the role of hydrothermal processes in concentrating high field strength elements in the strange lake peralkaline complex northeastern canada abstract the middle proterozoic peralkaline pluton at strange lake quebec labrador comprises hypersolvus to subsolvus phases which are unusually enriched in zr y rees nb be and f as exotic alkali and alkaline earth silicate minerals the highest concentrations of these elements are in subsolvus granite which underwent intense low temperature 200 c hydrothermal alteration involving hematization and the replacement of alkali high field strength element hfse minerals by calcic equivalents this alteration is interpreted to have been caused by meteoric or formational waters high temperature 350 c alteration attributed to orthomagmatic fluids is evident in other parts of the subsolvus granite by the replacement of arfvedsonite by aegirine comparisons of the chemical compositions of fresh and altered rocks indicate that rocks subjected to high temperature alteration were chemically unaffected except for depletion in zr y and hrees these elements were appreciably enriched in rocks that underwent low temperature alteration other elements affected by low temperature alteration include ca and mg which were added and na which was removed available data on hfse speciation in aqueous fluids and the chemistry of the pluton suggest that the hfses were transported as fluoride complexes if this was the case the low temperature fluid could not have been responsible for hfse transport because the high concentration of ca and low solubility of fluorite would have buffered f activity to levels too low to permit significant complexation we propose that hfse mineralization and accompanying alteration were the result of mixing in the apical parts of the pluton of a f rich essentially ca free orthomagmatic fluid containing significant concentrations of hfses with an externally derived meteoric dominated fluid enriched in ca as a result of interaction with calc silicate gneisses and gabbros according to this interpretation the latter fluid was responsible for the exchange of ca for alkalis mainly na in hfse rich minerals and by sharply reducing f activity in the mixed fluid through fluorite precipitation and or increasing ph destabilised the hfse fluoride complexes causing deposition of hfse bearing minerals an important implication of this study is that major hfse enrichment may be restricted to those rare cases where f rich ca free metal leaching environments and ca rich depositional environments are juxtaposed

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

short climatic oscillations in a western european loess sequence kesselt belgium this new study of the loess section at kesselt is focused mainly on the reconstruction of palaeoenvironments of the last glacial period in the belgian dutch region detailed grain size analyses in combination with the study of the palaeosols and periglacial structures indicate the occurrence of climatic cycles during loess deposition permafrost development coincided with enhanced deposition of relatively coarse loess and alternated with permafrost degradation decreased deposition of finer loess and tundra soil formation a newly designated palaeosol lafelt soil is described in detail particularly in terms of its micromorphological properties it is a luvisol and its chronostratigraphical position is still open to debate but radiocarbon dating places it in the weichselian middle pleniglacial 1998 john wiley sons ltd

ice deformation near sheba 1 the deformation rate of sea ice is a key parameter for determining the evolution of the ice thickness distribution it determines the rate of new ice formation through opening and the rate of ridging through closing and shear an extensive suite of ground based and satellite based measurements of ice motion is used to construct a daily time series of the ice velocity and deformation in the vicinity of the surface heat budget of the arctic ocean sheba ice camp that is suitable for forcing a model of the ice thickness distribution the velocity is interpolated to a square grid that remains centered on the camp has a spacing of 25 km is 400 km on a side and is determined for a 371 day period from 2 october 1997 to 7 october 1998 velocity measurements from buoys advanced very high resolution radiometer avhrr special sensor microwave imager ssmi and radarsat geophysical processing system rgps are merged using optimal interpolation and a kalman filter approach the deformation rate is taken directly from the rgps measurements when available the daily total deformation rate measured on a scale of 100 km near the camp averaged 2 21 d 1 and the standard deviation was 1 78 d 1 the divergence was positive in the early winter and negative through most of the spring and summer there were two major opening closing events one in january and one at the end of july the net divergence over the year was very near zero the vorticity indicated a net rotation of 87 over the year with the winter showing strong anticyclonic turning and the summer showing strong cyclonic turning

contemporary sand wedge development in seasonally frozen ground and paleoenvironmental implications abstract contemporary sand wedges and sand veins are active in seasonally frozen ground within the extensive discontinuous permafrost zone in northwest territories canada the region has a subarctic continental climate with 291 mm a 1 precipitation 4 1 c mean annual air temperature warm summers july mean 17 0 c and cold winters january mean 26 6 c five years of continuous observations indicate that interannual variation of the ground thermal regime is dominantly controlled by winter air temperature and snow cover conditions at sandy sites thin snow cover and high thermal conductivity promote rapid freezing high rates of ground cooling and low near surface ground temperatures 15 to 25 c resulting in thermal contraction cracking to depths of 1 2 m cracking potentials are high in sandy soils when air temperatures are

high resolution sea ice motions from amsr e imagery passive microwave remote sensing imagery has proven to be a useful source for sea ice motions because of its all sky capabilities however the low spatial resolution of the passive microwave sensors has not allowed the retrieval of small scale motion details such as lead and ridge formation the nasa earth observing system advanced microwave scanning radiometer amsr e has more than double the spatial resolution of previous passive microwave sensors allowing it to track the formation of moderate sized leads and yield much more detailed and more accurate ice motion estimates comparisons with buoys indicate that amsr e motions have errors 30 lower than ice motions derived from the previous passive microwave sensors while amsr e still cannot retrieve the same level of detail as synthetic aperture radars or visible infrared sensors amsr e s complete coverage can better capture the ephemeral motions of the sea ice cover on daily and potentially sub daily timescales

genesis of the carbonatite hosted fluorite deposit at amba dongar india evidence from fluid inclusions stability isotopes and whole rock mineral geochemistry the amba dongar carbonatite complex is located approximately 400 km northeast of bombay india and consists of a carbonatite ring dike and a number of syenitic intrusions which were emplaced into late cretaceous bagh sandstones and early to late eocene deccan volcanic rocks hydrothermal activity associated with intrusion of the carbonatite was responsible for fenitization of the surrounding sandstones and deposition of economic quantities of fluorite 11 6 mt of 30 caf 2 fluorite mineralization occurs as veins and vug fillings localized along fractures within the calcite carbonatite near its contact with the sandstone fluid inclusions in fluorite indicate a low temperature low salinity 42 and 3 5 respectively the presence of al and s in the fluid the molar equivalence of na and cl and the positive deviation of 18 o and d from the meteoric water line point to a small contribution from orthomagmatic fluids a model is proposed in which the intrusion of a carbonatite magma at high crustal levels caused faulting and fracturing of the surrounding country rocks and was accompanied by the release of orthomagmatic fluids expressed as extensive k and na metasomatism of the surrounding sandstones with the decline of orthomagmatic activity a meteoric water dominated hydrothermal system was initiated by the heat of the intrusion the interaction of ca bearing meteoric fluids with the last vestiges of f bearing orthomagmatic nacl brines caused deposition of large quantities of fluorite at the site of mixing

motion tracking of discontinuous sea ice the purpose of this paper is twofold 1 to develop a high resolution sea ice motion tracking system at the geospatial mesoscale 1 100 km2 and 2 to propose an algorithm that measures motion at close proximity to discontinuous regions here we present a motion tracking system that computes differential motion at 400 m resolution and validate the accuracy precision of this system via four studies the first study measures the accuracy against displacements measured from in situ global positioning system gps buoys deployed at the sea ice experiment dynamic nature of the arctic sedna and the surface heat budget of the arctic ocean sheba experiments the estimates are found to be statistically comparable with gps with an average error of 361 9 and 600 6 m for the experiments respectively the second study compares the estimated displacements to those measured by the radarsat geophysical processing system a precision error of 75 7 m is found between the two motion tracking systems the third study uses intensity warping of randomly sampled measurements to evaluate discontinuous motion tracking a one tailed wilcoxon signed rank test is used to validate these measurements at 0 01 results from this paper prove that anisotropic smoothing produces significantly smaller errors at discontinuous locations w 4240 and p 0 001 over conventional isotropic smoothing the fourth study compares displacements measured by anisotropic smoothing against manual measurements this paper demonstrates an average reduction of the estimation error by 50 m with the use of anisotropic smoothing over the conventional isotropic smoothing

the nature of orthomagmatic hydrothermal fluids in the oka carbonatite quebec canada evidence from fluid inclusions fluid inclusions in apatite monticellite and calcite from the oka carbonatite complex generally comprise either aqueous liquid vapour or aqueous liquid vapour halite some inclusions also contain a variety of trapped solids including calcite strontianite nahcolite and mirabilite microthermometry and raman spectroscopy indicate that co2 is not an important constituent of these fluids microthermometric data also indicate that the hydrothermal fluids liberated from the carbonatitic magma had a wide range of salinities 4 2 to 49 eq wt nacl and densities 0 77 to 1 26 g cm3 most of the fluids had relatively low concentrations of so42 and co32 6 wt however the nature of the trapped minerals and the phase behaviour of some inclusions indicate that some fluids may have had higher concentrations of so42 co32 and or hco3 textural relationships indicate that the crystallization sequence for the host minerals was monticellite apatite calcite which when combined with fluid inclusion data from the three minerals indicates that fluid salinity decreased and fluid density increased during progressive crystallization of the magma the density increase is thought to have been mainly caused by decreasing temperature isochoric projections indicate that the fluids were exsolved at minimum pressures of 4 to 8 kb these data provide a basis with which to assess the involvement of orthomagmatic aqueous fluids in the formation of hydrothermal rare element mineralization associated with carbonatites

large scale comparison between buoy and ssm i drift and deformation in the eurasian basin during winter 1992 1993 a method for comparing sea ice velocity divergence and shear at the large scale between buoys and special sensor microwave imager ssm i is presented for initial testing the method is applied in the eurasian basin because of its relatively simple circulation dominated by the wind using eight argos buoys 11 strain rate arrays 100 600 km in size are constructed daily 100 km resolution sea ice motion derived from ssm i 85 ghz brightness temperatures is sampled 100 1000 km from the center of the buoy arrays over this range of possible scales a minimum rms difference rmsd for deformation is used to identify an optimal inclusion radius of 600 km corresponding to a length scale of 1000 km this length scale is typical of local storms confirming a strong connection between wind and observed sea ice motion on the basis of all 11 arrays an average rmsd of 2 48 0 05 cm s 1 for velocity vector and 8 8 0 9 10 8 s 1 using all four deformation components ui j is found at the optimal inclusion radius corresponding to average correlation coefficients of 0 896 0 002 and 0 729 0 030 respectively rmsd are found to scale with the temporal and spatial uncertainties of the ssm i suggesting that even better results can be achieved with higher resolution instruments

volatiles in alkaline magmatism abstract gases extracted during fusion of volcanic glasses substantiate other sources of evidence that alkaline magmatism is distinguished from calc alkaline by higher co2 so2 contents with relatively smaller proportions of h2o in addition to higher c and s activity alkaline magmas are characterised by high cl and f which are released with alkalis during fusion experiments in a graphic reminder that alkalis should be regarded as mobile elements in magmatism the association of c s and halogens in alkaline magmatism is well shown in some high temperature residua characterized by assemblages such as calcite vishnevite calcium is an important cation in many aspects of alkaline magmatism and the links with carbonatite further emphasize the key position of c s cl and f throughout and the subordinate role of h2o

fram strait satellite image derived ice motions in order to develop an operational method for the u s navy noaa joint ice center to extract ice velocity vectors from sequential advanced very high resolution radiometer avhrr imagery we have combined the maximum cross correlation mcc method with a spatial filtering technique on the image inferred ice motion vectors we compute the cross correlations between images directly from the image brightness values rather than computing ffts the direct method allows greater flexibility in computational parameter settings and allows one to compute motion vectors near coastlines where irregular windows are required by using a combination of statistical and spatial filters we can then retrieve coherent ice motion vectors in the presence of cloud contaminated imagery a series of six satellite images of the fram strait region from april 1986 was used to compute sea ice motion from pairs of sequential images the resulting ice motion vectors were taken as a representation of the surface flow field derived objectively from the satellite imagery resulting vector motion fields were found to match well with manually tracked vectors for the same images thus verifying the validity of the objective mcc method of computing ice motion these techniques were applied to both the visible and infrared avhrr channels and to images with different spatial resolutions yielding an overall bias accuracy of about 0 5 cm s and standard deviations of about 0 9 cm s the mcc ice motion results were also compared with wind driven numerical model simulations of the region marked differences between the mcc image derived velocities and those from the numerical model were thought to be primarily due to a stronger ocean current than was present in the model

extracting quantitative information on coastal ice dynamics and ice hazard events from marine radar digital imagery marine radars have been employed to gather data in applications that require near continuous monitoring and tracking of objects over a wide area from a single viewpoint independent of weather and light conditions however little attention has been paid toward utilizing such systems for the study of long term phenomena and detecting anomalous environmental events or hazards that may occur infrequently but have potentially significant impacts on coastal populations in this paper we concentrate on tracking features in seasonally ice covered arctic coastal ocean environments we have developed tools for automated analysis of ground based radar images of landfast ice and moving sea ice to extract ice floe trajectories and velocity fields delineate the boundary of stable landfast ice detect events relevant to coastal populations and identify surface vessels we employ dense and feature based optical flow approaches to compute motion fields from the images active contours for delineation of stable landfast ice and hidden markov models for machine learning based event detection we present results from the analysis of sample images jointly with a quantitative evaluation of algorithm performance relative to operator based assessments

satellite remote sensing of sea ice thickness and kinematics a review observations of sea ice thickness and kinematics are essential for understanding changes in sea ice mass balance interactions between the ice cover and the ocean and atmosphere and for improving projections of sea ice response in a warming climate these parameters are not directly observable with current sensor technology but are derived from satellite altimetry and imagery while there is progress in the retrievals of arctic sea ice thickness from satellite altimetry approaches to address southern ocean ice thickness require additional attention on the other hand procedures to derive sea ice motion from satellite imagery are more mature and better understood and have been employed to produce useful results for more than a decade adequate sampling of sub daily ice motion however remains a challenge generally satellite instruments provide large scale coverage but the frequency of temporal sampling is limited by orbit characteristics in this review i focus on the approaches uncertainties sampling limitations and validation issues associated with the estimation of sea ice thickness and motion i provide a summary of current and anticipated capabilities for monitoring sea ice thickness and kinematics from space the prospects for continuing these measurements into the next decade from a satellite remote sensing perspective are discussed

atmospheric circulation impacts on winter maximum sea ice extent in the west antarctic peninsula region 1979 2001 increasing evidence exists that the strong warming of the west antarctic peninsula wap region since the 1950s is related to reduced sea ice that is likely to be due to changes in the atmospheric circulation over twenty years of sea ice extent ice motion and reanalysed near surface wind data are used to establish that winter ice extent in the west antarctic peninsula wap region is largely determined by the meridional north south atmospheric circulation a remarkably strong ice extent wind relationship is found in the wap no other antarctic or comparable sub arctic sea ice region shows this ice motion data confirm wind induced drift is crucial for extensive winter ice to occur reasons for winter ice extent and winds being more strongly correlated in the wap than in other parts of the antarctic are discussed along with implications for understanding the observed warming

ross sea ice motion area flux and deformation abstract the sea ice motion area export and deformation of the ross sea ice cover are examined with satellite passive microwave and radarsat observations the record of high resolution synthetic aperture radar sar data from 1998 and 2000 allows the estimation of the variability of ice deformation at the small scale 10 km and to assess the quality of the longer record of passive microwave ice motion daily and subdaily deformation fields and radarsat imagery highlight the variability of motion and deformation in the ross sea with the passive microwave ice motion the area export at a flux gate positioned between cape adare and land bay is estimated between 1992 and 2003 a positive trend can be seen in the winter march november ice area flux that has a mean of 990 103 km2 and ranges from a low of 600 103 km2 in 1992 to a peak of 1600 103 km2 in 2001 in the mean the southern ross sea produces almost twice its own area of sea ice during the winter cross gate sea level pressure slp gra

summer sea ice motion from the 18 ghz channel of amsr e and the exchange of sea ice between the pacific and atlantic sectors 1 we demonstrate that sea ice motion in summer can be derived reliably from the 18ghz channel of the amsr e instrument on the eos aqua platform the improved spatial resolution of this channel with its lower sensitivity to atmospheric moisture seems to have alleviated various issues that have plagued summer motion retrievals from shorter wavelength observations two spatial filters improve retrieval quality one reduces some of the microwave signatures associated with synoptic scale weather systems and the other removes outliers compared with daily buoy drifts uncertainties in motion are 3 4 km day using the daily motion fields we examine five years of summer ice area exchange between the pacific and atlantic sectors of the arctic ocean with the sea level pressure patterns during the summer of 2006 and 2007 favoring the export of sea ice into the atlantic sector the regional outflow is 21 and 15 of the total sea ice retreat in the pacific sector

thin film dawsonite in jurassic coal measure strata of the yaojie coalfield minhe basin china a natural analogue for mineral carbon storage in wet supercritical co2 abstract a large amount of thin film dawsonite has developed in coal cleats and also in fractures within the roof sandstone in jurassic co 2 rich coal measure strata of the yaojie coalfield minhe basin china the co 2 in these strata has been in a supercritical state since natural emplacement in this study the yaojie coalfield is considered a natural analogue site for co 2 capture utilization and storage ccus the thin film dawsonite in coal measure strata was analyzed to investigate the evolution of carbon in supercritical co 2 after ccus as it provides a possible example of the formation of carbonate minerals from a wet supercritical co 2 fluid the cleat and fracture filling dawsonite takes the form of white or silver white radial thin film crystals generally 2 and co 2 derived from the decomposition of basement marble which resulted from dynamic thermal metamorphism of the f19 fault zone the carbon isotopic compositions of the cleat filling dawsonite from different carbon sources are transitional and the carbon source for all of the sandstone fracture filling dawsonite is the co 2 released from the decomposed basement marble the morphological and mineralogical characteristics of the thin film dawsonite show that it most likely nucleated and grew directly in the liquid like water film formed by wet supercritical co 2 on solid phase surfaces rather than by epitaxial growth on the rocks surrounding the cleats and fractures probably via layer by layer crystallization the sodium and aluminum in the dawsonite were derived from formation water the formation of dawsonite in the coal measure strata of the yaojie coalfield indicates that some of the free state co 2 which increases in content due to desorption of the coal matrix can ultimately be converted into carbonate minerals during ccus

ice floe tracker an algorithm to automatically retrieve lagrangian trajectories via feature matching from moderate resolution visual imagery abstract satellite observations of sea ice along marginal ice zones suggest a strong coupling between sea ice transport and the underlying ocean turbulent eddy field moderate resolution imaging spectroradiometer modis satellite imagery spanning over almost two decades of daily observations at a resolution of up to 250 m provides a good resource for deriving long term ocean kinematics from sea ice dynamics in this paper we present a newly developed automatic algorithm to retrieve dynamic measurements of sea ice from these images we describe the methodology by presenting results acquired along the east greenland current ecg for 6 5 weeks in the spring of 2017 during this period our ice floe tracker was used to identify and track ice floes with length scales ranging from 8 to 65 km by effectively filtering atmospheric conditions from modis images ice floes were tracked for up to ten consecutive days and a total of 1061 trajectories were retrieved a southward mean sea ice flow associated with the ecg was observed along with deviations in both direction and magnitude suggesting the effect of an underlying turbulent eddy field the absolute position and tracking errors associated with our method are 255 m and 0 65 cm s respectively each derived from a comparison between manually and automatically identified ice floes going forward our methodology will be employed to process longer time sequences to analyze nonlinear interactions between drifting ice floes and the upper ocean turbulent eddy field in the ecg as well as to investigate other prominent regions of the arctic ocean

zirconolite allanite and hoegbomite in a marble skarn from the bergell contact aureole implications for mobility of ti zr and ree zirconolite allanite and hoegbomite are present as accessory phases in a metasomatically altered spinel calcite marble from the contact with the bergell intrusives switzerland italy textural relationships indicate a step wise alteration of spinel to 1 hoegbomite or corundum magnetite 2 margarite and 3 chlorite replacement of spinel by hoegbomite can be described by the substitution 1 94 mg2 fe2 zn2 mn2 ca2 ti4 0 12 oh where al3 and fe3 are held constant the average composition of the bergell hoegbomites is given by the formula fe 0 97 2 mg0 69zn0 04ti0 17al3 94fe 0 06 3 o7 98 oh 0 02 and seems to be imposed by the composition of pre existing spinel during the first two steps of spinel alteration calcite was replaced by anorthite phlogopite and the rare earth element ree bearing minerals zirconolite allanite and sphene were formed allanites have characteristic chondrite normalized ree patterns with enrichment in the light ree the zirconolite patterns show a marked increase in concentration from la to ce followed by an almost constant section sphene lacks detectable la and its ree patterns vary from grain to grain contemporaneous formation of phlogopite ree bearing minerals and hoegbomite during replacement of the spinel calcite marble indicates that the metamorphic fluid introduced potassium along with ree and other high valence cations ti4 zr4 u4 th4a3804265 nb5a3804265 y3a3804265 possibly as polynuclear complexes the abundance of fluorine bearing phlogopite and fluor apatite as well as their close association with ree bearing minerals and hoegbomite suggests f and po 4 3 as likely ligands for complexing of the above mentioned elements

sea ice motion from satellite passive microwave imagery assessed with ers sar and buoy motions observing the motion of sea ice from space is analogous to observing wind stress over the wet oceans both provide surface forcing for modeling ocean dynamics ice motion also directly provides the advective component of the equations governing the mass balance of the sea ice cover thus its routine observation from space would be of great value to understanding ice and ocean behavior to demonstrate the feasibility of creating a global multidecadal ice motion record from satellite passive microwave imagery and to quantitatively assess the errors in the estimated ice motions we have tracked ice every 3 days in the arctic ocean and daily in the fram strait and baffin bay during the 8 winter months from october 1992 to may 1993 and daily in the weddell sea during the 8 winter months from march to october 1992 the method which has been well used previously involves finding the spatial offset that maximizes the cross correlation of the brightness temperature fields over 100 km patches in two images separated in time by from 1 to 3 days the resulting ice motions are compared with contemporaneous buoyand sar derived ice motions the uncertainties in the displacement vectors between 5 and 12 km are better than the spatial resolution of the data both 85 ghz data with 12 km spatial resolution and 37 ghz data with 25 km resolution are tracked these trials with the 37 ghz data are new and show quite surprisingly that the error is only about 1 km larger with these data than with the 12 km 85 ghz data errors are typically larger than average in areas of lower ice concentration in the most dynamic regions particularly near the ice edge in the barents and greenland seas and in zones of high shear these passive microwave ice motions show a large increase in spatial detail over motion fields optimally interpolated from buoy and wind observations especially where buoy data are virtually absent such as near coasts and in some passages between the arctic ocean and its peripheral seas the feasibility of obtaining ice motion from the 37 ghz data in addition to the 85 ghz data should allow an important record of ice motion to be established for the duration of the scanning multichannel microwave radiometer smmr special sensor microwave imager ssm i and future microwave sensors that is from 1978 into the next millenium

a fluid inclusion study of vug minerals in dawsonite altered phonolite sills montreal quebec implications for hfse mobility ordovician limestones in the francon quarr on the island of montreal quebec are host to three sills of cretaceous age composed of phonolite that has been extensively altered to dawsonite an interesting feature of the sills is the presence of abundant vugs containing a wide variety of minerals including several in which one or more high field strength elements zr hf nb ti is a major component the most important of these latter minerals is weloganite a rare strontium zirconium hydrous carbonate first identified in the francon quarry four types of inclusions have been recognized in vug minerals aqueous aqueous carbonic carbonic and solidbearing aqueous inclusions homogenize at temperatures mainly between 70 and 170 c and between 230 and 390 c the homogenization temperatures of primary inclusions cluster around 350 c aqueous inclusions and the aqueous phase in aqueous carbonic inclusions have salinities ranging between 10 and 24 eq wt nacl equivalent primary aqueous carbonic inclusions have low xco2 0 7 carbonic inclusions are all secondary nahcolite dawsonite and weloganite occur as daughter minerals or trapped solids nahcolite and possibly natron or mirabilite appear to form in frozen inclusions analyses of fluid inclusion decrepitates detected high concentrations of na cl al s and c the extraordinarily high concentration of al in the fluid possibly exceeding 1 wt suggests a ph of approximately 10 pressure and temperature conditions estimated from stratigraphic reconstruction and the isochores of primary aqueous fluid inclusions were 450 bar and 360 to 400 c respectively the relatively high temperatures and compositions of primary fluid inclusions suggest that vug filling was the result of mineral precipitation from an orthomagmatic fluid a model is proposed in which a partially crystallized phonolite melt started exsolving a homogeneous low xco2 fluid immediately prior to or after intrusion sodium aluminium chlorine fluorine sulphur and hfse elements such as zr hf nb and ti were partitioned into the hydrous phase in the case of zr possibly to a concentration of 300 ppm the near horizontal orientation of the sills and the chilled margins produced by quenching of the magma created a tight seal that inhibited escape of the fluids as a result the phonolite stewed in its own juices long after crystallization giving rise to widespread replacement of primary igneous minerals by dawsonite and precipitation of this and other minerals in vugs once the sills had colled to temperatures between 200 and 300 c the aqueous fluid exsolved a high co2 fluid which was trapped as the secondary three phase type ii and type iii inclusions decreasing temperature is considered to have been the principal control of mineralization although in the case of the lower temperature minerals decreased bicarbonate or carbonate ion activity and a lower dielectric constant as a result of co2 exsolution may have played a role in the deposition of hfse bearing minerals

diagenetic f rich ferroan calcite and zircon in the offshore scotian basin eastern canada significance for understanding thermal evolution of the basin in the scotian basin offshore eastern canada an unusual combination of high heat flow in the cretaceous and the abundance of halite has resulted in unusual diagenetic minerals such as sphalerite the newburn h 23 well is the most distal well in the basin with good core samples and has two previously unknown diagenetic mineral occurrences fluorine rich ferroan calcite and diagenetic zircon this study uses sem backscattered electron images and eds analyses emp wds mineral analyses and raman spectroscopy to determine mineral chemistry and textures to investigate the diagenetic and thermal significance of these minerals late diagenetic fe calcite contains 1 2 5 wt fluorine mostly from adsorption but rarely as small fluorite crystals fluoride is also adsorbed on the surfaces of some framework minerals and chlorite fluoride was transported in highly saline formation brines derived from the argo salt formation zircon grains 20 40 m in size have crystal outlines that are straight adjacent to pores partially lobate filling porosity and cross cutting other grains these may be diagenetic some zoned detrital zircon grains show 1 3 m wide diagenetic outgrowths neoformation of diagenetic zircon requires temperatures of 250 c transport of zirconium is favored by ligands in low ph solution principally fluoride and phosphate anions with zirconium mobilized during the alteration of metamict detrital zircon under low grade metamorphic conditions the presence of diagenetic sphalerite and the documented mid cretaceous thermal event in the scotian basin indicate conditions that could have been suitable for the formation of diagenetic zircon in this well suitable geological conditions for such diagenetic formation of zircon will be found in a subsiding rift basin with early evaporites that are affected by a subsequent phase of volcanism due to new rifting or subduction

arctic wide operational sea ice drift from enhanced resolution quikscat seawinds scatterometry and its validation the near real time enhanced resolution quikscat seawinds qs scatterometry composite data are used for daily automatic 48 h sea ice tracking by maximum cross correlation over the entire arctic a correlation window of 61 spl times 61 pixels is used for best performance both qs polarizations vertical vv and horizontal hh are used independently which permits to filter the final results for erroneous vectors by comparing the two drift vectors u spl i oarr sub vv and u spl i oarr sub hh respectively additional filtering is performed by setting a minimum correlation coefficient and by considering the spatial consistency of the motion field the algorithm has been validated with winter 2002 2003 buoy data from the international arctic buoy program showing error standard deviations in the 48 h displacement of 3 1 and 3 2 km in the latitude and longitude direction respectively this corresponds to an error standard deviation in ice drift speed of just 2 6 cm s errors are largest in dynamic regions with lower ice concentrations as for example the southern fram strait the enhanced resolution data improve previous drift results by about 25 but are still blurred by the necessary 36 h period to produce the composites

an analysis of mechanisms of ice wedge casting based on geotechnical centrifuge simulations abstract here we interpret the outcomes of scaled geotechnical centrifuge simulation of ice wedge casting in terms of the likely significance of quaternary ice wedge pseudomorphs observed within different host sediments six experiments were completed in which 1 30th scale models of an ice wedge embedded within frozen host sediments beneath a 25 mm thick unfrozen active layer were thawed from the surface downwards in the geotechnical centrifuge under a 30 times gravity 30 g acceleration host sediment granulometry and or ice contents were varied in each model with host materials comprising medium sands fine sandy silts and silty clays the model ice wedge was 50 mm at the top 150 mm deep and extended across the full width of the 450 mm wide test box centrifuge scaling laws indicate that under an acceleration of 30 g stress distribution was equivalent to a 13 5 m long section of a 4 5 m high and 1 5 m wide full scale prototype ice wedge covered in an active layer of thickness equivalent to 0 75 m thermal regimes measured pore pressures during thaw observed thaw consolidation and measured host sediment geotechnical properties are utilised in the interpretation of casting mechanisms during a single uniform thaw event it is shown that arching of infilling sediment and the formation of a void is likely if negative pore pressures are developed in the host sediment in fine silt and clays high ice contents are more likely than in sands thaw consolidation is greater positive pore pressures encourage complete filling of the ice wedge void and soft sediment deformation is likely to cause deformation of the cast and reduce its width and depth though natural casting mechanisms are likely to be more complex than those simulated here modelling experiments highlight the need for care when inferring original ice wedge geometry from observed shape and size of quaternary ice wedge casts

the genesis of hydrothermal fluorite ree deposits in the gallinas mountains new mexico breccia hosted fluorite bastnaesite deposits associated with epizonal quartz syenite intrusions in the gallinas mountains new mexico provide an important example of hydrothermal rare earth element ree mineralization and an excellent opportunity to investigate the transport and deposition of the ree under hydrothermal conditions fluid inclusion studies show that mineralization commenced with the deposition of quartz at a temperature of approximately 400 c from sulfate rich nacl kcl brines having a salinity of 15 wt percent nacl equiv these fluids are interpreted to have been of orthomagmatic origin fluorite and bastnaesite deposition occurred at slightly lower temperatures and coincided with the introduction of separate co2 bearing and sulfate poor nacl brines into the system these fluids are considered to have been of external origin the latter being a formation water that circulated in surrounding permian sandstones and limestones evaluation of the available thermodynamic data on the aqueous speciation of ree and the preliminary data on the chemistry of the fluids obtained in this study suggest that the ree were dissolved primarily as fluoride complexes a model is proposed in which the ree were transported by the orthomagmatic fluids and deposited as bastnaesite owing to destabilization of ree fluoride complexes the latter occurred in response to the sharp reduction in f activity that accompanied large scale deposition of fluorite as a result of mixing of the orthomagmatic fluids and formation waters this mixing also led to the deposition of anhydrite and barite owing to the interaction of externally introduced calcium and barium ions with orthomagmatic sulfate ions the later stages in the evolution of the gallinas mountains hydrothermal system were marked by increased incursion of external fluids and the alteration of bastnaesite to ca bastnaesite and minor deposition of ca bastnaesite and parisite owing to lowered f batchmode documentclass fleqn 10pt legalpaper article usepackage amssymb usepackage amsfonts usepackage amsmath pagestyle empty begin document co 3 2 mbox end document ratios and or increased ca2 activity the study suggests that ca free ree fluoride bearing fluids are an important ingredient for ree mineralization that mixing of such fluids with ca carbonate bearing fluids or interaction with carbonate rocks is a major control of ree fluorocarbonate mineral deposition and that the occurrence of fluorite could provide an important guide in the exploration for economic ree deposits

high resolution sea ice motion estimation with optical flow using satellite spectroradiometer data the purpose of this paper is twofold 1 to propose an approach based on optical flow for the estimation of sea ice motion as an accurate dense and computationally efficient alternative to state of the art pattern matching approaches and 2 to investigate the potential of moderate resolution imaging spectroradiometer modis optical satellite data for combined daily and high resolution motion estimation a series of modis image pairs for a selected region in arctic ocean is employed and sparse pairwise correspondences between nonrigid patches are calculated an edge preserving sparse to dense interpolation is applied followed by variational energy minimization to compute the final optical flow a state of the art multiresolution pattern matching method based on phase correlation and normalized cross correlation is also implemented and evaluated for comparison thorough experimentation with different settings of input data preprocessing as well as varying scales of motion is performed the derived motion vectors are compared with coarser resolution operational sea ice motion vector products from combined buoy and microwave satellite data the proposed optical flow approach clearly outperforms the pattern matching method in most cases both in terms of accuracy and motion vector consistency the estimated motion vectors from the modis images highly correlate with the operational vector products in addition modis provides a vector field with spatial resolution two orders of magnitude higher than the operational products that are able to detect significantly smaller sea ice drifts

validating icesat over thick sea ice in the northern canada basin only in the past eight years has the feasibility of using satellite borne altimeters to estimate sea ice freeboard and thickness been demonstrated and these estimates still have uncertainties primarily associated with limited knowledge of snow loading on sea ice because accurate estimates of arctic wide sea ice thickness and volume are fundamental inputs to global climate models validation of satellite derived thickness estimates using independent data is required a detailed assessment of freeboard retrieved by the geoscience laser altimeter system glas aboard the ice cloud and land elevation satellite has been carried out using high resolution laser altimetry from the national aeronautics and space administration s airborne topographic mapper atm the delay doppler radar altimeter and digital photography collected along a 300 km segment of sea ice in the canada basin exploiting the repeat coverage of the aircraft flight line a correction was applied to glas footprint geolocations to adjust for sea ice drift that occurred during the time between satellite and aircraft acquisitions comparisons of glas and atm measurements over sea ice show excellent agreement about a 0 00 m mean with no apparent bias between data sets freeboard estimates were examined using data from glas and atm independently employing measurements over refrozen leads to estimate local sea surface heights sshs the results demonstrate the sensitivity of freeboard and thickness calculations to an accurate estimation of local ssh snow depth derived by differencing laser and radar data was combined with the freeboard estimates to yield a mean sea ice thickness of 5 5 m over a 250 km subsection of the flight track

sea ice drift characteristics revealed by measurement of acoustic doppler current profiler and ice profiling sonar off hokkaido in the sea of okhotsk

enhanced arctic sea ice drift estimation merging radiometer and scatterometer data satellites enable daily and global coverage of the polar oceans and provide a unique monitoring capability of sea ice dynamics sea ice drift maps can be estimated in arctic from several satellite sensors particularly from scatterometers and radiometers this study presents the benefits of combining single drift fields at the same resolution into a merged field built at three and six day lags during winters with a 62 5 km resolution it is shown that combining these drift fields not only increases the reliability of the displacement estimation and the number of estimated vectors to almost a full ice covered area but also expands the time period over which these estimations are reliable from freeze until the melt onset the autumn winter spring sea ice drift fields presented here are systematically produced at institut francais de recherche pour l exploitation de la mer centre d exploitation et de recherche satellitaire the sea ice drift 1992 2011 time series is available and the processing is ongoing these data are available for operational use and for the scientific community

comparison of sea ice extent and ice edge location estimates from passive microwave and enhanced resolution scatterometer data passive microwave sea ice concentration fields provide some of the longest running and most consistent records of changes in sea ice scatterometry based sea ice fields are more recently developed data products but now they provide a record of ice conditions spanning several years resolution enhancement techniques applied to scatterometer fields provide much higher effective resolutions 10km than are available from standard scatterometer and passive microwave fields 25 50km here we examine ice extent fields from both sources and find that there is general agreement between scatterometer data and passive microwave fields though scatterometer estimates yield substantially lower ice extents during winter comparisons with ice edge locations estimated from avhrr imagery indicate that enhanced scatterometer data can sometimes provide an improved edge location but there is substantial variation in the results depending on the local conditions a blended product using both scatterometer and passive microwave data could yield improved results

arctic ice ocean simulation with optimized model parameters approach and assessment 1 we present an optimized 1992 2008 coupled ice ocean simulation of the arctic ocean a green s function approach adjusts a set of parameters for best model data agreement overall model data differences are reduced by 45 the optimized simulation reproduces the negative trends in ice extent in the satellite records volume and thickness distributions are comparable to those from the ice cloud and land elevation satellite 2003 2008 the upper cold halocline is consistent with observations in the western arctic the freshwater budget of the arctic ocean and volume heat transports of pacific and atlantic waters across major passages are comparable with observation based estimates we note that the optimized parameters depend on the selected atmospheric forcing the use of the 25 year japanese reanalysis results in sea ice albedos that are consistent with field observations simulated pacific water enters the bering strait and flows off the chukchi shelf along four distinct channels this water takes 5 10 years to exit the arctic ocean at the canadian arctic archipelago nares or fram straits atlantic water entering the fram strait flows eastward merges with the st ana trough inflow and splits into two branches at the southwest corner of the makarov basin one branch flows along lomonosov ridge back to fram strait the other enters the western arctic circulates cyclonically below the halocline and exits mainly through the nares and fram straits this work utilizes the record of available observations to obtain an arctic ocean simulation that is in agreement with observations both within and beyond the optimization period and that can be used for tracer and process studies

an investigation of periglacial slope stability in relation to soil properties based on physical modelling in the geotechnical centrifuge results are presented from eight scaled centrifuge modelling experiments designed to investigate mass movement processes on thawing ice rich slopes four pairs of simple planar slope models were constructed one in each pair being of sufficient gradient to promote slope failure during soil thaw and the second having a gradient below the threshold for instability four frost susceptible soils were used three were normally consolidated and had different clay contents 2 12 and 20 and the fourth comprised the 20 clay soil but was over consolidated prior to model testing modelling protocols included freezing from the surface downwards under an open hydraulic system and thawing from the surface downwards under an enhanced gravitational field within the geotechnical centrifuge thereby utilising scaling laws to simulate correct prototype self weight stresses during thaw slopes below the stability threshold gradient were subjected to between 2 and 4 cycles of freezing and thawing simulating annual cycles those above the stability threshold were subjected to only one cycle since they failed during the first thaw phase thermal conditions pore water pressures surface movements and profiles of displacement are reported measured pore pressures are used in slope stability analyses based on a simple planar infinite slope model profiles of solifluction shear strain and mechanisms of slope failure are both shown to be sensitive to small changes in soil properties particularly clay content and stress history in all cases pore pressures rose rapidly immediately following thaw remained below the threshold for failure in low gradient models but exceeding the threshold to trigger landslides on steeper slopes upward seepage of melt water away from the thaw front contributed to loss of shear strength mechanisms of slope failure differed between test soils ranging from mudflow in non cohesive silt to active layer detachment sliding in over consolidated silt clay during solifluction shear strain was greatest at the surface in non cohesive silt and decreased rapidly with depth but in test soils containing clay the zone of maximum shear strain was located lower in the displacement profiles

mechanisms for the variation of sea ice extent in the northern hemisphere using daily sea ice data derived from satellite borne sensors and atmospheric data we examined processes controlling the variation of sea ice extent in the northern hemisphere the daily ice motion field was computed from imagery of the defense meteorological satellite program dmsp special sensor microwave imager ssm i for seven winters december to april from 1991 1992 to 1997 1998 by employing the maximum cross correlation method in order to examine mechanisms of the temporal variation of the ice extent we analyzed 50 specified lines across the daily ice edge although a high correlation between the ice motion and the geostrophic wind speed was observed in all the ice edge areas the degree for correlation between the speed of the ice edge displacement and the wind speed varied with region the degree for response of the ice edge speed to the wind speed largely depended upon that of the ice edge speed to the ice motion the following mechanisms controlling the variation of ice extent for regions in the northern hemisphere were anticipated in the barents sea bering sea and the sea of okhotsk the ice extent advances by wind driven ice advection and the daily scale variation of the ice extent were also controlled by the variation in wind speed in contrast the ice extent in the labrador sea and the greenland sea seemed to be considerably affected by oceanographic factors such as the location of the thermal front and was not related to the variation in wind speed the regional difference of the variation mechanism was also reflected in the interannual variation in maximum ice extent

variability of fram strait ice flux and north atlantic oscillation we estimate the winter sea ice export through the fram strait using ice motion from satellite passive microwave data sea ice motion october may is obtained by tracking the displacement of common features in sequential 85 and 37 ghz brightness temperature fields the average winter area flux over the 18 year record 1978 1996 is 670 000 km2 7 of the area of the arctic ocean the winter area flux ranges from a minimum of 450 000 km2 in 1984 to a maximum of 906 000 km2 in 1995 the daily monthly and interannual variabilities of the ice area flux are high there is an upward trend in the ice area flux over the 18 year record the average winter volume flux over the winters of october 1990 through may 1995 is 1745 km3 ranging from a low of 1375 km3 in the 1990 flux to a high of 2791 km3 in 1994 the sea level pressure gradient across the fram strait explains more than 80 of the variance in the ice flux over the 18 year record we use the coefficients from the regression of the time series of area flux versus pressure gradient across the fram strait and ice thickness data to estimate the summer area and volume flux the average 12 month area flux and volume flux are 919 000 km2 and 2366 km3 we find a significant correlation r 0 86 between the area flux and positive phases of the north atlantic oscillation nao index over the months of december march correlation between our 5 years of volume flux estimates and the nao index gives r 0 56 during the high nao years a more intense icelandic low increases the gradient in the sea level pressure by almost 1 mbar across the fram strait thus increasing the atmospheric forcing on ice transport correlation is reduced during the negative nao years because of decreased dominance of this large scale atmospheric pattern on the sea level pressure gradient across the fram strait

fram strait sea ice outflow 1 we summarize 24 years 1978 2002 of ice export estimates and examine over a 9 year record the associated variability in the time varying upward looking sonar uls thickness distributions of the fram strait a more thorough assessment of the pmw passive microwave ice motion with 5 years of synthetic aperture radar sar observations shows the uncertainties to be consistent with that found by kwok and rothrock 1999 giving greater confidence to the record of ice flux calculations interesting details of the cross strait motion profiles and ice cover characteristics revealed by high resolution sar imagery are discussed the average annual ice area flux over the period is 866 000 km2 yr between the 1980s and 1990s the decadal difference in the net exported ice area is 400 000 km2 approximately half the annual average except for the years with extreme negative nao correlation of winter ice area export with the nao index remains high r2 0 62 with thickness estimates from uls moorings we estimate the average annual ice volume flux 8 years to be 2218 km3 yr 0 07 sv over the 9 year uls ice thickness data set there is an overall decrease of 0 45 m in the mean ice thickness over the entire time series and a decrease of 0 23 m over the winter months december through march correspondingly the mode of the my ice thickness exhibits an overall decrease of 0 55 m and a winter decrease of 0 42 m these are significant trends whether these trends are indicative of the thickness trends of the arctic ocean is examined as the time varying behavior of the monthly uls thickness distributions can be related not only to the seasonal cycle in the basal growth and melt but also to the magnitude and pattern of ice motion in the arctic ocean and the proximity of the uls moorings to the ice edge

relict sand wedges in southern patagonia and their stratigraphic and paleo environmental significance abstract relict sand wedges are ubiquitous in southern patagonia at six sites we conducted detailed investigations of stratigraphy soils and wedge frequency and characteristics some sections contain four or more buried horizons with casts the cryogenic features are dominantly relict sand wedges with an average depth maximum apparent width minimum apparent width and h w of 78 39 3 8 and 2 9 cm respectively the host materials are fine textured silt loam silty clay loam clay loam till and the infillings are aeolian sand the soils are primarily calciargidic argixerolls that bear a legacy of climate change whereas the sand wedges formed during very cold 4 to 8 c or colder and dry ca 100 mm precipitation yr glacial periods petrocalcic horizons from calcium carbonate contributed by dustfall formed during warmer 7 c or warmer and moister 250 mm yr interglacial periods the paleo argillic bt horizons reflect unusually moist interglacial events where the mean annual precipitation may have been 400 mm yr permafrost was nearly continuous in southern patagonia during the illinoian glacial stage ca 200 ka the early to mid pleistocene ca 800 500 ka and on two occasions during the early pleistocene ca 1 0 1 1 ma

halo of ice deformation observed over the maud rise seamount 1 a distinctive halo of sea ice deformation was observed above the maud rise seamount in the eastern weddell sea in the winter of 2005 the deformation halo is coincident with a halo of low mean ice concentration that is often observed in the region monthly mean ice vorticity estimates for the months july through november reveal the deformation zone most clearly in an arc about 100 km northwest of the seamount where there is a strong gradient in the bathymetry at depths of 3000 5000 m the deformation was computed from satellite based ice motion vectors derived from envisat synthetic aperture radar backscatter images the deformation halo is evidence of a taylor cap circulation over the seamount which has been described and analyzed with modeling studies and concurrent oceanographic observations obtained during an extensive field campaign

a case study of old ice import and export through peary and sverdrup channels in the canadian arctic archipelago 1998 2005

on large outflows of arctic sea ice into the barents sea 1 winter outflows of arctic sea ice into the barents sea are estimated using a 10 year record of satellite ice motion and thickness the mean winter volume export through the svalbard franz josef land passage is 40 km3 and ranges from 280 km3 to 340 km3 a large outflow in 2003 is preconditioned by an unusually high concentration of thick perennial ice over the nansen basin at the end of the 2002 summer with a deep atmospheric low situated over the eastern barents sea in winter the result is an increased export of arctic ice the oct mar ice area flux at 110 103 km2 is not only unusual in magnitude but also remarkable in that 70 of the area is multiyear ice the ice volume flux at 340 km3 is almost one fifth of the ice flux through the fram strait another large outflow of arctic sea ice through this passage comparable to that in 2003 is found in 1996 this southward flux of sea ice represents one of two major sources of freshwater in the barents sea the other is the eastward flux of water via the norwegian coastal current the possible consequences of variable freshwater input on the barents sea hydrography and its impact on transformation of atlantic water en route to the arctic ocean are examined with a 25 year coupled ice ocean model

sea ice motion from low resolution satellite sensors an alternative method and its validation in the arctic 1 the retrieval of sea ice motion with the maximum cross correlation mcc method from low resolution 10 15 km spaceborne imaging sensors is challenged by a dominating quantization noise as the time span of displacement vectors is shortened to allow investigating shorter displacements from these instruments we introduce an alternative sea ice motion tracking algorithm that builds on the mcc method but relies on a continuous optimization step for computing the motion vector the prime effect of this method is to effectively dampen the quantization noise an artifact of the mcc it allows for retrieving spatially smooth 48 h sea ice motion vector fields in the arctic strategies to detect and correct erroneous vectors as well as to optimally merge several polarization channels of a given instrument are also described a test processing chain is implemented and run with several active and passive microwave imagers advanced microwave scanning radiometer eos amsr e special sensor microwave imager and advanced scatterometer during three arctic autumn winter and spring seasons ice motion vectors are collocated to and compared with gps positions of in situ drifters error statistics are shown to be ranging from 2 5 to 4 5 km standard deviation for components of the vectors depending on the sensor without significant bias we discuss the relative contribution of measurement and representativeness errors by analyzing monthly validation statistics the 37 ghz channels of the amsr e instrument allow for the best validation statistics the operational low resolution sea ice drift product of the eumetsat osi saf european organisation for the exploitation of meteorological satellites ocean and sea ice satellite application facility is based on the algorithms presented in this paper

thaw modification of frost fissure wedges richards island pleistocene mackenzie delta western arctic canada thaw modification is the general process whereby frost fissure wedges are modified during thaw and by which frost fissure pseudomorphs may develop specific processes of thaw modification are inferred from ice wedge pseudomorphs composite wedge pseudomorphs and deformed sand wedges in the pleistocene mackenzie delta i e thermal erosion collapse subsidence refreezing loading buoyancy spreading folding and shearing thaw modification is believed to result in selective preservation of pseudomorphs and wedges sand wedges are more likely to be preserved than are ice wedge pseudomorphs or compositewedge pseudomorphs because only those sand wedges that penetrate massive ice or icy sediments are prone to thaw modification furthermore whereas ice wedges preferentially develop in ice rich fine grained sediments thaw sensitive their pseudomorphs appear to be selectively preserved in ice poor coarse grained sediments thaw stable

reconstructing the origin and trajectory of drifting arctic sea ice recent studies have indicated that drifting arctic sea ice plays an important role in the redistribution of sediments and contaminants here we present a method to reconstruct the back ward trajectory of sea ice from its sampling location in the eurasian arctic to its possible site of ori gin on the shelf based on historical drift data from the international arctic buoy program this method is verified by showing that origins derived from the backward trajectories are generally con sistent with other indicators such as comparison of the predicted backward trajectories with known buoy drifts and matching the clay mineralogy of sediments sampled from the sea ice with that of the seafloor in the predicted shelf source regions the trajectories are then used to identify regions where sediment laden ice is exported to the transpolar drift stream from the new siberian islands and the central kara plateau calculation of forward trajectories shows that the kara sea is a major contributor of ice to the barents sea and the southern limb of the transpolar drift stream

validation of sea ice motion from quikscat with those from ssm i and buoy arctic sea ice motion for the period from october 1999 to march 2000 derived from quikscat and ocean buoy observations special sensor microwave imager ssm i data using the wavelet analysis method agrees well with ocean buoy observations results from quikscat and ssm i are compatible when compared with buoy observations and complement each other sea ice drift merged from daily results from quikscat ssm i and buoy data gives more complete coverage of sea ice motion based on observations of six months of sea ice motion maps the sea ice motion maps in the arctic derived from quikscat data appear to have smoother less noisy patterns than those from nscat especially in boundary areas possibly due to constant radar scanning incidence angle for late summer quikscat data can provide good sea ice motion information in the arctic as early as the beginning of september for early summer quikscat can provide at least partial sea ice motion information until mid june in the antarctic a case study shows that sea ice motion derived from quikscat data is consistent with pressure field contours

large scale drift of arctic sea ice retrieved from passive microwave satellite data a method of determining the large scale sea ice drift using 85 5 ghz special sensor microwave imager data are presented a cross correlation method is applied to sequential images of gridded data covering the entire arctic individual correlation results are validated with ice velocities derived from buoy data the satellite derived mean drift values and the variabilities of the ice drift correspond closely with the buoy data similarly time series of buoy data and associated satellite data are in good agreement even over large time periods an example of a satellite retrieved 3 day mean drift field demonstrates the potential of the method for providing large scale ice circulation patterns mean drift fields of the winter periods 1987 1988 and 1992 1993 indicate a considerable interannual variability of the sea ice drift pattern in the arctic ocean the arctic region is divided into seven larger areas and the area flux between these regions has been derived the kara sea and the laptev sea show the largest area ice export with 0 02 and 0 015 km 2 s 1 respectively the central arctic export through fram strait amounts to 0 12 sv during the winter of 1992 1993 with a maximum of 0 15 sv in january

sea ice extent mapping using ku band scatterometer data although spaceborne scatterometers such as the nasa scatterometer have inherently low spatial resolution resolution enhancement techniques can be used to increase the utility of scatterometer data in monitoring sea ice extent in the polar regions a key parameter in the global climate the resolution enhancement algorithm produces images of a and b where a is the normalized radar backscatter coefficient o at 40 incidence and b is the incidence angle dependence of o dual polarization a and b parameters are used to identify sea ice and ocean pixels in composite images the a copolarization ratio and vertically polarized b are used as primary classification parameters to discriminate between sea ice and open ocean estimates of the sea ice extent are obtained using linear and quadratic mahalanobis distance discriminant boundaries the distribution parameters needed for the quadratic estimate are taken from the linear estimate the o error variance is used to reduce errors in the linear and mahalanobis ice ocean classifications noise reduction is performed through binary image region growing and erosion dilation techniques the resulting edge closely matches the nasa team algorithm special sensor microwave imager derived 30 ice concentration edge a 9 month data set of global sea ice extent maps is produced with one 6 day average map every 3 days

wind forcing and ice motion in the weddell sea region the wind forcing on the ocean surface and temporal and spatial characteristics of ice motion are analyzed from data of automatic buoy stations drifting for 14 months on ice floes in the weddell sea generally fluctuations with periods from 2 to 5 days which are caused by synoptic scale atmospheric wind fields primarily contribute to the variance of ice drift peaks in the spectra of ice motion are also found at 12 hours due to inertial motion and weak tidal effects which are nearly coincident in this geographical region inertial motion is only missing in winter when the ice concentration is high in the western branch of the weddell gyre semidiurnal peaks are stronger over the continental shelf than over the deep ocean diurnal peaks are weaker than semidiurnal peaks they are found over the continental shelf and are missing over the deep ocean at the same time the tidal motion reflects non wind related coupling between water and ice motion for periods of 1 2 to 1 day the integral length scales of ice motion are between 550 and 680 km longitudinal correlation and between 360 and 540 km lateral correlation respectively when the ice concentration exceeds eight tenths in the marginal ice zone the lateral length scale of ice motion is reduced to 270 km the integral length scales of air pressure fields exceed the length scales of ice motion by a factor of at least 1 5 longitudinal and lateral length scales of ice motion in the weddell sea are slightly smaller than those published for the beaufort sea where the ice moves within a basin of similar diameter of approximately 1500 km the smaller scales in the weddell sea presumably are due to differences of the forcing fields about 70 to 95 of the variance of 12 hourly averaged drift velocities can be linearly related to the wind velocity except when the mean wind speed drops below 3 5 m s the correlation with geostrophic winds is close to that with locally measured winds the twelve hourly averaged ice drift amounts to about 3 5 of the actual surface wind velocity at a height of 3 m or to about 1 6 of the geostrophic wind velocity derived from surface pressure analyses the drift geostrophic wind ratio is 30 smaller in central winter with ice concentrations above nine tenths in the central weddell sea than during summer periods when the buoys are closer to the coast in the periphery of the gyre and in the marginal ice zone the drift local wind ratio scatters more than the drift geostrophic wind ratio the ice drift in winter for ice concentrations above eight tenths on an average is deflected by 20 degrees to the left of the surface wind direction and is parallel to the isobars in summer under reduced ice concentrations it deviates by 40 degrees to the left of the surface wind and by 10 to 15 degrees to the left of the geostrophic wind for periods of 1 month the ice drift is also linearly well correlated to geostrophic wind velocity winds in the weddell sea usually do not average out over longer time scales ocean currents are too weak to dominate mean ice motion

ice wedges growth thaw transformation and palaeoenvironmental significance frost cracking and ice wedge growth are fundamental processes within the permafrost environment extensive areas of contemporary permafrost terrain are characterised by frost fissure polygons formed by repeated thermal contraction cracking of the ground the incremental growth of ice veins and wedges along the axes of contraction cracks contributes significantly to the volume of ground ice in near surface permafrost in areas beyond the present limit of permafrost the recognition of ice wedge pseudomorphs provides one of the few unambiguous indications of the former existence of permafrost conditions an understanding of the processes of ice wedge growth and thaw transformation is essential if contemporary ice wedges are to be used as analogues for pleistocene frost fissure structures in palaeoenvironmental reconstructions

sea ice transport driving southern ocean salinity and its recent trends the southern ocean has freshened over the past few decades but the underlying mechanisms involved have remained unclear alex haumann and colleagues bring together multiple lines of evidence and despite large uncertainties in the underlying datasets they find that northward transport of sea ice formed around the antarctic coast can explain the bulk of the observed freshening

fluid inclusions as metamorphic process indicators in the southern aravalli mountain belt india fluid inclusions from a biotite garnet schist in the southern aravalli mountain belt india give information on both peak metamorphic conditions and post peak metamorphic processes during uplift a combination of careful petrography microthermometry and raman spectroscopy reveals the presence of at least five generations of enclosed fluids lower amphibolite facies pressure temperature conditions of the growth of garnet rims are reproduced by the highest fluid density of the relatively oldest inclusion type of co2 an2 rich compositions a calculated fluid composition in the coh system in equilibrium with the graphite buaer corresponds to a co2 rich fluid at metamorphic condi tions however the results of these calculations are very sensitive to small fluctuations in oxygen fugacity and the accuracy of thermodynamic properties of mineral equilibria re equilibration conceived by specific size density distribution and the absence of an aqueous phase in inclusions that contain nahcolite crystals is monitored in these inclusions as post peak metamorphic processes like partial decrepitation and preferential leakage the other fluid types represent heterogeneous fluid trapping of coexisting aqueous nacl bearing solutions with co2 ch4 rich vapour bubbles in healed cracks and probably the introduction of external fluids containing high salinity aqueous cacl2 rich solutions in nearly pure n2 vapour bubbles at lower p t conditions this study illustrates that fluid inclusions remain a valuable database of peak metamorphic conditions moreover alterations of the entrapped fluids and surrounding crystals are illustrative for specific exhumation evolutions

magmatic fluids in the fen carbonatite complex s e norway three different types of carbonatite magma may be recognized in the cambrian fen complex s e norway 1 peralkaline calcite carbonatite magma derived from ijolitic magma 2 alkaline magnesian calcite carbonatite magma which yielded biotite amphibole sovite and dolomite carbonatite and 3 ferrocarbonatite liquids related to 2 and or to alkaline lamprophyre magma damjernite apatite formed during the pre emplacement evolution of 2 contains inclusions of calcite and dolomite devitrified mafic silicate glass and aqueous fluid all of these inclusions have a magmatic origin and were trapped during a mid crustal fractionation event p 4 kbars t 625 c where apatite and carbonates precipitated from a carbonatite magma which coexisted with a mafic silicate melt the fluid inclusions contain water dissolved ionic species mainly nacl with minor polyvalent metal salts and in some cases co2 two main groups of fluid inclusions are recognized type a co2 bearing inclusions of approximate molar composition h2o 88 90 co 27 5 nacl 5 d 0 85 0 87 g cm3 type b co2 free aqueous inclusions with salinities from 1 to 24 wt nacleq and densities betwen 0 7 and 1 0 g cm3 more strongly saline type b inclusions salinity ca 35wt d 1 0 to 1 1 g cm3 contain solid halite at room temperature and occur in overgrowths on apatite type a inclusions probably contain the most primitive fluid from which type b fluids have evolved during fractionation of the magmatic system type b inclusions define a continuous trend from low towards higher salinities and densities and formed as a result of cooling and partitioning of alkali chloride components in the carbonatite system into the fluid phase available petrological data on the carbonatites show that the fluid evolution in the fen complex leads from a regime dominated by juvenile co2 h2o fluids during the magmatic stage to groundwater derived aqueous fluids during post magmatic reequilibration

arctic sea ice drift from wavelet analysis of nscat and special sensor microwave imager data wavelet analysis of nasa scatterometer nscat backscatter and dmsp special sensor microwave imager ssm i radiance data can be used to obtain daily sea ice drift information for the arctic region this technique provides improved spatial coverage over the existing array of arctic ocean buoys and better temporal resolution over techniques utilizing data from satellite synthetic aperture radars comparisons with ice motion derived from ocean buoys give good quantitative agreement both comparison results from nscat and ssm i are compatible and the results from nscat can definitely complement that from ssm i when there are cloud or surface effects then three sea ice drift daily results from nscat ssm i and buoy data can be merged as a composite map by some data fusion techniques the ice flow streamlines are highly correlated with surface air pressure contours examples of derived ice drift maps in december 1996 illustrate large scale circulation reversals over a period of 4 days these calibrated validated results indicate that nscat ssm i merged daily ice motions are suitably accurate to identify and closely locate sea ice processes and to improve our current knowledge of sea ice drift and related processes through the data assimilation of ocean ice numerical model

error analysis and assimilation of remotely sensed ice motion within an arctic sea ice model new sea ice motion fields available from remotely sensed data are potentially useful for assessing and improving models of the polar ice pack here we investigate the error characteristics of the observed ice motions relative to drifting buoys and a dynamic thermodynamic ice model a data assimilation approach is then used to assess the potential of the motion data for reducing model biases as well as the potential of the model to serve as an interpolation tool to generate improved ice motion data sets special sensor microwave imager ssm i derived and model simulated ice motions for the years 1988 through 1993 are compared with ice displacement observations from drifting buoys variability and biases are summarized for seasonal and regional means ssm i motions are assimilated into the model using an optimal interpolation method that accounts for the modeled and ssm i motion error variances and the number and distribution of the ssm i motions modeled and ssm i derived motions are found to have comparable mean errors with some notable regional and seasonal differences assimilation substantially reduces the error standard deviation and improves the correlation of the simulated motions relative to the buoy observations but some biases remain in the model framework used here assimilation of the ssm i data substantially alters average ice thickness in some regions of the arctic and affects ice mass outflow through the fram strait but has a small effect on mean ice concentration the assimilation yields an increase in the spatial and temporal variability in ice deformation the observations are particularly suited for improving the simulation of specific synoptic events where substantial differences can occur between simulated and observed ice transport

icesat measurements of sea ice freeboard and estimates of sea ice thickness in the weddell sea 1 sea ice freeboard heights in the weddell sea of antarctica are derived from the ice cloud and land elevation satellite icesat laser altimeter measurements which have a unique range precision to flat surfaces of 2 cm within 70 m footprints spaced at 172 m along track although elevations of flat surfaces can be obtained to an accuracy of 10 cm 1s per footprint direct determination of freeboard heights is precluded by errors in knowledge of the geoid and temporal variability of the ocean surface therefore freeboards are determined relative to an ocean reference level detected over areas of open water and very thin ice within the sea ice pack using an along track filtering method the open water thin ice selections show good agreement in the combined analysis of icesat segments and envisat synthetic aperture radar sar imagery the average residual between the icesat measured ocean level and the egm96 geoid is 1 4 m estimates of snow depth on the sea ice from amsr e passive microwave data along with nominal densities of snow water and sea ice are used to estimate sea ice thickness four periods of icesat data in may june fall and october november late winter of 2004 and 2005 between longitudes 298e and 360e are analyzed in the fall the mean freeboards are 0 28 m in 2004 and 0 29 m in 2005 and the mean thicknesses are 1 33 m in 2004 and 1 52 m in 2005 in late winter the freeboards grew to 0 37 m in 2004 and 0 35 in 2005 and the thicknesses grew to 2 23 m in 2004 and 2 31 m in 2005 the interannual differences in freeboard are small and the larger interannual change in estimated thickness mainly represents differences in the snow depth estimates seasonal changes in the spatial patterns of freeboard and thickness over the 4 months correlate with the expected circulation of sea ice in the weddell sea as indicated by sea ice velocity fields

geology and fluid geochemistry of the na metasomatism u deposits in the longshoushan uranium metallogenic belt nw china constraints on the ore forming process abstract the longshoushan belt in gansu province is a very important uranium metallogenic belt in northwest china and contains a series of different types magmatic na metasomatism supergenetic of uranium deposits and occurrences of all these mineralization types the na metasomatism type is the most predominant with great potential represented by two na metasomatism uranium deposits xinshuijing and jiling different from the fluorite illite quartz dominated alteration minerals in other hydrothermal uranium mineralization system the na metasomatism type uranium deposits are characterized by the unique albite dominated up to 90 vol alteration mineral assemblage which is referred to albitite in many literatures all the uranium orebodies in both the xinshuijing and jiling deposits are hosted within the metasomatic albitites and controlled by the subsidiary faults of the regional malugou fault the mineralization process in both deposits can be divided into four stages namely the na metasomatism stage u mineralization stage post mineralization stage and supergene mineralization stage the na metasomatism stage is predominantly composed of albite with hematite staining with minor chlorite and anatase while the u mineralization stage is characterized by the occurrence of uranium minerals mostly pitchblende intergrown with some tiny albite calcite chlorite pyrite apatite ree minerals and sometimes hydrothermal zircons the mineral assemblages of the na metasomatism stage and u mineralization stage are too intimately related to each other and might be the products of the evolution from the same ore forming fluids the post mineralization stage is mainly the calcite quartz veinlets or occur as aggregate clusters while the supergene mineralization stage includes mineral assemblage of secondary uranium mineralization clay minerals e g kaolinite limonite mineralogical studies and comparison of major and trace elements assay results between fresh biotite granite predominate host rocks albitite and uranium ores suggest that the ore forming fluids resulting in the formation of the na metasomatism alteration are oxidized and rich in na sc v cr co ni u th while the ore forming fluids of the u mineralization stage are relatively reduced and rich in heavy rare earth elements u th po34 fluid inclusion and calcite c o isotope studies indicate that the ore forming fluids are meteoric water dominated which circulated at depth 8 km by fluid inclusion geobarometer and scavenged uranium from the host biotite granites and metamorphic rocks of the longshoushan group the ore precipitation is mainly attributed to physicochemical changes fo2 temperature fluid composition from fluid rock interaction and further temperature decrease of the ore forming fluids while fluid boiling and fluid mixing processes are limited the proposed ore forming process is not only important for the understanding of the ore genesis for the na metasomatism mineralization systems in longshoushan but also highlights the significance of albite alteration which could be used as an important indicator during further uranium exploration

area balance of the arctic ocean perennial ice zone october 1996 to april 1997 we use national aeronautics and space administration scatterometer nscat radarsat and ice motion data to examine the perennial ice zone piz of the arctic ocean between october 1996 and april 1997 the piz is identified by a simple backscatter based classification of the gridded nscat backscatter fields the area of the piz at the beginning of october occupies an area of 5 32 106 km2 76 of the arctic ocean by the first of may only 4 54 106 km2 of that area remains a decrease of 0 78 106 km2 over the 7 month period this area loss can be explained almost entirely by ice export over this period the total area flux of sea ice through fram strait estimated using satellite passive microwave ice motion is 0 80 106 km2 or 12 of the arctic ocean approximately 0 70 106 km2 or 88 of the exported area is from the piz nares strait outflow is small at 34 000 km2 and is estimated by summing the high backscatter areas exported into northern baffin bay after accounting for the outflow through the fram and nares straits an unexplained residual of 46 000 km2 remains we attribute this residual to errors in our estimation process the unaccounted for ice flux through the canadian archipelago and the net divergence and convergence of the piz over the period our interpretation of the radiometry seems to be sound on the basis of the area balance arguments provided here this study shows that 1 the piz converage of the arctic ocean can be derived from nscat backscatter fields and 2 the decrease in piz area over the winter is a good estimate of the piz net ice area exported through fram strait

sea ice tracking by nested correlations spatial differences in sea ice displacement affect ice stress ice production and the mass balance of the ice cover our concepts about the spatial structure of this field have been undernourished because of a paucity of data with high spatial detail and because of the tedium of extracting such measurements from images manually a method is described that measures displacements from synthetic aperture radar digital imagery with fine spatial resolution and does so fully automatically many small areas of ice common to two images are identified by correlating the two images the strategy is to acquire a crude displacement field first from highly averaged images and to refine this field with images of successively higher resolution the median discrepancy between automatically and manually measured displacements is three pixels 0 075 km the algorithm operates successfully on compact ice with large floes and modest rotation rates we believe it will prove applicable to most of the arctic ice cover throughout the year