it in a turbulent upwelling flow along the submarine face that melts glacier ice to capture the effects of subglacial discharge on submarine melting we conducted 4 days of hydrographic transects during late summer 2012 at leconte glacier alaska a major rainstorm allowed us to document the influence of large changes in subglacial discharge we found strong submarine melt fluxes that increased from 9 1 1 0 to 16 8 1 3 m d 1 ice face equivalent frontal ablation as a result of the rainstorm with projected continued global warming and increased glacial runoff our results highlight the direct impact that increases in subglacial discharge will have on tidewater outlet systems these effects must be considered when modeling glacier response to future warming and increased runoff

impact of fjord dynamics and glacial runoff on the circulation near helheim glacier greenland to show that the melting circulation is affected by seasonal runoff from the glacier and by the fjord s externally forced currents and stratification the presence of light arctic and dense atlantic waters in the fjord in particular causes meltwater to be exported at depth and influences the vertical distribution of heat along the ice margin our results indicate that the melting circulation is more complex than hypothesized and influenced by multiple external parameters we conclude that the shape and stability of greenland s glaciers may be strongly influenced by the layering of the arctic and atlantic waters in the fjord as well as their variability

a reconciled estimate of glacier contributions to sea level rise 2003 to 2009 glaciers distinct from the greenland and antarctic ice sheets are losing large amounts of water to the world s oceans however estimates of their contribution to sea level rise disagree we provide a consensus estimate by standardizing existing and creating new mass budget estimates from satellite gravimetry and altimetry and from local glaciological records in many regions local measurements are more negative than satellite based estimates all regions lost mass during 2003 2009 with the largest losses from arctic canada alaska coastal greenland the southern andes and high mountain asia but there was little loss from glaciers in antarctica over this period the global mass budget was 259 28 gigatons per year equivalent to the combined loss from both ice sheets and accounting for 29 13 of the observed sea level rise

diamond garnet geobarometry the role of garnet compressibility and expansivity abstract we report p v and t v equations of state eos for synthetic single crystal pyrope py mg3al2si3o12 and the p v eos for synthetic single crystals of almandine alm fe3al2si3o12 as well as an intermediate composition py60alm40 as measured by in situ high pressure and high temperature x ray diffraction experiments the unit cell volumes of the three samples were measured at room temperature and different pressures and up to about 8 gpa in a diamond anvil cell the high temperature experiment was carried out using a micro furnace the pressure volume data were fitted to a third order birch murnaghan eos giving the following coefficients v0 1506 15 16 a3 kt0 163 7 1 7 gpa and k 6 4 4 for pyrope v0 1533 52 10 a3 kt0 172 6 1 5 gpa and k 5 8 5 for almandine and v0 1516 32 13 a3 kt0 167 2 1 7 gpa and k 5 6 5 for the intermediate py60alm40 composition the unit cell volume along the pyrope almandine join changes linearly within the error of measurement indicating ideality in the volume of mixing behaviour for the solid solution the first pressure derivative k for all three garnets is similar within experimental uncertainty with an average value of k 6 0 4 the thermal expansion parameters for end member pyrope as described using to the kroll type eos with the einstein temperature e fixed to 320 k are 303 k 1 bar 2 543 5 10 5 k 1 and v0 1504 64 4 a3 the determined thermoelastic parameters were combined in a thermal pressure type eos thermal p type eos to calculate the entrapment pressures pe for natural garnet inclusions in diamonds at mantle temperatures a calculated pressure of 5 8 gpa at t 1500 k using our newly determined thermoelastic parameters appears to be more consistent with diamond forming conditions compared to the higher pressures that range up to 6 8 gpa at t 1500 k which are obtained using thermoelastic data in the literature

the impact of glacier meltwater on the underwater noise field in a glacial bay ambient noise oceanography is proving to be an efficient and effective tool for the study of ice ocean interactions in the bays of marine terminating glaciers however obtaining quantitative estimates of ice melting or calving processes from ambient noise requires an understanding of how sound propagation through the bay attenuates and filters the noise spectrum measurements of the vertical structure in sound speed in the vicinity of the hans glacier in hornsund fjord spitsbergen made with o 130 ctd casts between may and november 2015 reveal high gradient upward refracting sound speed profiles created by cold fresh meltwater during summer months simultaneous recordings of underwater ambient noise made at depths of 1 10 and 20 meters in combination with propagation model calculations using the model bellhop illustrate the dominant role these surface ducts play in shaping the underwater soundscape the surface ducts lead to a higher intensity and greater variability of acoustic energy in the near surface layer covered by glacially modified waters relative to deeper waters indicating deeper zones as most appropriate for inter seasonal acoustic monitoring of the glacial melt surface waveguides in hornsund are relatively shallow and trap sound above o 1 khz deeper waveguides observed elsewhere will also trap low frequency sounds such as those generated by calving events for example finally the ambient noise field in hornsund is shown to be strongly dependent on the distribution of ice throughout the bay stressing the importance of performing complementary environmental measurements when interpreting the results of acoustic surveys this article is protected by copyright all rights reserved

unusually loud ambient noise in tidewater glacier fjords a signal of ice melt in glacierized fjords the ice ocean boundary is a physically and biologically dynamic environment that is sensitive to both glacier flow and ocean circulation ocean ambient noise offers insight into processes and change at the ice ocean boundary here we characterize fjord ambient noise and show that the average noise levels are louder than nearly all measured natural oceanic environments significantly louder than sea ice and nonglacierized fjords icy bay alaska has an annual average sound pressure level of 120 db referenced to 1 pa with a broad peak between 1000 and 3000 hz bubble formation in the water column as glacier ice melts is the noise source with variability driven by fjord circulation patterns measurements from two additional fjords in alaska and antarctica support that this unusually loud ambient noise in icy bay is representative of glacierized fjords these high noise levels likely alter the behavior of marine mammals

a century of mineral structures how well do we know them this decade marks the centenary of the discovery of x ray diffraction the development of mineralogy as a scientific discipline in which the properties of minerals are understood in terms of their atomic scale structures has paralleled the development of diffraction crystallography as diffraction crystallography revealed more precise details of mineral structures more subtle questions about mineral properties could be addressed and a deeper understanding of the relationship between the two could be attained we review the developments in x ray single crystal diffraction crystallography over the last century and show how its power to provide fundamental information about the structures of minerals has evolved with the improvements in data quality and the increased technological capacity to handle the data we show that modern laboratory x ray diffraction data are of the quality such that mineralogical results are no longer limited by the data quality but by the physical validity of the refinement models used to interpret the data

modeling acoustic propagation of airgun array pulses recorded on tagged sperm whales physeter macrocephalus in 2002 and 2003 tagged sperm whales physeter macrocephalus were experimentally exposed to airgun pulses in the gulf of mexico with the tags providing acoustic recordings at measured ranges and depths ray trace and parabolic equation pe models provided information about sound propagation paths and accurately predicted time of arrival differences between multipath arrivals with adequate environmental information a broadband acoustic pe model predicted the relative levels of multipath arrivals recorded on the tagged whales however lack of array source signature data limited modeling of absolute received levels airguns produce energy primarily below 250hz with spectrum levels about 20 40db lower at 1khz some arrivals recorded near the surface in 2002 had energy predominantly above 500hz a surface duct in the 2002 sound speed profile helps explain this effect and the beampattern of the source array also indicates an increased proportion of high frequency sound at near horizontal launch angles these findings indicate that airguns sometimes expose animals to measurable sound energy above 250hz and demonstrate the influences of source and environmental parameters on characteristics of received airgun pulses the study also illustrates that on axis source levels and simple geometric spreading inadequately describe airgun pulse propagation and the extent of exposure zones

miocene to recent structural development of an extensional accommodation zone northeastern baja california mexico the gulf of california extensional province in northeastern baja california contains a major structural transition from a northern domain of widely spaced basins and ranges to a southern domain of closely spaced nnw striking high angle faults in the northern domain the western boundary of the province the main gulf escarpment is a single listric normal fault the san pedro martir fault in the southern domain it is a 5 km wide zone of numerous e dipping high angle normal faults the western half of this structural transition studied here does not occur by a single transfer fault but rather by 1 transfer of displacement from the san pedro martir fault onto multiple fault zones in the footwall without intervening cross faults and 2 increased southward disruption of the hanging wall by wnw striking strike slip faults oblique to the extension direction and nnw striking normal faults and extension fractures this structural transition involves both the hanging wall and the footwall of the escarpment the lack of a discrete transfer structure is attributed either to insufficient extension 10 or to a gradual change in geometry of the basal detachment

directionality of the ambient noise field in an arctic glacial bay the directionality of ambient noise in an arctic tidewater glacier bay was measured using two horizontally spaced broadband hydrophones segments of noise were divided into two frequency bands and analyzed for arrival angle these data show that different classes of source radiate noise in distinct spectral bands and are spatially diverse a previously unidentified source the interaction of surface gravity waves with underside of ice ledges at the periphery of icebergs is described the generation of noise by ice wave interaction suggests that surface waves should be measured if ambient noise is to be used to monitor ice dynamics in glacial fjords

crystal chemistry of clinopyroxenes from mantle eclogites a study of the key role of the m2 site population by means of crystal structure refinement

source assemblage types for cratonic diamonds from x ray synchrotron diffraction abstract three single crystals of clinopyroxene trapped within three different gem quality diamonds from the udachnaya kimberlite siberia russia were analysed in situ by single crystal synchrotron x ray diffraction in order to obtain information on their chemical composition and infer source assemblage type a non destructive approach was used with high energy 60 kev 0 206 a at i15 the extreme conditions beamline at diamond light source a dedicated protocol was used to center the mineral inclusions located deep inside the diamonds in the x ray beam our results reveal that two of the inclusions can be associated with peridotitic paragenesis whereas the third is eclogitic this study also demonstrates that this non destructive experimental approach is extremely efficient in evaluating the origin of minerals trapped in their diamond hosts

underwater acoustic signatures of glacier calving climate driven ice water interactions in the contact zone between marine terminating glaciers and the ocean surface show a dynamic and complex nature tidewater glaciers lose volume through the poorly understood process of calving a detailed description of the mechanisms controlling the course of calving is essential for the reliable estimation and prediction of mass loss from glaciers here we present the potential of hydroacoustic methods to investigate different modes of ice detachments high frequency underwater ambient noise recordings are combined with synchronized high resolution time lapse photography of the hans glacier cliff in hornsund fjord spitsbergen to identify three types of calving events typical subaerial sliding subaerial and submarine a quantitative analysis of the data reveals a robust correlation between ice impact energy and acoustic emission at frequencies below 200 hz for subaerial calving we suggest that relatively inexpensive acoustic methods can be successfully used to provide quantitative descriptions of the various calving types

sound generation and air entrainment by breaking waves in the surf zone this paper presents the results of acoustic and optical measurements of individual breaking waves in the surf zone two hydrophones horizontally separated and deployed in 2 m of water off la jolla shores beach california were used to measure the source spectrum of breaking surf and characterize propagation through the surf zone over length scales of order 10 m the acoustic data show an acoustically active region within a wave which propagates shoreward the production of sound within the active region is associated with the formation of bubble plumes above 500 hz the sound is consistent with the radiation from individual bubble oscillations pictures were taken of the bubble plumes formed beneath the breaking surf providing estimates of the plume size and bubble size distribution and void fraction within a plume the density of bubbles scales as a 2 5 for a 1 mm where a is bubble radius and total void fractions of 0 3 0 4 were measured theoretical calculations show that ra

passive underwater acoustic evolution of a calving event direct measurements of processes occurring at the ice ocean boundary are difficult to acquire because of the dangerous and dynamic nature of the boundary yet these processes are among the least well understood in glaciology because sound travels well through water passive underwater acoustics offers a method to remotely sense activity at this boundary here we present passive acoustic measurements and spectral analysis of the evolution of a subaerial calving event and the subsequent mini tsunami and seiche at meares glacier alaska usa using two hydrophones to record sound from 1 to 40 000 hz we find that each phase of a calving event has distinctive spectral characteristics an event begins with an infrasound rumble 1 20 hz then the ice fractures 20 100 hz falls and impacts the water 200 600 hz high frequency 10 000 hz sound increases in intensity quickly as the iceberg oscillates creating turbulence spray and waves within 10 s the low frequency audible sound dissipates and the mini tsunami and seiche sounds dominate infrasound plus high frequencies and continue for over 10 min the specific frequencies and duration of each phase of a calving event depend on its size and location and the glacier and fjord characteristics

crystallographic orientations of magnesiochromite inclusions in diamonds what do they tell us we have studied by x ray diffractometry the crystallographic orientation relationships cors between magnesiochromite mchr inclusions and their diamond hosts in gem quality stones from the mines udachnaya siberian russia damtshaa botswana and panda canada in total 36 inclusions in 23 diamonds in nearly half of the cases n 17 111 mchr is parallel within error to 111 diamond but the angular misorientation for other crystallographic directions is generally significant this relationship can be described as a case of rotational statistical cor in which inclusion and host share a single axis 1 df the remaining mchr diamond pairs n 19 have a random cor 2 df the presence of a rotational statistical cor indicates that the inclusions have physically interacted with the diamond before their final incorporation of all possible physical processes that may have influenced mchr orientation those driven by surface interactions are not considered likely because of the presence of fluid films around the inclusions mechanical interaction between euhedral crystals in a fluid rich environment is therefore proposed as the most likely mechanism to produce the observed rotational cor in this scenario neither a rotational nor a random cor can provide information on the relative timing of growth of mchr and diamond some multiple iso oriented inclusions within single diamonds however indicate that mchr was partially dissolved during diamond growth suggesting a protogenetic origin of these inclusions