high integrated fluid rock ratios during metamorphism at naxos evidence from carbon isotopes of calcite in schists and fluid inclusions a dicussion of the paper by kreulen 1988 contributions to mineralogy and petrology 98 28 32

sea surface height determination in the arctic ocean from ers altimetry 1 accurate sea surface height measurements have been extracted from ers altimeter data in sea ice covered regions for the first time the data have been used to construct a mean sea surface of the arctic ocean between the latitudes of 60 degreesn and 81 5 degreesn based on 4 years of ers 2 data an rms value for the crossover differences of mean sea surface profiles of 4 2 cm was observed in the ice covered canada basin compared with 3 8 cm in the ice free greenland iceland norwegian seas comparisons are made with an existing global mean sea surface osumss95 highlighting significant differences between the two surfaces in permanently ice covered seas in addition we present the first altimeter derived sea surface height variability map of the arctic ocean comparisons with a high resolution coupled ocean sea ice general circulation model reveal a good qualitative agreement in the spatial distribution of variability quantitatively we found that the observed variability was on average a factor of 3 4 greater than model predictions

fluid rock ratios during metamorphism at naxos reply the comment by jansen et al on my paper high integrated fluid rock ratios during metamorphism at naxos evidence from carbon isotopes of calcite in schists and fluid inclusions kreulen 1988 offers a welcome opportunity to discuss in more detail some of the problems in estimating compositions of metamorphic fluids and the mass of fluid involved the fluid rock ratios in that paper were calculated from a model based on carbon isotope exchange the logic behind the model is as follows co2 rich fluids moved through the schists and exchanged 13c with calcite the change in isotopic composition of the calcite combined with the amount of this calcite is then a measure of the amount of fluid involved in the exchange process the results of the calculations of course depend critically on the input data the two main objections put forward by jansen et al 1989 are that 1 the fluid compositions derived from fluid inclusions may be wrong and most of the fluids may have been aqueous instead of co2 rich and 2 the calcites may have exchanged not only with metamorphic fluids but also or mainly with graphite i agree with jansen et al that in both cases the fluid rock calculations would give unrealistic results

a continuum model of melt pond evolution on arctic sea ice 1 during the northern hemisphere summer absorbed solar radiation melts snow and the upper surface of arctic sea ice to generate meltwater that accumulates in ponds the melt ponds reduce the albedo of the sea ice cover during the melting season with a significant impact on the heat and mass budget of the sea ice and the upper ocean we have developed a model designed to be suitable for inclusion into a global circulation model gcm which simulates the formation and evolution of the melt pond cover in order to be compatible with existing gcm sea ice models our melt pond model builds upon the existing theory of the evolution of the sea ice thickness distribution since this theory does not describe the topography of the ice cover which is crucial to determining the location extent and depth of individual ponds we have needed to introduce some assumptions we describe our model present calculations and a sensitivity analysis and discuss our results

increased arctic sea ice volume after anomalously low melting in 2013 changes in arctic sea ice volume are difficult to quantify five years of satellite data reveal a reduction in autumn sea ice volume in 2010 2012 but a sharp increase in 2013 and 2014 suggesting that ice volume can recover quickly

thinning and volume loss of the arctic ocean sea ice cover 2003 2008 1 we present our best estimate of the thickness and volume of the arctic ocean ice cover from 10 ice cloud and land elevation satellite icesat campaigns that span a 5 year period between 2003 and 2008 derived ice drafts are consistently within 0 5 m of those from a submarine cruise in mid november of 2005 and 4 years of ice draft profiles from moorings in the chukchi and beaufort seas along with a more than 42 decrease in multiyear my ice coverage since 2005 there was a remarkable thinning of 0 6 m in my ice thickness over 4 years in contrast the average thickness of the seasonal ice in midwinter 2 m which covered more than two thirds of the arctic ocean in 2007 exhibited a negligible trend average winter sea ice volume over the period weighted by a loss of 3000 km3 between 2007 and 2008 was 14 000 km3 the total my ice volume in the winter has experienced a net loss of 6300 km3 40 in the 4 years since 2005 while the first year ice cover gained volume owing to increased overall area coverage the overall decline in volume and thickness are explained almost entirely by changes in the my ice cover combined with a large decline in my ice coverage over this short record there is a reversal in the volumetric and areal contributions of the two ice types to the total volume and area of the arctic ocean ice cover seasonal ice having surpassed that of my ice in winter area coverage and volume became the dominant ice type it seems that the near zero replenishment of the my ice cover after the summers of 2005 and 2007 an imbalance in the cycle of replenishment and ice export has played a significant role in the loss of arctic sea ice volume over the icesat record

the mechanisms of sea ice melt pond formation and evolution 1 a series of observations were made on melting first year landfast arctic sea ice near barrow alaska to explore the seasonal evolution of melt pond coverage observations of pond coverage albedo and ice properties are combined with terrestrial lidar measurements of surface topography and meltwater balance to quantitatively identify the timing and role of mechanisms driving pond coverage the formation of interposed fresh ice is found to eliminate meltwater percolation through early pond formation and allow widespread ponding well above sea level pond drainage to sea level occurs principally by horizontal meltwater transport over the ice surface to macroscopic flaws freeboard loss caused by buoyancy decline as the ice thins controls pond growth late in the melt season after percolation begins the majority of the macroscopic flaws that drain melt ponds to sea level are observed to develop from brine drainage channels within the ice a simple thermodynamic model of meltwater percolation illustrates that fresh meltwater inflow causes pores in the ice to either shrink and freeze shut or enlarge based on initial size and ice temperature this threshold behavior of pore diameter controls both the blockage of smaller pores with interposed ice and the enlargement of larger brine drainage channels to allow meltwater drainage the results identify links between the temporal evolution of pond coverage and ice temperature salinity and thickness providing new opportunities to realistically parameterize ponds and summer ice albedo within sea ice models

relationship between sea ice freeboard and draft in the arctic basin and implications for ice thickness monitoring we have confirmed our earlier finding that the probability density function pdf of ice freeboard in the arctic ocean can be converted to a pdf of ice draft by applying a simple coordinate transformation based on the measured mean draft and mean elevation this applies in each of six 50 km sections north of greenland of joint airborne laser and submarine sonar profile obtained along nearly coincident tracks from the arctic basin north of greenland and tested for this study detailed differences in the shape of the pdf can be explained on the basis of snow load and can in principle be compensated by the use of a more sophisticated freeboard dependent transformation the measured density ratio r actually mean draft mean elevation ratio for each section was found to be consistent over all sections tested despite differences in the ice regime indicating that a single value of r might be used for measurements done in this season of the year the mean value r from all six sections is 7 89 on the assumption that all six values are drawn from the same population the standard deviation is 0 55 for a single 50 km section and thus 0 22 for 300 km of track in attempting to infer ice draft from laser measured freeboard we would therefore expect an accuracy of about 28 cm in 50 km of track if mean draft is about 4 m and about 11 cm in 300 km of track these accuracies are compatible with the resolution of predictions from numerical models a simple model for the variability of r with season and with mean ice thickness gives results in reasonable agreement with observations they show that although there is a large seasonal variability due to snow load there is a stable period from november to april when the variability is chiefly dependent on the mean ice thickness alone thus in principle r can be mapped over the arctic ocean as a basis for interpreting survey data better field data are needed on the seasonal and spatial variability of three key quantities area averaged snow load mean density of first year and multiyear ice including the effect of ridging with these two ice regimes and density of near surface water

aeromagnetic surveying using a simulated unmanned aircraft system carleton university and sander geophysics are developing an unmanned aircraft system uas for aeromagnetic surveying as an early indication of the expected performance of the unmanned aircraft system a simulated unmanned aircraft system suas was built the simulated unmanned aircraft system is a t shaped structure configured as a horizontal gradiometer with two cesium magnetometers spaced 4 67 m apart which is the same sensor geometry as planned for the unmanned aircraft system the simulated unmanned aircraft system is flown suspended beneath a helicopter an 8 5 km 2 area in the central metasedimentary belt of the grenville province near plevna ontario canada was surveyed with the simulated unmanned aircraft system suspended 50 m above ground the survey site was chosen on the basis of its complex geological structure the total magnetic intensity tmi data recorded were compared to that obtained during a conventional fixed wing survey and a ground survey transverse magneto gradiometric data were also recorded by the simulated unmanned aircraft system the simulated unmanned aircraft system total magnetic intensity data have a higher resolution than the conventional fixed wing data and were found to have a similar resolution to that of the ground survey data the advantages of surveying with the simulated unmanned aircraft system were 1 the acquisition of a detailed data set free of gaps in coverage at a low altitude above the terrain and 2 substantial saving of time and effort in the survey site the 4 67 m simulated unmanned aircraft system gradiometer measured the transverse magnetic gradient reliably up to an altitude of 150 m above ground

combined airborne laser and radar altimeter measurements over the fram strait in may 2002 knowledge of sea ice thickness is critical for the prediction of future climate and for assessing the significance of changes in thickness sea ice thickness can be calculated from radar or laser satellite altimetry measurements of freeboard however a lack of knowledge of snow depth introduces significant uncertainties into these calculations this paper compares the first coincident airborne laser and radar altimetry data over sea ice collected during the laser radar altimetry lara field campaign lara was a flight of opportunity that provided valuable data to explore techniques to validate satellite measurements of ice freeboard and the possibility of combining laser and radar measurements over snow covered sea ice to calculate the snow depth two new methods were created to analyse these data sets a new radar retracker and a radar power simulator which models radar returns from the laser data we present the first quantitative analysis of data from the lara laser and radar altimeters and demonstrate the potential of combining laser and radar altimetry to estimate snow depth lara elevation estimates compare well with elevations from the radar altimeter onboard ers 2 at the sub meter level and the study provides lessons for future validation of satellite altimetry data over sea ice laser elevations are consistently higher than the radar elevations over snow covered sea ice as lara was a flight of opportunity no coincident in situ measurements were available nevertheless the difference between the reflecting surface of the laser and radar is consistent with snow depth from climatology and the analysis techniques developed in this paper will be useful for future radar and laser altimetry comparisons

experimental aeromagnetic survey using an unmanned air system currently stratus aeronautics is developing an unmanned aircraft system uas called the venturer for aeromagnetic surveying on 2 october 2013 in southern alberta canada an experimental survey of the uas was conducted approximately 13 km of preprogrammed survey lines along with calibration maneuvers were flown providing 45 minutes worth of data collection the uas was stable in flight and only required operator intervention for takeoff and landing there was a 2 m offset from the nominal altitude of 150 m with variations of approximately 1 4 m deviations from a straight flight path were approximately 0 9 m along traverse lines and 25 m along tie lines the latter being affected mainly by crosswind the noise envelope for the magnetic data acquired during the survey was approximately 0 05 nt allowing a high quality total magnetic intensity map to be created

sea ice mass balance observations from the north pole environmental observatory in recent years the periphery of the arctic sea ice cover has undergone significant changes with a reduction in summer ice extent a thinning of the ice and a shift from multiyear to first year ice here we examine sea ice conditions during nine summers between 2000 and 2013 in the interior of the ice pack using autonomous measurements of sea ice mass balance deployed near the north pole results exhibit no definitive trends there is large interannual variability with surface melt ranging from 0 02 m to 0 50 m and bottom melt from 0 10 m to 0 57 m the largest amounts of bottom melt have occurred in the past few years for all 9 years the ice at the end of the melt season was at least 1 2 m thick

new hydrographic measurements of the upper arctic western eurasian basin in 2017 reveal fresher mixed layer and shallower warm layer than 2005 2012 climatology in 2017 ice atmosphere ocean observing system autonomous drifting platforms provided extensive physical and biogeochemical data in the upper 350 m of the western eurasian basin through their 8 month drift across the amundsen basin the gakkel ridge the nansen basin and western fram strait comparison with woa13 climatology indicates a fresher surface layer and shallower warm layer in 2017 than in 2005 2012 the ice atmosphere ocean observing system 2017 data feature two halocline eddies in the amundsen basin and two atlantic water aw mesoscale structures in the nansen basin analysis of the global 1 12 mercator ocean operational system suggests that the halocline eddies resulted from instabilities in the frontal zone between fresher makarov waters and saltier eurasian waters this frontal region appears to have shifted further southeast in 2017 near 88 n 10 e compared to 2005 2012 the operational system depicts the large aw structure in the nansen basin 140 km crossed as far as 83 7 n 34 5 e as an aw meander from the arctic circumpolar boundary current which turned into an anticyclonic eddy about a month after the platforms drifted away the aw structure at 82 8 n 3 w northwest of the yermak plateau corresponds to an aw recirculating branch detaching from the yermak plateau slope back toward fram strait

high integrated fluid rock ratios during metamorphism at naxos evidence from carbon isotopes of calcite in schists and fluid inclusions calcite in schists of the metamorphic complex at naxos is depleted both in 13c and in 18o with respect to massive marbles this effect is attributed to isotope exchange with circulating co2 rich fluids which had an x text co text 2 0 5 according to fluid inclusions the carbon isotopic composition of the calcites is close to equilibrium with fluid inclusion co2 at metamorphic temperatures mass balance calculations assuming initial 13c values of 0 for calcite and 5 for the fluid give integrated fluid rock volume ratios between 0 1 and 2 0 such high fluid rock ratios are supported by observations on the distribution of co2 h2o ratios of fluid inclusions carbon isotopic compositions of fluid inclusion co2 and oxygen isotope systematics of silicates

percolation blockage a process that enables melt pond formation on first year arctic sea ice melt pond formation atop arctic sea ice is a primary control of shortwave energy balance in the arctic ocean during late spring and summer the ponds determine sea ice albedo and how much solar radiation is transmitted into the upper ocean through the sea ice the initial formation of ponds requires that melt water be retained above sea level on the ice surface both theory and observations however show that first year sea ice is so highly porous prior to the formation of melt ponds that multi day retention of water above hydraulic equilibrium should not be possible here we present results of percolation experiments that identify and directly demonstrate a mechanism allowing melt pond formation the infiltration of fresh water into the pore structure of sea ice is responsible for blocking percolation pathways with ice sealing the ice against water percolation and allowing water to pool above sea level we demonstrate that this mechanism is dependent on fresh water availability known to be predominantly from snowmelt and ice temperature at melt onset we argue that the blockage process has the potential to exert significant control over inter annual variability in ice albedo finally we suggest that incorporating the mechanism into models would enhance their physical realism full treatment would be complex we provide a simple temperature threshold based scheme that maybe used to incorporate percolation blockage behavior into existing model frameworks this article is protected by copyright all rights reserved

the potential of rotary wing uav based magnetic surveys for mineral exploration a case study from central sweden abstract unmanned aerial vehicle uav based geophysical surveys are attractive for land mineral exploration and are gradually opening extraordinary opportunities in providing high resolution definition of geologic structures and for direct targeting of mineral deposits there are however challenges such as electromagnetic noise from the uav limited load capacity and short flight times if these are overcome there will be a new era in using uav based geophysical systems for mineral exploration and for a number of mining related purposes in this study we have tested the potential of rotary wing uav systems given their flight flexibility and robustness for direct targeting of iron oxide deposits in central sweden a walking mode high precision overhauser magnetometer was reassembled so that it could be lifted by the rotary wing system successful backyard tests were performed but during the real experiment several issues related to high uav noise level and extreme magnetic field from the mineraliza

sea ice is a mushy layer sea ice is a two phase two component reactive porous medium an example of what is known in other contexts as a mushy layer the fundamental conservation laws underlying the mathematical description of mushy layers provide a robust foundation for the prediction of sea ice evolution here we show that the general equations describing mushy layers reduce to the model of maykut and untersteiner 1971 under the same approximations employed therein

decline in arctic sea ice thickness from submarine and icesat records 1958 2008 1 the decline of sea ice thickness in the arctic ocean from icesat 2003 2008 is placed in the context of estimates from 42 years of submarine records 1958 2000 described by rothrock et al 1999 2008 while the earlier 1999 work provides a longer historical record of the regional changes the latter offers a more refined analysis over a sizable portion of the arctic ocean supported by a much stronger and richer data set within the data release area dra of declassified submarine sonar measurements covering 38 of the arctic ocean the overall mean winter thickness of 3 64 m in 1980 can be compared to a 1 89 m mean during the last winter of the icesat record an astonishing decrease of 1 75 m in thickness between 1975 and 2000 the steepest rate of decrease is 0 08 m yr in 1990 compared to a slightly higher winter summer rate of 0 10 0 20 m yr in the five year icesat record 2003 2008 prior to 1997 ice extent in the dra was 90 during the summer minimum this can be contrasted to the gradual decrease in the early 2000s followed by an abrupt drop to 55 during the record setting minimum in 2007 this combined analysis shows a long term trend of sea ice thinning over submarine and icesat records that span five decades

thermal evolution of permeability and microstructure in sea ice 1 the fluid permeability k of sea ice constrains a broad range of processes such as the growth and decay of seasonal ice the evolution of summer ice albedo and biomass build up such processes are critical to how sea ice and associated ecosystems respond to climate change however studies of k and its dependence on brine porosity and microstructure are sparse here we present a multifaceted theory for k which closely captures laboratory and field data x ray computed tomography provides an unprecedented look at the brine phase and its connectivity we find that sea ice displays universal transport properties remarkably similar to crustal rocks yet over a much narrower temperature range our results yield simple parameterizations for fluid transport in terms of temperature and salinity and permit more realistic representations of sea ice in global climate and biological models

evidence for thinning of the arctic ice cover north of greenland in may 1987 a british submarine carried out an ice profiling experiment in the arctic ocean in which the route closely approximated that of an earlier voyage in october 1976 over a zone extending more than 400 km to the north of greenland there is evidence of a significant decrease in mean ice thickness in 1987 relative to that found in 1976 this thinning amounts to a loss of volume of at least 15 over an area of 300 000 km2 the nature of the ice thickness distributions suggests that the thinning is primarily associated with the presence of a larger fraction of young and first year ice a consequence of wind driven divergence in the ice cover during the months preceding the 1987 observations such a large fluctuation in a region previously believed to possess consistently high ice thicknesses illustrates the importance of monitoring arctic ice thickness more systematically to determine whether such fluctuations fall within the limits of normal inter annual variability

when will the summer arctic be nearly sea ice free 1 the observed rapid loss of thick multiyear sea ice over the last 7 years and the september 2012 arctic sea ice extent reduction of 49 relative to the 1979 2000 climatology are inconsistent with projections of a nearly sea ice free summer arctic from model estimates of 2070 and beyond made just a few years ago three recent approaches to predictions in the scientific literature are as follows 1 extrapolation of sea ice volume data 2 assuming several more rapid loss events such as 2007 and 2012 and 3 climate model projections time horizons for a nearly sea ice free summer for these three approaches are roughly 2020 or earlier 2030 10 years and 2040 or later loss estimates from models are based on a subset of the most rapid ensemble members it is not possible to clearly choose one approach over another as this depends on the relative weights given to data versus models observations and citations support the conclusion that most global climate model results in the cmip5 archive are too conservative in their sea ice projections recent data and expert opinion should be considered in addition to model results to advance the very likely timing for future sea ice loss to the first half of the 21st century with a possibility of major loss within a decade or two

thin and thinner sea ice mass balance measurements during sheba 1 as part of a large interdisciplinary study of the surface heat budget of the arctic ocean sheba we installed more than 135 ice thickness gauges to determine the sea ice mass balance while installing these gauges during the fall of 1997 we found that much of the multiyear ice cover was only 1 m thick considerably thinner than expected over the course of the yearlong field experiment we monitored the mass balance for a wide variety of ice types including first year ice ponded ice unponded ice multiyear ice hummocks new ridges and old ridges initial ice thicknesses for these sites ranged from 0 3 to 8 m and snow depths varied from a few centimeters to more than a meter however for all of their differences and variety these thickness gauges sites shared a common trait at every site there was a net thinning of the ice during the sheba year the thin ice found in october 1997 was even thinner in october 1998 the annual cycle of ice thickness was also similar at all sites there was a steady increase in thickness through the winter that gradually tapered off in the spring this was followed by a steep drop off in thickness during summer melt and another tapering in late summer and early fall as freeze up began maximum surface melting was in july while bottom ablation peaked in august combining results from the sites we found an average winter growth of 0 51 m and a summer melt of 1 26 m which consisted of 0 64 m of surface melt and 0 62 m of bottom melt there was a weak trend for thicker ice to have less winter growth and greater net loss for the year however ice growth was also impacted by the snow depth considerable variability was observed between sites in both accretion and ablation the total accretion during the 9 month growth season ranged from zero for thick ridged ice to more than a meter for young ice ponds tended to have a large amount of surface melting while ridges had considerable bottom ablation

the lavrion pb zn fe cu ag detachment related district attica greece structural control on hydrothermal flow and element transfer deposition abstract the impact of lithological heterogeneities on deformation fluid flow and ore deposition is discussed based on the example of the lavrion low angle detachment partly accommodating gravitational collapse of the hellenides orogenic belt in greece the lavrion peninsula is characterised by a multiphase pb zn fe cu ag ore system with a probable pre concentration before subduction followed by progressive remobilisation and deposition coeval with the development of a low angle ductile to brittle shear zone the mylonitic marble below the detachment shear zone is composed of white layers of pure marble alternating with blue layers containing impurities sio2 al2o3 carbonaceous material ductile mylonitic deformation is more pervasive in the less competent impure blue marble we propose that localised deformation in the impure marble is associated with fluid circulation and dolomitisation which in turn causes an increase in competence of these layers mineralised cataclastic zones crosscutting the mylonitic fabric are preferentially localised in the more competent dolomitic layers oxygen and carbon isotopic signatures of marble invaded by carbonate replacement deposits during ductile to ductile brittle deformation are consistent with decarbonation coeval with the invasion of magmatic fluids mineralised cataclastic zones reflecting brittle deformation evolve from low 13c to low 18o signatures interpreted as local interaction with carbonaceous material that trends toward the contribution of a surface derived fluid these features indicate that the lavrion area records a complex deposition history influenced by the evolution of fluid reservoirs induced by the thermal and mechanical evolution of the marble nappe stack ore remobilisation and deposition associated with the activity of the low angle detachment is i firstly related to the intrusion of the plaka granodiorite leading to porphyry type and carbonate replacement mineralisation during ductile brittle deformation and ii then marked by progressive penetration of surface derived fluids guided by strain localisation in the more competent levels leading to epithermal mineralisation associated with brittle deformation

fluid inclusions in epidote minerals and fluid development in epidote bearing rocks the widespread occurrence of epidote minerals in metamorphic and igneous rocks as well as in many ore deposit types makes it a promising candidate for fluid inclusion studies apart from high to very high temperature and low to intermediate pressure conditions epidote minerals are stable over a wide range of pressure and temperature in the continental and oceanic crust e g poli and schmidt 1998 yet fluid inclusion studies on epidote minerals are surprisingly scarce even in fluid saturated environments like certain vein type deposits or hydrothermal volcanic vugs and druses for example epidote minerals are not mentioned in the subject index of roedder s 1984 outstanding summary and review of fluid inclusion studies and occurrences which lists more than sixty different host minerals for fluid inclusions nonetheless more recent studies showed fluid inclusions in epidote minerals to be the only direct witness of the physiochemical and compositional fluid evolution during certain geodynamic processes mainly found in fossil geothermal systems ore deposits and high pressure to ultra high pressure rocks the aim of this review is to outline and summarize some aspects and interpretations of geodynamic processes which are based on temperature t pressure p molar volume v and composition x data from fluid inclusions in epidote minerals as well as associated host minerals from various geological environments the review starts with a chapter on some typical mixed volatile solid fluid equilibria involving epidote minerals which are relevant for the here discussed environments this is followed by a short introduction into the basic concepts of fluid inclusion research and the role of epidote minerals the next section covers fluid inclusion studies on epidote minerals from active and fossil geothermal systems as well as low grade metamorphic rocks and constraints on the p t x properties of the fluids present in these systems this is followed by a short introduction

observations of flooding and snow ice formation in a thinner arctic sea ice regime during the n ice2015 campaign influence of basal ice melt and storms seven ice mass balance instruments deployed near 83 n on different first year and second year ice floes representing variable snow and ice conditions documented the evolution of snow and ice conditions in the arctic ocean north of svalbard in january march 2015 frequent profiles of temperature and thermal diffusivity proxy were recorded to distinguish changes in snow depth and ice thickness with 2 cm vertical resolution four instruments documented flooding and snow ice formation flooding was clearly detectable in the simultaneous changes in thermal diffusivity proxy increased temperature and heat propagation through the underlying ice slush then progressively transformed into snow ice flooding resulted from two different processes i after storm induced breakup of snow loaded floes and ii after loss of buoyancy due to basal ice melt in the case of breakup when the ice was cold and not permeable rapid flooding probably due to lateral intrusion of seawater led to slush and snow ice layers at the ocean freezing temperature 1 88 c after the storm the instruments documented basal sea ice melt over warm atlantic waters and ocean to ice heat flux peaked at up to 400 w m 2 the warm ice was then permeable and flooding was more gradual probably involving vertical intrusion of brines and led to colder slush and snow ice 3 c the n ice2015 campaign provided the first documentation of significant flooding and snow ice formation in the arctic ice pack as the slush partially refroze snow ice formation may become a more frequently observed process in a thinner ice arctic

large scale surveys of snow depth on arctic sea ice from operation icebridge 1 we show the first results of a large scale survey of snow depth on arctic sea ice from nasa s operation icebridge snow radar system for the 2009 season and compare the data to climatological snow depth values established over the 1954 1991 time period for multiyear ice the mean radar derived snow depth is 33 1 cm and the corresponding mean climatological snow depth is 33 4 cm the small mean difference suggests consistency between contemporary estimates of snow depth with the historical climatology for the multiyear ice region of the arctic a 16 5 cm mean difference climatology minus radar is observed for first year ice areas suggesting that the increasingly seasonal sea ice cover of the arctic ocean has led to an overall loss of snow as the region has transitioned away from a dominantly multiyear ice cover

circumpolar thinning of arctic sea ice following the 2007 record ice extent minimum september 2007 marked a record minimum in sea ice extent while there have been many studies published recently describing the minimum and its causes little is known about how the ice thickness has changed in the run up to and following the summer of 2007 using satellite radar altimetry data covering the arctic ocean up to 81 5 degrees north we show that the average winter sea ice thickness anomaly after the melt season of 2007 was 0 26 m below the 2002 2003 to 2007 2008 average more strikingly the western arctic anomaly was 0 49 m below the six year mean in the winter of 2007 2008 these results show no evidence of short term preconditioning through ice thinning between 2002 and 2007 but show that after the record minimum ice extent in 2007 the average ice thickness was reduced particularly in the western arctic citation giles k a s w laxon and a l ridout 2008 circumpolar thinning of arctic sea ice following the 2007 record ice extent minimum geophys res lett 35 l22502 doi 10 1029 2008gl035710

aerial magnetic mapping with an unmanned aerial vehicle and a fluxgate magnetometer a new method for rapid mapping and upscaling from the field to regional scale abstract magnetic measurements with an unmanned aerial vehicle are ideal for filling the gap between ground and airborne magnetic surveying however to obtain accurate aeromagnetic data the compensation of magnetic effects of the unmanned aerial vehicle is a challenge typically scalar magnetometers are towed several metres under the unmanned aerial vehicle to minimize its magnetic field in this study a fluxgate three component magnetometer is attached 42 cm in front of the unmanned aerial vehicle at the tip of a composite pipe using a scalar calibration the sensor can be calibrated and the permanent and induced magnetic fields of the unmanned aerial vehicle can be compensated the contributions of the magnetic measurements at different altitudes to the unmanned aerial vehicle results were tested over an area of 1 km in the northern vosges mountains the area is located in a hamlet surrounded by a forest where few geological outcrops are observed three magnetic surveys of the same area are obtained at different altitudes 100 30 and 1 m above the ground the unmanned aerial vehicle magnetic data are compared with a helicopter aeromagnetic survey at 300 m above the ground and a ground magnetic survey using upward continuations of the maps to compare the results the magnetic maps 300 100 30 and 1 m above the ground show very different magnetic anomaly patterns e g amplitude shape wavelength and orientation the magnetic data at different altitudes improve the understanding of the geology from the local to more general scales

desalination processes of sea ice revisited 1 we reexamine five processes that have been suggested to be important for the loss of salt from sea ice these processes are the initial fractionation of salt at the ice ocean interface brine diffusion brine expulsion gravity drainage and flushing with surface meltwater we present results from analytical and numerical studies as well as from laboratory and field experiments that show that among these processes only gravity drainage and flushing contribute to any measurable net loss of salt we show that during ice growth the salinity field is continuous across the ice ocean interface hence there is no immediate segregation of salt at the advancing front

aeromagnetic surveying with a rotary wing unmanned aircraft system a case study from a zinc deposit in nash creek new brunswick canada unmanned aircraft systems uass have been under rapid development for applications in the mineral exploration industry mainly for aeromagnetic surveying they provide improved detection of smaller deeper and weaker magnetic targets a traditional system flying an altitude of 100 m above ground level agl can detect a spherical ore body with a radius of 16 m and a magnetic susceptibility of 10 4 buried at a depth of 40 m a uas flying at an altitude of 50 or 2 m agl would require the radius to be 11 or 5 m respectively a demonstration survey was performed using the skylance rotary wing uas instrumented with a cesium vapour magnetometer in nash creek new brunswick canada the uas flew over a zinc deposit featuring three magnetic anomalies it acquired repeatable data that compared well with upward continuation maps of ground magnetic data dykes or faults that are dipping eastward at 25 and are approximately 1 5 m wide fit the observed response of the three anomalies captured on the uas magnetic data

tracer studies of pathways and rates of meltwater transport through arctic summer sea ice 1 at the surface heat budget of the arctic ocean sheba program s field site in the northern chukchi sea snow and ice meltwater flow was found to have a strong impact on the heat and mass balance of sea ice during the summer of 1998 pathways and rates of meltwater transport were derived from tracer studies h218o 7be and release of fluorescent dyes complemented by in situ sea ice permeability measurements it was shown that the balance between meltwater supply at the surface averaging between 3 5 and 10 5 mm d 1 and ice permeability between 10 9 m2 determines the retention and pooling of meltwater which in turn controls ice albedo we found that the seasonal evolution of first year and multiyear ice permeability and surface morphology determine four distinct stages of melt at the start of the ablation season stage 1 ponding is widespread and lateral melt flow dominates several tens of cubic meters of meltwater per day were found to drain hundreds to thousands of square meters of ice through flaws and permeable zones significant formation of underwater ice composed between 50 of meteoric water formed at these drainage sites complete removal of snow cover increase in ice permeability and reductions in hydraulic gradients driving fluid flow mark stage 2 concurrent with a reduction in pond coverage and albedo during stage 3 maximum permeabilities were measured with surface meltwater penetrating to 1 m depth in the ice and convective overturning and desalination found to dominate the lower layers of first year and thin multiyear ice enhanced fluid flow into flaws and permeable zones was observed to promote ice floe breakup and disintegration concurrent with increases in pond salinities and 7be advective heat flows of several tens of watts per square meter were derived promoting widening of ponds and increases in pond coverage stage 4 corresponds to freeze up roughly 40 of the total surface melt was retained by the ice cover within the ice matrix as well as in surface and under ice ponds with a total net retention of 15 based on this work areas of improvement for fully prognostic simulations of ice albedo are identified calling for parameterizations of sea ice permeability and the integration of ice topography and refined ablation schemes into atmosphere ice ocean models

high resolution unmanned aerial vehicle aeromagnetic surveys for mineral exploration targets abstract recent advancements in geophysical exploration have been realized through reliably integrating unmanned aerial vehicle platforms with lightweight high resolution magnetometer payloads unmanned aerial vehicle aeromagnetic surveys can provide a contemporary data product between the two end members of coverage and resolution attained using manned airborne and terrestrial magnetic surveys this new data product is achievable because unmanned aerial vehicle platforms can safely traverse with magnetometer payloads at flight elevations closer to ground targets than manned airborne surveys while also delivering an increased coverage rate compared to walking conventional terrestrial surveys this is a promising new development for geophysical and mineral exploration applications especially in variable terrains a three dimensional unmanned aerial vehicle aeromagnetic survey was conducted within the shebandowan greenstone belt northwest of thunder bay ontario canada in july 2017 a series of two dimensional grids 500 m 700 m were flown at approximate elevations of 35 45 and 70 m above ground level using a da ji ng innovations multi rotor unmanned aerial vehicle s900 and a gem systems inc potassium vapour magnetometer gsmp 35u in total over 48 line km of unmanned aerial vehicle aeromagnetic data were flown with a line spacing of 25 m the collected aeromagnetic data were compared to a regional heliborne aeromagnetic survey flown at an elevation of approximately 85 m above the terrain with a line spacing of 100 m as well as a follow up terrestrial magnetic survey the first vertical derivative of the gathered unmanned aerial vehicle total magnetic field data was calculated both directly between each of the different flight elevations and indirectly by calculating the values predicted using upward continuation this case study demonstrates that low flight elevation unmanned aerial vehicle aeromagnetic surveys can reliably collect industry standard total magnetic field measurements at an increased resolution when compared to manned airborne magnetic surveys the enhanced interpretation potential provided by this approach also aided in delineating structural controls and hydrothermal fluid migration pathways a pair of adjacent shear zones related to gold mineralization on site these structural features were not clearly resolved in the regional manned airborne magnetic data alone further demonstrating the utility of applying high resolution unmanned aerial vehicle aeromagnetic surveys to mineral exploration applications the conclusions and interpretations drawn from the unmanned aerial vehicle aeromagnetic data coupled with historical data were applied to make a new gold mineralization discovery on the site assayed at 15 7 g t