origin and tectonometamorphic history of the repulse bay block melville peninsula nunavut exotic terrane or deeper level of the rae craton the rae craton on melville peninsula nunavut comprises several lithotectonic domains including a structurally and lithologically distinct yet poorly known crustal terrane the repulse bay block rbb this study presents new lithological and petrographic observations combined with u pb zircon data to better understand the archean and paleoproterozoic crustal evolution of the rbb the new data demonstrate that the central eastern rbb consists of the following i upper amphibolite to granulite facies ca 2 73 2 71 ga intermediate granitoid gneisses and gabbroic sheets ii ca 2 69 ga two pyroxene charnockite to enderbite intrusions and iii thin slivers of both archean and paleoproterozoic supracrustal rocks inherited zircon also attests to the presence of a mesoarchean to paleoarchean substrate a semi pelitic gneiss from one of the paleoproterozoic supracrustal panels was deposited sometime after ca 1 89 ga and shows a similar detrital zircon age profile to a 1 92 ga semi pelitic gneiss fr

sea ice models for climate study retrospective and new directions scientific observations of sea ice began more than a century ago but detailed sea ice models appeared only in the latter half of the last century the high albedo of sea ice is critical for the earth s heat balance and ice motion across the ocean s surface transports fresh water and salt the basic components in a complete sea ice model must include vertical thermodynamics and horizontal dynamics including a constitutive relation for the ice advection and deformational processes this overview surveys topics in sea ice modeling from the global climate modeling perspective emphasizing work that significantly advanced the state of the art and highlighting promising new developments

decoupling of u pb dates from chemical and crystallographic domains in granulite facies zircon abstract high spatial resolution 12 m spot size and high density up to 22 spots per crystal u pb ion probe data were acquired for zircon crystals from a mafic granulite in the canadian shield the zircon grains are metamorphic in origin and were subjected to a subsequent high pressure granulite facies event 207pb 206pb dates span 650 ma and can be used to define discrete intracrystalline domains of dates by contouring the age results the boundaries of these domains cut at high angles across compositional zonation revealed by cathodoluminescence backscatter hf and u chemical mapping and electron backscatter diffraction misorientation data the results indicate decoupling of radiogenic pb behavior from other trace elements in the zircon crystals previously published u pb id tims data define a highly linear discordia array with an upper intercept at 2554 5 4 3 ma associated with initial zircon growth during granulite facies metamorphism and a lower intercept at 1896 0 18 0 ma associated with a second granulite facies metamorphic event that caused u pb discordance the intracrystalline patterns of ion probe dates are incompatible with multiple zircon growth events and are inconsistent with reported examples of zircon recrystallization in which resetting of the u pb systematics was accompanied by modification of zircon chemistry and cl patterns grains lack discernible core rim variations expected for diffusion profiles and diagnostic indicators of low temperature radiation damage enhanced pb loss are absent rather the data appear to require heterogeneous pb loss from non metamict metamorphic zircon during high temperature metamorphism implying that under certain circumstances other intracrystalline fast pathways facilitate pb loss in metamorphic zircon crystals this result is incompatible with conventional thinking regarding pb mobility in zircon and indicates that important aspects of pb behavior in zircon are not yet fully understood

collisional snowbird tectonic zone resurrected growth of laurentia during the 1 9 ga accretionary phase of the hudsonian orogeny the 2800 km long snowbird tectonic zone is one of the most controversial tectonic features of the canadian shield metamorphic and in situ geochronologic data reported here reveal that a 1 9 ga medium to high pressure belt extends along most of this tectonic zone in contrast to recent interpretations a collisional origin is indicated by the length of this metamorphic belt tectonic thickening documented in parts of it geological contrasts across it and subduction type microdiamonds within it this collisional event marks a pre 1 865 ga phase of the hudsonian orogeny involving microcontinent accretion that was fundamental to the growth of laurentia

age constraints on the paleoproterozoic tectonometamorphic history of the committee bay region western churchill province canada evidence from zircon and in situ monazite shrimp geochronology in situ u pb sensitive high resolution ion microprobe shrimp analyses of monazite from upper amphibolite facies paragneiss of the committee bay supracrustal belt central rae domain canada reveal three age populations ca 2350 1850 and 1780 ma the ca 1850 ma age also corresponds to growth of low th u zircon as indicated by u pb shrimp analyses of zircon separates from melanosome and leucosome the contextual advantage of the in situ monazite analysis allows evaluation of the geochronological data in terms of the regional structural and metamorphic evolution the region is dominated by a northeast striking s2 s1 fabric axial planar to tight northwest vergent f2 folds early garnet is enveloped by this biotite sillimanite cordierite s2 fabric garneti hosts ca 1850 ma monazite inclusions with ca 2350 ma cores placing a maximum age on garneti growth and s2 development d2 metamorphic conditions progressed through 3 5 kbar 1 kbar 100 mpa and 600 c to near peak conditions of 5 kbar and 675 c a minimum age for s2 is provided by unstrained ca 1820 ma monzogranite that locally and regionally truncates s2 dominantly ca 1780 ma matrix monazite is interpreted to date post s2 garnetii and cordierite which record 5 kbar and 675 c these data indicate that the committee bay region experienced penetrative d2 tectonometamorphism at ca 1850 1820 ma with a subsequent static overprint the absence of a ca 1 85 ga plutonic suite in the region suggests that low pressure metamorphism was a response to thick skinned crustal thickening initiated at ca 1870 ma the new data highlight the importance of paleoproterozoic reworking of the central rae domain in the hinterland of the trans hudson orogen

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

striding athabasca mylonite zone complex archean deep crustal deformation in the east athabasca mylonite triangle northern saskatchewan the geophysically defined snowbird tectonic zone is manifested in northernmost saskatchewan as a deep crustal multistage mylonitic structure the east athabasca mylonite triangle the triangle located at the northeastern apex of a stiff crustal scale lozenge is composed of mid archean annealed mylonites and late archean ribbon mylonites formed during two granulite facies events 850 1000 c 1 0 gpa the flow pattern in the mylonites is geometrically and kinematically complex and corresponds to that expected adjacent to the apex of a stiff elliptical volume subjected to subhorizontal regional extension parallel to its principal axis the late archean mylonites are divided into an upper structural deck entirely occupied by a dip slip shear zone and an underlying lower deck the latter is divided into two upright conjugate strike slip shear zones separated by a low strain septum which deformed by progressive coaxial flow the flow pattern in the mid archean mylonites is compatible with that of

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

modeling and measurement of c band radar backscatter from snow covered first year sea ice in this paper we present model and measurement results for c band hh and vv normalized radar cross sections nrcs from winter snow covered first year sea ice with average snow thicknesses of 16 4 and 3 cm the brine content in snow pack was low in all three case studies which is typical for cold winter conditions we used the first order approximation of the small perturbation theory accounting for surface scattering from the air snow and snow ice rough interfaces and continuously layered snow and sea ice the experimental data were collected during the circumpolar flaw lead system study in the winter of 2008 in the southern beaufort sea from the research icebreaker amundsen good agreement between the model and experimental data were observed for all three case studies the model results revealed that the scattering at the snow ice rough interface is usually stronger than that at the air snow interface furthermore both model and experimental nrcs values at vv and hh polarizations were considerably higher for thin snow cover compared with the thick snow cover case we associate this effect with the lower attenuation of the propagated wave within the thin snow pack in comparison to the thick snow pack we also demonstrated that different brine volume contents in snow with close thicknesses of 4 and 3 cm did not affect the backscattering coefficients at certain incidence angles and polarization our findings provide the physical basis for winter snow thickness retrieval and suggest that such retrievals may be possible from radar observations under particular scattering conditions

structure of a paleoproterozoic continent continent collision zone a lithoprobe seismic reflection profile across the trans hudson orogen canada abstract an 800 km reflection seismic profile across the trans hudson orogen northern saskatchewan and manitoba images crustal scale tectonic imbrication in an unprecedented picture of paleoproterozoic crustal accretion and continent continent collisional tectonism the profile is crudely symmetric about a crustal scale culmination in the western part of an accreted juvenile collage reindeer zone geologic and isotopic data suggest that this culmination is cored by microcontinental archean basement west of the culmination highly reflective juvenile crustal elements dip westward into the lower crust beneath the wathaman batholith and archean continental crust of hearne craton to the east strong reflections in the juvenile reindeer zone crust and reworked archean foreland of the thompson belt have eastward dips persisting into the middle crust and extending beneath the superior craton a continuous reflection moho well defined for 500 km in the western part of the profile shows marked relief 12 15 s including a prominent root below the crustal culmination these imaged structures give evidence of substantial crustal shortening and thickening via large scale imbrication consistent with collisional orogeny w dipping structures below the wathaman batholith and reworked hearne craton may reflect subduction polarity in this part of the orogen however geological evidence suggests that e dipping structures below superior craton are largely related to late post collisional deformation rather than to prior oceanic subduction polarity

sea ice thickness in the eastern canadian arctic hudson bay complex baffin bay abstract past observations of sea ice thickness in the eastern canadian arctic eca have generally been restricted to drill hole measurements at a few local sites on landfast ice here we use data from the laser altimeter icesat and the radar altimeter cryosat 2 to present a 14 year record 2003 2016 of high resolution and spatially extensive ice thickness observations for the eca and identify 12 sub regions with distinct patterns the mean sea ice growth rate within the seasonally ice covered eca from november to april is 23 cm mo 1 565 km 3 mo 1 with the fastest increase in thickness occurring through strong ice convergence and deformation in eastern hudson bay and foxe basin our results demonstrate characteristically asymmetrical distributions of sea ice thickness in both hudson bay and baffin bay but in opposing directions in hudson bay the spring ice cover is 40 cm thicker in the eastern region compared to the northwestern region whereas in baffin bay the ice is 20 cm thicker in the western half of the bay compared to the eastern half in hudson bay we find that years with strong and positive ice drift vorticity i e cyclonic and convergent conditions correlate with increasingly asymmetrical sea ice covers with the level of west east asymmetry varying from 2 to 11 cm per 100 km however in baffin bay the ice drift vorticity is typically negative i e anticyclonic and divergent with no obvious link to the asymmetry of the spring ice cover finally we estimate that large interannual variations in spring sea ice volume within the eca lead to 15 variations in the volume of freshwater available at the ocean surface during summer

multi mineral geochronology insights into crustal behaviour during exhumation of an orogenic root under rare conditions reworked cratons and their margins preserve the orogenic roots of ancient mountain building events however based on the preservation of high temperature 800 c middle and lower crustal metamorphic assemblages present day exposure of these terrains is not simply a result of protracted denudation but also must reflect a multifaceted exhumational history in situ analysis within thin section preserves the textural setting of target minerals that can be used as thermochronometers such as u pb of zircon monazite titanite and apatite and sm nd of apatite in situ analyses of these chronometers has the potential to provide critical timing constraints on exhumation processes related to decompression melting and cooling across large metamorphic terrains the repulse bay block of the rae craton preserves a large composite amphibolite granulite area 50 000 km2 of archean orthogneiss migmatite and slivers of proterozoic metasediments that underwent high grade metamorphism partial melting ductile flow and finally exhumation during the paleoproterozoic trans hudson orogeny the granulite domain preserves dry granitoid assemblages whereas the amphibolite domain is dominated by hydrated migmatites and orthogneiss metasediments occur in both domains and preserve mineral assemblages that are consistent with having undergone tectonometamorphic conditions of 9 kbar 800 c during burial u pb thermochronometers document identical cooling histories of the granulite and amphibolite domains through the u pb closure temperatures of titanite 650 c and apatite 450 c this suggests that melt loss from the underlying granulite domain and melt gain to the amphibolite domain prior to cooling through 650 c are a controlling factor of the metamorphic assemblages across the composite granulite amphibolite terrains such as the repulse bay block rather than significant differences in burial history cooling history and or reorganization of the crust

timescales and significance of high pressure high temperature metamorphism and mafic dike anatexis snowbird tectonic zone canada new geochronological isotopic and geochemical data for a spectacular swarm of deep crustal migmatitic mafic dikes offer important insight into processes operative during 1 9 ga high pressure high temperature metamorphism along the snowbird tectonic zone in northern saskatchewan high precision u pb zircon dates reveal anatexis of chipman mafic dikes at 1 896 2 0 3 ma during syntectonic and synmetamorphic intrusion at conditions of 1 0 1 2 gpa 750 c u pb zircon dates of 1 894 1 891 ma for cross cutting pegmatites place a lower bound on major metamorphism and deformation at the currently exposed crustal levels the persistence of elevated temperatures for 14 m y following peak conditions is implied by younger u pb titanite dates and by sm nd whole rock isotopic data that suggest the derivation of the pegmatites by melting of a mafic source limited melting of the host felsic gneiss at 1 9 ga despite high temperature is consistent with evidence for their previous dehydration by granulite facies metamorphism in the archean spatial heterogeneity in patterns of mafic dike and tonalitic gneiss anatexis can be attributed to lateral peak temperature and compositional variability we correlate 1 896 ma chipman mafic dike emplacement and metamorphism with substantial 1 9 ga mafic magmatism over a minimum along strike extent of 1 200 km of the snowbird tectonic zone this suggests a significant continent wide period of asthenospheric upwelling that induced incipient continental rifting extension was subsequently terminated by hinterland contraction associated with trans hudson accretion and orogenesis little activity in the lower crust for ca 650 m y prior to proterozoic metamorphism and mafic magmatism implies an extended interval of cratonic stability that was disrupted at 1 9 ga this episode of destabilization contrasts with the record of long term stability in most preserved cratons and is important for understanding the lithospheric characteristics and tectonic circumstances that control the destruction or survival of continents

insights into circum arctic sea ice variability from molecular geochemistry abstract geological records of past sea ice such as those contained in arctic marine sediments offer an opportunity to strengthen our understanding of long term sea ice variability provided unambiguous paleo sea ice proxies can be developed one such recently proposed proxy is ip25 a highly branched isoprenoid alkene biosynthesized exclusively by sea ice dwelling diatoms haslea spp which is well preserved in marine sediments and could be used to reconstruct past changes in spring sea ice extent however little is known about regional scale controls on ip25 production in sea ice limiting its wider applicability as a paleo sea ice proxy to address this issue we examined the distributions of ip25 and the marine productivity biomarkers dinosterol and brassicasterol in a suite of surface sediment samples distributed across the arctic we find a statistically significant logarithmic relationship between ip25 and spring sea ice cover in sediment samples from arctic and subarctic sites in the pacific n 96 r2 0 67 p

ocean surface wave evolvement in the arctic basin 1 recent basin scale changes to the compactness and thickness of arctic sea ice foreshadow that encroaching swells and locally generated waves will exert more influence there in the future indeed it is conceivable that waves may have already hastened the adjustments observed by breaking up ice floes yet waves advancing in sea ice attenuate due to being scattered from ice thickness variations and damped by ice inelasticity turbulence and friction while past research focuses on scattering by unnaturally perfect features in the ice the model reported herein assimilates realistic basin scale swathes of heterogeneous ice and parameterizes damping by way of example we show how an ocean wave train evolves during its passage in an 1670 km long arctic sea ice profile obtained from submarine

crustal history of the rae and hearne provinces southwestern canadian shield saskatchewan constraints from geochronologic and isotopic data abstract the cree lake zone hearne province and western granulite domain rae province in northern saskatchewan are contrasting parts of the variably reworked upper plate western hinterland of the paleoproterozoic trans hudson orogen their junction is defined by the virgin river shear zone a part of the more extensive snowbird tectonic zone subsurface extension of the 2 0 ga thelon orogen lies west of the western granulite domain we present u pb zircon ages sm nd and rb sr isotopic data from the cree lake zone and western granulite domain and from the junction granite which intrudes the virgin river shear zone data from the western granulite domain indicate that prevalent granulite facies metamorphism occurred between 2 3 and 2 0 ga but is imposed on archean protoliths 2 8 3 0 ga old low amphibolite facies retrogression which increases toward the virgin river shear zone probably postdates 2 1 ga data from the cree lake zone also yield archean protolith ages as old as 3 0 ga and some rocks yield interpreted high grade metamorphic overprint ages of 2 3 2 0 ga however two samples yield data indicating hudsonian high grade metamorphic overprint 1 87 to 1 81 ga the junction granite has a u pb zircon age of 1 82 0 30 ga but relict zircons and sm nd data show that it was derived by melting of archean crust high grade mid crustal thermal resetting in the western granulite domain may be coeval with the 1 9 2 0 ga thelon orogen although the data do not preclude an earlier event or events similar 2 3 2 1 ga reworking extends into the cree lake zone but high grade hudsonian 1 87 1 84 ga reworking is also evident in parts of this zone well to the west of the wollaston domain and may extend entirely across the zone to the virgin river shear zone relative importance of the thelon and hudsonian overprints in cree lake zone is unknown data from the junction granite and western granulite domain suggest that all recorded high strain events in the virgin river shear zone postdate 2 3 ga and are thus unrelated to deep crustal archean granulite facies mylonites in the tantato black lake segment of the snowbird tectonic zone north of the athabasca basin

evidence of arctic sea ice thinning from direct observations the arctic sea ice cover is rapidly shrinking but a direct longer term assessment of the ice thinning remains challenging a new time series constructed from in situ measurements of sea ice thickness at the end of the melt season in fram strait shows a thinning by over 50 during 2003 2012 the modal and mean ice thickness along 79 degrees n decreased at a rate of 0 3 and 0 2 m yr 1 respectively with long term averages of 2 5 and 3 m airborne observations reveal an east west thickness gradient across the strait in spring but not in summer due to advection from more different source regions there is no clear relationship between interannual ice thickness variability and the source regions of the ice the observed thinning is therefore likely a result of arctic wide reduction in ice thickness with a potential shift in exported ice types playing a minor role

u pb zircon geochronology and depositional history of the montresor group rae province nunavut canada paleoproterozoic metasedimentary successions of the northwestern canadian shield provide records of tectonic events but the definition of depositional ages has proved elusive although previously

coeval thrusting and extension during lower crustal ductile flow implications for exhumation of high grade metamorphic rocks numerical models of tectonic processes in large hot orogens offer insight into the styles controls and consequences of ductile flow of middle and lower orogenic crust we present results from crustal scale thermal mechanical models illustrating contrasting styles of syn and post convergent ductile flow crustal viscosity in the models is controlled by temperature dependent flow laws scaled to represent lithological strength variations an additional viscosity decrease at high temperature can be imposed to represent weakening during incipient partial melting two end member tectonic styles in which lower crustal flow is driven either by gravity or tectonics develop in response to the initial properties and evolving strength of the model crust homogeneous channel flow driven by the gravitational potential energy difference between a plateau and its foreland is characteristic of himalayan tibetan ht series models with relatively weak laterally homogeneous crust and moderately high heat production in contrast grenville orogen go series models with relatively strong laterally heterogeneous crust do not reach the low effective viscosity eff 1019 pa s required for gravity driven channel flow instead tectonically driven lateral flow and explusion of lower crust is triggered by underthrusting of a strong indentor the dominant structures are ductile fold nappes that may be transported hundreds of kilometres towards the foreland when tectonic convergence is turned off the model orogens undergo gravitational spreading in which ductile middle and lower crust flow laterally from the plateau towards the foreland driving thrusting on the orogenic flanks and ductile thinning in the orogenic core the resulting geometry can resemble that produced by syn convergent ductile flow except for the development of regional scale normal sense shear zones in the post convergent stage model feasibility is tested against data from the western grenville orogen in ontario the comparison suggests that high grade metamorphic rocks in the orogenic core record the effects of protracted syn and post convergent ductile flow whereas those on the flanks record mainly post convergent thrusting and extension the models suggest a number of ways to distinguish among different styles of syn and post convergent ductile flow metamorphic p t t paths alone are not diagnostic of tectonic process without additional information on crustal scale structure and timing in combination with erosion both types of flow may contribute to exhumation of regionally extensive high grade gneiss terranes

implications of fractured arctic perennial ice cover on thermodynamic and dynamic sea ice processes decline of the arctic summer minimum sea ice extent is characterized by large expanses of open water in the siberian laptev chukchi and beaufort seas and introduces large fetch distances in the arctic ocean long waves can propagate deep into the pack ice thereby causing flexural swell and failure of the sea ice this process shifts the floe size diameter distribution smaller increases floe surface area and thereby affects sea ice dynamic and thermodynamic processes the results of radarsat 2 imagery analysis show that a flexural fracture event which occurred in the beaufort sea region on 6 september 2009 affected 40 000 km2 open water fractional area in the area affected initially decreased from 3 7 to 2 7 but later increased to 20 following wind forced divergence of the ice pack energy available for lateral melting was assessed by estimating the change in energy entrainment from longwave and shortwave radiation in the mixed layer of the ocean following flexural fracture 11 54 mj m 2 of additional energy for lateral melting of ice floes was identified in affected areas the impact of this process in future arctic sea ice melt seasons was assessed using estimations of earlier occurrences of fracture during the melt season and is discussed in context with ocean heat fluxes atmospheric mixing of the ocean mixed layer and declining sea ice cover we conclude that this process is an important positive feedback to arctic sea ice loss and timing of initiation is critical in how it affects sea ice thermodynamic and dynamic processes

monazite and xenotime petrogenesis in the contact aureole of the makhavinekh lake pluton northern labrador high temperature 700 900 c metamorphism in the contact aureole of the makhavinekh lake pluton mlp northern labrador led to the growth of monazite and xenotime during progressive replacement of regional garnet bearing assemblages m1 by lower pressure symplectitic coronas of orthopyroxene cordierite m2 in the inner aureole 500 m from the contact where m1 garnet is strongly resorbed high y hree monazite xy hree 0 14 0 18 occurs as small isolated grains and as discontinuous rims on partially resorbed pre m2 monazites that were liberated from garnet xenotime also occurs as small isolated grains within m2 coronas ion microprobe dating of thin high y rims indicates that new monazite growth occurred during m2 monazite xenotime miscibility gap temperatures are consistent with al solubility in orthopyroxene thermometry estimates indicating that peak temperatures in the inner aureole are accurately recorded and preserved by monazite m2 monazite records therefore the temperature and timing of m2 metamorphism two net transfer reactions modelled using singular value decomposition in the system p y hree lree are proposed to account for the growth of m2 phosphates 1 38 grt1 1 mnz1 1 13 mnz2 and 2 737 grt1 1 ap 1 mnz2 3 4 xno2 reaction 1 conserves p and gave rise to locally coronitic high y overgrowths on partially resorbed pre m2 monazite whereas reaction 2 accounts for the growth of small new monazite and xenotime grains both reactions were highly localized within individual m2 coronas due to slow intergranular diffusion accompanying fluid undersaturated metamorphism in the mlp aureole similar monazite forming reactions are expected in other polymetamorphosed granulites

recent changes in the exchange of sea ice between the arctic ocean and the canadian arctic archipelago 1 sea ice is exchanged between the arctic ocean and canadian arctic archipelago caa but has not been quantified over long time periods the corresponding mechanisms responsible for recent variability and change also remain unidentified to address this we estimated the sea ice area flux between the arctic ocean and the m clure strait and queen elizabeth islands qei from 1997 to 2012 for the months of may to november over the period there was a mean flux of 1 103 km2 21 103 km2 at the m clure strait and mean flux of 8 103 km2 8 103 km2 at the qei positive and negative flux signs correspond to arctic ocean ice inflow and outflow respectively the m clure strait had a mean flux of 5 103 km2 from may to september and a mean flux of 7 103 km2 from october to november the qei gates had a mean flux of 4 103 km2 from august to september with negligible ice exchange from may to july and october to november more frequent high sea level pressure anomalies over the beaufort sea and canadian basin since 2007 have reduced arctic ocean multiyear ice myi inflow into the m clure strait the presence of myi in the caa originating from the arctic ocean has been maintained by inflow at the qei which has increased since 2005 these recent increases in arctic ocean myi inflow into the qei can be attributed to increased open water area within the caa that have provided more leeway for inflow to occur

geochronological constraints on metamorphism magmatism and exhumation of deep crustal rocks of the kramanituar complex with implications for the paleoproterozoic evolution of the archean western churchill province canada u pb and sm nd geochronology establishes an important paleoproterozoic 1 9 ga history for the kramanituar complex located in the interior of the archean western churchill province and provides further insight into the snowbird tectonic zone a crustal scale 2000 km feature whose role during precambrian time remains controversial the kramanituar complex is a window of deep crustal rocks dominated by a granulite facies metagabbroic suite of 1902 ma age with minor supracrustal rocks and charnockite these yield peak equilibrium conditions of 12 15 kbar and 850 900 c which are bracketed between 1910 ma the age of prograde metamorphic monazite in sillimanite and kyanite bearing paragneiss and 1901 ma the cooling ages of titanite and rutile in gabbroic and paragneissic rocks although mineral assemblages reflecting peak metamorphic conditions are widespread some rocks record near isothermal decompression to 8 kbar and 800 c the timing of uplift and exhumation is tightly bracketed between magmatic crystallization of gabbroic anorthosite under granulite facies conditions at 1902 ma and widespread rutile cooling ages of 1901 ma time averaged cooling rates of 100 c ma are estimated for gabbroic anorthosite and leucogranite rocks surrounding the kramanituar complex are mainly amphibolite facies archean plutonic and supracrustal rocks those to the north were at deep crustal conditions coeval with the complex whereas those to the south appear to preserve a record of older mainly neoarchean tectonometamorphic assemblages and fabrics the southern boundary of the complex is inferred to be a normal fault that accommodated tectonic unroofing of the kramanituar complex at 1 9 ga this geochronological data set highlights the protracted history of a segment of the geophysically defined snowbird tectonic zone a structure along which latest significant magmatism and tectonometamorphism has been interpreted as either 2600 or 1800 ma penetrative 1900 ma activity in the east trending chesterfield segment as documented at the kramanituar complex suggests that the complex may have represented a favorably oriented segment of a crustal scale archean fault that was reactivated during paleoproterozoic time possibly in response to collision between the slave and churchill cratons thelon orogen at 1 97 1 9 ga

early paleoproterozoic supracrustal assemblages of the rae domain nunavut canada intracratonic basin development during supercontinent break up and assembly abstract the basal paleoproterozoic supracrustal succession of the churchill province in northern canada comprises sedimentary basins overlying the archean rae and hearne domains the rae domain supracrustal succession e g amer ketyet river chantrey and montresor groups comprises four lithotectonic assemblages which include in ascending stratigraphic position 1 shallow marine fluvial quartzarenite with mainly neoarchean detrital zircons of local provenance 2 shallow marine quartzarenite with mainly local provenance that locally includes carbonates mafic volcanic flows 3 abrupt but conformable transition to basinal dark shales and overlying platformal carbonates that pass upward into siltstones and sandstones that record gradual emergence of the platform sandstones within this assemblage display a substantially different detrital zircon provenance signature dominated by early paleoproterozoic zircons with grains as young as 1 95 ga 4 unconformably to conformably overlying immature marine sandstones including turbidites with a significant component of 2 0 1 9 ga detritus probably derived from a combination of local and distal sources the thickness and relative compositional maturity of the basal lithotectonic assemblage 1 records a protracted period of enhanced weathering on a slowly subsiding but stable supercontinent e g kenorland this was followed by mafic volcanism and marine transgression consistent with partial rifting of the rae domain and crustal extension attending supercontinent break up lithotectonic assemblage 2 strata of lithotectonic assemblage 3 record basin flooding and deepening followed by platformal sedimentation along the margins of extended continental blocks assemblage 4 is interpreted to represent deposition in foreland basins during early amalgamation of laurentia part of nuna at ca 1 9 ga the stratigraphy and detrital zircon geochronology of the hurwitz group which overlies the hearne domain is broadly similar to the supracrustal sequence of the rae domain but differs through the presence of basal diamictites and lack of 2 5 ga detritus a major local source in the rae our data suggest that the rae and hearne domains were assembled together by max 1 91 ga i e max age of deposition of the uppermost hurwitz and amer groups the paleoproterozoic stratigraphic assemblage framework for the churchill province compares well with that of other cratons derived from break up of kenorland and ultimately amalgamated in nuna examples from laurentia include supracrustal rocks that overlie the southern margin of the superior province southern province e g huron supergroup animikie group marquette range supergroup whitewater group and mistassini otish group the paleoproterozoic assemblages of the southern and churchill provinces exhibit first order stratigraphic similarities that indicate a shared history of stable continental sedimentation followed by rifting basin opening and basin closure

out of the woods driftwood insights into holocene pan arctic sea ice dynamics the collation of 913 driftwood samples from across the western arctic with spatiotemporal distribution and available provenance data enabled the production of a high resolution proxy based reconstruction of holocene arctic ocean surface current and sea ice dynamics regionally bounded driftwood based sea ice reconstructions studies suggest spatiotemporally complex past arctic sea ice extent and movement however a large scale compilation of holocene arctic driftwood has not previously been developed sparse driftwood in the early holocene 8 2 cal ka b p deglacial period was followed by increased driftwood deposition in the warmer mid holocene 8 2 4 2 cal ka b p characterized by an enhanced transpolar drift tpd 7 cal ka b p leading to sea ice loss through the fram strait driftwood incursion peaks show spatial e w progression from the eurasian archipelagos to greenland and the canadian arctic archipelago suggesting a progressive shift in the orientation of the tpd on centennial millennial time scales and intermediate phases in the arctic oscillation late holocene cooling 4 2 cal ka b p is indicated by increased influx of probably north american picea via a strengthened beaufort gyre bg which enhanced sea ice recirculation starting in the western arctic and progressing eastward in recent millennia 2 cal ka b p a more variable driftwood record alternates between bg and tpd dominance on centennial time scales to further constrain a spatiotemporal reconstruction of variations in holocene ocean current and sea ice dynamics a more definitive determination of driftwood provenance is recommended to build upon the current framework such as through radiogenic isotope tracing and adna analysis

entrainment induced by near inertial drift of sea ice and its impact on under ice biogeochemical processes in marginal ice zones abstract mooring observation of hydrography hydrodynamics and suspended particles distribution under a drifting sea ice revealed the mixing and entrainment pattern in the upper mixed layer ml of the marginal ice zone the ice floe where the mooring system was installed drifted as near inertial motion with approximately 12 h cycle the mixing pattern induced by this near inertial drift can be divided into two distinct regimes first simple entrainment upward fluxes from the seasonal pycnocline to sea ice water boundary are induced by shear across ml and seasonal pycnocline during the period when ice floes drift toward pack ice the entrainment speed was in the range of 0 25 2 m h 1 which matches well with thickening and thinning of the ml during a near inertial period turbulent wakes on the boundary between sea ice and open water occurred behind the advancing edge of ice in the second regime when ice floes drift toward open ocean the turbulent wakes at the advancing edge of ice are combined with the entrainment caused by near inertial motion which results in a complex mixing pattern of both upward and downward fluxes in the ml the echo intensity observed by the acoustic doppler current profiler and beam attenuation from transmissometer revealed the elevated concentration of suspended particulate materials in the ml which can be direct evidence visualizing the mixing pattern results suggest that the mixing and entrainment found in our study sustain particulate matters in suspension within upper ml for a few months this may provide a potential mechanism to sustain abundant organic particulates in the ml and upper pycnocline for months after under ice bloom under strong wind events like storms the entrainment induced by near inertial motion may also get enhanced which causes elevated supply of nutrients from the deeper permanent pycnocline to the ml

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

the decline in arctic sea ice thickness separating the spatial annual and interannual variability in a quarter century of submarine data 1 naval submarines have collected operational data of sea ice draft 93 of thickness in the arctic ocean since 1958 data from 34 u s cruises are publicly archived they span the years 1975 to 2000 are equally distributed in spring and autumn and cover roughly half the arctic ocean the data set is strong we use 2203 values of mean draft each value averaged over a nominal length of 50 km these values range from 0 to 6 m with a standard deviation of 0 99 m multiple regression is used to separate the interannual change the annual cycle and the spatial field the solution gives a climatology for ice draft as a function of space and time the residuals of the regression have a standard deviation of 0 46 m slightly more than the observational error standard deviation of 0 38 m the overall mean of the solution is 2 97 m annual mean ice draft declined from a peak of 3 42 m in 1980 to a minimum of 2 29 m in 2000 a decrease of 1 13 m 1 25 m in thickness the steepest rate of decrease is 0 08 meters per year m a in 1990 the rate slows to 0 007 m a at the end of the record the annual cycle has a maximum on 30 april and a peak to trough amplitude of 1 06 m 1 12 m in thickness the spatial contour map of the temporal mean draft varies from a minimum draft of 2 2 m near alaska to a maximum just over 4 m at the edge of the data release area 200 miles north of ellesmere island

trans hudson orogen of north america and himalaya karakoram tibetan orogen of asia structural and thermal characteristics of the lower and upper plates 1 the trans hudson orogen tho of north america and the himalaya karakoram tibetan orogen hkto of asia preserve a paleoproterozoic and cenozoic record respectively of continent continent collision that is notably similar in scale duration and character in tho the tectonothermal evolution of the lower plate involves 1 early thin skinned thrusting and barrovian metamorphism 2 out of sequence thrusting and high t metamorphism and 3 fluid localized reequilibration anatexis and leucogranite formation the crustal evolution of the indian lower plate in hkto involves 1 early subduction of continental crust to ultrahigh pressure uhp eclogite depths 2 regional barrovian metamorphism and 3 widespread high t metamorphism anatexis and leucogranite formation the shallow depths of the high t metamorphism in hkto are consistent with early to mid miocene ductile flow of an indian lower plate midcrustal channel from beneath the southern tibetan plateau to the greater himalaya melt weakening of the lower plate in tho is not observed at a similar scale probably due to the paucity of pelitic lithologies tectonothermal events in the upper plate of both orogens include precollisional accretion of crustal blocks emplacement of andean type plutonic suites and high t metamorphism syncollisional to postcollisional events include emplacement of garnet biotite muscovite leucogranites anatectic granites and sporadic metamorphism up to 90 myr following the onset of collision in tho comparing the type and duration of tectonothermal events for tho and hkto supports the notion of tectonic uniformitarianism for at least the later half of dated earth history and highlights the complementary nature of the rock record in an older exhumed orogen compared to one undergoing present day orogenesis

reconstructing past sea ice cover of the northern hemisphere from dinocyst assemblages status of the approach abstract dinocysts occur in a wide range of environmental conditions including polar areas we review here their use for the reconstruction of paleo sea ice cover in such environments in the arctic ocean and subarctic seas characterized by dense sea ice cover islandinium minutum islandinium cezare echinidinium karaense polykrikos sp var arctic spiniferites elongatus frigidus and impagidinium pallidum are common and often occur with more cosmopolitan taxa such as operculodinium centrocarpum sensu wall dale cyst of pentapharsodinium dalei and brigantedinium spp canonical correspondence analyses conducted on dinocyst assemblages illustrate relationships with sea surface parameters such as salinity temperature and sea ice cover the application of the modern analogue technique permits quantitative reconstruction of past sea ice cover which is expressed in terms of seasonal extent of sea ice cover months per year with more than 50 of sea ice concentration or mean annual sea ice concentration in tenths the accuracy of reconstructions or root mean square error of prediction rmsep is 1 1 over 10 which corresponds to perennial sea ice such an error is close to the interannual variability standard deviation of observed sea ice cover mismatch between the time interval of instrumental data used as reference 1953 2000 and the time interval represented by dinocyst populations in surface sediment samples which may cover decades if not centuries is another source of error despite uncertainties dinocyst assemblages are useful for making quantitative reconstruction of seasonal sea ice cover

u pb geochronology of detrital zircons in metasedimentary rocks from southern baffin island implications for the paleoproterozoic tectonic evolution of northeastern laurentia a geochronological investigation of metasedimentary rocks from southern baffin island using the geological survey of canada shrimp ii sensitive high resolution ion microprobe has characterized the ages of detrital zircon populations to determine their provenance bracket timing of deposition and distinguish potentially distinct sequences of rocks four lithologically and structurally distinct metasedimentary packages have been identified each appears to have been derived from a different source region in the structurally lowest package all analysed zircons are archean and 90 have ages between 2 83 and 2 63 ga these rocks are interpreted as the northernmost exposures of the paleoproterozoic povungnituk group of the cape smith belt northern quebec with detritus derived from the superior craton occupying the intermediate structural levels the most abundant supracrustal rocks on southern baffin island are siliciclastic and carbonate units of the lake harbour group and the tasiuyak paragneiss

sedimentological and geochemical basin analysis of the paleoproterozoic penrhyn and piling groups of arctic canada abstract paleoproterozoic metasedimentary successions on the western churchill province record a history of regional tectonic events spanning the breakup and amalgamation of supercontinents metasedimentary successions in the northeastern part of the trans hudson orogeny including the penrhyn and piling groups of melville peninsula and baffin island respectively have been understudied with respect to their basin evolution records we present new sedimentological geochemical and geochronological data for the penrhyn and piling groups that record deposition on the rae craton new detrital zircon u pb age data indicate that deposition of the penrhyn group started after 1897 ma and post dates deposition of most of the piling group the new maximum age constraints and stratigraphy of the penrhyn group do not support previous lithostratigraphic correlation with the piling group deposition of the lower piling group likely occurred in an epicontinental basin setting the occurrence of detritus from the meta incognita microcontinent in the upper piling group bravo lake and longstaff bluff formations is interpreted to signal the onset of foreland basin deposition the details of sedimentation in the piling foreland basin provide an additional constraint to discerning the polarity of subduction between the rae craton and meta incognita microcontinent that closed the piling basin we conclude that the piling foreland system shows characteristics of a pro foreland basin implying that the rae craton was the lower plate in the collision with the meta incognita microcontinent finally with new stratigraphic and detrital zircon geochronological data for the penrhyn and piling groups we provide a comparison with other sedimentary successions on the rae craton whose histories were influenced by similar regional tectonic events

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

impact of the arctic ocean atlantic water layer on siberian shelf hydrography this paper examines the role of the arctic ocean atlantic water aw in modifying the laptev sea shelf bottom hydrography on the basis of historical records from 1932 to 2008 field observations carried out in april may 2008 and 2002 2009 cross slope measurements a climatology of bottom hydrography demonstrates warming that extends offshore from the 30 50 m depth contour bottom layer temperature time series constructed from historical records links the laptev sea outer shelf to the aw boundary current transporting warm and saline water from the north atlantic the aw warming of the mid 1990s and the mid 2000s is consistent with outer shelf bottom temperature variability for april may 2008 we observed on shelf near bottom warm and saline water intrusions up to the 20 m isobath these intrusions are typically about 0 2 c warmer and 1 1 5 practical salinity units saltier than ambient water the 2002 2009 cross slope observations are suggestive for the continental slope upward heat flux from the aw to the overlying low halocline water lhw the lateral on shelf wind driven transport of the lhw then results in the bottom layer thermohaline anomalies recorded over the laptev sea shelf we also found that polynya induced vertical mixing may act as a drainage of the bottom layer permitting a relatively small portion of the aw heat to be directly released to the atmosphere finally we see no significant warming up until now over the laptev sea shelf deeper than 10 15 m in the historical record future climate change however may bring more intrusions of atlantic modified waters with potentially warmer temperature onto the shelf which could have a critical impact on the stability of offshore submarine permafrost

three dimensional collisional structure of the trans hudson orogen canada abstract the three dimensional structure of the eastern trans hudson orogen tho part of a paleoproterozoic continent continent collision zone in central north america is revealed through a network of lithoprobe seismic reflection profiles the seismic images are interpreted to delineate a series of stacked thrust sheets essentially confined to the crust e w profiles show strong e dipping reflections extending throughout the crust while n s profiles record events outlining antiformal and synformal structures this allows the identification of decollements that may have localized along pre existing structures e g possible basin bounding extensional faults and at major rheological boundaries e g basement cover contact upper middle crust transition the present topographic surface displays oblique crustal sections with 10 15 km of structural relief generated during post collisional intracontinental transpression of tho as a result of crustal scale folding and faulting

the impact of surface mixing on the arctic river water distribution and stratification in a global ice ocean model abstractthe impact of oceanic vertical mixing on the near surface vertical structure of the arctic ocean is investigated in a global ice ocean model with a passive tracer lowering surface background vertical diffusivity and ignoring the effects of surface wave breaking under sea ice improves the model simulation of the horizontal arctic river water distribution this improvement is largely responsible for the freshening of the arctic surface salinity in the model although these modifications in the model vertical mixing scheme are applied over the whole global ocean the change in the surface salinity over the arctic is larger than that in the rest of the global ocean by one to two orders of magnitude in contrast when a reduced background vertical diffusivity is used at all depths the arctic vertical salinity stratification is improved below the surface as well as in the surface layer but the vertical structure and deep circulation in the rest of the global ocean are also strongly affected weaker s

comparison of viscoelastic type models for ocean wave attenuation in ice covered seas continuum based models that describe the propagation of ocean waves in ice infested seas are considered where the surface ocean layer including ice floes brash ice etc is modeled by a homogeneous viscoelastic material which causes waves to attenuate as they travel through the medium three ice layer models are compared namely a viscoelastic fluid layer model currently being trialed in the spectral wave model wavewatch iii and two simpler viscoelastic thin beam models all three models are two dimensional a comparative analysis shows that one of the beam models provides similar predictions for wave attenuation and wavelength to the viscoelastic fluid model the three models are calibrated using wave attenuation data recently collected in the antarctic marginal ice zone as an example although agreement with the data is obtained with all three models several important issues related to the viscoelastic fluid model are identified that raise questions about its suitability to characterize wave attenuation in ice covered seas viscoelastic beam models appear to provide a more robust parameterization of the phenomenon being modeled but still remain questionable as a valid characterization of wave ice interactions generally

variability of arctic sea ice thickness and volume from cryosat 2 we present our estimates of the thickness and volume of the arctic ocean ice cover from cryosat 2 data acquired between october 2010 and may 2014 average ice thickness and draft differences are within 0 16 m of measurements from other sources moorings submarine electromagnetic sensors icebridge the choice of parameters that affect the conversion of ice freeboard to thickness is discussed estimates between 2011 and 2013 suggest moderate decreases in volume followed by a notable increase of more than 2500 km 3 or 0 34 m of thickness over the basin in 2014 which could be attributed to not only a cooler summer in 2013 but also to large scale ice convergence just west of the canadian arctic archipelago due to wind driven onshore drift variability of volume and thickness in the multiyear ice zone underscores the importance of dynamics in maintaining the thickness of the arctic ice cover volume estimates are compared with those from icesat as well as the trends in ice thickness derived from submarine ice draft between 1980 and 2004 the combined icesat and cryosat 2 record yields reduced trends in volume loss compared with the 5 year icesat record which was weighted by the record setting ice extent after the summer of 2007

changes in the properties and distribution of the intermediate and deep waters in the fram strait abstract the fram strait is the only deep connection between the arctic ocean and the nordic seas greenland iceland and norwegian seas with a sill depth of approximately 2600 m consequently observations from this area reflect changes in the deep waters of the arctic mediterranean possible changes in the properties and distribution of the intermediate and deep water masses passing through the fram strait have been studied for the period from 1982 to 2008 at a zonal section at 79 n with special emphasis on the period from 1997 to 2008 the temperature of the arctic intermediate water shows large interannual variability where the period from 2002 to 2004 was especially cold indicating a strong winter convection in the nordic seas prior to those years the deep water originating from the norwegian sea has become warmer by about 0 10 c during the study period the changes in the properties of the norwegian sea deep water are caused by changes in its composition i e an increasing fraction of the eurasian basin deep water and a decreasing fraction of the greenland sea deep water each year if this trend continues the norwegian sea deep water will have similar characteristics as the eurasian basin deep water in about 15 years a prominent feature seen in the s diagrams from the deep fram strait is the disappearance of water with the characteristics of greenland sea deep water this very cold water temperature below 1 1 c was not observed after 1997 and the minimum temperature in the strait increased by 0 24 c between 1982 and 2008 in the fram strait the fraction of intermediate waters has increased while the fraction of deep waters from the nordic seas has decreased the fraction of deep waters originating from the arctic ocean shows no trend

on the arctic ocean ice thickness response to changes in the external forcing submarine and satellite observations show that the arctic ocean ice cover has undergone a large thickness reduction and a decrease in the areal extent during the last decades here the response of the arctic ocean ice cover to changes in the poleward atmospheric energy transport fwall is investigated using coupled atmosphere ice ocean column models two models with highly different complexity are used in order to illustrate the importance of different internal processes and the results highlight the dramatic effects of the negative ice thickness ice volume export feedback and the positive surface albedo feedback the steady state ice thickness as a function of fwall is determined for various model setups and defines what we call ice thickness response curves when a variable surface albedo and snow precipitation is included a complex response curve appears with two distinct regimes a perennial ice cover regime with a fairly linear response and a less responsive seasonal ice cover regime the two regimes are separated by a steep transition associated with surface albedo feedback the associated hysteresis is however small indicating that the arctic climate system does not have an irreversible tipping point behaviour related to the surface albedo feedback the results are discussed in the context of the recent reduction of the arctic sea ice cover a new mechanism related to regional and temporal variations of the ice divergence within the arctic ocean is presented as an explanation for the observed regional variation of the ice thickness reduction our results further suggest that the recent reduction in areal ice extent and loss of multiyear ice is related to the albedo dependent transition between seasonal and perennial ice i e large areas of the arctic ocean that has previously been dominated by multiyear ice might have been pushed below a critical mean ice thickness corresponding to the above mentioned transition and into a state dominated by seasonal ice

upper and lower plate juxtaposition deformation and metamorphism during crustal convergence trans hudson orogen quebec baffin segment canada abstract the lower plate of the quebec baffin segment of paleoproterozoic trans hudson orogen comprises parautochthonous archean crystalline basement of the superior province 3 22 2 74 ga and imbricated paleoproterozoic rift margin strata 2 04 1 92 ga the collisional upper plate contains 1 allochthonous ophiolitic units 2 00 ga 2 a continental arc terrane narsajuaq arc 1 86 1 82 ga 3 shelf sequence strata ca 1 86 ga and basement orthogneisses ca 1 95 ga 4 foreland basin deposits 1 86 ga and 5 a batholith which intrudes the shelf and foreland basin rocks cumberland batholith 1 86 1 85 ga lower and upper plate assemblages were juxtaposed during a 1 82 1 79 ga accretion collision event and deformed into regional scale folds during two post collisional folding episodes ca 1 76 1 74 ga as a result of the structural relief generated by the post collisional folding and subsequent exhumation all orogenic elements can be directly examined along a 400 km across strike transect in the external zone northern quebec lower plate rift margin units were internally imbricated cape smith belt and translated southward across the superior province basement paleoproterozoic amphibolite facies mineral growth is syn to post thrusting tectonic imbrication has resulted in a structural inversion of the accreted i e upper plate ophiolite stratigraphy north of the cape smith belt mid crustal plutonic units of the narsajuaq arc form an upper plate crystalline wedge whose sole thrust is localized near the thrust belt s basal decollement within narsajuaq arc syn magmatic granulite facies assemblages are retrogressed to amphibolite facies assemblages in proximity to major accretion collision faults in the internal zone southern baffin island a tripartite orogen scale tectonostratigraphy is exposed on the flanks of the post collisional fold structures at the lowest structural level lower plate superior province orthogneisses are imbricated with paleoproterozoic rift margin units and mineral growth is syn thrusting at intermediate structural level upper plate orthogneisses are correlated with the narsajuaq arc in northern quebec at the highest structural level a north facing shelf sequence is structurally overlain by an assemblage of clastic rocks interpreted as a foreland basin sequence dominantly monzogranite plutons of the cumberland batholith are restricted to the upper structural level and indicate pre emplacement imbrication of tectonostratigraphic units within both upper and lower plates granulite facies assemblages are retrogressed to upper amphibolite assemblages in proximity to 1 82 1 79 ga accretion collision structures exposures of superior province basement across the orogen document a progressive increase in the extent of reworking during accretion of upper plate units from a narrow shear zone in the external zone to km scale imbrication and more pervasive shear deformation in the internal zone a minimum of 160 km of basement underthrusting is constrained by the structural overlap of upper plate allochthons on lower plate units basement involvement during post collision shortening is manifest as thick skinned folding indicating coupling across the collisional basal decollement

u pb lu hf and ree in zircon from 3 2 to 2 6 ga archean gneisses of the repulse bay block melville peninsula nunavut abstract combined in situ u pb and lu hf isotope and ree analyses of zircons from the tonalite trondhjemite granodiorite ttg type gneisses and granitoids within the repulse bay block rbb of melville peninsula nunavut reveal that the block is composed of ca 2 86 ga and 2 73 2 71 ga granitoids that formed by reworking of a 3 25 3 10 ga basaltic crust the interpretation is supported by initial hf values for ca 2 86 ga and ca 2 73 2 71 ga gneisses of 2 7 to 0 7 and 4 8 to 2 3 respectively and the preservation of high uranium xenocrystic cores at 3 15 0 05 ga neoarchean plutonism also occurred at ca 2 69 2 66 ga and is characterized by two pyroxene bearing charnockite enderbite and hornblende biotite granitoid intrusions that yield initial hf values that range from 7 1 to 1 0 demonstrating that they were derived from juvenile magmas with significant assimilation of the existing crust the pyroxene and non pyroxene bearing granitoids also contain elevated lree in zircon a feature that is interpreted to reflect metasomatism of the source this study also demonstrates that in the rbb the results of lu hf isotopes in zircon combined with in situ u pb geochronology from inherited zircon cores differ from the results of whole rock sm nd isotopes

granulite microfabrics and deformation mechanisms in southern madagascar optical microstructures and crystallographic preferred orientations were studied in naturally deformed granulite to high amphibolite facies quartzo feldspathic rocks in southern madagascar the microstructures of coarse grained granulite suggest that feldspar and quartz accommodated deformation by both dislocation and diffusion creep in the absence of melt the extreme ductility of feldspar in dynamically recrystallized granulite is explained by activity of dislocation creep in conjunction with stress controlled intracrystalline diffusion in the studied rocks the considerable volume of quartz is not interconnected even at high strain the lack of its interconnectivity in coarse grained granulites and in amphibolite facies granoblastic platy quartz rocks is explained by an extreme stability of the load bearing framework structure at high temperatures in dynamically recrystallized granulite the feldspar viscosity decreases so that quartz becomes enveloped by a weak feldspar matrix which inhibits its coalescence and interconnectivity we predict an important decrease in strength of quartzo feldspathic granulites due to activity of diffusional creep and convergence of viscosity of recrystallized feldspar and quartz

localized accumulation and a shelf basin gradient of particles in the chukchi sea and canada basin western arctic transparent exopolymer particles tep particulate organic carbon poc and particles size range 5 2 119 m as determined by laser in situ scattering and transmissometry lisst were measured in the water column from the chukchi sea to the canada basin in the western arctic ocean during the late summer of 2012 in general the percentages of tep carbon to poc were high the mean values for the shelf and slope basin regions were 135 4 58 0 standard deviation n 36 and 187 6 73 3 n 58 respectively relative to the corresponding values reported for other oceanic regions suggesting that tep play an important role in regulating particle dynamics a hotspot extremely high concentration of particles accompanied by high prokaryote abundance and production was observed near the seafloor depth 50 m of the shelf region localized accumulation of particles was also found in the thin layer near the pycnocline depth 10 30 m and on the slope over a broader spatial scale particle concentration gradients were identified from the shelf to the basin in the upper water column 50 m the particle size distribution analysis indicated that relatively small particles were dominant in the shelf region compared to the slope basin region these results suggest that particles containing large amounts of tep are produced in the shelf region and are potentially delivered to the slope basin region along the pycnocline which might support productivity and material cycles in the nutrient depleted basin region of the western arctic ocean

thinning of the arctic sea ice cover comparison of sea ice draft data acquired on submarine cruises between 1993 and 1997 with similar data acquired between 1958 and 1976 indicates that the mean ice draft at the end of the melt season has decreased by about 1 3 m in most of the deep water portion of the arctic ocean from 3 1 m in 1958 1976 to 1 8 m in the 1990s the decrease is greater in the central and eastern arctic than in the beaufort and chukchi seas preliminary evidence is that the ice cover has continued to become thinner in some regions during the 1990s

the ice cloud and land elevation satellite 2 icesat 2 science requirements concept and implementation abstract the ice cloud and land elevation satellite icesat mission used laser altimetry measurements to determine changes in elevations of glaciers and ice sheets as well as sea ice thickness distribution these measurements have provided important information on the response of the cryopshere earth s frozen surfaces to changes in atmosphere and ocean condition icesat operated from 2003 to 2009 and provided repeat altimetry measurements not only to the cryosphere scientific community but also to the ocean terrestrial and atmospheric scientific communities the conclusive assessment of significant ongoing rapid changes in the earth s ice cover in part supported by icesat observations has strengthened the need for sustained high accuracy repeat observations similar to what was provided by the icesat mission following recommendations from the national research council for an icesat follow on mission the icesat 2 mission is now under development for planned launch in 2018 the primary scientific aims of the icesat 2 mission are to continue measurements of sea ice freeboard and ice sheet elevation to determine their changes at scales from outlet glaciers to the entire ice sheet and from 10s of meters to the entire polar oceans for sea ice freeboard icesat carried a single beam profiling laser altimeter that produced 70 m diameter footprints on the surface of the earth at 150 m along track intervals in contrast icesat 2 will operate with three pairs of beams each pair separated by about 3 km cross track with a pair spacing of 90 m each of the beams will have a nominal 17 m diameter footprint with an along track sampling interval of 0 7 m the differences in the icesat 2 measurement concept are a result of overcoming some limitations associated with the approach used in the icesat mission the beam pair configuration of icesat 2 allows for the determination of local cross track slope a significant factor in measuring elevation change for the outlet glaciers surrounding the greenland and antarctica coasts the multiple beam pairs also provide improved spatial coverage the dense spatial sampling eliminates along track measurement gaps and the small footprint diameter is especially useful for sea surface height measurements in the often narrow leads needed for sea ice freeboard and ice thickness retrievals the icesat 2 instrumentation concept uses a low energy 532 nm green laser in conjunction with single photon sensitive detectors to measure range combining icesat 2 data with altimetry data collected since the start of the icesat mission in 2003 such as operation icebridge and esa s cryosat 2 will yield a 15 year record of changes in ice sheet elevation and sea ice thickness icesat 2 will also provide information of mountain glacier and ice cap elevations changes land and vegetation heights inland water elevations sea surface heights and cloud layering and optical thickness

near inertial mixing in the central arctic ocean observations were made in april 2007 of horizontal currents hydrography and shear microstructure in the upper 500m from a drifting ice camp in the central arctic ocean an approximately 4 day long time series collected about 10 days after a storm event shows enhanced near inertial oscillations in the first half of the measurement period with comparable upward and downward propagating energy rough estimates of wind work and near inertial flux imply that the waves were likely generated by the previous storm the nearinertial frequency band is associated with dominant clockwise rotation in time of the horizontal currents and enhanced dissipation rates of turbulent kinetic energy the vertical profile of dissipation rate shows elevated values in the pycnocline between the relatively turbulent underice boundary layer and the deeper quiescent water column dissipation averaged in the pycnocline is near inertially modulated and its magnitude decays approximately at a rate implied by the reduction of energy over time observations suggest that near inertial energy and internal wave induced mixing play a significant role in vertical mixing in the arctic ocean

reconstructing hydrographic change in petersen bay ellesmere island canada inferred from sar imagery abstract synthetic aperture radar sar satellite imagery was used to reconstruct the change in limnological conditions adjacent to an arctic ice shelf by examining the backscatter values of coastal ice in mid winter scenes high sar backscatter values 6 db suggest that an ice dammed lake was present adjacent to the south coast of petersen bay from 1992 until 2005 following a large calving event of the adjacent petersen ice shelf 8 07 km2 in august 2005 the lake drained through a region where the ice shelf had separated from the coastline this loss of freshwater and replacement of lake ice with sea ice along the southern coast of petersen bay were confirmed from analyses of ice core samples and conductivity temperature depth ctd profiles the exception to this pattern was one distinct area where terrestrial streams entered the edge of petersen bay and freshwater continued to collect from 2006 to 2008 however this ephemeral area of freshwater has not reformed since 2009 due to the persistence of open water events in petersen bay observed in optical satellite imagery which likely facilitated mixing of freshwater with sea water based on the continued break ups of petersen ice shelf and the frequency of open water events it is unlikely that this ice dammed lake will reform the results of this study underscore the utility of sar for reconstructing past hydrographic conditions in the water column below

volume and freshwater transports through the canadian arctic archipelago baffin bay system 1 baffin bay connects the arctic ocean and the labrador sea it receives polar water through the canadian arctic archipelago and by the west greenland current the polar water is after transformation exported through davis strait with control sections both upstream and downstream baffin bay invites the use of an idealized geostrophic approach to estimate transports the baroclinic transports driven by the density differences between the arctic ocean and baffin bay are first determined the density and upper layer depth are assumed the same in lancaster sound nares strait and the west greenland current once the baroclinic transports are estimated the sea level difference between the arctic ocean and baffin bay is computed next the upper layer depth in nares strait and the west greenland current is reduced while the sea level difference is kept constant this allows for deep inflows through nares strait and the west greenland current to establish a deep outflow through davis strait a barotropic sea level slope between the arctic ocean and the labrador sea is estimated from two ideal water columns the transports are computed for different salinities in the polar water and the salinity giving mass balance in the deeper layers is determined the effects of possible increased melting of the greenland icecap are examined if the meltwater is added directly to baffin bay the effects are small but if it is incorporated in the east and west greenland current a significant reduction of the outflow through the archipelago might occur

temperatures of granulite facies metamorphism constraints from experimental phase equilibria and thermobarometry corrected for retrograde exchange this study assesses temperatures of formation of common granulites by combining experimental constraints on the p t stability of granulite facies mineral associations with a garnet orthopyroxene grt opx thermobarometry scheme based on al solubility in opx corrected for late fe mg exchange we applied this scheme to 414 granulites of mafic intermediate and aluminous bulk compositions our findings suggest that granulites are much hotter than traditionally assumed and that the p t conditions of the amphibolite granulite transition portrayed in current petrology textbooks are significant underestimates by over 100 c for aluminous and intermediate granulites mean corrected temperatures based on our method are 890 17 and 841 11 c respectively uncertainties reported as 95 confidence limits on the mean consistent with minimum temperatures for orthopyroxene production by fluid absent partial melting in these bulk compositions in contrast mean temperatures based on grt opx fe mg exchange equilibria using the same thermodynamic data are 732 22 and 723 11 c respectively well below the minimum temperatures for opx stability for mafic granulites the mean corrected temperature using our method is 816 12 c similar to the mean temperature of 793 13 c from fe mg exchange reasons for the differences between the mafic granulites and aluminous intermediate granulites are unclear but may be due to the lower al concentrations in opx in the mafic rocks and possible deficiencies in the thermodynamic modelling of these low concentrations we discuss a number of well known granulite terrains in the context of our findings including the adirondacks the acadian granulites of new england the incipient charnockites of southern india and sri lanka and the kerala khondalite belt our findings carry implications for thermotectonic models of granulite formation a computer program to perform our thermobarometry calculations rclc is available from the journal of petrology website at http www petrology oupjournals org or from the authors at http www geo ucalgary ca pattison drm pattison rclc htm

past present and impendent hydroelastic challenges in the polar and subpolar seas current and emergent advances are examined on the topic of hydroelasticity theory applied to natural sea ice responding to the action of ocean surface waves and swell with attention focused on methods that portray sea ice more faithfully as opposed to those that oversimplify interactions with a poor imitation of reality a succession of authors have confronted and solved by various means the demanding applied mathematics associated with ocean waves i entering a vast sea ice plate ii travelling between plates of different thickness iii impinging on a pressure ridge iv affecting a single ice floe with arbitrarily specified physical and material properties and v many such features or mixtures thereof the next step is to embed simplified versions of these developments in an oceanic general circulation model for forecasting purposes while targeted on specific sea ice situations many of the reported results are equally applicable to the interaction of waves with very large floating structures such as pontoons floating airports and mobile offshore bases

geometry and kinematics of wager shear zone interpreted from structural fabrics and magnetic data the wager shear zone wsz is characterized by progressive bending of northeast southwest trending aeromagnetic anomalies to the right as they merge with east west trending anomalies characterizing the shear zone this feature indicates dextral net shear mapping of abundant and diverse asymmetrical structural fabric elements within the shear zone where it is well exposed along the south coast of wager bay northwestern hudson bay consistently confirmed dextral shear sense pervasive dextral shear zone mylonites were deformed by folds with hinges parallel to the shear direction a folds as well as by discrete conjugate sinistral and dextral mylonitic shears to form a folds in mylonites it is necessary for the mylonitic fabric to rotate out of a stable orientation in the plane of shear and flattening and also to rotate about an axis parallel to the shear direction for which we have no general explanation we conclude with the speculation that the wsz is a strike slip fault related to terminal collisio

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

a combined optimal interpolation and nudging scheme to assimilate osisaf sea ice concentration into roms the ocean and sea ice satellite application facility osisaf of the european organisation for the exploitation of meteorological satellites eumetsat distributes satellite observations operationally in this paper we describe the development of a combined optimal interpolation and nudging coin scheme in the norwegian meteorological institute that assimilates osisaf sea ice concentration sic into a coupled sea ice ocean regional ocean modeling system roms the scheme modifies the modeled sic at every time step based on the difference between observation and forecast as well as on the ratio of observation error to model error snow and sea ice thickness are diagnostically modified to match the ice concentration field hindcast experiments of arctic sea ice are performed for the whole of 2009 the results are compared with osisaf and advanced microwave scanning radiometer for earth observing system amsr e sic showing a significant improvement in the analyzed sea ice edge and summer sic

the impact of an intense summer cyclone on 2012 arctic sea ice retreat 1 this model study examines the impact of an intense early august cyclone on the 2012 record low arctic sea ice extent the cyclone passed when arctic sea ice was thin and the simulated arctic ice volume had already declined 40 from the 2007 2011 mean the thin sea ice pack and the presence of ocean heat in the near surface temperature maximum layer created conditions that made the ice particularly vulnerable to storms during the storm ice volume decreased about twice as fast as usual owing largely to a quadrupling in bottom melt caused by increased upward ocean heat transport this increased ocean heat flux was due to enhanced mixing in the oceanic boundary layer driven by strong winds and rapid ice movement a comparison with a sensitivity simulation driven by reduced wind speeds during the cyclone indicates that cyclone enhanced bottom melt strongly reduces ice extent for about 2 weeks with a declining effect afterward the simulated arctic sea ice extent minimum in 2012 is reduced by the cyclone but only by 0 15 106 km2 4 4 thus without the storm 2012 would still have produced a record minimum

sea ice thickness variability in storfjorden svalbard results from electromagnetic induction surveys of sea ice thickness in storfjorden svalbard reveal large interannual ice thickness variations in a region which is typically characterized by a reoccurring polynya the surveys were performed in march 2003 may 2006 and march 2007 with helicopter and ship based sensors the thickness distributions are influenced by sea ice and atmospheric boundary conditions 2 months prior to the surveys which are assessed with synthetic aperture radar sar images regional quikscat backscatter maps and wind information from the european centre for medium range weather forecasts ecmwf reanalysis dataset locally formed thin ice from the storfjorden polynya was frequently observed in 2003 and 2007 mean thickness 0 55 and 0 37 m respectively because these years were characterized by prevailing northeasterly winds in contrast the entire fjord was covered with thick external sea ice in 2006 mean thickness 2 21 m when ice from the barents sea was driven into the fjord by predominantly southerly winds the modal thickness of this external ice in 2006 increased from 1 2 m in the northern fjord to 2 4 m in the southern fjord indicating stronger deformation in the southern part this dynamically thickened ice was even thicker than multi year ice advected from the central arctic ocean in 2003 mean thickness 1 83 m the thermodynamic ice thickness of fast ice as boundary condition is investigated with a one dimensional sea ice growth model 1dice forced with meteorological data from the weather station at the island of hopen southeast of storfjorden the model results are in good agreement with the modal thicknesses of fast ice measurements in all years

atmospheric response to anomalous autumn surface forcing in the arctic basin data from four reanalyses are analyzed to evaluate the downstream atmospheric response both spatially and temporally to anomalous autumn surface forcing in the arctic basin running weekly mean skin temperature anomalies were classified using the self organizing map algorithm the resulting classes were used to both composite the initial atmospheric state and determine how the atmosphere evolves from this state the strongest response was to anomalous forcing positive skin temperature and total surface energy flux anomalies and reduced sea ice concentration in the barents and kara seas analysis of the evolution of the atmospheric state for 12 weeks after the initial forcing showed a persistence in the anomalies in this area which led to a buildup of heat in the atmosphere this resulted in positive 1000 500 hpa thickness and high pressure circulation anomalies in this area which were associated with cold air advection and temperatures over much of central and northern asia evaluation of days with the opposite forcing i e negative skin temperature anomalies and increased sea ice concentration in the barents and kara seas showed a mirrored opposite downstream atmospheric response other patterns with positive skin temperature anomalies in the arctic basin did not show the same response most likely because the anomalies were not as strong nor did they persist for as many weeks following the initial forcing

isotopic evidence for neoarchean continuity across the snowbird tectonic zone western churchill province canada abstract the snowbird tectonic zone stz the ca 2800 km long boundary between rae and hearne domains of the western canadian shield remains of uncertain tectonic significance but is currently interpreted as a ca 1 9 ga suture the eastern rae domain is well studied and underlain by a 20 000 km2 region of high pressure granulites containing ca 2 60 ga arc rocks and granulite to amphibolite grade structures which formed at ca 2 57 ga d1 m1 and 1 90 ga d2 m2 the 1 85 ga legs lake shear zone juxtaposed the high p granulites of the eastern rae domain structurally above lower amphibolite to greenschist grade supracrustal gneisses of the hearne domain zircon u pb and hf isotopic analyses were acquired from igneous and metasedimentary rocks across the stz and rae hearne boundary to assess the validity of the suture model with specific focus given to the 5 km wide legs lake shear zone results indicate that both 2 60 2 55 ga magmatism and deformation continue unimpeded across the stz and rae hearne boundary furthermore hf isotopic data from igneous zircon from 2 60 ga plutonic rocks across the stz display little variation in ehf indicating that no major crustal break corresponds to the rae hearne boundary or any of the shear zones that parallel the stz on the ground older plutonic rocks show a greater variability in ehf which may indicate a disparate origin grade intensity and timing of paleoproterozoic features vary along the transect and display little continuity across the rae hearne domain boundary in conjunction with existing field and isotopic data we interpret that the rae and hearne domains were together by 2 60 ga and that the stz was host to repeated paleoproterozoic reactivation driven by the latter stages of taltson thelon orogenesis final indentation of the slave craton into the rae domain and accretionary processes on the southern periphery of the hearne domain from 1 93 to 1 84 ga furthermore assessing the viability of major shear zones within high grade terranes as potential sutures is complicated by the lateral and vertical heterogeneity of the crust juxtaposed by them

hydrothermal methane and manganese variation in the plume over the superfast spreading southern east pacific rise abstract onboard analyses of dissolved ch4 and mn were conducted on the water column along the southern east pacific rise between 13 50 and 18 40 s during the 1993 ridge flux cruise many hydrothermal plumes were identified by chemical anomalies which overlie more than half of the surveyed ridge crest the ch 4 mn ratio in the plumes shows wide variability ranges from about 0 05 to 3 9 due to wide range of ch 4 concentration the ch 4 rich plumes were detected in the region of 16 00 18 40 s where vigorous magmatic budget was confirmed by previous studies moreover the ch 4 mn ratio of the plumes is highly correlated with other volatile metal parameters such as the s fe ratio in plume particulate these results strongly suggest that volatile input caused by magmatic perturbation to hydrothermal systems is responsible for the ch 4 mn variability in the southern epr plumes based on analogy of the case at the epr 9 50 n site the detection of several volatile rich plumes and the extensive hydrothermal flux of volatile species are attributed to frequent magmatic events in the superfast spreading southern epr

comparison of freeboard retrieval and ice thickness calculation from als asiras and cryosat 2 in the norwegian arctic to field measurements made during the n ice2015 expedition we present freeboard measurements from airborne laser scanner als the airborne synthetic aperture and interferometric radar altimeter system asiras and cryosat 2 siral radar altimeter ice thickness measurements from both helicopter borne and ground based electromagnetic sounding and point measurements of ice properties this case study was carried out in april 2015 during the n ice2015 expedition in the area of the arctic ocean north of svalbard the region is represented by deep snow up to 1 12 m and a widespread presence of negative freeboards the main scattering surfaces from both cryosat 2 and asiras are shown to be closer to the snow freeboard obtained by als than to the ice freeboard measured in situ this case study documents the complexity of freeboard retrievals from radar altimetry we show that even under cold below 15 c conditions the radar freeboard can be close to the snow freeboard on a regional scale of tens of kilometers we derived a modal sea ice thickness for the study region from cryosat 2 of 3 9 m compared to measured total thickness 1 7 m resulting in an overestimation of sea ice thickness on the order of a factor 2 our results also highlight the importance of year to year regional scale information about the depth and density of the snowpack as this influences the sea ice freeboard the radar penetration and is a key component of the hydrostatic balance equations used to convert radar freeboard to sea ice thickness

small scale sea ice deformation during n ice2015 from compact pack ice to marginal ice zone we studied small scale 50 m to 5 km sea ice deformation from ship radar images recorded during the n ice2015 campaign the campaign consisted of 4 consecutive drifting ice stations floes 1 to 4 north of svalbard with a total duration of nearly 5 months deformation was calculated using 5 different time intervals from 10 min to 24 h and the deformation rate was found to depend strongly on the time scale floes 1 to 3 had a mean deformation rate within the range of 0 06 to 0 07 h 1 with the interval of 10 min and 0 03 to 0 04 h 1 with the interval of 1 h floe 4 represented marginal ice zone miz with very high deformation rate 0 14 0 08 h 1 with the interval of 10 min 1 h deep in the ice pack high deformation rates occurred only with high wind and drift speed while in miz they were found also during calm conditions the deformation rates were found to follow power law scaling with respect to length and time scale even on this small scales and in small domain 15 km 15 km the length scale dependence of deformation rate depends on the time scale the power law scaling exponent of the whole study period decreases from 0 82 to 0 52 with the time interval increasing from 10 min to 24 h ship radar images reveal the importance of the deformation history of the ice pack since the deformation events were initialized along the lines of previous damages

uncertainty in modeled arctic sea ice volume 1 uncertainty in the pan arctic ice ocean modeling and assimilation system piomas arctic sea ice volume record is characterized a range of observations and approaches including in situ ice thickness measurements icesat retrieved ice thickness and model sensitivity studies yields a conservative estimate for october arctic ice volume uncertainty of 1 35 103 km3 and an uncertainty of the ice volume trend over the 1979 2010 period of 1 0 103 km3 decade 1 a conservative estimate of the trend over this period is 2 8 103 km3 decade 1 piomas ice thickness estimates agree well with icesat ice thickness retrievals 0 1 m mean difference for the area for which submarine data are available while difference outside this area are larger piomas spatial thickness patterns agree well with icesat thickness estimates with pattern correlations of above 0 8 piomas appears to overestimate thin ice thickness and underestimate thick ice yielding a smaller downward trend than apparent in reconstructions from observations piomas ice volume uncertainties and trends are examined in the context of climate change attribution and the declaration of record minima the distribution of 32 year trends in a preindustrial coupled model simulation shows no trends comparable to those seen in the piomas retrospective even when the trend uncertainty is accounted for attempts to label september minima as new record lows are sensitive to modeling error however the september 2010 ice volume anomaly did in fact exceed the previous 2007 minimum by a large enough margin to establish a statistically significant new record

important role for ocean warming and increased ice shelf melt in antarctic sea ice expansion changes in sea ice significantly modulate climate change because of its high reflective and strong insulating nature in contrast to arctic sea ice sea ice surrounding antarctica has expanded1 with record extent2 in 2010 this ice expansion has previously been attributed to dynamical atmospheric changes that induce atmospheric cooling3 here we show that accelerated basal melting of antarctic ice shelves is likely to have contributed significantly to sea ice expansion specifically we present observations indicating that melt water from antarctica s ice shelves accumulates in a cool and fresh surface layer that shields the surface ocean from the warmer deeper waters that are melting the ice shelves simulating these processes in a coupled climate model we find that cool and fresh surface water from ice shelf melt indeed leads to expanding sea ice in austral autumn and winter this powerful negative feedback counteracts southern hemispheric atmospheric warming although changes in atmospheric dynamics most likely govern regional sea ice trends4 our analyses indicate that the overall sea ice trend is dominated by increased ice shelf melt we suggest that cool sea surface temperatures around antarctica could offset projected snowfall increases in antarctica with implications for estimates of future sea level rise

patterns of sea ice retreat in the transition to a seasonally ice free arctic abstractthe patterns of sea ice retreat in the arctic ocean are investigated using two global climate models gcms that have profound differences in their large scale mean winter atmospheric circulation and sea ice drift patterns the community earth system model large ensemble cesm le presents a mean sea level pressure pattern that is in general agreement with observations for the late twentieth century the community climate system model version 4 ccsm4 exhibits a low bias in its mean sea level pressure over the arctic region with a deeper icelandic low a dynamical mechanism is presented in which large scale mean winter atmospheric circulation has significant effect on the following september sea ice extent anomaly by influencing ice divergence in specific areas a lagrangian model is used to backtrack the 80 n line from the approximate time of the melt onset to its prior positions throughout the previous winter and quantify the divergence across the pacific and eurasian sectors of the arctic i

magma migration folding and disaggregation of migmatites in the karakoram shear zone ladakh nw india effi cient extraction of granitic magma from crustal sources requires the development of an extensive permeable network of melt bearing channels during deformation we investigate rocks that have undergone deformation and melting within the karakoram shear zone of ladakh nw india in which leucosome distribution is inferred to record the permeable network for magma extraction delicate structures preserved in these rocks record the development of this permeable magma network and its subsequent destruction to form a mobile mass of melt and solids resulting from the interplay between folding and magma migration during folding magma migrated from rock pores into layer parallel and axial planar sheets forming a stromatic migmatite or metatexite with two communicating sets of sheets intersecting parallel to the fold axis once the network was developed folding and stretching was eased by magma migration and slip along axial planar magma sheets folding and magma migration led to layer disaggregation transposition and the formation of a diatexite where rock coherency and banding were destroyed a number of structures developed during this process such as cuspate fold hinges disharmonic folds truncated layering shear along axial planar leucosomes and fl ow drag and disruption of melanosomes in this system magma migration was an integral part of deformation and assisted the folding and stretching of metatexites while folding gave rise to a magma sheet network now preserved as leucosomes as well as the pressure gradients that drove magma migration and the breakup of the metatexite thus metatexite folding increased melt interconnectivity while magma mobility increased strain rate and released differential stresses

geology geochronology and geochemistry of archean rocks in the eqe bay area north central baffin island canada constraints on the depositional and tectonic history of the mary river group of northeastern rae province results of stratigraphic u pb geochronological and geochemical study are reported for rocks in a 2800 km2 area along the southeastern margin of the archean rae province on north central baffin island archean rocks include a gneiss complex two greenstone belts of the mary river group and various younger plutonic rocks the 3000 2800 ma gneiss complex contains intrusions of orthogneiss dated at 2780 2770 ma intermediate felsic volcanism in overlying greenstone belts occurred at 2740 2725 ma and was accompanied and outlasted by calc alkaline plutonism 2730 2715 ma peraluminous plutonism at ca 2700 ma possibly associated with low to medium pressure metamorphism represents the culmination of the archean tectonic cycle dating of metamorphic zircon and titanite in archean gneissic rocks indicates that overprinting high grade metamorphism in the northwest part of the area footwall of the isortoq fault zone is paleoproterozoic ca 1820 ma a weaker somewhat older thermal disturbance ca 1850

sea ice thickness retrieval algorithms based on in situ surface elevation and thickness values for application to altimetry 1 in situ measurements of sea ice thickness i snow depth s and snow freeboard fsn from drilling profile lines from 15 cruises into the southern ocean antarctica were analyzed i was calculated from in situ fsn and s using an isostatic approach i was also directly estimated from fsn as can be obtained from laser altimetry the root mean square difference rmsd between observed and calculated i reduces and the correlation between fsn and i increases substantially when 1 using values averaged over the survey lines 50 m instead of single drill hole measurements 1 m and 2 treating positive and negative sea ice freeboard fi separately for small fi however s approximates fsn pointing toward an isostatic balance also between s and i our linear regression analysis between the in situ measurements suggests a direct conversion of fsn into i using a region specific set of equations rmsd values are similar to those obtained employing isostatic balance models and treating positive and negative fi separately however more data would have been needed to obtain significant differences between most of the various models suggested still our new approach gives a viable alternative for antarctic i retrieval from altimetric measurements of fsn alone correlation between in situ observations of fsn and s is high rmsd between observed and calculated s is small this suggests estimation of s from altimetric fsn measurements such s has an estimated precision of 5 cm and is neither affected by snow wetness or grain size nor limited to s 50 cm

neoarchean high potassium granites of the boothia mainland area rae domain churchill province u pb zircon and sm nd whole rock isotopic constraintsthis article is one of a series of papers published in this special issue on the theme of geochronology in honour of tom krogh the boothia mainland region of the north central rae domain is underlain by remnants of a neoarchean volcano sedimentary sequence dismembered by two regionally extensive neoarchean high potassium granitoid suites with rare occurrences of a structurally interleaved paleoproterozoic sedimentary cover sequence the granitoids and their gneissic equivalents are dominated by variably deformed and metamorphosed i type metaluminous polyphase commonly porphyritic to augen biotite hornblende monzogranite and subordinate granodiorite with rare tonalite new geochronological results the first for this area demonstrate that the widespread neoarchean granitoid plutonism is dominantly 2 61 2 59 ga with a less prominent 2 66 ga plutonic event the age of zircon recrystallization suggests that ca 2 60 ga archean metamorphism and fabric development s1 affected the 2 66 ga plutons prior to or contemporaneously with intrusion of the voluminous ca 2 6 ga suite end t for the ca 2 61 2 59 ga suite range from

composition of freshwater in the spring of 2014 on the southern labrador shelf and slope the labrador current is an important conduit of freshwater from the arctic to the interior north atlantic subpolar gyre here we investigate the spatial variability of the freshwater sources over the southern labrador shelf and slope during may june 2014 using measurements of seawater properties such as temperature salinity nutrients and oxygen isotopic composition we estimate the respective contributions of saline water of atlantic and pacific origins of brines released during sea ice formation and of freshwater from sea ice melt and meteoric water origins on the southern labrador shelf we find a large brine signal and pacific water influence indicating a large contribution of water from the canadian arctic the brine signal implies that more than 4 m of sea ice formed upstream either in the arctic or in baffin bay and the northern labrador sea over the midshelf and slope at 52 n we find a stronger influence of slope water from the west greenland current with a smaller contribution of pacific water and no brine signal thus there is advection of water from the slope region to the midshelf between 55 n and 52 n very freshwater with high meteoric content is found close to the coast in june 2014 observations from 1995 and 2008 suggest a higher fraction of brine and pacific water on the shelf compared to that observed in 2014

microstructural tectonometamorphic processes and the development of gneissic layering a mechanism for metamorphic segregation the mary granite in the east athabasca mylonite triangle northern saskatchewan provides an example and a model for the development of non migmatitic gneissic texture gneissic compositional layering developed through the simultaneous evolution of three microdomains corresponding to original plagioclase orthopyroxene and matrix in the igneous rocks plagioclase phenocrysts were progressively deformed and recrystallized first into core and mantle structures and ultimately into plagioclase rich layers or ribbons garnet preferentially developed in the outer portions of recrystallized mantles and with further deformation produced garnet rich sub layers within the plagioclase rich gneissic domains orthopyroxene was replaced by clinopyroxene and garnet and hornblende if sufficient water was present which were in turn drawn into layers with new garnet growth along the boundaries the igneous matrix evolved through a number of transient fabric stages involving s c fabrics s c c fabrics and ultramylonitic domains in addition quartz veins were emplaced and subsequently deformed into quartz rich gneissic layers moderate to highly strained samples display extreme mineralogical compositional segregation yet most domains can be directly related to the original igneous precursors the mary granite was emplaced at approximately 900 c and 1 0 gpa and was metamorphosed at approximately 750 c and 1 0 gpa the igneous rocks crystallized in the medium pressure granulite field opx pl but were metamorphosed on cooling into the high pressure grt cpx pl granulite field the compositional segregation resulted from a dynamic mutually reinforcing interaction between deformation metamorphic and igneous processes in the deep crust the production of gneissic texture by processes such as these may be the inevitable result of isobaric cooling of igneous rocks within a tectonically active deep crust