k feldspar muscovite andalusite quartz brine phase equilibria an experimental study at 25 to 60 mpa and 400 to 550 c abstract felsic magmas may evolve one or more water or chlorine rich fluid phases which can transport heat and solutes into associated hydrothermal systems and can contribute to alteration and ore deposition to understand the role of a high salinity aqueous phase in the magmatic hydrothermal environment the composition of a subcritical vapor undersaturated high salinity liquid phase brine in equilibrium with k feldspar muscovite quartz and muscovite andalusite quartz was determined for pressures and temperatures ranging from 25 mpa and 400 c to 60 mpa and 550 c with total cl nacl kcl hcl concentrations ranging from 3 42 to 8 56 moles of solute kg solution values of log 10 kcl hcl have been obtained for the equilibria 1 5 k feldspar hcl 0 5 muscovite 3 quartz kcland muscovite hcl 1 5 andalusite 1 5 quartz 1 5 h 2 o kcl for the k feldspar muscovite quartz brine equilibrium log 10 kcl hcl 1 6 0 1 0 81 0 06 0 54 0 04 and 0 42 0 08 at 25 mpa and 400 c 40 mpa and 450 c 50 mpa and 500 c and 60 mpa and 550 c pressures and temperatures of the experiments respectively for the muscovite andalusite quartz brine equilibrium log 10 kcl hcl 0 63 0 1 0 063 0 06 0 17 0 05 and 0 25 0 08 at the pressures and temperatures of the experiments respectively comparison of our results with previous studies conducted at higher pressures and with lower salinity aqueous phases show that the mineral stability fields in the k feldspar muscovite andalusite quartz system shift to lower kcl hcl values with increasing salinity and decreasing pressure

variability in categories of arctic sea ice in fram strait an attempt to quantify the temporal variability in the volume composition of arctic sea ice is presented categories of sea ice in the transpolar drift in fram strait are derived from monthly ice thickness distributions obtained by moored sonars 1990 2011 the inflection points on each side of the old ice modal peak are used to separate modal ice from ice which is thinner and thicker than ice in the modal range the volume composition is then quantified through the relative amount of ice belonging to each of the three categories thin modal and thick ice in the monthly ice thickness distributions the trend of thin ice was estimated to be negative at 8 8 per decade relative to the long term mean which was compensated for by increasing trends in modal and thick ice of 7 9 and 4 7 per decade respectively a 7 8 year cycle is apparent in the thin and thick ice records which may explain a loss of deformed ice since 2007 we also quantify how the categories contribute to the mean ice thickness over time thick predominantly deformed ice dominates the mean ice thickness constituting on average 66 of the total mean following the loss of deformed ice since 2007 the contribution of thick ice to the mean decreased from 75 to 52 at the end of the record thin deformed ice did not contribute to this reduction it was pressure ridges thicker than 5 m that were lost and hence caused the decrease in mean ice thickness

archean gold bearing quartz veins at the sigma mine abitibi greenstone belt quebec part i geologic relations and formation of the vein system the sigma deposit consists of an archean gold bearing vein system in metavolcanic rocks intruded by an irregular body of porphyritic diorite both affected by regional deformation and in turn cut by younger undeformed feldspar porphyry dikes the veins cut all rock types and are composed chiefly of quartz and tourmaline with minor amounts of carbonates pyrite chlorite scheelite and free gold they were emplaced during or after a greenschist facies metamorphism postdating the intrusion of feldspar porphyry dikes the veins were not significantly affected by any subsequent metamorphism or tectonism two principal types of veins occur in the mine subvertical veins and subhorizontal veins they are contemporaneous and cogenetic subvertical veins occur within steeply dipping east west trending ductile shear zones along which reverse subvertical displacements have taken place the veins occupy openings created by overriding of undulations and irregularities of foliation and slip planes during progressive shearing movements within the shears subhorizontal veins occupy extensional fractures which developed between ductile shear zones preferentially in the more competent host rocks these veins were formed by one or several episodes of open space filling geologic relations indicate that the mineralized veins were emplaced progressively in a dynamic tectonic environment during and shortly after the formation of ductile shear zones a structural analysis has shown that the ductile shear zones and the two vein types can be related to a single strain ellipsoid of the following orientation the z axis trending north south and horizontal the y axis plunging 10 degrees west and the x axis plunging 80 degrees east the deformation responsible for the generation of ductile shear zones and emplacement of the veins is ascribed to a late north south trending compression postdating regional deformation

gold quartz veins in metamorphic terranes and their bearing on the role of fluids in faulting gold quartz vein fields in metamorphic terranes such as greenstone belts provide evidence for the involvement of large volumes of fluids during faulting and may be products of seismic processes near the base of the seismogenic regime in the val d or district of the abitibi greenstone belt canada quartz tourmaline carbonate veins form a vein field 30 15 km in the hanging wall of a crustal scale fault zone which was the main channelway for upward migration of the deeply generated fluids the veins occur in small high angle reverse faults and in adjacent horizontal extensional fractures extending up to 75 m in intact rocks they have formed incrementally during active reverse faulting in response to crustal shortening at depths corresponding to those at the base of the seismogenic zone in actively deforming crust detailed structural and fluid inclusion studies provide evidence for generally lithostatic but fluctuating fluid pressures p of the order of 200 mpa and for cyclic stress reversals during vein formation and provide good support for the fault valve model a comparison of vein characteristics with standard earthquake rupture parameters suggests that each slip increment along veins in reverse faults was accompanied by a small earthquake 4 m 3 or less the large vein field thus represents both the extent of fluid dispersion in the hanging wall of a crustal scale channelway and the distribution of small earthquakes integrated over the lifetime of the hydrothermal system it is proposed that such small earthquakes along veins in reverse faults are related to large earthquakes m 6 nucleating near the base of the seismogenic regime along the nearby crustal scale fault either as aftershocks or as a precursory smarm

vapour loss boiling as a mechanism for fluid evolution in metamorphic rocks the calculation of fluid evolution paths during reaction progress is considered for multicomponent systems and the results applied to the ternary system co2 h2o nacl fluid evolution paths are considered for systems in which a co2 rich phase of lesser density vapour is preferentially removed from the system leaving behind a saline aqueous phase liquid such boiling leads to enrichment of the residual aqueous phase in dissolved components and for certain reaction stoichiometries to eventual saturation of the fluids in salt components distinctive textures particularly radiating growths of prismatic minerals such as tremolite or diopside are associated with saline fluid inclusions and solid syngenetic salt inclusions at a number of field localities the most thoroughly studied of these localities is campolungo switzerland where metasomatic rocks have developed in association with fractures and veins at 500 c and 2 000 bars of pressure the petrography of these rocks suggests that fluid phase separation into liquid and vapour has been an important process during metasomatism fracture systems with fluids at pressure less than lithostatic may facilitate the loss of the less dense vapour phase to conditions of the amphibolite facies

sea ice velocity in the fram strait monitored by moored instruments 1 the fram strait sea ice velocity was measured by means of a new method using moored doppler current meters in the period 1996 2000 almost 3 years of ice velocity observations near 79 n 5 w are analyzed the average southward ice velocity was 0 16 m s the correlation between the ice velocity and the cross strait sea level pressure slp difference was r 0 76 for daily means and r 0 79 for monthly means the same cross strait slp difference exhibits a positive trend since 1950 of 10 of the mean per decade by a simple linear model we compute mean sea ice area flux to 850 000 km2 year for the period 1950 2000 ice thickness monitored by means of upward looking sonars since 1990 is also discussed the combined data gave a monthly ice volume flux of 200 km3 during the last decade with no significant trend

accretion of archean oceanic plateau fragments in the abitibi greenstone belt canada the arc arc collision model is often applied to the evolution of archean greenstone belts this model predicts concordant stratigraphic relations among the various lithologies evolving generally from komatiitic tholeiitic affinities toward calc alkalic affinities new geological data from the malartic composite block of the abitibi greenstone belt indicate that this volcanic pile rather than representing a conformable sequence is composed of four distinct mafic lithotectonic domains that are overlain by a calc alkalic sequence the mafic domains are thought to be examples of accreted archean oceanic plateau material that were deformed during their collage state the younger calc alkalic sequence represents extension related volcanism that erupted through the ac creted and deformed plateau material possibly as a consequence of ridge subduction in a regime of oblique convergence the relations described here may represent a common feature of archean terranes

thickness and density of snow covered sea ice and hydrostatic equilibrium assumption from in situ measurements in fram strait the barents sea and the svalbard coast modern satellite measurements of sea ice thickness are based on altimeter measurements of the difference in elevation between the snow or ice surface and the local sea surface for retrieval of sea ice thickness it is assumed that the ice is in hydrostatic equilibrium and that the snow load on the ice and the density of the sea ice and sea water are known this study presents data from in situ sea ice thickness drillings and snow and ice density measurements from fram strait the barents sea and the svalbard coast in the european arctic the error in the altimetry ice thickness products is assessed based on the spatial variability of snow and ice density and snow thickness data ice thickness uncertainty related to snow depth was found to be 40 cm radar altimeter and 90 cm laser altimeter while uncertainty related to ice density is 25 cm for both techniques the assumption of hydrostatic equilibrium at the scales of the measurements 10 100 m was found to hold better in the case of level landfast ice near svalbard than for fram strait drift ice which consists of mixed ice types where the deviation between the calculated and measured ice thicknesses was on average 0 5 m

can we extend local sea ice measurements to satellite scale an example from the n ice2015 expedition knowledge of arctic sea ice conditions is of great interest for arctic residents as well as for commercial usage and to study the effects of climate change information gained from analysis of satellite data contributes to this understanding in the course of using in situ data in combination with remotely sensed data the question of how representative local scale measurements are of a wider region may arise we compare in situ total sea ice thickness measurements from the norwegian young sea ice expedition in the area north of svalbard with airborne derived total sea ice thickness from electromagnetic soundings a segmented and classified synthetic aperture radar sar quad pol alos 2 palsar 2 satellite scene was grouped into three simplified ice classes the area fractions of the three classes are 11 2 thin 74 4 level and 14 4 deformed the area fractions of the simplified classes from ground and helicopter based measurements are comparable with those achieved from the sar data thus this study shows that there is potential for a stepwise upscaling from in situ to airborne to satellite data which allow us to assess whether in situ data collected are representative of a wider region as observed by satellites

timing and kinematics of post timiskaming deformation within the larder lake cadillac deformation zone southwest abitibi greenstone belt ontario canada the larder lake cadillac deformation zone is one of several anastomosing zones of high strain within the abitibi greenstone belt in the kirkland lake area ontario the larder lake cadillac de

monitoring ice thickness in fram strait time series of ice thickness in fram strait are evaluated together with ice drift for estimation of the ice flux from the arctic ocean ice draft was measured from moored sonars every 4 min suggesting a nominal sampling interval of 30 m on the basis of these data the annual cycle of many statistics can be resolved the modal ice thickness shows a maximum of 3 15 m in may and a minimum in september of 2 43 m indicating an annual variation range of 0 72 m this compares with model results comprehensive drillings and most of the submarine observations during the last 2 3 decades indicating no significant long term ice thickness change this is also concurrent with the lack of significant temperature changes in the arctic ocean during the same period the mean ice thickness in the central core of the ice stream shows an annual amplitude of 1 m with a minimum in september of 2 25 m and a maximum in april may of 3 25 m the mean thickness of ice only open water excluded is 3 27 m and compares with 3 29 m which is the mean thickness of ice only from 17 submarine tracks in the arctic ocean 1960 1982 the mean annual ice export which is equal to the mean annual net production of ice in the arctic ocean is 2850 km 3 yr 1 for the period 1990 1996 this efflux shows significant variations from year to year with a minimum in 1990 1991 of 2050 km 3 yr 1 and a maximum in 1994 1995 of 4700 km 3 yr 1 this significant variation of nearly 130 is mainly caused by an increased atmospheric forcing and to a lesser degree by an increase in the annual mean ice thickness of 20 over the same period

the effect of structural porosity on the ablation of sea ice ridges 1 observations reveal that the decrease in ice thickness through melting in summer is much more rapid for ridges than for surrounding level ice a physical model that represents internal melting within ridge keels has been developed to explain this observed draft dependent ablation for first year pack ice in the beaufort sea the porous structure of a ridge keel permits percolation of a substantial fraction of the oncoming oceanic flow up to 20 for a feature with 30 porosity and 9 m draft the percolating flow delivers oceanic heat to a large surface area deep within the keel and increases melt rates relative to surrounding level ice by a factor of 5 when seawater temperatures are 0 18 degrees above freezing melt rates are sensitive to the internal geometry of ridges through keel porosity and block dimensions characteristics that vary widely between ridge features however the average rate of melting as a function of draft calculated for a realistic population of keels with average cross sectional shape and differing draft has the same draft dependence as the observations this concurrence suggests that the process of internal melting may be dominant in the ablation of ridged ice in addition internal melting during the summer may well hasten structural consolidation of surviving ridge keels through freezing during the following winter it appears that the evolution of the thickest ice within the arctic ice pack is dependent on the small scale structural characteristics of the ridged ice and its interaction with the upper layer of the ocean

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

u pb age constraints for the magmatic and tectonic evolution of the pontiac subprovince quebec new u pb zircon titanite and monazite ages help constrain the history of magmatism and tectonism within the pontiac subprovince of western quebec the pontiac subprovince resembles other metasedimentary belts of the superior province however the stratigraphic relationships between the dominantly sedimentary rocks of the pontiac and the adjacent volcanic dominated abitibi belt to the north and west remain controversial volcanic rocks of the belleterre volcanic zone in the southern part of the pontiac subprovince have been interpreted by other workers as klippen of abitibi strata that were thrust southward onto the pontiac subprovince however volcanic rocks in the belleterre zone give crystallization ages of 2689 2682 ma which are younger than any extrusive rocks dated thus far from the abitibi belt single detrital zircon grains from pontiac sedimentary rocks give ages as young as 2683 ma indicating that the sediments are similar in age or younger than the volcanic units the volcanic rocks pro

enrichment of co2 in fluid inclusions in quartz by removal of h2o during crystal plastic deformation abstract ductile strain induced leakage of h 2 o from mixed co 2 h 2 o fluid inclusions in quartz is proposed as a mechanism for producing occurrences of pure co 2 fluid inclusions in metamorphic rocks the h 2 o needed for hydrolytic weakening of quartz under stress may be provided by the h 2 o in fluid inclusions with dislocation creep as dislocations nucleate on the walls of fluid inclusions or intersect them h 2 o can be transported with the dislocations from the inclusion to the grain boundaries the process should continue so long as there is stress on the host quartz and the inclusion contains h 2 o the h 2 o taken to the grain boundaries would due to its wetting properties be wicked out along the grain boundaries if the h 2 o is totally removed from an inclusion by a flux of dislocations through the quartz during the crystal plastic flow then a residual inclusion bearing components other than water should remain a mixed co 2 h 2 o inclusion would as a consequence of the process become a pure co 2 fluid inclusion during dynamic recrystallization the co 2 would collect at grain boundary triple junctions and following grain boundary migration would become incorporated into the recrystallized quartz as fluid inclusions this mechanism of generating pure co 2 inclusions could result in co 2 fluid inclusions having densities appropriate for the pressure temperature conditions during deformation using estimates of temperature of deformation the total confining pressure during deformation could be determined from the density of the co 2 fluid in these inclusions

characterisation of amphibolite facies fluids of variscan eclogites from the orlica snieznik dome sudetes sw poland abstract eclogites from the orlica snieznik dome sudetes sw poland exhibit evidence for variscan high pressure metamorphism and a subsequent amphibolite facies overprint three main types of fluid inclusions were observed in quartz of partially retrogressed eclogites type 1 aqueous inclusions mostly two phase inclusions l v type 2 a co2 n2 ch4 inclusions normally one phase inclusions some contain graphite as daughter mineral b n2 ch4 inclusions one phase inclusions type 3 mixed h2o co2 n2 inclusions normally two phase inclusions lh2o lco2 vco2 consisting of 70 80 vol co2 the texturally earliest inclusions are the co2 n2 ch4 type 2a inclusions which were followed by h2o co2 n2 type 3 and h2o type 1 inclusions in chronological order late aqueous type 1 and n2 ch4 type 2b inclusions were the last to be trapped isochores for fluid inclusions are not conformable with peak metamorphic conditions which are estimated at temperatures between 640 and 790 c and minimum pressures of 14 kbar at least three possible explanations must be considered 1 no fluid phase was present during the eclogite facies metamorphism 2 all fluid inclusions which were trapped during the high pressure event decrepitated during retrogression 3 only under medium pressure conditions fluid inclusions were trapped we did not succeed to identify fluid inclusions which clearly are related to the eclogite facies metamorphism however the isochores derived from microthermometric measurements can be used to constrain the retrograde p t path the highest density isochore of the early co2 n2 ch4 inclusions indicates a pressure of 8 kbar at 600 c the isochores of the h2o co2 n2 the h2o inclusions and the re equilibrated co2 n2 ch4 inclusions suggest an almost isothermal decompressional uplift to 2 kbar at 600 c which was followed by isobaric cooling to 200 c therefore the rate of uplift was low relative to the rate of cooling indicating a relatively long period of tectonic inactivity

thinning of arctic sea ice observed in fram strait 1990 2011 1 time series 1990 2011 of sea ice thickness observed by moored sonars in the transpolar drift in fram strait are examined contrasting the post 2007 years against the 1990s three remarkable changes in the monthly ice thickness distributions are highlighted 1 the thickness of old level ice modal thickness is reduced by 32 2 the old ice modal peak width is reduced by 25 and 3 the fraction of ridged ice thicker than 5 m is reduced by 50 the combined effect on the mean ice thickness is a reduction from an annual average of 3 0 m during the 1990s to 2 2 m during 2008 2011 most of the thinning took place after 2005 2006 while the old ice modal thickness and peak width show signs of recovery after 2008 the decreasing trend in fraction of ridged ice and mean ice thickness persists until the end of the record in 2011 the ice observed in fram strait carries an integrated signal of arctic change due to the advection of ice from many sites in the arctic based on concurrence in timing we conclude that much of the thinning quantified here is reflecting recent change in the age composition of the arctic ice cover toward younger ice the old level ice remains thin and as such the ice cover remains preconditioned for new summers of very low sea ice extent

time variability in the annual cycle of sea ice thickness in the transpolar drift the annual cycle of modal and mean sea ice thickness was derived from upward looking sonar ice thickness observations 1990 2011 in fram strait the average annual peak to trough amplitude of the mode of 0 54 m is superimposed on interannual variability with peak to trough amplitudes of 0 73 m on time scales of 6 8 years which again is superimposed on a long term trend of 0 55 m decade over the observation period the long term trend is stronger for april than for august the average months of maximum and minimum modal thickness as a result the annual peak to trough modal thickness amplitude was reduced by 30 between the 1990s and the 2000s the average annual peak to trough amplitude of the mean ice thickness of 1 20 m is also superimposed on interannual variability with as much as 0 97 m thickness change over only 3 years these two modes of variability are superimposed on a long term trend of 0 35 m decade through the entire data set in contrast to the modal thickness the long term trend is weaker for the average month of maximum mean thickness june than for the average month of minimum september therefore the annual peak to trough amplitude of the mean ice thickness increased by 14 between the 1990s and the 2000s

characteristics and chronology of fracture fluid infiltration in the archean eye dashwa lakes pluton superior province evidence from h c o isotopes and fluid inclusions the archean eye dashwa lakes pluton 2672 24 ma has domains of mineralogically fresh isotropic granite domains that have undergone bulk hydrothermal alteration and at least eleven sets of sequential fracture arrays each with distinctive mineral assemblages fresh granite is characterized by whole rock 18o 8 1 to 8 6 and primary magmatic quartz feldspar 1 3 quartz biotite 5 2 to 5 4 and quartz magnetite 9 8 fractionations magmatic fluids had a calculated isotopic composition of 18o 7 9 0 5 and d 80 5 these isotropic volumes of the granite have not experienced significant incursion of external thermal waters pegmatites quartz molybdenite veins and phlogopite muscovite coated fractures are sporadically distributed in the granite and were precipitated from high temperature magmatic fluids where 18o 8 0 to 10 3 and d 80 5

hydrothermal fluid evolution within the cadillac tectonic zone abitibi greenstone belt canada relationship to auriferous fluids in adjacent second and third order shear zones the cadillac tectonic zone in the abitibi greenstone belt canada is spatially associated with world class gold deposits that are hosted in second and third order faults five types of hydrothermal quartz veins with distinct structural timing are distinguished in the cadillac tectonic zone in the val d or camp and are related to d 2 steep reverse faulting and d 3 oblique transcurrent movement fluid inclusions in gold bearing and barren hydrothermal quartz veins in the transcrustal cadillac tectonic zone record the progressive evolution of the hydrothermal fluids within the cadillac tectonic zone oldest h 2 o co 2 ch 4 nacl fluid inclusions which predate gold mineralization are superseded by gold associated dominantly carbonic co 2 ch 4 h 2 o nacl fluid inclusions on the basis of variable phase ratios and similar total homogenization temperatures in contemporaneous fluid inclusions trails the oldest h 2 o co 2 ch 4 nacl fluids are interpreted to have undergone phase separation the ch 4 content increases from the older x ch 4 0 03 0 24 to the younger x ch 4 0 15 0 71 fluid inclusions and the salinity is low to moderate in the older fluid inclusions mean 1 7 2 6 2 wt nacl equiv and increases in the younger fluid inclusions mean 1 16 2 6 0 wt nacl equiv trails of late stage co 2 ch 4 n 2 h 2 o and ch 4 c 2 h 6 c 3 h 8 fluid inclusions crosscut earlier carbonic aqueous fluid inclusion trails in all veins the texturally latest fluid inclusions occur in trails that crosscut earlier fluid inclusion trails and quartz deformation bands and are composed of h 2 o nacl cacl 2 postentrapment modifications are considered unlikely for most fluid inclusions in the cadillac tectonic zone the hydrothermal fluids in the cadillac tectonic zone were compared with those in second and third order fault zones in the world class sigma deposit to evaluate whether the two fluid systems are of similar derivation carbonic aqueous fluids that deposited quartz in veins and some gold in the cadillac tectonic zone are distinct from those that are hosted in structures of similar timing at sigma cadillac fluids have higher co 2 content and marginally higher salinity 0 6 15 3 wt nacl equiv and 1 10 wt nacl equiv in the cadillac tectonic zone and at sigma respectively but contain similar amounts of ch 4 the high salinity aqueous inclusions at sigma which are interpreted to represent the unmixed h 2 o rich end member of a combined co 2 ch 4 h 2 o nacl fluid are absent in the cadillac tectonic zone veins of d 3 timing which contain a high ch 4 component in the cadillac tectonic zone to 70 mole have not been documented at sigma the magnitude of the hydrothermal quartz vein field and the homogeneity of quartz vein mineralogy and textures in the val d or camp strongly suggest that the fluids that precipitated auriferous quartz veins in second and third order shear zones were not locally derived it is suggested that ore bearing fluids ascended along the cadillac tectonic zone and infiltrated the second and third order fault network an unknown amount of metamorphic h 2 o from the greenstone belt probably mixed with these fluids differences in the fluid composition in the cadillac tectonic zone and those in second and third order shear zones are explained by phase separation with preferential vapor loss into the upper portions of the cadillac tectonic zone and by in situ phase separation without vapor loss during ore deposition at sigma methane enrichment in the late fluids in the cadillac tectonic zone was most likely controlled by an increased fluid interaction with reduced carbon in sedimentary rocks but increasing mantle outgassing and cooling of an f o 2 buffered ascending fluid may also have contributed to the ch 4 budget the youngest aqueous brines in the cadillac tectonic zone are similar to fluids in late fracture fillings and to canadian shield basement brines

synoptic airborne thickness surveys reveal state of arctic sea ice cover 1 while summer arctic sea ice extent has decreased over the past three decades it is subject to large interannual and regional variations methodological challenges in measuring ice thickness continue to hamper our understanding of the response of the ice thickness distribution to recent change limiting the ability to forecast sea ice change over the next decade we present results from a 2400 km long pan arctic airborne electromagnetic em ice thickness survey in april 2009 the first ever large scale em thickness dataset obtained by fixed wing aircraft over key regions of old ice in the arctic ocean between svalbard and alaska the data provide detailed insight into ice thickness distributions characteristic for the different regions comparison with previous em surveys shows that modal thicknesses of old ice had changed little since 2007 and remained within the expected range of natural variability

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

n2 and co2 in deep crustal fluids evidence from the caledonides of norway abstract high pressure metamorphic rocks eclogites and high pressure granulites occur along the entire length of the norwegian caledonides and have formed from a variety of protoliths in some cases the relationship between protoliths high pressure rocks and their later retrogression products have been preserved in situ fluid inclusion data suggest a simple correlation between metamorphic grade and metamorphic fluid composition 1 eclogites and high pressure granulites contain n 2 bearing fluids pure n 2 or mixtures with co 2 or h 2 o with x n 2 5 in some eclogite facies rocks co 2 1bn 2 inclusions are associated with aqueous brine inclusions ca 30 wt nacl the two compositions representing immiscible fluids at peak metamorphic conditions 2 granulite facies protoliths and eclogites reworked in the granulite facies contain pure co 2 or co 2 dominated fluids with less than 2 5 n 2 3 rocks retrograded in the amphibolite facies contain h 2 o 1bnacl fluids immiscibility between brine and anhydrous n 2 1bco 2 fluid and between anhydrous fluid and waterbearing aluminosilicate melt have taken place in some eclogites during high grade metamorphism nitrogen may be incorporated in minerals as nh 4 substituting for k or it may occur as n 2 in the free fluid phase the partitioning of nitrogen between minerals and fluids depends upon the water activity and oxygen fugacity during metamorphism low a h 2 o and or high f o 2 partitioning nitrogen to the fluid phase a rock interacting with a carbonic fluid at granulite facies pt conditions will be depleted in mineralogically bound nitrogen in cases where the protoliths of high pressure rocks have been through a previous granulite facies event a local source for the nitrogen contained in high pressure fluid is therefore unlikely

a younger thinner arctic ice cover increased potential for rapid extensive sea ice loss 1 satellite derived estimates of sea ice age and thickness are combined to produce a proxy ice thickness record for 1982 to the present these data show that in addition to the well documented loss of perennial ice cover as a whole the amount of oldest and thickest ice within the remaining multiyear ice pack has declined significantly the oldest ice types have essentially disappeared and 58 of the multiyear ice now consists of relatively young 2 and 3 year old ice compared to 35 in the mid 1980s ice coverage in summer 2007 reached a record minimum with ice extent declining by 42 compared to conditions in the 1980s the much reduced extent of the oldest and thickest ice in combination with other factors such as ice transport that assist the ice albedo feedback by exposing more open water help explain this large and abrupt ice loss

the underside topography of sea ice over the continental shelf of the beaufort sea in the winter of 1990 a spatial section of draft across 348 km of sea ice was obtained by moored subsea sonars in the beaufort sea in the winter of 1990 the ice field was a mixture of first year and multiyear types with mean draft of the order of 3 m level ice of 0 to 4 m draft occupied approximately 50 of the section within this fraction draft values of 0 and 1 5 m were most common while at 2 to 3 m draft a noticeable contribution was made by rafted first year ice deformed ice was observed to a maximum draft of nearly 27 m keels within the section were identified using both the rayleigh criterion and a new criterion based on level ice both criteria defined exponentially distributed populations but with different e folding scales the observations revealed an ice cover whose statistical properties are consistent with other data from the periphery of the polar pack in the beaufort sea but which are much more severe than those of ice found in the seasonal ice zone only a few tens of kilometres to the south the cross sectional shape of individual keels was highly variable but on average the distribution of ice within a keel was an exponential function of draft the topography of both first year and old ice subsections of the data was fractal in character with a dimension of about 1 5 for both ice types the average mass of sea ice per unit area was estimated as 2540 2970 kg m 2 with 68 73 of this mass contributed by deformed ice the large uncertainties in these estimates arise because the porosity of keels and the burden of snow or melt water upon the ice are not known

interpretation of post entrapment fluid inclusion re equilibration at the three mile hill marvel loch and griffins find high temperature lode gold deposits yilgarn craton western australia abstract fluid inclusions that are interpreted to be related to vein filling of quartz veins at the three mile hill and marvel loch gold deposits in amphibolite facies rocks and the griffins find deposits in granulite facies rocks in the yilgarn craton of western australia are dominantly low salinity h 2 o co 2 ch 4 mixtures or co 2 ch 4 fluids at each deposit inclusions have a wide range of compositions with respect to both the aqueous carbonic ratio and the co 2 ch 4 ratio of the carbonic phase and most fluids could not have been in equilibrium with the mineral assemblage in the vein and adjacent rock inclusion densities suggest a range of p t conditions of entrapment and are in general not consistent with the conditions of vein formation indicated by vein assemblages diffusional addition of h 2 into inclusions diffusional loss of h 2 o and reduction of inclusion volume are possible during cooling and uplift along the inferred p t path the inclusion populations could have been derived from an originally uniform population of low salinity aqueous dominated h 2 o co 2 inclusions by a combination of these processes inclusion modification as the cause of the complex inclusion populations is supported by relations of molar volume to composition and to an extent by variations in fluid salinity if inclusion re equilibration is the cause of inclusion variability it was of variable intensity within a single vein system and within individual clusters of inclusions in some samples and is suggested to have been a function of the local petrological and textural environment

macflincor and its application to fluids in archean lode gold deposits abstract macflincor was developed to process laboratory data gathered on fluid inclusions and to calculate isochores for geologically important fluids composed of h2o c02 ch4 nacl and n2 within the program interactive diagrams are available to describe those chemical systems which cannot be adequately constrained numerically the user can choose from various published equations of state describing fluid behavior and can easily compare the results obtained by using different equations the program once the basic fluid parameters have been established allows the data to be used to determine the p t trapping conditions to evaluate possible pressure corrections and to compare different depths of formation based on the pressure calculations and given geothermal gradients for illustrative purposes macflincor has been utilized here to constrain different physical chemical parameters of fluid inclusions trapped in ore related quartz veins and breccias of archean lode gold deposits in western australia inferred pressures from individual deposits show a wide range of values which may be due to post entrapment modifications and or observational uncertainties including estimation of liquid vapor ratios

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

thin sea ice thick snow and widespread negative freeboard observed during n ice2015 north of svalbard in recent years sea ice conditions in the arctic ocean changed substantially toward a younger and thinner sea ice cover to capture the scope of these changes and identify the differences between individual regions in situ observations from expeditions are a valuable data source we present a continuous time series of in situ measurements from the n ice2015 expedition from january to june 2015 in the arctic basin north of svalbard comprising snow buoy and ice mass balance buoy data and local and regional data gained from electromagnetic induction em surveys and snow probe measurements from four distinct drifts the observed mean snow depth of 0 53 m for april to early june is 73 above the average value of 0 30 m from historical and recent observations in this region covering the years 1955 2017 the modal total ice and snow thicknesses of 1 6 and 1 7 m measured with ground based em and airborne em measurements in april may and june 2015 respectively lie below the values ranging from 1 8 to 2 7 m reported in historical observations from the same region and time of year the thick snow cover slows thermodynamic growth of the underlying sea ice in combination with a thin sea ice cover this leads to an imbalance between snow and ice thickness which causes widespread negative freeboard with subsequent flooding and a potential for snow ice formation with certainty 29 of randomly located drill holes on level ice had negative freeboard

nitrogen bearing aqueous fluid inclusions in some eclogites from the western gneiss region of the norwegian caledonides minerals in eclogites from different localities in the western gneiss region of the norwegian caledonides age 425 ma contain a variety of fluid inclusions the earliest inclusions recognized are contained in undeformed quartz grains protected by garnet and consist of h2o n2 with x text h text 2 text o geqslant 0 8 the reconstructed p v t x properties of these fluid inclusions are compatible with peak or early retrograde metamorphic conditions matrix minerals quartz garnet apatite plagioclase contain a complex pattern of mostly truly secondary inclusions dominated by co2 and n2 the textural patterns and p v t x properties of these inclusions are incompatible with the high pressures of the eclogite forming metamorphic event but suggest that they were formed during uplift by a combination of remobilization of preexisting inclusions and influx of external fluids the fluid introduced at a late stage was dominated by co2 and did not contain n2 the present data agree with theoretical predictions of eclogite fluids from mineral equilibria and highlight the differences between granulite co2 and eclogite h2o n2 fluid regimes the provenance of the nitrogen in the eclogite fluid inclusions represents an important but unsolved question in the petrology of high pressure metamorphic rocks